Highly efficient photocatalytic hydrogen production by ZnCdS composite catalyst modified with NiCoP nanosheets prepared by LDH precursor

Synergistic design of dual S-scheme heterojunction Cu2O/Ni2Al-LDH@MIL-53(Fe) for boosting photocatalytic hydrogen evolution

The development of heterojunctions is a proven strategy to augment the photocatalytic efficiency of materials. However, the enhancement in charge transfer facilitated by a single heterojunction is inherently constrained. To overcome these limitations, we synthesized a dual S-scheme heterojunction ternary composite photocatalyst, Cu2O/Ni2Al-LDH@MIL-53(Fe), designed for efficient visible-light-driven hydrogen (H2) production. The composite catalyst demonstrated a remarkable H2 production rate of 2093.9 μmol·g-1·h-1, which is 4.0-fold greater than that of pristine Cu2O (530.5 μmol·g-1·h-1), 56.7-fold higher than that of Ni2Al-LDH (36.9 μmol·g-1·h-1), and 5.9-fold superior to the single S-scheme heterojunction Ni2Al-LDH@MIL-53(Fe) (353.8 μmol·g-1·h-1). The improved photocatalytic performance is ascribed to the synergistic electrostatic forces and coordination interactions between MIL-53(Fe) and in-situ grown Ni2Al-LDH, which establish a closely contacted interface. Additionally, the incorporation of Cu2O mitigates electron transfer resistance and diminishes the recombination rate of photogenerated charge carriers. The engineered dual S-scheme heterojunction significantly increases the charge transfer pathways for photogenerated charge carriers and introduces minimal interfacial resistance, thus achieving efficient charge transfer. Comprehensive experimental characterizations and density functional theory (DFT) calculations substantiate that the migration of photogenerated electrons adheres to the dual S-scheme heterojunction mechanism. This work provides a design concept that integrates a surface in-situ growth strategy with heterojunction engineering, offering a novel approach for the fabrication of advanced photocatalytic composite materials.

Rh single atoms anchored in hollow microflower MoS2/sulfur-vacancy rich CdZnS with dual proton reduction sites for enhanced photocatalytic hydrogen generation

Modifying CdZnS with precious metal at the atomic scale is a promising approach for maximizing its photocatalytic performance. Herein, Rh single atoms (Rh1) were successfully anchored on hollow microflower MoS2/sulfur-vacancy-rich CdZnS (CZS-SVs) to boost H2 generation. The optimal catalyst Rh1@MoS2/CZS-SVs reaches a H2 productivity of 39,827 μmol h-1 g-1, representing 5.64 and 4.36-folds enhancement compared with pristine CZS and CZS-SVs, respectively. The enhanced H2 generation activity was due to Rh single atoms and sulfur-vacancy defects, both of which can effectively promote carrier separation and prolong carrier lifespan. Notably, density functional theory (DFT) calculations suggest that introducing Rh single-atom sites on MoS2/CZS-SVs significantly facilitated electron transfer, leading to efficient conversion of the H* intermediate to H2 (|ΔGH*| = 0.44 eV). Consistently, in situ Raman analysis confirmed Rh and S dual proton-reduction sites. Due to the accumulation of abundant electric charges, S atoms sites can also participate in H2 evolution process.

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.

Noble metal-free bimetallic phosphide-decorated Zn0.5Cd0.5S with efficient photocatalytic H2 evolution

The rapid recombination of charge carriers in semiconductor-based photocatalysts results in a low photocatalytic activity. Co-catalysis is considered a promising strategy to improve the photocatalytic performance of semiconductors. In this study, a bimetallic phosphide was grown by a facile in situ growth method. Loading the cocatalyst (7 wt% NiCoP) leads to activity enhancement by a factor of approximately 27 times in the visible-light-driven hydrogen evolution relative to the pristine Zn0.5Cd0.5S. The photocatalysis shows a high hydrogen evolution rate of 19.5 mmol g-1 h-1, which is much higher than that of the single metal phosphide (Ni2P: 7.0 mmol g-1 h-1; CoxP: 8.1 mmol g-1 h-1) and 7 wt% Pt modified Zn0.5Cd0.5S (0.3 mmol g-1 h-1). Its apparent quantum efficiency reaches 41.6% at 420 nm. Moreover, the photocatalyst exhibits a remarkable photostability for five consecutive cycles of photocatalytic activity measurements with a total reaction time of 15 hours. The excellent photocatalytic activity of the photocatalyst was attributed to the in situ-formed NiCoP cocatalyst, which not only acts as a reactive site but also accelerates the separation of charge carriers.