Study Of Preparation And Water Disinfection Of Graphene-Graphene Analogues And Silver Based Functional Materials

Microbial contamination has always been the challenge that threats the health of human being since the existence of human society.Many kinds of bacteria can lead to seriously and even deadly infections for people.The pathogenic microbials can be transmitted through different environmental media including water,soil and atmosphere,among which the water is the most popular and influential transmitting medium.The traditional bacterial inactivation methods such as chlorination and UV methods are popularly used.However,chlorination can produce carcinogenic disinfection byproducts and there are some free chlorine-resistant bacteria such as Mycobacterium avium.Additionally,UV light is not effective for some UV-resistant bacteria and some bacteria can regrow by photoreactivation after UV disinfection.Although the silver and gold based nanomaterials have notable bactericidal activity,their expensive cost limited the application of these two noble metal nanomaterials in practice.Moreover,they could not be recycled for being not separated from the water efficiently,which may result in second pollution and serious environmental risk.Therefore,developing safe,effective,low cost and environmental biocide is significant and necessary.Since the photon-based disinfection method by platinum-doped TiO₂ mediated photocatalysis was first reported in 1985,photocatalytic disinfection has been extensively investigated.The photocatalytic disinfection can produce reactvie species with strong oxidative power which can inactivate bacteria.Because it uses the abundant solar energy,the photocatalytic disinfection is regarded as a green and energy-saving disinfection technology.Firstly,the magnetic Ag-CoFe₂O₄-GO antimicrobial material was prepared by solvothermal reaction.The materials were characterized by TEM,XRD,FTIR,Raman,XPS,BET,CV and magnetic tests.The results showed that the dispersion of Ag and CoFe₂O₄ nanoparticles was improved by the addition of GO.Compared with CoFe₂O₄,Ag-CoFe₂O₄ and CoFe₂O₄-GO,Ag-CoFe₂O₄-GO showed the strongest bactericidal effect towards E.coli and S.aureus.At the concentration of 6.25μg/mL and contact time of 2 h,the bactericidal effect of Ag-CoFe₂O₄-GO towards E.coli and S.aureus was 98.8%and 73.4%,respectively.In the case of bacterial and Pb²⁺simultaneous contamination,the removal efficiency of bacteria and Pb²⁺was about 99%and 75%,respectively.Ag-CoFe₂O₄-GO has different disinfection mechanism towards E.coli and S.aureus.E.coli is inactivated by severe cell wall and membrane damage and the leakage of cell inclusions.S.aureus is inactivated by cell deformation and the inhibition of cell division.The superior sterilization effect of Ag-CoFe₂O₄-GO is the result of synergistic effect of nAg and GO,and the adsorption of Pb²⁺is achieved by electrostatic attraction.Secondly,magnetic Fe₃O₄-TNS photocatalyst was synthesized by lamellar reverse micelles and solvothermal method.The materials were characterized by TEM,SEM,XRD,BET,XPS and magnetic tests.In contrast to Fe₃O₄ and TNS,Fe₃O₄-TNS showed better photocatalytic efficiency,which was attributed to the formation of heterostructure in Fe₃O₄-TNS.It can be seen from the SEM picture that the sterilization mechanism of Fe₃O₄-TNS towards E.coli（G-）and S.aureus（G+）is different.For E.coli,the produced reactive species caused the damage of cell wall and membrane,brought serious oxidative pressure to the cell,and ultimately led to its death.For S.aureus,there was no obvious cell membrane damage.The S.aureus were adsorbed and bound by Fe₃O₄-TNS in form of group,giving physical pressure to the cells,triggering the dysfunction of cell membrane,and eventually leading to its death.The sterilization mechanism was studied by PL spectra and photocurrent experiments,which indicated that Fe₃O₄ can capture the photo-generated electrons from the conduction band of TNS and inhibit the recombination of electron-hole pairs.The addition of scavengers showed that h⁺and H₂O₂ were the key reactive species during the photocatalytic sterilization process.With repeated use of five times,the disinfection effect of Fe₃O₄-TNS was slightly decreased,but it was still more than90%.Thirdly,Ag/g-C₃N₄ plasmonic photocatalyst was prepared by thermal polymerization and photoreduction method.The results showed that nAg particles uniformly dispersed on the surface of g-C₃N₄ and formed heterogeneous structure without changing the crystal structure and morphology of g-C₃N₄.Compared with g-C₃N₄,Ag/g-C₃N₄ composite photocatalyst with different Ag doping content showed stronger sterilization efficiency,and Ag（3）/g-C₃N₄ had the best sterilization effect.With different pH（6.2,7.2,8.2）and humic acid（<1 mg/L）,Ag（3）/g-C₃N₄ still maintained its strong sterilization efficiency.SEM images showed that Ag（3）/g-C₃N₄induced oxidative destruction of E.coli cells from outside to inside.It led to the destruction of cell wall and membrane,induced cell oxidative stress,prolonged cell length,and caused the leakage of cell contents.Then the reactive species could come into the cell and damage cell components,eventually lead to the death of E.coli.The spectroscopy and photoelectrochemical tests indicated that the enhanced photocatalytic bactericidal effect was attributed to the hybrid effect from Ag and g-C₃N₄,which resulted in enhanced adsorption of visible light,reduced recombination of free charges,rapid separation and transportation of photogenerated electrons-holes,and long lifetime of free charges.The results of chemical scavengers and ESR showed that h⁺,e^-and·O₂^-were the key reactive species during the photocatalytic disinfection process.Finally,Ag/CeO₂-M plasmonic photocatalysts were prepared by hard template calcination and photodeposition.Compared with the bulk CeO₂-B,Ag/CeO₂-M had higher specific surface area and pore volume,and its crystal structure contained more oxygen vacancy,Ce³⁺,and chemically adsorbed oxygen species.Ag/CeO₂-M exhibited better photocatalytic disinfection effect than CeO₂-B and CeO₂-M,and Ag（2%）/CeO₂-M had the best effect.Low concentration of humic acid（<0.25 mg/L）can improve the sterilization effect,while high concentration of humic acid（>0.5 mg/L）showed a significant inhibitory effect.Ag/CeO₂-M can cause damage to E.coli from the outside to the inside including the rupture of cell membrane and the leakage of cell contents and the final death.By DFT calculations,it is found that there was an intermediate state above the CeO₂ conduction band after Ag doping,which can broaden the absorption range of visible light,capture free electrons and reduce the recombination rate of electron-hole.The spectroscopy and photoelectrochemical tests indicated that the enhanced photocatalytic bactericidal effect was attributed to enhanced and broadened adsorption of visible light,reduced recombination of free charges,increased separation and transportation of photogenerated electrons-holes,prolonged lifetime of free charges and enhanced oxidative power of hole.The results of chemical scavengers and ESR showed that h⁺was the key reactive species during the photocatalytic disinfection process.The Ag（2%）/CeO₂-M had the highest quantity of·O₂^-and·OH.