Performance evaluation of novel nanostructured modified mesoporous silica/polyetherimide composite membranes for the treatment of oil/water emulsion

Separation of oil-water emulsion by cellulose acetate ultrafiltration membranes

This study reports the separation of oil from water using cellulose acetate (CA) ultrafiltration (UF) membranes. The CA membranes were fabricated by varying bath temperatures such as 5 ± 2°C, 25 ± 2°C and 45 ± 2°C using the phase inversion technique and assess their performance based on the oil removal efficiency. Changing the coagulation bath temperature (CBT) at that stage of membrane formations affects the porosity, pore size, hydraulic resistance, morphological structure and performance of membranes. The obtained results revealed increased porosity and pore size and also decreased hydraulic resistance of the membranes as the CBT increases. Field Emission Scanning Electron Microscopy (FESEM) images indicate that a large number of surface pores are visibly found at the higher bath temperature. Atomic force Microscopy (AFM) images show increased average roughness (Ra) of the membrane as the CBT of the membrane increases. The water flux and permeate flux of all the membranes tend to increase with an increase in CBT. From Chemical Oxygen Demand (COD) studies, the oil removal efficiency was maximum for the lower bath temperature membrane. The results indicate that conditions of the coagulation bath significantly affect the porous structure, morphology and performance of the membrane.

ZnO/PDA/Mesoporous Cellular Foam Functionalized Thin-Film Nanocomposite Membrane towards Enhanced Nanofiltration Performance

Thin-film nanocomposite (TFN) membranes are the third-generation membranes being explored for nanofiltration applications. Incorporating nanofillers in the dense selective polyamide (PA) layer improves the permeability-selectivity trade-off. The mesoporous cellular foam composite Zn-PDA-MCF-5 was used as a hydrophilic filler in this study to prepare TFN membranes. Incorporating the nanomaterial onto the TFN-2 membrane resulted in a decrease in the water contact angle and suppression of the membrane surface roughness. The pure water permeability of 6.40 LMH bar^-1 at the optimal loading ratio of 0.25 wt.% obtained was higher than the TFN-0 (4.20 LMH bar^-1). The optimal TFN-2 demonstrated a high rejection of small-sized organics (>95% rejection for 2,4-dichlorophenol over five cycles) and salts-Na₂SO₄ (≈95%) > MgCl₂ (≈88%) > NaCl (86%) through size sieving and Donnan exclusion mechanisms. Furthermore, the flux recovery ratio for TFN-2 increased from 78.9 to 94.2% when challenged with a model protein foulant (bovine serum albumin), indicating improved anti-fouling abilities. Overall, these findings provided a concrete step forward in fabricating TFN membranes that are highly suitable for wastewater treatment and desalination applications.

Dual-bionic nano-groove structured nanofibers for breathable and moisture-wicking protective respirators

Coronavirus disease 2019 (COVID-19) pandemic makes protective respirators highly demanded. The respirator materials should filter out viral fine aerosols effectively, allow airflow to pass through easily, and wick away the exhalant moisture timely. However, the commonly used melt-blown nonwovens perform poorly in meeting these requirements simultaneously. Herein, dual-bionic nano-groove structured (NGS) nanofibers are fabricated to serve as protective, breathable and moisture-wicking respirator materials. The creativity of this design is that the tailoring of dual-bionic nano-groove structure, combined with the strong polarity and hydrophilicity of electrospinning polymer, not only endows the nanofibrous materials with improved particle capture ability but also enable them to wick away and transmit breathing moisture. Benefitting from the synthetic effect of hierarchical structure and the intrinsic property of polymers, the resulting NGS nanofibrous membranes show a high filtration efficiency of 99.96%, a low pressure drop of 110 Pa, and a high moisture transmission rate of 5.67 kg m^-2 d^-1 at the same time. More importantly, the sharp increase of breathing resistance caused by the condensation of exhaled moisture is avoided, overcoming the bottleneck faced by traditional nonwovens and paving a new way for developing protective respirators with high wear comfortability.

Designing of nanotextured inorganic-organic hybrid PVDF membrane for efficient separation of the oil-in-water emulsions

The separation of the emulsified oil/water is one of the critical environmental challenges. The PVDF membranes have been found helpful for separation, but rapid fouling makes them less attractive in treating oil-in-water emulsions. The design of antifouling membranes has become an area of deep interest. Herein, developing a novel modified PVDF ultrafiltration membrane was reported by doping the pyrrole and solidifying it in a ferric-containing coagulation bath, resulting in a unique nanotextured PVDF membrane (CCB-Fe/PP_np-PVDF) to separate the oil/water emulsions. The resultant CCB-Fe/PP_np-PVDF membrane was thoroughly characterized using the FTIR, FE-SEM, EDX, mapping, AFM, and contact analyzer. The hydrophilicity of the CCB-Fe/PP_np-PVDF was substantially improved, and the water contact angle was reduced from 81֯ ± 0.9֯ to 44֯ ± 1.7֯. The CCB-Fe/PPnp-PVDF membrane flux increased by 121% compared to the pristine PVDF membrane, with high separation efficiency of 99%. The hydrophilic nanotextured surface of the CCB-Fe/PP_np-PVDF membrane showed good antifouling behavior, with a flux recovery ratio (FRR) of more than 96%. Irreversible flux was just less than 4%. The high flux recovery ratio indicated that the nanotextured surface produced by the Fe/PP_np had prevented the blockage of the membrane pores and compact cake layer formation, which makes it an excellent membrane for oil/water emulsion separation. This strategy can be adopted for designing advanced membranes for separation applications.

Catalyst- and Stabilizer-Free Rational Synthesis of Ionic Polymer Nanoparticles in One Step for Oil/Water Separation Membranes

Ionic polymer nanoparticles (IPNs) were synthesized in one pot by quaternization precipitation polymerization (QPP) as a novel polymerization technique. QPP eliminated the usage of high-cost ionic monomers and reduced the number of steps for the preparation of IPN. The monomers 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 4-vinylbenzyl chloride (VBC) polymerized in the presence of azobisisobutyronitrile (AIBN) and underwent quaternization simultaneously, which yielded ionic poly(DMAEMA-co-VBC) nanoparticles in one step with the size of 50-80 nm without any stabilizer and catalyst. Similarly, 4-vinylpyridine (VP) and VBC polymerized in the presence of AIBN and underwent quaternization simultaneously, which yielded ionic poly(VP-co-VBC) nanoparticles in one step with the size of 70-90 nm without any stabilizer and catalyst. The as-synthesized IPN was further utilized for the fabrication of hydrophilic nanocomposite ultrafiltration membranes for oil/water separation. Fabricated hybrid membranes were characterized and studied for oil rejection properties. It exhibited an oil rejection of >96% with a pure water permeability of 219 L/m² h bar.

Bioinspired nanopillar surface for switchable mechano-bactericidal and releasing actions

Constructing safe and effective antibacterial surfaces has continuously received great attention, especially in healthcare-related fields. Bioinspired mechano-bactericidal nanostructure surfaces could serve as a promising strategy to reduce surface bacterial contamination while avoiding the development of antibiotic resistance. Although effective, these nanostructure surfaces are prone to be contaminated by the accumulation of dead bacteria, inevitably compromising their long-term antibacterial activity. Herein, a bioinspired nanopillar surface with both mechano-bactericidal and releasing actions is developed, via grafting zwitterionic polymer (poly(sulfobetaine methacrylate) (PSBMA)) on ZnO nanopillars. Under dry conditions, this nanopillar surface displays remarkable mechano-bactericidal activity, because the collapsed zwitterionic polymer layer makes no essential influence on nanopillar structure. Once being incubated with aqueous solution, the surface could readily detach the killed bacteria and debris, owing to the swelling of the zwitterionic layer. Consequentially, the surface antibacterial performances can be rapidly and controllably switched between mechano-bactericidal action and bacteria-releasing activity, guaranteeing a long-lasting antibacterial performance. Notably, these collaborative antibacterial behaviors are solely based on physical actions, avoiding the risk of triggering bacteria resistance. The resultant nanopillar surface also enjoys the advantages of substrate-independency and good biocompatibility, offering potential antibacterial applications for biomedical devices and hospital surfaces.

Modification of polyethersulfone membranes by Polyethyleneimine (PEI) grafted Silica nanoparticles and their application for textile wastewater treatment

In the current work, a novel nanocomposite membrane for wastewater treatment applications has been synthesized. A hydrophilic nature nanoadditive comprised grafting polyethylenimine (PEI) molecules onto the surfaces of silica nanoparticles (SiO₂ NPs) was synthesized then entrapped within a polyethersulfone polymeric matrix at disparate ratios via the classical phase inversion technique. A series of experimental tools were employed to probe the influence of SiO₂-PEI on the surface topography and morphological changes, hydrophilicity, porosity, surface chemistry as well as permeation and dyes retention characteristics of the new nanocomposite. Upon increasing the nanoadditives content (up to 0.7 wt. % SiO₂- PEI), clear cross-sectional changes were depicted along with a noticeable decline in the water contact angle by 29.7%. Performance evaluation measurements against synthetic dye solutions were disclosed explicit enhancement in both; retention and permeation characteristics of the nanocomposite membranes. Besides, prolonged permeation test has maintained high flux stability against real textile wastewater; implying better resistance and self-cleaning characteristics have been achieved.

A dual-functional layer modified GO@SiO2 membrane with excellent anti-fouling performance for continuous separation of oil-in-water emulsion

As the most significant target of membrane separation, the inadequacy of permeability and anti-fouling frequently constrain the application of the membrane in actual oily wastewater. Herein, a novel concept of membrane surface construction was proposed to mitigate this intractable problem, using SiO₂ as the support layer and graphene oxide (GO) as the isolation layer. The best co-localization proportion of the support layer (56 mg/L) and isolation layer (3.5 mg/L) was determined by the separation performance of the modified membranes for the simulated emulsion. The thin GO layer could effectively prevent contaminants from entering the membrane pores without affecting its roughness. Based on the synergistic action of the isolation layer and support layer, the GO@SiO₂ membrane could well implement emulsion purification with a stable permeability (654.11 LMHB) and high separation efficiency (99.41%). The superior anti-fouling performance of the membrane ensures its long-term cycling stability, with the permeability recovery rate of 89.75% (low-density oil) and 90.41% (high-density oil) after 10 repeated cycles. The storage stability also indirectly increases its value in practical applications. More importantly, the GO@SiO₂ membrane also shows great potential for industrial emulsion treatment with excellent purification and cycling stability (permeability recovery rate of 84.01%).

Modified hydrous zirconium oxide/PAN nanofibers for efficient defluoridation from groundwater

Fluoride contamination in groundwater is a worldwide problem that is related to human health. Zirconium-based adsorbents possess satisfactory selective defluoridation capacities. However, narrow efficiency pH range, easy aggregation and difficult separation are the main obstructions in practical application. In this study, the branched polyethyleneimine (bPEI) modified hydrous zirconium oxide (HZO)/polyacrylonitrile (PAN) nanofibers (NFs) are synthesized by immobilizing bPEI-HZO into PAN nanofibers via electrospinning. The resultant bPEI-HZO/PAN NFs exhibit a wide working pH range and an excellent adsorption capacity toward fluoride (67.51 mg·g^-1) even at neutral condition, indicating non-negligible superiority in the practical application of groundwater defluoridation. This enhanced adsorption performance along with extended wider working pH range are ascribed to the optimization of the adsorbents from both composition and structure. Compositionally, the modification of bPEI improves the surface property of HZO, and thus increases fluoride capacity in alkaline groundwater. Structurally, electrospinning conquers the drawbacks of nano-adsorbents for both easy aggregation and difficult separation. In addition, the effect of co-existing ions was further investigated and the X-ray photoelectron spectroscopy (XPS) as well as fourier transform infrared spectrum (FTIR) measurements were used to clarify the fluoride adsorption mechanism. Furthermore, the dynamic adsorption and regeneration performance were accomplished through the fixed-bed column experiment. All the results indicated that bPEI-HZO/PAN NFs are promising materials for defluoridation from groundwater.

Functionalized poly(arylene ether sulfone) containing hydroxyl units for the fabrication of durable, superhydrophobic oil/water separation membranes

The stability of superhydrophobicity is crucial for the long-term application of an oil/water separation membrane in harsh environments such as high temperatures and various aggressive solvents. However, achieving such a stable superhydrophobic membrane remains a challenge. In this study, high performance fibrous oil/water separation membranes with a highly stable superhydrophobicity were fabricated by designing a functional polymer containing hydroxyl units. The reaction of hydroxy groups in poly(arylene ether sulfone) with octadecyltrichlorosilane (OTS) produces stable covalent interactions, which greatly enhance the stability of OTS on the PAES-OH (polyarylene ether sulfone containing hydroxy units) fibrous membrane fabricated by electrospinning, thus improving the stability of superhydrophobicity of the membrane. The stability of the OTS layer was characterized by FT-IR, SEM and water contact angle measurement. The results suggest that OTS is highly stable on a PAES-OH membrane, while OTS on a polyethersulfone (PES) fibrous membrane is detached from the fiber during ultrasonic cleaning. The obtained membrane is superhydrophobic, with a water contact angle (CA) as high as 159.2° and a threshold sliding angle (TSA) as low as 7.8° even after ultrasonic cleaning for 3 h. In addition, the oil/water separation experiments indicate that this membrane has an excellent performance in the separation of oil from oil/water mixtures, and oil/water emulsions: the gravity driven flux is 7260-8720 L (m2 h)-1 and the water rejection is over 99%. This study provides a new approach for fabricating oil/water separation membranes with highly stable superhydrophobic properties from the perspective of designing new polymers.