Facile Preparation of Robust Superhydrophobic/Superoleophilic TiO2-Decorated Polyvinyl Alcohol Sponge for Efficient Oil/Water Separation

Synthesis of a new oil-absorbing PVC oil boom and its application to maritime oil spills

This paper aims to address the issue of environmental pollution resulting from marine oil spills by evaluating the oil adsorption performance of commonly used fence materials. Conventional oil adsorption materials exhibit limited rates and capacities for oil adsorption. Existing methods have proven insufficient in meeting the requirements for efficient and rapid oil-water separation. A new oil-absorbing barrier was developed by utilizing high oil adsorption resin as the primary material and hydroxypropyl methyl cellulose (HPMC) as the binder, leveraging the exceptional oil adsorption and hydrophobic properties of P(BMA-SMA-St)/MIL-101(Fe) resin. The oil-absorbing fence was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The oil adsorption rates of carbon tetrachloride, toluene, diesel and gasoline by the oil adsorption fence with 25 g/L resin content were 101.26 g/m2, 68.12 g/m2, 35.19 g/m2, and 46.69 g/m2, respectively. After 120 h of UV irradiation, the coating's oil absorption capacity remained nearly unchanged, and it demonstrated outstanding mechanical, chemical, and wear resistance. As a result, the oil adsorption fence possesses the capability to rapidly absorb oil from the water's surface during the process of containing oil pollution, leading to positive social and economic impacts.

Non-fluorinated lignin-based melamine sponges with superhydrophobic and photothermal properties for multi-functional applications

Frequent oil spills and the discharge of oily wastewaters become a significant threat to the environment and ecosystem. Herein, a non-fluorinated lignin-based melamine sponge with superhydrophobic and photothermal properties (labeled as MS@COF/LPs/PDMS) has been achieved by decorating with covalent organic framework (COF), lignin particles (LPs) and PDMS. The MS@COF/LPs/PDMS shows excellent surface superhydrophobicity with a water contact angle of 152.3° and a sliding angle of 6°. The adsorption capacities of the MS@COF/LPs/PDMS range from 38.4 g/g to 100.3 g/g for various oils and organic solvents, and the separation efficiency of the MS@COF/LPs/PDMS for CCl4 reaches 99.7 %. Furthermore, the maximum surface temperature of the MS@COF/LPs/PDMS reaches 61.2 °C because of the thermal vibration of LPs and COF under solar irradiation (1.0 kW/m2). Surprisingly, the MS@COF/LPs/PDMS can rapidly adsorb a droplet of crude oils within 32 s due to the superoleophilicity and excellent photothermal effect. Besides, the melting time of the MS@COF/LPs/PDMS (400 s) reduces by 70 % for an ice droplet under solar irradiation than that of pristine melamine sponge (1330 s). Thus, this study provides new insights into the rational design of low-cost lignin-based melamine sponges for the applications of oil/water separation, crude oil recovery, and de-icing.

Green Fabrication of Superhydrophilic/Underwater Superoleophobic Composite Membrane for High-Efficiency Oil/Water Separation in Harsh Environments

Due to the high oil spill incidence and industrial wastewater discharge including oil and emulsified oil, designing and synthesizing oil-water separation materials which can maintain stability under harsh environmental conditions with high separation efficiencies remains a great challenge. The present work developed an easy, green, cost-effective, and easily scaled-up approach for fabricating cellulose-based membranes. First, we coated polydopamine (PDA) onto fibers of filter membrane (FM). Then, the PDA-FM membrane was immersed into the mixed solution of poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) and further thermally cross-linked at 150 °C to create a superhydrophilic/underwater superoleophobic membrane (PVA/PAA@PDA-FM) to separate oil/water mixtures. The simple thermally cross-linking process promotes multiple covalent chemical bonds generation between cellulose filter membrane, PAA, PDA, and PVA, endowing membranes with excellent stability and resistance to acidity, alkalinity, and salinity. The PVA/PAA@PDA-FM membrane not only demonstrates great separation performance (>99.8%) and great flux (>1000 L m-2 h-1) in oil-water immiscible mixtures but also maintains high separation efficiency under conditions of high acidity, alkalinity, and salinity. Additionally, the PVA/PAA@PDA-FM membrane exhibits excellent separation capacity in oil-water emulsions, which can maintain the >99.6% separation efficiency even after 40 cycles in harsh environments, showing outstanding reusability. Thus, due to the multiple cross-linked networks in the membrane, the excellent performance makes the PVA/PAA@PDA-FM membrane a good application prospect in water purification and oily wastewater treatment.

Facile Preparation of Photothermal Superhydrophobic Melamine Sponge Decorated with MXene and Lignin Particles for Efficient Oil/Water Separation, Fast Crude Oil Recovery, and Active Deicing

Frequent oil spills and the discharge of oily wastewaters have caused a serious threat to the environment, ecosystems, and human beings. Herein, a photothermal and superhydrophobic melamine sponge (MS) decorated with MXene and lignin particles has been prepared for the separation of oil/water mixtures, the recovery of crude oils, and active deicing. The obtained superhydrophobic melamine sponge shows a water contact angle (WCA) of 152.3° and an oil contact angle of ∼0° and possesses good chemical stability, thermal stability, and mechanical durability in terms of being immersed in various liquids (i.e., corrosive solutions, organic solvents, and boiling water) and being abrased by sandpapers. This superhydrophobic MS displays a high oil adsorption capacity of CCl4, up to 91.6 times its own weight and a high separation efficiency of 99.4%. Furthermore, the maximum surface temperature of the superhydrophobic MS reaches 57.5 °C under sunlight irradiation (1.0 kW/m2) due to the excellent photothermal heating conversion performance of MXene and lignin particles. When exposed to sunlight, the superhydrophobic MS can quickly absorb viscous crude oils up to 72 times its own weight. Also, the WCA of the superhydrophobic MS remains above 146° after 50 icing/deicing cycles, showing excellent photothermal anti-icing properties. Thus, this study presents an easy and low-cost method for designing photothermal superhydrophobic melamine sponges and opens a new avenue to the applications of efficient oil/water separation, fast crude oil recovery, and active deicing.

Porous lignin-based composites for oil/water separation: A review

Frequent oceanic oil spill incidents and the discharge of industrial oily wastewaters have caused serious threats to environments, food chains and human beings. Lignin wastes with many reactive groups exist as the byproducts from bioethanol and pulping processing industries, and they are either discarded as wastes or directly consumed as a fuel. To make full use of lignin wastes and simultaneously deal with oily wastewaters, porous lignin-based composites have been rationally designed and prepared. In this review, recent advances in the preparation of porous lignin-based composites are summarized in terms of aerogels, sponges, foams, papers, and membranes, respectively. Then, the mechanisms and the application of porous lignin-based adsorbents and filtration materials for oil/water separation are discussed. Finally, the challenges and perspectives of porous lignin-based composites are proposed in the field of oil/water separation. The utilization of abundant lignin wastes can replace fossil resources, and meanwhile porous lignin-based composites can be used to efficiently treat with oily wastewaters. The above utilization strategy opens an avenue to the rational design and preparation of lignin wastes with high-added value, and gives a possible solution to use lignin wastes in a sustainable and environmentally friendly way.

A facile approach for oil-water separation using superhydrophobic polystyrene-silica coated stainless steel mesh bucket

Inspired by traditional shaduf technology in the irrigation field, we fabricated a superhydrophobic stainless steel mesh bucket by layering polystyrene and SiO2 nanoparticles through a facile dip coating technique for effective oil-water separation. The superhydrophobic steel mesh bucket could effectively lift oil as well as microplastic pollutants from the water surface. The water contact angle of a two-layered polystyrene-silica coating was 158.5° ± 2°, while the oil contact angle was nearly 0°. The oil-water separation performance of superhydrophobic mesh was tested using several kinds of oil. The separation efficiency achieved for low viscous oil was 99.33 %, while 86.66 % efficiency was recorded for high viscous oil. The superhydrophobic mesh showed high durability against mechanical tests including bending, folding, twisting, adhesive tape tearing (25 cycles), and sandpaper abrasion (20 cycles). The mesh presented admirable thermal and chemical durability. The present superhydrophobic steel mesh bucket is a suitable candidate for large-scale application.

Photothermal, Magnetic, and Superhydrophobic PU Sponge Decorated with a Fe3O4/MXene/Lignin Composite for Efficient Oil/Water Separation

Frequent oil spills and the discharge of industrial oily wastewaters have become a serious threat to the environment, ecosystem, and human beings. Herein, a photothermal, magnetic, and superhydrophobic PU sponge decorated with a Fe3O4/MXene/lignin composite (labeled as S-Fe3O4/MXene/lignin@PU sponge) has been designed and prepared. The obtained superhydrophobic/superoleophilic PU sponge possesses excellent chemical stability, thermal stability, and mechanical durability in terms of being immersed in corrosive solutions and organic solvents and boiling water and being abrased by sandpapers, respectively. The oil adsorption capacities of the S-Fe3O4/MXene/lignin@PU sponge for various organic liquids range from 29.1 to 70.3 g/g, and the oil adsorption capacity for CCl4 can remain 69.6 g/g even after 15 cyclic adsorption tests. The separation efficiencies of the S-Fe3O4/MXene/lignin@PU sponge for n-hexane and CCl4 are higher than 98% in different environments (i.e., water, hot water, 1 mol/L NaOH, 1 mol/L NaCl, and 1 mol/L HCl). More importantly, the introduction of three light absorbers (i.e., Fe3O4, MXene, and lignin) into the S-Fe3O4/MXene/lignin@PU sponge shows a synergistic effect in the photothermal heat conversion performance, and the maximum surface temperature reaches 64.4 °C under sunlight irradiation (1.0 kW/m2). The separation flux of the S-Fe3O4/MXene/lignin@PU sponge for viscous LT147 vacuum pump oil reaches 35,469 L m-2 h-1 under sunlight irradiation, showing an increase of 27.3% compared to that of oil adsorption processes without the photothermal effect. Thus, the rational design of superhydrophobic sponges by introducing proper photothermal heat absorbers provides new insights into facile and cost-effective preparation of sponges for efficient oil/water separation.

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

The development of continuous oil-water separation processes has applications in the treatment of industrial oily wastewater and effective management of oil spills. In this research, the performance of a superhydrophobic-superoleophilic (SHSO) membrane in oil-water separation is investigated through dynamic tests. We investigate the effects of the total flow rate and oil concentration on the separation efficiency using an as-fabricated SHSO mesh tube. To construct the SHSO membrane, a tubular stainless steel mesh is dip-coated into a solution, containing a long-chain alkyl silane (Dynasylan F8261) and functionalized silica nanoparticles (AEROSIL R812). The as-prepared SHSO mesh tube illustrates a water contact angle of 164° and an oil contact angle of zero for hexane. A maximum oil separation efficiency (SE) of 97% is obtained when the inlet oil-water mixture has the lowest flow rate (5 mL/min) with an oil concentration of 10 vol %, while the minimum oil SE (86%) is achieved for the scenario with the highest total flow rate (e.g., 15 mL/min) and the highest oil concentration (e.g., 50 vol %). The water SE of about 100% in the tests indicates that the water separation is not affected by the total flow rate and oil concentration, due to the superhydrophobic state of the fabricated mesh. The clear color of water and oil output streams also reveals the high SE of both phases in dynamic tests. The outlet oil flux increases from 314 to 790 (L/m²·h) by increasing the oil permeate flow rate from 0.5 to 7.5 (mL/min). The linear behavior of the cumulative amounts of collected oil and water with time demonstrates the high separation performance of a single SHSO mesh, implying no pore blocking during dynamic tests. The significant oil SE (97%) of the fabricated SHSO membrane with robust chemical stability shows its promising potential for industrial-scale oil-water separation applications.

Surface modification of TiO2 nanoparticles with organic molecules and their biological applications

In recent years, titanium(IV) dioxide nanoparticles (TiO₂NPs) have shown promising potential in various biological applications such as antimicrobials, drug delivery, photodynamic therapy, biosensors, and tissue engineering. For employing TiO₂NPs in these fields, their nanosurface must be coated or conjugated with organic and/or inorganic agents. This modification can improve their stability, photochemical properties, biocompatibility, and even surface area for further conjugation with other molecules such as drugs, targeting molecules, polymers, etc. This review describes the organic-based modification of TiO₂NPs and their potential applications in the mentioned biological fields. In the first part of this review, around 75 recent publications (2017-2022) are mentioned on the common TiO₂NP modifiers including organosilanes, polymers, small molecules, and hydrogels, which improve the photochemical features of TiO₂NPs. In the second part of this review, we presented 149 recent papers (2020-2022) about the use of modified TiO₂NPs in biological applications, in which specific bioactive modifiers are introduced in this part with their advantages. In this review, the following information is presented: (1) the common organic modifiers for TiO₂NPs, (2) biologically important modifiers and their benefits, and (3) recent publications on biological studies on the modified TiO₂NPs with their achievements. This review shows the paramount significance of the organic-based modification of TiO₂NPs to enhance their biological effectiveness, paving the way toward the development of advanced TiO₂-based nanomaterials in nanomedicine.

Investigation of Oil-Water Separation on an F-SiO2/TiO2-Based Superhydrophobic/Superoleophilic Surface: Experiment Evaluation and MD Simulation

Experiment evaluation and mechanism analysis of separation performance are crucial for oily wastewater treatment. In this work, a fluorinated superhydrophobic/superoleophilic (F-SHPB/SOPL) surface was fabricated on a steel mesh substrate by double depositions of SiO₂-TiO₂ nanoparticles for high-roughness improvement and composite modification of fluorine-alkyl groups for low-energy achievement. Measurements of SEM, XPS, FTIR, laser scanning confocal microscope (LSCM), and excitation-emission matrix (EEM) were carried out for surface property characterization. The oil-water separation performances at the prepared F-SHPB/SOPL surface were investigated from experimental and simulation aspects. Separation tests, flux tests, and anti-contamination tests were performed by experimental methods. The results indicated that the surface showed excellent separation efficiencies (>99.2%) for oil-water mixture and oil-in-water emulsion, high permeate flux (>3000 L·m^-2·h^-1) for organic oils, and perfect anti-pollution/self-cleaning capacity for liquid and solid contaminations. The interaction energies and interaction distances were measured by ab initio molecular dynamics simulation (AIMD) simulations. With lower interaction energy (E_oil = -456.52∼-1044.22 eV) than that of water molecules (E_water = -172.73 eV) and shorter distance (D_oil = 4.42∼5.13 Å) than that of water molecules (D_water = 11.49 Å), oil molecules showed higher interaction stability than water molecules on the F-SHPB/SOPL surface. The calculation revealed the essence of the oil-water separation phenomenon. This work not only proposes the fabrication methodology of the SHPB/SOPL material but also elucidates the intermolecular interaction for oil-water separation. The results can provide a fundamental basis for separation operation and removal treatment in industrial and domestic applications.

Recent Advances in Superhydrophobic Papers for Oil/Water Separation: A Mini-Review

The separation of oceanic spilled oils and industrial oily wastewaters becomes a great challenge, and it is highly desirable to develop efficient materials for oil/water separation. As abundant sustainable resources, superhydrophobic papers (SPs) have drawn much attention because of low-cost and efficient oil/water separation. Herein, this mini-review summarizes recent advances of SPs in terms of design, preparation, and properties. On the basis of the many excellent properties of SPs (i.e., self-cleaning, durability, chemical corrosion resistance, and reusability), the oil/water separation performances (i.e., separation efficiency, permeation flux, and recyclability) of SPs as well as the corresponding mechanisms are discussed. The efficient oil/water separation property and recyclability of SPs make them promising candidates in the field of oily wastewater treatment.

Rigid, eco-friendly and superhydrophobic SiO2-Polyvinyl alcohol composite sponge for durable oil remediation

Development of durable and eco-friendly adsorbents for oil remediation is in great demands. However, most of adsorbents were designed to pursue large capabilities while ignored their strength after adsorbing oil, which might cause secondary oil spilling during complex salvage process. Herein, an eco-friendly and superhydrophobic SiO₂-modified polyvinyl alcohol composite (H-SiO₂-G-PVA) sponge with extraordinary rigid structure after oil adsorption is designed for durable oil remediation. Through a two-step hydrolysis-condensation process including deposition of silica microparticles and introduction of hexadecyltrimethoxysilane (HDTMS), a superhydrophobic H-SiO₂-G-PVA sponge has been successfully constructed. The sponge presents stable superhydrophobicity in various complex environments，therefore it efficiently adsorbs oil from water (up to 6 g g^-1) and separate surfactant-stabilized water/oil emulsion with high efficiency (>99%). Noticeably, the H-SiO₂-G-PVA sponge maintains tough strength (3.5 MPa) after oil adsorption, which ideally overcomes secondary oil spilling problem and endows the sponge with excellent recycling performances (>20 cycles). Meanwhile, the excellent biocompatibility of the sponge (high cell viability of 91.85%) ensures the potential for practical applications. This rigid, eco-friendly oil-adsorbing sponge that achieves stable superhydrophobicity and recyclability, fulfills the application needs for durable oil remediation.

Mussel-Inspired Durable TiO2/PDA-Based Superhydrophobic Paper with Excellent Self-Cleaning, High Chemical Stability, and Efficient Oil/Water Separation Properties

Oceanic oil spill and the discharge of industrial oily wastewaters can cause significant threats to the ecological environment and human health. Herein, we design a durable TiO₂/PDA-based superhydrophobic paper for efficient oil/water separation. Bioinspired from mussel adhesive proteins, the mechanical durability of the as-prepared superhydrophobic paper is enhanced by the deposition of polydopamine (PDA) onto cellulosic fibers via self-polymerization of dopamine. The TiO₂/PDA-based superhydrophobic paper shows a high water contact angle of 168.2° and an oil contact angle of ∼0°, exhibiting excellent superhydrophobicity and superoleophilicity. Furthermore, the as-prepared superhydrophobic paper possesses excellent chemical stability, thermal stability, and mechanical durability in terms of being immersed in corrosive solutions and solvents and boiling water and being subjected to the sandpaper abrasion test, respectively. More importantly, the separation efficiency of the TiO₂/PDA-based superhydrophobic paper for an oil/water mixture is 97.2%, and it maintains a separation efficiency above 94.3% even after 15 cyclic separation processes. Furthermore, the separation efficiency for water-in-oil emulsions is higher than 93.7% after 15 cyclic separation tests, showing its excellent recyclable stability for water-in-oil emulsions. Therefore, the rationally designed TiO₂/PDA-based superhydrophobic paper shows great potential in the practical applications of self-cleaning, antifouling, and oil/water separation.