Water purification for human use, ecosystem management, agriculture, and industry is emerging as a leading global priority. Access to sufficient clean water ultimately requires improvements over the current state of water filtration technology. Membrane technologies for water purification have been actively pursued for decades, but with recent innovation of both analytical and fabrication tools, more advanced membrane technologies are surfacing. Here, we review the design, development, and application of new membrane materials, fabrication methods for controlling the filtration size regime, analytical tools for performance testing, and molecular modeling for transport and separation. Membrane chemical stability, fouling, and environmental impact as open questions are also presented.

Membrane materials for water purification: design, development, and application

Antifouling membrane surface construction: Chemistry plays a critical role

Novel magnetic nanocomposite hydrogel (m-CVP) beads were prepared by instantaneous gelation of carboxymethyl starch-g-polyvinyl imidazole (CMS-g-PVI), poly(vinyl alcohol) (PVA), and Fe3O4 mixture in boric acid solution followed by crosslinking by glutaraldehyde (GA). Highly porous m-CVP beads with magnetic sensitivity were fully characterized and used as eco-friendly adsorbent for the removal of crystal violet (CV) and congo red (CR) dye and Pb(II), Cu(II) and Cd(II) from water. Batch adsorption results showed that the sorbent had high affinity to the heavy metals and dyes in water. The adsorption kinetics results showed that the adsorption rates could be described by pseudo-second-order kinetics, indicating chemical sorption as the rate determining step. Sorption of Pb(II), Cu(II), Cd(II), CR and CV to m-CVP beads agreed well with the Langmuir adsorption model at different ionic strengths, with maximum adsorption capacities of 65.00, 83.60, 53.20, 83.66 and 91.58 mg g−1, respectively. Positive values of ΔH0 showed that the adsorption was chemisorption, and the negative values of ΔG0 indicated the spontaneity of the pollutant adsorption. Desorption and reusability of m-CVP beads was also investigated for tested heavy metal ions and dyes based on sequential adsorption–desorption cycles. All the studied results indicated that m-CVP beads were an efficient, low cost, and reusable adsorbent for the removal of dye and heavy metal ions from aqueous solutions.

Removal of dyes and heavy metal ions from water by magnetic hydrogel beads based on poly(vinyl alcohol)/carboxymethyl starch-g-poly(vinyl imidazole)

A bioinspired photocatalytic nanocomposite membrane was successfully prepared via polydopamine (pDA)-coated poly(vinylidene fluoride) (PVDF) membrane, as a secondary platform for vacuum-filtrated Au-TiO2 nanocomposites, with enhanced photocatalytic activity. The degradation efficiency of Au-TiO2/pDA/PVDF membranes reached 92% when exposed to visible light for 120 min, and the degradation efficiency of Au-TiO2/pDA/PVDF membranes increased by 26% compared to that of Au-TiO2 powder and increased by 51% compared to that of TiO2/pDA/PVDF nanocomposite membranes. The degradation efficiency remained about 90% after five cycle experiments, and the Au-TiO2/pDA/PVDF nanocomposite membranes showed good stability, regeneration performance, and easy recycling. The pDA coating not only served as a bioadhesion interface to improve the bonding force between the catalyst and the membrane substrate but also acted as a photosensitizer to broaden the wavelength response range of TiO2, and the structure of Au-TiO2/pDA/PVDF also improves the transfer rate of photogenerated electrons; the surface plasmon resonance effect of Au also played a positive role in improving the activity of the catalyst. Therefore, we believe that this study opens up a new strategy in preparing the bioinspired photocatalytic nanocomposite membrane for potential wastewater purification, catalysis, and as a membrane separation field.

Bioinspired Synthesis of Photocatalytic Nanocomposite Membranes Based on Synergy of Au-TiO2 and Polydopamine for Degradation of Tetracycline under Visible Light

Super hydrophilic PVDF based composite membrane for efficient separation of tetracycline

Temperature- and pH-responsive membranes based on poly (vinylidene fluoride) functionalized with microgels

Preparation and Catalytic property of PVDF composite membrane with polymeric spheres decorated by Pd nanoparticles in membrane pores

Combining catalysis and separation on a PVDF/Ag composite membrane allows timely separation of products during reaction process

In this study, we facilely introduce silver nanoparticles into Poly(N-isopropylacrylamide-co-acrylic acid)(Poly(NIPAM-co-AA)) microgels and specially focus on the effect of hydrophilic acrylic acid segments on the responsive catalytic performance of silver nanoparticles. The obtained Poly(NIPAM-co-AA)/AgNPs composites are characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The composites as catalysts are applied to the hydrogenation reaction of p-nitrophenol and the related conditions such as reaction temperature, concentration of p-nitrophenol, and the loadings of Ag nanoparticles are studied in detail. NIPAM segments of composites conveniently give silver nanoparticles a controllable characteristic for catalytic reaction by their conformation variation. AA segments of composites not only provide good stability and dispersibility for silver nanoparticles but also favor an easier diffusion of p-nitrophenol to Ag NPs. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Temperature‐responsive catalytic performance of Ag nanoparticles endowed by poly (N‐isopropylacrylamide‐co‐acrylic acid) microgels

The poly(vinylidene fluoride) (PVDF)/poly(N-isopropylacrylamide) (PNIPAM) blend membranes with different PNIPAM contents are prepared by phase inversion of PNIPAM and PVDF in aqueous medium The membranes are characterized by thermal gravimetric analyses, elemental analysis, Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, and scanning electron microscope photographs The results indicate that PNIPAM chains are largely distributed in membrane pore other than membrane surface, and furthermore, with the increase of PNIPAM content, the porous size, porosity, and water flux through the membrane increase, the hydrophilicity and antiprotein fouling are enhanced The blend membrane exhibits temperature-sensitive permeability to aqueous solutions, with the most drastic change being observed at the lower critical solution temperature (LCST) of PNIPAM (around 32°C) Below the LCST, the blend membrane shows a high protein rejection and a low water flux; above the LCST, the blend membrane shows a low protein rejection and a high water flux POLYM COMPOS, 2013 © 2013 Society of Plastics Engineers

Zeya Wang

Papers

Temperature- and pH-responsive membranes based on poly (vinylidene fluoride) functionalized with microgels

Preparation and Catalytic property of PVDF composite membrane with polymeric spheres decorated by Pd nanoparticles in membrane pores

Combining catalysis and separation on a PVDF/Ag composite membrane allows timely separation of products during reaction process

Temperature‐responsive catalytic performance of Ag nanoparticles endowed by poly (N‐isopropylacrylamide‐co‐acrylic acid) microgels

Structure and performance of poly(vinylidene fluoride) membrane with temperature‐sensitive poly(n‐isopropylacrylamide) homopolymers in membrane pores