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An increasing demand for freshwater inspires further understanding of the mechanism of water diffusion in reverse-osmosis membranes for the development of high-performance membranes for desalination. Water diffusion has a close relationship with the structural and dynamical characteristics of hydrogen bonds, which is not well-understood for the confining environment inside the polyamide membrane at the molecular level. In this work, an atomistic model of a highly cross-linked polyamide membrane was built with an equilibrated mixture of m-phenylenediamine and trimesoyl chloride monomers. The structure and dynamics of water in the regions from the bulk phase to the membrane interior were investigated by molecular dynamics simulations. Explicit hydrogen bond criteria were determined for hydrogen-bonding analysis. The local distribution and orientation of water reveal that the hydrogen-bonding affinity of the hydrophilic functional groups of polymers inhibits water diffusion inside the membrane. The affinity helps to produce percolated water channels across the membrane. The hydrogen-bonding structures of water in different regions indicate dehydration is required for the entry of water into the polyamide membrane, which dominates water flux across the membrane. This paper not only deepens the understanding of the structure and dynamics of water confined in the polyamide membrane but also stimulates the future work on high-performance reverse-osmosis membranes.

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Oxygen vacancies can capture and activate gaseous oxygen, forming surface chemisorbed oxygen, which plays an important role in the Hg 0 oxidation process. Fine control of oxygen vacancies is necessary and a major challenge in this field. A novel method for facet control combined with morphology control was used to synthesize Co 3 O 4 nanosheets preferentially growing (220) facet to give more oxygen vacancies. X-ray photoelectron spectroscopy (XPS) results show that the (220) facet has a higher Co 3+ /Co 2+ ratio, leading to more oxygen vacancies via the Co 3+ reduction process. Density functional theory (DFT) calculations confirm that the (220) facet has a lower oxygen vacancy formation energy. Furthermore, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results suggest that Co 3 O 4 nanosheets yield more defects during the synthesis process. These results are the reasons for the greater number of oxygen vacancies in Co 3 O 4 nanosheets, which is confirmed by electron energy loss spectroscopy (EELS), Raman spectroscopy, and photoluminescence (PL) spectroscopy. Therefore, Co 3 O 4 nanosheets show excellent Hg 0 removal efficiency over a wide temperature range of 100−350 °C at a high gas hourly space velocity (GHSV) of 180 000 h −1 . Additionally, the catalytic efficiency of Co 3 O 4 nanosheets is still greater than 83%, even after 80 h of testing, and it recovers to its original level after 2 h of in situ thermal treatment at 500 °C.