Publications

Effect of kaolin particle size and loading on the characteristics of kaolin ceramic support prepared via phase inversion technique

In this study, low cost ceramic supports were prepared from kaolin via phase inversion technique with two kaolin particle sizes, which are 0.04–0.6 μm (denoted as type A) and 10–15 μm (denoted as type B), at different kaolin contents ranging from 14 to 39 wt.%, sintered at 1200 °C. The effect of kaolin particle sizes as well as kaolin contents on membrane structure, pore size distribution, porosity, mechanical strength, surface roughness and gas permeation of the support were investigated. The support was prepared using kaolin type A induced asymmetric structure by combining macroporous voids and sponge-like structure in the support with pore size of 0.38 μm and 1.05 μm, respectively, and exhibited ideal porosity (27.7%), great mechanical strength (98.9 MPa) and excellent gas permeation. Preliminary study shows that the kaolin ceramic support in this work is potential to gas separation application at lower cost.

Omniphobic Braid-Reinforced Hollow Fiber Membranes for Dcmd of Oilfield Produced Water: Understanding the Effect of Process Conditions on Membrane Performance

Recent efforts to realize hollow fiber membranes for treatment of complex wastewater such as produced water has resulted in designing unique surfaces, for use in membrane distillation to combat wetting and fouling/scaling. However, HFMs suffer from mechanical inadequacies. Use of polyethylene terephthalate (PET) braid support to strengthen HFMs is gaining attraction, although their application in MD is scarce. Herein, we report omniphobic PET braid-reinforced HFMs (OBRMs) for application in direct contact membrane distillation (DCMD) of PW. The effects of feed type, velocity, temperature, and prolonged testing on performance OBRMs are reported. From the findings, a thin polymer layer with single-layer finger-like structure allowed for good flux (up to 15 kg/m 2 h) while omniphobic skin layer was instrumental in keeping oils and surfactants at bay. Complex PW feed is shown to have more adverse effect on strength of OBRMs than saltwater. Increased temperature negatively affects tensile strength while a turbulent flow keeps foulants at bay and mitigates fouling-assisted deterioration. Prolonged testing for nine DCMD cycles of treating PW recorded flux recovery up to 85%, with salt rejection remaining above 99.9%, a total organic carbon (TOC) rejection up to 98% and a decline in tensile strength of used membranes by 6.5%.

Ammonia removal by adsorptive clinoptilolite ceramic membrane: Effect of dosage, isothermal behavior and regeneration process

This work investigates the effectiveness of ammoniacal nitrogen (NH +4 -N) removal from contaminated water by adsorptive hollow fiber ceramic membrane (HFCM) derived from naturally made clinoptilolite. The technological value of this work is the simple mechanism of the adsorptive HFCM in removing gaseous ammonia in water by combining adsorption and separation. To test the technical feasibility of this proposed technology, clinoptilolite HFCM was fabricated via phase inversion-based extrusion/sintering technique and characterized by SEM and water permeation flux. The produced HFCM corresponds to the desired morphology of the asymmetric structure (dense and void formations) with outstanding adsorption performance of NH +4 -N. The effects of the HFCM’s operational parameters on its removal are examined in terms of membrane dosage and isothermal studies. The adsorption isotherm behavior exhibited that the adsorption process fitted the Freundlich isotherm model with outstanding removal performance even at trace concentration of ammonia. The low amount used by HFCM (4.75×10−4m2) resulted in over 96% ammonia removal, indicating a low cost of adsorption process. The regeneration of saturated HFCM suggests an outstanding recovery of the HFCM for its subsequent use for NH +4-N removal. This study also reveals the potential of adsorptive HFCM as a simple and cost-effective technology for ammonia removal from wastewater.

Chromium Removal from Aqueous Solution Using Natural Clinoptilolite

This work investigates the applicability of clinoptilolite, a natural zeolite, as a low-cost adsorbent for removing chromium from aqueous solutions using fixed bed studies. To improve its removal performance for the inorganic pollutant, the adsorbent is pretreated with NaCl to prepare it in the homoionic form of Na+ before undertaking ion exchange with Cr3+ in aqueous solution. This work also evaluates if treated effluents could meet the required effluent discharge standard set by legislation for the target pollutant. To sustain its cost-effectiveness for wastewater treatment, the spent adsorbent is regenerated with NaOH. It was found that the clinoptilolite treated with NaCl has a two-times higher Cr adsorption capacity (4.5 mg/g) than the as-received clinoptilolite (2.2 mg/g). Pretreatment of the clinoptilolite with NaCl enabled it to treat more bed volume (BV) (64 BV) at a breakthrough point of 0.5 mg/L of Cr concentration and achieve a longer breakthrough time (1500 min) for the first run, as compared to as-received clinoptilolite (32 BV; 250 min). This suggests that pretreatment of clinoptilolite with NaCl rendered it in the homoionic form of Na+. Although pretreated clinoptilolite could treat the Cr wastewater at an initial concentration of 10 mg/L, its treated effluents were still unable to meet the required Cr limit of less than 0.05 mg/L set by the US Environmental Protection Agency (EPA).

Preparation and Characterization of Bentonite - Based Ceramic Hollow Fiber Membrane

The use of low-cost clay materials for the fabrication of ceramic membrane has attracted much interest from researchers, and the outcome would be beneficial to the industries. In this study, low-cost bentonite was used for the preparation of hollow fiber ceramic (HFC) membrane. Bentonite powder was initially characterized by field emission scanning electron microscope (FESEM) for powder surface morphology. The bentonite membrane was fabricated through dope suspension mixing, using phase inversion-based extrusion method and sintering processes. The dope suspension was prepared by mixing quantified bentonite powder, dispersant, polymer binder, and organic solvent on a planetary ball mill. This was followed by the extrusion of the dope suspension at a bore fluid rate of 10 mL/min and air gap of 5 cm and finally subjected to the sintering temperatures of 950° C, 1000° C, 1050° C, and 1100° C. FESEM images revealed that bentonite powder has a compacted interlayer order of heterogeneous surface morphology. The resulting bentonite HFC membrane surface morphologies were examined by scanning electron microscopy (SEM), and the structures exhibit asymmetric structure, which was composed of sponge-like and finger-like structures. Due to, its superhydrophilic property and pore size; the membrane contact angle and water flux performance were obtained at 1.90° and ~326 L/m2 .h, respectively. Overall, the results suggest that bentonite can be used in the fabrication of ceramic-based hollow fiber membrane and in addition, can as well be utilized in microfiltration for wastewater treatment.

A Review of Titanium Dioxide (TiO2)-Based Photocatalyst for Oilfield-Produced Water Treatment

Oilfield produced water (OPW) has become a primary environmental concern due to the high concentration of dissolved organic pollutants that lead to bioaccumulation with high toxicity, resistance to biodegradation, carcinogenicity, and the inhibition of reproduction, endocrine, and non-endocrine systems in aquatic biota. Photodegradation using photocatalysts has been considered as a promising technology to sustainably resolve OPW pollutants due to its benefits, including not requiring additional chemicals and producing a harmless compound as the result of pollutant photodegradation. Currently, titanium dioxide (TiO2) has gained great attention as a promising photocatalyst due to its beneficial properties among the other photocatalysts, such as excellent optical and electronic properties, high chemical stability, low cost, non-toxicity, and eco-friendliness. However, the photoactivity of TiO2 is still inhibited because it has a wide band gap and a low quantum field. Hence, the modification approaches for TiO2 can improve its properties in terms of the photocatalytic ability, which would likely boost the charge carrier transfer, prevent the recombination of electrons and holes, and enhance the visible light response. In this review, we provide an overview of several routes for modifying TiO2. The as-improved photocatalytic performance of the modified TiO2 with regard to OPW treatment is reviewed. The stability of modified TiO2 was also studied. The future perspective and challenges in developing the modification of TiO2-based photocatalysts are explained.

List of contributors

Proton Transport Mechanisms in Nanofibers Ion Exchange Membrane

The importance of proton conductivity is enormous for biological systems and in devices such as electrochemical sensors, electrochemical reactors, electrochromic devices, and fuel cells. In the review, the phenomenon of proton conductivity in materials is discussed with a special emphasis on electrospinning as the fabrication method of proton exchange membranes (PEMs). In a fuel cell, PEMs have a profound influence on its performance. Many researchers have investigated the functionalization methods to solve the methanol crossover problem and to obtain low electronic conductivity, low electroosmotic drag coefficients, good mechanical properties, good chemical stability, good thermal stability, and high proton conductivity. The development and performance of high proton-conductive polymeric membrane, including electrospinning as the PEM fabrication method for fuel cells are discussed.

Recovering heavy metals from electroplating wastewater and their conversion into Zn2Cr-layered double hydroxide (LDH) for pyrophosphate removal from industrial wastewater

This work incorporated technological values into Zn2Cr-layered double hydroxide (LDH), synthesized from unused resources, for removal of pyrophosphate (PP) in electroplating wastewater. To adopt a resource recovery for the remediation of the aquatic environment, the Zn2Cr-LDH was fabricated by co-precipitation from concentrated metals of plating waste that remained as industrial by-products from metal finishing processes. To examine its applicability for water treatment, batch experiments were conducted at optimum M2 +/M3+, pH, reaction time, and temperature. To understand the adsorption mechanisms of the PP by the adsorbent, the Zn2Cr-LDH was characterized using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses before and after adsorption treatment. An almost complete PP removal was attained by the Zn2Cr-LDH at optimized conditions: 50 mg/L of PP, 1 g/L of adsorbent, pH 6, and 6 h of reaction. Ion exchange controlled the PP removal by the adsorbent at acidic conditions. The PP removal well fitted a pseudo-second-order kinetics and/or the Langmuir isotherm model with 79 mg/g of PP adsorption capacity. The spent Zn2Cr-LDH was regenerated with NaOH with 86% of efficiency for the first cycle. The treated effluents could comply with the discharge limit of <1 mg/L. Overall, the use of the Zn2Cr-LDH as a low-cost adsorbent for wastewater treatment has contributed to national policy that promotes a zero-waste approach for a circular economy (CE) through a resource recovery paradigm.

Chitosan-coated coconut shell composite: A solution for treatment of Cr(III)-contaminated tannery wastewater

Background Tannery industry generates a large amount of Cr(III)-contaminated wastewater daily. Unless properly treated, not only this effluent contaminates the water body, but also damages the environment and threatens public health. This batch study investigates the feasibility of chitosan-coated coconut shells as a low-cost material for removing Cr(III) from tannery wastewater. Both chitosan and coconut shell (CS) waste are abundantly available from local agricultural and fishery industries. Methods To enhance its treatment performance for Cr(III) removal, the CS was coated with chitosan as a composite. To sustain its cost-effectiveness, the saturated composite was regenerated with HNO3. Its performance for Cr(III) removal was evaluated and compared to other low-cost adsorbents in previous work. Findings At the same initial concentration of 20 mg/L, it was found that the composite had a higher Cr(III) removal (97%) than the chitosan alone under the optimized conditions of 4 g/L of dose, pH 6.5, 200 rpm of agitation speed, and 1 h of reaction time. The isotherm of Cr(III) removal by the adsorbents followed the Langmuir model, while the pseudo-second order reaction was representative to simulate the adsorption data. The Cr(III) removal by the composite was based on attractive columbic forces between the negative charge of the adsorbent's surface and the positive charge of the metal cation. The negative value of ΔG thermodynamic parameter suggests the spontaneous nature of adsorption. The efficiency of machine learning regression (MLR) model was assessed in predicting the experimental data of adsorption. In spite of promising results, treated effluents still could not comply with the required limit of discharge standards of less than 0.5 mg/L mandated by local legislation. Therefore, a subsequent treatment using activated sludge is required. Overall, this work reveals a contribution of unused resources from the coconut and shrimp industries in the form of composite for protecting the aquatic environment.

A review of water splitting <i>via</i> mixed ionic–electronic conducting (MIEC) membrane reactors

Coupling catalytic water splitting with a mixed ionic–electronic conducting (MIEC) membrane reactor has been demonstrated as a very promising approach to enhance the hydrogen production rate by extracting the oxygen produced.

Highly selective SPEEK/ENR blended polymer electrolyte membranes for direct methanol fuel cell

Sulfonated poly (ether ether ketone) (SPEEK) at higher degrees of sulfonation (DS) produced high proton conductivity, but it is impractical for DMFC application due to excessive swelling and severe methanol crossover. In this study, a novel blended membrane based on SPEEK at higher degrees of sulfonation (DS) of 80% and epoxidized natural rubber (ENR-50) are prepared at different mass ratio of SPEEK to ENR-50 (9.5:0.5, 9.0:1.0, 8.5:1.5, 8.0:2.0, and 7.5:2.5) via solution intercalation method. The influence of ENR-50 loading on the physical properties of SPEEK blends membranes was investigated and compared with the pristine SPEEK and Nafion117 membranes. The blended membranes were characterized by FTIR, which showed a successful chemical interaction between ENR-50 and SPEEK matrix. SEM images revealed a uniform dispersion of ENR-50 droplets in the polymer structure. The water uptake and methanol permeability of SPE50 membrane were found to be decreased with increasing of ENR-50 content. The highest proton conductivity of SPE50 membrane obtained was 47% higher than pure SPEEK, whereas the lowest permeability value obtained was 21 times lower than Nafion117 membrane. Consequently, incorporation of ENR-50 into SPEEK matrix has substantially enhanced the selectivity of the membrane by five folds. Apparently, this newly developed SPE blend membrane can be listed as one of the potential proton electrolyte membranes for the usage in DMFCs.

Polymer based Membrane Electrospun Fiber in Fuel Cell Application: A Short Review

usage which contributes to the environmental issues. Among the type of existing renewable energy, fuel cells is the most promising renewable energy sources since the energy can be directly converted from combustible of fuel. The proton exchange membrane (PEM) is the heart of the fuel cells system. The research and development on proton electrolyte membrane is keep burgeoned. Even though the studies of the electrolyte nanocomposite membrane for fuel cell application are quite various but only a few studies focused on the effect of electrospun nanocomposite membrane on the performance of proton electrolyte membrane. This review is focusing on the electrospinning process for the preparation of electrospun fiber membrane. This review is concentrates on polymer based membrane electrospun nanofiber and their influence on proton conductivity as well as on fuel crossover barrier properties. The proton conductivity and fuel crossover can be improved by fully exfoliated structure of nanocomposite electrolyte membrane via electropinning process and thus the membrane can be an alternative PEM for DMFC applications.

Effect of Pt–Pd/C coupled catalyst loading and polybenzimidazole ionomer binder on oxygen reduction reaction in high-temperature PEMFC

Polybenzimidazole (PBI) was studied as an ionomer binder at varying ratios (1–7) in a 20–40 wt% Pt–Pd/C cathode-coupled catalyst layer for the oxygen reduction reaction (ORR) in a high-temperature proton exchange membrane fuel cell (HT-PEMFC). Catalytic activity was examined by CV and LSV, while the properties of the catalysts were characterized by FESEM-EDX, N2 adsorption–desorption, XRD and FTIR. The results showed that the distribution of metals on the carbon surface, carbon wall thickness and the interaction between ionomer and coupled catalysts affected the ORR performance. The fabricated membrane electrode assembly with 5:95 PBI: 30 wt% Pt–Pd/C catalyst ratio exhibited the best performance and highest durability for HT-PEMFC at 170 °C, yielding a power density of 1.30 Wcm−2 with 0.02 mgPt/cm Pt loading. This performance of ultra-low metal loading of coupled Pt–Pd/C electrocatalyst with PBI binder was comparable to those reported by other studies, highlighting a promising catalyst for fuel cell application.

Rice husk-derived photothermal materials for membrane distillation

This study aimed to develop innovative photothermal materials derived from agricultural by-products (rice husk), with a primary focus on assessing the potential of both rice husk ash (RHA) and rice husk char (RHC) powders as effective photothermal for localised heating. A comparative analysis of their feasibility for membrane integration and photothermal performance was conducted through comprehensive physical, chemical, and optical characterisations. The RHC powder demonstrated superior qualities for utilisation in comparison with RHA. This superiority is attributed to several key factors: a notably high production yield (40.3 %), a smaller particle size of z-average (0.65 μm), a significantly larger effective BET surface area (301.78 m2 g−1), smaller pore size (2.78 nm) and an elevated total pore volume (0.21 cm³.g−1). Dominated by a significant carbon content of 38.5 %, RHC powder showcased minimal light reflection (<5 %) and excellent light absorption across the entire spectrum, while RHA exhibited reflectance of more than 40 %, with light absorption occurring solely in the UV region. Moreover, RHC powder displaced superior light-to-thermal conversion, evident in a 20.9 °C temperature rise (83.6 %) from a 90-min exposure to a 0.4 kW m−2 full spectrum light source. The findings of this study firmly established RHC powder as the preferred alternative option for sustainable photothermal materials, given its physical properties compatible with membrane integration and exceptional photothermal conversion ability.

Novel green hybrid processes for oily water photooxidation and purification from merchant ship

Two hybrid photooxidation systems consisting of two different reactors; photocatalytic reactor-ultrafiltration (PR-UF) and photocatalytic membrane reactor (PMR) have been investigated and compared for photolysis and separation of oily water. In both, oily water was irradiated by ultraviolet (UV) light. In PR, UV irradiation was made on the TiO2 photocatalyst suspended in oily water, followed by ultrafiltration (UF) to remove TiO2 particles and hydrocarbon residues. On the other hand, TiO2 was immobilized on the halloysite nanotube (HNT) and embedded in the UF membrane in PMR. In both systems, hydrocarbon concentration, chemical oxygen demand (COD), total dissolved solid (TDS), and hydrocarbon concentration were measured at each step of photooxydation and filtration. In UF, membrane flux, reduction in solute concentration, flux decline and flux recovery by backwashing were investigated. The experimental results showed that the reduction in TOC by PR-UF was ~10% higher than PMR. On the other hand, reduction in hydrocarbon concentration, COD and TDS was higher for PMR. The TiO2 concentration in UF permeate was 8ppm and 0.2ppm, respectively, for PR-UF and PMR.

Surface functionalization of bauxite hollow fibre membrane using copper oxide (CuO) and its reusability for photodegradation of bisphenol A from aqueous solution

This work developed and applied a CuO-impregnated bauxite hollow fibre membrane (BHFM) using hydrothermal method for bisphenol A (BPA) photodegradation. BHFM was synthesized through a phase inversion method at optimum sintering at 1300 °C. Subsequently, the physico-chemical properties of CuO-coated BHFM were characterized, while its performance for the BPA degradation was investigated at varying time of hydrothermal exposure and compared to ceramic hollow fibre membrane from alumina (AHFM) as control and commercial membranes. Oxidation by-products, resulting from BPA photodegradation, were identified and after treatment, the saturated membrane was regenerated to sustain its cost-effectiveness. As compared to the pristine BHFM membrane, we found that functionalizating BHFM surface with CuO significantly improved its mechanical strength by 130 % from 18.5 to 42.5 MPa. The removal of BPA was enhanced with the increasing hydrothermal time to 5 h due to the even distribution of CuO-impregnated BHMF on its membrane surface. 97 % of BPA removal with 10 mg/L concentration was substantially attained by the same CuO-impregnated BHFM under visible light (VIS) irradiation. Treated effluents, resulting from the BPA photocatalysis, could meet the required effluent limit of 20 mg/L set by national legislation. The possible oxidation by-products cover 4-(2-hydroxy-2-propanol)phenol, 4-isopropylphenol and dihydroxybenzene. With 25 % of efficiency, the saturated CuO-impregnated BHMF was subsequently regenerated for consecutive five cycles. This implies that functionalizing BHMF surface with CuO enabled it to possess outstanding stability and removal performance for treatment of BPA-laden wastewater.

A MORPHOLOGICAL STUDY OF NICKEL OXIDE HOLLOW FIBER MEMBRANES: EFFECT OF AIR GAP &amp; SINTERING TEMPERATURE

A systematic study of the air gap effects on morphology and mechanical strength of Nickel Oxide (NiO) hollow fiber membranes has been carried out. The hollow fibers were prepared using the dry-jet wet spinning process using a dope solution containing NiO/N-methyl-2-pyrrolidone (NMP)/Arlacel/Poly(ethylene sulphide) with a weight ratio of 70/22.9/0.1/7. Tap water was used as internal and external coagulants. The cross-sectional structure of precursors hollow fiber membrane was studied by scanning electron microscopy (SEM). The results showed that both inner and outer finger-like voids of the hollow membrane were determined by the air gap distance. Experimental results indicated that an increase in air gap distance, from 100 mm to 200 mm, gave a hollow fiber with a lower mechanical strength and higher percentages of cross section surface area covered by finger-like voids structures. This study also revealed that the air gap introduced an elongation stress because of gravity on the internal or external surfaces of the NiO hollow fibers. A more effective hollow fiber membrane which is in asymmetric structure instead of symmetric structure can be produced by using air gap higher than 200 mm.