Qianyu Wei, Guixin Hu, Huiyue Wang, Xueying Wen, Yan She, Xinyao Zhang, Hongrun Zhu, Hangyuan Du, Zhikun Dai, Ran Niu*, Jiang Gong*

When waste plastics meet with MOF: Upcycling waste polypropylene separator into carbon nanotube for efficient freshwater and hydroelectricity co-generation.

Sustainable Materials and Technologies (2025) Accept. (IF2025 = 9.2)

Coupling solar interfacial evaporation and electricity generation is one of the reliable solutions to address freshwater shortage and energy crisis. Carbon nanotube (CNT)-based evaporators exhibit high broadband light absorption capacity for water evaporation. However, developing low-cost, efficient CNT evaporators and revealing the influence of morphology and functional groups of CNT on the freshwater-electricity co-generation performance remain challenging. Herein, we report the conversion of waste polypropylene (PP) separator into CNT using a combined catalyst system of nickel-based metal-organic framework (MOF) and NiCl₂. The synthesized CNT is fabricated into evaporator for simultaneous interfacial water evaporation and power harvesting. To our knowledge, it is the first work on the employment of MOF to catalyze the conversion of waste PP into CNT. Owing to rich defects and abundant oxygen-containing groups of CNT, the CNT evaporator demonstrates good hydrophilicity and photothermal capacity. It achieves a high evaporation rate of 2.79 kg m^-2 h^-1 and a continuous voltage output of 259 mV, surpassing the performance of many advanced carbon-based evaporators. Molecular dynamics simulation results show that Na⁺ exhibits the stronger interaction force with the oxygen-containing functional groups of CNT than Cl^-, which promotes the selectivity of Na+ in the double-layer channel and eventually leads to voltage generation. This work not only provides a sustainable upcycling chemical method of waste plastics, but also contributes to the coupling of solar interfacial evaporation and electricity generation.