Photodegradation Of Formaldehyde Research Articles

Low-Temperature Preparation and Characterization of Nanocrystalline Anatase TiO2

Nanoanatase TiO2 of high crystallinity was prepared by a novel simple route at a temperature of 100 °C under mild conditions. Tetrabutyl titanate was used as a titanium precursor, Acetic acid was used as an inhibitor, and diethyl ether anhydrous was used as a solvent. X-ray powder diffraction (XRD), laser Raman spectroscopy (Raman), BET surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and UV−vis diffuse reflectance spectra (DRS) were applied to characterize the crystallinity, morphology, surface structure, and other physicochemical properties of the nanoanatase TiO2. The photocatalytic activity of the prepared photocatalyst was evaluated by the photodegradation of formaldehyde in aqueous solution and compared with the commercial photocatalyst, namely, Degussa P-25. The result showed that the sample prepared at low temperature showed photocatalytic activity. The activity of the sample prepared at 120 °C was high and close to the sample calcined at ...

The enhancement of WO3-catalyzed photodegradation of organic substances utilizing the redox cycle of copper ions

WO3 is a visible-light-responsive photocatalyst and an n-type semiconductor photocatalyst, but its photocatalytic activity toward organic substances is low. We utilized several transition metal ions as redox mediators in attempts to improve the photoactivity of WO3, and a drastic improvement was observed only when Cu2+ ions were utilized for WO3-catalyzed photodegradation of organic substances. More specifically, the CO2 generation rates for the photodegradation of formaldehyde and methanol in the presence of Cu2+ ions were about 1000 and 150 times as high, respectively, as the rates in the absence of Cu2+ ions. We confirmed that Cu2+ was reduced to Cu+ through the transfer of a photoexcited electron from WO3 and that Cu+ was easily re-oxidized to Cu2+ by oxygen in air. This redox cycle could assist in the reduction of oxygen in the photocatalytic reaction, and the reaction was particularly efficient when Cu2+ was introduced to the system as a CuCl2 solution. Photodegradation was achieved with a WO3 photoelectrode in a two-compartment cell in which the Cu2+ solution was separated from wastewater containing organic substances by an ion-exchangeable membrane, simulating practical use. The anodic photocurrent generated by the photodegradation of organic substances was observed at the WO3 photoelectrode without applying any external bias.

Photodegradation of Formaldehyde over Doped TiO<sub>2</sub> Prepared by Hydrothermal Method under Visible Light Irradiation

Titania particles doped with nitrogen were sol-gel and hydrothermally synthesized in autoclave from TiOCl 2 and mesoporous titania with 0.5 %(in mole) Fe 3+ , Cu 2+ , V 5+ and Pd 2+ as dopants were also prepared based on the above synthesis method. Structure of the samples was characterized by XRD, TEM, BET specific surface area, BJH pore size distribution and UV-vis/DRS. The photocatalytic activity was investigated under visible light irradiation(λ≥410 nm) and formaldehyde was taken as test gas. It is found that the prepared samples are anatase titania with average grain size of about 10 nm and the BET specific surface area of about 130 m 2 /g. Band gap of the titania samples doped with Fe 3+ , Cu 2+ , V 5+ , Pd 2+ and TiO 2 /N is 2.99, 2.93, 2.36, 2.92, 2.87 eV, respectively. The photo-degradation rate constant of titania samples with 0.5 %(in mole) Fe 3+ , Cu 2+ , V 5+ , Pd 2+ doping and TiO 2 N is 0.0063, 0.0086, 0.0049, 0.0031 and 0.0033/min, respectively. Good dispersion of Cu dopant onto the surface of titania, adequate surface area of Cu-TiO 2 /N photocatalyst may contribute to its comparatively higher photocatalytic activity.

Preparation of anatase F doped TiO2 sol and its performance for photodegradation of formaldehyde

Anatase fluoride doped TiO2 sol (F-TiO2) catalyst was prepared by a modified sol-gel hydrothermal method, using tetra butyl titanate as a precursor. The influences of F doping, temperature of hydrothermal, values of medium pH on the morphology and crystallization were studied. The microstructure and morphology of sol sample were characterized by XRD, TEM, FTIR, UV–Vis–DRS, particle size distribution (PSD) and XPS. The results showed that F-TiO2 particles in sol were spherical and partly crystallized to anatase structure, and dispersed in the aqueous medium homogeneously and that the average particle size was ca. 10.5 nm calculated from XRD and TEM results. It was also found that the addition of fluorine could improve the crystallization and adsorption of particles significantly, the photocatalytic activity for decomposition of formaldehyde were enhanced remarkably with the doping of fluorine. Possible mechanism of anatase F-TiO2 formed under hydrothermal conditions was discussed.

Visible-light-driven NaTaO 3− xN x catalyst prepared by a hydrothermal process

NaTaO 3− x N x catalyst has been successfully synthesized from N-doped Ta 2O 5 precursors by a simple hydrothermal process. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. Density functional theory calculations suggested that the valence band of the catalysts was composed of the hybrid O 2p and N 2p orbitals, and the visible-light sensitivity is due to the narrowing of the band gap by mixing N 2p and O 2p states. NaTaO 3− x N x catalyst could decompose the gaseous formaldehyde under the visible-light irradiation ( λ > 400 nm), and its photocatalytic activity depended on N dopant concentration. NaTaO 2.943N 0.047 showed the highest photoactivity for the formaldehyde photodegradation.

Photodegradation of formaldehyde by photocatalyst TiO2: effects on the presences of NO, SO2 and VOCs

Formaldehyde is a common indoor air pollutant and its removal by photocatalysis is investigated. Similar to other pollutants, however, formaldehyde is not the only pollutant which exists in the atmosphere but no study has yet reported the effects of the presence of other pollutants on the photodegradation of formaldehyde. In this study, common indoor air pollutants, namely nitrogen monoxide (NO), sulfur dioxide (SO2) and volatile organic compounds (VOCs) were selected to concurrently photodegradate with formaldehyde to identify their effects on formaldehyde. Formic acid was identified as the intermediate from the photodegradation of formaldehyde. The conversion of formaldehyde and the yield of formic acid decreased with increasing humidity levels. The presence of NO promoted the conversion of formaldehyde. The yield of formic acid was also higher under the presence of NO. Sulfate ion formed from the presence of SO2 inhibited the conversion of formaldehyde and the yield of formic acid. Similar inhibition effect is observed from the concurrent photodegradation of VOCs and formaldehyde. Intermediates generated from the photodegradation of VOCs inhibited the conversion of formaldehyde.

Structure and photocatalytic performances of glass/SnO 2/TiO 2 interface composite film

Glass/SnO 2/TiO 2, one interfacial composite semiconductor film with high photocatalytic activity, was prepared by depositing anatase TiO 2 film on rutile SnO 2 film. AES depth profile analyses of the film photocatalyst testified the bilayer structure of the sample. The glass/SnO 2/TiO 2 film with appropriate thickness of TiO 2 layer showed much higher photocatalytic activity in the case of formaldehyde photodegradation compared with glass/TiO 2 film. The results could be explained by efficient interfacial charge separation via the process of electron transfer from TiO 2 to SnO 2. However, when the thickness of TiO 2 layer was beyond some certain value, the photocatalytic activity of glass/SnO 2/TiO 2 film was nearly as same as glass/TiO 2 film. The reverse glass/TiO 2/SnO 2 composite film did not show higher photocatalytic activity than glass/TiO 2 film. This emphasized that the proper sequence for depositing individual semiconductor layer on glass substrate was important. A schematic mechanism of charge transfer was presented.

Photolytic demethylation of monuron and demethylmonuron in aqueous solution

AbstractPhotochemical demethylation of monuron [3‐(4‐chlorophenyl)‐1, 1‐dimethylurea] and of demethylmonuron [ 1‐(4‐chlorophenyl)‐3‐methylurea] in aqueous solution was investigated. The photoproducts identified in this study were formaldehyde, formic acid and carbon dioxide. These products indicate that demethylation occurs either by oxidation of a methyl group to hydroxymethyl which is readily cleaved to yield formaldehyde, or by further oxidation to an N‐formyl group, which is slowly hydrolysed under weakly acidic conditions to yield formic acid. Samples equilibrated either with air or oxygen (> 99 % purity) gave essentially the same yield of oxidation products. Experimental evidence indicated that extensive photodegradation of formaldehyde was occurring during photolysis, causing low recoveries of formaldehyde. Consequently, with [2H3‐methyl]demethylmonuron and deuterated water, only steady state concentrations of formaldehyde could be measured in an isotopic study.