线性和非线性方法估计单宁酸共存下形成的无定形铝氧化物上菲的吸附等温线参数比较

采用批实验研究了菲在单宁酸干扰下形成的不同晶形铝氧化物上的吸附现象,并用不同的吸附等温线方程对吸附平衡数据进行了拟合,重点比较了线性和非线性回归方法估计吸附等温线参数的差异。结果表明:菲在各种晶形的铝氧化物上都有明显的吸附,但并不是完全随着单宁酸含量和结晶度的变化而规律性变化。吸附平衡数据以Langmuir、Redlich-Peterson和Dubinin-Radushkevich吸附等温方程,用不同的回归方法估计的等温线参数值均有显著性差异。线性回归得到的参数有不确定性,表明用线性回归来判断吸附等温线能否对吸附平衡数据进行最优拟合是不可靠的。相反,非线性回归能较好地确定菲在不同晶形铝氧化物上的最佳吸附等温线及相应参数。采用R2和χ2共同检验发现,菲在4种不同结晶度(单宁酸与铝的摩尔比(MR)=0,10-3,10-2,10-1)铝氧化物上的最佳吸附等温线方程并不尽相同,分别为Freundlich,Freundlich,Dubinin-Radushkevich和Freundlich,反映了各种晶形的铝氧化物的表面异质性。修正的Freundlich方程比较不同晶形铝氧化物对菲的相对吸附容量顺序为:MR=10-3MR=10-2MR=0MR=10-1。由此,认为菲在无定形铝氧化物上的吸附是熵驱动的结果。

Comparative analysis of linear and non-linear method in estimating sorption isotherm parameters for phenanthrene sorption onto Al (oxy)hydroxides formed under influence of tannic acid

A batch experiment was conducted to study the sorption of phenanthrene onto AI (oxy)hydroxides formed under the influence of tannic acid. The sorption isotherms were employed to describe the sorption behavior. Linear and nonlinear regression methods were compared to select the optimal isotherm. Results showed that significant sorption of phenanthrene occurred on the surfaces of all A1 (hydro)oxides, but the sorption capacity didn't completely conform with tannic acid content and crystal form. Results generated with linear regression showed some uncertainties,indicating that linear regression was not good to determine the best fitting isotherm. In contrast, nonlinear regression was found to be better to obtain the parameters involved in the isotherms and also the optimal isotherm. By comparing R2 and x2 values, the optimal isotherm for sorption of phenanthrene onto different AI (oxy)hydroxides with different tannic acid/Al molecular ratios (MRs=0, 10-3 ,10-2, 10-1 ) were Freundlich, Frenndlich,Dubinin-Radushkevich and Frenndlich isotherm, respectively, which implied the heterogeneity of Al (oxy) hydroxides surfaces. Modified Freundlich isotherm was adopted to compare directly phenanthrene sorption characteristics of different Al (oxy)hydroxides formed under the influence of tannic acid and found the sorption capacity increasing with the order of MR=10-3