Adsorption of resorcinol from aqueous solution onto CTAB/NaOH/flyash composites: Equilibrium, kinetics and thermodynamics

•Coal fly ash: a thermal power plant waste used for synthesis of adsorptive materials.•CTAB/NaOH/flyash composite adsorbent shows higher uptake capacity for resorcinol than FA and NaFA.•Increasing removal efficiency on CTAB/NaOH/flyash composite attributed to the hydrophobicity imparted by surfactant leading to organic partioning.•The Redlich-Peterson isotherm was found to be best fitted model.•The adsorption was spontaneous and endothermic in nature.

The contamination of water by organic pollutant viz. phenolic compounds is a worldwide environmental problem due to their highly toxic nature. The resorcinol adsorption efficiencies for fly ash (FA), NaOH treated fly ash (NaFA) and surfactant modified NaOH treated fly ash (CTAB/NaOH/flyash composite) were compared. CTAB/NaOH/flyash composite presented higher resorcinol adsorption efficiency than FA and NaFA. This may be attributed to the hydrophobicity imparted by surfactant molecules on the surface of NaFA, consequently leading to organic partioning. The adsorption of resorcinol onto CTAB/NaOH/flyash composite as a function of initial resorcinol concentration, contact time, temperature, ionic strength and solution pH were investigated for their optimization. The adsorbent were characterized by X-ray diffraction (XRD), field emission scanning electro-microscope (FE-SEM), surface area and porosity measurement, Fourier transform infrared (FT-IR) etc. The adsorption kinetics of resorcinol followed a pseudo-second order model. The equilibrium adsorption data were best fitted by Redlich-Peterson isotherm. The resorcinol adsorption capacity slightly decreased with increasing ionic strength adjusted by NaCl. The adsorption was relatively high at solution pH 5.0-6.8 and decreased above pH 7.0. The value of ΔG°, ΔS° and ΔH° indicated spontaneous and endothermic adsorption process.

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