Z‑scheme Photocatalytic CO₂ Conversion on Three-Dimensional BiVO₄/Carbon-Coated Cu₂O Nanowire Arrays under Visible Light

Cuprous oxide (Cu₂O) is one of the most promising materials for photoreduction of CO₂ because of its high conduction band and small band gap, which enable the production of high-potential electrons under visible-light irradiation. However, it is difficult to reduce the CO₂ using a Cu₂O-based photocatalyst due to fast charge recombination and low photostability. In this work, we enhanced the photocatalytic CO₂ conversion activity of Cu₂O by hybridization of Cu₂O NWAs, carbon layers, and BiVO₄ nanoparticles. By construction of a Z-scheme charge flow on a 3-D NWA structure, the BiVO₄/carbon-coated Cu₂O (BVO/C/Cu₂O) NWAs show significantly enhanced charge separation and light harvesting property. As a result, CO formation rate of BVO/C/Cu₂O was 9.4 and 4.7 times those of Cu₂O mesh and Cu₂O NWAs, respectively, under visible light irradiation. In addition, the material retained 98% of its initial photocatalytic CO₂ conversion performance after five reaction cycles (20 h) because of the protective carbon layer and Z-schematic charge flow. We believe that this work provides a promising photocatalyst system that combines a 3-D NWA structure and a Z-scheme charge flow for efficient and stable CO₂ conversion

Amine-Functionalized Graphene/CdS Composite for Photocatalytic Reduction of CO₂

This study provides a significant enhancement in CO₂ photoconversion efficiency by the functionalization of a reduced graphene oxide/cadmium sulfide composite (rGO/CdS) with amine. The amine-functionalized graphene/CdS composite (AG/CdS) was obtained in two steps. First, graphene oxide (GO) was selectively deposited via electrostatic interaction with CdS nanoparticles modified with 3-aminopropyltriethoxysilane. Subsequently, ethylenediamine (NH₂C₂H₄NH₂) was grafted by an <i>N</i>,<i>N</i>′-dicyclohexylcarbodiimide coupling reaction between the amine group of ethylenediamine and the carboxylic group of GO. As a result, a few layers of amine-functionalized graphene wrapped CdS uniformly, forming a large interfacial area. Under visible light, the photocurrent through the AG/CdS significantly increased because of enhanced charge separation in CdS. The CO₂ adsorption capacity on AG/CdS was 4 times greater than that on rGO/CdS at 1 bar. These effects resulted in a methane formation rate of 2.84 μmol/(g h) under visible light and CO₂ at 1 bar, corresponding to 3.5 times that observed for rGO/CdS. Interestingly, a high methane formation rate (1.62 μmol/(g h)) was observed for AG/CdS under CO₂ at low pressure (0.1 bar), corresponding to a value 20 times greater than that observed for the rGO/CdS. Thus, the enhanced performance for photocatalytic reduction of CO₂ on the AG/CdS is due to the improved CO₂ adsorption related to the amine groups on amine-functionalized graphene, which sustains the strong absorption of visible light and superior charge-transfer properties in comparison with those of graphene