Standard Gibbs Free Energy Change Research Articles

Research on electrical conductive properties of thulium-doped calcium zirconate solid electrolyte

To further investigate the electrochemical performance of Tm doped CaZrO3 electrolyte, the CaZr1−xTmxO3−α (x = 0, 0.025, 0.05, 0.075 and 0.1) solid electrolyte specimens were prepared by high temperature solid state method. The phase structure and microstructure of the electrolyte samples were analyzed by Raman spectrum, XRD and SEM. The electrical conductivity of the specimen was measured at the temperature of 673∼1373K in hydrogen-rich and oxygen-rich atmosphere by the two-terminal AC impedance spectroscopy method. The H/D isotope effect of the specimen at different temperature was tested to confirm the dominant conducting carrier in predetermined temperature and atmosphere. It is found that proton is the dominant charge carrier both in oxygen-rich and hydrogen-rich atmosphere at the lower temperature below 1073 K. However, at higher temperature above 1073K, the predominant charge carrier seems to be oxygen ion vacancy in hydrogen-rich, whereas to be electron hole in oxygen-rich atmosphere, based on the analysis of the atmospheric dependence of the electrical conductivity. Moreover, partial conductivities of conducting species, the active doping amount of Tm and the standard Gibbs free energy changes for interstitial proton production by dissolution of water and hydrogen in Tm doped electrolyte were estimated based on crystal defect chemistry theory.

Thermodynamic investigation of biperiden hydrochloride and cyclodextrins supramolecular systems

Isothermal titration calorimetry (ITC) and theoretical calculations were used to investigate the interaction of cyclodextrins (CDs) with biperiden hydrochloride (BPR), a drug for Parkinson’s disease treatment. Among the natural CDs, βCD demonstrated the larger equilibrium constant (Keq = 9,020), demonstrating the cavity size dependency for the interaction. Carboxymethyl-β-cyclodextrin (CMβCD) demonstrated a stronger affinity and higher intermolecular complex stability. Additionally, the Keq for the CMβCD:BPR system varied from 68,100 at 298.15 K to 31,650 at 328.15 K, with a constant standard Gibbs free energy change. The theoretical calculations demonstrated the most stable structure for the CMβCD:BPR inclusion complex.

Elucidating the Mechanism of Copper-Induced Photoluminescence Quenching in 2-Phenylbenzimidazole-5-Sulfonic Acid.

To explore the possible impact of 2-Phenylbenzimidazole-5-sulfonic acid (PBSA) on the function of a sunscreen, in this work we investigate the binding of copper metal ions (Cu2+) to PBSA. Due to the existence of an intrinsic interaction phenomenon between Cu2+ ions and PBSA molecules, the photoluminescence (PL) quenching arises owing to the charge transfer from PBSA to Cu2+ ions. The mechanism of fluorescence quenching is probed experimentally following excitation at 306 nm by evaluating various quenching parameters with the help of the Stern-Volmer plot. Through the assessment of the values of the Stern-Volmer constant ( ) and bimolecular quenching rate constant ( ), it is deduced that the dynamic mode of PL quenching is operative between PBSA and Cu2+ ions. We evaluate the number of binding sites (n = 1) that advocate the presence of a single binding site in PBSA for Cu2+ ions. The numerical value of standard Gibbs free energy change, ~ -27.485 kJ.mol-1 implies the spontaneous binding between Cu2+ ions and PBSA molecules. The results obtained give an insight into the mechanism of metal-induced PL quenching of water soluble PBSA sunscreen.

Defective NH2-UiO-66 for effective Pb(II) removal: Facile fabrication strategy, performances and mechanisms

Defective NH2-UiO-66 adsorbent (named as NH2-UiO-66-SD) was successfully fabricated via post-synthesis method with the aid of both sodium carbonate anhydrous (Na2CO3) and diethylenetriaminepentaacetic acid (DTPA), in which the defective structure was confirmed by various characterizations. The as-obtained defective NH2-UiO-66-SD exhibited outstanding Pb(II) sorption capacity (172.21 ​mg ​g−1) and rapid diffusion rate (29.87 ​mg ​g−1 min−0.5) at room temperature with optimal pH being 5.47. The Pb(II) sorption behavior was conformed to pseudo-second-order kinetics and Langmuir model, demonstrating that the chemical sorption of the monolayer played a dominant model. As well, the thermodynamic parameters like standard Gibbs free energy change ΔGo (−31.21 ​kJ ​mol−1), standard enthalpy change ΔHo (12.79 ​kJ−1 ​mol−1) and standard entropy change ΔSo (146.73 ​J ​mol−1 ​K−1) revealed that the Pb(II) sorption process of NH2-UiO-66-SD was spontaneous, endothermic and disordered. Furthermore, the NH2-UiO-66-SD exhibited desirable desorption and recirculation performances (removal efficiencies >85 ​% in 5 runs) with ideal stability. Moreover, the Pb(II) sorption mechanism of NH2-UiO-66-SD mainly included the electrostatic attractions and coordinative interactions. Overall, this work offered an intriguing method of fabricating defective NH2-UiO-66 adsorbent, which vastly enhanced adsorption efficiency for toxic metal ions elimination from wastewater.

Synthesis, optical properties, DNA, β-cyclodextrin interaction, hydrogen isotope sensor and computational study of new enantiopure isoxazolidine derivative (ISoXD)

A novel isoxazolidine derivative (ISoXD) dye was successfully synthesized and comprehensively characterized. In this study, we conducted a thorough examination of its various properties, including optical characteristics, interactions with DNA and β-cyclodextrin (β-CD), molecular docking, molecular dynamic simulation, and density functional theory (DFT) calculations. Our investigation encompassed a systematic analysis of the absorption and emission spectra of ISoXD in diverse solvents. The observed variations in the spectroscopic data were attributed to the specific solvent's capacity to engage in hydrogen bonding interactions. Remarkably, the most pronounced intensities were observed in glycol, which can establish many hydrogen bonds with ISoXD.Furthermore, our study revealed a significant distinction in the fluorescence behavior of ISoXD when subjected to different solvents, particularly between CHCl3 and CDCl3. Moreover, we explored the fluorescence intensity of the ISoXD complex in the presence of various metals, both in ethanol and water. The ISoXD complex exhibited a substantial increase of fluorescence upon interaction with different metal ions. The utilization of DFT calculations allowed us to propose an intramolecular charge transfer (ICT) mechanism as a plausible explanation for this quenching phenomenon. The interaction of ISoXD with DNA and β-CD was studied using absorption spectra. The binding constant (K) and the standard Gibbs free energy change (ΔGo) for the interaction between DNA and β-CD with ISoXD were determined. In docking study, ISoXD exhibited significant docking scores (−6.511) and MM-GBSA binding free energies (−66.27 kcal/mol) within the PARP-1 binding cavity. Its binding pattern closely resembles to the co-crystal ligand veliparib, and during a 100ns MD simulation, ISoXD displayed strong stability and formed robust hydrogen bonds with key amino acids. These findings suggest ISoXD's potential as a PARP-1 inhibitor for further investigation in therapeutic development.

Removal of hexavalent chromium from electroplating wastewater by ion-exchange in presence of Ni(II) and Zn(II) ions

This study presents the ion-exchange elimination of hexavalent chromium [Cr(VI)] from electroplated industrial wastewater. The effects of experimental factors such as pH, contact time, adsorbent dose, temperature, and co-ions on Cr(VI) removal were investigated. The metal ions were maximally removed (up to 96.7 %) and obtained with a resin dosage of 3 g L−1 at pH 2 for 70 min. Thermodynamic parameters, such as the standard Gibbs free energy change (ΔG0), standard enthalpy change (ΔH0),and standard entropy change (ΔS0), were calculated. The negative value of ΔG0(−8.031 kJ/mol K)indicates the spontaneity of the ion exchange process. The Freundlich and Langmuir isotherms fit the adsorption data well. The adsorption kinetics of Cr(VI) on the Amberlite IRA400 resin were analyzed using reversible first-order kinetics. The presence of Zn(II) and Ni(II) increased the efficiency of the adsorption process in the order Zn(II) > Ni(II). Column experiments were conducted to determine the breakthrough point of the packed-bed resin column, and a break-even concentration of 0.1 mgL−1 was deducted after the treatment of 4.5 L of the effluent. The adsorption data from the column studies were fitted using the Adam–Bohart adsorption model and the results fit the model well. A mathematical approach to the regeneration process is described in this study. The reusability of the resin was tested for 30 cycles and its efficiency of the regenerated resin was found to be above 97 % after the 30th cycle.

Adsorption of aqueous Cr (VI) onto UiO66NH2 MOF: Isotherm, thermodynamics and mechanism studies

As a member of the UiO-66 family, UiO66NH2 MOF (UNH) possessed enhanced stability, high surface area, increased pore size, and pore volume. Additionally, its amino groups offer spectacular affinity to capture Cr (VI). With these propitious features, UNH was fabricated by a facile solvothermal route in this study. It was then characterized by XRD and FTIR to confirm its successful formation. Its affinity towards efficacious capture of aqueous Cr (VI) was explored with the help of isotherm models and thermodynamic parameters. The Langmuir isotherm model fits best the experimental data, demonstrating monolayer Cr (VI) sorption on a homogenous UNH surface. The maximum adsorption capacity was determined as 51 mg/g. Negative ΔG° values suggested that the Cr (VI) uptake process is spontaneous and favorable, while the endothermic nature of the sorption was evident from positive values ΔH°. Thermodynamic parameters such as standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard Gibbs free energy change (ΔG°) were determined as 6.651 kJ mol−1, –3.216 kJ mol−1, and 33.76 KJ K−1.mol−1 respectively. FTIR and pH studies evidenced that the sequestration of Cr (VI) onto UNH proceeds through the electrostatic attraction mechanism, supported by the fitted isotherm model and thermodynamic parameters’ results.

Cost-efficient and sustainable treatment of malachite green, a model micropollutant with a wide range of uses, from wastewater with Pyracantha coccinea M. J. Roemer plant, an effective and eco-friendly biosorbent

ABSTRACT Malachite green is a pestilential micropollutant with a wide range of uses. In this work, cost-efficient and sustainable treatment of malachite green from aqueous medium was first studied using the biosorbent material obtained from Pyracantha coccinea M. J. Roemer plant. The biosorption kinetics followed the pseudo-second-order model (R 2: 0.996). The standard Gibbs free energy change parameter ranging from −8.472 kJ mol−1 to −7.357 kJ mol−1 indicated a spontaneous and feasible treatment process. The biosorption isotherm was well described by Freundlich model with an R 2 of 0.991. SEM and FTIR studies showed an irregular and uneven biosorbent surface morphology rich in active site. The biosorbent exhibited a good biosorption performance compared to its competitors, with a capacity of 117.745 mg g−1. As a result, this study indicated that P. coccinea M. J. Roemer-based biosorbent could be a promising candidate for the economical, effective, eco-friendly and sustainable treatment of malachite green micropollutant.

Phase partitioning nature, interaction forces and thermodynamic parameters of triton X-100 and bovine serum albumin mixture: impacts of the composition of Na-salt

Herein, the assessment of interactions between a non-ionic surfactant (NIS) triton X-100 (TNX-100) and a globular protein bovine serum albumin (BSA) was explored through the determination of clouding nature in aqueous solution of sodium salts (Na-salts). Sodium chloride (NaCl), sodium acetate (NaOAc), sodium carbonate (Na2CO3), sodium oxalate (Na2Oxal), sodium sulphate (Na2SO4), and sodium phosphate (Na3PO4) have been chosen to assess their impacts on the clouding nature of TNX-100 + BSA mixture. The estimated cloud point (CP) values were noticed to be lowered with the enhancement of [Na-salts]. The lessening of CP values has been explained by the salting out effect of anions. The calculated standard Gibbs free energy change ( Δ G c o ) was positive at all examined conditions which illustrates the nonspontaneity of phase change. The standard enthalpy ( Δ H c o ) and entropy ( Δ S c o ) changes exhibited negative values at low contents of aq. Na-salts and positive values at high aq. Na-salts content. These consequences illustrate the presence of electrostatic interactions at low Na-salts concentration and hydrophobic interactions at high Na-salts concentration. Furthermore, enthalpy-entropy parameters were successfully computed and explained with proper clarification.

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.

The precipitation process for a rare earth leach solution with calcium oxide in the presence of ascorbate and calcination to oxide of high purity

Sulfate ions coprecipitate with rare earth metal ions to form alkaline rare earth sulfate (RE2(OH)4SO4) in the CaO precipitation process, leading to excessive content of sulfate in the mixed rare earth oxide. Due to the difference of coordination ability between ascorbate, sulfate, hydroxyl and rare earth metal ions, ascorbate is introduced into the pregnant leach solution (PLS) during the CaO precipitation process. It realizes the coprecipitation between ascorbate (C6H7O6−) and rare earth metal ions, reducing the formation of RE2(OH)4SO4 and improving the purity of mixed rare earth oxide. In this paper, the standard reaction Gibbs free energy changes of the possible reactions in the precipitation process were calculated using the group contribution method, to draw the species distribution equilibrium diagram with Newton's iteration method. When ascorbate exists, rare earth metal ions in the PLS tend to form the alkaline rare earth ascorbate (RE2(OH)4(C6H7O6)2) instead of RE2(OH)4SO4. Furthermore, the effect of the reaction conditions on the precipitation process were studied. When the molar ratio of rare earth metal ions to ascorbate was 1.17, the purity of the mixed rare earth oxide was 96.2 wt% and the sulfate content was 2.2 wt%. Finally, based on the results of the material balance calculation, FTIR, XRD and TG-DSC tests, it was further confirmed that ascorbate participated in the form of RE2(OH)4(C6H7O6)2, and effectively suppressed the generation of RE2(OH)4SO4. Consequently, the results facilitate the green and efficient extraction of rare earths from the ion-adsorption type ore.

Enhanced adsorption films of dendrimers on mild steel for super protection

ABSTRACT This study employed metronidazole skeletons based on the target branched molecules (TBMs) for achieving efficient anti-corrosion of mild steel in HCl solution. In contrast, the reference linear molecules (RLMs) carrying a single metronidazole framework were also made. The excellent corrosion resistance performance of the target dendrimers for mild steel electrodes in HCl solution was demonstrated. It is shown that the TBMs displayed a superior anti-corrosion effect for mild steel over RLMs in HCl medium at 298 K (at 0.15 mol/L, TBM1, 97.70% versus RLM1, 90.89%). It is shown that the standard Gibbs free energy changes of the adsorption of the TBMs on mild steel surface are below −33 kJ/mol (TBM1, −34.58 kJ/mol), thus an enhanced adsorption film was formed.

Effect of uni-divalent electrolyte in the interaction associated with solubility for the predominant form of L-isoleucine and L-serine in aqueous media

The study aimed to measure the solubilities of L-serine and L-isoleucine in an aqueous ammonium sulfate [(NH4)2SO4] solution at different temperatures (288.15 to 308.15 K) using a gravimetric technique. In pure aqueous media L-serine solubility is 4.1218 in mol•kg−1 of water while for L-isoleucine is 0.3094 mol•kg−1 at 298.15 K. The obtained solubility data was used to estimate the thermodynamic properties of the amino acids, such as the standard Gibbs free energy and standard entropy change during the solvation process. The analysis involved investigating the short range chemical interactions between the amino acids and the electrolyte solution, which significantly influenced the solvation thermodynamics. The study found that L-serine exhibited a salting in effect, meaning its solubility increased in the presence of ammonium sulfate, while L-isoleucine experienced a salting out effect, resulting in decreased solubility with the electrolyte. Additionally, solubility parameters were employed to assess the chemical strength of the amino acids and understand their solute–solvent interactions and relative solubilities in the solution. Overall, this experimental investigation provided valuable insights into the solvation behavior and chemical characteristics of L-serine and L-isoleucine in the presence of an electrolyte solution.

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.

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.

Influence of polyvinyl alcohol coated porous Al2O3 ceramic waste particles on cement properties in geothermal applications

To improve the low strength of the existing geothermal temporary sealing cement (GTSC) and figure out the influence of PACW on cement performances in geothermal applications, the hard porous Al2O3 ceramic waste (PACW) was introduced into oil well cement. The water-soluble PVA was coated on PACW particles to wrap the porous ceramic at relatively low temperature for geothermal drilling, and dissolve in water at ≥ 90 ℃ for hot water flow. The compressive strength, hydrates, pore structures and interface transition zone of cement with raw or modified PACW were tested. The results showed that 10% raw and modified PACW enhanced the compressive strength of oil well cement by 57.69% and 60.31% respectively, during the 90 ℃ water immersing. For the cement containing 10% raw and modified PACW, thermal weight loss related to degradation of hydrates and CH increased, meso pores fraction rose to 52.73% and 51.93 % respectively, and the deeper etch pits on surfaces of the mineral suggested the promoting effect of PACW on cement hydration. The promoted cement hydration and formed hydrates with their filling effect contributed to the cement strength enhancement. As the thermal weight loss attributed to AFm increased after immersion, the thermodynamic parameters of the possible transformation reaction of AFt to AFm were calculated. The standard molar Gibbs free energy change of the reactions are negative, and microstructure images showed that the PACW surface was covered by lots of flaky AFm crisscrossed with large hexagonal AFt crystals, proving that the alumina in PACW participated in and promoted the transformation of AFt to AFm. In addition to reservoir protection, simplifying construction procedures and reducing the time cost of geothermal development, the high-strength GTSC will further strengthen the hole wall and reduce the risk of borehole collapse.

Structural characterization of a cytosine-rich potential quadruplex forming sequence in the EGFR promoter

I-motifs are tetra-helixes that may form in cytosine-rich strands. They are based on cytosine–cytosine+ base pairs that require the N3 hemi-protonation of the nucleobases, and therefore, the stability of these non-canonical DNA arrangements depends on pH. These structures are promising targets for the development of new cancer therapies since they are enriched in the promoters of oncogenes where they can play a role in the regulation of transcription. The proximal promoter of the EGFR oncogene has multiple regions with a significant potential to form such a tetra-helix arrangement. Here, we present the thermodynamic characterization of a C-rich sequence located 37 nucleotides upstream of the transcription starting site of EGFR. We confirmed the ability of this sequence to fold into an I-motif. By applying a global analysis of calorimetric and spectroscopic data, we derived the dependency of the apparent standard Gibbs free energy change associated with the I-motif folding upon temperature and pH. The results showed that, in contrast to in silico prediction, only 4 CC+ base pairs formed while additional GC and TT base pairings were detected in the I-motif. Noteworthy, a single residue mutation at G14 largely shifts the equilibrium toward the formation of multimeric species.

Enhanced adsorption of target branched compounds including antibiotic norfloxacin frameworks on mild steel surface for efficient protection: An experimental and molecular modelling study

In this study, an approach was proposed to employ new target branched compounds (TBCs) including multiple antibiotic norfloxacin frameworks for intensified adsorption films to achieve super protection of mild steel in HCl medium. Thus, the TBCs containing bis/tri norfloxacin skeletons were synthesized by multi-step preparation route. In addition, the reference linear compound (RLC) including a single norfloxacin part was also synthesized. The chemical structures of these compounds were confirmed by various means. It was demonstrated that the TBCs could form the tough adsorption films on the surface of mild steel, which could be processed mainly through chemisorption effect. The electrochemical analysis suggested that the TBCs displayed superior corrosion inhibition performance for low carbon steel in 1.0 mol·L−1 HCl solution over the RLC (RLC, 87.80%; TBC1, 97.63%; TBC2, 98.35%), which was further understood by the molecular modelling. The isotherm adsorption plots were employed to analyze the spontaneous adsorption process of the TBCs on low carbon steel surface, and a prominent chemisorption could be inferred by the standard Gibbs free energy changes of the adsorption.

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.