Molar Surface Area Research Articles

Size-Dependent Thermodynamics and Kinetics of Adsorption on Nanoparticles: A Theoretical and Experimental Study.

Owing to their excellent adsorption properties compared with those of the corresponding bulk materials, nanoparticles have been widely applied in many fields. Their properties depend on the thermodynamics and kinetics of adsorption, which depend on the particle size. In this paper, we present universal theories of the thermodynamics and kinetics for nanoadsorption that have been developed over the past few years. Theoretically, we have derived relationships between the adsorption thermodynamic properties and the particle size, as well as those between the adsorption kinetic parameters and the particle size. Moreover, we discuss the regularities and mechanisms of influence of the particle size on the thermodynamics and kinetics of adsorption. Experimentally, taking the adsorption of methyl orange on nano-CeO2 in aqueous solution as a system, we have studied the size-dependent thermodynamics and kinetics of the system, and the size dependences were confirmed to be consistent with the theoretical relationships. The results indicate that particle size has a significant effect on the thermodynamic properties and kinetic parameters of adsorption: with decreasing particle size of nano-CeO2, the adsorption equilibrium constant K⊖ and the adsorption rate constant k increase, while the molar Gibbs free energy of adsorption Δads Gm⊖, the molar adsorption entropy Δads Sm⊖, the molar adsorption enthalpy Δads Hm⊖, the adsorption activation energy Ea, and the adsorption pre-exponential factor A all decrease. Indeed, ln K⊖, Δads Gm⊖, Δads Sm⊖, Δads Hm⊖, ln k, Ea, and ln A are each linearly related to the reciprocal of particle size. Furthermore, thermodynamically, Δads Gm⊖ and ln K⊖ are influenced by the molar surface area and the difference in surface tensions, Δads Sm⊖ is influenced by the molar surface area and the difference in temperature coefficients of surface tension, and Δads Hm⊖ is influenced by the molar surface area, the difference in surface tensions, and the difference in temperature coefficients of surface tension. Kinetically, Ea is influenced by the partial molar surface enthalpy of the nanoadsorbent, ln A is influenced by the partial molar surface entropy, and ln k is influenced by the partial molar surface Gibbs energy. The theories can quantitatively describe adsorption behavior on nanoparticles, explain the regularities and mechanisms of influence of particle size, and provide guidance for the research and application of nanoadsorption.

In-situ growth of ZIF-8 on layered double hydroxide: Effect of Zn/Al molar ratios on their structural, morphological and adsorption properties

In-situ growth of Zeolite imidazolate frameworks (ZIFs) on layered double hydroxides (LDHs) to form porous composites is a promising and challenging strategy to develop materials for separation application. Herein, the Zn-Al LDH with different Zn/Al molar ratios was prepared and used as matrix for the growth of ZIF-8 on its surface. The resulting composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, thermogravimetric (TG), scanning electron microscope (SEM) and elemental analysis followed by testing for AsV removal from aqueous solution. Results showed that ZIF-8 could form on the surface of LDH with different Zn/Al molar ratios. At low Zn/Al molar ratios, the morphology and surface area of the ZIF/LDH composites and the content of ZIF-8 in the composites were little affected by the Zn/Al molar ratio. With increasing Zn/Al molar ratio, ZIF-8/LDH exhibited a lower surface area, which resulted from reduced content of ZIF-8 caused by impurities generated in the LDH matrix. All ZIF-8/LDH samples showed high AsV adsorption capacity, which was significantly higher than that of pure LDH or ZIF-8.

Shape and curvature of surface tension isotherms for liquid mixtures

The different shapes of surface tension isotherms consistent with Butler’s ideal model for the planar surface phase of binary liquid mixtures are comprehensively worked out for the first time. Using the ratio of pure constituent molar surface areas and a parameter named surface factor, which depends only on pure-constituent properties, the Butler equation is expressed and solved as a function of these two independent parameters. The geometrical features for the plots of surface tension against the mole fraction of component with lower surface tension are established for every possible combination of those two parameters. Three main shape types are found, namely: concave up (positive curvature); concave down passing through an inflection point followed by concave up; and concave down (negative curvature). The range of parameter values leading to each shape type is obtained and shown graphically. It is demonstrated that Butler’s ideal model excludes the eventuality of a system presenting a shape with initial positive curvature, then an inflection point and continuing with negative curvature. All the above shapes will appear as a mirror image in the representation of surface pressure against mole fraction. Six organic–organic systems, including two ionic liquid solutions, taken from the literature are examined. It is shown that actual Gibbs adsorption isotherm shapes arise from the sum of ideal surface tension deviations with excess surface tensions, the latter being related to the equilibrium surface/bulk ratio of activity coefficients. It is also shown that this ratio is larger for the component with the greatest molar surface area. From the comparison of surface and bulk activity coefficients at the same chemical composition interesting insights into the surface phase are drawn.

Supramolecular Deoxyribose Nucleic Acid and Functionalized Carbon Nanotube Conjugate: Computational Modeling Approach

Objectives: To develop a robust, feasible and stable conjugate of functionalized Carbon Nanotube (f-CNT) and Supramolecular Nucleic Acid (DNA) which are compatible with each other in behavior. Method: A basic computational model of above mentioned conjugate is prepared with the help of Hyperchem® 7.5 obtained by steepest descent algorithm. Findings: This f-CNT-DNA conjugate model was then used to study various QSAR properties of CNT-DNA like molar refractivity, polarization, volume, Hydration Energy, Surface Area and Log P values to show its viability and potential in various biotechnical applications. Applications: Various conjugate models are studied and detected its feasibility and stability to work as a carrier for various biotechnical applications, ranging from biological transporters as a drug carrier and biosensors.

Size-dependent dissolution kinetics of CaCO3 nanoparticles in theory and experiment

In preparation and application of nanomaterials, the dissolution of nanoparticles is usually involved. However, it remains unclear about size dependent the dissolution kinetic parameters of nanoparticles. In this paper, kinetic model for the dissolution of nanoparticles is proposed, and the relations between dissolution kinetic parameters (rate constant, order, apparent activation energy and pre-exponential factor), respectively, and particle sizes were theoretically deduced by applying the transition state theory to the dissolution process, and then the influence regularity and mechanism of particle size on the kinetic parameters were discussed. Experimentally, the dissolution kinetic parameters of nano-CaCO3 with different particle sizes were determined by conductivity meter, and the quantitative influences of particle size on the dissolution kinetics were obtained. The experimental results are consistent with the theoretical relations. The results show that there are significant effects of the particle sizes of CaCO3 nanoparticles on dissolution kinetic parameters; with the particle diameter decreasing, the apparent activation energy and the pre-exponential factor correspondingly decrease, while the rate constant and the dissolution order increase sharply. When the diameter of nanoparticle exceeds 20 nm, the logarithm of the dissolution rate constant, the apparent activation energy, and the logarithm of the pre-exponential factor are all linearly related with the reciprocal of particle diameter. Furthermore, the apparent activation, the dissolution order, the pre-exponential factor, and the dissolution rate constant are influenced by the partial molar surface enthalpy, the partial molar surface area, the partial molar surface entropy, and the partial molar surface Gibbs energy, respectively.

Study on surface tension and surface phase of molten MCl-CeCl3 (M = Li, Na, K, Cs): A comparison of Butler's equation and a newly-proposed model

The thermodynamic optimization of NaCl-CeCl3 has been carried out through CALPHAD method, and a set of reliable parameters has been obtained to supplement the thermodynamic database. Based on Butler's equation and thermodynamic database established by CALPHAD method, the calculated surface tensions of molten salt mixtures MCl-CeCl3(M = Li, Na, K, Cs) agree quite well with experimental results reported in the literature. The model parameter β was determined to be 0.95, 1.04, 1.09 and 1.12 for LiCl-CeCl3, NaCl-CeCl3, KCl-CeCl3 and CsCl-CeCl3, respectively, by fitting the experimental data of surface tension of these mixtures, since it is out of the question to get a universal β applicable to all molten salt mixtures. The new model proposed lately by Santos et al. to describe the thermodynamics in surface phase of liquid solution has been reduced to a much simpler form which is nearly numerically equivalent to it by eliminating the derivative of molar surface area with respect to pressure. The surface compositions and surface activity coefficients from Butler's equation were compared with those from Santos model. For LiCl-CeCl3 and NaCl-CeCl3, the results from the two models are almost the same due to the similar surface tensions of LiCl, NaCl and CeCl3. Whereas for KCl-CeCl3 and CsCl-CeCl3, the mole fraction of CeCl3 in surface phase from Butler's equation is overestimated compared with that from Santos model, leading to a slight underestimation of surface activity coefficients of CeCl3 and also a slight overestimation of those of KCl and CsCl, since the surface tensions of KCl and CsCl are much smaller than that of CeCl3.

A semi-empirical equation for describing the surface tension of aqueous organic liquid mixtures

A thermodynamic analysis is made for the dependence on composition of the surface tension showing that the latter is a mechanical thermodynamic property which is linearly related to the reciprocal of each component standard molar surface area; and that there is no simple mixing formula linking the ideal surface tension to pure-component surface tensions.The ability of five current empirical equations to correlate the surface tension of the ideal and real binary systems water–ethanol or propan-2-ol or ethanenitrile or 1,4-dioxane at T = 298 K is examined. Polynomial equations are not able to describe the general, overall trend of surface tension variation across the entire composition range, where equations containing a hyperbolic term perform much better. This is the case of the proposed new equation in which two of its parameters can be estimated theoretically.

Relationship between surface tension and Gibbs energy, and application of Constrained Gibbs Energy Minimization

In the context of a boundary phase model, surface tension (σ) of a solution can be regarded as a system property of an equilibrium between a bulk phase and a surface phase. In the present article, a geometric relationship is shown among molar Gibbs energy of the bulk phase (g), that of the surface phase (gs), and corresponding surface tension of the system. The geometric relationship is based on a phase equilibrium between the bulk phase and the surface phase, under a constraint: constant surface area (A). The relationship is consistent with the proposal of Butler, Proc. R. Soc. Lond. A: Math. Phys. Eng. Sci., 135 (1932) 348 [1], and is mathematically equivalent to the Constrained Gibbs Energy Minimization (CGEM) for the surface tension calculation by Pajarre et al., Calphad 30 (2006) 196 [7]. The geometric relationship can be simply utilized by available CALPHAD type code, in order to calculate surface tension of a solution composed of any number of components. Role of various properties (surface tension (σi°) and molar surface area (Ai°) of pure components, excess Gibbs energy of the bulk phase and that of the surface phase) in the surface tension and surface concentration is examined using the CGEM.

Enhanced sulfamethazine removal by steam-activated invasive plant-derived biochar

Recent investigations have shown frequent detection of pharmaceuticals in soils and waters posing potential risks to human and ecological health. Here, we report the enhanced removal of sulfamethazine (SMT) from water by physically activated biochar. Specifically, we investigated the effects of steam-activated biochars synthesized from an invasive plant (Sicyos angulatus L.) on the sorption of SMT in water. The properties and sorption capacities of steam-activated biochars were compared with those of conventional non-activated slow pyrolyzed biochars. Sorption exhibited pronounced pH dependence, which was consistent with SMT speciation and biochar charge properties. A linear relationship was observed between sorption parameters and biochar properties such as molar elemental ratios, surface area, and pore volumes. The isotherms data were well described by the Freundlich and Temkin models suggesting favorable chemisorption processes and electrostatic interactions between SMT and biochar. The steam-activated biochar produced at 700°C showed the highest sorption capacity (37.7mgg−1) at pH 3, with a 55% increase in sorption capacity compared to that of non-activated biochar produced at the same temperature. Therefore, steam activation could potentially enhance the sorption capacities of biochars compared to conventional pyrolysis.

New thermodynamics for evaluating the surface-phase enrichment in the lower surface tension component.

Regarding the surface phase of liquid mixtures as a thermodynamic phase, ideal surface phases are designed so that at fixed bulk-phase composition, real and ideal surface phases have the same chemical composition and identical limiting slopes for the dependence of surface tension on mole fraction. Standard chemical potentials are introduced for surface phase components, and quasi-exact expressions are worked out to compute ideal surface tensions and surface-phase compositions of real liquid mixtures. Guidelines for choosing molecular models to estimate the molar surface area of pure constituents are given. Ideal and excess surface tensions are calculated by using literature data for aqueous ethanol solutions at 298 K. These results show treatment based on Butler's equations grossly overestimate predicted surface tensions, thus leading to lower ethanol content in the surface phase. These inaccuracies are ascribed to the use of molar surface areas in model equations that are too small.

QSPR prediction of chromatographic retention times of pesticides: Partition and fractal indices

The high‐performance liquid‐chromatographic retentions of red‐wine pesticide residues are modeled by structure–property relationships. The effect of different types of features is analyzed: geometric, lipophilic, etc. The properties are fractal dimensions, partition coefficient, etc., in linear and nonlinear correlation models. Biological plastic evolution is an evolutionary perspective conjugating the effect of acquired characters and relations that emerge among the principles of evolutionary indeterminacy, morphological determination and natural selection. It is applied to design the co‐ordination index that is used to characterize pesticide retentions. The parameters used to calculate the co‐ordination index are the molar formation enthalpy, molecular weight and surface area. The morphological and co‐ordination indices barely improve the correlations. The fractal dimension averaged for non‑buried atoms, partition coefficient, etc. distinguishes the pesticide molecular structures. The structural and constituent classification is based on nonplanarity, and the number of cycles, and O, S, N and Cl atoms. Different behavior depends on the number of cycles.

Study on the Size‐Dependent Oxidation Reaction Kinetics of Nanosized Zinc Sulfide

Numerous oxidation problems of nanoparticles are often involved during the preparation and application of nanomaterials. The oxidation rate of nanomaterials is much faster than bulk materials due to nanoeffect. Nanosized zinc sulfide (nano‐ZnS) and oxygen were chosen as a reaction system. The influence regularities were discussed and the influence essence was elucidated theoretically. The results indicate that the particle size can remarkably influence the oxidation reaction kinetics. The rate constant and the reaction order increase, while the apparent activation energy and the preexponential factor decrease with the decreasing particle size. Furthermore, the logarithm of rate constant, the apparent activation energy and the logarithm of preexponential factor are linearly related to the reciprocal of particle diameter, respectively. The essence is that the rate constant is influenced by the combined effect of molar surface energy and molar surface entropy, the reaction order by the molar surface area, the apparent activation energy, by the molar surface energy, and the preexponential factor by the molar surface entropy. The influence regularities and essence can provide theoretical guidance to solve the oxidation problems involved in the process of preparation and application of nanomaterials.

Aqueous Amine Spray Absorption and Droplet Distribution Data for CO2 Capture Applications

Spray columns can potentially be utilized for absorbing CO2 from large point sources such as flue gas exhausted by power plants. Low gas phase pressure drop, and the lack of internals which are susceptible to corrosion, make spray columns well suited for aqueous amine absorption. Design practices for spray columns are highly empirical and application specific. There is a paucity of data on absorption of CO2 in aqueous amine sprays. Mass transfer data for CO2-amine systems is required for robust design of spray columns. Further, the absorption efficiency of sprays is greatly influenced by the surface area of drops, which in turn depends on the droplet size distribution. However, experimental data for droplet size distributions inside aqueous amine sprays is non-existent. Measurement of droplet size distributions is critical in providing a fundamental insight into spray absorption. This work presents molar flux data coupled with droplet size distribution data for CO2 absorption into Monoethanolamine (MEA) spray. Both the molar flux measurements and the droplet size measurements are made inside a 0.2 m glass column. The droplet size distributions are measured using a Phase Doppler Interferometer (PDI). Further, a novel method is utilized to quantify the available surface area from the droplet size distribution measurements. The effect of MEA concentration on molar flux, droplet size, and surface area is presented.

Adsorption from n-heptane/benzene liquid mixture on acid leached bentonite powders

In this study, adsorption excess isotherms of n-heptane/benzene liquid mixture on hydrochloric acid leached bentonite powders were determined. Adsorptions were conducted at 25°C for 48h. Experimental results were evaluated with both Schay–Nagy (SN) and Everett (E) methods. Specific surface areas (SSN and SE) of the powders were calculated regarding monolayer adsorption capacity of the preferentially adsorbed benzene. Adsorption equilibrium constants (K≫1) were obtained by the E-method. The SE and SSN values are closed to each other. SE-values were found much lower than the corresponding Brunauer, Emmett and Teller (BET)-values. This difference was discussed with respect to the interaction of adsorbed molecules with solid surface, their collision diameter, molar cross sectional surface area and orientation in dense monolayer. Even the maximum for the SE was not associated with the maxima for K and nanopore volume (V), their values changed approximately parallel to each other with respect to the HCl% by the leaching.

Maxillary sinus floor extension and posterior tooth inclination in adolescent patients with Class II Division 1 malocclusion treated with maxillary first molar extractions

Our objective was to investigate potential associations between maxillary sinus floor extension and inclination of maxillary second premolars and second molars in patients with Class II Division 1 malocclusion whose orthodontic treatment included maxillary first molar extractions. The records of 37 patients (18boys, 19 girls; mean age, 13.2 years; SD, 1.62 years) treated between 1998 and 2004 by 1 orthodontist with full Begg appliances were used in this study. Inclusion criteria were white patients with Class II Division 1 malocclusion, sagittal overjet of ≥4 mm, treatment plan including extraction of the maxillary first permanent molars, no missing teeth, and no agenesis. Maxillary posterior tooth inclination and lower maxillary sinus area in relation to the palatal plane were measured on lateral cephalograms at 3 time points: at the start and end of treatment, and on average 2.5 years posttreatment. Data were analyzed for the second premolar and second molar inclinations by using mixed linear models. The analysis showed that the second molar inclination angle decreased by 7° after orthodontic treatment, compared with pretreatment values, and by 11.5° at the latest follow-up, compared with pretreatment. There was evidence that maxillary sinus volume was negatively correlated with second molar inclination angle; the greater the volume, the smaller the inclination angle. For premolars, inclination increased by 15.4° after orthodontic treatment compared with pretreatment, and by 8.1° at the latest follow-up compared with baseline. The volume of the maxillary sinus was not associated with premolar inclination. We found evidence of an association between maxillary second molar inclination and surface area of the lower sinus in patients treated with maxillary first molar extractions. Clinicians who undertake such an extraction scheme in Class II patients should be aware of this potential association andconsider appropriate biomechanics to control root uprighting.

The influence of dentition on the developing mandible in a mouse model

Developing dentition is considered an important influence on mandibular size and shape. Previously, it was shown that mandibular size and shape was affected in mice carrying an Fgfr2C342Y/+ mutation, specifically in the ramus rather than alveolar region. Here it is hypothesized that molar size will have a more significant correlation with size and shape of the mandibular alveolar region compared to the ramal region throughout ontogeny. Micro‐CT scans of adult (n=20), perinatal (n=9) and prenatal (n=9) wildtype and mutant mice were used to reconstruct total molar surface area and to collect 3‐D landmark data. Shape and size analyses for each region were conducted using EDMA. Partial correlations were used to test the influence of molar size.Results partly support the stated hypotheses. Principle coordinate plots demonstrate a clear separation in both alveolar and ramal shape between mutant and wildtype mice at each age range. Comparisons of geometric mean using t‐tests reveal that ramal size is significantly smaller in prenatal and adult mutants (p<0.05) but not in the alveolar region (p>;0.05). Partial correlations did not suggest that molar size had a stronger influence on alveolar regions. In conclusion, the alveolar region is less affected than the ramus, however it is not clear whether the dentition is driving this regional difference. It is possible that other ontogenetic factors are masking this signal.Grant Funding Source: NSF

Modeling of antitubercular activity of biphenyl analogs of 2-nitroimidazo[2,1-b][1,3]oxazine to rationalize their activity profile

The antitubercular activity of ortho-, meta- and para-substituted biphenyl analogs of 2-nitroimidazo[2,1-b][1,3]oxazine has been analyzed through combinatorial protocol in multiple linear regression using physicochemical and structural descriptors obtained from MOE software. The different electronic, hydrophobic, and steric descriptors have been identified for the model development. The study indicates that the ortho substituents with high LUMO (electron acceptor) and less dipole moment are favorable for the activity. The meta and para positions are mainly influenced by steric parameters. Here, the molar refractivity and volume surface area descriptors suggested that the small substituents are conducive for the activity. Also, the para substituents with negatively charged polar surface area are unfavorable for the activity. The identified physicochemical descriptors also indicate the nature of receptor surface in Mycobacterium tuberculosis for this class of compounds. The models and participating descriptors suggest that the substituted biphenyl analogs of 2-nitroimidazo[2,1-b][1,3]oxazine hold scope for further modification in the optimization of antitubercular activity.

Urchin-like cobalt incorporated manganese oxide OMS-2 hollow spheres: Synthesis, characterization and catalytic degradation of RhB dye

Urchin-like KxCoyMn8−yO16 hollow spheres assembled from nanoplate building blocks were successfully fabricated via a one-pot hydrothermal route using cobalt acetate and potassium permanganate as raw material. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometer, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) measurement. The thermal stability and surface areas of cobalt ion in the manganese sites of KMn8O16 structures were clearly evidenced by TGA and N2 adsorption–desorption isotherms curves. Based on time depended experiment results, a possible formation mechanism for this structures was proposed. The catalytic degradation of Rhodamine B (RhB) on KxCoyMn8−yO16 materials has, therefore been dependent for the molar precursor ratio and specific surface area of the as-fabricated products. UV–vis, LC–MS and barium hydroxide methods were utilized to monitor the temporal course of the catalytic reaction.

Molar surface area and mandibular mechanics: complex scaling relationships in primate masticatory systems

Primate evolutionary and comparative studies often rely on an understanding of scaling patterns in the primate masticatory complex. Recently, it was proposed that molar root size predicts masticatory loading and molar crown size predicts facial size. We hypothesize that root surface area (RSA) scales isometrically with mandibular strength, and crown surface area (CSA) scales isometrically with facial size. CT scans of Macaca (n=19) and Papio (n=18) were used to calculate M1 RSA, CSA and facial size (geometric mean of 9 linear distances). Mandibular strength (Zx) was calculated posterior to M1. RMA regressions were used to test scaling patterns among these properties.RSA was significantly correlated with Zx (r=0.76 and 0.69), exhibiting similar slope trajectories (p=0.182) in both species. Macaca scaled with isometry, however Papio was negatively isometric. RSA and facial size scaled isometrically in both taxa with similar slopes and elevations. In contrast, CSA displayed divergent scaling patterns relative to both Zx and facial size. For both variables, Papio possessed a significantly greater CSA slope trajectory. CSA scales isometrically with Zx and facial size in Papio, but with negative isometry in Macaca. Results partially support our hypotheses yet indicate that unique species‐specific scaling relationships exist for CSA and suggest that future studies should control for phylogenetic signals.Grant Funding Source : NIDCR (R03‐DE019816)

The Effects of Particle Size on the Kinetic Parameters in the Reaction of Nano-Nio with Sodium Bisulfate Solution

The kinetic parameters for the chemical reaction of nano-NiO of different particle sizes with aqueous sodium bisulfate solution were determined; additionally, the influence of particle size on the kinetic parameters were studied and were discussed. The results show that: there are clear effects of the particle size of nano-NiO on the rate constant, the reaction order, the apparent activation energy and the pre-exponential factor; thus the rate constant and the reaction order increase, and the apparent activation energy and the pre-exponential factor decrease, with decrease of the particle diameter; the logarithm of the preexponential factor, and the apparent activation energy, exhibit a linear relationship with the reciprocal of the particle diameter respectively. The bases of the role of the particle size are that the reaction order is influenced by the molar surface area of nano-NiO, the apparent activation energy by the molar surface energy, the preexponential factor by the molar surface entropy, and the rate constant by both the molar surface energy and the molar surface entropy.