Polyvinylidene Fluoride Hollow Fiber Research Articles

A facile and scalable fabrication procedure for PVDF-PDA/PEI/SiO2 hollow fiber composite ultrafiltration membranes: Integration of co-deposition and cross-linking

Polyvinylidene fluoride (PVDF) membranes, widely used for their stability, face limitations due to the hardly adjustable pore size in nanoscale and inherent hydrophobicity. To address this, we proposed a co-deposition method incorporating dopamine (DA), polyethyleneimine (PEI), and silicon dioxide (SiO2) nanoparticles with glutaraldehyde cross-linking for precise regulation of pore size and hydrophilicity in PVDF hollow fiber membranes. Notably, the pore diameter reduced from 119.0 ± 3.55 nm to 18.4 ± 0.36 nm, while the contact angle decreased from 107.7° to 40.9°. This simultaneous regulation led to a high-performance PDA/PEI/SiO2-PVDF hydrophilic ultrafiltration membrane with a rejection rate exceeding 99% for 20 nm nanoparticles in a long-term simulated separation experiment while achieving a significant protein permeability of 97% in BSA permeation experiments. Additionally, the membrane demonstrated exceptional long-term stability, offering a novel approach for tuning the performance of ultrafiltration/microfiltration membranes.

Construction of PDMS@ZIF-8 composite membrane on PVDF hollow fiber inner surface for ultrafast ethanol/water separation

Construction of ultra-thin and defect-free separation membrane on inner surface of hollow fiber supports is significant but challenging for molecular separation. In this study, the highly permeable PDMS@ZIF-8/PVDF composite membranes were successfully fabricated upon the inner-surface of polyvinylidene fluoride (PVDF) hollow fiber membrane for pervaporation (PV) ethanol/water separation. The efficient preparation of hierarchical PDMS@ZIF-8/PVDF composite membranes benefited from the precise regulation of ZIF-8 layer through interfacial synthesis and sequential coating of PDMS matrix. The thickness of the PDMS layer was only 16±2 nm, which admirably eliminated the non-selective defects in ZIF-8 layer. Owning to the optimal combination of MOF layer and ultra-thin polymer layer, the as-prepared membrane exhibited the excellent ethanol flux of 1.34 kg m-2 h-1 with an ethanol concentration in permeate of 31.3 wt.% for separating 5 wt.% ethanol aqueous solution at 40°C. The separation performance of the resultant membrane was superior to that of the other ethanol selective PV membranes. These findings herein provided a new way for preparing high-performance hollow fiber composite membranes for PV separation.

Hyperbranched polymer hollow-fiber-composite membranes for pervaporation separation of aromatic/aliphatic hydrocarbon mixtures

The separation of aromatic/aliphatic hydrocarbon mixtures is crucial in the petrochemical industry. Pervaporation is regarded as a promising approach for the separation of aromatic compounds from alkanes. Developing membrane materials with efficient separation performance is still the main task since the membrane should provide chemical stability, high permeation flux and selectivity. In this study, the hyperbranched polymer (HBP) was deposited on the outer surface of a polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane by a facile dip-coating method. The dip-coating rate, HBP concentration, and thermal cross-linking temperature were regulated to optimize the membrane structure. The obtained HBP/PVDF hollow fiber composite membrane had a good separation performance for aromatic/aliphatic hydrocarbon mixtures. For the 50%/50% (mass) toluene/n-heptane mixture, the permeation flux of optimized composite membranes could reach 1766 g·m–2·h–1 with the separation factor of 4.1 at 60 °C. Therefore, the HBP/PVDF hollow fiber composite membrane have great application prospects in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures.

Hydrophobic hollow fiber composite membranes based on hexadecyl-modified SiO2 nanoparticles for toluene separation

In this work, we present a cost-effective and affordable inorganic silicon material known as nano-SiO2. The purpose of this work is to enhance the performance of toluene separation by utilizing modified-SiO2/polydimethylsiloxane (PDMS) nanocomposite membranes. To achieve this, we successfully grafted hexadecyltrimethoxysilane (HDTMS) onto the surface of nano-SiO2 and systematically investigated the impact of SiO2 concentration on the separation efficiency. Various techniques such as scanning electron microscopy (SEM) and water contact angle (WCA) and Fourier transform infrared (FT-IR) spectrum analyses were employed to analyze the surface morphology, hydrophobic properties, and functional groups of modified polyvinylidene fluoride (PVDF) hollow fiber membranes. In brief, 400 ppm of each volatile organic compound (toluene) was injected into the module as a feed for 10 min at 25 °C under a pressure of 1 bar at room temperature. Gases in the retentate were analyzed by GC/FID in purge and trap analyzers at 250 °C. The VOCs were sampled using an Automated Purge & Trap Sampler. After comparing the chromatographic data to the reference compounds, the adsorption capacity was calculated to identify residual VOCs collected after separation by the nanocomposite membrane as present in the feed. Among the tested modules, 0.2HPM (hollow fiber membranes coated with 20 wt% PDMS and 0.2 wt% hexadecyl-modified SiO2) exhibited the highest toluene removal efficiency of 95.7 % under conditions of 400 mL/min flow rate and 1 bar pressure. The findings of this study provide valuable insight into the hydrophobic modification of nano-SiO2 and its potential application as a membrane-based separation technique.

Modification of PVDF hollow fiber membrane with ZnO structure via hydrothermal for enhanced antifouling property in membrane distillation

This study aims to provide a close insight into the possibilities and constraints associated with the development of ZnO structures on polyvinylidene fluoride (PVDF) hollow fiber membranes using the hydrothermal method to enhance membrane surface roughness for improved fouling resistance in membrane distillation (MD). Due to the flexible nature of polymeric hollow fiber membranes, there is a considerable risk of the ZnO structure detaching from the membrane surface when the membrane is bent. To address this issue, the hydrothermal duration was varied between 4 and 16 h to optimize the ZnO structure for high integrity, followed by fluorination. The results reveal that the membrane treated with hydrothermal for 8 h exhibits stable coating integrity, imparting the membrane with the highest contact angles with various liquids. This membrane demonstrates a flux of 4.0 kg/m2h and excellent salt rejection (>99.9 %) in direct contact MD (DCMD) when treating a 35 g/L saline solution. Additionally, the membrane exhibits outstanding antifouling performance with minimal flux reduction over 24 h when treating a saline solution containing humic acid. However, the upscaling of the hydrothermal approach may pose challenges due to the difficulty in maintaining the consistency of ZnO structure formation.

Efficient purification of high-salt rural groundwater in the areas along the Yellow River in Henan Province, China, by hollow fiber membrane distillation process

The vast rural drinking water sources along the Yellow River basin in Henan Province mainly come from the local high-salinity groundwater, which cannot be directly drunk. Zeolitic imidazolate framework-71/polyvinylidene fluoride hollow fiber composite membrane was applied to treat rural groundwater through membrane distillation technology. The variations of water quality parameters from 12 different rural regions after membrane distillation treatment were well analyzed and compared. Membrane separation performance for water samples from different regions during the membrane distillation process was investigated, including water flux and salt rejection. During a continuous 24-h membrane distillation process for the treatment of these water samples, hollow fiber membrane exhibits high solute retention rates (>99%) for salt ions, suspended solids and total dissolved solids, which are within the limits of national standards (GB 5749-2006), meanwhile membrane permeation water flux can remain stable. After the acid-cleaning for 180 min, all hollow fiber membranes can recover water flux well with a flux recovery rate above 98%. Even if the concentration ratio continued to increase, the water production rate of membrane distillation was basically maintained between 50% and 60%, which was obviously higher than the 30% of the reverse osmosis process. The economic analysis confirmed that the water production cost varied between US$0.45 and US$0.29/m3. With the extension of membrane service life, the specific membrane cost decreased rapidly in the first 6 years and then leveled off. The proposed vacuum membrane distillation process proved to be a promising water purification method for treating rural high-salinity groundwater.

A simple and effective method to adjust the size of micropores on the inner surface of Polyvinylidene fluoride hollow fiber membranes

AbstractPore‐forming agents affect phase thermodynamics of solution‐case membranes, hence influencing the structure and properties of the membrane. Polyvinylidene fluoride (PVDF) membrane has many advantages, but more in‐depth research is needed regarding directional control of membrane pore size. To solve this problem, a simple and efficient method is proposed. By adjusting the percentage of polyvinylpyrrolidone (PVP) in the casting solution, pore diameter is controlled between 0.01 and 10 μm. The number density and diameter of the inner surface increased significantly with increasing PVP content. The relevance of this study lies in the modulation of the inner surface micropore size of PVDF hollow fiber membranes in a simple and efficient procedure.Highlights Adjusting the size of micropores on the inner surface. The size range of the inner surface is controlled between 0.01 and 10 μm. It is possible to regulate the pore structure by limiting PVP concentration. Significant increase in the number and size of pore on the inner surface. A simple method for regulating the size of micropores.

Preparation of carbon-based monolith with macroporous-mesoporous structure derived from PVDF hollow fiber membranes for supercapacitors

In this work, a carbon-based monolith with macroporous-mesoporous structure derived from polyvinylidene fluoride (PVDF) hollow fiber membranes is reported. The Co2+ soaked PVDF hollow fiber membranes are treated with vinyltrimethoxysilane (VTMS) and calcined at relatively low temperatures (600 °C) to obtain a carbon-based material with a distinctive honeycomb porous structure. The VTMS treatment is the committed step, which provides a hard SiO2 protective layer for the PVDF hollow fiber membrane during the calcination process to support the skeleton structure and prevent the macrostructure collapse and also plays a role in expanding mesopores. The obtained hierarchically porous structure can improve the electrochemical activity of the carbon-based material. In a three-electrode system, the specific capacitance of 701.0 F g−1 can be achieved at a current density of 1 A g−1, and the retention rate is 112.1 % after 10,000 cycles at 10 A g−1. The assembled quasi-solid-state symmetric supercapacitor can be operated in a 0–1.4 V voltage window, and it demonstrates an energy density of 26.3 Wh kg−1 at the power density of 349.9 W kg−1.

Influence of NH2-MOF addition into PVDF and estimation of CO2 gas transport through membrane

Polyvinylidene fluoride (PVDF) had been vastly utilised for CO2/CH4 gas separation application. Nevertheless, pure polymeric membranes always suffer from a trade-off between permeability and selectivity as proven by Robeson in upper bound curves developed in gas separation applications. Thus, alternative modification like incorporating filler into polymer matrix to develop mixed matrix membranes (MMMs) is required. Besides, estimation of CO2 permeance of MMMs via unsuitable theoretical models would result in mismatch between experimental and predicted CO2 permeance data, subsequently causing troubles in membrane separation system designation. In the current work, PVDF hollow fiber mixed matrix membranes (HFMMMs) had been developed using NH2-MIL-125 (Ti) loadings of 1, 1.5, 2.5, and 3 wt%. The synthesized NH2-MIL-125 (Ti) and spun NH2-MIL-125 (Ti)/PVDF HFMMMs were characterized using Fourier transform infrared (FTIR). Furthermore, the Maxwell, Pal, modified Pal, Lewis–Nielson, Bruggeman and Bottcher model, were utilised to estimate the CO2 permeance of developed membranes. The additional FTIR peaks appeared at around 3440, 3358, 1478, 1430 cm−1 for developed HFMMMs when compared with pure PVDF indicate the presence of NH2-MIL-125 (Ti) in the HFMMMs. CO2 permeance estimation of 1.5 wt% PVDF HFMMM using all selected models yields around 1 absolute average relative error percent (AARE%). The remaining membranes displayed a high deviation, with an AARE% exceeding ± 5. AARE% obtained in the current work suggested that all the selected models can fit 1.5 wt% PVDF HFMMM.

Surface modification of PVDF hollow fiber ultrafiltration membranes for biopharmaceutical products, virus, and bacterial phage removal technology

In this study, radicals were chemically formed at the hydroxyl (-OH) sites on the surface of polyvinylidene fluoride (PVDF) hollow fiber membranes, and anionic-hydrophilic and hydrophobic materials were grafted onto the surface through -OH radical reaction to generate anions (−28, −41 mV). These membranes were then used as biomembranes (BMs) and showed excellent properties. We also studied the effects of chemical surface modification and reduction in pore size (60–130 nm) according to molecular weight. After anionic modification, the electrostatic repulsion between the pore surface and the bacteria prevents adsorption when anionic bacteria pass through the pores. Particles do not pass through the asymmetric pores due to agglomeration, resulting in separation. The hydrophilic membrane had a high initial water flux, but the flux gradually decreased due to fouling. In contrast, the hydrophobic modified membrane had a low initial water flux that eventually stabilized due to excellent fouling resistance. The protein recovery ratio (PRR) was 98.8 % for hydrophilic particles and 99.2 % for hydrophobic molecules, showing a higher PRR than the pristine membrane (96.4 %). An evaluation of removal of the gram-negative bacteria Brevundimonas diminuta (Bd) showed that no bacteria in membrane-purified solutions, confirming 100 % removal efficiencies. The developed membrane can be used in biopharmaceutical production and removal of proteins, retro viruses, and bacteria.

Preparation of a hollow fiber membrane made of antifouling PVDF/Zeolit using the dip-coating technique

The practical technique for membrane modification is dip coating. This study coats a PVDF hollow fiber membrane-based composite with a coating of zeolite. The composite is made of a polyvinylidene fluoride (PVDF) membrane. During water filtering, the separation capabilities and propensities of composite membranes for organic impurities were examined. SEM and Fourier-transform infrared spectroscopy analysis of the findings demonstrated that the Zeolite coating was successfully deposited on the PVDF membrane. The flux recovery ratio increases from 69% to 80% while the relative flux drop decreases from 63% to 50%. A composite PVDF membrane dip-coating of Fe2O3/Zeolite with a GA and H2SO4 ratio of 1:2 is needed to remove about 75% of humic compounds from effluent. The results of this study show that the addition of Fe2O3/Zeolite with a GA and H2SO4 layer can greatly improve the hydrophilicity, selectivity, and anti-organic fouling of the PVDF hollow fiber membrane.

Hydrophobic modification of a PVDF hollow fiber membrane by plasma activation and silane grafting for membrane distillation.

Polyvinylidene fluoride (PVDF) hollow fibers were hydrophobically modified using a simple and scalable method of plasma activation and silane grafting. The effects of plasma gas, applied voltage, activation time, silane type, and concentration were investigated according to the membrane hydrophobicity and direct contact membrane distillation (DCMD) performance. Two kinds of silane were used, including methyl trichloroalkyl silane (MTCS) and 1H,1H,2H,2H-perfluorooctane trichlorosilane silanes (PTCS). The membranes were characterized by techniques such as Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle. The contact angle of the pristine membrane was 88°, which increased to 112°-116° after modification. Meanwhile, the pore size and porosity decreased. In DCMD, the maximum rejection reached 99.95% by the MTCS-grafted membrane, while the flux decreased by 35% and 65% for the MTCS- and PTCS-grafted membranes, respectively. Treating humic acid-contained solution, the modified membrane showed steadier water flux and higher salt rejection than the pristine membrane, and 100% flux recovery was achieved by simple water flushing. This two-step method of plasma activation and silane grafting is very simple and effective to improve the hydrophobicity and DCMD performance of PVDF hollow fibers. However, further study on improving the water flux should be carried out.

Simulation Guided Coaxial Electrospinning of Polyvinylidene Fluoride Hollow Fibers with Tailored Piezoelectric Performance.

Electrospun polyvinylidene fluoride (PVDF) piezoelectric fibers have high potential applicability in mechanical energy harvesting and self-powered sensing owing to their high electromechanical coupling capabilities. Strategies for tailoring fiber morphology have been the primary focus for realizing enhanced piezoelectric output. However, the relationship between piezoelectric performance and fiber structure remains unclear. This study fabricates PVDF hollow fibers through coaxial electrospinning, whose wall thickness can be tuned by changing the internal solution concentration. Simulation analysis demonstrates an increased effective deformation of the hollow fiber as enlarging inner diameter, resulting in enhanced piezoelectric output, which is in excellent agreement with the experimental results. This study is the first to unravel the influence mechanism of morphology regulation of a PVDF hollow fiber on its piezoelectric performance from both simulation and experimental aspects. The optimal PVDF hollow fiber piezoelectric energy harvester (PEH) delivers a piezoelectric output voltage of 32.6V, ≈3 times that of the solid PVDF fiber PEH. Furthermore, the electrical output of hollow fiber PEH can be stably stored in secondary energy storage systems to power microelectronics. This study highlights an efficient approach for reconciling the simulation and tailoring the fiber PEH morphology for enhanced performances for future self-powered systems.

Green thermally induced phase separation (TIPS) process for braided tube reinforced polyvinylidene fluoride (PVDF) hollow fiber composite membranes with favorable bonding layer

BackgroundCurrently, membrane separation technology was used in the fields of water treatment, gas separation and electrodialysis. Among them, water treatment was still the main field of application of membrane separation technology, for example, in the treatment of industrial wastewater, membrane separation technology does not destroy or change the composition of wastewater during the treatment process, and valuable products can be recovered and used commercially. MethodsThe braided tube reinforced polyvinylidene fluoride (PVDF) hollow fiber composite membranes were successfully prepared by thermally induced phase separation (TIPS) method with no harmful diluent and additives (green preparation) based on concentric circle spinning process. Significant findingsThe membrane morphology was characterized by scanning electron microscopy (SEM) and confocal scanning microscopy (CSM). The effects of polyethylene oxide (PEO) content on the performance of the prepared hollow fiber membranes were investigated in terms of mechanical strength, pure water flux and bovine serum protein (BSA) rejection. The results showed that the addition of PEO promoted the phase separation process and inhibited the growth of PVDF spherical crystals. When the PEO content was 15wt%, the membrane has high pure water flux and excellent BSA rejection. In addition, the tensile strength of the reinforced hollow fiber membranes exceeded 100 MPa and exhibited favorable interfacial bonding.

Thin-Film Composite Matrimid-Based Hollow Fiber Membranes for Oxygen/Nitrogen Separation by Gas Permeation.

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O2 permeance of 30.8 GPU and O2/N2 selectivity of 4.7, with a thickness of about 5-10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.

Unveiling the residual membrane foulants in full-scale MBR plant after chemically enhanced backwash: Insights into microbe-associated compounds

Membrane fouling is a main bottleneck that limits the stable operation of membrane bioreactors (MBRs). However, the nature of residual foulants over frequent chemical cleaning remain elusive. Herein, we collected fouled membranes from a large-scale MBR with the treatment capacity of 200, 000 m3/d and explored the culprit for the key components resistant to chemically enhanced backwash. During 155 days of operation, transmembrane pressure increasing highly linked to the characteristics of membranes and bio-cakes. Fourier-transform infrared microscopy deciphered that a part of polyvinylpyrrolidone in the structure of polyvinylidene fluoride hollow fiber membrane was removed by NaOCl after chemical backwash. The stubborn uronic acids were mostly responsible for irreversible fouling due to pore constriction and the resistance to NaOCl. The fouling-related genera f_Rhodocyclaceae and f_Anaerolineaceae prevailed in the bio-cakes. According to the network analysis, the negative and competitive interactions on the bio-cake contributed more to severe membrane fouling than the positive and cooperative interactions. The keystone taxa c_WS6 (Dojkabacteria) and c_Deltaproteobacteria, which involved in secreting polysaccharides and hydrolyzing refractory matters, accelerated the accumulation of organic foulants. Our findings help to elucidate the key contributors to membrane fouling and anti-cleaning in full-scale MBR, which provide new insights for future fouling control.

Organic solvent-free constructing of stable zeolitic imidazolate framework functional layer enhanced by halloysite nanotubes and polyvinyl alcohol on polyvinylidene fluoride hollow fiber membranes for treating dyeing wastewater

In this study, zeolitic imidazolate framework (ZIF-8)/polyvinylidene fluoride (PVDF) loose nanofiltration (NF) hollow fiber membranes were fabricated by constructing ZIF-8 functional layer on the PVDF supporting membranes based on the vacuum-assisted assembly process. The ZIF-8 synthesis was completed in a water system, and the synthesized ZIF-8 suspension was directly added to polyvinyl alcohol (PVA) and halloysite nanotubes (HNTs) aqueous solution system without drying to prepare the casting solution, which could solve the agglomeration and poor dispersion problem of ZIF-8 particles. In addition, the embedded HNTs and the loaded PVA among the ZIF-8 layer could improve the bonding strength between the ZIF-8 layer and the supporting membranes. After constructing ZIF-8 functional layer, the pore size of supporting membranes decreased from more than 300 nm to several nanometers. Furthermore, the water contact angle reduced from 91.1° to 54.2°. Applied to treat dye wastewater, the prepared ZIF-8/PVDF membranes maintained high dye rejection (˃99.0 %) for Congo red (CR), but low salt rejection for NaCl (about 2 %). In addition, the flux could reach 21.6 L m-2h−1 after continuous filtration 360 min, exhibiting a potential for treating the dye/salt wastewater. In particular, there were no organic solvents used in the work, which provided a promising idea for solvent-free fabrication of loose NF membranes.

Potential effects of nano‐fumed silica particles (NFS)/PVDF mixed matrix hollow fiber membrane on the performance of direct contact membrane distillation

AbstractHydrophobic nano‐fumed silica (NFS) was incorporated in polyvinylidene fluoride (PVDF) hollow fiber (HF) membrane for improving direct contact membrane distillation (DCMD) performance. The NFS/PVDF mixed matrix hollow fiber membrane was fabricated by the phase inversion process. The potential effects of increasing the percentage of NFS additive (0–6 wt.%) in the dope solution on the hollow fiber membrane characteristics such as viscosity, membrane morphology, porosity, hydrophobicity, Fourier transformed infrared spectroscopy, and permeability were investigated. The performance outcomes showed that the dope solution incorporated with 1.5 wt.% NFS exhibited the most promising HF membrane for membrane distillation (MD). The optimal HF membrane demonstrated the highest flux through shorter and narrower finger‐like structure formation and targeted high porosity. The addition of NFS particle content in the dope solutions enhanced the hydrophobicity of the fabricated membranes while slightly decreasing the porosity due to increasing the viscosity of the dope solution. With a steady flux of 9.25 kg/m2 h compared with the neat membrane at 70°C/20°C of feed/permeate temperatures, 8 h operation, and above 99.9% salt rejection, this PVDF/NFS mixed matrix hollow fiber membrane could be of excellent potential and sustainability in desalination process through DCMD.

Ammonia removal using thermally induced phase separation PVDF hollow fibre membrane contactors

Hollow fibre membrane contactors (HFMCs) are a promising new technology for ammonia recovery but are limited by the mass transfer efficiency as well as their chemical resistance and physical strength. Thermally Induced Phase Separation (TIPS) Polyvinylidene Fluoride (PVDF) membranes offer a new HFMC option for ammonia recovery due to their superior removal performance and physicochemical properties. In this study, two chemically robust TIPS PVDF HFMCs were synthesized and evaluated for the recovery of ammonia from wastewater. The HFMCs displayed an uncompromised high tensile strength of up to 19.12 ± 0.93 MPa under a long-term chemical exposure against acids, alkalis, and oxidants over 60 days of immersion. The HFMCs had a high air permeance flux of up to 1.67 ± 0.26 mol/m2/s. The crystalline structure of the TIPS PVDF membranes affected the hydrophobicity of the membranes more than pore size. Optimisation of ammonia removal was achieved by the Taguchi method for design of experiments using five operational parameters namely pH, temperature, ammonia solution velocity, concentration, and air sparging rate. Empirical evidence showed that the TIPS PVDF HFMCs achieved the highest ammonia removal of greater than 99% and a mass transfer coefficient (Kov) of up to 4.53 × 10-5 m/s. Comparatively, the Kov and flux of both TIPS PVDF membranes in this study are up to one order higher than those previously reported and could even be higher with further improvements to operating conditions. Air sparging is for the first time used in HFMCs to improve ammonia removal and is known to simultaneously reduce membrane fouling.

Design of continuous flow membrane reactor for in-situ sonophotocatalytic degradation of ciprofloxacin

Antibiotics in the aquatic environments pose a severe threat to global public health. Hence, a sonophotocatalytic membrane reactor (SPMR) of sonophotocatalysis coupled membrane separation was designed to realize continuous and stable degradation of ciprofloxacin (CIP) by Bi2MoO6/FeVO4 in this study. The prepared catalysts were characterized by XRD, SEM, TEM, BET, UV–vis DRS, PL, and EIS. Under the optimal hydraulic retention time (HRT) of 55 min, 93.43% of CIP (10 mg/L) was degraded by Bi2MoO6/FeVO4 (500 mg/L) after 200 min sonophotocatalytic reaction in the presence of H2O2 (20 mM). The synergy index (SI) of sonocatalysis and photocatalysis was calculated to 1.80 during the catalytic process. The SPMR effluent turbidity was basically nil after 10 min separation of catalyst by polyvinylidene fluoride (PVDF) hollow fiber membrane. The changes of PVDF membrane before and after use in SPMR were observed by SEM and FTIR. The membrane fouling behavior in the SPMR was investigated by membrane water flux, flux recovery rate, and membrane resistances. The mechanisms of CIP degradation are attributed to·OH and·holes (h+) generated by Bi2MoO6/FeVO4 under ultrasonic and visible light irradiation. Besides, the solution matrix effects on sonophotocatalytic removal of CIP were investigated. The results proved that SPMR still maintained satisfactory sonophotocatalytic degradation efficiency in typical natural water bodies and simulated water matrices. In this work, the continuous operation process of CIP degradation and catalyst separation was realized, and the membrane fouling was alleviated by ultrasonic.