Modified hemp fibers as a novel and green adsorbent for organic dye adsorption: adsorption, kinetic studies and modeling

Synthetic dyes represent a serious hazard to aquatic environments. Many approaches for eliminating these contaminants have been devised and applied. This manuscript reports the production of a novel, low-cost and ecologically friendly bioadsorbent based on hemp fibers that are functionalized with graphite oxide through bridging with an organosilane. Methylene blue was selected as a typical pollutant to be removed from wastewaters. The adsorbent was characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared (FTIR) analysis. An investigation of the effects of pH and temperature on the adsorption process was carried out. The adsorption capacity increased with increasing contact time as well as with the temperature, proving that the process shows endothermic behavior. Moreover, the process was found to be dependent on the pH level and, to corroborate the collected results, the point of zero charge was evaluated. The maximum adsorption capacity was found to be 57 mg/g, which was achieved with the following parameters: pH = 7.5, T = 80 degrees C and an initial dye concentration equal to 5 mg/L. Reusability studies showed a 15% decrease in adsorption capacity after 30 adsorption tests, proving the possibility of reusing the produced adsorbent without any great decay in performance. Finally, a potential adsorption mechanism is reported and discussed. The reported results prove that it is feasible to apply the designed adsorbent of organic dyes to the purification of wastewaters.