Cheng Hefa, Reinhard Martin
Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020, USA.
Environ Sci Technol. 2007 Mar 15;41(6):1934-41. doi: 10.1021/es062332v.
Contaminant transformation rates in the subsurface can be slowed by sorption onto geosorbents. We evaluated the effect of micropore sorption on contaminant transformation in a model system consisting of dealuminated Y zeolites and 2,2-dichloropropane (2,2-DCP). 2,2-DCP dehydrochlorinates in water to 2-chloropropene (2-CP) at a rate of 2.93 x 10(-4) min(-1) at 24 degrees C. The Y zeolites used range from hydrophilic (CBV-300) to hydrophobic (CBV-720 and CBV-780). Wet zeolite samples were loaded with 2,2-DCP at 24 degrees C and reacted at 50 degrees C for 10 h. Results show that the hydrophobic zeolites (CBV-720 and CBV-780) sorbed nearly 900 times more 2,2-DCP than the hydrophilic CBV-300 under wet conditions. 2,2-DCP transformed less when sorbed in micropores of CBV-720 (6.3%) and CBV-780 (5.0%) than in micropores of CBV-300 (81.5%), and significantly less than in water (> 99.85%). Inhibition in hydrophobic micropores is interpreted as lack of water solvating the transition state of 2,2-DCP dehydrohalogenation and the H+ and Cl- formed. Near the micropore openings, the transformation was relatively fast, consistent with greater abundance of water associated with the hydrophilic edge sites. These results indicate that in the subsurface the half-lives of reactive organic contaminants may be longer than predicted from bulk water data.
污染物在地下的转化速率可因吸附到地质吸附剂上而减缓。我们在一个由脱铝Y型沸石和2,2 - 二氯丙烷（2,2 - DCP）组成的模型系统中评估了微孔吸附对污染物转化的影响。在24℃下，2,2 - DCP在水中脱氯化氢生成2 - 氯丙烯（2 - CP）的速率为2.93×10⁻⁴ min⁻¹。所使用的Y型沸石从亲水性（CBV - 300）到疏水性（CBV - 720和CBV - 780）不等。将湿的沸石样品在24℃下加载2,2 - DCP，并在50℃下反应10小时。结果表明，在潮湿条件下，疏水性沸石（CBV - 720和CBV - 780）对2,2 - DCP的吸附量几乎是亲水性CBV - 300的900倍。与在CBV - 300微孔中（81.5%）相比，2,2 - DCP在CBV - 720（6.3%）和CBV - 780（5.0%）微孔中的转化较少，且明显低于在水中（>99.85%）。疏水性微孔中的抑制作用被解释为缺乏水来溶剂化2,2 - DCP脱卤化氢的过渡态以及形成的H⁺和Cl⁻。在微孔开口附近，转化相对较快，这与亲水性边缘位点处更多的水相一致。这些结果表明，在地下，活性有机污染物的半衰期可能比从大量水体数据预测的更长。
