Omo-Okoro Patricia N, Curtis Christopher J, Marco Ana Miralles, Melymuk Lisa, Okonkwo Jonathan O
Department of Geography, Environmental Management and Energy Studies (GEMES), Faculty of Science, University of Johannesburg, P.O. Box 524, Auckland Park, 2006 South Africa.
Department of Environmental, Water & Earth Sciences, Faculty of Science, Tshwane University of Technology, Arcadia Campus, Private Bag X680, Pretoria, 0001 South Africa.
J Environ Health Sci Eng. 2021 Jan 7;19(1):217-236. doi: 10.1007/s40201-020-00597-3. eCollection 2021 Jun.
Per- and polyfluoroalkyl substances (PFAS) have been found to be widespread, extremely persistent and bioaccumulative with toxicity tendencies. Pre-synthesized nanocomposite-activated carbons, referred to, as physically activated maize tassel silver (PAMTAg) and chemically activated maize tassel silver (CAMTAg) were utilized in the present study. They were used for the removal of 10 PFAS from aqueous solutions.
The nanocomposite-activated carbons were characterized via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer Emmett Teller (BET) and other techniques. Batch equilibrium experiments were conducted in order to investigate the effects of solution pH, adsorbent dosage, initial PFAS concentration and temperature on the removal of PFAS using PAMTAg and CAMTAg. Langmuir and Freundlich adsorption isotherm models were used to analyse the equilibrium data obtained.
Maximum adsorption capacities of 454.1 mg/g (0.91 mmol/g) and 321.2 mg/g (0.78 mmol/g) were recorded for perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), respectively using CAMTAg. The values recorded for the Gibbs' free energy (ΔG°) for the adsorption of PFOS and PFOA onto PAMTAg and CAMTAg were negative; PFOS (-9.61, -9.99 and - 10.39), PFOA (-8.77, -9.76 and - 10.21) using PAMTAg; and PFOS (-13.70, -12.70 and - 12.37), PFOA (-12.86, -12.21 and - 11.17) using CAMTAg. Therefore, the adsorption processes were spontaneous and feasible. The values recorded for enthalpy (ΔH°) (kJ/mol) for the adsorption of PFOS (-26.15) and PFOA (-35.86) onto CAMTAg were negative, indicating that the adsorption mechanism is exothermic in nature. Positive values were recorded for ΔH° for the adsorption of PFOS (2.32) and PFOA (12.69) onto PAMTAg, indicative of an endothermic adsorption mechanism. Positive entropy (ΔS°) values (0.04 and 0.07) were recorded for PFOS and PFOA using PAMTAg; whereas negative values (-0.04 and - 0.08) were recorded for ΔS° using CAMTAg. A positive ΔS° indicates an increase in randomness of the adsorbate at the solid-solution interface and the reverse is the case for a negative ΔS°.
The interplay of electrostatic attraction and hydrophobic interactions enabled the removal of PFAS using PAMTAg and CAMTAg. Findings suggest that PAMTAg and CAMTAg are effective for the removal of PFAS from aqueous media and are good alternatives to commercially available activated carbons.
The online version contains supplementary material available at 10.1007/s40201-020-00597-3.
全氟和多氟烷基物质（PFAS）已被发现广泛存在、具有极强的持久性和生物累积性且具有毒性倾向。在本研究中使用了预先合成的纳米复合活性炭，即物理活化玉米穗银（PAMTAg）和化学活化玉米穗银（CAMTAg）。它们被用于从水溶液中去除10种PFAS。
通过扫描电子显微镜（SEM）、傅里叶变换红外（FTIR）光谱、布鲁诺尔-埃米特-特勒（BET）等技术对纳米复合活性炭进行表征。进行了批量平衡实验，以研究溶液pH值、吸附剂用量、初始PFAS浓度和温度对使用PAMTAg和CAMTAg去除PFAS的影响。使用朗缪尔和弗伦德利希吸附等温线模型分析所获得的平衡数据。
使用CAMTAg时，全氟辛烷磺酸（PFOS）和全氟辛酸（PFOA）的最大吸附容量分别记录为454.1 mg/g（0.91 mmol/g）和321.2 mg/g（0.78 mmol/g）。PFOS和PFOA吸附到PAMTAg和CAMTAg上的吉布斯自由能（ΔG°）值为负；使用PAMTAg时，PFOS为（-9.61、-9.99和-10.39），PFOA为（-8.77、-9.76和-10.21）；使用CAMTAg时，PFOS为（-13.70、-12.70和-12.37），PFOA为（-12.86、-12.21和-11.17）。因此，吸附过程是自发且可行的。PFOS（-26.15）和PFOA（-35.86）吸附到CAMTAg上的焓（ΔH°）（kJ/mol）值为负，表明吸附机制本质上是放热过程。PFOS（2.32）和PFOA（12.69）吸附到PAMTAg上时，ΔH°记录为正值，表明是吸热吸附机制。使用PAMTAg时，PFOS和PFOA的熵（ΔS°）值为正（0.04和0.07）；而使用CAMTAg时，ΔS°记录为负值（-0.04和-0.08）。正的ΔS°表明吸附质在固-液界面的随机性增加，而负的ΔS°情况则相反。
静电吸引和疏水相互作用的相互作用使得使用PAMTAg和CAMTAg能够去除PFAS。研究结果表明，PAMTAg和CAMTAg对于从水介质中去除PFAS是有效的，并且是市售活性炭的良好替代品。
在线版本包含可在10.1007/s40201-020-00597-3获取的补充材料。
