CdS-based Photocatalysts Research Articles

Photo-augmented PHB production from CO2 or fructose by Cupriavidus necator and shape-optimized CdS nanorods

Particulate photocatalysts developed for the solar energy-driven reduction of the greenhouse gas CO2 have a small product range and low specificity. Hybrid photosynthesis expands the number of products with photocatalysts harvesting sunlight and transferring charges to microbes harboring versatile metabolisms for bioproduction. Besides CO2, abiotic photocatalysts have been employed to increase microbial production yields of reduced compounds from organic carbon substrates. Most single-reactor hybrid photosynthesis systems comprise CdS assembled in situ by microbial activity. This approach limits optimization of the morphology, crystal structure, and crystallinity of CdS for higher performance, which is usually done via synthesis methods incompatible with life. Here, shape and activity optimized CdS nanorods were hydrothermally produced and subsequently applied to Cupriavidus necator for the heterotrophic and autotrophic production of the bioplastic polyhydroxybutyrate (PHB). C. necator with CdS NR under light produced 1.5 times more PHB when compared to the same bacterium with suboptimal commercially-available CdS. Illuminated C. necator with CdS NR synthesized 1.41 g PHB from fructose over 120 h and 28 mg PHB from CO2 over 48 h. Interestingly, the beneficial effect of CdS NR was specific to C. necator as the metabolism of other microbes often employed for bioproduction including yeast and bacteria was negatively impacted. These results demonstrate that hybrid photosynthesis is more productive when the photocatalyst characteristics are optimized via a separated synthesis process prior to being coupled with microbes. Furthermore, bioproduction improvement by CdS-based photocatalyst requires specific microbial species highlighting the importance of screening efforts for the development of performant hybrid photosynthesis.

Unique ternary Cd0.85Zn0.15S@WO3/WS2 core-shell nanorods for highly-efficient photocatalytic H2 evolution under visible-light irradiation

Development of noble-metal-free photocatalysts for efficient solar-powered water-splitting is of great interest yet still challenging to date. In this work, unique ternary Cd0.85Zn0.15S@WO3/WS2 (CZ0.15S@WO3/WS2) core-shell nanorods consisting of amorphous WO3 and few-layered WS2 nanosheets were synthesized through a two-step solvothermal method for the first time. The composition of WO3/WS2 shell is found to vary with the change of W content, which has a significant impact on the photocatalytic property of CZ0.15S@WO3/WS2 toward H2 evolution reaction (HER). Under visible-light irradiation (λ > 420 nm), the optimized CZ0.15S@WO3/WS2 composite (n (WO3): n (WS2) = 3:1) demonstrates a superior HER activity of 76.33 mmol h−1 g−1 (corresponding to an AQY of 23.9% at 420 nm), which can be further remarkably increased to 157.29 mmol h−1 g−1 when the reaction is driven by full Xe-lamp spectrum. The HER capability of CZ0.15S@WO3/WS2 is much better than that of Pt-decorated CZ0.15S and most CdS-based photocatalysts ever reported, due to the notably enhanced charge transfer and separation via the synergistic cooperation of Z-scheme and type-I charge transfer processes. The findings displayed here could inspire new strategies to optimize the charge separation of multi-component photocatalysts for highly-effective solar conversion and utilization.

Few-layered WS2 nanosheets onto 1D CdS@ZnCdS as efficient visible-light photocatalyst for hydrogen evolution

Exploiting highly efficient and non-expensive visible-light photocatalysts is a huge challenge for H2 photocatalytic production. Here we synthesized an efficient non-precious metal photocatalyst WS2/CdS@ZnCdS (WS2/CdS@ZCS) consisting of few-layered WS2 attached on the core/shell structure of CdS@ZnCdS (CdS@ZCS) via three-step hydrothermal and electrostatic adsorption methods, in which the morphology and structure of the components were regulated independently. The optimum photocatalytic H2 evolution rate of 8 wt% WS2/CdS@ZCS is 34860 μmol h−1 g−1, which is almost 5.2 times as high as that of pure CdS nanorods (6730 μmol h−1 g−1) and superior to most previously reported CdS-based photocatalysts. Moreover, it can maintain 91% of its initial hydrogen evolution rate after 20 hours photocatalytic experiment, indicating WS2/CdS@ZCS is very stable. A possible mechanism of H2 generation on WS2/CdS@ZCS photocatalyst is also proposed. It is thought that this work may provide a promising way to design nanosheets/1D core@shell heterostructured photocatalysts for high-performance and steady H2 production.

Efficient visible-light induced H2 evolution from T-CdxZn1-xS/defective MoS2 nano-hybrid with both bulk twinning homojunctions and interfacial heterostructures

Developing high-performance noble-metal-free photocatalysts for solar water splitting is of great urgency to address the growing energy and environmental crises. However, the current photocatalytic efficiency is unsatisfactory due to the low conversion of solar energy. Herein, we prepared a unique hybrid photocatalyst consisting of twinned CdxZn1-xS solid solutions grown with several layers of defect-rich MoS2 nanosheets (T-CdxZn1-xS/MoS2) to achieve a stable and efficient H2 evolution reaction (HER) activity. Noticeably, the alternating zinc blende/wurtzite (ZB/WZ) homojunctions in T-CdxZn1-xS and intimate heterojunctions formed between T-CdxZn1-xS and MoS2 facilitated the efficient separation and transfer of both bulk and surface charge carriers. Moreover, the good visible-light responses of T-CdxZn1-xS and MoS2 as well as the existence of abundant S22− and Mo5+ active species in defective MoS2 nanosheets also contributed significantly to the activity improvement of T-CdxZn1-xS/MoS2. Benefiting from the above advantages, T-CdxZn1-xS/MoS2 exhibited superior HER rates of 37.22 mmol∙h-1 g-1 in lactic acid solution and 69.25 mmol∙h-1 g-1 in Na2S/Na2SO3 solution, corresponding to the apparent quantum yield (AQY) of 36.3 % and 55.2 % at 420 nm, respectively. The HER capability of T-CdxZn1-xS/MoS2 exceeded that of Pt/T-CdxZn1-xS and most CdS-based photocatalysts reported previously. Our findings will facilitate the exploitation of advanced nanomaterials for sustainable energy conversion and utilization.

Recent developments and perspectives in CdS-based photocatalysts for water splitting

Over the past decades, visible-light-driven water splitting on CdS has gained substantial attention owing to its low cost, appropriate bandgap, and electron affinity that best fit the visible light absorption spectrum.

Fabrication of highly stable CdS/g-C3N4 composite for enhanced photocatalytic degradation of RhB and reduction of CO2

CdS/g-C3N4 (CdS/CN) type II heterojunction photocatalyst was prepared by an improved successive ionic layer adsorption and reaction process. TEM results show that the CdS nanoparticles (CdS NPs) were successfully loaded on the surface of CN. The results of PL and PEC display that the construction of CdS/CN heterojunction benefits the transmission of the photogenerated carriers and effectively inhibits the photogenerated carrier recombination in photocatalytic process. The photodegradation experiments exhibit that the 3-CdS/CN photocatalyst possesses the highest photodegradation performance over the other samples. The yields of H2 and CH4, in the presence of the best CdS/CN photocatalyst (1-CdS/CN) are 50 and 13 times stronger, respectively, than in the case of the pure CN in the photoreduction process of CO2. The CN coupling effectively improves the photocatalytic performance of CdS-based photocatalyst and inhibits the hole-induced photocorrosion of CdS NPs. A possible type II heterojunction photocatalytic mechanism has been provided.

Unique Cd1−xZnxS@WO3−x and Cd1−xZnxS@WO3−x/CoOx/NiOx Z-scheme photocatalysts for efficient visible-light-induced H2 evolution

Artificial Z-scheme photocatalytic systems have received considerable attention in recent years because they can achieve wide light-absorption, high charge-separation efficiency, and strong redox ability simultaneously. Nevertheless, it is still challenging to exploit low-cost and stable Z-scheme photocatalysts with highly-efficient H2 evolution from solar water-splitting so far. Herein, we report a novel all-solid-state Z-scheme photocatalyst Cd1− x Zn x S@WO3− x consisting of Cd1− x Zn x S nanorods coated with oxygen-deficient WO3− x amorphous layers. The Cd1− x Zn x S@WO3− x exhibits an outstanding H2 evolution reaction (HER) activity as compared with Pt-loaded Cd1− x Zn x S and most WO3- and CdS-based photocatalysts, due to the generation of stronger reducing electrons through the appropriate Zn-doping in Cd1− x Zn x S and the enhanced charge transfer by introducing oxygen vacancies (W5+/OVs) into the ultrathin WO3− x amorphous coatings. The optimal HER rate of Cd1− x Zn x S@WO3− x is determined to be 21.68 mmol h−1 g−1, which is further raised up to 28.25 mmol h−1 g−1 (about 12 times more than that of Pt/Cd1− x Zn x S) when Cd1− x Zn x S@WO3− x is hybridized by CoO x and NiO x dual cocatalysts (Cd1− x Zn x S@WO3− x /CoO x /NiO x ) through in - situ photo-deposition. Moreover, the corresponding apparent quantum yield (AQY) at 420 nm is significantly increased from 34.6% for Cd1− x Zn x S@WO3− x to 60.8% for Cd1− x Zn x S@WO3− x /CoO x /NiO x . In addition, both Cd1− x Zn x - S@WO3− x and Cd1− x Zn x S@WO3− x /CoO x /NiO x demonstrate good stability towards HER. The results displayed in this work will inspire the rational design and synthesis of high-performance nanostructures for photocatalytic applications.

Photostable core-shell CdS/ZIF-8 composite for enhanced photocatalytic reduction of CO2

Photocatalytic conversion of CO2 is recognized as a promising method to reduce CO2 emission and produce available chemical energy simultaneously. CdS-based photocatalysts have been intensively studied for CO2 reduction, due to their excellent optical response and suitable band structures. However, the photocorrosion of CdS seriously restricts their application. To reduce the photocorrosion, CdS/ZIF-8 composites with core-shell structures are prepared. The experimental results show that the modification of ZIF-8 shell can not only improve the photostability of CdS, but also enhance its CO2 adsorption capacity without impairing its light harvesting ability. CdS/ZIF-8 catalyst shows higher efficiency and better selectivity than that of unmodified CdS in photocatalytic reduction of CO2 to CO, which is attributed to its higher CO2 adsorption capability. Moreover, CdS/ZIF-8 composites exhibit high photostability.

Hydrothermal synthesis of MoS2-NiS/CdS with enhanced photocatalytic hydrogen production activity and stability

CdS is one of the most well-known photocatalysts for hydrogen production, while proper cocatalyst is indispensable to realize high hydrogen production performance. In this work, a three-component composite MoS2-NiS/CdS with dual cocatalysts was synthesized by a relatively facile and environmentally friendly three-step hydrothermal method and characterized by series of techniques. The as-prepared MoS2-NiS/CdS possesses good photostability and excellent photocatalytic hydrogen production performance. Under visible light irradiation of a 300 W Xe lamp (λ ≥ 420 nm), the H2 production rate reached a high value of 2525.2 μmol h−1 and the total amount of H2 evolved in 22 h achieved 40.5 mmol, further confirming that the photocatalysts with dual reduction cocatalysts possess higher photocatalytic performance than those with single cocatalyst. Especially, first study about the effect of pH of lactic acid aqueous solution on hydrogen production activity was carried out and the results indicated that increasing the pH from 1.5 to 3.0 leads to an obvious increase in H2-evolving activity. More importantly, an attempt on the photocatalytic hydrogen production under the irradiation of a 30 W LED lamp demonstrated that the H2 evolved was also up to 32.1 mmol in 48 h, showing the feasibility of using cheap and long lifetime LED lamp as light source for photocatalytic hydrogen production of CdS-based photocatalysts.

Glutathione-protected gold nanocluster decorated cadmium sulfide with enhanced photostability and photocatalytic activity

A Novel glutathione-protected gold nanocluster (Aux-GSH NC) decorated CdS photocatalyst was prepared using a chemical self-assembly method. After the photocatalyst was decorated with Aux-GSH NCs, the photocatalytic activity and photostability of CdS were remarkably enhanced. Compared to pure CdS, the as-prepared CdS-Pt-Auc photocatalyst exhibited 9 times of photocurrent and 2.85 times of photocatalytic activity. More importantly, the photocorrosion of CdS, which is a critical drawback for CdS-based photocatalysts, was significantly suppressed. It is believed that the heterostructures and matched energy levels between CdS and Aux-GSH NCs are the key for enhance catalytic activity and photostability. The level of LUMO and HOMO of Aux-GSH NCs is higher the conduction band and valence band of CdS respectively. Through the heterostructures, the photogenerated electrons of Aux-GSH NCs are injected into the CdS, while the photogenerated holes of CdS transferred to the Aux-GSH NCs. The opposite directions of charge migration improves the charge separation efficiency and average lifetime, which drastically enhances the photoactivity, and the rapid transferring of holes from CdS to Aux-GSH NCs significantly suppresses the photocorrosion of CdS.

CdS-Based photocatalysts

The review summarizes the recent progress in the synthesis, fundamental properties, morphology, photocatalytic applications and challenges of CdS-based photocatalysts.

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system.

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H2-production reaction are highly required for improving its photocatalytic H2-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H2-evolution reaction of CdxZn1-xS solid-solution photocatalysts in a sulfur-rich S2-/SO32- solution. Here, the suspensible CdxZn1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn2+/Cd2+ mixing ions in a sulfur-rich Na2S-Na2SO3 solution, and the resultant CdxZn1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S2-/SO32- on the surface of these CdxZn1-xS nanocrystals. It is found that the bandgap structure of CdxZn1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd2+/Zn2+ molar ratio. The photocatalytic experimental results suggested that the suspensible CdxZn1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H2-production performance, and the suspensible Cd0.6Zn0.4S nanocrystals exhibit the highest photocatalytic H2-generation performance of 717.19 μmol h-1, a value higher than that of the sole CdS (320.99 μmol h-1) and ZnS (5.89 μmol h-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S2- active site-mediated mechanism accounted for the high H2-production activity of the suspensible CdxZn1-xS nanocrystals, namely the numerous adsorbed S2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible CdxZn1-xS nanocrystals, but also serve as effective H+-capturing active sites to accelerate the interfacial H2-production reaction. Meanwhile, an optimum bandgap structure of suspensible CdxZn1-xS nanocrystals is also extremely required for promoting the photocatalytic H2-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Smart Utilization of Carbon Dots in Semiconductor Photocatalysis

Efficient capture of solar energy will be critical to meeting the energy needs of the future. Semiconductor photocatalysis is expected to make an important contribution in this regard, delivering both energy carriers (especially H2 ) and valuable chemical feedstocks under direct sunlight. Over the past few years, carbon dots (CDs) have emerged as a promising new class of metal-free photocatalyst, displaying semiconductor-like photoelectric properties and showing excellent performance in a wide variety of photoelectrochemical and photocatalytic applications owing to their ease of synthesis, unique structure, adjustable composition, ease of surface functionalization, outstanding electron-transfer efficiency and tunable light-harvesting range (from deep UV to the near-infrared). Here, recent advances in the rational design of CDs-based photocatalysts are highlighted and their applications in photocatalytic environmental remediation, water splitting into hydrogen, CO2 reduction, and organic synthesis are discussed.

Rational design and electron transfer kinetics of MoS2/CdS nanodots-on-nanorods for efficient visible-light-driven hydrogen generation

The efficiency of CdS-based photocatalysts for H2 evolution is limited by the ultrafast charge recombination. Here, we demonstrated the one-pot synthesis of a novel MoS2/CdS photocatalyst with the structure of partially crystalline MoS2 nanodots growing on single-crystalline CdS nanorods. This heterostructure not only effectively reduces the bulk and surface charge recombination owing to single-crystalline CdS nanorod matrix and efficient electron transfer, also provides plenty of active sites for hydrogen evolution reaction (HER) and accessible room for prompt hole extraction. The femtosecond transient absorption (TA) analysis reveals the effective electron transfer from CdS to MoS2 in ~20ps. As a result, MoS2/CdS exhibits extraordinary photocatalytic activity with a H2 evolution rate of 60.28mmol/g/h under visible light irradiation, far exceeding all previous HER photocatalysts with MoS2 as cocatalysts.

Screening and characterization for the optimization of CdS-based photocatalysts

The photocatalyst with a precursor composition In0.2–Cd0.8S showed the highest photocurrent under light illumination.

Insight into the Effect of Highly Dispersed MoS2 versus Layer-Structured MoS2 on the Photocorrosion and Photoactivity of CdS in Graphene–CdS–MoS2 Composites

Designing a semiconductor CdS-based photocatalyst for H2 evolution from water with high activity and stability is extremely desirable for practical application. We report the important morphological and structural influence of MoS2 cocatalyst on the photocorrosion and photoactivity of CdS that is carpeted on a graphene (GR) surface. Homogeneous dispersion of MoS2 nanoparticles by a controlled photodeposition (PD) method produces the GR–CdS–MoS2 (PD) composite, which does not have the characteristic stacked layer structure of MoS2. However, this GR–CdS–MoS2 (PD) composite exhibits much higher activity and particularly antiphotocorrosion than the hydrothermal synthesized GR–CdS–MoS2 (HT) counterparts, which feature the characteristic MoS2 layer structure, toward photocatalytic water splitting under visible light irradiation. The characterization results indicate that homogeneous dispersion of tiny MoS2 for GR–CdS–MoS2 (PD) markedly improves the separation and transfer of charge carriers and provides the inc...

Hydrogen production from water splitting on CdS-based photocatalysts using solar light

Hydrogen energy has been regarded as the most promising energy resource in the near future due to that it is a clean and sustainable energy. And the heterogeneous photocatalytic hydrogen production is increasingly becoming a research hotspot around the world today. As visible light response photocatalysts for hydrogen production, cadmium sulfide (CdS) is the most representative material, the research of which is of continuing popularity. In the past several years, there has been significant progress in water splitting on CdS-based photocatalysts using solar light, especially in the development of co-catalysts. In this paper, recent researches into photocatalytic water splitting on CdS-based photocatalysts are reviewed, including controllable synthesis of CdS, modifications with different kinds of cocatalysts, solid solution, intercalated with layered nanocomposites and metal oxides, and hybrids with graphenes etc. Finally, the problems and future challenges in photocatalytic water splitting on CdS-based photocatalysts are described.

Direct splitting of H2S into H2 and S on CdS-based photocatalyst under visible light irradiation

The conversion of H2S into H2 and S (H2S → H2 + S) is beneficial from both environmental and energy standpoints. Here we report that H2S can be splitted stoichiometrically into hydrogen and sulfur on CdS-based photocatalysts under visible light irradiation using ethanolamine as a H2S solvent and reaction media at room temperature. Raman spectra showed that the produced sulfur existed as S2−4 and S2−6 after photocatalytic reaction. The hydroxyls of the reaction media were found to be crucial for the hydrogen production, and the rate-determining step (RDS) of photocatalytic splitting H2S in diethanolamine is discussed. Electrochemical evaluation showed that the potential of H2S splitting in ethanolamine was greatly lowered and the photogenerated electrons could be fully used to reduce protons for hydrogen production. A free-radical-related one-electron electrochemical oxidation process on platinum electrode is suggested. This work demonstrates the possibility of the direct splitting H2S into S and H2 via photocatalysis.

Hydrogen production from sewage sludge solubilized in hot-compressed water using photocatalyst under light irradiation

Photocatalytic hydrogen production from a digested sewage sludge solubilized in hot-compressed water (573K) was investigated in order to develop a low-cost sacrifice agent for CdS-based photocatalysts from biomass. H 2 evolution occurred over a LaMnO 3/CdS composite photocatalyst under Xe lamp irradiation from water containing the solubilized sewage sludge and the amount of evolved H 2 reached more than 30 mmol/ g -catalyst for a 200 h -reaction; on the other hand, no H 2 was formed in the absence of the solubilized sewage sludge. The H 2 evolution rate was comparable to that when typical Na 2S–Na 2SO 3 sacrifice agents were used, suggesting the applicability of a biomass-derived sacrifice agent for photocatalysis. Organic compounds, such as methanol and formic acid, contained in the solubilized sewage sludge are responsible for the H 2 evolution observed.

Photocatalytic H 2 production with CdS-based catalysts from a sulphide/sulphite substrate: An effort to develop MgO-supported catalysts

CdS-based photocatalysts supported on MgO and γ-Al 2O 3 have been prepared, characterized and tested for dihydrogen evolution from a sulphide/sulphite substrate using a halogen lamp source. The effect of precursor salt for CdS preparation, the optimum loading of CdS on the support and the concentration of the catalyst in 50 ml of solution have been investigated. The effect of adding to CdS a semiconductor ZnS-Ag 2S and catalytic materials like Pt and RuO 2 have also been studied. The results obtained from the basic nature of MgO support are compared with the acidic nature of Al 2O 3 support. The importance of the acid-base properties of the support is substantiated by modifying the Al 2O 3 support with base materials like CaO BaO . Thus, the effect of the acid-base properties of the supports is highlighted.