The Modification Of Bismuth Molybdates And Their Excellent Photocatalytic Performance For Selective Oxidation Of Toluene Derivatives Under Visible Light Irradiation

Selective activation of primary C–H bonds for fine chemicals synthesis is of crucial importance for the sustainable exploitation of available feedstocks.Currently,there exist some main drawbacks of researches in this area,including low catalytic efficiency,narrow catalysts,and using of ultraviolet irradiation or noxious solvent.Bismuth molybdates are promising photocatalysts because of their suitable band location,nontoxicity as well as their superior spectral properties.It was reported that?-Bi₂MoO₆ exhibited a superior performance in the oxidation reactions of alcohols.Herein,sheet-like Bi₂MoO₆ was synthesized by a simple hydrothermal method,and the photocatalytic performance was enhanced by modification means such as construction of heterojunctions,doping and so on.On the other hand,we used the selective oxidation of aromatic alkanes undervisiblelightirradiation as reaction model to examine its photocatalytic performance.The physical and chemical properties of the as-prepared samples were characterized by varioustechniques and the relationship between strucutures and catalytic performances wasinvesitigated.Furthermore,we performed experiments with the addition of different scavengers to understand the role of photogenerated radical species and underlying reaction mechanism involved for photocatalytic selective oxidation of toluene over as-prepares samples under visible light irradiation.The main research contents and innovative results of the paper are summarized as follows:At first,TiO₂/Bi₂MoO₆heterostructure were successfully synthesized and found to show good phtotocatalytic performance towards the selective oxidation of aromatic alkanes into benzaldehyde derivatives under visible light irradiation,with benzaldehyde production rate of1036.8?mol g^-1h^-1.Compared with single component,the TiO₂/Bi₂MoO₆ heterostructures favor a high accessible surface area and good structural stability and shows better photocatalytic performance than Bi₂MoO₆ and TiO₂.The enhanced photocatalytic performance of TiO₂/Bi₂MoO₆ is mainly ascribed to the reduced electron–hole pair recombination due to the stepwise energy levels between Bi₂MoO₆ and TiO₂.Secondly,a simple protocol was developed for the synthesis of a Bi₂MoO₆-Bi₂Mo₃O₁₂heterostructure by adding Bi³⁺to control the phase transformation of Bi_3.64Mo_0.36O_6.55.55 for the first time.And the band structure of bismuth molybdates can be tuned through different extents of Bi self-doping.The synthesized Bi_2.1MoO₆-Bi_2.1Mo₃O₁₂2 composite is apt for the oxidation of saturated sp³ C–H bonds using dioxygen as oxidant and shows excellent visible-light-driven photocatalytic activity,stability,as well as selectivity.The good performance is attributed to the formation of heterostructure and molybdenum vacancies forming in the self-doping process.This method of using self-doped Bi₂MoO₆-Bi₂Mo₃O₁₂with heterostructure opens an environment-benign way for efficient synthesis of organic compounds that requires the activation of saturated alpha-carbon C–H bonds.Thirdly,a technology flow diagram was designed for the oxidation of toluene and the material balance,energy balance of the process have been calculated by the Aspen Plus software system to verify the feasibility of the process.The results showed that the mass flow rate of raw material equals the sum of the mass flow rate of the compound produced.Thus,the processaccords with the material balance.Each equipment accords with the energy balance,which means the whole system in line with the energy balance.This process was conduvcted at room temperature and atmosphere pressure,and the entire process greatly reduced the energy consumption.Therefore,the process conforms to the concept of green environmental and efficient production,which is economic and feasible.