Preparation And Photocatalytic Performance Of Metal Organic Framework MIL-125(Ti) Composite

Metal-organic frameworks?MOFs?are a new type of crystalline porous solid material that is bridged by metal ions or clusters as nodes and organic ligands.It has high specific surface area,multiple active sites,editability and functionalization.Thus it has received extensive attention in the field of photocatalysis.In particular,MIL-125?Ti?materials have made great progress in photocatalytic degradation of organic pollutants.However,it has a wide band gap,resulting in no absorption in the visible region.Therefore,the rational design and synthesis of MIL-125?Ti?with superior structure and morphology to improve its photocatalytic performance has important theoretical and practical application value.Here,the photocatalytic properties of MIL-125?Ti?were improved by dye sensitization and semiconductor composite methods.The specific conclusions are as follows.The metal organic framework MIL-125?Ti?with high specific surface area and porous structure was synthesized by hydrothermal method,and RhB/MIL-125 composite was synthesized by physical adsorption method with RhB as sensitizer.It was found that the sensitization of RhB not only broadens the visible light absorption range of MIL-125?Ti?semiconductor,but also effectively reduces the recombination efficiency of electrons and holes,which greatly improves the visible light photocatalytic performance of MO solution.The photocatalytic degradation test showed that the RhB/MIL-125composite saturated by RhB shows the best performance and its reaction efficiency constant(0.03 min^-1)is MIL-125?Ti?(0.0004 min^-1)75 times.The results of free radical trapping experiments show that superoxide radicals?·O₂^-?are formed by the electrons,transfer from RhB to the conduction band of MIL-125?Ti?,combined with the oxygen molecules adsorbed on MIL-125?Ti?surface;The holes?h⁺?remaining on the valence band and superoxide radicals?·O₂^-?act together as the main active species of the catalytic reaction to degrade the dye molecules.Constructing a semiconductor heterostructure is one of the effective methods for improving the performance of photocatalysts.SnS₂/amorphous MIL-125?Ti?composite materials were synthesized by hydrothermal method.It was found that the crystallinity of MIL-125?Ti?decreases and changes to amorphous during the composite process.The amorphous phase has more defect centers,which greatly increases the active sites and facilitates the catalytic reaction.However,this also leads to a decrease in the separation efficiency of electrons and holes.Though combing with SnS₂,the separation efficiency of electrons and holes can be effectively improved.The photocatalytic performance test showed that the SnS₂/amorphous MIL-125?Ti?heterojunction catalyst exhibited the best photocatalytic activity when the addition amount of MIL-125?Ti?was 0.5 g?SM-5?.Its efficiency constant(0.0734 min^-1)is 14 times and 122 times that of SnS₂(0.0052 min^-1)and MIL-125?Ti?(0.0006 min^-1).