Superhydrophilic and Underwater Superoleophobic Copper Mesh Coated with Bamboo Cellulose Hydrogel for Efficient Oil/Water Separation

Abstract

Super-wetting interface materials have shown great potential for applications in oil-water separation. Hydrogel-based materials, in particular, have been extensively studied for separating water from oily wastewater due to their unique hydrophilicity and excellent anti-oil effect. In this study, a superhydrophilic and underwater superoleophobic bamboo cellulose hydrogel-coated mesh was fabricated using a feasible and eco-friendly dip-coating method. The process involved dissolving bamboo cellulose in a green alkaline/urea aqueous solvent system, followed by regeneration in ethanol solvent, without the addition of surface modifiers. The resulting membrane exhibited excellent special wettability, with superhydrophilicity and underwater superoleophobicity, enabling oil-water separation through a gravity-driven "water-removing" mode. The super-wetting composite membrane demonstrated a high separation efficiency of higher than 98% and a permeate flux of up to 9168 L·m^-2·h^-1 for numerous oil/water mixtures. It also maintained a separation efficiency of >95% even after 10 cycles of separation, indicating its long-term stability. This study presents a green, simple, cost-effective, and environmentally friendly approach for fabricating superhydrophilic surfaces to achieve oil-water separation. It also highlights the potential of bamboo-based materials in the field of oil-water separation.

Keywords: bamboo cellulose; hydrogel coating; oil/water separation; wetting.

Figure 1

Schematic diagram of fabrication of the super-wetting membrane coated 1 wt% BC hydrogel on copper mesh substrate.

Figure 2

(a) The optical image of the super-wetting membrane. (b) SEM image of the super-wetting membrane. (c) XRD data of the raw BC (red line) and regenerated BC (black line). (d) FTIR data of the raw BC (red line) and regenerated BC (black line). Optical photographs of contact angle in air (e) and underwater oil (hexane) contact angle (f). (g) Low adhesion behavior of underwater oil droplet (1,2-dichloroethane) on the super-wetting membrane.

Figure 3

Oil/water separation of the super-wetting membrane. (a) Optical images of before/after oil/water separation; (b) Optical image of the oil intrusion pressure measurement. (c) The oil/water separation efficiency of various oil–water mixtures and underwater contact angles (insert pictures). (d) The fluxes of the super-wetting membrane for oil–water mixtures. (e) The separation efficiency of the super-wetting membrane with different mesh numbers. (f) The relationship between the recycle numbers and separation efficiency.

Figure 4

Schematic illustration of the liquid-wetting models. (a) Water penetrated the super-wetting membrane in air; (b) Oil intercepted the super-wetting membrane surface.