title: Azadirachta indica leaf powder as an effective biosorbent for dyes: a case study with aqueous Congo Red solutions.
abstract: In the present work, the leaves of Azadirachta indica (locally known as the Neem tree) in the form of a powder were investigated as a biosorbent of dyes taking aqueous Congo Red solution as a model system. The sorbent was made from mature Neem leaves and was investigated in a batch reactor under variable system parameters such as concentration of the aqueous dye solution, agitation time, adsorbent amount, pH, and temperature. An amount of 0.6 g of the Neem leaf powder (NLP) per litre could remove 52.0-99.0% of the dye from an aqueous solution of concentration 2.87 x 10(-2) mmol l(-1) with the agitation time increasing from 60 to 300 min. The interactions were tested with respect to both pseudo first-order and second-order reaction kinetics; the latter was found to be more suitable. Considerable intra-particle diffusion was found to occur simultaneously. The sorption process was in conformity with Langmuir and Freundlich isotherms yielding values of the adsorption coefficients in the following ranges: Freundlich n: 0.12-0.19, Kf: 0.1039-0.2648 L g(-1); Langmuir qm: 41.24-128.26 g kg(-1), b: 443.3-1898.0 l mmol(-1), which supported favourable adsorption. The Langmuir monolayer capacity (qm) was high and the values of the coefficient b indicated the equilibrium, dye + NLP = dye...NLP being shifted overwhelmingly towards adsorption. Thermodynamically, the sorption process was exothermic with an average heat of adsorption of -12.75 kJ mol(-1). The spontaneity of the sorption process was also confirmed by the favourable values of Gibbs energy (mean values: -1.09 to -1.81 kJ mol(-1)) and entropy of adsorption (range: -18.97 to -56.32 J mol(-1)K(-1)). The results point to the effectiveness of the Neem leaf powder as a biosorbent for removing dyes like Congo Red from water.
authors.affiliation: Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India. krishna111@sancharnet.in
authors.forename: Krishna G
authors.initials: KG
authors.lastname: Bhattacharyya
authors.forename: Arunima
authors.initials: A
authors.lastname: Sharma
mesh_terms: D000327:Adsorption; D031601:Azadirachta / Q000737:chemistry*; D001673:Biodegradation, Environmental; D004396:Coloring Agents / Q000737:chemistry* / Q000302:isolation & purification*; D003224:Congo Red / Q000737:chemistry* / Q000302:isolation & purification*; D007700:Kinetics; D010936:Plant Extracts; D018515:Plant Leaves; D011208:Powders; D018508:Water Purification / Q000379:methods*
chemical_list: D004396:Coloring Agents; D010936:Plant Extracts; D011208:Powders; D003224:Congo Red