Modification of Rice Husk with Ultrasound-Assisted Inorganic Treatment and Its Application for Catalytic Hydrogen Production

Rice husk is a massive byproduct of the agricultural sector, but less effort has been paid for its recycling. In this study, ultrasound-assisted inorganic treatment with HNO 3 , H 2 SO 4 , and H 2 O 2 was adopted to modify rice husk as a biosynthesized catalyst. The activity of produced biosynthesized catalyst was assessed in hydrogen production through the hydrolysis of sodium borohydride in an alkaline solution. The characterization of as-prepared biosynthesized catalysts revealed that HNO 3 was an efficient agent to protonate the surface of rice husk and make active sites available for the hydrolysis reactions. In addition, ultrasound-assisted HNO 3 treatment caused a constructive effect on the structural property of rice husk and increased the surface area from 1.9 m 2 /g to 17 m 2 /g and pore volume from 0.45 cm 3 /g to 3.9 cm 3 /g. According to optimum synthesizing conditions (45 wt% HNO 3 and 10 min ultrasonication), ARH-N 45 -10 could produce 745 mL/g hydrogen from the alkaline solution of NaBH 4 at ambient conditions. Based on the kinetic study, the catalytic hydrolysis of NaBH 4 by modified rice husk followed first-order kinetic concerning the NaBH 4 per fixed NaOH ratio. Moreover, the thermodynamic analysis indicated that hydrolysis of NaBH 4 and formation of hydrogen on the modified rice husk is an endothermic and spontaneous reaction, where the hydrogen generated at 55 °C (5280 mL/g) was seven times more than that at ambient temperature, and also activation energy was calculated 57.68 kJ/mol from Arrhenius plot.