Inorganic Membranes Research Articles

Effect of the coupling modes on EfOM degradation and fouling mitigation in ozonation-ceramic membrane filtration

To guide the practical application of ozonation coupled with tubular ceramic membranes (TCMs), the performance and the mechanism of mitigated membrane fouling by pre-ozonation-filtration (Pre-O/F) and in-situ ozonation-filtration (in-situ-O/F) were investigated. The in-situ-O/F mode exhibited a rejection performance 1.19 times better than that of Pre-O/F for effluent organic matter (EfOM) removal, but less membrane fouling mitigation. The backwashing efficiency of the in-situ-O/F mode was better than that of Pre-O/F, because backwashing loosened the in-situ-O/F membrane fouling layer and made it easier to remove by backwashing. SEM-EDX measurements were used to identify the components of the inorganic, organic, and biofouling membrane fouling layers. In Pre-O/F mode, EfOM, extracellular polymeric substances, and microorganisms in the effluent were destroyed by ozonation before filtration. In in-situ-O/F mode, the adhesion between irreversible membrane fouling and the pores/surfaces of TCMs was destroyed by ozonation, thus converting the irreversible membrane fouling to reversible membrane fouling. This led us to propose the process strategy of filtration coupled with ozonation for reclaimed water treatment. Pre-O/F is suitable for use in the treatment of large amounts of wastewater in short times because of the high-water flux. The in-situ-O/F mode is more suitable for normal use because of its lower operating cost and higher efficiency.

Tailor-Made Zeolitic Water Nanochannels for Liquid Fuel Production

Conversion of CO2 into valuable liquid fuels or other chemicals has been one of the attractive ways for effective utilization of CO2 produced by burning fossil fuels. However, this task is challenging due to the difficulties associated with the chemical inertness of CO2. In addition to research efforts devoted to the development of more active and selective catalysts for CO2 hydrogenation reaction, removing the by-product water from the system is proven beneficial for improving the reaction thermodynamics and kinetics toward desirable products. Therefore, highly water-selective membranes able to operate under reaction conditions like high temperature and pressure have long been pursued. In a recent study, Yu et al. reported a zeolite membrane with gas-impeding water-conduction nanochannels that selectively remove by-product water from CO2 dehydrogenation process, greatly enhancing CO2 conversion and methanol yield.

Preparation of Fe3O4@TiO2 blended PVDF membrane by magnetic coagulation bath and its permeability and pollution resistance

Fe3O4@TiO2 magnetic photocatalytic particles were synthesized and characterized. A composite PVDF separation membrane blended with Fe3O4@TiO2 particles was prepared by the phase inversion method. The main purpose was to explore the effect of magnetic fields on the performance of membranes during coagulation bath. The structure characterization, permeability, interception ability, and anti-pollution performance of inorganic particle blend membranes were then tested. Results showed that magnetic field coagulation baths have little effect on the pore structure and hydrophilicity of the membrane surface. When the liquid membranes was condensed under a magnetic field, the magnetic photocatalytic particles could migrate at a greater rate to the surface of the membrane. Through performance tests of the PVDF modified membranes, it was found that a magnetic coagulation bath could promote more Fe3O4@TiO2 to aggregate on the surface of the membrane, which led to the blend membrane formed under the magnetic coagulation bath had better antifouling performance against humic acid solution under ultraviolet light irradiation. Membranes with 0.5wt% magnetic photocatalytic particles in a magnetic field coagulation bath performed best. When filtered under the condition of ultraviolet light, its pure water flux was 1752L/(m2h), and the rejection rate of 20mg/L humic acid solution was 67.17%. The flux attenuation before and after filtration was 38.84%, the flux recovery rate was 91.10%, and the irreversible pollution index was only 8.90%.

Coupling of self-supporting geopolymer membrane with intercepted Cr(III) for dye wastewater treatment by hybrid photocatalysis and membrane separation

In this study, hazardous Cr(III) trapped by a geopolymer membrane was crystallized in situ and coupled with the membrane to afford dye wastewater treatment by hybrid photocatalysis and membrane separation for the first time. The X-ray powder diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy results confirmed that Cr(III) was highly dispersed on the membrane surface as nano Cr2O3 particles. The photoluminescence peak decreased with increasing Cr2O3 along with an increase in the photocatalytic degradation efficiency for basic green under static conditions (0 MPa downstream pressure). The photocatalytic performances under different downstream pressures confirmed that the degradation efficiency increased with increasing downstream pressure (below atmospheric pressure): 100 min was required for 100% degradation of basic green under static conditions, whereas only 50 min was required at 0.09 MPa owing to suitable membrane-induced concentration of the dyes. Density functional theory calculations indicated that the geopolymer membrane matrix was weakly nucleophilic, allowing it to effectively reject basic green, while the Cr2O3 was strongly nucleophilic, enabling it to adsorb basic green effectively for further photocatalytic degradation. The membrane reported here would be a brand-new choice for the wastewater treatment with inorganic membranes.

Selective electrochemical hydrogen evolution on cerium oxide protected catalyst surfaces

To date the only known solution to avoid the unwanted electrochemical reduction of hypochlorite and chlorate in industrial chlorate production, performed in undivided cells, is the addition of dichromate to the chlorate electrolyte. Because of the toxicity of this compound its use is restricted within the European Union to time limited authorization by REACH. Therefore, an alternative to sodium dichromate is essential to maintain, or even increase the process efficiency.The addition of cerium (III) salts to a hypochlorite solution increases the cathodic selectivity towards hydrogen evolution (HER), the preferred cathode process in industrial chlorate production. This is attributed to the deposition of a thin cerium oxide/hydroxide coating on the cathode, induced by the increased local alkalinity during electrolysis.Performing the electrodeposition of such protective coating ex situ, well-controlled coating thickness can be achieved. Optimizing the deposition conditions (time, current density), a coherent and stable coating is formed on the electrode surface. On this protected electrode surface the electrochemical reduction of hypochlorite is suppressed by ca. 90% compared to the bare Pt electrode, while the HER proceeds with high selectivity and unchanged kinetics. Interestingly, other electrochemical reactions (O2 reduction, H2O2 reduction and oxidation) are also suppressed by the protective coating, suggesting that the deposited layer acts as an inorganic membrane on the electrode surface.

Synthesis and Characterization of Novel Green Hybrid Nanocomposites for Application as Proton Exchange Membranes in Direct Borohydride Fuel Cells

Organic–inorganic nanocomposite membranes for potential application in direct borohydride fuel cells (DBFCs) are formulated from sulfonated poly(vinyl alcohol) (SPVA) with the incorporation of (PO4-TiO2) and (SO4-TiO2) nanotubes as doping agents. The functionalization of PVA to SPVA was done by using a 4-sulfophthalic acid as an ionic crosslinker and sulfonating agent. Morphological and structural characterization by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) confirmed the successful synthesis of the doping agents and their incorporation into the polymer. The influence of PO4-TiO2 and SO4-TiO2 doping and their content on the physicochemical properties of the nanocomposite membranes was evaluated. Swelling degree and water uptake gradually reduced to 7% and 13%, respectively, with increasing doping agent concentration. Ion exchange capacity and ionic conductivity of the membrane with 3 wt.% doping agents were raised 5 and 7 times, respectively, compared to the undoped one. The thermal and oxidative stability and tensile strength also increased with the doping content. Furthermore, lower borohydride permeability (0.32 × 10−6 cm2 s−1) was measured for the membranes with higher amount of inorganic doping agents when compared to the undoped membrane (0.71 × 10−5 cm2 s−1) and Nafion®117 (0.40 × 10−6 cm2 s−1). These results pave the way for a green, simple and low-cost approach for the development of composite membranes for practical DBFCs.

A comprehensive review of carbon molecular sieve membranes for hydrogen production and purification

Demand in clean alternative energy source together with fuel cells developments has attracted researchers towards utilization of hydrogen (H2). Common production of hydrogen from fossil fuels requires further pretreatment prior to the application, which makes separation and purification technology a very crucial component. Membrane reactors for water-gas shift reaction which was used for H2 generation by conversion of carbon monoxide revealed a good potential in shifting the reaction equilibrium. Two types of inorganic membranes widely studied for H2 separation and purification are dense phase metal and metal alloys and porous ceramic membranes. Among these two, microporous-type membrane was found to be more advantageous at harsh temperature during water-gas shift reaction. Sol-gel method employed for synthesised of porous ceramic membranes produced membranes with high stability and durability at high temperature and at tough hydrothermal environments. This work presents the critical issues regarding the membranes based on technical and economical perspective. Discussions are made on the significance of membrane technology advancement in order to strive for a clean environment with zero power technologies.

Low-cost and facile synthesis of geopolymer-zeolite composite membrane for chromium(VI) separation from aqueous solution

Inorganic membranes in wastewater treatment have captured increasing attention due to their numerous advantages. However, high cost and complicated producing process restricted their benign developments. This study proposed an novel inorganic geopolymer-zeolite composite membrane which was synthesized by using circulating fluidized bed fly ash (CFBFA) solid waste as initial material and via a low-cost and facile geopolymerization-hydrothermal treatment processes, further, the membrane was employed to separate Cr(VI) ion from aqueous solutions. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra results indicated that geopolymer-zeolite (Li-ABW) composite membrane was obtained successfully. Field emission scanning electron microscopy (FESEM) results demonstrated that the membrane had a compact zeolite layer with thickness about 1.5 μm. The effects of transmembrane pressures (TMP), Cr(VI) concentration, pH, ionic strength, and co-existing ions on Cr(VI) rejection were investigated, and the results revealed that the Cr(VI) rejection reached 85.45 % under 10 kPa of TMP, 1000 mg L−1 of Cr(VI), and pH 7. The separation mechanism of Cr(VI) on the geopolymer-zeolite composite membrane was considered to be size exclusion and electrostatic interaction. These results suggested that the geopolymer-zeolite composite membrane had a potential application for the effective removal of Cr(VI) contaminants from wastewater.

Influence of Host-Guest Interaction between Chiral Selectors and Probes on the Enantioseparation Properties of Graphene Oxide Membranes.

Graphene oxide (GO)-based membranes have displayed superior performances in the chiral resolution compared with conventional polymer-based and inorganic membranes. However, the effect of the host-guest interaction between chiral selectors and probes on the enantioseparation properties of GO-based membranes remains to be established. In this work, l-phenylalanine (l-Phe, as the chiral selector)-modified GO-based (l-Phe-GO) membranes were fabricated, and their enantioseparation performances toward various enantiomers, that is, d- and l-phenylalanine (d- and l-Phe), d- and l-methionine (d- and l-Met), N-acyl-d-phenylalanine (N-acyl-d-Phe) and N-acyl-l-phenylalanine (N-acyl-l-Phe), and N-acyl-d-methionine (N-acyl-d-Met) and N-acyl-l-methionine (N-acyl-l-Met), were detected. Results show that (i) l-Phe is preferential to transport d-enantiomers relative to l-enantiomers; (ii) as far as d-enantiomers are concerned, the d-Phe-like enantiomers move faster than d-Met-like ones through the l-Phe-GO membrane owing to their different host-guest interactions. The strength of interactions between chiral selectors and probes was further confirmed from both experimental and theoretical standpoints. In the former case, the enantioselective adsorption of l-Phe-GO nanosheets toward the aforementioned enantiomers demonstrates that l-Phe delivers a higher adsorption capacity to d-enantiomers relative to l-enantiomers, and meanwhile, d-Phe-like enantiomers are better than d-Met-like enantiomers in the adsorption capacity. In the latter case, the chiral separation mechanism is clarified using the periodical density functional theory (DFT) calculation, indicating that l-Phe interacts with d-enantiomers more strongly than l-enantiomers. Especially, our calculations unveil that the difference in the interaction strength is principally dominated by the nonstereoselective interactions between chiral probes and the GO surface. Therefore, our findings suggest that the nonstereoselective weak interaction can be employed to improve the enantioselectivity of GO-based membranes.

Development of robust and superhydrophobic membranes to mitigate membrane scaling and fouling in membrane distillation

Membrane distillation (MD) has attracted increasing attention for seawater and brackish water desalination, wastewater treatment, and concentration of juices and pharmaceutical solutions due to its feasibility of using low-grade energy and achieving high solute rejection. However, the successful implementation of MD technology is still impeded by membrane wetting resulted from membrane scaling by inorganic crystals and membrane fouling by organic matters in the feed solutions, especially when dealing with challenging wastewaters. Herein, this study describes a novel strategy to develop a robust and superhydrophobic membrane via electrospinning followed by electrospray to enhance membrane anti-wetting properties caused by scaling and fouling. The robust superhydrophobic membrane PDMS-3 comprised a superhydrophobic surface layer fabricated by electrospraying a PVDF/PDMS/silica fume blended solution and an electrospun nanofibrous PVDF support. The newly developed membrane PDMS-3 not only exhibited an outstanding superhydrophobicity with a water contact angle of 170⁰ ± 1⁰, but also showed a unique anti-abrasive feature, which still possessed a slippery superhydrophobic property after 40 abrasion cycles. Moreover, the DCMD tests revealed that this rigid superhydrophobic surface rendered PDMS-3 with the best anti-scaling and anti-fouling properties compared to the nanofibrous and commercial PVDF membranes. It could achieve a superior MD flux of 28 kg m−2 h−1and a stable salt rejection above 99.99% during a continuous 160-h DCMD operation when the feed and permeation solutions were 3.5 wt% NaCl solution at 333K and distillate water at 293 K, respectively. These results underline the importance of anti-abrasive superhydrophobic membrane development to deal with wastewaters containing diverse inorganic and organic matters via MD.

Permeation Properties of Ions through Inorganic Silica-Based Membranes.

The development of inorganic membranes has mainly found applicability in liquid separation technologies. However, only a few reports cite the permeation and separation of liquids through inorganic nanofiltration membranes compared with the more popular microfiltration membranes. Herein, we prepared silica membranes using 3,3,3-trifluoropropyltrimethoxysilane (TFPrTMOS) to investigate its liquid permeance performance using four different ion solutions (i.e., NaCl, Na2SO4, MgCl2, and MgSO4). The TFPrTMOS-derived membranes were deposited above a temperature of 175 °C, where the deposition behavior of TFPrTMOS was dependent on the organic functional groups decomposition temperature. The highest membrane rejection was from NaCl at 91.0% when deposited at 200 °C. For anions, the SO42− rejections were the greatest. It was also possible to separate monovalent and divalent anions, as the negatively charged groups on the membrane surfaces retained pore sizes >1.48 nm. Ions were also easily separated by molecular sieving below a pore size of 0.50 nm. For the TFPrTMOS-derived membrane deposited at 175 °C, glucose showed 67% rejection, which was higher than that achieved through the propyltrimethoxysilane membrane. We infer that charge exclusion might be due to the dissociation of hydroxyl groups resulting from decomposition of organic groups. Pore size and organic functional group decomposition were found to be important for ion permeation.

Preparation of a Self‐Supported SiO2 Membrane as a Separator for Lithium‐Ion Batteries

AbstractFor the first time, electrophoretic deposition (EPD) has been employed to prepare a self‐supported, inorganic membrane consisting of SiO2 nano‐fibers, as a separator for lithium‐ion batteries. The SiO2 nano‐fibers that were fabricated by a low‐cost force spinning technique were deposited by EPD directly onto LiNi0.8Co0.15Al0.05O2 cathode material. Citric acid charging agent and anhydrous acetone solvent were used. The resulting porosity and tortuosity of the EPD SiO2 separator were 71.42 %, and 1.70, respectively. The slightly higher tortuosity of the EPD‐SiO2‐fiber separator (60 μm) led to a lower rate capability in comparison to commercial GF/A glass fiber separator (260 μm). On the other hand, the latter exhibited lower self‐discharge than the former in full‐cells with a graphite anode; this is proposed to be related to the different purities of the two materials that impart different electronic properties or the presence of 20 wt % PVDF in the EPD‐SiO2 separator. Indeed, the deposited membrane has good characteristics as a battery separator and the EPD process is extremely feasible for the fabrication of miniaturized lithium‐ion batteries on wafer level.

Inorganic Nanoparticles Challenging Lamellar and Non-Lamellar Model Membranes

Nonlamellar lipid aqueous phases, such as reverse cubic or hexagonal phases, are ubiquitous in nature and they present a curve lipid aqueous interface on the nanoscale. The role of curvature for biomolecular interactions has been increasingly recognised. it has shown that synthetic planar lipid membranes can be used to mimic the interaction between inorganic nanoparticles (NPs) and membrane. Such studies provide relevant insights on the main factors implied in cellular trafficking and cytotoxic effects, but this type of particles are also used in nanomedicine to enhance imaging and also in therapeutic applications. The impact of NPs on curved membranes, i.e. nonlamellar phases, are much less studied. We are able to prepare lipid mesophase surface films with controlled and tuneable structure, which allows us to study the interaction of nanoparticles with lamellar and nonlamellar lipid films. The structural effects on the lipid films of gold nanoparticles (AuNPs) of different shape and surface functionalization have been studied using Neutron Reflectometry. We used spin coated layers of glycerol monooleate (GMO), forming a cubic phase, and mixtures of GMO/diphosphatidylcholine (DOPC) forming a lamellar phase. Hydrophobic and cationic particles added to the lamellar phase cause an increase in diffuse scattering, probing the presence of the particles in the film. Both the cationic and hydrophobized AuNPs seem to inserted in the cubic phase lipid film. The AuNP rods seems to perturb the lipid film structure and hydrophobic rods decrease the stability of the lipid film to a large extent. Complementary confocal microscopy imaging revealed the morphology changes of the film structure as a consequence of the particle addition. The results will be discussed in terms of particle shape and the curvature of the lipid aqueous interface.

An ion-conductive Li7La3Zr2O12-based composite membrane for dendrite-free lithium metal batteries

Lithium (Li) metal is pursued as the anode for next generation lithium batteries because of the highest energy density and the lowest reduction potential. However, the formation of lithium dendrite caused by nonuniform Li deposition exists. Moreover, the safety issue arising from hazardous Li dendrites hinders the practical application of lithium metal batteries (LMBs). In this work, an organic and inorganic composite protective membrane (CPM) consisting of PVDF-HFP and LLZO particles is prepared by a simple tape-casting method. The CPM modified Li symmetric cell exhibits no obvious voltage hysteresis over 500 h at 2 mA cm−2 and 1 mAh cm−2. Moreover, the CPM modified Li | LFP cell can stably run 800 cycles at 1C and retain a high average Coulombic efficiency of ~99.95%. Moreover, the in-situ formation of LiF between metallic Li anode and the C–F group in PVDF-HFP exhibits high modulus, effectively suppressing the growth of lithium dendrites. The uniform Li deposition is achieved owing to the high ionic conductivity and Li+ transference number of CPM. In addition, the high modulus LiF layer can stabilize interface and greatly reduce interfacial resistance after cycling.

Performance of H2-fed fuel cell with chitosan/silicotungstic acid membrane as proton conductor

Composite organic–inorganic proton exchange membranes for H2–O2 fuel cells were fabricated by ionotropic gelation process combining a biopolymer (chitosan) with a heteropolyacid (silicotungstic acid). According to scanning electron microscopy analysis, compact, homogeneous and free-standing thin layers were synthesized. X-ray diffraction proved the crystallinity of the fabricated membranes and showed the presence of Chitosan Form I polymorph soon after the reticulation step and of the Form II polymorph after the functionalization step. Fourier-transform infrared spectroscopy demonstrated that the Keggin structure of the heteropolyacid is maintained inside the membrane even after the fabrication process. These membranes worked properly as proton conductors in a low-temperature (25 °C) fuel cell apparatus using hydrogen as fuel recording a promising power density peak of 268 mW cm−2 with a Pt loading of 0.5 mg cm−2.

Thermal behaviour and phases evolution during the sintering of porous inorganic membranes

Anorthite-based highly porous membranes were successfully produced using calcined oyster shell to enhance the pore network. The calcined oyster shells produce CaO responsible for the crystallisation of gehlenite and anorthite at relatively low temperature. While the crystallisation produced nano and meso size of intergranular pores, vitrification of feldspar is responsible for development of the capillary porosities. The increasing sintering temperature from 1200 °C to 1300 °C implies the increase in average pores radius from 1.2 μm to 14.3 μm due to the formation of spherical pores from vitrification. The combination of different class of porosities in the matrices results in the interconnection with improvement of the permeability of the porous network. Porosity, permeability and chemical stability were improved with 20 wt.% of calcined oyster shell addition allowing the possible development of high strength porous network which is promising for the membranes support and other applications including liquid separation as well as liquid filtration where high pressure is used.

Recent Development of Enhanced Polymeric Blend Membranes in Gas Separation: A Review

Natural gas is the most rapid growing energy sources around the world. The presence of CO2 in natural gas lowers its calorific value and purification of a natural gas by removing CO2 is an essential process to increase its value. Several separation technologies are used to remove acidic gases like H2S and CO2 from natural gas. Among these technologies, membrane process is a feasible energy saving alternate to CO2 capture. The three types of membrane include polymeric, inorganic and mixed matrix membranes. Currently, polymer membranes and inorganic membranes were considered for gas separation, but inorganic membranes are too costly. Even mixed matrix membrane performance suffered defects caused by poor glassy polymer and particle interactions. Pure glassy and pure rubbery are problematic due to their instructive properties. The blending of glassy with rubbery polymers improve membrane properties for gas separation. To enhance the compatibility of the polymer blend, a third component is added such as alkanol amines. Although, the enhanced polymeric blend membranes have many advantages in terms of permeance, selectivity, thermal and chemical stability. Polymer blending also offers an effective technique to synthesize membranes with desirable properties.

Recent Development of Enhanced Polymeric Blend Membranes in Gas Separation: A Review

Natural gas is the most rapid growing energy sources around the world. The presence of CO2 in natural gas lowers its calorific value and purification of a natural gas by removing CO2 is an essential process to increase its value. Several separation technologies are used to remove acidic gases like H2S and CO2 from natural gas. Among these technologies, membrane process is a feasible energy saving alternate to CO2 capture. The three types of membrane include polymeric, inorganic and mixed matrix membranes. Currently, polymer membranes and inorganic membranes were considered for gas separation, but inorganic membranes are too costly. Even mixed matrix membrane performance suffered defects caused by poor glassy polymer and particle interactions. Pure glassy and pure rubbery are problematic due to their instructive properties. The blending of glassy with rubbery polymers improve membrane properties for gas separation. To enhance the compatibility of the polymer blend, a third component is added such as alkanol amines. Although, the enhanced polymeric blend membranes have many advantages in terms of permeance, selectivity, thermal and chemical stability. Polymer blending also offers an effective technique to synthesize membranes with desirable properties.

Fouling mechanism and control strategy of inorganic membrane

Compared with the traditional treatment technologies, inorganic membrane technology is gradually becoming the mainstream of the treatment of oily and salty wastewater, but membrane fouling has become the bottleneck restricting the development of membrane technology. In order to solve this problem, the mechanism of membrane fouling and the control strategies of membrane fouling are introduced in this paper. The atomic layer deposition technology and the preparation of TiO2 nanowires (NWs) film by impregnation method were mainly introduced, aiming to provide a more reliable industrial research status in the field of membrane fouling control.

Inorganic Porous Membranes for Separation in Organic Solvents

Inorganic Porous Membranes for Separation in Organic Solvents