Modified Of TiO₂ Photocatalyst And Wastewater With Bromamine Acid Treatment By Combined Freeze And Photocatalysis

Since dyes wastewater has the characters of containing much pollutant, high chromaticity and the fast change of pH value, it has become one of the difficult treatment wastewater. The photocatalyst was modified upon the base of production of our group, and the lacunaris coupling CdS/TiO₂ photocatalyst was prepared.The degraduation of bromamine acid solution by the lacunaris coupling CdS/TiO₂ photocatalyst and the freeze of bromamine acid solution were both studied. Then prelimimary research on dyes wastewater with bromamine acid treatment by combined freeze and photocatalysis was carried out in this paper.Lacunaris coupling CdS/TiO₂ photocatalyst which can be activated by visible light and easily separated from liquor was prepared by coupling CdS with lacunaris TiO₂ by a sol-gel process. Prelimimary research suggested that the optimal preparation condition is calcining temperature 700℃, and CdS adulterant proportion3%.The photocatalytic degradation by sunlight was investigated with bromamine acid as pollutant , and the effects of light intensity , initial concentration of the pollutant , dosage of photocatalyst , pH value , sodium chloride concentration and reaction time on the photocatalytic degradation were discussed . The results suggested the optimal degradation condition is higher light intensity , dosage of photocatalyst 2g/L , and pH value 12 for the bromamine acid solution of 30mg/L . Meanwhile the sodium chloride has a promote effect on degradation of the solution ,at the same time the removal rate of total organic carbon (TOC) has a slight decrease as the concentration of sodium chloride increased . Furthermore, the degradation rate decreased distinctly when the concentration of bromamine acid is higher than 50mg/L.When the synthetic wastewater with bromamine acid is frozen gradually, ice crystals grow from the pure water only, while pollutants are rejected into the liquid phase thus increasing their concentration. The results indicated a slower cooling rate was necessary to get the purer melted ice, and there was no obvious effect on the purity of melted ice when the concentration of bromamine acid is below a some value when the other condition was fixed, while when the concentration is too high, the separation efficiency would reduce. Meanwhile the existence of sodium chloride in the solution had no good for bromamine acid molecule being separated from ice crystals. Yet the bromamine acid had no obvious effect on inorganic ions in the separation process.The wastewater can be purified after freezing by the pollutants being rejected into the liquid phase. So the efficiency of photocatalytic degradation will be advanced if before which a freeze-concentration as a preprocess be inserted. The synthetic wastewater and industry wastewater treatments by combined freeze-concentration and photocatalysis was researched in this paper. After freezing, the synthetic wastewater with 500mg/L bromamine acid and 500mg/L sodium chloride was purified. When 70% of wastewater was frozen , the concentration of sodium ion Na+, total organic carbon (TOC) and chroma of melted ice fell from 209.88mg/L,208.9 mg/L and 8.12 to 19.06mg/L,24.80 mg/L and 0.638.Then the melted ice was degradated by lacunaris coupling CdS/TiO₂ photocatalyst under sunlight. After 6 hours, the removal rate of chroma and total organic carbon (TOC) reached 100% and 87.04%.The industry wastewater with high concentration dye(mainly bromamine acid) and salt (mainly sodium chloride) treatment by combined triple-stage freezing-concentration and photocatalysis was investigated too . It showed that the impurities of melted ice after triple-stage freezing were sharply decreased, and the removal rate of chroma and chemical demand of oxygen (COD) were 92.42% and 74.27% after the melted ice was photocatalytic degradated. But at the same time the volume of purer water which can be obtained from the process were limited. Thus the cycle-freezing of the concentrated solution should be considered.