Photodegradation Of Formaldehyde Research Articles

Novel Nanoarchitechtonics Olive-Like Pd/BiVO₄ for the Degradation of Gaseous Formaldehyde Under Visible Light Irradiation.

In this research, olive-like Pd/BiVO₄ was successfully prepared through a facile hydrothermal coreduction method for the photocatalytic degradation of formaldehyde under visible light irradiation. The structure, composition, and optical properties of the as-prepared Pd/BiVO₄ were characterized through X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectrophotometry, X-ray photoelectron spectroscopy, and photoluminescence. In addition, the photocatalytic activities of Pd/BiVO₄ were evaluated through the photodegradation of formaldehyde. The experimental results demonstrated that the degradation efficiency of formaldehyde increased with increasing irradiation time. Moreover, 1.0 wt% Pd/BiVO₄ exhibited the highest photocatalytic performance for formaldehyde degradation in 180 min, with the formaldehyde degradation rate as high as 87.5%.

Synthesis of immobilised Ni-doped TiO2 nanoparticles through hydrothermal route and their efficiency evaluation in photodegradation of formaldehyde

ABSTRACTThe aim of the present study was to synthesis Ni-doped TiO2 nanoparticles (NPs) in order to evaluate their effectiveness in photocatalytic degradation of formaldehyde in the aqueous phase. The Ni-doped TiO2 NPs were synthesised using a mild hydrothermal method. They were then immobilized on glass plates by the calcination method. Characterisation of Ni-doped TiO2 NPs was also carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The SEM images showed the uniform distribution of as-synthesised NPs on the surface of glass plates, with multidimensional crystalline structures. The results indicated that increasing the dopant weight ratio to 0.7% enhanced the photocatalytic degradation efficiency of formaldehyde; however, a further increase in the dopant weight ratio reduced the process efficacy. According to the results, increasing the initial pH from acidic and neutral to alkaline conditions decreased the efficacy of the process. Furthermore, the results showed that increasing the amount of nanocatalyst and decreasing the initial concentration of formaldehyde favoured the photocatalytic degradation of formaldehyde.

Visible Light Photodegradation of Formaldehyde over TiO2 Nanotubes Synthesized via Electrochemical Anodization of Titanium Foil.

In this study, a series of TiO2 nanotubes (NTs) were synthesized employing electrochemical anodization of titanium foil in an ionic liquid solution containing a mixture of glycerol and choline chloride, acting as electrolyte. The as-synthesized TiO2 NTs were calcined at 350, 450, or 550 °C for a 2 h duration to investigate the influence of calcination temperature on NTs formation, morphology, surface properties, crystallinity, and subsequent photocatalytic activity for visible light photodegradation of gaseous formaldehyde (HCHO). Results showed that the calcination temperature has a significant effect on the structure and coverage of TiO2 NTs on the surface. Freshly synthesized TiO2 NTs showed better-ordered structure compared to calcined samples. There was significant pore rupture with increasing calcination temperature. The transformation from anatase to rutile phase appeared after calcination at 450 °C and the weight fraction of the rutile phase increased from 19% to 36% upon increasing the calcination temperature to 550 °C. The band gaps of the TiO2 NTs were in the range from 2.80 to 2.74 eV, shifting the active region of the materials to visible light. The presence of mixed anatase–rutile TiO2 phases in the sample calcined at 450 °C showed enhanced photoactivity, which was confirmed by the 21.56 mg∙L−1∙g−1 removal of gaseous formaldehyde under 120 min of visible light irradiation and displayed enhanced quantum yield, ∅HCHO of 17%.

Effect of calcination time of a quadruple-element doped titania nanoparticles in the photodegradation of gaseous formaldehyde under blue light irradiation.

The photocatalytic degradation of gaseous formaldehyde using Ag/F/N/W-doped titanium dioxide was examined. The photocatalytic reaction was conducted using photocatalysts immobilized on glass tubular reactors illuminated under blue LED lights. Factors affecting gaseous formaldehyde degradation such as photocatalyst's calcination time and dosage, initial formaldehyde concentration, light intensity and operating temperature were studied. Results show that the photocatalytic degradation rate increases with pollutant concentration indicating no mass transfer limitations within the formaldehyde concentration range used. The photodegradation of the formaldehyde using catalyst calcined for 5h reached ∼88%. The photocatalyst concentration giving the highest degradation rate is found to be 0.10 gL-1. Which means that upon increasing the concentration of the immobilized photocatalysts will increase its thickness and it may not increase the number of the photo-induced particles. On the other hand, increasing light intensity and operating temperature increased the photocatalytic degradation of gaseous formaldehyde. The maximum light intensity and operating temperature were measured at 25 Wm-2 and 40°C, respectively. Langmuir-Hinshelwood kinetic type model was used to describe the photocatalytic reaction. The photocatalytic degradation behavior of gaseous formaldehyde on the modified photocatalyst follows a pseudo-first order rate equation based on a Langmuir-Hinshelwood kinetic type model.

Probing nanocolumnar silver nanoparticle/zinc oxide hierarchical assemblies with advanced surface plasmon resonance and their enhanced photocatalytic performance for formaldehyde removal

Recent advances in photocatalysis focus on the development of materials with hierarchical structure and on the surface plasmon resonance (SPR) phenomenon exhibited by metal nanoparticles (NPs). In this work, both are combined in a material where size‐controllable Ag‐NPs are uniformly loaded onto the hierarchical microporous and mesoporous and nanocolumnar structures of ZnO, resulting in Ag‐NP/ZnO nanocomposites. The embedded Ag‐NPs slightly decrease the hydrophobicity of fibrous ZnO, improve its wettability, and increase the absorption of formaldehyde (H2CO) onto the photocatalyst, all of this resulting in excellent photodegradation of formaldehyde in aqueous solution. Besides, we found that Ag‐NPs with optimal size not only accelerate the charge transfer to the surface of ZnO, but also strengthen the SPR effect in the intercolumnar channels of fibrous ZnO particles combining with high concentration of photo‐generated radical species. The micro‐to‐mesoporous ZnO is like a nanoarray packed Ag‐NPs. With Ag‐NPs of diameter 2.5 < ϕ < 6.5 nm, ZnO exhibits the most superior photodegradation rate constant value of 0.0239 min−1 with total formaldehyde removal of 97%. This work presents a new feasible approach involving highly sophisticated Ag‐NP/ZnO architecture combining the SPR effect and hierarchically ordered structures, which results in high photocatalytic activity for formaldehyde photodegradation.

The preparation and characterization of TiO2/r-GO/Ag nanocomposites and its photocatalytic activity in formaldehyde degradation

ABSTRACT A series of TiO2-rGO-Ag nanocomposites were prepared in this work via a facile one-pot hydrothermal method utilized for formaldehyde (HCHO) photodegradation; using TiO2, graphene oxide(GO) as well as AgNO3 as the raw materials, and sodium citrate as a reducing agent. Characterization by X-ray diffraction (XRD), Raman spectra, Transmission electron microscopy (TEM) and Field emission scanning electron microscopy (FESEM) demonstrated that GO and Ag+ were reduced during the formation of TiO2-rGO-Ag nanocomposites. X-ray photoelectron spectroscopy(XPS), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence spectra(PL) and Photocurrent spectrum measurement were applied to quantitatively characterize the bonding between TiO2 and rGO, the band gap energy of catalysts as well as electron–hole pairs recombination rate. The results revealed that the introduction of rGO sheets and Ag nanoparticles reduced the band gap energy of catalysts; it also suppressed the recombination of electron–hole pairs. However, C–O–Ti bond, which played a key role in photocatalysis, was reduced to some extent by the existence of Ag. Photodegradation results showed that, when the Ag loading was 9 mol% of TiO2, the reaction rate constant of formaldehyde (HCHO) removal improved distinctly, by about 22.3 times that of TiO2. The radical scavenger tests and electron paramagnetic resonance(EPR) analysis revealed that superoxide radical (·O2 −), hole (h+), and hydroxylradical (·OH) were reactive species of formaldehyde photodegradation.

Fabrication of Ag3PO4/TiO2 Composite and Its Photodegradation of Formaldehyde Under Solar Radiation

In order to improve the photocatalytic degradation performance of Ag3PO4 and reduce the cost of photocatalyst made of Ag3PO4, a kind of Ag3PO4/TiO2 composite was successfully fabricated via a simply precipitation method for the Ag3PO4 nanoparticles being loaded on the surface of commercial titanium dioxide (P25) to form a heterostructure. The Ag3PO4/TiO2 composite were characterized by FT-IR, XRD, XPS, FE-SEM, HR-TEM, DRS and PL and applied for the degradation of formaldehyde solution under solar radiation. The results showed that the degradation rat of Ag3PO4/TiO2 composite (0.01796 min−1) was much higher than that of pure Ag3PO4 (0.00775 min−1), indicating that the Ag3PO4/TiO2 composite possessed better photocatalytic degradation activity for the formaldehyde solution than pure Ag3PO4. The composite significantly decreased the dosage of silver for photocatalyst under solar radiation, thereby reduced the cost of the photocatalyst made from silver.

Ultrastable photodegradation of formaldehyde under fluorescent lamp irradiation by anti-reflection structure SnS2/TiO2 composite

In this work, mesoporous titanium dioxide sphere Mp-TiO2/SnS2 composites have been synthesized for the photodegradation of formaldehyde with fluorescent lamp. SnS2 nanosheets/nanoparticles were deposited on the surface of Mp-TiO2 sphere uniformly through an in-situ method. The morphology of SnS2 can be modulated through adjusting the Sn/Ti molar ratio. SnS2 nanosheet turned into nanoparticle when the Sn/Ti molar ratio changed from 0.05 and 0.10 to 0.15 and 0.20. The physical and chemical properties of as-prepared composite catalysts were thoroughly studied by X-ray diffraction (XRD), Raman, scanning electron microscope (SEM), Brunauer Emmett Teller (BET), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and UV–vis spectrophotometer. The photocatalytic performance of Mp-TiO2/SnS2 in the degradation of HCHO was assessed in a smog chamber with the irradiation of fluorescent light. A degradation efficiency of about 63% was achieved when the molar ratio of SnS2/TiO2 was 0.10. Through extending the light absorption range and hindering the recombination of photo-generated electron-hole pairs, the combination with SnS2 enabled the fabrication of hybrid photocatalysts with high photocatalytic activity and long-term stability.

Nanocrystalline TiO₂ Composite Films for the Photodegradation of Formaldehyde and Oxytetracycline under Visible Light Irradiation.

In order to effectively photodegradate organic pollutants, ZnO composite and Co-B codoped TiO2 films were successfully deposited on glass substrates via a modified sol-gel method and a controllable dip-coating technique. Combining with UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL) analyses, the multi-modification could not only extend the optical response of TiO2 to visible light region but also decrease the recombination rate of electron-hole pairs. XRD results revealed that the multi-modified TiO2 film had an anatase-brookite biphase heterostructure. FE-SEM results indicated that the multi-modified TiO2 film without cracks was composed of smaller round-like nanoparticles compared to pure TiO2. BET surface area results showed that the specific surface area of pure TiO2 and the multi-modified TiO2 sample was 47.8 and 115.8 m2/g, respectively. By degradation of formaldehyde and oxytetracycline, experimental results showed that the multi-modified TiO2 film had excellent photodegradation performance under visible light irradiation.

Photodegradation of formaldehyde by activated carbon loading TiO2 synthesized via microwave irradiation

A microwave-assisted synthetic method to form a series of AC/TiO2 for application as photocatalytic degradation of formaldehyde (HCHO) is presented. The influence of prepared conditions such as microwave power, microwave time, and the ratio of activated carbon and titanium dioxide sol (AC/TiO2-sel) on the degradation of HCHO was investigated. HCHO conversion of 58.68% was achieved by AC/TiO2 at microwave power of 700W for 15 min with AC/TiO2-sel ratio of 1: 2, which maintained multiple properties including high content of anatase and TiO2 largely distributed on AC without reunion, and possessed abundant functional groups for degradation. The influence of operation parameters on the degradation was also investigated: increasing dosage of catalyst and decreasing the initial concentration of HCHO could increase the conversion of HCHO. Acidic conditions can promote degradation effect. Stronger intensity of UV irradiating could improve efficiency of photocatalytic conversion of HCHO.

Modeling of Formaldehyde Photocatalytic Degradation in a Honeycomb Monolith Reactor Using Computational Fluid Dynamics

In this article, simulations were conducted on a pilot-scale honeycomb monolith reactor for the photodegradation of formaldehyde. The monoliths in the reactor were treated as porous media, and the local light intensity across the porous media was modeled by the discrete ordinates model with one adjustable parameter, namely, the absorption coefficient of the monolith channel wall. This absorption coefficient was estimated by a trial-and-error method based on the observed modeling results of light intensity in a single channel. Then, the formaldehyde degradation in a monolith reactor was simulated by the proposed model. The proposed model achieved a reasonable agreement between the simulation results and the published experimental data. Based on the modeling approach provided in this article, the effect of humidity on the photodegradation of formaldehyde was investigated. The data indicate that the reaction is first-order in the reactants for the intended applications such as purification of air in office b...

Visible-light-active ZnO via oxygen vacancy manipulation for efficient formaldehyde photodegradation

We developed a facile method for the synthesis of visible light responsive ZnO through the introduction of different concentrations of oxygen vacancy for efficient formaldehyde photodegradation under visible light irradiation. The visible light active ZnO was prepared using ZnO2 instead of traditional Zn(OH)2 as a precursor. According to the results of Raman and XPS, the concentrations of oxygen vacancy decreased with the increase of annealing temperatures. The effects of different concentrations of oxygen vacancy on the electronic structure of ZnO were investigated by density functional theory (DFT) simulation and the results were confirmed by UV–VIS spectra, which showed the oxygen vacancy narrowed the band gap of ZnO. ZnO with stable concentration of oxygen vacancy was used for formaldehyde photodegradation. The results of photocatalytic experiments reflected that oxygen vacancy can not only act as impurity levels in the band structure of ZnO but can also work as electron traps to accept the photogenerated electrons. The oxygen vacancy in ZnO effectively prohibited the recombination of electron–hole pairs, enhancing the photocatalytic activity of ZnO. The results of our study provide us useful information for the understanding of the mechanisms of the photocatalytic process of ZnO with oxygen vacancy.

Promotion effect of Pd on TiO2 for visible light photocatalytic degradation of gaseous formaldehyde.

TiO2 and Pd doped TiO2 (Pd/TiO2) nanoparticles were prepared by sol gel method. Pd/TiO2 material was characterized by XRD, TEM, TPR, XPS and BET. From XRD data, the crystalline type of TiO2 is known to as Anatase type. TiO2 and Pd/TiO2 were in the order of 9-10 nm and 10-13 nm respectively. The photocatalytic activities of the TiO2 and Pd/TiO2 nanomaterials were evaluated and compared for the photodegradation of formaldehyde (HCHO). HCHO degradation on Pd/TiO2 catalyst, at 60 min, the degradation rate of gaseous HCHO is 95%. Using Pd/TiO2, the rate was faster than TiO2 or doped with other metals (Au/TiO2; Ag/TiO2; Pt/TiO2).

TiO2 sol-gel for formaldehyde photodegradation using polymeric support: photocatalysis efficiency versus material stability

Photocatalysts supported on polymers are not frequently used in heterogeneous photocatalysis because of problems such as wettability and stability that affect photocatalysis conditions. In this work, we used polypropylene as support for TiO2 sol-gel to evaluate its stability and efficiency under UV radiation. We also tested the effect of the thermo-pressing PP/TiO2 system on the photocatalytic efficiency and stability under UV radiation. The films were characterized by scanning electron microscopy (SEM), UV-Vis spectroscopy and X-ray diffraction (XRD). The SEM micrographs showed that the films of TiO2 sol-gel onto PP has approximately 1.0-μm thick and regular surface and the generation of polypropylene nanowires on hot-pressed samples. XRD showed the formation of TiO2 anatase on the surface of the films made by dip-coating. All photocatalysts were tested in decontaminating air-containing gaseous formaldehyde (70 ppmv) presenting degradation of the target compound to the limit of detection. The photocatalysts showed no deactivation during the entire period tested (30 h), and its reuse after washing showed better photocatalytic performance than on first use. The photocatalyst showed the best results were tested for 360 h with no observed deactivation. Aging studies showed that the film of TiO2 causes different effects on the photostability of composites, with stabilizing effect when exposed to most energetic UVC radiation (λmax = 254 nm) and degradative effects when exposed to UVA radiation (λmax = 365 nm).

Study of Photocatalytic Activity and Properties of Transition Metal Ions Doped Nanocrystalline TiO2Prepared by Sol-Gel Method

Transition metal (Mn, Fe, Co,) doped TiO2nanoparticles were synthesized by the sol-gel method. All the prepared samples were calcined at different temperatures like 200°C to 800°C and characterized by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis. The studies revealed that transition metal (TM) doped nanoparticles have smaller crystalline size and higher surface area than pure TiO2. Dopant ions in the TiO2structure caused significant absorption shift into the visible region. The results of photodegradation of formaldehyde in aqueous medium under UV light showed that photocatalytic activity of TiO2nanoparticles was significantly enhanced by the presence of some transition metal ions. Chemical oxygen demand (COD) of formaldehyde solutions done at regular intervals gave a good idea about mineralization of formaldehyde.

Enhanced Photocatalytic Activity of Chemically Bonded TiO2/Graphene Composites Based on the Effective Interfacial Charge Transfer through the C–Ti Bond

Recently, graphene-based semiconductor photocatalysts have attracted more attention because of their enhanced photocatalytic activity caused by interfacial charge transfer (IFCT). However, the effect of a chemical bond is rarely involved for the IFCT. In this work, TiO2/graphene composites with a chemically bonded interface were prepared by a facile solvothermal method using tetrabutyl orthotitanate (TBOT) as the Ti source. The chemically bonded TiO2/graphene composites effectively enhanced their photocatalytic activity in photodegradation of formaldehyde in air, and the graphene content exhibited an obvious influence on the photocatalytic activity. The prepared composite with 2.5 wt % graphene (G2.5-TiO2) showed the highest photocatalytic activity, exceeding that of Degussa P25, as-prepared pure TiO2 nanoparticles, and the mechanically mixed TiO2/graphene (2.5 wt %) composite by a factor of 1.5, 2.6, and 2.3, respectively. The enhancement in the photocatalytic activity was attributed to the synergetic effect between graphene and TiO2 nanoparticles. Other than the graphene as an excellent electron acceptor and transporter, the enhanced photocatalytic activity was caused by IFCT through a C–Ti bond, which markedly decreased the recombination of electron–hole pairs and increased the number of holes participating in the photooxidation process, confirmed by XPS analysis, the gaseous phase transient photocurrent response, electrochemical impedance spectroscopy, and photoluminescence spectra. This work about effective IFCT through a chemically bonded interface can provide new insights for directing the design of new heterogeneous photocatalysts, which can be applied in environmental protection, water splitting, and photoelectrochemical conversion.

Photocatalytic Degradation of Formaldehyde by TiO<sub>2</sub> Nanoparticles Immobilized in Activated Carbon Fibers

Activated carbon fibers supported TiO2 nanoparticle photocatalyst was prepared by immersing activated carbon fibers in water suspended with TiO2 nanoparticles under sonication. X-ray diffraction and scanning electron microscopy were applied to characterize the crystallinity and morphology of the photocatalyst. The photocatalytic activity of the prepared photocatalyst was evaluated by the photodegradation of formaldehyde for indoor air purification. The result showed that the low-concentration formaldehyde in the polluted indoor air could be photocatalytically degraded over the prepared photocatalyst, with the formaldehyde concentration in the product air falling into the standard range that is specified by the Chinese Indoor Quality Standard.

High Photocatalytic Activity of Gd2O2S:Tb Modified Titanium Dioxide Films

<TEX>$Fe_2O_3,\;Ag_2O,\;CaWO_4$</TEX> and <TEX>$Gd_2O_2S$</TEX>:Tb loaded on titanium dioxide photocatalysts (P25, Degussa) were prepared by a calcination. Their composite films containing water-born polyurethane used as a material for immobilization were obtained by spray coating technique. The photocatalytic activity of the titanium dioxide films was characterized by decrease of UV-vis absorption spectra for methylene blue and gas chromatography for photocatalytic decomposition of formaldehyde diluted in water. It was shown that the <TEX>$Gd_2O_2S$</TEX>:Tb modified titanium dioxide films had good photocatalytic properties and followed the first-order kinetic model with regard to photocatalytic decoloration of methylene blue. Especially in formaldehyde photodegradation experiment, decrease rate of concentration of the titanium dioxide films with <TEX>$Gd_2O_2S$</TEX>:Tb modifying was about 35% larger than that of the unloaded titanium dioxide film.

Research on photodegradation of formaldehyde by nanocrystalline N-TiO2 powders under visible light irradiation

The photo-degradation of formaldehyde (HCHO) by nitrogen-doped nanocrystalline TiO2 (N-TiO2) powders under visible light irradiation has been systematically investigated. Experimental results show that the degradation ratio reached up to 42.6% after 2 h visible light irradiation when the amounts of N-TiO2 powders were 0.5 g, the initial concentration of the HCHO was set at 0.98 mg/m3, the illumination intensity was fixed at 10,000 lux, the ambient temperature was set at 26 °C, and the relative humidity was maintained at 33 ± 5%. Further research shows that the degradation ratios were all larger than 40% in ten repeated cycles of photodegradation of HCHO by N-TiO2 powders. The degradation ratio was as high as 82.9% after 2 h visible light irradiation when the amount of N-TiO2 was 5 g. The degradation ratio was increased from 25.5 to 59.6% when the illumination intensity of the visible light was increased from 0 to 30,000 lux. However, the degradation ratio could not be further increased by further increasing the illumination intensity.

Hydrothermal synthesis of (Fe, N) co-doped TiO2 powders and their photocatalytic properties under visible light irradiation

(Fe, N) co-doped titanium dioxide powders have been prepared by a quick, low-temperature hydrothermal method using TiOSO4, CO(NH2)2, Fe(NO3)3, and CN3H5 · HCl as starting materials. The synthesized powders were characterized by XRD, TEM, BET, XPS, and UV–Vis spectroscopy. Experimental results show that the as-synthesized TiO2 powders are present as the anatase phase and that the N and Fe ions have been doped into the TiO2 lattice. The specific surface area of the powders is 167.8 m2/g by the BET method and the mean grain size is about 11 nm, calculated by Scherrer’s formula. UV–Vis absorption spectra show that the edge of the photon absorption has been red-shifted up to 605 nm. The doped titanium dioxide powders had excellent photocatalytic activity during the process of photo-degradation of formaldehyde and some TVOC gases under visible light irradiation.