Statistical physics modelling of azo dyes biosorption onto modified powder of Acorus calamus in batch reactor

Abstract

The methylene blue adsorption was carried out on a natural material powder of Acorus calamus treated firstly with H2SO4 and then activated by KMnO4. The new material was called PACK. Fourier transform infrared (FT-IR) spectroscopy, pHpzc analysis, and SEM micrograph were carried out to characterize the material. Pseudo-first-order, pseudo-second-order and pseudo-nth order constant rates were calculated for analysis of the dynamics of the sorption process, showing that sorption kinetics followed a pseudo-nth order model. Among the tested isotherm models, the R-P isotherm was considered to be the most relevant to describe MB sorption onto PACK. Advanced statistical physics models, monolayer single-energy, monolayer two-energy, and double-layer two-energy were used to analyze the adsorption mechanism of methylene blue (MB) and to understand the PACK adsorbent performance. Based on the R2 values obtained, the monolayer two-energy model was found to be the most suitable to describe the MB adsorption onto the PACK material. From this, the adsorption of MB was assumed on two different sites of PACK with two different energies, E1 for the first site and E2 for the second site. These two different receptor sites can interact with a variable number of MB molecules (n), n1 with the first type of sites and n2 with the second type of sites. The sorption capacity of this material was about 1500 mg/g at 30 °C. The potential of PACK, a readily available material to use as an alternative biosorbent material to eliminate the MB color from aqueous solutions, was therefore confirmed.