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Chen, H.; Hao, J.; Wei, Y.; Huang, W.; Zhang, J.; Deng, T.; Yang, K.; Lu, K. Cobalt Sulfide-Based Composite Material for Photocatalysis. Encyclopedia. Available online: https://encyclopedia.pub/entry/42414 (accessed on 21 December 2024).
Chen H, Hao J, Wei Y, Huang W, Zhang J, Deng T, et al. Cobalt Sulfide-Based Composite Material for Photocatalysis. Encyclopedia. Available at: https://encyclopedia.pub/entry/42414. Accessed December 21, 2024.
Chen, Hui-Qi, Jin-Ge Hao, Yu Wei, Wei-Ya Huang, Jia-Lin Zhang, Tao Deng, Kai Yang, Kang-Qiang Lu. "Cobalt Sulfide-Based Composite Material for Photocatalysis" Encyclopedia, https://encyclopedia.pub/entry/42414 (accessed December 21, 2024).
Chen, H., Hao, J., Wei, Y., Huang, W., Zhang, J., Deng, T., Yang, K., & Lu, K. (2023, March 22). Cobalt Sulfide-Based Composite Material for Photocatalysis. In Encyclopedia. https://encyclopedia.pub/entry/42414
Chen, Hui-Qi, et al. "Cobalt Sulfide-Based Composite Material for Photocatalysis." Encyclopedia. Web. 22 March, 2023.
Cobalt Sulfide-Based Composite Material for Photocatalysis
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This entry is adapted from the peer-reviewed paper 10.3390/catal13030544

Photocatalysis, as an inexpensive and safe technology to convert solar energy, is essential for the efficient utilization of sustainable renewable energy sources. Earth-abundant cobalt sulfide-based composites have generated great interest in the field of solar fuel conversion because of their cheap, diverse structures and facile preparation.

photocatalysis cobalt sulfide synthesis strategies

1. Photocatalytic H2 Production

Semiconductor photocatalytic water decomposition has been improved by integrating appropriate co-catalysts. Due to the sufficient catalytic site and easy preparation, cobalt sulfide-based cocatalysts have been widely applied as co-catalysts for various semiconductors toward photocatalytic hydrogen evolution [1][2][3][4]. Fu et al. have illustrated that combining a hollow cobalt sulfide (CoSx) polyhedral cocatalyst with g-C3N4 can effectively accelerate the separation of photoinduced charges in g-C3N4 and provide an abundant active site to promote redox reactions [5]. In addition, the hollow structure of the CoSx polyhedron can also allow multiple reflections of light to enhance the light collection of g-C3N4. Thus, the photocatalytic performance of the 2% CoSx/g-C3N4 hybrids was significantly better than that of the blank g-C3N4. Obviously, the incorporation of cobalt sulfide could act as a cocatalyst to accelerate the separation and transfer of photo-generated electron-hole pairs and reduce the overpotential of the hydrogen production reaction. Qiu et al. reported that CdS nanorods loaded with CoS2 nanoparticles exhibited excellent photocatalytic hydrogen production activity, which was 13 times higher than that of pristine CdS NRs samples, and the optimized CoS2/CdS NRs photocatalyst had high stability and recyclability [6].
In addition to the cobalt sulfide single component cocatalyst, multicomponent cocatalysts exhibit superior co-catalytic activity than single component cocatalysts. For example, Li et al. have reported an excellent composite photocatalyst by combining CoS with Co(OH)2 on g-C3N4 to construct a dual cocatalyst [7]. The photocatalytic hydrogen production rate of the CoS/Co (OH)2/g-C3N4 composite photocatalyst is 311 times higher than that of pure g-C3N4, which is due to the synergistic effect of the dual cocatalysts. In the dual cocatalyst system, CoS cocatalyst acts as an electron acceptor to facilitate the separation of photogenerated carriers, and Co(OH)2 can also act as a conductor to diffuse photon-generated electrons. Moreover, in addition to acting as a co-catalyst, cobalt sulfide has also been reported as a semiconductor for H2 production. For example, Zhang et al. used a simple hydrothermal synthesis method to in situ grow two-dimensional ZnIn2S4 on one-dimensional hollow Co9S8 nanotubes to form a Co9S8/ZnIn2S4 heterostructure [8]. Type-I heterostructures are constructed when the Co9S8 nanotubes are covered with ZnIn2S4 nanosheets. When the Co9S8/ZnIn2S4 composites are excited to generate electron-hole pairs, the photogenerated electrons can migrate rapidly from the CB of ZnIn2S4 to that of Co9S8. Consequently, the Co9S8/ZnIn2S4 heterostructure achieves a higher photocatalytic activity than pure ZnIn2S4. 

2. Photocatalytic CO2 Reduction

In addition to being used as a cocatalyst for photocatalytic H2 production, cobalt sulfide can also be used as efficient photocatalytic for CO2 reduction [9][10]. For example, Zhang et al. have composited the hollow Co9S8 nanocages with ZnIn2S4 nanosheets and CdS quantum dots to construct a ternary composite photocatalyst [11]. The hollow structure of Co9S8 nanocages promotes multiple reflections of sunlight in the cavity, which enhanced the light absorption of ZnIn2S4 nanosheets and CdS quantum dots. In addition,, the ternary composite photocatalyst form a double Z-type heterojunction, which facilitates the separation and migration of photogenic electron hole pairs. Therefore, the photocatalytic performance of the Co9S8@ZnIn2S4/CdS hybrid is obviously better than that of blank CdS and ZnIn2S4.
Moreover, photocatalytic reduction of CO2 to methanol is another ideal approach for solar energy conversion. Ma et al. have prepared carbon nitride (CN) loaded with cobalt sulfide (CS) as a cocatalyst. The optimized CS/CN photocatalyst was 2.3 times more selective for CH3OH than CN [12]. It was confirmed that the introduction of cobalt sulfide can improve the selectivity of CH3OH. The cobalt sulfide not only provides the H2O oxidation center but also can significantly weaken the overpotential of the H2O oxidation half reaction, thus effectively avoiding the formation of strongly oxidized radicals.
Furthermore, Wang et al. have reported hierarchical FeCoS2-CoS2 double-shelled nanotubes as a composite photocatalyst for CO2 reduction [13]. FeCoS2-CoS2 composites can be obtained after ion-exchange reactions and sulfidation reactions with MIL-88A as precursors. FeCoS2-CoS2 composites present a uniform hierarchical nanosheet structure. When the Ru(bpy)32+ is used as the photosensitizer, the optimal FeCoS2-CoS2 composite shows excellent photocatalytic activity with a CO generation rate of 28.1 µmol h−1, which is better than the individuals of FeCoS2 and CoS2 and their physical mixtures sample. The unique hierarchical nanosheet structure reduces diffusion length and enhances scattering in the cavity, which inhibits electron-hole recombination and exposes active sites for redox reactions, thus improving the photocatalytic activity of the FeCoS2-CoS2 composite.

3. Photocatalytic Nitrogen Fixation

Neither humans nor the earth’s ecosystem can survive without the ability to synthesize ammonia [14]. The production of this foundation sustaining life on earth is based on both industrial and biological fixation levels of 200 × 106 tons per year [15]. At present, nitrogen fixation is principally carried out in three ways: (i) biological nitrogen fixation. Some micro-organisms, such as nitrogen-fixing bacteria, use their own nitrogenase to fix N2 molecules for biological nitrogen fixation; (ii) high-energy nitrogen fixation in geochemical processes, such as lightning; (iii) the energy-intensive Haber–Bosch method for industrial nitrogen fixation. However, biological and geochemical nitrogen fixation solely account for a tiny fraction of the fixed nitrogen supply. The Haber–Bosch process, which uses N2 and H2 as sources and iron-based compounds as the main material, is currently the main route for the synthesis of industrial ammonia. Nevertheless, this process requires a great deal of energy input while generating large emissions of by-products (such as carbon dioxide), which may cause environmental hazards. Hence, developing high-selectivity photocatalysts for nitrogen-reducing ammonia is challenging and interesting research [15]. Recently, Yuan et al. have demonstrated that loading Ru/CoSx to g-C3N4 nanosheets can effectively activate N2 molecules and facilitate the separation of light-induced electron-hole pairs in g-C3N4 [16]. In comparison with pure CN, Ru-Vs-CoS/CN shows obviously enhanced photocatalytic activity, reaching 1.28% apparent quantum efficiency at 400 nm and 0.042% solar-to-ammonia efficiency. The excellent nitrogen reduction reaction performance is attributed to the fact that the sulfur vacancies in CoSx can effectively promote the selective chemisorption of N2 molecules. In addition, an N2 molecule is bridged against the side-on Ru-Co center by the undercoordination of Ru and Co atoms at the Ru/CoSx interface. Furthermore, the plasmonic Ru/CoSx interface enhances light absorption to generate energetic charge-carriers, accelerates charge separation and transfer, and therefore kinetically facilitates the fixation of N2. This confirms that the presence of vacancies on the surface of cobalt sulfide-based nanomaterials exhibits excellent photocatalytic NRR performance, as it can modify the electronic structure, decrease the coordination number of surface atoms, facilitate the formation of dangling bonds, and greatly promote the formation of N2 chemisorption and activation. The N2-fixation mechanism indicates the hydrogen evolution reaction (HER) on Ru occurs easily due to its good free energy of hydrogen production (−0.07 eV). Meanwhile, the active hydrogen adsorption on Co and desorption on S limit the hydrogen evolution reaction (HER) on Ru.

4. Photocatalytic Degradation

Recent research shows that cobalt sulfide-based materials, such as CoS, CoS2, and Co3S4, are important candidate catalysts for photocatalytic organic pollutants degradation [17][18][19][20]. For instance, Co2.67S4 shows excellent photocatalytic degradation efficiency of methylene blue (MB) under UV, visible, and near-infrared irradiation [21]. The valence state change of cobalt ions effectively separates electrons from holes and accelerates electron transfer, thus enhancing the activity of photocatalytic degradation. In addition to single cobalt-based sulfide materials, cobalt sulfide, as a co-catalyst, can be combined with host semiconductors for photocatalytic degradation. For example, Tang et al. have designed a two-dimensional CoS/BiOBr heterojunction, which shows a 5.3-fold higher degradation rate as compared to pure BiOBr [22]. When the BiOBr and the CoS combine to construct the CoS/BiOBr heterojunction photocatalyst, the electrons on the CB of the CoS can be easily transferred to the CB of the BiOBr. In addition, the VB of BiOBr can oxidize glyphosate directly, producing small molecules or ions (PO43−, etc.). Simultaneously, some holes also migrate from BiOBr to CoS, leading to effective photogenerated charge carrier separation and thereby boosting the photocatalytic performance of the CoS/BiOBr composite.
Moreover, Zhang et al. have covered uniformly MoS2 nanosheets on CoS2 nanoparticles to construct CoS2/MoS2-nitrogen-doped graphene aerogels for photocatalytic organic pollutants degradation [23]. When MoS2 is combined with CoS2, the band gap of MoS2 can be narrowed and the optical response range can be expanded. At the same time, CoS2 can effectively accelerate the charge separation and increase the surface-active sites. Taking advantage of these advantages, the optimized three-dimensional CoS2/MoS2-nitrogen-doped graphene aerogel photocatalyst can degrade pollutants up to 97.1% within 60 minimums and still maintain 95.1% after three cycles.

References

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  2. Si, Y.; Lv, Z.; Lu, L.; Liu, M.; Wen, Y.; Chen, Y.; Jin, H.; Liu, J.; Song, W. Revealing important role of graphitic carbon nitride surface catalytic activity in photocatalytic hydrogen evolution by using different carbon co-catalysts. Appl. Surf. Sci. 2019, 491, 236–244.
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  20. Wu, Y.Y.; Zheng, H.L.; Li, H.; Sun, Y.J.; Zhao, C.; Zhao, R.; Zhang, C. Magnetic nickel cobalt sulfide/sodium dodecyl benzene sulfonate with excellent ciprofloxacin adsorption capacity and wide pH adaptability. Chem. Eng. J. 2021, 426, 127208.
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Subjects: Materials Science, Composites
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Hui-Qi Chen
,
Jin-Ge Hao
,
Yu Wei
,
Wei-Ya Huang
,
Jia-Lin Zhang
,
Tao Deng
,
Kai Yang
,
Kang-Qiang Lu
View Times: 377
Revisions: 2 times (View History)
Update Date: 27 Mar 2023
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