Carbon nanotubes decorated hollow metal–organic frameworks for efficient solar-driven atmospheric water harvesting

High equilibrium uptake capacity and rapid adsorption/desorption kinetics are essential to achieve efficient atmospheric water harvesting. In this work, carbon nanotubes decorated hollow MIL-101(Cr) particles (HMC-2) are prepared and utilized for solar-driven atmospheric water harvesting with nice water adsorption capacity and fast kinetics. The hierarchical porous hollow MIL-101(Cr) particles formed by post-etching show highly active defect sites and low mass transfer resistance, which promotes the adsorption and diffusion of water molecules. The resulted HMC-2 demonstrates a maximum water uptake of 1.074 g/g at 25 °C, 90% RH. Notably, the water adsorption capacity of HMC-2 in low humidity (40% RH) are increased by 113% and 202.6% compared to pure MIL-101(Cr) and carbon nanotubes decorated MIL-101(Cr). Due to the synergistic effect of CNTs and hollow MIL-101(Cr), the HMC-2 composites generate sufficient solar thermal heat and improve the desorption kinetics. The maximum adsorbed water of HMC-2 can be completely desorbed within 90 min under one sunlight. A single cycle of sorption–desorption of HMC-2 can be achieved within 210 min. This means that if the water harvesting cycle is performed three times daily, it is possible to harvest 3.22 L of water per kilogram of adsorbent at the area with high humidity. The water uptake and release rates of HMC-2 are competitive with even superior to most those reported. This may demonstrate a promising potential for atmospheric water generators.