| Abstract |
Biochars were successfully produced from rice straw and golden shower seed wastes and used to obtain agricultural waste-derived and low-cost adsorbents to remove methylene blue (MB) dye pollutants. The biochars were prepared using atmospheric pressure microwave plasma in a nitrogen environment at three individual flow rates of 7, 9, and 11 L/min for 5 min via pyrolysis. After pyrolysis, RS biochar's surface area and pore volume increased from 1.224 m(2)/g to 13.796 m(2)/g, 11.995 m(2)/g, 6.865 m(2)/g, and 0.006 cm(3)/g to 0.804 cm(3)/g, 0.168 cm(3)/g, 0.08 cm(3)/g, respectively, then GS increased from 11.874 m(2)/g to 40.423 m(2)/g, 45.731 m(2)/g, 73.067 m(2)/g, and 0.006 cm(3)/g to 0.181 cm(3)/g, 0.277 cm(3)/g, 4.227 cm(3)/g, respectively. FTIR results showed O-H stretching in hydroxyl groups, CO functional group, C-H bending of CH3, and C-H vibration aromatic compounds, essential for MB adsorption. The golden shower seed biochar activated by plasma gas flowrate 11 l/m (GS-11) and rice straw biochar activated by plasma gas flowrate 7 l/m (RS-7) had the highest adsorption capacity among all biochars, 344.82 mg/g, and 188.32 mg/g, respectively, which was 10.6 and 2.07 times higher than other golden shower and rice straw biochar from the previous research by much shorter pyrolysis duration of 24 and 48 times, respectively. In addition, both biochars had higher adsorption capacity than previous biochars from different biomass and pyrolysis methods even though they applied 5 times lower in dosage, 3 times higher on initial MB concentration, and 36-144 times shorter pyrolysis time. The equilibrium data fit well with the Langmuir model, and the adsorption kinetics followed pseudo-second-order kinetics. According to the current study, the atmospheric pressure microwave plasma can generate high-quality biochars quickly and be promoted as a recycling technology method. Then, the product biochars can reach high adsorption capacity with a low dosage, high initial MB concentration, low energy consumption, and no chemical added. Furthermore, the product can enhance the value of rice straw and golden shower seed waste, support a circular economy approach, reduce the waste released to the environment, and reduce air pollution generated. |