Synthesis and characterization of a novel organic-inorganic hybrid clay adsorbent for the removal of acid red 1 and acid green 25 from aqueous solutions

Abstract

Natural clay was grafted with 3-aminopropyl-trietoxisilane (APTES) for obtaining an organic-inorganic hybrid material. This material was successfully used as adsorbent for removal of Acid Red 1 (AR-1) and Acid Green 25 (AG-25) anionic dyes from aqueous solutions. This work demonstrates the effect of APTES concentration on the hydrophobic/hydrophilic characteristics and optical properties of the amino-functionalized materials. The adsorption capacity of the resultant hybrid materials were studied using anionic dyes. The physico-chemical properties of the materials was determined by several analytical techniques. It appears that the modified samples were more hydrophilic than the natural clay for ratios from 1.0 up to 2.0, due to the presence of amino group (—NH2) located at the end of the chain. The characterization data showed that APTES was successfully grafted on to the external as well as interlayer and broken edges of montmorillonite. Transmission electron microscopic images confirmed that the morphology of amino-functionalized material changed from sheet-like in the natural clay material to a conglobulated structure. The amino-functionalized material exhibited a surface area 6-times (SBET = 13.31 m2/g) lower than natural clay (SBET = 86.10 m2 g−1; Vtol = 0.126 cm3 g−1 and Dp = 4.72 nm). The total pore volume (Vtol = 0.041 cm3 g−1) and average pore diameter (Dp = 10.2 nm) was found to be 2-times lower than clay. Adsorption followed the general-order kinetic model for both dyes. Liu isotherm model was observed to be best fit and it displayed Qmax as 364.1 and 397.0 mg g−1 for AR-1 and AG-25, respectively at 50.0 °C. Electrostatic interaction was the main mechanism involved in the adsorption process. The Mrt-APTES0.5 seemed to be a good adsorbent for the treatment of synthetic effluents. The removal percentage of effluent A and B were 97.94% and 95.94%, respectively.