Preparation And Photocatalytic Degradation Properties Of Cellulose-based Composites

Recently,with the rapid industrialization development,ecological damage and environmental pollution,especially water pollution has become more and more seriously.Photocatalytic technology is considered as a promising sustainable strategy to solve the above problems,which has attracted great attentions for its lots of advantages including clean,efficiently,green environmentally friendly,no pollution and et.al.Most of semiconductors used for photocatalytic reaction are powder,which may cause particle agglomeration.Meanwhile,powder catalysts are difficult to separate and recover to hinder their practical application.To overcome these problems,we selected commercial mixed cellulose membrane（CNCA）and biological leaf veins（bio-veins）containing natural cellulose as the base materials.Series of porous cellulose membranes（Ag@Ag Cl/CNCA）with inorganic nanoparticle hybridization were prepared by impregnation-precipitation-photoreduction method,and BiOBr/Bio-veins composite materials were prepared by in situ method.The photocatalytic degradation activities of these prepared systems were studied,and related photocatalytic degradation mechanisms were explained.The main research results were shown as follows:（1）Investigation of photocatalytic properties of commercial hybrid cellulose films with inorganic nanomaterial hybrid.Series of hybrid cellulose composite films（Ag/CNCA,Ag Cl/CNCA,Ag@Ag Cl/CNCA）hybridized with nanomaterials were prepared by impregnation-precipitation-photoreduction method.The inorganic nanoparticles（Ag,Ag Cl,Ag@Ag Cl）were uniformly distributed on the CNCA.The loaded Ag@Ag Cl particles are ranged 200 to 500 nm with SEM analysis.The visible light adsorption of composite films is enhanced according from the results of UV-vis testing.And recombination of photogenerated electron-holes may be hindered by the charge transferring between CNCA and nanoparticles.Ag@Ag Cl/CNCA composite film shows best photocatalytic activity for degradation of methylene orange（MO）under visible light irradiation.Under the same conditions,about 96.01%of MO was degraded by Ag@Ag Cl/CNCA composite film within 120 min with calculated degradation rate is 0.0232 min^-1,which was 14.5 times higher than that of pure CNCA.The results of radical trapping experiments showed that holes（h⁺）and superoxide radicals（·O₂^-）were the main active groups for the photocatalytic degradation of MO by Ag@Ag Cl/CNCA composite film.At the same time,proper photocatalytic degradation mechanism was explored.（2）Investigation of photocatalytic properties of Osmanthus fragrans leaf veins.Bio-veins with different cleanliness degrees were successfully prepared by removing the mesophyll from osmanthus leaves with strong alkali method under high temperature.The completely untreated biological veins（0%-Bio-vein）were covered with a large amount of mesophyll,while cleaned leaf veins（100%-Bio-vein）were consisted of dendritic fibers.Comparing with 0%-Bio-vein,100%-Bio-vein has better visible light absorption.100%-Bio-vein showed the best photocatalytic activity for degradation of Rhodamine B（Rh B）within 2 hours,which the degradation rate of Rh B reached about 36.42%.（3）Investigation of the photocatalytic properties of the composite（BiOBr/Bio-veins）formed by BiOBr and natural cellulose（biological leaf veins）.A novel BiOBr/Bio-veins photocatalyst was prepared by a wet drop-in-situ generation method.The nanoparticles of BiOBr were uniformly distributed on Bio-veins with no obvious agglomeration,BiOBr particles size of BiOBr/Bio-veins composites became smaller for increasing active sites for catalytic reactions.After combing with Bio-veins,BiOBr/Bio-veins composite showed better visible light absorption and lower recombination rate of photogenerated electron-holes compared with pure BiOBr powder.As a result,the photocatalytic degradation performance of BiOBr/Bio-veins composites with different loadings of BiOBr showed better photocatalytic degradation activities than that of pure BiOBr or pure Bio-veins.The optimal sample（BiOBr/Bio-veins）_0.03,prepared with a concentration of BiOBr precursor of 0.03 mol/L,can degrade Rh B by 97.84%within 120 min under visible light conditions.The photocatalytic degradation rate of（BiOBr/Bio-veins）_0.03 reaches 0.02751 min^-1,which was 7.05 times and6.41 times higher than that of pure Bio-veins and pure BiOBr powder,respectively.Besides,BiOBr/Bio-veins composite had good cycling stability,and its photocatalytic degradation performance was still similar to that of pure Bio-veins and pure BiOBr samples after four cycling experiments.Meanwhile,the reactive species trapping experiments and EPR tests of（BiOBr/Bio-veins）_0.03 were operated,and superoxide radicals（·O₂^-）and holes（h⁺）were confirmed as the main active groups for photocatalytic degradation.At the same time,possible photodegradation mechanism of BiOBr/Bio-veins was explored.In conclusion,we have successfully prepared series of cellulose-based composite,which show great advantages including high catalytic efficiency,short synthesis process,easy separation and recycling,and low cost.Meanwhile,our works have also provided a new design idea for synthesis of cellulose-based photocatalysts with efficient photocatalytic activities.