Preparation And Catalytic Performance Of Composites Of Phosphotungstate And Ag Nanoparticles Loaded On Mesoporous TiO₂-ZrO₂

Polyoxometalates（POMs）has been widely used in catalysis,adsorption,electrochromatism,magnetism and materials science due to unique structures and special properties.However,POMs are easily soluble in polar solvents and difficult to be recycled and reused as the catalyst.Loading POMs on active carriers is one of the effective methods to address this disadvantage.At the same time,the catalytic activity of the catalyst can be effectively improved due to the synergistic effect between POMs and carriers.In this paper,phosphotungstic acid was loaded on mesoporous binary oxide Ti O₂-ZrO₂to prepare mTiO₂-ZrO₂/PTA composite（m represents the mesoporous）,and its catalytic performance on photocatalytic degradation pollutants in water was explored.Furthermore,Ag nanoparticles were further deposited to obtain Ag/PTA/mTiO₂-ZrO₂composite,and its photocatalytic and electrocatalytic performances for nitrogen reduction reactions were investigated.The main works are as follows:1. A series of novel mTiO₂-ZrO₂/PTA nanocomposites wereprepared by surfactant-assisted sol-gel co-condensation method combined with hydrothermal treatment technology using P123 as a template.The photocatalytic activity of the materials was evaluated by experiments of degradation of MO under simulated sunlight conditions and reduction of Cr⁶⁺under sunlight conditions.The experimental results show that when the molar ratio of titanium to zirconium is 3,the contant of phosphotungstic acid is 10 wt.%,the material has the best catalytic activity.The degradation efficiency of MO within 1 h was up to 100%,and the reduction efficiency of Cr⁶⁺reached 51.7%.Compared with a single component,the obtained mTiO₂-ZrO₂can strongly prevent the recombination of photo-generated electron and hole pairs,and the introduction of PTA can improve light absorption and photochemical stability,further promoting the photocatalytic activity effectively.At the same time,the synthesized catalyst has good stability.Catalytic cycling experiments showed that the material showed almost no reduction in activity after five cycles.2. A series of novel Ag/PTA/mTiO₂-ZrO₂ nanocomposites were prepared bysurfactant-assisted sol-gel co-condensation method combined with hydrothermal treatment technology using P123 as a template.The characterization results of the materials show that Ag metal phase and PTA Keggin structure are well dispersed on the carrier.The photocatalytic and electrocatalytic nitrogen fixation of the material were carried to explore the catalytic performance.It was found that Ag/PTA/mTiO2-ZrO2exhibited the excellent photocatalytic nitrogen fixation activity when the optimal Ag content was 1.0 wt.%(351.6μmol·g^-1_cat),and the electrocatalytic nitrogen fixation activity(208.2μg·mg^-1_cat·h^-1)and the maximum faraday efficiency（24.79%）.Mechanism experiments show that the introduction of Ag nanoparticles and PTA can effectively inhibit the recombination of photo-generated electrons and holes,further enhance light absorption and photochemical stability,and therefore can effectively improve photocatalytic activity.EPR and N₂-TPD characterizations indicate the presence of oxygen vacancies and the ability of strong chemisorb nitrogen in the material.The composite showed good stability,the activity remained almost unchanged after five photocatalytic nitrification cycles.In electrocatalytic nitrogen fixation,the nitrogen fixation efficiency and faraday efficiency maintained a consistent level after 10h of cycling.