Direct Determinations And Photocatalytic Reactions Of Pollutants In Suspension Systems

Titanium dioxide (TiO₂) photocatalysis technology that is used as one of the advanced oxidation technologies has remarkable advantages and prospective development. For its practical applications, TiO₂ photocatalytic suspension system is of simple operation, sufficient irradiation and high photocatalytic efficiency comparing with photocatalytic system of fixed membrane. However, it is difficult to recover the catalysts in suspension systems, and meanwhile the determinations of pollutants degraded are also a problem. At present, the methods for determining the pollutants mainly include electrochemistry, chromatography and its united technology, spectrophotometry and so on. Comparatively, spectrophotometry is characteristic by its simple equipment, low price and wide application range. Many heavy metallic ions, organic and inorganic compounds can be spectrophotometric determined, and it is possible to achieve the synchronous determination for multi-items and easy to achieve the on-line analysis by combining it with the flow injection analysis. But the problem is that the light dispersion caused by the tiny granules in test solution can inevitably interfere the spectrophotometric determination for pollutants in TiO₂ suspension system, especially for the ultrafine nanometer TiO₂, which can not be in a state of true solution even though centrifugal separation and membrane filtration processes have been adopted. In this case, it is difficult to indicate the true variations of pollutants in photocatalytic systems with the detecting results for the light dispersion caused by tiny granules in test solution, and in particularly, it is impossible to achieve on-line analysis by spectrophotometry and investigation on the reaction kinetics of photocatalytic degradation. On the consideration of the factors, a novel method for directly determining the concentrations of pollutants in TiO₂ suspension systems with three-wavelengths spectrophotometry that can efficiently eliminate the turbidity interference has been proposed, and the photocatalytic reactions of these pollutants have also been investigated based on the results of direct determination.Firstly, methyl orange (AO) was selected as a waste water model, and the possibilities for its concentrations which were directly determined three-wavelengths spectrophotometry that eliminated the turbidity interference and its effects of photocatalytic degradation which were represented based on the results of direct determination in TiO₂ suspension systems had been investigated in details. The results showed that the concentrations of AO in TiO₂ suspension systems couldbe directly determined in a wide range by three-wavelengths spectrophotometry which could efficiently eliminate the turbidity interference. The method was applied to the real system that AO had been degraded by T1O2 photocatalysis. It was found that the actual result was confirmed by agreement with the result from routine method, and the repeatability of measurement results in various turbidities was satisfying.On the basis of the conclusions, the degradation effects of methlyene blue (MB) with TiO2 photocatalysis were investigated by AA measured by three-wavelengths spectrophotometry. The results indicated that the chroma variations of MB in the course of photocatalytic degradation, and the effects of catalyst amounts, MB initial concentrations, light strength, pH, and salt effect on MB photocatalytic degradation rate, could be clearly reflected based upon the AA measured. Meanwhile, the aggregation of MB dye molecule in aqueous solution was also studied. Not only the molar absorption coefficient of MB monomer and the equilibrium constant of dimerazition had been obtained by computer programming method that coincided well with the results from constructive method, but also the molar absorption coefficient of MB dimer and the proportion coefficient of MB monomer in different concentrations had also been worked out.Furthermore, the concentrations of phenol in T1O2 suspension systems had been directly determined by three-wavelengths spectrophotometry. To compare with 4-aminoantipynin color-developing method and spectrophotometric method which detected phenol by maximum absorption wavelength at 270 nm, three-wavelengths spectrophotometry could eliminate interference caused not only by turbidity system but also by intermediates degraded, which could be more objective to reflect the degradation course of phenol photocatalysis. Meanwhile, the possibility of selective oxidation of high-strength phenol that was performed by T1O2 photocatalytic oxidation had also been discussed according to the HPLC results of phenol intermediates. It was indicated that the maximum main productions, hydroquinone and catechol, could be obtained by controlling different pH values under the conditions of direct UV irradiation and T1O2 photocatalysis respectively, while the minimum byproducts were formed accordingly.The concentrations of heavy metallic ion, Cr(VI) in T1O2 suspension system were uirectly detect by three-wavelengths spectrophotometry which was upon a color-developing reaction. Based upon it, the reactions of dark adsorption and TiC>2 photocatalytic reduction removal of Cr(VI) ion had been investigated in details, andthe effect factors, such as different initial concentrations, pH, competitive ions and reaction mechanism had also been discussed.On the basis of the above results, the photo-induced reaction and TiO2 photocatalytic reaction of Cr(A/I)-phenol coexist system were investigated. The results manifested that there were some redox reactions between the Cr(VI) and the photodegradation intermediates of phenol. It resulted in that Cr(VI) reduction rates of photo induction and photocatalysis had been improved dramatically. Meanwhile, the photo degradation rate of phenol had been somewhat increased in the beginning of the process and then decreased for the accumulation of phenol intermediates. The inhibition impact had been enhanced in the presence of TiC>2, and the photocatalytic degradation rate of phenol greatly decreased. It provides significant guidance for the efficient designs of photocatalytic system for complex pollution systems with both oxidation and reduction processes.At last, the technology of TiC>2 photocatalytic oxidation had been applied to analytic chemistry in this paper. A micro-reactor of TiO2 photocatalysis had been designed and made successfully. The pretreatment process of standard method for phosphor determination that added strong oxidants for digestion had been replaced by the method of TiC>2 photocatalysis, and the results from photocatalysis were contrast with that from standard methods. It was manifested that all kinds of classic organics containing phosphor could have been completely decomposed with the action of TiC>2 photocatalytic oxidation, and the degradation products with unitary form had been obtained, which could be quantified by three-wavelengths spectrophotometry after a color-developing reaction. The results of phosphor determination for various organics and environmental samples were satisfying with comparing with the results from standard methods. It was implied that the pretreatment processes in standard method could be replaced by the method of TiC>2 photocatalytic oxidation that was characteristic by simple operation, light-duty reaction and easy to be instrumental. It avoided the shortages of nanometer TiO2 in traditional use that was difficult to recover catalyst, high usage cost and cloudy interference since the use level was small for analysis and the determinations were directly fulfilled in suspension system, which provided a feasible method for further design and manufacture of on-line water quality monitor for TOP in environmental samples.