Heterostructured MoS2 quantum dot/GO lamellar membrane with improved transport efficiency for organic solvents inspired by the Namib Desert beetle

Whether membranes developed for organic solvent nanofiltration (OSN) tend to be hydrophilic or hydrophobic? ── a review

In the past few decades, organic solvent nanofiltration (OSN) has attracted numerous researchers and broadly applied in various fields. Unlike conventional nanofiltration, OSN always faced a broad spectrum of solvents including polar solvents and non-polar solvents. Among those recently developed OSN membranes in lab-scale or widely used commercial membranes, researchers preferred to explore intrinsic materials or introduce nanomaterials into membranes to fabricate OSN membranes. However, the hydrophilicity of the membrane surface towards filtration performance was often ignored, which was the key factor in conventional aqueous nanofiltration. The influence of surface hydrophilicity on OSN performance was not studied systematically and thoroughly. Generally speaking, the hydrophilic OSN membranes performed well in the polar solvents while the hydrophobic OSN membranes work well in the non-polar solvent. Many review papers reviewed the basics, problems of the membranes, up-to-date studies, and applications at various levels. In this review, we have focused on the relationship between the surface hydrophilicity of OSN membranes and OSN performances. The history, theory, and mechanism of the OSN process were first recapped, followed by summarizing representative OSN research classified by surface hydrophilicity and types of membrane, which recent OSN research with its contact angles and filtration performance were listed. Finally, from the industrialization perspective, the application progress of hydrophilic and hydrophobic OSN membranes was introduced. We started with history and theory, presented many research and application cases of hydrophilic and hydrophobic OSN membranes, and discussed anticipated progress in the OSN field. Also, we pointed out some future research directions on the hydrophilicity of OSN membranes to deeply develop the effect made by membrane hydrophilicity on OSN performance for future considerations and stepping forward of the OSN industry.

Bioinspired Graphene Aerogels with Hybrid Wettability for Solar-Driven Purification of Complex Wastewater

Salt deposition and pollutant enrichment greatly hamper efficient and sustainable water production for a solar evaporator. Inspired by the desert beetle, a dual-region hydrophobic graphene/hydrophilic titanium dioxide (TiO2) aerogel (GTA) with internal hydrophilic-hydrophobic hybrid wettability structure is prepared via a facile freeze-drying and thermal reduction method. The evaporator shows adjustable wettability, optimized water content, and a low energy loss in the evaporation process. Simultaneously, the hybrid wetting structure in aerogel subjects salt to a dynamic crystallization-dissolution process to prevent salt deposition. The GTA solar evaporator achieves an evaporation rate of 1.52 kg·m-2·h-1 with a 91.02% efficiency under 1 sun irradiation. Furthermore, GTAs achieve a stable evaporation rate in high salinity brine (25 wt % NaCl) under 1 sun irradiation for 100 h, which could compete well with other most advanced photothermal evaporation materials. Moreover, the synergistic effect of graphene and TiO2 endows GTAs with excellent photocatalytic degradation and self-cleaning properties, which can effectively reduce the enrichment of contaminants on the evaporator. Therefore, GTA evaporators can efficiently and stably obtain clean water from seawater and wastewater, which provides a feasible strategy for the purification of complex wastewater.

Cascaded compression of size distribution of nanopores in monolayer graphene

Monolayer graphene with nanometre-scale pores, atomically thin thickness and remarkable mechanical properties provides wide-ranging opportunities for applications in ion and molecular separations1, energy storage2 and electronics3. Because the performance of these applications relies heavily on the size of the nanopores, it is desirable to design and engineer with precision a suitable nanopore size with narrow size distributions. However, conventional top-down processes often yield log-normal distributions with long tails, particularly at the sub-nanometre scale4. Moreover, the size distribution and density of the nanopores are often intrinsically intercorrelated, leading to a trade-off between the two that substantially limits their applications5-9. Here we report a cascaded compression approach to narrowing the size distribution of nanopores with left skewness and ultrasmall tail deviation, while keeping the density of nanopores increasing at each compression cycle. The formation of nanopores is split into many small steps, in each of which the size distribution of all the existing nanopores is compressed by a combination of shrinkage and expansion and, at the same time as expansion, a new batch of nanopores is created, leading to increased nanopore density by each cycle. As a result, high-density nanopores in monolayer graphene with a left-skewed, short-tail size distribution are obtained that show ultrafast and ångström-size-tunable selective transport of ions and molecules, breaking the limitation of the conventional log-normal size distribution9,10. This method allows for independent control of several metrics of the generated nanopores, including the density, mean diameter, standard deviation and skewness of the size distribution, which will lead to the next leap in nanotechnology.

Simultaneous Regulation of Surface Properties and Microstructure of Graphene Oxide Membranes for Enhanced Nanofiltration Performance

The surface properties and microstructure of graphene oxide (GO)-based membranes are both crucial for enhanced nanofiltration performance. Herein, a GO nanofiltration membrane is fabricated with regulatable surface properties and microstructure via a facile two-step impregnation in KOH and following HCl aqueous solutions. The type and number of oxygen-containing groups in GO membranes change with fewer C-O-C/C-OH and C═O but more COOH groups, and they are readily regulated by alkaline treatment time, which enables enhanced surface hydrophilicity and larger surface ζ potentials. Meanwhile, a few tiny defects are present in the GO sheets, which could increase the number of pores and decrease the length of water nanochannels. Such surface properties and microstructure together determine the excellent nanofiltration performance of the GO membranes with fast and selective water permeation, e.g., ∼99.5% rejection toward CBB G250 and flux of 56.9 ± 1.0 L m-2 h-1. This work provides insights into the design of high-performance two-dimensional laminar membranes.

Cross-linked laminar graphene oxide membranes for wastewater treatment and desalination: A review

Two-dimensional (2D) lamellar graphene oxide (GO) membranes are emerging as attractive materials for molecular separation in water treatment because of their single atomic thickness, excellent hydrophilicity, large specific surface areas, and controllable properties. To yet, commercialization of GO laminar membranes has been hindered by their propensity to swell in hydrated conditions. Thus, chemical crosslinking of GO sheets with the polymer matrix is used to improve GO membrane hydration stability. This review focuses on pertinent themes such as how chemical crosslinking improves the hydration stability, separation performance, and antifouling properties of GO membranes.