Study On Biological Synthesis Of PbS Nanoparticles Using Desulfovibrio Desulfuricans

The PbS nanoparticles has a huge potential development and application value inthe optical, magnetic, electrical, and medicine fields because of its unique properties.Atpresent, the preparation methods of PbS nanoparticles are physical and chemical methodswhich have made significant progress in aspects of method, application or mechanism andaccumulated abundant of research results. With the proposal of environment friendly andgreen chemistry, people tend to look for a simpler and green synthetic method.Microbialmethod has the advantages of low cost, simple reaction process, more friendly to environment.It has broad prospect.In this study, PbS nanoparticles was biosynthesized by Desulfovibrio desulfuricans andthe factors which can effect on the structure, morphology, size and conversion of product wereinvestigated.The properties of photocatalysis, ultraviolet-visible absorption andphotoluminescence were measured. In final, biosynthesic mechanism was studied. There arethe following conclusions:(1)PbS nanoparticles was successfully prepared by Desulfovibrio desulfuricans. Theproducts were characterized by X-ray diffraction (XRD), high-resolution transmissionelectron microscopy(HRTEM) and energy dispersive spectrometer (EDS). Meantimes, thefactors such as pH value, temperature and inoculum size which have effects on thestructure, morphology, size and conversion of product were investigated in the preparationprocess.The results showed that the morphology of the products changed fromnearly spherical to granular and particle size increased from10~15nm to10~25nm, with thepH value increases from5to8.When pH is9, the shape of prepared PbS nanoparticles wasspecial irregular with granular inlay around the nearly spherical particles, the particle size isabout10~15nm.When pH is8, it has a highest conversion rate.The products have the samestructure, morphology and size in spite of different temperature, and they are at the range of 10~25nm.When the temperature is30℃,it has a highest conversion rate.With the increasingof inoculum size, the morphology ranged from spherical to granular whose size at the rangeof5~10nm to10~25nm. When inoculum size is about10%, it has a highest conversion rate.(2) Photocatalytic degradation of methyl orange and methylene blue solution wasfulfilled using the prepared PbS nanoparticles, the degradation process accorded with thefirst-order reaction dynamic law. The effect of photocatalytic degradation of PbSnanoparticles which prepared under different pH is pH9>pH8>pH7>pH6>pH5. The effect ofphotocatalytic degradation of PbS nanoparticles which preparedunder different temperature is30℃>25℃>15℃. The effect of photocatalyticdegradation of PbS nanoparticles which prepared under different inoculum size is5%>10%>20%, the prepared PbS nanoparticles under pH9was the best, the degradation rateof methyl orange and methylene blue solution respectively was77.37%and93.43%after6hunder ultraviolet irradiation.(3) Take the prepared PbS nanoparticles under pH9as catalyst, the effects of initial pHvalue of methyl orange and methylene blue solution and dosage of catalyst on degradationrate were investigated, the optimum degradation conditions is dosage of1.5g/L and pH3. Thedegradation rate of20mg/L methyl orange was99.04%after4h underultraviolet irradiation. Under dosage of1.8g/L and pH10, the degradation rate of8mg/Lmethylene blue was99.05%after4h under ultraviolet irradiation.(4) UV-Vis spectra and fluorescence spectra of the prepared PbS nanoparticles showeda obvious blue shift, indicating that the products with small particle size and resulting in theoccurrence of the quantum size effect.(5) Determination of specific activity of sulfate reductase and APS reductase indicatedthat the two enzymes showed a decreasing trend after increase at the first with the increase ofincubation time, and specific activity also reached a peak in83h. It showed that the twoenzymes had a simultaneously variation along with the culture time of strain. Comparison ofspecific activity of different pH, the specific activity of APS reductase reached highest atpH7. However, the specific activity of sulfite reductase reached highest at pH8. Comparison of specific activity of different temperature, the specific activity of two enzymes reachedhighest when culture temperature was30℃. Comparison of specific activity of differentinoculum size, the specific activity of two enzymes reached highest when inoculum size was10%. Combined with the results of conversion rate of lead ion underdifferent conditions, enzyme activity had a great influence on physiological metabolismof strain. The conversion rate of lead ion and yield of PbS nanoparticles is higher withenzyme activity increasing.(6) Subcellular fractionation analysises show that13.95%,66.90%and19.15%of thelead was in the cell wall, membraneand cytoplasm, respectively. It can be deduced that leadion may adsorbe with the cell membrane. The results of TEM and EDS of strains showed thatPbS nanoparticles was generated in the internal cell when biosynthesis of PbS nanoparticlesusing Desulfovibrio desulfuricans.