The Study Of Electrospun Chitosan-Based Membranes For Methyl Orange Adsorption And Photocatalysis

With the rapid development of industrial technology,water pollution caused by organic dyes pollutants has become more serious as an environmental issue and attracted worldwide attention.Organic dyes mainly come from the manufacturing,such as printing,paper,fabric and food processing.These organic dyes easily cause pollution to water and lead to bioaccumulation.Methyl orange?MO?is one of the organic dyes widely used in printing and dyeing industry,belongs to very important and typical azo dye.It can generate many kinds of aromatic compounds,destroying aquatic biological systems.If MO enters the food chain,it will induce human gene mutations and carcinogenesis.So MO is considered to be the most harmful pollutant to water resources.Up until now,among many methods for treating MO,adsorption has the advantages of high efficiency,low cost,and easy operation.Photocatalysis is considered as a"green"treatment method which uses solar energy to effectively degrade organic pollutants.This research work effectively combined the adsorption and photocatalysis methods in dealing with MO.Chitosan?CS?as the adsorbent because of a large number of amino?-NH₂?and hydroxyl?-OH?groups on the CS molecular chains,which can treat organic dyes by electrostatic attraction and chelation.At the same time,TiO₂ was added to the CS through electrospraying technology because of the outstanding chemical resistance,low cost,and good photocatalytic activity.It is expected that MO can be removed effectively by CS-based composite fiber membranes.In this work,based on CS composite fiber membranes were prepared by electrospinning and electrospraying methods.The adsorption and photocatalysis performance of composite membranes with different amounts of TiO₂ were studied.This research work included the following three parts:?1?CS was used as the carrier material,and 90%?v/v?acetic acid?AA?was used as solvent to prepare 2 wt%CS solution.The effect of adding different content of TiO₂ on morphology was studied by electrospraying.The humidity was controlled from 0%to 10%.When the conditions of electrospraying were 18 kV,15 cm,and 0.3 mL/h,uniformly distributed pure CS concave hemispheres were obtained.With the content of 1,2,3 wt%TiO₂,CS still maintained the concave hemisphere morphology,TiO₂ could be evenly distributed on the surface of CS concave hemispheres without any agglomeration.When the TiO₂ content was greater than 3 wt%,TiO₂ begun to agglomerate,and the original morphology of CS concave hemispheres gradually disappeared.?2?Based on cellulose acetate?CA?electrospun fibers,chitosan/TiO₂/cellulose acetate?C-T/CA?fiber membranes were successfully prepared by electrospraying CS-TiO₂ on the surface of CA fibers.The effects of pH,contact time,initial MO concentration,and TiO₂content on the adsorption and photocatalysis performance of MO were studied.When TiO₂content was 3 wt%,the highest MO removal amount for fiber membranes?C-T-3/CA?reached 98%at pH value 4 and MO concentration of 40 mg/L.The pseudo-second-order kinetic and Freundlich isotherm model were well fitted to kinetic and isotherm adsorption equilibrium of MO removal.Especially for C-T-3/CA,the fiber membrane exhibited multilayer adsorption behavior.By adding TiO₂ into the CS hemispheres,TiO₂ could not only be dispersed uniformly,but also be recovered after MO removal.The mechanism of adsorption and photocatalysis in the process of MO removal was discussed.?3?The CT/CS-CA multilayer structure was prepared by the electrospinning/electrospraying technology.As the upper and lower fiber layers,CS-CA composite nanofibers were fabricated by electrospinning the mixture of CS and CA solution.The humidity was controlled to 50%.As intermediate layer,CT composite nanospheres were fabricated by electrospraying the mixture of CS and TiO₂ solution.When TiO₂ content was 3wt%,the highest MO removal amount for fiber membranes?CT₃/CS-CA?reached 99%at pH value 4,MO concentration of 40 mg/L and reaction time of 40 min.The existence of multilayer structure enhanced the stability of intermediate layer.After five cycles,the MO removal rate still maintained 98%.The pseudo-second-order kinetic and Freundlich isotherm model were well fitted to MO removal by CT₃/CS-CA.Different from the monolayer adsorption of pure CS-CA fiber membrane,the multilayer structure changed the adsorption behavior during the MO removal process,exhibiting multilayer adsorption behavior.This work provided a possible method for developing a new photocatalyst with good catalytic activity,adsorption performance and recycling.