| TiO2 has become one of the most remarkable environmental purification materials due to its high photocatalytic activity, high chemical/heat stability, good accessibility, non-toxicity, non-negative effect on the environment and its thoroughgoing efficiency on catalyzing those matters difficult for biodegradation, and its utilization has been widely studied in environmental protection. However, some certain limits has made it difficult to utilize TiO2 in the practice of industrial wastewater treatment, of which the main limits are a photoresponse scope which is too narrow (that only responsive for UV-light ofλ<387 nm) and the difficulties in recovering/reuse. Currently, most of the studies are the preparation of nm-size TiO2 colloidal sols and powders, making it difficult to recover; there are also studies focusing on support-photocatalysts, yet problems such as insufficient stability of the supports and catalyst film falling off exist; in terms of property change, it's mainly about the improvement of the photocatalytic activity.This experiment fabricates TiO2- Al2O3 compound photocatalyst microballons which varies from 0.5mm to 2mm by adopting the granulating method of 'collosol-ultrasonic communion-gel-oil dripping'. XRD analyses of the samples from the compound photocatalysts fabricated in different Ti/Al moles rates and different calcination temperatures were conducted to identify the impact of different calcination temperatures on the formation of TiO2- Al2O3 crystals. We picked the catalyst of a certain rate and calcination temperature to examine its photocatalytic activity on the bio-toxic 2,4-dinitrophenol (2,4-DNP) which was chosen as the simulation pollutant, and used UV-light germicidal lamp as the light source.Tests of photocatalytic degradation, BAF biodegradation and photocatalytic-BAF combined degradation were conducted on the simulation wastewaters of different concentration of 2,4-DNP so that we could compare the characteristics of separate treatments and the combined treatment; UV-vis and HPLC were adopted to analyze the water samples and to observe the degradation outcome of 2,4-DNP.XRD analyses showed that the addition of Al evidently increased the phase-transition temperature of TiO2, that it transformed from anatase type to rutile type at 850℃; the absence of the diffraction peak of Al2O3 when TiO2:Al2O3< 1:2 implies the possibility that TiO2 might be distributed on the surface in non-crystal formations. The HPLC charts of the water samples showed that a kind of main intermediate material was detected in both the photocatalytic degradation and the BAF biodegradation, and sometimes several different ones. The UV-vis charts showed the occurrence of denitration in the first place during degradation, that nitro groups were replaced by hydroxyl groups. The lowering down pH during photocatalytic degradation showed that some carboxylic acid type intermediate products were generated during the reaction, which indicates the break of benzene rings. The principle process of the degradation might be as follows:nitro groups replaced-rings are broken-complete oxidization; the final products are NO3-,CO2,H2O.The outcome of the catalytic tests showed that the catalysts we prepared are endowed with relatively high photocatalytic activities under UV-light, and are easy to separate from the water solutions after having been used. Taking photocatalysis as a pretreatment and then use BAF bio-degradation, it turned out that the intermediate products of the photocatalysis oriented the microbes to the toxic wastewater better, and the degradation rate of 2,4-DNP was high improved compared to sole bio-degradation, leading to a dramatic shortening of the degradation time. |
PDF Full Text Request