Preparation Of TiO₂ Composite Photocatalysts Based On The Synergistic Effect Of Various Modification Technologies And Depth Analysis On The Process Of Degrading Organic Pollutants With Them

Since the beginning of the 21st century,with the progress of science and technology,rapid economic development and continuous improvement of living standards,human beings have to face severe problems such as global energy shortage and environmental pollution.How to get maximum output while reducing resource consumption,How to maximize the protection of the environment while developing resources,Photocatalysis technology with semiconductor materials as the core provides us with an ideal new idea of energy utilization and pollution control.Photocatalytic technology can use solar energy to split water to produce hydrogen,a green energy,to alleviate or partially solve the energy crisis.Photocatalytic technology can also use solar energy to degrade organic pollutants and reduce heavy metal ions to protect soil and water sources,thereby effectively improving our environment.Professor Fujishima discovered that titanium dioxide（TiO₂）can decompose water to generate hydrogen under the irradiation of ultraviolet light.Since then,TiO₂has become one of the most widely used catalysts in the field of photocatalysis due to its simple preparation method,low cost,stable physical and chemical properties,non-toxicity,and strong oxidizing ability.However,the inherent band gap of TiO₂is wide（about 3.2 e V）,and it can only be excited by ultraviolet light with a wavelength less than 387.5 nm to generate electrons and holes,which greatly limits the utilization of TiO₂for visible light.In addition,the photogenerated carriers of TiO₂are relatively easy to recombine,and these two problems severely limit the practical application of TiO₂.To improve the light absorption and utilization efficiency of TiO₂,the separation efficiency of photogenerated carriers and the surface photocatalytic reaction rate,researchers have carried out strategies such as element doping,dye sensitization,noble metal deposition,defect regulation and compounding with other semiconductors on TiO₂.This enables the photocatalytic activity of TiO₂,especially the photocatalytic activity under visible light,to be continuously improved.However,for those pollutants that are structurally stable and difficult to be degraded in the natural environment,sometimes the above single method is not effective.Therefore,the synergistic effect of various modification methods is expected to solve the problems of narrow light absorption range of TiO₂and low separation efficiency of photogenerated carriers at the same time.Based on this,a novel TiO₂-based composite photocatalyst that can efficiently degrade and deeply mineralize refractory pollutants under visible light is developed and constructed.In this dissertation,a series of novel TiO₂-based composite photocatalyst with visible light absorption and high photogenerated carrier separation efficiency were designed and fabricated by using various methods such as dye sensitization,morphology control,surface modification,bimetallic doping,and oxygen vacancy construction.The photocatalytic degradation of organic pollutants such as phenols,antibiotics and hormones was systematically studied.The mechanism of their photocatalytic was deeply analyzed and elucidated.The research work of this doctoral dissertation mainly consists of four aspects.The specific research contents are as follows:1.Preparation of Fe complex/TiO₂flower composite photocatalyst and its photocatalytic degradation of phenol and antibioticsUsing the complex formed by iron and 8-hydroxyquinoline-7-carboxylic acid（HQLC）as a sensitizer,and bonding with TiO₂by a hydrothermal method,two composite photocatalysts with different morphologies were obtained:Fe-HQLC/TiO₂particle and Fe-HQLC/TiO₂flower.Phenol and four antibiotics（ciprofloxacin,tetracycline,amoxicillin,and erythromycin）were used as target pollutants,and the photocatalytic activities of the two composite photocatalysts under visible light were investigated.The results showed that Fe-HQLC/TiO₂flower can rapidly degrade and mineralize phenol under visible light irradiation,and 50 mg Fe-HQLC/TiO₂flower can degrade 99%of phenol（concentration of 10mg/L）within 20 min.However,Fe-HQLC/TiO₂particle can only degrade 70%of phenol under the same conditions.The kinetic constant of Fe-HQLC/TiO₂flower to degrade phenol was 3.6 times that of Fe-HQLC/TiO₂particle and 52 times that of P25.Fe-HQLC/TiO₂flower can also quickly remove antibiotics in water.The removal rate of the four antibiotics by Fe-HQLC/TiO₂flower within 10 min was above 90%,and the maximum salinity reached78.6%.Antibiotic degradation products were analyzed by high-resolution mass spectrometry.The environmental toxicity and cytotoxicity of antibiotics and their degradation products were evaluated by bright luminescent bacteria experiments and cell experiments.Through the characterization of the structure,composition,morphology and surface properties of the composite photocatalyst,combined with the light absorption properties,photoelectric response properties and the properties of the active groups generated during the photocatalytic process,the analysis was carried out.The possible electron transport paths in the Fe-HQLC/TiO₂flower photocatalytic system and the mechanism of photocatalytic degradation of organic pollutants were proposed.2.Preparation of CDs@Cu complex/TiO₂flower composite photocatalyst and its photocatalytic degradation of phenol and glucocorticoid dexamethasoneThe complexes formed by copper and 8-hydroxyquinoline-5-carboxylic acid（HQAC）were used as sensitizers,bonded with TiO₂flower by hydrothermal method,and further surface-modified with carbon quantum dots（CDs）to obtain CDs@Cu-HQCA/TiO₂flower composite photocatalyst.Phenol and the glucocorticoid dexamethasone,which is extremely difficult to degrade naturally,were used as target pollutants,and the photocatalytic activity of the composite photocatalyst under visible light was investigated.The results showed that Cu-HQCA/TiO₂flower could rapidly degrade and mineralize phenol under visible light irradiation,but the degradation ability of dexamethasone was weak.In contrast,50 mg CDs@Cu-HQCA/TiO₂flower can degrade 99.6%of dexamethasone（at a concentration of 10mg/L）within 4 h.This was 1.3 times,1.5times and 7.6 times that of Cu-HQCA/TiO₂flower,TiO₂flower and P25,respectively.The salinity of CDs@Cu-HQCA/TiO₂flower to dexamethasone reached 77.4%.The sites vulnerable to free radical attack in the molecular structure of dexamethasone were predicted using theoretical calculations.At the same time,high-resolution mass spectrometry detection was carried out.Combining the above two results,the possible degradation products and degradation paths of dexamethasone were analyzed.The environmental toxicity of dexamethasone before and after photocatalytic degradation was also assessed.Through the characterization of the structure,composition,morphology and surface characteristics of the composite photocatalyst,combined with the light absorption characteristics,photoelectric response characteristics and characteristics of the active groups generated during the photocatalysis process,the analysis was carried out.Different electron transport pathways in four photocatalytic systems Cu-HQCA/TiO₂flower,CDs/TiO₂flower,Cu-HQCA@CDs/TiO₂flower and CDs@Cu-HQCA/TiO₂flower were proposed,and the mechanism of photocatalytic degradation of organic pollutants was analyzed.3.Preparation of EA@Nd-Fe-doped-oxygen vacancy TiO₂composite photocatalyst and its photocatalytic performance for the degradation of phenol and estrogen ethinylestradiolBy hydrothermal method and solid-phase thermal reduction method,neodymium-iron bimetallic doped titanium dioxide rich in oxygen vacancies was prepared,and then bonded with natural organic molecule ellagic acid（EA）to obtain a composite photocatalyst EA@Nd-Fe-（D-V_O）TiO₂.Phenol and the refractory estrogen ethinyl estradiol were used as target pollutants,and the photocatalytic activity of the composite photocatalyst under visible light was investigated.The results showed that under visible light irradiation,50 mg Nd-Fe-（D-V_O）TiO₂can only degrade about 58%of phenol（at a concentration of 10 mg/L）within 120 min.In contrast,EA@Nd-Fe-（D-V_O）TiO₂can completely degrade phenol within30 min,and 10 mg/L ethinyl estradiol can be completely degraded within 60 min,and the salinity of ethinyl estradiol was as high as 84%.The vunerable attacked sites of ethinyl estradiol were predicted by theoretical calculation,combined with the analysis of degradation products by high-resolution mass spectrometry,the possible degradation paths of ethinyl estradiol were proposed.The ecological risk of ethinylestradiol degradation products were further assessed.Through the free radical capture experiment,EPR,XPS and UPS characterization,combined with the characterization of the structure,composition,morphology and surface characteristics of the composite photocatalyst,the mechanism of the influence of bimetallic doping and the introduction of surface oxygen vacancies in the composite photocatalyst on the energy band structure of TiO₂was expounded.The possible electron transport paths in the photocatalytic system and the mechanism of photocatalytic degradation of organic pollutants were proposed.4.Preparation of water-soluble peryleneimide derivatives/TiO₂composite photocatalyst and its photocatalytic degradation of phenol and androgen trenbolone acetateThe water-insoluble PDI-SA and water-soluble PDI-ABS,4-Cl-PDI-ABS with broad spectral absorption and photothermal stability were used as sensitizers and bonded with TiO₂to obtain three composite photocatalysts PDI-SA/TiO₂,PDI-ABS/TiO₂and4-Cl-PDI-ABS/TiO₂.Phenol and the refractory male hormone trenbolone acetate were used as target pollutants,and the photocatalytic activity of the composite photocatalyst under visible light was investigated.The results showed that under visible light irradiation,50 mg of4-Cl-PDI-ABS/TiO₂can completely degrade 10 mg/L phenol within 20 min.The results were1.8 mes,2.8 imes and 14.3 times higher than those of PDI-SA/TiO₂,PDI-ABS/TiO₂and TiO₂,respectively.4-Cl-PDI-ABS/TiO₂could completely degrade 50 mg/L androgen trenbolone acetate within 60 min,and the salinity reached 72.3%.According to the theoretical calculation,the free radical reaction coefficient in the Fukui function was obtained,and the vulnerable sites in the Trenbolone acetate molecule were predicted.The degradation products were analyzed by high-resolution mass spectrometry,and the two were basically consistent.The change of the amount of degradation products with degradation time was tracked and analyzed,and the possible degradation pathway of trenbolone acetate was further proposed.Possible ecological risks were also assessed.Through the active radical trapping experiment and electron paramagnetic resonance（EPR）characterization,combined with the analysis of the photoelectric response characteristics of the composite photocatalyst and the built-in electric field of the peryleneimide derivative,the influence mechanism of the energy band structure of TiO₂was proposed.The band gap matching,possible electron transport paths and photocatalytic degradation mechanism of organic pollutants in three photocatalytic systems PDI-SA/TiO₂,PDI-ABS/TiO₂and 4-Cl-PDI-ABS/TiO₂were proposed.