Relative Humidity Conditions Research Articles

The Impact of Indoor Air Humidity on the Infiltration of Ambient Particles

Ambient particles contribute to occupant exposure as they infiltrate indoor environments through building envelope cracks, impacting indoor air quality. This study investigates the impact of indoor air humidity on the infiltration of ambient particles, highlighting humidity’s crucial role in influencing particle dynamics in indoor environments. Employing a controlled chamber system, we conducted experiments to quantify the infiltration of size-resolved particles under varying relative humidity (RH) conditions. Both the total number and the mass concentration of particles increased with RH in the experimental chamber. The smallest particles (0.3–0.4 μm) experienced reduced infiltration at higher RH levels due to hygroscopic growth, while intermediate-sized particles showed increased infiltration, resulted from coagulation effects. Large particles (>1.0 μm) demonstrated reduced infiltration factors, caused by lower penetration and higher deposition rates, with minimal impact from RH changes. Our findings reveal that RH influences particle hygroscopic growth, deposition rate, and coagulation process, thereby affecting indoor particle size distribution and concentration.

Influence of Humidity on Layer-by-Layer Growth and Structure in Coordination Networks.

Metal-organic frameworks (MOFs) are promising materials because of their high designability of pores and functionalities. Especially, MOF thin films and their properties have been investigated toward applications in nanodevices. Typically, MOF thin films are fabricated by using a bottom-up method such as layer-by-layer (LbL) growth in air. Because the water molecules can coordinate and be replaced with organic linkers during synthesis, humidity conditions will be expected to influence the LbL growth processes. In this study, we fabricated MOF thin films composed of Zn2+, tetrakis-(4-carboxyphenyl)-porphyrin (TCPP), and 4,4'-bipyridyl (bpy) at 10 and 40% relative humidity (RH) conditions. Then, we investigated the humidity effects on chemical compositions of TCPP and bpy, periodic structure, orientation, and surface morphology. At high RH, coordination replacement of water with the organic linkers becomes more competitive than that at low RH, resulting in a different TCPP/bpy composition ratio between the two RH conditions. Also, more frequent coordination replacements of water with the organic linkers at high RH led to the formation of phases other than that observed at low RH, loss of growth orientation, and rough surface. The findings clarified the importance of controlling the RH condition during LbL growth to obtain the desired coordination networks.

ErFeO3/α-Fe2O3 nanocomposites derived from MIL-100(Fe) for acetone sensing

Acetone, a flammable and volatile liquid, is toxic and can affect human well-being. Additionally, its presence in exhaled air can indicate the state of human respiratory health. Therefore, the investigation of an acetone gas sensor holds significant urgency in the realm of scientific research. Metal-organic frameworks (MOFs) exhibit significant promise in the field of gas detection due to their extensive surface areas, remarkable porosity, and the inclusion of unsaturated metallic sites. The study conducted the preparation of ErFeO3/α-Fe2O3 nanocomposites through impregnation and oxidation roasting methods. EF21 (MEr(NO3)3∙6H2O:MMIL-100(Fe) = 2:1) exhibited a large surface area of 43.7 m2/g and a high abundant oxygen vacancy of 12.5 %. Gas sensing experiments revealed that the EF21-based gas sensor exhibited a strong response of 55 towards 100 ppm acetone, with a low detection limit of 2 ppm (S = 3.3). Notably, the sensor demonstrated excellent selectivity towards acetone over other volatile organic compounds (e.g., ethanol, methanol, ammonia, ether, and toluene) in gas selectivity tests. Moreover, the EF21-based gas sensor maintained its responsiveness to acetone even under high relative humidity conditions (RH:90 %, S = 27) and demonstrated stability over a 15-day long-term test. The study provided a comprehensive explanation of the gas sensing mechanism responsible for the enhanced performance observed in ErFeO3/α-Fe2O3 through detailed analyses.

Formulation and Antimicrobial studies of Microencapsulated Musanga cecropioides Stem Bark Extract

Microencapsulation is the process of coating small droplets of liquid or solid materials with a continuous film of polymeric substances. The aim of the research was to formulate microparticles of Musanga cecropioides stem bark extract. The dried, powdered stem bark of Musanga cecropioides was extracted by maceration. The aqueous extract was microencapsulated using polymers such as alginate, pectin and hydroxylpropyl methylcellulose acetate succinate (HPMCAS) by counter-ion coacervation method using an electrostatic droplet generator. The formulated microcapsules were evaluated for flow properties, particle size, drug content, antimicrobial activity and in vitro release kinetics in simulated gastric and intestinal fluids. The microparticles were subjected to stability tests under different temperature (45°C, 25°C and 8°C) and relative humidity (100% RH, 78% RH and 0% RH) conditions for a period of three (3) months. The mean particle size of the microcapsules decreased with increasing applied voltage of the electrostatic generator. Particle size range for the batches of formulated microparticles was 68.20-223.84µm. The percentage entrapment efficiency of the batches of microparticles ranged from 80.26-86.58%. The microparticles lost a significant percent of its drug content after storage at different temperature and relative humidity conditions. The formulated microparticles and crude extract possess significant antibacterial action against both gram positive and negative bacteria as well as antifungal effect against C. albicans. Microparticles of M. cecropioides extract were formulated by counter-ion coacervation method using an electrostatic droplet generator which conferred advantages of sustained drug release, reduced frequency of dosing, masked unpalatable taste, improved stability and enhanced patient acceptance on the crude extract.

LIQUID AND SOLID SELF-EMULSIFYING DRUG DELIVERY SYSTEMS (SEDDS) CONTAINING VALSARTAN: STABILITY ASSESSMENT AND PERMEABILITY STUDIES

Objective: Valsartan (VST) is a Biopharmaceutical classification system (BSC) class II active ingredient with a bioavailability of approximately 25% and is utilized to treat high blood pressure (hypertension). This study aimed was to showcase the stability and increase the permeability of VST by developing self-emulsifying drug delivery systems (SEDDS) and solidified SEDDS (S-SEDDS) formulations. Material and Method: The ratios of the components were determined by the pseudo-ternary phase diagram, and the characterization studies were conducted in the previous study. Stability was performed in long-term (25±2˚C, 60±5% relative humidity) and accelerated (40±2˚C, 75±5% relative humidity) conditions. The intestinal permeability of SEDDS formulations was evaluated by Caco-2 cells. Result and Discussion: Formulations for 12 month, droplet sizes were found to be 67.52 ± 5.26 nm and 176.93 ± 17.34 nm for SEDDS of VST (VST-SEDDS) and S-SEDDS of VST (VST-S-SEDDS), respectively. During this period, polydispersity indexes were: VST-SEDDS, 0.56±0.1; VST-S-SEDDS, 0.58±0.05. Both formulations increased VST permeability across Caco-2 cells: VST-SEDDS by 2.32x (powder) and 2.18x (commercial); VST-S-SEDDS by 1.38x (powder) and 1.30x (commercial). The formulation components did not have cytotoxic effects. These results demonstrated that newly developed VST-SEDDS and VST-S-SEDDS formulations with high permeability may be a desirable approach for antihypertensive therapy.

The impact of environmental humidity on the mechanical property and microstructure of magnesium silicate hydrate cement

Environmental factors have a significant impact on the performance of cement-based materials. As a new type of low-carbon cementitious material, the performance of magnesium silicate hydrate cement (MSHC) under different environmental humidity conditions is crucial for its application. This study aimed to investigate the effects of environmental humidity on the hardening properties of MSHC. Compressive strength tests of MSHC were conducted under four different relative humidity (RH) conditions (RH of 33%, 58%, 75%, and 97%) and water curing (RH-w) condition. Microanalysis techniques were employed to reveal the strength mechanisms of MSHC under different environmental humidity conditions. The results showed that MSHC exhibited the optimal mechanical performance when RH was 75%, reaching 42.29 MPa. When RH was 58%, the compressive strength of MSHC was close to the optimal level, which was 41.02 MPa. However, under other humidity conditions (RH33, RH97, and RH-w), the compressive strength of MSHC was much lower than the optimal level, decreasing by 30.93%, 41.90%, and 63.66%, respectively. Pore structure analysis showed that the volume of detrimental pores (>100 nm) in the sample was the lowest when RH was 75%. Compared with RH75, the volume of detrimental pores in RH33, RH58, RH97, and RH-w increased by 20.47%, 9.83%, 36.77%, and 156.92%, respectively. In addition, the variation of environmental humidity resulted in different polymerization levels in the M-S-H gel, and higher degrees of polymerization were observed when RH was 58% and 75%.

Facile synthesis of natural stearic acid modified carbon adsorbent for toluene adsorption under high humidity conditions

The diminished adsorption efficiency of porous carbon for volatile organic compounds (VOCs) in high-humidity conditions poses a critical challenge that limits its widespread application. This study presents a facile method for enhancing the adsorption capacity of coffee grounds activated carbon in high-humidity environments through stearic acid modification. The incorporation of 20 % stearic acid (20 % ST-AC) significantly amplifies the saturated adsorption capacity and penetration duration of porous carbon for toluene under high-humidity conditions. Specifically, the toluene adsorption capacity improves from 230 mg/g to 498 mg/g in an 80 % relative humidity condition. However, increasing the stearic acid doping ratio beyond 20 % has a limited impact on moisture resistance while leading to micropore blockage, resulting in a significant reduction in toluene adsorption capacity. Additionally, 20 % ST-AC demonstrates excellent adsorption recycling performance over five cycles, maintaining 97 % of its original adsorption capacity. This study provides a novel perspective on the preparation of hydrophobic activated carbon, which helps to address the challenge of VOC adsorption in high-humidity flue gas environments.

Modeled versus Experimental Salt Mixture Behavior under Variable Humidity.

This study investigates the kinetics of salt mixture crystallization under relative humidity (RH) conditions, varying between 15 and 95% (at 20 °C), to inform applications in built heritage preservation, geology, and environmental sciences. We focused on commonly found, sulfate-rich and calcium-rich salt mixtures containing five to six ions, Cl-, NO3-, Na+, and K+, including or excluding less common Mg2+, and including either an excess of SO42- or Ca2+, with respect to gypsum. Using time-lapse micrographs and dynamic vapor sorption, we explore how crystallization and dissolution behavior depend on RH and mixture composition under constant temperature. A range of RH change rates were studied to simulate realistic weather events. Microstructural analyses through environmental scanning electron microscopy (ESEM) confirmed the crystal habit corresponding with RH transitions. Phases predicted from thermodynamic modeling (ECOS/RUNSALT) were confirmed using micro-Raman spectroscopy, X-ray diffraction (XRD), and elemental mapping via energy-dispersive X-ray spectroscopy (EDX). We identify a strong correlation between phase transition kinetics and RH change rates, with crystallization deviating by -15% and dissolution by +7% from modeled values under rapid (several seconds) and slow (several days) RH changes. These insights are important for preservation strategies in built heritage, salt deposition, and dissolution mechanisms in diverse geological and realistic environmental contexts, laboratory experiments, future modeling efforts, and the understanding of stone decay in general.

Impact of internal pre-damage due to drying shrinkage under various humidity conditions on DEF expansion in cement paste and mortar

This study explores the impact of internal pre-damage from early drying shrinkage on the delayed ettringite formation (DEF) expansion behavior of cement-based materials subjected to high-temperature processes. Specimens of cement paste and mortar with water-cement (W/C) ratios of 0.4, 0.5, and 0.6 were characterized after curing under relative humidity (RH) conditions of 50, 70, and 100 for 56 days. The parameters assessed were drying shrinkage, dynamic elastic modulus, and free water content. Subsequent DEF expansion over time was quantified, and the underlying mechanism was analyzed using XRD and SEM techniques after 270 days of underwater curing. Results indicate that: (1) a lack of adequate early curing humidity significantly reduces the dynamic elastic modulus with more than a 10% drop in cement paste following 56 days at RH50; (2) a higher W/C ratio and lower early curing humidity lead to more internal damage due to shrinkage, thereby promoting DEF expansion; (3) drying intensifies internal pre-damage in the interfacial transition zone (ITZ), causing an earlier deterioration of DEF expansion in mortar compared to cement paste. However, the presence of aggregates constrains this, leading to lesser DEF expansion in mortar; (4) dynamic elastic modulus changes as measured by ultrasonic methods can quantitatively characterize the extent of deterioration caused by DEF expansion, thus offering a tool for non-destructive testing and DEF expansion deterioration analysis.

Aging properties of a vegetable‐based polyurethane foam under high relative humidity and different temperatures

AbstractThe objective of this study is to assess, characterize, and forecast the aging effects on the mechanical properties of a vegetable‐based polyurethane foam (PUF) derived from castor oil under elevated relative humidity conditions and at two distinct load orientations (aligned with the expansion direction and perpendicular to it). Ten specimens were subjected to temperatures of 60, 75, and 90°C, along with a relative humidity of 90%, for a duration of up to 60 days. Compression tests, following ASTM D1621‐16 standards and supplemented by 3D digital image correlation, revealed nearly isotropic behavior with marginally lower compression strength in the expansion direction. On the other hand, the strength of the foams at 90°C was higher in that direction. This led to a smaller activation energy (Ea) in this property, which ended up showing a shorter lifespan prediction considering the strength retention in this direction. The stiffness values were proportionally more similar in both directions than the strength ones and this was observed in the Ea for those curves. In contrast to several other foams and polyurethanes, the one examined in this study exhibited consistently higher Ea values for its mechanical properties, particularly in the transverse direction to expansion, surpassing 94 kJ/mol. This indicates a robust diffusion and chemical stability, suggesting its potential for prolonged utilization compared to conventional oil‐based foams. A prediction was made that this foam would lose 50% of its stiffness and strength in around 9.8 and 9.5 years at 20°C, respectively, considering the directions more sensitive to the aging process. This research offers valuable insights for predicting lifespan based on operating temperatures and property retention needs, contributing to the advancement of sustainable materials in structural applications.Highlights Fifty specimens investigated for each of two directions. Evaluation of vegetable‐based PUF aging process unveils density changes. Unique behavior noted: different Ea values for each direction. High Ea values indicate enhanced mechanical stability over oil‐based foams. Lifespan prediction enhances material application prospects.

Research on the Effectiveness of Tetraethoxysilane-Reinforced Earthen Site: Influence of Soil Water Content and Curing Humidity

ABSTRACT To investigate the influence of soil water content and curing humidity conditions on the reinforcement effect of tetraethoxysilane on earthen sites, remolded rammed earth samples with 0%, 5%, 10%, and 14.5% water content were prepared and reinforced by tetraethoxysilane and then placed in the relative humidity conditions of 35%, 65%, and 85% for 28 days. The basic physical, mechanical, and durability properties of samples before and after reinforcement were evaluated, and the mechanism was clarified through microscopic analysis. Results showed that tetraethoxysilane strengthened the connection between soil particles and filled the pores by generating Si-O-Si groups mainly through a hydrolysis reaction. Under the same humidity condition, tetraethoxysilane had a better effect on the mechanical and durability properties of samples with low water content (0% and 5% in this paper), while it generated a weak reinforcement effect on the samples with high water content (10% and 14.5% in this paper). For samples with the same water content, too high a curing humidity condition (85% in this paper) was not favorable to the reinforcement effect of tetraethoxysilane. These conclusions were confirmed by microscopic analysis, including scanning electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy.

Infectiousness model of expelled droplets exposed to ultraviolet germicidal irradiation coupled with evaporation

Respiratory diseases propagated by droplet-based transmission are a serious public health hazard, leading, in extreme cases, to pandemics such as influenza and the recent Coronavirus outbreak. Droplet infectiousness evolves in response to the environment in such a way that it decreases with time and distance from the source. Droplets can also be treated with ultraviolet germicidal irradiation (UVGI) to accelerate the reduction in their survival rate. In addition, airflow management and furnishings in public spaces can be optimized to reduce exposure to expelled droplets. This introduces a role for engineered medical interventions based on precise modelling of the time evolution of droplet infectiousness. However, information is lacking on computational fluid dynamics (CFD) simulations of the time evolution of droplet infectiousness when exposed to both evaporation and UVGI at the same time. Therefore, in this study, we developed and presented algorithms for tracking droplet infectiousness in a CFD simulation. The variations of droplets’ infectiousness were investigated through the combination of parameters describing humidity and temperature, as well as the deployment of UVGI in confined public space environments. We have shown that, for airborne droplets, increased temperature leads to decreased infectiousness in propagation lengths and entrainment time, while increased humidity leads to increased infectiousness propagation lengths and entrainment times. Smaller droplets with diameters ≤ 110 μm remain entrained longer in the air, whereas droplets with a diameter ≥ 140 μm travel in the air stream for a relatively short time before falling to a surface due to gravity, depending on the specific relative humidity (RH) and temperature conditions. Thus, our data suggest that infectiousness of droplets is substantially reduced due to the influence of evaporation, and it is further decreased when exposed to UV irradiance. We also show that, due to the combined influence of UVGI and evaporation conditions, the infectiousness of droplets decreased faster. Our model can track droplet infectiousness, thus helping to understand how the spread of infectious droplets is reduced in a confined environment.

The effect of water activity on thermal resistance of Salmonella in chocolate products with different fat contents

Several instances of Salmonella outbreaks have been documented in association with chocolates. Conching, an important chocolate manufacturing step, may be designed for control of Salmonella if proper product temperature is maintained for sufficient time. A better understanding of thermal inactivation kinetics of Salmonella in different chocolate products is, however, highly desirable in evaluating the effectiveness of an existing conching process for Salmonella reduction or assessing the need for modification of manufacturing operations. Our previous study on milk chocolate (41.8% fat content) noted that aw and temperature are two key factors influencing Salmonella inactivation in a thermal process. In this research we studied the effect of different fat levels on Salmonella inactivation in chocolates at 80 °C. White and dark chocolates (fat content: 53.0% and 74.3%) were used in this study. The samples were conditioned to three water activity (aw) levels, 0.23, 0.33, and 0.43, at room temperature. The changes of aw in these samples were quantified when heated to 70 °C and 80 °C to reflect the real relative humidity conditions during the process. The data indicated an increase in the aw in the chocolate products, correlating with elevated temperatures. The thermal inactivation tests showed that D-values (time to achieve one log reduction at a fixed temperature) of Salmonella were between 33.9 and 46.5 min when treated at 80 °C, the corresponding aw,80 °C were 0.29 and 0.28 in white and dark chocolate samples, respectively. Our data suggests that the higher fat content contributed to a less increase in aw, leading to a higher heat tolerance of bacteria in the chocolates. The research results may offer useful insights for the chocolate manufactures to utilize conching process for the pathogen control of chocolate products made with different recipes.

Adsorption of DMMP and water vapor on granular activated carbon: An experimental and molecular simulation study

The adsorption behavior of Dimethyl methylphosphonate (DMMP), as a simulant of sarin nerve agent, especially in the presence of water vapor, is crucial for the design of efficient chemical protection equipment. Experimental results reveal DMMP's adsorption isotherm on granular activated carbon (GAC) as a typical type I. The adsorption process was a spontaneous and exothermic physical adsorption process, and the adsorption mechanism was in accordance with Dubinin's micropore filling theory. In the relative humidity range of 10 % ∼ 90 %, the isotherm remained I-type, and the effect of water vapor on the equilibrium adsorption capacity and apparent adsorption rate was weak. Molecular simulations also show that DMMP adsorption on GAC follows a type I isotherm, primarily driven by van der Waals forces of physical adsorption. The adsorption potential energy between DMMP and GAC surpasses that of water molecules, resulting in negligible effects from water vapor on DMMP adsorption equilibrium. Meanwhile, water molecules had minimal effect on the diffusion of DMMP molecules in the GAC pores, and the positional distribution of DMMP multilayer adsorption was consistent under different relative humidity conditions. Furthermore, the presence of polar functional groups such as hydroxyl groups significantly affects the adsorption equilibrium of DMMP.

VARIATIONS OF δ18О AND δ2H VALUES OF PRECIPITATION IN MOSCOW FROM 2017 TO 2019

To reveal variations in the iso topic composition of O and H in the atmospheric precipitation in Moscow and the processes influencing the isotope composition, all events of precipitation in 2017-2019 were sampled at the Meteorological Observatory of the Moscow State University: 158 samples in 2017, 119 samples in 2018 and 143 samples in 2019. The study is a prolongation of continuous measurements of the isotope composition of precipitation, started by authors in 2014. The study of the isotope composition of precipitation at the MSU Meteorological Observatory was supported by the IAEA and became a part of the Global Network of Isotopes in Precipitation (GNIP) database. It has been found that the intra-annual variability of the isotop e composition of precipitation has a pronounced seasonality. The most isotopically heavy precipitation falls from May to August, and the most isotop ically light precipitation at December-February, mainly due to seasonal air temperature variations. The ratio of the average monthly δ18O values in precipitation and air temperature for the study period varied from 0.34 to 0.39‰/°C, which is consistent with the previously obtained data for precipitation in Moscow. The δ2H-δ18O ratio in precipitation was clos e to that of the Global Meteoric Water Line, pointing to the equilibrium conditions during precipitation formation. It was established that in the summer months isotopic composition is significantly influenced by undercloud evaporation. The deuterium excess va lues in precipitation are not markedly seasonal; however, lower dexc values (below the 3-year average of 11‰) are typical for the summer months (July-August). It is most likely due to undercloud evaporation in conditions of low relative humidity and high air temperatures. Higher dexc values (above 11‰) prevailed from October to April.

Interface modification for efficient carbon-electrode CsPbI2Br perovskite solar cells using ionic liquid.

All-inorganic CsPbI2Br, as a promising photovoltaic (PV) material, have attracted extensive research attention in society for its outstanding thermal stability and appropriate trade-offs. Carbon-based perovskite solar cells (C-PSCs) without hole transporting layer (HTL) have shown great potential in terms of cost-effectiveness and stability. However, the inevitable defects on the surface of CsPbI2Br films severely hampers the development of high-efficiency CsPbI2Br C-PSCs. Surface engineering has emerged an effective approach to overcome this challenge. Herein, 1-decyl-3-methylimidazolium tetrafluoroborate (DMTT) ionic liquid was introduced between CsPbI2Br and carbon electrode to reduce non-recombination of charges, decrease defect states, minimize the energy-level mismatch, and greatly enhance the device stability. As a result, the HTL-free CsPbI2Br C-PSCs combined with DMTT as an interface modification achieved a higher power conversion efficiency (PCE) of 12.47% than that of the control devices with a PCE of 11.32%. Furthermore, without any encapsulation, the DMTT-optimized C-PSC remained approximately 84% of its initial PCE after over 700 h under room temperature and 25% relative humidity (RH) conditions. Additionally, when exposed to a temperature of 65 °C for over 400 h, the device still retained 74% of the initial PCE, demonstrating its thermal stability.

A Smoke Chamber Study on Some Low-Cost Sensors for Monitoring Size-Segregated Aerosol and Microclimatic Parameters

Low-cost sensors (LCSs) of Geekcreit PM1/PM2.5/PM10 (based on a PMS5003 sampler) and BOHU BH-1 models A3 and B3 (based on a Pando G7 sampler) were compared for different aerosol size ranges using a research-grade instrument (Grimm 1.109) under controlled laboratory conditions. An aerosol generator was utilized to produce various sizes of monodispersed particulate matter (PM), which was introduced into a laboratory smoke chamber under resistance heating/cooling and/or varying RH conditions. In addition, the accuracy of the air temperature (T) and relative humidity (RH) sensors of the LCSs were assessed against calibrated, laboratory-grade instruments. The study LCSs showed generally accurate readings for PM2.5, irrespectively of the slow T and/or RH changes, which provided apt conditions for accurate calibration slopes (S) and low intercepts/bias (b) of the linear fits. On the other hand, PM1 and PM10 readings slightly deviated from those observed with the reference monitor, likely due to the lower detection efficacy of the LCSs towards fine and coarse PM. Varying RH influenced the S and b values, showing its impact on the detection efficacy of LCSs. Under low/medium RH, homoscedastic calibration curves of PMx were found, whereas rather heteroscedastic calibration plots were observed at high RH. For T calibration, low RH in the smoke chamber provided more reproducible conditions in terms of lower measurement bias for LCSs as recorded against a calibrated, reference-grade thermometer.

On the dependence of electrical mobility on temperature, humidity and structure of alkylammonium ions

Insights into the effect of temperature (T) and relative humidity (RH) as well as structure and polarisation on ion mobility help the comparison and interpretation of mobility and mass-based data. We measured alkylammonium ions in air under different T (14 °C, 24 °C, 34 °C and 41 °C) and RH (0 %, 20 %, 40 %) conditions using two individual setups (in both cases a planar differential mobility analyser coupled with a time-of-flight mass spectrometer) and the results are in excellent agreement. Mobility increases with rising T and decreases with water vapour loading. When separating the measurement mobility by structures, clear mass dependence was observed. The measured mobilities exhibited large deviations from theoretically calculated results in dry conditions, which are possibly caused by adduct formation on the monomer ions via clustering (or reactions). This phenomenon seems to be unavoidably associated with light ions under atmospheric pressures, which is worth further exploration and bearing in mind when comparing measurements to calculations. Both methanol and oxygen (occasionally nitrogen or alkyl chain elongation) are possible candidates of the adduct. Under spherical assumption, we used the modified Mason–Schamp's approximation to link the measured mobility to the mobility equivalent diameter. The drag enhancement factor ξ and the effective gas-molecule collision diameter dg derived from our measurement data are comparable to literature values. Our data also exposed a non-linear dependence on the polarisation parameter ε*. Polarisation, ξ and dg were parameterised using linear models against ion structures, T, and RH for primary, secondary and tertiary alkylammonium ions with identical alkyl groups. Our model parametrisations predict mobilities within ±10 % deviation from the measured data. The model also has satisfying predicting power for alkylammonium ions with unidentical alkyl structures.

Doping/breath figure method triggered reversible diethylchlorophosphate vapor sensing

Aggregation-caused quenching (ACQ) is the key reason why thin-film fluorescence sensing studies have lagged. A facile two-step strategy combining doping with breath figure method (BF) is capable to suppress the ACQ effect without sacrificing the sensing property of the molecule. In this work, two long-wavelength fluorescent probes, Me4BOPHY-1 and Me4BOPHY-2, were synthesized by introducing one or two diethylaminophenyl group in the α-position of Me4BOPHY. Upon addition diethylchlorophosphate (DCP) to the solution of the probes, the initial intramolecular charge transfer (ICT) process is restrained. Thus, the intense fluorescence from Me4BOPHY core was released together with a dramatical color change. As the typical ACQ probes, Me4BOPHY-1 and Me4BOPHY-2 can’t be used in vapor-detection directly due to their weak fluorescence in the solid-phase. By means of being doped with polystyrene solution and being spin-coated under the optimal relative humidity conditions, porous films for DCP vapor detection were prepared with a high detection performance of a 162-ppb low detection limit. Moreover, it is exciting that these films show two outstanding characters of anti-interference to HCl gas and reversibility, which have not been reported in previous studies. This work breaks the application boundary of ACQ materials and provides an inspiration for the development of thin-film fluorescence sensors.

Selective Detection of NH3 Gas by Ti3C2Tx Sensors with the PVDF-ZIF-67 Overlayer at Room Temperature.

In the realm of NH3 gas-sensing applications, the electrically conductive nature of Ti3C2Tx MXene, adorned with surface terminations such as -O and -OH groups, renders it a compelling material. However, the inherent challenges of atmospheric instability and selectivity in the presence of gas mixtures have prompted the exploration of innovative solutions. This work introduces a strategic solution through the deposition of a mixed-matrix membrane (MMM) composed of poly(vinylidene fluoride) (PVDF) as the matrix and zeolitic imidazolate framework-67 (ZIF-67) as the filler. This composite membrane acts as a selective filter, permitting the passage of a specific gas, namely NH3. Leveraging the hydrophobic and chemically inert nature of PVDF, the MMM enhances the atmospheric stability of Ti3C2Tx by impeding water molecules from interacting with the MXene. Furthermore, ZIF-67 is selective to NH3 gas via acid-base interactions within the zeolite group and selective pore size. The Ti3C2Tx sensor embedded in the MMM filter exhibits a modest 1.3% change in the sensing response to 25 ppm of NH3 gas compared to the response without the filter. This result underscores the filter's effectiveness in conferring selectivity and diffusivity, particularly at 35% relative humidity (RH) and 25 °C. Crucially, the hydrophobic attributes of PVDF impart heightened stability to the Ti3C2Tx sensor even amidst varying RH conditions. These results not only demonstrate effective NH3 detection but also highlight the sensor's adaptability to diverse environmental conditions, offering promising prospects for practical applications.