Removal of direct blue 71 and methylene blue from water by graphene oxide: effects of charge interaction and experimental parameters

Abstract

Graphene oxide (GO) was synthesized by modified the Hummers method and used as an effective adsorbent for removing direct blue 71 (DB 71) and methylene blue (MB) from water. Surface characteristics of the produced GO materials and related physiochemical properties of the organic dyes were systematically examined to reveal removal mechanisms. Thermodynamics, kinetics, and regeneration of GO adsorbent were also studied to disclose the nature of the adsorption and the reusability of adsorbent. GO adsorbed the cationic MB better than the anionic DB 71 mainly due to the electrostatic attraction between negatively charged GO’s surface and the positively charged MB molecules. Langmuir isotherm better described MB and DB 71 adsorption than the Freundlich model. The adsorption capacities of GO of 476.19 mg/g (for MB) and 175.41 mg/g (for DB 71) were considerably higher than those of other adsorbents such as activated carbon, chitosan, and biochar. MB and DB 71 adsorption process was spontaneous, endothermic, and governed by both physisorption and chemisorption. GO could be regenerated by methanol and dilute HCl solutions, and reused as an efficient adsorbent. This study provides a comprehensive data on the MB and DB71 adsorption processes, and an efficient approach on the regeneration of GO adsorbent.