Research On Synthetic Of Cadmium Sulfide Nanoparticles By Sulfate-reducing Bacteria

Cadmium sulfide (CdS) is a kind of broadband gap semiconductor nanomaterials.Because its unique catalytic properties and optical properties has been widely used, theirpreparation and application of contemporary art has become a focus of concern in nanometer.Relative to conventional physical and chemical methods, microbiological method in recentyears gets more and more attention. Because its biotransformation process can be carried outat ambient temperature and pressure, the use of biological preparation of nano-materials, suchas low power consumption, low pollution and full use of the rich biological resources, canobtain higher stability of the nanoparticles. Therefore microbial sulfide nanomaterials is goingto go on line as a new method.In my study, Cd2+and sulfide produced by sulfate-reducing bacteria generate nanometerCdS particles,which uses sulfate-reducing bacteria to establish a pathway for the biosynthesisof nano-CdS.The results show that:（1）by measuring the growth curve of strain, it was found36hours for SRB is the bestincubation period. Adopting the use of LSD method at a calculation level α=0.05, Cd2+onthe safe concentration for the growth of sulfate-reducing bacteria is170mg L-1. The growthof sulfate-reducing bacteria and the best conditions for the conversion of Cd2+are determinedas follows: pH7, the30℃, anaerobic dark,10%inoculum, Cd2+conversion rate can reach at 98.76%. Cd2+initial concentration25,40,50,100,170mg L-1, the sulfate-reducing bacteriaCd2+transformation kinetics consistent with a half-life was24h,27h,28h,29h,30h.Transforming power learning equations are: C=31.566e-0.029t, C=47.631e-0.026t,C=58.987e-0.025t, C=109.35e-0.024t, C=183.57e-0.023t.（2）Examining the effects of different initial pH, reaction temperature and inoculumsize of CdS nanoparticles and using of XRD, SEM, HRTEM and EDS characterizationanalysis proved the products available are the well-distributed CdS nano-particles. CdScrystal at different pH values has the same structure and shape, particle size increases withincreasing pH, but when at pH5, no CdS nanoparticles generated, pH6, the smallest particlesize of CdS nanoparticle formed; different Preparation of CdS particle temperature crystalincreases with increasing temperature; and the change in the particle size of inoculums hasnegligible effect. Particle size of the product under the above conditions is between5~10nm.（3）Analyping the effect of different pH, temperature, inoculum size of sulfate-reducingbacteria to enzyme sulfite and APS reductase enzyme, the nesults shows that the optimumconditions for enzyme production is as follows: pH of7, the temperature is30℃, anaerobicdark inoculation amount of10%. The peak production of the enzyme is36h. Cd in thesulfate-reducing bacteria cells in different parts of the distribution of the results showed thatbacterial transformation of Cd2+focused on the cell membrane. Analysis of bacterial cellsobserved by a transmission electron microscope was found the bacterial cells in culturemedium with cadmium contains many high electron dense particles. While those growing inthe blank sample without Cd2+do not have such particulate matter. Through analysis of usingHRTEM and EDS, we know the particulate matter are nano-CdS particles of the substance.（4） Under different pH conditions may affect the synthesis of nano-CdS degradation rate of methyl orange. The experiments show that: where the smallest particle size pH6synthetic products of photocatalytic degradation of methyl orange was the best. After240minthe degradation rate can teach at98.8%; Nano-CdS prepared under different temperatureconditions will also affect the degradation rate of methyl orange. The smaller smapleparticles produced under15℃will be able to reach more than93percent of the degradationrate within240min reaction; CdS nanoparticles prepared under different inoculum had noeffect on the degradation rate of methyl orange.（5） It is found that, by UV-vis characterization of the samples, nano-CdS obsorptionpeak synthesized at different pH, temperature and inoculum has undergone a blue shiftrelative to the bulk, which is the result of quantum confinement effect; the samples arecharacterized by PL. Two emission peaks are both in spectra, one of which is located at398nm emission peak belonging to the band gap emission due to the electron-hole pairrecombination caused; another of which is located at422nm emission peak belonging to thesurface states emission, caused by a defect in the surface structure. Fluorescence spectrashows CdS nanoparticles prepared under different conditions with strong fluorescenceintensity, which has good luminescence properties.