SiC Membrane Research Articles

Photopolymerization enabled in-air highly oleophobic and hydrophilic SiC membranes with improved antifouling performance in oil-in-water emulsion separation

Ceramic membranes with tailored surface wettability have gained increasing attention for improving their separation efficiency and antifouling ability, while most of the previous work focused on the underwater oleophobic behavior. In this work, in-air highly oleophobic and hydrophilic SiC membranes were achieved through the UV irradiation triggered polymerization and controlled crosslinking between oleophobic perfluorodecyl acrylate (TFOA) and hydrophilic methacrylic acid (MAA). These key processing parameters including MAA content, soaking time and irradiation duration were systematically studied through examining the changes in porous microstructure, surface wettability and separation performance in oil-in-water emulsion. Results showed that the flux attenuation rate of SiC membranes can be effectively reduced by regulating the content of hydrophilic components. Due to the alternation of the surface wettability to highly oleophobic in air, the oil droplets can hardly attach on the surface of modified SiC membranes at the beginning of filtration process, and the membrane fouling was significantly slow down yet dominated by the intermediate blocking. Correspondingly, a combined cleaning procedure was proposed to regenerate the fouled SiC membranes. Further, the antifouling ability of modified and original SiC membranes was comparatively studied under the conditions of a fixed permeate volume (15 ml) and various oil concentrations (200 ∼ 1000 ppm) in the separation of oil-in-water emulsion. The advantages of modified SiC membranes become more notable when used for highly concentrated oil–water emulsion as reflected by the slower flux decline and higher stable flux. This work provides a feasible pathway to realize the in-air highly oleophobic and hydrophilic surface on ceramic membranes, and primarily demonstrates the advantages of antifouling ability in oil-in-water emulsion separation.

Surface oxidation via water plasma for increased H2 permselectivity of Allylhydridopolycarbosilane (AHPCS)-derived SiC membranes

Surface oxidation via water plasma for increased H2 permselectivity of Allylhydridopolycarbosilane (AHPCS)-derived SiC membranes

Silicon‐On‐Silicon Carbide Platform for Integrated Photonics

AbstractSilicon carbide (SiC)'s nonlinear optical properties and applications to quantum information have recently brought attention to its potential as an integrated photonics platform. However, despite its many excellent material properties, such as large thermal conductivity, wide transparency window, and strong optical nonlinearities, it is generally a difficult material for microfabrication. Here, it is shown that directly bonded silicon‐on‐silicon carbide can be a high‐performing hybrid photonics platform that does not require the need to form SiC membranes or directly pattern in SiC. The optimized bonding method yields defect‐free, uniform films with minimal oxide at the silicon–silicon–carbide interface. Ring resonators are patterned into the silicon layer with standard, complimentary metal–oxide–semiconductor (CMOS) compatible (Si) fabrication and measure room‐temperature, near‐infrared quality factors exceeding 105. The corresponding propagation loss is 5.7 dB cm−1. The process offers a wafer‐scalable pathway to the integration of SiC photonics into CMOS devices.

Integration of SiC Membrane and CePO4 Catalyst for the Simultaneous Efficient Removal of Dust and NO

Integration of SiC Membrane and CePO₄ Catalyst for the Simultaneous Efficient Removal of Dust and NO

Influence of initial powders morphology on structural-dimensional characteristics of porous ceramic materials based on SiC/MgO–SiO2

Synthesis of porous ceramic materials based on fine SiC with sintering silicon oxide and magnesia binders at T = 800–1300 °C is considered. Special attention is paid to the influence of the shape and morphology of the initial powder particles on structural parameters and characteristics of porous ceramic materials. The SiC membranes sintered at 1000–1300 °C had average pore sizes of 0.5–1 μm, open porosity - up to 50 %, bending strength - up to 48.5 MPa and high water permeance - up to 7890 l⋅m−2⋅h−1⋅bar−1. The established filtration efficiency was ∼99 % in the case of screening out model particles of D50 = 0.5 μm in size with maintaining stable permeance and physico-mechanical characteristics after multiple filtration-regeneration cycles.Comprehension of the initial powders morphology impact on the synthesized porous ceramics parameters makes it possible to forecast and ensure the preset structural, dimensional and physico-mechanical parameters of the materials under study properly. This work can be used for practical low-cost production of highly efficient SiC membranes for micro- and ultrafiltration processes, as well as base for catalysts.

La0·8Mn0·2FeO3 impregnated ceramic membrane for membrane fouling elimination via peroxymonosulfate activation

To endow SiC ceramic membranes a catalytic self-cleaning capability, a pore-functionalized SiC ceramic membrane with impregnated a perovskite-type catalyst La0·8Mn0·2FeO3 was fabricated by a urea-assisted one-step combustion method. Diffraction of X-ray (XRD), canning electronic microscopy (SEM) with an energy dispersion X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were employed to investigate the effects of the impregnating of La0·8Mn0·2FeO3 on SiC membrane pore-structure (La0·8Mn0·2FeO3-CM). The catalytic self-cleaning performance of the as-prepared membranes was assessed through peroxymonosulfate (PMS) activation under a cross-flow filtration mode. Results indicate that La0·8Mn0·2FeO3 has been successfully impregnated into the macropores of SiC membranes without pore blocking, and 92.4 % of the flux recovery rate (FRR) was achieved when the PMS concentration was 70 mM and catalytic flushing time was 45 min. Therefore, the La0·8Mn0·2FeO3 impregnated SiC membrane exhibited excellent catalytic self-cleaning property, which can effectively avoid the environmental pollution and the deterioration of membrane materials caused by chemical cleaning for membrane fouling. In addition, the radical quenching experiment and electron spin resonance (EPR) tests were conducted in the catalytic self-cleaning process, and the results suggested that the hydroxyl radical (⋅OH) and sulfate radical (SO4•‾) are simultaneously captured and ⋅OH is the dominant active species. This study embarks on a novel and environmental friendly membrane cleaning approach for irreversible fouling eliminates in diverse membrane separation applications.

Chemical vapor deposition of silicon carbide on alumina ultrafiltration membranes for filtration of microemulsions

Worldwide, a considerable amount of oily wastewater is generated, with oil droplets from 2 to 200 nm that are difficult to separate because of their size and colloidal stability. This study presents a novel approach for effectively separating microemulsions via cubic silicon carbide (3C-SiC)-coated alumina (Al2O3) membranes fabricated based on low pressure chemical vapor deposition (LPCVD). SiC was deposited at a relatively low temperature at 860 °C on 100 nm Al2O3 membranes using two precursors: SiH2Cl2 and C2H2. With the increase in deposition time, up to 25 min, the pore size decreased from 41 nm to 33 nm, which is a smaller pore size of a SiC membrane than previously used for oil/water separation. The polycrystalline 3C-SiC-coated membranes showed improved hydrophilicity (water contact angle of 15°) and highly negatively charged surfaces (−65 mV). Microemulsion filtration experiments were carried out at a constant permeate flux (80 Lm−2 h−1) for six cycles with varying deposition time, pH, surfactant types, and pore sizes. The fouling of the SiC-coated membrane was, compared to the Al2O3 membrane, effectively mitigated due to the enhanced electrostatic repulsion and hydrophilicity. Surfactant adsorption mainly occurred when the surface charge of the microemulsion and the membranes were opposite. Therefore, the surface charge of the alumina membrane changed from positive to negative when soaked in negatively charged microemulsions, whereas SiC-coated membranes remained negatively charged regardless of surfactant type. The membrane fouling was alleviated when the membrane and oil droplets had the same charge. Lastly, the 62 nm SiC-coated membrane with 20 min coating time was the best choice for the filtration of the microemulsion, because of the high rejection of the oil droplets and low fouling tendency.

Preparation of high performance porous SiC ceramic membrane support using zeolite and alumina as sintering additives

In-situ reaction bonded porous SiC ceramic membrane supports were successfully synthesized by economical way at 1300 °C in air using waste zeolite residue and alumina as sintering additive. The effects of additives content and sintering temperature on material, mechanical and permeabity properties were carefully investigated. The ceramics prepared at 1300 °C with a 20 % mixture of zeolite residue and alumina obtained with a very high mechanical strength of 114.85 MPa at a porosity of 28.90 vol% and exhibited pure water permeability of 1258 L.h-1.m-2.bar−1. Additionally, the support prepared in this study exhibited good chemical resistance in acid and alkali medium for long periods.The utilization of zeolite residue reduced the sintering temperature for fabrication of membrane support and provided a flexible strategy to control the mechanical performance and water permeability. The filtration and permeation results indicated that SiC membrane support prepared in this study is suitable for various applications, particularly in water treatment.

Efficient strategies for engineering high-permeance SiC ceramic membranes for gas/solid filtration: Prefilling method

The trade-off between gas permeance and filtration accuracy in SiC ceramic membranes has constrained their utilization in gas/solid filtration. Herein, a polyvinyl butyraldehyde (PVB) solution was introduced as a prefilling layer to impede membrane particles from penetrating the macroporous SiC support (average pore size: 23 μm). The PVB layer could be removed postsintering, thereby producing a ceramic membrane devoid of any intermediate layer, which showed great potential in enhancing the gas permeance. Initially, the PVB concentration was optimized to ensure membrane integrity and strong adhesion between the support and separation layer. Thereafter, suitable dispersants and drying conditions were investigated in detail. The resultant asymmetric SiC membranes fabricated under these optimized conditions had a thickness ranging between 50 and 60 μm. These membranes demonstrated exceptional gas permeance, varying from 71.1 to 178.1 m3 m−2 h−1 kPa−1 by tuning the membrane pore size from 1.02 to 3.03 μm. Additionally, the membranes achieved 99.94 % dust rejection for particles approximately 0.3 μm in size. When compared to traditional ceramic membranes with several intermediate layers, the prefilling approach employed herein circumvents the ceramic intermediate layer. This method resolves the mismatch between particle sizes of the ceramic support and the membrane layer, offering an effective strategy for developing high-permeance SiC membranes suited for gas/solid filtration applications.

A SiC membrane resistance recovery methodology based on dynamically dust cake layer analysis

Filter cake-induced resistance is a significant contributor to energy consumption in dust filtration processes. This can be optimized by adjusting inlet gas composition, membrane characteristics, and back-flushing parameters. In this study, calcium carbonate (CaCO3) dust with varying hygroscopicity was utilized to investigate the evolution mechanism of the filter cake on SiC membranes under different humidity conditions. The interacting force between particles and between the cake and membrane were analyzed to elucidate the fragmentation mechanism of the cake. It was observed that particles at higher relative humidity (increased RH from 40 % to 85 %) tend to form a more loosely packed cake (hydrophilic filter cake porosity and hydrophobic filter cake porosity increased from 70.8 % to 80.5 % and from 61.4 % to 69 %, respectively) with greater fragility (reduced cohesive force). This characteristic is advantageous for efficient backflushing operations. The strong adhesion between the filter cake and membrane hindered the recovery of the initial filtration resistance. For SiC membrane, the optimized back-flushing parameter is reservoir pressures of 0.2 and 0.15 MPa and pluse-jet intervals of 40 min to hydrophilic and hydrophobic dusts, respectively.

Sintering of silicomanganese slag-reinforced porous SiC ceramic membrane supports with high alkali corrosion resistance

Herein, we report the production of silicomanganese slag-reinforced porous SiC ceramic membrane supports with high alkali corrosion resistance through low-temperature sintering. The effects of the sintering temperature and particle size of the silicomanganese slag (SiMn-slag) on the properties of the membrane supports were studied. The optimal membrane support was obtained at 1150 °C with 20 μm SiMn-slag, which exhibited an open porosity of 41.03%, pore size of 3.15 μm, ultra-high pure water permeability of 120074.60 L·m−2·h−1·bar−1 and high bending strength of 43.18 ± 0.70 MPa. In addition to the excellent acid corrosion resistance, the prepared membrane support displayed high alkali corrosion resistance due to the neck connections that formed, comprising alkali resistant mullite, anorthite, and bustamite. This work is of great significance in guiding the production of high-performance SiC membranes at a low cost and offers a possible route for utilising solid waste as a value-added separation material.

Effects of the original state of sodium-based additives on microstructure, surface characteristics and filtration performance of SiC membranes

Sodium-contained compounds are promising sintering additives for the low-temperature preparation of reaction bonded SiC membranes. Although sodium-based sintering additives in various original states were attempted, their effects on microstructure and surface properties have rarely been studied. In this work, three types of sodium-based additives, including solid-state NaA zeolite residue (NaA) and liquid-state dodecylbenzene sulfonate (SDBS) and water glass (WG), were separately adopted to prepare SiC membranes, and the microstructure, surface characteristics and filtration performance of these SiC membranes were comparatively studied. Results showed that the SiC membranes prepared with liquid-state SDBS and WG (S-SDBS and S-WG) showed lower open porosity yet higher bending strength compared to those prepared with solid-state NaA (S-NaA). The observed differences in bending strength were further interpreted by analyzing the reaction process of each sintering additive and the composition of the bonding phase in the reaction bonded SiC membranes. Meanwhile, the microstructural differentiation was correlated to the original state of the additives. In addition, their surface characteristics and filtration performance for oil-in-water emulsion were examined and correlated to the membrane microstructure. The S-NaA samples showed higher hydrophilicity, lower surface roughness (1.80 μm) and higher rejection ratio (99.99%) in O/W emulsion separation than those of S-WG and S-SDBS. This can be attributed to the smaller mean pore size and higher open porosity, resulting from the originally solid-state NaA additives. Therefore, this work revealed the comprehensive effects of original state of sintering additives on the prepared SiC membranes, which could be helpful for the application-oriented fabrication by choosing additives in suitable state.

Construction of V2O5-WO3/TiO2 nanocones catalyst layer on SiC ceramic membrane for efficient removal of NO and dust

In this work, TiO2 nanocones grown on SiC membrane was used as the support of V2O5-WO3 species to prepare V2O5-WO3/TiO2@SiC (VWTi(C-X)@SiC) catalytic membrane for dust filtration and NH3-SCR denitration. On account of the large specific surface area, abundant surface acid sites and prominent redox property, the optimized VWTi(C-550)@SiC catalytic membrane shows >90% NO removal efficiency at the temperature of 280–360 °C, which are much higher than VWTi(P-550)/SiC catalytic membrane (TiO2 nanoparticles prepared by traditional vacuum coating titanium sol method was used as the support of V2O5-WO3 species, NO conversion <80% at whole tested temperature). Additionally, VWTi(C-550)@SiC displays superior stability during the SO2 + H2O resistance and 300 h long-term test at 300 °C, and exhibits an excellent dust filtration performance (2.5 μm SiO2 particles interception rate exceeded 99.99%) under all test conditions. More importantly, the structure of nanocones decrease the influence of tensile stresses due to the different thermal expansion coefficients of TiO2 and SiC membranes, which significantly suppress the fall of VWTi catalyst layer from the surface of SiC during pulse-jet cleaning. Among above results, it can be concluded that the optimized VWTi(C-550)@SiC catalytic membrane shows a prosperous application prospect for the simultaneously dust filtration and NH3-SCR denitration of medium–high temperature flue gas.

Base-activated persulfate strategy for ceramic membrane cleaning after treatment of natural surface water

The natural organic matters (NOM) have been proved to form the hydraulically irreversible membrane fouling, which limit the application of the membrane in water treatment processes. To solve the membrane fouling caused by NOM, a novel one-step chemical cleaning method for the ceramic membrane derived from the base-activated persulfate oxidation process was developed in this study. When the SiC ceramic membranes was used to filtrate practical river water, the permeate flux dropped 65% as ΔTMP reached 30 kPa. After 2 h immersion of the fouled membrane in the cleaning solution (2 mM PMS and 8 mM NaOH), the flux recovery rate nearly reached 100%. Direct backwash of the membrane by the above cleaning solution further reduced the cleaning time to 25 mins, while achieving similar cleaning effect. Then the cleaned membranes were immersed in NaClO solution to release all the residual foulants, but the fluorescence excitation-emission matrix spectra (EEM) and total organic carbon (TOC) of the solution were found insignificant, which demonstrated the base-activated persulfate strategy had effectively removed the irreversible membrane fouling. Free radical quenching experiments were carried out and·O2- was identified as the dominant ROS responsible for the removal of the membrane foulants. The permeate flux and filtration efficiency of the SiC membrane were stable after 5 consecutive fouling-cleaning cycles, and the membrane structure was not damaged. In summary, the base-activated persulfate strategy is an efficient and cleaner method for SiC membrane cleaning, which is potential to be applied in practical membrane water treatment process.

Insights into boosting SiC membrane superhydrophobic-superoleophilic property and oil purification performance by hierarchical structure control

Engineering of superhydrophobic-superoleophilic (SHB-SOL) ceramic membrane surface with hierarchical structures remains challenging and the relation between physicochemical structure-dependent wettability and separation performance lacks investigation. Herein, SHB-SOL SiC ceramic membranes with different hierarchical micro-nano structures were fabricated by ZnO nanoflower (NF) deposition and silane grafting. Three SiC ceramic membranes with different pore sizes were purposefully used as the pristine, these membranes displayed similar geometric structures in different scales. The modified SiC membrane surface becomes stronger in SHB-SOL property as the pore size decreases and the optimal membrane possessing the lowest pore size presented a water contact angle of 172.46° and a water sliding angle of 5°. When used for pure oil or oily mixture separation, all the SHB-SOL SiC membranes exhibited enhanced oil fluxes compared with their pristine forms. At a pressure of 0.5 bar, the optimal membrane could completely reject water droplets and graphite solids (D50 =4.8 µm) for the oil-water-solid mixture containing 0.05 wt% water and 0.05 wt% graphite, showing a stable oil (hexane) flux of 1383.8 L·m−2·h−1. This work also reveals the effects of the hierarchical structures on the SHB-SOL property formation and the resulting antifouling mechanism, which offers novel insights into boosting ceramic membranes with desired surface wettability for enhanced separation performance.

Reaction-bonded robust SiC ceramic membranes sintered at low temperature with coal gangue

Herein, we report an in-situ reaction-bonded SiC membrane sintered at low temperature using a solid waste (i.e. coal gangue) as the sintering aid to form strong neck connections. The effects of sintering temperature and coal gangue proportion on their properties regarding pore size, open porosity, bending strength and pure water permeability were investigated. The single-channel tubular SiC membrane sintered at 1300 °C with a coal gangue proportion of 12 wt% was optimal, exhibiting an average pore size of 2.78 μm, a open porosity of 47.08%, a bending strength of 34.01 ± 1.3 MPa and a high water permeability of 83967 L m−2 h−1 bar−1. The membrane could completely reject D50 = 0.87 μm SiC solids and presented a steady-state water permeability of 458 L m−2 h−1·bar−1. The SiC membrane could be regenerated through ultrasonication and its steady-state water permeability was almost unchanged for 3 cycles, proving its mechanical robustness. This work may appeal to the practical low-cost production of high-performance SiC membranes.

Comparison of MBR and MBBR followed by UV or electrochemical disinfection for decentralized greywater treatment

Greywater is an attractive source for water reuse at the household or building level, particularly for non-potable applications. Two greywater treatment approaches are membrane bioreactors (MBR) and moving bed biofilm reactors (MBBR), yet, their performance has not been compared so far within their respective treatment flowsheets, including post-disinfection. Two lab-scale treatment trains were operated on synthetic greywater: a) MBR with either polymeric (chlorinated polyethylene, C-PE, 165 days) or ceramic (silicon carbide, SiC, 199 days) membranes coupled with UV disinfection; and b) single-stage (66 days) or two-stage (124 days) MBBR coupled with an electrochemical cell (EC) for in-situ disinfectant generation. Water quality was constantly monitored, and Escherichia coli log removals were assessed through spike tests. Under low-flux operation of the MBR (<8 L·m − 2·h − 1), the SiC membranes delayed the onset of membrane fouling and needed less frequent cleaning compared to C-PE membranes. Both treatment systems met most water quality requirements for unrestricted greywater reuse, at a 10-fold lower reactor volume for the MBR than the MBBR. However, neither the MBR nor the two-staged MBBR allowed adequate nitrogen removal, and the MBBR did not consistently meet effluent chemical oxygen demand and turbidity requirements. Both EC and UV provided non-detectable E. coli concentrations in the effluent. Although the EC provided residual disinfection, scaling and fouling decreased its energetic and disinfection performance over time, making it less efficient than UV disinfection. Several outlines to improve the performance of both treatment trains and disinfection processes are proposed, thus, allowing a fit-for-use approach that leverages the advantages of the respective treatment trains. Results from this investigation will assist in elucidating the most efficient, robust, and low-maintenance technology and configurations for small-scale greywater treatment for reuse.

Influence of additive contents on the properties of SiC ceramic membranes and their performance in oil‐water separation

AbstractThe high processing cost is the key challenge for the economic industrial use of SiC membrane The aim of this research was to fabricate mullite bonded porous SiC ceramic membrane at low temperature from novel combinations of fly ash and alumina (FA) in weight ratio 44.5:55.5 as sintering additives. The influences of FA and pore former content on the porosity, morphology, crystalline phase composition, mechanical performance, permeability properties were investigated. The membrane prepared at 1300°C using 20 wt% FA showed pure water permeability 3690 Lm−2h−1bar−1 and exhibited high oil removal efficiency of ∼ 98% from the synthetic oil‐water emulsion having oil concentration of 1000 mg/L. The corrosion behaviour of silicon carbide membrane in the strong acid and alkali solution and its mechanism were investigated. The utilization of fly ash successfully reduced the raw material cost and sintering temperature and the use of alumina reduced the amount of oxidation of SiC as well as increased the amount of mullite bond phase which resulted excellent mechanical strength to the final ceramics.

Construction of Pt@CNTs/SiC Catalytic Membrane for High-Efficiency Removal of Formaldehyde and Dust

Catalytic membranes can achieve the simultaneous purification of particulate matter (PM) and gaseous pollutants, and their performance depends on the design of a catalyst and its combination with a membrane material. Herein, a novel Pt@CNTs/SiC catalytic membrane composed of a Pt@CNTs (carbon nanotubes) membrane layer and a porous SiC support was developed for the simultaneous removal of formaldehyde and PM at room temperature. The CNT membrane layer underwent vertically integrated growth on a porous SiC support, which provided the catalytic membrane with a pore size of 7.4 μm and a high gas permeance of 240.2 m3·m–2·h–1·kPa–1. The loading of Pt particles on CNTs slightly decreased the gas permeance of the catalytic membrane (219.9 m3·m–2·h–1·kPa–1) but endowed the membrane with catalytic formaldehyde degradation performance. The obtained Pt@CNTs/SiC catalytic membrane with a 240 μm thick CNT layer and 0.8% Pt loading exhibited 99.999% filtration efficiency for 300 nm SiO2 (face velocity = 1 m/min) and 72.1% formaldehyde degradation (gas flow = 49 mL/min), implying that the Pt@CNTs/SiC membrane has good application potential in the collaborative removal of various air pollutants.

Continuous preparation of water-in-heavy oil emulsion without emulsifier by SiC membranes at high temperature and its micro-explosion performance

Emulsified heavy oil as an alternative fuel is of great significance for reducing environmental pollution and settling energy crisis. The micro-explosion of the emulsion plays a vital role in improving the fuel efficiency as well as reducing harmful gas emissions. Here, the water-in-heavy oil emulsion was prepared by membrane emulsification at high temperatures (60–100 °C) without using any emulsifier, and its puffing and micro-explosion performance were investigated by the suspended drop method. The water droplet size (D90) of emulsions can be controlled from 3.8 μm to 7.0 μm by controlling the emulsification process parameters (i.e., membrane pore size, the flow rate ratio of the dispersed phase to the continuous phase, the flow rate of the continuous phase on the membrane surface and temperature of continuous phase) using SiC membranes. Moreover, the trend of droplet size can be predicted based on analyzing the forces on an individual droplet that govern by the emulsification parameters. The puffing and micro-explosion probability of the emulsions increased with the increasing water content and droplet size, which can also effectively reduce the coking of heavy oil at 500 °C. As a result, the highest probability of micro-explosion (90%) and the lowest probability of coking (10%) were realized at a water content of 5 vol% and an average droplet size of 6.5 μm. Therefore, the utilization efficiency of heavy oil can be improved by membrane emulsification process.