Wodyetia bifurcate structured carbon fabrics with durable superhydrophobicity for high-efficiency oil-water separation

Highlights

• A fascinating wodyetia bifurcate structured fibrous fabrics have been synthesized.

• The carbonization process is crucial for fabrics with superhydrophobicity.

• The fabric possesses substantial superhydrophobic durability.

• The fabric has anti-wetting, self-cleaning and oil-water separation performance.

• Our work gives a new way to prepare high-roughness fiber-based membranes.

Abstract

The superhydrophobic fiber-based membranes with features of high separation efficiency and low energy consumption for oil-water separation remains a formidable challenge. In this paper, a robust and durable superhydrophobic cotton-derived carbon fabric (CDCF) with wodyetia bifurcate-like structure is fabricated via in situ cobalt-nickel basic carbonate (CNC) deposition and 1 H, 1 H, 2 H, 2 H-perfluorooctyltriethoxysilane (POTS) coating. The combined action of rough surface structure and low surface energy makes CDCF/CNC/POTS with superhydrophobicity/superoleophilicity, anti-wetting, and self-cleaning performance. Intriguingly, the CDCF/CNC/POTS can keep its superhydrophobicity under of the water droplet impact pressure of 781 Pa. In addition to its robust dynamic superhydrophobicity, CDCF/CNC/POTS can also maintain its non-wetting property under harsh environmental conditions such as mechanical abrasion treatment, acidic, alkaline and salt solutions, and ultraviolet radiation. Importantly, the CDCF/CNC/POTS can separate various oil-water mixtures and emulsions under gravity with ultrahigh oil-water mixtures permeate flux (∼19,126 L/m²h), high surfactant-stabilized emulsion permeate flux (∼821 L/m²h), and high separation efficiency (> 98.60 %). Moreover, remarkable recyclability endow the CDCF/CNC/POTS with promising application in treating oily wastewater. This work may benefit the low-cost mass production of cotton-based carbon fabrics for developing eco-friendly high-efficiency separators.

Introduction

Superhydrophobic surfaces have received widespread attention in many practical applications, such as self-cleaning, anti-sticking, adsorption, anti-icing, oil-water separation, and so on (Krupa et al., 2017, Wang et al., 2015, Liang et al., 2015, Yang et al., 2022a, Yang et al., 2018, Liu et al., 2021a). Inspired by lotus leaves, gecko feet and petals in nature, many artificial superhydrophobic surfaces based on alternative surface superhydrophobicity have been obtained (Zorba et al., 2008, Pokroy et al., 2009, Feng et al., 2008, Shao et al., 2020). In general, the morphology and chemical composition of the contact surface are the two conditions required to build a superhydrophobic surface. Particularly, the use of the hierarchical (Yang et al., 2022a, Chen et al., 2018) and fractal structures (Yang et al., 2017, Zhang et al., 2018) can improve the roughness of surface microstructures. Based on this principle, many superhydrophobic membranes based on porous materials have been successfully prepared, including nanofibrous membrane, fabric, and metal mesh for oil/water separation (Li et al., 2019a, Ma et al., 2016, Ma et al., 2019, Zeng et al., 2017, Woo et al., 2021, Olabintan et al., 2022). Among them, fabrics-based membranes (e.g. cotton fabric, basalt fiber fabric, and glass fiber fabric) have been widely used as substrates for the preparation of superhydrophobic membranes for oil/water separation (Yang et al., 2022a, Yue et al., 2019, Guo et al., 2020, Zang et al., 2015, Saleh, 2020), because of its good mechanical properties, large-scale application, natural porous structure, easy chemical modification and so on.

For the ideal oil/water separation membrane, it should have strong mechanical strength and good chemical stability (Yang et al., 2020a). Commercial carbon fiber fabrics woven from carbon microfiber bundles have good chemical stability and high mechanical strength, which can meet these requirements, because they have a strong covalent bond skeleton (Yue et al., 2018, Zhang et al., 2017, Zhang et al., 2019a, Huang et al., 2020). In this regard, carbon fiber fabric plays an important role in oil-water separation because it can withstand harsh operating conditions. Nevertheless, the high cost seriously limits the large-scale application of commercial carbon fabric in separating oil/water mixture. Simple carbonization of biomass at high temperature provides a green and convenient method for preparing low-cost and conductive flexible carbon fiber fabrics (Li et al., 2020a, Yang et al., 2020b, Guo et al., 2019). The prepared carbon fiber fabric has light weight, good mechanical properties, and good porous structure is an ideal choice for oil/water separation membrane materials. However, if there is no other organic material to modify its surface, the obtained carbon fabric is difficult to have stable superhydrophobicity. Usually, a layer of low surface energy materials is used to improve the hydrophobicity of carbon fabric through post-treatment, but this will bring the risk of coating failure (Zulfiqar et al., 2021). Moreover, it is different to uniformly modify the whole carbon skeleton in the post-treatment process due to the poor chemical cutting ability and solubility of carbon fabric (Li et al., 2020b).

Ni-Co based carbonate has drawn increasing attention in water remediation because of its abundant reserves in nature, easy preparation, low temperature stability and sophisticated micronano structures. Combining the nanoparticles with large specific area and low surface energy with the membrane substrate to construct a novel self-supporting multifunctional material is a successful strategy to purify complex oily wastewater (Zhao et al., 2019a, Ma et al., 2020, Zhang et al., 2022a, Xie et al., 2021, Wang et al., 2021). It is worrying that the interaction between inorganic nanoparticles and the surface of carbon fabric is very weak, resulting in the shedding of nanoparticles, and the gradual loss of superhydrophobic in harsh environment (Zhao et al., 2018). Although lots of efforts have been made to enhance the durability of artificial superhydrophobic surfaces, the low mechanical strength and bond strength still hinder its practical application in industrial fields (Jia et al., 2018, Zhang et al., 2019b, Zhang et al., 2019c). Thus, it is highly desired to develop more facile and cost-effective method to stably load nanoparticles on carbon substrate to construct antifouling fiber fabric materials to deal with severe and complex water pollution. To date, there are few papers on the preparation of superhydrophobic cotton-derived carbon fabric (CDCF) by deposition modification process, let alone the use of these functional fabrics for further oil/water separation.

Here, inspired by the exquisite multiscale structures of Wodyetia bifurcata, cotton-derived carbon fabric/cobalt-nickel carbonate/1 H, 1 H, 2 H, 2 H-perfluorooctyltriethoxysilane (CDCF/CNC/POTS) fibrous fabrics were fabricated by a simple pyrolysis method, in-situ hydrothermal reaction, and hydrophobization, as shown in Fig. 1. Noteworthy, our system holds the following salient features. (I) The carbon fabrics with large amount of polar functional groups via a low temperture pyrolysis method improve the hydrophilicity of carbon fabric and regulate CNC uniform loading behavior. (II) Benefiting from the synergy of formed multiscale structures and low surface energy, the CDCF/CNC/POTS display the satisfactory superhydrophobicity/superoleophilicity, water repellency, and self-cleaning property. (III) The special surface structure of needle-like CNC free-standing formed on the surface of fabric similar to that of wodyetia bifurcate, endowed the CDCF/CNC/POTS excellent demulsification ability for surfactant-stabilized oil/water emulsion.