Selective and Continuous Oil Removal from Oil-Water Mixtures Using a Superhydrophobic and Superoleophilic Stainless Steel Mesh Tube

Highly Permeable Sulfonated Polydopamine Integrated MXene Membranes for Efficient Surfactant-Stabilized Oil-in-Water Separation

MXene is an incredibly promising two-dimensional material with immense potential to serve as a high-performing separating or barrier layer to develop advanced membranes. Despite the significant progress made in MXene membranes, two major challenges still exist: (i) effectively stacking MXene nanosheets into defect-free membranes and (ii) the high fouling tendency of MXene-based membranes. To address these issues, we employed sulfonated polydopamine (SPD), which simultaneously serves as a binding agent to promote the compact assembling of Ti3C2Tx MXenes (MX) nanosheets and improves the antifouling properties of the resulting sulfonated polydopamine-functionalized MX (SPDMX) membranes. The SPDMX membrane was tested for challenging surfactant-stabilized oil-in-water separation with an impressive efficiency of 98%. Moreover, an ultrahigh permeability of 1620 LMH/bar was also achieved. The sulfonation of PD helps in improving the antifouling characteristics of SPDMX by developing a strong hydration layer and enhancing the oleophobicity of the membrane. The underwater SPDMX membrane appeared superoleophobic with an oil contact angle of 153°, whereas the ceramic membrane exhibited an oil contact angle of 137°. The SPDMX membranes showed an improved flux recovery (31%) compared to the nonsulfonated counterpart. This work highlights the appropriate functionalization of MXene as a promising approach to developing MXene membranes with high permeation flux and better antifouling characteristics for oily wastewater treatment.

Underwater Superoleophobic and Underoil Superhydrophilic Copper Benzene-1,3,5-tricarboxylate (HKUST-1) Mesh for Self-Cleaning and On-Demand Emulsion Separation

Surfaces with underoil superhydrophilic (UOSHL) and underwater superoleophobic (UWOHB) have great potential for on-demand emulsion separation. However, the fabrication of underoil superhydrophilic based on wetting thermodynamic principles is quite challenging. Several previous studies have shown that some sarcocarps are able to spontaneously absorb water to moisturize themselves and have a unique UOSHL ability. By mimicking this unique ability of the sarcocarp, an outstanding UWOHB and UOSHL membrane was prepared. We choose 2300 mesh stainless steel mesh (SSM) as the substrate, then grow Cu and Cu(OH)₂ on SSM by a simple electrochemical method, and finally grow HKUST-1 crystals via a fast in situ growth method. The whole preparation process is simple, low cost, and does not require complex and long-term hydrothermal reactions. By growing HKUST-1 crystals, the prepared surface successfully achieved the required UOSHL and UWOHB properties. When the water droplets come into contact with the membrane under n-hexane, it will diffuse and can completely spread out in 2 s. The as-prepared membrane exhibits outstanding anti-fouling and self-cleaning properties for rapeseed oil and crude oil with high viscosity underwater due to the special wetting. By prewetting the surface with an appropriate amount of the dispersion medium, it can rapidly and efficiently on-demand separate different emulsions. The separation efficiencies of water-in-oil emulsions and oil-in-water emulsions are above 99.00 and 97.00%. With their outstanding performance in self-cleaning, on-demand emulsion separation, low cost, and fast preparation, the as-prepared UOSHL and UWOHB HKUST-1 meshes show excellent potential for treating oily wastewater in practical applications.