Amine-amide functionalized graphene oxide sheets as bifunctional adsorbent for the removal of polar organic pollutants

Effective mitigation of polar organic impurities from industrial effluents is a global environmental challenge. Here, we describe the solvothermal synthesis of ammonia-functionalized graphene oxide (NH3GO) sheets for adsorptive removal of diverse organic pollutants, such as cationic dye basic blue 41 (BB41), anionic dye methyl orange (MO), and ionic 4-nitrophenol (4-NP), in aqueous media. Structural analysis of NH3GO suggest a potent role of surface acidic and basic binding sites in adsorption of targets through an interplay of dynamic experimental variables, e.g., contact time, pH, initial adsorbate concentration, adsorbent mass, and temperature. At an initial pollutant concentration of 20 mg/L, equilibrium adsorption capacities for BB41, MO, and 4-NP were estimated at 199.5, 64.0, and 54.1 mg/g, respectively, with corresponding partition coefficients of 4156, 79.4, and 14.3 L/g, respectively. Experimental data of all three organic pollutants are best fitted by the pseudo-second-order kinetic model. The adsorption isotherm of BB41 follows a multilayer adsorption pattern, while those of MO and 4-NP fit into a monolayer adsorption pattern. The endothermic and spontaneous nature of the adsorption processes has also been explored for the three targets on NH3GO based on thermodynamic analysis. The prepared NH3GO sheets appear to be a promising adsorbent for the removal of polar organic dyes and aromatics in the solution phase. [Display omitted] •A facile solvothermal method of preparing ammonia-functionalized GO sheets is proposed.•Ammonia functionalization imparts amine-amide functionalities in the GO network.•Batch-mode adsorption of ionic dyes and 4-NP by ammonia-functionalized GO sheets is conducted.•Adsorption of ionic dyes is pH-independent, while 4-NP removal is influenced by solution pH.