Water Adsorption Capacity Research Articles

Insights into optimized synthesis conditions of hollow microspheres of silica for water vapor adsorption

Hollow microspheres of silica were synthesized with different ethanol/water ratios (0.4, 1.0, 2.0 and 6.0) to assess the influence of this parameter on the morphology/porosity of the samples and thus on their water adsorption capacity. The samples were characterized by N2 at 77 K and CO2 at 273 K adsorption isotherms, scanning electron microscopy, transmission electron microscopy and water vapor isotherms at 298, 313 and 328 K. The textural properties of the samples were slightly different: as the ethanol/water ratio increases, the pore volume and specific surface area decrease and the structure of the samples evolves into a well-defined spherical arrangement. In addition, water adsorption capacity of the samples was similar to that of commercial adsorbents used for gas drying at high relative pressures, but significantly lower at low relative pressures. Moreover, varying of the ethanol/water ratio did not lead to a noticeable improvement in the water adsorption capacity at low relative pressures and hence these samples are not suitable for deep gas drying. On the other hand, as they require less energy to be regenerated, HMS are alternatives to be considered in less demanding situations, such as coarse drying and water harvesting from air.

Nanoconfinement-Induced Conversion of Water Chemical Adsorption Properties in Nanoporous Photocatalysts to Improve Photocatalytic Hydrogen Evolution

The diffusion and adsorption properties of water molecules on active sites play a pivotal role in the performance of heterogeneous photocatalytic reactions. Water inside the microporous carbon nanocage (MCN) can form an ideal system for boosting such nanoconfined water molecules’ adsorption on the interior metal active sites compared with the bulk water system. The properties of water molecules adsorbed in the nanoconfined cavity and how they depend on the microporous pores and chemical functional groups of the carbon nanocage to promote water molecule adsorption on active sites have not been demonstrated before. Herein, we report a nano-constrained ZnIn2S4@C photocatalyst, maximizing water inside the MCN, and stabilization of its water molecules in the nanocavity can alter the localization electron distribution of water molecules at the ZnIn2S4 surface. This change demonstrates that the chemical adsorption capacity of the inside water on the photocatalyst can depend sensitively on the nanostructure, boosting the photocatalytic performance further. This work reveals an in-depth understanding of nano interior cavity effects on the water molecule adsorption process and provides a basis to understand how the nanoconfined space impacts the capability of water molecule chemical adsorption on the active sites of interior photocatalysts.

Binder‐Free Growth of Aluminum‐Based Metal–Organic Frameworks on Aluminum Substrate for Enhanced Water Adsorption Capacity

AbstractCoating metal–organic frameworks (MOFs) on metal substrates is an important research orientation in the applications of MOFs. However, the existing binder‐based coating method needs repetitive operations and unavoidably plugs the pores of MOFs, resulting in a reduction of the adsorption capacity. Herein, a binder‐free method is proposed to construct the MOF‐on‐metal structure. The well‐intergrown polycrystalline Al‐MOF layer on aluminum substrate is prepared by in situ synthesizing Al‐based MOFs (MIL‐96 and MIL‐100) with aluminum ions from the dissolution of aluminum substrates. The morphology and chemical compositions of the MOF coating layer are systematically characterized, and a pH‐controlled strategy is proposed to regulate the relative proportion of the hybrid MOFs. Importantly, the MOF‐on‐metal structure displays ultrahigh water adsorption capacity of 192.5 g m−2, which is the highest of all reported desiccant‐coated metal structures, and superior cycling stability. Further, the performance of a desiccant heat pump system utilizing MOF‐on‐metal structure is predicted, demonstrating that the operation period is 80% longer than a system with a binder‐based silica gel coating, and the average dehumidification capacity can reach 8.36 g kg−1 dry air. In conclusion, the new method enables the formation of binder‐free, low‐cost, and high‐performance MOF coating and has a broad prospect in energy‐efficient adsorption‐based applications.

Competitive coadsorption of ammonia with water and sulfur dioxide on metal-organic frameworks at low pressure

Purification of ammonia in semiconductor cleanrooms is crucial to improve semiconductor yields and ensure standardized production. In this study, adsorption isotherms for ammonia on HKUST-1, UIO-66, and MIL-100(Fe) were acquired. Density functional theory (DFT) calculations for ammonia illustrated the adsorption mechanism at low pressure. Adsorption isotherms and DFT calculations for water and sulfur dioxide (SO2) were used to investigate the effect of water and SO2 on ammonia adsorption.The ammonia adsorption capacity of HKUST-1 exceeded that of UIO-66 from 1.0 × 10−6 to 1.0 × 10−5 P/P0. The UIO-66 ammonia adsorption capacity was superior to that of MIL-100(Fe) at low pressure. The water adsorption capacity at 45% relative humidity followed an order of MIL-100(Fe) (24.040 mmol/g) > UIO-66 (16.300 mmol/g) > HKUST-1 (14.200 mmol/g). The SO2 adsorption capacity of MIL-100(Fe) exceeded that of HKUST-1 at low pressure.The order of interaction energies was HKUST-1 (−147.890 kJ/mol) > MIL-100(Fe) (−80.280 kJ/mol) > UIO-66 (−47.080 kJ/mol) for ammonia, ammonia (−147.890 kJ/mol) > SO2(O) (−78.890 kJ/mol) > SO2(S) (−74.790 kJ/mol) > water (−64.070 kJ/mol) on HKUST-1, ammonia (−80.280 kJ/mol) > SO2(O) (−64.910 kJ/mol) > water (−46.940 kJ/mol) > SO2(S) (−40.920 kJ/mol) on MIL-100(Fe), and SO2(O) (−71.670 kJ/mol) > SO2(S) (−65.720 kJ/mol) > ammonia (−47.080 kJ/mol) > water (−30.000 kJ/mol) on UIO-66. Ammonia is likely to displace preadsorbed SO2 and water due to ammonia's higher affinity for HKUST-1. Preadsorbed ammonia could be more difficult to displace with SO2 or water on MIL-100(Fe) and with water on UIO-66.

A Hydrolytically Stable Cu(II)-Based Metal-Organic Framework with Easily Accessible Ligands for Water Harvesting.

Water scarcity is a critical issue in desert and arid regions, and atmospheric water harvesting is a potential solution. The challenge is lacking ideal adsorbents that can efficiently capture water from low-humidity air and be regenerated readily. Herein, we report a hydrolytically stable metal-organic framework (MOF), [Cu2(AD)2(SA)] (Cu-AD-SA), with excellent performance in water harvesting. More importantly, this material can be facilely prepared from two easily accessible ligands adenine (HAD) and succinic acid (H2SA). Cu-AD-SA has a three-dimensional (3D) framework structure with the crs topology and intersecting channels of ∼5 Å in diameter. The channel surface is decorated by uncoordinated aromatic N atoms, amine groups, and alkyl moieties. Interestingly, Cu-AD-SA shows a high water adsorption capacity of 0.16 g g-1 at low pressure of 0.2 P/P0 and 25 °C. Furthermore, dynamic water adsorption-desorption cycling experiments demonstrated a stable working capacity of 0.13 g g-1 for uptaking water from a low-humidity air (water partial pressure: 0.85 kPa, 20% RH at 30 °C, 5.3% RH at 55 °C) at 30 °C and desorption at 55 °C. The water adsorption mechanism was also studied by analyzing its single-crystal structure after water loading. The results indicated the existence of strong H-bonding interactions between water molecules and uncoordinated N atoms and amine groups on the framework, which should play an important role in the high adsorption at low pressure. All the above features suggest great potential of Cu-AD-SA for water harvesting in arid regions.

Development and characterization of biopolymers films mechanically reinforced with garlic skin waste for fabrication of compostable dishes

The pollution caused by use of petroleum-derivate plastic materials is a major environmental problem. This has encouraged researchers to develop new compostable and environmental-friendly materials based on biopolymers and agro-industrial residues. The aim of this work was to study the addition of garlic skin (GS) particles and the changes in physicochemical, mechanical, and microstructural properties of films formulated with potato starch and gellan gum as well as the creation of an environmentally friendly dish. Different concentrations (1, 2 and 3% w/v) and sizes (1410-213 μm, 212-39 μm and 38-1 μm) of GS particles were used for the mechanical reinforcement of the films and as independent variables of the experimental design. Different response variables (phenolic content, color difference, thickness, film transparency, stress, strain, Young's modulus, water solubility, water adsorption capacity, fractal dimension and entropy of the images) were evaluated to select the optimal point using response surface methodology (RSM). Microscopy techniques and texture image analysis were used to explain the effect of adding GS particles to the microstructure and mechanical reinforcement of the films. Moreover, thermogravimetric analysis (TGA), principal component analysis (PCA) and RSM were used to select the best film for making a compostable dish using a low-cost molding process at laboratory level. A novelty of this study was proposing an alternative use of GS waste in a film with biopolymers, integrating different analytical tools to facilitate the selection of the suitable formulations to create compostable dishes in 60 days, which goes beyond the traditional studies of coatings and polymeric films reported.

Water vapor adsorption on metal-exchanged hierarchical porous zeolite-Y

The development of efficient zeolite-based adsorbents with high water uptake capacity is an essential requirement for water adsorption and moisture removal technologies. In the present study, zeolite-Y samples with interconnected hierarchical micro-mesoporous network were synthesized by employing a bifunctional cationic polymer (namely, polydiallydimethyl-ammonium chloride, PDDA), and ion-exchanged with several metal salts (such as Zn, Mg, Li) targeting high capacity water adsorption. We systematically investigated water adsorption behavior of hierarchically porous NaY (HP–NaY) samples and studied the influence of their distinct metal exchange analogues on water affinity and total adsorption capacity. The water affinity and water uptake increased for the HP-NaY samples compared to conventional NaY. HP-NaY samples demonstrating a high water adsorption capacity (17.32–17.98 mmol/g) at 303 K and 0.7 relative pressure (P/Po) when compared to commercial zeolite-Y (CBV-400, 14.83 mmol/g). A further improvement in water uptake was attained by introduction of distinct metal ions into the hierarchical porous zeolite-Y. HP-LiY exhibited the highest water adsorption capacity (19.08 mmol/g at 0.7 P/Po) amounting to 28% and 15% improvement when compared to CBV-400 and CBV-Li respectively. The observed improvements in water adsorption capacity are attributed to (i) the existence of interconnected micro-mesoporous channel network and higher total pore volume and (ii) the enhancement in accessibility of adsorption sites by H2O molecules. The adsorption data of the samples were also fitted using various adsorption models. Hierarchically porous zeolites displayed site heterogeneity, the latter being rendered by the existence of varying chemical environments between sites within the micropores and the mesopores and the nature of the host metals.

Poly(2-Hydroxyethyl methacrylate-co-N,N-dimethylacrylamide)-Coated Quartz Crystal Microbalance Sensor: Membrane Characterization and Proof of Concept.

Application-oriented hydrogel properties can be obtained by modifying the synthesis conditions of the materials. The purpose of this study is to achieve customized properties for sensing applications of hydrogel membranes based on poly(2-hydroxyethyl methacrylate), HEMA and N,N-dimethylacrylamide, DMAa. Copolymer p(HEMA-co-DMAa) hydrogels were prepared by varying the DMAa monomer ratio from 0–100% in 20% increments. Hydrogel membranes were characterized by attenuated infrared spectroscopy. Swelling and sorption were evaluated using cation solutions. Copolymers were also synthesized on the gold surface of quartz crystal microbalances (QCM) as coating membranes. A proof of concept was conducted for approaching the design and development of QCM sensors based on P(DMAa-co-HEMA)-membranes. Results showed that the water and ion adsorption capacity of hydrogel membranes increased with higher DMAa content. Membranes are not selective to a specific location but did show different transport features with each cation. The QCM coated with the selected membrane presented linear relationships between resonance frequency and ions concentration in solution (10–120 ppm). As a consequence, hydrogel membranes obtained are promising for the development of future biosensing devices.

Development of biomass based-activated carbon for adsorption dehumidification

Desiccant dehumidification systems can be utilized for decoupling moisture removal duty from the conventional mechanical vapor compression systems. Dehumidification using desiccant dehumidifiers is expected to exhibit a better energy efficiency. However, the high energy needed in the regeneration process limits its applicability. To realize the full potential of this technology, it is necessary to develop materials that can be regenerated using heat sources under 70 °C. In this study, activated carbons (ACs) derived from waste biomass were developed as desiccant materials. The ability of activated carbon (AC) to remove the moisture was controlled by carefully preparing the material to achieve the right operation window for optimum moisture sorption processes. The porous and surface characteristics of the newly-prepared AC were analyzed and compared with those of silica gel. The adsorption isotherm measurements were conducted, and the data were fitted with Henry–Sips and Do–Do isotherm models. The current ACs exhibit an excellent water adsorption capacity (up to 0.41 g/g). The efficacy of the ACs for dehumidification applications was assessed using the weather data from several regions of Indonesia, from North Sumatera to Papua. The results revealed that under the studied conditions, the new desiccant material showed a better dehumidification capacity than silica gel. Moreover, the reported AC can be regenerated using temperatures as low as 40 °C, which is readily available from waste heat, including the heat rejection from the condenser of an air-conditioning unit.

Preparation of MS/MIL-101(Cr) composite material and its properties of atmospheric water collection

In this study, we dispersed MIL-101(Cr) into melamine sponge (MS) by one-step hydro-thermal method and prepared MS/MIL-101(Cr) composite material (MM101CM). It is applied to atmospheric water harvest. The structure and properties of MM101CM were characterized by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), in situ attenuated total reflection fourier transform infrared spectroscopy (FT-IR) and comprehensive thermal analyzer (TG). The influence of temperature and humidity on atmospheric water collection performance of MM101CM was studied. The composite has good water stability and thermal stability, and its maximum water adsorption capacity can reach 1232 ​g/kg. This study found a simple and effective composite way for metal organic framework materials with hygroscopic properties, which will be conducive to the large-scale application of this kind of materials for atmospheric water collection.

Injectable Lignin-co-Gelatin Cryogels with Antioxidant and Antibacterial Properties for Biomedical Applications.

For several biomedical applications, it is essential to develop novel bioactive materials. Such biomaterials could potentially improve wound healing, prevent infections, or be used in immunoengineering. For example, bioactive materials that reduce oxidative stress without relying on antibiotics and other drugs could be beneficial. Hydrogel-based biomaterials, especially those derived from natural polymers, have been regarded as one of the most promising scaffolds for biomedical research. These multifunctional scaffolds can exhibit high water adsorption capacity, biocompatibility, and biomechanical properties that can match native tissues. Cryogels are a special type of hydrogels in which polymers are cross-linked around ice crystals. As a result, cryogels exhibit unique physical features, including a macroporous and interconnected network, flexibility, shape-memory properties, and syringe injectability. Herein, we developed a multifunctional, i.e., antibacterial, antioxidant, and injectable cryogel by combining lignin with gelatin. The cryogel with 0.2% lignin showed a compressive modulus of 25 kPa and a compressive stress of 140 kPa at 80% strain, which is, respectively, 1.8 and 7 times higher than those of the pure gelatin cryogels. Meanwhile, such a cryogel formulation could completely recover its shape after compression up to 90% and was needle-injectable. Additionally, the lignin-co-gelatin cryogel with 0.1-0.2 lignin showed 8-10 mm of inhibition zone against the most common surgical site infection-associated pathogenic bacteria. Furthermore, lignin-co-gelatin cryogel was found to scavenge free radicals and have good cytocompatibility, and the cryogels with up to 0.2% lignin minimally activate naïve mouse bone marrow-derived dendritic cells. Overall, the current approach shows great promise for the design of bioresource-based multifunctional cryogels for a wide range of biomedical applications.

Impact of heteroatom addition into mesoporous silica for water adsorption in the low partial pressure range.

Mesoporous silicas are known to be high-performing water adsorbents in high humidity levels due to their large pore volumes. However, for low humidity conditions, these materials typically present a less expressive performance, which is a drawback for many applications. In the present report, mesoporous silica SBA-15 was functionalized with Al, Ti, Zr and Li in order to improve their performance in this condition. The influence of functionalization in porosity, morphology and acidic sites was investigated. Samples with an increased number of acidic sites and with higher microporosity when compared to pure silica were produced. This was responsible for their enhanced performance for water adsorption in low moisture conditions. Sample functionalized with zirconium in SBA-15 synthesis improved the water adsorption capacity of pure silica by three times, reaching up to 127 g kg−1 at a relative pressure of 0.2 and 570 g kg−1 close to saturation pressure. This sample was found to be a promising material to be applied in processes which require high adsorption capacities in both low and high water partial pressure ranges. Moreover, the understanding of the mechanisms behind the heteroatom functionalization can be applied to any silica material in order to enhance its attractiveness towards any polar molecule.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10450-021-00336-6.

Experimental Study on Heat Transfer and Adsorption Cooling Performance of MIL-101/Few Layer Graphene Composite

MIL-101 is a promising metal-organic frameworks (MOFs) material in adsorption chiller application due to its high adsorption capacity for water and excellent adsorption/desorption cyclic stability. Few layer graphene (FLG) as the thermal conductive additive was added into MIL-101 to improve inferior heat transfer of MIL-101 in the adsorption cooling process. The heat transfer characteristic of MIL-101/FLG adsorber and the adsorption cooling performance of the MIL-101/FLG-water working pair were studied. Results show that thermal conductivity of MIL-101/20%FLG composite is 5.79-6.54 times that of MIL-101. Adding FLG is conducive to the formation of heat transfer channels in MIL-101/FLG adsorber and the rapid removal of adsorption heat. The heating and cooling rate of MIL-101/FLG adsorber is ~2.2 times that of MIL-101 adsorber. Under typical adsorption water chiller conditions, the specific cooling power (SCP) and coefficient of performance (COP) of the MIL-101/FLG-water working pair is 72.2–81.0 W kg−1 and 0.187–0.202, respectively, at desorption temperatures of 70 °C and 90 °C, which is 1.43–1.56 times higher than the MIL-101-water working pair. The excellent structural and adsorption/desorption cyclic stability of MIL-101/FLG composite is verified after 50 consecutive cycles. It can provide a promising adsorbent candidate (MIL-101/FLG composite) in adsorption water chiller process.

Zeolite-Polymer Composite Materials as Water Scavenger.

The influence of the charge compensating cation nature (Na+, Mg2+) on the water adsorption properties of LTA-type zeolites used as filler in composite materials (zeolite/polymers) was investigated. Large scale cation exchanges were performed on zeolite powder at 80 °C for 2 h using 1 M magnesium chloride (MgCl2) aqueous solutions. XRF, ICP, and EDX analyses indicate a successful cationic exchange process without the modification of the zeolite structure as shown by XRD and solid-state NMR analyses. Composite materials (granulates and molded parts) were manufactured using to extrusion and injection processes. In the case of MgA zeolite, nitrogen adsorption–desorption experiments allowed us to measure a microporous volume, unlike NaA zeolite, which is non-porous to nitrogen probe molecule. SEM and EDX analyses highlighted the homogeneous distribution of zeolite crystals into the polymer matrix. Water adsorption capacities confirmed that the trends observed in the zeolite powder samples are preserved after dragging zeolites into composite formulations. Granulates and molded parts composite samples containing the magnesium exchanged zeolite showed an increase of their water adsorption capacity up to +27% in comparison to composite samples containing the non-exchanged zeolite. The MgA composite is more promising for water decontamination applications due to its higher water adsorption properties than the NaA composite.

Development of green geo-adsorbent pellets from low fire clay for possible use in methylene blue removal in aquaculture

Mesoporous clay ceramic pellets have been prepared by sintering silica rich low fire clay at two different temperatures (650 °C and 850 °C). The prepared ceramic pellets were characterized using FTIR, SEM, XRF, compressive strength and water adsorption capacity. The methylene blue removal capacity of ceramic pellets was investigated and it was found that the uptake capacity of pellets was found to be increasing with increase in the initial dye concentration, while it was found to be decreasing with increase in pellet dose. Presence of co-ions and change in pH had no effect on the removal capacity. The adsorption isotherm followed the Langmuir model while the adsorption kinetics was well described by the pseudo-second order model. A simple device that can be used in aquariums, made from stainless steel wire mesh containing the ceramic pellets has been described which can slowly yet effectively remove MB from tap water at ultralow concentrations.

Green fabrication, characterization and water-oil separation properties of superhydrophilic/oleophobic grapefruit peel-derived aerogel

To develop novel interface and surface materials is a universal concern for water-oil separation. This research demonstrated a facile green synthetic method with one-step dipping modification to prepare an excellent modified grapefruit peel aerogel (M-GPA) with superhydrophilicity/oleophobicity. The BET surface area and pore volume of M-GPA were 16.42 m2/g and 0.042 cm3/g, respectively. The pore size distribution was presented within a range of 2–50 nm with an average pore diameter of 10.24 nm, belonging to mesoporous region. The static oil contact angle of M-GPA was 141.3° and the water contact angle was 0°. The superhydrophilic/oleophobic property of M-GPA was mainly attributed to the high porosity and coated chitosan-NaPFN/Fe3O4. The M-GPA showed not only a superior water adsorption capacity of 69.7 g/g from oil bulk, but also an excellent water-oil separation efficiency above 98%. In a continuous water-oil separation process the suction forces changed water contact angle inside the capillaries of M-GPA and equilibrium pressure to realize the continuous water transportation from oil. The lightweight superhydrophilic/oleophobic M-GPA was cheap with an estimated low cost of 0.33 US$/g. The economically attractive M-GPA shows a potential application in water-oil separation for pollution control of oil spilling and industrial oil product purification.

Microfracture-pore structure characterization and water-rock interaction in three lithofacies of the Lower Eagle Ford Formation

The microfracture-pore structures and water-rock interactions of eight samples of three typical lithofacies (three limestone, three wackestone, and two mudstone) from the Lower Eagle Ford Formation have been investigated using an integrated methodology. The methods used were X-ray diffraction (XRD), total organic carbon (TOC) content, pyrolysis, thin-section petrography, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), spontaneous water imbibition, and water vapor & nitrogen physisorption. Petrophysical properties such as organic richness, maturity, mineral composition, types and patterns of microfractures and pores, porosity, pore-throat size distribution, pore size distribution, pore connectivity, water adsorption and desorption behavior were determined from these methods, and the results compared among the three lithofacies. For example, the three limestone EAS samples and three wackestone DM samples show a low porosity range from 2.02–3.35%, whereas the two mudstone VRU samples exhibit a much large average porosity of 11.7% by MIP results. Nitrogen physisorption results show that pore size distributions have a good similarity in N2 adsorption volume for the samples with similar lithology. Microfractures are morphologically divided into seven types, with their definitions & pictorial examples presented and possible formation mechanisms proposed. In addition, the water vapor physisorption behavior and their controlling factors are discussed. The water adsorption capacity shows a positive relationship (R2 = 0.90) with clay content and a negative relationship (R2 = 0.99) with carbonate content. In general, this integrated study of microfracture-pore structure characterization and water-rock interaction provides some insights of water vapor adsorption behavior in different lithofacies and whether microfractures could be an important pathway for fluid flow.

Tuning the Physicochemical Properties of Cellulose Nanocrystals through an In Situ Oligosaccharide Surface Modification Method.

The trend to replace petroleum-based products with sustainable alternatives has shifted research efforts toward plant-based materials such as cellulose nanocrystals (CNCs). CNCs show promise in numerous applications (e.g., composites and rheological modifiers); however, maximizing their performance often requires surface modifications with complex chemistries and purification steps. Presented here is a novel surface modification method with the potential to tune CNC properties through the in situ deposition of cellulose phosphate oligosaccharides during CNC production. This was achieved by leveraging the selective solubility of oligosaccharides, which are soluble at a low pH (during the CNC hydrolysis) yet become insoluble and precipitate onto CNC surfaces upon increasing pH during quenching. Oligosaccharide-coated CNCs demonstrated subtle changes including higher surface charge densities and lower water adsorption capacities and viscosities than their unmodified counterparts. CNC surface coverage was tuned by controlling the oligosaccharide degree of polymerization. Overall, this fundamental study introduces an easily scalable modification route that opens the door for expanded CNC functionality and applications.

Development of Biomass Based-Activated Carbon for Adsorption Dehumidification

The demand for dehumidification in tropical regions contributes to a significant portion of the building energy consumption. Desiccant dehumidification can mitigate energy consumption by recovering the exergy potential from the waste heat and renewable energy sources. Material development is the bottleneck in realizing the full potential of desiccant dehumidification systems beyond conventional adsorbents such as silica gel and zeolite. Therefore, it is necessary to develop novel materials that can be regenerated using the heat source under 70°C. In this study, we developed activated carbons (ACs) as the desiccant materials derived from waste biomass. The ability of activated carbon (AC) to remove the moisture was controlled by carefully preparing the material using several conditions to achieve the right operation window for optimum moisture sorption processes. The porous and surface characteristics of the newly-prepared AC were analyzed and compared with those of silica gel. The adsorption isotherm measurements were conducted, and the data were fitted with Henry-Sips and Do-Do isotherm models. The current AC exhibited an excellent water adsorption capacity (up to 0.41 g/g). The efficacy of the ACs for dehumidification applications was assessed using the weather data from several regions of Indonesia, from North Sumatera to Papua. The results revealed that under the studied conditions, the new desiccant material showed a better dehumidification capacity than silica gel. Moreover, the reported AC can be regenerated using temperatures as low as 40°C, which is readily available from waste heat, including the heat rejection from the condenser of any air-conditioning unit.

Silane functionalization on zeolite 13X surface for direct steam generation in a solid sorption heat pump

High-temperature steam has been directly generated from hot water based on a solid sorption heat pump system by employing silane functionalized zeolite 13X (XS). The adsorbent is prepared by a liquid phase grafting method to modify functional groups on the zeolite surface with a silane coupling agent. The static water contact angle (WCA) and surface functional groups are analyzed by optical contact angle measuring instruments and Fourier transform infrared spectroscopy (FTIR), respectively. Analytical results confirm the successful preparation of surface hydrophobic zeolite. The water adsorption capacity of XS is slightly less than that of 13X, while the overall adsorption heat remains almost constant. Dry air at 130 °C is utilized for the regeneration of the wet zeolite in cyclic experiments. Steam at 207 °C is generated from input hot water at 72 °C in a packed bed filled with XS-25 (zeolite 13X functionalized by a saline solution concentration of 25%). The thermal response during the steam generation process is accelerated by utilizing XS. The mass of steam product does not change during the generation with XS, whereas cyclic time is shortened. Moreover, XS facilitates the regeneration process by decreasing the heat demand for the removal of free water. System evaluation results show that a higher Sp (steam productivity) is obtained for XS than that for zeolite 13X. COPh (coefficient of performance for heating) and SHP (specific heating power) are elevated by 23.6% and 5.7% for XS compared with those for zeolite 13X, respectively.