Effects and Mechanisms of Methyl Orange Removal from Aqueous Solutions by Modified Rice Shell Biochar

Abstract

Waste rice shell (RS) was used for modified biochar preparation via different activation methods. The types of modifiers, impregnation ratio, and pyrolysis temperature have significant effects on the characteristics of biochar and the adsorption capacity of methyl orange (MO). The physical and chemical properties of modified biochar and MO adsorption mechanisms were analyzed by N2-adsorption, X-ray diffraction (XRD), Fourier infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), thermogravimetric analyzer (TG), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the modified biochar (named Z2RT400) prepared at 400℃ with a mass ratio of 2:1 (ZnCl2:rice shell) had the highest adsorption capacity for MO. Under the following conditions with a solution pH value of 4, adsorbent dosage of 10 mg, initial MO concentration of 2000 mg·L-1, and reaction time of 420 min, the maximum adsorption capacity of Z2RT400 was 1967.72 mg·g-1. When the adsorbent dosage was 80 mg, the maximum removal rate reached 99.52%. The adsorption data fitted well with the pseudo-second order kinetic model and Freundlich isotherm model, which indicates that chemical adsorption is the main adsorption mechanism and physical adsorption is the auxiliary adsorption mechanism. Therefore, the waste rice shell derived biochar can be used as a highly efficient dye adsorbent in applications such as sewage treatment.