表面酸碱2步改性对活性炭吸附Cr(Ⅵ)的影响

研究了酸碱2步改性对活性炭吸附水相中Cr(Ⅵ)的影响.将活性炭(AC₀)在HNO₃溶液中氧化(AC₁),然后在NaOH和NaCl的混合液中处理(AC₂).分别采用平衡和连续吸附试验,测试Cr(Ⅵ)的吸附特征.以Boemh滴定法定量检测活性炭表面酸性官能团数量,结合元素分析结果定量表征活性炭的表面含氧官能团变化;以低温液氮(N₂/77K)吸附法分析活性炭的比表面积和孔径结构.结果表明:活性炭经2步改性后,其Cr(Ⅵ)的吸附容量和吸附速度均显著改变.吸附容量和吸附速度大小依次为AC₂>AC₁>AC₀.改性活性炭表面积下降,表面含氧酸性官能团数量增加.HNO₃液相氧化处理可使活性炭表面生成带正电含氧酸性官能团,第2步改性后活性炭表面酸性官能团H⁺部分被Na⁺取代,使活性炭表面酸性降低.表面较多的含氧酸性官能团(与AC₀相比)、适宜的表面pH(与AC₁相比)是AC₂所表现出较高Cr(Ⅵ)吸附容量的主要原因.

Effect of acid-base two steps surface modification on the adsorption of Cr(VI) onto activated carbon

Effect of HNO3-NaOH two steps surface modification on the adsorption of Cr(VI) from aqueous solution onto activated carbon was evaluated. Activated carbon was oxidized in HNO3 aqueous solution at first (AC1), then treated in the mixture of NaOH and NaCl solution (AC2). Batch equilibrium and continuous adsorption experiments were conducted to determine the adsorption characteristics. Boehm titration method, element analysis were used to characterize the surface properties. N2/77 K adsorption isotherm method was used to characterize the pore structure. The results reveal that adsorption capacity and adsorption rate increase significantly, which in the following order: AC2>AC1>AC0. Surface modification caused BET surface area decreased and the total number of surface oxygen acid groups increased. First oxidation modification in HNO3 solution produced positive acid groups on the surface of activated carbon. Subsequent 2nd modification replaced H+ of carbon surface groups by Na+, the acidity of AC2 was decreased. The main cause of higher Cr(VI) adsorption capacity and rate for AC2 was the more oxygen surface acid groups, and suitable solution pH provide by surface groups.