Standard Enthalpy Change Research Articles

Host-guest complexation between β-cyclodextrin and phosphonium-based ionic liquid and influence of its inclusion complex on the binding property of paracetamol drug

Current research aimed to examine the process of forming inclusion complexes (IC) between β-cyclodextrin and a phosphonium-based ionic liquid i.e., trihexyltetradecylphosphonium bis-(2,4,4-trimethyl pentyl) phosphinate [THTDPP] by UV–Vis spectroscopy and FTIR methods. The co-precipitation technique was utilized to produce the solid IC of [THTDPP] with β-CD, and the Job plot method was employed to understand the 1:1 M ratio stoichiometry and the binding affinity. The Benesi-Hildebrand equation was used to calculate the binding affinity at three unique temperatures, which revealed an increase in the association constant (K) with rising temperature. The Van't Hoff equation was utilized to investigate multiple thermodynamic properties, including the ΔH0 (standard enthalpy changes), ΔS0 (standard entropy changes), and ΔG0 (standard Gibbs free energy changes). The FT-IR analysis indicated notable changes in the IR stretching frequency, providing further evidence of the IC formation. Additionally, the IC was further used to study the aggregation of the Paracetamol drug by UV–Vis spectroscopy and the results indicated a significant improvement in the binding of Paracetamol. Overall, this study sheds important light on the development and properties of IC between β-CD and a phosphonium-based ionic liquid and demonstrates their potential application as an effective drug delivery system.

Environmentally friendly production, characterization, and utilization of ZrO2 nanoparticles for the adsorption of amoxicillin in water solutions

Green synthesis is a viable alternative for creating nanoparticles from environmentally friendly sources. Sonchus asper extract was used in this study to prepare ZrO2 nanoparticles that can adsorb amoxicillin from an aqueous solution as a reducing and stabilizing agent. The complex product was synthesized and then annealed for four hours at 500 °C, 600 °C, and 700 °C to produce fine ZrO2 powder. X-ray diffraction, BET, FTIR, and TEM were employed to explore these samples' structural characteristics. Structural analyses showed that a cubic phase with slight size variation at different annealing temperatures is present in nanocrystalline ZrO2 powder. We examined the influence of initial amoxicillin concentration, pH, and temperature on amoxicillin adsorption. Compared with other widely popular materials used to remove amoxicillin, the zirconia produced in this study had a much better adsorption capability. The adsorption processes were spontaneous and endothermic, following thermodynamic characteristics, including standard enthalpy change (H), Gibb's free energy change (G), and standard entropy change (S). The green production method and zirconia nanoparticles are promising to adsorb a developing contaminant.

Studies on synthesis, physicochemical properties, biological activities of two novel berberine-based salts with DL-mandelate and cinnamate anions

Berberine (BBR) is a natural quaternary isoquinoline alkaloid which is derived from the traditional Chinese medicine Coptis chinensis and exerts various pharmacological effects. However, low solubility in water has greatly limited its clinical application. This study prepared two novel berberine-based salts (berberine DL-mandelate ([BBR][MAN]) and berberine cinnamate ([BBR][CIN])) to improve the physicochemical properties and bioavailability of berberine. Many techniques, like 1H and 13C NMR, FTIR, ESI-MS, and thermogravimetric analyzes were utilized to characterize two salts. The solubility and octanol/water partition coefficient in water and simulated body fluids (simulated body, simulated intestinal and simulated gastric fluids) were determined. Self-aggregation behaviors of two salts in water have been investigated by conductometry at different temperatures. The obtained critical aggregation concentration (cac) was used for the calculation of various thermodynamic properties namely standard Gibbs energy change (ΔGm0), enthalpy change (ΔHm0), and entropy change (ΔSm0) in the aggregation progress. The volumetric properties including the infinite dilution apparent molar volumes (V2,φ0), infinite dilution apparent molar expansibility (Eφ0) and thermal expansion coefficient (β) for [BBR][MAN] were also determined to study its solvation behavior in aqueous solution. In addition, the antibacterial effect of two salts on three strains (Staphylococcus aureus, Bacillus subtilis and Candida albicans) was measured, and the minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values were obtained. The results show that [BBR][MAN] has better antibacterial effect than [BBR][CIN]. The esterase-like activity assay demonstrated a decrease in enzyme activity of BSA in presence of two berberine-based salts. Cytotoxicity evaluation shows that two salts have potent in vitro anticancer activities against B16-F10 cancer cell lines.

Batch and continuous adsorption of Cd(II) and Pb(II) on polycarboxylated sugarcane bagasse

A bioadsorbent composed of polycarboxylated sugarcane bagasse (PSB) was prepared in a one-step reaction by the esterification of sugarcane bagasse hydroxyl groups with butane-1,2,3,4-tetracarboxylic dianhydride. 13C SS NMR measurements showed that 0.3 butane-1,2,3,4-tetracarboxylic acid units were grafted per cellobiose unit. PSB was used in the batch adsorption of Cd(II) and Pb(II) from mono-, bi-, and multicomponent aqueous solutions. For upscaling of the technology aiming at practical applications, evaluation was made of 4 cycles of continuous adsorption of Cd(II) and Pb(II) on PSB in a fixed-bed column. The maximum adsorption capacities for Cd(II) and Pb(II) on PSB in batch and continuous modes were 0.55 and 1.164 mmol g−1 (62 and 241.2 mg g−1), and 0.58 and 0.71 mmol g−1 (65 and 153 mg g−1), respectively. The standard adsorption enthalpy change (ΔadsH°) values for Cd(II) and Pb(II) were 8.6 ± 0.5 and − 0.28 ± 0.03 kJ mol−1, respectively. The interactions involved in the adsorption of Cd(II) and Pb(II) on PSB were investigated. Multicomponent studies showed that Pb(II) and Cd(II) acted to suppress the adsorption of each other. In the presence of Cu(II) and Zn(II), the adsorption capacity followed the order: Pb(II) > Cu(II) > Cd(II) > Zn(II). Batch and continuous adsorption-desorption studies showed that PSB could be reused in at least 4 successive cycles, with desorption efficiencies of 88–100 %, which is essential for minimizing waste generation and reducing process costs.

Adsorptive Removal of Dye (Methylene Blue) Organic Pollutant from Water by Pine Tree Leaf Biomass Adsorbent

In this laboratory batch adsorption study, the raw pine tree leaf biomass solid waste adsorbent material was used for the removal of methylene blue (MB) dye from water at different physicochemical process conditions. The characteristics of adsorbents were determined for particle size, surface area, the existence of functional group identification, and the morphology of the adsorbent surface. The adsorption was performed at different process conditions, which include solution pH, dye concentrations, adsorbent doses, and temperature, respectively. In this study, it was found that MB dye adsorption increased with increases in solution pH and adsorbate MB dye concentration but decreased with adsorbent doses and temperature at fixed process conditions. The Langmuir isotherm model was best fitted with the experimental equilibrium data, with a higher linear regression coefficient (R2) value of 99.9% among the two widely used Langmuir and Freundlich adsorption isotherm model equations. The maximum Langmuir monolayer adsorption capacity of raw pine leaf was found to be 36.88 mg/g, which was comparable with other reported adsorbent capacities towards methylene blue (MB) dye adsorption. The value of the separation factor, RL, from the Langmuir isotherm model equation gives an indication of favorable adsorption. Thermodynamic parameters such as standard Gibbs free energy change (ΔG0), standard enthalpy change (ΔH0), and standard entropy change (ΔS0) indicated that the methylene blue (MB) dye adsorption by pine tree leaf biomass was spontaneous and exothermic in nature and that the mechanism of adsorption was mainly physical adsorption. Finally, limitations and future studies are also discussed here. The outcome of this batch adsorption study may result in the valorization of locally available large pine tree leaf residue waste, which could be used in water purification.

Acid-base treatment of lightweight expanded clay aggregate (LECA) for removal of paraquat from aqueous media

This study focuses on the modification of lightweight expanded clay aggregate (LECA) with sulfuric acid, potassium hydroxide, and sulfuric acid-potassium hydroxide to enhance the removal efficiency of the highly hazardous herbicide (paraquat) from the aqueous solution. The modification results showed that samples activated with sulfuric acid before KOH yielded higher removal efficiency (70.8%) than those activated with acid or base (25.6% and 35.8%, respectively). The paraquat uptake mechanism by LECA was investigated using XRD, XRF, FTIR, FESEM, BET, and zeta potential measurements. Batch adsorption tests were conducted under different conditions using LECA and acid-base-modified LECA. The results indicated the maximum removal efficiency for PQ at 240 min contact time, adsorbent dose of 3.5 g L−1, and pH 9 was achieved with the acid-base treated sample. Experimental data were evaluated with different isothermal, thermodynamic, and kinetic models. The pseudo-second-order model with a correlation coefficient of R2 > 0.99 was congruent with experimental results for LECA and acid-base-activated LECA through kinetic investigations. The highest adsorption capacities for the LECA and acid-base-activated LECA samples, respectively, were 6.12 mg g−1 and 21.23 mg g−1 according to the Langmuir equilibrium isotherm, which offered greater agreement with the experimental results. A negative standard enthalpy change (−21.09 kJ mol−1) and Gibbs free energy change for PQ uptake at 15, 25, and 35 °C indicated an exothermic and spontaneous process. Reusability studies confirmed that the treated adsorbent could successfully remove paraquat even after four regeneration cycles.

Solubilization and partitioning study of nickel fluoride complex [Ni(dmen)2F2].8H2O in the micellar media of sodium stearate by conductometric and spectroscopic techniques

This study was aimed to investigate the physicochemical behavior, solubilization and interaction of coordination complex [Ni(dmen)2F2].8H2O (NDC) with anionic surfactant sodium stearate (SS). The thermodynamic parameters of solubilization such as standard free energy (ΔGm0), enthalpy (ΔHm0) and entropy (ΔSm0) changes of micellization were evaluated by using conductometric measurements. These parameters revealed that the phenomenon of micellization is entropy driven and spontaneous due to the more negative value of (ΔGm0). The quantitative estimation of partitioning parameters such as partition coefficient (Kx), binding constant (Kb), standard energy of partition (ΔGpartO), and standard binding energy (ΔGbindO) revealed the complex-surfactant interaction. Spectroscopic study indicated the high degree of interaction and solubilization of NDC in SS micellar media.. The partitioning results not only governs the mechanism of solubilization but also gives understanding about the partitioning of NDC across membranes in biological systems.

Trace Ammonia Equilibrium Pressure of Zirconium Phosphate in Moisture.

Zirconium phosphate-absorbed ammonia gas and the ammonia concentration (pressure) decreased to 2 ppm (ca. 20 Pa). However, it has not been clarified what the equilibrium pressure of zirconium phosphate is during ammonia gas ab/desorption. In this study, the equilibrium pressure of zirconium phosphate during ammonia ab/desorption was measured using cavity ring-down spectroscopy (CRDS). For ammonia-absorbed zirconium phosphate, a two-step equilibrium plateau pressure was observed during the ammonia desorption in gas. The value of the higher equilibrium plateau pressure at the desorption process was about 25 mPa at room temperature. If the standard entropy change (ΔS0) of the desorption process is assumed to be equal to the standard molar entropy of ammonia gas (192.77 J/mol(NH3)/K), the standard enthalpy change (ΔH0) is about -95 kJ/mol(NH3). In addition, we observed hysteresis in zirconium phosphate at different equilibrium pressures during ammonia desorption and absorption. Finally, the CRDS system allows the ammonia equilibrium pressure of a material in the presence of water vapor equilibrium pressure, which cannot be measured by the Sievert-type method.

Environmental-friendly nanocomposite attapulgite modified by β-cyclodextrin and ionic liquid for the adsorption of thiamethoxam

Thiamethoxam (TH), extensively present in water environment, can adversely affect the ecological safety and human health. In this study, novel environmentally friendly β-Cyclodextrin/Attapulgite (β-CD/ATP) was synthesized by grafting method, followed by its further functionalization using 1-dodecyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide([C12MIM][NTF2]) ionic liquid to prepare [C12MIM][NTF2]-β-CD/ATP nanocomposites for efficient TH adsorption. The results of β-CD/ATP and [C12MIM][NTF2]-β-CD/ATP adsorption TH aqueous solution showed that the initial pH and adsorbent dosage had significant effects on the TH load amount. The optimum pH, initial concentration and adsorbent dosage for β-CD/ATP were 9, 100 mg/L and 0.01 g, respectively. The adsorption process can be described by Pseudo-second-order model and Freundlich model. Furthermore, the maximum experimental adsorption amounts at an TH initial concentration 140 mg/L in 318 K displayed the following order: β-CD/ATP (73.45 mg/g) > [C12MIM][NTF2]-β-CD/ATP (55.42 mg/g) > ATP (24.58 mg/g). The Gibbs free energy (−ΔG0) and standard enthalpy change (+ΔH0) confirm that the adsorption process is essentially a spontaneous heat absorption process, the system randomness increases (+ΔS0). In addition, the removal rate of β-CD/ATP for TH was still above 91 % after six sequential cycles of adsorption-desorption. This work showed the high efficiency of β-CD/ATP in TH adsorption and highlighted its great potential in efficient removal of TH from real water samples.

Investigation of the removal kinetics, thermodynamics and adsorption mechanism of anionic textile dye, Remazol Red RB, with powder pumice, a sustainable adsorbent from waste water.

Excessive growth and abnormal use of dyes and water in the textile industry cause serious environmental problems, especially with excessive pollution of water bodies. Adsorption is an attractive, feasible, low-cost, highly efficient and sustainable technique in terms of green chemistry for the removal of pollutants from water. This study aims to investigate the removal kinetics, thermodynamics and adsorption mechanism of Remazol Red RB, which was chosen as a representative anionic reactive dye, from synthetic wastewater using powdered pumice, taking into account various experimental parameters such as initial dye concentration, adsorption time, temperature and pH. Moreover, to support the proposed adsorption mechanism, before and after adsorption of the samples, the Fourier transform infrared spectrophotometer (FTIR) spectra, X-ray powder diffraction (XRD) diffractograms and High resolution transmission electron microscopy (HRTEM) images were also taken and used. The results show that powder pumice can be an efficient adsorbent for anionic dye removal with a relatively high adsorption capacity of 38.90mg/g, and it is very effective in 30-60min in mild conditions. The experimental data showed a high agreement with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm equation. In addition, thermodynamically, the process exhibited exothermic nature and standard isosteric enthalpy and entropy changes of -4.93kJ/mol and 16.11J/mol. K were calculated. It was determined that the adsorption mechanism was predominantly based on T-shaped pi-pi interactions and had physical characteristics.

Easy separable, floatable, and recyclable magnetic-biochar/alginate bead as super-adsorbent for adsorbing copper ions in water media

This work aimed to develop innovative material by combining properties of magnetic-biochar (derived from peanut shells) and hydrogel bead (MBA-bead) and apply it for adsorbing Cu2+ in water. MBA-bead was synthesized by physical cross-linking methods. Results indicated that MBA-bead contained ∼90% water. The diameter of each spherical MBA-bead was approximately 3 mm (wet form) and 2 mm in (dried form). Its specific surface area (262.4 m2/g) and total pore volume (0.751 cm3/g) were obtained from nitrogen adsorption at 77 K. X-ray diffraction data confirmed Fe3O4 presented in magnetic-biochar and MBA-bead. Its Langmuir maximum adsorption capacity for Cu2+ was 234.1 mg/g (30 °C and pHeq 5.0). The change in standard enthalpy (ΔH°) of the adsorption was 44.30 kJ/mol (dominant physical adsorption). Primary adsorption mechanisms were complexation, ion exchange, and Van der Waals force. Laden MBA-bead can be reused several cycles after desorbing with NaOH or HCl. The cost was estimated for producing PS-biochar (0.091 US$/kg), magnetic-biochar (0.303–0.892 US$/kg), and MBA-bead (1.369–3.865 US$/kg). MBA-bead can serve as an excellent adsorbent for removing Cu2+ ions from water.

Development and characterization of a clay-HDTMABr composite for the removal of Cr(VI) from aqueous solutions with special emphasis on the electrochemical interface

This research aims to study the removal of chromium in its toxic form, Cr (VI), from wastewater, using clay and modified clay with Hexadecyltrimethyl ammonium bromide (HDTMABr)as adsorbents. The modified clay is obtained by impregnating a known quantity of HDTMABr into the clay. The two materials were characterized by different techniques, such as X-ray diffraction, which is used to determine the inorganic composition and the phyllite structures it contains. Thermal analysis TGA isused to understand the thermal behavior as function of the sintering temperature. Nitrogen adsorption/desorption is used to get the pores' size and surface area, using the Brunauer-Emmett-Teller (BET) theory. Scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDAX) is used to study the surface morphology of the bare clay and the HDTMABr/clay. The operating conditions, such as contact times, pH, and adsorption temperatures, were studied, and optimized to improve the efficiency of the adsorption process. The adsorption is favored in acidic medium and room temperature, giving adsorption capacities for Cr(VI) of 12 mg/g and 250 mg/g for the clay and clay/HDTMABr, respectively. The reaction kinetics were studied and found to fit a pseudo-second-order model. The standard entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes indicate that the chromium (VI) adsorption process is a physical, spontaneous, endothermic process. Cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) are used for the electrochemical characterization of the raw clay and clay/HDTMABr in [Fe(CN)6]3-/4-/ 0.1 M KCl solution. The linear scan anodic stripping voltammetry (LSASV) is used for the reduction the Cr(VI) to Cr(III), indicating that Cr(VI) accumulates better at the surface of clay/HDTMABr compared to the bare graphite and the raw clay.

Insight of molecular interactions between short‐chain tetraalkylammonium bromides and cetyltrimethylammonium bromide: A spectroscopic and thermodynamic approach

AbstractThe influence of tetraalkylammonium salts, viz., tetraethylammonium, tetrapropylammonium, and tetrabutylammonium bromides (0.005, 0.010, 0.015 mol kg−1) on the micellar behavior of aqueous solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB, 0.2–2 mmol kg−1) over the 298.15–313.15 K temperature range has been studied by conductometric method. From conductivity versus surfactant concentration plots, the critical micelle concentration (CMC) of CTAB has been determined, which shows that the tetraalkylammonium bromides promote the formation of CTAB aggregates. Further, from the temperature dependence of CMC values, the degree of ionization, the counterion binding constant along with some thermodynamic parameters of micellization, such as standard free energy change (), standard enthalpy change (), standard entropy change () have been calculated. From the values of , and , it has been concluded that our ternary system is both enthalpy as well as entropy controlled. Similar CMC values were obtained from UV–Visible spectrometry measurements, using pyrene as a probe at ambient temperature. Also 1H‐NMR and FTIR methods give a greater understanding of the molecular scale interactions between the tetraalkylammonium bromides and the cationic surfactant.

Chloride sorption of nano-SiO2@MgAl-layered double hydroxides core-shell nanocomposite in simulated concrete pore solution: Equilibrium, thermodynamic and kinetic studies

Nano-SiO2@MgAl-layered double hydroxides (NS@MgAl-LDH) core-shell nano-composites were successfully synthesized by a co-precipitation method. The as-synthesized NS@MgAl-LDH was characterized by SEM, TEM, EDX, TGA and BET. The equilibrium, thermodynamic and kinetic studies on the chloride sorption of NS@MgAl-LDH were performed in simulated concrete pore solution (SCPS). The results show that NS@MgAl-LDH exhibits a higher specific surface area (SSA) compared to MgAl-LDH. Besides, the chloride sorption capacity of NS@MgAl-LDH is significantly higher than that of pure MgAl-LDH, which is obviously influenced by initial pH-value and amount of adsorbents addition. Also, the chloride sorption process can be fitted by the Langmuir-model thermodynamically and the pseudo-second-order kinetics kinetically. The negative values of Gibbs-free energy (ΔG0) and standard enthalpy change (ΔH0) indicate that the chloride sorption is spontaneous and exothermic. Furthermore, the outstanding chloride sorption capacity of NS@MgAl-LDH is mainly contributed to the ion-exchange of chloride ions with interlayer ions in the highly dispersed MgAl-LDH.

Electrochemical characterization and performance of phenothiazine derivatives as redox mediators

Two phenothiazine derivatives were synthesized as new redox mediators. Their electrochemical properties were compared with conventional redox mediators, such as thionine, ferricyanide(III), and hexaammineruthenium(III). Cyclic voltammetry experiments were performed under various conditions on glassy carbon and ultramicroelectrodes to investigate the proton-coupled electron transfer reaction mechanism, electrochemical reversibility, and chemical stability of the redox mediators. The number of intervening electrons and protons in the redox processes of redox mediators at each temperature was estimated accordingly. Furthermore, thermodynamic parameters (standard enthalpy change, standard entropy change, and standard Gibbs free energy) of redox mediators could be evaluated by analyzing their electrochemical behavior according to the reaction temperatures. The mediator performance was also analyzed for the oxidation of reduced nicotinamide adenine dinucleotide. These experimental and analytical results confirm that the performance of redox mediators is similar or superior to those of other mediators.

Synthesis of nanostructured novel ion-imprinted polymer for selective removal of Cu2+ and Sr2+ ions from reverse osmosis concentrated brine

This study aims to prepare an ion-imprinted polymer (IIP) using copper sulfate as a template and potassium persulfate as an initiator to selectively adsorb copper ions (Cu2+) from aqueous solutions and in an attempt to also test its applicability for removing strontium ions (Sr2+). The prepared polymer was denoted by IIP-Cu. Various physical and chemical characterizations were performed for the prepared IIP-Cu. The scanning electron microscopy and transmission electron microscopy analyses confirmed the cavities formed after the removal of the template. It also indicated that the IIP-Cu had a rough and porous topology. The X-ray photoelectron spectroscopy confirmed the successful removal of the Cu template from IIP-Cu. The Brunauer-Emmet-Teller revealed that the surface area of IIP-Cu is as high as 152.3 m2/g while the pore radius is 8.51 nm. The effect of pH indicated that the maximum adsorption of Cu2+ was achieved at pH 8 with 98.7%. Isotherm studies revealed that the adsorption of Cu2+ was best explained using Langmuir models with a maximum adsorption capacity of 159 mg/g. The effect of temperature revealed that an increase in temperature had an adverse impact on Cu2+ removal from the aqueous solution, which was further confirmed by thermodynamic studies. The negative value of standard enthalpy change (−4.641 kJ/mol) revealed that the adsorption of Cu2+ onto IIP-Cu was exothermic. While the continuous increase in Gibbs free energy from −6776 kJ/mol to −8385 kJ/mol with the increase in temperature indicated that the adsorption process was spontaneous and feasible. Lastly, the positive value of the standard entropy change (0.023 J/mol.K) suggested that the Cu2+ adsorption onto IIP-Cu had a good affinity at the solid-liquid surface. The efficiency of the prepared IIP-Cu was also tested by studying the adsorption capacity using Sr2+ and real brine water. The results revealed that IIP-Cu was able to remove 63.57% of Sr2+ at pH 8. While the adsorption studies revealed that the experiment was best described using the Langmuir model with a maximum adsorption capacity of 76.92 mg/g. Additionally, IIP-Cu was applied in a real brine sample, which consisted of various metal ions. The highest percentage of Cu2+ removal was 90.6% and the lowest was 65.63% in 1:4 and 1:1 brine ratios, respectively. However, this study indicates the successful application of IIP-Cu in a real sample when it comes to the effective and efficient removal of Cu2+ in a solution consisting of various competing ions.

Impacts of several salts on the clouding development, nature of interactions and associated physico-chemical variables of mixture of promethazine hydrochloride and conventional nonionic surfactant

Herein, in the presence of electrolytes, the cloud points (CPs) of the mixture of a conventional uncharged amphiphile (triton X-100 (TX-100)) and promethazine hydrochloride (PMH; phenothiazine medicine) were measured and explained in great details. The CP values of the employed surfactant + PMH system were reduced with enhancing salts contents (NaCl, Na2SO4, NH4Cl, and (NH4)2SO4)), while the CP values of the study system followed the trend: Na2SO4 < NaCl and (NH4)2SO4 < NH4Cl. The different thermodynamic parameters of phase separation, including standard free energy (ΔG 0 c), enthalpy (ΔH 0 c), and entropy (ΔS 0 c) changes were also calculated and discussed elaborately. The values of free energy change (ΔG 0 c) were obtained to be positive, indicating that the clouding phenomena are non-spontaneous. Different transfer properties (free energy (ΔG 0 c.t), enthalpy (ΔH 0 c,t ), and entropy (ΔS 0 c,t ) of transfer), intrinsic enthalpy gain (ΔH 0,*c) and compensation temperature (T c) of the inspected system have also been assessed and discussed.

Selective adsorption of gadolinium from real leachate using a natural bentonite clay

This article investigated the recovery of Gd3+ from real leachate of phosphogypsum (PG) using natural bentonite clay. Firstly, a detailed adsorption study was performed using synthetic Gd3+ solutions. Then, it was investigated the clay performance in the real PG leachate. The characterization results indicate classical bentonite characteristics, such as rugosity and an SBET 91.3 m² g−1, with meso (Dp =3.82 nm) and macroporous (Dp =52.6 nm). In addition, it was identified that the major functional groups are hydroxyl and silicate, with the presence of organic matter. The initial pH solution effect indicates that the optimum removal of Gd3+ is at pH (6), attributing to the pHpzc being at 5.75 and the negatively charged surface above the pHpzc. The Avrami fractional order model was the most suitable for describing the experimental kinetic data. The Langmuir was the proper model for describing the adsorption isotherms, indicating that the Gd3+ forms a monolayer at the surface of the bentonite. The maximum adsorption capacity at pH 6.0 was 121.5 mg g−1. The thermodynamic parameters indicate that the adsorption is spontaneous, with a standard enthalpy change of − 92.30 kJ mol−1, indicating an ionic exchange, where the Gd3+ tends to be organized at the surface, according to the standard entropy change of − 206.0 J K−1 mol−1. The fixed bed adsorption test showed that Gd3+ could be adsorbed for up to 200 min without regeneration. Regeneration results show that the citric acid is more efficient in desorbing the Gd3+ from the bentonite, reaching up to 8 cycles without efficiency loss. Finally, the bentonite clay could selectively recover Gd3+ from the real PG leachate.

Chlorine partial pressure measurements over CuCl2/CuCl by transpiration method with gas detector tubes

Copper-chlorine compounds often play important roles in many industrial processes, but no reliable values of their thermodynamic quantities have been established. In this work, we measured the equilibrium chlorine partial pressure over CuCl(s) and CuCl2(s) by the transpiration method to find accurate thermodynamic quantities of the copper-chlorine compounds. The temperature dependence of the equilibrium chlorine partial pressure is given by the following equation: logpCl2/bar=9.805±2.535-8633.1±1433.4T/K-1 (from 526 to 604 K), and the standard enthalpy change of the reaction (2 CuCl2(s) ⇌ 2 CuCl(s) + Cl2(g)) at 298.15 K is calculated as (161.7 ± 0.48) kJ mol−1 by the third-law method. This equation and value agree well with a thermodynamic data compilation Thermodynamic Properties of Individual Substances (L.V. Gurvich, I.V. Veyts, and C.B. Alcock, vol. 1, 1989 and V. S. Iorish et al., vol. 5, http://www.chem.msu.su/rus/tsiv/, accessed 18 September 2020).

Adsorptive Removal of Rhodamine B Dye Using Carbon Graphite/CNT Composites as Adsorbents: Kinetics, Isotherms and Thermodynamic Study.

The study of the adsorption efficiency of new carbon/CNT composites was undertaken to remove a cationic dye, Rhodamine B (RhB), from dye-contaminated wastewater. Indeed, we investigated the effect of different experimental parameters such as time, initial concentration of dye and temperature on the adsorption of RhB by the carbon composites (KS44-0 and KS44-20). The results showed that the adsorption uptake increased with the initial concentration and solution temperature while maintaining a relatively constant pH. The presence of the carbon nanotubes provided more active sites for dye removal and improved the adsorption behavior of Rhodamine B dye. The analysis of the experimental data was conducted using model equations, such as Langmuir, Freundlich and Temkin isotherms. As regards the Freundlich isotherm model, it was the best fit for the equilibrium data obtained from the experiments. The applicability of the pseudo-second-order equation could be explained assuming that the overall adsorption rate is limited by the rate of adsorbate transport that occurs on the pore surfaces of adsorbents. Furthermore, the intraparticle diffusion and Bangham models were used to investigate the diffusion mechanism of RhB absorption onto carbon composites. They showed that multiple adsorption stages occurred simultaneously via pore surface diffusion. Concerning the thermodynamic parameters (∆G°, ∆H°, and ∆S°), they were calculated and explained in the mean of the chemical structure of the adsorbate. Negative standard Gibbs free energy change values (ΔG°ads) at all temperatures suggested that the adsorption process was spontaneous, and the positive values of the standard enthalpy change of adsorption (∆H°ads) revealed the reaction to be endothermic. The values of standard enthalpy (ΔH°ads) and activation energy (Ea) indicated that the adsorption process corresponds to physical sorption. The mechanisms for the removal of Rhodamine B dye from wastewater using carbon composite were predicted. RhB is a planar molecule that is readily adsorbed, in which adsorbed molecules are bound by hydrophobic or other weak interactions due to the π-π interactions between the dyes' aromatic backbones and the hexagonal skeleton of graphite and carbon nanotubes. Thus, the graphite carbon/carbon nanotube composite is believed to play a major role in organic pollutant reduction.