共存物质对O_3/H_2O_2工艺降解2,4-D的影响(Ⅰ)2,4-D降解动力学

Effect of coexisting substances on degradation of 2,4-D in O_3/H_2O_2 process(Ⅰ)2,4-D degradation kinetics

采用少量无机盐、有机物添加至去离子水配制的2,4-D溶液及自来水、地表水配制2,4-D溶液的方法,模拟实际复杂水质对O3/H2O2工艺降解2,4-D的影响。结果表明不同共存物质对2,4-D降解动力学产生不同的影响,磷酸钠、碳酸钠、硅酸钠、碳酸氢钠、甲酸、硝酸钠、地表水、自来水促进2,4-D降解,氯化钠、叔丁醇、正丙醇、亚硝酸钠、乙酸抑制2,4-D降解。具促进作用的共存物质主要通过促进·OH间接反应来完成,具抑制作用的共存物质主要通过抑制·OH间接反应起作用。增强作用较强的磷酸钠、碳酸钠、硅酸钠及碳酸氢钠可增加溶液初始pH值,pH值不仅改变反应液里解离态2,4-D比例,还促进臭氧分解产生更多·OH,产生的二级自由基可帮助2,4-D降解。自来水和地表水中含有的物质种类和数量不同,对2,4-D降解有不同程度的增强。甲酸是·OH引发剂和促进剂,硝酸盐可同时促进间接反应和直接反应。亚硝酸根可消耗·OH,氯离子、叔丁醇、正丙醇、乙酸可湮灭·OH,由此对2,4-D降解具抑制效果。

In order to study the effect of complicated surroundings of water quality on 2,4-D degradation in O3/H202 process, different inorganic salts and organics were added in aqueous solution which was prepared by deionized water, and tap water and surface water were also used to prepare 2, 4-D solution. The results show that different coexisting substances have different influences on 2, 4-D degradation. Pseudo-first-order rate constants of 2,4-D degradation can be increased by sodium phosphate, sodium carbonate, sodium silicate, sodium bicarbonate, formic acid, sodium nitrate, tap water and surface water. On the contrary, they decreased by sodium chloride, tert-butyl alcohol, propanol, sodium nitrite and acetic acid. By promoting or retarding indirect reaction of them with ~ OH coexisting substances can enhance or restrain generally degradation reaction. The dissociation of 2,4-D and formation of hydroxyl radicals from ozone is increased by sodium phosphate, sodium carbonate, sodium silicate, sodium bicarbonate, because they can rise initial pH values of 2,4-D solution. Secondary, free radicals produced bythese coexisting substances can further promote 2,4-D degradation. Tap water and surface water contain generally different kind and amount of coexisting substances including sodium carbonate, sodium bicarbonate and so on, so they can also enhance 2,4-D degradation at some extent. Formic acid is initiator and promoter of hydroxyl radicals. Nitrate improves the indirect reaction and the direct reaction. Hydroxyl radical can be depleted by nitrite and annihilated by sodium chloride, tert-butyl alcohol, propanol and acetic acid, leading to the decrease of 2,4-D degradation.