Solar-driven efficient and selective ammonia recovery from ammonium-containing wastewater

Recovering ammonia (NH3) from ammonium (NH4+)-containing wastewater simultaneously achieves resource recovery and wastewater treatment. Given that NH3 recovery involves a reversible NH4+ hydrolysis reaction, traditional strategy requires alkaline reactants for promoting the reaction forward and energy-intensive heating for recovering NH3, resulting in substantial cost and energy consumption. Here we propose a solar-driven NH3 recovery strategy enabled by floatable amino-grafted (‒NH2) MXene (Ti3C2)-based sponge that possesses local alkaline environment and interfacial heat on water surface. Both H+ trapping via ‒NH2 groups and NH3 evaporating via interfacial solar heating thermodynamically facilitate efficient and sustainable NH3 recovery. Taking ammonia chloride (NH4Cl) wastewater for example, a NH3 recovery rate of 0.6 mol m−2 h−1 with a purity of 99.8% is obtained under 5 sun without extra reagents and energy consumption, and the recovered NH3 can be directly used as nitrogen fertilizer. Besides, the amino-grafted MXene-based sponge is also capable of being fully regenerated to its initial performance under 15 sun, and hydrochloric acid, a valuable by-product, can be obtained during this process. Life-cycle and techno-economic assessments highlight the advantages of solar-driven NH3 recovery in terms of environmental benefits and economic potential.