Benign-by-design N-doped activated carbon from wasted aqueous assisted hydrochar of leftover rice for efficient H₂S removal

The N-doped activated carbon is a potential material for H2S removal, reusing N-rich waste aqueous as a nitrogen source is promising to prepare in-expensive N-doped activated carbon. In this study, N-rich waste aqueous assisted hydrothermal carbonization and KOH activation were used to prepare activated carbon from starchy waste, concentrating on the effects of the nitrogen species (inorganic-N and organic-N) on the physicochemical characteristics and desulfurization performance of carbon material. Introducing inorganic-N (i.e., NH3H2O) can increase the defect degree and enhance the formation of micropores and mesopores for N-doped activated carbon, leading to high storage ability for desulfurization products and well oxidation performance. The organic-N (i.e., alanine) was conducive to forming pyridinic-N and quinonyl for N-doped activated carbon, resulting in a strong ability of adsorption, dissolution, and oxidation for H2S. The organic-N determined the high breakthrough sulfur capacity for hydrothermal aqueous doping activated carbon (110.7 mg/g), which was similar to 4.08 times than undoped activated carbon. The primary product of the desulfurization process was elemental sulfur (74.08%), with sulfuric acid and sulfonic acid as the subsequent by-products. After nitrogen doping, the contents of elemental sulfur and sulfuric acid increased by 5.65 and 1.73 times, respectively. The results revealed the correlations between nitrogen species in hydrothermal aqueous and the desulfurization performance of activated carbon, which could guide the selection of nitrogen-rich aqueous for synthesizing H2S removal N-doped activated carbon via the above novel method.