Thermodynamic analysis of sorption isotherms of chromium(VI) anionic species on reed biomass

A new sorbent material for removing Cr(VI) anionic species from aqueous solutions has been investigated. Adsorption equilibrium and thermodynamics of Cr(VI) anionic species onto reed biomass were studied at different initial concentrations, sorbent concentrations, pH levels, temperatures, and ionic strength. Equilibrium isotherm was analyzed by Langmuir model. The experimental sorption data fit the model very well. The maximum sorption capacity of Cr(VI) onto reed biomass was found to be 33 mg · g^?1. It was noted that the Cr(VI) adsorption by reed biomass decreased with increase in pH. An increase in temperature resulted in a higher Cr(VI) loading per unit weight of the adsorbent. Removal of Cr(VI) by reed biomass seems to be mainly by chemisorption. The change in entropy (ΔS^°) and heat of adsorption (ΔH^°) for Cr(VI) adsorption on reed biomass were estimated as 2205 kJ · kg^?1 · K^?1 and 822 kJ · kg^?1, respectively. The values of isosteric heat of adsorption varied with the surface loading of Cr(VI).     

The removal of uranium (VI) from aqueous solutions onto natural sepiolite

The adsorption of uranium (VI) from aqueous solutions onto natural sepiolite has been studied using a batch adsorber. The parameters that affect the uranium (VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of sepiolite and experimental results showed this to be 34.61 mg · g^?1. The experimental results were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (Q_o and b) were calculated. Thermodynamic parameters (ΔH° = ?126.64 kJ · mol^?1, ΔS° = ?353.84 J · mol^?1 · K^?1, ΔG° = ?21.14 kJ · mol^?1) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that sepiolite was suitable as sorbent material for recovery and adsorption of uranium (VI) ions from aqueous solutions.     

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C₁₄H₁₂O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be T_fus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Δ_fusH_m=(26.273±0.013) kJ · mol⁻¹ and Δ_fusS_m=(69.770±0.035) J · K⁻¹ · mol⁻¹. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Δ_cU(C₁₄H₁₂O, s)=−(7125.56 ± 4.62) kJ · mol⁻¹ and Δ_cH_m^∘(C₁₄H₁₂O, s)=−(7131.76 ± 4.62) kJ · mol⁻¹, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, Δ_fH_m^∘(C₁₄H₁₂O,s)=−(92.36 ± 0.97) kJ · mol⁻¹, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.     

The investigation of thermodynamic parameters of kinetic reaction between o-phenylenediamine and gold (III)

A visible spectrophotometric method has been developed for the reaction kinetics of o-phenylenediamine in the presence of gold (III). The method is based on the measurement of the absorbance of the reaction o-phenylenediamine and gold (III). Optimum conditions for the reaction were established as pH 6 at λ = 466 nm.When the reaction kinetic of o-phenylenediamine by gold (III) was investigated, it was observed that the following rate formula was found as ln (A/A₀) = −kt, according to absorbance measurements. The activation energy E_a and Arrhenius constant A were calculated from the Arrhenius equation as 1.009 kJ · mol⁻¹ and 3.46 · 10⁻² s⁻¹, respectively. Other activation thermodynamic parameters, entropy, ΔS (J · mol⁻¹ · K⁻¹), enthalpy, ΔH (kJ · mol⁻¹), Gibbs free energy, ΔG (kJ · mol⁻¹) and equilibrium constant, K_e were calculated at T = (283.2, 303.2, 323.2, and 343.2) K. The study was exothermic due to the decrease of entropy and was a non-spontaneous process during activation.     

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol^?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g^?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^°), enthalpy (ΔH^°), and entropy (ΔS^°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.     

Experimental study on the thermochemistry of 1-(2H)-phthalazinone and phthalhydrazide

The standard (p^° = 0.1 MPa) molar enthalpies of combustion of 1-(2H)-phthalazinone and phthalhydrazide, both in the solid phase, were measured at T = 298.15 K by static bomb calorimetry. Further, the standard molar enthalpies of sublimation, at T = 298.15 K, of these two phthalazine derivatives were derived from the Knudsen effusion technique. The combustion calorimetry results together with those obtained from the Knudsen effusion technique, were used to derive the standard molar enthalpies of formation, at T = 298.15 K, in the gaseous phase for 1-(2H)-phthalazinone and phthalhydrazide, respectively as, (79.1 ± 1.8) kJ · mol^?1 and ?(107.4 ± 2.4) kJ · mol^?1.     

Strain energy of phenanthrene

The strain energy of phenanthrene was derived to be (4.9 ± 2.8) kJ · mol⁻¹, on the basis of the latest standard enthalpies of formation of polycyclic aromatic hydrocarbons. This strain energy agrees well with those estimated from a semi-empirical calculation and from the basicity in hydrogen fluoride solution. The calculation again confirmed the standard enthalpy of formation of phenanthrene, Δ_fH⁰(g)=(201.7±2.9) kJ · mol⁻¹ at T=298.15 K, which was determined by Nagano (J. Chem. Thermodyn. 34 (2002) 377–383). The coupling constant J_4,5 in ¹H-n.m.r. spectrum of phenanthrene in CDCl₃ solution was determined to be 0.55 Hz, which indicates no significant through-space coupling between the 4- and 5-hydrogens.     

Standard molar enthalpies of formation of 2-furancarbonitrile, 2-acetylfuran,and 3-furaldehyde

The standard (p^° = 0.1 MPa) molar energies of combustion of 2-furancarbonitrile, 2-acetylfuran, and 3-furaldehyde were measured by static bomb combustion calorimetry; the Calvet high-temperature microcalorimetry was used to measure the enthalpies of vaporization of these liquid compounds. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of phase transition, as (106.8 ± 1.1) kJ · mol^?1, ?(207.4 ± 1.3) kJ · mol^?1, and ?(151.9 ± 1.1) kJ · mol^?1, for 2-furancarbonitrile, 2-acetylfuran, and 3-furaldehyde, respectively.Standard molar enthalpies of formation are discussed in terms of the isomerization ortho meta. Enthalpic increment values of the introduction of the functional groups –CN, –CHO, and –COCH₃ were also compared with some other heterocycles; i.e. thiophene and pyridine.     

Short chain lead (II) alkanoates as ionic liquids and glass formers: A d.s.c., X-ray diffraction and FTIR spectroscopy study

Three members of the lead (II) n-alkanoates (from etanoate to n-butanoate) have been synthesized, purified and studied by d.s.c., X-ray diffraction, and FTIR spectroscopy. Lead (II) acetate, propanoate, and butanoate present only a melting transition at T = (452.6, 398.2, and 346.5) K, with Δ_fH = (16.0, 13.1, and 15.6) kJ · mol⁻¹, and Δ_fS = (35.3, 32.8, and 45.1) J · mol⁻¹ · K⁻¹, respectively. These temperature data correct to a great extent the historical values reported in the literature. These three members readily quench into a glass state. Their corresponding T_g values are (314.4, 289.0, and 274.9) K, respectively, measured by d.s.c. at a heating rate of 5 K · min⁻¹.     

Sterically hindered and completely arrested nitrogen inversion in pyrazolidines

Syntheses of trans-1,2-di-tert-butylpyrazolidine 1, d,l- and semi-meso-1,2-diisopropyl-3,5-dimethylpyrazolidines, 2a and 2b, respectively, have been developed. Activation parameters of the nitrogen inversion in 1 (ΔG^≠ = 123 kJ mol⁻¹ at 110 °C, ΔH^≠ = 114 kJ mol⁻¹, ΔS^≠ = −15 J K⁻¹ mol⁻¹) have been determined. The steric veto of the nitrogen inversion in 2a has been confirmed. Chemical transformations of 1 have been studied, and the crystal structures of 2a·picrate and 2b·HCl determined.     

Thermodynamic properties of metal amides determined by ammonia pressure-composition isotherms

Thermodynamic properties of Mg(NH₂)₂ and LiNH₂ were investigated by measurements of NH₃ pressure-composition isotherms (PCI). Van’t Hoff plot of plateau pressures of PCI for decomposition of Mg(NH₂)₂ indicated the standard enthalpy and entropy change of the reactions were ΔH° = (120 ± 11) kJ · mol^?1 (per unit amount of NH₃) and ΔS° = (182 ± 19) J · mol^?1 · K^?1 for the reaction: Mg(NH₂)₂ → MgNH + NH₃, and ΔH° = 112 kJ · mol^?1 and ΔS^o = 157 J · mol^?1 · K^?1 for the reaction: MgNH → (1/3)Mg₃N₂ + (1/3)NH₃. PCI measurements for formation of LiNH₂ were carried out, and temperature dependence of plateau pressures indicated ΔH° = (?108 ± 15) kJ · mol^?1 and ΔS° = (?143 ± 25) J · mol^?1 · K^?1 for the reaction: Li₂NH + NH₃ → 2LiNH₂.     

Energetic effects of ether and ketone functional groups in 9,10-dihydroanthracene compound

The energetic effects caused by replacing one of the methylene groups in the 9,10-dihydroanthracene by ether or ketone functional groups yielding xanthene and anthrone species, respectively, were determined from direct comparison of the standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, of these compounds. The experimental static-bomb combustion calorimetry and Calvet microcalorimetry and the computational G3(MP2)//B3LYP method were used to get the standard molar gas-phase enthalpies of formation of xanthene, (41.8 ± 3.5) kJ · mol^?1, and anthrone, (31.4 ± 3.2) kJ · mol^?1. The enthalpic increments for the substitution of methylene by ether and ketone in the parent polycyclic compound (9,10-dihydroanthracene) are ?(117.9 ± 5.5) kJ · mol^?1 and ?(128.3 ± 5.4) kJ · mol^?1, respectively.     

Heat capacity and thermodynamic properties of germanium disulfide at temperatures from T = (2 to 1240) K

The heat capacity of polycrystalline germanium disulfide α-GeS₂ has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K^?1 · mol^?1, 87.935 J · K^?1 · mol^?1 and 12.642 kJ · mol^?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol^?1, respectively. The thermodynamic functions of α-GeS₂ were calculated over the range (0 ? T/K ? 1250).     

3,4,5-Trimethoxyphenol: A combined experimental and theoretical thermochemical investigation of its antioxidant capacity

The standard (p^° = 0.1 MPa) molar enthalpies of combustion and sublimation of 3,4,5-trimethoxyphenol were measured, respectively, by static bomb combustion calorimetry in oxygen atmosphere and by Calvet microcalorimetry. From these measurements, the standard molar enthalpy of formation in both the crystalline and gaseous phase, at T = 298.15 K, were derived: ?(643.4 ± 1.9) kJ · mol^?1 and ?(518.1 ± 3.6) kJ · mol^?1, respectively. Density functional theory calculations for this compound and respective phenoxyl radical and phenoxide anion were also performed using the B3LYP functional and extended basis sets, which allowed the theoretical estimation of the gaseous phase standard molar enthalpy of formation through the use of isodesmic reactions and the calculation of the homolytic and heterolytic O–H bond dissociation energies. There is good agreement between the calculated and experimental enthalpy of formation. Substituent effects on the homolytic and heterolytic O–H bond dissociation energies have been analysed.     

Determination of the energies of combustion and enthalpies of formation of nitrobenzenesulfonamides by rotating-bomb combustion calorimetry

The energies of combustion for 2-nitrobenzenesulfonamide (cr), 3-nitrobenzenesulfonamide (cr), and 4-nitrobenzenesulfonamide (cr) were determined using a recently described rotating-bomb combustion calorimeter. The condensed phase molar energies of combustion obtained were ?(3479.2 ± 1.0) kJ · mol^?1 for 2-nitrobenzenesulfonamide (cr), ?(3454.2 ± 1.1) kJ · mol^-1 for 3-nitrobenzenesulfonamide (cr), and ?(3450.1 ± 1.9) kJ · mol^-1 for 4-nitrobenzenesulfonamide (cr). From these combustion energy values, the standard molar enthalpies of formation in the condensed phase were obtained as: ?(341.3 ± 1.3) kJ · mol^?1, ?(366.3 ± 1.3) kJ · mol^?1, and ?(370.4 ± 2.1) kJ · mol^?1, respectively. Polyethene bags were used as an auxiliary material in the combustion experiments. The heat capacities and purities of the compounds were determined using a differential scanning calorimeter.     

Thermal reactivity of cis- and trans-bis(triphenylgermyl)bis(tertiary phosphine)platinum(II)

The complex cis-Pt(Ph₃Ge)₂(PMe₂Ph)₂ underwent smooth isomerization to give the trans-isomer at room temperature via an associative five-coordinated intermediate. Thermodynamic parameters and activation energy for the cis to trans isomerization were obtained, ΔH^# = 105 kJ mol⁻¹, ΔS^# = 12.5 J mol⁻¹ K⁻¹, and Ea = 107 kJ mol⁻¹, respectively. Heating of trans-Pt(Ph₃Ge)₂(PMe₂Ph)₂ at 50 °C for 36 days produced trans-PtPh(Ph₃Ge)(PMe₂Ph)₂ followed by the formation of trans-PtPh₂(PMe₂Ph)₂, Pt(PMe₂Ph)₄, and Ph₄Ge finally via elimination of the phenyl group from Ph₃Ge ligand with liberation of the Ph₂Ge unit and subsequent reductive elimination of the remaining Ph₃Ge ligand at 80 °C for 1 month.     

The molar enthalpies of solution and vapour pressures of saturated aqueous solutions of some cesium salts

Vapour pressures of water over saturated solutions of cesium chloride, cesium bromide, cesium nitrate, cesium sulfate, cesium formate, and cesium oxalate were determined as a function of temperature. These vapour pressures were used to evaluate the water activities, osmotic coefficients and molar enthalpies of vapourization. Molar enthalpies of solution of cesium chloride, Δ_solH_m(T = 295.73 K; m = 0.0622 mol · kg⁻¹) = (17.83 ± 0.50) kJ · mol⁻¹; cesium bromide, Δ_solH_m(T = 293.99 K; m = 0.0238 mol · kg⁻¹) = (26.91 ± 0.59) kJ · mol⁻¹; cesium nitrate, Δ_solH_m(T = 294.68 K; m = 0.0258 mol · kg⁻¹) = (37.1 ± 2.3) kJ · mol⁻¹; cesium sulfate, Δ_solH_m(T = 296.43 K; m = 0.0284 mol · kg⁻¹) = (16.94 ± 0.43) kJ · mol⁻¹; cesium formate, Δ_solH_m(T = 295.64 K; m = 0.0283 mol · kg⁻¹) = (11.10 ± 0.26) kJ · mol⁻¹ and Δ_solH_m(T = 292.64 K; m = 0.0577 mol · kg⁻¹) = (11.56 ± 0.56) kJ · mol⁻¹; and cesium oxalate, Δ_solH_m(T = 291.34 K; m = 0.0143 mol · kg⁻¹) = (22.07 ± 0.16) kJ · mol⁻¹ were determined calorimetrically. The purity of the chemicals was generally greater than 0.99 mass fraction, except for HCOOCs and (COOCs)₂ where purities were approximately 0.95 and 0.97 mass fraction, respectively. The uncertainties are one standard deviations.     

Thermochemical study of some methoxytetralones

The standard (p^° = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of 5-, 6- and 7-methoxy-α-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated, 5-methoxy-α-tetralone -(244.8 ± 1.9) kJ · mol^?1, 6-methoxy-α-tetralone ?(243.0 ± 2.8) kJ · mol^?1 and 7-methoxy-α-tetralone ?(242.3 ± 2.6) kJ · mol^?1.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of 8-methoxy-α-tetralone. Similar calculations were done for the 5-, 6-, 7- and 8-methoxy-β-tetralone, for which experimental work was not done.     

Removal of Cr(VI) from water by cork waste

The biosorption by cork powder is considered as a promising method for heavy metal removal from industrial waste waters such as chromium tanning factories. The aim of this study is to evaluate the efficiency extent of this method using cork powder as a biosorbent for Cr(VI). The Fourier Transform Infrared spectroscopy (FTIR) analysis permits to distinguish the type of functional groups likely to participate in metal binding. A linear form of BET isotherms for all the three used temperatures (i.e., 25, 35 and 45 °C) and a pseudo-second-order equation of adsorption kinetics are obtained. Other experimental results highlight the meaningful influence of parameters such as contact time, pH, concentration of Cr(VI) and the adsorbent particle size on Cr(VI) adsorption. 97% of Cr(VI) has been removed under definite conditions particularly a particle size of diameter d < 0.08 mm and pH of 2–3 values.