Purification Of Oily Wastewater Research Articles

Preparation of PVDF@TiO2 hybrid membrane and the research of the “hydration layer & rigid layer obstruction-electrostatic coalescence” anti-oil fouling mechanism

In this study, the 3-Aminopropyltriethoxysilane (APTES) was first grafted onto TiO2 nanoparticles (APTES-TiO2 nanoparticles), which were then introduced the membrane surface by reacting with anhydride on the membrane surface and Schiff base reaction with the PEI-TA. There are two types of hollow fiber hybrid membranes with varying nanoparticle distributions were constructed. The influence of hybrid mode on the ability of anti-oil fouling was researched. The results indicated that the PVDF@TiO2 hybrid membrane has a flux recovery rate of 96.68% and a total flux decline rate of 15.52%, indicating a good anti-emulsified oil fouling performance. By characterizing the anti-oil droplets adhesion, water-binding capacity, surface charge of membrane and concentrate system coacervate size, the coalescence ability of the hybrid membrane to the oil droplets and the spreading behavior of oil droplets on the surface were uncovered. Ultimately, the anti-fouling mechanism “hydration layer &rigid layer obstruction-electrostatic coalescence” was proposed, which can reasonably explain the weakness of the interplay between the membrane surface and oil droplets, thus slowing down the attaching and spreading of emulsified oil droplets. This study laid the foundation for developing hybrid membranes with high resistance to emulsified oil fouling ability. The proposed anti-fouling mechanism can provide new ideas for the efficient purification of oily wastewater.

Influence of photothermal nanomaterials localization within the electrospun membrane structure on purification of saline oily wastewater based on photothermal vacuum membrane distillation

Today, synergistic combination of special nanomaterials (NMs) and electrospinning technique has emerged as a promising strategy to address both water scarcity and energy concerns through the development of photothermal membranes for wastewater purification and desalination. This work was organized to provide a new perspective on membrane design for photothermal vacuum membrane distillation (PVMD) through optimizing membrane performance by varying the localization of photothermal NMs. Poly(vinylidene fluoride) omniphobic photothermal membranes were prepared by localizing graphene oxide nanosheets (GO NSh) (1) on the surface (0.2 wt%), (2) within the nanofibers structure (10 wt%) or (3) in both positions. Considering the case 1, after 7 min exposure to the 1 sun intensity light, the highest temperature (∼93.5 °C) was recorded, which is assigned to the accessibility of GO NSh upon light exposure. The case 3 yielded to a small reduction in surface temperature (∼90.4 °C) compared to the case 1, indicating no need to localize NMs within the nanofibers structure when they are localized on the surface. The other extreme belonged to the case 2 with the lowest temperature of ∼71.3 °C, which is consistent with the less accessibility of GO NSh during irradiation. It was demonstrated that the accessibility of photothermal NMs plays more pronounced role in the membrane surface temperature compared to the light trapping. However, benefiting from higher surface temperature during PVMD due to enhanced accessibility of photothermal NMs is balanced out by decrease in the permeate flux (case 1: 1.51 kg/m2 h and case 2: 1.83 kg/m2 h) due to blocking some membrane surface pores by the binder. A trend similar to that for flux was also followed by the efficiency. Additionally, no change in rejection was observed for different GO NSh localizations.

Lightweight, Elastic, and Superhydrophobic Multifunctional Organic-Inorganic Fibrous Aerogels for Efficient Oily Wastewater Purification and Electromagnetic Microwave Absorption.

Lightweight and robust aerogels with multifunctionality are highly desirable to meet the technological demands of current society. Herein, we designed lightweight, elastic, and superhydrophobic multifunctional organic-inorganic fibrous hybrid aerogels which were assembled with organic aramid nanofibers and inorganic hierarchical porous carbon fibers. Thanks to the organic-inorganic fiber hybridization strategy, the optimal aerogels possessed remarkable compressibility and elasticity. Benefiting from the microscopic hierarchical porous structure of carbon fibers and the macroscopic macroporous lamellar structure of aerogels, the optimal aerogels exhibited superb lightweight property, conspicuous electromagnetic microwave absorption ability, and outstanding oily wastewater purification capacity. As for electromagnetic microwave absorption, it achieved a strong reflection loss of -41.8 dB, and the effective absorption bandwidth reached 6.86 GHz. Besides, the oil adsorption capacity for trichloromethane reached as high as 93.167 g g-1 with a capacity retention of 95.6% after 5 cycles. Meanwhile, it could act as a gravity-driven separation membrane to continuously separate trichloromethane from a trichloromethane-water mixture with a high flux of 7867.37 L·m-2·h-1, even for surfactant-stabilized water-in-n-heptane emulsions of 3794.94 L·m-2·h-1. Such a strategy might shed some light on the construction of multifunctional aerogels toward broader applications.

A novel multifunctional photocatalytic membrane based on ternary heterojunction TiO2@PDA@BiOBr for biochemical oily wastewater purification

Membrane separation technology is a promising alternative for oily wastewater purification. However, developing membrane for the purification of biochemical oily wastewater is still challengeable. To this aim, a novel multifunctional photocatalytic membrane of PTPB-8 is fabricated by sequentially loading of TiO2, polydopamine (PDA), and BiOBr onto polyacrylonitrile (PAN) nanofibers in situ. PTPB-8 is of water contact angle (WCA) ∼ 0° and underwater oil contact angle (UOCA) 154.7 ± 2.5°, allowing it with outstanding separation and anti-fouling capability, and good reusability for emulsion separation under gravity (i.e., separation efficiency >90 %, permeation flux >300 L m-2h−1, and flux recovery rate >82 % for n-hexane-in-water emulsion after 15 cycles). Under simulated solar light, the ternary heterojunction TiO2@PDA@BiOBr is catalytically active with generating active species and the charge transfer pathway follows the mechanism of Z-type heterojunction. Consequently, PTPB-8 can kill E. coli and S. aureus by ∼ 100 % and degrade tetracycline by >90 %. The application trial results have demonstrated the great potential of PTPB-8 in the purification of biochemical oily wastewater containing bacteria and antibiotics. This study will also give a new idea for enhancing the photocatalytic activity of heterojunctions by PDA decoration.

Anti-fouling ampholytic polymer membrane with super-wetting surfaces for efficient oil-water emulsion separation

The development of highly efficient polymeric membranes with super-wetting surfaces (superhydrophilic/submerged superoleophobic) is one of the ideal options to achieve emulsified oily wastewater separation. However, this remains a challenging due to low fluxes and severe membrane contamination limitations. Here, we have demonstrated an ultra-hydrophilic, underwater super-oleophobic, highly anti-fouling and antibacterial (polydopamine/poly [2-(methacryloyloxy) ethyl] dimethyl- (3-sulfopropyl) ammonium hydroxide) PDA/PSBMA modified membrane by grafting amphoteric polymers via atom transfer radical polymerization (ATRP). Benefiting from PSBMA's superhydrophilicity and the unique adhesion of dopamine (DA), the PDA/PSBMA modified membrane shows superhydrophilic properties, superoleophobicity underwater, oil resistance, and fouling resistance. Meanwhile, PDA/PSBMA modified membrane reached a superb permeability to water as high as 5620 L·m−2·h−1·bar−1 and remarkable oil rejection rate of 98 % in separating diesel-in-water emulsions. Furthermore, the separating performance remained fairly constant over 10 emulsion filtration cycles. Besides, the PDA/PSBMA modified membranes have excellent acid and alkali resistance and antibacterial properties, showing its potential for oily wastewater purification. This work offers a simple and versatile strategy to fabricate superwetting efficient polymeric membranes to separate emulsified oily wastewater.

Preparation of Newly Polymer-Coated Microbial Pellets and Their Adsorption and Degradation Properties for Oil-Containing Wastewater.

Water is the lifeblood of everything on earth, nourishing and nurturing all forms of life, while also contributing to the development of civilization. However, with the rapid development of economic construction, especially the accelerated process of modern industrialization, the pollution of oily sewage is becoming increasingly serious, affecting the ecological balance and human health. The efficient elimination of pollutants in sewage is, therefore, particularly urgent. In this paper, a core-shell microbial reactor (MPFA@CNF-SA-AM) was fabricated by using nanocellulose and sodium alginate (SA) particles embedded with microorganisms as the core and lipophilic and hydrophobic fly ash as the outer shell layer. Compared with that of free microorganisms and cellulose and SA aerogel pellets loading with microorganisms (CNF-SA-AM), which has a degradation efficiency of 60.69 and 82.89%, respectively, the MPFA@CNF-SA-AM possesses a highest degradation efficiency of 90.60% within 240 h. So that this self-floating microbial reactor has selective adsorption properties to achieve oil-water separation in oily wastewater and high effective degradation of organic pollutants with low cost. The adsorption curves of MPFA@CNF-SA-AM for diesel and n-hexadecane were studied. The results showed that the adsorption follows the Freundlich model and is a multimolecular layer of physical adsorption. In addition, the degradation mechanism of diesel oil was studied by gas chromatography-mass spectrometry. The results showed that diesel oil was selectively adsorbed to the interior of MPFA@CNF-SA-AM, and it was degraded by enzymes in microorganisms into n-hexadecanol, n-hexadecaldehyde, and n-hexadecanoic acid in turn, and finally converted to water and carbon dioxide. Compared with existing oily wastewater treatment methods, this green and pollution-free dual-functional core-shell microbial reactor has the characteristics of easy preparation, high efficiency, flexibility, and large-scale degradation. It provides a new, effective green choice for oily wastewater purification and on-site oil spill accidents.

Superhydrophilic PANI/Ag/TA@PVDF Composite Membrane with Antifouling Property for Oil-Water Separation.

The current membrane materials used for oil-water separation suffer from low separation efficiency and poor durability, and membrane contamination is also a key issue that must be addressed urgently. In this paper, a superhydrophilic PANI/Ag/TA@PVDF composite membrane with PANI-Ag NPs heterojunction structure was prepared via chelation and reduction of Ag+ by tannic acid (TA) and in situ growth of hydrochloric acid-doped polyaniline (PANI). TA endows the prepared composite membrane with excellent superhydrophilicity and underwater oleophobicity, remarkable oil-water separation capacity (the separation efficiency of more than 97% for soybean oil), and extraordinary antifouling properties. Notably, the range of photodegradation is expanded from UV to visible light by the construction of a Schottky heterostructure between PANI and Ag NPs, the photocatalytic degradation ability of composite membrane for organic pollutants has been improved obviously, and the degradation efficiency for crystal violet (CV) is 97.9%. Considering these merits, the PANI/Ag/TA@PVDF composite membrane provides an effective strategy to overcome the shortcomings of existing membrane materials, presenting enormous potential in the treatment and purification of oily wastewater.

Antifouling macrocyclic-engineered PVDF membrane for the low-pressure separation of surfactant-stabilized oily wastewater

Fouling is a common phenomenon which affects the long-term efficacy of membranes in the practical treatment of oily wastewater. It often results in a dramatic decline in flux, and a consequent increase in maintenance and operational cost. To address this, various substrates have been incorporated during membrane fabrication to enhance the fouling resistance, and improve the separation efficiency. Herein, we report the fabrication of a novel symmetrical ball-copper phthalocyanine incorporated PVDF membrane (CuPc@PVDF) for the effective separation of surfactant-stabilized oil-in-water emulsions. The symmetrical ball-Cu phthalocyanine with four non-peripheral substituents synthesized ab-initio and characterized using UV–vis, FT-IR, 1H NMR, and MALDI-TOF spectroscopies was added to the casting solution during membrane fabrication resulting in the formation of highly hydrophilic and anti-fouling CuPc@PVDF membrane. In contrast to the PVDF membrane, having a water contact angle of 82.3° ± 0.7°, the CuPc@PVDF membrane demonstrated high hydrophilicity with a contact angle of 55.5° ± 0.5°, and pure water permeance up to 768 LMH at 3 bar. It further achieved 99.9 % rejection of oil with size in the range of 50–450 nm at 1 bar, and demonstrated high stability and excellent anti-fouling property during 10 cycles of continuous demulsification, with a flux recovery ratio (FRR) of 98.5 %, and extremely low irreversible flux of 1.5 %. Similarly, the CuPc@PVDF membrane exhibited high resistance to accelerated organic fouling, maintaining a steady flux and an FRR of 93.0 % during 1 hour of continuous operation with 10 ppm sodium alginate and Ca2+ ions. This study reports a novel strategy to enhance the fouling resistance of demulsification membranes, and could be further explored in the design of next generation of advanced membranes for the purification of oily wastewater.

Robust, all-state superhydrophobic-superoleophilic coating for ultrafast selective dye adsorption and oily wastewater purification

Superwettable surfaces have high application potential in liquid separation and dye adsorption, but considerable challenges remain in separately and quickly removing different contaminants in industrial wastewaters such as effluents from textile dying and wool scouring processes. Herein, a robust, all-state superhydrophobic-superoleophilic (SHP-SOI) composite coating was fabricated, using cobalt 2-methylimidazole nanoparticles (ZIF-67 NPs), polydimethylsiloxane (PDMS) and octadecylamine (ODA), and applied to various substrates via a facile two-step dip-coating method. The ZIF-67/PDMS-ODA coated fabrics turned superhydrophobic with a water contact angle (WCA) of over 150°, and oils could easily spread into the fabric with an oil contact angle (OCA) of 0° either in air or water. Owing to the synergistic effect of the coating components, the coating showed ultrafast and repeatable adsorption to anionic dyes (e.g. methyl orange, MO) with the maximum equilibrium adsorption capacity of 205.7 mg/g (MO concentration 100 mg/L, pH = 3). More importantly, 97.9 % of MO was adsorbed in only 5 min and the adsorption reached equilibrium in 30 min. In addition, owing to the coating’s strong affinity toward different oils, the treated fabrics could efficiently separate/adsorb oils from oil contaminated dye solutions. This all-state SHP-SOI coating was robust and could withstand various severe treatments without losing its original wettability and dye/oil adsorption/separation capability; it also exhibited heat induced self-healable property.

Biomass-based renewable, eco-friendly nanofiber membrane: Large-scale fabrication and application in PM0.3 capture and oily wastewater purification

Biomass-based poly (trimethylene 2,5-furandicarboxylate) (PTF) was synthesized by the simple and low-cost direct esterification method. The high number-average molecular weight (Mn) of about 39.6 kDa was achieved for PTF with a polydispersity index (PDI) of 2.0, which was suitable for spinning. The electrospun PTF nanofiber membranes were fabricated firstly and displayed adjustable diameters, excellent mechanical properties (lifting 550 g weight, foldability) and large-scale preparation potential (area of 100 cm × 50 cm). More impressively, high initial surface potential (13.5 kV) was found for the electrospun in-suit electret membranes, which facilitated the capture of ultrafine PM particles. Subsequently, the PTF membrane showed exceptional particle capture capability with a filtration performance of 99.96 %, low pressure drops of 78 Pa, and a satisfactory quality factor of 0.1 Pa−1. PTF filters also demonstrated long-term service capability for purifying high PM2.5 concentration smoke (15 cycles, 55 min), and could be flexibly introduced into various practical scenarios. Additionally, based on the selective oil/water wettability of PTF membranes, which showed outstanding separation effects of oily wastewater(＞99.88 %, 15 cycles). Therefore, the development and application of the PTF nanofibers provided a sustainable alternative for separation/purification and various fields in the future.

Sustainable recycling of waste poly(vinylidene fluoride) and rational design of Janus membrane with superhydrophilic/hydrophobic asymmetric wettability for efficient separation of surfactant-stabilized water-in-oil and oil-in-water emulsions

Membrane materials are great interest in the purification of oily wastewater due to their special wetting and high selectivity, however, the membrane fouling, poor recyclability and inferior efficiency significantly restrain the practical application. Herein, waste cellulose is used as the membrane matrix and modified with dopamine to obtain a super-hydrophilic polydopamine/cellulose membrane (PDA/CM). Secondly, poly(vinylidene fluoride) (PVDF) fiber membrane was electrospun on the surface of super-hydrophilic PDA/CM to form hydrophobic PVDF, and finally a Janus membrane (PVDF/PDA/CM) with asymmetric wetting properties was obtained for the separation of water-in-oil and oil-in-water emulsions. The structure, emulsion separation performance and mechanical properties of Janus membrane were discussed. The PDA/CM membrane side exhibits suphydrophilicity, which can separate various oil-in-water emulsions with efficiency of above 99%. Oppositely, the PVDF side owns hydrophobicity, which can separate various water-in-oil with efficiency of above 98.8%. After 10 cycles, the separation permeation flux remained over 14,000 L m−2 h−1 bar−1 for oil-in-water emulsions and 8000 L m−2 h−1 bar−1 for water-in-oil emulsions, demonstrating its good recycling ability. This work can provide a new strategy for designing laminated Janus separation membrane and realize the on-demand separation of surfactant-stabilized water-in-oil emulsions and oil-in-water emulsions by inversion of the membrane.

Simply Prepared, Wood‐Based Solar Evaporators for Highly Effective Oily Wastewater Purification

Oily wastewater has been causing serious water environment pollution and greatly affecting the safety of drinking water. Compared with superwettable oil‐water separation membrane technology, solar‐driven evaporators based on specific wettability can effectively remove not only oil but also ions, dyes, and other substances from wastewater. We report a longitudinally cut, porous, and wood‐based evaporator that exhibits superhydrophilic and underwater superoleophobic properties. By collaborating hydrophilic and oleophobic wettability, high porosity and the structural anisotropy of wood, the solar evaporators effectively remove different oils from oily emulsions. Separation efficiency of surfactant‐containing crude oil‐in‐water, peanut oil‐in‐water, silicone oil‐in‐water, diesel oil‐in‐water, and n‐dodecane‐in‐water emulsions can reach up to 99.57%, 99.1%, 99.86%, 99.75%, and 99.28%, respectively. The rate of evaporation increased by 1.83 times to 1.63 kg m−2 h−1 compared with the radially‐cut wood‐based evaporator. Meanwhile, it is also capable of purifying heavy metal ions, dyes, and acid‐base solution. This easily prepared and accessible solar evaporator provides a viable idea for obtaining pure water from oily wastewater treatment.

High permeability PEG/MXene@MOF membrane with stable interlayer spacing and efficient fouling resistance for continuous oily wastewater purification

Unstable interlayer spacing of lamellar membranes would be rapidly compressed and narrowed under normal high flowrates and concentration polarization effect contributes to reduced permeation and fouling resistance. Herein, a large permeability PEG/MXene@MOF membrane with stable interlayer spacing and superior antifouling property was created via facile interface self-assembly strategy. Metal-organic framework (MOF, UiO-66-NH2) nanoparticles as supports constructed an intercalation-induced structure with hierarchical Ti3C2Tx (MXene) nanosheets, which effectively regulated the interlayer spacing and improved permeability. Hydrophilic polyethylene glycol (PEG) further enhanced the stability of intercalation structure via hydrogen bonding, so that the PEG/MXene@MOF membrane demonstrated excellent swelling resistance with an average layer spacing expansion of only 0.05 nm even after immersion in water for 8 days. Moreover, MOF particles increased the lamellar roughness and interlayer water retention capacity, resulting in the PEG/MXene@MOF membrane with remarkable separation selectivity and powerful fouling resistance (UWOCA >156°, UWOSA <5.5°). Regarding the purification of oil-in-water emulsions stabilized by surfactants, the PEG/MXene@MOF membrane exhibited extremely stable high permeability (1246 ± 12 L m−2 h−1 bar−1) and excellent efficiency (>99.7 %), even during continuous separation of high-viscosity crude oil emulsions for 60 min. In addition, the PEG/MXene@MOF membrane also exhibited superior chemical durability and mechanical robustness in strong-corrosiveness and high-salty environments (72 h), ultrasonic treatments (120 min), bending experiments (100 times) and abrasion tests (20 times). Therefore, this work provided a promising strategy to construct highly permeable membrane with stable interlayer spacing and efficient fouling resistance for practical oily wastewater purification.

Robust PVA/GO@MOF membrane with fast photothermal self-cleaning property for oily wastewater purification

The poor mechanical durability and weak fouling resistance of oil/water separation membranes severely restrict their applications in industry. Herein, a robust PVA/GO@MOF membrane with fast photothermal self-cleaning capability was developed through facile chemical crosslinking and suction-filtration strategies. Attributed to the powerful underwater superoleophobicity, the PVA/GO@MOF membrane exhibited extraordinary anti-oil adhesion even for high-viscosity crude oil and continuous crude oil emulsion purification capability with stable flux (1020 L m−2 h−1 bar−1) and exceptional efficiency (> 99.3%) even after 60 min. Most importantly, in comparison to reported photocatalytic self-cleaning oil/water separation membranes, the PVA/GO@MOF membrane can degrade organic contaminants more rapidly with a higher degradation rate (99.9%) in 50 min due to the superior photothermal conversion capacity. The synergistic photothermal and photocatalytic effects significantly enhanced photodegradation efficiency, which created opportunities for in-depth treatment of complex oily wastewater. Besides, the obtained membrane displayed excellent chemical and mechanical durability with underwater oil contact angle (UWOCA) above 150° even in harsh environments, such as corrosive solutions, UV irradiation, ultrasound treatment, abrasion experiment and bending test. Therefore, the developed PVA/GO@MOF membrane with robust durability and fast photocatalytic self-cleaning property is highly expected to purify oily wastewater and degrade organic pollutants.

Plant Transpiration-Inspired Biomass-Based Device with Underwater Oleophobicity for Efficient General-Purpose Solar-Driven Oily Wastewater Purification.

The remediation of wastewater containing oily pollutants is imperative to mitigate the serious threats posed to the safety of fresh water, human well-being, and the environment. Current membrane separation technologies are severely restricted by their limitations for separating various types of oily pollutants with low sustainability. Herein, by imitating the plant transpiration in nature, we designed a solar-driven device composed of natural biomass sugar cane stem, chitosan/carboxymethyl cellulose, and graphite powders to separate versatile oily pollutants from the wastewater. Owing to its superior solar absorption capacity, microchannels for water transportation, and underwater oleophobicity, the resultant evaporator not only exhibited an excellent evaporation rate of 1.41 kg m-2 h-1 but also demonstrated an admirable purification efficiency of 99.9% for oily wastewater. Moreover, the device can maintain a stable evaporation rate and the original structure even in oily wastewater containing strong acid, alkali, or hypersaline components. Therefore, this work provides an effective approach to producing clean water from versatile wastewater.

Design of photocatalytic self-cleaning poly (arylene ether nitrile)/nitrogen-doped Bi2O2CO3 composite membrane for emulsified oily wastewater purification

Membrane separation technique offers unique advantages for treating the emulsified oily wastewater with the oil droplet diameter less than 20 µm. However, the complicated membrane fouling originating from oils and soluble matters pose the huge challenges to membrane separation technique, which has stimulated the development of advanced membrane materials. Herein, we reported the photocatalytic and super-wetting poly (arylene ether nitrile) (PEN) fibrous composite membrane with high permeability and enhanced anti-fouling ability. The nitrogen-doped Bi2O2CO3 (N-Bi2O2CO3) was prepared by low-temperature chemical modification method and modified by dopamine (DA)-polyethyleneimine (PEI), which was further self-assembled on porous PEN support backbone. The hydrophilicity provided by the cross-linking reaction between PDA and PEI and micro-/nano- rough surface constructed by the flower-like N-Bi2O2CO3 contributed to the super wetting properties (WCA=0°, UOCA>150°), which imparted the membrane with ultra-low oil adhesion. In particular, the arrangement of flower-like N-Bi2O2CO3 effectively regulated the water channel of membrane, further increasing the permeate flux. Therefore, the fibrous composite membranes showed superior separation flux (632.79–762.81 L·m−2·h−1) and separation efficiency (>99.16%) for various oil-in-water emulsions, even under harsh conditions (90 ℃ and 2 M NaCl solution). More importantly, the N-Bi2O2CO3 rendered the membrane excellent degradation rates for various dyes (MO: 95.53%, MeB: 96.40%, CV: 96.45%, CR: 87.14%), achieving favorable photocatalytic self-cleaning ability. This work opens an alternative strategy to fabricate fibrous composite membrane with synergistically enhanced anti-fouling for the treating complicated emulsified oily wastewater in petrochemical industry.

Double network cross-linked hydrogel coating membrane with photocatalytic self-cleaning performance for efficient oil-water separation

Oil-water separation is one of the most attractive areas in the field of energy and the environment. However, the synthesis of oil-water separation membranes with high separation efficiency and anti-fouling via simple methods is still a challenge. In this work, a double network with tannic acid and g-C3N4 cross-linked gelatin hydrogel coating membrane was prepared via ultrasound and coating. The prepared hydrogel had excellent mechanical properties and swelling resistance and also endowed the membrane with underwater superoleophobicity. For stratified oil-water mixtures, the separation flux achieved 40,355 ± 1957 L·m−2·h−1 and separation efficiency higher than 99 %. Moreover, after 40 cycles, there was no decrease significantly in separation performance. For oil-in-water emulsions, the separation efficiency is >99.90 % under gravity. The adsorption of MB by the GE-CNTA-PP membrane conformed to a pseudo-first-order kinetic process (R2 = 0.99906), which was consistent with the Langmuir isothermal adsorption model (R2 = 0.99932). The contaminated membrane could self-clean via photocatalytic reaction, which mechanism was explained through theoretical investigation of the band structure of g-C3N4 by DFT. Due to these obvious advantages, the practical application of the gelatin-based hydrogel membrane in the purification of oily wastewater is promising.

Cellulose cryogels from herbal residues for oily wastewater purification

Recycling herbal residues for oily wastewater purification is a potential way to use the wastes to treat wastes. Cellulose extracted from herbal residues is a fine material for cryogel fabrication. However, the cellulose cryogels were not suitable for oily wastewater treatment due to their amphiphilicity. To address this issue, the cryogels were modified with methyltrimethoxysilane (MTMS), which made them hydrophobic and reduced their surface energy. In this study, the herbal residues (Ficus microcarpa L. f) were used in cryogel preparation for the first time. The cryogels exhibit super lightweight and low density. The modified cryogels show excellent sorption capacity for free oils, especially silicone oil (51.22 g/g), and outperformed some recent sorbents. They also effectively separated water-in-toluene emulsion stabilized by Span 80, with a separation efficiency of 98.57 % and a flux of 1474.67 L/m2h. This study demonstrated a novel application of waste herbal residues in the field of environmental remediation.

Super-amphiphobic arabic gum-based coatings on textile for on-demand oily and dye wastewater treatment

Different membrane materials have broadly been constructed for oil-containing water separation, but most of preparation routes involve corrosive or toxic chemicals and especially many materials have only single superwetting property. Herein, a novel and eco-friendly cellulose-based textile membrane is developed by incorporating the composite coating consisting of arabic gum (AG), attapulgite (APT), and iron (Fe) onto cellulose textiles. The functionalized textile is superoleophobic underwater and superhydrophobic underoil. As a result, the textile prewetted with water or oil can be employed to separate light oil layer/water and heavy oil layer/water mixtures, respectively, and the separation efficiency to the two types of mixtures is larger than 98.3 %. Results also reveal that the decorated textile possesses superior stability and recyclability in purifying oily wastewater. More importantly, such coated textile is capable of filtrating water-soluble contaminants (dyes) from polluted water. Due to the versatility and environmental compatibility of product as well as the accessibility as agricultural and forestry product as raw materials, the advanced textiles may offer effective solutions to oily wastewater purification and water-soluble contaminant removal.

Preparation and characterization of electrospun PVDF/PVP/SiO2 nanofiber membrane for oil-water separation

For oily wastewater purification, polyvinylidene fluoride (PVDF) nanofiber membranes have been widely noticed for their excellent mechanical strength and corrosion resistance. However, it is prone to serious oil fouling problems during use, resulting in reduced flux and inability to be used repeatedly. It has become a hot research topic to develop simple methods to realize its hydrophilic modification for oily wastewater treatment to address this problem. Herein, a novel separation membrane was prepared by doping polyvinylpyrrolidone (PVP) and hydrophilic silica nanoparticles (SiO2 NPs) into PVDF using a facile one-step electrospinning method. The modified membrane shows hydrophilicity, water contact angle (WCA) is 0°, oleophobicity in water, and oil contact angle (OCA) is more than 145° and has good separation efficiency and flux for both oil-water mixtures and emulsions. After 30 times of mixture and emulsion separation tests, the separation efficiency is above 99.5 % and 97 %, respectively, showing good separation and reusability. Besides, compared with hydrophilic modification methods such as surface coating and grafting, the proposed modification method is simpler and has great potential in treating oily wastewater.