Synthesis of TiO<Subscript>2</Subscript> nanotubes using different alkaline media and their applications in photocatalysis and DSSCs

TiO₂ nanotubes (TNTs) were successfully synthesized from different alkaline media (i.e., NaOH and KOH) by using a microwave hydrothermal process. The effects of different alkaline media on the formation of TiO₂ nanotubes and their physicochemical properties were investigated. The phases of different TiO₂ nanostructures were studied by using X-ray diffraction patterns. Morphologies of the nanostructures were observed with a transmission electron microscope. The optical properties of the nanostructures were evaluated through the absorption behavior using UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of the TiO₂ nanostructures were evaluated by the degradation of methylene blue aqueous dye solution under the simulated solar light irradiation. Similarly, the photovoltaic efficiencies of the prepared samples were investigated by making photo-anode layers in the Dye Sensitized Solar Cells (DSSCs). The results revealed that in comparison to the single layered TiO₂ nanostructures in the DSSC, creation of a double layer structure significantly enhanced the efficiency of DSSC.     

Three-dimensionally ordered macroporous metal oxide–silica composite for removal of mercaptan

A series of 3DOM and non-3DOM metal oxide–silica composites were prepared and tested dynamically in a packed-bed reactor at room temperature to remove ethanethiol from a gas stream containing ethyl mercaptan in moist N_2.The obtained sorbents were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption techniques. The experimental results showed that the adsorption ability of different kinds of metal oxide–silica composites with 3DOM structure decreased in the sequence: 3D-CuO/SiO₂ > 3D-NiO/SiO₂ > 3D-Co₃O₄/SiO₂ > 3D-ZnO/SiO₂. The best ratio of CuO to SiO₂ of 3DOM copper–silicon oxide sorbents for ethanethiol removal was found to be 1:2. The 3DOM structure could improve the removal activity of sorbents remarkably because of the high porosity with ordered interconnected macropores as well as the large surface area and high dispersion of CuO. It was also found that a moist atmosphere greatly benefited the adsorption of ethanethiol at ambient condition.     

Understanding Behavior of Polycaprolactone–Gelatin Blends under High Pressure CO<Subscript>2</Subscript>

Polycaprolactone (PCL) is widely used in biomedical applications as electrospun fibers or porous foams. As PCL is synthetic polymer, many researchers have explored blends of PCL–gelatin to combine mechanical and bioactive properties of individual components. High pressure carbon dioxide (CO2) has been studied to foam and impregnate many biocompatible polymers. In case of PCL–gelatin blends, certain compositions can be swelled reversibly under high pressure CO₂ without permanent deformation. This allows successful impregnation of PCL–gelatin blends under CO₂. This study summarizes effect of different treatments adopted during impregnation process including high pressure CO2 on several blend compositions of PCL–gelatin blends. Stress relaxation, polymer melting and dissolution were observed during several treatments which affects porosity and scaffold structure significantly. Results summarized in this study will aid in optimum selection of PCL–gelatin blend composition for biomedical applications. Furthermore, CO₂ solubility in polymers is restricted due to thermodynamic limitations but can be altered in the presence of a co-solvent to produce better foams. PCL can be foamed using supercritical CO₂. However, CO₂ foaming of PCL–gelatin blend becomes challenging to simultaneous swelling of PCL and compression of gelatin providing blend structural stability. This study has demonstrated ability of supercritical CO₂ to foam PCL–gelatin blends in presence of water to create porous structure. These foams were subjected post-fabrication crosslinking and supercritical CO₂ without losing porosity of foams. Thus, creating a strategy to use environmentally benign processes to fabricate, crosslink and impregnate porous scaffolds for biomedical applications.     

Mechanically-induced dimensional extensibility of fibers towards tough fiber networks

The beneficial effect of materials with high aspect ratio as composite reinforcement has prompted continuous interest towards cellulosic fibers. Besides providing stiffness, fibers can potentially contribute to composite extensibility. While mechanical treatments are typically used to adjust the physical and surface properties of fibers, less is known about ensuing effects on their extensibility and that of associated networks. Fiber network dimensional extensibility of 16% was achieved by processing the precursor aqueous fiber dispersions following a simple mechanical treatment with a judicious combination of low (PFI refining) and high concentrations and temperatures (Wing defibrator). Consequently, deformation of fibers and increased inter-fiber bonding resulted in a three-fold increase in strength to rupture of the fiber network leading to the structures with unprecedented toughness.     

Analysis of moisture sorption in lyocell-polypropylene composites

The preparation of composites by thermoforming of intermingled fibre slivers is an efficient method to receive high performance and lightweight materials. Cellulosic fibres have benefits like low density and sustainability but the sorption of water due to the high hydrophilicity of the cellulose requires attention. The swelling of the wet fibres changes the fibre-matrix adhesion and as a consequence, the mechanical strength of the composite is influenced negatively. In this study, the thermoplastic polypropylene was combined with lyocell fibres as reinforcement. Moisture sorption isotherms of cellulose/polypropylene composites were recorded as function of relative humidity. Additionally, the specific surface area was analysed by the Brunauer–Emmett–Teller model. It has been found, that the moisture sorption is influenced by the polypropylene (PP) ratio in the composites. At 60% relative humidity the moisture uptake of the lyocell fibres was reduced from 10.8 to 5.8% for lyocell embedded in a composite with 50% polypropylene. Besides the hysteresis between moisture sorption/desorption cycles was found to be proportional to the increased content of PP. The “Parallel Exponential Kinetics” (PEK) model was used to analyse the kinetics of moisture sorption of these composites in more detail. With the help of the PEK model the sorption/desorption kinetics were described by a fast and slow moisture sorption/desorption process. The capacity for rapid moisture sorption is reduced by the formation of PP layers on the lyocell surface. The share of slow moisture sorption increased with increasing PP content in the composite. The results support understanding of the interaction of water with cellulose containing composites.     

Heuristic analysis of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> bark depolymerization via acid-liquefaction

A clear, direct and rapid analysis of the preliminary results concerning the acid liquefaction of Eucalyptus globulus’ bark is herein presented. The results led to a methodology for the selective liquefaction of hemicellulose and amorphous cellulose. Liquefaction was conducted at various temperatures, as well as different reaction times. The process results are heuristically explained in view of the experiments of ATR-FTIR, hydroxyl number, and acid value. The procedure method allows reusing the wastes arising from the paper industry. Valuable products and chemical building blocks from lignocellulosic biomass, mostly based on cellulose can be thus accessed.     

Stability enhancement of nanofibrillated cellulose in electrolytes through grafting of 2-acrylamido-2-methylpropane sulfonic acid

This study aimed to improve the stability of nanofibrillated cellulose (NFC) in an electrolyte containing system, which was achieved by the grafting of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) via the ceric ammonium nitrate-induced polymerization process. The results indicated that upon grafting the salt resistance and thermal stability of NFC were significantly improved. Moreover, the stability of the modified NFC increased with the AMPS loading. Compared to the control (the original NFC), the poly-AMPS/NFC (357.5 mg/g AMPS) exhibited much improved stability in a 400 mmol/L NaCl solution, and its viscosity was 350 mPa s. The thermogravimetric analysis results showed that the initial decomposition temperature of the modified NFC increased from 265 to 330 °C. Transmission electron microscopy (TEM) observations showed that the main morphologic features of NFC were not altered, suggesting that the grafting reaction occurred on the fiber surface. The modified NFC can have promising industrial applications, such as oil recovery.     

Recent advances in anion recognition

By linkage of 1,5-naphthalenedisulfonate (1,5-NDS) anion fluorophore, 3D cucurbit[7]uril (CB[7]) framework has been constructed. The maximum solid-state fluorescence wavelength of the CB[7] framework exhibits blue-shift from 406 to 340 nm in comparison with that of 1,5-NDS, which was ascribed to increased excited energy from 0.10 to 0.13 eV according to theoretical calculations.     

Physical properties and thermal behavior of reconstituted tobacco sheet with precipitated calcium carbonate added in the coating process

Addition of precipitated calcium carbonate (PCC) to cellulosic products can reduce production costs and modify their physical properties. This study investigated the effects of adding PCC on the properties of reconstituted tobacco sheet (RTS), a cellulosic product. Scanning electron microscopy (SEM) analysis showed that adding PCC to the coating could modify the surface microstructure of RTS. With increasing PCC addition, the strength and tar release per cigarette of RTS decreased. However, the filling capacity, bulk, and CO release content in the mainstream smoke reached optimal values when the proportion of PCC in the coating was 8%. Thermogravimetry (TG) and differential thermogravimetry (DTG) analysis indicated that the main thermal pyrolysis stage occurred in the range of 200–400 °C, similar to cellulosic components. The Coats–Redfern equation was used to analyze the thermal pyrolysis mechanism. The fitting results showed that, in the range of 200–280 °C, the best fit model for RTS with 4 or 8% PCC was diffusion-controlled reaction (D1) with fitting correlation coefficient (r ²) of 0.9630 and 0.9576, respectively. Meanwhile, in the range of 280–400 °C, the most reliable fitting model for RTS with 4% PCC was chemical reaction (F2) with r ² = 0.9681. One reaction model could not describe the thermal pyrolysis of RTS with 12% PCC in the main decomposition stage. The thermal kinetic parameters suggested that addition of PCC to RTS coatings could modify the thermal pyrolysis mechanism, but did not change the peak temperatures in the main thermal decomposition stage. This study demonstrates that addition of PCC to RTS coating is a promising method to improve its quality.     

Aerogel microspheres based on cellulose nanofibrils as potential cell culture scaffolds

Crosslinked poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) hybrid aerogel micro-spheres with two different particle sizes were fabricated via a combination of the water-in-oil (W/O) emulsification process and the freeze-drying process. The aerogel micro-spheres were highly porous with a bulk density as low as 0.0047 g/cm³ for the large microspheres. The pore size of the microspheres ranged from nano- to micro-meters. Preliminary biocompatibility assays of the aerogel microspheres were investigated with NIH 3T3 cells to explore their potential application as cell culture scaffolds. The highly crosslinked aerogel microspheres were robust and were able to maintain their shape during the cell culture process. The live/dead assay showed that the cells could be seeded, attached, and proliferated on the surface of PVA/CNF aerogel microspheres. The fluorescence images showed that some of the cells migrated into the inner pores of the microspheres. Moreover, the large microspheres with larger average pore sizes had a higher cell count than that of the small microspheres. This study confirms that the PVA/CNF aerogel microspheres fabricated in this work are nontoxic and biocompatible. Furthermore, the interconnected, highly porous nanofibrous structure of the microspheres can successfully facilitate cell attachment, differentiation, and proliferation.