Hydrophobic Sponge Research Articles

Synergistic enhancement of oil-water separation and flame retardant properties of melamine sponges based on 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and perfluorinated compounds

Facing the escalating issue of industrial wastewater discharge and its profound environmental repercussions, the creation of novel sponge materials that excel in oil-water separation while incorporating flame retardancy becomes critically urgent. Despite their superior absorption capabilities, conventional oil-water separation sponges typically overlook flame retardant features, a limitation that curtails their applicability. To address this gap, we have developed a multifunctional hydrophobic sponge through a sophisticated multi-step chemical self-assembly process. This method grafts 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and perfluorinated compounds onto melamine foam (MF), yielding a composite material designated as DOPO-PF@MF. DOPO-PF@MF boasts a dual functionality of hydrophobicity and flame retardance. Its modified surface exhibits a pronounced hydrophobic-lipophilic balance, with a static water contact angle of 134°. It also displays favorable wetting characteristics towards various organic solvents, such as methanol, ethanol, dimethylformamide, dichloromethane, and hexane. This material demonstrates an impressive adsorption capacity for these solvents, with the adsorption-desorption capacity for ethanol remaining consistent over ten cycles. Furthermore, DOPO-PF@MF efficiently separates emulsions of methylene chloride and water, showcasing its versatility. Moreover, DOPO-PF@MF exhibits commendable chemical resilience under extreme temperatures, ranging from 0 °C to 100 °C, and withstands both acidic and alkaline conditions (pH 1–14), preserving its structural integrity against corrosive substances. Most notably, it surpasses unmodified melamine foam in flame retardancy. The incorporation of DOPO fortifies the material's resistance to high-temperature ignition, effectively inhibiting flame propagation and reducing burn rate, enhancing safety measures.

Sustainable waste valorization: hydrophobic sponge from coconut fibers and expanded polystyrene for effective oil–water separation

Sustainable waste valorization: hydrophobic sponge from coconut fibers and expanded polystyrene for effective oil–water separation

Efficient cleanup of highly viscous spilled oil using a fast solar-heating and super hydrophobic sponge

A solar-heating sponge, in which the polypyrrole (PPy) coating plays the role of photothermal converter and carbon nanotubes (CNTs) act as the thermal conductor, was fabricated. The sponge can effectively convert sunlight into heat and fast conduct heat so that the temperature can rise to 80 °C within 30 s under 1 sun irradiation. Besides, the temperatures of the other parts rise synchronously with the top surface, unlike most reported sponges which had temperature differences between different parts. This advantage can avoid the decrease of diffusion rate of the oil in application. The sponge also exhibits super hydrophobility with a high water contact angle of 151.2°. The excellent solar-heating ability and hydrophobility make the sponge an efficient viscous oil adsorbent. The sponge can continuously and rapidly remove the spilled oil under solar irradiation. The coating composed of interconnected PPy nanosheets is firmly fixed on the surface of the elastic matrix via multiple H bonds. After 10 adsorption-desorption cycles, the adsorption capacity still maintains 97.2 %, without any change in hydrophobility. These advantages including fast solar-heating, super hydrophobility and high regenerability demonstrate that the sponge has great potential in oil spill treatment, especially highly viscous oils.

Same volume, larger output: 3D trapezoidal multi-interface solar evaporator for concentrated seawater desalination and wastewater treatment

With the scarcity of freshwater resources, solar desalination of seawater is a promising strategy for freshwater production. Compared to 2D evaporators with limited evaporation area, 3D evaporators can increase the evaporation area. However, traditional 3D evaporators cannot fully utilize the internal space of the evaporator for evaporation. In this study, a 3D trapezoidal multi-interface evaporator (Evap1), which composed of superhydrophilic sponges and superhydrophobic sponges arranged by alternate permutation for making full use of the inside structure of the evaporator to expand the actual evaporation area and achieve effective thermal management, were developed. The selective water transport channels and heat transfer channels were constructed by alternate permutation of hydrophilic and hydrophobic sponges in Evap1, while the top trapezoidal structure prevented heat from accumulating on the top surface of Evap1, which can enhance the efficiency of photothermal conversion. The Evap1 exhibited excellent evaporation rate of 3.6 kg m−2 h−1 under 1 sun illumination, and the evaporation rate was almost unchanged in brine with 20 wt% concentration for 8 h working. In addition, the Evap1 can achieve efficiently purificaiton of waste water containing dye, and the potential practical application of Evap1 was further proved by repeated and outdoor evaporation experiments.

Graphitic carbon nitride based fluorine-free hydrophobic sponges for the mitigation of microplastics, oil spillage, and harmful microbial growth in water

Water pollution poses significant environmental challenges due to the pervasive presence of microplastics, frequent oil spillage, and the proliferation of harmful microbial populations. Addressing these multifaceted pollution issues often necessitates distinct treatment strategies, potentially compromising the economic viability and causing secondary pollution. In response, this study presents a novel approach by developing three-dimensional sponges with interconnected pores to simultaneously combat these environmental concerns. In this work, Hexadecyltrimethoxysilane functionalized graphitic carbon nitride (h-GCN) hydrophobic sponges were fabricated in a simple and scalable method. The sponges with varying porosity and hydrophobicity were fabricated by controlling the amount of NaCl as the hard sacrificial agent incorporated into the Polydimethylsiloxane matrix. The hierarchical surface irregularity and surface energy of the sponges were influenced by the addition of h-GCN content. The resulting sponges showed remarkable properties of oil/organic solvent-water separation ability of 116 % for mineral oil to 832 % for chloroform. Leveraging their extensive porosity and hydrophobic nature, the sponges demonstrated near-complete removal of Poly (methyl methacrylate) (PMMA) microplastic particles from aqueous solutions. The hydrophobic sponges also showed excellent bacteriostatic properties by inhibiting the growth of Escherichia coli and Staphylococcus aureus. We anticipate that these fluorine-free hydrophobic sponges, with their multifaceted capability to mitigate diverse water pollutants and exhibit robust recyclability, hold promise for a range of environmental remediation applications.

Fluorine-Functionalized Covalent Organic Framework Superhydrophobic Modified Melamine Sponge for Efficient oil-water Separation.

Hydrophobic sponges have attracted significant interest in oil spills and water-oil separation as potential absorption materials due to their desirable absorptivity, selectivity, and elasticity. In this paper, a hydrophilic melamine sponge (MS) is transferred into a superhydrophobic sponge via polydimethylsiloxane (PDMS) modification followed by in situ growth of fluorine-functionalized covalent organic framework (denoted as TFA-COF) nanoparticles. Therefore, the PDMS@TFA-COF@MS sponge was successfully prepared for efficient oil-water separation. The resultant PDMS@TFA-COF@MS exhibits superhydrophobic properties with a water contact angle of 156.7°. The superhydrophobic sponge has selectivity adsorption for different organic solvents and oils from water as well as oil-water separation efficiency (96% after 30 cycles) and oil absorption capacity (12 646% after 30 cycles). Meanwhile, the PDMS@TFA-COF@MS sponge exhibits strong thermal stability and flame retardancy in addition to having exceptional resistance to chemical corrosion in acidic, alkaline, and salt solutions. Moreover, the surfactant-stabilized oil-in-water emulsion could be efficiently separated by the sponge. Therefore, the prepared superhydrophobic PDMS@TFA-COF@MS sponge demonstrates possible uses for long-life oil-water separation applications.

Rapid cell isolation in breastmilk in a non-clinical setting by a deterministic lateral displacement device and selective water and fat absorption.

Breastmilk is a reliable source of biomarker-containing, sloughed breast cells that have the potential to give valuable health insights to new mothers. Furthermore, known DNA-based markers for pregnancy-associated breast cancer are chemically stable and can be safely stored on a commercially available FTA® Elute Micro (EM) card, which can subsequently be mailed to a testing facility for the cost of a stamp. In theory, this archiving process can be performed by nonprofessionals in very low-resource settings as it simply requires placing a drop of breastmilk on an EM card. Although this level of convenience is paramount for new mothers, the low cell density of breastmilk complicates archiving on an EM card as such commercial products and associated protocols were designed for high-cell density physiological fluids such as blood. In this study, we present the use of a deterministic lateral displacement (DLD) device combined with porous superabsorbent polymers and hydrophobic sponges to achieve simple and low-cost cell enrichment in breastmilk. As the critical separation diameter in a DLD device is more heavily dependent on lithographically controlled pillar layout than fluid or flow properties, our use of DLD microfluidics allowed for the accommodation of both varying viscosities in human breastmilk samples and a varying pressure of actuation resulting from manual, syringe-driven operation. We demonstrate successful cell enrichment (>11×) and a corresponding increase in the DNA concentration of EM card elutions among breastmilk samples processed with our hybrid microfluidic system. As our device achieves sufficiently high cell enrichment in breastmilk samples while only requiring the user to push a syringe for 4 min with reasonable effort, we believe that it has high potential to expand EM card DNA archiving for diagnostic applications with low-cell density physiological fluids and in low-resource settings.

Transparent Oil-Water Separating Hydrophobic Sponge Prepared from a Pickering High Internal Phase Emulsion Stabilized by Octadecyltrichlorosilane Grafting Carbon Nanotubes.

Increasingly, oil spills and industrial discharges are wreaking havoc on the water environment; in order to efficiently separate oil and water from sewage containing oil or organic solvents, a novel porous polymer (P(EHA-co-BA)) was prepared by Pickering high internal phase emulsion (HIPE) template method. To obtain polyHIPE with better oil/water separation capacities, octadecyltrichlorosilane (OTS)-modified carbon nanotubes (CNTs) and surfactants were used as costabilizers for HIPE, which improved the stability of HIPE as well as the mechanical properties and the separation efficiency of polyHIPE. In the presence of 1 wt % OTS-CNT adding in the oil phase, 1%OTS-CNT polyHIPE has high porosity (92.21%), favorable hydrophobicity (a water contact angle of 128°), and excellent mechanical properties. As a result, 1%OTS-CNT polyHIPE has high absorption of oils and oily solvents, e.g., dichloromethane up to 36 g/g, and maintains an absorption efficiency of >97% after 20 reapplications. In the formulation of polyHIPE, cinnamaldehyde (CA) has been added to provide superior antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). It appears that the novel polyHIPE proposed in this work is a reusable antibacterial porous polymer with promising applications for oil-water separation.

Study on the Influence of the Reduced Graphene Oxide Coating on the Hydrophobicity of PU Sponge for Oil Recovery

In order to produce a hydrophobic material for oil removal from surface waters, in this study, the reduced graphene oxide coated PU sponges (rGO@PU) were prepared by ultrasonication of PU sponges with suspension of rGO in ethanol. The chemical structure of the rGO coatings was investigated by X-ray diffraction and FT-IR spectroscopy methods. The surface morphology of the obtained materials was also examined by SEM. The influence of the rGO loadings and the number of coatings on the hydrophobicity of the materials was investigated. The testing on the surface hydrophobicity indicated that the water drops were remained on the surface of rGO@PU for 4.5 - 5 hours. The results indicated that the best hydrophobic sponge was obtained at the rGO loading of 3 mg/mL and after three times of coatings. The water contact angle (WCA) of the optimal rGO@PU was up to 119°. The kerosene oil absorption capacity of the rGO@PU in 5 minutes is 32.34 g/g. Besides, the oil-water separation ability of the material was also investigated by passing the kerosene-water mixture through a filter funnel containing the synthesized porous material rGO@PU. The result indicated that the separation efficiency of the material was 85%. The recyling test was conducted by squeezing the saturated absorbed sponges and applying the desorbed sponges for the next cycle tests. After 10 times of recycling, the amounts of kerosene absorption on the rGO@PU were maintained from 4.39 - 5.33 g, implying the excellent recyclability of the material.

Hydrophobic sponge derived from natural loofah for efficient oil/water separation

Polymer sponge and carbon aerogel have received widespread attention because of their high specific surface area and controllable wettability. However, the complex manufacturing processes and non-renewable raw materials of these porous materials have limited their practical applications. Herein, we conducted the thermal chemical vapor deposition (CVD) of hydrophobic methyltrichlorosilane (MTCS) on loofah sponge (LS), which led to the formation of a novel oil-adsorbing hydrophobic MTCS-coated loofah sponge (MTCS-LS). The obtained MTCS-LS retained the interconnected 3D porous structure and robust structure stability of natural LS, while exhibited dramatically improved hydrophobicity with contact angle of 137° in the pH range of 2–12. This unique characteristic conferred MTCS-LS selective oil removal ability from water, and MTCS-LS possessed oil sorption capacity of 13 times of its dry weight and high separation efficiency (>92%). Results of the adsorption-squeezing tests proved that the excellent reversible compressibility of natural LS was maintained after the silanization modification. Compared to other known oil-adsorbing materials, the MTCS-LS displayed apparent advantage in adsorbing oils with high viscosity (e.g. crude oil). Our study provides a simple approach to exploitation of biomass in pollutants removal.

Inside Cover Picture

In nature, the leaf veins skeleton and mesophyll are distinctly different in both structure and composition, however, the robust integration synergistically contributes to the unique combination of various properties, and fulfills specific functions. Inspired by such structure‐property relationship, a simple yet effective strategy is developed to integrate the hydrophobic sponge skeleton with hydrogel networks with robust interface. More details are discussed in the article by Liu et al. on page 2635—2640.image

Polydimethylsiloxane-carbon nanotubes-based hydrophobic sponge for treatment of palm oil mill effluents with enhanced reusability

Improper treatment and discharge of palm oil mill effluents (POME) into the water bodies have become one of the leading causes of aqueous contamination due to the release of a large volume of POME into the environment. This study reports the development of poly(dimethylsiloxane) (PDMS) and carbon nanotubes (CNTs) supported sorbent material to reduce the oil and grease (O&G) content of POME. The morphology and chemical properties of the prepared material were characterized using SEM-EDX, FTIR, Raman spectroscopy, XRD, TGA, water contact angle, and pH point of zero charge (pHPZC) analysis. CNT-PDMS optimal O&G removal capacity has been determined using batch experiments with varying parameters, including CNT wt%, contact time, pH, and initial POME concentration. The introduction of CNT significantly improves the oil sorption capacity almost three times as compared to pure PDMS. The maximum sorption capacity achieved was 658.09 ± 7.21 mg/g with the O&G removal of 84% within 8 min using initial POME concentration (1:20) and at room temperature. The study shows that the O&G sorption process using PDMS and CNT-PDMS-0.8 followed the pseudo-second-order kinetic model. Moreover, the adsorption isotherms study revealed that the adsorption process can be described by the Freundlich isotherm model based on the R2 values of 0.98075 and 0.99981 for PDMS and CNT-PDMS-0.8, respectively. Furthermore, the composites also show excellent reusability, retaining high O&G sorption and removal even after the tenth cycle.

The effect of chemical bond and solvent solubility parameter on stability and absorption value of functionalized PU sponge

Seawater pollution from various sources such as industrial effluents, ship washing at sea, and oil spills harm humans and the marine environment. Therefore, finding ways to eliminate this pollution is crucial. This study successfully modified a polyurethane sponge through a simple dip-coating method with functionalized graphene oxide incorporating octadecylamine and oleic acid, resulting in a hydrophobic sponge capable of absorbing crude oil and various organic solvents. Characterization analyses confirmed the synthesis. The absorption capacity of the modified sponges was examined, for example, the PU sponge has absorbed 4 g/g engine oil, while the modified GO-ODA-PU sponge has increased its absorption to 36 g/g. The GO-ODA-PU sponge demonstrated great reusability compared to the GO-OA-PU sponge owing to the strong covalent bond formed between GO and ODA, which is superior to the weak hydrogen bond formed between GO and OA. The absorption capacity of the GO-OA-PU sponge decreased by 30%. The contact angle test showed that GO-ODA-PU and GO-OA-PU sponges had contact angles of 131° and 115°, respectively. Additionally, the GO-ODA-PU sponge performed optimally for semi-polar solvents in the solubility parameter range of 18–19, with its absorption capacity reaching its maximum value. The amount of oil recycling is even possible up to 98%.

One-step preparation of robust elastic plastic polyvinyl chloride sponges with a layered structure for highly efficient separation of water-in-oil emulsions

To address the environmental pollution and human health issues caused by oily wastewater and PVC plastic waste, a practical zero-waste solution has been developed. In this study, PVC sponges with superlipophilic and superhydrophobic properties were prepared using vapor induced phase inversion and recycling PVC food wrap, without the use of any additives. This sponge effectively separates oil and water. The pore size of PVC sponges could be adjusted by varying the PVC concentration and solvent ratio, which led to improvements in pore density, specific surface area, porosity, oil sorption capacity, and emulsion separation performance. The emulsion separation experiment demonstrated that the 7 wt% PVC sponge (7-0-1) can efficiently separate oil from water-in-oil emulsion, with excellent separation efficiency and a flux of 161.5 L·m−2·h−1·bar−1. Moreover, the sponge exhibits impressive properties such as elastic recovery, flexibility, self-cleaning, and mechanical strength. Remarkably, even after recycling, the sponge maintains its hydrophobicity and emulsion separation performance. This hydrophobic sponge has great potential for mass production and oil–water separation such as in oil spill accidents.

Hierarchical Sponge‐Hydrogel Hybrid Structures with Robust Interfaces†

Comprehensive SummarySoft materials including elastomers and hydrogels are playing critical roles in a variety of fields, including bioelectrodes, batteries, supercapacitors, biomedical scaffolds, and solar vapor absorbents. Integrating hydrophobic sponges (i.e., mechanical robustness, elasticity and macroscopic porous structure) and hydrophilic hydrogels (i.e., autonomous water absorption and transportation, biocompatibility) within one unit could readily combine the complementary characters from each component, making a number of future research directions and applications possible. We propose a simple yet effective strategy to construct sponge‐hydrogel hybrid structures with robust hydrophobic‐hydrophilic interface. The sponge scaffold imparts the sponges‐hydrogel hybrids with desirable mechanical robustness, elasticity and macroscopic pores. On the other hand, the incorporated hydrogel component endows the hybrids with high water content (98 wt% hydrogel and 2 wt% sponge), superior compatibility, and nanoscale pores allowing for storage and transportation of various chemical and biological molecules. We further demonstrate that the introduction of hydrophilic hydrogel components could effectively improve the liquid absorption capability, blood coagulation rate, hemostatic capacity and hemocompatibility, thus promising as hemostatic agents.

Facile fabrication of robust superhydrophobic polyurethane sponge modified with polydopamine- silica nanoparticle for effective oil/water separation

Porous superhydrophobic materials with high mechanical stability have a significant amount of potential for oil-water separation in practice. In this study, a superhydrophobic material with strong hydrophobic coating adhesion was developed using a polyurethane sponge. The interior and exterior surfaces of the porous polyurethane material were coated using a two-step technique. The sponge was treated with poly (dopamine) to modify its skeleton, allowing the second layer to adhere readily. The second layer of silica applied to the surface of the sponge functions as a superhydrophobic layer. The modified sponge's water contact angle was approximately 156.2° ± 5°, compared to 78° ±2° for the original sponge, demonstrating its superhydrophobic nature. The fabricated sponge is capable of separating and absorbing 43.3–51 times of its initial mass from an oil-water mixture, depending on the type of oil used in the test. Fifteen cycles of oil-water separation were followed by chemical cleaning of the hydrophobic sponge. After undergoing these cycles, the hydrophobic nature and absorption capacity of the produced sponge were preserved. Over a broad pH range, the hydrophobicity of the superhydrophobic sponge was studied, and the results indicated that hydrophobicity was substantially maintained even under harsh pH operating conditions. The water contact angle of the sponge was measured to be 145° ± 1° and 140° ± 1°, respectively, after 12 h of immersion in strong acids and bases.

Facile fabrication of hydrophobic covalent organic framework decorated melamine sponge for efficient separation of immiscible oil-water mixture and water-in-oil emulsion

Frequent oil spills and oily sewage have caused serious environmental problems. Sponges have attracted great attention in oil-water separation due to their low cost and high porosity, but it still remains challenge to hydrophobic modification of sponge in facile and scalable manner. Here is reported a facile fabrication of porous and hydrophobic sponge composite (MS@COF) with effective oil-water separation by in-situ growth of hydrophobic TFB-BD(Me)2 COF on the surface of melamine sponge. Combining the porous structure of the sponge and hydrophobicity of COF, the composite can separate oil-water mixture and water-in-oil emulsions in a fast way. The prepared MS@COF showed oil adsorption capacity up to 160 g g-1. In addition, continuous separation of oil-water mixture was demonstrated using a peristaltic pump with a separation rate of 50 mL min-1. More importantly, the composite could separate surfactant-stabilized water-in-oil emulsions with separation efficiency of 98.8%. The oil-water mixture and oil-water emulsion separation ability of the composite persisted after 50 separation cycles thereby demonstrating good recyclability. The composite also showed good chemical stability, mechanical and flame retardancy. This work introduces a new approach for the synthesis of hydrophobic sponge decorated with COF nanoparticles for oily wastewater treatment and organic pollutant removal on water surfaces.

A solvent-template ethyl cellulose-polydimethylsiloxane crosslinking sponge for rapid and efficient oil adsorption

Lipophilic adsorbents for oil-water separation are usually synthesized using the template method, in which hydrophobic materials are coated on a ready-made sponge. Herein, a novel solvent-template technique is used to directly synthesize a hydrophobic sponge, by crosslinking polydimethylsiloxane (PDMS) with ethyl cellulose (EC) which plays a vital role in the formation of 3D porous structure. The as-prepared sponge has advantages of strong hydrophobility, high elasticity, as well as excellent adsorption performance. In addition, the sponge can be readily decorated by nano-coatings. After the sponge was simply dipped in nanosilica, the water contact angle increases from 139.2° to 144.5°, and the maximum adsorption capacity for chiroform rises from 25.6 g/g to 35.4 g/g. The adsorption equilibrium can be reached within 3 min, and, the sponge can be regenerated by squeezing, without any change in hydrophobility or evident decline in capacity. The simulation tests of emulsion separation and oil-spill cleanup demonstrate that the sponge has great potential in oil-water separation.

Self-stratifying coating enables facile fabrication of robust superhydrophobic sponges for oil-water mixture separation

Superhydrophobic polymer sponges are a promising solution to the serious environmental crisis caused by oil spills in modern society, given their excellent sorption capacity and high selectivity, if designed well. However, realizing such hydrophobic sponges in an eco-friendly, easy, and cost-effective way is still a challenging task, despite several reported methods. Here, we report a facile approach to obtaining a superhydrophobic sponge using self-stratifying coating technology. The process briefly involves dip coating a pre-made commercial sponge in our prepared self-stratifying resin, followed by curing. The prepared superhydrophobic sponges showed excellent oil sorption capacity towards various organic solvents, with adsorptive capacity values ranging from ∼100 to 200 g/g and the capability to be reused >20 times with an adsorption retention capacity of above 95 % of the first cycle. In addition, the modified sponge presented good mechanical stability and thermal stability (up to 350 °C). With the advantages of the fabrication method and the benefits in oil-water separation, the modified sponge has promising applications in the field of oil spill treatment and environmental remediation.

Facile fabrication of solar-heating and Joule-heating hyperelastic MXene-modified sponge for fast all-weather clean-up of viscous crude oil spill

Developing rational sorbent for viscous crude oil clean-up is still a daunting challenge, which requires rapid oil-uptake capability and scalable fabrication process. Herein, a heatable hydrophobic sponge sorbent (H-MXene/PVA/MS) with excellent light/Joule-heating performances was fabricated by a simple and feasible top-down approach. MXene nanosheets firmly coated on the substrate skeleton gave the sorbent outstanding ability to convert solar/electricity into heat rapidly due to the localized surface plasmon resonance (LSPR) effect and ultrahigh metallic conductivity. The surface temperature of H-MXene/PVA/MS could reach about 80 ℃ under 1.0 sun irradiation within 30 s and 125 ℃ under a low applying voltage of 6 V within 25 s. The rapid and sufficient heat generation on the sorbent would effectively warm the surrounding oil and accelerate its absorption. The oil absorption rate under 1.0 sun irradiation (1 kW/m2) improved about 41.5 times compared to the unheated sorbent. Moreover, the sorbent showed practical application potential in harsh environments due to its high coating firmness, durability, elasticity, and suitability for large-scale production and operations. Thus, the easily-prepared H-MXene/PVA/MS sorbent, which mainly focuses on solar-heating, supplemented by Joule-heating, provides an efficient and energy-efficient strategy for addressing large-scale viscous oil spill clean-up.