Unit Surface Area Research Articles

Catalytic performance and insight into the mechanism of CeO2 nanorod catalysts in phenol ozone oxidation reaction

In order to effectively remove phenol wastewater and improve the utilization of ozone in non-homogeneous catalytic ozone oxidation, we synthesized cerium oxide catalysts with different morphologies and characterized the prepared catalysts. It was found that the dissolution/recrystallization rate was positively correlated with base concentration, with nanoparticles forming at low base concentrations. When the base concentration increases, the chemical potential to drive the anisotropic growth of the nuclei is higher, forming nanorods. At even higher concentrations of base, the nuclei are oxidized to have a nanocube morphology. The exposed surfaces of CeO2 nanorods and nanocubes are in the (110) and (100) planes, respectively, so they have a higher catalytic activity per unit surface area, this results in higher oxygen storage capacity and catalytic activity. The removal of phenol by ozone oxidation catalyzed by nr(nanorod)-CeO2 could reach 100% in a reaction of 30 min. The ESR technique demonstrated that ·OH, ·O2− and 1O2 produced during the reaction process are the main ROS that enhance catalytic ozone oxidation and participate in the degradation of phenol, which is decomposed into small molecule acids through substitution and ring opening reactions, and ultimately converted into CO2 and H2O. These results indicate that CeO2 nanorods exhibit stable and high performance in catalytic ozone oxidation, and controlling the morphology is an effective strategy to improve the catalytic performance.

Thermal Stability and Resistance to Biodegradation of Humic Acid Adsorbed on Clay Minerals

This article studies sorption regularities and evaluates thermal stability and resistance to microbial degradation of humic acid during three sorption cycles on bentonite clay, kaolinite, and muscovite using TGA/DSC, XRD, hydrophobic chromatography, light and electron microscopy, etc. The experiment revealed that kaolinite sorbed more humic acids (HAs) in terms of unit surface area (1.03 × 10−3 C, g/m2) compared to bentonite (0.35 × 10−3 C, g/m 10−3 g/m2). Sorption at pH 4.5 showed HA fractionation in amphiphilicity and chemical composition. HA was sorbed on the surface of all sorbents, mainly via hydrophobic components. No intercalation of HA into the interlayer spaces of montmorillonite was observed during sorption. Sorption via hydrophilic interactions was mostly performed on muscovite and bentonite rather than on kaolinite. Sorption of HA resulted in changes in its chemical composition and decreased C/N compared to free HA, which demonstrated selective sorption of nitrogen-containing compounds more typical of muscovite. All minerals adsorbed only a relatively thermolabile HA fraction, while its thermal stability increased compared to that before the experiment. The thermal stability and ratio of the Exo2/Exo1 peak areas on the DSC curves of sorbed HA increased with each subsequent sorption cycle. We revealed the following relationship between thermal stability and resistance to microbial oxidation of the sorbed HA: The higher the thermal stability, the less available the sorbed HA becomes for utilization by microorganisms.

Lenticels are sites of initiation of microcracking and russeting in 'Apple' mango.

The mango cultivar 'Apple' is an important fruitcrop in Kenya, but it is highly susceptible to russeting. The objective was to establish whether lenticels predispose cv. 'Apple' mango to russeting. Fruit mass and surface area increased in a sigmoidal pattern with time. The frequency of lenticels per unit surface area decreased during development. The number of lenticels per fruit was constant. Lenticels were most frequent in the apex region and least common in the cheek and nak (ventral) regions. The cheek region also had lenticels with the largest core areas, whereas the lenticel core areas in the apex region were significantly smaller. Microscopy revealed stomata became covered over with wax deposits at 33 days after full bloom (DAFB). By 78 DAFB, periderm had formed beneath the pore. At 110 and 161 DAFB, cracks had developed and the periderm had extended tangentially and radially. The presence of lenticels increased the strain released upon excision of an epidermal segment, further strain releases occurred subsequently upon isolation of the cuticle and on extraction of the cuticular waxes. The number of lenticels per unit surface area was negatively correlated with the fruit surface area (r2 = 0.62 **), but not affected by fruit size. Mango cv. 'Apple' had fewer, larger lenticels and more russet, compared with 'Ngowe', 'Kitovu' or 'Tommy Atkins' mango. In cv. 'Apple', the lowest lenticel frequency, the largest lenticels and the most russeting occurred at a growing site at the highest altitude, with the highest rainfall and the lowest temperature. Moisture exposure of the fruit surface resulted in enlarged lenticels and more microcracking of the cuticle. Our results establish that russeting in 'Apple' mango is initiated at lenticels and is exacerbated if lenticels are exposed to moisture.

Ammonia Decomposition over Alkali Metal (Li, K, Cs)-Promoted Bulk Mo2N Catalyst

Ammonia (NH3), which has a 17.7 wt% gravimetric hydrogen density, has been considered as a potential hydrogen storage material. This study looked at the thermocatalytic decomposition of NH3 using a bulk Mo2N catalyst that was boosted by alkali metals (AM: 5 wt% Li, K, Cs). The K-Mo2N catalyst outperformed all other catalysts in this experiment in terms of catalytic performance. At 6000 h−1 GHSV, 100% conversion of NH3 was accomplished using the K-Mo2N, Cs-Mo2N, and Mo2N catalysts. However, when compared to other catalysts, K-Mo2N had the highest activity, or 80% NH3 conversion, at a lower temperature, or 550 °C. The catalytic activity exhibited the following trend for the rate of hydrogen production per unit surface area: K-Mo2N > Cs-Mo2N > Li-Mo2N > Mo2N. Up to 20 h of testing the K-Mo2N catalyst at 600 °C revealed no considerable deactivation.

Turkey's Green Economy Initiative: An Experimental Evaluation of Hydrogen Energy

Green economy is a concept that aims to achieve sustainable economic growth without harming the environment. Reducing carbon footprint is an important tool for the green economy. The contribution of reducing carbon footprint to the green economy is to measure the impact of economic activities on the environment and guide the development of green economy practices. Through green economy practices, carbon footprint can be reduced, environmentally friendly production and consumption habits can be promoted, and natural resources can be used more efficiently. Turkey is in a moderate position in terms of carbon footprint worldwide. As of 2019, Turkey's carbon footprint was calculated as 370 million tons of carbon dioxide (CO2) equivalent. The energy sector, industrial activities, transportation and agriculture sectors are among the largest sources of carbon footprint in Turkey. In this study, the evaluation of hydrogen gas production for reducing carbon footprint during Turkey's transition to the green economy is discussed. The production and evaluation of the cathode electrode used in hydrogen gas production with the alkaline electrolysis system were conducted. For this purpose, a novel, cheap and accessible cathode material containing transition metal was used for the first time in the literature, which was produced by a triple coating of nickel (Ni), iron (Fe), and molybdenum (Mo) on a nickel foam electrode surface at different potentials (2.1 V - 3 V) and different times (5-30 minutes) with two electrode techniques to produce hydrogen gas. According to the results, the amount of hydrogen gas produced per unit surface area (m2) of the electrode during a 30-minute period was approximately 516 L, and the energy value determined by the Lower Heating Value (LHV) was 5533.2 kJ/kg H2.

Conversion of clay minerals to photocatalysts for CrVI reduction and salicylic acid decomposition

This study investigates the conversion of biotite, a subgroup of clay minerals, into photocatalysts through heat treatment with CaCl2. The resulting reaction products were analyzed in terms of their composition, structure, optical properties, and photocatalytic activity against CrVI and salicylic acid (SA). Biotite and CaCl2 mixtures could be heated to 600 °C while retaining the biotite crystal structure, whereas heating to 700 °C resulted in transformation to octahedral wadalite crystals. The band gap of the wadalite obtained after heat treatment was approximately 3.10 eV. The photocatalytic reduction rate per unit surface area increased markedly with increasing heat-treatment temperature, and the CrVI reduction and SA degradation rates of the sample calcined at 800 °C were approximately 18 and 9 times greater, respectively, than those of the sample calcined at 500 °C. Leaching tests of the reaction products revealed that the elution of Ca2+ and Cl− was particularly significant. Even the samples that retained the biotite structure after heat treatment displayed some photocatalytic activity, indicating that this method may be applicable to preparing photocatalysts from mica and related minerals with similar structures.

Surface roughness and overgrowth dynamics: The effect of substrate micro-topography on calcite growth and Sr uptake

Substrate roughness influences epitaxial nucleation, growth, and trace element incorporation. We qualitatively and quantitatively examine the role of calcite surface roughness on overgrowth morphology and Sr concentration. Surfaces were made by cleaving optically clear Iceland spar, then abrading calcite cleavage surfaces with sandpaper (physical weathering analogues), or by attacking the cleavage surface with dilute HCl (chemical weathering analogues). Calcite precipitated on “weathered” surfaces have morphologies that vary systematically from one substrate type to the next. Growth on the abraded substrate was shingled, didn't form a continuous growth layer, and was poorly adhered to the seed crystal. Growth on the acid etched substrate mostly formed a continuous growth layer in optical continuity with the seed crystal. Differences in overgrowth morphology are interpreted to be due to differences in island coalescence dynamics on the different substrates. Rough substrates have a high density of island nuclei per unit surface area, which inhibits island coalescence due to interfacial misfit between individual islands. In contrast, overgrowths on smooth substrates coalesced into a single crystalline overgrowth layer. There is a weak positive correlation between the initial fractal dimension of the substrate and average Sr concentration in the overgrowth.

Dimensional and Physiological-Biochemical Parameters of Erythrocytes and Gill and Heart Indices in Some Benthic Fish of the Black Sea Coast of the Southeastern Crimea

The dimensional and physiological-biochemical parameters of erythrocytes, as well as the gill and heart indices were studied in five species of marine benthic fish. The black scorpionfish Scorpaena porcus Linnaeus, 1758 and the shore rockling Gaidropsarus mediterraneus Linnaeus, 1758 differed from the other species in a larger mass of the heart and gill apparatus, which indicates more efficient transport capabilities of the circulatory system of these fish. The linear size characteristics of erythrocytes of a cartilaginous fish, the thornback ray Raja clavata Linnaeus, 1758, were 1.5–2 times higher than those of erythrocytes of S. porcus, which were the largest among the studied teleosts. The sizes of erythrocytes of three other teleost species differed insignificantly. The amount of hemoglobin per unit surface area of erythrocyte, which reflects the efficiency of hemoglobin saturation with oxygen, insignificantly varied (0.05 to 0.071 pg/mm2) among the bony fish stu-died. In contrast, in the thornback ray this parameter was 2.7–3.8 times lower. The intracellular glycogen concentration, which characterizes the degree to which the erythrocyte is independent of glycemic fluctuations, was highest in cells of S. porcus (305.2 ± 35.1 mg %), while it was lowest in erythrocytes of the thornback ray R. clavata (142.8 ± 15.1 mg %). The ecto-ATPase activity was higher in large erythrocytes of S. porcus, R. clavata, and Uranoscopus scaber (4.8, 3.1, and 1.6 µmol Pin/min/mL of erythrocytes, respectively) than in smaller erythrocytes of Crenilabrus tinca and Gaidropsarus mediterraneus (0.5 and 0.4, µmol Pin/min/mL of erythrocytes, respectively). This confirms the assumption that erythrocytes use the thermal energy from hydrolysis of extracellular ATP to “warm up” their own membrane, which leads to the change in the rheological characteristics of blood in the capillary blood flow.

Machine learning for prediction of delirium in patients with extensive burns after surgery.

Machine learning-based identification of key variables and prediction of postoperative delirium in patients with extensive burns. Five hundred and eighteen patients with extensive burns who underwent surgery were included and randomly divided into a training set, a validation set, and a testing set. Multifactorial logistic regression analysis was used to screen for significant variables. Nine prediction models were constructed in the training and validation sets (80% of dataset). The testing set (20% of dataset) was used to further evaluate the model. The area under the receiver operating curve (AUROC) was used to compare model performance. SHapley Additive exPlanations (SHAP) was used to interpret the best one and to externally validate it in another large tertiary hospital. Seven variables were used in the development of nine prediction models: physical restraint, diabetes, sex, preoperative hemoglobin, acute physiological and chronic health assessment, time in the Burn Intensive Care Unit and total body surface area. Random Forest (RF) outperformed the other eight models in terms of predictive performance (ROC:84.00%) When external validation was performed, RF performed well (accuracy: 77.12%, sensitivity: 67.74% and specificity: 80.46%). The first machine learning-based delirium prediction model for patients with extensive burns was successfully developed and validated. High-risk patients for delirium can be effectively identified and targeted interventions can be made to reduce the incidence of delirium.

Oxidation behavior of the CVD-Al2O3 coatings on tungsten substrate at 1000 °C

In this paper, TiN/TiCN/Al2O3 coating, as a classic coating system for cemented carbide tools, was prepared by chemical vapor deposition (CVD) on pure tungsten substrate for improved oxidation resistance. It is found that the oxidation weight gain per unit surface area of the coated sample is 7.45 mg/cm2 after 5 h oxidation at 1000 °C, significantly lower than that of 218.44 mg/cm2 in uncoated specimen. Due to the difference of thermal expansion coefficient, a network of microcracks were formed within the top Al2O3 layer during fabrication process. These microcracks provide a diffusion path for titanium ions and oxygen ions in the initial oxidation stage (0−1h), which produces TiO2 at cracking regions. As oxidation time prolongs (1–5 h), the oxidation of nitride layer beneath the microcracking region creates short-circuit oxygen diffusion paths towards the metal substrate. The generation of volcanic-like WO3 breaks the graded structure of CVD coating and expands the channel between oxygen and substrate. Nevertheless, the weight gain is still limited at this stage as the main area of Al2O3 coating is dense and protective. Finally, the oxidation kinetics accelerate at 5–10 h when coating failure occurs and severe breakaway oxidation appears in tungsten.

The anatomical distribution of lentiginous melanoma (lentigo maligna and lentigo maligna melanoma): Differences according to sex.

The anatomical distribution of lentiginous melanoma (lentigo maligna and lentigo maligna melanoma): Differences according to sex.

Turbulent/turbulent interfacial layers of a shearless turbulence mixing layer in temporally evolving grid turbulence

Turbulent/turbulent interfacial (TTI) layers are investigated with direct numerical simulation of temporally evolving grid turbulence. The present study considers a temporally evolving wake of two parallel-bar grids with different mesh sizes, which generate homogeneous isotropic turbulent regions with large and small turbulent kinetic energies (TKE). A shearless mixing layer of turbulence forms between the large- and small-TKE regions. The TTI layer bounded by the large- or small-TKE region is identified with a passive scalar field, and the flow statistics are evaluated as functions of a position with respect to the TTI layer. Statistics of a velocity gradient tensor suggest that the center and edges of the TTI layer are dominated by vortex sheets and vortex tubes, respectively. Because of the configuration of these vortical structures, the flow toward the TTI layer in the layer-normal direction generates a compressive strain, which is important to sustain the thin layer structure. The mean velocity jump due to the compressive strain is about 3 u η and is observed over a length of about 20 η, where u η and η are the Kolmogorov velocity and length scales, respectively. The thickness of the TTI layer is about 12 η, which hardly depends on time. The TTI layer has a large surface area when it is bounded by the large-TKE region. Consequently, the shearless mixing layer tends to entrain more amount of fluid from the large-TKE region than from the small-TKE region although the entrainment rate per unit surface area normalized by the Kolmogorov velocity is similar for both regions.

Investigation of the process of bimetallic castings formation for crushing and grinding equipment

The analysis of the state of production of wear-resistant materials showed that one of the promising directions for improving their quality is the use of bimetallic castings, which have a complex of properties differentiated by the volume and surfaces of the products. However, the problem of obtaining a high-quality connection of the base and the working layer has not been solved until now. The article examines the influence of the chemical composition, temperature parameters, and mass ratio of alloys of bimetallic pairs on the process of bimetallic castings formation. The purpose of the study was to study the growth kinetics and structural-phase composition of the transition diffusion layers of bimetallic castings depending on the chemical composition, temperature parameters and the ratio of the masses of the alloys of the bimetallic pairs. As a research result, it was established that the formation of transition layers of bimetallic castings is determined by the processes of diffusion and structural-phase transformations in the interaction zone - "solid - liquid metal". The processes largely depends on the chemical composition of bimetallic pairs, temperature parameters, and the mass ratio of the layers. It was determined that in bimetallic castings obtained by pouring liquid metal onto a preheated solid billet, the transition layer is characterized by the presence of two zones - pearlitic, from the side of the base metal and without the carbide region of the matrix of the working layer. It has been established that the formation of transition layers in bimetallic castings obtained by successive pouring of melts into the mold through autonomous pouring systems is accompanied by the saturation of steel by carbon from cast iron to a depth of 600-800 microns and the formation of a zone with a lamellar pearlite structure along the border of the alloy junction, and the transition layer between cast iron and steel consists of pearlite in the form of a narrow strip and a zone of chromic ferrite from the side of cast iron. As a result of the study of the peculiarities of the formation of transitional layers of bimetallic castings when liquid metal is poured onto a solid billet, it was established that the degree of dissolution of the base metal in liquid cast iron increases with an increase of the billet preheating temperature and the temperature of the melt, as well as the ratio of the mass of liquid cast iron to a unit surface area of the metal base. At the same time, the rate of dissolution is proportional to the gradient between the temperatures of the contact surface and the cast iron solidus. It was established that the formation of a reliable diffusion bond for bimetallic pairs "carbon (low-alloy) steel - high-chromium cast iron" is ensured if the temperature of the contact surface exceeds the temperature of the eutectic transformation of cast iron. The mechanism is revealed of formation of the transition zone structure. The materials of the article can be used by scientists for further research and practitioners in the selection of materials for work in extreme conditions. Keywords: steel, cast iron, temperature, transitional layer, solidus, liquidus, melt, solidification.

Hydration states of europium(III) adsorbed on silicas with nano-sized pores

The confinement in small spaces influences the complicated reaction involving water molecules under electrostatic potentials at the solid–liquid interface. It is unclear, in particular, how the hydration state of metal ions adsorbed on the surface changes as a function of the pore size. This study analyzed the adsorption states of europium aqua ions (Eu3+) on mesoporous silicas with different pore distributions in comparison with nonporous silica using time-resolved laser-induced fluorescence spectroscopy. The parallel factor analysis was used to differentiate the contribution of different chemical species of Eu3+ to the fluorescence signal and determine the influence of the pore size on each chemical species. The results show that Eu3+ mainly form outer-sphere complexes with silica below pH 6, where Eu3+ adsorption is low. Within nano-sized pores, distortion of the hydration structure and a decrease in the hydration number were suggested in this pH range. As the concentration of the silicate ions derived from the dissolution of silica increases with increasing pH, Eu3+ form the silica/Eu3+/silicate ternary surface complexes. Within nano-sized pores, the concentration of silicate ions decreases due to the overlap of the electric double layer, which inhibits the formation of the ternary surface complex. Furthermore, at high pH, Eu3+ multinuclear complexes formed only on the mesoporous silica surface. This adsorption behavior specific to nano-sized pores could not be concluded by macroscopic adsorption experiments alone because the amount of Eu3+ adsorbed per unit surface area did not differ between the mesoporous and nonporous silicas. Consideration of the silicate complexes should be indispensable in future studies on the adsorption of lanthanide ions using mesoporous silica.

Passive acoustic exploration of the ocean

Encoded in the spectral density, spatial variability, and directionality (spatial coherence) of the ambient sound field is information on the generation mechanisms of sound and the properties of the ocean propagation environment and its boundaries. Through field and observatory measurements, and analytical and computational models of the underwater sound field, a research program has been pursued that asks, “What can we learn about the ocean by listening?” Large acoustic data sets have been exploited to develop an estimate of the effective source level per unit area of surface generated noise. In complement, a methodology for precisely partitioning the sound field into ship generated and wind generated components by exploiting the vertical noise directionality has been demonstrated. Models of the spatial properties of wind driven and ship generated sound have further been used to estimate the geoacoustic properties of the seabed, the depth of mix layer, depth-averaged pH, and localize a source in bearing and azimuth using only a pair of vertically oriented omnidirectional hydrophones. An autonomous passive acoustic profiler, The Deep Acoustic Lander (DAL), recently made measurements of the ambient sound field from the surface to the bottom of the Challenger Deep, Mariana Trench, precisely determining the mixing of a locally- and distantly generated contributions to the sound field. Meanwhile, DAL measurements at the Endeavour hydrothermal vent field have revealed components of the sound field generated by vent activity.

Effect and Mechanism of Cu Foams with Different Porosity on Kinetic Parameters of Ga Electrodeposition: Accompanied by Hydrogen Evolution Reaction

The process of Ga electrodeposition is usually accompanied by intense hydrogen evolution reaction, so the escape rate of hydrogen bubbles from the electrode surface has a great influence on Ga electrodeposition. In this paper, Cu foams with different porosity are applied to research the effect of escape rate of hydrogen bubbles on Ga electrodeposition. When Ga electrodeposition is controlled by mass transport process, Cu foams with high porosity exhibit a higher reaction rate of Ga electrodeposition because of its faster bubble escape rate. The larger pore channel diameter of Cu foam with low porosity reduces the escape rate of hydrogen bubbles and hinders the mass transfer process. The addition of surfactant accelerates the escape rate of bubbles from the electrode surface, thus promoting the mass transfer process and leading to the increase of the current efficiency of Ga electrodeposition. It is also found that the process of Ga electrodeposition is controlled by nucleation rate at the early stage. Due to the rapid separation of hydrogen bubbles, Cu foams with high porosity provide more effective sites per unit surface area. Therefore, Cu foams with high porosity have a higher nucleation rate and a lower induced time for Ga electrodeposition.

A COMPARATIVE STUDY BETWEEN PRESSURE OFFLOADING DEVICE DRESSING VERSUS CONVENTIONAL BETADINE AND NORMAL SALINE DRESSINGS IN TREATMENT OF PLANTAR DIABETIC FOOT ULCER

Ofoading is redistribution of weight bearing from a small area to a large area, reducing unit of load per unit surface area of foot, thereby decreasing pressure over plantar ulcers . A Randomised Controlled Study conducted in GGH, Vijayawada in plantar diabetic foot ulcers, based on exclusion and inclusion criteria allocated to Ofoading device dressing(50), Conventional Dressing(50).Forefoot ulcers (19), hindfoot ulcers (81) were included with a mean size of ulcers at week 0 among control group(5.32cm) and study group(5.91cm) respectively. A reduction in size to 2.28 cm, 1.25 cm has been noticed at end of 6 weeks respectively (p= < 0.0001). Control group and study group had 40 and 46 Grade2 ulcers respectively. A reduction in grade to Grade1 has been noticed at end of 6 weeks in 25 and 45 patients respectively. Necrotic tissue score on ulcers at week 0 among control group and study group were, Grades (2 =26, 3 = 24 and 2 =28, 3 =24) (p= 0.38) respectively. A reduction in percentage of necrotic tissue to has been noticed at end of 6 weeks respectively ( p= 0.0001).Granulation tissue score on ulcers at week 0 among control group and study group were Grades (1 = 35, 2 =15 and 1 = 28 ,2= 22 respectively) . An increase in granulation tissue score to Grades (4 = 20 ,3= 28 and 4 =44 and 3 = 4), has been noticed at end of 6 weeks respectively (p= 0.0001). Number of debridements required for the ulcer healing until week 6 among the control group and study group was 27( 2), 22 (1) and 36 (1) , 13 (2) respectively (p =0.0006). A statistically signicant difference in patient satisfaction was noted. Mandakini Ofoading Device is cost-effective, easily available, efcient ,technically easy, less time consuming, good patient compliance and satisfaction, less restriction to mobility, fewer secondary infection rates, fewer recurrence rates, earlier reduction in size of ulcers

Application of molecularly imprinted polymer and ZnO nanoparticles as a novel electrochemical sensor for tartrazine determination

Tartrazine (Tz) is one of the synthetic dyes used in food that should be monitored and controlled due to its toxicity and pathogenicity. For this purpose, we have built an ultrasensitive electrochemical sensor to measure and determine Tz. In the first step, a carbon paste electrode (CPE) was modified with zinc oxide (ZnO) nanoparticles and in the next step, Tz was used as a template during poly-arginine (PArg) electropolymerization via the cyclic voltammetrymethod. The reason for using ZnO nanoparticles is to increase the number of imprint sites per unit surface area of the electrode. To characterize the ZnO/MIP-PArg these techniques were used: FE-SEM,HR-TEM, ATR-FTIR, AFM, and EIS.DPV results showed two linear response ranges 0.008–0.112 µM and 0.25–5.0 µM with a low detection limit of 2.7 nM (S/N = 3). Also, the built-in sensor was used to determine Tz in orange jelly powder and soft drinks and the results were satisfactory.

Adsorption of cesium and strontium on mesoporous silicas.

Studies are underway on the adsorption reactions of metal ions in confined spaces at the solid-water interface, but it is unclear how the effects of confinement differ for different types of ions. We investigated the effect of the pore size on the adsorption of two cations with different valence, Cs+ and Sr2+, on mesoporous silicas with different pore size distributions. The amount of Sr2+ adsorbed per unit surface area did not differ significantly among the silicas, whereas that of Cs+ was particularly high for silicas with a larger fraction of micropores. The results of X-ray absorption fine structure analysis showed that both ions form outer-sphere complexes with the mesoporous silicas. The results of adsorption experiments were analyzed by fitting using a surface complexation model with the cylindrical Poisson-Boltzmann equation and optimized capacitance of the Stern layer for different pore sizes, and we found that the intrinsic equilibrium constant for the adsorption of Sr2+ is constant regardless of the pore size, whereas that of Cs+ increases as the pore size decreases. The decrease in the relative permittivity of water inside pores with a decrease of the pore size can be interpreted to cause a change in the hydration energy of Cs+ in the second coordination sphere upon adsorption. The reasons for the different confinement effects on the adsorption reactions of Cs+ and Sr2+ were discussed based on the distance of the adsorbed ions from the surface and the chaotropic and kosmotropic nature of Cs+ and Sr2+, respectively.

Adsorption of CO2 and N2 on bimetallic Mg-Al hydrotalcites and Z-13X zeolites under high pressure and moderate temperatures

The adsorption of carbon dioxide on a commercial hydrotalcite (HT) was investigated using gravimetric analysis at 473 K, 573 K and 673 K and pressures up to 10 bar. The CO2 adsorption performance of HT was correlated with a wide range of physicochemical characterisation techniques. For further understanding and comparative purposes, the same adsorption and characterisation measurements are reported for a commercial zeolite 13X (Z-13X). The HT exhibited higher adsorption capacities per unit mass of sorbent at relatively low pressures and per unit surface area over the whole range of pressures analysed, compared to zeolite 13X. However, HT showed adsorption-desorption isotherms with a hysteresis loop indicating a stronger binding energy. The HT also presented deactivation upon cycling (up to ∼ 10%, depending on conditions) suggesting the need for future studies focused on improvement of its regenerability. The same performance regarding hysteresis and deactivation was observed in the presence of N2. The CO2 adsorption isotherms of HT were successfully fitted to the Freundlich model. The values of heat of adsorption calculated -56 and -84 kJ mol−1 for the 1st and 5th cycle, are indicative of a chemisorption process. The data of this work provide information regarding fundamentals of CO2 adsorption of the materials that is useful in the design of realistic adsorption units in conventional and novel H2Carbon Dioxide Capture processes, especially in the sorption-enhanced H2 reaction process.