Removal of chromium (VI) and bisphenol A from water using a novel spoilt milk-derived adsorbent: material characterisation and adsorption mechanisms

Abstract

This work aims to turn spoilt milk into a high specific surface area activated carbon exploitable in wastewater treatment. Spoilt milk was hydrothermally carbonised to generate hydrochar which was activated with potassium hydroxide at 800°C. The activated carbon displayed a high specific surface area of 1465 m2g−1, with a remarkable microporous character. The activated carbon exhibited excellent maximum monolayer adsorption of 472 mgg−1 and 640 mgg−1 for bisphenol A and chromium (VI), respectively. The adsorption equilibrium was achieved rapidly within 20 min for bisphenol A and 60 min for chromium (VI). Both adsorption processes were spontaneous (∆G° < 0). The adsorption was exothermic in the case of bisphenol A adsorption (∆H° = −56.28 kJmoL−1) and endothermic for potassium dichromate (∆H° = 25.14 kJmoL−1). The bisphenol A was adsorbed on the activated carbon via π-π donor-acceptor interactions, whereas the potassium dichromate was removed through chemical adsorption that included ion exchange, electrostatic interaction, complexation, and redox reaction. Overall, spoilt milk proved to be an excellent precursor of activated carbon for the removal of bisphenol A and dichromate from water.