Investigation In Photocatalytic Oxidation Of Glucose With Two Kinds Of Composite Catalyst

In recent years,it has caused the continuous increase of the price of petrochemicals by the continuous under-supply of petroleum,and the production of petrochemicals have caused environmental pollution.That is promoting the development of alternative energy sources such as agricultural by-products or biomass to get rid of dependence on non-renewable fossil resources.As an important component of biomass,glucose is not only the constituent monomer of lignin and cellulose,but also the most widely distributed monosaccharide in nature.It is considered to be an ideal raw material for the production of biofuels and platform chemicals.A large amount of glucose can be obtained directly from plants or indirectly by hydrolyzing cellulose and starch.Through the selective oxidation of glucose,a variety of industrial raw materials and high value-added chemicals can be obtained.In this paper,based on the selective oxidation of glucose,CoPz/ZnO and WO₃/g-C₃N₄ photocatalysts containing no precious metals were prepared by porphyrin photosensitization and semiconductor composites to form heterojunctions to enhance the catalytic activity of single-phase catalysts.For the first time,they were used as catalysts for photocatalytic oxidation of glucose in a neutral aqueous solution with molecular oxygen as an oxygen source and at normal temperature and pressure.The experimental results show that the photocatalytic performance of ZnO is effectively improved after loading cobalt thioporphyraines?CoPz?.Under the optimal conditions,the glucose conversion rate was 45.4%?more than 4 times that of ZnO?for reacting 3 hours,and the selectivity of gluconic acid and glucaric acid was 10%and 1.4%respectively,as well as products such as arabinose,formic acid,and glycerol.CoPz/ZnO has a wider absorption light wavelength range and higher photogenerated electron-hole separation efficiency than ZnO proved by solid ultraviolet diffuse reflection and surface photocurrent.Electron paramagnetic resonance and quenching experiments show that the main reactive oxygen species in this reaction system are hydroxyl radical?·OH?,singlet oxygen?¹O₂?,hole?h⁺?and superoxide anion(O₂^·-).And four reactive oxygen species are involved in the reaction.CoPz/ZnO produces more hydroxyl radicals and singlet oxygen than ZnO.WO₃/g-C₃N₄(W₁₀G)obtained by compounding WO₃ and g-C₃N₄ at a mass ratio of 10:1 as a catalyst,reacted under optimal reaction conditions for 4 hours,glucose can be converted by 58.6%,with the selectivity of gluconic acid and glucaric acid are27.8%and6.9%respectively.The conversion rate is significantly higher than that of WO₃ and g-C₃N₄ alone as a catalyst,while the selectivity remains unchanged basically.It has proved by electron paramagnetic resonance and reactive oxygen species quenching experiments,there are four reactive oxygen species in the reaction system:hydroxyl radical?·OH?,singlet oxygen?¹O₂?,superoxide anion(O₂^·-)and hole?h⁺?.The concentration of hydroxyl radical,singlet oxygen and superoxide anion produced by W₁₀G under illumination is significantly higher than that of pure WO₃and g-C₃N₄,so the composite catalyst showed higher catalytic performance.Comparing the surface photocurrent intensities of WO₃,g-C₃N₄ and W₁₀G,it is proved that W10G has higher efficiency for the separation of photogenerated electron-holes,and more photogenerated electrons and holes participate in the reaction.