Efficient adsorption of methylene blue from aqueous solution by graphene oxide modified persimmon tannins

With the rapid development of dye and textile industry, the pollution of dye wastewater has aroused widespread public concern due to the potential risk to human health. Therefore, it is of significance for the removal of dye pollutants from wastewater. In this work, a green and efficient bio-adsorbent, graphene oxide modified persimmon tannin (PT-GO), has been fabricated through glutaraldehyde crosslinking method for efficient adsorption of methylene blue (MB) from aqueous solutions. The prepared PT-GO bio-adsorbent was analyzed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectra (XPS) and Brunauer-Emmett-Teller (BET) analysis. The adsorption behavior of the PT-GO bio-adsorbent towards MB dye in a batch adsorption process was investigated. The maximum MB adsorption capacity achieved 256.58 mg g^-1 with MB concentration of 35 mg L^-1 at 323 K. The Freundlich equilibrium isotherm and the pseudo-second order model fit the adsorption behavior very well. Thermodynamics data revealed that the adsorption of MB onto PT-GO bio-adsorbent was feasible, spontaneous and endothermic. Redox reactions, electrostatic interactions and π-π interactions dominated the adsorption of MB onto PT-GO bio-adsorbent. In addition, the regeneration of the PT-GO was efficiently achieved and MB removal efficiency remained high (88.3%) after fifth cycles. All these results indicated that PT-GO bio-adsorbent could be a promising biomass adsorbent for the removal of organic dye contaminants with non-toxic, efficient and low cost.