Study On Emulsification Behavior And Interfacial Catalytic Performance Of Cross-Linked Enzyme-Carrying Chitosan

Pickering emulsions are widely used in various fields due to the advantages of low emulsifier usage,easy recovery and separation.In catalytic reactions,Pickering emulsion systems can shorten the diffusion distance of material and increase the mutual contact area between two-phase of substances,which is beneficial to improve the catalytic efficiency.Among the materials that used to stabilize Pickering emulsions,chitosan can form emulsions under ultrasound without adding any surfactants and cross-linking agents.Due to its biodegradability,biocompatibility and non-toxic property,chitosan has become a potential Pickering emulsion stabilizer.At the same time,chitosan has a large amount of amino and hydroxyl groups,it is an excellent carrier for immobilizing enzymes,so that it can be used as both emulsifier and catalyst to construct a Pickering emulsion catalytic system.Enzyme is a highly efficient green catalyst.Free enzyme will be inactivated in the presence of high temperature or organic solvents.Therefore,it can be used in the catalytic reaction system by immobilizing enzyme instead of free enzyme.However,there is no report on chitosan cross-linked enzyme-loaded Pickering emulsion catalytic system.The immobilized enzyme chitosan composite surface with oppositely charged phytosterol particles obtained by cross-linking the enzyme is used to stabilize the Pickering emulsion,so that the enzyme can be stably present at the water-oil interface,which is conducive to maintaining its stability and catalytic activity,increasing the contact between the enzyme and the reaction substrate,thereby increasing the reaction rate of the catalytic system.(1)Preparation and emulsification behavior of CSMPs.Firstly,CSMPs were prepared by emulsion template method using paraffin oil as oil phase,chitosan acetic acid solution as water phase and glutaraldehyde as crosslinking agent.The aldehyde groups of glutaraldehyde reacted with the amino groups of CS to form Schiff base for crosslinking,CSMPs were obtained.The morphology and structure of CSMPs which were prepared under different experimental conditions were analyzed by SEM,TEM,FTIR,Size,Zeta potential,contact angle and other characterization methods,also investigated the differences between CSMPs and CS emulsified water and n-hexane.The results show that CSMPs with high ballability,uniform particle size and good monodispersity can be obtained when the mass fraction of CS was 2.5%,the volume ratio of water to oil was 1:2 and the concentration of glutaraldehyde was 25%.Both CS and CSMPs could emulsify water and n-hexane to form O/W Pickering emulsions,but CS emulsified water and n-hexane emulsions did not occur serious demulsification after standing at room temperature for 36 h,the emulsification performance of CS is better than CSMPs.(2)Preparation of immobilized enzyme chitosan and its catalytic performance at water-oil interface.Firstly,PPL was immobilized by Schiff base reaction using CSMPs and CS as carriers respectively,glutaraldehyde as crosslinking agent,obtained immobilized enzyme particles CSPPL and CSMPPL.The morphology and structure were analyzed by SEM,Zeta potential,contact angle and other characterization methods.After cross-linking immobilized the enzyme,the morphology of CSMPs was maintained,CS showed a multi-layer flaky structure.Then,the emulsifying properties of CS and CSPPL were investigated.Subsequently,the W/O Pickering emulsion catalytic system was prepared by using CSPPL composite PS particles which the surface with oppositely charged.The catalytic performance of the system was studied by using the template reaction of catalytic esterification to synthesize PSA.Finally,the effects of different catalytic systems on the esterification rate of esterification reaction were compared.The results showed that the enzyme loading of CSMPs was 302.05 mg/g and the enzyme loading of CS was 262.0 mg/g when the mass ratio of enzyme to carrier was 1:1,the concentration of crosslinking agent was 2% and the reaction time was 8 h.Both CS and CSPPL particles can stabilize water and white oil to form the stable O/W Pickering emulsions.However,when the amount of CSPPL was less than CS,the emulsion droplet diameter was smaller,so the emulsification performance becomes better after cross-linking immobilized enzyme.The esterification rate of Pickering emulsion catalytic system for 24 h reached 84.51% when the amount of CSPPL was 0.02 g,which was nearly 30 times than that of homogeneous catalytic system.The catalyst could be recovered by simple centrifugation,and the recovered particles still maintained good catalytic performance after 5 cycles of reaction.