In situ construction of 0D CoWO4 modified 1D Mn0.47Cd0.53S for boosted visible-light photocatalytic H2 activity and photostability

CdS/ZnS core-shell nanorod heterostructures co-deposited with ultrathin MoS2 cocatalyst for competent hydrogen evolution under visible-light irradiation

Hydrogen generation via semiconductor photocatalysts has gained significant attention as a sustainable fuel generation process. To demonstrate the performance of nanoscale core-shell heterostructure in photocatalytic hydrogen production, we have fabricated CdS nanorods coated with ZnS photocatalyst via wet-chemical reaction followed by deposition of ultrathin MoS2 nanosheets by photo reduction process. The effect of ZnS content and suitable amount of MoS2 loading over the visible-light induced photocatalytic hydrogen evolution was examined in Na2S and Na2SO3 aqueous solutions. Interestingly, it is apparent that a close connection (or heterojunction) between CdS and ZnS is believed to easily tunnel the charge carriers to the surplus surface states, making its electrons and holes energetically favourable to transfer from ZnS to MoS2 for photocatalytic reactions and subsequently, enhances the H2 evolution activity in CdS/ZnS type I core-shell heterostructures. The optimal MoS2 concentration is resolved to be 7 mol% and the subsequent visible-light induced H2 generation rate was 13589 μmol h-1g-1, which is 19 and 158 fold higher than pristine CdS and ZnS respectively. The probable photocatalytic mechanism of CdS/ZnS type I core-shell heterostructure with MoS2 cocatalyst is proposed. Our inexpensive and convenient preparation strategy may offer novel prospects in the engineering of desirable nanoheterostructures with better performance.

Design of p-n heterojunction between CoWO4 and Zn-defective Zn0.3Cd0.7S for efficient photocatalytic H2 evolution

To enhance the efficiency of photocatalytic H2 evolution, numerous methods are employed by increasing the utilization of photogenerated charge carriers (PCCs), including catalyst design, defect regulation, and selection of suitable H+ resources. Using self-assembly method, CoWO4/ZnxCd1-xS with p-n heterojunction was synthesized. Although CoWO4 (CW) cannot produce H2 under visible light irradiation, it can provide photogenerated electrons (e-) to Zn0.3Cd0.7S (ZCS), and largely increase the photocatalytic activity of ZCS. The optimal CW/ZCS composite can reach 15.58 mmol·g-1·h-1, which is 45.8 and 24.3 times higher than the values of the pure CdS and ZCS, respectively. The largely enhanced photocatalytic H2 production is attributed to the Zn vacancies (VZn), p-n heterojunction, and p-chlorobenzyl alcohol (Cl-PhCH2OH) as the H+ source of H2 production. VZn on the ZCS surface as the capture center of photogenerated holes (h+), can regulate the carrier distribution, which results in more photogenerated e- and less generated h+. The combination of p-n heterojunction and VZn can enhance the separation and transfer efficiency of PCCs, and effectively inhibit the recombination of charge carriers. To further improve the utilization rate of PCCs, the photocatalytic H2 evolution is proceeded by Cl-PhCH2OH oxidation in N,N-dimethylformamide solution, with 4-chlorobenzaldehyde (Cl-PhCHO) generated. The separated photogenerated e- and h+ both participated in the redox reaction of H+ reduction and Cl-PhCH2OH oxidation, considering that the amount of H2 and Cl-PhCHO products are close to 1:1. This work not only facilitates the separation and transfer of PCCs, but also provides directions for the design of efficient photocatalysts and H2 evolution in the organic phase.

Achieving improved full-spectrum responsive 0D/3D CuWO4/BiOBr:Yb3+,Er3+ photocatalyst with synergetic effects of up-conversion, photothermal effect and direct Z-scheme heterojunction

The key to obtain effective photocatalysts is to increase the efficiency of light energy conversion, and thus the design and implementation of full-spectrum photocatalysts is a potential approach to solve this problem especially by extending the absorption range to near-infrared (NIR) light. Herein, the improved full-spectrum responsive CuWO₄/BiOBr:Yb³⁺,Er³⁺ (CW/BYE) direct Z-scheme heterojunction was prepared. The CW/BYE with CW mass ratio of 5% had the best degradation performance, and the removal rate of tetracycline reached 93.9% in 60 min and 69.4% in 12 h under visible (Vis) and NIR light, respectively, which were 5.2 and 3.3 times of BYE. According to the outcome of experimental, the reasonable mechanism of improved photoactivity was put forward on the basis of (i) the up-conversion (UC) effect of Er³⁺ ion to convert NIR photon to ultraviolet or visible light, which can be used by CW and BYE, (ii) the photothermal effect of CW to absorb the NIR light, increasing the local temperature of photocatalyst particle to accelerate the photoreaction, and (iii) the formed direct Z-scheme heterojunction between BYE and CW to boost the separation of photogenerated electron-hole pairs. Additionally, the excellent photostability of the photocatalyst was verified by cycle degradation experiments. This work opens up a promising technique for designing and synthesizing full-spectrum photocatalysts by utilizing synergetic effects of UC, photothermal effect and direct Z-scheme heterojunction.

Strong synergy between gold nanoparticles and cobalt porphyrin induces highly efficient photocatalytic hydrogen evolution

The reaction efficiency of reactants near plasmonic nanostructures can be enhanced significantly because of plasmonic effects. Herein, we propose that the catalytic activity of molecular catalysts near plasmonic nanostructures may also be enhanced dramatically. Based on this proposal, we develop a highly efficient and stable photocatalytic system for the hydrogen evolution reaction (HER) by compositing a molecular catalyst of cobalt porphyrin together with plasmonic gold nanoparticles, around which plasmonic effects of localized electromagnetic field, local heating, and enhanced hot carrier excitation exist. After optimization, the HER rate and turn-over frequency (TOF) reach 3.21 mol g^-1 h^-1 and 4650 h^-1, respectively. In addition, the catalytic system remains stable after 45-hour catalytic cycles, and the system is catalytically stable after being illuminated for two weeks. The enhanced reaction efficiency is attributed to the excitation of localized surface plasmon resonance, particularly plasmon-generated hot carriers. These findings may pave a new and convenient way for developing plasmon-based photocatalysts with high efficiency and stability.

Insight into the enhanced photocatalytic activity mechanism of the Ag3VO4/CoWO4 p–n heterostructure under visible light

A novel Ag3VO4/CoWO4 p–n heterostructure was designed and prepared by an in situ growth method. The physicochemical properties were characterized by multiple techniques, and the photocatalytic performances in Cr(vi) reduction and TC degradation were also evaluated under visible-light irradiation.