Superhydrophobic PDMS@TiO2 wood for photocatalytic degradation and rapid oil-water separation
Graphical abstract
Introduction
One of the byproducts of the rapid industrial development seen in recent decades is an increase in the discharge of waste [1]. A large proportion of this waste consists of oily wastewater, which can cause serious damage to ecological environments [2]. To mitigate the potential harm caused by oily wastewater, the development of economical and highly efficient oil-water separation technology has become a focus of research interest [3], [4], [5]. At present, common methods for the treatment of oily wastewater include gravity sedimentation [6], centrifugal separation [7], membrane separation [8], [9], [10], and chemical flocculation [11]. However, these traditional technologies are often expensive to implement and suffer from serious shortcomings such as complex and tedious processes, high energy consumption, low efficiency, and secondary pollution [12], [13], [14], [15].
In recent years, superhydrophobic materials have attracted significant attention owing to their high separation efficiency towards the treatment of oil-water mixtures [16], [17], [18]. Inspired by lotus leaves in nature, superhydrophobic materials with water contact angle greater than or equal to 150o are constructed by combining the hierarchical roughness with low-surface-energy substances. For example, many studies have been carried out on the design and fabrication of hydrophobic woods for oil-water separation [19], [20], [21], as natural wood is a renewable resource with a special longitudinal pore structure, excellent mechanical properties, and high chemical stability [22], [23], [24]. Fu et al. [25] created a superhydrophobic/superoleophilic wood material with a water contact angle (WCA) of 140o and an oil absorption capacity of 15 g/g by making use of the mesoporous three-dimensional structure of natural wood in conjunction with its hydrophobic modification using epoxy resin. Huang et al. [26] adopted chemical treatment, graphene oxide (GO) coating and reduction, and fluoroalkyl silane (FAS) grafting modification methods to prepare a highly hydrophobic rGO/FAS wood sponge with electrothermal properties for the clean-up of viscous crude oil. Ma et al. [27] prepared a superhydrophobic wood material with oil-water separation efficiency >97.0% and effective flame-retardant performance by assembling chitosan, polyethylenimine, ammonium polyphosphate, and sodium alginate, and conducting the hydrophobic modification of 3-aminopropyltriethoxysilane/silicon dioxide. However, the permeation fluxes were found to be unsatisfactory, as these were limited by the small channels in the wood. It is important to note that, to achieve high hydrophobicity, the wood is usually modified using nondegradable low-surface-energy chemicals [28], [29], [30], resulting in secondary pollution to the environment. Unfortunately, little attention has been focused on the post-treatment of hydrophobic wood after oil-water separation.
In this study, we propose a method for the production of superhydrophobic wood wrapped with titanium dioxide (TiO2) and polydimethylsiloxane (PDMS) for rapid oil-water separation and subsequent photocatalytic degradation. As a renewable material with a naturally porous structure, balsa wood was selected as substrate and chemically treated to achieve unimpeded longitudinal channels, followed by coating with anatase-phase TiO2 and modification with PDMS through simple immersion. The anatase-phase TiO2 and PDMS were utilized to endow the wood with photocatalytic degradation capability and to decrease its surface energy, respectively. The results from this study are expected to provide valuable guidance towards the fabrication of functional superhydrophobic wood with photocatalytic degradation ability for efficient oily wastewater treatment.
Section snippets
Materials
Natural balsa wood with density of 130–180 kg/m3 was provided by Guangzhou Sinokiko Balsawood Trading Co., Ltd. (China), and was cut into pieces with scale at 35 × 35 × 3 mm for use. Titanium tetrachloride (TiCl4), sodium hydroxide (NaOH), anhydrous sodium sulfite (Na2SO3), tetrahydrofuran, toluene were purchased from Aladdin Reagent Co., Ltd. (China). Hydrogen peroxide (H2O2, 30%) was bought from Tianjin Damao Chemical reagent factory (China). Cyclohexane, ethanol and dichloromethane were
Preparation and characterization of superhydrophobic PDMS@TiO2 wood
As a natural renewable source, balsa wood possesses the advantages of low density, high mechanical strength and an anisotropic porous structure [32], [33], [34]. First, the wood was chemically treated using NaOH, Na2SO3 and H2O2 to remove hemicellulose and lignin, and then freeze-dried to create a porous structure with unobstructed longitudinal channels. Second, the wood was immersed into aqueous TiO2 solution to increase its surface roughness and allow it to obtain photocatalytic ability.
Conclusions
In this study, a superhydrophobic PDMS@TiO2 wood with excellent photocatalytic performance for fast oil-water separation was successfully fabricated through delignification, TiO2 coating, and PDMS modification. The PDMS@TiO2 wood possessed an anisotropic porous structure with vertically-arranged enlarged channels, and showed strong superhydrophobicity (WCA of 160°). Due to its excellent water repellency, unobstructed longitudinal channels, and the strong capillary action of its porous
CRediT authorship contribution statement
Zhuohan Chen: Methodology, Investigation, Validation, Writing-original draft, Writing-review & editing. Xiaojing Su: Validation, writing-review & editing. Wenjian Wu: Validation, Writing-review & editing, Supervision. Siting Chen: Methodology. Xiaofan Zhang: Conceptualization. Yunhui Wu: Conceptualization. Huali Xie: Investigation, Writing-review & editing. Kunquan Li: Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Zhuohan Chen and Xiaojing Su contributed equally to this work. This study was supported by the Special Project for Key Areas of Guangdong Higher Education Institutions, China (2020ZDZX2024), the National Nature Science Foundation of China (51903059), the Guangdong Basic and Applied Basic Research Foundation, China (2019A1515110343).
References (45)
- et al.
A review on emerging contaminants in wastewaters and the environment: current knowledge, understudied areas and recommendations for future monitoring
Water Res.
(2015) - et al.
A review of treating oily wastewater
Arab. J. Chem.
(2017) - et al.
Ultralight, robustly compressible and super-hydrophobic biomass-decorated carbonaceous melamine sponge for oil/water separation with high oil retention
Appl. Surf. Sci.
(2019) - et al.
PDA-PEI copolymerized highly hydrophobic sponge for oil-in-water emulsion separation via oil adsorption and water filtration
Surf. Coat. Technol.
(2021) - et al.
Preparation of carbon cloth membrane with visible light induced self-cleaning performance for oil-water separation
Surf. Coat. Technol.
(2020) - et al.
A novel interface-active cationic flocculant for the oil-water separation of oily wastewater produced from polymer flooding
J. Mol. Liq.
(2019) - et al.
Rational construction of highly transparent superhydrophobic coatings based on a non-particle, fluorine-free and water-rich system for versatile oil-water separation
Chem. Eng. J.
(2018) - et al.
Freely switchable super-hydrophobicity and super-hydrophilicity of sponge-like poly(vinylidene fluoride) porous fibers for highly efficient oil/ water separation
J. Hazard. Mater.
(2021) - et al.
A mussel-inspired method to fabricate reduced graphene oxide/g-C3N4 composites membranes for catalytic decomposition and oil-in-water emulsion separation
Chem. Eng. J.
(2017) - et al.
Surfaces with controllable super-wettability and applications for smart oil-water separation
Chem. Eng. J.
(2019)
Efficient separation of free organic liquid mixtures based on underliquid superlyophobic coconut shell coated meshes
Sep. Purif. Technol.
One-step hydrothermal synthesis of the modified carbon cloth membrane: towards visible light driven and self-cleaning for efficient oil-water separation
Surf. Coat. Technol.
Highly hydrophobic F-rGO@wood sponge for efficient clean-up of viscous crude oil
Chem. Eng. J.
Facile fabrication of wood-inspired aerogel from chitosan for efficient removal of oil from water
J. Hazard. Mater.
Direct coating of a DKGM hydrogel on glass fabric for multifunctional oil-water separation in harsh environments
Chem. Eng. J.
Photo-oxidative resistance and adjustable degradation of poly-lactic acid (PLA) obtained by biomass addition and interfacial construction
Polym. Degrad. Stab.
Facile fabrication of superhydrophobic wood slice for effective water-in-oil emulsion separation
Sep. Purif. Technol.
The synthesis strategies and photocatalytic performances of TiO2/MOFs composites: a state-of-the-art review
Chem. Eng. J.
Superhydrophobic and photocatalytic PDMS/TiO2 coatings with environmental stability and multifunctionality
Colloids Surf. A Physicochem. Eng. Asp.
Superwettable janus nylon membrane for multifunctional emulsion separation
J. Membr. Sci.
Simple fabrication of superhydrophobic PLA with honeycomb-like structures for high-efficiency oil-water separation
Chin. Chem. Lett.
Photocatalytic degradation of RhB from an aqueous solution using Ag3PO4/N-TiO2 heterostructure
J. Mol. Liq.
Cited by (32)
Creation of a high strength, hydrophobic and fireproof surface on wood by polyamide acid under mild and simple conditions
2024, Progress in Organic CoatingsEfficient preparation of multifunctional superhydrophobic surfaces on Zr-based bulk metallic glass by electrochemical machining
2023, Colloids and Surfaces A: Physicochemical and Engineering AspectsA superhydrophobic graphene@copper mesh irradiated by laser for efficient oil/water separation
2023, Surface and Coatings TechnologyA comprehensive review of lignocellulosic biomass derived materials for water/oil separation
2023, Science of the Total Environment