Showing papers on "Enthalpy published in 2019"

Evaluation of thermodynamic parameters for adsorption of heavy metals by green adsorbents

Abstract: Thermodynamic parameters ΔG°, ΔH° and ΔS° are indicators of the possible nature of adsorption. This review summarizes the thermodynamic properties of metal adsorption by green adsorbents. Conclusively, the adsorption of heavy metals ions by green adsorbents is spontaneous in most cases (ΔG° < 0). Since the thermodynamic parameters were evaluated from very different adsorbent/adsorbate combinations, it is not possible to note a correlation between the corresponding enthalpy change (ΔH°) and entropy change (ΔS°) following adsorption.

Dielectric properties and electrocaloric effect of high-entropy (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic

Abstract: Single-phase homogeneous (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 powder with high configurational entropy was synthesized by using a solid-state method. Calculations of thermodynamic parameters and related experiments indicate that both entropy and enthalpy drive the formation of a stable system. To further research the material's performance, we sintered the powder into a ceramic, which exhibited relaxation behavior because of the disorder of the microscopic composition. In addition, an applied electric field of 145 kV/cm produces a discharge energy density of 1.02 J/cm3. Meanwhile, the adiabatic temperature is 0.63 K at 60 kV/cm. These properties suggest that the electrocaloric effect of the (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic is attractive for applications such as solid-state refrigeration and energy storage. High-entropy perovskite oxides are also highly tolerant to ions, and their properties can be tailored by tuning their composition, making them attractive for a broad range of applications.

Methylene Blue removal using polyamide-vermiculite nanocomposites: Kinetics, equilibrium and thermodynamic study

Abstract: A novel low-cost adsorbent was produced from clay mineral of vermiculite using chemical modification. The vermiculite was modified with polyamide through in-situ interfacial polymerization. Adsorption performance of the modified adsorbent was investigated for methylene blue removal from aqueous solution. The influence of various operational parameters of the adsorption process was studied through kinetics, thermodynamics, and equilibrium. Noticeable enhancement in methylene blue removal was achieved for modified vermiculite compared to that of un-modified samples. The obtained equilibrium results were fitted to Langmuir, Freundlich, Temkin, Dubinin – Radushkevich, and Sips, where Langmuir model was best followed. Maximum removal uptake was found to be 76.42 mg/g, whereas maximum removal efficiency of 99% was achieved. Pseudo-second order kinetic model was best followed for the experimental kinetics. The modified vermiculite was characterized by scanning electron microscope coupled with energy dispersive spectrometer (SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer–Emmett–Teller (BET). The characterization outcome revealed that polymer chain was successfully attached to the vermiculite surface. The thermodynamic investigations showed that negative values of the free energy ΔG were reported, and the negativity was found to increase with increasing the temperature, which implies that the adsorption is spontaneous, energetic and favorable. Moreover, a positive value of enthalpy ΔH (10.98 KJ/mole) was reported, which indicated that the nature of adsorption is endothermic.

Adsorption of metronidazole antibiotic using a new magnetic nanocomposite from simulated wastewater (isotherm, kinetic and thermodynamic studies)

Abstract: This experimental study was conducted on a laboratory scale to synthesize a new magnetic nano-adsorbent and to examine its efficiency in removing metronidazole antibiotic from aqueous solutions. In this research, a new FeNi3/SiO2/CuS magnetic nanocomposite was first synthesized and its physical and structural characteristics were analyzed using FESEM, TEM, FTIR, XRD, VSM, and TGA techniques. To determine the thermodynamic parameters, the equilibrium isotherms, and adsorption process kinetics, the effect of parameters including pH (3–11), contact time (5–180 min), initial concentration of pollutant (10–30 mg/L), nanocomposite dose (0.005–0.1 g/L), and temperature (50-5 °C) were studied. Finally, the residual metronidazole concentration was determined using a UV–Vis spectrophotometer T80+ at a wavelength of 320 nm. The results related to the physical properties of the synthesized magnetic nanocomposite indicated that the particle size lied within the range of 20–65 nm and the structure of this new nano-absorbent was amorphous. Also, the FeNi3/SiO2/CuS nanocomposite had a good magnetism and its magnetic saturation was 18.42 emu/gr. Considering the efficiency of the newly synthesized nanocomposites in metronidazole absorption, the highest percentage of the pollutant adsorption was observed at pH = 7, contact time = 180 min, nanocomposite dose = 0.1 g/L, and temperature = 20 °C. With the increase in the synthesized nano-absorbent dose, the absorption percentage increased significantly (from 24.18 to 62.18). Similarly, with in the growth of the initial concentration of metronidazole from 10 to 30 mg/L, the absorption percentage declined from 85.26 to 44.6% due to the restriction of the absorption sites. Notably, as the temperature rose, the absorption percentage increased (from 37.73% to 65.15%), suggesting that the adsorption reaction was endothermic. The data obtained from Langmuir (R2 = 0.9991) and Freundlich (R2 = 0.8148) equilibrium isotherms revealed that the metronidazole absorption process through the synthesized magnetic nanocomposite was consistent with the Langmuir model. Also, the data obtained from the reaction kinetic calculations showed that the absorption of metronidazole by the adsorbent was described in accordance with a pseudo-second-order model. According to the results of the thermodynamic studies including the entropy changes (ΔS) (82.12% J/mol k), the enthalpy changes (ΔH) (0.056 kJ/mol) and the Gibbs negative free energy (ΔG), it could be concluded that the adsorption process was endothermic. In this study, the efficiency and the reusability of the synthesized magnetic nanoadsorbent were examined in the removal of metronidazole. The findings indicated that following five adsorption – desorption cycles, the efficiency of the nanoadsorbent in the removal process have a slight decrease. Regarding the results of this study, it is suggested that the magnetic nanocomposite (FeNi3/SiO2/CuS) can be a suitable new absorbent for absorption of metronidazole antibiotic from aqueous solutions. The reason is that in addition to its excellent efficiency, it can be separated from an in-vitro setting by an external magnetic field due to its great magnetic properties.

Thermodynamic Properties for Carbon Dioxide.

Abstract: We first report three reliable analytical expressions of the entropy, enthalpy and Gibbs free energy of carbon dioxide (CO2) and perform predictions of these three thermodynamic quantities on the basis of the proposed analytical expressions and in terms of experimental values of five molecular constants for CO2. The average relative deviations of the calculated values from the National Institute of Standards and Technology database over the temperature range from 300 to 6000 K are merely 0.053, 0.95, and 0.070%, respectively, for the entropy, enthalpy, and Gibbs free energy. The present predictive expressions are away from the utilization of plenty of experimental spectroscopy data and are applicable to treat CO2 capture and storage processes.

Thermodynamics of adsorption on nanocellulose surfaces

Abstract: Understanding the thermodynamic interactions of cellulose nanomaterials with their environment is important to understand the forces behind their self-organization and co-organisation with other compounds, and to be able to use self-assembly to form new functional multicomponent materials. This review analyzes published studies that determined the thermodynamic parameters of the surface interactions of and adsorption of various compounds (proteins, polymers, and small molecules/ions) onto cellulose nanomaterials. We compiled the data reported and performed a meta-analysis for better comparison and to find trends in the published data. We first introduce the methods employed and describe the adsorption isotherm models typically used to describe the adsorption thermodynamics on nanocellulose surfaces. We then discuss and analyze the published results for the interaction of the various compounds with nanocellulose surfaces. The systems that have been reported on most were adsorption of natural binding proteins and various pollutants from water, such as heavy metal ions, dyes, and drugs. Interactions between cellulose surfaces and the cellulose binding module were generally both enthalpy- and entropy-driven, where the negative binding enthalpy indicates the formation of specific interactions between peptides and the carbohydrate backbone. On the other hand, interactions with charged molecules were mostly endothermic and purely entropy-driven, indicating that the adsorption on nanocellulose surfaces can be described as an interaction between opposite charges, where the entropy increase that arises from the release of surface-structured water molecules and counterions from the electronic double layer supplies the major contribution to the free energy of adsorption. We performed a meta-analysis on all published data, and found a linear relationship between ∆H and ∆S with the slope equal to the reference temperature, irrespective of whether the interacting compound is a specific cellulose binding protein, a non-specific binding protein, a polymer, or a small molecule/ion. This indicates that the process of adsorption is the same for all compounds and takes place with a constant change in Gibbs free energy of interaction, ∆G, where a change in interaction enthalpy is offset by change in entropy change upon binding and vice versa.

Removal of heavy metals by chitin: equilibrium, kinetic and thermodynamic studies

Abstract: Adsorption is one of the most commonly used methods for the wastewaters treatment. In this work, we studied the impact of experimental conditions on the adsorption of heavy metals M(II) (M = Cd, Ni, Cu, Pb and Zn) in batch system using chitin obtained from crab shells. This biomaterial is selected because of its low cost, availability and efficiency. The M(II) adsorption was found to be dependent on the initial pH, contact time, initial concentration of M(II) and biomass dose. The kinetic models of Elovich, pseudo-first-order and pseudo-second-order kinetic models were successfully applied, providing the best fitting of the experimental data. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms and the thermodynamic parameters were also discussed. The adsorption capacity peaks at: 50, 47.61, 43.4, 40 and 38.46 (mg L−1) for Pb(II), Cu(II),Ni(II), Cd(II) and Zn(II), respectively. The negative free energy (∆G°) and positive enthalpy (∆H°) indicated spontaneous and endothermic adsorption.

Ionic association analysis of LiTDI, LiFSI and LiPF6 in EC/DMC for better Li-ion battery performances

Abstract: New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF6), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and 7Li self-diffusion coefficient have been deeply investigated. Moreover, as these properties are directly linked to the nature of the interionic interactions and ion solvation, a better understanding of the structural properties of electrolytes can be obtained. The Li salt concentration has been varied over the range of 0.1 mol L−1 to 2 mol L−1 at 25 °C and the working temperature from 20 °C to 80 °C at the fixed concentration of 1 mol L−1. Experimental results were used to investigate the temperature dependence of the salt ion-pair (IP) dissociation coefficient (αD) with the help of the Walden rule and the Nernst–Einstein equation. The lithium cation effective solute radius (rLi) has been determined using the Jones–Dole–Kaminsky equation coupled to the Einstein relation for the viscosity of hard spheres in solution and the Stokes–Einstein equation. From the variations of αD and rLi with the temperature, it is inferred that in EC/DMC LiFSI forms solvent-shared ion-pairs (SIP) and that, LiTDI and LiPF6 are likely to form solvent separated ion-pairs (S2IP) or a mixture of SIP and S2IP. From the temperature dependence of αD, thermodynamic parameters such as the standard Gibbs free energy, enthalpy and entropy for the ion-pair formation are obtained. Besides being in agreement with the information provided by the variations of αD and rLi, it is concluded that the ion-pair formation process is exergonic and endothermic for the three salts in EC/DMC.

Preparation, Characterization, and Application of Metakaolin-Based Geopolymer for Removal of Methylene Blue from Aqueous Solution

Abstract: Metakaolin-based geopolymers are aluminosilicate materials that can be used as cationic dye adsorbents in aqueous system treatment. Our aim in this paper is to study the ability of geopolymer powder produced from metakaolin and alkaline activators to act as an adsorbent to remove methylene blue (MB). The solid materials were systematically analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectrometery (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and the point of zero charge. XRF, FTIR, XRD, SEM, and EDX analyses confirmed the formation of a geopolymer composite by geopolymerization reaction. The influence of various experimental factors such as geopolymer dosage, pH, initial dye concentration, contact time, and temperature was assessed. Adsorption isotherms were evaluated by Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms. Kinetics data were studied using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The thermodynamic parameters, namely, Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), were determined. The results indicated that the maximum decolorization was found in high pH values. The collected isotherm data were best fitted by the Langmuir isotherm, and the maximum adsorption capacity of dye onto the geopolymer was 43.48 mg/g. The experiment kinetics followed the pseudo-second-order kinetic models. The thermodynamic results demonstrated that the adsorption of the obtained material occurs spontaneously as an endothermic process. The results confirmed that the prepared adsorbent can be used for remediation of water contaminated by MB dye.

The Reaction Thermodynamics during Plating Al on Graphene Process

Abstract: This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C2H5)3Al. In this reaction, the ΔH(enthalpy) was 10.64 kcal/mol, the ΔG(Gibbs free energy) was 19.87 kcal/mol and the ΔS(entropy) was 30.9 cal/(mol·K); this was an endothermic reaction. In the second stage, the (C2H5)3Al decomposed into Al atoms, which were gradually deposited on the surface of the graphene and the Al plating formed. At 298.15 K, the ΔH was −20.21 kcal/mol, the ΔG was −54.822 kcal/mol, the ΔS was 116.08 cal/(mol·K) and the enthalpy change was negative, thus indicating an endothermic reaction.