Photocatalytic Oxidation Of Ethylene Research Articles

Effect of ligand substitution in UiO-66 metal-organic frameworks on the photocatalytic oxidation of acetaldehyde

A series of functionalized X-UiO-66 (X = NH2, H, Br and NO2) materials were prepared using a hydrothermal method and modified with various ligands. Their photocatalytic activity was evaluated by the oxidation of acetaldehyde. Experimental results show that the introduction of different ligands significantly influences the physicochemical properties of UiO-66. Br-UiO-66 exhibited the highest photocatalytic activity and CO2 selectivity of 85.6% and 85.7%, respectively. Photochemical properties reveal that -Br functional group facilitate the separation of photogenerated electrons and holes, significantly improving their transfer and oxygen reduction. As a result, an increased number of hydroxyl and superoxide radicals can form, improving the efficiency of the photocatalytic reaction. Br-UiO-66 accumulates fewer intermediates on its surface and still shows excellent photocatalytic activity and structural stability after 24 h of dynamic reaction. This work demonstrates the excellent adsorption and catalytic oxidation performance of Br-UiO-66 towards acetaldehyde and may provide new ideas for researching catalysts in the photocatalytic degradation of pollutants.

Evidence of Synergy Effects between Zinc and Copper Oxides with Acidic Sites on Natural Zeolite during Photocatalytic Oxidation of Ethylene Using Operando DRIFTS Studies

In this article, the role of surface sites of modified zeolites with semiconductor nanoparticles as alternative photocatalyts for protecting post-harvest foodstuff from the detrimental effects of ethylene is addressed. Two single and one double catalyst based on zinc and copper oxides supported over modified zeolite samples were prepared. Physical, chemical, and surface properties of prepared materials were studied by several characterization methods. UV-Vis absorption spectra show that the applied modification procedures increase the optical absorption of light in the UV and visible regions, suggesting that an increase in the photocatalytic activity could take place mainly in the obtained co-impregnated catalyst. An ethylene conversion around 50% was achieved when the parent natural zeolite support was modified with both transition metal oxides, obtaining higher removal efficiency in comparison to single oxide catalysts. Adsorption and photocatalytic oxidation experiments were also performed using single and double catalysts supported over fumed silica, attaining lower ethylene conversion and thus highlighting the role of zeolite surfaces as adsorption sites for ethylene during photocatalytic reactions. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that a synergistic mechanism occurs, involving ethylene adsorption at acidic sites of zeolite and its photocatalytic oxidation due to the generation of radicals by the light activation of nanoparticles of zinc and copper oxides.

ASSESSMENT OF THE INDOOR AIR PURIFICATION BY PHOTOCATALYTIC PAINTS

Photocatalytic building materials containing TiO2 were extensively studied for outdoor applications using solar radiation. Nowadays, the market offers a wide variety of these materials with self-cleaning and air purification functionalities. However, heterogeneous photocatalysis applied in indoor construction materials was less developed. The objective of this work is to investigate the photocatalytic performance of carbon doped TiO2 in replacement of the normal pigments in indoor wall paint formulations. To achieve this goal, the photocatalytic oxidation of acetaldehyde in gas phase was carried out. The air decontamination process was conducted using regular indoor light in a bench scale chamber photoreactor simulating a room. The main environmental conditions that affect the photocatalytic process were varied: air flow rate, irradiance, relative humidity and acetaldehyde concentration. The results were analyzed through the response surface methodology and revealed the air purifying power of photocatalytic paints under indoor conditions.

Photocatalytic oxidation of acetaldehyde by hybrid Pt/WO3–MOR photocatalysts under visible or sunlight irradiation

A hybrid photocatalyst was prepared from visible light-responsive Pt/WO3 and siliceous mordenite (MOR) zeolite by simple impregnation with an aqueous solution of (NH4)10W12O41·5H2O. Unmodified Pt/WO3 had low photocatalytic activity in gas phase oxidation of acetaldehyde because of its low surface area (3–5 m2/g). In contrast, the Pt/WO3–MOR had higher photocatalytic activity under focused sunlight and Xe lamp irradiation. Pt/WO3–MOR with low WO3 content (<20 wt%) adsorbed sufficient acetaldehyde, but absorption of light in the visible region was low. The optimum zeolite content enhancing the photocatalytic activity of Pt/WO3 was estimated to be 30–50 % (w/w). Adsorption of the gaseous reactants and the efficiency of absorption of incident light are both important aspects of high photocatalytic activity.

Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling

Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.

Photocatalytic oxidation of acetaldehyde with ZnO-quantum dots

In this paper, the comparison study of photocatalytic oxidation properties of TiO2 and ZnO-quantum dots (QDs) in gaseous phase was designed and performed to degrade acetaldehyde (CH3CHO) first time. The obtained results showed that the 1st order rate constant for the prepared QDs of ZnO (1.9×10−2/min) is one magnitude higher than that of Degussa P-25 (8.3×10−3/min). The efficiencies were found to be 70% and 92% for Degussa P-25 and ZnO-QDs respectively in 120min of reaction time. The QDs were prepared from zinc nitrate hexahydrate (Zn(NO3)⋅6H2O), n-propylamine and SDS surfactant in 6h refluxing. The crystallinity of the product was analyzed with X-ray diffraction (XRD) and it reveals that prepared QDs size is very small and it exhibit wurzite phase. The general morphology of prepared QDs were observed with using FESEM and TEM, which showed that the average size are in the range of ∼6–7nm. The elemental and compositional analysis was also carried out with FTIR spectroscopy.

Selective synthesis of TiO2-based nanoparticles with highly active surface sites for gas-phase photocatalytic oxidation

This work demonstrated the absence of surface terminal hydroxyl groups plays a key role in the photocatalytic oxidation of low concentration volatile organic compounds. Probed by 1H MAS NMR spectroscopy, we showed the synthesis of bare and F-TiO2 nanoparticles with undetectably low content of terminal hydroxyl groups (TiOH) on the surface of TiO2 could be obtained through a sol–gel process. The characterization results by N2 adsorption, XRD, HRTEM, Raman, and XPS show that the bare TiO2 and F-TiO2 have almost identical bulk and surface structural properties. The photocatalytic activity was evaluated by photocatalytic oxidation of acetaldehyde and ethanol. Due to the absence of terminal TiOH in the bare TiO2 and F-TiO2, both materials exhibit 100% photodegradation of acetaldehyde and ethanol. No deactivation was observed during the experimental period of 8 days. The activities surpassed the photodegradation performance of the benchmarking Aeroxide P25 TiO2 under similar conditions (93%). On the bare TiO2, only stoichiometric CO2 production was observed and no detectable by-product existed in the product stream, resulting in no expanded off-odor problems. On the contrary, ethanol photodegradation on F-TiO2 produced minor acetaldehyde as a by-product, but the amount of acetaldehyde produced was still lower than that produced on Aeroxide P25.

Quenching of TiO2 photo catalysis by silver nanoparticles

Abstract The plasmon resonance of metal nanostructures affects neighboring semiconductors, quenching or enhancing optical transitions depending on various parameters. These plasmonic properties are currently investigated with respect to topics such as photovoltaics and optical detection and could also have important consequences for photocatalysis. Here the effect of silver nanoparticles of a size up to 30 nm and at maximum 0.50 monolayers on the photocatalytic oxidation of ethylene on TiO2 is studied. Since the plasmon resonance energy of silver nanoparticles is comparable with the TiO2 band gap, dipole–dipole interaction converts excitons into heat at the silver nanoparticle. This indicates that plasmonic interaction with TiO2 semiconductor catalysts can reduce the photo catalytic activity considerably.

Sol-Gel Preparation, Characterization and Photocatalytic Activity of Nanostructured TiO2 Nanoparticles

ABSTRACTTo establish a promising method for the purification of air containing volatile organic compounds, TiO2 nanoparticles with interesting physicochemical properties were prepared by the sol-gel method to perform the photocatalytic decomposition of acetaldehyde. The obtained samples were characterized by the x-ray diffraction -Rietveld refinement, transmission electron microscopy (TEM) and the Brunauer, Emmet and Teller (BET) model. According to the results, the sample that presented the highest activity (96.4%) in the photocatalytic oxidation of acetaldehyde was the one annealed at 200 °C. This material showed the presence of a mixture of the anatase (higher proportion) and brookite phases, nanometric crystal size (7.03 nm) and high surface area (189 m2g-1). The physicochemical properties present in the TiO2-P-200°C nanoparticles suggest that they may establish a photoassisted reaction process for air purification, in which volatile organic compounds are photocatalitically decomposed.

Photocatalytic Degradation of Acetaldehyde by Sol-Gel TiO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles: Effect of the Physicochemical Properties on the Photocatalytic Activity

Nowadays, nanostructured semiconductor materials offer promising opportunities for a new generation of materials such as TiO2nanoparticles with improved properties for their application in the environmental catalysis field. It is well known that the phocatalytic activity of the TiO2nanoparticles is strongly dependent on the surface area, crystal size, phase composition and synthesis method. Thus, the preparation conditions clearly affect the photocatalytic activity of the TiO2nanoparticles. This work deals with the study of the structure of TiO2nanoparticles that were synthesized by the sol-gel method (using isopropanol as solvent), and calcined at 200 and 500°C. The obtained samples were characterized by the XRD-Rietveld refinement, BET and TEM techniques; and tested in the photodecomposition of acetaldehyde. The evaluations were carried out at room temperature by using CH3CHO (300 ppmv), O2(2.0 %) in helium balance in a quartz glass photoreactor (gas phase) with a 365-UV light lamp. According to the results, the sample that presented the highest activity in the photocatalytic oxidation of acetaldehyde (96.4%) was the one annealed at 200 °C. This sample showed the following proportion of phases: anatase (62.88%) with a tetragonal structure (a=0.3790926, b=0.3790926, c=0.9495732) nm; and b) brookite (37.12%) with an orthorhombic structure (a=0.9167624, b=0.5416461, c=0.5210546) nm. The surface area was 189 m2/g and the average crystal size was 7.03 nm. From the results, it can be seen that this material showed high activity in the photocatalytic degradation of acetaldehyde because of: the presence of a mixture of the anatase (higher proportion) and brookite phases, nanometric crystal size and high surface area obtained in this TiO2material. According to the aforementioned, this material can be considered as a good option for the decomposition of acetaldehyde and other volatile organic compounds (VOCs) in confined spaces.

Effect of H2O vapor addition on the photocatalytic oxidation of ethanol, acetaldehyde and acetic acid in the gas phase on TiO2 semiconductor powders

The effect of H2O vapor addition on the photocatalytic oxidation of ethanol, acetaldehyde and acetic acid on TiO2 semiconductor powders under UV light irradiation were investigated. The photocatalytic oxidation of acetaldehyde and acetic acid on TiO2 surfaces was enhanced by the addition of H2O vapor, its extent depending on the pressure while, on the other hand, the photocatalytic oxidation of ethanol was depressed by its coexistence with the H2O vapor. Since the Ti4+ sites on the TiO2 surfaces work as trap sites for the photo-formed electrons, the carbonyl compounds strongly adsorbed on the Ti4+ sites are not directly oxidized by the holes. However, when optimal amounts of H2O molecules exist in the reaction system, the OH radicals formed by the photo-oxidation of H2O molecules indirectly oxidize such organic species on the Ti4+ sites. In contrast, although ethanol molecules promptly interact with the photo-formed holes on the hydroxyl groups, the coexistence of H2O molecules in the reaction system lessens the efficient interaction between ethanol and the hydroxyl groups on TiO2 surfaces, resulting in a suppression of photocatalytic reactivity. In this way, the correlation of the different surface sites, such as Ti4+ or the hydroxyl groups, on which organic compounds adsorb and the photo-formed carriers are trapped, is not clearly understood but is observed to play an important role in the efficient photocatalytic oxidation of various organic compounds on TiO2 semiconductor in the presence or the absence of an H2O vapor.

Synthesis, characterization, and photocatalytic application of novel TiO2 nanoparticles

Novel TiO 2 nanoparticles (TNP) having a high specific surface area were successfully synthesized in a vortex reactor by sol–gel process with optimized operating parameters. These 10–20 nm TNP were characterized and compared with TiO 2 synthesized by solution combustion (TSC) method and commercially available TiO 2 (degussa P25 and anatase by Aldrich). Characterization was performed by X-ray diffraction spectroscopy (XRD), specific surface area analysis, energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), diffuse reflectance ultraviolet–visible spectroscopy (DR/UV–vis), and Fourier transformed-infrared spectroscopy (FT-IR). TNP showed comparatively smaller size with little porosity between them, good crystalline anatase with small rutile phase, higher BET surface area, confined band gap energy, and higher OH groups. Photocatalytic oxidation of ethylene (a naturally occurring gas produced by plant tissues, engine exhausts, and plant and fungi metabolism) has been investigated at ambient temperature in an ad hoc designed pyrex glass photocatalytic reactor, by using these TNP and compared with TSC, and commercial TiO 2 . Higher photocatalytic conversion of ethylene was observed for TNP compared to TSC and commercial TiO 2 . Mixed phase of TN with high surface area might induce the adsorption of ethylene pollutant and water with generation of OH groups (oxidizing agent) on the surface of TNP leading to higher photocatalytic activity.

Photocatalytic oxidation of ethylene by ammonium exchanged ETS-10 and AM-6

ETS-10 and AM-6 in the as-prepared and ammonium form have been characterized using Raman, X-ray powder diffraction, N2 adsorption, energy dispersive X-ray (EDX) analysis, UV/vis spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Upon NH4+ ion exchange, AM-6 shows the loss of the characteristic V–O–V stretch in the Raman spectrum similar to the effects observed for NH4+ ion exchanged ETS-10. The UV/vis spectrum of NH4+ ion exchanged AM-6 also shows similar changes to NH4+ ion exchanged ETS-10, though the band gap in AM-6 is not red shifted as it is in ETS-10. Heating the NH4+ exchanged AM-6 to form H-AM-6 changes the coordination environment of the vanadium from an octahedral coordination to a tetrahedral coordination, but does not cause the partial collapse of the AM-6 structure. The oxidation of ethylene under oxygen on as-synthesized AM-6 only produces partial oxidation products while the NH4+ ion exchanged AM-6 was able to completely oxidize ethylene to CO2.

Effects of reaction medium and crystallite size on Ti3+ surface defects in titanium dioxide nanoparticles prepared by solvothermal method

Abstract Titanium dioxide nanoparticles were prepared using solvothermal methods in 1,4-butanediol and toluene. Three different crystallite sizes (10 nm, 13 nm, and 17 nm) of titania as anatase crystals were produced and were then employed as catalysts in photocatalytic oxidation of ethylene in gas phase. As the crystallite size of titania increased, more Ti3+ surface defects were observed. The amounts of surface defects on titania were determined by temperature-programmed desorption using carbon dioxide as a probe molecule. Despite the smaller specific surface area, titania with larger crystallite size exhibited higher photocatalytic activity, which was attributed to more surface defects in the catalyst.

Photocatalytic oxidation of acetaldehyde with oxygen on TiO 2/ZSM-5 photocatalysts: Effect of hydrophobicity of zeolites

TiO 2 photocatalysts hybridized with ZSM-5 were prepared by the impregnation of (NH 4) 2[TiO(C 2O 4) 2] aqueous solution. This is one of the most ideal green processes in establishing TiO 2 photocatalysts because of an organic solvent-free preparation method. The highly hydrophobic H-ZSM-5 with low Al 2O 3 content was effective as an adsorbent for acetaldehyde molecules. These results suggest the close relationship between the hydrophobicity of the zeolite and the high photocatalytic reactivity of TiO 2 prepared on zeolites compared with unloaded TiO 2 catalysts. However, acetaldehyde molecules were strongly trapped on the Na + sites of ZSM-5 and their efficient diffusion onto the TiO 2 sites was inhibited, resulting in low photocatalytic reactivity. The photocatalytic oxidation of acetaldehyde over TiO 2/ZSM-5 was improved in the coexistence of H 2O vapor. The role of the H 2O molecules was estimated to be the efficient formation of OH radicals and the prevention of strong adsorption of acetaldehyde on the TiO 2 sites.

酸化チタン／ＺＳＭ‐５ゼオライト光触媒によるアセトアルデヒドの完全酸化分解反応

TiO2 hybridized with ZSM-5 zeolites were prepared by the impregnation of (NH4)2[TiO(C2O4)2] aqueous solution. This is one of the most ideal green processes in establishing TiO2 photocatalysts because of an organic solvent-free preparation method. The highly hydrophobic H-ZSM-5 having low Al2O3 content was effective as an adsorbent for acetaldehyde. On the other hand, acetaldehyde molecules were strongly trapped on the Na+ sites of ZSM-5 and their efficient diffusion onto the TiO2 sites was inhibited. These results suggest the close relationship between the interaction of reactant with zeolite surfaces and the photocatalytic reactivity of TiO2 prepared on the zeolites as compared to unloaded TiO2 catalysts. The photocatalytic oxidation of acetaldehyde on TiO2/ZSM-5 was improved in the presence of H2O vapor.

Catalytic Properties of Ti-HMS with High Titanium Loadings

Ti-HMS samples in which titanium species exist in various forms of isolated tetrahedral state, finely dispersed <TEX>$TiO_2$</TEX> cluster, and some in extra-framework anatase phase were prepared via a direct synthesis route using dodecylamine (DDS) as a structure directing agent by systematically varying the titanium loadings between 2 and 50 mol% Ti/(Ti+Si) in substrate composition. Physicochemical properties of the materials were evaluated using XRD, SEM/TEM, N2 adsorption, UV-vis and XANES spectroscopies. Catalytic properties of Ti-HMS in cyclohexene and 2,6-di-tert-butyl phenol (2,6-DTBP) oxidation using aqueous <TEX>$H_2O_2$</TEX>, and vapor phase photocatalytic degradation of acetaldehyde were evaluated. High <TEX>$H_2O_2$</TEX> selectivity was obtained in cyclohexene oxidation, and cyclohexene conversion was found primarily dependent on the amount of tetrahedrally coordinated Ti sites. For bulky 2,6-DTBP oxidation and photocatalytic oxidation of acetaldehyde, on the other hand, conversions were found dependent on the total amount of Ti sites and maintaining an uniform mesoporous structure in the catalysts was not critical for efficient catalysis.

Photocatalytic activity of metal ion (Fe or W) doped titania

Iron or tungsten-doped nano TiO2 were successfully synthesized from TiCl4. All of the samples showed anatase phase of TiO2. For the iron-doped TiO2, Iron ion was well dispersed in the TiO2 lattice. However, tungsten-doped TiO2 formed 12-tungstate with anatase TiO2. As the concentration of tungsten increased, 12-tungstate disappeared. The photocatalytic oxidation of acetaldehyde was evaluated to examine the photocatalytic characteristics of metal-doped TiO2. Because of the surface containing metal oxide or metal precursors at high concentration metal ion, increasing the concentration of W or Fe ion decreased the reactivity. The reaction rate was drastically increased after 300 °C heat treatment. Furthermore, the photocatalytic activity of iron- or tungsten-doped TiO2 was higher than that of synthesized pure TiO2 and commercial TiO2.

Catalytic and Photocatalytic Oxidation of Ethylene on Titania-Based Thin-Films

The effect of reaction temperature on the catalytic and photocatalytic oxidation of ethylene on unplatinized and platinized versions of a TiO2/ZrO2 mixed-oxide thin-film catalyst is presented in this study. Ethylene conversion data collected using a recirculating tubular reactor are analyzed using a half order model of reaction kinetics. When operated in the presence of UV, both catalysts exhibit significant (95% confidence) increases in the reaction rate constant at 70 °C compared to 30 °Cno difference is observed between unplatinized and platinized versions at these two temperatures. However, only the platinized catalyst performs better at 107 °C compared to its performance at 70 °C. Also, at 107 °C in the presence of UV, the reaction rate constant obtained for the platinized catalyst is a factor of 2 larger than that obtained using the unplatinized catalyst. Catalytic reaction rate constants for the platinized catalyst were 1 (107 °C) to 2 (70 °C) orders of magnitude lower than corresponding photocatal...

Aldol condensation of acetaldehyde to form high molecular weight compounds on TiO 2

Temperature-programmed desorption, hydrogenation, and oxidation are used to show that acetaldehyde undergoes continued aldol condensation beyond crotonaldehyde formation on Degussa P-25 titania to form hexan-2,4-diene-al and higher molecular weight compounds containing conjugated C=C bonds. Aromatic compounds also form, and at higher temperatures coke forms. Degussa P-25 TiO2 has more sites that catalyze chain propagation reactions beyond formation of C4 species than do pure anatase or rutile surfaces. These reactions may be responsible for deactivation observed during photocatalytic oxidation of acetaldehyde at elevated temperatures.