Enhancement of Cr(VI) Ion Removal Using Nanochitosan Coated on Bituminous Activated Carbon Wanida Chooaksorn 1 , Rachnarin Nitisoravut 1, *, Chongrak Polprasert 2 , Sandhya Babel 1 , Kritapas Laohhasurayotin 3 , Wiyong Kangwansupamonkon 3 ABSTRACT: Bituminous activated carbon (AC) has been widely used as a sorbent for adsorption of non-polar species, but its performance for removal of ionic species such as heavy metals has not been as efficient. In this study, AC was modified with chitosan nanoparticles (CN) using facile methods of dip coating and wet impregnation. The CN-coated AC demonstrated an increase in Cr(VI) removal efficiency in both kinetics and adsorption capacity. The adsorption capacity of the CN-coated AC (mg/g) was more than twice that of the uncoated AC (36.36 mg/g), or pure chitosan (32.57 mg/g). The sizes of the synthesized CN (160-2,000 nm) can be controlled by varying the concentration of the chitosan/ reagents used. The adsorption isotherms are better described using the Freundlich rather than the Langmuir model and are in agreement with the heterogeneity of the surfaces. Adsorption kinetics followed that of the pseudo-second-order kinetics, suggesting chemisorption as a rate limiting step. Water Environ. Res., 88, 2150 (2016). KEYWORDS: Adsorption isotherms, adsorption kinetics, bituminous activated carbon, chitosan, Cr(VI) ion, nanosorbent. doi: Introduction Chromium pollution is one of the most significant environ- mental problems due to its hazards for human and ecological systems (Kim et al., 2001; Hani and Hassan, 2004; Chen and Wang, 2011). Chromium in wastewater can be from anthropo- genic and natural sources. The most common anthropogenic source of chromium is from wastewater resulting from mining operations, electroplating, tanning, textile dying, paper pulping, petroleum refining, and metal finishing processes (Boddu et al., 2003; Suksabye et al., 2008). For natural sources, chromium may be from rock erosion and volcanic eruptions. There are two existing forms of chromium in water (chromium (III) and chromium (VI)). Chromium(III) is much less toxic than chromium (VI). It is an essential nutrient for some plants and animals. Cr(VI) has gained considerable attention because of its mobility in the environment and high toxicity to living organisms (Babel and Kurniawan, 2004; Gil et al., 2006; Sugashini and Sheriffa Begum, 2013). Conventional approaches for removal of chromium (VI) from wastewater include precipitation, coagulation and flocculation, solvent extraction, ion-exchange, electrochemical treatment, and reverse osmosis (Boddu et al., 2003; Kobya, 2004; Sharma, 2003; Kumar and Chakraborty, 2009; Gupta et al., 2010; Dalida et al., 2011). These technologies are effective but inefficient, especially when heavy metal concentration is higher than 100 ppm (Juang and Shao, 2002; Patricia et al., 2006). Moreover, they are also relatively high in operational and maintenance costs. Among the physicochemical treatment processes, adsorption is highly effective, inexpensive, and easy to operate. The use of biosorbents has been proposed as an alternative, as this has been proven effective at low concentration. Biosorption is of industrial interest, not only for its ability to remove metals from wastewaters, but also for the possibility of recovering metals. Different adsorbents have been used for chromium removal, including clarified sludge, bark, oak saw dust, fly ash, olive cake, peanut husk, pine needles, almond shells, cactus leaves, coconut shell charcoal, commercial activated carbon, activated alumina, chitin, lignin, modified wool, and seaweeds (Dakiky et al., 2002; Baral et al., 2006; Bhattacharya et al., 2008). Among these materials, chitosan has proven to be a promising adsorbent (Bailey et al., 1999). Chitosan is of interest because it is biodegradable, inexpensive, and made of natural polymers. It has been shown to be an effective sorbent for heavy metal removal from aqueous solutions (Lin and Wu, 2001; Juang and Shao, 2002; Birgit et al., 2004). Recent advances in nanotechnology suggest that nanosorb- ents can be useful in solving problems of heavy metal pollution. New adsorbents have superior performance due to their high specific surface area (Onundi et al., 2011). Unique properties of nanoadsorbents are being exploited by researchers for develop- ing effective sorbents and improving the existing ones for metal ion removal and recovery from effluents. Nanoparticle adsor- bents, such as activated carbon/nanoscale zero-valent iron composites, activated carbon modified by silver bimetallic nanoparticles, have been used to remove Cr(VI) (Wu et al., 2013; Babak et al., 2014). From these results, the nanosorbent showed a high adsorption capacity for Cr(VI) removal due to 1 School of Bio-Chemical Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12120, Thailand 2 Department of Civil Engineering, Faculty of Engineering, Thammasat University, Pathum Thani 12120, Thailand. 3 National Nanotechnology Center, National Science and Technology Development Agency, Pathum Thani 12120, Thailand * School of Bio-Chemical Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12120, Thailand; e-mail: snitisor@siit.tu.ac.th 2150 Water Environment Research, Volume 88, Number 11 10.1002/j.1554-7531.2016.tb00146.x