Formaldehyde Capture Research Articles

Co-adsorption enhancement of formaldehyde/carbon dioxide over modified hexagonal boron nitride for whole-surface capture purification

Simultaneous capture of formaldehyde (HCHO) and carbon dioxide (CO2) in indoor air is promising of achieving indoor-air purification. Of all potential adsorbents, hexagonal boron nitride (h-BN) is one of the most suitable species owing to facile formation of attraction points. Therefore, in this study, performances of HCHO and CO2 being adsorbed over pure/modified h-BN are systematically investigated via density functional theory (DFT) calculations. Minutely speaking, direct interaction between HCHO and CO2, single-point adsorption enhancement of HCHO over modified h-BN, co-adsorption reinforcement of HCHO/CO2 as well as relevant thermodynamic characteristics are major research contents. According to calculation results, there is relatively strong attraction between HCHO and CO2 owing to hydrogen bonds, which is in favor of co-adsorption of HCHO/CO2. As to single-adsorption of HCHO, C-doped h-BN shows better adsorption features than P-doped h-BN and C/P-doped h-BN is slightly weakened in adsorption ability due to surficial deformation caused by P atoms. For co-adsorption of HCHO/CO2, CO2 is the protagonist via formation of quasi-carbonate with the help of delocalized π-orbital electrons. Regarding effects of temperatures on adsorption strengths, they depend on interelectronic interactions among dopant atoms and finally derives from dispersion of π bonds across adsorbents. Overall, this study provides detailed mechanisms for co-capture of HCHO/CO2 to accomplish indoor-air purification.

Graphene oxide a promising formaldehyde scavenger of phenolic resin‐bonded plywood: From elaboration to evaluation

AbstractA long‐standing manufactured and most frequently used resin is phenol‐formaldehyde resin, which has currently reached new horizons by incorporating nano reinforcements, even at lower loadings. Nanostructured materials, particularly graphene, have gained considerable interest in recent years because of their fascinating characteristics. Herein, this study explores for the first time the potential of prepared graphene oxide (GnO) as an effective formaldehyde scavenger in the development of plywood panels containing PF resins. The addition of 1% of GnO to the system resulted in a significant improvements in the mechanical properties by more than 45% in the shear strength (SS), 35% in modulus of elasticity, and 25% in modulus of rupture when compared with the reference panel. While the moisture resistance of panels were found to remarkably enhanced showing an increase in SS by 25% and 37% After 24 h in cold water (20°C) and 12 h of immersion in boiling water, respectively. The results also demonstrated that GnO exhibited exceptional formaldehyde capture efficiency, surpassing 60% reduction compared with the control. This innovative research not only unveils the novel potential of GnO in improving the performance of PF resins but also ushers in a new way of developing eco‐friendly wood‐based materials.

Experimental study of adsorption characteristic of novel pyrazole-based metal-organic frameworks for volatile organic compounds

Volatile organic compounds (VOCs) are the major indoor air pollutants that affect human health, comfort, and working performance. Sorbent material and adsorption technology are considered to be one of the most effective and economical ways to remove VOCs from indoor air. Among many sorbent materials, metal-organic frameworks (MOFs) have received more and more attention because of their superior performance in capturing a variety of compounds. In this work, the adsorption characteristic of a newly synthesized pyrazole-based metal-organic framework (Al-pda) for different VOCs was investigated. First, the single-pass VOC adsorption rates of Al-pda and activated carbon were tested under different low-concentration VOCs mixture, which is in line with the practical application in the indoor environment. The results showed that Al-pda had an especially high adsorption ability for formaldehyde. The single-pass efficiency of formaldehyde adsorption was up to 89% at the beginning of the test and gradually stabilized at 66%. Compared with activated carbon, Al-pda had significantly higher selectivity and adsorption efficiency for the capture of formaldehyde. Then the effect of relative humidity on formaldehyde adsorption was investigated. After increasing the relative humidity from 15% to 65%, Al-pda’s formaldehyde single-pass adsorption rate almost remained at a similar level. Preliminary research showed that Al-pda is a promising material for the selective adsorption of indoor formaldehyde under humid conditions. More work is needed to probe this new MOF’s adsorption mechanism and application method.

Evaluation of properties and formaldehyde removal efficiency of biocarbon prepared at variable pyrolytic temperatures

Biocarbon (BC) represents a potential material for application in air remediation. This study investigated the efficiency of BC particles in the removal of formaldehyde. BC samples were prepared from Arundo donax (AD) and olive stone (OS) feedstocks at variable pyrolysis temperatures (from 300°C to 800°C). The BC particles were characterized using proximate, Fourier transform infrared, water contact angle, particle size, and physisorption analyses. The formaldehyde removal capacity was tested using an electrochemical formaldehyde sensor in a batch experiment. The physicochemical and structural properties depended on the pyrolysis temperature at which the BC was produced. The increase in pyrolysis temperature increased the BC’s pH, hydrophobicity, and porosity. All the samples achieved a formaldehyde removal capacity ranging between 26% and 64% for BC pyrolyzed at 300°C and 800°C, respectively. In BC pyrolyzed at temperatures under 500°C, the formaldehyde capture was governed by a partitioning mechanism through diffusion in the noncarbonized organic fraction. In comparison, formaldehyde capture was controlled by a physical adsorption mechanism through pore filling for BC pyrolyzed at 500°C or above. BC pyrolyzed at 800°C was more efficient for formaldehyde adsorption due to the well-developed microporous structure for both AD and OS. AD-derived BC prepared at 800 °C (AD-BC800) was selected for the re-usability test, using thermal regeneration to remove the adsorbed components. The regenerated sample maintained a comparable formaldehyde removal capacity up to four re-use cycles. Moreover, the comparison between non-activated and activated AD-BC800 revealed that physical activation significantly enhanced BC’s adsorptive ability.

Rational design of the double hydrogen-bonds sites in IL@MOF composites for efficient and selective formaldehyde capture

Long-term exposure to volatile organic compounds (VOCs) represented by formaldehyde (HCHO) poses a serious threat to human health. However, traditional adsorption materials cannot meet the needs of efficient and selective formaldehyde capture because of the weak host-guest interaction. Herein, a double hydrogen-bonds strategy was proposed to boost the HCHO affinity by rich -NH3Cl sites in ionic liquids (ILs) named carbamide chloride ([CAM][Cl]). In order to fully expose these sites, MIL-101(Cr), as a kind of mesoporous metal-organic frameworks (MOFs) with large porosity, was used to construct the IL@MOF composites. As expected, the resulting [CAM][Cl]@MIL-101(Cr)-15% exhibits high HCHO uptake of 9.53 mmol·g−1, which is 2.3-fold higher than that in MIL-101(Cr) (4.10 mmol·g−1). Surprisingly, breakthrough experiments reveal that the HCHO concentration can be reduced from 800 ppm at the inlet to less than 1 ppb at the outlet within a time range of up to 1636 min·g−1, achieving efficient deep HCHO removal even under humidity conditions. Mechanism researches prove that the double hydrogen-bonding (Hδ+(-NH3Cl)···Oδ−(HCHO)) interactions play a significant role for the HCHO adsorption of [CAM][Cl]@MIL-101(Cr). More importantly, this work not only reports an adsorbent with excellent HCHO capture performance, but also innovatively highlights the important of double hydrogen-bonds for HCHO capture.

High-efficient capture and degradation of formaldehyde based on the electric-field-enhanced catalytic effect

Enhancing the generation of active groups is of great significance for alleviating the catalyst deactivation of formaldehyde (HCHO) by accelerating the decomposition of intermediate products. Herein, an electric-field-enhanced catalytic effect was proposed for the efficient capture and degradation of HCHO base on carbon cloth loaded manganese oxide catalyst (MnOx-CC). Under the action of electric field, MnOx can generate more hydroxyl radicals (•OH) and superoxide radicals (•O2-), thus accelerating the degradation of HCHO and intermediates at room temperature. After the introduction electric field (∼1 ×104 V/m), •O2- and •OH radical on the surface of MnOx-CC catalyst can be increased by 8 times and 23 times, respectively. At weight hourly space velocity of 300,000 mL/(gcat h) for ∼15 ppm HCHO, MnOx-CC-Electric Field catalyst reached the removal efficiency of 99.4%, and the CO2 conversion efficiency of 81.2%, without decrease significantly within 80 h. Theoretical calculation shows that the electric field can increase the electron state density of Mn atom at the Fermi level and reduce the adsorption energy of HCHO, O2 and H2O, thus promoting the generation of active groups and degradation of intermediate products. The electric-field-enhancement catalytic effect provides a new approach for the degradation of Volatile Organic Compounds.

In Silico Screening of Metal-Organic Frameworks for Formaldehyde Capture with and without Humidity by Molecular Simulation.

Capturing formaldehydes (HCHO) from indoor air with porous adsorbents still faces challenges due to their low capacity and poor selectivity. Metal-organic frameworks (MOFs) with tunable pore properties were regarded as promising adsorbents for HCHO removal. However, the water presence in humid air heavily influences the formaldehyde capture performance due to the competition adsorption. To find suitable MOFs for formaldehyde capture and explore the relationship between MOFs structure and performance both in dry air and humid air, we performed grand canonical Monte Carlo (GCMC) molecular simulations to obtain working capacity and selectivity that evaluated the HCHO capture performance of MOFs without humidity. The results reveal that small pore size (~5 Å) and moderate heat of adsorption (40-50 kJ/mol) are favored for HCHO capture without water. It was found that the structure with a 3D cage instead of a 2D channel benefits the HCHO adsorption. Atoms in these high-performing MOFs should possess relatively small charges, and large Lennard-jones parameters were also preferred. Furthermore, it was indicated that Henry's constant (KH) can reflect the HCHO adsorption performance without humidity, in which the optimal range is 10-2-101. Hence, Henry's constant selectivity of HCHO over water (SKH HCHO/H2O) and HCHO over mixture components (H2O, N2, and O2) was obtained to screen MOFs at an 80% humidity condition. It was suggested that SKH for the mixture component overestimates the influence of N2 and O2, in which the top structures absorb a quantity of water in GCMC simulation, while SKH HCHO/H2O can efficiently find high-performing MOFs for HCHO capture at humidity in low adsorption pressure. The ECATAT found in this work has 0.64 mol/kg working capacity, and barely adsorbs water during 0-1 bar, which is the promising candidate MOF for HCHO capture.

Hole-embedding block strategy to synthesize the NMOFs-NADH model: Selective capture and reduction of formaldehyde in aqueous and gaseous phases

A new NMOFs-NADH model (UiO-66-NADH) had been designed and synthesized utilizing the hole-embedding block strategy for self-adaptive pore radius to FA, and could selectively capture and confined reductive remove of FA as a good donor of hydrogen proton in aqueous and gaseous phases. With the catalysis of tetra(carboxyphenyl)porphyrin iron (Ⅱ) (Fe-TCPP), UiO-66-NADH could selectively convert FA to methanol deeply and efficiently up to 98.6% within 40 min. In addition, the regeneration of UiO-66-NAD+/UiO-66-NADH was performed by g-C3N4 via photocatalysis, and the recycled UiO-66-NADH still had high reduction activity after three cycles. While, a fixed bed reactor filled with UiO-66-NADH/Fe-TCPP mixture was employed for the selective absorption and removal of gaseous FA, also in the aqueous solution of some real samples. These results demonstrated that UiO-66-NADH/Fe-TCPP system had a great potential in environmental protection. The hole-embedding block strategy could be extended to related applications in air purification and environmental protection.

Novel B and N Sites of One-Dimensional Boron Nitride Fiber: Efficient Performance and Mechanism in the Formaldehyde Capture Process.

Identification of adsorption centers with atomic levels of adsorbents is crucial to study the adsorption of formaldehyde (HCHO), especially for an in-depth understanding of the mechanism of HCHO capture. Herein, we investigate the HCHO adsorption performance of one-dimensional (1D) nanoporous boron nitride (BN) fiber, and explore the adsorption mechanism by density functional theory (DFT) calculations, including adsorption energy change and Bader charge change, and experimental study as well. Research shows that the 1D nanoporous BN fiber possesses a high concentration of Lewis pairs, which act as Lewis acid and Lewis base sites associated with the fiber’s electron-deficient and electron-rich features. It is worth noting that the HCHO removal efficiency of a typical sample is as high as 91%. This work may open the door to the field of adsorption of other pollutants by constructing Lewis pairs in the future.

Identifying promising covalent organic frameworks for HCHO/O2 + N2 adsorption from indoor air pollution using high-throughput computational screening

Formaldehyde is regarded as a member of Group 1 carcinogen to humans by the International Agency for Research on Cancer (IARC). Effective capture of indoor formaldehyde is especially important. In this work, we perform a high-throughput computational screening of ∼470 experimentally realizable covalent organic frameworks (COFs) structures to identify the best candidate that can separate formaldehyde from indoor air pollution. Several performance metrics: working capacity, adsorption selectivity and adsorbent performance factor to assess the performance of the COFs in the database. COF-LZU8 was identified with the highest selectivity and adsorbent performance factor, outperforming the most of the promising hMOFs by high-throughput computational screening reported to date. In addition, based on the radial distribution functions, snapshots and contour plots of the center of mass, thioether-functionalized linkers in the COF-LZU8 framework had an effective approach to significantly strengthen COF separation capability.

Introducing Polyhydroxyurethane Hydrogels and Coatings for Formaldehyde Capture.

Formaldehyde (FA) is a harmful chemical product largely used for producing resins found in our living spaces. Residual FA that leaches out the resin contributes to our indoor air pollution and causes some important health issues. Systems able to capture this volatile organic compound are highly desirable; however, traditional adsorbents are most often restricted to air filtration systems. Herein, we report novel waterborne coatings that are acting as a FA sponge for indoor air decontamination. These coatings, of the poly(hydroxyurethane) (PHU) type, rich in primary amine groups, are prepared by the polyaddition of a hydrosoluble dicyclic carbonate to a polyamine in water at room temperature under catalyst-free conditions. We highlight the importance of the choice of the polyamine on the curing rate of the formulation and on the FA capture ability of PHU. The excellent FA capturing ability of the best candidate is rationalized by investigating the action mode of the polyamine used to construct PHUs. With poly(vinyl amine), FA is covalently and permanently bound to PHU, with no release over time. The performance of the coating in FA abatement is impressive, with more than 90% of captured FA after one day of contact. The facility to prepare these transparent and colorless coatings from waterborne formulations gives access to new efficient indoor air depolluting solutions, potentially applicable to various surfaces of our living spaces (wall, ceiling, etc.).

Conjugated microporous poly(aniline)s for removal of low-concentration formaldehyde

Removal of indoor formaldehyde is important but challenging due to the very low concentration. Here, we showed the applicability of a new class of conjugated microporous poly(aniline)s (CMPAs) in this formaldehyde capture. The unique properties of rich ultramicroporosity and benzenoid amine (–NH–) groups made the resulting CMPAs ideal platforms for the efficient low-concentration formaldehyde adsorption, through the interaction between benzenoid amine groups and formaldehyde via Mannich reaction and H-bond in the ultramicropore. They therefore exhibited ultrafast adsorption, receiving > 80% removal efficiency for ca 0.7 ppm formaldehyde within 60 min, and benchmarking storage capacity, achieving ca. 2679.68 mg·g−1 for CMPA-2. Our CMPAs also worked well in a self-assembled air clean unit, keeping kinetically reducing average 98% of formaldehyde after treatment of 4000 BV polluted air (with ca. 25 ppm formaldehyde) without break-through. Outcomes highlighted the potential of CMPAs for the clean-up of airborne formaldehyde for human health protection in next generation.

Passive Control of Indoor Formaldehyde by Mixed-Metal Oxide Latex Paints.

This work reports the incorporation of mixed-metal oxides (MMOs) such as Si/Ti and Si/Zr into latex paints in the form of thin coatings for permanent trapping of indoor formaldehyde. The formaldehyde removal performance of the surface coatings was evaluated in a lab-scale indoor air chamber, and the results were compared with those of powder analogues. Due to the pore blockage by the latex, the incorporation led to 6-30% reduction in adsorption capacity and 50-70% drop in the adsorption rate for MMO-latex paints relative to their powder MMO analogues. Under the operating conditions of concentration, temperature, and relative humidity, the Si/Zr-latex paints outperformed the Si/Ti counterparts. It was also observed that performance could decrease over excessive loading, for example, Si/Zr-latex paint with 15/1 Si/Zr weight ratio showed a 20% lower adsorption capacity than that of the Si/Zr-latex paint with 25/1 Si/Zr ratio at 5 ppmv, 25 °C, and 70% RH. While high temperature greatly reduced the adsorption rate of the MMO-latex paints, high humidity slightly promoted the rate of formaldehyde capture. In 10 L, flow-through chamber tests, 25Si/Zr-latex paint reduced 5 ppmv formaldehyde by up to 60% at 25 °C and 70% RH with an adsorption rate of 0.34 ppmv/h. Overall, this study highlights the potential of MMO-latex paints with optimized formation for the efficient abatement of indoor aldehydes.

Machine learning and high-throughput computational screening of hydrophobic metal–organic frameworks for capture of formaldehyde from air

Aiming to efficiently capture the formaldehyde (HCHO) with low content in the air exceeding the standard, 31,399 hydrophobic metal–organic frameworks (MOFs) were first selected from 137,953 hypothetical MOFs to calculate their formaldehyde adsorption performance, namely, adsorption capacity (NHCHO) and selectivity (SHCHO/N2+O2) by molecular simulation and machine learning (ML). To combine the SHCHO/N2+O2 and NHCHO, a new performance metric, the tradeoff between selectivity and capacity (TSC) was proposed to identify more reasonably the top-performing MOFs. The MOFs were divided into three datasets (i.e., all of the MOFs (AM), MOFs with top 5% of SHCHO/N2+O2 (PS) and MOFs with top 5% of NHCHO (PN)) to scrutinize and explore the characteristics of different materials capturing formaldehyde from the air (N2 and O2). Furthermore, after four ML algorithms (the back propagation neural network (BPNN), support vector machine (SVM), extreme learning machine (ELM), and random forest (RF)) are applied to quantitatively assess the prediction effects of performance indexes in different datasets, RF algorithm with the most accurate prediction revealed that the TSC has strong correlations with the MOF descriptors in PS dataset. In view of 14.10% of the promising MOFs occupied PN, the design paths of excellent adsorbents for six MOF descriptors were quantitatively determined, especially for the Henry's coefficient (KHCHO) and heat of adsorption of formaldehyde (Q0st). Their probabilities of obtaining excellent MOFs could reach 100% and 77.42%, respectively, and both the relative importance and the trends of univariate analysis coherently confirm the important positions of KHCHO and Q0st. Finally, 20 best MOFs were identified for the single-step separation of formaldehyde with low concentration. The microscopic insights and structure-performance relationship predictions from this computational and ML study are useful toward the development of new MOFs for the capture of formaldehyde from air.

Three-dimensional carbon foam supported MnO2/Pt for rapid capture and catalytic oxidation of formaldehyde at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is one of the most viable approaches to indoor HCHO pollution abatement. Herein, three-dimensional (3D) carbon foam decorated with Pt/MnO2 nanosheets (Pt/MnO2-CF) was in-situ synthesized for room-temperature catalytic oxidation of HCHO. The 3D Pt/MnO2-CF with a low platinum content of 0.3 wt% exhibited excellent catalytic activity because of its hierarchically porous structure facilitating the diffusion of reactant molecules. Moreover, an abundance of active oxygen species resulting from oxygen vacancies are favorable for HCHO oxidation. In addition, the carbon foam substrate exhibited a very good HCHO adsorption capability, which helps achieve prompt reduction in HCHO concentration in the gas-phase and subsequent complete oxidation of adsorbed HCHO. The combination of adsorption and oxidation was more favorable for oxidative decomposition of HCHO. This work demonstrates that such 3D nanocomposites with low noble metal loading have promising application for indoor HCHO removal and air purification.

Health risk assessment of formaldehyde released from several Chinese dishes cooking activities

To study the effect of Chinese dishes cooking activities on the health risk for domestic cook, numerical simulations are executed under different air flow rates for three oil-based Chinese dishes cooking activities. The concentration of formaldehyde in respiratory area during cooking process is obviously influenced by the cooking dishes. And the effect of air flow rate of range hood on the formaldehyde capture is not as significant as that of the cooking method. The predicated results show that the formaldehyde concentration is 4.5-5.5, 2.8-3.6 and 1.2-1.5 times of the prescribed limit when cooking the dishes of stir-fried mutton, pan-fried chicken with onion and deep-fried pork, respectively. The high air flow rate is recommended for improving formaldehyde capture efficiency (CE) of range hood. The potentially benefit effects induced by higher air flow rate is reliable in the cooking activity of stir-fry mutton. Using high air flow rate of 19m3/min can reduce the risk by 11.86% compared with using low air flow rate of 10m3/min. Low air flow rate is more suitable for cooking activities with low release rate of cooking oil fumes (COFs), in order to better protect the health of cooks.

Computer aided design of water-resistant adsorbent for formaldehyde abatement

Formaldehyde is a well-known indoor air pollutant that is regulated by authorities worldwide. Formaldehyde has adverse health effects in humans, especially as a sensory irritant to the eyes and to the upper air way, and more importantly, it is a known carcinogen. Adsorption by carbon adsorbents is an old, but indispensable cleaning technology for combating indoor formaldehyde. In this study, we report isotherms and 2D-density distributions by conducting comprehensive Monte Carlo simulation. The effects of the functional group and pore size were investigated. We found that formaldehyde has a different response when the number of functional group and pore size change from that of water. Therefore, by tuning pore size and functionalities it may be feasible to produce real materials that retain effective capture of formaldehyde but which avoid pore blocking by water based on the differences in adsorption properties between water and formaldehyde.

Selective adsorption of formaldehyde and water vapors in NaY and NaX zeolites

Abstract Coadsorption of formaldehyde and water vapors on NaX and NaY zeolites is studied at 298 K in the pressure range 0–2 hPa by manometry coupled with gas phase chromatography and calorimetry. Coadsorption isotherms, adsorption selectivities and coadsorption heats are measured. Results show that the coadsorption process is selective for water at low filling and for formaldehyde at high filling. The adsorption selectivity for formaldehyde over water is however too low to consider the possibility of using such adsorbents for the development of air handling units. On the other hand, a preliminary study carried out on the adsorption of formaldehyde and water in pure gas phase on a hydrophobic FAU zeolite reveals that high silica zeolites could be promising adsorbents for the capture of formaldehyde in the presence of water.

Biomass Bricks with Excellent Indoor Formaldehyde Capture and Transformation Performance

Indoor formaldehyde capture and conversion to nontoxic materials, a widespread focal problem, is crucial for human health and suitable residence and also sufficiently challenging. Herein we present a kind of practical construction of biomass/wooden bricks with excellent indoor formaldehyde capture and transformation performance. These biomass bricks are prepared from Ca(OH)2, waste poplar wood fiber, corn stalk fiber, and nano-TiO2, presenting excellent compressive strength (average 2.94 MPa) and capacity for indoor formaldehyde removal. In the HCHO adsorption test (desiccator testing methods), the concentration of HCHO decreased to 25% of the initial value in 3 days, and the HCHO concentration after the biomass brick absorption experiment is lower than the E2 limiting one (GB 18580-2001 national standard, China), creating a relatively safe indoor environment. On the basis of the results of a series of tests, including scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance, etc., indo...

Advanced nanonetwork-structured carbon materials for high-performance formaldehyde capture

Facile design and construction of advanced materials for eliminating the indoor formaldehyde pollution is still a great challenge but very desirable to provide clean air for human life. Herein, we report a high-performance formaldehyde adsorbent, i.e., a new type of nanonetwork-structured carbon (NNSC) with a hollow nanosphere as network unit by developing a facile, efficient and post-treatment-free strategy. The NNSCs can be easily obtained by a simple carbonization of a mixture, in which natural wheat husk and Teflon are used as carbon precursor and biotemplate-in-situ-remover, respectively. The as-constructed NNSC exhibits a unique three-dimensional interconnected micro-, meso- and macroporous nanonetwork. Benefiting from such a valuable hollow nanosphere-interconnected network structure, the NNSCs show surprising formaldehyde gas adsorption properties including super-high storage capacity, ultrafast adsorption rate and efficient adsorptively active surface. Remarkably, their specific adsorption capacity and maximum adsorption rate are as high as 120.3 mg g−1 m−3 and 44.6 mg g−1 m−3 h−1, which make 18-fold and 41-fold enhancement when compared to activated carbon commercially used for formaldehyde adsorption, respectively. This work highlights an efficient solution to develop high-performance formaldehyde adsorbents by facile and rational construction of novel porous structure, simultaneously to provide a new avenue to high-value advanced materials for challenging environmental issue.