Photocatalytic Inhibition Of Growth Of Cyanobacteria By Metal Ions（V,La,Ag）Doped With Nano-TiO₂

At present,the eutrophication of lake waters is becoming more and more serious,and the Cyanobacteria blooms are an important indicator of eutrophication of water bodies.66%of freshwater lakes and reservoirs in China have been invaded by Cyanobacterial blooms for many years,seriously endangering human life and production.Nanomaterial photocatalysis technology has opened a new door for the treatment of water pollution.In this research field,semiconductor materials such as ZnO,Fe2O3,W03 and TiO2 are widely used,and TiO2 has been widely studied due to its unique properties such as low cost,no toxicity and high efficiency.In this paper,a typical bloom Cyanobacteria,Microcystis aeruginosa was selected as a research object,and a series of doped modified TiO2 photocatalytic materials were prepared.Moreover,the photocatalytic properties of modified nano-TiO2 on Microcystis aeruginosa were studied,and the algae cells were discussed.Photocatalytic removal mechanism.The main research contents and results of this paper are as follows:1.In this thesis,the growth curve of Microcystis aeruginosa was determined,and then we select the logarithmic algae cells growing to about 7-10 days as the best experimental object.The transition metal(V),lanthanide(La)and noble metal(Ag)ion doped nano-TiO2 photocatalysts were prepared by sol-gel method.The doping concentration was divided into V:Ti=0.1%,0.2%,0.3.%,0.4%V-TiO2;La:Ti=0.2%,0.4%,0.5%,0.8%La-TiO2;Ag:Ti=0.2%,0.5%,0.8%,1.0%Ag-TiO2.The optimum process conditions for preparation were pH=2.5 and heat treatment temperature of 500℃.The growth inhibition efficiency of three different elements(V,La,Ag)doped TiO2 on Microcystis aeruginosa under different conditions was tested.(1)0.3%V-TiO2,0.5%La-TiO2,0.5%Ag-TiO2 three groups of materials with higher photocatalytic efficiency of microcystis cells,the removal rate under ultraviolet light irradiation can reach 30.32%,53.21%,88.11%.(2)The amount of catalyst will affect the photocatalytic effect,and will not exhibit the concentration-dose effect.The optimal experimental results show that the optimum dosage is 100 mg/L.(3)Continuous ultraviolet light irradiation inhibited the growth of Microcystis aeruginosa,but this is a reversible mechanism.By comparing the photocatalytic effects of the three photocatalytic materials,0,5%Ag-TiO2 has a more efficient photocatalytic effect,and the cell removal rate of P.aeruginosa cells can reach 98%.(4)Structural characterization by XRD,TEM,UV-Vis,PL,etc.Compared with TiO2 the doping modification of metal ions increases the content of anatase phase.The 0.3%V ion doped TiO2 expands the visible light spectral response range of TiO2,and the V ions enter the TiO2 lattice,which reduces the recombination rate of photogenerated electron-hole pairs.However,its photocatalytic effect on algae cells is low,probably due to problems such as particle size and agglomeration.0.5%La-TiO2 due to the addition of La ions,the surface Ti-O-La bond formation causes lattice distortion,resulting in the crystal size of TiO2 becoming smaller than 11 nm,and has a large specific surface area,and the adsorption performance is enhanced,which is beneficial to its Adsorbed on the surface of algae cells.However,due to the local surface plasmon resonance effect of Ag ions,the average crystallite size of nanoparticles decreases from 14.8 nm to 11 nm,and can act as an electron trap,reducing the recombination of photogenerated electron-hole pairs.High photocatalytic efficiency under both ultraviolet and visible light conditions.3.The mechanism of cell destruction of Microcystis aeruginosa under the photocatalytic activity of 0.5%Ag-TiO2 was investigated.The results show that the photocatalytic process can be divided into three parts:(1)destruction of cell wall and membrane.Infrared spectroscopy changes in the infrared vibration peaks of the functional groups of proteins,polysaccharides and phospholipids on the cell surface and the results of the permeability of the algae cell membrane can prove that the photocatalytic reaction produces reactive oxygen species binding to the surface structure of the cell membrane,thereby destroying the cell membrane structure.(2)cause cellular oxidative stress.The increase of antioxidant enzyme activity(SOD)and malondialdehyde(MDA)content indicates that the active oxygen species can also cause oxidative stress of algal cells and damage the internal structure of algae cells while the cells are active.(3)Effects on extracellular organic matter(EOM).In a short period of time,the photocatalytic reaction will cause cell rupture and release intracellular cytoplasm,which will increase the content of aromatic proteins,soluble organic matter and humic acids.After a certain period of photoreaction,the change of EOM will be stable.