Alga-based Carbon Modified TiO₂ Composites For Photocatalytic Degradation Of Organic Pollutant

In recent years,the alga green tide frequently breaks out and intrudes into coastal waters for many times owning to the eutrophication of water bodies and the greenhouse effect,which has a serious impact on marine environmental protection and marine economic development.As a natural resource with abundant output which is widely distributed,cheap and easy to obtain,seaweed is expected to be transformed into high value-added products.The seaweed enteromorpha is rich in polysaccharides,protein,minerals,cellulose and so on,which can be deeply developed and prepared for a variety of high value-added derivatives.Based on the current research,choosing the Qingdao offshore enteromorpha as carbon source,two kinds of algae-based carbon materials,algae-based carbon quantum dots（CDs）and activated carbon（AC）were designed and prepared,and then combined them with semiconductor material TiO₂,which can build a safe,non-toxic,high efficient degradation of organic pollutants as well as create some environmental and economic benefits.Choosing rhodamine B as the model organic pollutant,it focuses on the photocatalytic degradation performance of the algae base light catalyst on the organic pollutant under visible illumination.The results are listed as follows:Firstly,choosing solid waste as carbon source,seaweed algae-based CDs was synthesized by one-step microwave hydrothermal method.Then,the CDs-Cu-TiO₂ composites was synthesized by combing the CDs with TiO₂ nanoparticles through hydrothermal method,and using copper doping modification,which was used to catalyze pollutant degradation under visible light.The results showed that CDs,Cu and TiO₂are closely combined in the composite material,causing the remarkable improvement absorption of visible light region and the reduction of fluorescence emission efficiency.The synergistic effect of CDs and doped Cu reduced the band gap to 2.35e V,and effectively inhibited the electron-hole recombination.Using rhodamine B as a pollutant model,the photocatalytic degradation experiments showed that the first-order reaction rate constant of CDs-Cu-TiO₂ composites could reach 6.4 times than that of pure TiO₂ nanoparticles under visible light irradiation.Secondly,using algae as carbon source,we prepared the activated carbon（AC）with a specific surface area of 2190 m2/g by adjusting different activation methods and environments.The surface of AC was rich in oxygen-containing functional groups,reaching to 2.28 mmol/g.Using AC as carbon carrier and carbon source,3-ammonia propyl triethoxy silane（APTES）as inducers and coupling agent,2（2-hydroxyl acrylic acid）dihydrooxy diammonium titanium（Ti-BALDH）as organic titanium precursor of TiO₂,TiO₂-AC composite material was prepared in a green controllable preparation process using bionic way of in-situ growth of TiO₂nanoparticles on activated charcoal.To further expand the visible absorption,TiO₂-Cu-AC composite materials was synthesized with copper doping modification based on the above work.The forbidden band width of the composite materials is 2.38 e V and the photocatalytic degradation rate constant of rhodamine B solution is 12 times that of pure TiO₂,showing excellent photocatalytic activity,which could be attributed to the synergistic effect between TiO₂,AC and copper doping enhanced the intensity of light absorption.The strong adsorption property of AC can increase the local concentration of organic pollutants around the photoactivation site,thus enhancing photocatalytic effect.While the doping of copper can reduce the band gap width of TiO₂ and expand the absorption and utilization of visible light.