Etherified Moringa oleifera gum as rapid and effective dye adsorbents

Abstract

Plant gums serve as low-cost, non-toxic and biodegradable resource for development of functional materials for use in environmental protection applications. Herein Moringa oleifera gum (MOG), plant waste, was utilized to synthesize new nanoscale dimension (nano-R-O-MOGs) dye adsorbents via a simple etherification reaction protocol using alkyl halides, of different chain length, viz. butylbromide (C4H9Br), octylbromide (C8H17Br) and hexadecylbromide (C16H21Br) to obtain corresponding nano-C4-O-MOG, nano-C8-O-MOG and nano-C16-O-MOG. These were well characterized by different techniques and later evaluated as adsorbents for different dyes, but these showed higher preference for malachite green (MG) than other dyes. These adsorbents showed property-structure relationship as nano-C4-O-MOG and nano-C8-O-MOG showed highly rapid dye removal nearly 100% within 90 min, whereas nano-C16-O-MOG showed complete removal of MG in 120 min at 25 °C and pH 7.0. MG adsorption process followed pseudo-second order kinetics and Langmuir isotherm with maximum adsorption capacities of 213.66 mg/g, 227.27 mg/g and 207.04 mg/g for nano-C4-O-MOG, nano-C8-O-MOG and nano-C16-O-MOG, respectively. All the synthesised products were found to be reusable for many repeat cycles with cumulative adsorption capacities of 1141.92 mg/g, 1166.37 mg/g and 1107.82 mg/g for nano-C4-O-MOG, nano-C8-O-MOG and nano-C16-O-MOG, respectively, after 15th repeat cycle.