Effect of various sodium hydroxide treatment parameters on the adsorption efficiency of rice husk for removal of methylene blue from water

In this paper, the effect of various sodium hydroxide (NaOH) treatment parameters on the adsorption efficiency of rice husk for the removal of methylene blue (MB) from water is studied. Various NaOH-based adsorbents were prepared by treating rice husk with different concentrations of NaOH solution as well as by varying the treatment time and temperature. The adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and N2 adsorption studies. FTIR and TGA studies indicated that NaOH treatment results in the degradation and removal of hemicellulose, lignin, and silica of rice husks. The MB adsorption studies were done by varying parameters such as pH, adsorbent dosage, contact time, and initial concentration. These studies indicated that increasing the concentration of NaOH solution as well as time and temperature during the treatment of rice husk makes the adsorption process faster and improves its adsorption efficiency. The pseudo-second-order model was found to give the best fit among various models applied to the experimental data. The second-order rate constant for adsorption by adsorbent prepared by treating rice husk with 1 N NaOH at 90℃ for 4 h was more than three times greater than bare rice husk. Among various isotherms such as Freundlich, Langmuir, Temkin, and Redlich-Peterson applied to equilibrium data, the last one was found to give the best fit, indicating the heterogeneous nature of adsorbents. The maximum monolayer adsorption capacity was found to be 123.39 mg.g−1 and 71.28 mg.g−1 for NaOH-treated and bare rice husk, respectively.