Study On The Preparation And Application Of Novel Nano-Photocatalyst Driven By Visible Light

Worldwide energy resource crisis and environment pollution are becoming more severe with each passing day. In the 21st century, environmental problems caused by noxious and nonbiodegradable organic pollutions such as dyes and PPCPs have deeply affected the survival and development of human beings. Such pollution is difficult to solve with traditional environment technology. How effective use of sunlight to solve environment pollution problems has become the focus to the world. With the public concern for environmental problems increased, novel treatment methods being promoted and developed. Photocatalysis has gained a great deal of attention in the field of pollutant degradation. Photocatalytic technology, an advanced oxidation technology, is a green utilization of solar energy. Studies have proven that photocatalysis oxidation technology is able to treat many kinds of organic pollutants. In recent years, many researchers have focused on modified nano titanium dioxide and binary or ternary compound photocatalysts, because of extending the photoresponse rangea and increasing the efficiency of charge separation.We are motivated to work in this direction in the present dissertation, and summarized the mechanism and influencing factors of photocatalysis techniques, and reviewed the study on development and application of modified nano-titanium dioxide and coupled oxide semiconductors visible light-activated photocatalysts. As well as treatment effect of photocatalysis of dye and antibiotic wastewater are illustrated in details.Based on a sufficient understanding of the relationship between the organic pollution and photocatalyst specialty, two series of novel nanocomposite photocatalysts are successfully prepared using simple methods. One type comprises rare earth and nonmetal elements co-doped TiO2 photocatalyst. whereas the other comprises ternary nano-composite photocatalysts. Subsequently, the effects of photocatalysts synthesis and reaction conditions on photocatalytic activity are systematically analyzed. Dye wastewater (Reactive Blue 19 and Acid Blue 62) and antibiotic wastewater [sulfadiazine (SD) and chlortetracycline (CTC)]. the target compounds in source water and the most widely used antibiotics, respectively, have been chosen as the study samples. The effects of main factors of photochemical degradation, degradation mechanisms, kinetics, and reaction pathways of the processes under simulated sunlight irradiation are amply studied. Some important valuable achievements and conclusions have been obtained in the current thesis, offering theoretical and experimental guidelines with practical applications for the degradation of organic pollutants. The current dissertation contains the following major parts:1. Preparation and characterization of lanthanum and iodine co-doped TiO2 photocatalystThe novel visible-light-activated La/I/TiO2 nano-composition photocatalyst was successfully synthesized using precipitation-dipping method, and characterized by XRD, BET, TEM, XPS, TG-DSC, and UV-Vis DRS. The characterization results of XRD, TEM, and BET indicate that the La/I/TiO2 photocatalyst calcined at 350℃for 2 h resulted in bigger BET surface area and smaller crystal size, in comparison with La/TiO2 or I/TiO2 photocatalysts. Characterization results also reveal that the lanthanum and iodine co-doped can hinder the aggregation and growth of TiO2 particles, which cause the decrease in particle sizes and the increase internal surface areas. The La optimal doping concentration is 1.5% in the present dissertation. In addition, the XPS spectra indicate that Ti atoms exist in the form of Ti4+ state and that part of I5+ replaced Ti4+ of the prepared photocatalysts. La2O3 was converted on the surface of nano TiO2 particles, resulting in the separation of electrons and holes and structural deformation of TiO2 The crystal size of the TiO2 particles was restrained after the La3+ elements were doped onto the crystal lattice. The UV-Vis-DRS of the as-prepared La/I/TiO2 photocatalysts shows that the absorption edge of the lanthanum and iodine co-doped TiO2 shifting significantly to the visible-light region in comparison with the TiO2, and this work may provide new insights into the development of novel sunlight photocatalysts.2. Photocatalytic activity of visible-light-driven TiO2 photocatalyst co-doped with lanthanum and iodine under simulated sunlightThe photocatalytic activity of lanthanum and iodine co-doped TiO2 photocatalyst was evaluated by studying the photodegradation of Reactive Blue 19 and SD as a probe reaction under Xe light irradiation. Studies have indicated that the La/I/TiO2 photocatalyst calcined at 350℃could effectively mineralize Reactive Blue 19 and SD under simulated sunlight irradiation. In addition, the degradation kinetics of reactive blue 19 and SD in aqueous La/I/TiO2 suspensions follow pseudo-first-order kinetics under simulated sunlight irradiation, when both of the concentration is in the range of investigation, demonstrating that La/I/TiO2 photocatalyst has remarkable photocatalytic activity.Under simulated sunlight irradiation, the degradation of Reactive Blue 19 aqueous solution reached 98.6% in 80 min, and the removal rate of TOC was about 90% when the initial concentration of Reactive Blue 19 solution was 50 mg/L, the pH value was approximately 3 to 7, whereas the concentration of La/I/TiO2 photocatalyst was 1.0 g/L. These results show that La/I/TiO2 photocatalyst maximal photocatalytic activity. Furthermore, the degradation of Reactive Blue 19 on La/I/TiO2 photocatalyst under irradiation of different light sources shown in the simulated sunlight system was the best. The possible reason is that the gathering of intermediates adsorbed on the photocatalysts surface will cause the catalysts poisoning, however, the ultraviolet rays in the simulated sunlight can effectively mineralize the intermediates and prevents photocatalysts from poisoning. Experimental results indicate that the La/I/TiO2 photocatalysts can degrade and mineralize the industry dye wastewater when the reaction time is in the range of investigation, and can reach a removal rate of COD was approximately 90%.The La/I/TiO2 photocatalyst also exhibited strong photocatalytic activity in photodegradation of SD wastewater, the degradation of SD aqueous solution reached 90% in 90 min under simulated sunlight irradiation.·OH radicals are the most important oxidizing species which can attack and transform the organic molecules to inorganic micro molecule. The mechanism of La/I/TiO2 degradation SD may involved in high oxidation ability of active hydroxyl radicals(·OH) which are strongly enough to break the S-N and C-S bond of SD.-SO2 functional group was removed from SD molecule, generated the intermediate product 4-(2-iminopyrimidine-1(2H)-vl) aniline under the condition of simulated sunlight irradiation. And then·OH again attacks, SD is broken into inorganic micro molecule through different Pathway. After many times of recycle use, La/I/TiO2 photocatalysts still keep high photocatalytic activity, which shows that La/I/TiO2 photocatalysts are promising catalysts in the industrialization field.3. Preparation, characterization and photocatalytic activity of La/CuO-SnO2 in simulated sunlight irradiationSnO2 is an n-type semiconductor and it has the similar to rutile TiO2 crystal structure. In view of these properties, La/CuO-SnO2 ternary nano-composite photocatalysts were prepared under different calcination temperatures using a simple co-precipitation method in the current dissertation. With different calcining temperatures, the characterization results of XRD, BET, TEM. and UV-Vis display that the samples particle size, crystalline structures, photo absorption and surface area varied significantly. The photocatalytic experimental results show that the maximum specific photocatalytic activity of the La/CuO-SnO2 nano-composite photocatalysts appears after calcination at 450℃for 2.5 h, the molar ratio of CuO to SnO2 of 1:1, and doping concentration of La at 2.0% because of the good crystallization, high BET surface areas (110.35 m2/g), small crystal size (15.4 nm) and strong optical absorption of the sample. The photocatalytic activity of La/CuO-SnO2 nanocomposite oxide was evaluated using the photodegradation efficiency of acid blue 62 as a probe under Xe light.irradiation. Under simulated sunlight irradiation, the degradation kinetics of Acid Blue 62 in aqueous La/CuO-SnO2 suspensions followed pseudo-first-order kinetics, and when the concentration of Acid Blue 62 in the range of investigation, as the initial Acid Blue 62 concentration increased, the degradation rates decreased. The degradation of Acid Blue 62 aqueous solution can reach a removal rate of TOC was approximately 68%, and the degradation rate of 97.71% in 2 h when the initial concentration of Acid Blue 62 solution of 50 mg/L, the concentration of La/CuO-SnO2 photocatalyst was 1.0 g/L, and the pH value was approximately 5.35, showing that the La/CuO-SnO2 nanocomposite photocatalyst has a much higher photocatalytic activity than the standard Degussa P25 photocatalyst.4. Photocatalytic degradation of chlortetracycline over La/CuO-SnO2 photocatalysts under simulated sunlightThe paper chose CTC as the object, and analyzed the feasibility of CTC treatment by La/CuO-SnO2 photocatalysis. The experiment result shows that the La/CuO-SnO2 ternary nano-composite photocatalysts exhibits excellent photocatalytic activity. The paper reviewed the optimal condition of CTC initial concentration, La/CuO-SnO2 photocatalyst concentration, different pH values, and different lights for CTC treatment by La/CuO-SnO2 photocatalysis. In addition, the effect of various oxidant supplies and the dynamics of CTC treatment by photocatalysis were studied. The maximum degradation ratio of CTC by photocatalysis was 88.7% under the following conditions:CTC initial concentration 50 mg/L, La/CuO-SnO2 photocatalyst concentration 1.5 g/L, and pH 3, and COD removal efficiency could reach up to 93% in 120 min. Meanwhile, the value of BOD5/COD> 0.3 of wastewater after 40 min irradiation, it showed chemical and biologic properties were improved. The addition of oxidant also improved the photocatalysis result. When the concentration exceeded 300 mg/L of H2O2 added into the reaction system, the time was cut down. The rate of degradation of CTC can be described by the Langmuir-Hinshelwood equation. A series of photo-oxidation and subsequent chemical reactions were involved on degradation of CTC chemical mechanisms during the photo-catalytic processes. A variety of bicyclic and tricyclic compounds were included in intermediate products of CTC. Polycyclic compounds were opened up, and then small molecular compounds were produced. Ultimately, some inorganic products were investigated. The results indicated that La/CuO-SnO2 photocatalysts have high photocatalytic activity, and have important value in practical application.