Phosphate-regulated Nickel Phthalocyanine/BiVO₄ Ultrathin Composites For Total Water Splitting Photocatalyst Synthesis

Using solar energy to drive the photocatalytic overall water splitting to generate clean fuel hydrogen and available oxygen is one of the effective ways to solve current energy and environmental problems.Semiconductor photocatalysis technology can convert solar energy into chemical energy that is easier to use.In the solar spectrum,the energy of visible light accounts as much as 44%.Therefore,the development of narrow band gap semiconductors with high-efficiency visible light response is the key to achieving high-efficiency photocatalytic activity.BiVO₄ is a cheap and easy-to-obtain,narrow band gap semiconductor which is widely used in photocatalysis.However,due to the poor reduction ability of BiVO₄ photogenerated electrons,the overall water splitting performance needs to be improved.Constructing Z-scheme heterojunction is an effective strategy to improve the overall water splitting performance of BiVO₄.However,the traditional BiVO₄-based Z-scheme heterojunction lacks surface catalytic active sites and the light absorption range of two semiconductor components are relatively close,which makes it difficult to further broaden the light response range of the system.Therefore,this work has developed a new Z-scheme NiPc/BiVO₄ ultrathin nanocomposite with a wide spectrum response and rich in surface catalytic active centers which is different from the traditional Z-scheme,committed to improving the activity of BiVO₄ overall water splitting,and studying the activity enhancement mechanism.This paper is mainly divided into two parts.First,the NiPc/BiVO₄ ultrathin nanocomposites with a wide spectral response was successfully constructed by the method of hydroxyl-induced assembly.The experimental results show that NiPc and BiVO₄have independent light absorption ranges,and NiPc modification significantly broadens the visible light response of BiVO₄.The close interface between BiVO₄ and NiPc through hydrogen bonding makes the new Z-scheme NiPc/BiVO₄ ultrathin nanocomposite exhibit excellent charge transfer and separation performance,and the photocatalytic overall water splitting activity is significantly improved.In addition,the Z-scheme charge transfer mechanism between NiPc and BiVO₄is proved.Second,introducing phosphate to induce controllable assembly of highly dispersed NiPc and BiVO₄.Experimental results show that phosphate regulation can significantly improve the dispersion of NiPc,make NiPc highly dispersed on the surface of BiVO₄nanosheets in a state of 1-2 layers,and significantly improve its photocatalytic overall water splitting activity.It can be revealed by exploring the mechanism of improving photocatalytic activity,phosphate modification greatly increases the loading of NiPc on BiVO₄（from 1 wt.%to 2.6 wt.%）,and significantly promotes the Z-scheme between NiPc and BiVO₄ charge transfer and separation.In addition,phosphate modification can form a negative surface field,induce the photogenerated holes of BiVO₄ to migrate to the surface,further promote Z-scheme charge transfer and separation,and synergistically improve its overall water splitting activity.