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Motivated by recents results for the double‐layer on Pt(111), I reexamine the theory of weak adsorption on double‐layer properties, and use it to explore the capacitance at low electrolyte concentrations. Even a very weak adsorption enhances the double layer capacitance, so that it may exceed the value CGC predicted by Gouy‐Chapman theory. A Parsons‐Zobel plot of 1/C vs. 1/CGC for the experimental capacity C does not result in a straight line of unit slope, but roughly follows a linear relation with smaller slope. These results are in line with older data on Ag(111), and with the new data on Pt(111). [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Pomelo (Citrus grandis) is the largest citrus fruit, the peel of which is a well‐known agricultural wastes. Disposal of pomelo peel after consumption is a serious environment problem. As a natural, versatile bio‐absorbent, pomelo peel has shown excellent adsorption capacity for several pollutants, attributed to its micro‐pores; however, there is no relevant report on its adsorption capacity for natural products or food ingredients. The ability of pomelo peel to adsorb epigallocatechin‐3‐gallate (EGCG) was examined in this study. The physicochemical characterizations of pomelo peel were determined by Fourier transform infrared spectroscopy, scanning electron microscopy and high‐performance liquid chromatography. The adsorption process of EGCG onto pomelo peel from aqueous solution was carried out at a range of concentrations (50–800 mg L−1) and temperatures (25, 40 and 55 °C). RESULTS: The main components of pomelo peel are composed of dietary fiber, which provide sufficient adsorption sites during the adsorption process. The adsorption of EGCG onto pomelo peel showed excellent fitness with a pseudo‐second‐order model. Both Langmuir and Freundlich models were able to describe the isothermal adsorption of EGCG onto pomelo peel. The results of thermodynamic analysis suggested that adsorption is spontaneous and endothermic in nature, and that the process is likely to be dominated by a physisorption mechanism. CONCLUSION: The results of this study indicate that pomelo peel has potential adsorption capacity for EGCG, which can be used as an effective, low‐cost carrier for delivery of natural products in functional food and dietary supplement applications. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Silicate‐bearing hectorites (laponite) were synthesized by hydrothermal method, and the laponite sample was characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), zeta potential, Brunauer‐Emmett‐Teller (BET) surface area, and pore size analyses. The adsorption of Ni(II) from aqueous solution on laponite as a function of contact time, pH, ionic strength, laponite dosage, and temperature was studied via batch technique. The maximum removal of 99% (approx) could be achieved at the optimum adsorbent dosage of 2.5 g L−1 and near‐neutral pH. Adsorption of Ni(II) on laponite is strongly dependent on pH but independent on ionic strength. At low pH, the adsorption of Ni(II) was dominated by ion exchange with Li+ on laponite surfaces, whereas inner‐sphere surface complexation and surface precipitation were the main adsorption mechanisms at near‐neutral pH and alkaline environment, respectively. The adsorption kinetic data of Ni(II) on laponite were well described by the pseudo‐second‐order kinetics model. The intraparticle diffusion was involved in the adsorption process but was not the only rate‐controlling step. The adsorption isotherms of Ni(II) on laponite can be described well by the Langmuir model and the maximum Ni(II) adsorption capacity of laponite obtained from Langmuir model was 65.79 mg g−1. The thermodynamic studies indicated that the adsorption of Ni(II) on laponite was endothermic and spontaneous. The laponite exhibited excellent adsorption properties for Ni(II) uptake compared with various adsorbents, indicating that it is a suitable material as an adsorbent for preconcentration and immobilization of Ni(II) from aqueous solution. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 942–950, 2018 [ABSTRACT FROM AUTHOR]

Cerium oxide (CeO2) nanoparticles of size 3–5 nm and surface area 257 m2 g−1 were synthesized using simple, single‐pot, and surfactant‐free aerogel process. Efforts were made to tune the surface area and porosity of CeO2 nanoparticles by changing the concentration of precursors. CeO2 nanoparticles were characterized by TEM, SEM, XRD, N2‐BET, and FTIR. Prepared CeO2 was used to remove As(III) and As(V) from water at variable contaminant concentrations (25–100 ppm) and pH (3–10). The adsorption process found extremely fast for the first few minutes of exposure. CeO2 nanoparticles indicated adsorption capacities of 71.9 and 36.8 mg g−1 against As(III) and As(V), respectively. The adsorption data best fitted with Redlich–Peterson model, depicting monolayer adsorption. The adsorption followed pseudo‐second‐order kinetics and intraparticle diffusion with three‐step diffusion process. The effect of co‐existing anions (H2 PO 4 −, SO 4 2 −, and HCO 3 −) indicated 80–96% reduction in adsorption capacity. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 221–231, 2018 [ABSTRACT FROM AUTHOR]

In this study, a natural loess soil was evaluated as an adsorbent of Li+ in seawater. Only Li+ was adsorbed preferentially by loess over other cations in seawater despite having the lowest concentration. The adsorption studies of Li+ with loess were assessed using the batch equilibration method. In batch adsorption experiment, the various factors such as agitation time, initial concentration, and amount of dose were investigated. Adsorption isotherm and kinetic studies were performed to quantify the adsorption capacity and adsorption rate of Li+ by loess from seawater. The equilibrium data of adsorption were fitted by using the Freundlich and Langmuir isotherm models. It was seen that the Langmuir isotherm is better in describing the adsorption process of Li+ by loess due to its higher correlation coefficient R2 value. The maximum adsorption capacity of loess for Li+ obtained by Langmuir isotherm was 0.193 mg/g. The pseudo-first-order, the pseudo-second-order, and the intra-particle diffusion kinetic models were employed to analyze the time-dependent adsorption rate of Li+. It was found that the adsorption of Li+ closely follows the pseudo-second-order kinetic model, from which a very accurate estimation of the equilibrium adsorption capacity ( qe,cal) was achieved, as well as the higher R2. Because of its low-cost and high selectivity towards Li+, loess could be probably an applicable adsorbent for the recovery of Li+ from seawater. [ABSTRACT FROM AUTHOR]

This article presents the immobilization of nanostructured biosilica within calcium alginate biopolymer and its potential for the adsorption of Direct Red 12B (DR12B) as an azo dye in batch flow mode reactors. The immobilization of biosilica was performed well according to the images of scanning electron microscopy. Moreover, the results of Fourier transform infra-red analysis confirmed strong binding of dye molecules by surficial functional groups. The adsorption process was pH-dependent and increasing initial pH from 3 to 11 led to the decrease in adsorbed dye from 16.02 to 11.88 mg/g, respectively. Increasing adsorbent dosage from 0.5 to 4 g/L led to decreasing the adsorption of DR12B from 75.13 to 12.10 mg/g, respectively. Among various isotherm models, Langmuir isotherm had the highest correlation coefficient (R2 = 0.9924) with a maximum adsorption capacity of 33.78 mg/g. The value of mean free energy (E = 15.81 KJ/mol) related to Dubinin-Radukevisch (D-R) model demonstrated chemical nature of the adsorption process. The results of kinetic study revealed the fitness of experimental data to pseudo-second order model. The negative values of Gibbs free energy (ΔG°) and enthalpy change (ΔH°) suggested a simultaneous and exothermic adsorption process, respectively. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1435-1443, 2015 [ABSTRACT FROM AUTHOR]

Activated carbon was prepared from Citrus limettioides seed (CLSC), a novel waste material by chemical modification with sulfuric acid was applied for the adsorption Ni(II) from aqueous solutions. The effect of contact time, pH, adsorbent dose, initial metal ion concentration, and temperature were studied in batch experiments. According to the experimental results, the equilibrium time, optimum pH range, and adsorbent dosage were found to be 3 h, pH = 4.0-8.0 and 1 g L−1, respectively. In addition, raw Citrus limettioides seeds (CLS) were used as adsorbents at the same parameters. Ni(II) removal for CLSC and CLS were obtained 99.00% and 37.00% in turn. The equilibrium data agreed well with Langmuir model, which confirmed the monolayer coverage of Ni(II) ions onto CLS and CLSC. The Langmuir monolayer adsorption capacity of the CLSC was found to be 36.06 mg g−1 which was significantly about 3.5 times greater than that of CLS (10.23 mg g−1) at 300 K. The kinetic data followed pseudo-second order model and intra-particle diffusion was not the sole rate-controlling factor. Surface morphology and structural analysis of CLSC prior to and after adsorption were characterized by SEM and EDX. The presence of hydroxyl, carboxylic, and sulfonic acid groups are confirmed by FTIR spectra. The adsorbents were also tested for the removal of Ni(II) from electroplating wastewater in connection with the reuse and selectivity of the adsorbents. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1384-1395, 2015 [ABSTRACT FROM AUTHOR]

Prediction of multicomponent adsorption equilibria has been investigated for several decades. While there are theories available to predict the adsorption behavior of ideal mixtures, there are few purely predictive theories to account for nonidealities in real systems. Most models available for dealing with nonidealities contain interaction parameters that must be obtained through correlation with binary-mixture data. However, as the number of components in a system grows, the number of parameters needed to be obtained increases exponentially. Here, a generalized procedure is proposed, as an extension of the predictive real adsorbed solution theory, for determining the parameters of any activity model, for any number of components, without correlation. This procedure is then combined with the adsorbed solution theory to predict the adsorption behavior of mixtures. As this method can be applied to any isotherm model and any activity model, it is referred to as the generalized predictive adsorbed solution theory. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2600-2610, 2015 [ABSTRACT FROM AUTHOR]

The aim of the present study is to explore the possibility of utilizing fly ash, loess and activated charcoal for the adsorption of Li in aqueous solution. Batch adsorption experiments were performed to evaluate the influences of various factors like initial concentration, contact time, and temperature. The adsorption data showed that fly ash and activated charcoal are not effective for the adsorption of Li. On the contrary, loess showed much higher adsorption capacity for Li. The adsorption of Li on loess was highly concentration dependent. It was found that the adsorption capacity of loess is favored at a lower Li concentration. At equilibrium, approximately 95% of adsorption was achieved by loess. The equilibrium data were fitted well to the Freundlich isotherm model. The pseudo-second-order kinetic model appeared to be the better-fitting model because it has higher R2 compared to the pseudo-first-order kinetic models. The thermodynamic parameters such as free energy Δ G, the enthalpy Δ H, and the entropy Δ S were calculated. [ABSTRACT FROM AUTHOR]

A study on the removal of hexavalent chromium ions from aqueous solution by using activated carbon prepared from Ricinus communis has been done. In this process, it was carbonised and activated by treating with concentrated sulphuric acid followed by heating for 5 h at 500°C. Batch adsorption experiments are also carried out as a function of pH, contact time, initial concentration of the adsorbate, adsorbent dosage and temperature. The experimental data are fitted well to the Freundlich adsorption isotherm. Thermodynamic parameters such as Δ H°, Δ S° and Δ G° are calculated, which indicated that the adsorption is spontaneous and endothermic in nature. Adsorbent used in this study is characterised by FT-IR and SEM before and after the adsorption of Cr(VI). © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]

The potential of eggshell-a domestic waste to remove hazardous Malachite Green dye from aqueous solution was investigated in a batch experimental setup. Adsorption conditions were studied with respect to particle size, initial solution pH, adsorbent dose, contact time, initial dye concentration, and temperature. The optimum conditions for Malachite Green removal were found to be pH = 9.0, contact time = 90 min, adsorbent dose = 2.0 g L−1, initial dye concentration = 50 mg L−1. The temperature had a strong influence on the sorption process. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and surface area analysis were used to characterize the adsorbent material. FTIR analysis revealed that OH, CO, and PO4 functional groups were mainly responsible for the adsorption process. The rate of the adsorption reaction followed the pseudo second-order kinetics while the sorption equilibrium data well fitted to the Freundlich and the Langmuir isotherm models. The Arrhenius and Eyring equations were used to evaluate the activation parameters. A thermodynamic study showed spontaneous and endothermic nature of the adsorption process. Owing to its low cost and high dye uptake capacity, eggshells seem to be one of the most promising adsorbents for removal of Malachite Green from aqueous solutions. © 2011 American Institute of Chemical Engineers Environ Prog, 2011 [ABSTRACT FROM AUTHOR]

The frictional behaviors of methyl oleate (MO), methyl palmitate (MP), methyl laurate (ML), and methyl stearate (MSt) as additives in hexadecane have been examined in a boundary lubrication test regime using steel contacts. It was found that the transient attributes of coefficient of friction (COF)-time spectra are a sensitive measure of adsorption equilibria. Critical additive concentrations were defined and used to perform novel and simple Langmuir analyses that provide an order of adsorption energies: MSt > MP > MO > ML. Application of Langmuir, Temkin, and Frumkin-Fowler-Guggenheim adsorption models via nonlinear fitting of a general cooperative model demonstrates the necessary inclusion of cooperative effects in the applied model. In agreement with the qualitative features of steady-state COF-concentration plots, MSt modeling requires minimal cooperative interaction terms. However, MO, MP, and ML data require large attractive interaction terms to be adequately fitted. Primary adsorption energies calculated via the cooperative model are necessarily decreased, whereas total adsorption energies correlate well with values obtained via critical concentration analyses. These results and comparisons with previous adsorption studies of MO and MSt suggest that primary (ester-surface) and secondary (alkyl-surface) adsorbate-adsorbent, adsorbate-adsorbate, and (free-additive) adsorpt-adsorpt interactions collectively determine both the calculated primary and the cooperative interaction energies. [ABSTRACT FROM AUTHOR]

A new isotherm is presented for adsorption of proteins, the available area isotherm. This isotherm has a steric basis, unlike the (steric) mass action model. The shape of the available area isotherm is determined only by geometric exclusion. With the new isotherm, experimental results can be fitted equally well as with existing ones, such as the steric mass action model. However, it has several advantages. For fitting of single-protein isotherms one less parameter is needed, its theoretical basis is more realistic, it can be extended consistently to many components, it is applicable to adsorption by both ion-exchange and hydrophobic interaction, and it can easily be combined with equations describing the effect of pH and ionic strength to obtain a complete description of adsorption behavior. [ABSTRACT FROM AUTHOR]