Photocatalytic Hydrogen Evolution from Water Splitting Using Core-Shell Structured Cu/ZnS/COF Composites

Abstract

Hydrogen is considered to be a very efficient and clean fuel since it is a renewable and non-polluting gas with a high energy density; thus, it has drawn much attention as an alternative fuel, in order to alleviate the issue of global warming caused by the excess use of fossil fuels. In this work, a novel Cu/ZnS/COF composite photocatalyst with a core–shell structure was synthesized for photocatalytic hydrogen production via water splitting. The Cu/ZnS/COF microspheres formed by Cu/ZnS crystal aggregation were covered by a microporous thin-film COF with a porous network structure, where COF was also modified by the dual-effective redox sites of C=O and N=N. The photocatalytic hydrogen production results showed that the hydrogen production rate reached 278.4 µmol g−1 h−1, which may be attributed to its special structure, which has a large number of active sites, a more negative conduction band than the reduction of H+ to H2, and the ability to inhibit the recombination of electron–hole pairs. Finally, a possible mechanism was proposed to effectively explain the improved photocatalytic performance of the photocatalytic system. The present work provides a new concept, in order to construct a highly efficient hydrogen production catalyst and broaden the applications of ZnS-based materials.

Covalent Organic Frameworks Based Inorganic/Organic Composite Materials for Photocatalytic Applications

“…Reproduced with permission. [43] Copyright 2021, MDPI. (c) Schematic illustration for fabrication of AuSP/COFs and AuCP/COFs with supposed electron transfer processes, respectively; TEM, HAADF-STEM and EDS-Mapping images of (d, f) Au3SP/COFs and (e, g) Au3CP/COFs hybrids, respectively.…”

“…By ultrasonically treating Cu/ZnS microspheres and imine-based COFs with high intensity (700 W, 20 kHz), Wang et al prepared Cu/ZnS/COFs hybrid materials with core-shell structures (Figure 2b). [43] Due to the abundant hydrogen bonds within this system, COFs with 2D porous network structure would wrap up ZnS/Cu to form an organic COFs shell. The energy of ultrasound enables the imine bonds of the COFs to achieve dynamic covalent equilibrium, which realizes their crystallization into ordered structure.…”

“…(b) Schematic synthesis of Cu/ZnS/COFs photocatalyst. Reproduced with permission [43] . Copyright 2021, MDPI.…”

“…By ultrasonically treating Cu/ZnS microspheres and imine‐based COFs with high intensity (700 W, 20 kHz), Wang et al. prepared Cu/ZnS/COFs hybrid materials with core‐shell structures (Figure 2b) [43] . Due to the abundant hydrogen bonds within this system, COFs with 2D porous network structure would wrap up ZnS/Cu to form an organic COFs shell.…”

Covalent Organic Framework‐Semiconductor‐Based Heterostructures for Photocatalytic Applications

“…Given that Cu had a mass of negative charge near the interface, while ZnS/COF possessed abundant positive charges, resulting in the construction of a space charge layer at the interface and a Schottky junction between ZnS/COF. The doped Cu efficiently captured photo‐induced electrons as a trap, therefore restraining the recombination of the electron/hole pairs and significantly improving the catalytic performance [122] . In contrast, semiconductor‐semiconductor‐based Z‐scheme heterojunctions not only shorten the carrier transport distance but also eliminate the light shielding effect of noble metal nanoparticles‐based redox mediators and thus further improve the efficiency of the photocatalytic system [123] .…”