Photocatalytic Oxidation Of 2-propanol Research Articles

Synergetic effect of oxygen vacancies and morphology of ZnO photocatalyst prepared by non-hydrolytic sol-gel route for the photo-oxidation of 2-propanol in a gas-solid system

The effects of the nature of some carboxylic acids (oxalic, malic, citric, and tartaric acid) and of the annealing temperature in the preparation of the ZnO photocatalyst by a non-hydrolytic sol-gel route (using zinc acetate as the precursor) have been studied for oxidation of 2-propanol in air as probe reaction in a gas-solid regime. The physico-chemical characterization by XRD, SEM/EDX and UV–vis-DRS revealed a synergetic effect of the presence of oxygen vacancies and morphology of ZnO on the reaction performance. Oxygen vacancies were found to increase with decreasing annealing temperature, and this result indicates the possibility of their production in situ without the addition of a doping agent.XRD results showed that ZnO samples present a pure wurtzite structure with an average crystal size ranging from 21 nm to 42 nm. The specific surface area of samples ranged from 3.0 m2·g–1 to 18 m2·g–1and SEM observation indicated the presence of different agglomeration of both faceted and non-faceted particles. The lowest band gap energy of ZnO was 3.2 eV. The photocatalytic oxidation of 2-propanol in gas-solid regime was carried out in oxygen atmosphere. An increase of acid concentration during the ZnO preparation caused a decrease on the activity of the photocatalyts. An increasing amount of zinc acetate with respect to acid during the preparation of the photocatalysts enhanced the oxygen vacancies in the solid, which induced an increase of the 2-propanol oxidation rate constant. The increasing of the annealing temperature decreased the oxygen vacancies and hence the photocatalytic activity of ZnO. The highest 2-propanol oxidation rate (kapp = 4.00·10–2 min–1) was obtained by using the ZnO sample prepared with a 1:2 molar ratio of zinc acetate:oxalic acid, and annealed at 400 °C. This photocatalyst showed an oxidation rate 80 times higher than that of the least active photocatalyst (kapp = 5.00·10–4 min–1) obtained using zinc acetate:tartaric acid at 1:1 molar ratio and annealed at 500 °C.

Au/TiO2-CeO2 Catalysts for Photocatalytic Water Splitting and VOCs Oxidation Reactions

Photocatalytic water splitting for H2 production and photocatalytic oxidation of 2-propanol, an example of volatile organic compounds, were investigated over TiO2 catalysts loaded with gold and/or ceria. In the water splitting reaction the presence of gold only slightly affected the performance of TiO2 whereas the presence of CeO2 had a more remarkable positive effect. In the 2-propanol oxidation Au/TiO2 was the most active sample in terms of alcohol conversion whereas Au/TiO2-CeO2 exhibited the highest CO2 yield. On the basis of characterization experiments (X-Ray Diffraction (XRD), Energy Dispersive X-ray Analysis EDX, surface area measurements, Diffuse Reflectance Spectroscopy (DRS) and Raman spectroscopy), it was suggested that the interaction of Au with TiO2 causes an increase in the charge separation between the photo-excited electron/hole pairs, leading to an enhanced photocatalytic activity (to acetone over Au/TiO2 and to CO2 over Au/TiO2-CeO2), whereas the presence of ceria, acting as a hole trap, positively mainly affects the formation of hydrogen by water splitting.

Photocatalytic oxidation of 2-propanol under visible light irradiation on TiO2 thin films prepared by an RF magnetron sputtering deposition method

Visible light-responsive TiO2 (Vis-TiO2) thin films able to absorb UV and visible light in wavelength regions of 250-600 nm were successfully developed by applying a radio-frequency magnetron sputtering deposition method. These Vis- TiO2 thin films exhibited high activity for the photocatalytic oxidation of 2-propanol diluted in water even under visible light irradiation (k C 450 nm). The photocata- lytic activity of Vis-TiO2 thin films was dramatically enhanced by the deposition of Pt particles on the surface. Secondary ion mass spectrometry measurements revealed that Pt particles are distributed from the top surface to the deep bulk of Vis- TiO2 thin films with a columnar structure. The unique columnar structure of Vis- TiO2 thin films plays an important role in the high photocatalytic performance.

Influence of the Ti content on the photocatalytic oxidation of 2-propanol and CO on TiSiBEA zeolites

TixSiBEA (x = 1.5, 3.2 and 5.8 Ti wt.%) zeolites were prepared by a two-step postsynthesis method reported earlier (Chem. Commun. 1998, 87). Diffuse reflectance (DR) UV–vis and photoluminescence data suggest that mainly isolated tetrahedral framework Ti ions are present in Ti1.5SiBEA and Ti3.2SiBEA zeolites. These ions which in their excited triplet state easily interact with CO molecules as shown by photoluminescence data, are believed to be the active sites of the photocatalytic liquid phase oxidation of 2-propanol by dissolved oxygen and of photocatalytic gas phase oxidation of CO by N2O as suggested by catalytic measurements.

Photocatalytic treatment of indoor air: Optimization of 2-propanol removal using a response surface methodology (RSM)

This paper presents an experimental design methodology for the optimization of the photocatalytic removal of 2-propanol also called isopropyl alcohol (IPA) at indoor air concentration level (ppbv). The response surface methodology (RSM) for the modelization and optimization of the photodegradation of 2-propanol in the presence of titanium dioxide was used. The effect of four different process parameters on the yield of 2-propanol mineralization was determined. Experiments were performed using an annular flow-through reactor with TiO2 as photocatalyst, 2-propanol as a volatile organic compound (VOC) model, under different ranges of relative humidity (RH: 0–60%), inlet concentration (100–700ppbv) and flow rate (100–500mLmin−1), TiO2 loading (5–20gm−2). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled with gas chromatography–mass spectrometry (ATD–GC–MS) whereas a gas chromatograph equipped with a pulsed discharge helium photoionization detector (GC–PDHID) was used for on-line measurements of CO and CO2 at ppbv level. RH was found as the principal parameter that affect significantly the mineralization and the formation of acetone, the principal reaction intermediate from the photocatalytic oxidation of 2-propanol. For example an immediate and total removal of 2-propanol at very low % of RH along with a high rate of mineralization without any by-products was found. Many strong interactions between the parameters were also found ([2-propanol]–flow rate, RH–[TiO2], [2-propanol]–RH). The model obtained (R2=0.9965) shows a satisfactory correlation between the values of experimental data and predicted values of 2-propanol mineralization (CO2).

Effect of dissolved oxygen and lanthanide ions in solution on TiO2 photocatalytic oxidation of 2-propanol

The photocatalytic degradation of 2-propanol in D2O solution under UV irradiation was investigated. The conversion yield from 2-propanol to acetone was studied by 1H-NMR measurements. The study was carried out to elucidate effects of O2 in the reaction medium and lanthanide ion modification on the TiO2 surface. Under aerobic conditions, acetone formation was clearly increased in comparison with anaerobic conditions. On the modification of TiO2 with lanthanide ion, the conversion yield decreased with the increase in the ionic radius. Yb3+ ion modification increased the acetone formation by approx. 5% in comparison with the unmodified case. Appreciably large effects of the counter ion in lanthanide salts were also observed. The role of OH˙ radical formation in the first step of photocatalysis was emphasized in the experimental results.

Effect of Irradiation Sources and Oxygen Concentration on the Photocatalytic Oxidation of 2-Propanol and Acetone Studied by in Situ FTIR

The photocatalytic oxidation (PCO) of 2-propanol and acetone was studied on TiO2 powder at high coverage (>2 monolayers) at various oxygen concentrations using in situ FTIR. Two UV irradiation sources, either a continuous-wave UV lamp or an excimer laser, were applied to investigate the effect of the UV source on the PCO. It was found that higher oxygen concentrations increased the PCO rate of 2-propanol and acetone. The excimer laser source accelerated the PCO rate of 2-propanol while decelerating that of acetone as compared to the continuous-wave source. This effect was found to be larger at higher oxygen concentrations. Factors such as multiphoton adsorption or a pulsed irradiation were excluded as possible explanations for the irradiation source effect. More likely, the laser source changes the reaction mechanism by introducing an abrupt temperature increase, and hence the thermal decomposition, that is, dehydration of 2-propanol to propene, is effectively initiated on the surface. The PCO of 2-propanol was found to proceed along two routes: one was through the chemisorbed species, 2-propoxide, to form CO2 directly; the other was through conversion of H-bonded 2-propanol to acetone, followed by thermal fragmentation of mesityl oxide (aldol condensation product of acetone) to form formate species, and finally to CO2. It was also found that the acetone decay rate during acetone PCO was much faster than that of acetone formed as an intermediate during 2-propanol PCO at the same oxygen concentration. This was likely due to the presence of other species competing for reaction sites on the catalyst surface.

Photocatalytic Oxidation of 2-Propanol on TiO2 Powder and TiO2 Monolayer Catalysts Studied by Solid-State NMR

The adsorption and photocatalytic oxidation of 2-propanol was studied by solid-state NMR spectroscopy over TiO2 powder and a TiO2 monolayer catalyst anchored on porous Vycor glass (TiO2 /PVG). Two adsorbed 2-propanol species were identified on the TiO2 powder, a hydrogen-bonded species and a 2-propoxide species, whereas only the H-bonded 2-propanol species was observed on TiO2/PVG. The photooxidation of 2-propanol proceeded along two parallel routes. The first occurred through the formation of acetone from the H-bonded 2-propanol species and was followed by the aldol condensation of acetone to form mesityl oxide. The subsequent photooxidation of mesityl oxide progressed slowly. Under dark conditions, mesityl oxide and its fragmentation products, acetaldehyde and isobutylene, were found to be in thermal equilibrium. The second route occurred through the relatively rapid and complete oxidation of 2-propoxide to CO2. In addition, the mobility of H-bonded 2-propanol was found to be important in the photooxida...