Search

The studies on the batch experiments and transport of 90Sr and 241Am were respectively conducted under unsaturated flow conditions in silty clay column. The results show that the linear correlation coefficient r2 of adsorption and desorption isotherms for 90Sr and 241Am in silty clay medium is greater than 0.9, which indicates that the Freundlich isotherm adsorption model can better describe the adsorption and desorption process of different nuclides in silty clay. The adsorption capacity of strongly adsorbed nuclides 241Am is much greater than that of 90Sr. As for 90Sr, the first-order rate coefficient(named as β) between the dissolved phase and the adsorbed phase was considered in the non-equilibrium adsorption model by transport column. The calculated concentration distribution curve is good agreement with the measured values. The fitting results show that the distribution coefficient(named as Kd) and β of 90Sr in the fine sand aquifer are 3.6 mL/g and 0.55/h. Respectively, in terms of 241Am, the radionuclides concentration distribution curves in equilibrium adsorption model and non-equilibrium adsorption model are in good agreement with the measured values. It shows that the stronger adsorption capacity of the nuclides have the faster rate of the adsorption-desorption in the soil, meanwhile the shorter time for the system reaction equilibrium. At this time, the fitting results of the equilibrium adsorption mode and the non-equilibrium adsorption model are closer to each other. Meanwhile the calculated Kd value by equilibrium adsorption model is 3×103 mL/g.

In order to provide technical support and evaluation basis for the development of remediation technology of radioactive contaminated sites and the site selection, design and construction of radioactive waste disposal facilities, the reliable longterm risk assessment for potential nuclear waste repositories and decommissioning of nuclear facilities requires detailed knowledge on the migration behavior of radionuclides in natural, it is necessary to understand the reaction mechanism of radionuclides in the complex geological environment of aquifers. The batch experiments and dynamic undisturbed soil column migration experiments of 90Sr, 137Cs, 238Pu and 241Am were carried out under saturated steadystate flow conditions in fine sand column, a theoretical model of nuclide migration in soil and groundwater environment was constructed, and the irreversible adsorption reaction mechanism of the microinterface was studied through static adsorptiondesorption and dynamic undisturbed soil column migration experiments, and the environmental migration flux of nuclides was calculated. The static adsorption and desorption experiments adopt batch method, and the test medium is fine sand with saturated porous media from an arid mining area in Gansu Province. The fine sand and soil samples according to the solidliquid ratio of 1 g∶9 mL were added into the centrifuge tube, and the nuclide activity concentration was measured after adsorption and desorption equilibriums to obtain the adsorption and desorption isotherms. Dynamic column method used undisturbed soil to ensure the continuity of soil sample medium, original connectivity of void channels and authenticity of stratum. The design and advantages of dynamic column method is to take into account various physical, chemical and biogeochemical reaction processes and complex migration paths of tracers during migration in soil. And the dynamic migration and transformation process of 90Sr, 137Cs, 238Pu and 241Am were studied in saturated porous media with anisotropic timevarying hydrologic characteristics by artificial spraying under controlled laboratory initial conditions and boundary conditions. The results show that the absorption isotherm of 90Sr doesn’t coincide with its desorption isotherm, with an angle at 3238° between them. According to the metastable equilibrium adsorption theory, 90Sr has an irreversible adsorptiondesorption process, and ions exchange is the dominated action for its adsorption. As for 137Cs, 238Pu and 241Am, reversible adsorptiondesorption process are shown, and their adsorptions are mainly attributed to surface complexation. Equilibrium adsorption theory and nonequilibrium adsorption model can be used to describe the migration peak phenomenon of different nuclides in the dynamic soil column experiment, which can be effectively integrated into chemical nonequilibrium and physical nonequilibrium processes. Considering the superposition of convectiondispersion and chemical reaction on solute migration, solute migration equations were established based on the reaction rate equation, and the calculated and measured concentration distribution curves were fitted reasonably to obtain a reaction model that can accurately describe and predict nuclide migration. As for 90Sr, the nonequilibrium adsorption model by transport column was taken into account the firstorder rate coefficient (β) between the dissolved phase and the adsorbed phase. The calculated concentration distribution curve is good agreement with the measured concentration. The fitting results show that the distribution coefficient (Kd) and β of 90Sr in the fine sand aquifer are 085 mL/g and 016 h-1, respectively, in terms of 137Cs, 238Pu and 241Am, the radionuclides concentration distribution curves in equilibrium adsorption and nonequilibrium models are in good agreement with the measured values. Meanwhile the calculated results by two different adsorption models are almost similar, and the Kd are 49×102, 21×104, and 6.0×103 mL/g for 137Cs, 238Pu and 241Am. It shows that the stronger adsorption capacities of the nuclides have the faster rate of the adsorption-desorption in the soil, meanwhile the shorter time for the system reaction equilibrium. At this time, the fitting results of the equilibrium adsorption mode and the nonequilibrium adsorption mode are closer to each other.

The simultaneous high-capacity and fast removal of radioactive barium ion (Ba2+) from nuclear wastewater is necessary but still faces large challenge. In this study, a novel adsorbent containing sulfonic group, MOF-808-SO3H, was prepared based on the oxidation of –SH group. Characterizations confirm the successful introduction of –SO3H, good porosity, and stability of the material. The adsorbent exhibits excellent capture ability for Ba2+ due to strong hard acid-base and electrostatic interactions, with the adsorption capacity of 152.0 mg g−1 and fast equilibrium adsorption time, superior to other reported materials. Optimal pH was found to be almost neutral and temperature cannot affect the adsorption largely. Besides, the irreversible adsorption was demonstrated and thereby the secondary pollution may be avoided. Therefore, our work provides an efficient adsorbent for capturing Ba2+ irreversibly, and proposes a feasible strategy for constructing adsorbents with simultaneous high adsorption capacity and fast kinetics.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We investigate the irreversible adsorption of poly(3-hexylthiophene) (P3HT) polymer thin films on silicon dioxide/silicon (SiO 2 /Si) substrates during thermal annealing at a temperature below the melting temperature ( T m ) but far above the glass transition temperature ( T g ), i.e., T , and its effect on their crystalline ordering and charge transport properties. It was found that short-time annealing enhances the molecular ordering of P3HT films, while prolonged thermal annealing gradually disrupts the crystalline structures and reduces the overall crystallinity of the film. Concurrently, thermal annealing at this temperature facilitates the slow irreversible adsorption of P3HT chains at the polymer-solid interface, resulting in the formation of a 1.7 g ≪ T /Si substrates that is fully amorphous and contains a large fraction of loosely adsorbed chains. We postulate that such irreversible adsorption is responsible for the reduced crystalline packing of P3HT at the polymer-solid interface at T m , and its effect on their crystalline ordering and charge transport properties. It was found that short-time annealing enhances the molecular ordering of P3HT films, while prolonged thermal annealing gradually disrupts the crystalline structures and reduces the overall crystallinity of the film. Concurrently, thermal annealing at this temperature facilitates the slow irreversible adsorption of P3HT chains at the polymer-solid interface, resulting in the formation of a 1.7 R g -thick (∼18 nm thick) adsorbed layer on SiO 2 /Si substrates that is fully amorphous and contains a large fraction of loosely adsorbed chains. We postulate that such irreversible adsorption is responsible for the reduced crystalline packing of P3HT at the polymer-solid interface at T g ≪ T < T m , which further disrupts the molecular ordering of the entire 46 nm thick P3HT film by a long-range perturbation effect. Electrical measurements using an organic field-effect transistor (OFET) device reveal that the enhanced charge carrier mobility of P3HT films correlates with an optimized annealing time at T g ≪ T < T m , which achieves a balance between maximizing molecular ordering and minimizing the impact of irreversible chain adsorption. These findings provide new insights into the underlying mechanism of thermal annealing in tailoring the structure and property of conjugated polymer thin films prepared on solid substrates.

Per- and polyfluoroalkyl substances (PFASs) are used in industrial production and manufacturing but were repeatedly detected in agricultural soils and therefore in cash crops in recent years. Dissipation of perfluoroalkyl acids (PFAAs), a sub-group of PFASs, in the environment was rather attributed to the formation of non-extractable residues (NER) than to degradation or transformation. Currently, there are no models describing the fate of PFAAs in the soil-plant continuum under field conditions, which hampers an assessment of potential groundwater and food contamination. Therefore, we tested the ability of the pesticide-leaching model MACRO to simulate the leaching and plant uptake of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in a field lysimeter using two concepts of adsorption: a kinetic two-side sorption concept usually applied for pesticide leaching (scenario I) and the formation of NER (scenario II). The breakthrough of substances could be simulated adequately in scenario II only. Scenario I, however, was not able to reproduce sampled leaching concentrations. Plant uptake was simulated well in the first year after contamination but lacked adequacy in the following years. The model results suggest that more than 90% of PFOA and PFOS are in the pool of NER after 8 years, which is more compared with other studies. However, since NER formation was hypothesized to be a kinetic process and our study used a PFASs leaching time series over a period of 8 years, the results are reasonable. Further research is required on the formation of NER and the uptake of PFAAs into plants in order to gain a better model performance and extend the simulation approach to other PFAAs. [ABSTRACT FROM AUTHOR]

Presented in this work is an investigation of co-deposits of Pt and Bi on Au disk (Pt-Bi/Au) toward formic acid oxidation (FAO) using voltammetry and X-ray photoelectron spectroscopy (XPS). The co-deposits of Pt and Bi on Au were prepared using an irreversible method in a mixed solution of Pt ion (1 mM) and Bi ion (5 mM), and the amount of co-deposits was controllable by the number of deposition cycles. The voltammetric studies revealed that the Pt-Bi/Au surfaces presented the characteristics of Pt, Bi, and Au depending on the number of deposition cycles. A detailed analysis of semi-quantitative results of XPS combined with hydrogen coverage on Pt and covered fraction of Au surface suggested two aspects of Pt-Bi co-deposits. One is that during co-adsorption, Bi adsorbing with a low efficiency enhanced irreversible adsorption of Pt. The other is that the Pt-Bi co-deposits would be an alloy of Pt-Bi when the Pt amount was low or Pt deposits enriched with Bi in surface regions when the Pt amount was high. The best FAO catalytic efficiency among the investigated Pt-Bi/Au surfaces was ~ 14 mA/cm2, which was higher than that of plain Pt deposits on Au (~ 6 mA/cm2) and comparable to that of sequentially prepared Bi-modified Pt deposits on Au (Bi/Pt/Au, ~ 20 mA/cm2). Because of a similarity in compositions and catalytic performances of the best Pt-Bi/Au and Bi/Pt/Au, the preparation procedure was concluded not to be critical so that the co-deposition method was more beneficial in terms of the number of deposition cycles in manufacturing electrocatalysts toward FAO. [ABSTRACT FROM AUTHOR]

This work presents the formic acid oxidation (FAO) behavior on three model Pt deposit catalysts on Au. The investigated model Pt catalysts were single-layered Pt deposits, plateau-type Pt deposits and tall conical Pt deposits, produced via irreversible adsorption of Pt ions according to the protocols of conventional route, CO route and iodine route, respectively. The shapes and populations of the model Pt deposits were controlled by the deposition protocols and number of deposition cycles. The most effective Pt deposit catalyst in FAO was verified to be single-layered one with a population of ∼50% which inhibited dehydration (poison formation) and promoted dehydrogenation. As the population of Pt deposits became higher than 50%, the dehydration process activated to decrease the FAO catalytic efficiency. Furthermore, multiple layered Pt deposits such as conical ones were not so efficient due to activation of dehydration even at a population below 50%. More detailed analysis of the observed voltammograms in the negative-going scan suggested that dehydrogenation took place at two different potentials depending on the shapes and populations of Pt deposits. One was low potential dehydrogenation occurring on separated single-layered Pt deposits at 0.14 V; the other was high potential dehydrogenation taking place on continuous Pt surface at 0.34 V. This particular suggestion was successfully applicable to explaining the FAO voltammograms of Pt electrodes of disk and nanoparticle. Image 1 [ABSTRACT FROM AUTHOR]

Multimodal chromatography adsorbents are novel materials with promising properties for downstream processing of therapeutic glycoproteins. This work analyzes the properties of a salt-tolerant membrane, Sartobind STIC, for the purification of recombinant human erythropoietin (rhEPO) produced by human embryonic kidney cells. Batch adsorption experiments were carried out to determine equilibrium properties of the membrane as a function of pH and NaCl concentration. It was found that the membrane adsorbs strongly both rhEPO and impurity proteins but the selectivity of binding is low independent of process conditions. Since the membrane demonstrated strong salt tolerance, flow experiments were designed to elucidate the effect of elution conditions on the bound proteins desorption. These experiments have revealed irreversible character of protein adsorption on the multimodal adsorbent probably caused by protein unfolding on the hydrophobic groups of the adsorbent. The recovery degree was especially low in case of rhEPO with the maximum at about 45% even when solutions of kosmotropic agents were used as desorbents. [ABSTRACT FROM AUTHOR]

• Time dependent irreversible adsorption was observed on chromatographic resins. • L-arginine can help prevent protein unfolding and reduce irreversible adsorption. • L-arginine sulfate is more effective than l -arginine chloride. • The choice of counter-ions also affects irreversible adsorption. Immobilized metal affinity chromatography (IMAC) is a powerful technique for capture and purification of relevant biopharmaceuticals in complex biological matrices. However, protein recovery can be drastically compromised due to surface induced spreading and unfolding of the analyte, leading to fouling of the stationary phase. Here, we report on the kinetics of irreversible adsorption of a protease on an IMAC resin in a time span ranging from minutes to several hours. This trend correlated with the thermal data measured by nano differential scanning calorimetry, and showed a time-dependent change in protein unfolding temperature. Our results highlight that 'soft' proteins show a strong time dependent increase in irreversible adsorption. Furthermore, commonly used co-solvents for preservation of the native protein conformation are tested for their ability to reduce fouling. Thermal data suggests that the amino acid l -arginine is beneficial in preventing unfolding, which was confirmed in batch adsorption experiments. The choice of counter-ions has to be considered when using this amino acid. These results show that l -arginine sulfate decelerates the irreversible adsorption kinetics of proteins on the IMAC stationary phase to a greater extent than l -arginine chloride. [ABSTRACT FROM AUTHOR]

Abstract This work demonstrated a method, termed iodine route, to produce height-controllable Pt deposits on Au using irreversible adsorption. Characterization of Pt deposits was performed utilizing scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy and cyclic voltammetry. The iodine route sequentially utilized iodine adsorption, selective replacement of adsorbed iodine on Pt deposits with CO, and removal of adsorbed CO to produce adsorbate-free Pt deposit surfaces on iodine-covered Au surface. Execution of additional Pt deposition on the particular surface permitted selective growth of Pt on the existing Pt deposits to produce conical tall multiple-layered Pt deposits of height of 4–6 atomic layers without rim of single-layered Pt-Au alloy. A comparison of Pt deposits formed via iodine route with those produced via CO and conventional routes revealed that their physical and chemical properties depended on deposition route. Pt deposits of conventional route were double-layered plateau with wide rims of single-layered Pt-Au alloy, while CO route yielded single-layered Pt-Au alloyed deposits. The adsorption stoichiometries of CO and hydrogen on Pt deposits were evaluated using electrochemical coverages of the adsorbates and STM coverage of surface Pt. A strong correlation between adsorption stoichiometric values and physical shapes of Pt deposits was revealed. Adsorption of CO and hydrogen on single-layered Pt-Au alloy enhanced so that the adsorption stoichiometries were verified to be ∼2, ascribable to adsorption on Au atoms in the Pt-Au alloy. On multiple-layered Pt deposits the adsorption stoichiometry of CO was similar to that on polycrystalline Pt, while that of hydrogen was ∼0.5. The observation was discussed in terms of mutual interactions between Pt and Au and crystallographic effect of highly stepped surfaces of conical tall multiple-layered Pt deposits. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Irreversibly adsorbed polymer layers represent an intriguing new class of materials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. These extremely thin layers (thickness < few tens of nanometers) are obtained via a short list of successive steps, easily reproducible in a laboratory environment: a polymer melt is placed in contact with an adsorbing substrate and non‐adsorbed chains are washed away by soaking the sample in a good solvent. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying the performance of polymer coatings without affecting the interfacial chemistry. Here, after providing an introduction to the kinetics of irreversible adsorption, we discuss on the most commonly used methods to determine the thickness of adsorbed layers. We conclude with a brief perspective on future possible applications of adsorbed layers. [ABSTRACT FROM AUTHOR]

Most of radioactive nuclides emitted into the air eventually fall to the ground, after then 80% of cesium fallout is fixed in soil and the other 20% is mobile as exchangeable fraction. It is most difficult to remove cesium from the soil after contamination because of the strong adsorption onto clay mineral especially illite, compared to other radionuclides and clay minerals. All the experiments were conducted using the 2:1 lattice minerals which as illite, hydrobiotite (vermiculite + biotite) and montmorillonite with 133-cesium chloride. In this study, illite had 0.25 mol/kg of frayed edge site (FES). Furthermore using the TEM-EDS confirmed selective adsorption of cesium. The selective and irreversible adsorption mechanism of cesium on illite was summarized by hydrated ion size, charge density and hydration energy. And the mechanism was proved by using barium. When cesium coexisted with barium, the adsorption efficiency to FES decreases. And when cesium adsorbed on FES was desorbed using various cations, the desorption rate was in order of ammonium > potassium > barium > calcium > magnesium, which follows the hydration energy. [ABSTRACT FROM AUTHOR]

Growing experimental evidence shows that the behavior of polymer chains confined at the nanoscale level strongly depends on the degree of adsorption correlated to the number density of monomers pinned onto the supporting substrate. In this contribution, after introducing the physics behind the mechanisms of irreversible adsorption, we review recent experimental observations on how adsorption affects properties of polymer melts confined in 1D, focusing on those related to the thermal glass transition, maximum water uptake, viscosity and crystallization. These findings strongly support a new physical framework of confined soft matter, not trivially limited to finite size effects and interfacial interactions, but also enriched by non-equilibrium phenomena. [ABSTRACT FROM AUTHOR]

The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation – narrow micropores (<7 Å) in the oxygen-deficient samples and midsize micropores (7–12 Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials. [ABSTRACT FROM AUTHOR]

This work presents a correlation of the oxidative behavior of formic acid to various Pt deposits on Au and bulk Pt in the absence and presence of Bi, studied by electrochemical means and X-ray photoelectron spectroscopy (XPS). Deposition of Pt on Au was performed using irreversible adsorption of Pt precursor ions, followed by electrochemical reduction, and a strategy of multiple Pt deposition was employed to control the deposited amount of Pt. Modification of the surfaces of Pt deposits and bulk Pt with Bi was carried out using irreversible adsorption of Bi. The amount of deposited Pt on Au, measured using coulometry and XPS, implied that most of Pt deposits are islands consisting of Pt monolayers partially covered with the second Pt layer. On such Pt deposits on Au, formic acid oxidation was enhanced by suppression of dehydration path and promotion of dehydrogenation path. In the presence of Bi on Pt deposits, dehydrogenation path was boosted further to increase the electrocatalytic activity by a factor of 4 below 0.4 V. On the other hand adsorbed Bi of coverage 0.25 on bulk Pt completely inhibited dehydration path and enormously sped up dehydrogenation path to be best among the scrutinized Pt surfaces. The enhancement factor of Bi-modified bulk Pt was 3 times compared to Bi-modified Pt deposits. The roles of Bi on Pt were discussed in terms of ensemble effect to suppress dehydration path and electronic effect to promote dehydrogenation path. In addition, electronic effect was found strongly to depend on the Pt thickness underneath adsorbed Bi. [ABSTRACT FROM AUTHOR]

The adsorption of asphaltenes on mineral surfaces is important in petroleum production and in oilsands extraction. Adsorption of Athabasca asphaltenes from toluene solutions onto kaolinite was investigated over a wide range of asphaltene and kaolinite concentrations. Although the adsorption appeared to follow the functional form of the Langmuir isotherm, the amount adsorbed depended on the kaolinite concentration so that the result depended on the experimental path, not the final solution concentration of asphaltenes. The results are consistent with kinetically limited adsorption, analogous to proteins, with a functional dependence on the asphaltene/kaolinite ratio. Multiple contacts between dried asphaltene-coated kaolinite and fresh asphaltene solutions, and between “spent” asphaltene solutions and fresh samples of kaolinite further confirmed that conventional isotherms were inadequate to describe the adsorption behavior. Repeated contact of asphaltene solution with kaolinite adsorbed up to 98% of the asphaltenes, therefore, the adsorption was not selective for specific species in the asphaltene mixture. Kaolinite samples before and after multiple contacts with asphaltene were analyzed by elemental analysis and X-ray photoelectron spectroscopy (XPS). The adsorption density of asphaltene on kaolinite increased dramatically after each contact with a fresh asphaltene solution, but the surface composition detected by XPS on the kaolinite surface was unchanged. The presence of Al and Si, detectable even at high asphaltene adsorption density, proved that asphaltene adsorption layer is not continuous on the kaolinite surface, and that subsequent asphaltene adsorption occurred preferentially on the asphaltenes already adsorbed on the kaolinite surface. [ABSTRACT FROM AUTHOR]

The effect of activated carbon’s pore size distribution (PSD) on heel formation during adsorption of organic vapors was investigated. Five commercially available beaded activated carbons (BAC) with varying PSDs (30–88% microporous) were investigated. Virgin samples had similar elemental compositions but different PSDs, which allowed for isolating the contribution of carbon’s microporosity to heel formation. Heel formation was linearly correlated (R 2 = 0.91) with BAC micropore volume; heel for the BAC with the lowest micropore volume was 20% lower than the BAC with the highest micropore volume. Meanwhile, first cycle adsorption capacities and breakthrough times correlated linearly (R 2 = 0.87 and 0.93, respectively) with BAC total pore volume. Micropore volume reduction for all BACs confirmed that heel accumulation takes place in the highest energy pores. Overall, these results show that a greater portion of adsorbed species are converted into heel on highly microporous adsorbents due to higher share of high energy adsorption sites in their structure. This differs from mesoporous adsorbents (low microporosity) in which large pores contribute to adsorption but not to heel formation, resulting in longer adsorbent lifetime. Thus, activated carbon with high adsorption capacity and high mesopore fraction is particularly desirable for organic vapor application involving extended adsorption/regeneration cycling. [ABSTRACT FROM AUTHOR]

Synthetic resin adsorbents comprise agglomerated gel-type microparticles. Although the excellent adsorption capacities of resins are useful in adsorbing various organic substances, the adsorbed molecules cannot be completely desorbed. A majority of the irreversible adsorbed molecules can be attributed to slow mass transfer within microparticles of resins and it may lower the recovery efficiency of resins. This study focuses on reducing the irreversible adsorption that occurs within a resin (FPX-66) to improve the overall recovery efficiency of the adsorbate. In order to reduce the irreversible adsorption capacity of the resin, styrene monomer was polymerized in microparticles of the resin. Effects of polymerized styrene concentrations and multi-cycle polymerization on irreversible adsorption capacity of the resin were investigated. The experimental results indicated that using one cycle of polymerization with 30-40 vol% of styrene solution is the most effective modification process. The irreversible adsorption capacity could be lowered by half with the above process. [ABSTRACT FROM AUTHOR]

Sufficient uniformity of the gas phase and surfaces within a catalytic bed is an essential prerequisite for precise kinetic characterization of heterogeneous catalysts. In addition to uniformity, the gas transport regime must be mathematically well-defined and allow for controlled alterations of the catalyst state. The Thin-Zone Temporal Analysis of Products (TZTR) reactor satisfies these requirements for industrially-relevant powdered catalysts. Numerical simulations of pulse-response experiments were used to chart the conditions of spatial uniformity within the TZTR for very fast (Da II up to 100) irreversible reactions, such as strong chemisorption or oxidation reactions. The simulations demonstrated that even when an initial catalyst state is so reactive that uniformity cannot be readily achieved, a series of reactant pulses eventually creates a catalyst state which is spatially uniform and at the same time reactive enough for kinetic characterization. This point on the scale of possible catalyst states is attained when the total amount of pulsed molecules exceeds the initial number of active sites in the sample, i.e. the theoretical monolayer coverage. Simulations also indicated that the rate at which the catalyst bed becomes more uniform from one pulse to the next is sensitive to reaction order: the desired uniformity is established for a second order adsorption after smaller amount of pulses than for a first order adsorption. Thus, a wider range of spatially uniform, yet kinetically-relevant catalyst states can be characterized for a second order adsorption. These results not only expand the range of validity for the TZTR approach, but also set new bounds for generally achievable precise kinetic measurements. [ABSTRACT FROM AUTHOR]

In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial PtRu/C were studied as catalysts for ethanol oxidation. The prepared trimetallic catalysts showed enhanced properties for ethanol oxidation through a wide range of surface coverages. However, coverage higher than 0.7 of Sb on PtRu/C causes the decrease of the catalytic activity suggesting that specific sites composed of 3 metals are necessary to achieve the highest performance. In situ Fourier Transform Infrared Spectroscopy experiments were also performed to compare the reaction products of the bimetallic and trimetallic catalysts. The catalysts were also tested under fuel cell conditions. Also in this case, higher power densities, higher open-circuit voltages and better stability than the bimetallic substrate were found. With this catalyst preparation method, the catalysts showed 2 times higher current densities than for the PtRu catalysts and 6 times better than for pure Pt anodes. [ABSTRACT FROM AUTHOR]

The adsorption of neutral organophosphorous compounds on a charged polycrystalline Ni electrode is studied by differential capacitance and impedance measurements in methanol solutions. Analysis of capacitance measurements reveals that tributylphosphine oxide, tri( n)octylphosphine oxide, and triphenylphosphine follow Langmuir adsorption isotherm. Saturation capacitance C, potential of maximum adsorption E, limiting surface concentration Γ, and standard Gibbs energy of adsorption ΔG at E are determined. The cathodic reduction of (NiOCH) film formed on Ni surface at positive potentials, introducing a faradaic contribution in addition to the electrostatic charging of the interface, is supported by linear sweep voltammetric and impedance measurements. High values of electrode coverage and strong depression of faradaic currents are attained, indicating that these adsorbates may be suitable as corrosion inhibitors. [ABSTRACT FROM AUTHOR]

We report, for the first time, the electrochemical behavior of thallium irreversibly adsorbed on Pt (111) and platinum stepped surfaces composed of (111) terraces and monoatomic steps. Similar to the case of thallium UPD, the voltammograms obtained after thallium irreversible adsorption present three characteristic features. After a careful analysis of the effect of the thallium concentration, the concentration and nature of the anion of the supporting electrolyte and the pH of the solution on these voltammetric features, we have been able to ascribe these processes to Tl/Tl + oxidation and anion adsorption on the Tl-modified surface. In addition, the results obtained with stepped surfaces, indicate that some of the features are clearly associated to the presence of (111) surface domains, and thus they could be used for the quantification of these sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • New kinetic model of electrodeposition of composite coatings has been developed. • The model implies irreversible adsorption of dispersed particles on a metal matrix. • The model is compared to experimental data for electrodeposition of Ni–TiO 2 composite coatings. A kinetic model of electrochemical deposition of composite coatings has been developed, which assumes irreversible adsorption of dispersed particles on a growing metal matrix. The irreversibility of particle adsorption is due to energy consumption required for the complete or partial removal of adsorption layers and solvate shells present on the surfaces of dispersed particles and a metal matrix, which is a necessary condition for the formation of a strong adhesive bond. The corresponding kinetic equations are derived that reflect the dependence of the content of a dispersed phase in the composite on the concentration of particles in the electrolyte, their average size and current density of metal deposition. The resulting equations are used to calculate adsorption rate constants on the basis of experimental data on the electrodeposition of nickel–titania composite coatings from an aqueous electrolyte and an electrolyte based on a choline chloride-containing deep eutectic solvent. The influence of current density on the adsorption rate constants in these electrolytes is revealed and interpreted. [ABSTRACT FROM AUTHOR]

Determining the long-term performance of adsorbents is crucial for the design of air treatment systems. Heel buildup i.e., the accumulation of non-desorbed/ non-desorbable adsorbates and their reaction byproducts, on the surface/pores of the adsorbent is a primary cause of adsorption performance deterioration. However, due to the complexity of heel buildup mechanisms, theoretical models have yet to be developed to map the extent of heel buildup to the adsorption/desorption parameters. In this work, two machine learning (ML) algorithms (XGBoost and neural network (NN)) were applied to predict volatile organic compounds (VOCs) cyclic heel buildup on activated carbons (ACs) by considering the adsorbent characteristics, adsorbate properties and regeneration conditions. The NN algorithm showed better performance in prediction of cyclic heel buildup (R2 = 0.94) than XGBoost (R2 = 0.81). To analyze interaction between heel buildup and adsorbent characteristics, adsorbate properties, and regeneration conditions, partial dependency plots were generated. The proposed ML-based heel prediction methods can be ultimately used to: (i) optimize adsorption/desorption operating conditions to minimize heel buildup on activated carbon in cyclic adsorption/desorption processes and (ii) quickly screen various adsorbents for efficient adsorption/desorption of a particular family of VOCs by excluding adsorbents prone to high heel formation. [Display omitted] • Heel buildup reduces activated carbon (AC) service life. • Two machine learning (ML) algorithms were developed to predict heel buildup on AC. • XGBoost & Neural network (NN) algorithms were trained & tested. • NN can predict heel build with high accuracy and low overfitting error (R2 = 0.94). • ML related heel buildup to adsorbent/adsorbate properties, & regeneration condition. [ABSTRACT FROM AUTHOR]

This work presents a structural evolution of irreversibly adsorbed Bi on Pt(111) studied by electrochemical scanning tunneling microscopy and electrochemistry. The irreversibly adsorbed Bi showed a stable redox couple at 0.33 V whose maximum charge corresponded to the coverage of 0.33. The pristine layer of irreversibly adsorbed Bi grew from islands to large domains of the first monolayer, eventually to large domains of the monolayer with scattered protrusions of the second layer. During an electrochemical treatment from open circuit potential (∼0.25 V) to 0.1 V, the domains of the pristine Bi layer shrunk and the Bi in the second layer moved to the first layer to form a compressed layer of elemental Bi. When the elemental Bi was re-oxidized at 0.35 V, there was no structural change to denote that the structures of the pristine and re-oxidized layers of oxygenated Bi differ from each other. The structural evolution during the electrochemical treatments is discussed in terms of removal and reinsertion of oxygen species. [ABSTRACT FROM AUTHOR]

Oil in water (o/w) emulsions are ubiquitous in food systems, where the stabilization of a homogeneous biphasic texture is necessary. In this study, binary protein particles (CRPs) with hydrophilic shells (cod proteins) and hydrophobic cores (rice proteins) were fabricated as stabilizers of o/w emulsions. To circumvent their instability at the interface due to conformational changes, the CRPs were further reinforced by starch nanocrystals (SNCs) to form a secondary complex (CRP@SNCs). Results from cryo-scanning electron microscope and confocal laser scanning microscope confirmed the stable adsorption of SNC-reinforced CRPs on the biphasic interface with excessive SNCs as the spacers separating the adjacent oil droplets, leading to emulsions featuring both Pickering-type and steric-type stabilization. At the optimum SNCs/CRPs mass ratio, the emulsions showed undetectable phase-separation and negligible changes in droplet size during the tested storage for up to 28 days. Our study presents a facile strategy for innovating novel stabilization protocols for emulsions. [Display omitted] • Interface absorption of proteins was improved by starch nanocrystals (SNCs). • Interaction between proteins and SNCs modulated the amphiphilicity. • Emulsion stability was enhanced due to Pickering-type and steric-type mechanisms. [ABSTRACT FROM AUTHOR]

Highlights: [•] CBC amendment strongly enhance the sorption irreversibility to natural soils. [•] HI increased exponentially with the increase of CBC%. [•] HI decreased exponentially with the increase of SOM%. [•] q irr and I irr are well proportional to the amount of CBC in soils. [•] DOM may affect the irreversible sorption to soils and CBC-amended soils. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pd-Bi/C catalysts were easily prepared by irreversible adsorption of Bi on Pd/C surface. [•] The adsorption of Bi increases the oxygen-containing species obviously on Pd-Bi/C surface. [•] Only a little amount of Bi on Pd-Bi/C can play a significant role in ethanol oxidation reaction (EOR). [•] Current density of EOR on Pd-Bi/C (20:1) is 2.4 times higher than that on Pd/C. [•] Anti-poisoning ability and durability of Pd-Bi/C (20:1) is greatly enhanced. [ABSTRACT FROM AUTHOR]