Role In Adsorption Phenomena Research Articles

The Role of Adsorption Phenomena in ac Conductivity Measurements of Dielectric Nanoparticle Suspensions

The authors of numerous measurements of conductivity for suspensions of nanoparticles of various types carried out in the last decade came to the general conclusion that the well-known Maxwell’s theory is not applicable to quantitative explanation of the properties of such systems. In the present work, we demonstrate that the Maxwell’s theory can be still applicable even for such systems, but the specifics of the standard ac measurements have to be correctly taken into account. Namely, the dependence of the capacitance of “metal–electrolyte” cuvette boundaries on nanoparticle adsorption, which in its turn dramatically depends on nanoparticle concentration, has to be taken into account. The latter circumstance strongly (via the RC characteristic of the circuit) affects the results of conductivity measurements. We propose the new algorithm of the impedance measurement data analysis for the particles’ concentration dependence of conductivity σ(ϕ) (where ϕ is the volume fraction of nanoparticles in suspension) for the suspensions of the diamante nanoparticles in alcohol which demonstrates the adequate correspondence of the Maxwell’s theory to the available experimental findings.

Pt nanoparticles decorated WO 3 -MWCNTs nanocomposites: Preparation, characterization, and adsorption behavior

Abstract A novel multi-walled carbon nanotubes–WO3–Pt nanocomposite (Pt-WO3-MWCNTs) was synthesized using a simple facile two-step precipitation method. Several analytical techniques such as X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, were used for the surface characterization of the synthesized nanocomposites and the specific surface area of the synthesized nanocomposites i.e. WO3-MWCNTs and Pt-WO3-MWCNTs using BET method was found to be 24.31 and 37.81 m2/g respectively. Effective parameters such as pH, reaction time, temperature, and initial concentrations which plays a significant role in adsorption phenomenon of typical hazardous pharmaceutical waste on Pt-WO3-MWCNTs was optimized using the batch adsorption experiments and the optimized values of pH, and contact time is 5, and 1 h respectively. It was observed that the warfarin uptake decreases from 141.2 mg/g to 121.1 mg/g as the solution pH increases from 5 to 9. Non-linear regression method was adopted to analyze the obtained equilibrium data in terms of Langmuir, Freundlich, and Temkin models. The Langmuir isotherm fitted the equilibrium data best among the four models, and the adsorption capacity increased with the temperature increased from 5 °C to 35 °C. Hence, Pt-WO3-MWCNTs could be used as an efficient adsorbent for adsorption of warfarin.

Removal of amitraz from aqueous solutions on clay by adsorption technique at industrial scale

Abstract Amitraz (AZ) that is used as acaricide was extracted by using clay adsorbent. The experimental data were modeled via Langmuir and Freundlich isotherms in which adsorption data fit well. The monolayer adsorption capacity was found as 28.53 mg × g−1 at a temperature of 30 °C. The effects of the phases contact time, the initial solution pH value and the initial pesticide concentration were investigated regarding the points of adsorption equilibrium and yield. The adsorption kinetics were investigated by applying pseudo-first-order, pseudo-second-order and intra-particle diffusion laws. Adsorption of AZ was found to be best fitted by the pseudo-second-order model. The intra-particle diffusion also plays an important role in adsorption phenomenon. This adsorption is a physical and spontaneous phenomenon. The pesticide removal by adsorption technique was successfully applied in industrial plants.

Role of Adsorption Phenomena in Cubic Tricalcium Aluminate Dissolution.

The workability of fresh Portland cement (PC) concrete critically depends on the reaction of the cubic tricalcium aluminate (C3A) phase in Ca- and S-rich pH >12 aqueous solution, yet its rate-controlling mechanism is poorly understood. In this article, the role of adsorption phenomena in C3A dissolution in aqueous Ca-, S-, and polynaphthalene sulfonate (PNS)-containing solutions is analyzed. The zeta potential and pH results are consistent with the isoelectric point of C3A occurring at pH ∼12 and do not show an inversion of its electric double layer potential as a function of S or Ca concentration, and PNS adsorbs onto C3A, reducing its zeta potential to negative values at pH >12. The S and Ca K-edge X-ray absorption spectroscopy (XAS) data obtained do not indicate the structural incorporation or specific adsorption of SO42- on the partially dissolved C3A solids analyzed. Together with supporting X-ray ptychography and scanning electron microscopy results, a model for C3A dissolution inhibition in hydrated PC systems is proposed whereby the formation of an Al-rich leached layer and the complexation of Ca-S ion pairs onto this leached layer provide the key inhibiting effect(s). This model reconciles the results obtained here with the existing literature, including the inhibiting action of macromolecules such as PNS and polyphosphonic acids upon C3A dissolution. Therefore, this article advances the understanding of the rate-controlling mechanism in hydrated C3A and thus PC systems, which is important to better controlling the workability of fresh PC concrete.

Adsorption of phenolic compounds and color from bleached Kraft mill effluent using allophanic compounds

Synthetic and natural allophanic compounds were used to evaluate the phenolic compounds and color removal capacity from a biological treated softwood bleached Kraft mill effluent. Kinetics studies and solid/solution relationship using synthetic allophanic compounds were studied and compared with powder activated carbon adsorption. On the other hand, the pH effect (4 to 9) on allophanic compounds adsorption was studied. The adsorption capacity of three allophanic soil profiles (10–20, 20–40 and 40–60 cm) activated by washing the soil with H 2SO 4, 0.1 M, and by calcination at 550°C was also evaluated. Kinetics studies showed that the adsorption half-time was 2 min in both activated carbon and synthetic allophanic compounds and more than 90 and 70% removal occurred in the first 5 min, respectively. The adsorption of color and phenolic compounds increased with decreasing solid/solution ratio in both activated carbon and synthetic allophanic compounds. pH plays an important role in adsorption phenomena. Phenolic compounds and color removal increased with the decreasing of suspension-effluent pH, obtaining the optimum at pH 5.0 with 87 and 96% removal, respectively. Phenolic compounds and color removal were near 90 and 75% when 20–40 cm acidified and calcinated soil profile was used, respectively. The organic matter content in the 10–20 cm soil profile and the low content of the fine colloidal fraction in the 40–60 cm profile reduced the removal capacity of the allophanic soil.

The role of adsorption phenomena in capillary gas‐liquid‐solid chromatography

AbstractThe method of invariant relative retention value determination using commerciallly produced fused silica open‐tubular columns with different contents of stationary liquid phase has been tested. Invariant retention values are determined only by interaction of analyzed compound with stationary liquid phase and are independent of the adsorptive interactions in the studied system.

Role of adsorption phenomena in the electrocatalytic reduction of nitric acid at a platinized platinum electrode

The electrocatalytic reduction of nitric acid was studied at a platinized platinum electrode in the presence of different supporting electrolytes. It has been found that at low HNO 3 concentrations the polarization behaviour, the shape of the polarization curves and the reduction rate depend significantly upon the supporting electrolyte. (For instance, one maximum in HClO 4, two maxima in H 2SO 4.) With increasing nitric acid concentrations the differences in the character of the polarization curves gradually disappear. The phenomena observed can be explained by the role of competitive adsorption between nitric acid and ions of the supporting electrolyte. Strongly adsorbing chloride ions exert a very pronounced influence on the reduction rate and induce periodical phenomena under certain experimental conditions. The adsorption of chloride ions was studied by a radiotracer method. Results of this study confirm the view on the importance of adsorption competition in the polarization behaviour. On the basis of simple adsorption models an attempt was made to explain the phenomena observed.

Surface chemical compounds on siliceous adsorbents and their role in adsorption phenomena : I. Ye. Neimark, Neftekhimiya 3, No. 1, 149–158, 1963

Surface chemical compounds on siliceous adsorbents and their role in adsorption phenomena : I. Ye. Neimark, Neftekhimiya 3, No. 1, 149–158, 1963