An overview of superhydrophobic ceramic membrane surface modification for oil-water separation

The discharge of oily wastewater and offshore oil spills contaminates the biotic and aquatic environment and ultimately result in the destruction of the ecosystem. Recently, the application of ceramic membranes has gained prodigious attention due to its efficiency in oil-water separation process. Ceramic membranes developed from inorganic materials are considered as the most promising technology for the treatment of industrial wastewater. Besides, different types superhydrophobic-superoleophilic substrates are being developed using various substrate materials to tailor its purpose for higher efficiency. Nonetheless, fouling and clogging phenomena restrict the performance of ceramic membrane in oil-water separation. This review emphasizes the recent innovation on superhydrophobic methods for the modification of ceramic membranes for oil-water recovery. It comprises of an overview of the preparation technique of ceramic membrane using various techniques. Moreover, the different types of hydrophobic ceramic membrane modification using chemical agents and consequent effects on oil-water separation were discussed in detail. Furthermore, the technical challenges and issues associated with the applications of superhydrophobic-superoleophilic ceramic membrane for oil-water separation were discussed. Finally, future direction in the research of cost-efficient approach to produce superhydrophobic ceramic membranes for oil-water filtration process is enumerated

Facile approach in development of superhydrophobic-superoleophilic kaolin-based hollow fibre ceramic membrane

A silane coupling agent is an organosilicon compound with special structure possessing organic functional groups and hydrolysable groups. In this study, a superhydrophobic-superoleophilic nano-silica film on ceramic membrane was constructed by a modified Stöbertechnique by using tetraethoxy-silane (TEOS) and fluoroalkyl silane (FAS). The colloidal nano-silica based silane sol coating solution was synthesized via co-hydrolysis and co-condensation of TEOS and FAS. Particle size distribution of the colloidal nano-silica based silane sol was evaluated using particle size analyzer as depicted. The contents of the relative elements of the colloidal nano-silica based silane sol were examined using energy dispersive x-ray (EDX) spectra. Extent of superhydrophobicity-superoleophilicity was determined using the contact angle measurements. The surface wettability of superhydrophobicity-superoleophilicity was determined using the contact angle measurements. Also, the effects of grafting times and coating cycles on the wettability of the modified kaolin-based hollow fiber membrane were determined. The results revealed that the modified kaolin-based hollow fiber membrane exhibited oil contact of 0o and water contact angle of 160o and, demonstrating its considerable antiwetting applications like in oil-water filtration process. While, with an increase in grafting times and coating cycles, the wettability of the superhydrophobic-superoleophilic nano-silica film was enhanced due to increase in surface roughness provided by the hydrolysable groups on the surface of the ceramic membrane. In conclusion, this study presents a feasible route to the surface superhydrophobicity-superoleophilicity testing of ceramic membrane

Facile purification of palygorskite and its effect on the performance of reverse osmosis thin film nanocomposite membrane

BACKGROUND: Palygorskite (PAL) is a naturally occurring nanoclay characterized by a distinctive tubular structure and fibrous morphology, exhibiting chemical and thermal stability as well as large specific surface area. The tubular structure of PAL promotes the selective transportation of water molecules, hence can serve as an interesting candidate for liquid separation. In this work, a membrane substrate was fabricated using the purified PAL to enhance the flux of the thin film composite reverse osmosis. Purification of PAL enhances its interaction with polymer chain to further promote nanofiller dispersion and improves the hydrophilic properties. The water flux as well as salt rejection of the developed membranes was examined using a dead end filtration system. The membrane performance with respect to pure water flux and salt rejection was evaluated using reverse osmosis water and 2000 ppm sodium chloride solution at 15 bar operation pressure. RESULTS: The physico-chemical characterization evidenced the role of purified PAL (P-PAL) in increasing the number of pores and promoting the formation of finger like structure in the substrate layer. The water flux of thin film nanocomposite (TFN) containing P-PAL exhibited 114.6% and 43.1% improvement compared to that of neat and TFN membrane incorporated with pristine PAL respectively without compromising the salt rejection performance. CONCLUSIONS: This study highlights the purification of palygorskite and its effects on membrane water permeability in the field of water desalination. © 2021 Society of Chemical Industry (SCI)

Photocatalytic degradation of recalcitrant aromatic hydrocarbon compounds in oilfield-produced water: A critical review

Oilfield-produced water (OPW) contains a complex mixture of toxic and hazardous organic and inorganic compounds. Refractory polycyclic aromatic hydrocarbons (PAHs) and polyaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX) chemical compounds present in OPW which result from hydrocarbon sources and chemicals added during the oil recovery process, have become a source of global concern. Their continuous presence in the OPW requires suitable technology to remove them before their discharge to the environment. When the OPW contains harmful pollutants combined with oil in minute size, the treatment performance of various water technologies appears insufficient due to the generation of secondary by-products, which are also recalcitrant and toxic. To consolidate scattered knowledge of OPW in the field of water pollution control, this article critically reviews and evaluates the technical feasibility of heterogeneous photocatalysis for OPW treatment, their bottlenecks in applications, and the way forward for the removal of recalcitrant hydrocarbon compounds from OPW. This work also presents the nature, composition, and health implications of these compounds in the OPW. Pertinent factors for effective photodegradation were presented. It also critically evaluates and discusses a variety of pilot and commercial-scale applications of photocatalysis in water treatment and its limitations. It was conclusively evident from 239 published articles (1988–2022) that heterogeneous photocatalytic degradation is a powerful approach for the removal of the hydrocarbon compounds such as PAHs, BTEX, and phenol with an average of over 80% of degradation efficiency. The photocatalytic process can be scaled up to the commercial scale with the proper design of photocatalytic reactors and the synthesis of advanced photocatalys

Recent development in modification of polysulfone membrane for water treatment application

Polysulfone (PSF) membranes have been widely used for wastewater treatment due to their desired properties like stability, high mechanical strength and ease of modification. The modification of PSF membranes presents a great opportunity in improving their performance in the field of wastewater treatment. This review presents a comprehensive review of PSF ultrafiltration (UF) and microfiltration (MF) membranes modification via various techniques as well as novel modifiers for water purification by paying attention to various issues inherent in the modification process. Recent studies on nanomaterial as well as hydrophilic macromolecules used for the modifications of PSF UF/MF membranes for water treatment application have been comprehensively analysed. These modified membranes exhibited a remarkable improvement with regards to water permeability, salt rejection and anti-fouling features of PSF modified membranes when compared to the neat PSF membranes. The modification techniques such as coating, grafting/blending, layer by layer and deposition are discussed. Besides, the impacts of these modifiers on the performance of the membranes for wastewater treatment as well as their environmental impacts are discussed. Based on the literature review, it is obvious that nanomaterial/hydrophilic macromolecules modified PSF membranes have unique features that can contribute to the advancement of innovative nanocomposite membranes with enhanced capacities for wastewater treatment

The influence of pretreatment step on hollow braided PET fabric as a potential membrane substrate

Self-supporting polymeric hollow fiber membranes prepared using non-solvent induced phase separation (NIPS) often suffer deterioration in mechanical properties due to asymmetric fingerlike and spongelike morphology giving a porous and fragile structure. Hollow braided fibers of Polyethylene terephthalate (PET) have been used as substrate to increase the strength of hollow fiber membranes. However, problems arise from poor interfacial bonding between the braid and coating polymer resulting in peeling off or delamination at the interface. In this work, we report a method of braid treatment and selection with two alkali treatment steps (NaOH and KOH) to study their effect on pure water flux, water contact angle, tensile strength as well as braid morphology of three different braid samples (B1, B2 and B3). B2 sample treated in KOH demonstrated the highest water flux of 1388 L/m2h. Examination of surface morphology of the braids revealed a washing effect and enlargement of braid interspaces making them more porous and hence increased permeability, with a contact angle of 0° with water. The sample also exhibited zero weight loss as well as a remarkable tolerance for high temperature with negligible reduction in tensile strength of only about 0.9%. Membrane fabricated with B2-K was demonstrated to have better adhesion between polymer-braid interface in comparison to the control. The pre-treatment step provides a good braid selection basis for onward membrane development with KOH showing the most favorable outcome without losing braid quality

Hydrothermal synthesis of tio2 nanoflower deposited on bauxite hollow fibre membrane for boosting photocatalysis of bisphenol a

The special physical and chemical properties of titanium dioxide (TiO2), including the environmental friendliness and facile fabrication, have made it the most widely studied photocatalyst. The use of TiO2 largely relies on its morphological traits, crystal structure, and phase dimension. The uniqueness of TiO2nanoflower structure with a coarse texture and arranged structures demonstrates higher photocatalytic activity for organic pollutants. A simple hydrothermal synthesis was used in this study with TiO2 nanoflowers implanted on the surface of bauxite-based hollow fibre membrane (BHFM). The modification was done to enhance the photocatalytic performance of the BHFM as this membrane naturally possesses catalytic property. The decorated BHFM was then subjected to catalytic degradation of bisphenol A (BPA) under irradiation of UV light. The synthesis of TiO2 nanostructure on the membrane surface was successfully performed based on SEM images, and it has good water permeability of 323.76, 309.32 and 280.42 L/h.m2.bar for 2.5 h, 5.0 h and 7.5 h of hydrothermal time respectively. A significant difference of 25 % between the modified and unmodified BHFM was notable, which indicates its potential as a new material for photocatalyst. As a conclusion, the modified BHFM possessed enhanced photocatalytic properties under both UV light and visible light

Bisphenol A Removal Using Visible Light Driven Cu₂O/PVDF Photocatalytic Dual Layer Hollow Fiber Membrane

Bisphenol A (BPA) is amongst the endocrine disrupting compounds (EDCs) that cause illness to humans and in this work was removed using copper (I) oxide (Cu2O) visible light photocatalyst which has a narrow bandgap of 2.2 eV. This was done by embedding Cu2O into polyvinylidene fluoride (PVDF) membranes to generate a Cu2O/PVDF dual layer hollow fiber (DLHF) membrane using a co-extrusion technique. The initial ratio of 0.25 Cu2O/PVDF was used to study variation of the outer dope extrusion flowrate for 3 mL/min, 6 mL/min and 9 mL/min. Subsequently, the best flowrate was used to vary Cu2O/PVDF for 0.25, 0.50 and 0.75 with fixed outer dope extrusion flowrate. Under visible light irradiation, 10 mg/L of BPA was used to assess the membranes performance. The results show that the outer and inner layers of the membrane have finger-like structures, whereas the intermediate section of the membrane has a sponge-like structure. With high porosity up to 63.13%, the membrane is hydrophilic and exhibited high flux up to 13,891 L/m2h. The optimum photocatalytic membrane configuration is 0.50 Cu2O/PVDF DLHF membrane with 6 mL/min outer dope flowrate, which was able to remove 75% of 10 ppm BPA under visible light irradiation without copper leaching into the water sample

Impact of organosilanes modified superhydrophobic-superoleophilic kaolin ceramic membrane on efficiency of oil recovery from produced water

BACKGROUND: Novel hybrid absorption coupled with membrane filtration technology is proposed for the recovery of oil from produced water. This study aims at developing a low cost superhydrophobic-superoleophilic kaolin-based hollow fiber ceramic membrane using phase inversion and sintering technique for the recovery of oil from synthetic produced water. The influence of different organosialanes, such as methyltriethoxysilane (MTES), octadecyltrimethoxysilane (OTMS), 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS), trichloro(octadecyl)silane, and chlorotrimethylsilane, was investigated for the modification process. RESULTS: Field emission scanning electron microscopy results clearly indicated that membrane morphology was altered with coating of the organosilanes. The surface functionality of the organosilanes on kaolin membranes was also confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. From the atomic force microscopy studies, membrane surface roughness was observed to be higher for MTES, FAS, and OTMS coated kaolin membranes. Contact analysis show that the membranes coated with MTES, FAS and OTMS organosilane agents possessed superhydrophobicity of 161.3°, 155.6°, and 150.2° as well as superoleophilicity of 0°, 1.5°, and 2.3°, respectively. CONCLUSION: Crude oil with a concentration of 2 g L−1 displayed a higher oil flux of 80 L m−2h−1 and absorption of 90% for MTES coated kaolin membrane. This study extends the frontier of knowledge in ceramic membrane application for produced water treatment