Moisture Adsorption Desorption Research Articles

Multi-plateau water adsorption of pyrene-based covalent organic frameworks for potential humidity control

Indoor air humidity significantly influences air quality, human health, and work performance. Covalent organic frameworks (COFs) have been proven effective in humidity regulation; however, challenges remain in broadening their range of humidity control. This study designs and synthesizes a series of pyrene-based crystalline COFs as humidity control materials, investigating the moisture adsorption–desorption characteristics under structural modulation. Among these, PY-3,3′-BPY-COF exhibits unique multi-step adsorption isotherms, achieving the highest water uptake capacity (1 g/g) and efficient water uptake-release cycles. Theoretical and experimental analyses reveal a linear relationship between the maximum water uptake rate and the specific surface area, while the adsorption inflection points are influenced by the water binding energy and pore size distribution. Importantly, the introduction of strong binding sites promotes multi-step adsorption phenomena, significantly enhancing the humidity control capabilities of COFs across a wide range of humidity levels. This research introduces an innovative approach for broad-spectrum indoor humidity control and reveals the fundamental relationship between the structure characteristics of COFs and their capabilities in water adsorption and release.

Biomimetic bilayer phase change hydrogels with enhanced water adsorption and desorption for evaporative cooling

Hygroscopic hydrogels, reliable carriers for water-based evaporative materials, undergo shrinkage after evaporative cooling, and the consequent reduction in hygroscopic sites can significantly impair their recyclability in cooling period. To realize cyclic evaporative cooling for rapid regeneration and evaporation, bilayer phase change hydrogel (BPH) concept combining an upper layer of hygroscopic polymer film (CaCl2@ carboxymethyl cellulose/konjac glucomannan films, CaCl2@CMC/KGM, MAF) with a lower layer of hygroscopic hydrogel (CaCl2@poly(vinyl alcohol)/sodium tetraborate decahydrate hydrogel, CaCl2@PVA/Borax, PCH), is presented in this paper. The high liquid–vapor phase change enthalpy of BPH (1274 J/g) enables it to continuously and rapidly remove heat. Benefiting from the MAF hygroscopic porous skeleton, the saturated BPH exhibited a faster water evaporation rate (2.15 kg m−2 h−1) and comparable water vapor transmission rate (1.61 kg m−2 h−1) at 50 °C. After being heated at 50 °C for 1 h, BPH requires 9h to regain its initial mass at 25 °C, 90 % RH. Fifteen moisture adsorption–desorption cycles demonstrate the excellent cyclic regeneration capability of BPH. COMSOL Multiphysics simulation results indicate that evaporative cooling in BPH provides excellent heat dissipation (reduced by about 27 °C). BPH reduces the peak temperatures of a mobile phone by 7.8 °C while charging and 6.5 °C while gaming. This design will contribute to the future cooling of heat-related devices and global sustainability.

Moisture Adsorption-Desorption Behaviour in Nanocomposite Copolymer Films.

Dehumidifying air via refrigerant cooling method consumes a tremendous amount of energy. Independent humidity control systems using desiccants have been introduced to improve energy efficiency. This research aimed to find an alternative to the commonly used solid desiccant, silica gel, which has weak physical adsorption properties. It also aimed to overcome the limitation of liquid desiccants that may affect indoor air quality and cause corrosion. This study reports on the synthesis of poly(vinyl alcohol-co-acrylic acid), P(VA-AA), through solution polymerisation by hydrolysing poly(vinyl acetate-co-acrylic acid), P(VAc-AA). This viable copolymer was then incorporated with graphene oxide (GO) at different concentrations (0 wt.%, 0.5 wt.%, 2 wt.% and 5 wt.%) to enhance the adsorption-desorption process. The samples were tested for their ability to adsorb moisture at different levels of relative humidity (RH) and their capability to maintain optimum sorption capacity over 10 repeated cycles. The nanocomposite film with 2% GO, P(VA-AA)/GO2, exhibited the highest moisture sorption capacity of 0.2449 g/g for 60-90% RH at 298.15 K, compared to its pristine copolymer, which could only adsorb 0.0150 g/g moisture. The nanocomposite desiccant demonstrated stable cycling stability and superior desorption in the temperature range of 318.15-338.15 K, with up to 88% moisture desorption.

Structural properties of volcanic precursors-based geopolymers before and after natural weathering

The structural properties of geopolymers based on locally available volcanic feedstocks were here investigated in the optics of the development of sustainable non-structural building materials. Geopolymer binders and mortars based on two volcanic pyroclastic residues from Mt. Etna (ejected ash and a paleosoil, named “ghiara”) were studied to assess the effects of natural weathering.The strength and durability of the resultant products were examined before and after six months of outdoor exposure by comparing ultrasound pulse velocity (UPV), specific weight, Brazilian Disk test (BD) and Digital Image Correlation (DIC) together with Dynamic Vapour Sorption (DVS) results. DVS data were also compared to those of pure salts (e.g. sulphates and carbonates) commonly occurring in geopolymers as efflorescences.The results obtained on unexposed and exposed samples and the relationship between the moisture transportation, efflorescence development, and structure degradation have shown a better response of the volcanic ash-based geopolymers to weathering in the hot summer Mediterranean climate zone than ghiara-based products. The latter are more affected by exposure conditions as revealed by the decrease of UPV, the influence of efflorescences on moisture adsorption-desorption curves and the consequent worsening of mechanical performances.The correlation between UPV and DVS applied for the first time to the study of volcanic precursors-based geopolymers exposed to natural weathering has proven to be an effective and useful tool for assessing the durability of materials.

Engineering and scaling-up ceramic tiles with humidity self-regulation functionality

The humidity regulation in the interior spaces of buildings by means of passive solutions that do not require energy consumption is a topic of great interest due to the current needs for comfort and energy efficiency. This paper addresses the engineering of humidity regulating ceramic tiles that incorporate a functional coating formulated from gibbsite together with other common raw materials whose moisture regulating capacity has been demonstrated previously. A multi-layer coating tile system has been proposed, consisting of the following elements: an engobe layer, the functional coating with the regulating capacity, a decoration by inkjet technology and a protective topcoat glaze.This system has been analysed with moisture adsorption–desorption tests. The moisture regulation capacity and the effect of the coating thickness on this property have been determined, allowing to optimise the functionality.Finally, an analysis of the humidity regulation has been performed on the basis of demonstrators or small-sized cubicles that simulate the conditions of final use in rooms of buildings. The results show the different behaviour of the demonstrator with functional tiles in relation to conventional tiles, with an indoor ambient humidity that remains in the comfort zone for longer periods of time.

Moisture adsorption-desorption full cycle power generation

Environment-adaptive power generation can play an important role in next-generation energy conversion. Herein, we propose a moisture adsorption-desorption power generator (MADG) based on porous ionizable assembly, which spontaneously adsorbs moisture at high RH and desorbs moisture at low RH, thus leading to cyclic electric output. A MADG unit can generate a high voltage of ~0.5 V and a current of 100 μA at 100% relative humidity (RH), delivers an electric output (~0.5 V and ~50 μA) at 15 ± 5% RH, and offers a maximum output power density approaching to 120 mW m−2. Such MADG devices could conduct enough power to illuminate a road lamp in outdoor application and directly drive electrochemical process. This work affords a closed-loop pathway for versatile moisture-based energy conversion.

A simple method to valorize silica sludges into sustainable coatings for indoor humidity buffering

In this study, the production of indoor humidity-buffering coatings (IHC-s) from recycling waste silica sludges by using a room-temperature sol-gel method which is a simple and energy-efficient route is reported. The properties of these IHC-s are identified by scanning electron microscope, X-ray diffraction, X-ray fluorescence spectrometer, laser particle size analyzer, N2 adsorption-desorption isotherms and toxicity characteristic leaching procedure (TCLP). The moisture adsorption-desorption tests show that the IHC-s have moisture buffering values of ca. 270–316 g m− 2 and moisture contents of 23.6–26.7% in the range of 50–90% relative humidity (RH). Furthermore, the humidity buffering capacities, moisture adsorption-desorption rate and stability are significantly superior to commercially available coatings in the range of 50–75% RH. The enhancement may be due to the formation of porous structure in the coatings via the dispersed waste silica sludges and gypsum which transformed from bassanite by self-assembly process. Most importantly, the prepared IHC-s show surpassing antimicrobial efficacy (> 99.99%) and no detectable leaching heavy metals based on TCLP tests, which provides an economic and environmental-friendly route for recovering and valorizing industrial wastes.

Air dehumidification with advance adsorptive materials for food drying: A critical assessment for future prospective

In food processing, drying is an important unit operation for preserving the product quality by moisture content reduction. However, some drying processes suffer from technical and economical drawbacks mainly related to low process efficiency, high energy cost, and product quality degradation. Drying food products using dehumidified air at low temperature is one of the smart options to solve the abovementioned problems. This review presents some challenges and opportunities for dehumidifying air to enhance the driving force for drying. The potential of some solid materials, namely zeolite, silica-based materials, activated carbons (ACs), and other biomass-based materials, as moisture adsorbents for air dehumidification in food drying applications is also discussed. This paper also comprehensively reviews the recent perspectives and emerging technologies in the development of efficient adsorbent materials for air dehumidification, moisture adsorption–desorption characteristics, and its potential for food drying application. Moreover, some crucial parameters for advancing the research and development of adsorptive dehumidification systems are criticized in this review paper.

Freezing-induced hierarchical porous manganese dioxide with excellent humidity tolerance for indoor formaldehyde removal

The K-Birnessite type MnO2 was recognized to be a promising material to remove indoor low-level formaldehyde at room temperature. However, moisture was considered to significantly affect the activity of MnO2 for working durably in the complex indoor environment. Here, we prepared a hierarchical porous δ-MnO2 with modest moisture adsorption–desorption content. The formaldehyde removal efficiency exceeds 90% for 200 h test at high gas-hourly space velocity (GHSV: 600 L·g−1·h−1) in both high and low humidity environments, indicating an excellent humidity tolerance. This work provides a meaningful long lifetime catalyst for using in an indoor environment.

High-performance humidity control coatings prepared from inorganic wastes

Valorization of industrial wastes in an economic and environmental-friendly way is important. In the present study, the preparation of humidity control coatings (HCCs), which is an energy-saving method to regulate indoor humidity, are developed by recycling inorganic sludges (i.e., enhancement silica fume (ESF) and spent fluid catalytic cracking catalysts (sFCCC)). Bassanite, kaolin, sodium silicates and acrylic resins are combined with ESF and sFCCC in different amounts to prepare HCCs. Experimentally, moisture adsorption–desorption performance of the HCCs increases as ESF increases. Moreover, the humidity control performance can be enhanced in the range of medium relative humidity (50–75%) upon the addition of sFCCC which results in the formation of more micropores in the HCCs. However, excessive amounts of sFCCC could reduce the moisture adsorbed capacities in the humidity range of 50–90% relative humidity due to the decrease of mesopore volume. As a result, the HCCs with 38% of ESF and 10% of sFCCC have the optima ratios of mesoporous and microporous structure showing the moisture adsorbed value and content of 309 g m−2 and 27.0%, respectively, which are much better than commercial coatings (58.7 g m−2 and 11.4%). Moreover, the prepared HCCs can reach the coating benchmark of level 2 (based on Japanese Industrial Standards (JIS A 1470-1)) at medium relative humidity range (50–75%). In the simulation tests with variable temperatures, the HCCs exhibit a narrow amplitude change of moisture (7% relative humidity) which is smaller than commercial coatings (11–13% relative humidity). Most importantly, the HCCs have good film hardness, 99.99% of antimicrobial efficacy and environmental friendliness according to the pencil, antibacterial activity and toxicity characteristic leaching procedure (TCLP) tests, respectively.

Hydration Characteristics and Humidity Control Performance of Calcium Silicate Board Prepared from Mine Tailing and Diatomite

The feasibility of utilizing molybdenum tailing and diatomite as siliceous materials to prepare calcium silicate board was explored. The influences of molybdenum tailing/diatomite proportion on hydration characteristics, thermal conductivity, water absorption, flexural strength and moisture adsorption-desorption property of calcium silicate board were investigated in detail. The experimental results reveal that molybdenum tailing is environmentally friendly to prepare building materials. The main hydration products in calcium silicate board under autoclaved condition are C-S-H with low crystallinity and tobermorite. Molybdenum tailing is favorable to the formation of tobermorite. The flexural strength and bulk density of the calcium silicate board gradually increase when the content of molybdenum tailing increases. Netlike C-S-H is formed with the increase of diatomite content during autoclaved curing process, resulting in the enhancement of moisture adsorptiondesorption performance and the reduction of thermal conductivity. The optimal content of molybdenum tailing is 20%, furthermore, the flexual strength and thermal conductivity of calcium silicate board at this content meet the Chinese standard JC/T564.1-2008.

Colorful Wall-Bricks with Superhydrophobic Surfaces for Enhanced Smart Indoor Humidity Control.

Humidity-control materials have attracted increasing attention because of energy savings and smart regulation of indoor comforts. The current research is a successive work to face challenges, such as poor performance, limitations for large-scale production, and surface contamination. Here, we report a smart humidity-control wall-brick manufactured from sepiolite using CaCl2 as an additive. Low-temperature sintering generated a super hygroscopic interior structure, and further silane modification produced bricks with superhydrophobic surfaces. These superhydrophobic surfaces can promote the moisture storage and prevent the CaCl2 solution from leaking even after the surface is wiped 100 times. Meanwhile, the superhydrophobic surfaces make the wall-bricks easy to clean; also, these materials possess antifouling and antifungal properties. The 24 h and saturated moisture adsorption–desorption contents reached 630 and 1700 g·m–2, respectively. Furthermore, a test was performed using model houses in a real environment, which indicates that the wall-bricks can narrow the daily indoor humidity fluctuations by more than 20% in both wet and dry seasons. The white wall-brick can also be dyed with different colors and thus shows promise for applications in interior decorations of houses.

新たなデシカント材料（PEDOT/PSS）の動的吸放湿性能測定と数値解析による検討

新たなデシカント材料（PEDOT/PSS）の動的吸放湿性能測定と数値解析による検討

Moisture adsorption desorption characteristics of stainless steel tubing measured by ball surface acoustic wave trace moisture analyzer

A ball surface acoustic wave (SAW) trace moisture analyzer (TMA) was applied to measuring the adsorption and desorption (AD) characteristics of a stainless steel tube. For the first time, two-frequency measurement for precise temperature compensation was attempted at intervals of 3 s using a burst waveform undersampling circuit. We succeeded in measuring the variations of moisture transit time and dry-down dynamics caused by inner surface treatments such as bright annealing (BA), electropolishing (EP), and electrochemical buffing (ECB) using a sample-tube length of only 100 mm at a flow rate of 0.1 L/min. Net moisture adsorption was evaluated from the measured adsorption subtracted by the background adsorption. As a result, it was found that the adsorption on the ECB tube was smaller than those on EP and BA tubes by 1/3 and 1/4, respectively, at a baseline concentration of 13 ppbv. From these results, it was demonstrated that the ball SAW TMA could be used for measuring the AD characteristics of stainless steel tubes with various surface treatments.

Humidity control materials prepared from diatomite and volcanic ash

The preparation of humidity control materials has been studied by sintering a mixture of diatomite and volcanic ash with and without the addition of sodium perborate. The final products were analyzed to identify moisture adsorption–desorption performances, porous and mechanical properties. In addition, effects of sintering temperature and various mixed portions on the final products were also investigated. The sintered products have mesoporous structure with the pore diameter tends to be in the range of 2–50nm, and the porous properties reach from 14.1±1 to 65±3m2/g in BET surface area and from 65.23±3 to 70.84±5% in porosity. In addition, moisture adsorption–desorption ability of the humidity control materials increases as diatomite content increases. The results indicate that the adsorbed moisture amount of the best products manufactured from the mixture of 90% diatomite, 8% volcanic ash and 2% sodium perborateat sintering temperature of 1000°C and 1100°C reach 65±4 and 55±2g/m2, respectively. The best products show excellent performance as a humidity control building material with fine mechanical properties and can be used for various construction applications at low cost.

Laboratory test on moisture adsorption-desorption of wall paintings at Mogao Grottoes, China

Moisture adsorption-desorption tests (MATs) were conducted on simulated mural plaster specimens under different air temperatures (ATs) and relative humidity (RH) to investigate the possible effect of seasonal alteration and visitors’ breath on the deterioration of Mogao Grottoes, Dunhuang, China. Saturated salt solutions were used to maintain a constant RH, and plant growth cabinets were used to maintain a constant or varying temperature in the simulation test. The weight of specimen was periodically measured to determine the adsorbed or desorbed moisture. Test data illustrate that the desorption process is far quicker than the adsorption one, indicating that it is possible to inhibit the disadvantage effect from visitors, such as shortening the staying time in caves. In case of high humidity, an accumulated moisture adsorption was found to correspond to the varying temperature. On the other hand, in case of low humidity, accumulated moisture desorption corresponded. Test data imply that opening caves more often to visitors in humid seasons should be avoided so as to prevent continuous wetting of wall paintings.

Preparation of humidity-controlling porous ceramics from volcanic ash and waste glass

This work investigated the preparation of a humidity-controlling porous ceramic via sintering of a mixture of volcanic ash soil and waste glass at 800–815 °C for 5–10 min. The final products were analyzed to identify the porous and mechanical properties, the moisture adsorption–desorption performance characteristics, and the adsorbed moisture amount. The most superior ceramic product, manufactured by mixing 30% weathered volcanic ash and 70% waste glass, was sintered at 800 °C for 5 min. The porous properties included a BET surface area of 163.73 ± 12 m 2/g, porosity of 52.08 ± 2.1%, and a pore size of approximately 9 nm in diameter. The total amount of water adsorbed by the superior ceramic product was 0.047 cm 3/g. In addition, the mechanical characteristics, including a bulk density of 1.34 ± 0.2 g/cm 3, 2.61 ± 0.1% shrinkage, 4.64 ± 0.3% ignition loss, and 6.58 ± 0.4 MPa bending strength, are consistent with those of commercial porous ceramics. The leaching concentration of heavy metals in the final products were all well below the TCLP regulation limits. Thus, the most superior products meet the standards for commercial porous ceramics.

Moisture adsorption–desorption isotherms of Citrus reticulata leaves at three temperatures

The equilibrium moisture contents of Citrus reticulata leaves were measured by the gravimetric static method. The equilibrium was achieved after 12 days for desorption and 10 days for adsorption at 30, 40 and 50 °C with water activity ranging from 5% to 90%. The sorption isotherms of C. reticulata leaves decreased with increase in temperature at constant relative humidity. An hysteresis effect was observed. The experimental data of sorption were fitted by six models (Modified Henderson, Modified Chung-Pfost, Modified Oswin, Modified Halsey, GAB and Modified BET). Only the GAB and modified BET models were found to be the most suitable for describing the sorption curves. The net isosteric heat of sorption of C. reticulata leaves decreases with an increase in moisture content and was found to be a polynomial function of moisture content for adsorption and desorption.

Moisture sorption isotherms and heat of sorption of bitter orange leaves ( Citrus aurantium)

Moisture adsorption–desorption isotherms (EMC/e.r.h.) of Citrus aurantium leaves were determined at 30, 40, and 50 °C using the standard gravimetric static method over a range of relative humidity from 0.05 to 0.9. The experimental sorption curves were fitted by six equations: modified Chung–Pfost, modified Halsey, modified Oswin, modified Henderson, modified BET, and GAB. The modified Halsey and the modified BET models were found to satisfactorily describe the desorption isotherms of Citrus aurantium leaves. For adsorption, GAB and modified BET models were the best fit. The net isosteric heats of sorption of water were determined from the equilibrium data at different temperatures.

珪藻土を添加した無機質系塗材の吸放湿性に関する研究 その3 現場で珪藻土を添加した場合の実大実験における吸放湿性に関する研究

珪藻土を添加した無機質系塗材の吸放湿性に関する研究 その3 現場で珪藻土を添加した場合の実大実験における吸放湿性に関する研究