Synthesis, Characterization And Application Of "All-in-One" TiO₂Composite Photocatalysts In Wastewater Treatment Process

Environmental pollution by toxic compounds can be detrimental to human health and the environment. Dinitrophenolic compounds and dyestuffs are widely avknowledged to be two types of hazardous compounds. These hazardous compounds are introduced into environment from its manufacturing and application processes. Although much benefits is obtained from their uses, dinitrophenolic compounds and dyestuffs have some undesirable side effects, such as toxicity and carcinogenity, and these hazardous compounds can be hardly destroyed by using conventional wastewater treatment methods. Therefore, the removal of dinitrophenolic compounds and dyestuffs from aqueous solution is necessary and very important. The direct photocatalytic reaction by using semiconductor particles as photocatalyst has attracted much attention as a promising method to degrade organic pollitants in recent20years. Among these semiconductor materials, TiO2as photocatalyst has been widely used to photodegrade organic pollutants for its relatively high catalytic reactivity, nontoxicity, physical and chemical stability, avirulence and cost-effectiveness. However, uses of TiO2nanoparticles in applications such as wastewater treatment have been limited because there are major bottleneck drawbacks associated with TiO2photocatalysts, namely, low photo-quantum efficiency arising from the fast recombination of photo-generated electrons and holes, low efficiency for utilizing solar light due to its large band gap, low capacity for the adsorption of organic pollutants and the problem of separation and recovery of nanometer sized TiO2particles from water. The preparation of TiO2composite photocatalysts by using doping, sensitizing, intelligent polymeric hydrogel supporting and surface modification methods are reported in this work. The application of these TiO2composite photocatalysts in the photocatalytic degradation of dinitrophenols and dyes containing wastewater is also investigated thoroughly in the thesis. The main results are as follows:1. The TiO2-GO composite photocatalyst was prepared by doping graphene oxide (GO) into the nanosized TiO2particles. The microstructure and morphology of the photocatalyst were characterized by XRD, SEM, TEM, FT-IR, UV-vis and TG-DTA techniques. The results showed that the addition of GO can enhance the degree of dispersion and adsorption capacity of TiO2particles can be enhanced significantly by doping TiO2with GO. The TiO2-GO composite photocatalyst can cause an obvious red shift of UV-vis spectra compared with pure TiO2. The photocatalytic degradation of2-.sec-butyl-4,6-dinitrophenol (DNBP) was studied with TiO2-GO composite photocatalyst under visible light illumination. The effect of experimental parameters such as pH values, initial concentration of DNBP, catalyst dosage, irradiation time, etc. on the photocatalytic degradation efficiency of DNBP were systematically studied in the work. The results indicated that the TiO2-GO composite photocatalyst showed much higher adsorption capacity and photocatalytic degradation efficiency than the pure TiO2catalyst. The photocatalytic reaction was discussed in terms of Langmuir-Hinshelwood model and followed pseudo-first order kinetics in low concentration of DNBP. A plausible DNBP degradation pathway was also suggested on the basis of analysis of degradation products.2. Poly-o-phenylenediamine (PoPD) sensitized TiO2-GO composite photocatalyst (PoPD-TiO2-GO) was successfully synthesized by’in situ’polymerization ofPoPD in the presence of TiO2-GO particles with ultraviolet light photoinitiating method. The prepared PoPD-TiO2-GO composite photocatalyst was characterized by XRD, SEM, TEM, FT-IR, UV-vis techniques. The results demonstrated that a dense conductive PoPD layer with reasonable thickness deposited on the surface of TiO2-GO composite particles, which can enhance adsorption of organic pollutants and make more use of visible light. The photocatalytic decolorizadation of methylene blue (MB) was evaluated with PoPD-TiO2-GO composite photocatalyst under visible light irradiation. The effect of experimental parameters such as pH values, initial concentration of DNBP, catalyst dosage, irradiation time, etc. on the photocatalytic decolorizadation of MB were systematically investigated. In terms of Langmuir-Hinshelwood model the photocatalytic decolorization reaction followed pseudo-first order kinetics in low concentration. The PoPD-TiO2-GO composite photocatalyst showed much higher adsorption capacity and photocatalytic degradation efficiency than the pure TiO2catalyst. Moreover, the composite photocatalyst has high reusable ability.3. A novel composite photocatalyst of Poly(N-isopropylacrylamide-co-acrylic acid-co-cobalt tetra(N-carbonylacrylic) aminephthalocyanine)/(titanium dioxide-graphene oxide)(Poly(NIPAM-co-AAc-co-CoMPc)/(TiO2-GO)) was successfully prepared via free radical polymerization method. The microstructure and morphology of the photocatalyst were characterized by XRD, TEM, FT-IR, UV-vis techniques. The results show that TiO2particles were successfully encapsulated in the copolymer carrier in spherical shapes and the composite photocatalyst was activated by visible light. The thermo-and pH-responsive properties of the composites were investigated by using swelling ratio measurements. The photocatalytic activity of obtained Poly(NIPAM-co-AAc-co-CoMPc)/(TiO2-GO) composite catalyst in visible light was estimated by measuring the degradation efficiency of DNBP in an aqueous solution. The effect of pH of the solution, catalyst concentration, irradiation time and initial DNBP concentration were examined as operational parameters. The thermo and pH sensitive composite photocatalysts exhibited easy separation and less deactivation after several runs. The results showed the feasible and potential use of the multisensitive composites in photodegradation of organic pollutants by controlling temperature and pH simply.4. A series of triazine. compounds such as2,4-bis(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine were successfully synthesized by using anisole and cyanuric chloride as raw materials. The synthesized triazine compounds can be used as ultraviolet absorbers. TiO2-GO composite photocatalyst modified with the synthesized triazine compounds showed much higher adsorption capacity than the pure TiO2catalyst.