Jianqiang Meng

A Scalable Method toward Superhydrophilic and Underwater Superoleophobic PVDF Membranes for Effective Oil/Water Emulsion Separation

A superhydrophilic and underwater superoleophobic PVDF membrane (PVDFAH) has been prepared by surface-coating of a hydrogel onto the membrane surface, and its superior performance for oil/water emulsion separation has been demonstrated. The coated hydrogel was constructed by an interfacial polymerization based on the thiol-epoxy reaction of pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) with diethylene glycol diglycidyl ether (PEGDGE) and simultaneously tethered on an alkaline-treated commercial PVDF membrane surface via the thio-ene reaction. The PVDFAH membranes can be fabricated in a few minutes under mild conditions and show superhydrophilic and underwater superoleophobic properties for a series of organic solvents. Energy dispersive X-ray (EDX) analysis shows that the hydrogel coating was efficient throughout the pore lumen. The membrane shows superior oil/water emulsion separation performance, including high water permeation, quantitative oil rejection, and robust antifouling performance in a series oil/water emulsions, including that prepared from crude oil. In addition, a 24 h Soxhlet-extraction experiment with ethanol/water solution (50:50, v/v) was conducted to test the tethered hydrogel stability. We see that the membrane maintained the water contact angle below 5°, indicating the covalent tethering stability. This technique shows great promise for scalable fabrication of membrane materials for handling practical oil emulsion purification.

Surface glycosylation of polysulfone membrane towards a novel complexing membrane for boron removal.

In this study, a novel complexing membrane was synthesized for boron removal from aqueous solution. A glycopolymer, poly(2-gluconamidoethyl methacrylate) (PGAMA), was grafted onto the chloromethylated polysulfone (CMPSF) microporous membrane via surface-initiated ATRP (SIATRP). The glycosylated PSF (GlyPSF) membrane was characterized by attenuated total refection-Flourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). It was demonstrated that PGAMA was successfully anchored onto the membrane surface and the grafting yield can be tuned in a wide range up to 5.9 mg/cm(2) by varying the polymerization time. The complexing membrane can adsorb boron rapidly with the equilibrium reached within 2h and has a remarkable high boron adsorption capacity higher than 2.0 mmol/g at optimized conditions. Freundlich, Langmuir, and Dubinin-Radushkevich adsorption isotherms were applied, and the data were best described by Langmuir model. Kinetic data were analyzed, and the data fitted very well to the pseudo-second-order rate expression. The optimal pH for boron uptake is in a wide range of 6-9, and the optimal initial boron concentration is over 300 mg/L. Studies of ionic strength effects indicated the formation of inner-sphere surface complexes. The complexed boron can be leached quantitatively under acid condition.

Hyperbranched grafting enabling simultaneous enhancement of the boric acid uptake and the adsorption rate of a complexing membrane

Efficient polymeric adsorbents, including complexing membranes, attract increasing attention due to the global occurrence of micropollutants in water resources. Grafting polyhydroxy polymers onto a microporous membrane surface to prepare a complexing membrane for flow-through boron removal is also an emerging method. However, it remains a great challenge to develop efficient sorbents with both high capacity and high adsorption rate. In this work, hyperbranched polyols are grafted onto a polyacrylonitrile (PAN) membrane surface to prepare complexing membranes with high capacity and high adsorption rate, which utilize the structural characteristics of hyperbranched molecules to optimize the three-dimensional distribution of the chelating ligands. First, the PAN membrane was grafted with three hyperbranched polyethyleneimine (HPEI) macromolecules through a water mediated hydrolysis and amidation reaction in an autoclave followed by a ring opening reaction with glycidol. ATR-FTIR, XPS, FESEM and WCA methods were used to characterize the modified membranes. The results demonstrated that HPEI was successfully anchored onto the membrane surface and reacted with glycidol. Large quantities of hydroxyl groups were enriched on the surface of the membranes leading to rougher and superhydrophilic surfaces. The study on boron adsorption shows that the complexing membrane can absorb 3.2 mmol g−1 within only 4 min, which is superior to other reported sorbents. The adsorption isotherm can be described by the Langmuir model and the kinetic adsorption data fit very well with the pseudo-first-order expression. In addition, the boron adsorption can be completely regenerated for ten cycles of use by 15 min acid leaching without obvious degradation. The rapid boron removal and high regeneration are believed to benefit from the hyperbranched scaffold thanks to the high density and good accessibility of the ligands.

One-step bimodel grafting via a multicomponent reaction toward antifouling and antibacterial TFC RO membranes

Simple methods for dual functional modification of membrane surfaces have been rarely reported but are highly desirable for the fabrication of antifouling and antibacterial membranes. In this work, we exploit a multicomponent reaction, Ugi-4CR (Ugi four-component reaction), to prepare novel antifouling and antibacterial reverse osmosis (RO) membranes. With the aid of the high number of residual carboxyl groups on a commercial polyamide RO membrane as the anchor and methyl isocyanoacetate as a component, a hydrophilic macromolecular component, methoxy poly(ethylene glycol) aldehyde (MPEG-CHO), and an amino-terminated antibacterial component, tris(2-aminoethyl)amine (TAEA) or sulfamethoxazole (SMZ), were grafted onto the surface in a single step via the Ugi-4CR. The surfaces of the original and modified membranes were characterized by ATR-FTIR, XPS, TG, WCA, FESEM and AFM measurements. The antifouling performance was evaluated by cross-flow filtration of protein and inorganic salt solution. The antibacterial performance was assessed by the shake flask method. The results show that the Ugi-4CR was successfully conducted on the RO membrane surface and that MPEG-CHO and the antibacterial agents were successfully grafted. The surface roughness decreased and surface the hydrophilicity improved upon modification. After 48 h fouling experiments, the obtained PA-g-PEG/TAEA and PA-g-PEG/SMZ membranes showed obviously lower flux attenuation ratios and higher flux recovery ratios than the original membrane in both cases when fouled by protein or inorganic salt. In addition, the bacterial concentrations in the suspensions shook with the modified membranes were much lower than that of the original membrane. As for the PA-g-PEG/SMZ membrane, hardly any bacterial growth was seen, even after 24 h culture. In contrast to current multi-step grafting processes, this work reports a “one pot” procedure with two functional groups grafted simultaneously under very mild conditions without the use of any catalyst.

Green facile scalable synthesis of titania/carbon nanocomposites: new use of old dental resins.

A green facile scalable method inspired by polymeric dental restorative composite is developed to synthesize TiO2/carbon nanocomposites for manipulation of the intercalation potential of TiO2 as lithium-ion battery anode. Poorly crystallized TiO2 nanoparticles with average sizes of 4-6 nm are homogeneously embedded in carbon matrix with the TiO2 mass content varied between 28 and 65%. Characteristic discharge/charge plateaus of TiO2 are significantly diminished and voltage continues to change along with proceeding discharge/charge process. The tap density, gravimetric and volumetric capacities, and cyclic and rate performance of the TiO2/C composites are effectively improved.

Synthesis of membrane adsorbers via surface initiated ATRP of 2-dimethylaminoethyl methacrylate from microporous PVDF membranes

Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to tether poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) onto microporous PVDF membranes in order to synthesize membrane adsorbers for protein adsorption. The alkaline treatment and bromine addition reaction were used to anchor ATRP initiators on membrane surface. Then PDMAEMA was grafted from the membrane surface via SI-ATRP. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) revealed the chemical composition and surface topography of the PVDF-g-PDMAEMA membrane surfaces. These results showed that PDMAEMA was grafted from the membrane surface successfully and a grafting yield as high as 1500 μg/cm2 was achieved. The effects of the grafting time and the density of initiators on the static and dynamic binding capacity of bovine serum albumin (BSA) were systematically investigated. Both the static and dynamic binding capacities increase with the bromination and polymerization time. However, the benefits of the initiator density on binding capacities are limited by the graft density of PDMAEMA chains.

Silicon Oxycarbide/Carbon Nanohybrids with Tiny Silicon Oxycarbide Particles Embedded in Free Carbon Matrix Based on Photoactive Dental Methacrylates

A new facile scalable method has been developed to synthesize silicon oxycarbide (SiOC)/carbon nanohybrids using difunctional dental methacrylate monomers as solvent and carbon source and the silane coupling agent as the precursor for SiOC. The content (from 100% to 40% by mass) and structure (ratio of disordered carbon over ordered carbon) of the free carbon matrix have been systematically tuned by varying the mass ratio of methacryloxypropyltrimethoxysilane (MPTMS) over the total mass of the resin monomers from 0.0 to 6.0. Compared to the bare carbon anode, the introduction of MPTMS significantly improves the electrochemical performance as a lithium-ion battery anode. The initial and cycled discharge/charge capacities of the SiOC/C nanohybrid anodes reach maximum with the MPTMS ratio of 0.50, which displays very good rate performance as well. Detailed structures and electrochemical performance as lithium-ion battery anodes have been systematically investigated. The structure-property correlation and corresponding mechanism have been discussed.

Poly(p-phenylene terephthamide) embedded in a polysulfone as the substrate for improving compaction resistance and adhesion of a thin film composite polyamide membrane

A new approach to improving the compaction resistance and polyamide skin layer adhesion onto the substrate in thin film composite (TFC) membranes was developed. It was based on in situ polymerization of p-phenylene terephthamide (PPTA) in a polysulfone (PSf) solution prior to membrane casting via the phase inversion process, thereby forming a PPTA-embedded PSf substrate. The TFC membrane was prepared by interfacial polymerization on such (PPTA/PSf) substrates. The crystal structure of the PPTA polymerized in the PSf/NMP solution was investigated by XRD and TEM. The immobilization of PPTA in the PSf substrate was confirmed by FTIR and XPS. The surface properties of the PPTA/PSf substrates were characterized by FESEM, AFM and WCA measurements. Incorporating PPTA into the substrates resulted in more open porous structures and a thinner dense layer, as well as a rougher and more hydrophilic surface. Both the compaction resistance of the TFC membrane and the polyamide skin layer adhesion onto the substrates were improved by the presence of PPTA. The TFC membranes exhibited a typical nanofiltration performance with salt rejections in the order of Na2SO4 > MgSO4 > MgCl2 > NaCl.

Declined ionic flux through the nano-pores of vertically aligned carbon nanotubes filled with PNIPAm hydrogel

We demonstrate a novel nano-porous membrane of 10 nm diameter multiwall carbon nanotubes (MWCNTs) filled with thermally sensitive poly(N-isopropylacrylamide) (PNIPAm) hydrogel. High-resolution transmission electron microscopy (HRTEM), micro FT-IR spectroscopy and confocal laser scanning fluorescence microscopy are used to confirm that the MWCNTs are filled with the hydrogel. An improvement in the hydrophilicity of the gel-filled nano-channels is expected to promote the migration of aqueous solutions and the transportation of water. Meanwhile a decrease in ion flux is observed after the nano-pores of MWCNTs are filled with the hydrogel. This new hydrogel filled-CNT material shows potential for nano-chromatography, water purification and use as intelligent ionic channels.

Facile Scalable Synthesis of TiO2/Carbon Nanohybrids with Ultrasmall TiO2 Nanoparticles Homogeneously Embedded in Carbon Matrix

A facile scalable synthesis of TiO2/C nanohybrids inspired by polymeric dental restorative materials has been developed, which creates ultrasmall TiO2 nanoparticles homogeneously embedded in the carbon matrix. The average size of the nanoparticles is tuned between about 1 and 5 nm with the carbon content systematically increased from 0% to 65%. Imaging analysis and a scattering technique have been applied to investigate the morphology of the TiO2 nanoparticles. The composition, nature of carbon matrix, crystallinity, and tap density of the TiO2/C nanohybrids have been studied. The application of the TiO2/C nanohybrids as lithium-ion battery anode is demonstrated. Unusual discharge/charge profiles have been exhibited, where characteristic discharge/charge plateaus of crystalline TiO2 are significantly diminished. The tap density, cyclic capacities, and rate performance at high current densities (10 C, 20 C) of the TiO2/C nanohybrid anodes have been effectively improved compared to the bare carbon anode and the TiO2/C nanohybrids with larger particle size.