Degradation Of HCHO Research Articles

Valence state heterojunction Mn3O4/MnCO3: Photo and thermal synergistic catalyst

The valence state Mn3O4/MnCO3 heterojunctions were synthesized using a facile, wet chemical oxidation method during hydrothermal process. Their crystal structures, morphologies and optical properties were systematically investigated. The obtained Mn3O4/MnCO3 exhibited photo and thermal synergistic catalysis which have been estimated via degradation of methylene blue (MB) and HCHO under visible light (λ>420nm) irradiation at different temperature (20°C, 60°C and 80°C). Mn3O4 and MnCO3 possessed matching band potentials that could prevent the recombination rate of photogenerated electrons and holes in the reaction, which proved by the PL intensity of the samples, resulting in a great enhancement on their catalytic efficiency. Catalytic activity of Mn3O4/MnCO3 under photo and thermal effect was not the simple summation of photocatalysis and thermocatalysis, but a synergistic effect was existed in Mn3O4/MnCO3 composites which possessed much lattice oxygen to capture the holes leading to efficiently oxidizing reaction at high temperature. A possible mechanism was proposed based on valence state heterojunction to illustrate the synergistic effect between photo and thermal catalysis on degradation of organic pollutions.

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.

Photocatalytic Decomposition of Formaldehyde by Combination of Ozone and AC Network with UV365nm, UV254nm and UV254+185nm

Formaldehyde (HCHO) is one of the most common indoor pollutants. Long time exposure to the environment with HCHO concentration above 0.1mg/m3 can cause harm to human body. In order to remove HCHO efficiently, The TiO2/AC network film was prepared by loading nanometer particle TiO2 on the surface of activated carbon. The photocatalytic degradation of gaseous HCHO was performed by TiO2/AC network film under the irradiation of UV365nm, UV254nm and UV254+185nm, respectively. The results show that the adsorption of AC network and byproduct ozone (O3) oxidation simultaneously can promote the degradation of the HCHO; under the illumination of UV254+185nm, HCHO can be degraded more effectively. The produced ozone can also be degraded below 0.214mg/m3 that are required by Chinese indoor air quality standard.

Solar Photocatalytic Degradation of Typical Indoor Air Pollutants Using TiO2Thin Film Codoped with Iron(III) and Nitrogen

A type of iron and nitrogen codoped titania thin film was prepared by sol-gel method to degrade three typical indoor air pollutants: formaldehyde (HCHO), ammonia (NH3), and benzene (C6H6) under solar light. X-ray diffraction (XRD), UV-Vis spectroscopy, and energy dispersive spectra (EDS) were employed to characterize the photocatalysts. The results showed that the Fe/N codoped TiO2had a stronger absorption in the visible region than pure, Fe-doped, and N-doped TiO2and exhibited excellent photocatalytic ability for the degradation of indoor HCHO, NH3, and C6H6. When the three pollutants existed in indoor air at the same time, the removal percentages of HCHO, NH3, or C6H6after 6 h photocatalytic reaction under solar light reached 48.8%, 50.6%, and 32.0%. The degradation reaction of the three pollutants followed the pseudo-first-order kinetics with the reaction rate constants in the order of 0.110 h−1for ammonia, 0.109 h−1for formaldehyde, and 0.060 h−1for benzene. The reaction rate constant decreased with the increase of initial reactant concentration, which reflected that there was oxidation competition between the substrate and its intermediate during the photocatalytic process.

Catalytic oxidation of formaldehyde in water by calcium phosphate-based Pt composites

Catalytic degradation of HCHO begins with the dissolution of O2gas from atmosphere into an HCHO solution. O2and HCHO in a solution are then adsorbed onto active sites of PtNPs catalyst, and the complete oxidation happens to generate CO2and H2O.

Theoretical investigation on the role of mineral dust aerosol in atmospheric reaction: A case of the heterogeneous reaction of formaldehyde with NO2 onto SiO2 dust surface

The role of mineral dusts on the heterogeneous reaction of formaldehyde with NO2 was investigated using a quantum chemical approach. SiO2 was selected as a model of mineral dust to investigate the heterogeneous reaction mechanism and kinetics because the mineral dust is comprised of ∼60% of SiO2. Compared with NO2, formaldehyde was easily adsorbed onto SiO2 model, indicating SiO2 was a sink for formaldehyde. Further data showed that the presence of SiO2 reduced the reaction barrier, but did not change reaction mechanism. The kinetics calculation using the canonical variational transition state theory plus small curvature tunneling correction showed that the presence of SiO2 could accelerate the atmospheric reaction rate of formaldehyde with NO2 to produce HONO. The effect of the altitudes was also considered, and the heterogeneous reaction rate decreased with increasing the altitude due to the atmospheric temperature decrease, suggesting that the degradation of atmospheric HCHO onto available mineral dusts might be competitive with the corresponding homogeneous reaction, especially in dusty urban and desert environments. This work can lay the foundation on the atmospheric heterogeneous reaction of VOCs, probe the role of mineral dust and establish the atmospheric transformation models, to better understand pollution mechanism.

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).

Acrylonitrile-Vinylidene Chloride Copolymer Film with Activated Carbon and MnO2 for Formaldehyde Degradation

Abstract Acrylonitrile-vinylidene chloride (AN-VDC) copolymer films containing activated carbon, manganese dioxide nanoparticles were fabricated via casting method. The formaldehyde degradation capacity of copolymer film was investigated. The results showed that formaldehyde eliminating rate was obviously improved when copolymer film was blended with MnO2 or activated carbon, respectively. The HCHO removal rate increased with concentration of MnO2 or activated carbon. HCHO degradation rate of AN-VDC copolymer film without addition was 45 % for 48 h, while it was up to 90–95 % with the treatment time of 36 h after 3 wt.-% MnO2 or activated carbon addition. Furthermore, the complex effect of MnO2 and activated carbon on the degradation has also been studied. When 3 wt.-% MnO2 and 1 wt.-% activated carbon was mixed into copolymer, the HCHO removal rate was about 90 % for 36 h treatment. The results demonstrated that the formaldehyde eliminating rate was enhanced by complex addition of both MnO2 and activated carbon compared to films with single additions. The enhancement of HCHO eliminating efficiency occured due to a double effect of physical absorption of activated carbon and catalytic oxidation of MnO2.

Efficient photocatalytic degradation of gaseous formaldehyde by the TiO2/tourmaline composites

The TiO2 supported tourmaline composites were prepared by a sol–gel method and used as a photocatalyst for the degradation of formaldehyde (HCHO). The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption–desorption, Fourier transform infrared (FT-IR) spectroscopy and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The results indicate that the mixed-phase of anatase and rutile exists in the TiO2/tourmaline composites. The specific surface area of the TiO2/tourmaline composites is much higher than that of the pure TiO2. The TiO2/tourmaline composites exhibited excellent photocatalytic activity for the degradation of HCHO, which was 6 times higher than that of the pure TiO2. Moreover, the excellent photocatalytic activity of the composites was fully maintained after five photocatalytic cycles, which may be attributed to the physicochemical property of tourmaline and the mixed-phase of anatase and rutile in the TiO2/tourmaline composites.

Experimental study on visible-light induced photocatalytic oxidation of gaseous formaldehyde by polyester fiber supported photocatalysts

Heterogeneous photocatalytic oxidation (PCO) has shown large potentials in controlling airborne gaseous pollutants such as volatile organic compounds (VOCs). This article addresses PCO of gaseous formaldehyde (HCHO) by VIS-active photocatalysts which were immobilized on polyester fiber filter through a spray coating method under room temperature. The coatings showed good dispersion and strong adhesion on the fiber surface as supported by the SEM images and the stability test result. High PCO efficiency was achieved by the spray-coated filter under typical room light illumination. The effects from various reaction parameters, such as volumetric flow rate, pollutant initial concentration, relative humidity, illumination strength, as well as photocatalyst loading amount, on the PCO efficiency were also evaluated systematically. A Langmuir–Hinshelwood model was used to examine the kinetics of VIS-PCO of HCHO. One of the important findings was that changes of relative humidity had little influence on the PCO efficiency at either low or high HCHO concentrations. Different from the UV-PCO process where hydroxyl radical (OH) is the major oxidative species, the VIS-generated holes, hVIS+, as well as the superoxide radical (O2-) were considered to contribute predominantly to the degradation of HCHO under visible light illumination.

Degradation of selected indoor air pollutants: Comparison study of photocatalytic, ozone-assisted photocatalytic and amine adsorption processes

Indoor air pollutants impact human health, comfort and productivity. The method of photocatalysis has been applied mainly in flow reactors and little information is available on indoor air pollutant removal in airtight reactors. In the paper, experiments were carried out to remove formaldehyde (HCHO), ammonia (NH3) and volatile organic compounds (VOCs) in the airtight and ventilated chambers. Results demonstrated that 90.4% of HCHO, 92.3% of NH3 and 57.9% of VOCs were removed in the amine adsorption process, while 67.5% (hereinbefore, these are the mass fraction) of HCHO, 60.0% of NH3, and 61.2% of VOCs were removed in the photocatalytic process. However, ozone-assisted photocatalytic process showed great potential to degrade indoor air pollutants in the ventilated chamber. Factors and mechanisms of the photocatalytic degradation of HCHO, NH3 and VOCs were also discussed.

TiO2 nanoparticles with increased surface hydroxyl groups and their improved photocatalytic activity

TiO2 nanoparticles with improved photocatalytic activity (TiO2NPs-NaCl(R)) were synthesized through a well controlled sol–gel process in the presence of NaCl. Instead of being incorporated into the lattice of TiO2, the added sodium chloride can be completely removed from the resultant TiO2NPs-NaCl(R) by DI water. The results showed that TiO2NPs-NaCl(R) has 2 times more surface hydroxyl groups than that in TiO2NPs prepared without adding NaCl. Consequently TiO2NPs-NaCl(R) exhibits an enhanced photocatalytic activity for degradation of methylene blue (MB) and HCHO under UV irradiation. This research provides a simple and economic approach to improve photocatalytic performance of TiO2 related materials.

Photocatalytic Decompositions of Gaseous HCHO over Ag/TiO2 Nanotube Arrays

TiO2 nanotube arrays prepared by electrochemical anodization method attract considerable interest as a practical air purifier, as the nanotube arrays may form a TiO2 film with a porous surface and straight gas diffusion channel. Here, the TiO2 and Ag/TiO2 nanotube arrays with different Ag amount are used to degrade gaseous HCHO pollutants. The photocatalytic results confirm that the HCHO-degrading efficiency of the TiO2 nanotube arrays may vary with the amount of Ag nanoparticles, and the Ag amount within a certain range significantly improves the degradation rate of HCHO molecules. The main final product after HCHO degradation is detected to be CO2. Ag nanoparticles effectively act as electron trappers prohibiting the recombination of photo-excited electrons and holes, hence increasing the photocatalytic efficiency. However, excessive Ag nanoparticles form new recombination center of photo-excited electrons and holes to decrease the photocatalytic efficiency.

Kinetics and Reaction Pathways of Formaldehyde Degradation Using the UV‐Fenton Method

This study was based on the purpose of investigating the reaction rules of formaldehyde (HCHO) as an intermediate product in the degradation of many other organic wastewaters. The process conditions of UV-Fenton method for the degradation of the low concentrations of HCHO were studied in a batch photochemical reactor. The results showed that, when the original HCHO concentration was 30 mg/L, at an operating temperature of 23 degrees C, pH = 3, an H202 dosage of 68 mg/L, and an H2O2-to-Fe2+ mole ratio (H2O2:Fe2+) of 5, 91.89% of the HCHO was removed after 30 minutes. The degradation of HCHO in the UV-Fenton system was basically in accordance with the exponential decay. The kinetic study results showed that the reaction orders of HCHO, Fe2+, and H2O2 in the system were 1.054, 0.510, and 0.728, respectively, and the activation energy (Ea) was 9.85 kJ/mol. The comparison of UV/H2O2, Fenton, and UV-Fenton systems for the degradation of HCHO, and the results of iron catalyst tests showed that the mechanism of UV-Fenton on the degradation of HCHO was through a synergistic effect of Fe2+ and UV light to catalyze the decomposition of H2O2. The introduction of UV irradiation to the Fenton system largely increased the degradation rate of HCHO, mainly as a result of the accelerating effect on the formation of the Fe2+/Fe3+ cycle. The reaction products were analyzed by gas chromatography-mass spectrometry and a chemical oxygen demand (COD) analyzer. The effluent gases also were analyzed by gas chromatography. Based on those results, the reaction pathways of HCHO in the UV-Fenton system were proposed. The qualitative and quantitative analysis of the reaction products and the COD showed that the main intermediate product of the reaction was formic acid, and the further oxidation of it was the rate-limiting step for the degradation of HCHO.

Effects of peptizing conditions on nanometer properties and photocatalytic activity of TiO 2 hydrosols prepared by H 2TiO 3

TiO 2 hydrosols were prepared from metatitanic acid (H 2TiO 3) by chemical precipitation–peptization method under various peptizing conditions. The effects of peptizing conditions on nanosized properties and photocatalytic activity of TiO 2 hydrosols were investigated. The crystal structure, crystallinity, particle size distribution, and transparency ( T%) of as-obtained hydrosols were characterized by means of X-ray diffraction, transmission electron microscopy, light-scattering size analyzer, and UV–vis transmittance spectra. The results showed that the properties of hydrosols depended on peptizing conditions including a molar ratio of H +/Ti, temperature, and solid content. The photoactivity of TiO 2 hydrosols was evaluated in terms of the degradation of rhodamine B (RhB) in aqueous solution, and formaldehyde (HCHO) and methyl mercaptan (CH 3SH) in gaseous phase. The results showed that increase in H +/Ti ranging 0.19–0.75 led to the decrease in particle size and the increase in transparency. With increasing of temperature, particle sizes increased while the transparency and photoactivity decreased steadily when the temperature was higher than 65 °C. The particle size, transparency and photoactivity of the hydrosols hardly depended on solid content when it was not less than 2%. It should be confirmed that the hydrosols with higher crystallinity, smaller particle size and higher transparency could have the higher photoactivity for the degradation of RhB, CH 3SH, and HCHO. In this study, the optimal peptizing conditions were determined to be H +/Ti = 0.75, temperature = 65 °C and solid content = 2–6%.

Solid-State, Planar Photoelectrocatalytic Devices Using a Nanosized TiO2 Layer

Solid-state planar photoelectrocatalytic devices using a nanosized Ti02 layer have been fabricated and used in the photodegradation of gaseous formaldehyde (HCHO). It is discovered for the first time that in the photocatalytic degradation of HCHO over TiO2 film, besides a well-known process of exciton dissociation expressed as TiO2* --> e(-) + h+ (process A), there exists an HCHO-involved process of exciton dissociation expressed as TiO2 + HCHO* --> TiO2(-) + HCHO+ (process B); these two processes have comparable contributions to the electron photogeneration. A biased photocatalytic device is unable to photodegrade HCHO under the nitrogen condition, but under the air condition, a positive synergic effect of bias on the photodegradation of HCHO over the planar photoelectrocatalytic device has been observed, mainly attributed to it that the horizontal electric field can displace electrons generated via process B away from their counterparts, effectively suppressing hole-electron recombination on TiO2 surface and thereby leading to the enhanced formation of O2- species. The current research points out that the planar photoelectrocatalytic device can provide the in-depth investigations on the mechanisms of the photocatalytic degradation over nanosized semiconductor oxide films, and also have potential application in decomposing and mineralizing organic gas-phase pollutants.

Investigation of air–water exchange of formaldehyde using the water surface sampler: Flux enhancement due to chemical reaction

Laboratory ( n = 30 ) and field ( n = 89 ) experiments were conducted using the water surface sampler (WSS) to investigate the air–water exchange of formaldehyde (HCHO). Average gas-phase overall mass transfer coefficients ( K g) calculated using concurrently measured gas-phase fluxes and air concentrations were 0.58±0.21 and 0.25±0.12 cm s −1 for laboratory and field experiments, respectively. K g values were compared to the predictions of two different models, one previously developed based on experiments performed with the WSS (considering no enhancement, Model I) and, one previously published by others (accounting the enhancement due to chemical reaction, Model II). The predictions of Model I (0.17±0.07 cm s −1) significantly underestimated the laboratory determined K g while the predictions of Model II (0.58±0.17 cm s −1) were in excellent agreement with those measured. Under the laboratory conditions, the flux enhancement of HCHO mass transfer due to chemical reaction ranged between 2.8 and 4.1 times (average±SD, 3.6±0.4). For field studies, the average measured K g was significantly lower than the average predictions of Model I (0.44 cm s −1) and the Model II (0.90 cm s −1). It was shown that the difference between the modeled and experimental K g values was due to the propagated effect of interfering factors with the measured gas-phase flux (i.e., decreased deposition due to non-zero water concentration, sulfite/bisulfite interference, and losses due to chemical degradation or transformation). The results of this study indicated that the formaldehyde transfer into the surface waters is significantly enhanced due to chemical reaction and air–water exchange may be an important removal mechanism for atmospheric HCHO. The results also suggest that transformation and degradation of aqueous HCHO may be significant under field conditions.