Study On The Modification Of Diatomite-sodium Ferric Silicate For Removing Organic Pollutants Behavior

Water resource pollution is a serious environmental crisis for the development of human society.Organic pollutants in water,such as organic dyes and antibiotics,have the characteristics of strong stability,self-degradation,difficult and easy to accumulate,which caused irreversible damage to human health and ecological environment.The photocatalytic/photo-Fenton catalytic oxidation technology based on cheap mineral materials is considered as a large-scale environmental purification method due to its advantages of low cost,high efficiency,and non-pollution.In this thesis,based on mineral materials such as diatomite and ferric sodium silicate,the design modification was carried out from various perspectives,including construction of carrier composites,preparation of novel catalyst,the introduction of metal defect,ion surface doping and the preparation of magnetic ternary composite.With the common and persistent organic pollutants rhodamine B（Rh B）,ciprofloxacin（CIP）,levofloxacin（CIP）and tetracycline（TC）as the target degradants,the degradation performance of prepared and modified catalyst materials was evaluated.Meanwhile,the catalytic removal behavior and mechanism of various organic compounds by different catalysts through photocatalysis/photo-Fenton catalysis were systematically explored.The main research contents and results are as follows:The red phosphorus/diatomite（RP/Dt）composite was constructed by the hydrothermal treatment,on the surface of diatomite supported using disk diatomite as carrier.When the loading capacity of diatomite was 15 wt%,the optimum degradation rate of pollutant Rh B by red phosphorus/diatomite composite was 95.9%,which was1.92 times of the original red phosphorus.The presence of Si O₂ and RP in the composite was proved by a series of structural characterization.The micrography images showed that the diatomite in the composite maintained intact disk geometry structure,indicating that the hydrothermal process would not destroy the diatomite disk.It also proved that the diatomite as a carrier could support nano RP well and reduce the aggregation of RP.The specific surface area results showed that the specific surface area of red phosphorus/diatomite composite constructed by hydrothermal deposition was larger than that of physical mixed red phosphorus&diatomite.The diatomite can also be used as a dispersant to improve the dispersion of red phosphorus.At the same time,photoelectric performance tests showed that the composite has higher carrier concentration and lower interfacial charge transfer resistance,which are attributed to the reduction of nano-RP agglomeration and more active sites.The intermediate product of Rh B degradation was determined by liquid chromatography-mass spectrometry,and the possible degradation path was given.The main active species of Rh B degradation was h⁺,and the corresponding photocatalytic degradation mechanism was proposed.In order to further improve the application range and application value of diatomite,low-grade diatomite as Si source was used to prepare the novel sodium ferric silicate（SFS）photocatalyst.The SFS catalyst with abundant surface Fe defects was successfully prepared by ball milling and pickling modification.The highest oxidation/reduction efficiency for CIP and Cr（VI）of Fe-deficient SFS(D_Fe-SFS)was5.12 and 2.83 times of the original SFS,respectively.The mechanical ball milling process can selectively destroy Fe-O bonds,so that Fe³⁺ions can be released from the SFS lattice.The surface iron oxide species were removed by pickling to expose Fe defects.The sample showed that the uneven distribution of Fe/Si elements after the introduction of Fe defects.At the same time,Fe defect concentration can be accurately controlled by controlling the ball milling time.The optical absorption and photoelectric performance test results show that the introduction of Fe defect level can not only enhance the light absorption,but also act as an electron trapping trap and improve the separation efficiency of photogenerated charge,which increases the conversion efficiency of Fe（III）/Fe（II）pairs.The exposed Fe defective active sites can effectively activate H₂O₂ and OA to produce·OH and·CO₂^-.The radical quenching experiments showed that the main active species were·OH and[Fe^II（C₂O₄）₃]^2-species in photo-Fenton REDOX CIP and Cr（VI）.In addition,the intermediate products and three possible degradation paths of ciprofloxacin were analyzed by liquid chromatography-mass spectrometry.Based on the surface abundant Fe defects of SFS,a Cu/Fe double transition metal catalyst（Cu-SFS）was constructed by impregnation-calcination method,in which Cu²⁺ions were doped to the surface Fe defects in the way of vacancies filling.Compared with undoped SFS,the performance of activating peroxymonosulfate（PMS）Cu-SFS catalyst to degrade LEV was significantly improved.The performance of Cu-SFs catalyst was the best when the Cu doping amount was 3 mol%,which was 3.49 times that of SFS.Due to the negative charge of the metal defects,Cu²⁺can be adsorbed on the metal defects on the surface of SFS by water-bath pretreatment,and then converted into Cu-O bond by roasting to achieve Cu²⁺surface doping of SFS.Cu²⁺enters the SFS lattice by doping rather than adhesion on the surface in the form of Cu O.Surface doping of Cu²⁺can effectively improve the photogenerated charge separation efficiency.Meanwhile,the free radical signal test proved that Cu-SFS could activate PMS more effectively to produce·SO₄^-,·OH,·O₂^-and ¹O₂ radicals.The improvement of catalytic degradation performance can be attributed to the synergistic interaction between the fast photogenerated charge separation efficiency and the Fe/Cu bimetallic catalyst.In order to simplify the synthesis process and realize the purpose of catalyst recycling,magnetic sodium ferric silicate/ferroferric oxide-ferric oxide（SFS/M-FO）ternary composite was prepared by one-step in situ method.Compared with the ternary composites and bare catalyst,SFS/M-FO showed the optimal photo-Fenton catalytic performance,that is,the degradation efficiency of antibiotic tetracycline（TC）reached91.8%and the mineralization rate was 54.2%within 50 min of visible light irradiation.Density functional theory（DFT）,X-ray photoelectron spectroscopy and band structure demonstrated that the S-scheme path transport of photogenerated charge at the interface of SFS andα-Fe₂O₃,which ensures effective carrier separation and maintaining strong REDOX capacity.In situ growth promotes the formation of a semi-coherent interface between the SFS andα-Fe₂O₃ components,which can significantly reduce the transfer resistance of photogenerated charge.The introduction of magnetic Fe₃O₄ not only improves the photogenerated electron transfer efficiency,but also makes the material easier to recycle.The radical quenching experiments verified that h⁺and·OH active species played major roles.The intermediate products and proposed three possible tetracycline degradation routes were proposed by liquid chromatography-mass spectrometry.