Biological Preparation And Controll Of Nanoscale Semiconductor Metal Sulfides And Selenides

With the rapid development of industry,heavy metals pollution has gradually emerged,and recovery and utilization of heavy metals by biotechnology treatment system has aroused more and more attention.Metal sulfide and selenide semiconductor nanomaterials display attractive application prospect and broad application range due to outstanding performance in photoelectric convert,photoelectric catalysis,photoluminescence and so on.Using the biological reduction preparation technology of semiconductor nanomaterials to recycle and utilize heavy metal ions,and developing energy-saving,eco-friendly,low cost,efficient,resourceful treatment of heavy metal and green technology for biosynthesis of nano materials have been a hot issue for a long time.Bio-synthesis of sulfide and selenide semiconductor nanomaterials will be investigated deeply in this proposal because biological preparation technology represents the green chemistry well.The specific microorganisms which can reduce SO₄^2-ions and SeO₃^2-ions using organic matters as electron donor will be isolated,the optimum conditions for bio-synthesis of sulfide and selenide semiconductor nanomaterials will be established.Some organic polymer compounds and chemical reductant are used to control the morphology,crystal structure,particle size and composition of sulfide and selenide nanomaterials in microbial system.The structure and property of the bio-synthesized sulfide and selenide nanomaterials are characterized using X-ray diffraction?XRD?,scanning electron microscope?SEM?and transmission electron microscope?TEM?,X-ray energy dispersive spectroscopy?EDS?,X-ray Photoelectron Spectroscopy?XPS?,Fourier transfer infra-red?FTIR?,UV-Vis and fluorescence spectroscopic analysis.Finally,the photocatalytic activity of sulfide and selenide nanomaterials and the formation mechanism of Cu/Se compound nanoparticles are revealed.The results showed that:1.A new sulfate-reducing bacteria,Clostridiaceae sp.was successfully filtered out,and reduced SO₄^2-ions into S^2-ions in their metabolic process,then S^2-ions combined with free Pb²⁺or Zn²⁺ions to generate PbS nanocrystals or ZnS quantum dots.2.PbS nanocuboids with a particle size 50nm×50nm×100nm,PbS nanosheets with a thickness size ca.10nm and PbS nanoparticles with a uniform diameter of ca.60nm were successfully controlled and synthesized in biological reduction system by changing the concentration of polyethylene glycol 2000?PEG,4mM,12mM,20mM?;From PbS nanocuboids,nanosheets to nanoparticles,their UV-Vis absorption peak occurred red shift,the band gap decreased in turn,the photo-catalytic activity reduced in turn;It is interesting that the factor affecting their catalytic activities is not the specific surface area but the number of[200]crystal plane with photo-catalytic activity.3.The?-ZnS quantum dots with wurtzite structure and diameter of 6-10nm and the?-ZnS quantum dots with sphalerite structure and diameter of 3-5nm were successfully controlled and synthesized in biological reduction system by changing the concentration of hydroxypropyl starch?HPS,0.08mg/L,0.20mg/L,0.32mg/L,0.40mg/L,0.80mg/L?;The bio-prepared ZnS quantum dots were wrapped by a small amount of extracellular proteins and HPS,and had a better stability and bio-compatibility;The?-ZnS and?-ZnS quantum dots had a strong fluorescence at 400-460nm and a weak fluorescence at 590-690nm,but the?-ZnS quantum dots obtained from a microbial system containing 0.80mg/L of HPS only had a very strong fluorescence at 407nm;Compared with?-ZnS quantum dots,?-ZnS quantum dots had stronger photo-catalytic activity because of its bigger specific surface area.4.A new selenite-reducing bacteria,Pantoea agglomerans was successfully filtered out and used to synthesize Cu_2-x Se nanospheres with cubic structure and diameter of ca.80nm,CuSe nanospheres with hexagonal structure and diameter of 100-200nm and Cu₂Se nanospheres with tetragonal structure and diameter of ca.100nm in biological reduction system by changing the concentration of NaBH₄?0.0g/L,0.2g/L,0.4g/L?;The bio-prepared Cu/Se compound nanospheres were wrapped by a small amount of extracellular proteins,and had a better stability and bio-compatibility;Cu_2-x Se and Cu₂Se had larger band gap width,but had a poor photo-catalytic activity.5.The biosynthetic mechanism of the extracellular biosynthesis of CuSe,Cu_2-x Se and Cu₂Se nanospheres all contained three processes.First,part or all of the Cu²⁺ions were reduced into Cu⁺ions by reducing agent and SeO₃^2-ions were reduced into Se namoparticles by cell metabolic process under the catalysis of extracellular enzymes;Second,Se namoparticles were further reduced into Se^2-ions by cell metabolic process under the catalysis of Cu⁺ions;Third,the Cu²⁺and Cu⁺ions in solution and Se^2-ions combined to generate Cu/Se compound nanoparticles.