Adsorption Isotherm Measurements Research Articles

Carbon-dot hydrogels as superior carbonaceous adsorbents for removing perfluorooctane sulfonate from water

Efficiently removing perfluorooctane sulfonate (PFOS) from wastewaters is a hot topic in environmental field. Herein, crosslinking the nano-sized and zero-dimensional carbon dots (CDs) with polyethylene glycol diglycidyl ether (PEG) and polypropylene glycol diglycidyl ether (PPG) resulted in CD hydrogels that were verified by TEM, SEM, FTIR and XPS. The obtained CD hydrogels could efficiently adsorb PFOS from water through their CD moieties. The kinetic curves were fitted well by the pseudo-second order model, indicating the involvement of chemisorption in the rate-limiting step. The adsorption isotherm measurements showed that the hydrogel with the highest CD content had a PFOS maximum uptake capacity of ca. 2.82 g/g (5.64 mmol/g) in the neutral water, which was much higher than the ever-reported carbonaceous materials, and also ranked the top three among the superior positively-charged adsorbents. The superior PFOS adsorption of CD hydrogels could be attributed to good dispersion of the nanoscale CDs in the PEG/PPG hydrogel matrix, leading to the substantial exposure of the binding sites of CDs towards PFOS molecules. Moreover, CD hydrogels did not show pronounced loss of adsorption capacity after experiencing five adsorption-desorption cycles. As for the real wastewaters, CD hydrogels could efficiently treat not only the high concentration of PFOS in the neutral firefighting wastewaters, but also the extremely low concentration of PFOS in the neutral environmental wastewater, where the residual PFOS concentration could be reduced less than 5 ng/L, satisfying the standard of the U.S. Environmental Protection Agency.

Transformation of solid plastic waste to activated carbon fibres for wastewater treatment

In this study, the solid waste plastic was converted into activated carbon fibres through carbonization and chemical activation process. The morphological structure, composition, thermal stability and pore structure of the produced activated carbon materials were characterized. The results revealed that the activation process substantially increases the specific surface area of carbon materials via forming large micropores and mesopores (0.01–0.85 cm3g-1) within average nano size range of 50–100 nm. This study provides an effective means to remove the thymol blue dye via adsorption over activated carbon (ACs) as adsorbent. Batch adsorption of thymol blue was conducted to verify the effect of variety of pH, dye concentrations, contact time, adsorbent dose and temperature. The highest dye removal efficiency (approximately 98.05%) of ACs generated from waste plastic polybags, cups and bottles was observed at 10 ppm of thymol blue dye. The results also exhibited that the dye adsorption was favourable at basic pH (9.0) and increasing amount of adsorbent dosage promotes the dye removal efficiency. The excellent dye removal performance was primarily due to the presence of higher available surface area on the surface of developed carbon fibres. In addition, the current results have given the large overview and useful information of dye removal properties by adsorption isotherm and kinetic measurements. The adsorption kinetics and thermodynamic prospective of formed ACs explored the physical, spontaneous and endothermic adsorption process. The as prepared ACs provided easy regeneration of adsorbents with fast response which further suggests the efficiency of nanoparticles to promote their usage up to 5 consecutive cycles. The current work illustrated that better means to transform solid waste plastic into carbon fibres for providing effective and cheap viable option for the fast removal of thymol blue dye from waste water samples.

Mechanism of CO2 Capacity Reduction of Flexible Metal-Organic Framework Caused by Water Adsorption

Elastic layer-structured metal-organic framework (MOF)-11 {ELM-11: [Cu(BF4)2 (4,4′-bipyridine)2]}, which is a crystalline porous material, is a promising adsorbent for high-throughput and high-efficiency separation processes of CO2 because of its peculiar adsorption characteristics originating from the flexibility of the crystal framework. However, the exposure of ELM-11 to water vapor has been reported to reduce its CO2 capacity, which is problematic for processing feed gases that contain a certain concentration of water vapor. In this study, we investigated the stability of ELM-11 against water vapor exposure to reveal the mechanism of CO2 capacity reduction. Our combined measurements of adsorption isotherms and X-ray diffraction patterns indicated that the CO2 capacity reduction was caused by the partial formation of a crystalline subphase upon adsorption of water molecules and the subsequent formation of an amorphous phase to relax the crystalline grain boundaries. Because a higher supply rate of water molecules resulted in a larger amount of subphase formation, we concluded that the structural subphase was a metastable kinetically controlled structure, formed through the rate-dependent adsorption of water molecules. These results suggest that slowing the adsorption rate is an effective approach to suppress the formation of the subphase; therefore, we proposed the covering of ELM-11 surfaces with porous shells. We used ELM-12 {[Cu(CF3SO3)2 (4,4′-bipyridine)2]} as a shell material because of its robust stability against water adsorption and affinity with ELM-11. The ELM-12 shell decreased the adsorption rate of water molecules compared with that of bare ELM-11, resulting in the suppression of subphase formation and preventing CO2 capacity reduction. Although further optimization of the shell thickness and coverage is required to keep the capacity completely unchanged, controlling the adsorption rate of water molecules is successfully demonstrated to be possible with shell formation, which is key for industrial applications of ELM-11.

Digitization of Adsorption Isotherms from "The Thermodynamics and Hysteresis of Adsorption".

Sorption isotherms collected from tables in the seminal dissertation, “The Thermodynamics and Hysteresis of Adsorption” by A. J. Brown, have been digitized and made publicly available, along with supporting software scripts that facilitates usage of the data. The isotherms include laboratory measurements of xenon, krypton, and carbon dioxide adsorption (and, when possible, desorption) isotherms on a single sample of Vycor glass1, at various temperatures including subcritical conditions for xenon and krypton. The highlight of this dataset is the collection of “scanning” isotherms for xenon on Vycor at 131 K. The scanning isotherms examine numerous trajectories through the adsorption-desorption hysteresis region, such as primary adsorption and desorption scanning isotherms that terminate at the hysteresis boundary, secondary scanning isotherms made by selective reversals that return to the boundary, and closed scanning loops. This dataset was originally used to test the independent domain theory of adsorption and continues to support successor theories of adsorption/desorption scanning hysteresis including more recent theories based on percolation models. Through digital preservation and release of the tables from Brown’s dissertation, these data are now more easily accessible and can continue to find use in developing models of adsorption for fundamental and practical applications.

Water vapor diffusion models in asphalt mortar considering adsorption and capillary condensation

Water vapor diffusion persistently and extensively existing in asphalt pavement is one of the important contributors to moisture-induced damage. Non-Fickian diffusion of water vapor in asphalt mortar has not been deeply understood due to the lack of quantitative characterization of water molecular transport in micropores affected by the adsorption and capillary condensation. The objective of this study is to establish diffusion models considering the effects of the adsorption and capillary condensation and quantitatively characterize the dependence of diffusion coefficient on the humidity and sample thickness. The diffusion characteristics of water vapor in asphalt mortar with various thicknesses under various humid conditions were investigated using a standard wet cup method. The results suggest that in the steady diffusion the measured mass loss of diffusive water vapor linearly increases with time. The apparent diffusion coefficients determined by the first Fick’s law demonstrate a nonlinear rapid reduction from 51.45×10–9 m2/s to 12.66×10–9 m2/s while the relative humidity varies from 22% to 95%. The diffusion coefficient nonlinearly decreases from 40.92×10–9 m2/s to 24.71×10–9 m2/s while the sample thickness increases from 3.62 mm to 16.34 mm. The molecular transports in gaseous flow, surface flow, and capillary condensate flow were introduced to formulate the effects of adsorption and capillary condensation. Combining the measured adsorption isotherm of water vapor in asphalt mortar, a diffusion model considering adsorption was derived and quantitatively characterizes the diffusion coefficients varying with the relative humidity. The dependence on relative humidity is attributed to the thickening of adsorbed water film in high humidity that changes the diffusivities in gaseous flow and surface flow. Another diffusion model considering capillary condensation was established to formulate the thickness-dependent diffusion coefficients in asphalt mortar. The dependence on the sample thickness is explained as the variable ratio of the diffusion in capillary condensate flow to the overall diffusion in a thick sample. This study provides a feasible approach to quantifying the environment-dependent diffusion characteristics and promotes the understanding of non-Fickian diffusion of water vapor in asphaltic materials.

Silver nanoparticles supported on UiO-66 (Zr): As an efficient and recyclable heterogeneous catalyst and efficient adsorbent for removal of indigo carmine

As incorporating silver nanoparticles (Ag NPs) into zirconium metal-organic frameworks (UiO-66) offer an extensive potential in numerous applications such as wastewater treatment and catalysis, we herein synthesized UiO-66, followed by incorporating different contents of Ag NPs into UiO-66. The prepared UiO-66 composites were identified by means of various techniques like X-ray-diffraction patterns (XRD), nitrogen adsorption desorption (BET), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) analysis. Besides, acidic properties of composites were examined using FTIR of chemisorbed pyridine and non-aqueous potentiometric titration. The results displayed that UiO-66 crystals exhibited sizes of 180 and 240 nm. Their surface area and total pore volume respectively reached 1593 m 2 g −1 and 0.834 m 3 g −1 , and decreased by incorporating Ag NPs to 863 m 2 g −1 and 0.432 m 3 g −1 at 5.0 wt% Ag/UiO-66. TGA data manifested that adding Ag NPs could improve the thermal stability of the primitive UiO-66. The as-synthesized composites were tested towards indigo carmine (IC) adsorption from aqueous media and in synthesis of 3,4-dihydro-pirimidin-2(1H)-ones (3,4-DHPs). The adsorption data showed that silver nanoparticles incorporation enhanced IC removal performance of UiO-66 and adsorption capacity was augmented from 87.2 mg g −1 (UiO-66) to 312.8 mg g −1 at 2.0 wt% Ag/UiO-66. This performance was efficient relying on adsorption isotherm measurements, indicating that incorporating Ag NPs augmented the number of adsorption sites and π–π interactions between adsorbate and adsorbent were enhanced, resulting in improved adsorption capacity towards anionic dyes. Also, incorporated Ag NPs show better catalytic activity in the preparation of DHPs and the yield reached 88% using 2.0 wt% Ag/UiO-66, imparting excellent recyclability for four cycles.

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.

Re-evaluating adsorbed and free methane content in coal and its ad- and desorption processes analysis

Discriminating methane mass stored between free and adsorbed states in coal and shale is crucial in devising optimal gas recovery strategies and greenhouse control. Existing methods of estimating free and adsorbed gas contents in core plugs cannot fully discriminate between methane phases due to high levels of compaction and the resulting complex architecture of micropores. We propose a method using nuclear magnetic resonance (NMR) spectroscopy to define adsorbed/free methane ratios in powdered coal at pressures up to 15 MPa and to verify its fidelity against standard isothermal adsorption measurements. The methane T2 spectra exhibit four distinct peaks in the intervals 0.01–1, 1–20, 20–100, and ~ 1000 ms, respectively. The three peaks located < 100 ms all correspond to surface relaxation indicating the presence of adsorbed (0.01–1 ms) and free (1–100 ms) methane. The free methane can be interpreted as occupying both small (1–20 ms) and large (20–100 ms) pores as indicated by relaxation times and their pressure-dependency. The adsorption capacity generally reaches a maximum at ~ 10 MPa with free methane content only lower than adsorbed content below ~ 5 MPa. Adsorbed/free methane ratios recovered by NMR compare favorably with isothermal adsorption results with NMR also capable of calibrating absolute adsorbed methane contents.

Synthesis of a porous MOF, UiO-67-NSO2CF3, through post-synthetic method

We newly synthesized an anionic porous MOF, UiO-67-NSO2CF3 ((HPy)6[Zr6O4(OH)4(BPDC-NSO2CF3)6](guest)n (H2BPDC-NSO2CF3 = (4,4′-dicarboxy-[1,1′-biphenyl]-2-yl)((trifluoromethyl)sulfonyl)amide, HPy+ = pyridinium), having large pore size through post-synthetic method. The amino groups (–NH2) on the UiO-67-NH2 were converted into –NSO2CF3– groups. The sample was characterized with X-ray powder diffraction, scanning electron microscope observations, SEM combined with energy-dispersive X-ray spectroscopy, infrared spectra, thermogravimetry, and N2 adsorption isotherms measurements. These measurements revealed that the successful synthesis of the porous MOF, UiO-67-NSO2CF3.

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.

The effect of nanosilica sizes in the presence of nonionic TX100 surfactant on CO2 foam flooding

The aim of this research is to study the effect of hydrophilic silica nanoparticles, sizes as CO2 foam stabilizer in the presence of nonionic TX100 surfactant. Two nanosilica sizes, 15 and 70 nm, have been examined thoroughly. Physisorption of TX100 on silica nanoparticles (nanosilica) was characterized by adsorption isotherm and surface tension measurement, while CO2 foams stability was quantified based on their foamability, foam stability, particle partitioning in the foams, and bubble sizes. Results show that direct contact of TX100 with nanosilica does altered the wettability of hydrophilic nanosilica surface, enable them to lengthen CO2 foams life at certain surfactant and nanoparticles concentrations. For 15 nm nanosilica, CO2 foam stability shows excellent performance at 0.1 and 0.5 wt% TX100 concentrations. As for 70 nm nanosilica, CO2 foam demonstrates longer lifetime at much lower TX100 concentration, 0.01 wt%. Without the presence of TX100, CO2 foams exhibit undesirable lifetime performances for both nanosilica sizes. Nanosilica partitioning in CO2 foams structures demonstrate consistent relation with contact angle measurement. Estimated bubble sizes shows insignificant effect on CO2 foams life. With the assists of nanosilica and TX100, enhanced oil recovery via CO2 foam injection succeeds in increasing oil production by 13–22% of original oil-in-place (OOIP).

Bisindole [3]arenes—Indolyl Macrocyclic Arenes Having Significant Iodine Capture Capacity

Bisindole [3]arenes—Indolyl Macrocyclic Arenes Having Significant Iodine Capture Capacity

Investigating Methylene Blue Removal from Aqueous Solution by Cysteine-Functionalized Mesoporous Silica

In this study, mesoporous silica nanoparticles (MSNs) were synthesised using the Stober method and functionalised with cysteine (MSN-Cys) for removal of Methylene Blue (MB) from aqueous solution using the batch method. The adsorbent nanoparticles were characterised by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), FTIR, BET, and TGA. Several influential factors on the adsorption of MB onto the surface of MSN-Cys particles were investigated, including pH, initial concentration, and contact time. The adsorption capacity of MB from aqueous solution increased from circa 70 mg/g MSN-Cys in acidic media to circa 140 mg/g MSN-Cys in basic media. Adsorption isotherms and kinetic models of adsorption were used to clarify the adsorption process. The measured adsorption isotherm was fitted with a Freundlich model for all solutions, and the kinetic model was determined to be pseudo-second-order.

High‐performance adsorptive desulfurization by ternary hybrid boron carbon nitride aerogel

AbstractSeparation of aromatic organosulfur compounds is vital for upgrading the feed to clean fuel products, however, it remains a formidable challenge for the present adsorbents. Herein, a series of novel aerogel‐like boron carbon nitride (BCN) with three‐dimensional interconnected porous networks were fabricated via a hydrogel template and freeze‐casting strategy. The as‐prepared aerogel‐like BCN had a variable carbon content and a flexible size of graphene domain on its porous structure. The optimal BCN aerogel represents the top‐level of adsorptive desulfurization (ADS) capacity for aromatic organosulfur compounds (30.8 mg S/g adsorbent), strikingly higher than the state‐of‐the‐art aerogels adsorbents (17.1 mg S/g adsorbent) reported under similar conditions. A selective adsorption for dibenzothiophene in the presence of aromatic hydrocarbons, nitrogen compounds were also achieved on BCN aerogel. The adsorption isotherm and XPS measurement reveal heterogeneous adsorption on the BCN aerogel via π–π and Lewis acid–base interactions.

An automated multi-component gas adsorption system (MC GAS)

The knowledge gap on adsorption of complex mixtures in the literature relative to single component data represents a persistent obstacle to developing accurate process models for adsorption separations. The collection of mixed gas adsorption data is an imminent need for improved understanding of the behavior of adsorbent systems in these diverse adsorption applications. Current approaches to understanding mixture adsorption using predictive theories based on pure component adsorption experiments often fail to capture the behavior of more complex, non-ideal systems. In this work, we present an automated volumetric instrument for the measurement of mixed gas adsorption isotherms. This instrument was validated by comparison to other in-house instruments and data available in the literature, and the binary adsorption measurements were found to be thermodynamically consistent. The automation of this instrument allows for rapid collection of high-quality mixture adsorption data.

Synthesis, characterization and electrochemical evaluation of hydrogen storage capacity of graphitic carbon nitride and its nanocomposites in an alkaline environment

Herein, synthesis of graphitic carbon nitride (g-C3N4) and its nanocomposites with monometallic nickel (Ni-g-C3N4), and bimetallic zirconium-nickel (ZrNi-g-C3N4) is reported. New materials for high storage performance are investigated eagerly in electrochemical energy applications. With this aim, the electrochemical method is used for the evaluation of hydrogen storage capacity (HSC) of the samples in the present research work. Synthesis of samples were carried out using a combination of thermal and hydrothermal methods. The evaluation of electrochemical hydrogen sorption and storage capability of g-C3N4 and its nanocomposites was done after sample characterization. Characterization techniques followed were powder X-ray diffraction (XRD), Nitrogen adsorption and desorption isotherms measurements at 77 K, thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry (EDS). Cyclic voltammetric and chronopotentiometry measurements carried out in an alkaline medium helped to calculate the HSC. The discharge capacity was measured to be 82 mAhg−1 for g-C3N4, 182 mAhg−1 for Ni-g-C3N4 and 380 mAhg−1 for ZrNi-g-C3N4 at 1 mAg−1 of current density. Catalytic properties of the metal nanoparticles augment the storage capability of the g-C3N4 nanocomposites. These nanocomposites help to store hydrogen which serves as safe carrier in fuel cell applications.

Kinetic Modeling for Photo-Assisted Penicillin G Degradation of (Mn0.5Zn0.5)[CdxFe2-x]O4 (x ≤ 0.05) Nanospinel Ferrites.

Penicillin G is an old and widely used antibiotic. Its persistence in the environment started to appear in many environmental samples and food chains. The removal of these emerging pollutants has been a challenging task for scientists in the last decades. The photocatalytic properties of Cd2+ doped Manganese- Zinc NSFs with chemical formula (Mn0.5Zn0.5)[CdxFe2−x]O4 (0.0 ≤ x ≤ 0.05) NSFs are herein evaluated. The Manganese- Zinc N.S.F.s nanomaterials were deeply characterized, utilizing UV-Vis (reflectance) spectroscopy, X-ray diffraction, N2 adsorption isotherm measurements, and S.E.M., SEM-EDX mapping, and T.E.M. The Kinetic model for the photodegradation of penicillin G (as a model molecule) is investigated using visible light as a source of energy. The kinetic study shows that our results fit well with the modified pseudo-first-order model. The Pen G degradation are 88.73%, 66.65%, 44.70%, 37.62% and 24.68% for x = 0.5, 0.4, 0.3, 0.2 and 0.1, respectively, against 14.68% for the free Cd spinel sample. The pseudo-rate constant is bandgap dependent. From the intra-diffusion rate constant (Kd), we developed an intra-diffusion time (τ) model, which decreases exponentially as a function of (x) and mainly shows the existence of three different domains versus cadmium coordination in spinel ferrite samples. Hence, Cadmium’s presence generates spontaneous polarization with a strong opportunity to monitor the charge separation and then open the route to a new generation of “assisted” photocatalysts under visible light.

Measurement and interpretation of unary supercritical gas adsorption isotherms in micro-mesoporous solids

Gas adsorption at high pressures in porous solids is commonly quantified in terms of the excess amount adsorbed. Despite the wide spectrum of adsorbent morphologies available, the analysis of excess adsorption isotherms has mostly focused on microporous materials and the role of mesoporosity remains largely unexplored. Here, we present supercritical CO2 adsorption isotherms measured at T=308 K in the pressure range p=0.02{-}21 MPa on three adsorbents with distinct fractions of microporosity, phi_2, namely a microporous metal-organic framework (phi_2=70%), a micro-mesoporous zeolite (phi_2=38%) and a mesoporous carbon (phi_2<0.1%). The results are compared systematically in terms of excess and net adsorption relative to two distinct reference states–the space filled with gas in the presence/absence of adsorbent–that are defined from two separate experiments using helium as the probing gas. We discuss the inherent difficulties in extracting from the supercritical adsorption isotherms quantitative information on the properties of the adsorbed phase (its density or volume), because of the nonuniform distribution of the latter within and across the different classes of pore sizes. Yet, the data clearly reveal pore-size dependent adsorption behaviour, which can be used to identify characteristic types of isotherm and to complement the information obtained using the more traditional textural analysis by physisorption.

Data-driven Modeling of the Methane Adsorption Isotherm on Coal Using Supervised Learning Methods: A Comparative Study

Methane adsorption isotherm on coals is key to the development of coalbed methane (CBM). Laboratory measurement of adsorption isotherm is time-consuming. This paper presents a comparative study on the accuracy and robustness of seven supervised learning (SL) methods in estimating the methane adsorption isotherm based on coal properties. The SL methods used include the Gaussian process regression (GPR), kernel ridge regression (KRR), classifier and regression tree (CART) and four ensemble decision tree methods (random forests (RF), Adaboost, gradient boosting decision tree (GBDT) and extreme boosting (XGBoost)). The results show that all these SL methods are capable of correlating methane adsorption amounts with the feature variables with reasonable accuracies in the training stage. However, the KRR, GBDT and XGBoost are demonstrated to outperform other SL techniques in terms of the robustness and generalization capability, which therefore are recommended for fast estimation of the methane adsorption isotherms on coals.

Evaluating liquid-water generation in catalyst layers of polymer electrolyte fuel cells based on adsorption isotherm measurements and lattice density functional theory calculations

Evaluating liquid-water generation in catalyst layers of polymer electrolyte fuel cells based on adsorption isotherm measurements and lattice density functional theory calculations