In Situ Growth Facilitating the Piezo-Photocatalytic Effect of Zn1-xCdxS/ZnO Nanorods for Highly Efficient H2 Production.

Photocatalytic H2 production holds promise for alleviating energy and environmental issues. The separation of photoinduced charge carriers plays vital roles in enhancing the activity of photocatalytic H2 production. The piezoelectric effect has been proposed to be effective in facilitating the separation of charge carriers. However, the piezoelectric effect is usually restricted by the noncompact contact between the polarized materials and semiconductors. In this study, Zn1-xCdxS/ZnO nanorod arrays on stainless steel for piezo-photocatalytic H2 production are fabricated by an in situ growth method, achieving an electronic-level contact between Zn1-xCdxS and ZnO. The separation and migration of photogenerated charge carriers in Zn1-xCdxS are significantly improved by the piezoelectric effect induced by ZnO under mechanical vibration. Consequently, under solar and ultrasonic irradiation, the H2 production rate of Zn1-xCdxS/ZnO nanorod arrays achieves 20.96 µmol h-1 cm-2, which is 4 times higher than that under solar irradiation. Such a performance can be attributed to the synergies of the piezoelectric field of bent ZnO nanorods and the built-in electric field of the Zn1-xCdxS/ZnO heterostructure, which efficiently separate the photoinduced charge carriers. This study provides a new strategy to couple polarized materials and semiconductors for highly efficient piezo-photocatalytic H2 production.

Enhanced Photocatalytic Hydrogen Production of ZnIn2S4 by Using Surface-Engineered Ti3C2Tx MXene as a Cocatalyst.

Developing efficient and stable photocatalysts is crucial for photocatalytic hydrogen production. Cocatalyst loading is one of the effective strategies for improving photocatalytic efficiency. Here, Ti3C2Tx (Tx = F, OH, O) nanosheets have been adopted as promising cocatalysts for photocatalytic hydrogen production due to their metallic conductivity and unique 2D characterization. In particular, surface functionalized Ti3C2(OH)x and Ti3C2Ox cocatalysts were synthesized through the alkalization treatment with NaOH and a mild oxidation treatment of Ti3C2Fx, respectively. ZnIn2S4/Ti3C2Tx composites, which were fabricated by the in-situ growth of ZnIn2S4 nanosheets on the Ti3C2Tx surface, exhibited the promoted photocatalytic performance, compared with the parent ZnIn2S4. The enhanced photocatalytic performance can be further optimized through the surface functionalization of Ti3C2Fx. As a result, the optimized ZnIn2S4/Ti3C2Ox composite with oxygen functionalized Ti3C2Ox cocatalyst demonstrated excellent photocatalytic hydrogen evolution activity. The characterizations and density functional theory calculation suggested that O-terminated Ti3C2Ox could effectively facilitate the transfer and separation of photogenerated electrons and holes due to the formation of a Schottky junction, with the largest difference in work function between ZnIn2S4 and Ti3C2Ox. This work paves the way for photocatalytic applications of MXene-based photocatalysts by tuning their surface termination groups.

Construction of TiO2 /SrTiO3 Heterojunction Derived from Monolayer Ti3 C2 MXene for Efficient Photocatalytic Overall Water Splitting.

Construction of heterojunction at the atomic scale to ensure efficient charge separation for improvement of photocatalytic water splitting is challenging. Herein, a facile hydrothermal method has been applied for the in situ fabrication of TiO2 /SrTiO3 heterojunction, using the monolayer Ti3 C2 MXene as the template and reactant. It is found that the sample with the hydrothermal reaction time of 60 min exhibits the highest H2 evolution rate with the sacrificial reagent, due to the efficient charge separation of TiO2 /SrTiO3 heterojunction as Ti3 C2 derivative. In addition, the sample shows the best overall water splitting performance at a hydrothermal reaction time of 120 min, where TiO2 is nearly converted to SrTiO3 , due to the fast kinetic process and low structural defects of SrTiO3 . This work not only provides a simple strategy for the fabrication of heterojunction photocatalysts but also demonstrates the difference in optimization of half-reaction and overall water splitting reaction.