Skip to main content
NCBI home page
RSC Advances logoLink to RSC Advances
. 2022 Apr 5;12(17):10401–10408. doi: 10.1039/d2ra01067d

A facile chemical synthesis of nanoflake NiS2 layers and their photocatalytic activity

Mohammed M Gomaa 1,✉, Mohamed H Sayed 1,2, Mahmoud S Abdel-Wahed 3, Mostafa Boshta 1
PMCID: PMC8981175  PMID: 35425001

Abstract

A single-phase and crystalline NiS2 nanoflake layer was produced by a facile and novel approach consisting of a two-step growth process. First, a Ni(OH)2 layer was synthesized by a chemical bath deposition approach using a nickel precursor and ammonia as the starting solution. In a second step, the obtained Ni(OH)2 layer was transformed into a NiS2 layer by a sulfurization process at 450 °C for 1 h. The XRD analysis showed a single-phase NiS2 layer with no additional peaks related to any secondary phases. Raman and X-ray photoelectron spectroscopy further confirmed the formation of a single-phase NiS2 layer. SEM revealed that the NiS2 layer consisted of overlapping nanoflakes. The optical bandgap of the NiS2 layer was evaluated with the Kubelka–Munk function from the diffuse reflectance spectrum (DRS) and was estimated to be around 1.19 eV, making NiS2 suitable for the photodegradation of organic pollutants under solar light. The NiS2 nanoflake layer showed photocatalytic activity for the degradation of phenol under solar irradiation at natural pH 6. The NiS2 nanoflake layer exhibited good solar light photocatalytic activity in the photodegradation of phenol as a model organic pollutant.

A single phase nanoflake NiS2 layer synthesized by a facile chemical bath deposition showed good solar light photocatalytic degradation of phenol with good stability and reusability.graphic file with name d2ra01067d-ga.jpg

Introduction

In the last decades, nanostructured transition metal sulfides (NTMSs) have received considerable attention in different fields because of their unique optical, magnetic and catalytic properties.1–3 The properties of these materials are strongly dependent on the dimension, size, and morphologies of fabricated materials,4–6 making these materials very promising for numerous advanced applications such as adsorbents for dye removal,7 supercapacitors,8 rechargeable lithium-ion batteries,9 hydrodesulfurization catalysts,10 hydrogen evolution reaction,4,11,12 and catalysts in the degradation of organic dyes.13

Metal sulfide materials such as zinc sulfide,14 manganese sulfide,15 silver sulfide,16 iron sulfide,17 molybdenum sulfide,18 nickel sulfide,12 and copper sulfides, have been reported and studied extensively.19 Among the metal sulfides, nickel sulfides are more favorable in terms of earth-abundant resources, forming numerous phases such as NiS, NiS2, Ni3S2, Ni3S4, Ni7S6, and Ni9S8, which are suitable as alternative materials for different applications.20–23 Nickel disulfide (NiS2) crystallizes in a pyrite-like structure (FeS2), with a cubic phase Pa3̄ symmetry.10,24,25 Nanostructured pyrite NiS2 with a cubic structure has interesting optical, electronic, and magnetic properties.3,10,26 NiS2 nanostructures with controlled morphology such as nanoparticles, nanowires, nanosheets and hollow microspheres,27–29 have been considered as promising semiconducting materials for catalytic applications due to their low-cost, nontoxicity and chemical stability.30,31 However, the catalytic performance of NiS2 in the degradation of organic pollutants such as endocrine disrupting compounds (EDCs) is still less competitive compared to other catalytic materials based on phosphides and noble metals.4,13 In this regard, numerous techniques have been used to develop and fabricate nickel sulfide nanostructures with good physical and chemical properties including hydrothermal methods,23,32,33 solvothermal,34 decomposition of single-source precursors,35 microwave-assisted synthesis,36,37 solventless route in air,38 sonochemical,39 and ultrasonic spray pyrolysis.10 Most of these methods are suitable for preparing nickel sulfides in powder form with other different phases sometimes accompanying.22,29,38 The different possible phases of nickel sulfide make the synthesis of single-phase nickel disulfide very complicated.20,29,34 Therefore, the demand for an alternative approach to prepare a single phase of nickel disulfide layers with a high specific area and uniform morphology is still a major challenge, and will open doors to various opportunities for advanced applications.

Endocrine disrupting compounds (EDCs) such as phenol and its derivatives are a category of dangerous persistent organic pollutants, which are usually present in low concentrations in water environments. Phenol molecules are considered very harmful to human health, marine creatures and living organisms due to their carcinogenic, mutagenic, stability, and bioaccumulation nature, even in low concentrations. Phenolic compounds are discharged to ecology through effluent from many industries for instance, paint production, processing of petroleum, tanning, and pharmaceuticals.40–42 The conventional treatment is not very effective for the removal of these hazardous pollutants. Thus, the development of novel techniques is essential to address this issue. Morphological control is one of the effective approaches for promoting the photodegradation of phenol using NiS2 with nanoflake morphology. One of the big problems in the photocatalyst process is separation and recovery restriction of the photocatalyst from effluent after the treatment process. Therefore, herein, this problem is overcome through immobilizing prepared nickel sulfide on a glass substrate as layers.

In this study, single-phase NiS2 nanoflake layers were successfully processed via a facile two-step fabrication process. First, Ni(OH)2 nanoflake layers were grown on glass substrates by the chemical bath deposition method, followed by the phase transformation of Ni(OH)2 into NiS2via a sulfurization process. Structural, morphological and optical properties as well as the catalytic activity of the obtained NiS2 layer were studied. The unique nanoflake-like morphology of NiS2 serves as an efficient photocatalyst for the degradation of destructive organic pollutants (phenol as the model organic compound).

Experimental

NiS2 layers deposition

First, the chemical bath deposition (CBD) approach was used for the synthesis of the nanoflake-structured nickel hydroxide layer. The glass substrates were ultrasonically cleaned using acetone and ethyl alcohol for 20 min followed by distilled water, then dried with nitrogen gas, prior to loading into the reaction bath. 0.1 M aqueous solution of nickel chloride (NiCl2·6H2O – Sigma Aldrich) and ammonia solution were used as the source of Ni2+ and complexing agent for layer deposition, respectively. In a typical experimental procedure, the ammonia solution was added drop wise into the nickel chloride solution under continuous magnetic stirring to produce a clear and homogeneous aqueous solution as the starting solution. The precleaned glass substrates were vertically immersed in the solution bath at optimum deposition temperature, (Td = 50 °C) and pH 11 during the synthesis process. After 2 h, the blue-colored solution changed to a greenish white color with the formation of Ni(OH)2 layer on the surface of the substrate by the adsorption and nucleation of the nickel cations on the substrate. The as-deposited Ni(OH)2 layers were transferred into a tube furnace with excessive sulfur powder and subsequently sulfurized at 450 °C for 1 h in nitrogen atmosphere to obtain a nickel sulfide layer.43,44 For the ease of understanding, the facile CBD and synthesis process for the nanoflake structured NiS2 layer is schematically described in Fig. 1.

Fig. 1. Schematic description of the synthesis of porous NiS2 nanoflake layers.

Fig. 1

Open in a new tab

The formation mechanism of the nanoflake-structured nickel disulfide layer is divided into two processes: first, the formation of a nickel hydroxide phase via the chemical bath deposition route, as indicated by the following equations:

Ni2+ + 2OH− → Ni(OH)2↓ 1
Ni(OH)2 + 4NH3 → [Ni(NH3)]4+ + 2OH− 2
[Ni(NH3)]4+ + 2OH− → Ni(OH)2↓ + 4NH3↑ 3

The detailed mechanism of the formation of nickel hydroxide by chemical bath deposition (CBD) can be found elsewhere.45,46

Second, the transformation of as deposited Ni(OH)2 layers to nickel disulfide2 due to reaction of Ni(OH)2 with sulfur atoms at 450 °C according to the following reactions:

Ni(OH)2 + S ↔ NiS + 2OH− 4
NiS + S → NiS2 5

Characterization of prepared immobilized NiS2

In this study, the structural investigation and phase identification of the as-prepared NiS2 layer was analyzed by X-ray powder diffraction (XRD) with a Panalytical X'Pert diffractometer using Cu Kα1 radiation at 45 kV and 40 mA. Scanning electron microscopy (SEM) (QUANTA FEG250) was used for the surface morphology imaging of the obtained layers. X-ray photoelectron spectroscopy (XPS) was collected on K-Alpha (Themo Fisher Scientific, USA) with monochromatic X-ray Al K-alpha radiation at pressure 10−9 mbar to determine the elemental composition and electronic states of the NiS2 layer. Raman analysis was performed on a confocal Raman microscope model WITec Alpha 300 RA under the laser excitation of 532 nm. Diffuse reflectance spectra were carried out using a UV/Vis/NIR spectrophotometer (Jasco V770) in the wavelength range 250–1000 nm.

Evaluation of the photocatalytic performance of the as-prepared immobilized NiS2 layer

The photocatalytic performance of the as-prepared NiS2 layer was established by photodegradation of phenol as a model organic pollutant. For this purpose, the NiS2 slide is primarily fixed by a silicon adhesive on a 2 cm-height edge inside a 150 mL beaker. After that, 90 mL of 10 mg L−1 phenol solution was placed in dark and stirred by a magnetic stirrer for 30 min to achieve adsorption desorption equilibrium. The beaker was irradiated vertically in a solar system (UVA CUBE 400, Dr Hönle AG UV Technology, Germany) equipped with a halogen lamp (model: SOL 500), which is simulated to the natural sunlight (1000 W m−2). At definite time intervals, a 1 mL sample was withdrawn from the beaker and 1 mL double distilled water was inserted instead to keep the distance between the light source and meniscus of solution constant all over the experiment duration. Phenol concentration in the withdrawn samples was determined by a high-performance liquid chromatograph (HPLC, Agilent 1260, USA) equipped with an analytical column Zorbax reverse-phase C18 and a diode-array detector at 280 nm wavelength. Each point was measured in triplet and the average was recorded. The column temperature was kept at 25 °C during the analysis. Gradient elution was obtained using water (mobile phase A) and acetonitrile (mobile phase B). 75% A mobile phase was eluted for 1 min, and then decreased to 60% A for 2 min. The flow rate of the mobile phase was kept at 0.5 mL min−1. The generation of redox reactive species by NiS2 after solar irradiation excitation was inspected by 1 mmol ammonium oxalate (AO) as the hole (h+) scavenger agent, 1 mmol para-benzoquinon (p-BQ) as the superoxide radical (O2˙−) scavenger and 1 mmol isopropyl alcohol (IPA) as the hydroxyl radical (˙OH) scavenger.

Results and discussion

Structural and elemental composition properties

The XRD and Raman data for the as-prepared NiS2 layer are presented in Fig. 2. The XRD pattern of the NiS2 layer (Fig. 2(a)) show sharp and dominant characteristic peaks of the NiS2 cubic structure (JCPDS card no. 00-011-0099),45 with no additional peaks related to any other crystalline nickel compounds such as nickel oxide, nickel hydroxide and other phases of nickel sulfides, indicating the complete transformation of the Ni(OH)2 phase to NiS2 phase.47–49 The XRD analysis well matched with reported studies in literature.28,30,31,50 The average crystallite size (D) of the NiS2 layer was calculated using the Scherrer–Debye formula (eqn (6)) for the (200) reflection plane.

graphic file with name d2ra01067d-t1.jpg 6

where K is the Debye constant, λ is the X-ray wavelength, β is the line broadening at full width at half maximum of the diffraction peak, and θ is the Bragg's angle.51 The calculated crystallite size of the NiS2 layers was approximately 26 nm.

Fig. 2. (a) XRD pattern and (b) Raman spectrum of nanoflake NiS2 layer.

Fig. 2

Open in a new tab

The surface Raman spectrum measured at room temperature of the NiS2 layer (Fig. 2(b)) shows the dominant characteristic peaks of the NiS2 phase.20 The peaks at 279 and 476 cm−1 are assigned to Eg and Ag photons, respectively. The observed peaks shifted towards a lower frequency compared with the NiS2 single crystal. The obtained spectrum shows no noticeable characteristic peaks related to possible secondary phases and is consistent with previous reports.11,28

In order to study the elemental compositions and electronic states of the nanoflake NiS2 layer, X-ray photoelectron spectroscopy (XPS) measurements were performed in this study. Fig. 3(a) presents the high-resolution XPS spectrum of Ni 2p for the nanostructured NiS2 layer, which has two main peaks appearing at 854.12 and 871.63 eV, fitting to the binding energy of Ni 2p3/2 and Ni 2p1/2, respectively. In addition, both Ni 2p3/2 and Ni 2p1/2 have shake-up satellite peaks located at 860.1 eV and 875.59 eV, respectively. Peak fitting analysis to separate overlapping peaks was made for the Ni 2p3/2 component, which indicates that it can be de-convoluted into a pair of peaks located at 854.12 and 856.05 eV, corresponding to Ni2+ and Ni3+ in NiS2, respectively. The existence of Ni3+ results from the surface oxidation of NiS2, which is in agreement with literature. The collected XPS results of the deconvolution of Ni 2p are in agreement with the reported binding energy values for Ni2+ and Ni3+.4,36 In addition, the spectral deconvolution of the S 2p spectrum (Fig. 3(b)) consists of two strong peaks at 162.91 (S 2p3/2) and 164.38 eV (S 2p1/2), implying the presence of unsaturated S atoms on the Ni–S and S–S bonds in NiS2. These results fit well with NiS2 single crystal XPS data.22,29,52

Fig. 3. XPS spectra of nanoflake NiS2 layers: (a) Ni 2p and (b) S 2p.

Fig. 3

Open in a new tab

Morphological properties

The morphology of the NiS2 layer was investigated by SEM. Fig. 4(a–d) shows the SEM images of the surface with different magnification, and cross section of the NiS2 layer, synthesized on the glass substrate. The top view images of the as-prepared NiS2 layer show that the surface of the NiS2 sample reveals a rough nanoflake-like structure, with homogeneous and uniform distribution as well as a pinhole free layer. Moreover, the magnified view images show that the cross-linked nanoflakes are compact and uniform, resulting in a network architecture on the substrates. Also, the rough nanoflake edges observed clearly in Fig. 4(c) can be associated with the sulfurization process of the as-deposited Ni(OH)2 layer as a result of gas release and dehydration during annealing, leading to the formation of NiS2 with a high surface area structure.44 The high surface area and rough morphology can significantly influence the photocatalytic performance of materials.20,28 A cross-sectional image (Fig. 4(d)) exhibits that the NiS2 layer has a uniform thickness in the range of approximately 950 nm.

Fig. 4. (a–c) SEM images of NiS2 with different magnifications, and (d) cross section of the NiS2 layer.

Fig. 4

Open in a new tab

Optical properties

The energy bandgap of NiS2 was derived from the diffuse reflectance of the obtained layer using the Kubelka–Munk (KM) function53,54, as indicated by the following equation:

graphic file with name d2ra01067d-t2.jpg 7

where F(R) is the (KM) function, R is the diffused reflectance, α is the absorption coefficient, and S is the scattering coefficient. The optical band gap energy (Eg) of the NiS2 layer can be calculated by the Tauc's equation:55

αhν = A(hν − Eg)n 8

where (hν) is the incident photon energy, α is the absorption coefficient, A is a constant, (Eg) is the optical band gap energy. Based on the KM function and Tauc's equation, the optical bandgap energy of the NiS2 layer can be estimated using the following equation:

F(R)hν = A(hν − Eg)n 9

The plots of (F(R)hν)2vs. hν for indirect allowed transition are shown in Fig. 5. It was found that the estimated value of Eg for the NiS2 layer was 1.19 eV, which is in agreement with reported values.33,56 The low Eg value would allow the utilization of this material in photocatalytic applications under solar radiation.29,57

Fig. 5. (F(R)hν)1/2vs. hν plot of the nanoflake NiS2 layer.

Fig. 5

Open in a new tab

Photocatalytic activity measurements

The photocatalytic activity performance of the NiS2 sample (5 cm2) was examined using phenol as the model organic pollutant, two NiS2 samples and at natural pH of 10 mg L−1 phenol. The variation of phenol relative concentration (C/C0) is offered in Fig. 6 with the matching values of the 1st order apparent rate constants. Phenol presented insignificant photolysis under solar light. On the other hand, the rate of phenol photodegradation under solar light in the presence of the as-prepared NiS2 layer was improved. This is due to the presence of the as-prepared NiS2 slide, which absorbs solar light and photogenerates e−/h+ pairs utilized in photodegradation.

Fig. 6. Photocatalytic performance of NiS2, phenol conc. = 10 mg L−1, and natural pH 6.

Fig. 6

Open in a new tab

The main active species used in pollutant photodegradation are e−, h+, ˙OH and O2˙−. The active species produced by NiS2 are identified in Fig. 7. The active species identification was done by adding 1 mmol of each scavenger agent (AO, p-BQ and IPA) with 10 mg L−1 phenol and NiS2 layer compared to the experiment done without any scavenger. As shown in Fig. 7, the primary active species is O2˙− and h+ is a secondary species, which are used as redox species in phenol photodegradation. Therefore, the proposed mechanism of the photocatalytic reactions is indicated by the following equations:

NiS2 + hν → NiS2(h+, e−) 10
NiS2(e−) + O2 → NiS2 + O2˙− 11
O2˙− + h+ + phenol → photodegradation product 12

Fig. 7. Effect of scavengers on phenol removal efficiency.

Fig. 7

Open in a new tab

On the other hand, the NiS2 reusability process is a very important issue, making the treatment process more economical. Fig. 8 shows a five cycle reusability test for NiS2 phenol photodegradation. The removal efficiency was slightly decreased after the first cycle. Thereafter, there was no change in the phenol removal efficiency after each cycle.

Fig. 8. Reusability of NiS2, phenol conc. = 10 mg L−1, and natural pH 6.

Fig. 8

Open in a new tab

Conclusion

A NiS2 layer with a nanoflake-like structure was successfully synthesized by a facile two-step growth process. The Ni(OH)2 layer was deposited on a glass substrate by chemical bath deposition, followed by a sulfurization process to obtain a single phase NiS2 layer. The XRD and Raman analysis confirmed the formation of single-phase NiS2. SEM revealed that the NiS2 layer consisted of overlapping nanoflakes. XPS measurements revealed that the observed peaks from Ni 2p and S 2p spectra were attributed to NiS2. The NiS2 displayed a narrow optical bandgap of 1.19 eV. The NiS2 nanoflake layer showed photocatalytic activity for the degradation of phenol under the irradiation of solar light at natural pH 6. The NiS2 nanoflake layer exhibited good solar light photocatalytic degradation of phenol with good stability and reusability. The as-prepared NiS2 layer can absorb solar irradiation and generate e−/h+ pairs. Hence, the NiS2 layer is a promising photocatalyst for the photodegradation of destructive organic pollutants.

Author contributions

Mohammed M. Gomaa: conceptualization, data curation, formal analysis, investigation, methodology, writing – original draft. Mohamed H. Sayed: conceptualization, data curation, formal analysis, investigation, methodology, writing – original draft. Mahmoud S. Abdel-Wahed: conceptualization, methodology, data curation, formal analysis, investigation, writing – original draft. Mostafa Boshta: funding acquisition, project administration, resources, supervision, validation, writing – original draft.

Conflicts of interest

The authors declare no competing interests

Supplementary Material

Acknowledgments

The authors acknowledge the financial support from the National Research Centre Fund, through in-house projects number TT111001 and 12040110.

Notes and references

  1. Zhu W. Cheng Y. Wang C. Pinna N. Lu X. Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications. Nanoscale. 2021;13:9112. doi: 10.1039/d1nr01070k. [DOI] [PubMed] [Google Scholar]
  2. An G. Chenguang L. Hou Y. Zhang X. Liu Y. Transition metal dichalcogenide materials: solid-state reaction synthesis of nanocrystalline nickel disulfide. Mater. Lett. 2008;62:2643. [Google Scholar]
  3. Li J. Jiménez-Calvo P. Paineau E. Ghazzal M. N. Metal chalcogenides based heterojunctions and novel nanostructures for photocatalytic hydrogen evolution. Catalysts. 2020;10:89. [Google Scholar]
  4. Liang Y. Yang Y. Xu K. Yu T. Yao S. Peng Q. Yuan C. Crystal plane dependent electrocatalytic performance of NiS2 nanocrystals for hydrogen evolution reaction. J. Catal. 2020;381:63. [Google Scholar]
  5. Lai C. H. Lu M. Y. Chen L. J. Metal sulfide nanostructures: synthesis, properties and applications in energy conversion and storage. J. Mater. Chem. 2012;22:19. [Google Scholar]
  6. Dai M. Wang R. Synthesis and applications of nanostructured hollow transition metal chalcogenides. Small. 2021;17:1. doi: 10.1002/smll.202006813. [DOI] [PubMed] [Google Scholar]
  7. Gadisa B. T. Appiah-Ntiamoah R. Kim H. Amorphous iron sulfide nanowires as an efficient adsorbent for toxic dye effluents remediation. Environ. Sci. Pollut. Res. 2019;26:2734. doi: 10.1007/s11356-018-3811-3. [DOI] [PubMed] [Google Scholar]
  8. Peng L. Ji X. Wan H. Ruan Y. Xu K. Chen C. Miao L. Jiang J. Nickel sulfide nanoparticles synthesized by microwave-assisted method as promising supercapacitor electrodes: an experimental and computational study. Electrochim. Acta. 2015;182:361. [Google Scholar]
  9. Zhao J. Zhang Y. Wang Y. Li H. Peng Y. The application of nanostructured transition metal sulfides as anodes for lithium ion batteries. J. Energy Chem. 2018;27:1536. [Google Scholar]
  10. Mondal D. Villemure G. Li G. Song C. Zhang J. Hui R. Chen J. Fairbridge C. Synthesis, characterization and evaluation of unsupported porous NiS2 sub-micrometer spheres as a potential hydrodesulfurization catalyst. Appl. Catal., A. 2013;450:230. [Google Scholar]
  11. Ma Q. Hu C. Liu K. Hung S. Ou D. Ming H. Nano energy identifying the electrocatalytic sites of nickel disulfide in alkaline hydrogen evolution reaction. Nano Energy. 2017;41:148. [Google Scholar]
  12. Wang J. Liu Z. Zhan C. Zhang K. Lai X. Tu J. Cao Y. 3D hierarchical NiS2/MoS2 nanostructures on CFP with enhanced electrocatalytic activity for hydrogen evolution reaction. J. Mater. Sci. Technol. 2020;39:155. [Google Scholar]
  13. Molla A. Sahu M. Hussain S. Synthesis of tunable band gap semiconductor nickel sulphide nanoparticles: rapid and round the clock degradation of organic dyes. Sci. Rep. 2016;6:1. doi: 10.1038/srep26034. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Fang X. Zhai T. Gautam U. K. Li L. Wu L. Bando Y. Golberg D. ZnS nanostructures: from synthesis to applications. Prog. Mater. Sci. 2011;56:175. [Google Scholar]
  15. Chen X. Zhang J. Zeng J. Shi Y. Lin S. Huang G. Wang H. Kong Z. Xi J. Ji Z. MnS coupled with ultrathin MoS2 nanolayers as heterojunction photocatalyst for high photocatalytic and photoelectrochemical activities. J. Alloys Compd. 2019;771:364. [Google Scholar]
  16. Kumari P. Chandran P. Khan S. S. Synthesis and characterization of silver sulfide nanoparticles for photocatalytic and antimicrobial applications. J. Photochem. Photobiol., B. 2014;141:235. doi: 10.1016/j.jphotobiol.2014.09.010. [DOI] [PubMed] [Google Scholar]
  17. Heift D. Iron sulfide materials: catalysts for electrochemical hydrogen evolution. Inorganics. 2019;7:75. [Google Scholar]
  18. Ma G. Peng H. Mu J. Huang H. Zhou X. Lei Z. In situ intercalative polymerization of pyrrole in graphene analogue of MoS2 as advanced electrode material in supercapacitor. J. Power Sources. 2013;229:72. [Google Scholar]
  19. Rakspun J. Kantip N. Vailikhit V. Choopun S. Tubtimtae A. Multi-phase structures of boron-doped copper tin sulfide nanoparticles synthesized by chemical bath deposition for optoelectronic devices. J. Phys. Chem. Solids. 2018;115:103. [Google Scholar]
  20. Dai C. Li B. Li J. Zhao B. Wu R. Ma H. Duan X. Controllable synthesis of NiS and NiS2 nanoplates by chemical vapor deposition. Nano Res. 2020;13:2506. [Google Scholar]
  21. Yang Y. Zhu H. Meng H. Ma W. Wang C. Ma F. Hu Z. Nickel foam-supported starfish-like Ni(OH)2@CoS nanostructure with obvious core–shell heterogeneous interfaces for hybrid supercapacitors application. J. Mater. Sci. 2021;56:3280. [Google Scholar]
  22. Jiang N. Tang Q. Sheng M. You B. Jiang D. E. Sun Y. Nickel sulfides for electrocatalytic hydrogen evolution under alkaline conditions: a case study of crystalline NiS, NiS2, and Ni3S2 nanoparticles. Catal. Sci. Technol. 2016;6:1077. [Google Scholar]
  23. Zhang D. Zhou X. Ye K. Li Y. Song C. Cheng K. Cao D. Wang G. Li Q. Synthesis of honeycomb-like NiS2/NiO nano-multiple materials for high performance supercapacitors. Electrochim. Acta. 2015;173:209. [Google Scholar]
  24. Ulbrich K. F. Nishida E. N. Souza B. S. Campos C. E. M. NiS2-NiS nanocrystalline composite synthesized by mechanochemistry and its performance for methylene blue dye adsorption. Mater. Chem. Phys. 2020;252:123226. [Google Scholar]
  25. Pan Q. Xie J. Liu S. Cao G. Zhu T. Zhao X. Facile one-pot synthesis of ultrathin NiS nanosheets anchored on graphene and the improved electrochemical Li-storage properties. RSC Adv. 2013;3:3899. [Google Scholar]
  26. Akbarzadeh R. Dehghani H. Behnoudnia F. Sodium thiosulfate-assisted synthesis of NiS2 nanostructure by using nickel(ii)-salen precursor: optical and magnetic properties. Dalton Trans. 2014;43:16745. doi: 10.1039/c4dt02232g. [DOI] [PubMed] [Google Scholar]
  27. Guo Y. Guo D. Ye F. Wang K. Shi Z. Synthesis of lawn-like NiS2 nanowires on carbon fiber paper as bifunctional electrode for water splitting. Int. J. Hydrogen Energy. 2017;42:17038. [Google Scholar]
  28. Yang S. L. Bin Yao H. Gao M. R. Yu S. H. Monodisperse cubic pyrite NiS2 dodecahedrons and microspheres synthesized by a solvothermal process in a mixed solvent: thermal stability and magnetic properties. CrystEngComm. 2009;11:1383. [Google Scholar]
  29. Karthikeyan R. Thangaraju D. Prakash N. Hayakawa Y. Single-step synthesis and catalytic activity of structure-controlled nickel sulfide nanoparticles. CrystEngComm. 2015;17:5431. [Google Scholar]
  30. Chen W. Zhang X. Mo L. E. Feng Z. Chen S. Zhang X. Zhang Y. Hu L. Ligands induced NiS2 quantum dots for synchronous high specific capacity and robust stability of advanced electrochemical energy storage. Chem. Eng. J. 2019;375:121981. [Google Scholar]
  31. Rahman M. M. Ahmed J. Asiri A. M. Siddiquey I. A. Hasnat M. A. Development of 4-methoxyphenol chemical sensor based on NiS2-CNT nanocomposites. J. Taiwan Inst. Chem. Eng. 2016;64:157. [Google Scholar]
  32. Vu T. T. Park S. Park J. Kim S. Mathew V. Alfaruqi M. H. Kim K. H. Sun Y. K. Hwang J. Y. Kim J. Investigation of superior sodium storage and reversible Na2S conversion reactions in a porous NiS2@C composite using: in operando X-ray diffraction. J. Mater. Chem. A. 2020;8:24401. [Google Scholar]
  33. Huerta-Flores A. M. Torres-Martínez L. M. Moctezuma E. Singh A. P. Wickman B. Green synthesis of earth-abundant metal sulfides (FeS2, CuS, and NiS2) and their use as visible-light active photocatalysts for H2 generation and dye removal. J. Mater. Sci.: Mater. Electron. 2018;29:11613. [Google Scholar]
  34. Yang X. Zhou L. Feng A. Tang H. Zhang H. Ding Z. Ma Y. Wu M. Jin S. Li G. Synthesis of nickel sulfides of different phases for counter electrodes in dye-sensitized solar cells by a solvothermal method with different solvents. J. Mater. Res. 2014;29:935. [Google Scholar]
  35. Buchmaier C. Glänzer M. Torvisco A. Poelt P. Wewerka K. Kunert B. Gatterer K. Trimmel G. Rath T. Nickel sulfide thin films and nanocrystals synthesized from nickel xanthate precursors. J. Mater. Sci. 2017;52:10898. [Google Scholar]
  36. Lu M. Gao N. Zhang X. J. Wang G. S. Reduced graphene oxide decorated with octahedral NiS2/NiS nanocrystals: facile synthesis and tunable high frequency attenuation. RSC Adv. 2019;9:5550. doi: 10.1039/c8ra10633a. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Arivazhagan M. Shankar A. Maduraiveeran G. Hollow sphere nickel sulfide nanostructures-based enzyme mimic electrochemical sensor platform for lactic acid in human urine. Microchim. Acta. 2020;187:468. doi: 10.1007/s00604-020-04431-3. [DOI] [PubMed] [Google Scholar]
  38. Schmachtenberg V. A. V. Tontini G. Koch J. A. Semione G. D. L. Drago V. Low temperature solventless syntheses of nanocrystalline nickel sulfides with different sulfur sources. J. Phys. Chem. Solids. 2015;87:253. [Google Scholar]
  39. Kristl M. Dojer B. Gyergyek S. Kristl J. Synthesis of nickel and cobalt sulfide nanoparticles using a low cost sonochemical method. Heliyon. 2017;3:1. doi: 10.1016/j.heliyon.2017.e00273. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Zakaria W. F. W. Jalil A. A. Hassan N. S. Ibrahim M. Azami M. S. Visible-light driven photodegradation of phenol over niobium oxide-loaded fibrous silica titania composite catalyst. J. Chem. Technol. Biotechnol. 2020;95:2638. [Google Scholar]
  41. Rehman G. U. Tahir M. Goh P. S. Ismail A. F. Hafeez A. Khan I. U. Enhancing the photodegradation of phenol using Fe3O4/SiO2 binary nanocomposite mediated by silane agent. J. Phys. Chem. Solids. 2021;153:110022. [Google Scholar]
  42. Tzompantzi F. Castillo-Rodríguez J. C. Tzompantzi-Flores C. Pérez-Hernández R. Gómez R. Santolalla-Vargas C. E. Che-Galicia G. Ramos-Ramírez E. Addition of SnO2 over an oxygen deficient zirconium oxide (ZrxOy) and its catalytic evaluation for the photodegradation of phenol in water. Catal. Today. 2021 doi: 10.1016/j.cattod.2021.07.027. [DOI] [Google Scholar]
  43. Chen X. Liu Q. Bai T. Wang W. He F. Ye M. Nickel and cobalt sulfide-based nanostructured materials for electrochemical energy storage devices. Chem. Eng. J. 2021;409:127237. [Google Scholar]
  44. Ju B. Song H. J. Lee G. H. Sung M. C. Kim D. W. Nickel disulfide nanosheet as promising cathode electrocatalyst for long-life lithium–oxygen batteries. Energy Storage Mater. 2020;24:594. [Google Scholar]
  45. Surendran S. Sankar K. V. Berchmans L. J. Selvan R. K. Polyol synthesis of α-NiS particles and its physico-chemical properties. Mater. Sci. Semicond. Process. 2015;33:16. [Google Scholar]
  46. Gomaa M. M. Boshta M. Farag B. S. Osman M. B. S. Structural and optical properties of nickel oxide thin films prepared by chemical bath deposition and by spray pyrolysis techniques. J. Mater. Sci.: Mater. Electron. 2016;27:711. [Google Scholar]
  47. Xiong D. Li W. Liu L. Vertically aligned porous Nickel(II) hydroxide nanosheets supported on carbon paper with long-term oxygen evolution performance. Chem.–Asian J. 2017;12:543. doi: 10.1002/asia.201601590. [DOI] [PubMed] [Google Scholar]
  48. Ede S. R. Anantharaj S. Kumaran K. T. Mishra S. Kundu S. One step synthesis of Ni/Ni(OH)2 nano sheets (NSs) and their application in asymmetric supercapacitors. RSC Adv. 2017;7:5898. [Google Scholar]
  49. Kashale A. A. Ghule A. V. Chen I. W. P. Active edge site exposed β-Ni(OH)2 nanosheets on stainless steel mesh as a versatile electrocatalyst for the oxidation of urea, hydrazine, and water. ChemCatChem. 2021;13:1165. [Google Scholar]
  50. Bhardwaj R. Jha R. Bhushan M. Improved electrocatalytic performance with enlarged surface area and reduced bandgap of caterpillar and cabbage-like nickel sulphide nanostructures. Appl. Nanosci. 2020;10:3757. [Google Scholar]
  51. Hjiri M. Aida M. S. Neri G. NO2 selective sensor based on α-Fe2O3 nanoparticles synthesized via hydrothermal technique. Sensors. 2019;19:167. doi: 10.3390/s19010167. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Lonkar S. P. Pillai V. V. Alhassan S. M. Scalable solid-state synthesis of MoS2-NiS2/graphene nanohybrids as bifunctional electrocatalysts for enhanced overall water splitting. Adv. Mater. 2020;1:794. [Google Scholar]
  53. Sharma S. Khare N. Sensitization of narrow band gap Bi2S3 hierarchical nanostructures with polyaniline for its enhanced visible-light photocatalytic performance. Colloid Polym. Sci. 2018;296:1479. [Google Scholar]
  54. Patel M. Chavda A. Mukhopadhyay I. Kim J. Ray A. Nanostructured SnS with inherent anisotropic optical properties for high photoactivity. Nanoscale. 2016;8:2293. doi: 10.1039/c5nr06731f. [DOI] [PubMed] [Google Scholar]
  55. Gomaa M. M. Sayed M. H. Chikoidze E. Dumont Y. Boshta M. V-doped ZnO diluted magnetic semiconductor prepared by chemical spray pyrolysis. Mater. Sci. Semicond. Process. 2020;109:104944. [Google Scholar]
  56. Anand J. S. Rajan R. K. M. Abdul Aziz M. Z. B. Electrosynthesized NiS2 thin films and their optical and semiconductor studies. Rep. Electrochem. 2013;3:25. [Google Scholar]
  57. Schuster C. Gatti M. Rubio A. Electronic and magnetic properties of NiS2, NiSSe and NiSe2 by a combination of theoretical methods. Eur. Phys. J. B. 2012;85:1. [Google Scholar]

Articles from RSC Advances are provided here courtesy of Royal Society of Chemistry

RESOURCES