Search Results (210)

Kefiran, the extracellular polysaccharide produced from the Generally Recognized as Safe (GRAS) bacteria in kefir grains, with its well-documented functional and health-promoting properties, constitutes a promising biopolymer with a variety of possible uses. Its compatibility with other biopolymers, such as milk proteins, and its ability to form standalone cryogels allow it to be utilized for the fabrication of films with improved properties for applications in the food and biomedical–pharmaceutical industries. In the present work, the properties of kefiran films were investigated in the presence of milk proteins (sodium caseinate, native and heat-treated whey proteins, and their mixtures), alongside glycerol (as a plasticizer) and cryo-treatment of the film-forming solution prior to drying. A total of 24 kefiran films were fabricated and studied for their physical (thickness, moisture content, water solubility, color parameters and vapor adsorption), mechanical (tensile strength and elongation at break), and optical properties. Milk proteins increased film thickness, solubility and tensile strength and reduced water vapor adsorption. The hygroscopic effect of glycerol was mitigated in the presence of milk proteins and/or the application of cryo-treatment. Glycerol was the most effective at reducing the films’ opacity. Heat treatment of whey proteins proved to be the most effective in increasing film tensile strength, reducing, at the same time, the elongation at break, while sodium caseinates in combination with cryo-treatment resulted in films with high tensile strength and the highest elongation at break. Cryo-treatment, carried out in the present study through freezing followed by gradual thawing of the film-forming solution, proved to be the most effective factor in decreasing film roughness. Based on our results, proper selection of the film-forming solution composition and its treatment prior to drying can result in kefiran–glycerol films with favorable properties for particular applications. Full article

The development of high-performance adsorbent materials is crucial for any sorption-based energy conversion process. In such a context, composite sorbent materials, although promising in terms of performance and stability, are often challenging to shape into complex geometries. Additive manufacturing, also known as 3D printing, has emerged as a powerful technique for fabricating intricate structures with tailored properties. In this paper, an innovative three-dimensional structure, constituted by zeolite as filler and sulfonated polyether ether ketone as matrix, was obtained using additive manufacturing technology, which is mainly suitable for sorption-based energy conversion processes. The lattice structure was tailored in order to optimize the synthesis procedure and material stability. The complex three-dimensional lattice structure was obtained without a metal or plastic reinforcement support. The composite structure was evaluated to assess its structural integrity using morphological analysis. Furthermore, the adsorption/desorption capacity was evaluated using water-vapor adsorption isobars at 11 mbar at equilibrium in the temperature range 30–120 °C, confirming good adsorption/desorption capacity. Full article

The development of effective oil adsorbents has attracted a great deal of attention due to the increasingly serious problem of oil pollution. A light and porous collagen (COL)/polyvinyl alcohol (PVA)/vanadium carbide (V₂CT_x) composite aerogel was synthesized using a simple method of blending, directional freezing, and drying. After modification with methyltriethoxysilane (MTMS) via chemical vapor deposition, the aerogel possessed an excellent hydrophobicity and its water contact angle reached 135°. The hydrophobic COL/PVA/V₂CT_x composite aerogel exhibits a porous structure with a specific surface area of 49 m²/g. It also possesses prominent mechanical properties with an 80.5 kPa compressive stress at 70% strain, a low density (about 28 mg/cm³), and outstanding thermal stability, demonstrating a 61.02% weight loss from 208 °C to 550 °C. Importantly, the hydrophobic COL/PVA/V₂CT_x aerogel exhibits a higher oil absorption capacity and stability, as well as a faster absorption rate, than the COL/PVA aerogel when tested with various oils. The hydrophobic COL/PVA/V₂CT_x aerogel has the capacity to adsorb 80 times its own weight of methylene chloride, with help from hydrophobic interactions, Van der Waals forces, intermolecular interactions, and capillary action. Compared with the pseudo first-order model, the pseudo second-order model is more suitable for oil adsorption kinetics. Therefore, the hydrophobic COL/PVA/V₂CT_x aerogel can be used as an environmentally friendly and efficient oil adsorbent. Full article

The aim of this work was to obtain biochar materials from plant biomass and to determine the changes occurring under the conditions of the pyrolysis process and physical activation, as well as to characterize the physicochemical characteristics of the produced products in terms of their practical use. The pyrolysis process was carried out at a temperature of 700 °C, under the flow of a protective gas, i.e., carbon dioxide, at a rate of 5.0 L/min. The pyrolysis processes were carried out in the absence and presence of an activating agent. For ecological safety, physical activation using water vapor was chosen. In the next stage of the work, biochars were produced and subjected to detailed physicochemical analysis. A scanning electron microscope with energy-dispersive SEM/EDS was used to determine the microstructure and changes in the chemical composition of the biochars. FTIR spectrophotometry was used to identify the functional groups present in the structures of biochars and to indicate changes occurring in the biomass during pyrolysis. Meanwhile, Raman spectroscopy was used to assess the ordering of the biochar structures based on the identification of spectral signals. The description of the specific surface areas of the biochars was made possible by studies conducted using a physical and chemical adsorption analyzer. Based on the obtained research results, the elementary structure, surface development, presence of functional groups on the surfaces of biochars and changes in the structure before and after activation with water vapor were determined. It was found that the biochars had functional groups, a well-developed specific surface area that increased after activation with water vapor, micropores and mesopores, as well as changes in structure under the influence of physical activation. It has been shown that the presence of functional groups influences the hydrogen sulfide sorption capacity. Full article

The aim of this study is to investigate a green and efficient hydrothermal synthesis method for obtaining a high-purity MIL-100(Fe) metal–organic framework (MOF) without using hazardous HF acid or other toxic reagents. The influence of various synthesis conditions (reactant ratios and reaction times) and washing protocols on the MOF’s properties and crystallinity was investigated. Additionally, the adsorption capacities of the synthesized MIL-100(Fe) for hydrogen (H₂), carbon dioxide (CO₂), and water vapor were evaluated at different temperatures and pressures. By analyzing the adsorption behavior, this research study aims to assess the potential of this material for thermal or specific gas storage applications. MF-S1 synthesis, using less iron and water, produces the purest MIL-100(Fe), as confirmed by XRD and FTIR. MF-S1-W2, with additional washing, is ideal for gas adsorption due to its crystallinity, purity, and high surface area. It effectively stores hydrogen (0.25 wt.% at 5 °C), CO₂ (32.6 wt.% at 5 °C), and water vapor (47.5 wt.% at 30 °C). Full article

The present study aims to investigate a Pd catalyst on a complex multi-oxide medium-entropy support interlayer La₂O₃-CeO₂-ZrO₂-Al₂O₃ and its possible use as catalysts for methane abatement applications. The low-temperature N₂-adsorption, XRD, TEM, XPS, TPD, and TPR techniques were used to characterize the catalyst. The palladium deposition on the supports leads to the formation of PdO. After the catalytic tests, the metal-Pd phase was observed. The complete oxidation of methane on Pd/La-Ce-Zr-Al catalyst takes place at temperatures above 250 °C, and in the presence of water vapor, the reaction temperature increases to about 70 °C. The careful choice of constituent oxides provides a balance between structural stability and flexibility. The alumina and lanthanum oxide ensure the high specific surface area, while the simultaneous presence of zirconia and ceria leads to the formation of a mixed-oxide phase able to interact with palladium ions by incorporating and de-incorporating them at different conditions. The mechanism of Mars–van Kerevelen was considered as the most probable for the reaction of complete methane oxidation. The possibility of the practical application of Pd-modified La-Ce-Zr-Al catalyst is evaluated. The use of a mix of multiple rare and abundant oxides makes the proposed catalyst a cost-effective alternative. Full article

Activated carbons (ACs) are employed in the nuclear industry to mitigate the emission of potential radioactive iodine species. Their retention performances towards iodine are mainly dependent on the relative humidity due to the competitive effect induced by adsorbed water molecules. Thus, this work will focus on the prediction of AC behavior toward the capture of water vapor to better assess the poisoning effect on radiotoxic iodine removal. For the first time, H₂O breakthrough curves (BTCs) on nuclear grade ACs are predicted through a specific methodology based on the combination of transport phenomena with adsorption kinetics and equilibrium. Three ACs, similar to those deployed in the nuclear context, are considered within the present study. Our model is based on the Linear Driving Force Model (LDF), governed by an intraparticle diffusion mechanism, notably surface and Knudsen diffusions. In addition, the type V isotherms obtained for H₂O and the investigated carbon supports were described through the Klotz equation, taking into account the formation and progressive growth of H₂O clusters within the internal porosity. This methodology allowed us to successfully simulate the H₂O adsorption by a non-impregnated AC, where only physisorption phenomena are involved. In addition, promising results were highlighted when extrapolating to the two other impregnated ACs (AC 5KI and AC Nuclear). Full article

The water adsorption property was shown to be the critical process limiting the thermal output in the adsorption heat storage driven by the air humidity process, which was different for the physical adsorbent and the physical/chemical adsorbent. In this study, coconut shell-based activated carbon (CAC), a hierarchically porous material that is both low-cost and mass-producible, was utilized as a physical adsorbent and as a matrix for loading calcium chloride (CAC/Ca). The incorporation of calcium chloride in CAC, with a 24% content, resulted in a 4~102% increase in water uptake capacity. The water uptake dynamics of high-thickness adsorbents are inhibited, especially for CAC/Ca. In the context of the adsorption test conducted within a fixed-bed reactor, an increase in air velocity was observed to facilitate water vapor supply, thereby culminating in higher output temperatures for both CAC and CAC/Ca, indicating a higher hydration conversion. The maximum discharge powers of CAC/Ca increased from 2 kW/m³ to 20 kW/m³, with the air velocity increasing from 0.5 m/s to 2.5 m/s. The heat-release densities of CAC and CAC/Ca at the air velocity of 2.5 m/s were 156 kJ/kg and 547 kJ/kg, respectively. Full article

Given the high cost and limited availability of noble-metal-based catalysts in acidic media water electrolysis, developing cost-effective and high-performance non-noble metal catalysts is crucial for realizing large-scale hydrogen production. In this study, Fe-, Co-, and Ni-doped MoSe₂ nanomaterials were synthesized via chemical vapor deposition, and their electrocatalytic performance for the hydrogen evolution reaction (HER) was systematically evaluated. Characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy were used to confirm the incorporation of doping elements and investigate their effects on the crystal structure and morphology of MoSe₂. Electrochemical tests, including linear sweep voltammetry and cyclic voltammetry, revealed that the doping of Fe, Co, and Ni significantly enhanced the HER catalytic activity of MoSe₂, with the Co-doped sample exhibiting the best performance, showing an overpotential of 0.293 V at 100 mA/cm⁻² and a Tafel slope of 47 mV/dec. Furthermore, density functional theory calculations were employed to analyze the adsorption energy of hydrogen atoms on the catalysts, providing deeper insights into the role of doping in tuning the catalytic activity of MoSe₂. This study offers new theoretical support and experimental evidence for the application of transition metal-doped MoSe₂ in electrocatalysis. Full article

Nowadays, Pt-based catalysts are widely applied in carbon monoxide (CO) removal at room temperature. However, the effects of abundant hydroxyl groups (OH*) on the decomposition of intermediate products and catalyst durability have rarely been studied. In this work, a novel hydroxyl-rich structured mesh-type Pt/Mn/γ-Al₂O₃/Al catalyst using a water vapor treatment (WVT) strategy to generate OH* in situ was developed. Firstly, density functional theory (DFT) calculations indicated that Mn-modification enhanced the adsorption capacity of CO and reduced the work function and the energy barrier of the catalytic reaction. Meanwhile, the water molecule dissociation ability of the Pt catalyst was improved. Secondly, the effects of WVT on the selected catalysts were investigated, and a possible reaction mechanism was proposed. XPS, FTIR, and TG results showed that WVT increased the content of OH*. Moreover, in situ FTIR further indicated that the increase of OH* content could alter the reaction path (from carbonate to formate pathway), thus enhancing the activity and durability of the catalyst. The selected catalyst exhibited excellent durability with 100% conversion within 200 h for 1000 ppm CO at room temperature. Full article

Zeolite is increasingly recognized for its enhancement of low-frequency acoustic performance in microspeakers. The aging characteristics of zeolite have been regarded as the critical factor for the commercial viability of mobile phones products, but the mechanism remains ambiguous. Here, the low-frequency acoustic performance of hierarchically structured ZSM-5 was investigated through aging with water and acetic acid (AA). It was discovered that water vapor augmented the resonance offset as it enhanced the structure of the zeolite, resulting in a lower water content. The resonance offset of ZSM-5 significantly decreased after the adsorption of AA vapor, as excessive AA was adsorbed through both physical and chemical adsorption, causing partial destruction of supermicropore and mesopores. The performance of ZMS-5 stored with vapor of AA and water mixture did not significantly deteriorate, indicating that water effectively protected the pores of zeolite to prevent excessive adsorption of AA. This was attributed to the fact that water was adsorbed by Brønsted acid sites of ZSM-5 more preferentially than AA, thereby avoiding excessive adsorption of AA. Full article

This research aimed to assay the impact of convective drying (CD) or infrared–convective (IR–CD) drying methods on the physical and techno-functional properties, FTIR spectra, and mathematical modeling of adsorption kinetics of black soldier fly larvae powders. By using convective drying, insect powder exhibited higher water content and water activity but lower hygroscopicity than powder dried with the infrared–convective method. After drying with the convective method, the powder exhibited a significantly lower loose and tapped bulk density and oil holding capacity (OHC). Furthermore, this powder was lighter and more yellow. The FTIR spectrum of the CD-dried powder showed lower absorption at key wavenumbers for the protein (1625 and 1350–1200 cm⁻¹), indicating lower denaturation and less ability to bind water and water vapor. The mathematical modeling of the water vapor adsorption kinetics of insect powders via the second Fick’s law for transient diffusion showed that this equation is suitable for adjusting the experimental data based on the high coefficient of determination (0.997–0.999) and the low root mean square (2.50–3.34%). This study revealed that the drying method influences insect powder properties, and the IR–CD method seems better in terms of obtaining better techno-functional properties. Full article

Atmospheric water harvesting (AWH) is a promising alternative to address immediate water needs. Desiccant-based AWH could compete effectively with other commercially available AWH technologies. One of the primary challenges facing desiccant-based AWH is the energy required to desorb the captured water vapor from the desiccant. This work presents a multi-faceted approach targeted explicitly at low-humidity and arid regions, aiming to overcome the limitations of the refrigerant-based AWH system. It includes assessing common desiccants (zeolite, activated alumina, and silica gel) and their forms (beads, powdered, or coated on a substrate). A bench-scale test rig was designed to evaluate different types and forms of desiccants for adsorption and desorption cycles and overall adsorption capacity (g/g), kinetic profiles, and rates. Experimental results indicate that beaded desiccants possess the highest adsorption capacity compared to powdered or coated forms. Furthermore, coated desiccants double the water uptake (1.12 vs. 0.56 g water/g desiccant) and improve adsorption/desorption cycling by 52% compared to beaded forms under the same conditions. Additionally, Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and dynamic vapor sorption (DVS) analysis show the pore geometry, morphology, and sorption capacity. The goal is to integrate these performance improvements and propose a more effective, energy-efficient desiccant-based AWH system. Full article

Traditional water purification systems often rely on synthetic materials that pose environmental risks due to their non-biodegradability and the potential release of harmful substances. To address these concerns, natural polymer-based membranes are being developed as a sustainable and environmentally friendly alternative for water treatment due to their biodegradability, low toxicity, and chemical versatility. These materials are particularly suitable for removing a wide range of contaminants due to their high selectivity and water permeability. Despite their benefits, challenges such as improving mechanical strength, durability, and resistance to fouling persist. Ongoing research continues to optimize the performance of electrospun membranes to meet modern water treatment demands. For this purpose, crosslinking via thermal initiators azobisisobutyronitrile (AIBN) and 2,2’-azobis(2-amidinopropane)dihydrochloride (V50) and chemical crosslinking by glutaraldehyde (GA) vapor have been studied for methacrylated chitosan and alginate. In addition, biocharcoal has been introduced into the membranes to enhance their functional properties. The development of natural polymer-based membranes combined with biocharcoal presents a promising and scalable solution for sustainable water purification, playing a crucial role in reducing pollution and preserving vital water resources for future generations. In this study, we demonstrate that the crosslinking effect plays a key role in maintaining the stability of alginate-based membranes in an aqueous environment while enhancing their adsorption capacity for methylene blue dye, making them promising for water purification applications. Full article

The presence of abundant water vapor in industrial organic waste gases greatly reduces the selective adsorption of volatile organic pollutants (VOCs). The polarity of the adsorbent and VOC molecules plays an important role in the adsorption process, especially in the presence of water vapor. In this paper, commercial coconut shell activated carbon (CSC) was modified by a thermal reduction treatment to obtain heat-treated coconut shell activated carbon (HCSC). CSC and HCSC exhibited similar pore structure characteristics but differed significantly in surface oxygen content (10.97% and 7.55%, respectively). Dynamic adsorption breakthrough experiments were conducted to determine the dynamic adsorption capacities of toluene on both adsorbents under varying relative humidity levels. HCSC demonstrated superior toluene/water vapor adsorption selectivity. Further analyses of toluene adsorption kinetics, activation energy, and water vapor adsorption isotherms revealed that the lower surface oxygen functional group content of HCSC resulted in a weaker surface polarity, facilitating the adsorption of weakly polar toluene. This was attributed to stronger toluene–HCSC interactions and weaker water–HCSC interactions. The dynamic adsorption capacities of three VOCs with varying polarities were also tested on HCSC. The observed VOC/water vapor adsorption selectivity had the following order: toluene > n-heptane > 1,2-dichloroethane. Grand Canonical Monte Carlo (GCMC) simulations were employed to quantify the relationship between the adsorption selectivity of eight VOCs with varying polarities and their molecular polarity. The results indicated a decrease in adsorption selectivity with increasing VOC polarity. A mechanistic analysis suggests that more polar VOCs prefer to adsorb polar oxygen-containing functional groups, competing with water molecules for adsorption sites. Under high humidity, hydrogen bonding leads to the formation of water clusters, exacerbating this competition. This research holds significant implications for the efficient selective adsorption of VOCs with varying polarities in humid industrial conditions. Full article