Study On The Tunable Degradability Of Chitosan Membranes Modified By Silver Nanoparticles

A wide application of membranes for water treatment has greatly improved the water treatment efficiency and water quality.Membranes,mostly made of polymeric materials derived from petroleum,are eventually disposed of to landfill or incinerated after reaching their service life.Improper disposal of used membranes sometime occur,however,which may pollute the natural environment.It is therefore desirable to develop membranes made of natural polymeric materials that are available at low cost and particularly,are subject to degradation in the environment so there is no permanent environmental impact.Chitosan is a polysaccharide that can be easily obtained from chitin shells of shrimp and other crustaceans.Water treatment membrane made of chitosan had been prepared with good biocompatibility and hydrophilicity when LiOH/KOH/urea system was applied to dissolve chitosan.Chitosan membrane has the desirable property of biodegradability after its service life.A conundrum is how to make sure the membrane is not degraded by microorganisms during its active applications for water treatment.What we need is a membrane that its degradation is controllable,i.e.,the membrane is not subject to degradation during the service but could be degradable after its service life.The goal of this work was to develop a membraene with controlable biodegradability using chitosan as a model membrane material.The anti-degradation properties of chitosan membranes were imparted by embedding the silver nanoparticles into the membrane.Since the release time and rates of silver nanoparticles from the membrane depend on the amounts and protocols of silver nanopartilce embedding,we could potentially control the duration of silver release and thus the duration prior to which the biodegradation would have been suppressed.In this study,the release rates of silver nanoparticles from the modified chitosan membrane were controlled by changing the membrane forming temperature and the embedded amount of silver nanoparticles.From the SEM imaging and silver release experiments,we found the membrane forming temperature could significantly influence on the membrane structure and release rates of silver nanoparticles from the chitosan membrane.For the membrane formed at 20℃,the stable release rate of silver is 0.025μg/cm~2/h;For the membrane formed at-20℃,the stable silver release rate is 0.075μg/cm~2/h.The anti-degradation performance of chitosan membrane was assessed by the lysozyme activity for chitosan degradation.When the concentration of silver in the solution was 10μg/L,the lysozyme activity of chitosan degradation was 24%of the control without silver;and when the concentration of silver in the solution was 40μg/L,the lysozyme activity of chitosan degradation was less than5%.Silver nanoparticles modified chitosan membrane similarly showed a strong inhibitory effect on microbial activity.The duration of anti-degradation of chitosan membrane modified with silver nanoparticles containing 1%silver nanoparticles at 20℃and-20℃was 196 h and 73 h,respectively.