Study On The Copper And Zinc Loaded X Zeolite Synthesized From Natural Diatomite And Its Antimicrobial Performance

X zeolite is a kind of porous material,which is widely used in chemical industry,environmental protection,light industry,pharmaceuticals and other fields.Meanwhile,X zeolite doped with the biocidal cations of Cu2+ and Zn2+ ions is kind of antlbacterial materials with excellent antimicrobial activity and slow release performance.It can replace antibiotic to kill Enterotoxingenic Escherichia coli,causing diarrhea in newborn livestock,which is safe and long-term.However,The novel antibacterial agents with great practical significance and economic value for livestock industry is still dependent on imports.Diatomite is a biogenic siliceous sedimentary rock,its main chemical composition is amorphous SiO2,and low-grade diatomite also contains a certain amount of Al2O3.Therefore,diatomite can replace sodium silicates and aluminum salt to serve as the silica source in the synthesis of zeolites,which will simplify the synthesizing process.In the paper,we use diatomite as the Si source to synthesize X zeolite via hydrothermal methods.The structure and performance were systematically characterized and the formation mechanism was deeply investigated.The biocidal cations of Cu2+ and Zn2+ were loaded on X zeolite via ion exchange.Furthermore,the adsorption activity of the as-prepared samples and the adsorption mechanism were systematically investigated.Finally,the antimicrobial activity of the as-prepared samples were evaluated for the disinfection of K88 Escherichia coli and Staphylococcus aureus.Meanwhile,the antimicrobial activity of Cu2+-zeolite for different kinds of gram-negative bacteria(K88,K99 and 987 Escherichia coli)and gram-positive bacteria Enterococcus Faecium and lactobacillus plantarum)was investigated,and the antimicrobial mechanism was also analyzed.The main achievements of this paper are as follows:(1)In this work,zeolite X powder was synthesized using natural low-grade diatomite as the main source of Si but only as a partial source of A1 via a simple and green hydrothermal method.In addition,the optimum preparation conditions of zeolite X were 5 h of crystallization time,110? of crystallization temperature,30? of aging temperature,30 min of aging time,H2O/Na2O ratio of 40 and Na2O/SiO2 ratio of 1.4.The prepared zeolite X possess high crystallinity,unique meso-microporous structure,remarkable thermal stability and excellent calcium ion exchange performance.The proposed crystallization mechanism of zeolite can be divided into three steps:(1)gel transformation.(2)nucleation,(3)crystal growth.(2)The cations of Cu2+ and Zn2+ were hosted on the surfaces and in the cavities of X zeolite via ion exchange.The optimum preparation conditions of copper-loaded X zeolite are 0.20 mol/L of initial ion concentration,20:1 of liquid-solid ratio,3.62 of solution pH,60 min of exchanging time,70? of exchanging temperature.In addition,the exchanging amount of copper ions reached 179.19 mg/g.The optimum preparation conditions of zinc-loaded X zeolite are 0.15 mol/L of initial ion concentration,25:1 of liquid-solid ratio,4.64 of solution pH,60 min of exchanging time,70? of exchanging temperature.Meanwhile,the exchange amount of zinc ions reached 127.35 mg/g.(3)The pseudo-second order model and Langmuir isotherm model can best describe the adsorption kinetics and isothenns of Cu2+ and Zn2+,respectively.And the maximum adsorption capacities of Cu2+ and Zn2+can reach 145.99 mg/g and 194.93 mg/g,respectively.The adsorption free energy of Cu2+ are higher than those of Zn2+,and the adsorption mechanism of Cu2+ and Zn2+ is chemical adsorption and ion exchange,respectively.Meanwhile,the adsorption process of Cu2+and Zn2+ are both endothermic and spontaneous in nature.At the same initial concentration,the Polanyi adsorption potential energy of Cu2+ and Zn2+ increased with the increase of the adsorption capacities.At the same temperature,the Polanyi adsorption potential energy of Cu2+ and Zn2+ decreased with the increase of the adsorption capacities,and the surface coverage and micropore filling of X zeolite increased with the increase of adsorption capacities.(4)The adsorption of Cu2+ and Zn2+ by X zeolite synthesized from diatomite is mainly chemical adsorption by ion exchange,and accompanied by physical adsorption.The excellent adsorption activity could be attributed to the meso-microporous structure.It can improve its mass diffusion and transport of ions with its large cavity volumes and mesopore channels,thus increasing the meso-microporous contact area and accelerating the adsorption process.Therefore,the X zeolite synthesized from diatomite is a promising and potentially cost-effective adsorbent for the efficient disposal of heavy metals from industrial effluent.(5)The as-prepared samples showed excellent antimicrobial activity towards K88 Escherichia coli and Staphylococcus aureus.Furthermore,the disinfection process fitted well with the first order model,and the apparent rate constants(k)of Cu2+-zeolite are higher than those of Zn2+-zeolite.The apparent rate constants(k)of Cu2+-zeolite for Staphylococcus aureus are higer than those of K88 Escherichia coli,and the apparent rate constants(k)of Zn2+-zeolite for K88 Escherichia coli are higer than those of Staphylococcus aureus.The antibacterial performance of Cu2+-zeolite for K88 Escherichia coli and Staphylococcus aureus are higher than those of Zn2+-zeolite.Moreover,the antibacterial performance of Cu2+-zeolite for Staphylococcus aureus are higer than those of K88 Escherichia coli,and the antibacterial performance of Zn2+-zeolite for K88 Escherichia coli are higer than those of Staphylococcus aureus.The Cu2+-zeolite showed excellent antibacterial performance on different kinds of gram-positive bacteria(Enterococcus Faecium and lactobacillus plantarum)and gram-negative bacteria(K88,K99 and 987 Escherichia coli),and the Cu2+-zeolite showed better antibacterial performance on gram-positive bacteria than on gram-negative bacteria.