Diffusion Of Formaldehyde Research Articles

Discussion on the calculation method for formaldehyde diffusion coefficient in building materials

Many scholars have utilized Bodalal’s mathematical model in the development of environmentally friendly building materials to describe the physical diffusion process of volatile organic compounds. In the model, the key to calculating the diffusion coefficient of volatile organic compounds in building materials is the value of the auxiliary parameter α1 and q. This paper improves the method of solving auxiliary parameter values by using extreme value theory. Several other calculation methods are also presented. The process of solving it is explained in detail, and an example is used to verify its accuracy. As these methods are very easy to learn and easy to implement on a computer, they can greatly reduce error rates, which makes them popular and useful.

Simulation of Formaldehyde Distribution Characteristics under Different Indoor Conditions and Optimization of Monitoring Methods

The distribution of indoor formaldehyde concentration is affected by many factors, which makes the concentration distribution of formaldehyde in different indoor positions uneven, which has a negative impact on the monitoring accuracy. Firstly, through orthogonal experiment and numerical simulation, it is determined that the airflow organization and the location of pollution source have a great influence on the monitoring accuracy. Further research found that the relative position of the air supply airflow and the pollution source affected the diffusion of formaldehyde in the room. Through Computational Fluid Dynamics(CFD) simulation, the error and correction basis of the monitoring data caused by different monitoring conditions were obtained. Finally, the accurate optimal monitoring position is given by genetic algorithm optimization. In the optimization process of 17 working conditions, 76% of the working conditions only need one sensor and correction, which can make the monitoring effective coefficient λ reach more than 80%, and 24% of the working conditions need two sensors.

The performance analysis of a novel photocatalytic-thermal-catalytic-photovoltaic-Trombe wall system integrated with compound parabolic concentrator

This paper proposes a novel photocatalytic-thermal-catalytic-photovoltaic-Trombe wall system integrated with compound parabolic concentrator (CPC/PTCPV-TW), which can make full use of outdoor solar radiation and make the system have multiple functions of heating, purification and photovoltaic power generation. The experimental detection platform of CPC/PTCPV-TW system was built and then turbulent natural convection model and indoor formaldehyde diffusion and transfer model were established to study the performance of CPC/PTCPV-TW system. The results were: (1) In the photocatalytic flow channel, the average daily thermal efficiency and the single pass rate of formaldehyde were 0.36 and 0.25–0.56, respectively. In the thermal catalytic flow channel, the average daily thermal efficiency and the single pass rate of formaldehyde were 0.26 and 0.18–0.38, respectively. The average daily photoelectric conversion efficiency of CPCPTCPV-TW system was 6.68%; (2) The greater the solar irradiation intensity and the lower the air inlet temperature, the higher the instantaneous thermal efficiencies of the photocatalytic channel and thermal catalytic channel and the photoelectric conversion efficiency of the system. The lower the formaldehyde inlet concentration, the greater the amount of clean air delivery rate (CADR) and the smaller ventilation times, the better the degradation effect of formaldehyde in the room equipped with CPC/PTCPV-TW system, and the lower the indoor formaldehyde concentration in a stable state.

Effect of Temperature on Formaldehyde Diffusion in Cellulose Amorphous Region: A Simulation Study

A formaldehyde-cellulose amorphous region model at the micro-level was established using the molecular dynamics software Materials Studio to simulate the change of cellulose and formaldehyde molecules in an external temperature field. The diffusion coefficients of formaldehyde molecules increased as the temperature increased. Moreover, the total number of hydrogen bonds decreased, and the interaction energy in the formaldehyde-cellulose model was reduced, which confirmed this conclusion and indicated that temperature increase could enhance the diffusion of formaldehyde in cellulose. The mechanical parameters of cellulose were analyzed in terms of Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, and the ratio of bulk modulus to shear modulus (K/G), which were affected by the temperature. The elastic modulus (E, G, and K) of cellulose decreased as the temperature increased, while the Poisson’s ratio V and K/G values increased. The results of the research explain how elevated temperature can promote the release of formaldehyde in furniture from a microscopic perspective, which supports each other with the results of previous experimental data and practical applications in production.

Distribution of transient formaldehyde concentration in confined small glass desiccators and its impact on emission rate measurement

The headspace method is used frequently for measuring the emissions rates of chemical compounds from building materials when operating labeling systems for these materials. A numerical investigation of transient formaldehyde concentration distribution in confined small glass desiccators was conducted in this study. To clarify the impact of the desiccator geometry on the formaldehyde emission and diffusion characteristics, three-dimensional (3D) laser-based measurement was first conducted to define the detailed inner geometries of the different commercial desiccators. A petri dish containing water was used as the sorbent for test specimens of formaldehyde emission sources produced inside the desiccators. Fundamental experiments concerning formaldehyde emission rates and sorption onto the sorbent were next performed using high- and low-emission types of building materials in the desiccators. Transient and steady numerical analyses were conducted for formaldehyde emissions from the building materials, molecular diffusion, and sorption onto the water sorbent. Transient analysis of the formaldehyde diffusion field over 24 h revealed that the total amount of dissolution of formaldehyde in the water was not significantly affected by the desiccator geometry in the building material of the inner diffusion control type. For evaporative/external diffusion emission-type, however, the formaldehyde emission rate was strongly affected by the desiccator shape. To obtain reproducible emission rate measurements in desiccators with different geometrical shapes, substantial adjustment is needed for the relative positions of the emission source and the sorbent in terms of the equivalent diffusion length, Ld.

Development of a formaldehyde biosensor with application to synthetic methylotrophy.

Formaldehyde is a prevalent environmental toxin and a key intermediate in single carbon metabolism. The ability to monitor formaldehyde concentration is, therefore, of interest for both environmental monitoring and for metabolic engineering of native and synthetic methylotrophs, but current methods suffer from low sensitivity, complex workflows, or require expensive analytical equipment. Here we develop a formaldehyde biosensor based on the FrmR repressor protein and cognate promoter of Escherichia coli. Optimization of the native repressor binding site and regulatory architecture enabled detection at levels as low as 1 µM. We then used the sensor to benchmark the in vivo activity of several NAD-dependent methanol dehydrogenase (Mdh) variants, the rate-limiting enzyme that catalyzes the first step of methanol assimilation. In order to use this biosensor to distinguish individuals in a mixed population of Mdh variants, we developed a strategy to prevent cross-talk by using glutathione as a formaldehyde sink to minimize intercellular formaldehyde diffusion. Finally, we applied this biosensor to balance expression of mdh and the formaldehyde assimilation enzymes hps and phi in an engineered E. coli strain to minimize formaldehyde build-up while also reducing the burden of heterologous expression. This biosensor offers a quick and simple method for sensitively detecting formaldehyde, and has the potential to be used as the basis for directed evolution of Mdh and dynamic formaldehyde control strategies for establishing synthetic methylotrophy.

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

To provide a microcosmic theoretical support for the reduction of formaldehyde in building material, the diffusion process was investigated by molecular dynamics simulation. In addition, the diffusion model of formaldehyde molecules in crystalline and amorphous cellulose was built, and diffusion coefficients at different temperatures and electric fields were studied. The simulation temperature was from 293 to 393 K and electric field was from 0 to 400 kV/m. Diffusion coefficient increased with greater temperature and electric field both in crystalline and amorphous region. However, the diffusion coefficient in amorphous region could be ignored for it was two orders of magnitude lower than diffusion coefficient in crystalline region. The relationship between diffusion coefficient and temperature, and the relationship between diffusion coefficient and electric field were obtained by simulation, verified by the experiment. Temperature was shown to have a significant contribution to formaldehyde diffusion than electric field. Compared with experimental studies, the molecular dynamics simulation could only analyse the diffusion coefficient qualitatively because of the difference between micro-scale and macro-scale.

Improvement of the performance of a simple box model using CFD modeling to predict indoor air formaldehyde concentration

The purpose of this study is to improve the predictive potential of a simple box model by using CFD simulation. In this easy-use box model, the material/air mass transfer is governed by a convective coefficient of pollutant through the boundary layer settling on the surface of material (hoi) which is a key parameter for the prediction of indoor air pollution. The aim of this study is to better assess this parameter as function of several variables (material surface emissions, room configurations and ventilation conditions) by means of CFD simulations. First, dimensional analysis method is applied to CFD results to establish a new relationship between physical parameters involved in the transfer of compounds in air, particularly room characteristic length, mean air velocity in inlet section area and molecular diffusion of formaldehyde in air. Thus, the validity of this relation is tested by CFD modeling for large range of room sizes, mean air velocities and inlet section locations. Lastly, results of a first measurement campaign show the improvement of the prediction of the box model compared to the previous version including this new relation by a better assessment of indoor material contributions to indoor air formaldehyde concentration.

Release and absorption of formaldehyde by textiles

Formaldehyde has been one of the most widely and most controversially debated substances in indoor spaces. Its classification as a human carcinogen by the International Agency for Research on Cancer in 2004 and the EU in 2015 has given rise to further studies into possible indoor emission sources. It is known that the utilization of formaldehyde-containing chemicals in textiles is widespread. As a result, the question arises as to whether, and to what extent, textiles can contribute to contamination of indoor air with formaldehyde. However, there is hardly any information available on this subject, as the formaldehyde content in textiles is generally determined through extraction procedures. In contrast, the procedure used in this work is focused on the conditions of the indoor space. The release of formaldehyde into the ambient air from various textiles is followed using intensive demand intervals under defined climatic conditions in emission chambers. Additionally, extractions are taken in order to determine the content of free formaldehyde. Doping tests enable the differing properties of various textiles to be investigated with respect to the adsorption and desorption processes of formaldehyde. Through the application of a special double chamber, the diffusion of formaldehyde through textile membranes can be determined. The results demonstrate that extraction procedures do not necessarily correctly reveal the emission behavior of textiles.

Diffusion of Formaldehyde on Rutile TiO2(110) Assisted by Surface Hydroxyl Groups

As the photo-dissociation product of methanol on the TiO2 (110) surface, the diffusion and desorption processes of formaldehyde (HCHO) were investigated by using scanning tunneling microscope (STM) and density functional theory (DFT). The molecular-level images revealed the HCHO molecules could diffuse and desorb on the surface at 80 K under UV laser irradiation. The diffusion was found to be mediated by hydrogen adatoms nearby, which were produced from photodissociation of methanol. Diffusion of HCHO was significantly decreased when there was only one H adatom near the HCHO molecule. Furthermore, single HCHO molecule adsorbed on the bare TiO2(110) surface was quite stable, little photo-desorption was observed during laser irradiation. The mechanism of hydroxyl groups assisted diffusion of formaldehyde was also investigated using theoretical calculations.

Active monitoring of formaldehyde diffusion into histological tissues with digital acoustic interferometry.

The preservation of certain labile cancer biomarkers with formaldehyde-based fixatives can be considerably affected by preanalytical factors such as quality of fixation. Currently, there are no technologies capable of quantifying a fixative's concentration or the formation of cross-links in tissue specimens. This work examined the ability to detect formalin diffusion into a histological specimen in real time. As formaldehyde passively diffused into tissue, an ultrasound time-of-flight (TOF) shift of several nanoseconds was generated due to the distinct sound velocities of formalin and exchangeable fluid within the tissue. This signal was resolved with a developed digital acoustic interferometry algorithm, which compared the phase differential between signals and computed the absolute TOF with subnanosecond precision. The TOF was measured repeatedly across the tissue sample for several hours until diffusive equilibrium was realized. The change in TOF from 6-mm thick ex vivo human tonsil fit a single-exponential decay ([Formula: see text]) with rate constants that varied drastically spatially between 2 and 10h ([Formula: see text]) due to substantial heterogeneity. This technology may prove essential to personalized cancer diagnostics by documenting and tracking biospecimen preanalytical fixation, guaranteeing their suitability for diagnostic assays, and speeding the workflow in clinical histopathology laboratories.

Effect of high-voltage electric field on formaldehyde diffusion within building materials

An experimental study concerning the diffusion of formaldehyde within building material in different high-voltage electric fields was conducted. Formaldehyde concentration was tested under electric field intensities of 0, 33.3, 66.6 and 100 kV/m. The Capsule Concentration Footprint Method (CCFM) was proposed to analyse the resulting experimental data. It was found that both equilibrium concentration and emission rate increased under greater electric field intensity. In addition, the experimental data indicated that high-voltage electric fields have a significant effect on partition coefficient, little effect on initial concentration and nearly no influence on diffusion coefficient. The partition coefficient decreased remarkably, while initial concentrations increased slowly due to the increasing electric field intensity. A formula was obtained to explain the relationship between partition coefficient and electric field intensity. A simulation of the adsorption between the formaldehyde and building material was conducted to illustrate the decrease in adsorption potential due to the greater electric field intensity, which helps to understand the principle established by the experimental data. The results of this study confirmed the feasibility of a new method for the reduction of formaldehyde in the man-made boards.

Experimental Study of Formaldehyde Diffusion with in Building Materials in Different High-Voltage Electric Field

An experiment of formaldehyde diffusion within building materials in different high-voltage electric field using different samples had been done. High Density Fiberboard(HDF) was also tested under uniform and nonuniform electric field respectively. The experimental result indicated that formaldehyde emitted from Middle Density Fiberboard (MDF) and HDF were both affected strongly in the action of high-voltage electric field. The influence of electric field to MDF and HDF were obvious and almost same in low electric intensity, while the enhancement of equilibrium concentration of MDF was greater than that of HDF in higher electric intensity. However, the uniform and nonuniform electric field had no obvious different influence to formaldehyde diffusion. It can conclude that it was easier for formaldehyde to emit from both MDF and HDF in high voltage field. The formaldehyde diffused in the building materials can be speeded up under the action of the high-voltage electric field, which provided the feasibility of removing formaldehyde in man-made boards.

Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity

The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, “green” gypsum wallboard, and “green” carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The “green” materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K ma) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in “green” wallboard and “green” carpet. At the same relative humidity level, the “green” wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings. Implications: Based on the results of this study, the sink effects of these commonly used materials (conventional and “green” gypsum wallboards, “green” carpet) on indoor formaldehyde concentration could be estimated. The effects of relative humidity on the diffusion and partition coefficients of formaldehyde were found to differ for materials and for different humidity levels, indicating the need for further investigation of the mechanisms through which humidity effects take place.

Hierarchical structured TiO2 nano-tubes for formaldehyde sensing

Hierarchical structured TiO2 nano-tubes were prepared following a two-step method: the highly ordered uniform TiO2 nanotube arrays were first grown by the conventional electrochemical anodization of the Ti metal sheet followed by mechanical milling of the as-fabricated TiO2 nanotube arrays. The obtained nanotubes with a length around 400nm and opening diameter ∼100nm were formed mixed with the spherical TiO2 single crystals with a diameter around 10nm indicating hierarchical nanostructure. The as-synthesized TiO2 hierarchical nanotubes based resistive-type chemical sensor exhibits good sensitivity to formaldehyde at room temperatures with or without UV-irradiation. The response of the sensor increased almost linearly as a function of the concentration of formaldehyde from 10–50ppm under UV irradiation. The response of the sensor to different relative humidity and other possible interferents such as ammonia, methanol and alcohol was investigated. The larger response of the sensor to formaldehyde relative to these interferents is suggested to be due to the deeper diffusion of formaldehyde into the TiO2 nanotubes.

Modeling and simulations of the removal of formaldehyde using silver nano-particles attached to granular activated carbon

A combined reaction, consisting of granular activated carbon (GAC) adsorption and catalytic oxidation, has been proposed to improve the removal efficiencies of formaldehyde, one of the major indoor air pollutants. In this study, silver nano-particles attached onto the surface of GAC (Ag-GAC) using the sputtering method were evaluated for the simultaneous catalytic oxidation and adsorption of formaldehyde. The evolution of CO 2 from the silver nano-particles indicated that formaldehyde was catalytically oxidized to its final product, with the oxidation kinetics expressed as pseudo-first order. In addition, a packed column test showed that the mass of formaldehyde removed by the Ag-GAC was 2.4 times higher than that by the virgin GAC at a gas retention time of 0.5 s. However, a BET analysis showed that the available surface area and micro-pore volume of the Ag-GAC were substantially decreased due to the deposition of the silver nano-particles. To simulate the performance of the Ag-GAC, the homogeneous surface diffusion model (HSDM), developed for the prediction of the GAC column adsorption, was modified to incorporate the catalytic oxidation taking place on the Ag-GAC surface. The modified HSDM demonstrated that numerical simulations were consistent with the experimental data collected from the Ag-GAC column tests. The model predictions implied that the silver nano-particles deposited on the GAC reduced the adsorptive capacity due to decreasing the available surface for the diffusion of formaldehyde into the GAC, but the overall mass of formaldehyde removed by the Ag-GAC was increased due to catalytic oxidation as a function of the ratio of the surface coverage by the nano-particles.

Coupled heat and formaldehyde migration in dry porous building materials

Due to a lack of accurate description of the coupled heat and formaldehyde migration in dry porous building materials, the characteristics of the heat and mass transfer have not been fully revealed. An improved model of coupled heat and formaldehyde migration is developed and analyzed to investigate the transport features in dry porous building materials. Based on the theory of non-equilibrium thermodynamics and molecular kinetics, the mechanisms of the heat and formaldehyde migration process in dry porous building materials are discussed. The effect of temperature on the transfer coefficients, such as the infiltration coefficient, migration coefficient, apparent thermal conductivity and thermal infiltration coefficient is also presented. The coupled heat and formaldehyde migration process in an ordinary particle board is simulated using a finite difference method. The simulated results indicate that the effect of temperature on the formaldehyde migration in dry porous building materials is obvious. In contrast to the formaldehyde diffusion process, the heat transfer process in the particle board approaches to a steady state more quickly. The formaldehyde emission levels from the particle board in the early stage increase with the increasing temperature gradient, while the formaldehyde concentration remained in the particle board decreases with the increasing temperature gradient. The peak concentration in the chamber increases with the increase of the initial formaldehyde concentration. The reasonability of the present model is verified by the similarity between the numerical results and the experimental data available in the literatures.

On-site determination of formaldehyde: A low cost measurement device for museum environments

A trapping reagent for formaldehyde, based on the pararosaniline reaction, was evaluated as a method of determination of formaldehyde in the aqueous or vapour phase. Collection of formaldehyde vapour relied upon passive diffusion of formaldehyde into the trapping media and quantitative results were obtained without the need for liquid impingers, bubblers or active sampling pumps. Moreover, a novel, hand-held absorption spectrophotometric measurement device was designed to provide on-site, quantitative measurements. It is proposed that the full measurement system devised would be ideally suited to specific sampling applications such as those found in museum enclosures.

Molecular dynamics study of diffusion of formaldehyde in ice

We report a Molecular Dynamics simulation study of the diffusion process of formaldehyde (CH 2O) in proton-disordered ice Ih at atmospheric pressure, in the temperature range 200–273 K. CH 2O molecules diffuse in ice predominantly by jumping between B sites (bond-breaking mechanism), but substitutional diffusion can also be observed. At 260 K, the diffusion constant is predicted to be 4 × 10 −7 cm 2/s with the TIP4P–Ew water model, and 3 × 10 −7 cm 2/s with the TIP4P/Ice water model.

Mass transfer effect in electrochemical oxidation of methanol at platinum electrocatalysts

The influence of the mass transfer on the electrochemical oxidation of methanol was investigated at a rotating disk electrode with smooth polycrystalline Pt and high area carbon supported Pt (Pt/C) as the electrocatalysts. It was found that the reaction rate at the smooth Pt is suppressed significantly by the convection of the electrolyte. The Tafel slope and the reaction order with respect to methanol were also influenced by the convection of the electrolyte. On the contrary, mass transfer influenced neither the reaction rate nor the kinetic parameters of methanol oxidation at the Pt/C electrocatalyst. It was proposed that a reaction path via formaldehyde as a soluble intermediate is operative at both electrocatalysts, but with hindered diffusion of formaldehyde from the corrugated surface of the Pt/C.