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•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.
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•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.
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•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).
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•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.
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•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.
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•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.
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The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization ...conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters.
Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies.
The optimal immobilization conditions for a laccase concentration of 3.75μL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis–Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.
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•Exfoliated carbon nitride obtained after thermal and ultrasonic post-treatments.•Exfoliation treatments decreased the hydrodynamic particle size from 25 to 3.2 μm.•Photoefficiency ...depends on the nature of the p-substituents in benzyl alcohol.•Few-layer carbon nitride nanosheets avoid the blockage of the microfluidic channels.
Benzyl alcohol and a set of para-substituted derivatives (–NO2, –Cl, −CH3, −OCH3 and −OH) were converted to the corresponding aldehydes in a commercial continuous-flow microfluidic reactor. Due to the dimension and the rigidity of the commercial microfluidic reactor channels, a stable suspension with few-layer graphitic carbon nitride nanoparticles (GCN-TS) was used to avoid the blockage of the photocatalyst in the channels of the reactor. Preliminary photocatalytic batch experiments revealed that different reaction yields were obtained depending on the aromatic ring activating/deactivating nature of the substituent groups. Regarding the experiments under continuous-flow, the highest aldehyde production was obtained for the reactions with 4-methoxybenzyl alcohol as starting molecule, corresponding to 0.19 mM at a retention time of merely 0.75 min. The results show the possibility of employing microfluidic reactors for the selective photocatalytic conversion of aromatic alcohols for both process intensification and screening applications due to the drastic decrease of reaction time.
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•Semi-conductive g-C3N4 photocatalysts outperformed the commercial TiO2 P25.•Metal loaded g-C3N4 increased photocatalytic conversion.•The best performance was obtained for g-C3N4 ...loaded with Ru (1wt.%).•1%Ru/g-C3N4 could be used in 3 consecutive runs without loss of activity.
Replacement of traditional thermal synthesis of fine chemicals by selective photocatalysis can lead to more environmental friendly processes, carried out at milder conditions, using ambient temperature, atmospheric pressure, with more ecological and economic solvents such as water. Because benzaldehyde (BAL), as fine chemical building block, has an enormous range of applications in pharmaceutical, fragrance and agricultural industries, we analyzed its route of synthesis by the photocatalytic oxidation of benzyl alcohol (BA).
In this work, we used graphitized-carbon nitride (g-C3N4) as photocatalyst for the selective synthesis of benzaldehyde from benzyl alcohol. The solid matrix of the photocatalyst was modified by loading different metals such as Au, Ru, Pd, Pt, Ir, Ag and Rh. Conversion, yield and selectivity were compared against benchmark commercial photocatalyst P25 TiO2 (by Evonik). The influence of the physical-chemical nature of the medium, by means of the pH, on the efficiency of the photocatalytic process was also evaluated. The 1wt.% Ru/g-C3N4 photocatalyst had the best compromise between conversion (73%) and selectivity (72%) for a 4h of irradiation time using 390nm activation by a light emitting diode source and it proved to be stable up to 3 consecutive runs.
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•A GCN-T/PVDF film was successfully tested in the degradation of MPs under visible light.•GCN-T/PVDF film showed great stability under batch and continuous flow modes.•The ...photocatalytic treatment did not lead to increased toxicity in the mobility of the D. magna.
The presence of micropollutants (MPs) in aquatic compartments poses a great risk to the ecosystems and human health. Advanced oxidation processes (AOPs), such as light-induced systems employing a variety of powder optical semiconductors, have been widely investigated to remove MPs from water and wastewater. In this work, a metal-free photocatalyst (GCN-T) immobilized in the form of a film (GCN-T/PVDF) was activated by visible light (λexc = 417 nm) and successfully tested in both batch and continuous flow mode reactors for the degradation of two pharmaceutical model compounds (metoprolol and venlafaxine) spiked in ultrapure water (UP) and urban wastewater (WW) samples. A total removal of MPs was reached after 3 h reaction using GCN-T/PVDF film in a batch reactor. Under continuous mode operation, a steady state was attained after 2 h, with ca. 64 % removal for both MPs being obtained. The photocatalytic system was also examined using a non-spiked WW sample to study its performance to remove trace concentrations of these and other MPs in this type of complex matrix. MPs, such as bezafibrate, carbamazepine, diclofenac, isoproturon, and tramadol, were detected and efficiently degraded using the GCN-T/PVDF film. Finally, the ecotoxicity of the WW samples was also investigated using the aquatic invertebrate microcrustacean Daphnia magna. The results showed that the toxicity of WW samples decreases with the photocatalytic treatment.
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