Water Vapor Sorption Research Articles

Abnormal adsorption properties of the MOF CALF-20 as revealed by water and methanol vapor sorption

Abnormal adsorption properties of the MOF CALF-20 as revealed by water and methanol vapor sorption

Porphyrin-Based Aluminum Metal-Organic Framework with Copper: Pre-Adsorption of Water Vapor, Dynamic and Static Sorption of Diethyl Sulfide Vapor, and Sorbent Regeneration.

Metal-organic frameworks (MOFs) are hybrid inorganic-organic 3D coordination polymers with metal sites and organic linkers, which are a "hot" topic in the research of sorption, separations, catalysis, sensing, and environmental remediation. In this study, we explore the molecular mechanism and kinetics of interaction of the new copper porphyrin aluminum metal-organic framework (actAl-MOF-TCPPCu) compound 4 with a vapor of the volatile organic sulfur compound (VOSC) diethyl sulfide (DES). First, compound 4 was synthesized by post-synthetic modification (PSM) of Al-MOF-TCPPH2 compound 2 by inserting Cu2+ ions into the porphyrin ring and characterized by complementary qualitative and quantitative chemical, structural, and spectroscopic analysis. Second, the interaction of compound 4 with DES vapor was analyzed dynamically by the novel method of in situ time-dependent attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy at controlled humidity levels. The sorbent-adsorbate interactions, as analyzed by the shifts in IR peaks, indicate that the bonding includes the hydroxy O-H, carboxylate COO-, and phenyl groups. The kinetics of sorption obeys the Langmuir pseudo-first-order rate law. The pre-adsorption of water vapor by compound 4 at the controlled relative humidity under static (equilibrium) conditions yields the binary stoichiometric adsorption complex (Al-MOF-TCPPCu)1.0(H2O)8.0. The pre-adsorption of water vapor makes the subsequent sorption of DES slower, while the kinetics obey the same rate law. Then, static pre-adsorption of water vapor was followed by static sorption of DES vapor, and the ternary adsorption complex (Al-MOF-TCPPCu)1.0(H2O)8.0(DES)3.8 was obtained. Despite the pre-adsorption of significant amounts of water, the binary complex adsorbs a large amount of DES: ca. 36.6 wt. % (per compound 4). Finally, the ternary complex is facilely regenerated by gentle heating under vacuum. Compound 4 and related MOFs are promising for adsorptive removal of vapor of DES and related VOSCs from dry and humid air.

Synthesis of fluorinated ether free aromatic backbone copolymers containing trifluoromethyl and dimethylamino groups for CO2 separation: Investigation of pure and mixed gas performance under dry and humid conditions

A novel series of linear, high molecular weight aromatic copolymers containing trifluoromethyl and dimethylamino groups was synthesized via facile super-acid catalyzed polyhydroxyalkylation and investigated as CO2 gas separation membrane materials. The molar ratio of the two ketone comonomers used in copolymerization, trifluoroacetophenone (TFAp) and N,N-dimethylamino trifluoroacetophenone (dMATFAp), was systematically varied to produce five copolymers with different dMATFAp contents ranging from 12 to 73 %. The influence of dMATFAp content on physicochemical and mechanical properties as well as pure gas and water vapor separation performance was studied. All synthesized copolymers displayed excellent film forming ability, high thermal stability and high Tg values (Tgs > 380 °C). Pure gas permeability measurements revealed that the increase of dMATFAp molar content from 12 % to 34 % resulted in improved gas permeability, while, on the contrary, further increase of dMATFAp content from 34 to 73 % led to substantial gas permeability decrease ascribed to FFV decrease. In particular, among copolymers, the one with dMATFAp content of 34 % presented the highest CO2 permeability value of 290 Barrer due to its highest CO2 diffusion and CO2 solubility coefficients associated with its higher FFV value. The CO2/CH4 performance of synthesized copolymers fell very close to 2008 upper bound limit and exceeded most of the super-acid catalyzed copolymer membranes reported in the literature and commercial membranes. CO2/CH4 and CO2/N2 selectivity values for the different synthesized copolymers were in the range of 29.9–40 and 22.7–44, respectively. The study of the effect of dMΑTFA on water permeability unveiled that the membrane with the highest dMΑTFAp molar content (73 %) showed the highest water permeability value (23,100 Barrer) as well. This was attributed to the increased concentration of N-methyl substituent of dMΑTFAp which can interact with water molecules thereby increasing solubility. Under process gas stream conditions using a mixture of 3 % H2O-48.5 % CO2-48.5 % CH4, both CH4 and CO2 permeability were significantly reduced (by 35 % and 47 %, respectively) due to the preferential sorption of water vapor over other gases present in the mixture, highlighting the negative effect of water vapor on gas permeability. Accordingly, the CO2/CH4 separation factor was slightly increased from 23.8 to 29. Finally, stability test of the copolymer (BP-TFAp)66-(BP-dMATFAp)34 at 40 °C under humid mixed gas conditions showed that CO2 and CH4 permeability remained unchanged for one month after an initial condition stabilization that is required implying that these copolymer structures are promising materials for CO2 separation.

Bipolar Membrane (BPM)-Based Direct Seawater Electrolysis

I will introduce direct seawater electrolysis with a bipolar membrane (BPM) as a separator for controlling inorganic precipitates. Seawater is acidified to pH 2 despite the significant generation of hydroxide ions in the hydrogen evolution reaction (HER). This acidification results from the cooperative effect of hydroxide ions trapped by inorganic precipitates at the cathode and proton flux from water dissociation in the BPM. The acidified seawater continuously dissolves the Mg(OH)2 formed on the cathode surface, keeping the deposits very thin. In addition, the thermodynamic potential of the HER moves in the positive direction, which has the advantage of decreasing the cell voltage. Using Brunauer–Emmett–Teller (BET) analysis, water vapor sorption, and electrochemical impedance analysis, it is confirmed that the Mg(OH)2 film has a hierarchical mesoporous structure and high affinity for water, which maintained mass transport. The unique properties of the Mg(OH)2 film under seawater acidification contributes to a lower rate of increase in the cathodic potential than that under seawater alkalization, where very thin inorganic deposits are formed.

Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation.

Pore engineering is commonly used to alter the properties of metal-organic frameworks. This is achieved by incorporating different linker molecules (L) into the structure, generating isoreticular frameworks. CPO-27, also named MOF-74, is a prototypical material for this approach, offering the potential to modify the size of its one-dimensional pore channels and the hydrophobicity of pore walls using various linker ligands during synthesis. Thermal activation of these materials yields accessible open metal sites (i.e., under-coordinated metal centers) at the pore walls, thus acting as strong primary binding sites for guest molecules, including water. We study the effect of the pore size and linker hydrophobicity within a series of Ni2+-based isoreticular frameworks (i.e., Ni2L, L = dhtp, dhip, dondc, bpp, bpm, tpp), analyzing their water sorption behavior and the water interactions in the confined pore space. For this purpose, we apply water vapor sorption analysis and Fourier transform infrared spectroscopy. In addition, defect degrees of all compounds are determined by thermogravimetric analysis and solution 1H nuclear magnetic resonance spectroscopy. We find that larger defect degrees affect the preferential sorption sites in Ni2dhtp, while no such indication is found for the other materials in our study. Instead, strong evidence is found for the formation of water bridges/chains between coordinating water molecules, as previously observed for hydrophobic porous carbons and mesoporous silica. This suggests similar sorption energies for additional water molecules in materials with larger pore sizes after saturation of the primary binding sites, resulting in more bulk-like water arrangements. Consequently, the sorption mechanism is driven by classical pore condensation through H-bonding anchor sites instead of sorption at discrete sites.

Reversible Co(II)-Co(III) Transformation in a Family of Metal-Dipyrazolate Frameworks.

Transformation between oxidation states is widespread in transition metal coordination chemistry and biochemistry, typically occurring in solution. However, air-induced oxidation in porous crystalline solids with retention of crystallinity is rare due to the dearth of materials with high structural stability that are inherently redox active. Herein, we report a new family of such materials, four isostructural cobalt-pyrazolate frameworks of face-centered cubic, fcu, topology, fcu-L-Co, that are sustained by Co8 molecular building blocks (MBBs) and dipyrazolate ligands, L. fcu-L-Co were observed to spontaneously transform from Co(II)8 to Co(III)8 MBBs in air with retention of crystallinity, marking the first such instance in metal-organic frameworks (MOFs). This transformation can also be achieved through water vapor sorption cycling, heating, or chemical oxidation. The reverse reactions were conducted by exposure of fcu-L-Co(III) to aqueous hydrazine. fcu-L-Co(II) exhibited high gravimetric water vapor uptakes of 0.55-0.68 g g-1 at 30% relative humidity (RH), while in fcu-L-Co(III) the inflection point shifted to lower RH and framework stability improved. Insight into the transformation between fcu-L-Co(II) and fcu-L-Co(III) was gained from single crystal X-ray diffraction and in situ spectroscopy. Overall, the crystal engineering approach we adopted has afforded a new family of MOFs that exhibit cobalt redox chemistry in a confined space coupled with high porosity.

Modification of polyvinyl alcohol with borates

Modification of polyvinyl alcohol (PVA) with borates allows to regulate the main performance indicators of water-soluble films - temperature and time of solubility, strength. The need to increase the water resistance of PVA-based films is associated with specific areas of their application, for example, when creating protective shells in plant growing or eco-friendly disposable tableware, etc. The aim of the work is a comparative assessment of the main performance indicators of PVA films with different molecular weights modified with borates of different nature. Objects of study: film samples of low-hydrolyzed PVA of three different grades (05-88, 17-88, 24-88) having the same degree of hydrolysis (88%), but differing in molecular weight (MW) and, as a consequence, solution viscosity (for PVA 05-88, 17-88, 24-88 comprising 4.5÷6.5, 20.0÷26.0, 44.0÷56.0 mPa*s, respectively), modified with borates in different ratios (sodium tetraborate in an amount of 0.125÷2.0 wt.% and boric acid in an amount of 2.5÷10.0 wt.%). Research methods: water solubility of samples was assessed visually by immersion in water with a temperature of 20°C, water vapor sorption was assessed using the standard static (desiccator) method for determining water vapor sorption isotherms by polymeric materials, strength properties of films in a dry and vapor-saturated state were determined according to GOST 11262-17 using an RM-50 tensile testing machine with Stretch Test software. It was found that the influence of the crosslinker nature on the properties of modified films differs significantly for PVA with different MW. Sodium tetraborate leads to rapid gelation of the PVA solution, which is more intense with an increase in the MW of the polymer, therefore its introduction is limited to 2.0, 1.0 and 0.5 wt.%, respectively, for PVA 05-88, 17-88 and 24-88; when crosslinking with boric acid, the gelling effect is absent. Sodium tetraborate is ineffective in increasing the water resistance of low-MW PVA, although it improves its strength properties; boric acid effectively crosslinks PVA (especially high-MW), which is manifested in a significant increase in the dissolution time of the films. The maximum crosslinking effect, accompanied by a significant increase in water resistance, was observed in the case of modification of medium- and high-molecular PVA with boric acid in an amount of at least 5.0 wt.% of the polymer weight.

Water in the micropores of CPO-27 metal-organic frameworks: A comprehensive study

The metal-organic framework CPO-27 exhibits free coordination sites (open metal sites) and can be prepared with a wide range of metals that influence its properties. It is therefore an intriguing structure to study sorption phenomena. We analyze the water resistance and sorption behavior of these frameworks, with particular attention to the sorption mechanism in detail and the structure of the confined water molecules. For this purpose, we use manometric water vapor sorption analysis and FTIR spectroscopy. The respective metal center orchestrates both the adsorption behavior and the arrangement of the water molecules in the micropores of the framework. The extent to which water molecules form hydrogen bonds (with each other and with framework oxygen atoms) plays a crucial role in the stability of the framework towards water. Water adsorption is governed by the coordination of water molecules to the open metal sites (except for CPO-27-Cu) and subsequent H-bonding. A stepwise adsorption of water is observed, with significant differences depending on the choice of metal.

Shrinkage reduction mechanism of low Ca/Si ratio C-A-S-H in cement pastes containing fly ash

Understanding the drying shrinkage of low Ca/Si ratio cement pastes is crucial for promoting the use of low-clinker ratio cementitious materials and reducing the environmental impact of cement production. We prepared well-hydrated cement paste samples with various fly ash replacement and water-to-cement ratios. The long-term drying shrinkage was measured by 1 mm-thick samples. Results showed that fly ash containing samples exhibited lower shrinkage and the irreversible part of drying shrinkage was less compared to those without fly ash. Chemical composition analysis of the calcium aluminate-silicates hydrate (C-A-S-H) was conducted using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). Additionally, water vapor sorption isotherms and proton nuclear magnetic resonance (1H NMR) relaxometry were used to determine specific surface area and pore structure. By analyzing these results in conjunction with the C-A-S-H model, we attributed the reduced and more reversible drying shrinkage in fly ash cement to lower Ca ion amounts in the interlayer space and fewer trapped larger pores.

Diffusion and sorption of water vapor by polyamide‐imides

AbstractThe study of sorption and diffusion characteristics of glassy polymers based on polyamide‐imides was carried out using the methods of static sorption, dilatometry, electron microscopy. Water sorption isotherms of polyamide‐imides based on trimellitimido‐N‐acetic acid (PAI‐A) and trimellitimido‐N‐p‐benzoic acid (PAI‐B) with different intramolecular ‘hinges’ in the diamine fragment were obtained. The isotherms are S‐shaped and occupy an intermediate position between polyheteroarylenes and aliphatic polyamides. The dual sorption model was used to interpret the results. It is shown that the Langmuir component of the isotherms is determined by the thermal prehistory of glassy polymers, while the sorption component associated with water dissolution according to Flory‐Huggins is determined by the chemical nature of the functional groups included in the monomeric unit. The diffusion coefficients of water and the temperature and concentration dependences of the diffusion coefficients of sorbed water molecules were determined.

Color Modifications of a Maxillofacial Silicone Elastomer under the Effect of Cigarette Smoke.

Although it is known (from the observations of medical professionals) that cigarette smoke negatively affects maxillofacial prostheses, especially through staining/discoloration, systematic research in this regard is limited. Herein, the color modifications of M511 maxillofacial silicone, unpigmented and pigmented with red or skin tone pigments, covered with mattifiers, or with makeup and mattifiers, and directly exposed to cigarette smoke, were investigated by spectrophotometric measurements in the CIELab and RGB color systems. The changes in color parameters are comparatively discussed, showing that the base silicone material without pigmentation and coating undergoes the most significant modifications. Visible and clinically unacceptable changes occurred after direct exposure to only 20 cigarettes. By coating and application of makeup, the material is more resistant to color changes, which suggests that surface treatments provide increased protection to adsorption of the smoke components. The dynamic water vapor sorption (DVS) measurements indicate a decrease of the sorption capacity in pigmented versus unpigmented elastomers, in line with the changes in color parameters.

Tailoring the structural and physicochemical properties of rice straw cellulose-based cryogels by cell-mediated polyhydroxyalkanoate deposition

This study presents a novel biotechnological approach for creating water vapor-resistant cryogels with improved integrity. Rice straw cellulose was transformed into nanofibrils through TEMPO-mediated oxidation and high-pressure homogenization. The resulting cryogels remained firm even when immersed in aqueous media, whose pores were used by live cell to deposit polyhydroxyalkanoate (PHA) particles inside them. This novel method allowed the compatibilization of PHA within the cellulosic fibers. As a consequence, the water sorption capacity was decreased by up to 6 times having just 4 % of PHA compared to untreated cryogels, preserving the cryogel density and elasticity. Additionally, this technique can be adapted to various bacterial strains and PHA types, allowing for further optimization. It was demonstrated that the amount and type of PHA (medium chain length and small chain length-PHA) used affects the properties for the cryogels, especially the water vapor sorption behavior and the compressive strength. Compared to traditional coating methods, this cell-mediated approach not only allows to distribute PHA on the surface of the cryogel, but also ensures polymer penetration throughout the cryogel due to bacterial self-movement. This study opens doors for creating cryogels with tunable water vapor sorption and other additional functionalities through the use of specialized PHA variants.

The effect of traditional processing craft on the hygroscopicity of palm leaf manuscripts

Palm leaf manuscripts, which are crucial carriers of historical, religious, scientific, and artistic information in East and Southeast Asia, specifically encapsulate significant aspects of Buddhist culture and thus require comprehensive research and preservation efforts. The base material of palm leaf manuscripts is processed palm leaves, which are hygroscopic and profoundly affected by environmental humidity. Currently, there is a research gap regarding the impact of traditional processing crafts and natural aging on the hygroscopicity of palm leaf manuscripts. Utilizing dynamic water vapor sorption (DVS), the hygroscopic properties of palm leaves from various years were assessed before and after traditional processing in Yunnan Province, China. The results show that traditional processing slightly increases the equilibrium moisture content (EMC) in environments with 0 to 60% relative humidity (RH), but significantly lowers EMC in high humidity environments, with reductions up to 19.01%. Additionally, hysteresis doubled post-processing, indicating enhanced stability under fluctuating humidity conditions. Sorption models suggest that traditional processing increases the number of adsorption sites while reducing physical adsorption or capillary condensation. FT-IR (Fourier-transform infrared spectroscopy) analysis indicates that the relative contents of cellulose and hemicellulose were reduced by 39.90% and 3.97%, respectively. Degradation occurring in both the crystalline and amorphous regions of cellulose. After natural aging, the hygroscopicity of processed palm leaves improved across the entire humidity range of 0 to 95%, and there was a slight increase in hysteresis. This is due to the increase in both adsorption sites and physical adsorption capabilities. FT-IR results also indicate that the relative contents of cellulose and hemicellulose were decreased by 57.52% and 19.83% after nature aging, respectively. These findings confirm that traditional processing improves the writability and humidity resilience of the leaves, while natural aging enhances their overall hygroscopic properties. This research contributes to our understanding of how humidity damages palm leaf manuscripts. aids in determining optimal RH ranges for storage, and assesses the effectiveness of consolidation treatments in their long–term preservation.

Leveraging Isoreticular Principle to Elucidate the Key Role of Inherent Hydrogen-Bonding Anchoring Sites in Enhancing Water Sorption Cyclability of Zr(IV) Metal-Organic Frameworks.

Water adsorption/desorption cyclability of porous materials is a prerequisite for diverse applications, including atmospheric water harvesting (AWH), humidity autocontrol (HAC), heat pumps and chillers, and hydrolytic catalysis. However, unambiguous molecular insights into the correlation between underlying building blocks and the cyclability are still highly elusive. In this work, by taking advantage of the well-established isoreticular synthetic principle in Zr(IV) metal-organic frameworks (Zr-MOFs), we show that the inherent density of hydrogen atoms in the organic skeleton can play a key role in regulating the water sorption cyclability of MOFs. The ease of isoreticular practice of Zr-MOFs enables the successful syntheses of two pairs of isostructural Zr-MOFs (NU-901 and NU-903, NU-950 and SJTU-9) from pyrene- or benzene-cored carboxylate linkers, which feature scu and sqc topological nets, respectively. NU-901 and NU-950 comprised of pyrene skeletons carrying more hydrogen-bonding anchoring sites show distinctly inferior cyclability as compared with NU-903 and SJTU-9 built of benzene units. Single-crystal X-ray crystallography analysis of the hydrated structure clearly unveils the water molecule-involved interactions with the hydrogen-bonding donors of benzene moieties. Remarkably, NU-903 and SJTU-9 isomers exhibit outstanding water vapor sorption capacities as well as working capacities at the desired humidity range with potential implementations covering indoor humidity control and water harvesting. Our findings uncover the importance of hydrogen-bonding anchoring site engineering of organic scaffold in manipulating the framework durability toward water sorption cycle and will also likely facilitate the rational design and development of highly robust porous materials.

Hydration and deliquescence behavior of calcium chloride hydrates

The phase transitions of calcium chloride between various hydrates and solid–liquid phase transitions are common in many natural and industrial processes. Recent studies have revealed some discrepancies in investigating the hydration and deliquescence of calcium chloride using different methods. In this study, water vapor sorption analysis and Raman measurements on CaCl2·2H2O and CaCl2·6H2O and their dehydration products were conducted. The results indicate two possible hydration sequences from lower hydrates to deliquescence at 298.15 K: (1) Hydration of the monohydrate to the dihydrate, followed by the formation of β-CaCl2·4H2O, ending with its deliquescence at 18.5 % RH; (2) Hydration of the monohydrate to the dihydrate, followed by the formation of α-CaCl2·4H2O and of the hexahydrate, ending with its deliquescence at 29 % RH. It was observed that the transition from pure dihydrate to β-CaCl2·4H2O occurs spontaneously, instead of hydration to the thermodynamically stable α-CaCl2·4H2O. The latter phase is only formed in the presence of crystal seeds of α-CaCl2·4H2O that remained after dehydration. Additionally, direct deliquescence of β-CaCl2·4H2O and thus absence of hydration to hexahydrate at 298.15 K is reported for the first time, which could be explained by the more similar lattice structure of CaCl2·2H2O (orthorhombic) and β-CaCl2·4H2O (monoclinic) than α-CaCl2·4H2O (triclinic). Apart from that, an explanation for the observed transformation sequence is proposed, considering the impact of the enhanced solubility of β-CaCl2·4H2O compared to the α-CaCl2·4H2O. The resulting water to salt ratio below six may contribute to the absence of CaCl2·6H2O formation. A Raman spectrum of CaCl2·H2O not reported previously is also provided.

Modulation of Water Vapor Sorption by Pore Engineering in Isostructural Square Lattice Topology Coordination Networks.

We report a crystal-engineering study conducted upon a platform of three mixed-linker square lattice (sql) coordination networks of general formula [Zn(Ria)(bphy)] [bphy = 1,2-bis(pyridin-4-yl)hydrazine, H2Ria = 5-position-substituted isophthalic acid, and R = -Br, -NO2, and -OH; compounds 1-3]. Analysis of single-crystal X-ray diffraction data of 1-2 and the simulated crystal structure of 3 revealed that 1-3 are isomorphous and sustained by bilayers of sql networks linked by hydrogen bonds. Although similar pore shapes and sizes exist in 1-3, distinct isotherm shapes (linear and S shape) and uptakes (2.4, 11.6, and 13.3 wt %, respectively) were observed. Ab initio calculations indicated that the distinct water sorption properties can be attributed to the R groups, which offer a range of hydrophilicity. Calculations indicated that the significantly lower experimental uptake in compound 1 can be attributed to a constricted channel. The calculated water-binding sites provide insights into how adsorbed water molecules bond to the pore walls, with the strongest interactions, water-hydroxyl hydrogen bonding, observed for 3. Overall, this study reveals how pore engineering can result in large variations in water sorption properties in an isomorphous family of rigid porous coordination networks.

The Effect of Macromonomer Surfactant Microstructure on Aqueous Polymer Dispersion and Derived Polymer Film Properties.

Water-borne coatings were prepared from poly(methyl methacrylate-co-butyl acrylate) latexes using different methacrylic acid containing macromonomers as stabilizers, and their physical properties were determined. The amphiphilic methacrylic acid macromonomers containing methyl, butyl, or lauryl methacrylate as hydrophobic comonomers were synthesized via catalytic chain transfer polymerization to give stabilizers with varying architecture, composition, and molar mass. A range of latexes of virtually the same composition was prepared by keeping the content of methacrylic acid groups during the emulsion polymerization constant and by only varying the microstructure of the macromonomers. These latexes displayed a range of rheological behaviors: from highly viscous and shear thinning to low viscous and Newtonian. The contact angles of the resulting coatings ranged from very hydrophilic (<10°) to almost hydrophobic (88°), and differences in hardness, roughness, and water vapor sorption and permeability were found.

Comprehensive analysis of water vapor sorption kinetics and mechanisms using biosorbent pellets from canola meal and oat hull

Agricultural residues, specifically canola meal (CM) and oat hull (OH), have been innovatively utilized to develop biosorbents for sorbing water vapor from the air. These biomaterials are comprised of hydrophilic functional groups that effectively perform air dehydration. Air, being non-polar, was used as a model gas in this study to simulate gas dehydration. In the current research, these materials were formed into pellets to produce high-quality biosorbents with controlled size, shape, and enhanced moisture uptake capacity. CM (309.48 mg/g) and OH (233.07 mg/g) pellets had higher or comparable water sorption capacities than commercialized adsorbents used for drying gases. The mixed-order kinetic model described the sorption process well and identified both mass transfer and sorption on active site steps (R 2 > 0.991 and χ 2 < 16.0). Regarding the OH pellet, sorption on active sites was the predominant kinetic mechanism at the beginning, followed by intraparticle diffusion until equilibrium. However, sorption on CM pellets was delayed at 4.2 min at the initial stage, owing to the external mass transfer resistance; then, intraparticle diffusion controlled the process until equilibrium. Adding sodium lignosulfonate (LSNa) lowered the initial sorption rate but enhanced the water uptake and strength of pellets. The addition of LSNa resulted in a 25% and 14% increase in the water uptake capacity of oat hull and canola meal pellets, respectively; conversely, it also caused an increase in the delay time for sorption on CM pellets at the beginning of the process, extending it to 9.50 min.

Cellulose acetate/chitosan composite film loaded with ground cinnamon for active packaging: water vapor sorption kinetic, compounds release, and antimicrobial effect

This study evaluated structural, physical, and water sorption properties of cellulose acetate/chitosan composite film incorporated with ground cinnamon as an antimicrobial. The controlled release of antimicrobial compounds and antimicrobial effects on Escherichia coli and Staphylococcus aureus were also monitored. The composite film formed highly porous and fibrous materials with higher thermal resistance. A higher ratio of chitosan in the film improved the swelling degree and water-vapor absorption capacity but reduced adsorption rates. Consequently, antimicrobial compounds, including eucalyptol, naphthalene, and β-caryophyllene, were more quickly released from the composite film with a larger chitosan ratio, affecting stronger antimicrobial effects. The inclusion of ground cinnamon with residual fat content in the film contributed to an extended inhibition of microbial growth in an indirect packaging system. Understanding the chitosan/cellulose acetate ratio in the film composite formation and the incorporation of ground cinnamon is important to control the compounds' release and generate long-term antimicrobial effects of active packaging materials on fresh food products.

Heat and mass transfer analysis of desiccant-coated heat exchanger with desiccants and metal-organic framework for bus air conditioning applications

Desiccant-coated heat exchangers (DCHEs) in air conditioning offer advantages like independent temperature and humidity control, reduced energy consumption, and high performance. However, the availability of desiccants with high water adsorption and low thermal energy requirements is limited. The present study proposes that aluminum fumarate (Al-Fum) MOF-coated heat exchangers will outperform conventional desiccants, especially at low regeneration temperatures (around 50°C). In order to evaluate this hypothesis, the performance of DCHEs was evaluated with a validated analytical model for different solid desiccant coatings: silica gel, zeolite, and Al-Fum MOF. Water vapor sorption characteristics, heat and mass transfer, and adsorption and desorption capacities were determined. The results showed that the Al-Fum MOF-coated heat exchanger outperformed silica gel and zeolite at low regeneration temperatures under adiabatic conditions. The MOF exhibited superior water uptake capacity (0.39 g/g) between 20% and 80% RH compared to the other studied conventional desiccants. Moreover, the MOF achieved the lowest outlet air temperature. At 19.5 g/kgda, the MOF demonstrated higher adsorption rates (4 % and 0.3 %) than zeolite and silica gel. These findings highlight the potential of Al-Fum MOFs as energy-efficient solutions for controlling indoor air humidity, particularly for latent-sensible heat separation systems with conventional vapor compression bus air-conditioning systems.