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Copper phosphides are promising materials for energy conversion applications because of their unique electronic structure and controllable composition. Two stoichiometric copper phosphides, CuP2 and Cu3P, were prepared by direct wet-chemical synthesis using red phosphorus. They were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy. The precursor selection, reaction temperature, time and solvent composition were also studied. CuP2 is the thermodynamically more stable product, but Cu3P is more commonly obtained. This work demonstrated that higher temperature helps in CuP2 formation. More importantly, using more trioctylphosphine oxide helps control the morphology leading to crystal growth along the crystallographic a-axis. CuP2 and Cu3P were tested for hydrogen evolution, oxygen evolution, and oxygen reduction reactions. CuP2 works better for HER in acidic conditions and OER in general, and Cu3P showed better activity than CuP2 for HER and ORR in an alkaline medium. This study has led to a simple approach to the synthesis of CuP2 nanowires.

The construction of a heterojunction by coupling two semiconductor photocatalysts with appropriate band positions can effectively reduce the recombination of photogenerated charge carriers, thus improving their catalytic efficiency. Recently, ZnO photocatalysts have been highly sought after in the synthesis of semiconductor heterostructures due to their wide band gap and low conduction band position. Particularly, transition metal-doped ZnO nanoparticles are attractive due to the additional charge separation caused by temporary electron trapping by the dopant ions as well as the improved absorption of visible light. In this paper, we compare the effect of doping ZnO nanoparticles with 3d (Co and Mn) and 4d (Ag) transition metals on the structural and optical properties of ZnO/CdZnS heterostructures and their photocatalytic performance. With the help of scanning electron microscopy, the successful anchoring of doped and undoped ZnO nanoparticles onto CdZnS nanostructures was confirmed. Among the different heterostructures, Ag-doped ZnO/CdZnS exhibited the best visible-light-driven degradation of rhodamine B at a rate of 1.0 × 10−2 min−1. The photocurrent density analysis showed that AgZnO/CdZnS has the highest amount of photogenerated charges, leading to the highest photocatalytic performance. The reduction in the photocatalytic performance in the presence of hole scavengers and hydroxyl radical scavengers confirmed that the availability of photogenerated electrons and holes plays a pivotal role in the degradation of rhodamine B.