Metal-organic Frameworks And The Composites In Photocatalysis And Photo-piezocatalysis For Hydrogen Evolution

Metal-organic frameworks（MOFs）have attracted great interest in the field of photocatalysis in recent years,but their activity is hampered by the issue of severe carrier recombination.To enhance photogenerated charge transfer and migration,a variety of strategies have been developed,including defect engineering,cocatalyst decoration,formation of heterojunction,etc.Among them,MOFs own abundant coordination bonds and non-absolute crystalline order structure,thereby the rational design of MOFs and their composites effectively promote the photogenerated carriers’migration and separation,which presents a broad development prospect.Based on a comprehensive review of the mechanism of photocatalysis and piezo-photocatalysis,material composition and characteristics,application system,and prospect,this article through a carboxyl group assisted coordination route promotes efficiently photocatalytic water splitting.And piezoelectric potential drives the internal polarization of MOFs,thereby promoting the catalytic activity in the case of orderly migration and separation of photogenerated charges.The details are listed below:1.through a carboxyl group-assisted coordination route,MXene decorated with carboxyl groups provides chelation sites enabling coordination with Ui O-66-NH₂（Zr/Ti）to fabricate a tightly connected Ui O-66-NH₂（Zr/Ti）/carboxyl-functionalized MXene（UZT/CFMX）heterostructure.This is the first instance of direct chemical bonding of MOF-involved heterostructure via a coordination bond.The critical role of decorated carboxyl groups can be determined that 1)they can help to establish a strong coordination bond between two materials;2)act as a bridge to promote the electrons transfer from MOFs to MXene,thus relieving carrier recombination,and 3)most interestingly,the carbon atom on the carboxyl group forms a bond with the oxygen from water stimulating the water to dissociate into OH*and H*,thus adding additional reaction pathways for promoting photocatalytic water splitting.Accordingly,the resulting UZT/CFMX shows efficient solar-driven photocatalytic performance for water splitting.The H₂ evolution rate is as high as 2187μmol g^-1 h^-1.This work provides an efficient carboxyl group-assisted coordination route to establish strong interactions in a MOF-based composite,thus promoting the charge transfer process and photocatalytic performance,and such a method can be extended to the future design of high-performance photocatalytic heterojunctions.2.The classical MIL-125-NH₂（Ti）was used to explore piezo-photocatalytic hydrogen production.T0 with{001}crystal facet showing disk and T1 with{111}crystal facet showing octahedron were successfully fabricated with different morphologies.In the process of catalytic application,we found that T0 and T1 can promote water splitting under ultrasonic conditions,and explored the effect of crystal facet on piezo-photocatalysis.Importantly,T1 with{111}crystal facet has higher electrical conductivity and better piezoelectric transient current response under the influence of piezoelectric potential,which promotes the rapid migration and separation of carriers and effectively suppresses the recombination of electron-hole pairs.The piezo-photocatalytic hydrogen evolution of T1 showed better activity.Furthermore,piezoelectric deposition experiments proved that under piezoelectric action,MIL-125-NH₂（Ti）could generate some electrons to migrate to the surface of MOFs to promote water splitting.This work preliminarily explores the combination of the advantages of piezoelectric catalysis and photocatalysis to create a built-in electric field in MOFs as the driving force for charge separation and provides a unique problem-solving idea for the establishment of piezo-photocatalysis in pure MOFs.The methods of restoration of water splitting are diversified.