Enhanced water permeation through the terahertz-induced phase and diffusion transition in metal-organic framework membranes.

Freshwater scarcity is a pressing global concern, and water desalination has emerged as a promising solution. Metal-organic framework (MOF) membranes have demonstrated exceptional potential in this regard. However, previous efforts to improve the permeability of MOFs have primarily focused on chemical modifications and synthesis rather than exploring physical methods. Using molecular dynamics simulations, we propose that the use of terahertz waves at a specific frequency of 7.5 ± 1.0 THz significantly enhances water permeability across MOF membranes, up to 27-fold, while maintaining effective ion rejection capabilities throughout the process. The mechanism behind this enhancement involves the resonance between the terahertz wave and the hydrogen bond vibrations of water within the MOF. This resonance amplifies the rotational kinetic energy of water molecules, disrupting the hydrogen bonds and causing a phase transition from quasi 1D square ice to a gas-like phase. Additionally, the diffusion behavior shifts from Fickian diffusion to sub-diffusion, resulting in improved water permeation across the MOF membrane. This study highlights the potential of terahertz waves as a physical tool to enhance the permeability of MOFs in water desalination, providing new avenues for efficient water treatment and resource sustainability.

Fabrication and properties of TiO2 nanofilms on different substrates by a novel and universal method of Ti-ion implantation and subsequent annealing.

We report a new, novel and universal method to fabricate high-quality titanium dioxide (TiO2) nanofilms on different substrates by a solid phase growth process of ion implantation and subsequent annealing in oxygen atmosphere. Ti ions were implanted into fused silica, soda lime glass, Z-cut quartz, or (0001) α-sapphire by a metal vapor vacuum arc (MEVVA) ion source implanter to fluences of 0.75, 1.5 and 3 × 10(17) ions cm(-2) with a nominal accelerating voltage of 20 kV. To understand the influence of the annealing temperature, time, and substrate on the formation and phase transformation of the TiO2 nanofilms, the Ti-ion-implanted substrates were annealed in oxygen atmosphere from 500 to 1000 °C for 1-6 h. The formation of TiO2 nanofilms resulted from the slow out-diffusion of implanted Ti ions from the substrates which were then oxidized at the surfaces. The thickness and phase of the nanofilms can be tailored by controlling the implantation and annealing parameters. Since the TiO2 nanofilms are formed under high temperature and low growth rate, they show good crystallinity and antibacterial properties, with good film adhesion and stability, suggesting that the TiO2 nanofilms formed by this method have great potential in applications such as antibacterial and self-cleaning transparent glass.