Negative Gibbs Free Energy Research Articles

A novel magnetic chitosan/clinoptilolite/magnetite nanocomposite for highly efficient removal of Pb(II) ions from aqueous solution

A novel nanocomposite (with components of chitosan, clinoptilolite and magnetite) was synthesized featuring magnetic properties, and was used for the removal of Pb(II) as a toxic heavy metal from aqueous solutions. The effects of temperature, contact time, Pb(II) concentration, pH value of the solution and adsorbent dosage on the adsorption capacity of the nanocomposite were investigated. The kinetics data of adsorption process were analyzed by the models of pseudo-first order, pseudo-second order, the Elovich and intra-particle diffusion. The adsorption kinetics was well described by the pseudo-second order equation. The adsorption isotherms were more accurately fitted by the Langmuir equation and the maximum theoretical Pb(II) adsorption capacity of the nanocomposite was found to be 136.99mg/g at pH6 and 333K. The negative Gibbs free energy values of adsorption illustrated the spontaneity of the adsorption of Pb(II) ions on the nanocomposite. The magnetic nanocomposite gave a saturation magnetization value of 9.50emu/g, therefore, it was efficiently separated from the solution by a fast and simple magnetic separation process. Desorption of the Pb(II) ions from the nanocomposite was achieved by using 0.01M HNO3, CaCl2 and NaCl solutions. The prepared nanocomposite exhibited proper magnetic property, high thermal strength and large specific surface area while being synthesized at low cost. Hence, it offers possibilities for future practical use.

Effective adsorption of antimony(III) from aqueous solutions by polyamide-graphene composite as a novel adsorbent

Graphene was modified with polyamide by using a facile interfacial polymerization method to obtain an effective composite. The produced polyamide-graphene (PAG) was characterized by Fourier transform infrared spectroscopy (FTIR), Scanning Electron microscopy (SEM) equipped with Energy-Dispersive X-ray spectroscopy (EDX), Thermogravimetric analyzer (TGA), and Brunauer–Emmett–Teller (BET) analysis methods. The adsorption efficiency of the adsorbent for the removal of Sb(III) was evaluated under the effects of concentration, temperature, contact time, medium pH, and re-usability. The results of the study showed very good adsorption performance and high regeneration efficiency. The Langmuir modeling results revealed that the synthesized PAG sorbent had a considerably high adsorption capacity (158.2mg/g) for Sb(III) ions from aqueous solution. The adsorption data fitted well into pseudo-second order model. The exothermic enthalpy change of −65.6kJ/mol and negative Gibbs free energy change assured the viability of the adsorption process under the considered temperature conditions. Moreover, by taking into account all results it was concluded that the PAG composite material leverages its cheap source and ease of regeneration in combination with its high and fast uptake capacities to offer a great promise for the remediation of Sb(III) ions from aqueous solutions.

Study on surface appearance, geometry size, and delta-ferrite content of ZrO2-aided TIG welding of AISI 316LN stainless steel

This study investigated the influence of oxide with a more negative Gibbs free energy (ΔG) on the surface appearance, geometry size, and delta-ferrite (δ-Fe) content of AISI 316LN stainless steel subjected to flux-aided tungsten inert gas (TIG) welding. Powdered ZrO2 of various particle sizes mixed with 80 % water/20 % acetone solution was used as flux. The potential advantages of ZrO2-aided TIG welding were also demonstrated. The results show that nanoscale ZrO2 flux produces a TIG weld with a slag-free surface, but it did not significantly increase the depth-to-width ratio of the weld. The present work also found that ZrO2 flux slag influences the δ-Fe content of AISI 316LN stainless steel weld. ZrO2-aided TIG welding has low tendency to form undercut ting and allows high-speed welding. The potential advantages of the ceramic slag created by the ZrO2 flux are a small tem-perature difference between the center and edges of welding pool surface, a low solidified rate of liquid metal at the rear of the welding pool, as well as alleviation of the arc pressure at the front of the welding pool.

Replacement micro-mechanism of CH4 hydrate by N2/CO2 mixture revealed by ab initio studies

Ab initio calculations and molecular dynamics simulations were performed to investigate the thermodynamic and kinetic feasibility of the replacement of CH4 from its hydrate by N2/CO2 mixture. Substitution of CH4 in small and large cages with N2 and CO2 has negative Gibbs free energy, whereas the substitution by CO2 in small cages is structurally unfavorable. The calculations show that the replacement process should be the substitution with CO2 in large cages followed by N2 in small cages, featuring with the produce of mixed N2-CO2 hydrate. Further, the simulations results indicate N2 exhibits a faster diffusion motion than CO2 in hydrate, implying the substitution by N2 is more kinetically favorable to occur. Our results highlights that the replacement process should include the thermodynamically dominated CO2 substitution simultaneous to the kinetically dominated N2 substitution.

Synthesis, characterization of magnetic chitosan/active charcoal composite and using at the adsorption of methylene blue and reactive blue4

In this study, a chitosan/activated charcoal (or carbon) (CTN/AC-Fe3O4) composite was obtained in one step, characterized several techniques such as by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, Brunauer-Emmet-Teller, thermogravimetric analysis/differential thermal analysis and differential scanning calorimetry techniques. The sorption the composite were investigated as kinetically and thermodynamically for removal of methylene blue (MB) and reactive blue4 (RB4) from aqueous solution. Effects of several parameters, such as initial temperature and initial concentration on removal of MB and RB4 from aqueous solution by the composite were investigated as a function of contact time. Maximum adsorption capacity (Qmax) was found to be 500 mg g−1 at and 250 mg g−1 at 318 K for MB, 298 K for RB4 respectively. Also, thermodynamic parameters such as ΔH0, ΔG0 and ΔS0 were calculated by Langmuir adsorption isotherm model. Negative Gibbs free energy (ΔG0) implies that the adsorption is spontaneous and positive adsorption enthalpy (ΔH0) demonstrates the process is endothermic for MB while negative adsorption enthalpy (ΔH0) demonstrates the process is exothermic for RB4, respectively.

Syntheses of planar 1,5,2,4,6,8-dithiotetrazocine derivatives and thermodynamic study on intermolecular charge transfer for developing efficient organic solar cell

A series of planar 1,5,2,4,6,8-dithiotetrazocine derivatives were synthesized for study on charge transfer at donor/acceptor interface. The fluorescence quenching spectra, and the highest occupied molecular orbital (−6.10 ∼ −6.25 eV) and the lowest unoccupied molecular orbital (−3.45 ∼ −3.58 eV) energy levels of these 1,5,2,4,6,8-dithiotetrazocine derivatives show that they would be potential acceptor materials. Based on theoretical calculations, thermodynamic study on charge transfer at donor/acceptor interface was carried out. The results of experiments and theoretical calculations show that the electrons could transfer spontaneously from poly(3-hexylthiophene) to these acceptors. The percentages of fluorescence quenching increase with negative Gibbs free energy values increasing in the charge transfer procedures. Therefore, short circuit current values of organic solar cells would increase with the Gibbs free energy values increasing. This paper suggests a useful way for developing efficient organic solar cells.

활성탄을 이용한 Acid Yellow 14 흡착에 대한 평형, 동역학 및 열역학 파라미터의 연구

Adsorption experiments of Acid Yellow 14 dye using activated carbon were carried out as function of adsorbent dose, pH, initial concentration, contact time and temperature. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Temkin isotherm model. The experimental data were best represented by Freundlich isotherm model. Base on the estimated Freundlich constant (1/n=0.129~0.212) and Langmuir separation factor (), this process could be employed as effective treatment method. The heat of adsorption of Temkin isotherm model was 5.101~9.164 J/mol indicated that the adsorption process followed a physical adsorption. Adsorption kinetics experimental data were modeled using the pseudo-first-order and pseudo-second-order kinetic equation. It was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. Base on the negative Gibbs free energy (-4.81~-10.33 kJ/mol) and positive enthalpy (+78.59 kJ/mol) indicate that the adsorption is spontaneous and endothermic process.

N-H bond cleavage of ammonia on graphene-like B36 borophene: DFT studies.

Ammonia N-H bond cleavage at metal-free substrates has attracted great attention because of its industrial importance. Here, we investigate the dissociative adsorption of ammonia onto the surface of a B36 borophene sheet by means of density functional theory calculations. We show that the N-H bond may be broken at the edges of B36 even at room temperature, regarding the small energy barrier of 14.1-19.3kcalmol(-1) at different levels of theory, and more negative Gibbs free energy change. Unlike basis set size, the kind of exchange correlation functional significantly affects the electronic properties of the studied systems. Also, by increasing the percentage of Hartree Fock (HF) exchange of density functionals, the activation and adsorption energies are lowered. A linear relationship between the highest occupied molecular orbital or lowest unoccupied molecular orbital of B36 borophene and the %HF exchange of functionals is predicted. Our work reveals that pure whole boron nanosheets may be promising metal-free materials in N-H bond cleavage, which would raise the potential application of these sheets.

Adsorption Equilibrium of CO2 and CH4 and Their Mixture on Sichuan Basin Shale

Adsorption equilibrium isotherms of CO2, CH4, and mixtures of CO2/CH4 on shale sampled from Nanchuan, southeastern Sichuan Basin, were measured at 278, 298, and 318 K by an accurate gravimetric method. The adsorption equilibrium data of CO2 and CH4 were fitted using both the virial model and the Brunauer–Emmett–Teller (BET) model, and the isotherms of CO2/CH4 mixtures were fitted by an extended BET model. On the basis of adsorption data, the adsorption selectivity factors for CO2 over CH4 (αCO2/CH4) and thermodynamic parameters were estimated. Nanchuan shale was characterized with a high total organic carbon (TOC), having inorganic minerals and wide pore size distribution ranges. The adsorption heat, negative Gibbs free energy change, and negative surface potential of CO2 are larger than those of CH4, and the entropy loss of CO2 is larger than that of CH4, suggesting that adsorbed CO2 is in a more highly ordered arrangement than CH4 on shale. αCO2/CH4 values at different temperatures are all larger than 2.5.

BIOSSORPTION OF Pb(II) BY URUCUM SHELLS (Bixa orellana) IN AQUEOUS SOLUTIONS: KINETIC, EQUILIBRIUM AND THERMODYNAMIC STUDY

This study describes the application of new and low cost biosorbent, shells of urucum (Bixa Orellana), for removal of lead ions (Pb(II)) from water solution. The urucum shells were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Batch adsorption experiments were performed in order to evaluate the effect of pH, agitation speed, adsorbent dosage, contact time, temperature, presence of interfering ions and matrix effect on the adsorption of process. The kinetics of biosorption followed pseudo-second-order model. Langmuir and Freundlich isotherm models were applied to describe the biosorption of Pb(II) by urucum shells. The Langmuir model showed better fit and the estimated biosorption capacity was 43.6 mg g-1. The negative Gibbs free energy, ΔG°, confirms the spontaneous nature and positive value of enthalpy, ΔH°, the endothermic character of the process. Furthermore, we also performed an evaluation of matrix and others ions effect on the biosorption process.

Quantum chemical insight into the reactivity of 1,3-dipoles on coronene as model for nanographenes

In this paper, we present a systematic investigation into reactivity of 1,3-dipoles on coronene as model for nanographenes using the density functional theory (DFT). The calculations show that the dipole nature mainly involving the structure and electrical effect is the major influence on reactivity. The 18-valence-electron azomethine ylides shows more active than the other two types of 1,3-dipoles with 16-valence-electron to NG, which may due to a smaller singlet-triple splitting. The more electronegative terminate group leads a higher stability and chemical inertness of the 1,3-dipole. There the reactivity order is oxide < imine < ylide. The varied distortion energy which determines the activation energy depends on the deformation of the 1,3-dipole. It can be obviously observed the distortion energy increases as the strengths of two resonance bonds of the 1,3-dipole increase in each series. The less electronegative terminate group leads the more electron-deficient and the less electron delocalization of the 1,3-dipole and even the more stable of the intermediate, which leads the cycloaddition proceed easier. The trend that the activation energy decreases as the strengths differences of the two new bonds of intermediate is also very clear in each series. All the reactivities are consistent analyzing in frontier molecular orbitals (FMO) theory. Unlike the 1,3-DC toward some other dipolarophiles, the vast majority of the studied 1,3-dipole cycloaddtions (DC) are of largely negative Gibbs free energies (ΔG≠) values which are spontaneous at the temperature. There is correlation between the extent of spontaneous of reaction and the activation energy. There is also good relationship between the activation energy and the reaction energy, which follows the Hammond postulate.

입상 활성탄에 의한 Safranin의 흡착에 관한 평형, 동력학 및 열역학에 관한 연구

Abstract Adsorption of Safranin using granular activated carbon from aqueous solution was investigated. Batch experiments were car-ried out as a function of adsorbent dose, initial concentration, contact time and temperature. The equilibrium adsorption data were fitted to Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. Based on an estimated Langmuir separation factor, R L = 0.183~0.254 and a Freundlich separation factor, 1/n = 0.518~0.547, this process could be employed as an effec-tive treatment method. Adsorption data were also modeled using the pseudo-first and second-order kinetic equations. It was shown that the pseudo-second-order kinetic equation could best describe the adsorption kinetics. The negative Gibbs free en-ergy (△G = -3.688~-7.220 kJ/mol) and positive enthalpy (△H = 33.126 kJ/mol) indicated that the adsorption process was spontaneous and endothermic. Keywords: safranin, dye adsorption, adsorption, adsorption kinetic, adsorption thermodynamics 1)1. 서 론

Dissolution Engineering of Platinum Alloy Counter Electrodes in Dye‐Sensitized Solar Cells

AbstractThe dissolution of platinum (Pt) has been one of the heart issues in developing advanced dye‐sensitized solar cells (DSSCs). We present here the experimental realization of stable counter‐electrode (CE) electrocatalysts by alloying Pt with transition metals for enhanced dissolution resistance to state‐of‐the‐art iodide/triiodide (I−/I3−) redox electrolyte. Our focus is placed on the systematic studies of dissolution engineering for PtM0.05 (M=Ni, Co, Fe, Pd, Mo, Cu, Cr, and Au) alloy CE electrocatalysts along with mechanism analysis from thermodynamical aspects, yielding more negative Gibbs free energies for the dissolution reactions of transition metals. The competitive reactions between transition metals with iodide species (I3−, I2) could protect the Pt atoms from being dissolved by redox electrolyte and therefore remain the high catalytic activity of the Pt electrode.

Dissolution Engineering of Platinum Alloy Counter Electrodes in Dye-Sensitized Solar Cells.

The dissolution of platinum (Pt) has been one of the heart issues in developing advanced dye-sensitized solar cells (DSSCs). We present here the experimental realization of stable counter-electrode (CE) electrocatalysts by alloying Pt with transition metals for enhanced dissolution resistance to state-of-the-art iodide/triiodide (I(-)/I3(-)) redox electrolyte. Our focus is placed on the systematic studies of dissolution engineering for PtM0.05 (M=Ni, Co, Fe, Pd, Mo, Cu, Cr, and Au) alloy CE electrocatalysts along with mechanism analysis from thermodynamical aspects, yielding more negative Gibbs free energies for the dissolution reactions of transition metals. The competitive reactions between transition metals with iodide species (I3(-), I2) could protect the Pt atoms from being dissolved by redox electrolyte and therefore remain the high catalytic activity of the Pt electrode.

Adsorption in simple batch experiments of Coomassie blue G-250 by apricot stone activated carbon—Kinetics and isotherms modelling

The preparation of an activated carbon from apricot stones (ASAC) with H3PO4 activation and its ability to remove the Coomassie blue (CB) from aqueous solutions are reported in this study. The spectroscopy method is used to get information on interactions between the functional groups of the adsorbent and the CB. Batch adsorption experiments were first undertaken to assess the effect of various parameters on the removal efficiency of CB. It was observed that under optimized conditions up to 98.022 mg/g could be removed from solution at 50°C. The equilibrium experimental data were analysed using Langmuir and Freundlich isotherm equations. An error-based statistic study showed that the isotherm data are well described by the Freundlich model. The suitability of the kinetic models for the adsorption of CB onto ASAC was also investigated. It was found that the adsorption kinetics of the dye obeyed pseudo-second-order kinetic model. The evaluation of thermodynamics parameters such as activation energy of adsorption (Ea: 66.161 kJ/mol) predicted the chemisorption nature of the sorption process. The negative Gibbs free energy (−ΔG° = 15.21–19.27 kJ/mol) and negative enthalpy change (ΔH° = −55.088 kJ/mol) indicated, respectively, the spontaneous and exothermic nature of the reaction.

Succinate-bonded pullulan: An efficient and reusable super-sorbent for cadmium-uptake from spiked high-hardness groundwater

Chemically modified pullulan was evaluated for its sorption efficiency and selectivity to remove cadmium (Cd) from spiked high-hardness groundwater (GW). Pullulan esterified with succinic anhydride using dimethylaminopyridine showed a fairly high degree of substitution value as confirmed by 1H NMR spectroscopy. Pullulan succinate (Pull-Suc) was converted into the sodium salt (Pull-Suc-Na). The effect of contact time (5–200min) and pH (2–8) on Cd-uptake by the sorbent (Pull-Suc-Na) was investigated. The sorbent showed more than 90% Cd-removal in first 15min from distilled water (DW) and GW solution, respectively. Comparison of Pull-Suc-Na with other polysaccharidal sorbents suggested its high efficiency (DW 476.2mg/g and GW 454.5mg/g) and selectivity for the removal of Cd by an ion exchange mechanism, which is further supported by the negative Gibbs free energy values calculated from Langmuir isotherms. A Langmuir isotherm kinetic model provided the best fit for the sorption of Cd using Pull-Suc-Na. The sorbent showed a negligible decrease in Cd-uptake over three regeneration cycles. The thermal stability testing of the sorbents indicated that Pull-Suc-Na (sorbent) is more stable than Pull-Suc.

Investigation of adsorption of Basic Blue 41, Acid Violet 17 and Reactive Red 23 dyestuffs on Çatalağzı Thermal Power Plant flyash

In this study the various dyestuffs in industrial wastewaters (Basic Blue 41, Acid Violet 17, Reactive Red 23) was investigated adsorption on fly ash whiche is a waste. Dyestuff adsorption on fly ash carried out in batch system has been investigated as a function of medium pH, temperature and the amount of adsorbent. In the other part of the study, fly ash samples treated using H 2 SO 4 and heat have been studied for dye adsorption. After acid and heat treatment, the specific surface area of the fly ash and the dye adsorption capacity increased. The results of adsorption equilibrium obtained by untreated of fly ash were examined for compliance of Langmuir and Freundlich isotherm models. Dye adsorption systems data were fitted better to the Langmuir izoterm. The Gibbs free energy of adsorption (ΔG 0 ), enthalpy (ΔH 0 ) and entropy (ΔS 0 ) were calculated using the adsorption isotherms obtained at different temperatures. Negative Gibbs free energy shows the dye adsorption onto flyash is spontaneous.

Comparative study on the inhibitive effect of Sulfadoxine–Pyrimethamine and an industrial inhibitor on the corrosion of pipeline steel in petroleum pipeline water

The corrosion inhibition characteristics of Sulfadoxine plus Pyrimethamine (S&P) was evaluated and compared with the inhibition performance of an industrial corrosion inhibitor (S-Ind) under anaerobic condition. Modified gravimetric and electrochemical techniques were used. The corrosion inhibition efficiencies of both S&P and S-Ind were comparable for all the techniques applied. S&P gave slightly higher inhibition efficiency, while S-Ind gave a more steady corrosion protection. The corrosion inhibition efficiencies increased with increased concentration of both substances. The polarization curves showed mixed inhibition behavior for both S&P and S-Ind. A mechanism of chemisorption was proposed for the adsorption of S&P and S-Ind on pipeline steel surface, while the negative Gibbs free energy of adsorption values indicates a spontaneous adsorption process. The adsorption characteristics of the inhibitors were fitted into Langmuir adsorption isotherm.

석탄계 입상 활성탄에 의한 Brilliant Blue FCF 염료의 흡착 동력학 및 열역학에 관한 연구

Adsorption of brilliant blue FCF dye using coal based the granular activated carbon from aqueous solution was investigated. Batch experiments were carried out as a function of the adsorbent dose, initial concentration, contact time and temperature. The equilibrium adsorption data were fitted to Langmuir, Freundlich and Temkin models. The results indicate that Freundlich model provides the best correlation of the experimental data. Base on the estimated Freundlich constant (1/n = 0.129∼0.212), this process could be employed as an effective treatment method. Adsorption data were modeled using the pseudo-first-order and pseudo-second-order kinetic equations. It was shown that the pseudo-second-order kinetic equation could describe well the adsorption kinetics. The negative Gibbs free energy value (-4.81∼-10.33 kJ/mol) and positive enthalpy value (+78.59 kJ/mol) indicated that the adsorption was a spontaneous and endothermic process.

Adsorption characteristics and mechanisms of high-levels of ammonium from swine wastewater using natural and MgO modified zeolites

This paper focuses on the effectiveness of removing ammonium by both natural and MgO modified zeolites and the theoretical aspects of adsorption including mechanisms. Results have demonstrated that the zeolite synthesized by integrated calcination with MgO at 400°C performances a good ammonium adsorption capacity as high as 24.9 mg g−1, an increase by 97.6 and 68.2% compared to that of natural zeolite itself and natural zeolite that heated in 400°C for 4 h (12.6 and 14.8 mg g−1, respectively), when its dose was adjusted at 27 g L−1 with solution pH of 8.3 and agitation speed of 280 r min−1 at 25°C. Negative Gibbs free energy change indicated the spontaneous nature of the adsorption. In addition, both ion-exchange and molecular adsorption being the main mechanisms, in which ion-exchange dominated the ammonium adsorption process near neutral pH, and the molecular adsorption was of secondary importance, and contributed less to the total ammonium removal according to the experimental results under neutral pH conditions.