Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment

An effective adsorbent of methylene blue was synthesized from coal fly ash (FA; waste material from a coal power plant) by a denaturing process with an alkaline solution at 90 °C. The denatured fly ash (D-FA) has a surface area and pore volume of 66.39 m(2) g(−1) and 15.33 cm(3) g(−1), respectively, whereas the values of the original FA are negligible, i.e., 3.55 m(2) g(−1) and 0.02 cm(3) g(−1). The removal of methylene blue (MB) in aqueous solution by D-FA was increased in the range of initial MB concentration (10–20 mg L(−1)); contact time (0–120 min); pH (2–8); D-FA dosage (1–4 g L(−1)). However, a larger value of those operational parameters would not improve the removal activity. Furthermore, the methylene blue adsorption on the denatured FA was fitted with the Langmuir model with R(2) = 0.9991; the maximum adsorption capacity was determined as 28.65 mg g(−1) from the model. Overall, the highest removal efficiency of MB using D-FA with the dosage of 4 g L(−1) was 97.1% in 30 mg L(−1) solution of methylene blue at pH = 7. The alkaline hydrothermal denaturation of waste FA is a promising approach to produce an adsorbent with beneficial environmental engineering applications.