Preparation And Performance Of The Modified TiO₂Photocatalysts

Photocatalytic oxidation, one of advanced oxidation technologies, has importantroles to water-splitting for hydrogen production, photocatalytic synthesis and thedegradation of organic contaminants. Photocatalytic oxidation has importantapplication feature in global warming, energy problems and environmental issues, etc.The widely explored TiO2has been accepted as an excellent photocatalyst among thesemiconductors due to its advantages of stability, low toxicity and high activity.However, the large band–gap energy (3.2eV) of TiO2considerably limits theutilization of natural solar light or artificial visible light. Photosensitization isconsidered to be an efficient and general method to modify the photoresponseproperties of TiO2.In this thesis, using commercial organic pigments and graphene as modifier tomodify TiO2to expand visible light absorption performance of TiO2. The structuresand property of modified catalyst were studied. There are three main parts in thisthesis:(1) TiO2photocatalyst sensitized with commercial organic pigment wasconveniently prepared and characterized by FT-IR, UV-Vis, XRD, SEM and N2adsorption-desorption isotherms. The adsorption capacities and photocatalyticactivities of the new photocatalyst were evaluated by photocatalytic degradation ofseveral kinds of representative pollutants under visible light irradiation. The resultsindicated that the new photocatalyst extends the photoresponse of TiO2from the UVto the visible region. The degradation rates of dyes RB (Rhodamine B), ACBK (AcidChrome Blue K) and MO (Methyl Orange) were24.8%,34.8%and9.4%respectivelyat their initial pH values in a fixed time under visible light irradiation with pure TiO2as the catalyst, while the degradation rates reach up to93.5%,94.6%and89.2%respectively in the present of BYH3G/TiO2(Benzimidazolone Yellow H3G/TiO2)under the same conditions. There was no appreciable loss of photocatalytic activityobserved when the photocatalyst was used four times, which demonstrates excellentstability and recyclability factors. Furthermore, sensitized TiO2with Pigment Red254,Pigment Red151, Pigment Red179, Phthalocyanine Green G, Pigment Red122wereprepared, and they all display better visible light catalytic activity than pure TiO2inthe degradation of MO and RB test under visible light irradiation. The mechanism ofaction was also discussed. (2) Graphene/TiO2(GE/TiO2) was prepared by hydrothermal treating of a mixedsuspension of TiO2and graphite oxide. The prepared catalyst was characterized byFT-IR, UV-Vis, XRD and SEM. The adsorption capacity of GE/TiO2for RB、MB(Methlyene Blue) and MO was better than pure TiO2. Pure TiO2has a little bit ofdegradation capacity for RB and MB, but has no degradation capacity for MO, thevisible-light degradation ability of GE/TiO2was better than the pure TiO2. In addition,the degradation rate in the presence of UV light was far better than that of visible light.The degradation rate of MO was95.6%in70min under UV light irradiation, thedegradation rate of RB was99.1%in60min, and the degradation rate of MB was99.4%in70min. The mechanism of action was also discussed.(3) Phenol photocatalytic oxidation experiment was carried out under ultravioletand visible light irradiation with the pure TiO2, GE/TiO2and BYH3G/TiO2catalysts.Under visible light irradiation, phenol was relatively stable and only a little catecholwas produced when use BYH3G/TiO2as the catalyst. While under UV-lightirradiation, there were obvious photocatalytic oxidations for phenol, and most phenolwas hydroxylated to pyrocatechol (CAL) and hydroquinone (HQE), others werephotocatalytic oxidized into benzoquinone or other materials. The effects of variousparameters on photocatalytic oxidation of phenol were studied. When using TiO2ascatalyst, the highest conversion of phenol was66.9%, and the yield of CAL and HQEwere12.6%and4.6%respectively, and the selectivity of the reaction was25.7%.Using GE/TiO2as catalyst, the highest conversion of phenol was92.1%, and the yieldof CAL and HQE yield were19.8%and11.2%, the selectivity was33.6%. UsingBYH3G/TiO2as catalyst, the highest conversion of phenol was63%, the yield ofCAL and HQE can reach28.7%and27.6%respectively, and the selectivity of thereaction was up to89.3%. From high yield of CAL and HQE perspective,BYH3G/TiO2was the best hydroxylation catalyst, the second was GE/TiO2, and theworst was pure TiO2. The mechanism of photocatalysis of the catalysts was inferred.