Study On The Modification Of Bismuth Molybdate And Its Photocatalytic Performances In Selective Oxidation Of Toluene

The photocatalytic process for the selective oxidation of hydrocarbons under mild conditions to prepare value-added oxygenated organic chemicals is of great significance in the chemical industry.Compared with traditional catalytic technology,the reaction conditions can be green and mild by photocatalysis.Heterogeneous photocatalysts have attracted extensive attention due to their low cost and easy separation from products.However,low catalytic efficiency prevents their practical applications.By constructing heterojunction has become one of the most commonly used method to enhance activity because the absorption of light can be broadened,and the built-in electric field can be constructed on heterojunctions to promote interface charge transfer and separation.Bi₂MoO₆ has attracted attention from the photocatalytic community due to its suitable band gap,visible light absorption,low cost and stable characteristics.In recent years,Bi₂MoO₆ exhibited good catalytic activity in the oxidation of aromatic hydrocarbons and aromatic alcohols.However,due to the short life and high recombination rate of photogenerated carriers,the application of Bi₂MoO₆ is restricted.Based on this,adjusting the morphology and construction of heterojunctions with g-C₃N₄ and Bi₂WO₆ to enhance the activity of Bi₂MoO₆ are proposed.Possible reaction mechanism for selective oxidation of toluene over the as-prepared catalysts is proposed based on the results of ESR and control experiments.The conclusions of this paper are as follows:Synthesis of Bi₂MoO₆/g-C₃N₄ zero-dimensional/two-dimensional?0D/2D?heterojunction.Bi₂MoO₆ quantum dots?QDs?anchored on 2D g-C₃N₄ nanosheets was successfully prepared by a simple two-step hydrothermal method.Not only the charge migration distance be shortened,the visible light absorption range be broadened,but also a rich catalytic active sites can be provided over the composite.Excellent catalytic performance in selective oxidation of toluene to benzaldehyde achieved onver Bi₂MoO₆/g-C₃N₄ when oxygen was used as the oxidant.When the mass ratio of Bi₂MoO₆ QDs:2D g-C₃N₄ was 2:10,the composite photocatalyst showed the highest activity,and the rate of benzaldehyde formation is 850.7?mol g^-11 h^-1 under the condition of visible light??>400 nm?without solvent.Synthesis of ultra-thin Bi₂MoO₆-Bi₂WO₆ 2D/2D heterojunction.In order to improve the contact area of the heterojunction of the composite photocatalyst,CTAB was used as the structure directing agent,and the heterojunctions between Bi₂MoO₆ and Bi₂WO₆ nanosheets were controllable fabricated by a two-step hydrothermal method.Due to the construction of the 2D/2D heterojunction,the migration of photogenerated carriers is enhanced and the recombination of charge carriers is inhibited.When the molar ratio of Bi₂WO₆ to Bi₂MoO₆ is1:2,the formation rate of benzaldehyde under visible light reaches 984.7?mol g^-1 h^-1.