Azo-dye derived oxidized-nitrogen rich carbon sheets with high adsorption capability for dye effluent under both batch and continuous conditions

The removal of methyl blue (MB) from wastewater using graphene and its derivative is very successful due to their high aromaticity which drives adsorption via π-π and electron-donor-acceptor (EDA) interactions; however, graphene is expensive and difficult to synthesize, which limit its practical application. Meanwhile, low aromatic carbon materials (LACM) derived from farm-water and other materials are cheaper and easier to synthesize but have limited π-π and EDA interactions and low adsorption capacity. Herein, we demonstrate that LACM with oxidized-nitrogen (N–O-) functionality overcomes this limitation via chemisorption of MB through a combination of hydrophobic-hydrophobic interactions and EDA interactions. This is confirmed using XPS analysis of LACM/N–O- post MB adsorption. Consequently, a remarkable adsorption capacity of 3904 mg g−1 is achieved under batch condition which is the highest ever reported for any MB adsorbent. Furthermore, LACM/N–O- works equally well under continuous-flow adsorption conditions which shows its practicability. Amongst several LACM precursors tested, only Azo-dyes are able to generate LACM/N–O- implying that the NN moiety is key to N–O- formation. A carbonization temperature of 700 °C generates the highest N–O- sites hence the highest adsorption capacity. Characterization of LACM/N–O- is done mainly using BET, XPS, Raman, TGA, and FTIR analysis. [Display omitted] •Oxidize nitrogen (N–O-) laden carbon sheets synthesized via Azo-dye carbonization.•Maximum adsorption capacity of 3904 mg g−1 achieved for Methyl blue (MB) dye.•Adsorption process governed by synergy between electrostatic and chemisorption.•N–O- interacts with MB via electron-donor-accepter reaction.•The adsorbent exhibits fast kinetics, high efficiency and recyclability.