Durable super-hydrophobic PDMS@SiO2@WS2 sponge for efficient oil/water separation in complex marine environment

Mechanical and optical properties assessment of an innovative PDMS/beeswax composite for a wide range of applications

Polydimethylsiloxane (PDMS) is an elastomer that has received primary attention from researchers due to its excellent physical, chemical, and thermal properties, together with biocompatibility and high flexibility properties. Another material that has been receiving attention is beeswax because it is a natural raw material, extremely ductile, and biodegradable, with peculiar hydrophobic properties. These materials are applied in hydrophobic coatings, clear films for foods, and films with controllable transparency. However, there is no study with a wide range of mechanical, optical, and wettability tests, and with various proportions of beeswax reported to date. Thus, we report an experimental study of these properties of pure PDMS with the addition of beeswax and manufactured in a multifunctional vacuum chamber. In this study, we report in a tensile test a 37% increase in deformation of a sample containing 1% beeswax (BW1%) when compared to pure PDMS (BW0%). The Shore A hardness test revealed a 27% increase in the BW8% sample compared to BW0%. In the optical test, the samples were subjected to a temperature of 80 °C and the BW1% sample increased 30% in transmittance when compared to room temperature making it as transparent as BW0% in the visible region. The thermogravimetric analysis showed thermal stability of the BW8% composite up to a temperature of 200 °C. The dynamic mechanical analysis test revealed a 100% increase in the storage modulus of the BW8% composite. Finally, in the wettability test, the composite BW8% presented a contact angle with water of 145°. As a result of this wide range of tests, it is possible to increase the hydrophobic properties of PDMS with beeswax and the composite has great potential for application in smart devices, food and medicines packaging films, and films with controllable transparency, water-repellent surfaces, and anti-corrosive coatings.

Superelastic chitin nanofibril/chitosan aerogel for effective circulating and continuous oil-water separation

Elastic and hydrophobic aerogels have received a lot of attention in dealing with the increasing oil pollution due to their recyclable properties. Herein, we present an ultralight and superelastic aerogel with highly oriented polygon structure based on chitin nanofibril (ChNF) and chitosan (CS) by directional freezing. The chemical cross-linking enables good mechanical strength at low aerogel density. After 500 compression-release cycles, the aerogel can retain the deformation recovery rate of 88 % in air, demonstrating the excellent resilience. The bio-based aerogel has high absorption capacity (52-114 g/g) for various oils and organic solvents, and it is able to achieve the absorption retention of 90 % even after 20 absorption-extrusion cycles. Moreover, owing to the good elasticity, the pore size of the aerogel can be adjusted by compression to selectively separate water-in-oil emulsions of different particle sizes with separation efficiencies higher than 99.5 %. The bio-based aerogel with good cycle performance has broad application prospects in the field of oil-water separation.

Assessment of various forms of cellulose-based Luffa cylindrica (mat, flakes and powder) reinforced polydimethylsiloxane composites for oil sorption and organic solvents absorption

Oil spillage has damaged public health noticeably and contributed to significant environmental deterioration. As a result, a significant amount of effort has been spent on investigating and developing the sorbent materials capable of separating oil from water. Thus, the sorbent materials that could be effective particularly in oil spill disposal and resolve such environmental issue remain to be explored. We have proposed luffa cylindrica (LC)-polydimethylsiloxane (PDMS) composite forms to remove the oil and organic components that might be hazardous to aquatic organisms. The scaffolds were fabricated using hand lay-up method with various forms of luffa cylindrica i.e., LC mat, flakes and powder. Various characterizations such as scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), effective porosity, surface wettability, mechanical stability, cytotoxicity and sorption behavior with respect to oil, phosphate buffer saline (PBS) and few organic solvents were performed. The results showed that the scaffold in combination with P-L flakes was highly effective in eradicating oil spills and removing harmful components of crude oil. Scaffolds composed of P-L mat, P-L flakes, P-L powder, and PDMS (P) exhibited oil absorption efficacy around 16.09 ± 4.62 %, 24.49 ± 3.55 %, 15.52 ± 2.67 % and 5.52 ± 1.44 %, respectively. We anticipate that the proposed scaffolds have the tremendous potential to provide a solution to this significant environmental remediation issue and to serve as a cost-effective method for removing oil spills and hazardous crude oil components.

Robust Superhydrophobic PDMS@SiO2@UiO66-OSiR Sponge for Efficient Water-in-Oil Emulsion Separation

A major challenge in oil/water separation is the processing of surfactant-stabilized emulsions from the water medium. One of the feasible schemes of emulsion separation is the porous melamine sponge coupled with functional particles. Here, we proposed a novel superhydrophobic metal-organic framework (MOF)-based sponge for water-in-oil emulsion separation. The porous melamine sponge was combined with poly(dimethylsiloxane) (PDMS)-coated hydrophobic SiO₂ and UiO66-OSiR particles were prepared for demulsification via the one-step dipping method for the first time. The PDMS@SiO₂@UiO66-OSiR sponge revealed excellent superhydrophobicity at a water contact angle of 160.7° and superlipophilicity at an oil contact angle of 0°. Compared with the pristine melamine sponge, the size-controllable PDMS@SiO₂@UiO66-OSiR sponge could separate stabilized water-in-oil emulsions with ultrahigh separation efficiency (>98.64%) and high flux (e.g., 970 L·m^-2·h^-1). Meanwhile, the PDMS@SiO₂@UiO66-OSiR sponge exhibited superior durability and mechanical reusability. Under harsh conditions such as strong acid and alkali, organic solvent corrosion, etc., all water contact angles of the PDMS@SiO₂@UiO66-OSiR sponge were over 152°. Furthermore, the stress decreased by 5% when the sponge was subjected to 10 loading/unloading compression cycles at a constant strain of 60%. These results demonstrate that the PDMS@SiO₂@UiO66-OSiR sponge can efficiently separate water-in-oil emulsions through its adjustable porous structure coupled with demulsification and hydrophobic particles. This study provides a step forward in developing a feasible strategy for the MOF-based sponge for emulsion separation.

Preparation of 2D Materials and Their Application in Oil-Water Separation

The problems of environmental pollution are increasingly severe. Among them, industrial wastewater is one of the primary sources of pollution, so it is essential to deal with wastewater, especially oil and water mixtures. At present, biomimetic materials with special wettability have been proven to be effective in oil-water separation. Compared with three-dimensional (3D) materials, two-dimensional (2D) materials show unique advantages in the preparation of special wettable materials due to their high specific surface area, high porosity, controlled structure, and rich functional group rich on the surface. In this review, we first introduce oil-water mixtures and the common oil-water separation mechanism. Then, the research progress of 2D materials in oil-water separation is presented, including but not limited to their structure, types, preparation principles, and methods. In addition, it is still impossible to prepare 2D materials with large sizes because they are powder-like, which greatly limits the application in oil-water separation. Therefore, we provide here a review of several ways to transform 2D materials into 3D materials. In the end, the challenges encountered by 2D materials in separating oil-water are also clarified to promote future applications.

Hygroscopic ramie fabrics for recovering highly viscous low sulfur fuel oil

Low sulfur fuel oils (LSFOs) with less than 0.5% sulfur content have been mandated for marine vessels by the International Maritime Organization since 2020. However, owing to the low dispersibility and high viscosity of LSFOs, their oceanic spills are difficult to clean using conventional response systems. In this study, we propose a superhydrophilic and hygroscopic ramie to clean spilled LSFO. To this end, a raw ramie fiber, which is intrinsically hydrophobic, was treated using a mild alkali to remove its waxy, rough, and gummy veneer and reveal a smooth surface. This substantially improved its hygroscopic nature, superhydrophilicity, and water-retention, while preserving its mechanical durability in dry and wet environments. The hygroscopic ramie exhibited underwater superoleophobicity and self-cleaning abilities against highly adhesive LSFOs. Two proofs-of-concept are demonstrated in this study-an oil-proof glove for maximizing oil repellency and a direct oil-scooping device for simple and continuous recovery of spilled oil with high efficiency.

Phytic acid and graphene oxide functionalized sponge with special-wettability and electronegativity for oil-in-water emulsion separation in single-step

Developing an emulsion separation material with one-step in-situ purifying capability and improved security in applications, especially for subsequent scale-up, is valuable but remains a challenge. Herein, the amphiphilic sponge (PA@RGO@MS) was prepared via impregnation and in-situ growth of the negatively charged hydrophilic phytic acid (PA) and the hydrophobic reduced graphene oxide (RGO) on the surface of the melamine sponge (MS) and applied in emulsion purification. The mechanics, wettability, absorption performance of the PA@RGO@MS were analyzed to identify its potential for stable demulsification. Results show that the PA@RGO@MS could purify emulsions (turbidity removal rate = 99.7%; TOC removal rate = 94.14%) in-situ in one step by simple shock absorption, profited from the hydrophilic and demulsification capability of PA, oil absorption of RGO, and wide reaction and storage space of MS. Targeting the emulsion with distinct properties (density, viscosity, and concentration) of the oil phase, the PA@RGO@MS could efficiently enable the purification. Meanwhile, the powerful flame-retardant granted from PA ensures the safe shipment and storage of sponges. The favorable cyclability (turbidity removal rate > 98.5% and TOC removal rate > 89.5% after 10 cycles) and diversified operating modes enhance the practical value of the PA@RGO@MS.

Superhydrophobic polyurethane sponge based on sepiolite for efficient oil/water separation

Massive oil leakage accidents and illegal discharge of oily wastewater have not just destroyed the sustainability of the ecological environment but caused permanent damage to marine ecosystems, which makes it urgent to handle it. In this paper, by means of sol-gel, micro-nan silica that grew from the surface of fibrous sepiolite was organically modified with 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane (PFDS). The superhydrophobic sepiolite/silica firmly attached to the surface of polyurethane sponge under the action of oily epoxy resin with strong adhesion. The sponge exhibited superhydrophobicity and excellent selective oil adsorption capacity (19.98-40 times of their own weight). More importantly, besides the effective separation of immiscible oil-water mixtures (the separation rate reached 98.72%), it could also efficiently separate oil with water and oil with salt solution emulsions. In addition, the sponges kept hydrophobic even after floating in extremely corrosive liquids for 20 h, showing a strong resistance to strong acidic as well as alkaline liquids. After 100 times of mechanical compression, the three-dimensional structure of sponge held still and the water contact angle was greater than 144°, demonstrating an excellent mechanical stability, which provided a reference for its practical application in oil-water separation.

Low-Cost Multifunctional Vacuum Chamber for Manufacturing PDMS Based Composites

Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in several areas of activity, due to its excellent characteristics and properties, such as biocompatibility, flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other materials promotes the desired changes to broaden its range of applications in various fields of science. However, the heating, mixing and degassing steps of the manufacturing process have not received much attention in recent years when it comes to blending with solid materials. For instance, PDMS has been extensively studied in combination with waxes, which are frequently in a solid state at room temperature and as a result the interaction and manufacturing process are extremely complex and can compromise the desired material. Thus, in this work it is proposed a multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing process of PDMS composites combined with additives, blends and different kinds of solid materials. The MVC developed in this work allows to control the mixing speed parameters, temperature control and internal pressure. In addition, it is a low cost equipment and can be used for other possible modifications with different materials and processes with the ability to control those parameters. As a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the heating and mixing step and approximately 200% at the last degassing step. Regarding the complete manufacturing process, it is possible to achieve an improvement over 150%, when compared with the conventional manufacturing process. When compared to maximum tensile strength, specimens manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The samples have also shown a 9% improvement in transparency at room temperature and 12% at a temperature of about 75 °C. It should be noted that the proposed MVC can be used for other blends and manufacturing processes where it is desirable to control the temperature, agitation speed and pressure.

A facile and effective strategy to develop a super-hydrophobic/super-oleophilic fiberglass filter membrane for efficient micron-scale water-in-oil emulsion separation

In order to achieve efficient micron-scale water-in-oil emulsion separation, a facile and effective strategy is developed to prepare a super-hydrophobic/super-oleophilic fiberglass filter membrane (FGm). Methyl-trichlorosilane (MTS) is successfully cross-linked on the surface of the fiberglass filter membrane (FGm) and aggregates into a 3D nanowire array to provide low surface energy. Nano fumed hydrophobic silica (SH-SiO₂) is used to construct the well-defined nanosphere structure on the surface of FGm and enhance the ability of the membrane to resist extreme conditions. The optimally modified membrane displays outstanding super-hydrophobic properties with a contact angle of 156.2°. It is impressive to find that the MTS@SH-SiO₂@FGm not only demonstrates the ability to separate water-in-oil emulsions with a particle size of less than 20 μm, but also the removal efficiency of separation has reached 99.98%. More attractively, the membrane still has stable super-hydrophobic features and reusable water-in-oil emulsion separation performance even under exposure to diverse harsh conditions, including extremely acidic corrosive solutions and ultra-high temperature systems.

In order to achieve efficient micron-scale water-in-oil emulsion separation, a facile and effective strategy is developed to prepare a super-hydrophobic/super-oleophilic fiberglass filter membrane (FGm).

Polydimethylsiloxane Composites Characterization and Its Applications: A Review

Polydimethylsiloxane (PDMS) is one of the most promising elastomers due its remarkable proprieties such as good thermal stability, biocompatibility, corrosion resistance, flexibility, low cost, ease of use, chemically inertia, hyperplastic characteristics, and gas permeability. Thus, it can be used in areas such as microfluidic systems, biomedical devices, electronic components, membranes for filtering and pervaporation, sensors, and coatings. Although pure PDMS has low mechanical properties, such as low modulus of elasticity and strength, it can be improved by mixing the PDMS with other polymers and by adding particles or reinforcements. Fiber-reinforced PDMS has proved to be a good alternative to manufacturing flexible displays, batteries, wearable devices, tactile sensors, and energy harvesting systems. PDMS and particulates are often used in the separation of liquids from wastewater by means of porosity followed by hydrophobicity. Waxes such as beeswax and paraffin have proved to be materials capable of improving properties such as the hydrophobic, corrosion-resistant, thermal, and optical properties of PDMS. Finally, when blended with polymers such as poly (vinyl chloride-co-vinyl acetate), PDMS becomes a highly efficient alternative for membrane separation applications. However, to the best of our knowledge there are few works dedicated to the review and comparison of different PDMS composites. Hence, this review will be focused on PDMS composites, their respective applications, and properties. Generally, the combination of elastomer with fibers, particles, waxes, polymers, and others it will be discussed, with the aim of producing a review that demonstrates the wide applications of this material and how tailored characteristics can be reached for custom applications.

Highly Efficient Amorphous Carbon Sphere-Based Superhydrophobic and Superoleophilic Sponges for Oil/Water Separation

In this experimental study, a commercially available polyurethane (PU) sponge coated with amorphous carbon spheres (ACSs) is investigated for oil/water separation. The ACSs synthesized using chemical vapor deposition are embedded in the PU sponge by a simple dip-coating method. The superhydrophobic ACS-PU sponge exhibits a water contact angle (WCA) of 156.2 ± 1° and a sliding angle <5°. The prepared sponge exhibits high absorption capacity, removal of oil spills from water, and demulsification of an oil-in-water emulsion. Absorption capacities of 32-68 times the ACS-PU sponge weight were obtained for different organic solvents and oils. It was found that the prepared ACS-PU sponge can effectively absorb oils under both static and turbulent conditions. Compared with the reported studies on the loading of different carbon materials in sponges for oil/water separation, ACSs in PU have a low loading percentage of ∼7 wt % and better absorption recyclability. The method proposes a simple and cost-effective preparation technique of highly hydrophobic and oleophilic ACS-PU sponges for effective oil/water separation.