HCHO Removal Efficiency Research Articles

Electrothermal regeneration by Joule heat effect on carbon cloth based MnO2 catalyst for long-term formaldehyde removal

Carbon-based materials (e.g., activated carbon) have been widely used as contaminant removal media due to their unique adsorption properties. However, some of their other characteristics, such as electrothermal properties, have been greatly ignored in the field of environmental remediation. Herein, a kind of carbon cloth (CC)-supported MnO2 composite (MnO2-CC) was prepared and investigated for catalytic oxidation of gaseous formaldehyde (HCHO) under the assistance of electric power. The MnO2-CC composite exhibited unique Joule heat property and could efficiently convert electrical energy into heat energy. The surface temperature of MnO2-CC composite could be increased to as high as 138 °C within 20 s when 8 V input voltage was imposed. In addition, porous MnO2 nanosheets dispersed uniformly on the surface of CC surface, forming a kind of hierarchical core-shell structure. The close contacted interface could reduce energy loss during heat transfer. As a result, the used MnO2-CC composite could exhibit long-term HCHO removal efficiency by highly effective electrothermal regeneration. This work represents a convenient and fast approach that allows direct utilization of electric power to accelerate the complete mineralization of HCHO. The in-situ fast electric heating process along with the uniform dispersion of porous MnO2 on CC make the MnO2-CC fabric an excellent material for indoor HCHO abatement.

Effect of redox state of Ag on indoor formaldehyde degradation over Ag/TiO2 catalyst at room temperature

Ag/TiO2 catalysts were prepared via in-situ synthesis and impregnation methods. The effect of redox state of Ag species on catalytic activity of Ag/TiO2 catalysts was studied. The Ag-i-300 catalyst with partially oxidized state of Ag species shows superior catalytic activity, keeping HCHO removal efficiency at an extraordinary level of 100% during the 200 min's reaction. The Ag/TiO2 catalysts were characterized by XPS, UV–Vis, BET, XRD, TEM, and in-situ DRIFTS technologies. XPS and TEM results exhibit that the partially oxidized state of Agδ+ (0 < δ < 1) and high dispersion of Ag species are beneficial for the oxidation of HCHO over Ag/TiO2 catalysts. According to the above results, a reaction pathway for HCHO oxidation over Ag-i-300 catalyst was also proposed.

Effect of K+ ions on efficient room-temperature degradation of formaldehyde over MnO2 catalysts

δ-MnO2 was prepared via a facile in-situ redox reaction and used for catalytic oxidation of HCHO, a major indoor air pollutant. The washing treatment during catalyst preparation could impose great effect on content of K+ and catalytic activity. δ-MnO2 catalyst without washing treatment contains the highest content of K+ ion and exhibits the best catalytic activity among various δ-MnO2 samples. The HCHO removal efficiency keeps at 100% for first 600 min. The δ-MnO2 samples were characterized by advanced technologies including XRD, Raman, XPS, TPR, TPD and in-situ DRIFTS. The XPS results indicates that K+ ions increases the AOS value of Mn and the ratio of surface-adsorbed oxygen over δ-MnO2. The content of K+ ions improves the amount and redox ability of surface mobile oxygen species, enhancing catalytic oxidation of HCHO.

Promotional removal of HCHO from simulated flue gas over Mn-Fe oxides modified activated coke

A series of MnxFey/AC catalysts synthesized by impregnation method were investigated on the efficient and stable removal of HCHO in the fix-bed reactor. Extensive characterizations, BET, SEM, XRD, H2-TPR, XPS and FT-IR, were conducted to study the physicochemical properties, HCHO oxidation and surface reaction of catalysts. The optimal Mn0.75Fe6.02/AC showed enhanced HCHO removal efficiency of 98.30%, as well as excellent performance for simultaneous removal of HCHO (89.96%) and Hg0 (77.51%). NO and SO2 balanced in N2 would inhibit the removal of HCHO, while the addition of 6% O2 weakened the negative effect of SO2 and NO + 6% O2 facilitated the removal of HCHO. Besides, the slight promotion effect of water vapor was contributed to the regeneration of consumed −OH via the activation of surface oxygen by adsorbed H2O. Characterization results indicated that Mn0.75Fe6.02/AC possessed larger BET surface area, well-developed porosity and better dispersion of active components. Mn0.75Fe6.02/AC exhibited higher reducibility due to the synergistic effect between MnOx and FeOx, and the interaction between Mn-Fe oxides and AC support. At the same time, the oxygen-containing functional groups (C-O-, COO), abundant active surface oxygen and –OH facilitated both adsorption and oxidation of HCHO. Besides, the formate and carbonate intermediates formed on the surface of Mn0.75Fe6.02/AC in HCHO removal process, which could be further oxidized into CO2 and H2O. On the basis of above investigations, the mechanism of enhanced HCHO catalytic removal over MnxFey/AC was proposed.

Study of the structure and characteristics of mesoporous TiO2 photocatalyst, and evaluation of its factors on gaseous formaldehyde removal by the analysis of ANOVA and S/N ratio.

This study differs from previous studies of TiO2/SiO2 in that 0.5–10 μm microsized TiO2-rutile based catalysts (TR catalysts) with varying proportions of titanium and silicon were synthesized using a one-step modified hydrothermal method. At Ti/Si = 1/9, a two-dimensional channel-structured catalyst with a morphology resembling that of SBA-15 was obtained. In contrast, at Ti/Si = 3/7 or 5/5, a three-dimensional porous structure was formed, and Ti–O–Si–C bonds appeared. The structure of the TR catalyst transformed due to the decrease in C–Si bond content and the increase in C–C bond content with increasing Ti/Si ratio. The results indicated that the rutile phase was the main crystal phase of the TR catalyst. The small crystal size and large rutile phase content of the mesoporous TR catalyst contributed to the low band gap energy below 3.0 eV. Under 2 × 10 W lamp irradiation with either UVA or visible light, the three TR catalysts showed better formaldehyde (HCHO) removal efficiency than P25. Furthermore, the Taguchi method was employed to evaluate the catalytic factors by analysis of variance (ANOVA) and S/N ratio. The results revealed the contributions of each of the three factors to HCHO removal efficiency over TR catalysts to be as follows: space velocity (62%), Ti ratio (32%), and time on stream (5%). The TR catalyst with Ti/Si = 1/9 showed good HCHO removal efficiency with a high SBET (787.1 m2 g−1) and large pore volume (0.95 cm3 g−1) for a residence time of over 2.29 × 10−1 s under visible light irradiation. Microwave-assisted EG reduction was successfully applied to dope a TR catalyst with nanosized Pt particles in a short synthesis time. After Pt doping, the removal efficiency in the stream improved and stabilized. The Pt particles were Pt0 and proved effective for improving the photocatalytic removal of HCHO over the TR catalyst by prolonging the separation time of the electron–hole pairs. Overall, the Pt/TR catalyst is a potential material for pollutant removal and can be easily separated from the pollutant removal system since the catalysts are microsized.

The synthetic evaluation of CuO-MnOx-modified pinecone biochar for simultaneous removal formaldehyde and elemental mercury from simulated flue gas.

A series of low-cost Cu-Mn-mixed oxides supported on biochar (CuMn/HBC) synthesized by an impregnation method were applied to study the simultaneous removal of formaldehyde (HCHO) and elemental mercury (Hg0) at 100-300°C from simulated flue gas. The metal loading value, Cu/Mn molar ratio, flue gas components, reaction mechanism, and interrelationship between HCHO removal and Hg0 removal were also investigated. Results suggested that 12%CuMn/HBC showed the highest removal efficiency of HCHO and Hg0 at 175°C corresponding to 89%and 83%, respectively. The addition of NO and SO2 exhibited inhibitive influence on HCHO removal. For the removal of Hg0, NO showed slightly positive influence and SO2 had an inhibitive effect. Meanwhile, O2 had positive impact on the removal of HCHO and Hg0. The samples were characterized by SEM, XRD, BET, XPS, ICP-AES, FTIR, and H2-TPR. The sample characterization illustrated that CuMn/HBC possessed the high pore volume and specific surface area. The chemisorbed oxygen (Oβ) and the lattice oxygen (Oα) which took part in the removal reaction largely existed in CuMn/HBC. What is more, MnO2 and CuO (or Cu2O) were highly dispersed on the CuMn/HBC surface. The strong synergistic effect between Cu-Mn mixed oxides was critical to the removal reaction of HCHO and Hg0 via the redox equilibrium of Mn4+ + Cu+ ↔ Mn3+ + Cu2+.

Efficient MnOx supported on coconut shell activated carbon for catalytic oxidation of indoor formaldehyde at room temperature

MnOx was supported on peracetic acid modified coconut shell activated carbon (MnOx/AC) via facile in-situ redox reactions and used for catalytic oxidation of HCHO which is a major indoor air pollutant. The MnOx/AC catalysts were characterized by XRD, Raman, XPS, BET and in-situ DRIFTS technologies. The prepared MnOx was δ-type structure with poor crystalline. With the addition of methanol as a reducing agent during preparation, the MnOx/AC-methanol catalyst exhibited superior catalytic activity and stability toward HCHO oxidation at room temperature. The HCHO removal efficiency was kept nearly at 100% for a reaction time of 1000 min and remained highly stable even after six repetitive cycles. The rich Mn3+ and surface oxygen groups were beneficial for the catalytic activity. The in-situ DRIFTS results showed lower accumulation and faster decomposition of intermediates on the surface of the MnOx/AC-methanol catalyst, which may account for its superior catalytic efficiency and stability.

Oxidation of gaseous formaldehyde with ozone over MnOx/TiO2 catalysts at room temperature (25 °C)

The TiO2 support materials were synthesized by a chemical vapor condensation (CVC) method and the subsequent MnOx/TiO2 catalysts were prepared by an impregnation method in our previous studies. Catalytic oxidation of formaldehyde on the MnOx/TiO2 catalysts was examined with ozone. Formaldehyde (HCHO) is a specific volatile organic compound (VOC) found in indoor air of both residential places and workshops and must be removed to improve air quality. Catalytic oxidative decomposition of HCHO at room temperature (25°C) is considered one of the most promising strategies for this. In this study, MnOx/TiO2 was prepared using chemical vapor condensation (CVC) as a HCHO ozone (O3) catalyst that operates at 25°C. In this catalytic oxidation experiment, the HCHO of the gas stream on the MnOx/CVC-TiO2 catalyst was completely oxidized to CO2 with the addition of O3. The removal efficiency of HCHO increased from 35.3% to 100% as the O3:HCHO ratio increased from 1 to 5. COX selectivity also increased significantly with the increasing O3:HCHO ratio. As the relative humidity (RH) increased, HCHO removal efficiency and mineralization to CO2 increased. The HCHO removal efficiency increased to 100% at RH=50%, whereas it was 85% at RH=10%. The mineralization to CO2 increased to 100% at RH=80%, and was 15% at RH=10%.

The catalytic oxidation removal of low-concentration HCHO at high space velocity by partially crystallized mesoporous MnOx

Efficient removal of low-concentration HCHO at room temperature and high space velocity without using noble metals is still a great challenge to date. In this work, we have fabricated partially crystallized mesoporous MnOx by redox precipitation reaction between potassium permanganate and oxalic acid, followed by NaBH4 post-treatment at room temperature. The as-synthesized MnOx was coated on honeycomb ceramics and the obtained monolithic catalyst exhibited high efficiency in removing low-concentration HCHO (1ppm and 0.2ppm) at a space velocity of ∼48,000h−1. When operated at 85°C, the monolithic catalyst showed further improved HCHO removal efficiency and durable performance. And with humidity, the catalyst also showed enhanced catalytic activity and prolonged life. The multiple valence states of Mn, high surface area together with the high content of surface-adsorbed oxygen species have been identified and proposed to be responsible for its high catalytic activity in HCHO oxidation removal.

Using Box Modeling to Determine Photodegradation Coefficients Describing the Removal of Gaseous Formaldehyde from Indoor Air

Human exposure to volatile organic compounds (VOCs) indoors is receiving increasing attention. Formaldehyde (HCHO) is the most common VOC emitted from household materials and is associated with many health risks, including sick building syndrome. In this study, a simple box model was developed and applied to help understand the fate and degradation mechanisms of HCHO in the indoor environment. The model was validated using observations from an air handling system under different conditions. A UV/TiO2 filter reactor was installed in a closed box with the air conditioning unit. Three parameters, temperature, relative humidity, and circulation wind speed, were investigated for their effects on the performance of the air handling system. Our results show that the operation mode of the air handling system has a greater effect on the removal of HCHO than any of the air conditioning parameters. From a kinetic perspective, the removal of gaseous HCHO from a constant-volume box clearly represents a zero-order reaction. After UV irradiation with a TiO2 filter for 2 hours, the removal efficiency of gaseous HCHO increases to approximately 90%. Contributions to the removal of gaseous HCHO from natural dissipation, photodegradation, and photocatalytic oxidation decomposition are 12%, 30%, and 58%, respectively. Our results have implications for reducing indoor air pollution and reducing stress on air conditioning systems. Meeting these goals is beneficial for human health and energy conservation in modern society.

Ultrathin manganese dioxide nanosheets for formaldehyde removal and regeneration performance

Ultrathin manganese dioxide (MnO2) nanosheets with the thickness of 1–2nm were synthesized by chemical oxidation of Mn2+ ions in the presence of tetramethylammonium cations in an aqueous solution. The composite material MnO2/PET (polyethylene terephthalate) was prepared by impregnating PET into MnO2 nanosheets colloid. The impregnation time has a great influence on HCHO adsorption and removal efficiency. When the PET was impregnated in nanosheets colloid for 1h at room temperature, the concentration of HCHO decreased quickly within initial 10min and finally reached about 81% removal efficiency with an initial HCHO concentration of ∼200ppm. Moreover, the used MnO2/PET can be simply regenerated by heating at 105°C without any rinse treatment. Based on in-situ DRIFTS and TG-MS studies, the mechanism of formaldehyde removal and regeneration was proposed. All the results showed that as-synthesized MnO2/PET can be used as an effective, affordable, and recyclable materials to removal and oxide toxic HCHO in indoor air.

Highly dispersed and active supported Pt nanoparticles for gaseous formaldehyde oxidation: Influence of particle size

Abstract A series of Pt/TiO 2 catalysts with various Pt particle sizes and chemical properties were facilely synthesized by NaBH 4 reduction and heated at different temperatures. They were used to catalytically oxidize gaseous formaldehyde (HCHO) at ambient temperature. The influence of structural nature of Pt NPs on catalytic activity was investigated. The as-prepared Pt NPs are highly dispersed and very active for HCHO oxidation even at room temperature. The maximum Pt dispersion and HCHO removal efficiency reached 73.4% and 81.3%, respectively. The turnover frequencies (TOFs) of Pt NPs present size-dependent effect. The Pt NPs with average size of 10.1 nm had the highest TOF of 4.39 s −1 for HCHO oxidation.

NaOH-Modified Ceramic Honeycomb with Enhanced Formaldehyde Adsorption and Removal Performance

NaOH-modified ceramic honeycombs (Na-CH) were simply prepared by impregnating ceramic honeycombs (CH) into NaOH aqueous solution. It was clearly shown that the surface modification incurs higher specific surface area and smaller grain sizes of the CH without destruction of their integrity. Moreover, the introduced surface NaOH can trigger Cannizzaro disproportionation of surface-absorbed formaldehyde (HCHO) on Na-CH, resulting in catalytic transformation of HCHO into less-toxic formate and methoxy salts. The NaOH concentration during impregnating treatment has a great influence on HCHO adsorption and removal efficiency, while the impregnation time and temperature have little influence on the efficiency. When the CH was impregnated in 1 M NaOH aqueous solution for 0.5 h at room temperature, the HCHO removal efficiency at ambient temperature can reach about 80% with an initial HCHO concentration of 250 ppm. Moreover, the used Na-CH can be facilely regenerated via 1 min blow using a common electric hair dryer, with the generation of less toxic HCOOH and CH3OH and recovery of NaOH. Using such a mild, fast, and practical regeneration method, the regenerated Na-CH showed slight degradation in adsorption and removal capability toward HCHO. The enhanced performance of Na-CH obtained was attributed to the presence of NaOH and increase of specific surface area and surface hydroxyl groups. Considering no demand of noble metal for HCHO removal at ambient temperature and practical reusable capability of Na-CH under mild conditions, this work may provide some new insights into the design and fabrication of advanced catalysts for indoor air purification.

A Novel Approach of Chitosan Additive to Remove Formaldehyde from Building Materials

Formaldehyde (HCHO) which emitted from building materials, such as plywood and adhesive, is a carcinogenic substance in indoor air. Chitosan is produced from the structural element in the exoskeleton of crustaceans (such as crabs and shrimp), and has the ability to absorb HCHO. In this study, the HCHO removal efficiency by chitosan additives was evaluated for two building materials - adhesive and plywood. The experiments were performed in a small chamber based on the method of Japanese Industrial Standards (JIS) A1901 to evaluate the HCHO emission from adhesive and plywood before and after the application of chitosan additives. Both the HCHO concentration in the chamber and the HCHO emission factor of two adhesives, urea-formaldehyde (UF) resin and Poly Vinyl Acetate (PVAC) resin, were reduced from 0.02~0.21 ppm and 0.12~1.05 mg/m2h to 0~0.14 ppm and 0.12~0.63 mg/m2h after using chitosan additives. The best HCHO removal efficiency was adding 9% chitosan additives in the adhesives. The amount of absorbed HCHO is proportional to the amount of chitosan additives, and approximate 0.02 mg of HCHO can be absorbed by per mg of chitosan additive (i.e. absorption capacity 0.02 g HCHO/g Chitosan).

Effect of OH Radicals on Formaldehyde Removal in Dielectric Barrier Discharge

The removal of formaldehyde by dielectric barrier discharge in a coaxial cylindrical reactor has been studied at atmospheric pressure. The emission spectra of OH (A 2 Σ→X 2 Π, 0-0) emitted from the dielectric barrier discharge have been successfully recorded. The relationship between the removal efficiency of formaldehyde and the emission intensity of OH (A 2 Σ→X 2 Π, 0-0) has been investigated at different applied voltages, driving frequencies, concentrations of argon and oxygen. We find that the removal efficiency of HCHO increases when the emission intensity of OH (A 2 Σ→X 2 Π, 0-0) increases with rising applied voltage, driving frequency, and concentration of argon. However, the removal efficiency of HCHO decreases when the emission intensity of OH (A 2 Σ→X 2 Π, 0-0) decreases with an increase in the concentration of oxygen. The removal efficiency of HCHO is 93.8% in N2+HCHO mixed gas at 11.5 kV applied voltage and 9 kHz driving frequency.

Formaldehyde removal from gas streams by means of NaNO2 dielectric barrier discharge plasma

Destruction of formaldehyde by means of NaNO2 ferro-electric packed bed dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. The difference among four kinds of NaNO2 ferro-electric reactors was compared in terms of specific energy density (SED), energy yield (EY), and HCHO decomposition. In addition, by-products during the decomposition of HCHO and destruction mechanism were also investigated. The removal efficiency of HCHO increased by means of NaNO2 DBD plasma significantly and enhanced with increasing SED distinctly. More amount of NaNO2 contributed to higher HCHO removal efficiency in the reactors. Reactor C had the highest HCHO removal efficiency among the reactors. As an important by-product, ozone concentration increased with higher SED. The possible main products in the outlet effluent were CO, CO(2) and H(2)O.