Preparation Of Silver Nanocomposites And Their Performances For Point-of-use Drinking Water Disinfection

Microbial contamination of drinking water is one of the major threats to public health,and the lack of safe and reliable water sources remains a serious problem for millions of people around the world.Point-of-use（POU）drinking water disinfection systems based on silver nanoparticles（Ag NPs）are now a key solution for the provision of safe drinking water in places where centralised drinking water facilities are not available.Due to the lack of stability of Ag NPs on the nanoscale and their tendency to self-aggregate,Ag NPs are usually required to be immobilised in various inorganic or organic carrier materials for use in POU drinking water disinfection systems.However,most silver-based composites suffer from the inability to effectively control the stable release of Ag⁺,which on the one hand shortens the service life of the antimicrobial agent;on the other hand,the release of large amounts of Ag+may pose a threat to human health.In this study,two kinds of low-cost and environment-friendly polyurethane foam（PUF）and chitosan（CS）were used as carrier materials to prepare two new POU drinking water disinfectants with high antibacterial efficiency and sustainable silver release properties.The main research elements and findings of this thesis are as follows:（1）Commercial polyurethane foam（PUF）was used as the carrier material and modified by the introduction of calcium alginate（CA）gel,which was then impregnated with Ag NO₃solution and reduced by propanetriol to produce a nano-silver laden calcium alginate/polyurethane complex（CA/PUF@Ag）.The physicochemical properties of CA/PUF@Ag,such as morphology,functional group structure,crystalline structure,elemental chemical state,swelling properties and mechanical strength,were characterised by various means.The sustainable release of silver ions from CA/PUF@Ag was assessed,and the antibacterial effect of CA/PUF@Ag was systematically investigated using Escherichia coli（E.coli）as the pathogen model.The resμlts show that CA/PUF@Ag prepared with0.25%w/v sodium alginate（SA）has a higher water absorption capacity with a swelling rate of 8.0 g/g,which is higher than that of unmodified silver loaded polyurethane（PUF@Ag）（6.0 g/g）,and the water coμld be squeezed out by slight pressure stimμlation.Compared with PUF@Ag,the synthesized CA/PUF@Ag has higher Ag NPs loading and can slow down the release of Ag NPs in solution.After 14 days of exposure,the leaching level of Ag NPs in CA/PUF@Ag（44.35μg/L）was much lower than the drinking water limit recommended by WHO（100μg/L）.CA/PUF@Ag exhibits good long-term bacterial inhibition activity,with100%sterilisation of squeezed water recovered from CA/PUF@Ag within 5 operating cycles.In addition,the bacteriostatic column filled with CA/PUF@Ag also showed high bacteriostatic efficiency.Therefore,it can be concluded that the CA/PUF@Ag has potential applications in the disinfection of drinking water in POU and that the technology may be significant in remote areas and in emergency applications.（2）In order to enhance the antibacterial activity and realize the controlled release of silver ions,chitosan（CS）was used as the main material to covalently graft sμlfonate betaine zwitterionic monomer[2-（methacryloxy）ethyl]dimethyl-（3-sμlfopropyl）ammonium hydroxide（SBMA）to form CS/SBMA hydrogel ball.Then silver-loaded chitosan/[2-（methacryloxy）ethyl]dimethyl-（3-sμlfonpropyl）ammonium hydroxide graft copolymer gel spheres（CS/SBMA@Ag）were prepared by in-situ reduction of silver nitrate solution with sodium borohydride.On the one hand,because of its three-position network structure and rich functional groups,more Ag NPs can be introduced and fixed to improve the antibacterial activity of CS/SBMA@Ag;on the other hand,the introduction of SBMA can endow CS/SBMA@Ag with good resistance to contamination and unique high critical solution temperature（UCST）thermosensitive properties to realize the controlled release of silver nanoparticles.The ideal preparation conditions of CS/SBMA@Ag gel spheres were determined as follows:the molar ratio of CS to SBMA was 3:1,the concentration of Magne Ag No3 was 5 mmol/L.The test resμlts showed that the CS/SBMA gel spheres prepared at a CS to SBMA molar ratio of 3:1 had a higher water absorption capacity,with a swelling rate of 9.4 g/g,which was higher than that of the unmodified chitosan gel spheres（CS）（3.8 g/g）.Compared with the unmodified nano-silver loaded chitosan gel spheres（CS@Ag）,the synthesized CS/SBMA@Ag has higher Ag NPs loading and excellent anti-biocontamination properties.After 14 days of exposure,the leaching level of Ag NPs in CS/SBMA@Ag（33.10μg/L）was much lower than the drinking water limit recommended by WHO（100μg/L）.CS/SBMA@Ag showed good long-term bacterial inhibition activity,with100%sterilisation of the CS/SBMA@Ag treatment solution being achieved within 5 test cycles.In addition,the bacteriostatic column filled with CA/PUF@Ag also showed high bacteriostatic efficiency.