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. 2023 Jan 4;8(2):2723–2732. doi: 10.1021/acsomega.2c07364

Synthesis of CuOx/TiO2 Photocatalysts with Enhanced Photocatalytic Performance

Li Li †,*, Xinhong Chen ‡, Xuejun Quan †, Facheng Qiu †, Xingran Zhang †
PMCID: PMC9850735  PMID: 36687026

Abstract

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CuOx/TiO2 co-photocatalysts with various Cu loading contents were synthesized by an impregnation method, and their photocatalytic activities were evaluated by photodegradation of organic pollutants under visible light illumination. The as-prepared CuOx/TiO2 composites exhibited a unique structure, in which CuOx clusters with about 2–3 nm nanocrystals were uniformly distributed on the TiO2 cube. The mesoporous Ti3+/TiO2 substrate with a uniform pore structure greatly improved the uniformity of the loaded Cu, wherein Ti3+ acted as a reducing agent for reducing Cu2+ to Cu+ and Cu0. The reversible process of the Cu species between Cu+ and Cu0 markedly enhanced the photocatalytic activity of the CuOx/TiO2 co-photocatalyst, by promoting the transfer of photogenerated electrons and suppressing the recombination of photogenerated electron and hole pairs. The synergistic effect between CuOx and TiO2 also played an important role in enhancing the photocatalytic activity of the CuOx/TiO2 co-photocatalyst. The results indicated that CuOx/TiO2-1 had the highest photocatalytic efficiency, which was 1.5 times higher than that of the commercial nano-TiO2 P25 under visible light, and demonstrated a good stability even after five recycles. This structural design and the valence control strategy for the Cu atom provide an idea that facilitates the utilization of visible light and the improvement of the photocatalytic activity of TiO2, promoting the practical application of the TiO2 photocatalyst.

1. Introduction

Due to its wide band gap (3.2 eV) and higher recombination of charge carries, in practical applications, pure titanium dioxide (TiO2) has low solar efficiency and quantum efficiency; hence, it is not a good photocatalyst.1−3 In recent years, much effort has been focused on enhancing the photocatalysis efficiency.4,5 One approach is to improve the specific surface area and surface-active site of TiO2 by changing its crystal size, exposure crystal plane, and surface morphology, which is conducive to the transfer and diffusion of reactants and products.6−8 Another approach is to dope various transition metal cations, non-metal elements, or other semiconductor materials, which results in the light response changing from UV irradiation to visible light.9,10 The doped metal cations can act as efficient electron traps based on the charge transfer mechanism, inhibiting the photoelectron–hole pair recombination and improving the photoluminescence quantum yields.11−14 In particular, doping noble metal nanoparticles can improve the photocatalytic activity of TiO2 efficiently owing to its excellent resistance of oxidation, the surface plasmon resonance (SPR) effect will be generated on the surface of noble metal nanoparticles, and the effective transport of electrons from the metal particles to the TiO2 conduction band will be promoted. Therefore, immense efforts have been devoted to studying both theoretically and experimentally the photoactivity of TiO2 by doping noble metals.

Compared with Au, Pt, Pd, Rh, Ru, Ag, and other precious metals, the transition metal Cu is suitable for large-scale commercial applications owing to its cost effectiveness.15−19 Since the ionic radius of Cu2+ (0.073 nm) is close to that of Ti4+ (0.068 nm), the loaded Cu can enter the TiO2 matrix by occupying the position of the Ti atom.20−23 When the TiO2 surface is loaded with copper, it will introduce the d intermediate state to form an intermediate energy level, which functions as “charge carrier traps” and broadens the spectrum response range.24,25 It is beneficial to improve the separation efficiency of the photogenerated electron–hole pairs. Docao et al.21 synthesized Cu-loaded TiO2 by a wet impregnation method using copper acetate monohydrate as a precursor. Under AM 1.5 sunlight irradiation, Cu/TiO2 can effectively split water vapor to produce H2 and O2, which is an important method to convert solar energy into chemical energy. Lee et al.20 synthesized a site-specific single-atom Cu/TiO2 photocatalyst by a hard template method. Through an atomic-level design and synthesis strategy, the Cu/TiO2 catalyst showed a reversible and cooperative photoactivation process, with reversible photoelectric performance and enhanced photocatalytic hydrogen production activity. In addition, copper is an excellent antibacterial agent. Doping Cu into the TiO2 matrix has dual advantages; it not only can reduce the recombination of electron–hole pairs but also can realize antibacterial and antiviral functions, which promote the application of TiO2 composite materials in photocatalysis, biomedicine, and antibacterial coatings.25

From the perspective of green chemistry that focuses on the synthesis of an environmentally friendly photocatalyst, a cooperative photoactivation process for enhancing the photocatalysis performance is imperatively demanded. To date, a variety of high-performance visible light catalysts have been synthesized through combining element loading and special configurations (mesoporous, hollow, oxygen vacancies) together, to realize a cooperative photoactivation process, and applied in photocatalysis, biocatalysis, and new energy storage.26−29 Park et al.30 synthesized a CuxO–TiO2 photocatalyst in a simple way, which showed high CO2 photoreduction efficiency due to the mesoporous p-type/n-type heterojunction structure. In addition, porous materials have a large specific surface area and uniform pore structure, which are conducive to the diffusion of the metal precursor solution and uniform loading at the molecular level. Li et al.31 reported a sol–gel method to synthesize a mesoporous silica-supported Cu/TiO2 co-catalyst, which had a high surface area (300 m2·g–1) and exhibited enhanced CO2 photoreduction ability, and the quantum yield reached 1.41%. Although the metal was not loaded on the mesoporous TiO2 with a defective structure, this approach could offer potential advantages compared with the pure TiO2-loaded metal co-catalyst.

In this paper, we used Ti3+/TiO2 powder synthesized earlier as the substrate to synthesize CuOx/TiO2 by an impregnation method. The CuOx/TiO2 had a special configuration that offers several advantages for photocatalytic application owing to its defective structure. In the process of loading CuOx, the uniform pore structure and high specific surface area of mesoporous Ti3+/TiO2 particles are conducive to the uniform loading of Cu2+, and Ti3+ is used as a reducing agent to reduce Cu2+ to Cu+ partially. With these unique configurations, CuOx/TiO2 can be expected to be a more effective alternative to remove organic pollutants in aqueous solution, such as rhodamine B.

2. Experimental Section

2.1. Materials

Titanium sulfate (Ti(SO4)2) and oxalic acid (H2C2O4) were obtained from Sinopharm Chemical Regent Co., Ltd. (Shanghai, China). Copper nitrate (Cu(NO3)2·2H2O), copper sulfate (CuSO4·5H2O), copper acetate monohydrate (Cu(CH3COO)2·H2O), and rhodamine B (RhB) were all obtained from Chengdu Ke Long Regent Co., Ltd. (Chengdu, China). Nano-TiO2 (P25) was obtained from Degussa (75% anatase and 25% rutile). They were all used directly without any further treatment. The water used in the experiments was double-distilled water.

2.2. Synthesis

According to the hydrothermal method reported by the research group,32 Ti3+ self-doped TiO2 was synthesized using Ti(SO4)2 as a precursor and oxalic acid as a reducing agent. CuOx/TiO2 was prepared by the wet impregnation method. A total of 0.2 g of Ti3+/TiO2 powder was dispersed in 20 mL of H2O and ultrasonically treated for 20 min. Then, a certain amount of copper nitrate (the mole ratio of the amount of Cu to TiO2 ranging from 0.5, 1.0, and 2.0 to 3.0%) was added and stirred in a water bath kept at 90 °C for 2 h. The obtained solution was dried at 80 °C for 12 h and then calcined at 400 °C for 4 h under an air atmosphere. The samples obtained under different conditions are denoted as CuOx/TiO2-N, where N refers to the mole ratio of the amount of Cu to TiO2.

2.3. Characterization

The XRD pattern was recorded using an X-ray diffractometer (EMPYREAN, Panalytical) with Cu Kα radiation. The morphology and crystal size of the sample were characterized by transmission electron microscopy (TEM, Talos F200S, Thermo Fisher). The crystal phase was measured by Raman spectroscopy (LabRAM HR Evolution, HORIBA Jobin Yvon S.A.S.) with an Ar ion laser source. The UV–vis diffuse reflection spectra were obtained with BaSO4 as a reference using ultraviolet–visible light (UV–vis) spectroscopy (TU-1901, PERSEE). The specific surface area and porous structure of the products were evaluated using nitrogen adsorption–desorption measurements (equipment: 3S-2000PSI, BeiShiDe). The X-ray photoelectron spectroscopy (XPS) analysis was carried out using an X-ray photoelectron spectrometer (ESCALAB 250Xi, Thermo Fisher) equipped with monochromatized Al Kα radiation. The binding energy was calibrated using C 1s (284.8 eV) a as reference. Photoluminescence (PL) emission spectra were recorded using a fluorescence spectrophotometer (XRF-1800, SHIMADZU) with a laser excitation at 300 nm (450 W xenon lamp).

2.4. Measurement of Photocatalytic Activity

The photocatalytic activity of the products was evaluated by the photodegradation of RhB in solution under 300 W xenon lamp (Sirius300PU, λ > 420 nm) irradiation with a UV-cut filter. Typically, a 50 mg CuOx/TiO2 sample was suspended in 100 mL of RhB solution (2 × 10–5 mol L–1) and then stirred for 30 min to achieve the adsorption–desorption equilibrium in the dark. The distance between the lamp and the surface of the liquid was 15 cm. At the defined time, solutions of about 5 mL were taken out and centrifuged to remove the particles. Finally, the concentration of RhB was monitored using an UV–vis spectrophotometer at 554 nm.

3. Results and Discussion

Figure 1 shows the XRD patterns of unloaded and loaded TiO2 samples with different amounts of copper. All the diffraction peaks can be well indexed to the anatase phase of TiO2 (JCPDS 21-1272). The diffraction peaks around 2θ = 25.3, 37.7, 48.0, 53.9, and 55.0° can be indexed to the (101), (004), (200), (105), and (211) planes of the anatase titania, respectively.33,34 This indicates that the loading of copper does not affect the phase of TiO2, regardless of the amount of the loaded CuOx. No characteristic diffraction peaks related to CuOx and other impurities were observed. This may be because the content of CuOx was low and CuOx was highly dispersed in TiO2 particles, and the loaded Cu ions were imbedded into the TiO2 matrix by occupying the position of Ti atoms.21 The amplifying diffraction patterns in the 2θ range between 35 and 50° are shown in Figure 1b. It is observed that after loading CuOx, the diffraction peak intensity of the (004) crystal plane of TiO2 decreases significantly. The possible reason is that CuOx anchored in the pore channel could change the X-ray scattering contrast between the pore channels and the walls of mesoporous CuOx/TiO2.34 The average crystal sizes and cell parameters (a, b, c) of the samples before and after loading were calculated using Scherrer’s formula, as shown in Table 1. The results demonstrate that the cell volume of TiO2 increases after loading CuOx, especially along the c-axis direction. This is because the radius of Cu2+ is larger than that of Ti4+, and then, the crystal size increases after Cu2+ enters the TiO2 matrix.

Figure 1.

Figure 1

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(a, b) XRD patterns of the CuOx/TiO2 samples.

Table 1. Physical Properties of the CuOx/TiO2 Sample.

samples crystal size(nm) a, b (Å) c (Å) band gap (eV)
CuOx/TiO2-0 41.1 3.7865 9.4993 2.92
CuOx/TiO2-0.5 41.7 3.7884 9.5009 2.90
CuOx/TiO2-1 47.4 3.7877 9.5022 2.88
CuOx/TiO2-2 48.9 3.7875 9.5045 2.87
CuOx/TiO2-3 45.3 3.7891 9.5069 2.84
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Furthermore, the Raman spectra were analyzed for the samples to study the crystal structure characteristics. As shown in Figure 2, all samples exhibit five Raman active modes located at 141, 197, 394, 516, and 636 cm–1 that are identified as anatase peaks, which were consistent well with the XRD results.35 Among them, the Eg peaks at 141, 197, and 636 cm–1 correspond to the stretching vibration of O–Ti–O, the B1g peak at 394 cm–1 corresponds to the bending vibration of O–Ti–O, and the A1g peak at 516 cm–1 corresponds to the antisymmetric bending vibration of O–Ti–O.36,37 It is worth noting that there are two peaks shifting from 141 and 194 cm–1 to 144 and 197 cm–1, respectively, with increasing concentration of Cu.25 These blue shifts in the peak position indicate that there is an adjustment in the cell size of the CuOx/TiO2 sample.

Figure 2.

Figure 2

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Raman scattering spectra of the CuOx/TiO2 samples.

The UV–vis diffuse reflectance spectra show a significant difference before and after loading copper samples. As shown in Figure 3a, the spectrum of the CuOx/TiO2-0 sample without the Cu loading contains only one absorption peak at ca. 410 nm, which corresponds to the band-to-band transition of anatase TiO2. The Cu-loaded TiO2 samples exhibit a shoulder peak at ∼450 nm except the absorption peak near 410 nm compared to the CuOx/TiO2-0 sample. This shoulder peak is attributed to the existence of Cu, which induces electron transfer from the valence band (VB) of TiO2 to the Cu atom. The broad band at 700–800 nm corresponds to the d–d transition of Cu.38 According to the absorption spectrum data, the band gaps of all samples were calculated, and the results are shown in Table 1. It can be seen that the band gap of the CuOx/TiO2 sample decreases with increasing amount of the Cu loading. This is helpful for the utilization of solar light.

Figure 3.

Figure 3

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(a) UV–vis diffuse reflection spectra and (b) PL spectra of the CuOx/TiO2 samples.

In addition, the photoluminescence spectra were characterized to understand the impact of the Cu loading on the efficiency of transfer and separation of electrons and holes. As shown in Figure 3b, there are two emission bands in all spectra. The peaks at around 460 nm in the PL spectra are attributed to the band–band radiation transition, and the peaks at about 520–530 nm are mainly derived from the excitation PL phenomenon.39,40 The loaded copper has an important effect on the PL intensity of the samples. Once copper is loaded on the Ti3+/TiO2 sample, the emission intensity of the PL spectra decreases significantly. It is clear that CuOx/TiO2-1 has the weakest PL intensity, indicating that it possesses the highest photocharge separation efficiency and the lowest carrier recombination rate.20 The main reason is that TiO2 generates photogenerated electrons and holes under photoexcitation. After being loaded with Cu, there is indeed a transfer of electrons from TiO2 to Cu, preventing the recombination of photogenerated electrons and holes. BET analyses did not evince any significant changes of the CuOx/TiO2 co-photocatalyst with respect to the unloaded Cu sample. All the adsorption–desorption curves can be categorized as IUPAC type III, with the BET surface area ranging between 31and 34 m2·g–1. All samples showed the characteristics of a mesoporous structure, which is conducive to the adsorption and removal of organic pollutants and makes the photocatalytic reaction easier.

To investigate the valence state of Cu and Ti elements throughout the co-photocatalyst, the CuOx/TiO2 samples were characterized by XPS. The survey spectra (Figure 4a) exhibit the characteristic peaks of Cu 2p, Ti 2p, and O 1s, indicating that the Cu element is successfully loaded onto the sample surface. As shown in Figure 4b, the Ti 2p spectra of the samples show two typical peaks located at 458.67 and 464.50 eV, which are assigned to the binding energies of Ti4+ 2p3/2 and Ti4+ 2p1/2, respectively.15,41,42Figure 4c–f shows the XPS spectra of Cu 2p. The spectrum of the CuOx/TiO2-0.5 sample shows mangy burrs, due to the high background noise caused by the low content of Cu. When the content of Cu is greater than 1%, two characteristic peaks are shown at 951.94 and 932.37 eV, corresponding to the electron binding energies of Cu 2p1/2 and Cu 2p3/4 of Cu0 and Cu+, respectively, and weak satellite peaks of Cu+ are also observed at 940–945 eV.31,43−45 Because CuOx/TiO2 was synthesized using Ti3+/TiO2 as a raw material, Ti3+ with strong reducibility would reduce Cu2+ to Cu+ or Cu0. However, it should be noted that no binding energy peaks of Cu2+ near 935 and 955 eV are observed in all the samples, indicating that the Cu species on the samples exist in the form of Cu2O or Cu rather than as CuO.46

Figure 4.

Figure 4

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XPS spectra of the CuOx/TiO2 samples and (a) full-range XPS spectra, (b) Ti 2p and (c–f) Cu 2p.

The phase structure of the typical sample CuOx/TiO2-0.5 was investigated by low- and high-resolution TEM, as shown in Figure 5. The TEM images exhibit a cubic structure with a length of about 50 nm and homogeneous mesoporous structure. The HRTEM images show clearly uniform lattices, which confirm that the sample is highly crystallized. In summary, the morphology and crystal structure of the Ti3+/TiO2 cube were not changed after Cu loading.32 To further validate the existence and the content of the loaded Cu on the Ti3+/TiO2 particles, the samples, CuOx/TiO2-N (N = 0.5, 1, 2, 3), were analyzed by EDS (Figure S2 and Table S1), which is a chemical microanalysis technique used together with TEM. When Cu is loaded at less than 1%, the samples CuOx/TiO2-0.5 and CuOx/TiO2-1 show a homogeneous dispersion of very weak Cu species (Figure 6a,b). With increasing loading content, the CuOx/TiO2-2 sample shows a small number of aggregated Cu species (Figure 6c), and the aggregation is more obvious in the CuOx/TiO2-3 sample (Figure 6d). It assigns these well-dispersed Cu species as CuOx clusters consisting of about 2–3 nm nanocrystals. It has been reported that CuOx clusters are attached to the surface of TiO2 through the combination of O atoms and unsaturated 5C-Ti atoms.22

Figure 5.

Figure 5

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(a, b) TEM and (c, d) HRTEM images of the CuOx/TiO2-0.5 sample.

Figure 6.

Figure 6

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EDS mapping of the CuOx/TiO2 samples, (a) CuOx/TiO2-0.5; (b) CuOx/TiO2-1; (c) CuOx/TiO2-2; and (d) CuOx/TiO2-3.

The full spectral light and visible light photocatalytic activities of the co-photocatalysts were evaluated by RhB degradation to explore the effect of the Cu loading. For comparison, commercial nano-TiO2 (P25) was also tested under the same conditions. Figure 7a,b shows the photodegradation activities versus Cu loading quantity under full spectral light irradiation. It can be seen that the loaded Cu has a great influence on the photocatalytic activities of the co-photocatalyst. The sample CuOx/TiO2-1 demonstrates strong photocatalytic activity with a RhB degradation rate of 99% after 20 min, which is similar to that of P25. The photodegradation constants within the first 20 min were calculated, in the following order: P25 (K = 0.391 min–1) > CuOx/TiO2-1 (K = 0.283 min–1) > CuOx/TiO2-0.5 (K = 0.264 min–1) > CuOx/TiO2-2 (K = 0.041 min–1) > CuOx/TiO2-3 (K = 0.040 min–1). It can be seen from Figure 7e that with the increase of the photodegradation reaction time, the absorption peak of RhB aqueous solution blue-shifts gradually from 554 to 532 nm. At the same time, the color of the reaction suspension gradually changes from red to light pink and finally becomes transparent. This is because the conjugated structure of RhB was destroyed to form N,N,N triethyl rhodamine (TER) with the absorption peak at 532 nm.47

Figure 7.

Figure 7

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(a, b) Photocatalytic activities and reaction rate constant of the CuOx/TiO2 samples for the RhB degradation(under full spectral light); (c, d) photocatalytic activities and reaction rate constant of the CuOx/TiO2 samples for the RhB degradation (under visible light); and (e) UV–vis spectrum changes of RhB over CuOx/TiO2-1 (under full spectral light) and (f) under visible light.

The photocatalytic activities of the samples under visible light exhibit a increase first followed by a decline with increasing amounts of the Cu loading, and the optimum amount of Cu loading is 1.0%, as shown in Figure 7c,d. Different from the results under full spectral light irradiation, the photodegradation performance of CuOx/TiO2-1 is higher than that of P25, and its apparent reaction rate constant is 1.5 times greater than that of P25. The results of these comparative experiments indicate that the spectral response range of Cu-loaded TiO2 is widened, which leads to the enhanced photocatalytic activity. However, there is an optimal Cu loading amount, and when the loading amount is less than the optimal value, the Cu species can trap electrons to inhibit the photogenerated electron–hole recombination, and then, the catalytic activity increases with the increase in the loading amount of Cu. On the contrary, the high concentration of CuOx species may cover the light irradiation on the TiO2 surface and can also act as recombination centers of photogenerated electron–hole pairs.31 Furthermore, to understand the reusable nature of the co-photocatalyst, repeating experiments were carried out on CuOx/TiO2-1. As shown in Figure 8a,b, the CuOx/TiO2-1 exhibited excellent stability both under the full spectral and UV light irradiation during five continuous cycles. The main reason is that the organic dye material adsorbed on the surface of the sample falls off after repeated washing.48

Figure 8.

Figure 8

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(a) Repetitive test curves of CuOx/TiO2-1 under full spectral light and (b) repetitive test curves of CuOx/TiO2-1 under visible light.

The effects of different copper precursors and the TiO2 substrate on the photocatalytic activity were also discussed (Figures S3 and S4). The results show that the sample synthesized using Cu(NO3)2 exhibited the highest photocatalytic activity under both visible light irradiation and full spectral light irradiation. Especially under visible light, the photodegradation rate constants of the sample synthesized using Cu(NO3)2 (K = 0.012 min–1) are 7.5 and 6.7 times those of the sample synthesized using Cu(OAc)2 (K = 0.0016 min–1) and CuSO4 (K = 0.0018 min–1), respectively. As shown in Figure S3c, characteristic peaks at 934.24 and 954.58 eV, corresponding to the electron binding energies of Cu2+ 2p3/2 and Cu2+ 2p1/2, respectively, and a satellite peak at 943.33 eV are observed, indicating that the Cu species on the sample synthesized using P25 exist in the form of CuO. The photodegradation activity of the sample (P25 + Cu(NO3)2) synthesized using P25 is lower than that of the sample synthesized using Ti3+/TiO2 under visible light irradiation (Figure S4c,d). These results further confirm the beneficial effect of the valence state of Cu species on charge transfer in photocatalytic processes.

To further investigate the photodegradation mechanism, capture experiments of the active substances were carried out on CuOx/TiO2-1. As shown in Figure 9, after adding IPA and EDTA-2Na, the photodegradation rate of RhB decreased sharply, while that of AgNO3 was moderate. During photocatalysis, EDTA-2Na and IPA act as a hole-trapping agent and a hydroxyl scavenger, respectively, and AgNO3 is used as an electron-trapping agent.49,50 The result indicates that holes and hydroxyl radicals play major roles and electrons play a supplementary role in photocatalysis. Loading Cu could produce the d-orbital underneath the CB of TiO2 and as a result could enhance the visible light response. On the other hand, the CuOx clusters on the surface of the CuOx/TiO2 co-photocatalyst exhibit high reversibility between Cu+ and Cu0, which can promote the electron migration greatly. This can prevent the recombination of the photogenerated electron–hole pairs and thus efficiently prolong the hole life.34 The photogenerated holes that have strong oxidability can react with the adsorbed H2O to form hydroxyl radicals (•OH), and the photogenerated electrons are trapped by O2 to form reactive oxygen species (•O2). These crucial reactive species destroy the molecular structure of RhB, oxidizing it into CO2 and H2O.

Figure 9.

Figure 9

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Photocatalytic activity of CuOx/TiO2-1 after adding different trapping agents.

4. Conclusions

CuOx/TiO2 co-photocatalysts were synthesized using a mesoporous Ti3+/TiO2 cube as a substrate by an impregnation method, in which CuOx clusters with 2–3 nm nanocrystals were loaded uniformly on the TiO2 cube. They exhibited excellent photodegradation performance toward RhB under visible light illumination. Among all samples, CuOx/TiO2-1 exhibited the highest photodegradation efficiency, which was 1.5 times higher than that of the commercial nano-TiO2 P25. During the co-photocatalyst synthesis process, the uniform mesoporous structure of the substrate greatly improved the uniformity of the loaded Cu, and the valence state of the loaded Cu atoms was changed by the Ti3+ defects in the Ti3+/TiO2 substrate. This valence change promoted photogenerated electron transfer from the TiO2 CB to the CuOx species. Furthermore, it demonstrated that the synergistic effect between the CuOx species and TiO2 was also the reason for enhancement of the photocatalytic activity of the co-photocatalyst. Therefore, the cooperative interaction between the loaded metal and the oxygen defects should not be overlooked in the design of heterogeneous catalyst structures.

Acknowledgments

The authors gratefully acknowledge the support of the Scientific Research Foundation of Chongqing University of Technology (0115220003) and the Science and Technology Research Program of Chongqing Municipal Education Commission (KJQN202201118).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c07364.

  • N2 adsorption–desorption isotherms and the corresponding pore size distribution of the CuOx/TiO2 samples, EDS spectrum and the mass ratio of different elements of the CuOx/TiO2 samples, Cu 2p XPS spectra of the samples synthesized with different precursors, and photocatalytic activities and reaction rate constant of the samples synthesized with different precursors for the RhB degradation (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao2c07364_si_001.pdf (384.6KB, pdf)

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