The capacity of mesoporous fly ash grafted with ultrathin film of polydiallyldimethyl ammonium for enhanced removal of phenol from aqueous solutions

This study investigates the feasibility of coating cationic polydiallydimethyl ammonium chloride (PDDA) onto mesoporous acid-treated fly ash (AFA) and its capacity to adsorb phenol from aqueous solution. The PDDA-FA and its AFA substrate were characterized using a scanning electron microscope with energy-dispersive x-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and thermogravimetric analysis (TGA) to ascertain successful film coating. Batch adsorption studies were carried out to evaluate the effects of solution pH, initial concentration, adsorbent dosage, contact time, shaking speed and temperature on the removal of phenol using PDDA-FA and AFA. Characterization revealed that the coating of cationic polyelectrolyte film onto FA introduced surface polarity which enhanced the mass transfer of phenol to the PDDA-FA surfaces. Importantly, the results showed that synthesized PDDA-FA is 4-fold more efficient than precursor AFA in removing phenol from aqueous solution. The sorption equilibrium isotherm of adsorbent was described by Freundlich, Langmuir and Temkin models. The adsorption rate of both adsorbents followed the pseudo-second-order kinetic model, while the thermodynamic studies of PDDA-FA sorption of phenol indicated a favorable endothermic and physical adsorption mechanism. The PDDA-FA also has a higher adsorption capacity than other reported modified FA. In conclusion, an ultrathin coating of fly ash with cationic polyelectrolyte offers a viable potential as an alternative adsorbent from waste. This work has the advantages of cleaner production of adsorbents from waste, and wastewater decontamination.