Photooxidation Of Ethanol Research Articles

Charge carrier recombination processes, intragap defect states, and photoluminescence mechanisms in stoichiometric and reduced TiO2 brookite nanorods: an interpretation scheme through in situ photoluminescence excitation spectroscopy in controlled environment.

The study of titanium dioxide (TiO2) in the brookite phase is gaining popularity as evidence has shown the efficient photocatalytic performance of this less investigated polymorph. It has been recently reported that defective anisotropic brookite TiO2 nanorods display remarkable substrate-specific reactivity towards alcohol photoreforming, with rates of hydrogen production significantly (18-fold) higher than those exhibited by anatase TiO2 nanoparticles. To elucidate the basic photo-physical mechanisms and peculiarities leading to such an improvement in the photoactive efficiency, we investigated the recombination processes of photoexcited charge carriers in both stoichiometric and reduced brookite nanorods via photoluminescence excitation spectroscopy in controlled environment. Through an investigation procedure employing both supragap and subgap excitation during successive exposure to oxidizing and reducing gaseous agents, we firstly obtained an interpretation scheme describing the main photoluminescence and charge recombination pathways in stoichiometric and reduced brookite, which includes information about the spatial and energetic position of the intragap states involved in photoluminescence mechanisms, and secondly identified a specific photoluminescence enhancement process occurring in only reduced brookite nanorods, which indicates the injection of a conduction band electron during ethanol photo-oxidation. The latter finding may shed light on the empirical evidence about the exceptional reactivity of reduced brookite nanorods toward the photo-oxidation of alcohols and the concomitant efficiency of photocatalytic hydrogen generation.

Effect of different Cu:Co film concentrations on photocatalytic reactions of ethanol, MB, AMX, and Cr(VI): A study of film properties & effects of photooxidation

Wastewater treatment is an urgent challenge of the 21st century, and photocatalysis represents a promising approach. However, much of the research has focused on powdered photocatalysts and complex, costly methods, leading to limitations in practical applications. This study introduces an innovative approach to produce Cu:Co thin films with different weight ratios (70:30, 50:50, and 30:70) by the low-cost dip-coating technique. The photocatalytic activity of Cu:Co films was investigated through the photooxidation of alcohol (EtOH), degradation of dye (MB), antibiotic (AMX), and photoreduction of heavy material ions (Cr(VI)) under sunlight irradiation. The results clearly show that higher Cu concentration ratios (70:30%) resulted in smoother surfaces (49.7 nm), higher droplet contact angle (72.43°), smaller particles (67 nm), lower film thickness (365 nm), narrower band gap (1.68 eV), higher transmittance (26.7%), and improved degradation of MB (78% for 4 h) and amoxicillin (43% for 45 min). Conversely, higher Co ratios may yield contrasting effects in most cases. The photoreduction of Cr(VI) showed similar results for Cu:Co films with 70:30 and 50:50 ratios, reaching 42.81% and 43.82% for 30 min, respectively. The effect of the ethanol photooxidation process significantly reduced the roughness, film thickness, and band gap in all Cu:Co films while enhancing transmittance, except for the 50:50 Cu:Co ratio. Cu:Co films are ideal for practical applications such as photoreaction processes due to their efficiency, sustainability, and stability.

Efficient photocatalytic oxidation of VOCs using ZnO@Au nanoparticles

The emission of toxic VOCs (Volatile Organic Compounds) in the environment causes serious problems and, if from one side there are directives to reduce this threat, from the other side there are stringent necessities for their removal. Several methods have been proposed to remove toxic VOCs, but little attention has been paid towards their photooxidation using materials with improved photodetection. For these reasons, we account here on the good photocatalytic performance of semiconducting ZnO@Au nanostructures that revealed to be excellent for both ultraviolet and visible light detection, thanks to the wide ZnO band gap and visible Au surface plasmon resonance, towards the photooxidation of some toxic Volatile Organic Compounds. In particular, we tested these peculiar materials for the removal of some common VOCs as toluene, ethanol and formaldehyde under solar light irradiation. The ZnO@Au showed excellent performance in the total oxidation of toluene (95% of conversion) and formaldehyde (85%) with the consequent formation of only CO2 and water as by-products. This good activity was also confirmed in the photooxidation of ethanol that allowed to obtain the 72% of CO2 selectivity. Furthermore, in all tests the catalysts showed a good stability after several consecutive runs. The efficient electronic communication between the gold core and the zinc oxide shell permitted to enhance the overall photodetection of the solar irradiation, improving also the charge carriers separation. The ZnO@Au nanostructures can be considering promising candidates as photocatalysts for air purification.

One-Pot Ethyl Acetate Production from Ethanol Photooxidation on Rutile TiO2(110): Strong Photon Energy Dependence.

Ethyl acetate (EA) production from sequential ethanol (EtOH) photooxidation on a rutile(R)-TiO2(110) surface has been investigated by the temperature-programmed desorption (TPD) method at 355 and 266 nm. Significant EA product is detected under 266 nm irradiation, which is most likely to be formed via cross-coupling of primary dissociation products, aldehyde (CH3CHO) and ethoxy groups. On the contrary, EA formation at 355 nm is negligible. In addition, the initial rate of EA formation from EtOH at 266 nm is nearly 2 orders of magnitude faster than that at 355 nm. Quantitative analysis suggests that EA formation from sequential EtOH photooxidation on R-TiO2(110) is strongly dependent on photon energy or the energy of hot holes. This experimental result raises doubt about the traditional photocatalysis model on TiO2 where charge carriers relax to their respective band edges prior to charge transfer to adsorbates during the photocatalytic process, leading to no dependence on photon energy in TiO2 photocatalysis.

Local Silver Site Temperature Critically Reflected Partial and Complete Photooxidation of Ethanol Using Ag–TiO2 as Revealed by Extended X-ray Absorption Fine Structure Debye–Waller Factor

The critical factors in choosing the reaction pathway for photocatalysis are often unclear. In this study, for a typical Ag–TiO2 photocatalyst, the control factors of partial and complete oxidation of ethanol were investigated using kinetics, UV–visible and emission spectroscopy, and silver K-edge extended X-ray absorption fine structure. Low concentrations of O2-derived intermediate species that were not detected by curve-fitting analysis could be monitored under the photocatalytic conditions based on the local temperature of Ag sites provided by the Debye–Waller factor and the correlated Debye model. The site temperature monitoring was extended to Ag nanoparticles growing from 0.5 to 3.6 nm under photocatalytic reaction conditions. The Ag site temperature reached 404 K under reductive conditions to dehydrogenate ethanol into acetaldehyde, whereas it was 363–368 K under oxidative conditions owing to O2-derived species forming CO2, CH4, and H2O to suppress localized surface plasmon resonance. Under UV light, partial ethanol oxidation to acetaldehyde and O2 activation for complete oxidation to CO2 and H2O proceeded over TiO2. However, under visible light, the C–C bond cleavage to CO2 and CH4 and complete oxidation to CO2 and H2O combined with the O2-derived species transferred from the TiO2 surface proceeded over Ag0 nanoparticles.

Nanocubes phase adaptation of In2O3/TiO2 heterojunction photocatalysts for the dye degradation and tracing of adsorbed species during photo-oxidation of ethanol

This work reports an efficient method to prepare In2O3/TiO2 heterojunction photocatalysts containing different micro-structures including nanorods (ITNR) and nanocubes (ITNC) with a coordination chemical approach followed by thermal treatments. The as-prepared materials were characterized by various physicochemical tests, to verify the structural properties and the associated photocatalytic properties. In addition, malachite green (MG) dye and ethanol were used to examine their photooxidation properties. Both experiments demonstrated the photocatalytic activity of the as-prepared samples were in the order of ITNC > ITNR > TiO2 > In2O3. This tendency implied that the formation of semiconductor-semiconductor heterojunction in ITNC and ITNR. Reduced the lower recombination rate of electron-hole pair, along with the lower electrical resistance, and higher OH adsorption sites. In addition, ITNC has a larger surface area and a wide absorption spectrum under visible light region than that of the ITNR. The scavenger study of dye degradation shows that more than 70% of the MG dye was degraded through OH radicals, which was further confirmed by the diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). The results illustrated the adsorbed gas-phase ethanol was converted to CO2 and H2O through different reaction pathways, which revealed that both surface-adsorbed OH radicals and the photogenerated holes were contributed to the higher photocatalytic activity.

Enriched silver plasmon resonance activity on the sonochemical synthesis of ZnO flowers with α-Fe2O3 as an efficient catalyst for photo-Fenton reaction and photo-oxidation of ethanol

We report the preparation of flower-shaped ZnO bunches with the α-Fe2O3 photocatalyst using the sonochemical method followed by the photodeposition of Ag nanoparticles. The Ag-ZnO/α-Fe2O3 photocatalyst was utilized for the removal of the environmental pollutant Methylene Blue (MB) dye. From our results, it was found that the Ag-ZnO/α-Fe2O3 photocatalyst exhibited higher photocatalytic activity when compared to ZnO/α-Fe2O3 with the addition of H2O2. Moreover, the higher plasmon resonance activity of the Ag with a photocatalyst degraded the MB dye within 30 min in the presence of H2O2. The different pH and the molar ratio of H2O2 were influenced by the degradation performance. In addition, the ZnO@α-Fe2O3 and Ag-ZnO/α-Fe2O3 photocatalysts were used for the generation of the OH radicals and the formation of formaldehyde and CO2 as analyzed by diffuse reflectance infra-red transmission (DRIFT) spectroscopy.

Photo-substitution reactions of perylene red dyes

Irradiation of Lumogen Red 305 (3) in ethyl acetate with intense blue LED light led to very slow bleaching, showing a high photochemical stability. However, irradiation in ethanol led to the formation of a low yield product in which one of the phenoxy groups is substituted by an acetoxy group, the oxidized form of an ethoxy group. This reaction product was only formed in the presence of blue light and oxygen. Adding a small amount of acetic acid to the solutions resulted in a much higher yield of the product, indicating a possible photo oxidation of ethanol to acetic acid during the process in this solvent. A similar dye (5) containing less phenoxy side groups than Lumogen Red 305 showed the same reaction although the product formed showed lower chemical stability. The photo-substitution of phenoxy groups by acetoxy groups is a new reaction. The results are used to discuss the structural effects on the stability of these type of fluorescent dyes under irradiation conditions, potential reaction mechanisms and the possibility of using the photochemical transformations for preparative purposes.

Surface Plasmon Resonant Gold-Palladium Bimetallic Nanoparticles for Promoting Catalytic Oxidation

AbstractColloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

Visible Light-Promoted Plasmon Resonance to Induce “Hot” Hole Transfer and Photothermal Conversion for Catalytic Oxidation

Titanium dioxide (TiO2) semiconductor photocatalysts were photosensitized to the visible spectrum with gold nanospheres (AuNSs) and gold nanorods (AuNRs) to study the ethanol photo-oxidation cycle, with an emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. The photocatalysts exhibited a localized surface plasmon resonance (SPR) that was harnessed to drive the complete photo-oxidation of formic acid (FA) and ethanol (EtOH) via augmented carrier generation/separation and photothermal conversion. Contributions of transverse and longitudinal localized SPR modes were decoupled by irradiating AuNSs–TiO2 and AuNRs–TiO2 with targeted wavelength ranges to probe their effects on plasmonically assisted photocatalytic oxidation of FA and EtOH. Photocatalytic performance was assessed by monitoring the yield of gaseous products during photo-oxidation experiments using a gas chromatography–mass spectrometry–multiple headspace extraction (GC–MS–MHE) analysis method. The complete oxidation of E...

Selective photo-oxidation of ethanol to acetaldehyde and acetic acid in water in presence of TiO2 and cupric ions under UV–simulated solar radiation

The selective oxidation of ethanol to acetaldehyde and acetic acid in aqueous solution, through sacrificial TiO2 photocatalysis in the presence of cupric ions at ambient temperature, under acidic conditions and artificial sunlight, has been investigated. Different commercial TiO2 photocatalyst samples and loads have been tested. The influence of starting cupric ion and ethanol concentrations has been investigated. Ethanol conversion, overall product selectivity, and product yield have been calculated and compared with the aim of maximizing the recovery of valuable commodity chemicals. For the run corresponding to optimal values of ethanol conversion, overall product selectivity and yields, a value of process photoefficiency equal to 33% has been calculated.Based on the experimental results, the main focus of the study has been the development of a photo-oxidation mechanism and a new kinetic model constituted by a set of mass balance equations for the main species involved in the photocatalytic oxidation process. The model has been employed for analyzing data collected at different starting substrates and cupric ion concentrations. A reliable prediction of the concentrations of cupric ions and organic species during selective photo-oxidation runs has been achieved.The modeling investigation has allowed to estimate for the first time the kinetic parameters not available in the literature review, such as the equilibrium adsorption constants and the rate constants for the hole-capture by sacrificial agents.A new alternative strategy to convert ethanol from biorefinery wastewaters into valuable fine chemicals, by using water as solvent, a low-cost catalyst, solar radiation and ambient temperature, has been proposed and kinetically characterized. The model presented can be easily applied to other photocatalytic systems for the oxidation of organic species over metal doped photocatalysts.

Rapid photocatalytic reduction of graphene oxide indirectly activated by the domino effect of ethanol oxidation on a titanium dioxide film

Deoxygenation of graphene oxide is a low-cost and effective way to yield graphene (i.e., reduced graphene oxide - RGO) for many applications. However, choices of reduction approach and reduction time need consideration due to damaging pre-existing materials on electronic devices. Here, we found a facile and eco-friendly route that was based on the photo-oxidation of ethanol (diluted in water) on a catalytic TiO2 film to rapidly induce the formation of RGO within 15 min under UV (20 mW/cm2) or sun lights (1 sun = 100 mW/cm2). Our reduction route was indirectly activated by chain reactions of ethanol and TiO2 (so-called domino effect) because the GO deoxygenation occurred even when the samples were placed around and not in contact with TiO2 film. To obtain the highest reduction, the samples should stay on the catalytic film to receive lights for activation and acceleration of reactions. Furthermore, effects of exposure time (1–20 min), ethanol concentration (14.3–100%), and light intensity on RGO quality explored with the use of chemiresistive devices. The results of demonstrative sensing measurements towards NO2 and NH3 indicate that our method is promising for electrical applications using solution processable RGO.

Effect of the addition of different doping agents on visible light activity of porous TiO2 photocatalysts

The influence of the addition of different doping agents (N, W and Hf) on the macroporous TiO2 photoactivity toward the Rhodamine B degradation and ethanol photo-oxidation was evaluated. The samples were characterized by XRD, XPS, SEM, TEM, N2 adsorption-desorption, UV–vis Diffuse Reflectance and Photoluminescence spectroscopies to study also the changes in the physico-chemical properties due to the presence of dopants.The photonic effect and the high ordered porous structure of the macroporous TiO2 that lead to increase the path length of the light, were the key factors that allow to enhance the catalytic activity towards the dye and VOC degradation under visible and solar light irradiation of these materials compared to the commercial TiO2 anatase. A significant improvement of the catalytic performances was achieved when the amount of the dopant was low, the ionic exchange of Ti4+ ions by doping ions and the consequent substitution in the crystal lattice of TiO2 was favoured, and/or the formation of non-stoichiometric Ti-compound on the TiO2 surface was promoted.

(Invited) Ethanol Photoreaction over Anatase TiO2(101) and Rutile TiO2(110) Single Crystals. A Combined STM and Online Mass Spectrometry

The reactions of ethanol have been investigated over anatase TiO2(101) and rutile TiO2 (110) single crystals by STM and on-line mass spectrometry to determine the adsorbate species in the dark and post UV illumination, in the presence and absence of O2 or Au nanoclusters, in order to extract initial reaction parameters under photo-excitation. On anatase (101) TiO2 single crystal the reaction rate for the photo-oxidation of ethanol to acetaldehyde is found to be strongly dependent on O2 partial pressures and surface coverage with an order of the reaction for O2 close to 0.15. Carbon-carbon bond dissociation leading to CH3 radicals in the gas phase was found to be a minor pathway, which is contrary to the case of TiO2 rutile (110) single crystal, as previously reported by our group and others. Our STM images distinguished two types of surface adsorbates upon ethanol exposure that can be attributed to its molecular and dissociative modes. Upon UV exposure at (and above) 3×10-8 mbar O2, a third species is identified as a reaction end-product, which can be tentatively attributed to acetate/formate species, in line with XPS C1s measurements. The room temperature photo-oxidation of ethanol has also been investigated over a rutile TiO2(110) single crystal by STM and on-line mass spectrometry, in the presence of O2 to determine adsorbate species remaining post UV exposure and emitted gas phase products. In addition to acetaldehyde, methyl radical was detected in the mass spectrometry resulting from the photo-fragmentation of an acetaldehyde-O complex. Formic acid species bound to Ti5c in a bi-dentate mode were identified by STM on the surface after the reaction. The effect of O2 partial pressure on the reaction selectivity demonstrated a dominance of the photo-fragmentation process with increasing pressure unlike the case of anatase TiO2(101) single crystal. In addition the effect of Au particles on the reaction of the TiO2(110 rutile has been investigated for hydrogen production under photo-irradiation in UHV conditions. It was found that particle size in the range 4 to 8 nm do not change the reaction rate yet particle density does. Detailed reaction mechanism for both reduction and oxidation reactions are addressed based on structural and kinetic information from the UHV systems and compared to those of their corresponding powder forms in liquid-solid photocatalytic reactions conditions.

Mechanism of Ethanol Photooxidation on Single-Crystal Anatase TiO2(101)

Despite the proven properties of the anatase phase of TiO2 related to photocatalysis, detailed mechanistic information regarding a photooxidation reaction has not yet been derived from single-crystal studies. In this work, we have studied the photooxidation of ethanol (as a prototype hole-scavenger organic molecule) adsorbed on the anatase TiO2(101) surface by STM and online mass spectrometry to determine the adsorbate species in the dark and under UV illumination in the presence of O2 and to extract kinetic reaction parameters under photoexcitation. The reaction rate for the photooxidation of ethanol to acetaldehyde was found to depend on the O2 partial pressure and surface coverage, where the order of the reaction with respect to O2 is close to 0.15. Carbon–carbon bond dissociation leading to the formation of CH3 radicals in the gas phase was found to be a minor pathway, which is contrary to the case of the rutile TiO2(110) single crystal. Our STM images distinguished two types of surface adsorbates upo...

Mechanistic study of the role of Au, Pd and Au–Pd in the surface reactions of ethanol over TiO2in the dark and under photo-excitation

In situinfrared spectroscopy (FTIR) and catalytic reactions are employed to explore the photo-oxidation and photo-reforming of ethanol over TiO2and M/TiO2(M = Au, Pd and Au–Pd) catalysts.

Slow photon amplification of gas-phase ethanol photo-oxidation in titania inverse opal photonic crystals

Here we describe the successful fabrication of six titania inverse opal (TiO2 IO) photocatalysts with fcc[111] pseudo photonic band gaps (PBGs) tuned to span the UV–vis region. Photocatalysts were fabricated by a colloidal crystal templating and sol-gel approach – a robust and highly applicable bottom-up scheme which allowed for precise control over the geometric and optical properties of the TiO2 IO photocatalysts. Optical properties of the TiO2 IO thin films were investigated in detail by UV–vis transmittance and reflectance measurements. The PBG along the fcc[111] direction in the TiO2 IOs was dependent on the inter-planar spacing in the [111] direction, the incident angle of light and the refractive index of the medium filling the macropores in the IOs, in agreement with a modified Bragg’s law expression. Calculated photonic band structures for the photocatalysts revealed a PBG along the Γ→L direction at a/λ∼0.74, in agreement with the experimental optical data. By coupling the low frequency edge of the PBG along the [111] direction with the electronic absorption edge of anatase TiO2, a two-fold enhancement in the rate of gas phase ethanol photo-oxidation in air was achieved. This enhancement appears to be associated with a ‘slow photon’ effect that acts to both enhance TiO2 absorption and inhibit spontaneous emission (i.e. suppress electron-hole pair recombination).

Investigating the photo-oxidation of model indoor air pollutants using field asymmetric ion mobility spectrometry

We have developed a versatile measurement system utilising field asymmetric ion mobility spectrometry (FAIMS) to study the photocatalytic degradation of VOCs at concentrations comparable to indoor air. FAIMS allows continuous monitoring of chemical species in the gas phase, whilst having a high separation selectivity and sensitivity, so can be used to identify multiple species concurrently at ppb concentrations, which are clear advantages over traditional characterization techniques used in photocatalytic air purification such as gas chromatography. Here we demonstrate the methodology with the photo-oxidation of 2-propanol, ethanol and acetone using a commercial titanium dioxide felt. To the best of our knowledge, this is the first time FAIMS has been used in photocatalytic air purification applications.

Photocatalysis of ethanol oxidation by tetrachloroferrate(III) supported on Dowex 2‐X8

FeCl4− heterogenized on a Dowex 2‐X8 anion exchange resin catalyzes the photooxidation of ethanol to acetaldehyde under visible and near‐UV irradiation (>345 nm). The rate of reaction is proportional to the oxygen partial pressure up to 1 atm. Oxidation is suggested to occur through the formation of 1‐hydroxyethylhydroperoxide, initiated by the photodissociation of a chlorine atom. The hydroperoxide re‐oxidizes the iron(II) species, both the oxidation and reduction steps producing acetaldehyde. This mechanism is consistent with the increases in yield with ethanol concentration in ethanol–toluene mixtures towards an asymptotic limit. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of colloidal graphene oxide on photocatalytic activity of nanocrystalline TiO2 in gas-phase ethanol and benzene oxidation

Impregnation of the nanocrystalline TiO2 Degussa/Evonik P25 by colloidal graphene oxide produced by the Hummers method (H-GO) results in a 4-fold acceleration of photocatalytic gas-phase oxidation of ethanol and benzene vapors by air oxygen as a result of enhanced separation of the photogenerated charge carriers between TiO2 and H-GO. Preliminary photochemical reduction of H-GO decreases drastically its activity in ethanol photooxidation but does not affect appreciably photocatalytic oxidation of benzene. More deeply oxidized colloidal GO produced by the Brodie method (B-GO) almost does not affect the photocatalytic properties of titania in benzene photooxidation. It is concluded that the catalytic properties of GO in the photooxidation of ethanol and benzene depend on a balance between the capabilities of the GO sheets (i) to accept photoelectrons from titania nanocrystals and (ii) to bound to the TiO2 surface. The former factor depends on the aromaticity of GO particles and increases from B-GO to H-GO to photoreduced H-GO, while the latter factor depends on the density of the functional groups on GO sheets and increases in the opposite direction.