Removal Of Acetaldehyde Research Articles

Influence of humidity on the photo-catalytic degradation of acetaldehyde over TiO2 surface under UV light irradiation

We have studied the influence of water vapors on the activity of the photo-catalytic oxidation of acetaldehyde on the surface of TiO2 film under UV light (365nm) irradiation. Photo-catalysis experiments were performed at atmospheric conditions under various humidity levels (0, 16.8, and 33.6 relative humidity%) using a high vacuum chamber equipped with online gas-chromatography as a batch-type reactor. Acetaldehyde and H2O molecules competitively adsorbed on the surface of TiO2 film and the increase in the humidity decreased both the acetaldehyde removal and CO2 evolution rates. The rate of CO2 evolution was even more influenced by the humidity level of the gas mixture compared to the acetaldehyde removal rate, particularly over the certain level of relative humidity. We evidenced that the total oxidation of acetaldehyde was majorly mediated by oxygen molecules rather than H2O vapor under our experimental conditions. It is suggested that photo-catalytic total oxidation of acetaldehyde was promoted by the presence of large active sites ensemble near the adsorbed acetaldehyde, which were available to oxygen. Increase of humidity level disturbed this large ensemble, resulting in the reduction of photo-catalytic degradation rate of acetaldehyde under UV light irradiation.

Improved Photocatalytic Air Cleaner with Decomposition of Aldehyde and Aerosol-Associated Influenza Virus Infectivity in Indoor Air

ABSTRACTAir pollution caused by fine particulate matter (PM2.5), volatile organic compounds, and bioaerosols is a major environmental risk to health. We developed a photocatalytic air cleaner for reducing the pollution levels of indoor air; we improved the photocatalytic system by using UV-LED for the removal of acetaldehyde and PM2.5 and by reducing the weight and size of the system. The efficiency of photocatalysis depends on the surface area and materials. Therefore, we prepared a nanosized titanium dioxide (TiO2)-coated aluminum plate irradiated by UV-LED lamps (wavelength: 375 nm) as a photocatalytic air cleaner. Passing air continuously through a TiO2-coated aluminum plate (5 × 10 × 1 cm) under black light for 200 min decomposed 90% of 5 ppm acetaldehyde (12.4 µmol h–1) and generated two carbon dioxide molecules (25.43 µmol h–1) at a molar ratio of 1:2, indicating complete decomposition of acetaldehyde with high efficiency. This photocatalytic air cleaner was applied to the decomposition of acetaldehyde and inactivation and removal of aerosol-associated influenza virus. Acetaldehyde (20 ppm) in a 1-m3 cubic space was eliminated in 60 min at a half-life of 8 min. The aerosol-associated infectivity and the RNA genome of influenza virus A/PR/8/1934 (H1N1) produced by a nebulizer in a 779-L cubic space were eliminated within 7 min; however, they were detectable for up to 28 minutes when the functional photocatalytic air cleaner was not used. The presence of intermediate breakdown products of influenza virus indicated that the virus was broken down by photocatalysis. Thus, the photocatalytic air cleaner efficiently decomposed and eliminated organic chemicals, acetaldehyde, and aerosol-associated influenza virus infectivity and viral RNA, indicating that it can clean and detoxify the indoor air in a closed space for maintaining a safer environment.

An efficient photo-catalytic VOC removal process by one-pot synthesized N-F/TiO2 nanoparticles in fluidized-spouted bed reactor

ABSTRACTPhotocatalytic degradation under visible light irradiation is an important task of using solar energy for the removal of environmental pollutants. N-F/TiO2 nanoparticles were synthesized in one-pot sol–gel condition using tetra-isopropyl-orthotitanate as the TiO2 precursor and NH4F as the N-F doping source. Diffuse reflectance spectroscopy (DRS) analysis of the material has shown a reduction of band gap energy and shifting absorption edge to the visible wavelengths. A fluidized-spouted bed reactor equipped with the light source was designed and constructed for the oxidation process of VOC from the high airflow rate under Hg lamp irradiation using synthesized N-F/TiO2 nanoparticles. Acetaldehyde was used as the air pollutant model molecule of VOC in this process. The effluent acetaldehyde concentration was analyzed continuously along the time by an online Gas Chromatography (GC) from the start up to reaching steady conditions. The results have revealed significant enhancement of acetaldehyde removal by the N-F/TiO2 sample fabricated with an equal weight ratio of NH4F/Ti. After steady conditions, almost 100% removal of acetaldehyde was observed in the spouted bed reactor from a high airflow stream of 5 L/min polluted with 1000 ppm acetaldehyde at room-temperature conditions, under 80 W Hg with 500 Lux intensity.

Synthesis and Characterisation of Porous Titania-Silica Composite Aerogel for NO(x) and Acetaldehyde Removal.

In this study, the synthesis of porous titania-silica (TiO2-SiO2) composite aerogel at ambient pressure by using non-hazardous chemicals as a source of silica was investigated. TiO2-SiO2 composite aerogels were characterised and their photocatalytic performances were investigated for the removal efficiency of acetaldehyde and NO(x) under UV light. Results showed that porous composite aerogel with aggregated morphology, high surface area and an increased mesoporosity were formed. TiO2-SiO2(1.8) composite, with high Ti/Si ratio, showed the best results in terms of photocatalytic removal of acetaldehyde and nitrogen oxide.

Formation of TiO2/Mica Composite for Photocatalysis

The design results of the composites TiO2/mica photocatalytic active sheet are presented. For producing of initial powders elements of sol-gel and freeze-drying were used. The tape casting of TiO2/mica water slurry with using of doctor blade apparatus were used for forming of sheets. The phase composition, the specific surface area, the porous distribution and morphology of the produced powders and materials were investigated. It is established that the resulting TiO2 pillared mica sheet possesses good photocatalytic properties determined by gaseous acetaldehyde removal measurement.

Removal of acetaldehyde gas using wet scrubber coupled with photo-Fenton reaction

The feasibility of the combined air-cleaning method, which consisted of a wet scrubber and the photo-Fenton reaction, in the removal of gaseous acetaldehyde was evaluated. An acetaldehyde-gas removal efficiency of 99% was achieved in the one-pass test (residence time of 17 s) using an inlet acetaldehyde-gas concentration of 1000 ppb at an initial total-iron-ion concentration of 50 mg L−1 and initial hydrogen peroxide concentration of 630 mg L−1. Even at the low initial total-iron-ion concentration of 4 mg L−1, a removal efficiency of 92% was achieved. The acetaldehyde removal efficiency was relatively independent of the initial hydrogen peroxide concentration. UV irradiation further augmented the rate of the photo-Fenton reaction leading to enhanced acetaldehyde-gas removal.

Adsorption and Photocatalytic Kinetics of Visible-Light Response N-Doped TiO2Nanocatalyst for Indoor Acetaldehyde Removal under Dark and Light Conditions

Understanding the removal nature of the indoor volatile organic compounds under realistic environment conditions would give clear guidance for the development of air purification devices. The study investigated the removal of indoor acetaldehyde using visible-light-responsive N-doped TiO2(N-TiO2) photocatalyst under visible-light irradiation (light) and in the absence of light (dark). The adsorption kinetics of acetaldehyde onto N-TiO2followed a pseudo-second-order model. The magnitude of acetaldehyde adsorption is proportional to temperature, and the results were fitted to the Langmuir isotherm model. Moreover, the effect of initial acetaldehyde concentration and visible-light intensity on the photooxidation of acetaldehyde was well described by the Langmuir-Hinshelwood model. Results show that the mesoporous N-TiO2catalyst had a high ability to absorb acetaldehyde in the dark condition, and then acetaldehyde was subsequently photooxidized under visible-light irradiation. The adsorption capacity was found to increase with decreasing temperature. The negative value ofΔG° and the positive value ofΔS° indicate that the adsorption of acetaldehyde onto N-TiO2was a spontaneous process. Finally, a reaction scheme for removal process of indoor acetaldehyde by N-TiO2was proposed.

Development of a novel dual-stage method for metaldehyde removal from water

A dual-stage method was developed to first efficaciously degrade metaldehyde into acetaldehyde, before subsequent removal of acetaldehyde using an amine functionalized ion-exchange resin. A range of Macronets, with different surface areas, pore volumes, pore size distributions and extents of functionalization were evaluated for the depolymerisation of metaldehyde. Nuclear magnetic resonance spectroscopy was used to confirm the compete degradation of metaldehyde by the selected Macronets. Kinetic studies showed that the rates of catalytic degradation were primarily determined by the porous structure of the materials rather than the extent of surface functionalization, since high levels of acid surface groups were observed to decrease the porosity significantly. The rate constants obtained show excellent correlation with non-micro pore volumes, which are of import as the only pores that are accessible to hydrogen bonded metaldehyde molecules; Macronet MN502 exhibits the largest non-micro pore volume and, hence, demonstrated the best kinetic performance. The effect of competing ions on catalytic performance was also studied and the results demonstrate that competing ions compromise the performance of the proposed system to some extent, however, it is notable that a good level of performance is maintained even for competing ion concentrations as high as 100 times that of metaldehyde. Isothermal studies of acetaldehyde onto ion-exchange resin A830, including kinetic evaluation, showed that acetaldehyde could be chemically adsorbed by the resin. Consequently, a dual-column system was proposed, which was determined to effectively degrade metaldehyde (MN502) and remove the resulting by-product, acetaldehyde, via a second fixed bed adsorber (A830); this method could easily be adapted to existing facilities in water treatment works, making it very cost-effective and of great practical interest.

Rapid removal and decomposition of gaseous acetaldehyde by the thermo- and photo-catalysis of gold nanoparticle-loaded anatase titanium(IV) oxide

Gold nanoparticles (NPs) with a mean particle size ranging from 2.1 to 7.4nm were loaded on anatase TiO2 particles (Au/TiO2) by the heating temperature-varied deposition precipitation technique. This study has shown that Au/TiO2 with Au particle size <3nm and TiO2 surface area >50m2g−1 can be a promising environmental catalyst for the rapid removal and decomposition of gaseous acetaldehyde in a closed space. The Au loading on TiO2 causes a drastic enhancement of the acetaldehyde adsorption in the dark, and the adsorption amount increases as the Au particle size decreases. This result originates from the thermocatalytic activity of Au/TiO2 for the oxidation of acetaldehyde to acetic acid under ambient conditions. The resulting acetic acid spontaneously moves to the TiO2 surface due to the great adsorptivity for the carboxyl group. Consequently, the acetaldehyde adsorption amount strongly depends on the TiO2 surface area in addition to the Au particle size. UV-light irradiation of acetaldehyde (or acetate)-adsorbed Au/TiO2 leads to the complete decomposition to carbon dioxide by the high photocatalytic activity of anatase TiO2.

Rapid removal and subsequent low-temperature mineralization of gaseous acetaldehyde by the dual thermocatalysis of gold nanoparticle-loaded titanium(IV) oxide

Under ambient humid conditions, the adsorption of acetaldehyde on unmodified TiO2 is small and weak. In contrast, loading Au particles smaller than 3nm on TiO2 with surface area larger than 17.5m2g−1 (Au/TiO2) causes the rapid and strong adsorption of gaseous acetaldehyde from a closed space. This striking adsorption phenomenon initiates from the aerobic oxidation of acetaldehyde to acetic acid by the thermocatalysis of Au/TiO2 at room temperature. Acetic acid is moved to the TiO2 surface to be dissociated to acetate ion and proton, which are adsorbed on the Lewis acid and base sites on the surface, respectively. The resulting reproduction of the catalytic sites for the acetaldehyde oxidation enables the continuous removal of acetaldehyde without the release of the harmful product. Further, the adsorbed species on Au/TiO2 are completely oxidized to CO2 by the post-heating at 548K, whereas the oxidation degree of acetate adsorbed on unmodified TiO2 remains several % even at 570K with harmful products (Quah et al., 2010).

Cyanohydrin reactions enhance glycolytic oscillations in yeast

Synchronous metabolic oscillations can be induced in yeast by addition of glucose and removal of extracellular acetaldehyde (ACAx). Compared to other means of ACAx removal, cyanide robustly induces oscillations, indicating additional cyanide reactions besides ACA to lactonitrile conversion. Here, 13C NMR is used to confirm our previous hypothesis, that cyanide directly affects glycolytic fluxes through reaction with carbonyl-containing compounds. Intracellularly, at least 3 cyanohydrins were identified. Extracellularly, all signals could be identified and lactonitrile was found to account for ~66% of total cyanide removal. Simulations of our updated computational model show that intracellular cyanide reactions increase the amplitude of oscillations and that cyanide addition lowers [ACA] instantaneously. We conclude that cyanide provides the following means of inducing global oscillations: a) by reducing [ACAx] relative to oscillation amplitude, b) by targeting multiple intracellular carbonyl compounds during fermentation, and c) by acting as a phase resetting stimulus.

Modified manganese oxide octahedral molecular sieves M′-OMS-2 (M′ = Co,Ce,Cu) as catalysts in post plasma-catalysis for acetaldehyde degradation

Metal ions-modified cryptomelane-type manganese oxide octahedral molecular sieves M′-OMS-2 (M′=Co,Ce,Cu) were synthesized and characterized by XRD, BET, EDS, ICP, TEM, XPS, FTIR, H2-TPR in this work. The obtained materials were supported on Al2O3 pellets and investigated for acetaldehyde degradation in a post plasma-catalysis system. The results showed that the introduction of M′-OMS-2/Al2O3 catalysts improved acetaldehyde removal efficiency and inhibited ozone formation of plasma significantly, while the intermediates such as acetic acid, amine and nitromethane were suppressed. Co-OMS-2/Al2O3 exhibited the best catalytic activity to combine with plasma among all the prepared catalysts. The excellent activity is ascribed to the redox property, oxygen vacancies, oxygen mobility and surface area of catalyst. It can be inferred that, ozone formed in plasma was catalytically dissociated into active oxygen species by metal ions in M′-OMS-2 catalysts and contributed to acetaldehyde oxidation and intermediates removal.

Activated carbon fibers modified by metal oxide as effective structured adsorbents for acetaldehyde

Novel efficient adsorbents for acetaldehyde removal from diluted gas streams (∼1300ppmv) have been developed. The adsorbents combine the properties of activated carbon fibers (ACF) and nanoparticles (NPs) of basic metal oxides (La2O3, CaO, MgO, ZnO, Al2O3). The adsorbents have been prepared by wetness impregnation of ACF using different precursors. The NPs are well dispersed and have average particle size below 2nm. The ACFs-based adsorbents have an open regular macrostructure with low resistance to gas-flow (low pressure drop) and allow fast adsorption without any diffusion resistance. The NPs deposition provides up to 10-fold increase of acetaldehyde amount adsorbed as compared to non-modified ACF. The adsorption capacity increased with the basicity of metal oxides attaining 20wt.% on La2O3/ACF. The materials are characterized by different techniques including temperature-programmed desorption (TPD) and high resolution scanning transmission electron microscopy (HRSTEM).

Optimized porous clay heterostructure for removal of acetaldehyde and toluene from indoor air

Adsorption is the most widely used technology for the removal of indoor volatile organic compounds (VOCs). However, existing adsorbent-based technologies are inadequate to meet the regulatory requirement, due to their limited adsorption capacity and efficiency, especially under high relative humidity (RH) conditions. In this study, a series of new porous clay heterostructure (PCH) adsorbents with various ratios of micropores to mesopores were synthesized, characterized and tested for the adsorption of acetaldehyde and toluene. Two of them, PCH25 and PCH50, exhibited markedly improved adsorption capability, especially for hydrophilic acetaldehyde. The improved adsorption was attributed to their large micropore areas and high micropore-to-mesopore volume ratios. The amount of acetaldehyde adsorbed onto PCH25 at equilibrium reached 62.7 mg·g−1, eight times as much as the amount adsorbed onto conventional activated carbon (AC). Even at a high RH of 80%, PCH25 removed seven and four times more of the acetaldehyde than AC and the unmodified raw PCHs did, respectively. This new PCH optimized for their high adsorption and resistance to humidity has promising applications as a cost-effective adsorbent for indoor air purification.

Are TiO2 nanotubes worth using in photocatalytic purification of air and water?

Titanium dioxide nanotubes (TNT) have mainly been used in dye sensitized solar cells, essentially because of a higher transport rate of electrons from the adsorbed photo-excited dye to the Ti electrode onto which TNT instead of TiO2 nanoparticles (TNP) are attached. The dimension ranges and the two main synthesis methods of TNT are briefly indicated here. Not surprisingly, the particular and regular texture of TNT was also expected to improve the photocatalytic efficacy for pollutant removal in air and water with respect to TNP. In this short review, the validity of this expectation is checked using the regrettably small number of literature comparisons between TNT and commercialized TNP referring to films of similar thickness and layers or slurries containing an equal TiO2 mass. Although the irradiated geometrical area differed for each study, it was identical for each comparison considered here. For the removal of toluene (methylbenzene) or acetaldehyde (ethanal) in air, the average ratio of the efficacy of TNT over that of TiO2 P25 was about 1.5, and for the removal of dyes in water, it was around 1. This lack of major improvement with TNT compared to TNP could partially be due to TNT texture disorders as seems to be suggested by the better average performance of anodic oxidation-prepared TNT. It could also come from the fact that the properties influencing the efficacy are more numerous, their interrelations more complex and their effects more important for pollutant removal than for dye sensitized solar cells and photoelectrocatalysis where the electron transport rate is the crucial parameter.

Acetaldehyde removal using an atmospheric non-thermal plasma combined with a packed bed: Role of the adsorption process

This work is an attempt in order to help towards understanding the influence of the adsorption process on the removal of a VOC (acetaldehyde, CH3CHO) using cyclic non thermal plasma (NTP) combined with a packed-bed of a catalyst support, α-Al2O3. In the first part, the results obtained by placing the saturated alumina pellets inside the plasma discharge zone are discussed, in terms of acetaldehyde removal, CO and CO2 production. In the second part, adsorption of CH3CHO, CO, CO2 and O3 was carried out, from single and multicomponent mixtures of the different compounds. The results showed that (i) the adsorption capacities followed the order CH3CHO ≫ CO2 > CO; (ii) O3 was decomposed on the alumina surface; (iii) CO oxidation occurred on the surface when O3 was present. In the third part, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to follow the alumina surface during acetaldehyde adsorption. DRIFTS measurements demonstrated that besides the bands of molecularly adsorbed acetaldehyde, several absorptions appeared on the spectra showing the intermediate surface transformation of acetaldehyde already at 300K. Finally, the relationship between the adsorption results and the NTP combined with a packed-bed process is discussed.

Removal of Volatile Organic Compounds (VOCs) at Room Temperature Using Dielectric Barrier Discharge and Plasma-Catalysis

Non-thermal plasma (NTP) was produced in a dielectric barrier discharge reactor for degradation of acetaldehyde and benzene, respectively. The effect of volatile organic compounds (VOCs) chemical structure on the reaction was investigated. In addition, acetaldehyde was removed in different background gas. The results showed that, no matter in nitrogen, air or oxygen, NTP technology always exhibited high acetaldehyde removal efficiency at ambient temperature. However, it also caused some toxicity by-product such as NOx and ozone. Meanwhile, some intermediates such as acetic acid, amine and nitromethane were formed and resulted in low carbon dioxide selectivity. To solve above problems, Co–OMS-2 catalysts were synthesized and combined with plasma. It was found that, the introduction of catalysts improved VOCs removal efficiency and inhibited by-product formation of plasma significantly. The plasma-catalysis system was operated in a recycling experiment to investigate its stability. The acetaldehyde removal efficiency can be kept at 100 % in the whole process. However, slight deactivation in ozone control was observed at the later stage of the experiment, which may be ascribed to deposition of VOCs on the catalysts surface and reduction of catalysts surface area.

Enhanced photocatalytic activity of titanium dioxide/allophane mixed powder by acid treatment

The TiO2/allophane mixed powders at various mixing ratios were acid-treated to obtain a highly active photocatalyst. It was found that amorphous silica surrounding TiO2 particles was formed after acid treatment by selective dissolution of alumina component in the allophane. The photocatalytic activity of the mixed powder, evaluated by the photocatalytic decomposition rate for gaseous acetaldehyde, was improved by the acid treatment when the mixing ratio of allophane was higher than 5mass% in spite of the decrease of specific surface area (SSA), while that of the pure-TiO2 powder was decreased maybe because of the increase of Ti3+ defects density on its surface. As for the pure-allophane powder, SSA and adsorption rate for acetaldehyde were decreased by acid treatment. In addition, it was found that the acid treatment of allophane was needed to be performed in the presence of TiO2 to obtain a highly active photocatalyst from the result of the comparative experiments using mixed powder of acid-treated TiO2 powder and acid-treated allophane powder. Based on these results, it was concluded that the silica-dispersed microstructure of the nanocomposite was suitable for the efficient removal of acetaldehyde.

Post plasma-catalysis for VOCs degradation over different phase structure MnO2 catalysts

MnO2 catalysts with different phase structure were supported on Al2O3 pellets and applied in a post plasma-catalysis system for volatile organic compounds (VOCs) degradation. The introduction of MnO2/Al2O3 catalysts improved the acetaldehyde removal efficiency and the carbon dioxide selectivity significantly, while the formation of ozone and NOx in plasma was inhibited. Among different phase structure MnO2 catalysts, α-MnO2 was superior to β-MnO2 and γ-MnO2 with respect to the degradation efficiency, the carbon dioxide selectivity and ozone suppression. The excellent activity may be ascribed to OH groups, VOCs adsorption capacity and mobility of oxygen. Compared with acetaldehyde, the degradation of benzene by plasma-catalysis had lower removal efficiency, less production of NOx and more residual ozone. On the other hand, amine and nitromethane were observed by on-line fast FTIR in the acetaldehyde degradation by plasma. It is speculated that some nitrogen-containing intermediates are oxidized into NOx, while acetaldehyde also contributes its oxygen to the formation of NOx in non-thermal plasma.

Effect of oxygen on the conversion of acetaldehyde in homogeneous plasmas of N2/O2/CH3CHO mixtures

A photo-triggered discharge producing a homogeneous plasma was used to investigate, experimentally and with the help of a self-consistent 0D model, the decomposition processes of acetaldehyde (concentration up to 0.5%) in N2/O2/CH3CHO mixtures containing up to 20% oxygen, at a total pressure of 460 mbar. This work follows a previous one about N2/CH3CHO, having provided the necessary data about the quenching of the N2 metastable states by the acetaldehyde molecule. For the condition of the experiment, it was shown that oxygen has a weak influence on the acetaldehyde removal. Nevertheless, the kinetic reactions involved drastically change when the oxygen percentage is increased. Quenching reactions gradually give way to oxidation reactions by O(3P) and OH. Oxidation by OH dominates for a high acetaldehyde concentration or a high oxygen percentage. Moreover, CH3 is an important primary compound for the formation of CH4 and C2H6. Ethane is less populated than methane in the whole range of oxygen percentage values studied, and there are still hydrocarbon molecules in the gas mixture at 20% oxygen. This is well explained by the adopted kinetic scheme.