Surface modification of polymeric foams for oil spills remediation

A review of the prospects, efficacy and sustainability of nanotechnology-based approaches for oil spill remediation

Numerous marine oil spill incidents and their environmental catastrophe have raised the concern of the research community and environmental agencies on the topic of the offshore crude oil spill. The oil transport through oil tankers and pipelines has further aggravated the risk of the oil spill. This has led to the necessity to develop an effective, environment-friendly, versatile oil spill clean-up strategy. The current review article analyses various nanotechnology-based methods for marine oil spill clean-up, focusing on their recovery rate, reusability and cost. The authors weighed the three primary factors recovery, reusability and cost distinctively for the analysis based on their significance in various contexts. The findings and analysis suggest that magnetic nanomaterials and nano-sorbent have been the most effective nanotechnology-based marine oil spill remediation techniques, with the magnetic paper based on ultralong hydroxyapatite nanowires standing out with a recovery rate of over 99%. The chitosan-silica hybrid nano-sorbent and multi-wall carbon nanotubes are also promising options with high recovery rates of up to 95-98% and the ability to be reused multiple times. Although the photocatalytic biodegradation approach and the nano-dispersion method do not offer benefits for recovery or reusability, they can nevertheless help lessen the negative ecological effects of marine oil spills. Therefore, careful evaluation and selection of the most appropriate method for each marine oil spill situation is crucial. The current review article provides valuable insights into the current state of nanotechnology-based marine oil spill clean-up methods and their potential applications.

Enhanced Cement Foam Composite with Biochar for Eriochrome Black T Dye Removal

Cement-based foam composites have gained attention as innovative and high-performing adsorbents for wastewater treatment due to their lightweight, porous, and structurally robust properties. This study investigates the adsorption of Eriochrome Black T dye onto biochar-modified cement foam, providing a cost-effective solution for industrial wastewater management. The integration of biochar into cement foam enhances its surface area and adsorption capabilities while maintaining structural stability and tunable porosity. The composites were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy to verify quality and functionality. The adsorption process adhered to the Freundlich isotherm model (R2 = 0.967), indicating multilayer adsorption, with a maximum capacity of 13.33 mg/g under optimal conditions. Kinetic studies showed a pseudo-first-order fit (R2 = 0.981), while thermodynamic analysis revealed a spontaneous and endothermic process, with ΔH° = 28.84 KJ/mol and ΔG° values ranging from -0.457 to -2.36 KJ/mol. These results demonstrate the composite's exceptional efficiency and scalability, making it a sustainable and practical option for removing persistent dyes such as Eriochrome Black T. This work contributes significantly to the advancement of environmentally friendly wastewater treatment technologies.

Development of a superhydrophobic and superoleophilic halloysite nanotube/phenyltriethoxysilane-coated melamine sponge sorbent material with high performance in supercritical CO2 atmosphere for the selective and effective oil spill cleanup and oil-water separation

In this study, activated halloysite nanotube (HNT) and phenyltriethoxysilane (PTES) were utilized for the first time to fabricate modified HNT materials and coat them onto melamine sponge (MS) substrate in the supercritical carbon dioxide (scCO2) atmosphere. The successful coating of MS substrate was confirmed using SEM, EDS, XPS, and contact angle measurements. The drainage technique applied in the CO2 medium achieved the uniform coating of both the inner and outer surfaces of the MS. Water and oil contact angles of the fabricated sorbent material (MS-PTES) were measured as 167.1° and 0°, respectively. MS-PTES sorbent having superhydrophobic and superoleophilic properties demonstrated sorption capacities ranging from 47.6 g/g to 132.2 g/g for 13 different pollutants, including various petroleum products, oils, and organic solvents. Moreover, the MS-PTES sorbent material showed outstanding separation efficiency (99.99%) for the diesel-water mixture using a continuous separation process. It also displayed high selectivity for oil and organic solvent pollutants under acidic, saline, and alkaline conditions, along with excellent reusability, chemical stability, robustness, and mechanical flexibility. MS sorbent material coated with HNT-modified PTES nanoparticles, produced in the scCO2 atmosphere using the drainage technique, represents a promising solution for the removal of petroleum derivatives, oils, and organic solvents from water.

Polyurethane Foam and Algae-Based Activated Carbon Biocomposites for Oil Spill Remediation

This study investigates the incorporation of algae-based activated carbon into polyurethane foam to improve a biocomposite for gasoil sorption. The biocomposites were thoroughly analyzed using various techniques to examine the properties of both the blank foam and the algae activated carbon foam with a carbon content of 4.41 mass% and particle diameter of 500 µm. These techniques included Scanning Electron Microscopy (SEM), thermogravimetric analysis (TGA), and density analysis. The TGA analysis revealed that the biocomposites had an impact on the onset temperature (Tonset) of the foams. Higher concentrations of the biocomposites resulted in a decrease in Tonset from approximately 310 °C in the blank foam (PUF0) to 300 °C in the composite (PUF3B). The final residue percentage also decreased from around 20% in PUF0 to 10% in PUF3B. Density analysis showed that the apparent density of the foam increased from 0.016 g/cm3 in the blank foam to 0.020 g/cm3 in the biocomposite (PUF3B), while the real density slightly decreased from 0.092 g/cm3 to 0.076 g/cm3, indicating a reduction in overall porosity from 82.5% to 74.4%. All foams that were modified showed an increase in their ability to absorb gasoil in a PUF/gasoil/water system. The optimized biocomposite (PUF1B), with 1.14 mass% of 500 µm algae carbon, displayed the highest sorption capacity, starting at approximately 50 g/g at 1.5 h and increasing to 53 g/g over 72 h. The analysis of adsorption kinetics revealed that by utilizing adsorption isotherms, particularly the Langmuir isotherm, a more accurate fit to the data was achieved. This allowed for the prediction of the maximum gasoil adsorption capacity. This study aims to further develop, analyze, and utilize biocomposites made from algae-based activated carbon and polyurethane. These materials offer a sustainable and environmentally friendly approach to cleaning up oil spills.

Modification of polyurethane foams with zinc sulfide nanoparticles and their novel composites with multani mitti and charcoal for oil spill cleanup

With the rapid growth of the automobile industry, the excessive number of industrial pollutants, particularly oil spills, has become a huge threat to the natural environment. Therefore, an environmentally benign and sustainable solution is required for an effective oil spill cleanup. To enhance the sorption capacity of pristine polyurethane (PU) foam used in oil spill cleanup, ZnS nanoparticles were deposited on PU foam via a coprecipitation approach. Additionally, the effect of Fuller's earth, locally known as Multani Mitti (MM), and charcoal (CC) on the sorption properties of the PU foam were investigated and compared. Polyvinyl alcohol (PVA) was used as a binder during the modification procedure. The morphology, chemical composition, and thermal stability of ZnS/MM/PVA- and ZnS/CC/PVA-modified PU sorbents were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray photon spectroscopy (XPS). The modified PU foam exhibited outstanding properties including a high sorption capacity, high selectivity to different types of used oils such as vegetable oil, hydraulic oil, lube oil, and gear oil, and superior reusability in comparison to pristine PU foam. ZnS/CC/PVA has a sorption capacity of 16.78 g g-1 while ZnS/MM/PVA exhibited a sorption capacity of 16 g g-1. In addition, after 10 cycles of oil sorption-squeezing experiments, the oil sorption capacity remained unchanged, and the absorbed used oil could be removed and collected by an easy squeezing procedure prior to reuse. This work reveals that the ZnS/CC/PVA- and ZnS/MM/PVA-modified PU foams have a promising potential for oil spill removal and environmental protection.

Recent progress in surface engineering methods and advanced applications of flexible polymeric foams

Polymeric foams, also known as three-dimensional (3D) polymeric sponges, are lightweight, flexible, compressible, and possess a high surface area compared with other bulk polymers. These sponges have traditionally been used for mattresses or seat cushions in homes, offices, aircraft, automobiles, and trains, and to insulate against heat, electricity, and noise. Recently, the demand for modern materials has expanded the application of polymeric foams to various high-value technologies, including in areas that need high flame retardancy, flame sensors, oil/water separation, metal adsorption, solar steam generation, piezoresistivity, electromagnetic interference shielding, thermal energy storage, catalysis, supercapacitors, batteries, and triboelectric energy harvesting. Proper modification of foams is a prerequisite for their use in high-value applications. Several new strategies for the surface coating of 3D porous foams and novel emerging applications have been recently developed. Therefore, in this review, current advances in the field of surface coating and the application of 3D polymeric foams are discussed. A brief background on 3D polymeric foams, including the unique properties and benefits of polymeric sponges and their routes of synthesis, is presented. Different coating strategies for polymeric sponges are discussed, and their advantages and drawbacks are highlighted. Different advanced applications of polymeric sponges, in conjunction with specific and detailed examples of the above-mentioned applications, are also described. Finally, challenges and potential applications related to the coating of polymeric foams are discussed. We envisage that this review will be useful to facilitate further research, promote continued efforts on the advanced applications mentioned above, and provide new stimuli for the design of novel polymeric sponges for future modern applications.

Evaluation of factors causing lateral migration of light non-aqueous phase liquids (LNAPLs) in onshore oil spill accidents

Contamination of groundwater by harmful substances poses significant risks to both drinking water sources and aquatic ecosystems, making it a critical environmental concern. Most on-land spill events release organic molecules known as light non-aqueous phase liquids (LNAPLs), which then seep into the ground. Due to their low density and organic composition, they tend to float as they reach the water table. LNAPLs encompass a wide range of non-aqueous phase liquids, including various petroleum products, and can, over time, develop carcinogenic chemicals in water. However, due to frequent changes in hydraulic head, the confinement may fail to contain them, causing them to extend outward. When it contaminates water wells, people cannot reliably consume the water. The removal of dangerous contaminants from groundwater aquifers is made more challenging by LNAPLs. It is imperative to analyze the mechanisms governing LNAPL migration. As a response to this need and the associated dispersion of contaminants into adjacent aquifers, we have conducted a comprehensive qualitative literature review encompassing the years 2000-2022. Groundwater variability, soil structure, and precipitation have been identified as the three primary influential factors, ranked in the following order of significance. The rate of migration is shown to rise dramatically in response to changes in groundwater levels. Different saturation zones and confinement have a major effect on the lateral migration velocity. When the various saturation zones reach a balance, LNAPLs will stop moving. Although higher confinement slows the rate of lateral migration, it speeds up vertical migration. Beyond this, the lateral or vertical movement is also influenced by differences in the permeability of soil strata. Reduced mobility and tighter containment are the outcomes of migrating through fine-grained, low-porosity sand. The gaseous and liquid phases of LNAPLs move more quickly through coarse-grained soils. Due to the complexities and uncertainties associated with LNAPL behavior, accurately foreseeing the future spread of LNAPLs can be challenging. Although studies have utilized modeling techniques to simulate and predict LNAPL migration, the inherent complexities and uncertainties in the subsurface environment make it difficult to precisely predict the extent of LNAPL spread in the future. The granular soil structure considerably affects the porosity and pore pressure.

3D Oleophilic Sorbent Films Based on Recycled Low-Density Polyethylene

Recycling low-end, one-time-use plastics-such as low-density polyethylene (LDPE)-is of paramount importance to combat plastic pollution and promote sustainability in the modern green economy. This study valorizes LDPE waste by transforming it into 3D oleophilic swellable thin films through a process involving dissolution, phase separation, and extraction. These films are subsequently layered using a customized polypropylene (PP) based nonwoven fabric separator and securely sealed in a zigzag pattern. The zigzag-shaped seal enhances the adhesion of pollutants to the sorbent by providing wire curvatures that increase retention time and uptake capacity. As a result, the sorbent exhibits impressive oil uptake capacities, with immediate and equilibrium values of 120 g/g and 85 g/g, respectively. Notably, the as-prepared sorbent demonstrates low water retention and high selectivity for oil, outperforming commercially available oil sorbents. The unique design involving a 3D-film structure, superposed films, and a zigzag-shaped seal offers a sustainable and value-added solution to the issues of LDPE waste and oil spills on water surfaces.

A biomimetic design for efficient petrochemical spill disposal: CoFe-PBA modified superhydrophobic melamine sponge with mechanical/chemical durability and low fire risk

Due to frequent petrochemical spills, environmental pollution and the threat of secondary marine fires have arisen, necessitating an urgent need for petrochemical spill treatment strategies with high-performance oil-water separation capabilities. To address the challenges of poor durability, instability in hydrophobic conditions, and difficulty in absorbing high-viscosity crude oil associated with hydrophobic absorbent materials, the authors of this study took inspiration from the unique micro and nanostructures of springtails' water-repellent skin. We engineered a superhydrophobic melamine sponge using interfacial assembly techniques designated as Si@PBA@PDA@MS. This material demonstrated improved mechanical and chemical durability, enhanced photothermal performance, and reduced fire risk. The metal-organic framework (MOF)-derived cobalt-iron Prussian blue analog (CoFe-PBA) was firmly anchored to the sponge framework by the chelation of cobalt ions using polydopamine (PDA). The results demonstrated that Si@PBA@PDA@MS demonstrated excellent superhydrophobicity (WCA=163.5°) and oil absorption capacity (53.4-97.5 g/g), maintaining high durability even after 20 cycles of absorption-squeezing. Additionally, it could still exhibit excellent mechanical properties, hydrophobic stability, and absorption performance across a wide temperature range (0-100 °C), pH range (1-14), and high compression strength (ε = 80%), with excellent mechanical/chemical durability. Furthermore, Si@PBA@PDA@MS demonstrated remarkable photothermal performance and low fire risk, offering efficient, safe, and sustainable practical value for effective petrochemical spill treatment.

Complex treatment of oily polluted waters by modified melamine foams: from colloidal emulsions to a free oil removal

This study deals with the efficient, low-cost, and scalable treatment of oily polluted waters including colloidal emulsions, oil-in-water mixtures, and free oil removal using melamine foams (MFs) modified by ferric chloride (FeCl3). Modified foams have superhydrophobic character due to the coordination of Fe3+ with free electron pairs on nitrogen and oxygen atoms within the melamine structure. The water contact angles (WCA) were 146° ± 2°, 148° ± 4°, 153° ± 2°, and 150° ± 4° for foams modified by the solutions with concentrations of 0.001 M, 0.005 M, 0.01 M, and 0.02 M, respectively. This modification enables the efficient treatment of various oil/water systems, including oil/water colloidal emulsions (99 vol% of the droplets have dimensions below 500 nm), oil-in-water mixtures up to 40 weight % of the oil component, and "free" oil removal as it was demonstrated in this study for the first time. The emulsions containing 100 ppm diesel oil (DO) were separated with 91.4% efficiency, and the mixtures containing 20 and 40 weight % DO were separated with 99.9% efficiency. Modified foams also quickly remove free DO from the water surface, absorbing 95 g/g DO, whereas water sorption was negligible. The separation of colloidal oil in water emulsions represents the key finding of this study as it indicates the applicability of the treated MFs for the treatment of emulsified industrial wastewater. The demulsification mechanism is based on multiple diffusion processes running at different time scales, including diffusion of the emulsion into the foam and diffusion of oil droplets within the foam, combined with parallel adsorption of oil droplets onto the solid skeleton of the foam. A multiplied usage of these foams for all these niche operations was also proven. The application of our current study with previous studies on modified MFs and polyurethane for water oil separation utilization is summarized in Table S1 ESI.

C-shaped porous polypropylene fibers for rapid oil absorption and effective on-line oil spillage monitoring

Development of efficient absorbent materials for detection and treatment of offshore oil spillages remained a challenge. In this work, C-shaped polypropylene oil-absorbent fibers with sub-micron internal pores were prepared by combining spun-bonding technique and thermally induced phase separation (TIPS). The effect of drawing speed on the phase separation and the porous morphology of the shaped fiber non-woven fabric (NWF) was investigated. C-shaped NWF with porous morphology had large water contact angle, higher porosity, larger specific surface area, and increased oil absorption speed and capacity. An online oil spillage detection system was developed using porous C-shaped NWF and an oxygen sensing probe, showing shorter response time and higher signal-to-noise (STN) ratio. The response time for detecting the spillage of soybean oil and diluted crude oil (0.5 mL/0.8 L) in water were only 24 s and 10 s, respectively. The reliable oil detection low detection limit (RLDL) of the oxygen sensing probe was reduced 173 times (from 36.5 g/L to 0.21 g/L) when combined with C-shaped porous fiber NWF.

Oil/Water Mixtures and Emulsions Separation Methods-An Overview

Catastrophic oil spill accidents, oily industrial wastewater, and other types of uncontrolled release of oils into the environment are major global issues since they threaten marine ecosystems and lead to a big economic impact. It can also affect the public health of communities near the polluted area. This review addresses the different types of oil collecting methods. The focus of this work will be on the different approaches to materials and technologies for oil/water separation, with a special focus on water/oil emulsion separation. Emulsified oil/water mixtures are extremely stable dispersions being, therefore, more difficult to separate as the size of the droplets in the emulsion decreases. Oil-absorbent materials, such as sponges, foams, nanoparticles, and aerogels, can be adjusted to have both hydrophobic and oleophilic wettability while displaying a porous structure. This can be advantageous for targeting oil spills in large-scale environmental and catastrophic sets since these materials can easily absorb oil. Oil adsorbent materials, for example, meshes, textiles, membranes, and clays, involve the capture of the oily material to the surface of the adsorbent material, additionally attracting more attention than other technologies by being low-cost and easy to manufacture.

Sustained release of alpha-methylacyl-CoA racemase (AMACR) antibody-conjugated and free doxorubicin from silica nanoparticles for prostate cancer cell growth inhibition

This article presents silica nanoparticles for the sustained release of AMACR antibody-conjugated and free doxorubicin (DOX) for the inhibition of prostate cancer cell growth. Inorganic MCM-41 silica nanoparticles were synthesized, functionalized with phenylboronic acid groups (MCM-B), and capped with dextran (MCM-B-D). The nanoparticles were then characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, zeta potential analysis, nitrogen sorption, X-ray diffraction, and thermogravimetric analysis, before exploring their potential for drug loading and controlled drug release. This was done using a model prostate cancer drug, DOX, and a targeted prostate cancer drug, α-Methyl Acyl-CoA racemase (AMACR) antibody-conjugated DOX, which attaches specifically to AMACR proteins that are overexpressed on the surfaces of prostate cancer cells. The kinetics of sustained drug release over 30 days was then studied using zeroth order, first order, second order, Higuchi, and the Korsmeyer-Peppas models, while the thermodynamics of drug release was elucidated by determining the entropy and enthalpy changes. The flux of the released DOX was also simulated using the COMSOL Multiphysics software package. Generally, the AMACR antibody-conjugated DOX drug-loaded nanoparticles were more effective than the free DOX drug-loaded formulations in inhibiting the growth of prostate cancer cells in vitro over a 96 h period. The implications of the results are then discussed for the development of drug-eluting structures for the localized and targeted treatment of prostate cancer.

MOF-derived LDH modified flame-retardant polyurethane sponge for high-performance oil-water separation: Interface engineering design based on bioinspiration

Frequent petrochemical spill accidents and secondary fire hazards have threatened the ecological environment and environmental safety. The traditional purification technology has the problems of high energy consumption and secondary pollution, which also brings new challenges to spill disposal. Herein, we demonstrate a biomimetic structure-based flame-retardant polyurethane (PU) sponge (FPUF@MOF-LDH@HDTMS) for continuous oil-water separation. Inspired by desert beetle and lotus leaf, the biomimetic micro-nano composite structure was constructed by in-situ growth of metal-organic framework-derived layered double hydroxide (MOF-LDH) on the surface of the PU sponge. After grafting MOF-LDH with hexadecyltrimethoxysilane, FPUF@MOF-LDH@HDTMS showed excellent superhydrophobic/superoleophilic performance (water contact angle=153° and oil contact angle=0°). FPUF@MOF-LDH@HDTMS can easily and quickly adsorb oily liquids suspended/settled in the water thanks to the unique bionic structure. FPUF@MOF-LDH@HDTMS has excellent oil/organic solvents absorption capacity; even after 20 cycles of use still maintains high adsorption capacity. More importantly, the continuous oil-water separation through FPUF@MOF-LDH@HTMS has achieved a separation efficiency of up to 99.1%. In addition, the bionic superhydrophobic sponge has excellent flame retardancy, which reduces the possibility of secondary fire caused by PU sponges. Thus, the biomimetic micro-nano composite structure provides a new design strategy for the more high-performance oil-water separation sponges.

A review on the effectiveness of nanocomposites for the treatment and recovery of oil spill

The introduction of unintended oil spills into the marine ecosystem has a significant impact on aquatic life and raises important environmental concerns. The present review summarizes the recent studies where nanocomposites are applied to treat oil spills. The review deals with the techniques used to fabricate nanocomposites and identify the characteristics of nanocomposites beneficial for efficient recovery and treatment of oil spills. It classifies the nanocomposites into four categories, namely bio-based materials, polymeric materials, inorganic-inorganic nanocomposites, and carbon-based nanocomposites, and provides an insight into understanding the interactions of these nanocomposites with different types of oils. Among nanocomposites, bio-based nanocomposites are the most cost-effective and environmentally friendly. The grafting or modification of magnetic nanoparticles with polymers or other organic materials is preferred to avoid oxidation in wet conditions. The method of synthesizing magnetic nanocomposites and functionalization polymer is essential as it influences saturation magnetization. Notably, the inorganic polymer-based nanocomposite is very less developed and studied for oil spill treatment. Also, the review covers some practical considerations for treating oil spills with nanocomposites. Finally, some aspects of future developments are discussed. The terms "Environmentally friendly," "cost-effective," and "low cost" are often used, but most of the studies lack a critical analysis of the cost and environmental damage caused by chemical alteration techniques. However, the oil and gas industry will considerably benefit from the stimulation of ideas and scientific discoveries in this field.

Development of a Hydrophobic Carbon Sponge Nanocomposite for Oil Spill Cleanup

Oil leaks (or spills) into the aquatic environment are considered a natural disaster and a severe environmental problem for the entire planet. Samples of polyurethane (PU) composites were prepared with high specific surface area carbon nanotubes (CNT) to investigate crude oil sorption. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), density measurements, and mechanical compression tests were used to characterize the polyurethane-carbon PU-CNT prepared samples. The spongy composites exhibited good mechanical behavior and a contact angle of up to 119°. The oleophilic character resulted in increased hydrophobicity, a homogeneous oil distribution inside the sponge, and a sorption capacity in a water/oil mixture of 41.82 g/g. Stress-strain curves of the prepared samples showed the good mechanical properties of the sponge, which maintained its stability after more than six sorption desorption cycles. The CNT-PU composites may prove very effective in solving oil pollution problems.

Preparation of Three-Dimensional MF/Ti3C2Tx/PmPD by Interfacial Polymerization for Efficient Hexavalent Chromium Removal

Heavy metal pollution is a serious threat to human health and the ecological environment, but adsorption technology based on nano adsorbents can effectively treat the crisis. However, due to the nanoscale effect, nano adsorbents have some crucial shortcomings, such as recycling difficulty and the loss of nanoparticles, which seriously limit their application. The feasible assembly of nano adsorbents is an accessible technology in urgent need of a breakthrough. In this study, three-dimensional (3D) adsorbent (MF/Ti3C2Tx/PmPD) with excellent performance and favorable recyclability was prepared by interfacial polymerization with melamine foam (MF) as the framework, two-dimensional (2D) titanium carbide (Ti3C2Tx) as the bridge and Poly (m-Phenylenediamine) (PmPD) as the active nano component. The morphology, structure, mechanical property of MF/Ti3C2Tx/PmPD and reference MF/PmPD were investigated through a scanning electron microscope (SEM), Fourier transformed infrared spectra (FT-IR), Raman scattering spectra and a pressure-stress test, respectively. Owning to the regulation of Ti3C2Tx on the morphology and structure of PmPD, MF/Ti3C2Tx/PmPD showed excellent adsorption capacity (352.15 mg/g) and favorable cycling performance. R-P and pseudo-second-order kinetics models could well describe the adsorption phenomenon, indicating that the adsorption process involved a composite process of single-layer and multi-layer adsorption and was dominated by chemical adsorption. In this research, the preparation mechanism of MF/Ti3C2Tx/PmPD and the adsorption process of Cr(VI) were systematically investigated, which provided a feasible approach for the feasible assembly and application of nano adsorbents in the environmental field.

The Separation of Oil/Water Mixtures by Modified Melamine and Polyurethane Foams: A Review

Melamine (MA) and polyurethane (PU) foams, including both commercial sponges for daily use as well as newly synthesized foams are known for their high sorption ability of both polar and unipolar liquids. From this reason, commercial sponges are widely used for cleaning as they absorb a large amount of water, oil as well as their mixtures. These sponges do not preferentially absorb any of those components due to their balanced wettability. On the other hand, chemical and physical modifications of outer surfaces or in the bulk of the foams can significantly change their original wettability. These treatments ensure a suitable wettability of foams needed for an efficient water/oil or oil/water separation. MA and PU foams, dependently on the treatment, can be designed for both types of separations. The particular focus of this review is dealt with the separation of oil contaminants dispersed in water of various composition, however, an opposite case, namely a separation of water content from continuous oily phase is also discussed in some extent. In the former case, water is dominant, continuous phase and oil is dispersed within it at various concentrations, dependently on the source of polluted water. For example, waste waters associated with a crude oil, gas, shale gas extraction and oil refineries consist of oily impurities in the range from tens to thousands ppm [mg/L]. The efficient materials for preferential oil sorption should display significantly high hydrophobicity and oleophilicity and vice versa. This review is dealt with the various modifications of MA and PU foams for separating both oil in water and water in oil mixtures by identifying the chemical composition, porosity, morphology, and crosslinking parameters of the materials. Different functionalization strategies and modifications including the surface grafting with various functional species or by adding various nanomaterials in manipulating the surface properties and wettability are thoroughly reviewed. Despite the laboratory tests proved a multiply reuse of the foams, industrial applications are limited due to fouling problems, longer cleaning protocols and mechanical damages during performance cycles. Various strategies were proposed to resolve those bottlenecks, and they are also reviewed in this study.

Joule-heatable bird-nest-bioinspired/carbon nanotubes-modified sepiolite porous ceramics: An efficient, sturdy, and continuous strategy for oil recovery

Oil-spill accident is a severe globally concerned environmental issue. In this work, a Joule-heatable bird-nest-bioinspired/carbon nanotubes-modified sepiolite porous ceramic (JBN/CM-SC) was developed, using inexpensive sepiolite porous ceramics as the substrate and carbon nanotubes (CNTs) derived from waste plastics as the modifier. The former exhibited outstanding mechanical property (1.7 MPa of compressive strength), gas permeability (9.1 × 10^-11 m²), thermal conductivity (0.215 W·m^-1·K^-1) and thermal/chemical stability. As expected, the deposited CNTs not only conferred a hydrophobic surface, but also resulted in a Joule-heating ability of intrinsically non-conductive ceramics. As-prepared JBN/CM-SC demonstrated a separation rate as high as 120-200 kg·s^-1·m^-2 for oil recovery and a high selectivity of over 95%. The Joule heat generated by the heated JBN/CM-SC could in-situ reduce the oil-viscosity, remarkably increasing the oil-diffusion. The separation rate was enhanced by ~12 times with respect to that of the non-heated counterpart. In addition, the idea of modular design was proposed. By simply combining JBN/CM-SC components with pipes and a pump, a continuous in-situ collection of oil from an oil/water mixture was realized, providing an efficient, sturdy, and continuous approach to recover the spilled oil in an oil-spill accident.

Polyurethane Foams Loaded with Carbon Nanofibers for Oil Spill Recovery: Mechanical Properties under Fatigue Conditions and Selective Absorption in Oil/Water Mixtures

Marine pollution due to spillage of hydrocarbons represents a well-known current environmental problem. In order to recover the otherwise wasted oils and to prevent pollution damage, polyurethane foams are considered suitable materials for their ability to separate oils from sea-water and for their reusability. In this work we studied polyurethane foams filled with carbon nanofibers, in varying amounts, aimed at enhancing the selectivity of the material towards the oils and at improving the mechanical durability of the foam. Polyurethane-based foams were experimentally characterized by morphological, surface, and mechanical analyses (optical microscopy observation, contact angle measurement, absorption test according to ASTM F726-99 standard and compression fatigue tests according to ISO 24999 standard). Results indicated an increase in hydrophobic behavior and a good oleophilic character of the composite sponges besides an improved selective absorption of the foam toward oils in mixed water/oil media. The optimal filler amount was found to be around 1 wt% for the homogeneous distribution inside the polymeric foam. Finally, the fatigue test results showed an improvement of the mechanical properties of the foam with the growing carbon filler amount.

Multifunctional metal-organic frameworks in oil spills and associated organic pollutant remediation

The release of toxic organic compounds into the environment in an event of oil spillage is a global menace due to the potential impacts on the ecosystem. Several approaches have been employed for oil spills clean-up, with adsorption technique proven to be more promising for the total reclamation of a polluted site. Of the several adsorbents so far reported, adsorbent-based porous materials have gained attention for the reduction/total removal of different compounds in environmental remediation applications. The superior potential of mesoporous materials based on metal-organic frameworks (MOFs) against conventional adsorbents is due to their intriguing and enhanced properties. Therefore, this review presents recent development in MOF composites; methods of preparation; and their practical applications towards remediating oil spill, organic pollutants, and toxic gases in different environmental media, as well as potential materials in the possible deployment in reclaiming the polluted Niger Delta due to unabated oil spillage and gas flaring.

Microwave Foaming of Materials: An Emerging Field

In the last two decades, the application of microwave heating to the processing of materials has to become increasingly widespread. Microwave-assisted foaming processes show promise for industrial commercialization due to the potential advantages that microwaves have shown compared to conventional methods. These include reducing process time, improved energy efficiency, solvent-free foaming, reduced processing steps, and improved product quality. However, the interaction of microwave energy with foaming materials, the effects of critical processing factors on microwave foaming behavior, and the foamed product's final properties are still not well-explored. This article reviews the mechanism and principles of microwave foaming of different materials. The article critically evaluates the impact of influential foaming parameters such as blowing agent, viscosity, precursor properties, microwave conditions, additives, and filler on the interaction of microwave, foaming material, physical (expansion, cellular structure, and density), mechanical, and thermal properties of the resultant foamed product. Finally, the key challenges and opportunities for developing industrial microwave foaming processes are identified, and areas for potential future research works are highlighted.

Superhydrophilic Coating with Antibacterial and Oil-Repellent Properties via NaIO4-Triggered Polydopamine/Sulfobetaine Methacrylate Polymerization

Superhydrophilic coatings have been widely used for the surface modification of membranes or biomedical devices owing to their excellent antifouling properties. However, simplifying the modification processes of such materials remains challenging. In this study, we developed a simple and rapid one-step co-deposition process using an oxidant trigger to fabricate superhydrophilic surfaces based on dopamine chemistry with sulfobetaine methacrylate (SBMA). We studied the effect of different oxidants and SBMA concentrations on surface modification in detail using UV-VIS spectrophotometry, dynamic light scattering, atomic force microscopy, X-ray photoelectron spectroscopy, and surface plasmon resonance. We found that NaIO4 could trigger the rate of polymerization and the optimum ratio of dopamine to SBMA is 1:25 by weight. This makes the surface superhydrophilic (water contact angle < 10°) and antifouling. The superhydrophilic coating, when introduced to polyester membranes, showed great potential for oil/water separation. Our study provides a complete description of the simple and fast preparation of superhydrophilic coatings for surface modification based on mussel-inspired chemistry.

Rapid UV-radiation synthesis of polyacrylate cryogel oil-sorbents with adaptable structure and performance

Macro-porous poly(lauryl acrylate) cryogel sheets as oil-sorbents were prepared through UV-radiation cryo-polymerizations in 1, 4-dioxane at low temperatures (-5, -2 and 0 °C) within 30 min. The influences of total monomer concentration, crosslinking monomer amount and polymerization temperature on the formation of cryogels were studied. The chemical structure and porous morphology were characterized through the techniques of Fourier transform infrared spectroscopy, thermal gravimetric analysis, contact angle measurement and scanning electron microscopy, confirming the features of high hydrophobicity, macro-porosity and good thermal stability. As well, the comparison between conventional gels prepared at room temperature and cryogels at lower temperatures was made, showing the higher rate of cryo-polymerization than conventional polymerization under the same UV-radiation condition. The swelling investigation was carried out with several organic solvents and oils. Enhanced performance of oil absorption was observed for those cryogels considering the absorption capacity and absorption rate. Variation of initiator amount and acrylate monomers could also modulate the absorption capacity. Those cryogel oil-sorbents exhibited wide adaptability, good reusability and high-temperature tolerance. Thus, this rapid and low-cost fabrication opens out a novel pathway to prepare efficient oil-sorbents used in waste water treatment.

Non-Invasive Approaches for the Evaluation of the Functionalization of Melamine Foams with In-Situ Synthesized Silver Nanoparticles

The use of polymeric nanocomposites has arisen as a promising solution to take advantage of the properties of nanoparticles (NPs) in diverse applications (e.g., water treatment, catalysis), while overcoming the drawbacks of free-standing nanoparticles (e.g., aggregation or accidental release). In most of the cases, the amount and size of the NPs will affect the stability of the composite as well as their performance. Therefore, a detailed characterization of the NPs present on the nanocomposites, including their quantification, is of vital importance for the optimization of these systems. However, the determination of the NPs load is often carried out by destructive techniques such as TGA or ICP-OES, the development of non-invasive approaches to that aim being necessary. In this work, the amount of silver NPs synthesized directly on the surface of melamine (ME) foams is studied using two non-invasive approaches: colorimetry and X-ray radiography. The obtained results show that the amount of silver NPs can be successfully determined from the luminosity and global color changes of the surface of the foams, as well as from the X-ray attenuance.

Plant-Inspired Layer-by-Layer Self-Assembly of Super-Hydrophobic Coating for Oil Spill Cleanup

A versatile, facile, energy-saving, low-cost and plant-inspired self-assembly strategy was used to prepare super-hydrophobic coating in this study. Concretely, an appealing super-hydrophobicity surface was obtained by designing a molecular building block phytic acid (PA)-Fe (III) complex to anchor the substrate and hydrophobic thiol groups (HT). The facile and green modification method can be applied to variety of substrates. The as-prepared PA-Fe (III)-HT coated melamine composite sponge possesses both super-hydrophobic and superlipophilicity property. Moreover, it displays superior efficiency to separate the oil-water mixture and splendid oil spill cleanup.

Superswelling Hybrid Sponge from Water Glass for Selective Absorption of Crude Oil and Organic Solvents

A lightweight super hydrophilic hybrid sponge is designed and demonstrated out of water glass and an organic polymer, which has a macroporous flaky nature and is superflexible with an apparent density of 0.069 g cc^-1, ∼97% porosity, and 3000% water uptake. The octadecyltrimethoxy silane-modified hybrid sponge exhibits selective absorption of oil and organic solvents in open water. An absorption capacity in the range 12-23 g g^-1 for the test liquids light crude oil, engine oil, paraffin oil, chloroform, kerosene, and hexane is revealed. Absorption capacity by a weight basis was directly proportional to the density and inversely proportional to the viscosity of test liquids. Trials under both stagnant and turbulent conditions verify selective uptake of oil from sea water. Complete regeneration of the absorbent was possible for ten cycles for the test liquids. The work provides design of an affordable water clean-up material alternative to commonly used polyurethane sponges.

Macroporous Oil-Sorbents with a High Absorption Capacity and High-Temperature Tolerance Prepared through Cryo-Polymerization

The facile preparation and admirable performance of macro-porous poly(lauryl acrylate)-based oil-sorbents for organic solvents and oils are reported in this manuscript. Cryo-polymerizations of lauryl acrylate (LA) with ethylene glycol dimethacrylate (EGDMA) as the cross-linker were carried out at temperatures below the freezing point of the polymerization mixture. The polymerization medium and pore-forming agent was 1,4-dioxane. The influences of the total monomer concentration, EGDMA content and cryo-polymerization temperature on the structure of the obtained P(LA-co-EGDMA) cryogels were investigated with the techniques of Fourier transform infrared spectroscopy, scanning electron microscopy, contact angle measurement and thermo-gravimetric analysis. Through the modulation of the crosslinking density and porosity of these cryogels, the P(LA-co-EGDMA) oil-sorbents demonstrated a high absorption capacity for organic solvents and oils, recyclability and high-temperature tolerance. The absorption capacity reached 20-21 and 16-17 g/g for toluene and gasoline oil, respectively. Those fabricated sorbents survived high temperatures up to 150 °C without any change in absorption capacity as well as porosity. Considering the convenient synthesis process and absorption performance, the present work offers a remarkable opportunity to bring polymer cryogels to practical application in waste oil clean-up.

Removal of heavy crude oil from water surfaces using a magnetic inorganic-organic hybrid powder and membrane system

Oil spills are among the most significant threats to aquatic ecosystems. The present work describes the synthesis of different organic-inorganic hybrid matrices with magnetic properties, obtained in the forms of powders and membranes. The powders were synthesized using the following biomass wastes to form the organic phase: coconut mesocarp, sugarcane bagasse, sawdust, and water hyacinth. The resulting powders were denoted HMG-CO, HMG-CN, HMG-SE, and HMG-AP, respectively. Membranes (denoted MHMG-PES) were prepared using polyethersulfone polymer. In both cases, the inorganic phase was cobalt ferrite. The materials were evaluated in terms of their efficiencies in removing crude oil from water surfaces. The presence of organic matter, polyethersulfone, and cobalt ferrite in the structures of the materials was confirmed by XRD and FTIR analyses. The efficiencies of the materials were determined using the Standard Test Method for Sorbent Performance of Adsorbents (ASTM F726-99). Among the hybrids in powder form, the HMG-CN material presented the highest oil removal efficiency (85%, adsorptive capacity of 17 g g^-1), which could be attributed to the fibrous nature of the sugarcane bagasse. The MHMG-PES membrane was able to remove 35 times its own mass of oil (adsorptive capacity of 35 g g^-1). In addition to this high removal efficiency, an important advantage of MHMG-PES, compared to the HMG-CN hybrid powder, was that the oil could be mechanically removed from the membrane surface, eliminating the need for subsequent time-consuming extraction steps requiring large volumes of organic solvents and additional energy expenditure. When the two materials were used simultaneously, it was possible to remove 45 times their own mass of oil (adsorptive capacity of 45 g g^-1), with the adsorptive capacity of HMG-CN increasing by 23%. This high adsorptive capacity was due to the retaining barrier formed by the HMG-CN hybrid powder, which prevented the oil patch from spreading and enabled its homogeneous removal, which was not possible using MHMG-PES alone. It could be concluded that use of the magnetic hybrids synthesized using biomass wastes, together with the hybrid magnetic membrane, provided an effective and inexpensive technological alternative for the removal of oil from water surfaces.

Cobalt oxyhydroxide as an efficient heterogeneous catalyst of peroxymonosulfate activation for oil-contaminated soil remediation

The persulfate/Fe²⁺ system has been proposed for the chemical oxidation for soil remediation, however, the homogeneous iron catalyst was hard to reuse which limited the further application. Cobalt oxyhydroxide (CoOOH) existed as a mineral in nature, which was environmentally friendly. Thus, in this study, CoOOH was selected as an efficient heterogeneous catalyst for peroxymonosulfate (PMS) activation to remediate oil contaminated soil by chemical oxidized reaction. 88.3% of oil at the initial concentration of 78-99 mg/kg can be removed within 24 h under the conditions of 1.0 g/L CoOOH and 0.1 M PMS at room temperature. The residual oil content was approximately 11.5 mg/kg which was lower than the standard of petroleum hydrocarbons for residential land (30 mg/kg), published by the Canadian Council of Ministers of the Environment (CCME). Specifically, the PMS/CoOOH system had a relatively high apparent reaction rate constant (0.3078 h^-1), which was approximately twice that of the PS/Fe²⁺ system (0.1601 h^-1). Furthermore, multiple radicals and reactive oxygen species (ROS), such as SO₄^-, O₂^- and ¹O₂, were involved in the oil removal oxidation reaction. Moreover, 73% total organic carbon (TOC) had been removed after the reaction. The findings of this study suggested that the oil-contaminated soil and CoOOH could both be recycled after remediation using the PMS/CoOOH system. In summary, the results indicated that CoOOH is a promising heterogeneous catalyst, and the PMS/CoOOH system could be considered as a feasible alternative to the PS/Fe²⁺ system for the remediation of oil-contaminated soil.

The investigation on Fe3O4 magnetic flocculation for high efficiency treatment of oily micro-polluted water

For the low-concentration oily micro-polluted water formed by the leakage of refined oil products, an unexpensive and high-efficiency magnetic enhanced flocculation method was introduced in this study. First, the performance of magnetic flocculation(MF) to remove oily contaminants was discussed. The results indicated that it achieved more than 95% removal in only 1min with 50mg/L-Polyaluminum chloride(PAC), 50mg/L-Fe₃O₄ and10mg/L- Polyacrylamide (PAM). The novel indexs R_δand S_i were proposed to evaluate the oil removal with UV-Abs in-situ method. According to the adsorption kinetics of oil contaminants, the adsorption kinetics changed from pseudo-first-order to pseudo-second-order kinetics after the addition of Fe₃O₄ on the basis of conventional coagulation (CF). It was transformed into intraparticle diffusion kinetics when the PAM continued to be added. Combined with the Fe-O-Al bond in the FTIR spectrum of flocs, the main mechanism of MF is enhanced charge neutralization and hydrogen bond adsorption. In addition, it was shown that satisfactory oil removal after recover, which indicated the great potential of a sustainable way by reusing low-cost magnetic seeds.

Superhydrophobic foam prepared from high internal phase emulsion templates stabilised by oyster shell powder for oil-water separation

In this paper, poly(styrene-divinylbenzene) foams were synthesized using a high internal phase emulsion (HIPE) technique with Span 80 and with 900 °C calcined oyster shell powder as a co-emulsifier, 2,2'-azobisisobutyronitrile (AIBN) as an initiator and deionized water as the dispersing phase. SEM images revealed that the materials possess a hierarchical porous structure of nano/micro size, which resulted in saturated oil adsorption in only half a minute. The dispersing phase amount was investigated for its effect on adsorption. The optimized foams have 24.8-58.3 g g-1 adsorbencies for several organic solvents, and they demonstrated superhydrophobicity and excellent oleophilicity with the water contact angle (WCA) even close to 149° and oil contact angle approaching 0°. Moreover, the foams displayed high oil retention under pressure. The adsorption-centrifugation cycling results indicated high repeatability of the recovered foams. All of these features predicted the potential applications of superhydrophobic foams in oil-water separation.

Preparation of a porous superhydrophobic foam from waste plastic and its application for oil spill cleanup

In order to cope with the increasing oil spill accidents and the intentional discharge of oily wastewater, a new oil-adsorbing material with superhydrophobicity and reusability is needed. In this paper, waste plastic was used to fabricate an alveolate polystyrene (PS) foam to reduce secondary pollution. The PS foam was synthesized from a high internal phase Pickering emulsion (HIPPE) technique in a one-step process. The emulsion was stabilized by a co-Pickering system of Span 80 surfactant and SiO₂ particles. To explain the super stability of the HIPPE, a novel model of the water-in-oil droplet was promoted. The obtained SiO₂@PS foam exhibited a multi-order-porous structure, and displayed superhydrophobicity and superoleophilicity. It can selectively remove various oily contaminants from water with a high adsorption capacity of 20.4–58.1 g g⁻¹ at a fast rate. The oil-adsorbed material can be reused by simple centrifugation, and no more than a 1% decline was obtained in the oil adsorption after 10 cycles. Therefore, the SiO₂@PS foam has a great potential application in oily water treatment.

In this paper, waste polystyrene (PS) plastic was used to fabricate alveolate PS foam via a high internal phase Pickering emulsion (HIPPE) which was stabilized by Span 80 and silica particle as a co-Pickering emulsifier in one-step progress.

Facile Oil Removal from Water-in-Oil Stable Emulsions Using PU Foams

Superhydrophobic and oleophilic polyurethane foams were obtained by spray-coating their surfaces with solutions of thermoplastic polyurethane and hydrophobic silicon oxide nanoparticles. The developed functionalized foams were exploited as reusable oil absorbents from stable water-in-oil emulsions. These foams were able to remove oil efficiently from a wide range of emulsions with oil contents from 10 to 80 v.%, stabilized using Span80. The modified foams could reach oil absorption capacities up to 29 g/g, becoming a suitable candidate for water-in-oil stable emulsions separation.

Polybenzoxazine-Functionalized Melamine Sponges with Enhanced Selective Capillarity for Efficient Oil Spill Cleanup

Severe environmental and ecological issues arising from frequent oil spill accidents have been great worldwide concerns. Considering the abruptness, complex condition, and long-term perniciousness of the spilled oil, the development of economic and versatile materials to quickly remove oil contaminants, especially for oil with high viscosity from a large water body, is of significant importance but remains a big challenge. Herein, we demonstrated a facile strategy to fabricate a versatile hierarchical structured sponge with superhydrophobicity and powerful oil capillarity via the in situ polymerization of a novel phenolic resin (polybenzoxazine) composite open-cell sponges. The tunable hierarchical structures of the as-prepared sponge significantly improved its water repellence and oil capillarity; meanwhile, a plausible mechanism is also proposed. With the merits of high porosity, excellent water repellence, enhanced oil capillarity, and robust mechanical stability, the obtained sponge exhibited an intriguing oil spill cleanup performance with fast oil absorption speed, good recyclability, and high absorption capacity. Besides that, the modified sponge could also be utilized for the separation of oil/water mixture with individual phase and the surfactant-stabilized emulsion solely under the drive of gravity. The robust oil/water separation performance, low cost, and facile synthesis strategy make the resultant sponges a competitive material for the large-scale oil spill emergency remediation.

Superhydrophobic/superoleophilic cotton-oil absorbent: preparation and its application in oil/water separation

A superhydrophobic and superoleophilic oil sorbent was prepared by attaching SiO₂ particles onto a cotton fiber surface by a sol–gel method and subsequent octadecyltrichlorosilane modification. The surface formation was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and an observation of the water behavior on the cotton surface. The sorption capacity of the modified cotton in pure oil and in an oil/water mixture, the oil adsorption and the reusability were investigated. Compared with raw cotton, the as-prepared cotton absorbed different oils rapidly up to in excess of 25–75 g g⁻¹ its own weight, and the water adsorption was nearly 0 g g⁻¹. The modified cotton fiber could separate oil/water mixtures efficiently through a flowing system. After 10 cycles, the as-prepared cotton was still highly hydrophobic with a 6-times greater adsorption than raw cotton. By a simple modification, a low-cost, high-adsorption and environmentally friendly modified cotton could be prepared that can be considered a promising alternative to organic synthetic fibers to clean up oil spills.

A superhydrophobic and superoleophilic oil sorbent was prepared by attaching SiO₂ particles onto a cotton fiber surface by a sol–gel method and subsequent octadecyltrichlorosilane modification.