RESEARCH ARTICLE Functionalized activated carbon for the adsorptive removal of perchlorate from water solutions Rovshan MAHMUDOV, Chinglung CHEN, Chin-Pao HUANG (✉) Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA © Higher Education Press and Springer-Verlag Berlin Heidelberg 2015 Abstract Two types of activated carbon, namely, Filtrasorb 400 and Nuchar SA, were functionalized by quaternary ammonium salts (quats), as to enhance perchlorate adsorption. Results showed that the adsorption of quats on Nuchar SA increased with increase in chain length (hydrophobicity) of quats. Filtrasorb 400, however, had limited uptake of long-chain quats such as dodecyl- trimethylammonium and hexadecyltrimethylammoium (HDTMA). Results indicated that perchlorate removal by the functionalized activated carbon was directly related to the chain length of the modifying quats. Perchlorate removal by functionalized activated carbon increased with increase in chain length of the modifying quats and became less pH-dependent. Modified Nuchar SA had higher overall perchlorate removal capacity than the modified Filtrasorb F400, but was more strongly affected by pH than Filtrasorb 400. Activated carbon treated with HDTMA exhibited the best perchlorate removal capacity among all quats studied. Results indicated that tailoring the activated carbon surface with HDTMA rendered the activated carbon surface positively charged, which resulted in substantial increase in perchlorate removal compared to unfunctionalized activated carbons. Keywords perchlorate, activated carbon, removal, func- tionalization, quaternary ammonium salts 1 Introduction Perchlorate is suspected of disrupting the uptake of iodide by thyroid for the synthesis of hormones, and subsequently causing malfunction of metabolic processes [1,2]. EPA has included perchlorate in the Candidate Contaminant List (CCL) with a reference dose of 0.7 g$d –1 $kg –1 of body weight, which is equivalent to approximately 24 g$L –1 in drinking water [3]. Perchlorate has been used mostly as an oxidant in solid fuel rocket propellants, explosives, pyrotechnics, and to a lesser extend in the manufacturing of commercial products ranging from electronics to pharmaceuticals [4–7]. The main problem in removing perchlorate from drinking water supply sources is its concentration being several orders of magnitude lower than that of other anions, namely, sulfate, nitrate, and chloride. Subse- quently, methods such as anion exchange for the removal of common anions are often not effective. Major anions especially nitrate can compete with perchlorate, particu- larly at low concentration, when treated with other methods such as microbial and catalytic reduction, thereby leading to unfavorable efficiency [8,9]. Therefore, there is a need to pre-concentrate perchlorate from dilute streams as to enhance the performance of microbial or catalytic reduction techniques. At elevated concentrations compar- able to that of other major anions, specifically, nitrate, perchlorate can be more effectively and favorably disposed by catalytic chemical reduction. Perchlorate specific anion exchange resins have been shown to greatly improve the selectivity towards perchlorate removal [10–13]. Wang et al. [14] have recently synthesized a perchlorate permselective membranes for pre-concentration of per- chlorate in water. However, the cost of ion exchange resins and membranes can still limit their wide-scale applications. Modifying the surface functional groups of solid substrates to enhance the removal of contaminants of interest has been suggested for the treatment of impaired water while lowering the treatment cost. Surface modifica- tion of solid adsorbents, such as activated carbon has been shown to be an effective alternative compared to other anion exchange methods. Incorporating functional groups to the surface of common sorbents such as activated carbon and clay and its related minerals enables to substantially improve the removal of the target contaminants of concern such as perchlorate and the treatment efficiency. Quater- Received January 8, 2015; accepted May 12, 2015 E-mail: huang@udel.edu Front. Chem. Sci. Eng. DOI 10.1007/s11705-015-1517-3