Preparation Of Zinc Oxide Nanoparticles@Calcium Alginate And Their Application For Water Disinfection

Nano-zinc oxide?ZnO?is zinc oxide with a size of less than 100 nm.Nano ZnO has been used in the fields of light-emitting devices,photoelectric detection,piezoelectric devices,photocatalysis and cell imaging,etc.Due to its stronger luminescence characteristics,piezoelectric characteristics and catalytic characteristics compared to bulk materials.In addition to the above fields,ZnO has excellent antibacterial properties,especially when the size is reduced to the nanometer level,the antibacterial properties are significantly improved.Therefore,it can be used as an inorganic antibacterial agent and has a very large application prospect in the field of the biological environment.Micro-organisms are closely related to human life.Beneficial bacteria can promote people's production and life,help people ferment food,regulate intestinal balance,improve the body's immunity and other effects.Harmful pathogenic bacteria can cause food spoilage,water pollution,wound infection,suppuration,and even threaten people's lives.Therefore,it is very necessary to disinfect the water.At present,the simplest and most effective method of disinfection is chlorine disinfection.Chlorine gas reacts with water to form hydrochloric acid and hypochlorous acid.Among them,the strong oxidation of hypochlorous acid can destroy the enzymes and proteins of disease-causing bacteria in the water,which in turn leads to the death of bacteria in the water and achieving disinfection.Although chlorine disinfection offer rapid oxidation capabilities,these powerful oxidants may react with natural organic matter in polluted water to form disinfection byproducts?DBP?,which have been identified as carcinogens by the World Health Organization?WHO?.Therefore,it is urgent to research and use new disinfection methods to replace the traditional chlorine disinfection to provide safe and clean water without producing DBP.Nano-antibacterial material is a new type of antibacterial material that responds to the problem of serious resistance of bacteria caused by the abuse of antibiotics.After more than ten years of development,the nano-antibacterial materials have been used in various fields,including medical and health,water disinfection,food preservation and other fields.Nanoparticles?NPs?including Ag,Ti O₂ and ZnO NPs have been reported for their good bactericidal properties,some of them have been used for disinfection of water.Water purification devices based on nano-antibacterial materials and related compounds can quickly and efficiently remove pathogenic bacteria in water in a short time.Among these antibacterial nanoparticles,nano ZnO is favored by researchers because of its high stability,low-cost,and low-toxicity.There have been some studies on the use of ZnO NPs for the inactivation of bacteria in drinking water.However,these studies are far from satisfactory because the ZnO NPs used in the above mentioned studies are relatively large in particle size and non-hydrophilic,leading to a time-consuming and inefficient disinfection process.Therefore,it is meaningful to prepare nano ZnO with high antibacterial activity and water solubility to expand the application of ZnO and promote the development of new and convenient water disinfection devices.In addition,in order to ensure the safety of water use,nanomaterials after disinfection in the water residue must be strictly limited to avoid additional pollution.To address these problems,we have adopted the following solutions:improve the surface status of ZnO with a suitable surface modifier.Improve its hydrophilicity,which in turn improves the antibacterial properties in aqueous solution.Subsequently,choosing a suitable carrier to wrap the nano-ZnO can not only exert the antibacterial ability of the nano-ZnO,but also limit the residual of the nano-particles in water.Calcium alginate is a natural polysaccharide with good biocompatibility.It is widely used in food processing,drug delivery and other fields,and because of its internal cross-linked network structure,it is very suitable as a carrier for nanomaterials.In summary,we chose the silane coupling agent to modify the alcohol-soluble ZnO NPs to make the amino groups and silicon-oxygen bonds onto the surface of the ZnO,which improved the dispersibility in water and the affinity of bacteria.The antibacterial properties of the prepared ZnO NPs are superior to commercial nano ZnO,which can be attributed to the good hydrophilicity of ZnO NPs,the large contact area with bacteria in the solution,and the increase of active oxygen.For the first time,hydrophilic ZnO nanoparticles@calcium alginate composite has been prepared by embedding hydrophilic ZnO nanoparticles?NPs?into calcium alginate,and the bactericidal rate of the composite against Staphylococcus aureus and Escherichia coli can reach up to 99%in water.At the same time,the composite can also limit the residual of ZnO NPs in water and avoid secondary pollution.The results of this paper are as follows:?1?The ZnO NPs with small particle size and uniform morphology were prepared by a sol-gel method.Then the ZnO NPs were modified with a silane coupling agent,and amino groups,silicon oxides and other groups were modified on the surface to endowed with hydrophilic properties.By testing the antibacterial properties,it is found that at the same concentration,the hydrophilic ZnO NPs have significantly better antibacterial properties than ordinary commercial nano-ZnO.?2?In order to limit the residual of ZnO NPs in water,the hydrophilic ZnO NPs were embedded in calcium alginate hydrogels to form hydrophilic ZnO nanoparticles@calcium alginate composite,and the bactericidal rate of the composite against bacterium?Staphylococcus aureus and Escherichia coli?can reach up to 99%in water.Subsequently,we used the prepared composite for the disinfection of real surface water.The disinfected water quality met the World Health Organization's standards for drinking water quality in terms of microbial content.?3?The disinfection mechanism of the composite was analyzed.The removal of organic substances is mainly due to the three-dimensional structure of calcium alginate,which endowed with a high adsorption capacity.Sterilization mechanism studies show that the ZnO NPs can cause excessive oxidative stress in cells,inducing bacteria to produce large amounts of intracellular reactive oxygen species?ROS?,leading to the apoptosis of the bacteria,which is the dominant bactericidal mechanism.