Enhancing Water Treatment Performance of Porous Polysulfone Hollow Fiber Membranes through Atomic Layer Deposition.

Polysulfone (PSF) is one of the most used polymers for water treatment membranes, but its intrinsic hydrophobicity can be detrimental to the membranes' performances. By modifying a membrane's surface, it is possible to adapt its physicochemical properties and thus tune the membrane's hydrophilicity or porosity, which can achieve improved permeability and antifouling efficiency. Atomic layer deposition (ALD) stands as a distinctive technology offering exceedingly even and uniform layers of coatings, like oxides that cover the surfaces of objects with three-dimensional (3D) shapes, porous structures, and particles. In the context of this study, the focus was on titanium dioxide (TiO2), zinc oxide (ZnO), and alumina (Al2O3), which were deposited on polysulfone hollow fiber (HF) membranes via ALD using TiCl4, diethyl zinc (DEZ), and trimethylamine (TMA), respectively, and H2O as precursors. The morphology and mechanical properties of membranes were changed without damaging their performances. The deposition was confirmed mainly by energy-dispersive X-ray spectroscopy (EDX). All depositions offered great performances with a maintained permeability and BSA retention and a 20 to 40° lower water contact angle (WCA) than the raw PSF HF membrane. The deposition of TiO2 offered the best results, showing an enhancement of 50% for the water permeability and 20% for the fouling resistance of the PSF HF membranes.

Enhanced sieving from exfoliated MoS2 membranes via covalent functionalization.

Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS2) nanosheets. The functionalized MoS2 membranes demonstrate >90% and ~87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS2 membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability.

Enhanced visible light photocatalysis by TiO2-BN enabled electrospinning of nanofibers for pharmaceutical degradation and wastewater treatment.

Boron nitride (BN) nanosheets are promising support materials for catalysts. A series of TiO2-BN enabled electrospun nanofibers were synthesized for the photocatalytic treatment of ibuprofen and secondary wastewater effluent under visible light. X-ray photoelectron spectroscopy confirmed the existence of B-O-Ti bonds between the BN nanosheets and TiO2 nanofibers, resulting in energy rearrangement, narrowed band gaps, and enhanced light utilization efficiency of the TiO2-BN nanocomposites in the visible light spectrum. Transient photocurrent measurements revealed that the BN enhanced the transport of photogenerated holes from the bulk TiO2 nanofibers to its surface, resulting in more efficient separation and less recombination of the charge carriers. A kinetic study of ibuprofen degradation indicated the enhanced photocatalytic performance of TiO2-BN catalysts with a higher BN content in the nanocomposites. The kinetic rate constant of the TiO2-10% BN catalysts was 10 times higher than that of the pure TiO2 nanofibers. The degradation of organic contaminants in wastewater followed the same trend as ibuprofen and improved with increasing BN content. The stability of the TiO2-BN nanocomposites as an effective solar photocatalyst was demonstrated by multiple cycles of wastewater treatment. The results proved that TiO2-BN is an appealing photocatalyst under visible light.

Porous Gelatin Membrane Obtained from Pickering Emulsions Stabilized by Graphene Oxide.

This article presents a novel procedure for preparing porous membranes from water-soluble polymers involving the formation of a Pickering emulsion. Gelatin is a biodegradable biopolymer obtained by the partial hydrolysis of collagen. A biopolymer such as gelatin is capable of adsorbing at an oil/water interface, resulting in decreased interfacial energy. Hence, gelatin is widely employed as an alternate for synthetic surfactants to stabilize emulsions in the food industry. However, high-molecular-weight gelatin leads to large emulsion droplets and poor emulsion stability. The amphoteric nature of graphene oxide (GO) nanosheets was helpful in stabilizing the oil/water interface and allows for the preparation of a stable gelatin/GO emulsion. Membranes fabricated using gelatin/GO have a uniformly distributed porous structure. However, prepared membranes are highly hydrosoluble, so the membranes were cross-linked without affecting their morphology. XRD results evidenced that gelatin effectively exfoliated the graphite oxide which is essential to stabilizing the emulsion. Fabricated gelatin/GO membranes possess uniformly distributed pores and are highly stable in aqueous solution. Pure water filtration tests were conducted on the membranes. The permeability results proved that the membranes fabricated by a Pickering emulsion are promising materials for filtration.

Nanocomposites through the Chemistry of Single-Source Precursors: Understanding the Role of Chemistry behind the Design of Monolith-Type Nanostructured Titanium Nitride/Silicon Nitride.

Monolith-type titanium nitride/silicon nitride nanocomposites, denoted as TiN/Si3 N4 , have been prepared by a reaction of polysilazanes with a titanium amide precursor, warm pressing of the resultant polytitanosilazanes, and subsequent pyrolysis of the green bodies at 1400 °C. Initially, a series of polytitanosilazanes was synthesized and the role of the chemistry behind their synthesis was studied in detail by using solid-state NMR spectroscopy, elemental analysis, and molecular-weight measurements. The intimate relationship between the chemistry and the processability of these precursors is discussed. Polytitanosilazanes display the appropriate requirements for facile processing in solution and as a melt, but they must be treated with liquid ammonia to be adapted for solid-state processing, that is, warm-pressing, to design dense and mechanically stable structures after pyrolysis. We provide a comprehensive mechanistic study of the nanocomposite conversion based on solid-state NMR spectroscopy coupled with thermogravimetric experiments. HRTEM images coupled with XRD and Raman spectroscopy confirmed the unique nanostructural features of the nanocomposites, which appear to be a result of the molecular origin of the materials. The as-obtained samples are composed of an amorphous Si3 N4 matrix, in which TiN nanocrystals are homogeneously formed in situ in the matrix during the process. The hardness and Young moduli were measured and are discussed.

Molecular-Level Processing of Si-(B)-C Materials with Tailored Nano/Microstructures.

The design of Si-(B)-C materials is investigated, with detailed insight into the precursor chemistry and processing, the precursor-to-ceramic transformation, and the ceramic microstructural evolution at high temperatures. In the early stage of the process, the reaction between allylhydridopolycarbosilane (AHPCS) and borane dimethyl sulfide is achieved. This is investigated in detail through solid-state NMR and FTIR spectroscopy and elemental analyses for Si/B ratios ranging from 200 to 30. Boron-based bridges linking AHPCS monomeric fragments act as crosslinking units, extending the processability range of AHPCS and suppressing the distillation of oligomeric fragments during the low-temperature pyrolysis regime. Polymers with low boron contents display appropriate requirements for facile processing in solution, leading to the design of monoliths with hierarchical porosity, significant pore volume, and high specific surface area after pyrolysis. Polymers with high boron contents are more appropriate for the preparation of dense ceramics through direct solid shaping and pyrolysis. We provide a comprehensive study of the thermal decomposition mechanisms, and a subsequent detailed study of the high-temperature behavior of the ceramics produced at 1000 °C. The nanostructure and microstructure of the final SiC-based ceramics are intimately linked to the boron content of the polymers. B4 C/C/SiC nanocomposites can be obtained from the polymer with the highest boron content.

Inverse Pickering Emulsion Stabilized by Exfoliated Hexagonal-Boron Nitride (h-BN).

The formation of inverse Pickering emulsions using exfoliated hexagonal boron nitride (h-BN) as an effective particulate stabilizer without using any surfactants is reported for the first time. The stability and the type of h-BN Pickering emulsions formulated with different BN concentrations and by varying oil/water (o/w) ratios are studied and discussed. First the emulsion structure is analyzed microscopically through optical and epifluorescence microscopy and macroscopically by the study of the rheological behavior. The average droplet size decreases with h-BN concentration whereas the emulsions achieve good stability at 2 wt % BN concentrations and for a 1:1 o/w ratio. In all formulations, the emulsions are of water-in-oil (w/o) type due mainly to the hydrophobicity of h-BN.

Polymer-Derived Silicoboron Carbonitride Foams for CO2 Capture: From Design to Application as Scaffolds for the in Situ Growth of Metal-Organic Frameworks.

A template-assisted polymer-derived ceramic route is investigated for preparing a series of silicoboron carbonitride (Si/B/C/N) foams with a hierarchical pore size distribution and tailorable interconnected porosity. A boron-modified polycarbosilazane was selected to impregnate monolithic silica and carbonaceous templates and form after pyrolysis and template removal Si/B/C/N foams. By changing the hard template nature and controlling the quantity of polymer to be impregnated, controlled micropore/macropore distributions with mesoscopic cell windows are generated. Specific surface areas from 29 to 239 m(2) g(-1) and porosities from 51 to 77 % are achieved. These foams combine a low density with a thermal insulation and a relatively good thermostructural stability. Their particular structure allowed the in situ growth of metal-organic frameworks (MOFs) directly within the open-cell structure. MOFs offered a microporosity feature to the resulting Si/B/C/N@MOF composite foams that allowed increasing the specific surface area to provide CO2 uptake of 2.2 %.

Key study on the potential of hydrazine bisborane for solid- and liquid-state chemical hydrogen storage.

Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during dehydrogenation) but can be used for the synthesis of derivatives with improved dehydrogenation properties. In liquid-state chemical hydrogen storage, it can be studied for room-temperature dehydrogenation, but this requires the development of an active and selective metal-based catalyst. HBB is a thus a candidate for chemical hydrogen storage.

Tuning of ZnO 1D nanostructures by atomic layer deposition and electrospinning for optical gas sensor applications.

We explored for the first time the ability of a three-dimensional polyacrylonitrile/ZnO material-prepared by a combination of electrospinning and atomic layer deposition (ALD) as a new material with a large surface area-to enhance the performance of optical sensors for volatile organic compound (VOC) detection. The photoluminescence (PL) peak intensity of these one-dimensional nanostructures has been enhanced by a factor of 2000 compared to a flat Si substrate. In addition, a phase transition of the ZnO ALD coating from amorphous to crystalline has been observed due to the properties of a polyacrylonitrile nanofiber template: surface strain, roughness, and an increased number of nucleation sites in comparison with a flat Si substrate. The greatly improved PL performance of these nanostructured surfaces could produce exciting materials for implantation in VOC optical sensor applications.

Dynamics of polymer nanoparticles through a single artificial nanopore with a high-aspect-ratio.

The development of nanometric Coulter counters for nanoparticle detection is an attractive and promising field of research. In this work, we have studied the influence of the nanopore surface state on charged polymer nanoparticle translocations. To make this, the translocation of carboxylate modified polystyrene microspheres (diameter 40, 70 and 100 nm) has been investigated through two kinds of high aspect ratio nanopores (negative and uncharged). The latter were tailored by a single track-etched and atomic layer deposition technique. It was shown that the mobility and the energy barrier are strongly dependent on nanopore surface charge. Typically if the latter exhibits negative surface charge, the microsphere mobility increases and the global energy barrier of entrance inside the nanopore decreases with its diameter, converse to the uncharged nanopore.

Cobalt-based catalysts for the hydrolysis of NaBH4 and NH3BH3.

Cobalt has been widely used as the main component of catalysts for the hydrolysis of sodium borohydride NaBH4 and, to a lesser extent, for the hydrolysis of ammonia borane NH3BH3. Though active in these reactions, the cobalt-based catalyst generally suffers from rapid deactivation. As emphasized in a perspective paper finalized in 2009 [Phys. Chem. Chem. Phys., 2010, 12, 14651], the nature of the catalytically active phase and the reasons for its deactivation are rather unknown. However, since 2010, significant advances have been reported. Therefore, after 4 years of fruitful research, the present perspective paper aims to (i) answer the questions asked in our previous contribution, (ii) give an overview of the new insights, and (iii) identify the nature of the catalytically active phase of cobalt. The literature of the period 2010-2013 has been exhaustively surveyed while paying attention to the characterization results and problems, the experimental conditions, and the authors' interpretations. Our main observation is that the research groups involved in the field have shown scientific curiosity and dynamism, and demonstrated ingenuity to circumvent the characterization difficulties. Thus, each group has contributed to highlight the nature of the catalytically active phase of cobalt as well as the reasons for its deactivation.

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment.

The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.

Hydrazine borane: synthesis, characterization, and application prospects in chemical hydrogen storage.

Hydrazine borane (N(2)H(4)BH(3)) is the novel boron- and nitrogen-based material appearing to be a promising candidate in chemical hydrogen storage. It stores 15.4 wt% of hydrogen in hydridic and protic forms, and the challenge is to release H(2) with maximum efficiency, if possible all hydrogen stored in the material. An important step to realize this ambitious goal is to synthesize HB with high yields and high purity, and to characterize it fully. In this work, we report a 2-step synthesis (salt metathesis and solvent extraction-drying) through which N(2)H(4)BH(3) is successfully obtained in 3 days, with a yield of about 80% and a purity of 99.6%. N(2)H(4)BH(3) was characterized by NMR, IR, XRD, TGA and DSC, its stability in dioxane and water was determined, and its thermolysis by-products were characterized. We thus present a complete data sheet that should be very useful for future studies. Furthermore, we propose a discussion on the potential of HB (with H(2) released by either thermolysis or hydrolysis) in chemical hydrogen storage.

Design and Manufacturing of Si-Based Non-Oxide Cellular Ceramic Structures through Indirect 3D Printing.

Additive manufacturing of Polymer-Derived Ceramics (PDCs) is regarded as a disruptive fabrication process that includes several technologies such as light curing and ink writing. However, 3D printing based on material extrusion is still not fully explored. Here, an indirect 3D printing approach combining Fused Deposition Modeling (FDM) and replica process is demonstrated as a simple and low-cost approach to deliver complex near-net-shaped cellular Si-based non-oxide ceramic architectures while preserving the structure. 3D-Printed honeycomb polylactic acid (PLA) lattices were dip-coated with two preceramic polymers (polyvinylsilazane and allylhydridopolycarbosilane) and then converted by pyrolysis respectively into SiCN and SiC ceramics. All the steps of the process (printing resolution and surface finishing, cross-linking, dip-coating, drying and pyrolysis) were optimized and controlled. Despite some internal and surface defects observed by topography, 3D-printed materials exhibited a retention of the highly porous honeycomb shape after pyrolysis. Weight loss, volume shrinkage, roughness and microstructural evolution with high annealing temperatures are discussed. Our results show that the sacrificial mold-assisted 3D printing is a suitable rapid approach for producing customizable lightweight highly stable Si-based 3D non-oxide ceramics.

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping.

The conversion of CO2 into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO2 into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C2+ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C2+ formation of ≈80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm-2 for C2+ products.

Fabrication of 3D printed antimicrobial polycaprolactone scaffolds for tissue engineering applications.

Synthetic polymers are widely employed for bone tissue engineering due to their tunable physical properties and biocompatibility. Inherently, most of these polymers display poor antimicrobial properties. Infection at the site of implantation is a major cause for failure or delay in bone healing process and the development of antimicrobial polymers is highly desired. In this study, silver nanoparticles (AgNps) were synthesized in polycaprolactone (PCL) solution by in-situ reduction and further extruded into PCL/AgNps filaments. Customized 3D structures were fabricated using the PCL/AgNps filaments through 3D printing technique. As demonstrated by scanning electron microscopy, the 3D printed scaffolds exhibited interconnected porous structures. Furthermore, X-ray photoelectron spectroscopy analysis revealed the reduction of silver ions. Transmission electron microscopy along with energy-dispersive X-ray spectroscopy analysis confirmed the formation of silver nanoparticles throughout the PCL matrix. In vitro enzymatic degradation studies showed that the PCL/AgNps scaffolds displayed 80% degradation in 20 days. The scaffolds were cytocompatible, as assessed using hFOB cells and their antibacterial activity was demonstrated on Escherichia coli. Due to their interconnected porous structure, mechanical and antibacterial properties, these cytocompatible multifunctional 3D printed PCL/AgNps scaffolds appear highly suitable for bone tissue engineering.

Synthesis, characterization, and crystal structure of a new trisodium triborate, Na(3)[B(3)O(4)(OH)(4)].

The preparation of a new trisodium triborate, Na(3)[B(3)O(4)(OH)(4)], and its complete characterization in terms of molecular structure and thermal behavior are reported. Synthesis of this compound was achieved either by NaBH(4) hydrolysis or by thermal treatment of Na[B(OH)(4)].2H(2)O. The crystal structure was determined by single-crystal X-ray diffraction. The trisodium triborate crystallized in the monoclinic system (a = 12.8274(6) A, b = 7.7276(4) A, c = 6.9690(3) A, and beta = 98.161(3) degrees ), space group Cc, Z = 2. The structure of Na(3)[B(3)O(4)(OH)(4)] comprised [B(3)O(4)(OH)(4)](3-) polyanions, based on B-O-containing rings with two tetracoordinated boron atoms and one tricoordinated boron atom in the fragments BO(2)(OH)(2) and BO(3), respectively. These polyanions are interconnected by four intermolecular hydrogen bonds and presented a tilt of 10.470(4) degrees compared to the a axis. Thus, they are stacked by rotation of about 180 degrees around an axis defined by the three-coordinated boron atoms and parallel to the c axis. Such polyanions were only observed previously in two synthetic compounds, M(3)[B(3)O(4)(OH)(4)].2H(2)O with M = K and Rb, which were isostructural. The originality of the present work was the synthesis and the description of a different crystallographic structure containing this polyanion. Characteristic peaks ranging from 500 to 1500 cm(-1) and around 3300 cm(-1) highlighted the presence of the B-O rings and hydroxyl groups, respectively. The decomposition temperature T = 155 degrees C was obtained by thermogravimetric analysis, and the following equivalent formula in terms of hydration degree was proposed: NaBO(2).(2)/(3)H(2)O. Na(3)[B(3)O(4)(OH)(4)] decomposed into Na(3)[B(3)O(5)(OH)(2)] in equilibrium with its vapor.

Iron-based 1D nanostructures by electrospinning process.

Iron-based 1D nanostructures have been successfully prepared using an electrospinning technique and varying the pyrolysis atmospheres. Hematite (Fe(2)O(3)) nanotubes and polycrystalline Fe(3)C nanofibers were obtained by simple air or mixed gas (H(2), Ar) annealing treatments. Using the air annealing treatment, a high control of the morphology as well as of the wall thickness of the nanotubes was demonstrated with a direct influence of the starting polymer concentration. When mixed gases (H(2) and Ar) were used for the annealing treatments, for the first time polycrystalline Fe(3)C nanofibers composed of carbon graphitic planes were obtained, ensuring Fe(3)C nanoparticle stability and nanofiber cohesion. The morphology and structural properties of all these iron-based 1D nanostructures were fully characterized by SEM, TEM, XRD and Raman spectroscopy.

Synthesis of polystyrene coated SiC nanowires as fillers in a polyurethane matrix for electromechanical conversion.

Grafting of polystyrene (PS) from silica coating of silicon carbide nanowires (SiCNWs) has been performed by a two-step nitroxide mediated free radical polymerization (NMP) of styrene. First, an alkoxyamine based on N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (DEPN) was covalently attached onto NWs through free surface silanol groups. To immobilize the alkoxyamine initiator on the silica surface, alkoxylamine was formed in situ by the simultaneous reaction of polymerizable acryloxy propyl trimethoxysilane (APTMS), azobis isobutyronitrile (AIBN), and DEPN, which was used as a radical trap. Polystyrene chains with controlled molecular weights and narrow polydispersity were then grown from the alkoxyamine-functionalized NWs surface in the presence of a 'free' sacrificial styrylDEPN alkoxyamine. Both the initiator and polystyrene chains were characterized by FTIR and (13)C solid-state NMR and quantified by TGA. Ensuing nanocomposites were characterized by FEG-SEM, TEM and Raman spectroscopy. EDX analysis performed on functionalized nanowires during FEG-SEM analysis also gave evidence of grafting by a strong increase in the average C/Si atomic ratio. Incorporation of 2 wt% NWs into the polyurethane (PU) matrix has been carried out to prepare homogeneous nanocomposite films. The electric field induced thickness strain response has been investigated for the polystyrene-grafted silica coated SiC NWs (PU-SiC@SiO(2)@PS) nanocomposites and compared to pure polyurethane film and PU-SiC@SiO(2) nanocomposite without polystyrene grafting. At a moderate electric field of 10 V microm(-1), SiC@SiO(2)@PS loading increased the strain level of pure PU by a factor of 2.2. This improvement came partially due to polystyrene grafting since PU-SiC@SiO(2) films showed only a 1.7 times increase. The observed higher strain response of these nanocomposites makes them very attractive for micro-electromechanical applications.