Study On The Preparation Of Floating BiOCl-based Photocatalyst And Its Algae Removal Performance

In recent years,with the rapid development of cities and the increasing discharge of industrial and agricultural wastewater,a large amount of nutrients have flowed into water,resulting in serious eutrophication of water,which makes harmful algal blooms and other environmental problems occur frequently.The large-scale reproduction of algae not only affects the landscape environment,but also pollutes water sources,thus threatening the safety of drinking water.The application of traditional treatment methods is limited because of the defects such as high cost and unstable effect.Compared with the shortcomings of the current mainstream algae removal technology,photocatalytic technology has been gradually applied in the environmental field in recent years due to its environmental friendliness,high efficiency,low cost,and good degradation effect.Bismuth oxychloride（BiOCl）,as one of the semiconductor materials,has attracted extensive attention of scholars due to its excellent electron transport capability and high optical stability.However,due to the large band gap value of BiOCl,it only shows good activity under ultraviolet light,so its practical application has certain limitations.At the same time,the phototaxis of algae makes it float on the surface of water layer,and it is difficult for the photocatalyst to fully contact the algae,which affects the removal efficiency.In view of the above urgent problems,based on bismuth oxychloride（BiOCl）,Microcystina aeruginosa（dominant algae species）as the target pollutant,the experiment modifies BiOCl by constructing solid solution and combining with semiconductor materials,and then prepared floating photocatalyst.The morphological characteristics of the samples and photocatalytic inactivation of Microcystis aeruginosa under visible light are studied.The main contents are as follows:1.The floating BiOCl_0.6I_0.4/GO/EP photocatalyst was successfully synthesized by water bath method and in-situ precipitation method with expanded perlite（EP）as the carrier.The composition and morphology of synthesized samples were characterized by XRD（X-ray diffracation）,SEM（Scanning electron microscope）,FTIR（Fourier Transform Infrared Spectrometer）,UV-Vis DRS（UV-Vis diffuse reflectance spectroscopy）and XPS（X-ray photoelectron spectroscopy）.The results of photocatalytic algae removal experiments indicate that BiOCl_0.6I_0.4/GO/EP composite have a wider photoresponse range and better algae removal performance than that of BiOCl_0.6I_0.4/EP and GO/EP.Even after four cycles reuse,the composite still shows better photocatalytic activity.Furthermore,free radical capture experiment proves that photo-generated holes（h⁺）are the main active species for the inactivation of algae in photocatalytic process.2.Zinc oxide（Zn O）was synthesized by water bath method,precipitation method and calcination method and loaded on the surface of expanded perlite,and then combined with BiOCl_0.6I_0.4to form p-n heterostructures.The composition,morphology,chemical states,optical properties of the photocatalyst were also characterized.The results indicate that the composite has stronger photocatalytic activity than a single BiOCl_0.6I_0.4and Zn O,and the removal rate of chlorophyll a is89.28%after 6 h of photocatalytic reaction.The photosynthetic system is destroyed and cell membrane of algae ruptured under photocatalysis,resulting in the decrease of phycobiliprotein components and the release of a large number of ions(K⁺,Ca²⁺and Mg²⁺).Finally,active species trapping experiment determines that holes（h⁺）and superoxide radicals（·O₂^-）are the main active substance for the inactivation of algae,and the p-n mechanism of photocatalyst is proposed.