The Zr‐containing metal–organic frameworks (MOFs) formed by terephthalate (UiO‐66) and 2‐aminoterephthalate ligands UiO‐66(NH2) are two notably water‐resistant MOFs that exhibit photocatalytic ...activity for hydrogen generation in methanol or water/methanol upon irradiation at wavelength longer than 300 nm. The apparent quantum yield for H2 generation using monochromatic light at 370 nm in water/methanol 3:1 was of 3.5 % for UiO‐66(NH2). Laser‐flash photolysis has allowed detecting for UiO‐66 and UiO‐66(NH2) the photochemical generation of a long lived charge separated state whose decay is not complete 300 μs after the laser flash. Our finding and particularly the influence of the amino group producing a bathochromic shift in the optical spectrum without altering the photochemistry shows promises for the development of more efficient MOFs for water splitting.
Let there be light! We describe the photocatalytic hydrogen generation of water/methanol using UiO‐66 as photocatalyst. We show that this photocatalytic activity can be increased by rational design of the material and by adding a hydrogen evolution co‐catalyst. By using laser flash photolysis, the photocatalytic activity for hydrogen formation has been correlated with the generation of charge separated states.
Display omitted
•N-doped CNT/ZnO materials are efficient photocatalysts for vanillin production.•N-doping improves CNTs’ electron availability and mobility in CNT/ZnO hybrids.•The best performance, ...in yield and selectivity, was obtained using 5.0%N-CNT/ZnO.•N-CNT act as photosensitizer and as e− scavenger for ZnO, inhibiting recombination.
ZnO synthesized by solid-state thermal process was combined with different contents of nitrogen-doped carbon nanotubes (N-CNT). The materials were characterized by several techniques including thermogravimetric analysis, N2 adsorption-desorption isotherms, scanning and transmission electron microscopies, and diffuse reflectance UV–vis and photoluminescence spectroscopies. The performance of neat ZnO and N-CNT/ZnO composite materials was evaluated in the selective photocatalytic oxidation of vanillyl alcohol into vanillin under UV-LED irradiation. The presence of the carbon phase in the composite materials (from 5.0 to 10 wt.%) revealed to be crucial for increasing the performance of the photocatalysts. The best performance for vanillyl alcohol oxidation was obtained using the composite containing 5% of carbon phase (5.0%N-CNT/ZnO), with an increase of 22% in vanillin concentration comparing to neat ZnO after 2 h of reaction. This enhancement in the efficiency of ZnO by the introduction of the carbon phase is attributed to the action of N-CNT as effective electron scavengers for ZnO, as revealed by the photoluminescence quenching, inhibiting the recombination of electrons and holes.
Display omitted
•Photocatalytic oxidation of benzyl alcohol in water by g–C3N4 is selective to benzaldehyde.•Mechanical and chemical post-treatments widen-up g–C3N4 photocatalyst band-gap.•Thermal ...post-treatments of bulk g–C3N4 significantly increase benzaldehyde yield.•Benzaldehyde production by photocatalysis with g–C3N4 is clean, safe and efficient.
The selective photocatalytic conversion of benzyl alcohol to benzaldehyde was studied in aqueous medium, as alternative to common organic solvents, in combination with environmentally friendly conditions: metal-free catalysts based on graphitic carbon nitride (g-C3N4), natural pH, ambient temperature and pressure, and light emitting diodes (LEDs) as high efficient lighting source. g-C3N4 was synthesized by thermal condensation of dicyandiamide and the photocatalytic performance evaluated in terms of different post-treatment routes: thermal, mechanical and chemical. Several temperatures (400, 450 and 500°C), times of mechanical treatment (1.5, 3.0 and 8.0h) and protic acids (H2SO4, HCl and HNO3) were tested. The post-treatments significantly enhance photocatalytic conversion and yield, with minimal compromise on selectivity. The photocatalyst obtained upon thermal pos-treatment of g-C3N4 at 500°C, which had the better performance (66% conversion, 59% yield, and 90% selectivity at four hours of irradiation), was found to have the highest BET surface area (87m2g−1).
Display omitted
•ZnO materials were loaded with gold nanoparticles by a double impregnation method.•Bare ZnO efficiency depends on both textural and surface properties.•Depending on the ZnO support ...Au nanoparticles act as electron sinks or sensitizers.•Photogenerated holes play a major role in phenol degradation but free radicals are also important.
Gold nanoparticles were loaded on ZnO materials by a double impregnation method. Materials were characterized by spectroscopic, microscopic and N2 adsorption techniques, and tested on the photocatalytic oxidation of phenol in aqueous solutions, under simulated solar light. Compared with bare ZnO, the Au-loaded catalysts presented increased activity, which has been evaluated in terms of the pseudo-first-order kinetic constant (kapp) and phenol mineralization. The best activities were obtained with the Au-loaded ZnO samples produced by chemical vapor deposition, and by thermal decomposition of zinc acetate (kapp=5.6min−1mgAu−1 for both materials), achieving mineralizations of 92% and 82%, respectively. Depending on the ZnO material, on the gold nanoparticle dimensions and on the irradiation wavelength used, gold particles may act as electron sinks or light harvesters. Selective trapping of photogenerated holes and radicals by selective scavengers showed that holes are crucial, but free radicals do also participate on phenol’s photodegradation pathway.
Abstract The study assessed the effect of velocity of arm movement on anticipatory postural adjustments (APAs) generation in the contralateral and ipsilateral muscles of individuals with stroke in ...seating. Ten healthy and eight post-stroke subjects were studied in sitting. The task consisted in reaching an object placed at scapular plane and mid-sternum height at self-selected and fast velocities. Electromyography was recorded from anterior deltoid (AD), upper (UT) and lower trapezius (LT) and latissimus dorsi (LD). While kinematic analysis was used to assess peak velocity and trunk displacement. Differences were found between the timing of APAs on ipsi and contralateral LD and LT in both movement speeds and in ipsilateral UT during movement of the non-affected arm at a self-selected velocity. A delay on the contralateral LD to reach movement with the non-affected arm at fast velocity was also observed. The trunk displacement was greater in post-stroke subjects. Individuals with stroke demonstrated a delay of APAs in the muscles on both sides of the body compared to healthy subjects. The delay was observed during performance of the reaching task with the fast and self-selected velocity.
The development of biodegradable curative systems containing antibacterial drug are fundamental for the promotion of therapeutic actions, reducing the infections caused by microorganisms and being ...able to substitute conventional dressings which are not biodegradable polymers in their composition. Meeting those needs, poly (butylene adipate‐co‐terephthalate) (PBAT) and PBAT/gentamicin (GT) fibers were electrospun using different concentrations of GT. The physical–chemical, morphological, thermal, antibacterial, and biological properties of the PBAT and PBAT/GT fibers were characterized. The presence of GT modified the mean diameter, roughness, and wettability of the prepared fibers. The degree of swelling was altered with the addition of GT. PBAT/GT fibers showed antibacterial activity against Escherichia coli strains reaching an inhibitory activity above 90% in the films with 2%, 5%, and 10% of GT. In addition, the fibers did not present cytotoxicity according to ISO 10993‐5 standard. The obtained results reinforce that PBAT can be used as a curative system.
Display omitted
•A Fe3O4/g-C3N4 photocatalyst with magnetic response was efficiently synthetized.•Photocatalytic oxidation of benzyl alcohol into benzaldehyde was investigated.•Benzaldehyde was ...produced for the first time with a magnetic g-C3N4 photocatalyst.•The hybrid photocatalyst shows reasonable stability in three consecutive runs.•Hydrogen was produced simultaneously with benzaldehyde.
Selective production of aromatic aldehydes is an important challenge in the synthesis of fine chemicals. This study presents a viable strategy for the production of benzaldehyde using a magnetic recoverable photocatalyst. Graphitic carbon nitride was submitted to a thermal post-treatment, for partial exfoliation (g-CN-T) and combined with magnetic nanoparticles of Fe3O4. The composite containing 18 wt.% of Fe3O4 shows a remarkable magnetic response. The efficiency of this composite was evaluated in the selective photocatalytic conversion of benzyl alcohol into benzaldehyde. A good compromise was observed in terms of selectivity for benzaldehyde formation and ability of recovery at the end of the photocatalytic reaction by the application of a magnetic field. Reutilization experiments using this hybrid material revealed a slight decrease of efficiency after the first run only. Moreover, hydrogen was generated during the photocatalytic production of benzaldehyde. Thus, the combination of gCN-T and magnetic nanoparticles provided an impetus to design a photocatalyst with easy and inexpensive features for selective synthesis of organic compounds.
Display omitted
•Metal-free carbon nitride catalyst (GCN-500) obtained through thermal exfoliation.•GCN-500 was more efficient than TiO2 in the photocatalytic degradation of parabens.•The oxidative ...pathway is mainly dominated by O2•− and h+ in the VB of GCN-500.•Degradation of parabens decrease due to organics and ions in tap and river waters.•GCN-500 coated glass rings (GCN-500-GR) show good stability under continuous mode.
Metal-free graphite-like carbon nitride (GCN-500) was obtained by thermal post-treatment of bulk polymeric carbon nitride at 500 °C. The catalyst was thoroughly characterized by morphological, optical and textural analysis techniques. The efficiency of GCN-500 was evaluated under visible (λexc = 417 nm) LED excitation for the photocatalytic degradation of methyl-, ethyl- and propyl-paraben in different water matrices either isolated or in a mixture of the three compounds. The GCN-500 proved to be more efficient than the benchmark TiO2 P25, with complete conversion of the individual parabens within 20 min of irradiation, contrasting with 120 min needed for total degradation using TiO2. Experiments in the presence of selected scavengers confirmed the high importance of superoxide radicals in the photocatalytic oxidation of parabens using GCN-500. The effect of the nature of the aqueous matrix in the kinetics of the photocatalytic process was assessed using ultrapure, tap and river waters spiked with a mixture of the three parabens. Although still very efficient, the complexity of the real water samples turned the degradation process slower due to the presence of other components such as ions and dissolved organic matter. GCN-500 proved to be stable in a continuous-flow system using GCN-500 coated glass rings (GCN-500-GR) to remove MP, EP and PP from real water matrices.
Currently, there is a strong demand to identify the most sustainable methods for the production of nanostructured materials. In particular, for carbon nitride photocatalysts, with numerous attractive ...qualities, it is essential to assess the impact of different precursors on the microwave synthesis of these materials and understand the respective influence on the resulting photocatalytic performances. In the present work, the synthesis procedure comprises two microwave steps and six distinct precursors (dicyandiamide, melamine, guanidine carbonate, guanidine hydrochloride, thiourea, or urea) to obtain materials with varying exfoliated nanosheets-like disordered structures, among other morphological, structural and optical properties. The different characteristics of the photocatalysts produced are described, and correlations are established between these properties and the respective photocatalytic results for phenol degradation and selective hydrogen peroxide evolution with phenol or isopropanol. The best performing photocatalyst for phenol (kapp = 0.065 min−1) and total organic carbon removal (71.0%) was that prepared with the urea precursor and after a two-step microwave treatment, ascribed to the higher surface area, increased pore volume and hypsochromic photoluminescence emission. The larger rates of H2O2 were achieved in specific experiments with isopropanol (15026 µmol gcat−1 h−1) and using a guanidine hydrochloride as the photocatalyst precursor. Expectantly, these results will contribute to developing more effective and sustainable synthesis methods of graphitic carbon nitride materials.
Display omitted
•Microwave synthesis was successful to achieve photoactive carbon nitride (CN).•Novel CN materials were prepared from six C- and N-rich precursors.•Textural properties are the most significant in phenol degradation/mineralisation.•Surface chemistry and photoluminescence support H2O2 evolution rates.•Selection of precursor molecule is imperative for high photocatalytic activity.
PDF
