Efficient sono-sorptive elimination of methylene blue by fly ash-derived nano-zeolite X: Process optimization, isotherm and kinetic studies

Sono-assisted adsorptive elimination of dyes from industrial effluent is proved to be a fast, efficient and clean technique. Highly pure nanozeolite X (nFAZX) was synthesized from waste coal post-combustion fly ash (CFA) by pre-fusion hydrothermal method. Rapid sono-assisted adsorptive elimination of methylene blue (MB) dye from water solution was studied in presence nFAZX, CFA and commercial zeolite X (CZX). As-synthesized nFAZX, raw CFA, and CZX have been characterized by means of X-ray fluorescence (XRF), X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscopy (TEM), field emission Scanning electron microscopy (FESEM), and Brunauer Emmett Teller (BET) adsorption/desorption isotherms for surface area analysis. The influence of adsorption variables, for example solution pH (3-11), adsorbent dose (0.05–0.25 g/100 ml), sonication time (2.50–12.50 min), and initial dye concentration (12.50–62.50 mg/L), on the % elimination of MB was explored by response surface methodology (RSM). Maximum MB removal (64.52% by CFA, 99.30% by nFAZX, and 96.57% by CZX) was obtained at pH 8.25, 0.164 g/100 ml of adsorbent, 9.92 min sonication time, and 25 mg/L MB concentration. The adsorption isotherms and kinetic models were best fitted with Langmuir isotherm and pseudo 2nd order model respectively for all three adsorbents. Also, the maximum Langmuir adsorption capacity of CFA, nFAZX and CZX for MB were 78.22 mg/g, 345.36 mg/g, and 250.41 mg/g respectively for 0.160 g/100 ml adsorbents. The experimentation demonstrated a route of development of a cheap, eco-friendly sorbent nFAZX as well as a green, rapid and highly efficient protocol of treating synthetic dyes which are often present in real textile wastewater.