纳米二氧化钛光催化转化甲基砷的研究

二甲基胂酸(DMA)和一甲基胂酸(MMA)是环境中甲基砷的主要种类.由于农药滥用及含砷废水的释放等,严重危害人类健康.本文应用实验室人工合成纳米TiO2研究了甲基砷(DMA和MMA)光催化转化过程,考察了光照和pH对光催化转化过程的影响,通过测定液相及固相中的不同化学形态,解析光催化转化产物.结果表明:UV光照下,相比自然光时,纳米TiO2对DMA和MMA的去除率在不同pH条件下均有提高.pH值的影响为:在低pH条件(pH为3、5)下去除率高,而在高pH条件(pH为7、9)下去除率低,这主要是取决于纳米TiO2的等电点(pHpzc=5.8).转化产物解析结果表明:无光条件下,DMA和MMA均不发生转化;在自然光条件下,纳米TiO2催化少量DMA和MMA发生一步转化,分别形成MMA和As(V);在紫外光条件下,纳米TiO2能够催化几乎全部的DMA和MMA彻底转化,形成As(V).因此,在UV光下,纳米TiO2能够催化DMA和MMA转化为As(V),同时此纳米TiO2对As(V)有较强的吸附能力,所以,UV光照能够显著提高纳米TiO2对DMA和MMA的去除率.

Photocatalytic transformation of dimethylarsinicand monomethylarsonic acids by NanoTiO2

Photocatalytic transformation of dimethylarsinic acid (DMA) and monomethylasonic acid (MMA) with nano titanium dioxide (TiO₂) was investigated by exploring the effect of light condition and pH, and by analyzing the catalytic transformation products. In the presence of UV irradiation, the removal rate of DMA and MMA was higher than that with normal light under any pH conditions. The removal rate was high at pH 3~5 and decreased as the pH increase from 7 to 9. This pH effect could be attributed to the point of zero charge of nano TiO₂(pH_pzc=5.8). In the dark, DMA and MMA remained the same species; under the natural light illumination, little DMA and MMA were catalytically transformed into MMA and As (V), respectively, in the presence of TiO₂; under the UV irradiation, almost all DMA and MMA were catalytically transformed into As(V) by TiO₂. The results showed that DMA and MMA could be photocatalytically transformed into As(V) by Nano-TiO₂ under UV irradiation, and readily removed from aqueous phase because of the high adsorption capacity of Nano-TiO₂ for As(V).