In situ growth of MIL-100(Fe) onto the rice straw-derived biochar for efficient adsorption of gaseous ammonia

Ammonia (NH3) is the primary odor-causing substance in compost waste gas, which can cause irreversible damage to the environment and humans, and is also a significant contributor to the formation of PM2.5. In this study, a novel composite adsorbent (MIL-100/RSB) for efficient adsorption of NH3 was fabricated by in situ growth of MIL-100(Fe) onto biochar derived from waste rice straw through hydrothermal synthesis. The resulting optimized MIL-100/RSB-0.5-700-0.4 (where 0.5 represented the mass ratio of K2CO3 activator to rice straw, 700 denoted pyrolysis temperature and 0.4 corresponded to the mass ratio of Fe-MOFs to biochar) was acquired by rationally adjusting the activation ratio, pyrolysis temperature and loading amounts of Fe-MOFs. The MIL-100/RSB-0.5-700-0.4 delivered a superior NH3 adsorption capability of 6.7 mmol/g at 298 K and 100 kPa with a rapid adsorption kinetics (achieving about 96 % of equilibrium sorption capacity after 30 min). In contrast, the inactivated biochar (carbonization without activator) only exhibited a much lower adsorption capacity at approximately 1.85 mmol of NH3/g. Additionally, the MIL-100/RSB showed favorable regeneration ability, retaining 3.62 mmol/g after undergoing six regeneration cycles. The adsorption mechanism of MIL-100/RSB was found to involve both physical and chemical adsorption process. Therefore, the as-prepared MIL-100/RSB composite offers a potentially promising carbon-based adsorbent for practical applications in the NH3 capture field.