Waste-derived aluminium based metal-organic framework for atmospheric moisture harvesting and photocatalytic hydrogen production

Abstract

• This work integrates principles of waste-to-value recycling with the development of advanced functional materials. • The synthesis of MIL-53(Al) was achieved through a hydrothermal process involving Al(NO₃)₃.9H₂O and BDC. • The materials demonstrated varying levels of water adsorption capacity • The distillation and TGA-FTIR hyphened technology used to investigate the water collection kinetics. • The TGA adsorption kinetic followed a pseudo-second-order model. • The hydrogen evolution experiments revealed that MIL-53(Al) catalyst produced 1253 μmol of hydrogen gas Green hydrogen production via photocatalytic water splitting is a promising and environmentally friendly route towards sustainable energy. However it relies on freshwater source, which is limited in regions facing water scarcity. Herein, we report a waste-to-value approach in which aluminium nitrate nonahydrate (Al(NO₃)₃.9H₂O), benzene 1,4 dicarboxylic acid (BDC), and the metal-organic framework (MIL 53(Al)) were synthesised from waste aluminium cans and PET bottles contributing to recycling. The materials were characterised by FTIR, XRD, SEM-EDS, TGA, and BET. MIL-53(Al) exhibited a water-responsive porous structure with a water harvesting capacity of 180 g.kg⁻¹, while Al(NO₃)₃.9H₂O showed a superior capacity of 420 g.kg⁻¹. Kinetic studies revealed that water desorption followed pseudo second order kinetics, indicating site specific interactions. Reusability tests showed that MIL-53(Al) maintained nearly constant water production over five cycles (95% retention), whereas Al(NO₃)₃·9H₂O exhibited a gradual decline due to particle agglomeration. The water harvested from the atmosphere was used directly as the reaction medium for photocatalytic hydrogen production. MIL-53(Al) demonstrated a hydrogen production rate of 418 µmol. g⁻¹.min⁻¹ under visible light, with an apparent activation energy of 1.79 kJ·mol⁻¹ and retained 96% of its activity after five cycles. The individual precursors show negligible photocatalytic activity. This work demonstrated a closed loop, waste-derived pathway that couples atmospheric water harvesting with solar driven hydrogen production, contributing to circular economy and sustainable energy.