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. 2024 Mar 13;9(12):14101–14117. doi: 10.1021/acsomega.3c09594

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior

Esakkimuthu Shanmugasundaram †, Kannan Vellaisamy †, Vigneshkumar Ganesan †, Vimalasruthi Narayanan †, Na’il Saleh ‡,*, Stalin Thambusamy †,*
PMCID: PMC10976396  PMID: 38559980

Abstract

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Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4–CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4–CQD composite has been studied using a three-electrode system. The results show that at 1 A g–1, the composite delivers a higher capacitance of 1209 F g–1. The asymmetric supercapacitor (Co3O4–CQD//AC) provided 13.88 W h kg–1 energy and 684.65 W kg–1 power density with a 96% capacitance retention. The Co3O4–CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4–CQD composite is a promising material for commercial energy storage and environmental applications.

1. Introduction

The energy crisis and environmental pollution are major issues in the modern world, as they affect the quality of human life.1 Most industries rely on nonrenewable energy sources such as coal, oil, and natural gas, which release large amounts of carbon dioxide (CO2) gas into the environment when burned. This contributes to the environmental pollution and global warming. Therefore, it is vital to find an alternative energy source to maintain a clean and green environment. Additionally, industries, such as leather, pharmaceuticals, textiles, and plastics, release harmful organic pollutants that affect the environment. To address these challenges, scientists are focusing on developing efficient technology that can produce bifunctional materials for resolving energy and environmental issues.2,3

There are several techniques available for energy conversion and storage, such as solar cells,4,5 batteries,6,7 and supercapacitors.8 These methods have been developed to address energy shortage problems while minimizing the environmental impact. Among them, supercapacitors (SCs)9 have attracted the attention of the scientific community due to their unique properties, such as higher power density than batteries, long cycle stability, and rapid charge–discharge process. However, the low energy density remains a significant challenge for large-scale applications of SCs. It is well-known that commercial carbon-based materials (electric double-layer capacitors; EDLC) have a limited energy density of 10 W h kg–1.10 Pseudocapacitive materials such as transition metals,11,12 metal–organic frameworks (MOFs),13−15 polymers,16 sulfides,17 and nitrides18 are recommended as an alternative source to EDLC materials because they deliver a higher energy density. Among transition metal oxides, those such as TiO2,19 WO220, NiO,21 RuO2,22 MnO4,23 and Co3O424 are involved in faradic redox reactions and can provide higher energy density due to their higher voltage range capacity and ion diffusion properties. Among these metal oxides, cobalt oxide (Co3O4)25 has been considered a promising material for supercapacitor applications due to its higher theoretical capacity (3650 F g–1),26 faradic activity, low-cost, better electrochemical performance, good cycle stability, and reversibility.

Co3O4 is a material that has recently gained attention in the field of photocatalytic applications due to its superior catalytic performance, high surface area, and good thermal and chemical stability. In a study by Chen et al., Co3O4 hollow spheres were found to be effective in degrading methyl orange dye under UV light radiation,27 while 3D porous/urchin nanostructured Co3O4 prepared by pulsed laser deposition showed 81% dye degradation.28 However, few studies have recently shown that Co3O4 has a high potential for photocatalytic application. Meanwhile, the Co3O4 has limited specific capacitance and electronic conductivity, whose properties hinder the commercial usage of these materials for SC applications.

To overcome this issue, additive materials like carbon,29 nitrides,30 sulfides,31 and metals are doped with Co3O4. This doping process can improve the electrical and optical properties of the Co3O4. Particularly, carbon sources like graphene oxide (GO),32 carbon nanotube (CNT),33 carbon nitride (g-C3N4),34 and carbon quantum dot (CQD)35 have great potential to improve the electrochemical and optical properties of Co3O4 because they have an ultrafine porous structure and surface area, higher conductivity and life-cycle stability.

Among them, carbon quantum dot (CQD) is an emerging carbon material that is used in different applications such as applications including photocatalysis,36 bioimaging,37 sensor,38 and photovoltaic applications39 due to their high solubility and chemical stability. The unique properties of CQD make it an excellent additive material for improving the electrochemical and optical behaviors of metal oxides. Recently, studies have shown that metals like nickel,40 and cobalt-doped CQD materials can provide high capacitance and exceed cyclic stability. Two cobalt-based materials, CoS-CQD41 and Co3O4–Ag-CQD,42 showed a capacitance of 808 and 1052 F g–1 at 1 A g–1, respectively. Additionally, TiO2-doped ascorbic acid-derived CQD is utilized as a photocatalyst for dye degradation.43 In previous research, conducting polymers such as polyaniline, polypyrrole, and polythiophene have been combined with ascorbic acid-derived CQD for their electrochemical and photophysical properties in organic solar cell applications.44,45

In this work, we used an ascorbic-acid-derived CQD to improve the optical and electrical properties of Co3O4. We achieved this by using a one-pot hydrothermal method to produce the Co3O4–CQD composite. The resulting composite was characterized both photophysically and electrochemically and demonstrated multifunctional capabilities. In a three-electrode electrochemical system, the Co3O4–CQD composite exhibited high specific capacitance and efficient cycle stability. Additionally, the asymmetric device (Co3O4–CQD//AC) displayed superior energy and power density, with a recorded 13.88 W h kg–1 and 684.65 W kg–1 respectively. Furthermore, the Co3O4–CQD composite exhibited excellent photocatalytic activity, with a 90% dye degradation rate within 60 min under UV light, outperforming the pristine Co3O4. Efficient electrochemical and catalytic performance suggests Co3O4–CQD composite’s wide use as electrode material for supercapacitors and photocatalytic material for environmental remediation.

2. Experimental Section

2.1. Chemicals

Cobalt nitrate (Co (NO3)2·6H2O), ascorbic acid, potassium hydroxide (KOH), and poly(vinyl alcohol) (PVA) were purchased from Sigma-Aldrich Chemicals Pvt. Ltd., India, and used without purification.

2.2. Preparation of Co3O4–CQD

A one-pot hydrothermal synthesis method was used to prepare Co3O4–CQD. First, 20 mmol of cobalt nitrate and 20 mmol of ascorbic acid were dissolved in 50 mL of water. The resulting solution was then transferred to a 100 mL Teflon autoclave and heated at 180.0 °C for 18 h. Next, the suspension solution was heated at 250 °C in a muffle furnace for 5 h. Finally, black Co3O4–CQD powder was collected and can be used for further purposes. The same procedure was followed to prepare Co3O4 and CQD separately using cobalt nitrate and ascorbic acid as precursors.

3. Results and Discussion

3.1. Physicochemical Characterization

In Figure 1a, the UV–vis spectra of Co3O4 show two absorption peaks at 262 and 517 nm. These peaks correspond to the charge transfer processes of the Co3O4 spinel structure, specifically the O2––Co2+ and O2––Co3+ transitions.46 Meanwhile, Figure 1b shows the CQD’s two absorption peaks at 277 and 356 nm, which are attributed to the π–π* transition (C=C bond) and n−π* transition (C=O bond), respectively.44 When Co3O4 and CQD are combined (Figure 1c), their absorption peaks are shifted to 303 and 510 nm. The (O2––Co2+) transition is red-shifted to a longer wavelength, indicating that the CQD (π–π* transition) interacts with the cobalt charge transfer process. Moreover, the extra peak at 361 nm confirms the CQD’s n−π* transition (carbonyl group) and the fact that Co3O4 is linked to the CQD.47

Figure 1.

Figure 1

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UV–visible spectra of (a) Co3O4, (b) CQD, and (c) Co3O4–CQD.

In Figure 2, the fluorescence spectra show that the Co3O4 emission peak appears at around 480 nm (green emission) when excited at 365 nm. The visible region emission is due to impurities and structural defects in the nanocrystal.48 Normally, CQD has higher fluorescence emission behavior, which is confirmed by the excitation-dependent fluorescence study (280–380 nm), as shown in Figure S1a. The fluorescence intensity of the CQD is gradually increased and the peaks are red-shifted and reaching a high intensity at 360 nm, then decreased. The intensity changes and peak shifts indicate various size carbon dots and emission trap states are presented in the CQD. In Figure S1b, the CQD is shining by various light source regions (visible and UV light) that show the yellow color in the visible region. Meanwhile, it emits strong fluorescence in the UV region (green color). The CQD has a more intense peak at 490 nm, which may be the transition of π → π* graphitic sp2 core in the CQD structure. The peak also appeared in Co3O4–CQD, but its intensity was lower than others. The low-intensity emission peak of Co3O4–CQD reveals that the recombination of the photogenerated electron–hole pair is highly inhibited. This poor electron–hole pair recombination can increase the photocatalytic reactions.49

Figure 2.

Figure 2

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Fluorescence spectra of Co3O4, CQD, and Co3O4–CQD.

Figure 3a shows the FT-IR spectrum of Co3O4, which consists of five bands ranging from 4000 to 500 cm–1. The two bands at 603 and 859 cm–1 correspond to the characteristic bands of Co–O, which represent the rocking vibration of the metal oxide. These bands confirm the spinel structure of Co3O4, with Co3+ occupying octahedral sites and Co2+ occupying tetrahedral sites. The bands at 3402 and 1649 cm–1 represent the O–H stretching and bending vibrations of the absorbed water molecules. Additionally, the peak at 1094 cm–1 denotes the coordination of the Co–OH.50,51 In Figure 3b, the O–H and C–H stretching vibration bands are presented at 3428 and 2925 cm–1, respectively. The carbonyl groups C=O and C–O bands52 are located at 1703 and 1047 cm–1. The aromatic C–H stretching band appeared at 556 cm–1. The Co3O4–CQD spectrum (Figure 3c) shows vibration bands similar to those of the Co3O4 spectrum but with shifted positions due to the interaction of CQD and Co3O4. For instance, the rocking vibration of the metal oxide is presented53 at 584 and 862 cm–1. Additionally, one band observed at 1710 cm–1 corresponds to the carbonyl functional group of CQD, confirming the presence of CQD in the Co3O4 composite.

Figure 3.

Figure 3

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FT-IR spectra of (a) Co3O4, (b) CQD, and (c) Co3O4–CQD.

The XRD analysis was used to characterize the phase form of Co3O4, CQD, and the Co3O4–CQD. The patterns shown in Figure 4a indicate that Co3O4 has a cubic structure nature, with diffraction peaks at 31.59°, 36.90°, 44.70°, 60.00°, and 65.54° corresponding to the 220, 311, 400, 511, and 440 planes of Co3O4 (JCPDS card no: 073-1701).54 CQD, on the other hand, exhibits a broad diffraction peak at 24.20° (002), indicating the lattice carbon disordered structure of CQD.55 Interestingly, the Co3O4 planes 220, 311, 400, 511, and 440 are also present in the Co3O4–CQD composite, but the position is slightly shifted and the peaks have sharply appeared. These results confirm that CQD is present in the Co3O4–CQD composite, where it acts as a surfactant and improves the crystalline nature of the cobalt.47

Figure 4.

Figure 4

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XRD (a) and Raman spectra (b) of Co3O4, CQD, and Co3O4–CQD.

The composite has been confirmed by Raman spectral data. In Co3O4, the peak appears at 585 cm–1, and the Eg and A1g mode56 of cobalt oxide is ascribed to 678 cm–1, as shown in Figure 4b. The CQD has two major peaks at 1360 and 1590 cm–1, which are attributed to the D and G bands. The D band corresponds to the vibration peak of the terminal graphite carbon (sp3) planes, and the G band denotes the vibration of the hexagonal lattice of two-dimensional carbon. Moreover, the peak at 3000 cm–1 corresponds to the 2D band that confirms the number of sp2 layers presented in the CQD.57 The same type of peaks appeared in the Co3O4–CQD composite, which proves the carbon network presented in the Co3O4–CQD composite. Additionally, another three peaks at 597, 678, and 1013 cm–1 for the Co3O4–CQD are attributed to the Eg, A1g symmetric stretching and the O–H [Co (OH)2] deformation mode.58 The XRD and Raman results confirm the formation of the Co3O4–CQD.

X-ray photoelectron spectroscopy (XPS) analysis was used to determine the element composition and surface valence state of Co3O4–CQD. The composition included Co, C, H, and O elements, which were identified in the survey spectrum (Figure 5a). The peaks observed in Figure 5b at 284.23, 285.66, and 287.86 eV were attributed to different carbon bonds, such as C–C/C=C for the CQD carbon skeleton, and C–OH/C–O and C=O bonds for the surface functional groups of CQD. The O 1s spectrum in Figure 5c displayed peaks at 530.31, 531.56, and 532.82 eV, which corresponded to the C–OH/Co–O, C–O–C, and C=O bonds, respectively,59 confirming the presence of CQD in the composite materials. Additionally, the Co 2p peaks at 778.19 and 793.63 eV in Figure 5d were attributed to the presence of Co2+ in 2p3/2 and 2p1/2 chemical states, respectively, which indicates the formation of cobalt oxide in the composite. The peaks at 787.12 and 802.56 denoted the satellite peak of the 2p3/2 and 2p1/2, confirming the formation of Co3+ on the surface.60 Compared to Co3O4,61 the Co3O4–CQD Co 2p region is shifted to the lower binding energies, indicating the reduction of the Co valence state due to the formation of Co–O and Co–C formation after the addition of CQD’s oxygen and carbon in the Co3O4 skeleton structure. The CQD zeta potential value is −14 mV (Figure S2), the value confirms the CQD has a greater number of electronegative atoms so that it can easily interact with the Co atom by their surrounding electrons.62 The formation of interstitial compound (Co–O) induces more active sites and defects, which can improve the interaction between electrode–electrolyte ions. The interaction can boost the charge transfer mobility and storage capacity of the composite material. The XPS finding illustrates the coexistence of cobalt and CQD in the Co3O4–CQD composite.

Figure 5.

Figure 5

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XPS deconvoluted spectra of Co3O4–CQD. (a) Survey scan, (b) C 1s, (c) O 1s, and (d) Co 2p.

The structure and surface morphology of Co3O4, CQD, and Co3O4–CQD were characterized by SEM and TEM, as shown in Figure 6. Figure 6a–c displays the SEM images of Co3O4, CQD, and Co3O4–CQD, respectively. The Co3O4 images indicate a uniform distribution of Co3O4, which has a woven sphere shape, whereas the CQD has a spherical ball-shaped structure.63 The Co3O4–CQD has a brush-like structure64 which is entirely different from Co3O4, and this structural change is due to CQD acting as a surfactant. In addition, the side position brushes bind to each other, creating bundles.65 The TEM images in Figure 6d–g show that the composite material has a highly porous honeycomb-like structure. The TEM image of CQD (Figure S3) shows that the CQD has a spherical shape with a diameter of 2–10 nm. The spherical shape dots are also presented in the Co3O4–CQD composite, representing the CQD anchored on the cobalt oxide surface. The SAED patterns of Co3O4–CQD values 220, 311, 222, 400, 422, 511, and 440 (inward to outward) direction confirm the binding of Co3O4 and CQD54,66 to form a composite, which is consistent with the XRD result. The SEM and TEM results indicate that the Co3O4–CQD composite electrode can be easily exposed to the electrolyte, and its brush and mesoporous nature enhances the electrochemical performance.

Figure 6.

Figure 6

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SEM images of (a) Co3O4, (b) CQD, (c) Co3O4–CQD, and TEM images of Co3O4–CQD (d–f), and SAED patterns of Co3O4–CQD (g).

The EDX analysis was used to determine the percentage of elements in the composite, as shown in Figure 7. In Co3O4 (Figure 7a), two peaks were observed, corresponding to the cobalt and oxygen present in the material. Using the peak intensities in the EDX profile, the amounts of cobalt and oxygen were found to be 55.92 and 44.08%, respectively.67 The CQD, shown in Figure 7b, consists of 75.25% carbon and 24.75% oxygen. In Figure 7c, the Co3O4–CQD composite contains 34.27% cobalt, 50.48% oxygen, and 15.26% carbon. The carbon peaks confirm the presence of CQD in the Co3O4.68

Figure 7.

Figure 7

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EDX images of (a) Co3O4, (b) CQD, and (c) Co3O4–CQD.

The surface area and pore diameter of Co3O4 and Co3O4–CQD were evaluated using nitrogen adsorption and desorption isotherm measurements, specifically the Brunauer–Emmett–Teller (BET) method. Figure 8a and b show that the surface area and pore size diameter of Co3O4 are 127.04 m2/g and 4.17 nm, respectively. The CQD surface area and pore size diameter (Figure S4a,b) are 9.63 m2/g and 2.15 nm, respectively. On the other hand, the surface area of Co3O4–CQD (Figure 8c) is higher than that of Co3O4 and CQD, measuring 209.24 m2/g, while the pore size is smaller at 2.54 nm (Figure 8d). The reason for the surface area elevation of the composite is the distribution of cobalt ions with the carbon matrix. To the best of our knowledge, the surface area of Co3O4–CQD is higher than previous reports based on Co3O4 composites.69−71 This higher surface area is a key factor that affects the interfacial electrochemical behavior of the electrode material72 and its photocatalytic application. Additionally, the small porous structure of Co3O4–CQD enhances ion diffusion in supercapacitors73 and improves the sorption ability of dye molecules in photocatalytic applications.

Figure 8.

Figure 8

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Nitrogen adsorption–desorption isotherms for (a) Co3O4 and pore size distributions of (b) Co3O4; nitrogen adsorption–desorption isotherms for (c) Co3O4–CQD, and (d) pore size distributions of Co3O4–CQD. The inset of (b) and (d) exhibits a magnified view of mesopore distribution.

3.2. Electrochemical Analysis of the Three-Electrode System

The three-electrode system’s cyclic voltammogram (CV) for Ni foam, Co3O4, CQD, and Co3O4–CQD in 1 M KOH at 10 mV/s during the 0.1–0.7 V potential window is shown in Figure 9a. The Co3O4 current density and curve area increased while the redox peaks shifted to Ni foam and CQD. The reversible redox process in the different valent states of cobalt in the Co3O4 can attributed to the redox peaks. Based on earlier reports,74,75 the electrochemical reaction mechanism involving Co3O4 and electrolyte anions (OH–) can be expressed (eqs 1 and 2).

3.2. 1
3.2. 2

Figure 9.

Figure 9

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(a) CV study of Co3O4, CQD, and Co3O4–CQD, (b) CV different scan rate study of Co3O4–CQD, and (c) proportion of capacitive and diffusion capacitance for charge storage contributions of Co3O4–CQD at 10 mV/s. (d) Comparison of the stored charge at scan rates of 5, 10, 15, 20, 25, and 30 mV/s.

Compared to Co3O4, Co3O4–CQD delivered a higher current density, suggesting the carbon source (CQD) can improve electrochemical active sites during that redox process. It is a well-known factor that the CV area curve is positively related to the capacitance performance.76 The CV area curve of Co3O4–CQD is higher than that of Co3O4 which indicates that Co3O4–CQD has higher capacitance than Co3O4. Moreover, the result suggests that the CQD improves the electron transport and diffusion ion process within the Co3O4–CQD composite with the help of the synergistic effect, the reason the composite has higher energy storage capacity.77

To further investigate the charge transfer property of the Co3O4–CQD composite, the electrode involves different potential scan rate studies in the CV, and the results are in Figure 9b. With increasing scan rate, the position of the redox peak shifted toward the positive voltage direction due to the diffusion polarization effect, and the current range increased because of the improvement of the capacitance behavior of the electrode material. To identify the capacitance ratio of the Co3O4–CQD composite, the capacitive and diffusion behavior of the composite was investigated. The current response of the Co3O4–CQD composite is estimated by the separation of capacitive and diffusion-controlled processes.78 As per the reports from the Dunn group, eq 3(79) helps to calculate the capacitive effects.

3.2. 3

where Ip denotes the current density (A g–1) corresponding to the redox peaks, k1 and k2 denote constant coefficients, v is the scan rate (mV/s), k1v is the current from the surface capacitance, and k2v0.5 is the process of diffusion-controlled intercalation.

Figure 9c shows the capacitive (shaded region) and diffusion capacitances for charge storage contributions at 10 mV/s. It exhibits that the contribution rate of diffusion capacitance is 47% whereas the surface capacitance is 53%. Figure 9d, the contribution rates of the Co3O4–CQD composite in different scan rates are given in which the low scan rate (5 mV/s), the capacitive contribution, is lower (46%) than the diffusion contribution (54%). Based on the scan rate improvement, the capacitive contribution (surface capacitance) gradually increased and reached 93% at 30 mV/s. The Co3O4–CQD composite electrode contains higher capacitive contribution due to the higher ion accessibility with sufficient surface-active sites80 and rapid ions/electron migration between electrode/electrolyte interface. Based on the scan rate improvement, the capacitive contribution rate is increased which confirms the fast reaction kinetics ability81 of the Co3O4–CQD electrode. It is the main factor for achieving superior rate capability and cyclic performance at high current density during charge–discharge processes.82

The EIS is a great tool to analyze electron transfer and kinetics of ions between the electrode and electrolyte. The Co3O4, CQD, and Co3O4–CQD impedance spectra involve an electrochemical fitting process, as exhibited in Figure 10a–c. The fitting process gives the equivalent circuits containing solution resistance (Rs), charge transfer resistance (Rct), Warburg impedance element (W), and constant phase element (CPE).83,84 A Nyquist plot has two distinct parts which include a semicircle in the higher-frequency region and a sloped straight line in the higher-frequency region.85 The Rs values of the prepared materials are Co3O4 (2.83 Ω), CQD (1.68 Ω), and Co3O4–CQD (1.54 Ω), and the Rct values are Co3O4 (5.53 Ω), CQD (4.50 Ω), and Co3O4–CQD (4.20 Ω). All among the Co3O4–CQD have lower Rs and Rct, so the electron and charge transfer between the electrolyte and electrode is high.86 It is a crucial factor for electrochemical energy devices since the minimum resistance can enhance the conductivity with the help of a speed redox reaction. The results are consistent with those of the CV study. Furthermore, the material porosity can generate the CPE.87 The CPE calculated from the following (eq 4),

3.2. 4

where n and TCPE are frequency-independent constants and w is the angular frequency. The 'n' is a correction factor that is related to the electrode material roughness. The values n = 0–0.5 denote a Warburg behavior, while n = 0–1 denotes the CPE as an ideal capacitor. The Co3O4–CQD 'n' value is 0.61, which indicates that the electrode has ideal supercapacitor behavior (pseudo capacitance). The result reveals that the solution resistance and charge transfer between the electrode and electrolyte is more significant, the behavior is responsible for higher capacitance property.

Figure 10.

Figure 10

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EIS spectra and the equivalent circuits of (a) Co3O4, (b) CQD, and (c) Co3O4–CQD.

Galvanostatic charge–discharge (GCD) analysis helps determine the capacitance behavior of the electrode materials. The Co3O4, CQD, and Co3O4–CQD specific capacitance are 784, 102, and 1209 F g–1 at 1 A g–1. The Co3O4 electrode GCD curve exhibits pseudocapacitive behavior whereas the Co3O4–CQD curve has a hybrid capacitive nature due to the electrochemical double-layer capacitance behavior of CQD, as shown in Figure 11a. The GCD study at different current densities (1–20 A g–1) is exhibited in Figure 11b. When the current density is increased (Figure 11c), the specific capacitance is gradually decreased due to the insufficient time for the Faraday reaction in the fast charge–discharge process.88 However, Co3O4–CQD has 452 F g–1 capacitance at the 20 A g–1 range is 38% of the original capacitance whereas Co3O4 is 14% of the original capacitance, these results suggest that the CQD not only accelerates the ion and electron transport of the Co3O4 composite but also restrict the diffusion opposition throughout the charge–discharge processes. Long-term cyclic stability is one of the crucial parameters for commercial supercapacitor applications. As shown in Figure 11d, the Co3O4–CQD electrode material involves a charge–discharge cycle test at 20 A g–1, and the result exhibits 100% capacitance retention after 5000 cycles. The material was also analyzed by XRD and XPS study after 5000 cycles to understand the phase and composition of the material. In the XRD spectra (Figure S5), the cobalt oxide corresponding patterns such as 220, 311, 400, 511, and 440 are presented before and after cycling. The XRD spectrum has no phase change but the peaks are slightly shifted in their position which may be the addition of binding polymer and conducting carbon added in the composite. In XPS spectra of the Co3O4–CQD composite before cycling (Figure S6), the carbon spectrum peaks are presented at 284.03 (C–C/C=C), 286.34 (C–OH/C–O) and 288.48 eV (C=O) and the oxygen peaks located at 530.31 (C–OH/Co–O) and 531.42 eV(C–O–C), respectively. The same peaks are presented in the Co3O4–CQD composite after the cycling test (Figure S7). Meanwhile, the peaks of the Co spectrum (before cycle) 2p3/2 and 2p1/2 are presented at 779.90 and 795.11 eV, and the peak at 782.11 and 796.81 eV which corresponds to the Co2+ and Co3+ chemical state of cobalt oxide, respectively. After the cycle, the peaks are slightly shifted and located at (780.84 and 796.42 eV-Co2+) and (785.03 and 799.56 eV-Co3+) which is more similar to the before cycle. The slight intensity shift and full width at half-maximum aspects may be the substrate (Ni foam) and the addition of binding polymer in the composite. The result indicates that the material is stable, and the charge storage mechanism involved a complete reversible reaction near/on the surface of the material.

Figure 11.

Figure 11

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(a) GCD study of Co3O4, CQD, and Co3O4–CQD, (b) different current density, (c) specific capacitance values, and (d) cycle stability study of Co3O4–CQD.

For our understanding and comparative studies for the different electrode materials, respective capacitance and its cycle stability are tabulated briefly in Table 1.

Table 1. Electrochemical Performance of Co3O4–CQD in Comparison with Reported Cobalt and Other Metal-Oxide-Doped CQD-Based Materials.

s. no. electrode material capacitance cycle stability ref
1 CQDs/CoS2 808 F g–1 at 1 A g–1 98.75% (10,000) (41)
2 MnO2/CQDs/GA 721 F g–1 at 1 A g–1 92.3% (10,000) (89)
3 CuS@CD-GOH 920 F g–1 at 1 A g–1 90%, (5000) (90)
4 CuS@CQDs@C HNS 618 F g–1 at 1 A g–1 95%, (4000) (91)
5 CQD-MnO2 189 F g–1 at 0.14 A g–1 100%, (1200) (92)
6 CQD-Bi2O3 343 F g–1 at 0.5 A g–1 95%, (2500) (93)
7 CQDs-MnO2 340 F g–1 at 1 A g–1 80%, (10,000) (94)
8 RCQD/RuO2 594 F g–1 at 1 A g–1 96%, (5000) (95)
9 NiS/C-dot 880 F g–1 at 2 A g–1 100%, (1000) (40)
10 MoS2/NCDs 149.21 F g–1 at 0.5 A g–1 100%, (2000) (10)
11 CuMnO2/GQD 520.2 F g–1 at 0.5 A g–1 83.3% (5000) (96)
12 Co3O4-CQD 1209 F g–1 at 1 A g–1 100%, (5000) this work
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3.3. Electrochemical Analysis of Supercapacitor Two-Electrode System

For commercial applications, a two-electrode asymmetric supercapacitor device is fabricated by using Co3O4–CQD as a positive electrode and activated carbon as a negative electrode. Before solid-state analysis, the two-electrode potential window is determined by a three-electrode system using 1 M KOH as an electrolyte; it is shown in Figure 12a. The abovementioned analysis and its result suggest that the potential window of two electrodes is 0–1.6 V. Figure 12b depicts different potential window CV studies of the (Co3O4–CQD//AC). In Figure 12c, the CV curve current range is gradually increased and achieves a higher current range (4 mA), and it has a proper redox peak with a rectangular-shaped CV curve. The CV redox peaks are retained very well even at 100 mV/s the results suggest that the device possesses higher power capability. The EIS exhibits (Figure 12d) the semicircle that corresponds to the double layer and charges transfer resistance which is 1.69 and 9.28 Ω. The low resistance behavior confirms that the device has higher electrical conductivity due to the synergistic effect between the cobalt ion with CQD. The small Rct value demonstrated the fast ion and charge transfer kinetics of the electrode–electrolyte interface.

Figure 12.

Figure 12

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(a) CV study of AC and Co3O4–CQD at 50 mV/s in 1 M KOH in three-electrode systems, (b) different potential windows, (c) different scan rates, and (d) EIS study of Co3O4–CQD//AC asymmetric two electrode devices.

Furthermore, the Co3O4–CQD//AC device potential window is analyzed and finally determined at 0.8–1.4 V, it is shown in Figure 13a. The GCD curves (0.5–10 A g–1) are exhibited in Figure 13b. The capacitance value of the device is 51 F g–1 at 0.5 A g–1 and 19 F g–1 at 10 A g–1 which is calculated from the GCD curves.60 Energy and power density are crucial merit factors in energy storage devices that help to determine the performance of SCs for real applications. In Ragone plot (Figure 13c), exhibits the relationship between the energy density and power density97 and the values are 13.88 W h kg–1 energy density and 684.65 W kg–1 power density, respectively. The long cycling life is an essential parameter of the SCs device in which the charge–discharge measurement is repeated 5000 times at 10 A g–1 in the potential window 0–1.4 V as shown in Figure 13d. The capacitance range slightly decreased and delivered 96% retention after 5000 cycles; this result indicates the high electrochemical stability and the excellent performance of the device. The amorphous nature of the carbon network-induced Co3O4–CQD electrode material controls the volume change during the charge–discharge process that property can improve the cyclic performance of the electrode. The results suggest that this device is suitable for practical SC applications.

Figure 13.

Figure 13

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(a) Different voltage GCD, (b) different current density GCD, (c) Ragone diagram, and (d) cycle stability study of Co3O4–CQD//AC asymmetric two electrode devices.

3.4. Photocatalytic Application

The study on the photodegradation of MB under UV irradiation is presented in Figure 14. A blank test was conducted without a catalyst, and the initial absorption spectra of MB showed a negligible decrease after 60 min of UV irradiation (Figure 14a). In the pristine Co3O4 test, the absorption of MB gradually decreased upon UV irradiation, as shown in Figure 14b. The absorption spectra range of MB slightly decreased after exposure to UV irradiation for 10 min in the presence of Co3O4. With continuous UV irradiation for 10–60 min, the MB absorption spectra considerably decreased. After 60 min of UV irradiation, the absorption intensity range decreased by approximately 50% from its initial range. This degradation pattern was observed in the pristine CQD as well, as shown in Figure 14c. However, Co3O4–CQD (Figure 14d) exhibited efficient degradation of MB under UV irradiation, with a 90% decrease in the absorption intensity range at 60 min. This intensity loss was higher than those observed in Co3O4 and CQD.

Figure 14.

Figure 14

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Photocatalytic performance of (a). Without catalyst, (b). Co3O4, (c). CQD, (d). Co3O4–CQD under UV irradiation for about 60 min.

The efficiency of dye degradation rates under UV irradiation in the presence of Co3O4, CQD, and Co3O4–CQD is shown in Figure 15a,b. The photocatalytic degradation efficiency is calculated based on the initial and final absorbance range of the dye molecule.98 The Co3O4–CQD composite degraded 90% of the dye in just 60 min. However, without a catalyst, pristine Co3O4 and CQD only degraded 3, 52, and 45%, respectively. The improved catalytic activity of the Co3O4–CQD composite can be attributed to its higher surface area and chemical composition. In addition, the Co3O4–CQD composite exhibits an enhanced photocatalytic effect due to the synergistic effect between CQD and Co3O4. This synergistic effect is explained in the electrochemical performance section, which results in improved quick charge transport and reduced recombination of electron/hole (e–/h+) during the photocatalytic reaction.99 These separations of e–/h+ generate a greater amount of active oxygen radicals such as OH and O2– from H2O and O2, which can effectively degrade dye molecules. Moreover, the presence of CQD (carbon source) increases the surface area of the Co3O4–CQD composite (as demonstrated in the N2 adsorption–desorption isotherm study), facilitating the absorption of dye molecules on the surface of the composite during degradation. The stability of the photocatalyst is a crucial aspect of its practical applications.

Figure 15.

Figure 15

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(a) Comparative degradation rate of MB dye under UV irradiation. (b) Degradation efficiency of dye degradation based on different catalysts. (c) Percentage of dye degradation in Co3O4–CQD at different cycles of reuse. (d) XRD pattern of Co3O4–CQD before and after dye degradation.

The study aimed to evaluate the photocatalytic reusability and stability of Co3O4–CQD, which underwent three consecutive cycles under UV irradiation. The results showed that the photocatalytic activity (Figure 15c) of Co3O4–CQD for MB dye degradation decreased by only 2% (from 90 to 88%), indicating that it is a stable photocatalyst for dye degradation. The structure stability and crystalline nature of Co3O4–CQD were also assessed (Figure 15d), and the XRD pattern showed no change even after three photocatalytic experiment cycles. Additionally, there was no phase transformation during UV light illumination, indicating that Co3O4–CQD has good chemical stability and reusability properties.

3.4.1. Plausible Mechanism for Photodegradation of Co3O4–CQD

The band gap analysis is a crucial tool for understanding the photocatalytic mechanism of prepared materials. The band gap is calculated using Tauc plot100 (eq 5).

3.4.1. 5

α—absorption coefficient, h—Planck’s constant, t—light frequency, A—constant’s value, Eg—bandgap energy, and n—number of transitions in the semiconductor. The formula mentioned above is used to compute the bandgap. The bandgap of Co3O4, CQD, and Co3O4–CQD is computed using the formula mentioned above. The obtained values are 2.68, 3.20, and 2.24 eV, respectively, as shown in Figure 16.

Figure 16.

Figure 16

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Band gap study of (a) Co3O4, (b) CQD, and (c) Co3O4–CQD composites.

Moreover, the valence band (VB) and conductance band (CB) potential ranges are calculated using the following eqs 6–8101,102

3.4.1. 6
3.4.1. 7
3.4.1. 8

where ECB and EVB are edge potentials, Eg is the band gap of the semiconductor material, Ec is the energy of free electrons on the hydrogen scale (4.5 eV), χ represents the Mulliken electronegativity, and a, b, and c represent the number of atoms in the compound. The calculated electronegativity of the Co3O4, CQD, and Co3O4–CQD is 5.9, 7.5, and 6.7 eV respectively. The ECB and EVB values are calculated with the help of χ and Eg and summarized in Table 2. Figure 17 demonstrates the energy level diagram of the Co3O4, CQD, and Co3O4–CQD composite.

Table 2. Values of the Bandgap (Eg), Conduction Band (ECB), and Valence Band (EVB) Edge Potentials.
materials Eg (eV) ECB (V) EVB (V)
Co3O4 2.68 0.06 2.74
CQD 3.20 1.74 4.94
Co3O4–CQD 2.24 1.14 3.30
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Figure 17.

Figure 17

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Band gap structure of Co3O4, CQD and Co3O4–CQD composite.

Figure 18 illustrates the possible mechanism of dye degradation and charge transfer process between Co3O4 and CQD. During the photodegradation process under UV light irradiation, the Co3O4 and CQD in the Co3O4–CQD composite absorb the photon energy. In the first step, Co3O4 absorbs the UV light and excites the electron from the VB to the CB, creating an electron (e–) in the CB and holes (h+) in the VB. The CB electron of Co3O4 can transfer to the CQD CB, while the CQD also undergoes an excitation process and produces electrons and holes in the CB and VB band, respectively. The electrons that are collected during the photocatalytic103 process are trapped by the oxygen vacancy. This helps to prevent the recombination of electron–hole pairs (e–/ h+), which, in turn, enhances the photocatalytic activity. During the reduction process, the electrons react with H2O to produce the O2·– and ·OH radicals. On the other hand, during the oxidation process, the holes react with H2O to produce ·OH radicals. These radicals play a crucial role in the degradation of MB, breaking down its aromatic bonds and converting it into smaller molecules104 such as CO2 and H2O. The photodegradation process of MB in the presence of Co3O4–CQD under UV irradiation can be summarized by the following mechanism105 steps (eqs 9–13).

3.4.1. 9
3.4.1. 10
3.4.1. 11
3.4.1. 12
3.4.1. 13
Figure 18.

Figure 18

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Schematic diagram of dye degradation and the electron charge transfer mechanism of Co3O4–CQD under UV irradiation.

4. Conclusions

The Co3O4–CQD nanocomposite has been successfully synthesized by using the hydrothermal method. The composite has a uniform nanobrush structure, as confirmed by a surface morphology study. SEM and TEM analysis have also verified that the CQD is attached to the outer surface of the cobalt. By using CV, EIS, and GCD techniques, the composite shows significant improvement over Co3O4 in terms of charge mobility, capacitance, cycle stability, and rate capability. The material has a high capacitance of 1209 F g–1 at 1 A g–1, and it retains 100% of its capacitance after 3000 cycles. Additionally, the asymmetric supercapacitor device delivers 13.88 W h kg–1 energy and 684.65 W kg–1 power density with a wide voltage window of 0–1.4 V, using Co3O4–CQD//AC. Moreover, the Co3O4–CQD exhibits 90% dye degradation efficiency under UV light irradiation, thanks to its higher surface area and suitable band gap. These findings suggest that Co3O4–CQD is a promising material for energy storage and environmental applications.

Acknowledgments

Na’il Saleh acknowledges the financial support by United Arab Emirates University (Grant # 12S106).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.3c09594.

  • Physical characterization and electrochemical characterization, asymmetric supercapacitor fabrication, photocatalytic activity test, different excitation fluorescence study of CQD (280–380 nm), photographs of CQD in visible and UV light (254 and 365 nm), zeta potential of CQD, TEM images of CQD, nitrogen adsorption–desorption isotherms for CQD and pore size distributions of CQD, XRD patterns of Co3O4–CQD before and after 5000 cycles, and XPS deconvoluted spectra of Co3O4–CQD before and after 5000 cycles (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao3c09594_si_001.pdf (997.8KB, pdf)

References

  1. Gong X.; Liu G.; Li Y.; Yu D. Y. W.; Teoh W. Y. Functionalized-Graphene Composites: Fabrication and Applications in Sustainable Energy and Environment. Chem. Mater. 2016, 28 (22), 8082–8118. 10.1021/acs.chemmater.6b01447. [DOI] [Google Scholar]
  2. Niu X.; Li Y.; Zhou Q.; Shu H.; Wang J. Arsenene-Based Heterostructures: Highly Efficient Bifunctional Materials for Photovoltaics and Photocatalytics. ACS Appl. Mater. Interfaces 2017, 9 (49), 42856–42861. 10.1021/acsami.7b14842. [DOI] [PubMed] [Google Scholar]
  3. Zeng L.; Li X.; Fan S.; Mu J.; Qin M.; Wang X.; Gan G.; Tadé M.; Liu S. Seaweed-Derived Nitrogen-Rich Porous Biomass Carbon as Bifunctional Materials for Effective Electrocatalytic Oxygen Reduction and High-Performance Gaseous Toluene Absorbent. ACS Sustain. Chem. Eng. 2019, 7 (5), 5057–5064. 10.1021/acssuschemeng.8b05863. [DOI] [Google Scholar]
  4. Ali M. H.; Al Mamun M. A.; Haque M. D.; Rahman M. F.; Hossain M. K.; Islam A. Z. M. T. Performance Enhancement of an MoS2-Based Heterojunction Solar Cell with an In2Te3 Back Surface Field: A Numerical Simulation Approach. ACS Omega 2023, 8 (7), 7017–7029. 10.1021/acsomega.2c07846. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Esakkimuthu S.; Manikandan G.; Khan M. I.; Vigneshkumar G.; Vimalasruthi N.; Kannan V.; Rajamohan R.; Stalin T. Electrospun and Electropolymerized Carbon Nanofiber–Polyaniline–Cu Material as a Hole Transport Material for Organic Solar Cells. Carbon Lett. 2023, 33, 2233–2235. [Google Scholar]
  6. Elia G. A.; Marquardt K.; Hoeppner K.; Fantini S.; Lin R.; Knipping E.; Peters W.; Drillet J. F.; Passerini S.; Hahn R. An Overview and Future Perspectives of Aluminum Batteries. Adv. Mater. 2016, 28 (35), 7564–7579. 10.1002/adma.201601357. [DOI] [PubMed] [Google Scholar]
  7. Liu S.; Kang L.; Jun S. C. Challenges and Strategies toward Cathode Materials for Rechargeable Potassium-Ion Batteries. Adv. Mater. 2021, 33 (47), 2004689 10.1002/adma.202004689. [DOI] [PubMed] [Google Scholar]
  8. Say M. G.; Brett C. J.; Edberg J.; Roth S. V.; Söderberg L. D.; Engquist I.; Berggren M. Scalable Paper Supercapacitors for Printed Wearable Electronics. ACS Appl. Mater. Interfaces 2022, 14 (50), 55850–55863. 10.1021/acsami.2c15514. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Liu S.; Kang L.; Zhang J.; Jun S. C.; Yamauchi Y. Sodium Preintercalation-Induced Oxygen-Deficient Hydrated Potassium Manganese Oxide for High-Energy Flexible Mg-Ion Supercapacitors. NPG Asia Mater. 2023, 15 (1), 9. 10.1038/s41427-022-00450-z. [DOI] [Google Scholar]
  10. El Sharkawy H. M.; Dhmees A. S.; Tamman A. R.; El Sabagh S. M.; Aboushahba R. M.; Allam N. K. N-Doped Carbon Quantum Dots Boost the Electrochemical Supercapacitive Performance and Cyclic Stability of MoS2. J. Energy Storage. 2020, 27, 101078 10.1016/j.est.2019.101078. [DOI] [Google Scholar]
  11. Kate R. S.; Khalate S. A.; Deokate R. J. Overview of Nanostructured Metal Oxides and Pure Nickel Oxide (NiO) Electrodes for Supercapacitors: A Review. J. Alloys Compd. 2018, 734, 89–111. 10.1016/j.jallcom.2017.10.262. [DOI] [Google Scholar]
  12. Zhang G.; Xiao X.; Li B.; Gu P.; Xue H.; Pang H. Transition Metal Oxides with One-Dimensional/One-Dimensional-Analogue Nanostructures for Advanced Supercapacitors. J. Mater. Chem. A 2017, 5, 8155–8186. 10.1039/C7TA02454A. [DOI] [Google Scholar]
  13. Wang K.; Li Q.; Ren Z.; Li C.; Chu Y.; Wang Z.; Zhang M.; Wu H.; Zhang Q. 2D Metal–Organic Frameworks (MOFs) for High-Performance BatCap Hybrid Devices. Small 2020, 16 (30), 2001987 10.1002/smll.202001987. [DOI] [PubMed] [Google Scholar]
  14. Wang K.; Chen C.; Li Y.; Hong Y.; Wu H.; Zhang C.; Zhang Q. Insight into Electrochemical Performance of Nitrogen-Doped Carbon/NiCo-Alloy Active Nanocomposites. Small 2023, 19 (23), e2300054 10.1002/smll.202300054. [DOI] [PubMed] [Google Scholar]
  15. Wang K.; Guo Y.; Zhang Q. Metal–Organic Frameworks Constructed from Iron-Series Elements for Supercapacitors. Small Struct. 2022, 3, 2100115. [Google Scholar]
  16. Fong K. D.; Wang T.; Smoukov S. K. Multidimensional Performance Optimization of Conducting Polymer-Based Supercapacitor Electrodes. Sustain. Energy Fuels. 2017, 1 (9), 1857–1874. 10.1039/C7SE00339K. [DOI] [Google Scholar]
  17. Iqbal M. F.; Ashiq M. N.; Zhang M. Design of Metals Sulfides with Carbon Materials for Supercapacitor Applications: A Review. Energy Technol. 2021, 9 (4), 2000987 10.1002/ente.202000987. [DOI] [Google Scholar]
  18. Ghosh S.; Jeong S. M.; Polaki S. R. A Review on Metal Nitrides/Oxynitrides as an Emerging Supercapacitor Electrode beyond Oxide. Korean J. Chem. Eng. 2018, 35, 1389–1408. 10.1007/s11814-018-0089-6. [DOI] [Google Scholar]
  19. Ates M.; Bayrak Y.; Yoruk O.; Caliskan S. Reduced Graphene Oxide/Titanium Oxide Nanocomposite Synthesis via Microwave-Assisted Method and Supercapacitor Behaviors. J. Alloys Compd. 2017, 728, 541–551. 10.1016/j.jallcom.2017.08.298. [DOI] [Google Scholar]
  20. Mandal D.; Routh P.; Nandi A. K. A New Facile Synthesis of Tungsten Oxide from Tungsten Disulfide: Structure Dependent Supercapacitor and Negative Differential Resistance Properties. Small 2018, 14 (4), 1702881 10.1002/smll.201702881. [DOI] [PubMed] [Google Scholar]
  21. Xia Q. X.; Yun J. M.; Mane R. S.; Li L.; Fu J.; Lim J. H.; Kim K. H. Enhanced Electrochemical Activity of Perforated Graphene in Nickel-Oxide-Based Supercapacitors and Fabrication of Potential Asymmetric Supercapacitors. Sustain. Energy Fuels 2017, 1 (3), 529–539. 10.1039/C6SE00085A. [DOI] [Google Scholar]
  22. Suktha P.; Phattharasupakun N.; Sawangphruk M. Transparent Supercapacitors of 2 Nm Ruthenium Oxide Nanoparticles Decorated on a 3D Nitrogen-Doped Graphene Aerogel. Sustain. Energy Fuels 2018, 2 (8), 1799–1805. 10.1039/C8SE00177D. [DOI] [Google Scholar]
  23. Li Z.; Mi Y.; Liu X.; Liu S.; Yang S.; Wang J. Flexible Graphene/MnO2 Composite Papers for Supercapacitor Electrodes. J. Mater. Chem. 2011, 21 (38), 14706–14711. 10.1039/c1jm11941a. [DOI] [Google Scholar]
  24. Salunkhe R. R.; Tang J.; Kamachi Y.; Nakato T.; Kim J. H.; Yamauchi Y. Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework. ACS Nano 2015, 9 (6), 6288–6296. 10.1021/acsnano.5b01790. [DOI] [PubMed] [Google Scholar]
  25. Xie L. J.; Wu J. F.; Chen C. M.; Zhang C. M.; Wan L.; Wang J. L.; Kong Q. Q.; Lv C. X.; Li K. X.; Sun G. H. A Novel Asymmetric Supercapacitor with an Activated Carbon Cathode and a Reduced Graphene Oxide-Cobalt Oxide Nanocomposite Anode. J. Power Sources 2013, 242, 148–156. 10.1016/j.jpowsour.2013.05.081. [DOI] [Google Scholar]
  26. Xu J. M.; Yan A. L.; Wang X. C.; Wang B. Q.; Cheng J. P. A Review of Cobalt Monoxide and Its Composites for Supercapacitors. Ceram. Int. 2021, 47 (16), 22229–22239. 10.1016/j.ceramint.2021.04.262. [DOI] [Google Scholar]
  27. Chen Y.; Hu L.; Wang M.; Min Y.; Zhang Y. Self-Assembled Co3O4 Porous Nanostructures and Their Photocatalytic Activity. Colloids Surfaces A Physicochem. Eng. Asp. 2009, 336 (1–3), 64–68. 10.1016/j.colsurfa.2008.11.018. [DOI] [Google Scholar]
  28. Warang T.; Patel N.; Santini A.; Bazzanella N.; Kale A.; Miotello A. Pulsed Laser Deposition of Co3O4 Nanoparticles Assembled Coating: Role of Substrate Temperature to Tailor Disordered to Crystalline Phase and Related Photocatalytic Activity in Degradation of Methylene Blue. Appl. Catal. A Gen. 2012, 423–424, 21–27. 10.1016/j.apcata.2012.02.037. [DOI] [Google Scholar]
  29. Ramesh S.; Karuppasamy K.; Kim H. S.; Kim H. S.; Kim J. H. Hierarchical Flowerlike 3D Nanostructure of Co3O4@MnO2/N-Doped Graphene Oxide (NGO) Hybrid Composite for a High-Performance Supercapacitor. Sci. Rep. 2018, 8 (1), 16543 10.1038/s41598-018-34905-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Gonçalves R.; Paiva R. S.; Lima T. M.; Paixão M. W.; Pereira E. C. Carbon Nitride/Polypyrrole Composite Supercapacitor: Boosting Performance and Stability. Electrochim. Acta 2021, 368, 137570 10.1016/j.electacta.2020.137570. [DOI] [Google Scholar]
  31. Liu T.; Liu J.; Zhang L.; Cheng B.; Yu J. Construction of Nickel Cobalt Sulfide Nanosheet Arrays on Carbon Cloth for Performance-Enhanced Supercapacitor. J. Mater. Sci. Technol. 2020, 47, 113–121. 10.1016/j.jmst.2019.12.027. [DOI] [Google Scholar]
  32. Numan A.; Duraisamy N.; Saiha Omar F.; Mahipal Y. K.; Ramesh K.; Ramesh S. Enhanced Electrochemical Performance of Cobalt Oxide Nanocube Intercalated Reduced Graphene Oxide for Supercapacitor Application. RSC Adv. 2016, 6 (41), 34894–34902. 10.1039/C6RA00160B. [DOI] [Google Scholar]
  33. Sarkar A.; Chakraborty A. K.; Bera S.; Krishnamurthy S. Novel Hydrothermal Synthesis of CoS2/MWCNT Nanohybrid Electrode for Supercapacitor: A Systematic Investigation on the Influence of MWCNT. J. Phys. Chem. C 2018, 122 (32), 18237–18246. 10.1021/acs.jpcc.8b04137. [DOI] [Google Scholar]
  34. Rabani I.; Zafar R.; Subalakshmi K.; Kim H. S.; Bathula C.; Seo Y. S. A Facile Mechanochemical Preparation of Co3O4@g-C3N4 for Application in Supercapacitors and Degradation of Pollutants in Water. J. Hazard. Mater. 2021, 407, 124360 10.1016/j.jhazmat.2020.124360. [DOI] [PubMed] [Google Scholar]
  35. Syed Zainol Abidin S. N. J.; Mamat M. S.; Rasyid S. A.; Zainal Z.; Sulaiman Y. Electropolymerization of Poly(3,4-Ethylenedioxythiophene) onto Polyvinyl Alcohol-Graphene Quantum Dot-Cobalt Oxide Nanofiber Composite for High-Performance Supercapacitor. Electrochim. Acta 2018, 261, 548–556. 10.1016/j.electacta.2017.12.168. [DOI] [Google Scholar]
  36. Han M.; Zhu S.; Lu S.; Song Y.; Feng T.; Tao S.; Liu J.; Yang B. Recent Progress on the Photocatalysis of Carbon Dots: Classification Mechanism and Applications. Nano Today. 2018, 19, 201–218. 10.1016/j.nantod.2018.02.008. [DOI] [Google Scholar]
  37. Cao L.; Yang S. T.; Wang X.; Luo P. G.; Liu J. H.; Sahu S.; Liu Y.; Sun Y. P. Competitive Performance of Carbon “Quantum” Dots in Optical Bioimaging. Theranostics 2012, 2 (3), 295–301. 10.7150/thno.3912. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Molaei M. J. Principles, Mechanisms, and Application of Carbon Quantum Dots in Sensors: A Review. Anal. Methods. 2020, 12, 1266–1287. 10.1039/C9AY02696G. [DOI] [Google Scholar]
  39. Mistry B.; Machhi H. K.; Vithalani R. S.; Patel D. S.; Modi C. K.; Prajapati M.; Surati K. R.; Soni S. S.; Jha P. K.; Kane S. R. Harnessing the N-Dopant Ratio in Carbon Quantum Dots for Enhancing the Power Conversion Efficiency of Solar Cells. Sustain. Energy Fuels 2019, 3 (11), 3182–3190. 10.1039/C9SE00338J. [DOI] [Google Scholar]
  40. Sahoo S.; Satpati A. K.; Sahoo P. K.; Naik P. D. Incorporation of Carbon Quantum Dots for Improvement of Supercapacitor Performance of Nickel Sulfide. ACS Omega 2018, 3 (12), 17936–17946. 10.1021/acsomega.8b01238. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Arsalani N.; Ghadimi L. S.; Ahadzadeh I.; Tabrizi A. G.; Nann T. Green Synthesized Carbon Quantum Dots/Cobalt Sulfide Nanocomposite as Efficient Electrode Material for Supercapacitors. Energy Fuels 2021, 35 (11), 9635–9645. 10.1021/acs.energyfuels.1c00369. [DOI] [Google Scholar]
  42. Wang X.; Zhang X.; Han W.; Mu X.; Zhang Y.; Zhao X.; Chen Y.; Yang Z.; Su Q.; Xie E.; Lan W. Embedded Ag Quantum Dots into Interconnected Co3O4 Nanosheets Grown on 3D Graphene Networks for High Stable and Flexible Supercapacitors. Electrochim. Acta 2017, 224, 260–268. 10.1016/j.electacta.2016.12.073. [DOI] [Google Scholar]
  43. Ke J.; Li X.; Zhao Q.; Liu B.; Liu S.; Wang S. Upconversion Carbon Quantum Dots as Visible Light Responsive Component for Efficient Enhancement of Photocatalytic Performance. J. Colloid Interface Sci. 2017, 496, 425–433. 10.1016/j.jcis.2017.01.121. [DOI] [PubMed] [Google Scholar]
  44. Shanmugasundaram E.; Ganesan V.; Narayanan V.; Perumalsamy M.; Kuppu S. V.; Guruviah P. K.; Stalin T. Preparation and Characterization of Quantum Dot Doped Polyaniline Photoactive Film for Organic Solar Cell Application. Chem. Phys. Lett. 2021, 771, 138517 10.1016/j.cplett.2021.138517. [DOI] [Google Scholar]
  45. Esakkimuthu S.; Stalin T. Investigations of the Optical and Electrical Properties of Carbon Quantum Dots Doped Conducting Polymers for Organic Solar Cell Applications. Indian J. Chem. Technol. 2022, 29 (6), 771–775. 10.56042/ijct.v29i6.67382. [DOI] [Google Scholar]
  46. Abdallah A. M.; Awad R. Study of the Structural and Physical Properties of Co3O4 Nanoparticles Synthesized by Co-Precipitation Method. J. Supercond. Nov. Magn. 2020, 33 (5), 1395–1404. 10.1007/s10948-019-05296-1. [DOI] [Google Scholar]
  47. Bankole O. M.; Olaseni S. E.; Adeyemo M. A.; Ogunlaja A. S. Microwave-Assisted Synthesis of Cobalt Oxide/Reduced Graphene Oxide (Co3O4-RGO) Composite and Its Sulfite Enhanced Photocatalytic Degradation of Organic Dyes. Z. Phys. Chem. 2020, 234 (10), 1524. 10.1515/zpch-2019-1524. [DOI] [Google Scholar]
  48. Gajendiran J.; Sivakumar N.; Parthasaradhi Reddy C.; Ramya J. R. The Effect of Calcination’s Temperature on the Structural, Morphological, Optical Behaviour, Hemocompatibility and Antibacterial Activity of Nanocrystalline Co3O4 Powders. Ceram. Int. 2020, 46 (4), 5469–5476. 10.1016/j.ceramint.2019.10.261. [DOI] [Google Scholar]
  49. Vennela A. B.; Mangalaraj D.; Muthukumarasamy N.; Agilan S.; Hemalatha K. V. Structural and Optical Properties of Co3O4 Nanoparticles Prepared by Sol-Gel Technique for Photocatalytic Application. Int. J. Electrochem. Sci. 2019, 14 (4), 3535–3552. 10.20964/2019.04.40. [DOI] [Google Scholar]
  50. Packiaraj R.; Devendran P.; Venkatesh K. S.; Asath Bahadur S.; Manikandan A.; Nallamuthu N. Electrochemical Investigations of Magnetic Co3O4 Nanoparticles as an Active Electrode for Supercapacitor Applications. J. Supercond. Nov. Magn. 2019, 32 (8), 2427–2436. 10.1007/s10948-018-4963-6. [DOI] [Google Scholar]
  51. Alem A. F.; Worku A. K.; Ayele D. W.; Wubieneh T. A.; Teshager A. A.; Kndie T. M.; Admasu B. T.; Teshager M. A.; Asege A. A.; Ambaw M. D.; Zeleke M. A.; Shibesh A. K.; Yemata T. A. Ag Doped Co3O4 Nanoparticles for High-Performance Supercapacitor Application. Heliyon 2023, 9 (2), e13286 10.1016/j.heliyon.2023.e13286. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Ren H.; Ge L.; Guo Q.; Li L.; Hu G.; Li J. The Enhancement of Photocatalytic Performance of SrTiO3 Nanoparticles: Via Combining with Carbon Quantum Dots. RSC Adv. 2018, 8 (36), 20157–20165. 10.1039/C8RA02103A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Mussa Y.; Ahmed F.; Abuhimd H.; Arsalan M.; Alsharaeh E. Enhanced Electrochemical Performance at High Temperature of Cobalt Oxide/Reduced Graphene Oxide Nanocomposites and Its Application in Lithium-Ion Batteries. Sci. Rep. 2019, 9 (1), 44. 10.1038/s41598-018-37032-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Naushad M.; Ahamad T.; Ubaidullah M.; Ahmed J.; Ghafar A. A.; Al-Sheetan K. M.; Arunachalam P. Nitrogen-Doped Carbon Quantum Dots (N-CQDs)/Co3O4 Nanocomposite for High Performance Supercapacitor. J. King Saud Univ. - Sci. 2021, 33 (1), 101252 10.1016/j.jksus.2020.101252. [DOI] [Google Scholar]
  55. Chaudhary S.; Kumar S.; Kaur B.; Mehta S. K. Potential Prospects for Carbon Dots as a Fluorescence Sensing Probe for Metal Ions. RSC Adv. 2016, 6 (93), 90526–90536. 10.1039/C6RA15691F. [DOI] [Google Scholar]
  56. Zhao Y.; Chen S.; Sun B.; Su D.; Huang X.; Liu H.; Yan Y.; Sun K.; Wang G. Graphene-Co3O4 Nanocomposite as Electrocatalyst with High Performance for Oxygen Evolution Reaction. Sci. Rep. 2015, 5, 7629. 10.1038/srep07629. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Zheng C.; Huang L.; Guo Q.; Chen W.; Li W.; Wang H. Facile One-Step Fabrication of Upconversion Fluorescence Carbon Quantum Dots Anchored on Graphene with Enhanced Nonlinear Optical Responses. RSC Adv. 2018, 8 (19), 10267–10276. 10.1039/C8RA00390D. [DOI] [PMC free article] [PubMed] [Google Scholar]
  58. Patil U. M.; Ghorpade R. V.; Nam M. S.; Nalawade A. C.; Lee S.; Han H.; Jun S. C. PolyHIPE Derived Freestanding 3D Carbon Foam for Cobalt Hydroxide Nanorods Based High Performance Supercapacitor. Sci. Rep. 2016, 6, 35490 10.1038/srep35490. [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Omer K. M.; Tofiq D. I.; Hassan A. Q. Solvothermal Synthesis of Phosphorus and Nitrogen Doped Carbon Quantum Dots as a Fluorescent Probe for Iron(III). Microchim. Acta 2018, 185 (10), 466. 10.1007/s00604-018-3002-4. [DOI] [PubMed] [Google Scholar]
  60. Liu Y.; Chang X.; Wang M.; Guo H.; Li W.; Wang Y. Hierarchical CuCo2O4/CuO Nanoflowers Crosslinked with Carbon Nanotubes as an Advanced Electrode for Supercapacitors. J. Alloys Compd. 2021, 871, 159555 10.1016/j.jallcom.2021.159555. [DOI] [Google Scholar]
  61. Liu S.; Yin Y.; Shen Y.; Hui K. S.; Chun Y. T.; Kim J. M.; Hui K. N.; Zhang L.; Jun S. C. Phosphorus Regulated Cobalt Oxide@Nitrogen-Doped Carbon Nanowires for Flexible Quasi-Solid-State Supercapacitors. Small 2020, 16 (4), 1906458 10.1002/smll.201906458. [DOI] [PubMed] [Google Scholar]
  62. Kang L.; Huang C.; Zhang J.; Zhang M.; Zhang N.; Liu S.; Ye Y.; Luo C.; Gong Z.; Wang C.; Zhou X.; Wu X.; Jun S. C. Effect of Fluorine Doping and Sulfur Vacancies of CuCo2S4 on Its Electrochemical Performance in Supercapacitors. Chem. Eng. J. 2020, 390, 124643 10.1016/j.cej.2020.124643. [DOI] [Google Scholar]
  63. Zheng H.; Niu P.; Zhao Z. Carbon Quantum Dot Sensitized Pt@Bi2WO6/FTO Electrodes for Enhanced Photoelectro-Catalytic Activity of Methanol Oxidation. RSC Adv. 2017, 7 (43), 26943–26951. 10.1039/C7RA01867C. [DOI] [Google Scholar]
  64. Liu Y. B.; Lin L. Y.; Huang Y. Y.; Tu C. C. Investigation of the Electroactive Capability for the Supercapacitor Electrode with Cobalt Oxide Rhombus Nanopillar and Nanobrush Arrays. J. Power Sources 2016, 315, 23–34. 10.1016/j.jpowsour.2016.03.035. [DOI] [Google Scholar]
  65. Kang X.; Wu L.; Xu J.; Liu D.; Song Q.; Hu Y. Preparation and Photoelectrochemical Properties of Porous Silicon/Carbon Dots Composites. IOP Conf. Ser.: Mater. Sci. Eng. 2020, 892, 012025 10.1088/1757-899X/892/1/012025. [DOI] [Google Scholar]
  66. Yang W.; Gao Z.; Ma J.; Wang J.; Wang B.; Liu L. Effects of Solvent on the Morphology of Nanostructured Co3O4 and Its Application for High-Performance Supercapacitors. Electrochim. Acta 2013, 112, 378–385. 10.1016/j.electacta.2013.08.056. [DOI] [Google Scholar]
  67. Chakraborty P.; Deka N.; Patra D. C.; Debnath K.; Mondal S. P. Hydrothermally Grown Porous Cobalt Oxide Nanostructures for Enzyme-Less Glucose Detection. J. Electron. Mater. 2021, 50 (6), 3699–3705. 10.1007/s11664-021-08852-5. [DOI] [Google Scholar]
  68. Raeisi M.; Alijani H. Q.; Peydayesh M.; Khatami M.; Bagheri Baravati F.; Borhani F.; Šlouf M.; Soltaninezhad S. Magnetic Cobalt Oxide Nanosheets: Green Synthesis and in Vitro Cytotoxicity. Bioprocess Biosyst. Eng. 2021, 44 (7), 1423–1432. 10.1007/s00449-021-02518-6. [DOI] [PubMed] [Google Scholar]
  69. Fan H.; Yi G.; Tian Q.; Zhang X.; Xing B.; Zhang C.; Chen L.; Zhang Y. Hydrothermal-Template Synthesis and Electrochemical Properties of Co3O4/Nitrogen-Doped Hemisphere-Porous Graphene Composites with 3D Heterogeneous Structure. RSC Adv. 2020, 10 (60), 36794–36805. 10.1039/D0RA06897G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Xie S.; Liu Y.; Deng J.; Yang J.; Zhao X.; Han Z.; Zhang K.; Dai H. Insights into the Active Sites of Ordered Mesoporous Cobalt Oxide Catalysts for the Total Oxidation of O-Xylene. J. Catal. 2017, 352, 282–292. 10.1016/j.jcat.2017.05.016. [DOI] [Google Scholar]
  71. Wang Y.; Zhong Z.; Chen Y.; Ng C. T.; Lin J. Controllable Synthesis of Co3O4 from Nanosize to Microsize with Large-Scale Exposure of Active Crystal Planes and Their Excellent Rate Capability in Supercapacitors Based on the Crystal Plane Effect. Nano Res. 2011, 4 (7), 695–704. 10.1007/s12274-011-0125-x. [DOI] [Google Scholar]
  72. Rakhi R. B.; Chen W.; Cha D.; Alshareef H. N. Substrate Dependent Self-Organization of Mesoporous Cobalt Oxide Nanowires with Remarkable Pseudocapacitance. Nano Lett. 2012, 12 (5), 2559–2567. 10.1021/nl300779a. [DOI] [PubMed] [Google Scholar]
  73. Xu J.; Xu C.; Zhao Y.; Wu J.; Hu J. Hollow Co3O4@MnO2 Cubic Derived From ZIF-67@Mn-ZIF as Electrode Materials for Supercapacitors. Front. Chem. 2019, 7, 831. 10.3389/fchem.2019.00831. [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Yang J.; Xu X.; Zhou X.; Jiang S.; Chen W.; Shi S.; Wang D.; Liu Z. Ultrasmall Co3O4 Nanoparticles Confined in P, N-Doped Carbon Matrices for High-Performance Supercapacitors. J. Phys. Chem. C 2020, 124 (17), 9225–9232. 10.1021/acs.jpcc.0c01539. [DOI] [Google Scholar]
  75. Zallouz S.; Réty B.; Vidal L.; Le Meins J. M.; Matei Ghimbeu C. Co3O4 Nanoparticles Embedded in Mesoporous Carbon for Supercapacitor Applications. ACS Appl. Nano Mater. 2021, 4 (5), 5022–5037. 10.1021/acsanm.1c00522. [DOI] [Google Scholar]
  76. Ding Y.; Peng Y.; Chen S.; Li Z.; Zhang X.; Falaras P.; Hu L. A Competitive Coordination Strategy to Synthesize Co3O4@carbon Flower-like Structures for High-Performance Asymmetric Supercapacitors. Appl. Surf. Sci. 2019, 495, 143502 10.1016/j.apsusc.2019.07.244. [DOI] [Google Scholar]
  77. Wu C. L.; Chen D. H. Fabrication of RGO/CoSx-RGO/RGO Hybrid Film via Coassembly and Sulfidation of 2D Metal Organic Framework Nanoflakes and Graphene Oxide as Free-Standing Supercapacitor Electrode. J. Alloys Compd. 2021, 872, 159702 10.1016/j.jallcom.2021.159702. [DOI] [Google Scholar]
  78. Liu S.; Ni D.; Li H. F.; Hui K. N.; Ouyang C. Y.; Jun S. C. Effect of Cation Substitution on the Pseudocapacitive Performance of Spinel Cobaltite MCo2O4 (M = Mn, Ni, Cu, and Co). J. Mater. Chem. A 2018, 6 (23), 10674–10685. 10.1039/C8TA00540K. [DOI] [Google Scholar]
  79. Wang X.; Wang Y.; Jiang Y.; Li X.; Liu Y.; Xiao H.; Ma Y.; Huang Y.; Yuan G. Tailoring Ultrahigh Energy Density and Stable Dendrite-Free Flexible Anode with Ti3C2Tx MXene Nanosheets and Hydrated Ammonium Vanadate Nanobelts for Aqueous Rocking-Chair Zinc Ion Batteries. Adv. Funct. Mater. 2021, 31 (35), 2103210 10.1002/adfm.202103210. [DOI] [Google Scholar]
  80. Liu S.; Kang L.; Hu J.; Jung E.; Henzie J.; Alowasheeir A.; Zhang J.; Miao L.; Yamauchi Y.; Jun S. C. Realizing Superior Redox Kinetics of Hollow Bimetallic Sulfide Nanoarchitectures by Defect-Induced Manipulation toward Flexible Solid-State Supercapacitors. Small 2022, 18 (5), 2104507 10.1002/smll.202104507. [DOI] [PubMed] [Google Scholar]
  81. Liu S.; Yin Y.; Ni D.; Hui K. S.; Ma M.; Park S.; Hui K. N.; Ouyang C. Y.; Jun S. C. New Insight into the Effect of Fluorine Doping and Oxygen Vacancies on Electrochemical Performance of Co2MnO4 for Flexible Quasi-Solid-State Asymmetric Supercapacitors. Energy Storage Mater. 2019, 22, 384–396. 10.1016/j.ensm.2019.02.014. [DOI] [Google Scholar]
  82. Zhang Y. S.; Lu C.; Hu Y. X.; Zhang B. M.; Li J.; Tian C. Y.; Zhang D. T.; Kong L. B.; Liu M. C. Assemble from 0D to 3D: Anchored 0D Molybdenum Carbide on 3D Octahedral Amorphous Carbon with Excellent Capacitive Properties. J. Mater. Sci. 2020, 55 (32), 15562–15573. 10.1007/s10853-020-05119-y. [DOI] [Google Scholar]
  83. Liu S.; Yin Y.; Hui K. S.; Hui K. N.; Lee S. C.; Jun S. C. High-Performance Flexible Quasi-Solid-State Supercapacitors Realized by Molybdenum Dioxide@Nitrogen-Doped Carbon and Copper Cobalt Sulfide Tubular Nanostructures. Adv. Sci. 2018, 5 (10), 1800733 10.1002/advs.201800733. [DOI] [PMC free article] [PubMed] [Google Scholar]
  84. Xie Y. Synthesis and Electrochemical Performance of an Electroactive Nitrogen-Doping SnO2 Nanoarray Supported on Carbon Fiber. J. Chem. Res. 2021, 45 (7–8), 738–746. 10.1177/1747519821994252. [DOI] [Google Scholar]
  85. Liu S.; Lee S. C.; Patil U.; Shackery I.; Kang S.; Zhang K.; Park J. H.; Chung K. Y.; Chan Jun S. Hierarchical MnCo-Layered Double Hydroxides@Ni(OH)2 Core-Shell Heterostructures as Advanced Electrodes for Supercapacitors. J. Mater. Chem. A 2017, 5 (3), 1043–1049. 10.1039/C6TA07842G. [DOI] [Google Scholar]
  86. Mugheri A. Q.; Tahira A.; Aftab U.; Abro M. I.; Mallah A. B.; Memon G. Z.; Khan H.; Abbasi M. A.; Halepoto I. A.; Chaudhry S. R.; Ibupoto Z. H. An Advanced and Efficient Co3O4/C Nanocomposite for the Oxygen Evolution Reaction in Alkaline Media. RSC Adv. 2019, 9 (59), 34136–34143. 10.1039/C9RA07224A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Li J.; Cui M.; Lai Y.; Zhang Z.; Lu H.; Fang J.; Liu Y. Investigation of Polyaniline Co-Doped with Zn2+ and H+ as the Electrode Material for Electrochemical Supercapacitors. Synth. Met. 2010, 160 (11–12), 1228–1233. 10.1016/j.synthmet.2010.03.014. [DOI] [Google Scholar]
  88. Zhang M.; Liu W.; Liang R.; Tjandra R.; Yu A. Graphene Quantum Dot Induced Tunable Growth of Nanostructured MnCo2O4 Composites for High-Performance Supercapacitors. Sustain. Energy Fuels 2019, 3 (9), 2499–2508. 10.1039/C9SE00341J. [DOI] [Google Scholar]
  89. Lv H.; Yuan Y.; Xu Q.; Liu H.; Wang Y. G.; Xia Y. Carbon Quantum Dots Anchoring MnO2/Graphene Aerogel Exhibits Excellent Performance as Electrode Materials for Supercapacitor. J. Power Sources 2018, 398, 167–174. 10.1016/j.jpowsour.2018.07.059. [DOI] [Google Scholar]
  90. Ghosh K.; Srivastava S. K. Enhanced Supercapacitor Performance and Electromagnetic Interference Shielding Effectiveness of CuS Quantum Dots Grown on Reduced Graphene Oxide Sheets. ACS Omega 2021, 6 (7), 4582–4596. 10.1021/acsomega.0c05034. [DOI] [PMC free article] [PubMed] [Google Scholar]
  91. De B.; Kuila T.; Kim N. H.; Lee J. H. Carbon Dot Stabilized Copper Sulphide Nanoparticles Decorated Graphene Oxide Hydrogel for High Performance Asymmetric Supercapacitor. Carbon N. Y. 2017, 122, 247–257. 10.1016/j.carbon.2017.06.076. [DOI] [Google Scholar]
  92. Prasath A.; Athika M.; Duraisamy E.; Sharma A. S.; Elumalai P. Carbon-Quantum-Dot-Derived Nanostructured MnO2 and Its Symmetrical Supercapacitor Performances. ChemistrySelect. 2018, 3 (30), 8713–8723. 10.1002/slct.201801950. [DOI] [Google Scholar]
  93. Prasath A.; Athika M.; Duraisamy E.; Selva Sharma A.; Sankar Devi V.; Elumalai P. Carbon Quantum Dot-Anchored Bismuth Oxide Composites as Potential Electrode for Lithium-Ion Battery and Supercapacitor Applications. ACS Omega 2019, 4 (3), 4943–4954. 10.1021/acsomega.8b03490. [DOI] [PMC free article] [PubMed] [Google Scholar]
  94. Lv H.; Gao X.; Xu Q.; Liu H.; Wang Y. G.; Xia Y. Carbon Quantum Dot-Induced MnO2 Nanowire Formation and Construction of a Binder-Free Flexible Membrane with Excellent Superhydrophilicity and Enhanced Supercapacitor Performance. ACS Appl. Mater. Interfaces. 2017, 9 (46), 40394–40403. 10.1021/acsami.7b14761. [DOI] [PubMed] [Google Scholar]
  95. Zhu Y.; Ji X.; Pan C.; Sun Q.; Song W.; Fang L.; Chen Q.; Banks C. E. A Carbon Quantum Dot Decorated RuO2 Network: Outstanding Supercapacitances under Ultrafast Charge and Discharge. Energy Environ. Sci. 2013, 6 (12), 3665–3675. 10.1039/c3ee41776j. [DOI] [Google Scholar]
  96. Ashourdan M.; Semnani A.; Hasanpour F.; Moosavifard S. E. Synthesis of CuMnO2/Graphene Quantum Dot Nanocomposites as Novel Electrode Materials for High Performance Supercapacitors. J. Energy Storage 2021, 36, 102449 10.1016/j.est.2021.102449. [DOI] [Google Scholar]
  97. Zhang C.; Xiao J.; Lv X.; Qian L.; Yuan S.; Wang S.; Lei P. Hierarchically Porous Co3O4/C Nanowire Arrays Derived from a Metal-Organic Framework for High Performance Supercapacitors and the Oxygen Evolution Reaction. J. Mater. Chem. A 2016, 4 (42), 16516–16523. 10.1039/C6TA06314D. [DOI] [Google Scholar]
  98. Khan M. A. M.; Khan W.; Ahamed M.; Ahmed J.; Al-Gawati M. A.; Alhazaa A. N. Silver-Decorated Cobalt Ferrite Nanoparticles Anchored onto the Graphene Sheets as Electrode Materials for Electrochemical and Photocatalytic Applications. ACS Omega 2020, 5 (48), 31076–31084. 10.1021/acsomega.0c04191. [DOI] [PMC free article] [PubMed] [Google Scholar]
  99. Wang Q.; Li J.; Tu X.; Liu H.; Shu M.; Si R.; Ferguson C. T. J.; Zhang K. A. I.; Li R. Single Atomically Anchored Cobalt on Carbon Quantum Dots as Efficient Photocatalysts for Visible Light-Promoted Oxidation Reactions. Chem. Mater. 2020, 32 (2), 734–743. 10.1021/acs.chemmater.9b03708. [DOI] [Google Scholar]
  100. Shanmugasundaram E.; Ganesan V.; Narayanan V.; Vellaisamy K.; Rajamohan R.; Lee Y. R.; Kaliyamoorthy S.; Thambusamy S. Heteroatom (Boron, Nitrogen, and Fluorine) Quantum Dot-Doped Polyaniline-Photoactive Film Preparation and Characterization for Organic Solar Cell Applications. New J. Chem. 2023, 47, 13127–13137. 10.1039/D3NJ02435K. [DOI] [Google Scholar]
  101. Peng P.; Chen Z.; Li X.; Wu Y.; Xia Y.; Duan A.; Wang D.; Yang Q. Biomass-Derived Carbon Quantum Dots Modified Bi2MoO6/Bi2S3 Heterojunction for Efficient Photocatalytic Removal of Organic Pollutants and Cr (VI). Sep. Purif. Technol. 2022, 291, 120901 10.1016/j.seppur.2022.120901. [DOI] [Google Scholar]
  102. Yan M.; Wu Y.; Zhu F.; Hua Y.; Shi W. The Fabrication of a Novel Ag3VO4/WO3 Heterojunction with Enhanced Visible Light Efficiency in the Photocatalytic Degradation of TC. Phys. Chem. Chem. Phys. 2016, 18 (4), 3308–3315. 10.1039/C5CP05599G. [DOI] [PubMed] [Google Scholar]
  103. Asaithambi S.; Sakthivel P.; Karuppaiah M.; Yuvakkumar R.; Velauthapillai D.; Ahamad T.; Khan M. A. M.; Mohammed M. K. A.; Vijayaprabhu N.; Ravi G. The Bifunctional Performance Analysis of Synthesized Ce Doped SnO2/g-C3N4 Composites for Asymmetric Supercapacitor and Visible Light Photocatalytic Applications. J. Alloys Compd. 2021, 866, 158807 10.1016/j.jallcom.2021.158807. [DOI] [Google Scholar]
  104. Ayu D. G.; Gea S.; Andriayani N.; Telaumbanua D. J.; Piliang A. F. R.; Harahap M.; Yen Z.; Goei R.; Tok A. I. Y. Photocatalytic Degradation of Methylene Blue Using N-Doped ZnO/Carbon Dot (N-ZnO/CD) Nanocomposites Derived from Organic Soybean. ACS Omega 2023, 8 (17), 14965–14984. 10.1021/acsomega.2c07546. [DOI] [PMC free article] [PubMed] [Google Scholar]
  105. Asaithambi S.; Sakthivel P.; Karuppaiah M.; Balamurugan K.; Yuvakkumar R.; Thambidurai M.; Ravi G. Synthesis and Characterization of Various Transition Metals Doped SnO2@MoS2 Composites for Supercapacitor and Photocatalytic Applications. J. Alloys Compd. 2021, 853, 157060 10.1016/j.jallcom.2020.157060. [DOI] [Google Scholar]

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