Surface Desorption Research Articles

Effect of surfactant concentration, compression ratio and compression rate on the surface activity and dynamic properties of a lung surfactant

This paper reports dynamic surface tension experiments of a lung surfactant preparation, BLES, for a wide range of concentrations, compression ratios and compression rates. These experiments were performed using Axisymmetric Drop Shape Analysis–Constrained Sessile Drop (ADSA–CSD). The main purpose of the paper is to interpret the results in terms of physical parameters using the recently developed Compression–Relaxation Model (CRM). In the past, only the minimum surface tension was used generally for the characterization of lung surfactant films; however, this minimum value is not a physical parameter and depends on the compression protocol. CRM is based on the assumption that the dynamic surface tension response is governed by surface elasticities, adsorption and desorption of components of the lung surfactant. The ability of CRM to fit the surface tension response closely for a wide variety of parameters (compression ratio, compression rate and surfactant concentration) and produce sensible values for the elastic and kinetic parameters supports the validity of CRM.

Time of flight secondary ion mass spectrometry and high-resolution transmission electron microscopy/energy dispersive spectroscopy: A preliminary study of the distribution of Cu 2+ and Cu 2+/Pb 2+ on a Bt horizon surfaces

Relatively new techniques can help in determining the occurrence of mineral species and the distribution of contaminants on soil surfaces such as natural minerals and organic matter. The Bt horizon from an Endoleptic Luvisol was chosen because of its well-known sorption capability. The samples were contaminated with Cu 2+ and/or Pb 2+ and both sorption and desorption experiments were performed. The preferential distribution of the contaminant species ( 63Cu and 208Pb) to the main soil components and their associations were studied together with the effectiveness of the surface sorption and desorption processes. The results obtained were compared with non-contaminated samples as well as with previous results obtained by different analytical techniques and advanced statistical analysis. Pb 2+ competes favorably for the sorption sites in this soil, mainly in oxides and the clay fraction. Cu 2+ and Pb 2+ were mainly associated with hematite, gibbsite, vermiculite and chlorite. This study will serve as a basis for further scientific research on the soil retention of heavy metals. New techniques such as spectroscopic imaging and transmission electron microscopy make it possible to check which soil components retain heavy metals, thereby contributing to propose effective measures for the remediation of contaminated soil.

Differentiation of various kinds of Fructus schisandrae by surface desorption atmospheric pressure chemical ionization mass spectrometry combined with Principal Component Analysis

Various kinds of Fructus schisandrae were studied by surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS) without any sample pretreatment. The volatile components in F. schisandrae were detected in the ambient environment and the analytical time for each sample was only 30 s. F. schisandrae are produced mainly in 5 different geographical regions (Elunchun, Mudanjiang, Tonghua, Tieling and Shangluo), and they could be successfully differentiated according to their chemical markers by Principal Component Analysis (PCA). A total of 8 components which gave more contribution for PCA analysis were unambiguously identified by comparison of the MS 2 data of chemical markers to the data of reference compounds as reported in the literature. Similarly, wild grown and cultivatable species of F. schisandrae were well separated by the above-mentioned method. In addition, raw and processed cultivatable F. schisandrae (steamed by water, alcohol, vinegar, or honey, and fried by honey) were found to be clustered at different location, respectively. Furthermore, the clustered degree of differently processed products was correlated with their clinical effects. Our results demonstrated that DAPCI-MS in combination with PCA was a feasible technique for high-throughput differentiation of various kinds of F. schisandrae. It is also possible that DAPCI-MS could become a powerful technology in the studies of traditional Chinese medicine studies and in situ analysis of Chinese herbs.

The growth of SAPO 34 membrane layer on support surface for gas permeation application

The formation stage of SAPO 34 zeolite membrane on a tubular mullite support has been investigated. XRD, FESEM, IR and EDAX analysis techniques were used to explain the changes in crystallization stages as well as formation of membrane on tubular clay–alumina support with time. From the studies, the evidence tends to support that crystallization of SAPO 34 started from initial gel, proceed through cluster formation and accumulation followed by segregation and crystallization process. The study also showed the gradual incorporation of Si into AlPO 4 phase and form cubical CHA phase after 120 h of synthesis time. Single gas permeation of CO 2 and H 2 showed that upto 300 KPa of feed pressure permeability of CO 2 is more than that of H 2. But at higher pressure the results show the reverse trend, flux is more for H 2. This may be due to more adsorption of CO 2 on SAPO 34 surface and less desorption from the surface than hydrogen with increasing pressure. The selectivity of H 2/CO 2 increases from 0.85 to 2.67.

Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

DIFFUSION, SEGREGATION AND DESORPTION OF POTASSIUM FROM K2Fe22O34 FERRITE

The samples of K 2 Fe 22 O 34 phase were synthesized and characterized by XRD, BET, SEM-EDX and XPS. K+ diffusion was investigated by impedance spectroscopy, whereas the surface segregation and desorption were monitored by Kelvin Probe (changes in work function) and Species Resolved Thermal Alkali Desorption, at the temperature range of 600–1000 K. The analysis of changes in work function and desorption signals ( K and K+ ) at various temperatures allowed to resolve the kinetic parameters (flux, rate constants, activation energies) of potassium diffusion, surface accumulation and desorption. Based on the obtained results, the simple, functional model of bulk and surface changes of K -β-ferrite was proposed.

Synthesis of carbon xerogels at varying sol–gel pHs, dye adsorption and chemical regeneration

Several carbon xerogels were synthesized at varying sol–gel pHs of 6–10 using KOH as a catalyst. The porous structure, dye adsorption and regeneration by chemical oxidation of the carbon xerogels were comprehensively investigated. It was found that sol–gel pH significantly affected the porous structure and adsorption properties of carbon xerogels. The sol–gel pHs of 6–9 did not have a significant influence on surface area, micropore surface area, crystalline structure, combustion and desorption behavior of carbon xerogels, however, the pore size was different with development of mesopores at higher pH. When the pH was higher than 9, the carbon xerogel still possessed a highly porous structure. The surface area, micropore surface area, and combustion temperature could be reduced by 30%. Adsorption tests demonstrated high capacity of the carbon xerogels in dye adsorption. Due to loss of surface area and pore volume, the carbon xerogel synthesized at higher pH (>9) exhibited lower dye adsorption. For different types of dye, the carbon xerogels exhibited strong adsorption capacity for methylene blue and acid blue 40, but low adsorption of reactive black 5. Regeneration of the carbon xerogels using a chemical oxidation with Co 2+/oxone recovered the adsorption capacity by 70%.

THE EFFECTS OF GRAIN SIZE AND GRAIN GROWTH ON THE CHEMICAL EVOLUTION OF COLD DENSE CLOUDS

We investigate the formation of molecules during the chemical evolution of a cold dense interstellar cloud using a gas-grain numerical code in order to study the effects of grain-size distribution and grain growth on molecular abundances. Three initial size distributions have been used, based on earlier models. To incorporate different granular sizes, we divided the distribution of sizes utilized into five logarithmically equally spaced ranges, integrated over each range to find its total granular number density, and assigned that number density to an average size in that range. We utilized rate coefficients for surface reactions, accretion, and desorption as functions of grain size. We then followed the chemical evolution of the surface populations of the five average-sized grains along with the gas-phase chemistry. We find that the total effective granular surface area of a distribution is an important parameter in the determination of surface abundances, with and without grain growth. The effect on gas-phase abundances can also be sizable. Grain growth with time increases the rate of depletion of molecules, such as CO, produced in the gas phase. Use of a size distribution for grains in gas-grain models does not improve the agreement of calculated and observed abundances, in the gas or on grains, as compared with models containing grains of a fixed radius of 0.1 μm. This result helps to verify the quality of the classical grain approximation for cold cloud models. Further, it provides an important basis for future gas-grain models.

Laboratory H2O:CO2ice desorption data: entrapment dependencies and its parameterization with an extended three-phase model

Ice desorption affects the evolution of the gas-phase chemistry during the protostellar stage, and also determines the chemical composition of comets forming in circumstellar disks. From observations, most volatile species are found in H2O-dominated ices. The aim of this study is first to experimentally determine how entrapment of volatiles in H2O ice depends on ice thickness, mixture ratio and heating rate, and second, to introduce an extended three-phase model (gas, ice surface and ice mantle) to describe ice mixture desorption with a minimum number of free parameters. Thermal H2O:CO2 ice desorption is investigated in temperature programmed desorption experiments of thin (10 - 40 ML) ice mixtures under ultra-high vacuum conditions. Desorption is simultaneously monitored by mass spectrometry and reflection-absorption infrared spectroscopy. The H2O:CO2 experiments are complemented with selected H2O:CO, and H2O:CO2:CO experiments. The results are modeled with rate equations that connect the gas, ice surface and ice mantle phases through surface desorption and mantle-surface diffusion. The fraction of trapped CO2 increases with ice thickness (10 - 32 ML) and H2O:CO2 mixing ratio (5:1 - 10:1), but not with one order of magnitude different heating rates. The fraction of trapped CO2 is 44 - 84 % with respect to the initial CO2 content for the investigated experimental conditions. This is reproduced quantitatively by the extended three-phase model that is introduced here. The H2O:CO and H2O:CO2:CO experiments are consistent with the H2O:CO2 desorption trends, suggesting that the model can be used for other ice species found in the interstellar medium to significantly improve the parameterization of ice desorption.

Microwave treated activated carbon from industrial waste lignin for endosulfan adsorption

AbstractBACKGROUND: Disposal of large amounts of recurring industrial waste lignin is a big problem for the paper industries and there is need for a rational alternative to utilize this waste lignin. Thus highly porous activated carbons (ACs) were prepared from lignin using H3PO4 as an activating chemical with and without microwave treatment in a self‐generated environment at 600 °C and the influence of different types of impregnation on the adsorption–desorption capacities of endosulfan from a liquid phase was studied.RESULT: The maximum adsorption capacities (Xm) for ACs prepared by a microwave treatment and using a simple impregnation method were 6.2422 mg g−1 and 3.9557 mg g−1, respectively. Equilibrium adsorption time determined from kinetic experiments was 5 h and the experimental kinetic data were described by a pseudo‐second‐order rate model. Surface characteristics and desorption patterns showed considerable difference between the two ACs with the microwave treated AC showing less hysteresis, greater Xm and established overall superiority over the other.CONCLUSION: Use of microwave treatment produced more oxygen surface functional groups. Results indicate that surface chemistry of the microwave treated sample is more important than the textural properties for the higher adsorption of endosulfan. The microwave treated sample also resulted in less hysteresis and fewer carbonyl surface groups. Desorption patterns cannot be predicted from adsorption alone. Copyright © 2011 Society of Chemical Industry

Differentiation of human kidney stones induced by melamine and uric acid using surface desorption atmospheric pressure chemical ionization mass spectrometry

Clinically obtained human kidney stones of different pathogenesis were dissolved in acetic acid/methanol solutions and then rapidly analyzed by surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS) without any desalination treatment. The mass spectral fingerprints of six groups of kidney stone samples were rapidly recorded in the mass range of m/z 50-400. A set of ten melamine-induced kidney stone samples and nine uric acid derived kidney stone samples were successfully differentiated from other groups by principal component analysis of SDAPCI-MS fingerprints upon positive-ion detection mode. In contrast, the mass spectra recorded using negative-ion detection mode did not give enough information to differentiate those stone samples. The results showed that in addition to the melamine, the chemical compounds enwrapped in the melamine-induced kidney stone samples differed from other kidney stone samples, providing useful hints for studying on the formation mechanisms of melamine-induced kidney stones. This study also provides useful information on establishing a MS-based platform for rapid analysis of the melamine-induced human kidney stones at molecular levels.

Sinapine Detection in Radish Taproot Using Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Plant research and natural product detection are of sustainable interests. Benefited by direct detection with no sample preparation, sinapine, a bioactive chemical usually found in various seeds of Brassica plants, has been unambiguously detected in radish taproot (Raphanus sativus) tissue using a liquid-assisted surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS). A methanol aqueous solution (1:1) was nebulized by a nitrogen sheath gas toward the corona discharge, resulting in charged ambient small droplets, which affected the radish tissue for desorption/ionization of analytes on the tissue surface. Thus, sinapine was directly detected and identified by tandem DAPCI-MS experiments without sample pretreatment. The typical relative standard deviation (RSD) of this method for sinapine detection was 5-8% for six measurements (S/N=3). The dynamic response range was 10(-12)-10(-7) g/cm2 for sinapine on the radish skin surface. The discovery of sinapine in radish taproot was validated by using HPLC-UV methods. The data demonstrated that DAPCI assisted by solvent enhanced the overall efficiency of the desorption/ionization process, enabling sensitive detection of bioactive compounds in plant tissue.

The effect of layer number and substrate on the stability of graphene under MeV proton beam irradiation

The use of graphene electronics in space will depend on the radiation hardness of graphene. The damage threshold of graphene samples, subjected to 2 MeV H + irradiation, was found to increase with layer number and also when the graphene layer was supported by a substrate. The thermal properties of graphene as a function of the number of layers or as influenced by the substrate argue against a thermal model for the production of damage by the ion beam. We propose a model of intense electronically-stimulated surface desorption of the atoms as the most likely process for this damage mechanism.

Reactivity of Silicon Surfaces in the Presence of Adsorbed Hydrogen and Chlorine

AbstractThe desorption of hydrogen and hydrogen chloride from Si surfaces is the rate‐determining step of the low temperature CVD of silicon from both hydrogenated and chlorinated precursors. Thus, in order to model the deposition process, the rate of these reactions must be known to a high level of accuracy. In this work, the surface desorption kinetics of H2 and HCl from the Si(100)2 × 1 surface is investigated by modeling the surface through clusters of various dimensions (up to 60 Si atoms) and determining the reaction energies at the B3LYP, and coupled cluster methodology with inclusion of single, double and a perturbative estimation of triple excitations (CCSD(T)) levels. The investigated mechanisms are the pairwise intradimer and the 4H‐2H reaction pathways. The desorption activation energy (57.4 kcal mol−1) and adsorption barriers (15.9 kcal mol−1) calculated for H2 for the 4H and 2H pathways are in good agreement with experimental data, confirming that these are the H2 main desorption and adsorption routes. The reaction mechanism of HCl is different to that of H2. The calculations in fact indicate that the less activated desorption pathway (65.0 kcal mol−1) is the intradimer mechanism, followed by the 2H pathway (67.1 kcal mol−1), which might thus compete with the intradimer pathway at low surface coverage. The HCl adsorption barrier on Si dimers is small (0.6 − 4.8 kcal mol−1), confirming the high reactivity of HCl with Si surfaces.

Smoothing of microfabricated silicon features by thermal annealing in reducing or inert atmospheres

In this work, high-temperature annealing of reactive ion etched silicon microstructures in H2 and Ar gases is studied. Three types of structural features were etched with four different masks into ⟨100⟩-oriented silicon wafers. Scanning electron microscope and atomic force microscope (AFM) results show that when smoothing due to surface diffusion and desorption of silicon is taking place in both the argon and hydrogen gas environments, the three types of features respond differently to the treatments. The surface diffusion was observed to be strongly dependent on temperature in argon, whereas the transport was more linear and controllable in the hydrogen gas environment. For hydrogen, AFM studies were performed to observe the details of the smoothing process. Finally, some potential applications of these transport phenomena are discussed.

A semi-detailed kinetic model of char combustion with consideration of thermal annealing

The present paper presents a semi-detailed kinetic model of coal char combustion which embodies consideration of thermal annealing as a mechanism leading to the loss of char combustion reactivity along burn off. The distinctive feature of this model is that deactivation induced by thermal annealing is followed along with combustion. Thermodeactivation is modelled according to the power-law equation proposed by Senneca and Salatino [1]. A semi-detailed combustion mechanism was taken after Hurt and Calo [2] and includes three steps: formation of carbon–oxygen complexes (chemisorption), switch-over of surface oxides and desorption of oxygen complexes to yield combustion products. Computation results allow to discuss the impact of thermal annealing on char combustion under conditions of practical interest.

Tracing Origins of Complex Pharmaceutical Preparations Using Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

A novel strategy to trace the origins of commercial pharmaceutical products has been developed based on the direct chemical profiling of the pharmaceutical products by surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS). Besides the unambiguous identification of active drug components, various compounds present in the matrixes are simultaneously detected without sample pretreatment, providing valuable information for drug quality control and origin differentiation. Four sources of commercial amoxicillin products made by different manufacturers have been successfully differentiated. This strategy has been extended to secerning six sources of Liuwei Dihuang Teapills, which are herbal medicine preparations with extremely complex matrixes. The photolysis status of chemical drug products and the inferior natural herd medicine products prepared with different processes (e.g., extra heating) were also screened using the method reported here. The limit of detection achieved in the MS/MS experiments was estimated to be 1 ng/g for amoxicillin inside the capsule product. Our experimental data demonstrate that DAPCI-MS is a useful tool for rapid pharmaceutical analysis, showing promising perspectives for tracking the entire pharmaceutical supply chain to prevent counterfeit intrusions.

Surface desorption and bulk diffusion models of tritium release from Li 2TiO 3 and Li 2ZrO 3 pebbles

The release of tritium from Li 2TiO 3 and Li 2ZrO 3 pebbles, in batch experiments, is studied by means of temperature programmed desorption. Data reduction focuses on the analysis of the non-oxidized and oxidized tritium components in terms of release limited by diffusion from the bulk of ceramic grains, or by first or second order surface desorption. By analytical and numerical methods the in-furnace tritium release is deconvoluted from the ionization chamber transfer functions, for which a semi-empirical form is established. The release from Li 2TiO 3 follows second order desorption kinetics, requiring a temperature for a residence time of 1 day ( T 1dRes) of 620 K, and 603 K, of the non-oxidized, and the oxidized components, respectively. The release from Li 2ZrO 3 appears as limited by either diffusion from the bulk of the ceramic grains, or by first order surface desorption, the first possibility being the more probable. The respective values of T 1dRes for the non-oxidized component are 661 K, according to the first order surface desorption model, and 735 K within the bulk diffusion limited model.

Interaction and Reaction of Coadsorbed NO and CO on a Rh(100) Single Crystal Surface

In order to assess the possibility to follow surface reactions in a quantitative way by vibrational spectroscopy, a combination of temperature programmed reaction spectroscopy (TPRS) and reflection absorption infrared spectroscopy (RAIRS) has been used to study the decomposition of NO and the reaction between NO and CO on Rh(100). NO adsorbs in two configurations: in an almost parallel position at coverages below 0.18 ML and, in addition, in an upright position, probably on a bridge site, at all coverages. Coadsorbing NO and CO has only a minor influence on NO binding, whereas CO shifts gradually from top toward the bridge site under the influence of NO. Combining TP-RAIRS with TPRS during the reaction between CO and NO enabled us to simultaneously study site occupation and obtain qualitative surface coverages and desorption rates. At low surface coverages, NO dissociation is observed at lower temperatures than CO(2) formation. Near saturation, NO dissociation becomes blocked and shifts up in temperature. NO dissociation occurs simultaneously with CO(2) formation. To decompose NO, free surface sites have to be generated through surface diffusion or desorption of some CO. During NO decomposition, the formed oxygen atoms react with CO to form CO(2), creating more empty sites. This may lead to an explosive surface reaction.

Adsorption of antimony(III) and antimony(V) on bentonite: Kinetics, thermodynamics and anion competition

This research attempted to study the adsorption of Sb(III) and Sb(V) on bentonite using batch experiments. The effects of reaction time, temperature, initial Sb concentration, and competitive anions at different concentrations on the adsorption of Sb(III) and Sb(V) were investigated. Kinetic studies suggested that the adsorption equilibriums for both Sb(III) and Sb(V) were reached within 24 h. The desorption of Sb adsorbate on the bentonite was observed following Sb(III) adsorption, probably due to the oxidation of Sb(III) on the bentonite surface and subsequent desorption of Sb(V). In addition, oxidation of Sb(III) can occur in the solution medium also, which decreases the concentration of Sb(III) in the solution thereby driving the equilibrium in the direction of desorption from the surface. The adsorption data at three temperatures were successfully modeled using Langmuir (r 2 > 0.82) and Freundlich (r 2 > 0.99) isotherms. The thermodynamic parameters (ΔG 0, ΔH 0, and ΔS 0) were calculated from the temperature dependence, suggesting that the adsorption process of Sb(III) is spontaneously exothermic, while the adsorption process of Sb(V) is spontaneously endothermic. Competitive anions such as NO 3 − , SO 4 2 − , and PO 4 3 − hardly affected the Sb(III) adsorption on bentonite, while SO 4 2 − and PO 4 3 − could compete with Sb(OH) 6 − for adsorption sites. The competition between PO 4 3 − and Sb(OH) 6 − on adsorption sites was presumably due to the formation of surface complexes and the surface accumulation or precipitation of PO 4 3 − on bentonite surface.