Purification Of Oily Wastewater Research Articles

Thermally stable and superhydrophobic foam prepared by high‐internal phase emulsion for oil/water separation with good recycling capacity

AbstractSuperhydrophobic polymeric foams, with good thermal stability and high‐recycling capacity to remove oil from oily wastewater, are highly desirable for current oily wastewater purification. Herein, poly (styrene‐acrylic acid 2,2,3,4,4,4‐hexafluoro‐butyl ester‐divinylbenzene) foam with porosity as high as 99.27% has been prepared through high‐internal phase emulsions. Therein, poly (cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) microspheres, and Span80 act as co‐emulsifier to stabilize the emulsion system. The as‐prepared foams exhibited super hydrophobicity with a water contact angle of 150.3° and thermal stability. Additionally, the oil adsorption capacity of the porous material could reach up to 25.6–53.4 times its mass with accessible and high‐recycling capacity. These aforementioned outstanding properties make our superhydrophobic foam hold potential applications in oil/water separation.

Recent Progress in Superhydrophilic Carbon-Based Composite Membranes for Oil/Water Emulsion Separation.

The purification of stabilized oil/water emulsions is essential to meet the ever increasing demand for monitoring water in the environment, which has been addressed with superwetting carbon-based separation membranes. These include superhydrophilic carbon-based membranes whose progress in recent years and perspectives are reviewed in this paper. The membrane construction strategy is organized into four parts, vacuum-assisted self-assembly, sol-gel process, electrospinning, and vacuum-assisted filtration. In each section, the design strategies and their responding disadvantages have been comprehensively discussed. The challenges and prospects concerning the superhydrophilic carbon-based separation membranes for oily wastewater purification are also summarized to arouse researchers to carry out more studies.

Durable, self-healing superhydrophobic nanofibrous membrane with self-cleaning ability for highly-efficient oily wastewater purification

It is of great significance while challenging to develop separation materials with integrated functionalities including self-healing, self-cleaning, and efficient separation capabilities for the remediation of oily wastewater and oil spills. In this work, a facile method is developed to fabricated polyimide (PI) nanofibrous membrane with self-healing superhydrophobicity. The designed membrane presents remarkable separation efficiency towards a range of oil/water mixtures and water-in-oil emulsions. Furthermore, the membrane demonstrates desirable adaptability in harsh environment due to the synergistic environmental stability of the PI membrane and polydimethylsiloxane/octadecylamine (PDMS/ODA) coating. Of particular interest is the fact that the as-prepared membrane displays outstanding self-healing and self-cleaning abilities, possessing multifunctional integration. These features make the membrane a promising separation material for efficient oil/water separation in realistic environment.

One-step preparation of tubular nanofibers and micro/nanospheres covered membrane with 3D micro/nano structure for highly efficient emulsified oil/water separation

Facile fabrication of superwetting materials is urgently desired, which remains a challenging issue for industrial oily wastewater treatment. In this study, a novel tubular nanofibers and micro/nanospheres covered PVDF/graphene (GE) composite membrane (TPGCM) was prepared via one-step simultaneous electrospinning/electrospraying process with the polyethylene terephthalate (PET) braided tube (BrT) as the support. This simple combined technique allowed the uniform integration of PVDF micro/nanospheres and GE nanosheets into the PVDF nanofibrous network to form a 3D hierarchical micro/nano structural composite membrane. The resultant membrane exhibited superoleophilicity in air with oil contact angle of 0°, and showed under oil superhydrophobicity with corresponding contact angle of 159 ± 0.8°. Furthermore, the morphology of the covered micro/nanospheres was simply controlled by adjusting GE nanosheets content in electrospraying precursor. As-prepared TPGCM can effectively separate a series of Span-80-stabilized water-in-oil emulsions, which showed outstanding separation efficiency of up to 99.8 %. Moreover, the robust recyclability was also presented with separation efficiency of more than 99.3 % after 10 cycles. Our strategy possesses the advantages of simplicity and cost saving, avoiding complicated reaction or post treatment, thus indicating its scalable application for practical oily wastewater purification.

A facile and green route to fabricate fiber-reinforced membrane for removing oil from water and extracting water under slick oil

Except the good separation performance, the membranes used for oil-water mixture separation should be fabricated with as little wastewater produced as possible. Thus, we proposed a green tactic--water vapor induced phase inversion to prepare the high-strength and superhydrophilic/underwater superoleophobic nonwoven fabric-based cotton/PA6/PAN membranes which is based on the polymer/solvent/nonsolvent ternary system analysis. Differing from adding additives in polymer solution or coagulation bath, above proposed strategy has an “subtractive effect” with the advantages of constructing three-dimensional porous structure and greatly reducing the organic wastewater produced during preparation process. Moreover, the obtained cotton/PA6/PAN membranes exhibited unexpected performances for separating oil-in-water emulsions. An ultrahigh permeation flux of up to 478,000 L m−2 h−1 bar−1 with a separation efficiency of > 99.9% was obtained under the driving pressure of 1.6 KPa, which was one order of magnitude higher than the conventional separation membranes with similar properties. In addition, it is surprising that the cotton/PA6/PAN membranes can also extract water from the slick oil/water immiscible mixture. Therefore, it is expected that the cotton/PA6/PAN membranes can be used in practical oily wastewater purification.

Wettable copper hydroxide cotton fabric for oil-water separation made by surface micro-dissolution

Cotton textiles with special surface wettability, high adsorption capacity and low cost have a promising future for oily wastewater purification. A facile and efficient surface microdissolution technology was used to generate micro-nanostructure copper hydroxide on the surface of cotton fabric, and super-hydrophilic and underwater superoleophobic functional textiles were prepared. The underwater contact angle of the developed Cu(OH)2@Cotton Fabric is more than 152.9°. Driven by gravity, the oil/water mixture can be successfully separated by CH@CF with high flux of 2043–3843 L/m2h and high separation efficiency of 98.75%. After soaking in the harsh environment (high alkali and salt solution) for 24 h, CH@CF still keep good oil-water separation ability. The prepared fabric is efficient in the separation of water-in-oil emulsion driven by a constant current pump (200 mL/min) and the efficiency is greater than 99.1%. After repeated separation experiments for 25 times, the separation efficiency of the CH@CF for oil-water mixture keep more than 98.93%. This method can produce fabrics made of low-cost and available materials, expected to be a potential and feasible and efficient solution for oily wastewater purification, which has a promising future for oil/water separation.

Repeatable oil-water separation with a highly-elastic and tough amino-terminated polydimethylsiloxane-based sponge synthesized using a self-foaming method

A 3D porous sponge based on amino-terminated polydimethylsiloxane (PDMS) and graphene oxide (GO) was prepared using a simple one-pot method under mild conditions. Condensing agents combined GO and PDMS with covalent bonds, and simultaneously acted as the pore-foaming agents. Scanning electron microscopy and Mercury intrusion porosimetry revealed that the joint action of GO and condensing agents contributes to the formation of the porous structure. Cyclic compression demonstrated high toughness and elasticity. No deformation occurs after 20 compression cycles at over 80% strain, owing to the assistance of dynamic hydrogen bonds. GO content significantly influences the mechanical strength, hydrophobicity, as well as adsorption capacity for oil. Notably, the sponge can be repeatedly used with a simple squeezing method, and the adsorption capacity can still reach 96.30% of the first adsorption after 30 cycles of adsorption. Besides, the sponge was used to adsorb oil on the seawater surface experimentally. The stable structure, high mechanical strength, and excellent adsorption property suggest the sponge be a promising material for the treatment of oil leakage and oily wastewater purification in practice. This self-foaming method can be a common method for fabricating porous and stable porous materials.

Facile synthesis and characterization of Zno-HNT additive for enhancement of polysulfone membrane for Oil-In-Water separation

In this study, a novel nanocomposite of Zinc Oxide-Halloysite Nanotubes (ZnO-HNT) has been synthesized and incorporated into polysulfone membrane for the purpose of oily wastewater separation and purification. ZnO-HNT nanocomposite was synthesized as additives that can improve the hydrophilicity as well as the oleophobicity of the membrane. The nanocomposite was incorporated into PSf membrane in three different loading of ZnO and HNT. The novel nanocomposite has been characterized for its morphological characteristics using SEM, TEM and its physicochemical properties were also analyzed by FTIR and XRD. The performance of the modified polysulfone membrane was studied in terms of hydrophilicity, oil rejection and antifouling properties. The FTIR spectra recorded significant –OH peak at 3200 to 3500 cm−1 which contributes to the improve hydrophilicity of the membrane. XRD analysis shown that there are significant peaks at 2θ that attributes to both ZnO and HNT in which the nanocomposite exhibited more intense peak at 56.7° denoting increased amount of hydroxide groups. Additionally, the modified PSf membrane with ZnO-HNT additives has shown improved oil contact angle of 165°, water contact angle of 48.6° and 99% total rejection for oily wastewater indicating the improve performance of PSf through incorporation of ZnO-HNT.

Efficient purification of oily wastewater by a single-stage filtration with diatomite/carbon membranes

Efficient purification of oily wastewater by a single-stage filtration with diatomite/carbon membranes

Multifunctional charged hydrogel nanofibrous membranes for metal ions contained emulsified oily wastewater purification

Efficiently purifying metal ions contained emulsified oily wastewater has become a great challenge. Herein, a novel charged hydrogel nanofibrous membrane (CHNM) with negative surface charges, favorable mechanical ability and anti-fouling capacity was prepared via electrospinning and twice crosslinking process. The obtained CHNM with a surface potential of -32.9 mV at pH = 7.2 possesses outstanding oil-in-water emulsion separation performance with high permeation flux of around 10800 L h-1 m-2 bar-1 for surfactant free emulsion and high permeation flux of around 7100 L h-1 m-2 bar-1 for surfactant stabilized emulsion. The excellent oil/water emulsion separation performance can be attributed to the surface charge demulsification (SCD), which is theoretically demonstrated by a finite element analysis simulation. In addition, CHNM can absorb many kinds of metal ions (Fe3+, Ni2+ and Al3+) due to the chelation effect between high-density phosphate groups and metal ions. With outstanding separation performance for oil/water emulsion and good adsorption capacity for metal ions, the multifunctional CHNM may offer a promising approach to develop a new-generation membrane for treating metal ions contained oily wastewater.

Facile fabrication of TiO2-functionalized material with tunable superwettability for continuous and controllable oil/water separation, emulsified oil purification, and hazardous organics photodegradation

The sustainable development of modern industry and the frequent emergence of marine oil spills have caused a significant and far-reaching impact on water resources, prompting individuals to develop an advanced technology or material for the solution of oily wastewater. Therefore, a functionalized material herein has been successfully fabricated by decorating cotton surface with photocatalytic titanium dioxide (TiO2) nanoparticles and chemical components containing pH-sensitive carboxyl groups through a simple, green and cost-effective approach. By combining the nano-roughness structure of the surface with the suitable surface components, endowing the as-obtained cotton with the splendid properties of adjustable surface wettability, photocatalytic degradation and durability. Based on the tunable wettability of the resulted cotton, it can intelligently separate two forms of oil/water mixtures involving stratified oil-water mixtures and surfactant-stabilized emulsions with prominent separation efficiency. Simultaneously, by virtue of the resultant superwettable cotton, the high-speed and high-efficiency in-situ purification of oily wastewater driven by negative pressure is successfully realized. More interestingly, benefitting from the photocatalytic property of TiO2, this resulting cotton can be also exploited for degrading water-soluble dyes to achieve water purification. In light of the unique predominance of the above-mentioned modified cotton, this newly developed economical strategy can promote the extensive development of multipurpose superwetting materials, providing tempting potential for the treatment of intricate oily wastewater.

3D-Printed Membranes with a Zwitterionic Hydrogel Coating for More Robust Oil–Water Separation

Three-dimensional (3D)-printed membranes via stereolithography (SLA) are promising in oil–water separation, which is the key in the purification of industrial oily wastewater. To achieve gravity-dr...

Optimal synthesis of high fouling-resistant PVC-based ultrafiltration membranes with tunable surface pore size distribution and ultralow water contact angle for the treatment of oily wastewater

The effects of salt and alkali in coagulation bath for the synthesis of Pluronic F127/polyacrylonitrile/bentonite (PF127/PAN/bentonite-) blended polyvinyl chloride (PVC) ultrafiltration (UF) membrane with ultralow water contact angle and tunable surface pore size distribution have been established and the synthesized membrane has been tested for the purification of oily wastewater. The UF membranes are prepared via a single-step phase inversion technique using different coagulation baths involving (i) water, (ii) KCl, (iii) aqueous KOH solution, and (iii) KCl + aqueous KOH solution, and the effect of coagulation on membrane morphology, structure and performance have been studied. The best performing membrane is obtained by maximizing pure water flux using casting solution involving PF127, PAN and bentonite, and KOH-induced KCl-salt coagulation bath. The optimally synthesized membrane performs very well for the purification of oilfield oily wastewater, and a significant increment in permeate flux is obtained with oil rejection > 97.0%. The optimally synthesized UF membrane results in reduced surface pore size distribution with exceptionally high surface pore density, ultralow oil-adhesion, and improved antifouling performance maintaining with stable permeate flux for a long-time run. The synthesized PVC/PF127/PAN/bentonite-blended UF membranes using KOH-induced KCl-salt coagulation bath have shown great promise for the purification of oilfield oily wastewater, especially with low oil concentration below 200 ppm.

Robust superhydrophilic depth filter and oil/water separation device with pressure control system for continuous oily water treatment on a large scale

As oily wastewater treatment has emerged as an urgent global issue, oil/water separation using functional filters is attracting significant attention as an environmentally friendly method of oily wastewater purification. Although functional filters based on wetting characteristics have already been developed, it is difficult to use them in the oil/water separation field due to their inability to handle a large amount of wastewater continuously. Herein, a strategy to continuously treat large amounts of oily water for practical application is reported. For the first time, we fabricate a robust superhydrophilic depth filter using a hydrogel material. This filter has great potential for treating large amounts of wastewater because of its large effective area, excellent mechanical and chemical durability, self-cleaning ability and high oil/water separation efficiency. Using this filter, we further develop a device to treat a large amount of wastewater continuously. The promising results demonstrated in this work show the potential applicability of our filter and device in the field of wastewater treatment.

MnO2-x nanowires on carbon cloth based superamphiphilic and under-oil superhydrophilic filtration membrane for oil/water separation with robust anti-oil fouling performance

Filtration membranes (FMs), with robust anti-fouling performance, are highly desirable for practical oily wastewater purification but still a challenge to be realized without water pre-wetting procedure. Herein, we demonstrate a novel and effective route to address this challenge by decorating MnO2-x nanowires on carbon cloth membrane (MCM) via simple hydrothermal method, in which the existence of oxygen vacancies on the outer surface of MnO2-x nanowires can greatly enhance the H2O adsorption capacity even under oil, thus the oil-fouling problem can be solved by simply immersing the oil-polluted membrane into water and shaking. Besides the superamphiphilic performance in air and underwater superoleophobic (underwater oil contact angle > 155° against diverse oils), our MCM also exhibits unexpected under-oil superhydrophilic properties, Moreover, high separation efficiency for diverse oil/water mixtures (>99.8%) and oil-in-water emulsions (>98.3%) have been also achieved based on our product. These outstanding properties make our sample hold a great potential in practical oily/water purification.

Flexible PDA@ACNTs decorated polymer nanofiber composite with superhydrophilicity and underwater superoleophobicity for efficient separation of oil-in-water emulsion

Nanofibrous membranes with superwetting performance have promising applications in oil adsorption or oil/water separation. However, the development of superwettable, stretchable and durable nanofiber composite for efficient separation of oil-in-water emulsion is still a challenge. Herein, a simple and versatile method was proposed to prepare flexible, superhydrophilic and electrically conductive polymer nanofiber composite with a core/shell structure by acidified carbon nanotubes (ACNTs) decoration onto polyurethane (PU) nanofibers and subsequent polydopamine (PDA) modification. Multiple interfacial hydrogen bonding among ACNTs, PDA and PU nanofibers results in the enhancement of both the tensile strength and Young's modulus of the PU nanofibrous membrane and also ensures the excellent stretchability, surface stability and durability of the nanofiber composite. The obtained superhydrophilic/underwater superoleophobic nanofiber composite exhibits superior anti-fouling property and can be used for high efficiency separation of oil-in-water (even corrosive) emulsion with outstanding recyclability. The flexible and multifunctional nanofiber composite with a unique PDA/ACNTs shell and polymer nanofiber core structure shows great potentials in practical oily wastewater purification.

Superhydrophilic and underwater superoleophobic Ti foam with robust nanoarray structures of TiO2 for effective oil-in-water emulsion separation

In this work, a superhydrophilic and underwater superoleophobic Ti foam with TiO2 nanoarrays was facilely fabricated via the hydrothermal treatment and proton exchange method. Taking advantages of the constructed hierarchical structures and the high surface energy of TiO2, the Ti foam exhibits excellent superwetting behaviors to water and ultralow oil adhesion property with the underwater oil contact angle (OCA) of 166° and the sliding angle (OSA) lower than 3°. Meanwhile, the as-prepared foam can be applied for separating various oil-in-water emulsions with 99% separation efficiency and high permeation fluxes. Additionally, it performed good anti-fouling and self-cleaning property, which had stable separation performance even for 50 cycles of repeated use. Importantly, the hierarchical structured sample showed outstanding chemical stability and robust mechanical durability under various chemical corrosions, physical abrasion and vibration without obvious reduction of the separation efficiency. It is expected that superhydrophilic Ti foam with nanoarray structures constructed by this facile method would be a practical candidate in oily wastewater purification, due to its excellent wetting property, good self-cleaning capacity, robust mechanical durability, as well as superior chemical stability.

Engineering of ultrafine polydopamine nanoparticles in-situ assembling on polyketone substrate for highly-efficient oil-water emulsions separation

Environmental issues caused by oily pollutants is one of the most severe challenges for the global ecosystem and public health. To develop the advanced membrane materials with superior antifouling property is urgently needed for highly efficient oily wastewater purification. In this study, an ultrathin polydopamine layer with a controllable thickness of ~90 nm was decorated onto a porous polyketone substrate via an extremely simple and scalable surface modification process. The ammonia initiator facilitated the ultrafine polydopamine nanoparticles (with its size about 30 nm) in-situ assembling. Benefiting from the ultrathin surface modification, the resultant polydopamine decorated polyketone (PDA-d-PK) membrane performed ultrahigh water permeance up to 11600 L m−2 h−1 bar−1. This membrane also exhibited a superior oily emulsions separation property with remarkably high permeance up to 8300–10600 L m−2 h−1 bar−1, and high rejection ratio more than 99.9% against various oily phases, including hexane, hexadecane, petroleum ether, and soybean oil. The hierarchical nanosphere-like polydopamine layer with superhydrophilicity/underwater superoleophobicity also endowed the PDA-d-PK membrane with an excellent antifouling performance against the oily emulsions containing surfactant, protein, and natural organic material. The PDA-d-PK membrane also featured a superior tolerance and durability under challenging conditions of salty, strong acid/alkali solutions, and a variety of organic solvents. This work provides an insight into the facile preparation of an ultrathin polydopamine membrane with simultaneous enhancement in separation and antifouling properties for highly-efficient oil-water emulsions separation.

Biomimetic Durable Multifunctional Self-Cleaning Nanofibrous Membrane with Outstanding Oil/Water Separation, Photodegradation of Organic Contaminants, and Antibacterial Performances.

Wastewater pollution has always been one of the most severe worldwide environmental problems. In addition, in light of the frequent oil spills that have occurred in recent years, the treatment of oily wastewater is particularly important. In this work, a novel zeolitic imidazolate framework-8@thiolated graphene (ZIF-8@GSH) composites-based polyimide (PI) nanofibrous membrane was developed via a facile electrospinning and in situ hydrothermal synthesis approaches for effective purification of oily wastewater. The membrane showed superhydrophobicity/superoleophilicity and high separation efficiency (>99.9%) for a wide range of oil/water mixtures and water-in-oil emulsions. Besides, the membrane demonstrated excellent photocatalytic dye degradation, antibacterial, self-cleaning, and mechanochemical durable abilities, showing high potential in oily wastewater treatment and water remediation.

Facile preparation of petaliform-like superhydrophobic meshes via moisture etching for oil-water separation

Developing a facile strategy for high-efficiency mixture separating is highly necessary, especially for the purification of oily wastewater and the refinement of organic solvents. In this work, robust superhydrophobic meshes (Cu@E-Zn@SA) with ribbon-shaped coating and controllable pore size were prepared via the electrodeposition of laminated Zinc coating, further moisture etching and post-modification with stearic acid. In particular, the moisture etching process, which was facile and environment-friendly, were applied to form the rough petaliform structure and adjust the pore size. Through carefully coordinated regulating the electrodeposition time, moisture etching time and post-modification process, the average pore size of the mesh could be precisely tuned in the range from 38 μm to 6 μm. The influences of the textured roughness and chemical composition on the surface wettability were systematically investigated. The Cu@E-Zn@SA exhibited superhydrophobicity with water contact angles of larger than 150° and sliding angles of lower than 8°. Besides, the Cu@E-Zn@SA could maintain their superhydrophobicity after sandpaper abrasion and sand impact for 50 cycles, displaying remarkable environmental durability and mechanical robustness. Moreover, the prepared superhydrophobic meshes could be applied for the on-demand separation of the oil-water immiscible mixture and water-in-oil emulsions with high efficiencies over 99.3%. Thus, these findings may provide insights in constructing robust superwetting metallic meshes with great application potential in oil-water separation.