Showing papers on "Enthalpy published in 2016"
TL;DR: Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decomposition to lead iodide and methylammonium iodide, thus limiting its long-term use in devices.
Abstract: Hybrid perovskites, especially methylammonium lead iodide (MAPbI3), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chemical and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decomposition to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl3, MAPbBr3, MAPbI3, with only the chloride having a negative heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodynamic guide for seeking chemical substitutions to enhance stability.
314 citations
TL;DR: It is argued that the activation enthalpy reduction is directly related to the photoelectrochemical potential built-up on the Au nanoparticle under steady-state light excitation, analogous to electrochemical activation.
Abstract: The activation energy of a catalytic reaction serves not only as a metric of the efficacy of a catalyst but also as a potential indicator of mechanistic differences between the catalytic and noncatalytic reaction. However, activation energies are quite underutilized in the field of photocatalysis. We characterize in detail the effect of visible light excitation on the activation enthalpy of an electron transfer reaction photocatalyzed by plasmonic Au nanoparticles. We find that in the presence of visible light photoexcitation, the activation enthalpy of the Au nanoparticle-catalyzed electron transfer reaction is significantly reduced. The reduction in the activation enthalpy depends on the excitation wavelength, the incident laser power, and the strength of a hole scavenger. On the basis of these results, we argue that the activation enthalpy reduction is directly related to the photoelectrochemical potential built-up on the Au nanoparticle under steady-state light excitation, analogous to electrochemical...
172 citations
TL;DR: In this paper, the cosmological constant is interpreted as thermodynamic pressure and treated as a thermodynamic variable in its own right, whereas the mass of the black hole is identified with the chemical enthalpy.
Abstract: We review recent developments on the thermodynamics of black holes in extended phase space, where the cosmological constant is interpreted as thermodynamic pressure and treated as a thermodynamic variable in its own right. In this approach, the mass of the black hole is no longer regarded as internal energy, rather it is identified with the chemical enthalpy. This leads to an extended dictionary for black hole thermodynamic quantities, in particular a notion of thermodynamic volume emerges for a given black hole spacetime. This volume is conjectured to satisfy the reverse isoperimetric inequality - an inequality imposing a bound on the amount of entropy black hole can carry for a fixed thermodynamic volume. New thermodynamic phase transitions naturally emerge from these identifications. Namely, we show that black holes can be understood from the viewpoint of chemistry, in terms of concepts such as Van der Waals fluids, reentrant phase transitions, and triple points. We also review the recent attempts at extending the AdS/CFT dictionary in this setting, discuss the connections with horizon thermodynamics, applications to Lifshitz spacetimes, and outline possible future directions in this field.
165 citations
15 Sep 2016
TL;DR: Copper(II) oxide nanoparticles were synthesized at low temperature using cold finger assisted magnetron sputtering technique and were applied as adsorbent for the rapid removal of noxious Cr(VI) ions from the solvent phase and were in good agreement with the pseudo second order kinetic behaviour.
Abstract: Copper(II) oxide nanoparticles were synthesized at low temperature using cold finger assisted magnetron sputtering technique and were applied as adsorbent for the rapid removal of noxious Cr(VI) ions from the solvent phase. The average size of CuO nanoparticles from TEM analysis was found to be 8 nm in addition to this the BET surface area (84.327 m2/g) was found to be significantly high in comparison to the previously CuO nanoparticles synthesized via green route. The synthesized CuO nanoparticles is crystalline in nature and exhibits monoclinic phase, which was confirmed using various analytical techniques such as SAED, XRD and Raman analysis. The impact of influential parameters including pH, adsorbent dose, contact time, stirring speed, initial Cr(VI) ions concentration, and temperature were optimized using batch adsorption method in order to obtain maximum removal of Cr(VI) ions. From the thermodynamic parameters, the positive value of enthalpy (ΔH) and negative value of Gibbs free energy (ΔG) indicate the endothermic and spontaneous nature of Cr(VI) ions adsorption, respectively. The adsorption kinetics data was well fitted and found to be in good agreement with the pseudo second order kinetic behaviour.
131 citations
TL;DR: In this article, a simple composite of paraffin with cross-linking phase-change structure was used to obtain novel phase change materials with high phase change enthalpy and form-stable characteristics.
121 citations
TL;DR: In this article, a chitosan/activated charcoal (or carbon) composite was obtained in one step, characterized several techniques such as by Fourier transform infrared spectroscopy, scanning electron microscopy and dynamic light scattering, Brunauer-Emmet-Teller, thermogravimetric analysis/differential thermal analysis and differential scanning calorimetry techniques.
121 citations
TL;DR: In this article, the thermodynamic properties of four doped lanthanum manganites, namely La0.6A 0.6Ca 0.1−yAlyO3 (A, Ca, Sr and y = 0, 0.4MnO3 by the divalent Ca but also increases significantly when additionally doping 40%% Al to the Mn-site.
115 citations
TL;DR: This article reports on the calibration and validation of a new GROMOS-compatible parameter set 2016H66 for small organic molecules in the condensed phase, based on 62 organic molecules spanning the chemical functions alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, amide, thiol, sulfide, and disulfide, as well as aromatic compounds and nucleic-acid bases.
Abstract: This article reports on the calibration and validation of a new GROMOS-compatible parameter set 2016H66 for small organic molecules in the condensed phase. The calibration is based on 62 organic molecules spanning the chemical functions alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, amide, thiol, sulfide, and disulfide, as well as aromatic compounds and nucleic-acid bases. For 57 organic compounds, the calibration targets are the experimental pure-liquid density ρliq and the vaporization enthalpy ΔHvap, as well as the hydration free energy ΔGwat and the solvation free energy ΔGche in cyclohexane, at atmospheric pressure and at (or close to) room temperature. The final root-mean-square deviations (RMSD) for these four quantities over the set of compounds are 32.4 kg m(-3), 3.5 kJ mol(-1), 4.1 kJ mol(-1), and 2.1 kJ mol(-1), respectively, and the corresponding average deviations (AVED) are 1.0 kg m(-3), 0.2 kJ mol(-1), 2.6 kJ mol(-1), and 1.0 kJ mol(-1), respectively. For the five nucleic-acid bases, the parametrization is performed by transferring the final 2016H66 parameters from analogous organic compounds followed by a slight readjustment of the charges to reproduce the experimental water-to-chloroform transfer free energies ΔGtrn. The final RMSD for this quantity over the five bases is 1.7 kJ mol(-1), and the corresponding AVED is 0.8 kJ mol(-1). As an initial validation of the 2016H66 set, seven additional thermodynamic, transport, and dielectric properties are calculated for the 57 organic compounds in the liquid phase. The agreement with experiment in terms of these additional properties is found to be reasonable, with significant deviations typically affecting either a specific chemical function or a specific molecule. This suggests that in most cases, a classical force-field description along with a careful parametrization against ρliq, ΔHvap, ΔGwat, and ΔGche results in a model that appropriately describes the liquid in terms of a wide spectrum of its physical properties.
108 citations
TL;DR: In this paper, the results showed that the optimum removal efficiency of 69% was achieved at a current density of 0.1 µm − 2 and pH of 7.0 µm.
101 citations
TL;DR: In this article, the adsorption is controlled by an entropy effect rather than an enthalpy change and the maximum removal has been achieved in the pH range of 4-8 at 150-rpm.
91 citations
TL;DR: In this article, the solubility of sulfamethazine (SMT) in {methanol (1) + water (2)} co-solvent mixtures was determined at five different temperatures from (293.15 to 313.15)
TL;DR: This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites, and yields results that agree with experiment within chemical accuracy limits.
Abstract: The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre-exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude).
TL;DR: In this article, the third generation cephalosporin antibiotic drug ceftriaxone sodium trihydrate (CFT) with a cationic conventional surfactant cetyltrimethylammonium bromide (CTAB) has been carried out by conductometric technique in water and in the presence of various salts such as NaCl, Na2SO4 and Na3PO4 at varying temperatures with gaps of T = 5 K.
TL;DR: In this article, a thermochemical energy storage media with CaBxMn1-xO3-δ perovskites was proposed for concentrating solar power plants.
Abstract: Developing efficient thermal storage for concentrating solar power plants is essential to reducing the cost of generated electricity, extending or shifting the hours of operation, and facilitating renewable penetration into the grid. Perovskite materials of the CaBxMn1-xO3-δ family, where B = Al or Ti, promise improvements in cost and energy storage density over other perovskites currently under investigation. Thermogravimetric analysis of the thermal reduction and reoxidation of these materials was used to extract equilibrium thermodynamic parameters. Lastly, the results demonstrate that these novel thermochemical energy storage media display the highest reaction enthalpy capacity for perovskites reported to date, with a reaction enthalpy of 390 kJ/kg, a 56% increase over previously reported compositions.
TL;DR: In this paper, the authors demonstrate that a liquid-cooled Au-based metallic glass can achieve very high kinetic stability by an optimal annealing treatment to yield a large increase in Tg,h of 28 K, which is 3-5 times larger than the increase usually reported.
TL;DR: A quasi-harmonic approximation is coupled with fragment-based hybrid many-body interaction calculations to predict thermal expansion and finite-temperature thermochemical properties in crystalline carbon dioxide, ice Ih, acetic acid and imidazole.
Abstract: Molecular crystals expand appreciably upon heating due to both zero-point and thermal vibrational motion, yet this expansion is often neglected in molecular crystal modeling studies. Here, a quasi-harmonic approximation is coupled with fragment-based hybrid many-body interaction calculations to predict thermal expansion and finite-temperature thermochemical properties in crystalline carbon dioxide, ice Ih, acetic acid and imidazole. Fragment-based second-order Moller-Plesset perturbation theory (MP2) and coupled cluster theory with singles, doubles and perturbative triples [CCSD(T)] predict the thermal expansion and the temperature dependence of the enthalpies, entropies and Gibbs free energies of sublimation in good agreement with experiment. The errors introduced by neglecting thermal expansion in the enthalpy and entropy cancel somewhat in the Gibbs free energy. The resulting ∼ 1-2 kJ mol(-1) errors in the free energy near room temperature are comparable to or smaller than the errors expected from the electronic structure treatment, but they may be sufficiently large to affect free-energy rankings among energetically close polymorphs.
TL;DR: In this article, the adsorption of CH4 and CO2 onto illitic clay was investigated at the temperatures 298, 313, 328, 358, and 423 K (25, 40, 55, 85, and 150 °C) over a range of pressures up to 50 MPa using GCMC simulations.
Abstract: The adsorption of CH4 and CO2 onto illitic clay was investigated at the temperatures 298, 313, 328, 358, and 423 K (25, 40, 55, 85, and 150 °C) over a range of pressures up to 50 MPa using grand canonical Monte Carlo (GCMC) simulations. Our simulation results showed spontaneous and exothermic adsorption behavior of illite for CH4 and CO2 with enthalpy changes of −3.50 kJ/mol and −25.09 kJ/mol, respectively. Our results indicated that the interlayer counter cations (K+) play an important role in CO2 adsorption. Methane adsorption is mainly affected by the clay surface layers rather than the interlayer counter cations. The density and volume of CH4 and CO2 in their adsorbed phase at saturation were extrapolated from the linear portion of the excess adsorption isotherm. The resulting values were compared with available experimental data, and possible factors causing inconsistency were described. We discussed some issues associated with the Langmuir fit to experimental excess adsorption data in the case of lo...
TL;DR: In this paper, a binary Fe(III)-Sn(IV) mixed oxide-coated sand (ITOCS) has shown 89.33 and 93.59% efficiencies from their 500μg/L solutions, respectively.
TL;DR: In this article, the solubility of N-phenylanthranilic acid in nine pure organic solvents including methanol, ethanol, acetone, acetonitrile, ethyl acetate, n-propanol, isopropanol, 1-butanol and toluene was determined experimentally by using the isothermal saturation method within the temperature range from (283.15 to 318.15) K under atmosphere pressure.
TL;DR: Characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorbate-adsorbate enthalPies of MOF-801 are nearly constant for a wide range of vapor uptakes.
Abstract: Water adsorption is becoming increasingly important for many applications including thermal energy storage, desalination, and water harvesting. To develop such applications, it is essential to understand both adsorbent-adsorbate and adsorbate-adsorbate interactions, and also the energy required for adsorption/desorption processes of porous material-adsorbate systems, such as zeolites and metal-organic frameworks (MOFs). In this study, we present a technique to characterize the enthalpy of adsorption/desorption of zeolites and MOF-801 with water as an adsorbate by conducting desorption experiments with conventional differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). With this method, the enthalpies of adsorption of previously uncharacterized adsorbents were estimated as a function of both uptake and temperature. Our characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorption enthalpies of MOF-801 are nearly constant for a wide range of vapor uptakes.
TL;DR: In this article, the adsorption equilibrium isotherms of CO on the adsorbents at temperatures up to 333 K can be well fitted by both the Langmuir and Sips models.
TL;DR: In this paper, the adsorbent of Fe3O4-chitosan hybrid nano-particles has been prepared and the adsorption of humic acid (HA) from aqueous solutions using batch adaption technique was performed using FTIR, XRD, TEM, EDX, BET and TGA.
Abstract: The adsorbent of Fe3O4-chitosan hybrid nano-particles have been prepared. In this process, these materials were initially synthesized by chemical co-precipitation and then cross-linked with chitosan to coat on the surface of Fe3O4 nano-particles. The characterization of the synthesized Fe3O4-chitosan hybrid nano-particles was performed using FTIR, XRD, TEM, EDX, BET and TGA. Finally, the Fe3O4-chitosan hybrid nano-particles were used for the adsorption of humic acid (HA) from aqueous solutions using batch adsorption technique. The influences of contact time, pH, adsorbent dosages, initial concentration of HA and temperatures on the adsorption process were studied. The adsorption isotherms were better fitted by Langmuir isotherm with the adsorption capacity was found to be 44.84 mg/g. The results of the kinetic study showed that the adsorption of HA onto Fe3O4-chitosan hybrid nano-particles could be described by the pseudo second order kinetic model with a rate constant in the range of 0.032–0.104 g mg−1 min−1, respectively. Thermodynamic parameters data indicated that the HA adsorption process was non spontaneous and endothermic under the experimental conditions, with the values of Gibbs free energy (ΔGo) were in the range of 2.92–4.65 kJ/mol; as well as the values of enthalpy (ΔHo), entropy (ΔSo) and the activation energy (Ea) were found to be 21.80 kJ/mol, 57.55 J/mol and 19.27 kJ/mol, respectively. The computational chemistry study showed that the interaction between adsorbent and HA was occurred through the interaction between amine groups of chitosan and phenol groups of HA. The adsorption of HA from real sample using the prepared adsorbents showed that the Fe3O4-chitosan hybrid nano-particles has higher adsorption percentages than both Fe3O4 nano-particles and pure chitosan.
TL;DR: In this paper, the effect of L-phenylalanine methyl ester hydrochloride (PMEH) on the corrosion of mild steel (MS) in 1 M HCl solution was investigated at different concentrations and temperatures (30-60 °C) by using weight loss measurements, potentiodynamic polarization measurement, electrochemical impedance spectroscopy, and UV-visible spectrophotometry, and quantum chemical calculations.
Abstract: The inhibitive effect of L-phenylalanine methyl ester hydrochloride (PMEH) on the corrosion of mild steel (MS) in 1 M HCl solution was investigated at different concentrations and temperatures (30–60 °C) by using weight loss measurements, potentiodynamic polarization measurement, electrochemical impedance spectroscopy (EIS), UV-visible spectrophotometry, and quantum chemical calculations. The obtained results revealed that PMEH is a good inhibitor for the corrosion of MS in HCl solution. The inhibition efficiency (IE) increased with the inhibitor concentration up to 400 ppm as well as with a rise in temperature, which is suggestive of a chemical adsorption mechanism. The adsorption of inhibitor onto the MS surface was found to obey the Langmuir adsorption isotherm. Thermodynamics of adsorption such as enthalpy of adsorption (ΔH), entropy of adsorption (ΔS), equilibrium of adsorption (Kads), Gibbs free energy (ΔG°), activation and synergism parameters (S1) were calculated and discussed. Corrosion attack morphologies as observed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) qualitatively verify the results obtained by gravimetric as well as electro-chemical methods. The results obtained from all the techniques are in good agreement.
TL;DR: In this article, the removal of toxic metal, cadmium, by using adsorption into Algerian cork biomass was investigated, and the results showed that equilibrium was reached within 1h.
TL;DR: In this paper, the Pitzer-Simonson-Clegg (PSC) model was used to simulate the thermodynamic properties of binary salt lake brine systems, including water activity, osmotic coefficient, mean ionic activity coefficient, enthalpy of dilution and solution, relative apparent molar entropy, heat capacity of aqueous phase and solid phases.
Abstract: This study is part of a series of studies on the development of a multi-temperature thermodynamically consistent model for salt lake brine systems. Under the comprehensive thermodynamic framework proposed in our previous study, the thermodynamic properties of the binary systems (i.e., NaCl+H2O, KCl+H2O, MgCl2+H2O and CaCl2+H2O) are simulated by the Pitzer–Simonson–Clegg (PSC) model. Various thermodynamic properties (i.e., water activity, osmotic coefficient, mean ionic activity coefficient, enthalpy of dilution and solution, relative apparent molar enthalpy, heat capacity of aqueous phase and solid phases) are collected and fitted to the model equations. The thermodynamic properties of these systems are reproduced or predicted by the obtained model parameters. Comparison to the experimental or model values in the literature suggests that the model parameters determined in this study can describe all of the thermodynamic and phase equilibria properties over wide temperature and concentration ranges. This modeling study of binary systems provides a solid basis for property predictions of salt lake brines under complicated conditions.
TL;DR: In this article, the feasibility of using dried plants to remove As(V) from aqueous solution under different experimental conditions was reported. And the experimental data were analyzed using Freundlich, Langmuir, and Temkin isotherm models to determine the mechanistic parameters related to the adsorption process.
TL;DR: In this article, the solubility of terephthaldialdehyde in ten solvents of ethanol, n-propanol, 1-butanol, isopropanol, benzyl alcohol, 2-butanone, acetonitrile, and isopentanol were determined by an isothermal saturation method at temperatures ranging from (273.15 to 318.15) K under atmospheric pressure.
TL;DR: In this paper, HCl activated (HK) and untreated (UnK) Egyptian (Sinai) kaolin were characterized and the adsorption parameters of Pb(II) on UnK and HK were examined in aqueous solutions.
Abstract: HCl activated (HK) and untreated (UnK) Egyptian (Sinai) kaolin were characterized. The adsorption parameters of Pb(II) on UnK and HK were examined in aqueous solutions. The equilibrium adsorption data were described using Langmuir and Freundlich adsorption isotherm models. The monolayer adsorption capacities were 34.5 and 23.8 mg g −1 at pH 5.5 and 25 °C for the HK and UnK, respectively. The experimental data fitted well the pseudo-second-order kinetics model. The thermodynamic parameters standard Gibbs free energy (Δ G °), enthalpy (Δ H °) and entropy changes (Δ S °) for the adsorption process were calculated. The negative value of the Gibbs free energy confirms that the adsorption processes are spontaneous and thermodynamically favorable while the positive value of Δ H ° supports the endothermic physical adsorption process. HK was applied successfully for removing Pb(II) (67.5–99.3%) from spiked water samples and >98% of the loaded Pb(II) ions was recovered by 1 mol L −1 HNO 3 . The successful removal of Pb(II) from the studied water samples indicates that HK can be used efficiently for pollution remediation of fresh water from lead.
TL;DR: In this article, the solubility of CO2 in five deep eutectic solvents (DESs) at temperatures (303.15-333.15) K with 10 K intervals under a pressure of (0-600.0)kPa using isochoric saturation method.
TL;DR: In this article, the authors used the exact muffin-tin orbital method combined with coherent potential approximation (EMTO-CPA) for over 2700 compositions of the NiFeCrCo alloy as a single-phase solid solution in paramagnetic state.