Sonochemical Synthesis Of ZnS Nanolayers On The Surface Of Microbial Cells And Their Application In The Removal Of Heavy Metals

As we all know,more and more heavy metals produced in industr ia l production processes are dischar ged into the environme nt in the for m of waste water,waste gas,and waste slag.In addit io n,a lar ge number of ma n-made pollut io n sources,such as the random d isposa l of che mica l fert ilizers,pestic ides,and munic ipal so lid wastes,as well as the nat ural pheno me na of eroded and weathered geology have aggravated the proble m of heavy metal pollut io n in the living environment.Heavy meta l conta minants are very sta b le in water bodies and are difficult to re move.The y are often prone to be absorbed by suspended partic les in water bodies and submer ged into underwater silt,thereby becoming a source of long-term heavy meta l contaminat ion of water bodies.Many bio logica l materia ls represented by bacteria,algae,yeast,fungi ha ve been paid more and more attent ion for heavy meta l remova l because of the ir large adsorption capacity,lar ge ava ilabilit y,low cost,and no secondary pollut ion.Nanotechno logy a lso has great potentia l for environme ntal re med iat ion and wastewater treatment.N ano-partic les wit h large s urface area,self-assemb ly potentia l,high specific it y,high reactivit y and cata lyt ic potent ia l are the first cho ic e for water pollut io n treatment.I f the comb inat ion o f microorga nis ms and nanomater ia ls is used in the treatment of wastewater containing hea vy metals,it is expected that the remova l effic ienc y will be significant ly improved,and the practical applicat ion of adsorption to remove heavy metals will be greatly expanded.This study referred to the method of sonochemica l synt hes is of hollow ZnS nanopartic le structure us ing bio logical cells as temp lates.Using the fungus phanerochaete chrysosporium as the temp late,by strict ly contro lling the ultrasonic reactio n time,the ZnS nanopartic le layer was successfully synthes ized on the sur face of the microorga nis m w itho ut damaging its cell str ucture.The composite materia l（hereina fter referred to as ZnS-cells）were characterized by X-ray diffract ion（XRD）,scanning electron microscopy（SEM）,trans miss ion electron microscopy（TEM）,energy d ispersive X-ray spectroscopy（EDS）and Fourier trans for m infrared spectroscopy（FTIR）.The characterizat ion results showed that the co mposite of nano-ZnS and microbia l ce lls was successfully synt hesized.The structure of nano-ZnS is w urtzite wit h an average partic le s ize between 20-30 nm.The synthes is of the partic le la yer is related to the carboxyl gro ups on the surface of microbia l cell walls.The ZnS-cells not only ma inta ins t he integr ity of t he microb ial ce lls and does not affect its biosorption e ffect,but also uses the nanopartic le la yer protective film on the sur face of t he microbes to enhance t he strengt h o f the b iosorbent.More important ly,ZnS has an excellent ion exc hange capacity to remove heavy metals,which can make the adsorption of biological cel s more prominent.In addit ion,t he heavy meta l adsorption properties of ZnS-cells were measured,and the results showed that ZnS-cells had a higher adsorptio n effic ie ncy for Pb²⁺and Cd²⁺.The remo val rate of Pb²⁺and Cd²⁺by ZnS-cells was 140%and 160%higher than that of pure P.chrysogenum respectively.Among the influe nc ing factors of adsorption reaction,p H is the lar gest influe nce on the adsorption react ion,the optima l p H value is about 5-6,and the te mperature is t he sma llest influence.The adsorption reactio n can reach equilibr ium w ithin 4 h.O verall,the composite adsorbent has excellent heavy meta l adsorptio n performa nce,and provides a feas ible new met hod for the treatme nt of wastewater conta ining heavy metals by preparing an adsorbent comb ining microbia l cells and nano materia ls.Its excellent perfor mance makes ZnS-cells to have great application potential in actual water treatment.The stud y results on t he adsorptio n mechanis m o f the co mposite showed that t he adsorption mec hanis m to heavy metals by ZnS-cells is heterogeneous,the adsorption capacity is changed by the concentrat ion of hea vy metal ions in the solut ion,and the adsorption of ZnS-cells to Pb²⁺is better than Cd²⁺.The adsorption rate of ZnS-cells to heavy meta ls is controlled by t he chemica l adsorption mechanis m.The ent ire adsorption process can be divided into three parts:t he first rapid reactio n stage is ma inly controlled by the ion excha nge syste m,and the second stage is ma inly the biolo gical adsorptio n process,which is relat ive ly slow,and third stage gradually reached the adsorption equilibr ium.The ZnS-cells’adsorptio n to heavy meta ls ma inly depends on t he ion exc hange of ZnS nanopart icles and t he comple xat ion o f the microbia l ce ll sur face,and the ma in contr ib ut ion o f adsorpt ion is t he io n exc hange of ZnS nanopartic les.The comp lex of microbia l cells to heavy meta l ions ma inly involves hydroxyl,carboxyl,amide and other groups on the cell surface.