Viologen-Modified Platinum Clusters Acting as an Efficient Catalyst in Photocatalytic Hydrogen Evolution

摘要

A highly efficient photocatalytic system for hydrogen evolution with dihydronicotinamide coenzyme (NADH) as a sacrificial agent in an aqueous solution has been constructed by using water-soluble platinum clusters functionalized with methyl viologen-alkanethiol (MVA~(2+)) and a simple electron-donor dyad,9-mesityl-10-methylacridinium ion (Acr~+-Mes),which is capable of fast photoinduced electron transfer but extremely slow back electron transfer.The mean diameter of the platinum core was determined as R_(CORE)=1.9 nm with a standard deviation a=0.5 nm by transmission electron microscopy (TEM).As a result,the hydrogen-evolution rate of the photocatalytic system with MVA~(2+)-modified platinum clusters (MVA~(2+)-PtC) is 10 times faster than the photocatalytic system with the mixture of the same amount of MVA~(2+) and platinum clusters as that of MVA~(2+)-PtC under otherwise the same experimental conditions.The radical cation of NADH has been successfully detected by laser flash photolysis experiments.The decay of the absorbance due to NAD~(centre dot),produced by the deprotonation from NADH~(centre dot+),coincides with the appearance of the absorption band due to Acr~(centre dot)-Mes.This indicates electron transfer from NAD~(centre dot) to Acr~+-Mes to give Acr~(centre dot)-Mes,which undergoes the electron-transfer reduction of MVA~(2+)-PtC,leading to the efficient hydrogen evolution.