Study On Antibacterial Properties And Mechanism Of Hydrotalcite-Like Compounds Loaded And Combined With Heavy Metals

With the development of science and technology and the upgrading of human needs,environmental deterioration is described as a complex and diverse situation.Such as heavy metal pollutants and acid-base salts from industry and manufacturing,pathogens or antibiotic pollutants from medical treatment and pharmaceutical manufacturing,etc.,could pass through the sewage treatment process and soil-atmosphere-water ecological cycle,and finally enter the water.Therefore,two or multiple kinds of toxic and harmful pollutants coexist side by side,which causes difficulty in the treatment and restoration of water.Thereinto,heavy metal is one of the pollutants that once enter the environment can hardly be removed and cause irreversible harm to the human being.In addition,with the development of medicine and the widespread use of antibiotics,the drug resistance of pathogenic pollutants(viruses,germs,parasites,etc.)develops rapidly.Antibiotic resistant bacteria(ARB)and antibiotic resistance genes(ARG)occurred and spread widespread by water as a medium,increasing the risk of people poisoned,cancer,and infectious diseases.Heavy metal and bacterial pollutants widespread into the water,and then migration,accumulation dramatically.Therefore,clean and effective technologies or materials should be developed to take the advantage of the biological toxicity of heavy metals in sterilization,or the microbial metabolism in heavy metals precipitate out.To develop a synthetic material that combines one type of pollutant to treat the other pollutant in the direction and hotspot of future research.Hydrotalcite,also known as layered double hydroxides(LDHs),has remarkable structural characteristics with good intercalation performance,large surface area,good thermal stability,which can capture inorganic and organic ions,encapsulate and fix cells.Aiming at the complex pollution treatment in the environment,this article uses hydrotalcite-like compounds(HTLCs)as a precursor to synthesize different composite metal oxide materials to adsorb/load heavy metals,and use its biological toxicity to efficiently remove resistant bacteria and resistance genes.In order to improve the adsorption efficiency and stability of LDHs to heavy metals in industrial waste water treatment,magnetic doped Fe-LDHs was synthesised via hydrothermal method,using Fe-LDHs to remove heavy metals cadmium(Cd),chromium(Cr),lead(Pb)and copper(Cu)from water.The iron material is distributed on the surface of LDHs,which effectively improves the loading capacity.When p H=6,Fe-LDHs showed the best capacity effect on heavy metals:The saturated loading capacities of Cd(II),Pb(II)and Cu(II)are 117.31,133.04,91.15 and 160.50 mg/g,respectively.The capacity of Fe-LDHs on Cr(VI)conforms to the pseudo-second-order kinetic model and Langmuir isotherm adsorption model.The saturated adsorption capacities of Fe-LDHs in actual water bodies for Cr(VI),Cd(II),Pb(II)and Cu(II)are 111.58,130.64,91.12 and 150.67mg/g,respectively.Under the action of desorbent Na HCO3,the loading capacity efficiency is still higher than 70%after 5 times of recycling.Fe-LDHs and chemical precipitating agents are used in combination to treat a certain special machinery processing wastewater:The effluent quality is stable;The effluent indicators of Cr(VI),total nickel,petroleum,and total phosphorus are 0.06,0.08,1.56,and 0.22mg/L,respectively,which are higher than electroplating pollution emissions standards.When combined with antibacterial metal ions,hydrotalcite compounds was synergistically effective against bacteria.Layered double oxides(LDOs)were prepared with P123 as a template,and then antibacterial metals Cr,Cu and Zn were embedded to remove bacteria E.coli and B.subtilis.The P123 template is removed by step-gradient firing and the resistant metal is doped into the X-LDOs laminate in the form of solid solution.The results show that the morphology and size of X-LDOs nanosheets doped with Cr,Cu and Zn are uniform,the crystallinity is higher than that of LDHs.The inhibition ability of X-LDOs on bacteria E.coli and B.subtilis:Cr-LDOs>Cu-LDOs>Zn-LDOs>LDHs.Because of the difference of the structure of cell membrane,the antibacterial material show better inhibition on Gram-negative bacteria E.coli than Gram-positive bacteria B.subtilis.At an exposure concentration of 50μg/m L,the antibacterial efficiency of Cr-LDOs against E.coli and B.subtilis was 91.51%and 90.86%.At an exposure concentration of 100μg/m L,the antibacterial efficiencies of LDHs,Cu-LDOs and Zn-LDOs against B.subtilis were 22.56%,96.19%and 80.93%,respectively;the antibacterial efficiencies against E.coli were 34.54%,97.67%and 97.67%respectively.E.coli and B.subtilis exposed to 100μg/m L X-LDOs.Analysis of cell metabolites showed that X-LDOs lead to physically damagement of cell membranes,cellular oxidative stress,membrane lipid peroxidation,and inhibition of protein synthesis.The toxicity of X-LDOs to bacteria depends on many factors such as chemical composition,surface charge and shape.In order to further understand the removal mechanism of HTLCs combined with heavy metals on bacteria,improve the antibacterial efficiency,Mixed metal oxides(MMOs)were prepared to load the chromium to remove the resistant bacteria E.coli NDM-1.It was found that the capacity of Cr(VI)by MMOs could be 98.80 mg/g.The MMOs loaded with Cr(VI)had good stability,would not release heavy metals into the environment and cause secondary pollution.Inhibition of Cr-MMOs on E.coli NDM-1 is more efficiently than MMOs and LDHs.when the exposure concentration of Cr-MMOs is 50μg/m L,the activity of E.coli NDM-1 is completely inhibited.p H=4,the Cr(VI)loading was 19.70 mg/g,Cr-MMOs had optimal inhibition performance on E.coli NDM-1.When the exposure concentration was 100 mg/L,the bacterial concentration of E.coli NDM-1decreased from～10~8 to～10~3 CFU/m L.Cr-MMOs can specifically bind to the choline group of the cell membrane,helping MMOs effectively capture E.coli NDM-1 and physically damage to cell membranes.And then Cr(VI)enters the cell,interacting with cell enzymes and destroying the cell protein structure,eventually leading to the death of E.coli NDM-1.In addition,after lysis of E.coli NDM-1 the resistance gene bla NDM-1 was also captured by Cr-MMOs,realizing the simultaneous removal of ARBs and ARGs in water.