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Sorbitol-based organogelators were used to obtain nanostructured, robust polyolefin gels that could be freeze-dried into aerogels. Finding the ideal ratio of polymer to gelator led to homogeneous, fine structures with good mechanical stability and low thermal conductivity. The influence of polymer type, molecular weight and concentration was studied with regard to structure, compressive strength and thermal conductivity and a mechanism for the structure formation was postulated. Moreover, Soxhlet extraction was shown as a route to optimize the drying process and partially recover the gelator that is required as a structure-directing component, but partially also necessary in the final composite. The materials presented here are novel and useful composite aerogels with potential applications as insulating materials, porous supports, adsorbents, catalyst carriers and membranes. [ABSTRACT FROM AUTHOR]

Stimuli-responsive separation membranes with tunable molecular scale pore size, which are desirable for on-demand sieving of targeted macromolecules, have attracted increasing attention in recent years. In this study, novel magneto-hydrogel pore-filled composite membranes with excellent magneto-responsivity and tunability for molecular sieving have been developed. Such membranes comprising magnetic nanoparticles (MNPs) as localized heater which can be excited by high frequency alternating magnetic field (AMF), poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network as the sieving medium and actuator, and polyethylene terephthalate (PET) track-etched membrane as robust support, have been prepared via in situ reactive pore-filling functionalization. Rheological study has been carried out first to investigate the influence of MNPs and initiation methods on gelation kinetics and microstructure of the MNP–PNIPAAm composite hydrogels, and to identify proper conditions for further pore-filling functionalization. Then AMF distribution of chosen field condition and its heating effectiveness for MNPs and MNP–PNIPAMm composite hydrogel were studied. Pre-functionalization of the PET membranes with linear polymer chains with different composition were compared with respect to their effects for achieving desired MNP loading and fixation of the hydrogel network in the pores. At last, in situ reactive pore-filling functionalization was carried out to immobilize robust magneto-hydrogel in the pores of the membranes. Conditions were investigated and optimized to obtain functionalized membranes with high MNP loading and suited PNIPAM network properties, i.e. good stimuli-responsivity and sieving in the ultrafiltration range. The excellent thermo- and magneto-responsivity of obtained pore-filled membranes was proved by its large and reversible change of water permeability in response to switching on and off the AMF. Finally, it was demonstrated by filtration of dextrans with different molecular weights that the membranes had ultrafiltration properties and that large changes of their molecular sieving performance could be obtained by “remote control” with the external AMF. [ABSTRACT FROM AUTHOR]

The application of magnetic nanoparticles (NPs) in membrane technology is still very new and combinations of such NPs and separation membranes are essentially unexplored. By the integration of NPs into polymeric membranes it is possible to create new functionalities based on the synergies of the materials. Here nanoparticle polymer hybrid membranes were created by immobilizing (super)paramagnetic Fe3O4 NPs on the walls of track-etched polyethylene terephthalate pores and further functionalization with poly(N-isopropylacryl amide) (PNIPAAm). The hybrid system can be controlled via local heat generation by the NPs induced by an external high frequency electromagnetic field, i.e., effective membrane pore size can be switched by the magnetic field due to the synergy between the nanoparticle functionality and the temperature-responsive properties of PNIPAAm. Analytical characterizations showed a successful and stable NP integration and the feasibility of functionalization with grafted PNIPAAm in the presence of immobilized NPs on the membrane pore surface. The valve function of the nanoparticle polymer hybrid materials with an external control via a high frequency electromagnetic field was demonstrated in water permeability experiments, but such systems will have significant potential for other applications such as drug release or mass separation. [ABSTRACT FROM AUTHOR]

Molecularly imprinted polymers (MIP) offer in principle a robust, cost-efficient alternative to antibodies, but it is still a challenge to develop such materials for protein recognition. Here, we report the molecular imprinting of a functional polymeric hydrogel layer with lysozyme as the template in a two-step grafting procedure by a novel initiation approach on track-etched polyethylene terephthalate membrane surface. This is based on surface functionalization with aliphatic C–Br groups which can be used as an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated copolymerization. At first, the scaffold poly(methacrylic acid) (PMAA) was obtained through SI-ATRP of poly(tert-butyl methacrylate) and subsequent hydrolysis. Thereafter, it was assembled with the template to form a stable PMAA/lysozyme complex. In the second step, a polyacrylamide (PAAm) hydrogel was synthesized via UV-initiated surface grafting/crosslinking copolymerization around the scaffold/protein complex. Finally, the template was eluted to yield the grafted hydrogel layer with binding sites having complementary size, shape and appropriate arrangement of the functional groups to rebind lysozyme. The selectivity of lysozyme recognition, relative to cytochrome C with a similar size and isoelectric point, was increased by optimization of the scaffold chain length, UV grafting/crosslinking time and the chemical crosslinking degree of the PAAm-based hydrogel. The feasibility for the development of protein MIP in a straightforward way by independent optimization of crucial parameters – structures of scaffold with functional groups and of the crosslinked hydrogel matrix – have been demonstrated. [ABSTRACT FROM AUTHOR]

Polymeric hydrogels are a most interesting class of “soft matter” with several established and many more possible applications as functional materials. In this review we will focus on the combination of polymeric hydrogels and porous membranes which leads to composites with promising functionality for, e.g., mass separations, sensing and analytics, (bio)catalysis, biomedical engineering and micro-system technologies. The combination of a rigid porous membrane with a soft functional hydrogel by a suited preparation technique enables that the functionality of the hydrogel can be applied in a unique way. The most important preparation strategies for hydrogel composite membranes, i.e., pore-filling, various surface-grafting methods and combinations thereof, will be discussed. The structural diversity of the hydrogels is based on the use of a wide range of synthetic monomers, but biopolymers or their derivatives can also be applied. The interplay of the membrane pore structure, the structure of the hydrogel and the distribution of the hydrogel in the pore space can lead to different types of composite membranes with completely different potential applications. The focus will be on promising examples for the various types of functional composite membranes, i.e., macroporous membrane adsorbers, anti-fouling filtration membranes, hydrogel-based ultrafiltration membranes, other separation membranes with pore-filling hydrogel as selective material, stimuli-responsive membranes and porous membrane valves and gates, as well as biocompatible or bioactive membranes. [ABSTRACT FROM AUTHOR]

Nitrogen-containing porous carbons prepared by the pyrolysis of adequate biopolymer-based precursors have shown potential in several electrochemical energy-related applications. However, it is still of crucial interest to find the optimal precursors and process conditions which would allow the preparation of carbons with adequate porous structure as well as suitable nitrogen content and distribution of functional groups. In the present work we suggested a straightforward approach to prepare N-doped porous carbons by direct pyrolysis under nitrogen of chitosan : coffee blends of different compositions and using KOH for simultaneous surface activation. The synthetized carbon materials were tested for the electrochemical oxygen reduction to hydrogen peroxide (H 2 O 2 ). A higher fraction of chitosan in the precursor led to a decrease in meso- and nano-porosity of the formed porous carbons, while their activity towards H 2 O 2 generation increased. The nitrogen species derived from chitosan seem to play a very important role. Out of the synthesized catalysts the one with the largest content of pyridinic nitrogen sites exhibited the highest faradaic efficiency. The faradaic efficiencies and current densities of the synthesized materials were comparable with the ones of other commercially available carbons obtained from less renewable precursors., Competing Interests: The authors declare that they have no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

This work describes how the control of grafting density and grafted chain length of a thermo-responsive polymer in membrane pores can be utilized to tune the pore size and the switchability of size-based selectivity in the ultrafiltration range. Using a previously established methodology for controlled synthesis, surface-initiated atom transfer polymerization (ATRP) of poly( N -isopropylacrylamide) (PNIPAAm) to the pore walls of poly(ethylene terephthalate) track-etched membranes with experimentally determined pore diameters of 35 nm (PET30) and 110 nm (PET80) is performed. Characterization in this study is mainly done with filtration experiments, making use of the well-defined pore structure of the base membranes. It is demonstrated that both the gravimetrically determined degree of functionalization and the effective pore size determined from water permeability are a linear function of ATRP time. For the grafted PET30 membranes, it is shown that the rejection of lysozyme (diameter ∼ 4 nm) can be switched between 99% at 23 °C and 65% at 45 °C for the membrane with the highest degree of functionalization. For the grafted PET80 membranes, it is found that two different types of membranes can be obtained. Membranes with long grafted chains at low grafting density show very large changes of water permeability as a function of temperature (effective pore size switching ratio of up to 10) and, for example, rejection for 20 nm silica particles of 95% and 23% at 23 °C and 45 °C, respectively. Membranes with PNIPAAm at high grafting density show much lower switching ratios (as low as 1.4, for long enough grafted chains). Effective pore size and thermo-responsive change of pore size can therefore be tuned by the combination of both synthesis parameters, initiator density and ATRP time. The switchable thermo-responsive separation of two colloids with a tailored membrane is demonstrated for mixtures of bovine serum albumin (BSA; ∼7 nm) and silica nanoparticles (20 nm); at 23 °C silica is completely rejected and only BSA is in the permeate; at 40 °C both colloids permeate through the membrane., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

MoS 2 is a very attractive material and has been well studied for potential applications in various areas. However, due to the wide variety of factors affecting the molecular and electronic structure of MoS 2 , several contradictory reports about the adsorptive and photocatalytic properties of such materials have been published. In most of these reports, the effect of the actual phase of the materials on the properties was neglected. Here, different phases of MoS 2 nanosheets (1T/2H, 1T/3R and 2H) have been obtained using the hydrothermal method with different Mo : S molar ratios and different autoclave filling ratios. The obtained materials have been thoroughly characterized using Raman, UV-vis, powder XRD, SEM, TEM and XPS measurements in order to accurately identify the existing phases in each material. A comparative study of the photocatalytic organic dye degradation efficiency under white light irradiation has been conducted using methyl orange to correlate the different activity of each material to the respective phase composition. The results indicate a much higher performance of the 1T/2H phase compared to the 2H and 3R phases. Detailed computational studies of the different phases revealed the emergence of mid-gap states upon introducing 1T sites into the 2H lattice. This leads to the improvement of the photocatalytic activity of 1T/2H compared to the other prepared materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The application of magnetic nanoparticles (NPs) in membrane technology is still very new and combinations of such NPs and separation membranes are essentially unexplored. By the integration of NPs into polymeric membranes it is possible to create new functionalities based on the synergies of the materials. Here nanoparticle polymer hybrid membranes were created by immobilizing (super)paramagnetic Fe 3 O 4 NPs on the walls of track-etched polyethylene terephthalate pores and further functionalization with poly(N-isopropylacryl amide) (PNIPAAm). The hybrid system can be controlled via local heat generation by the NPs induced by an external high frequency electromagnetic field, i.e., effective membrane pore size can be switched by the magnetic field due to the synergy between the nanoparticle functionality and the temperature-responsive properties of PNIPAAm. Analytical characterizations showed a successful and stable NP integration and the feasibility of functionalization with grafted PNIPAAm in the presence of immobilized NPs on the membrane pore surface. The valve function of the nanoparticle polymer hybrid materials with an external control via a high frequency electromagnetic field was demonstrated in water permeability experiments, but such systems will have significant potential for other applications such as drug release or mass separation.