Negative Standard Free Energy Research Articles

Dynamic modulation and epoxy functionalization of protein-mediated enoate ester-based hybrid cryogels

The current work is focused on the preparation of protein-mediated poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) copolymer as a self-template for in situ synthesis of hybrid gels. Gelatin, collagen, biotin, and l-arginine were used to create hybrid materials with adjustable swelling and elastic properties. Hybrid cryogels tended to swell more than hybrid hydrogels due to their porous nature. Collaged-doped cryogels had the highest swelling, whereas gelatin-doped hybrids showed enhanced elastic modulus. All hybrid gels exhibited pH-sensitive swelling to controlled release applications depending on the degree of protonation of NH2 and COOH groups in the side chains. At low pH conditions, hybrid cryogels exhibited a higher swelling tendency compared to hydrogels. Ion-stimulus-response of hybrid gels was studied to evaluate the effect of salt concentration and features of ambient ions on swelling. Depending on the polyelectrolytic or polyampholytic nature, the extent of swelling in NaCl and KCl solutions varied according to the charge distribution in the network chains. Hybrid gels showed excellent adsorption performance for methyl orange by the presence of epoxy, hydroxyl groups, amino and carboxyl groups providing sufficient active sites. Adsorption capacity of hybrid cryogels is higher than that of hydrogels. The removal rate 97/%, reached an equilibrium state in a short period, suggested that collagen-doped hybrid cryogels have a potential application to remove dyestuff from wastewater. In relation to the decrease of methyl orange concentration in solution, adsorption process followed pseudo-second-order kinetic model. Avrami model has provided a better experimental-calculated fit and adsorption thermodynamics analysis indicated that the adsorption was a spontaneous process with a negative standard free energy. The characteristic findings from this research will provide insights into the design and application of enoate-ester and protein-based combinations in the food, biomedical and cosmetic fields.

Phosphate abatement using calcium silicate hydrate synthesized from alum factory solid waste residue

ABSTRACT Calcium silicate hydrate (CSH), synthesized from the solid waste residue (SWR) of Awash Melkassa Alum Factory was examined for phosphate removal from an aqueous solution. The synthesized CSH was characterized using BET surface area analyzer, Scanning Electron Microscopy, Powder X-ray diffraction, and Fourier-transform infrared spectroscopy. Response surface methodology (RSM) adapted to assess a model equation that correlates the phosphate removal efficiency (R %) with the factors affecting adsorption such as initial phosphate concentration (Co), adsorbent dosage, pH, and time (t). Optimum removal efficiency of 95.69% attained at Co =5.5 mg/L, dose = 5 g/L, pH = 5, and t = 90 min at which consecutive experiments conducted. The adsorption kinetics experimental data fitted well to both pseudo-second-order model (R2 = 0.999) and Elovich model (R2 = 0.996) imply that chemisorption is dominant adsorption mechanism for phosphate adsorption on CSH. The isotherm experimental data fitted well to the Langmuir model (R2 = 0.965). The maximum phosphate adsorption capacity (qm) of 82.58 mg/g obtained at 45°C. The attained negative standard free energy (ΔGo = −5.18 kJ/mol) and positive enthalpy (ΔHo = 7.10 kJ/mol) confirms the spontaneity and endothermic nature of phosphate adsorption by CSH. The synthesized CSH tested for its phosphate removal (R = 63.78%) using real wastewater collected from a local wastewater treatment plant. Bicarbonate and sulfate observed to compete for active sites on the adsorbent during phosphate removal. Generally, the synthesized CSH can be considered as a low-cost silicate material for phosphate abatement.

Use of Ionic Liquid Pretreated and Fermented Sugarcane Bagasse as an Adsorbent for Congo Red Removal

A large amount of industrial wastewater containing pollutants including toxic dyes needs to be processed prior to its discharge into the environment. Biological materials such as sugarcane bagasse (SB) have been reported for their role as adsorbents to remove the dyes from water. In this study, the residue SB after fermentation was utilized for the dye removal. A combined pretreatment of NaOH and methyltrioctylammonium chloride was given to SB for lignin removal, and the pretreated SB was utilized for cellulase production from Bacillus aestuarii UE25. The strain produced 118 IU mL−1 of endoglucanse and 70 IU mL−1 of β-glucosidase. Scanning electron microscopy and FTIR spectra showed lignin and cellulose removal in fermented SB. This residue was utilized for the adsorption of an azo dye, congo red (CR). The thermodynamic, isotherm and kinetics studies for the adsorption of CR revealed distinct adsorption features of SB. Untreated SB followed Langmuir isotherm, whereas pretreated SB and fermented SB obeyed the Freundlich isotherm model. The pseudo-second-order model fitted well for the studied adsorbents. The results of thermodynamic studies revealed spontaneous adsorption with negative standard free energy values. Untreated SB showed a 90.36% removal tendency at 303.15 K temperature, whereas the adsorbents comprised of pretreated and fermented SB removed about 98.35% and 97.70%, respectively. The study provided a strategy to utilize SB for cellulase production and its use as an adsorbent for toxic dyes removal.

Interaction of cephalexin monohydrate with surfactants in aqueous and sodium chloride solution at variable temperatures: Conductivity and spectroscopic measurements

Cephalexin monohydrate (CLM) is a well-known antibiotic applied for prohibiting bacterial growth. Herein, the mode of interaction of CLM with both ionic (cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS)), and nonionic (triton X-100 (TX-100)) surfactants, was investigated using the conductivity measurement and UV–Visible spectroscopic techniques in H2O and NaCl + H2O media at numerous temperatures ranging from 293.15 to 328.15 K. In the current study, the critical micelle concentration (CMC) of CLM + CTAB and CLM + SDS mixed systems was estimated from a sudden and clear breakpoint of specific conductivity (κ) versus the concentration of surfactant plot. A single CMC was found for both CLM + CTAB and CLM + SDS systems in entirely experimental cases studied. The value of CMC of surfactants undergoes a drop in presence of CLM in an aqueous phase and hence, the drug causes an enhancement of the extent of micellization of surfactants. Also, the CMC values of CLM + CTAB and CLM + SDS mixed systems were found to reduce in NaCl + H2O medium and the CMC values were observed to experience a further reduction with increasing concentration of NaCl salt. A negative standard free energy change (∆Gmo) of micellization discloses that the CLM + ionic surfactant micellization is spontaneous. The different thermodynamic parameters of transfer and the enthalpy-entropy compensation parameters of micelle formation were also measured and demonstrated appropriately. The binding constant (Kb) of the CLM + TX-100 mixture has been evaluated from the Benesi-Hildebrand equation and the values were found to be dependent on CLM concentration and temperature. The ∆Hbo and∆Sbo values of CLM + TX-100 mixture reveal the survival of the electrostatic force of interaction along with the presence of hydrophobic interaction developed between the CLM drug and TX-100 surfactant.

Preparation and utilization of cigarette filters based activated carbon for removal CIP and SDS from aqueous solutions

The smoked cigarette filters were used to prepare high-surface-area activated carbons by KOH activation. The highest BET specific surface area of cigarette-filters-based activated carbon (CFAC) was 2726 m2·g−1 obtained at the activation parameter of carbonized materials/KOH = 1:5 and activation temperature of 900 °C, which could concluded that smoked cigarette filters were excellent raw materials for preparation activated carbons. The ciprofloxacin (CIP) and Sodium dodecyl sulfat (SDS) adsorption isotherms, adsorption kinetics and adsorption thermodynamics from aqueous solution using cigarette filters based activated carbon were investigated. The results indicated that Langmuir model and pseudo-second-order models were suitable to describe the CIP and SDS adsorption process of CFAC. More negative standard free energy (ΔG) and positive entropy change (ΔS) of CIP adsorption with increasing temperature indicated the spontaneous nature and increasing randomness of the CIP adsorption process. While More positive ΔG and negative ΔS of SDS adsorption indicated the non-spontaneous processes. The both positive enthalpy change (ΔH) indicated endothermic of CIP and SDS adsorption process.

Adsorptive removal of Cr(VI) from simulated wastewater in MOF BUC-17 ultrafine powder

A water-stable metal-organic framework [Co3(tib)2(H2O)12](SO4)3 (BUC-17) with 2D graphene-like crystal structure was tuned to produce ultrafine powder via the introduction of absolute ethanol. The BUC-17 powders were further characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Zeta potential analysis. The BUC-17 ultrafine powder exhibited excellent adsorption performance toward Cr(VI) from simulated wastewater, in which the maximum uptake capacity is 121 mg g−1 at pH = 4. The kinetics fitting results revealed that the adsorption process is more suitably described by the pseudo-second-order kinetics model. The negative standard free energy change ΔG°, positive enthalpy change ΔH°, and positive entropy change ΔS° of the adsorption process implied that the adsorption between BUC-17 and Cr(VI) was spontaneous and endothermal. As well, the influencing factors of the adsorption process like pH, adsorbent dosage, initial concentration and foreign ions were investigated. Finally, the adsorption mechanism of BUC-17 toward Cr(VI) was proposed.

Adsorption and inhibitive properties of methanol extract of Eeuphorbia Heterophylla for the corrosion of copper in 0.5 M nitric acid solutions

Abstract The adsorption and the inhibitive properties of methanol extract of Euphorbia heterophylla on copper in 0.5 M HNO3 have been studied by weight loss method at different temperatures (30-50°C), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Also, the surface morphology was analyzed by scanning electron microscopy (SEM). It was found that the inhibition efficiency increases with increasing extract doses and decreased with increasing temperature. The polarization data revealed that this extract acts as mixed type inhibitor. The adsorption process was more favored at lower temperatures with larger negative standard free energy. The extract was adsorbed physically on the copper surface followed Frumkin isotherm.

Preparation of Activated Carbon From Polygonum orientale Linn. to Remove the Phenol in Aqueous Solutions.

Phenol components are major industry contaminants of aquatic environment. Among all practical methods for removing phenol substances from polluted water, activated carbon absorption is the most effective way. Here, we have produced low-cost activated carbon using Polygonum orientale Linn, a wide spreading species with large biomass. The phenol adsorption ability of this activated carbon was evaluated at different physico-chemical conditions. Average equilibrium time for adsorption was 120 min. The phenol adsorption ability of the P. orientale activated carbon was increased as the pH increases and reached to the max at pH 9.00. By contrast, the ionic strength had little effect on the phenol absorption. The optimum dose for phenol adsorption by the P. orientale activated carbon was 20.00 g/L. The dominant adsorption mechanism of the P. orientale activated carbon was chemisorption as its phenol adsorption kinetics matched with the pseudo-second-order kinetics. In addition, the equilibrium data were fit to the Langmuir model, with the negative standard free energy and the positive enthalpy, suggesting that adsorption was spontaneous and endothermic.

Adsorption of 1,1-dimethylhydrazine (UDMH) from aqueous solution using magnetic carbon nanocomposite: kinetic and thermodynamic study

In this work, removal of UDMH as a pollutant with considerable toxicity is studied using activated carbon magnetic nanocomposite with fast and easy separation. To optimize the process, effective parameters, such as pH, adsorbent dosage, contact time, and temperature, have been investigated. More than 90% UDMH removal efficiency obtained within 30 min of contact time, 20 mg of adsorbent at pH 6 and room temperature. The adsorption behavior was evaluated based on equilibrium data, using both the Langmuir and Freundlich isotherm models. It was found that adsorption data were interpreted by Freundlich model better than Langmuir model with regression coefficient of 0.9971. Besides, the adsorption data were well described by the pseudo-second-order kinetic model. The adsorption thermodynamic parameters showed that the adsorption process is endothermic and spontaneous with positive standard enthalpy of 2.74 J mol−1 and negative standard free energy of 29.08 kJ mol−1, respectively. Also standard entropy changes of 97.56 J mol−1 k−1 was calculated.

Adsorption behavior of long alkyl chain imidazolium ionic liquids at the n-butyl acetate + water interface

The adsorption behavior of amphiphilic long alkyl chain imidazolium ionic liquids (ILs), 1-alkyl-3-methylimidazolium chloride {[Cnmim][Cl], n=12, 14, 16} at the interface of n-butyl acetate+water system was studied. Within IL bulk concentration range of 1.00·10−5–1.00·10−2mol/dm3 and temperature of 293.2–318.2K, the used ILs act as excellent surfactants and reduce the interfacial tension significantly. The corresponding interfacial activity appeared logically in the order of [C16mim][Cl]>[C14mim][Cl]>[C12mim][Cl]. An almost linear decrease in interfacial tension was also relevant by temperature. For modeling, the Szyszkowski adsorption equation was used to reproduce the experimental data. The consistent fittings confirm the ideal adsorption of the used IL molecules at the interface. Results also show that adsorption effectiveness increases with the alkyl chain length; however, it declines with temperature. On the other hand, adsorption tendency increases with alkyl chain length as well as with temperature. Negative standard free energy values indicate simultaneous adsorption for all cases.

Pectin as promising green corrosion inhibitor of aluminum in hydrochloric acid solution

The present article describes the use of promising green eco-friendly pectin natural polymer as successful corrosion inhibitor on the surface of aluminum metal in acidic media. The inhibition efficiency first increased linearly up to 2.0g/L, and then it continues steady exponential increase until it reached plateau. The maximum inhibition efficiency obtained at 10°C using pectin concentration=8.0g/L was ∼91%, whereas at 40°C it severely declined to 31%. As pectin concentration increased, higher activation energy, enthalpy of activation and entropy of activation were obtained. In presence of 2.0M HCl, the aluminum sheet showed longitudinal parallel grooves together with huge amount of irregular deep voids distributed along the sheet, whereas in the presence of inhibitor and acidic medium the number of deep voids diminished. The adsorption process was more favored at lower temperatures with larger negative standard free energy. Adsorption of pectin macromolecules on aluminum surface demonstrated proper Langmuir isotherm fit.

Formation of an aluminum-alloyed coating on AZ91D magnesium alloy in molten salts at lower temperature

An aluminum-alloyed coating was formed on an AZ91D magnesium alloy in molten salts containing AlCl3 at a lower temperature of 380°C. The microstructure and phase constitution of the alloyed layer were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectrum and X-ray diffraction. The nano-hardness of the coating was studied by nanoindentation associated with scanning probe microscopy. The corrosion resistance of the coated specimen was evaluated in a 3.5wt.% NaCl solution by electrochemical impedance spectroscopy and cyclic potentiodynamic polarization. The results show that the aluminum-alloyed coating consists of Mg2Al3 and Mg17Al12 intermetallic layers. The formation of the coating is dictated by the negative standard free energy of the reaction: 2AlCl3+3Mg=3MgCl2+2Al. This process is associated with a displacement reaction mechanism and diffusion process that takes place during the molten salt treatment. High activity of Al elements in molten salts contributes to the lower temperature formation of the Al-alloyed coating. The alloyed coating markedly improves the hardness as well as the corrosion resistance of the alloy in comparison with the untreated AZ91D magnesium alloy, which is attributed to the formation of the intermetallic compounds.

Sorptive removal of methylene blue from aqueous solutions by polymer/activated charcoal composites

AbstractIn this study, a new sorbent, a poly(acrylamide‐co‐itaconic acid) [P(AAm‐co‐IA)]/activated charcoal (AC) composite, was prepared by the aqueous polymerization of acrylamide and itaconic acid in the presence of AC with N,N′‐methylene bisacrylamide as a crosslinker and potassium persulfate as an initiator. The P(AAm‐co‐IA)/AC composite sorbent showed a fair capacity to adsorb the cationic dye methylene blue. The maximum sorption capacity, as studied at 23, 37, and 50°C and determined with the Langmuir isotherm model, was found to be 909.0, 312.5, and 192.3 mg/g, respectively. For an initial concentration of 5 mg/L, the kinetic uptake data were studied with various kinetic models. The pseudo‐second‐order equation was found to fairly fit the uptake data with a regression value of 0.999. The dye uptake increased with the pH of the sorbate solution, and the optimum pH was found to be in the range of 7–10. Intraparticle diffusion was also observed to take place, and the coefficient of intraparticle diffusion was evaluated to be 26.51 × 10−2 mg g−1 min−1/2. The various thermodynamic parameters were also determined to predict the nature of the uptake process. The sorption process was found to be spontaneous, as indicated by a negative standard free energy change. The negative standard enthalpy change suggested an exothermic nature for the uptake. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Equilibrium, kinetic and thermodynamic studies on the adsorption of the toxins of Bacillus thuringiensis subsp. kurstaki by clay minerals

The persistence of Bacillus thuringiensis ( Bt) toxins in soil is further enhanced through association with soil particles. Such persistence may improve the effectiveness of controlling target pests, but impose a hazard to non-target organisms in soil ecosystems. In this study, the equilibrium adsorption of the Bt toxin by four clay minerals (montmorillonite, kaolinite, goethite, and silicon dioxide) was investigated, and the kinetic and thermodynamic parameters were calculated. The results showed that Bt toxin could be adsorbed easily by minerals, and the adsorption was much easier at low temperature than at high temperature at the initial concentration varying from 0 to 1000 mg L −1. The adsorption fitted well to both Langmuir and Freundlich isotherm models, but the Freundlich equation was more suitable. The pseudo-second-order (PSO) was the best application model to describe the adsorption kinetic. The adsorption process appeared to be controlled by chemical process, and the intra-particle diffusion was not the only rate-controlling step. The negative standard free energy ( Δ G m θ r ) values of the adsorption indicated that the adsorption of the Bt toxin by the minerals was spontaneous, and the changes of the standard enthalpy ( Δ H m θ r ) showed that the adsorption of the Bt toxin by montmorillonite was endothermic while the adsorption by the other three minerals was exothermic.

Investigation of interactions between some anionic dyes and cationic surfactants by conductometric method

The interactions of cationic surfactants with anionic dyes were studied by conductometric method. Benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl) and benzyltributylammonium chloride (BTBACl) were used as cationic surfactants and indigo carmine (IC) and amaranth (Amr) were chosen as anionic dyes. The specific conductance of dye–surfactant mixtures was measured at 25, 35 and 45 °C. A decrease in measured specific conductance values of dye–surfactant mixture was caused by the formation of non-conducting or less-conducting dye–surfactant complex. The equilibrium constants, K 1, the standard free energy changes, Δ G 1 ° , the standard enthalpy changes, Δ H 1 ° and the standard entropy changes, Δ S 1 ° for the first association step of dye–surfactant complex formation were calculated by a theoretical model. The results showed that the equilibrium constants and the negative standard free energy change values for all systems decreased as temperature increased. Also these values decreased for all systems studied with increasing alkyl chains of surfactants due to the steric effect. When the equilibrium constant values, K 1, for the first association step of IC–surfactant and Amr–surfactant systems with the same surfactant were compared, the values of K 1 for IC–surfactant system were higher than that of Amr–surfactant system.

Effect of phenols on the potentiometric response of a nitrate-ion-selective electrode

The effect of phenols containing different electron-withdrawing substituents on the potentiometric responses of several liquid PVC membranes containing the complex trioctylmethylammonium–nitrate, TOMA +NO 3 −, is analyzed. The results make it possible to separate these phenols into two groups; those phenols containing electron-releasing groups, which produce almost Nernstian slopes, and those containing electron-withdrawing substituents, which generate sub-Nernstian slopes. The highly negative standard free energy of transfer of the aryl phenolic group from water to a cationic polar head suggests that these phenols are mainly located in the membrane phase associated with TOMA + via a cation– π interaction. It seems that the strength of this interaction, and hence of the nitrate dissociation, is affected by the presence of phenols in an extension which correlates well with the kind of phenol present in these membranes and, consequently, with the type of their potentiometric responses.

Micellar properties of some surface active mixed copper(II) chelates

Abstract Micellar properties of surface active mixed copper(II) chelates, [Cu(R-tmed)(acac)X] (where R-tmed = N,N,N′-trimethyl-N′-alkylethylenediamine, R = C12H25 to C16H33, acac = acetylacetonate and X = Cl, Br) and [Cu(C12-tmed)(acac)Cl] (where C16-dmed = N,N′-dimethyl-N-cetylethylenediamine) were investigated by surface tensiometry, conductivity, viscosity and light scattering studies. In aqueous solution, they have a large negative standard free energy of adsorption at the air/water interface and a negative standard free energy of micellization. The degree of dissociation of the halide ions from the positively charged micelles falls in the range 0.22–0.29, with the [Cu(C12-tmed)(acac)Cl] micelle having the largest degree in the series studied. Viscosity and light scattering experiments suggest that the shape of the [Cu(C12-tmed)(acac)Cl] micelle is a sphere and that of its C16 analogue is an ellipsoid.

Transient kinetic and isotopic tracer studies of the myosin adenosine triphosphatase reaction

From transient kinetic studies of the Mg2+-dependent adenosine triphosphatase of myosin subfragment 1, prepared from rabbit skeletal muscle, a seven-step mechanism has been proposed. Features of this mechanism include two-step processes for ATP and ADP binding in which the binary complex isomerizes in addition to a rapid nucleotide association step. In the case of ATP a large negative standard free energy change is associated with the isomerization. An overall rate-limiting isomerization of the myosin-product complex prior to product release has been identified. Studies on the mechanism of cleavage of ATP bound to the active site indicate the process is readily reversible and can account for the observation that more than one oxygen of the product phosphate arises from water. This proposal has been substantiated by the finding that the oxygen atoms of the gamma-phosphoryl group of bound ATP also undergo extensive exchange with water.