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Abstract--A high-charge smectite from Arizona [cation-exchange capacity (CEC) = 120 meq/100 g] and a low-charge smectite from Wyoming (CEC = 90 meq/100 g) were used to prepare homoionic tetramethylammonium (TMA)-clay complexes. The adsorption of benzene, toluene, and o-xylene as vapors by the dry TMA-clays and as solutes from water by the wet TMA-clays was studied. The adsorption of the organic vapors by the dry TMA-smectite samples was strong and apparently consisted of interactions with both the aluminosilicate mineral surfaces and the TMA exchange ions in the interlayers. In the adsorption of organic vapors, the closer packing of TMA ions in the dry high-charge TMA-smectite, compared with the dry low-charge TMA-smectite, resulted in a somewhat higher degree of shape-selective adsorption of benzene, toluene, and xylene. In the presence of water, the adsorption capacities of both samples for the aromatic compounds were significantly reduced, although the uptake of benzene from water by the low-charge TMA-smectite was still substantial. This lower sorption capacity was accompanied by increased shape-selectivity for the aromatic compounds. The reduction in uptake and increased selectivity was much more pronounced for the water-saturated, high-charge TMA-smectite than for the low-charge TMA-smectite. Hydration of the TMA exchange ions and/or the mineral surfaces apparently reduced the accessibility of the aromatic molecules to interlamellar regions. The resulting water-induced sieving effect was greater for the high-charge TMA-smectite due to the higher density of exchanged TMAions. The low-charge Wyoming TMA-smectite was a highly effective adsorbent for removing benzene from water and may be useful for purifying benzene-contaminated water.

A viable and cost-effective technology was explored in this present task for removal of heavy metal ions such as Cu 2+ , Ni 2+ , Zn 2+ , Cd 2+ , and Pb 2+ from aqueous solution using three fruit peels such as orange peel (OP), lemon peel (LP), and banana peel (BP). The surface of the LP and lemon peel cellulose (LPC) was chemically modified. All these adsorbents were characterized by FT-IR, BET, and SEM. The widely used Langmuir adsorption isotherms were used to describe the adsorption equilibrium process. The adsorption capacity of metal ions such as Cu 2+ and Ni 2+ was found to be more than that of other metal ions. Upon comparison of the adsorbents, surface modified LPC (LPCACS) was found to show enhanced adsorption activity. A comparative study of adsorption was carried out with activated carbon (AC) also from which it was inferred that the order of the adsorption capacity is as follows: LPCACS > LPC > AC > LP.

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For orange peel (OP), lemon peel (LP), and banana peel (BP) as adsorbents for removal of heavy metal ions such as Cu2+, Ni2+, Cd2+, Pb2+, and Zn2+ from aqueous solution, a simple FT-IR technique was used and discussed to study the variation in functional groups upon modification. Metal−carbon bond formation was witnessed by FT-IR during metal ion adsorption. All of these adsorbents were characterized by FT-IR, BET, and SEM. The presence of carboxylic and hydroxyl groups was confirmed by FT-IR. The FT-IR spectrum of lemon peel cellulose (LPC) showed well resolved peaks for carboxylic acid and hydroxyl groups compared to LP indicating the appreciable contents of carboxylic acid and hydroxyl groups in LPC. The widely used Langmuir adsorption isotherms were used to describe the adsorption equilibrium process. The adsorption capacity of the metal ions such as Cu2+ and Ni2+ was found to be more than those of other metal ions. Upon comparison of the adsorbents, surface modified LPC (LPCACS) was found to show enhanced adsorption activity. A comparative study of adsorption was carried out with commercially available activated carbon (AC) also from which it was inferred that the order of the adsorption capacity is as follows: LPCACS > LPC > AC > LP > OP > BP.