Free Energy Change Of Adsorption Research Articles

N-Doping Coupled with Co-Vacancies Activating Sulfur Atoms and Narrowing Bandgap for CoS Toward Synergistically Accelerating Hydrogen Evolution.

The combination of hetero-elemental doping and vacancy engineering will be developed as one of the most efficient strategies to design excellent electrocatalysts for hydrogen evolution reaction (HER). Herein, a novel strategy for N-doping coupled with Co-vacancies is demonstrated to precisely activate inert S atoms adjacent to Co-vacancies and significantly improve charge transfer for CoS toward accelerating HER. In this strategy, N-doping favors the presence of Co-vacancies, due to greatly decreasing their formation energy. The as-developed strategy realizes the upshift of S 3p orbitals followed by more overlapping between S 3py and H 1s orbitals, which results in the favorable hydrogen atom adsorption free energy change (ΔGH ) to activate inert S atoms as newborn catalytical sites. Besides, this strategy synergistically decreases the bandgap of CoS, thereby achieving satisfactory electrical conductivity and low charge-transfer resistance for the as-obtained electrocatalysts. With an excellent HER activity of -89.0mV at 10.0mA cm-2 in alkaline environments, this work provides a new approach to unlocking inert sites and significantly improving charge transfer toward cobalt-based materials for highly efficient HER.

Extractive adsorption of 1,3-propanediol on a novel polystyrene macroporous resin enclosing medium and long-chain alcohols as extractant

Extractive adsorption is an integrated separation method employing a novel resin with both particle and liquid characteristics in terms of adsorption and extraction. In this study, the novel extractive adsorption polystyrene-divinylbenzene (PS-DVB) macroporous resin was synthesized by suspension polymerization, in which n-octanol (OL-PS-DVB) or mixed alcohols of n-octanol, undecyl alcohol, and tetradecyl alcohol (MA-PS-DVB) were added as porogen and enclosed in the resin skeleton after the reaction. The characterization of the two novel resins of OL-PS-DVB and MA-PS-DVB showed that they have large specific surface areas of 48.7 and 17.4 m2/g, respectively. Additionally, the two synthesized resins have much higher static adsorption capacities of 1,3-propanediol (511 and 473 mg/g) and dynamic adsorption capacities (312 and 267 mg/g) than traditional resins, because extractants enclosed in the resin can increase the adsorption capacity. Through Langmuir equation, the theoretical static maximum adsorption capacity of the mixed alcohols resin is 515 mg/g at 298 K and Gibbs free energy change of adsorption was -3781 J/mol, indicating that the adsorption process was spontaneous. In addition, the sorbent concentration effect in the resin was generated at high 1,3-propanediol (1,3-PDO) concentrations. The fitting of the Flocculation model can reveal that there is a possible relation between adsorption and flocculation. Compared to OL-PS-DVB, MA-PS-DVB showed better performance in the recovery yield of 1,3-PDO and other byproducts, the removal rates of the inorganic salt and protein, and the efficiency of recycled resin. For MA-PS-DVB, the recovery of 1,3-PDO, butyrate acid, acetic acid, and residual glycerol was 97.1%, 94.7%, 93.3%, and 90.3%, respectively. Simultaneously, the resin of MA-PS-DVB could remove 93.8% of inorganic salts and 90.9% of proteins in the concentrated fermentation broth. The two synthesized resins of OL-PS-DVB and MA-PS-DVB still had 90% or 92% of capacity for extractive adsorption of 1,3-propanediol after 10 times of recycling, which exhibited potential application in the separation of 1,3-propanediol from fermentation broth.

Benzethonium chloride as a tungsten corrosion inhibitor in neutral and alkaline media for the post-chemical mechanical planarization application

The cleaning solution for the post-chemical mechanical planarization (post-CMP) process of tungsten in neutral-alkaline media requires corrosion inhibitors as an additive, especially for advanced devices where the device node size shrinks below 10 nm. In the present study, the corrosion inhibition performance of benzethonium chloride (BTC) is evaluated in neutral-alkaline conditions. The electrochemical impedance spectroscopy (EIS) analysis showed ∼ 90 % of corrosion inhibition efficiency with an optimum concentration of 0.01 wt% BTC at both pH 7 and 11. Langmuir adsorption isotherm, frontier molecular orbital theory, molecular simulation, contact angle, precipitation study, and X-ray photoelectron spectroscopy analysis were performed to identify the inhibition mechanism of the BTC molecule on the W surface. Based on the proposed mechanism, the electrostatic attraction between the positively charged N atom in the BTC molecule and the negatively charged W surface initiates the adsorption of the molecule. The high dipole moment and large molecular size enhance the physical adsorption of the molecule to the surface. In addition to this, the adsorption isotherm analysis shows that possible chemical interaction with a moderate value of Gibbs free energy change of adsorption exists between the W and BTC molecule. The excellent corrosion inhibition efficiency of BTC on W is confirmed by the frontier molecular orbital theory and molecular dynamic simulation analysis.

Effect of polylactic acid on the micellization of SDS and CTAB: physicochemical studies on surfactants aggregation

Abstract This study reports the aggregation behavior of polylactic acid (PLA) with ionic surfactants e.g. sodium dodecyl sulphate (SDS) and hexadecyltrimethylammonium bromide (CTAB) at different temperatures. Surface tension and conductivity techniques were used to investigate these physicochemical properties. Surface tension measurements were carried out to find out critical micelle concentration (CMC), free energy change of micellization (ΔG m), free energy change of adsorption (ΔG ads) and surface excess concentration (Γ). Conductivity measurements were used to determine CMC, degree of ionization (α) and degree of counter ion binding (β). The values of α and β obtained for SDS were (0.389 and 0.611 respectively), while for CTAB the values of α and β were (0.239 and 0.761 respectively). This type of electrostatic interactions is very important which can be applied in various industrial applications (e.g. pharmaceutical, industrial foaming, oil recovery etc.).

Can the Langmuir adsorption coefficient be used to derive the adsorption Gibbs energy?

To explore the inhibition mechanism of corrosion inhibitors for metals in aqueous solution, the Langmuir adsorption isotherm has been widely used to ascertain the adsorption mode of the inhibitors on the metal surface. Meanwhile the obtained Langmuir adsorption coefficients have been further applied to calculate Gibb free energy change in the adsorption processes. However, the relationship between the Langmuir adsorption coefficients and Gibbs free energy change of adsorption has been misused for plant extracts (as inhibitors) whose composition and/or content were unknown. Herein, the relationship between the Langmuir adsorption coefficients and Gibbs free energy change is derived detailedly. And the applicable conditions of the relationship are analyzed and discussed for correct application and avoiding misuse.

The Adsorptive Removal of Bengal Rose by Artichoke Leaves: Optimization by Full Factorials Design

Currently, the dye industry is increasing its production as a consequence of the growing need for their products in different manufacturing sectors, such as textiles, plastics, food, paper, etc... Thereafter, these industries generate very large volumes of effluents contaminated by these dyes, which require proper removal treatment before final discharge of the effluents into the environment. In this study, artichoke leaves were used as an economical and eco-friendly bio-adsorbent for Bengal Rose (BR) dye removal. Bio-adsorbent obtained from artichoke leaves was ground to powder size. The resulting powder was characterized by different methods, such as Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy(SEM), X-ray Diffraction (XRD), Fourier transfer infrared (FTIR), pH at point of zero charge (pHpzc), equilibrium pH, iodine number, methylene blue number, phenol number, density, Energy dispersive X-ray spectroscopy (EDX) and Thermo-gravimetric analysis (TGA). Thereafter, the bio-adsorbent was used to study its capability for removing BR dye by testing contact time, initial concentration of dye and temperature. The results show that the saturation of bio-sorbent was reached after 40 min and the removal rate of BR dye by artichoke leaves powder (ALP) was 4.07 mg/g, which corresponds to a removal efficiency of 80.1%. A design of experiences (DOE) based on a two-level full factorial design (23) was used to study the effects of different parameters, such as pH, temperature and bio-adsorbent dosage on BR dye removal efficiency. The obtained results show that the highest removal efficiency was 86.5% for the optimized values of pH (4), temperature (80 °C) and bio-adsorbent dosage (8 g/L). Furthermore, a satisfying accordance between experimental and predicted data was observed. The kinetic and isotherm studies show that the pseudo-second order model simulated adequately the obtained data and it was found that Langmuir and Temkin isotherm models are liable and suitable for evaluating the adsorption process performance. Free energy change of adsorption (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were furthermore calculated to predict the nature of the adsorption process.

Manipulating the d-band centers of transition metal phosphides through dual metal doping towards robust overall water splitting

By modulating the d band center via dual metal doping, and thus optimizing the adsorption free energy change for intermediates, the as prepared Ni–Mn–FeP exhibits outstanding catalytic performance toward both the OER (η10 = 185 mV) and HER (η10 = 103 mV).

In-situ construction of N-doped carbon nanosnakes encapsulated FeCoSe nanoparticles as efficient bifunctional electrocatalyst for overall water splitting

The development of bifunctional electrocatalysts with high activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for efficient overall water splitting but still challenging. Herein, we propose a facile and effective polymerization–pyrolysis–selenization (PPS) strategy for in-situ synthesis of N-doped carbon nanosnakes (NCNSs) encapsulated Fe-doped CoSe nanoparticles (NPs) derived from predesigned trimetallic Zn/Fe/Co polyphthalocyanine conjugated polymer networks. Benefiting from the synergistic effect between the regulation of Fe atoms and CoSe NPs as well as the confinement effect of in situ formed porous conductive carbon nanosnakes, the FeCoSe@NCNSs catalyst exhibited the excellent electrocatalytic activity for HER with small overpotentials (142 and 99 mV in 0.5 M H2SO4 and 1 M KOH) and OER (320 mV in 1 M KOH) at the current density of 10 mA cm−2. Particularly, it also can be used as an efficient bifunctional electrocatalyst with a cell voltage of 1.66 V to achieve a current density of 10 mA cm−2 and superior stability for overall water splitting. Density functional theory study reveals that the doping of Fe atoms on CoSe enhanced the splitting and delocalization of metal-d orbitals close Fermi level, and modifies the distribution of Se-p orbitals close Fermi level, which improved the flexibility of electron donor-acceptor system and the hydrogen adsorption free energy change on metal-metal bridge sites in FeCoSe@NCNSs. Additionally, beneficial from the accepting of Fe-Se bridge site, the overpotential of OER which following intramolecular oxygen coupling mechanism is also decreased, thus accelerating the electrocatalytic performance. This work presents a novel strategy to regulate the activity and stability of transition metal selenides and facilitating the rational design of bifunctional electrocatalysts for overall water splitting applications.

Piperazine-modified activated carbon as a novel adsorbent for CO2 capture: modeling and characterization.

In this study, activated carbon and piperazine-modified activated carbon adsorbents were prepared and used for CO2 adsorption. The effect of various parameters including adsorbent particle size, adsorbent amount, piperazine weight percent, pressure, and temperature were investigated on the CO2 adsorption capacity. The adsorbents were characterized using nitrogen adsorption/desorption isotherms and FTIR analyses. The results showed that the adsorption capacity decreases with temperature increasing and increases with pressure increasing. In addition, the surface modification of activated carbon improved the CO2 adsorption capacity more than the unmodified adsorbent, and the highest CO2 adsorption was obtained 203.842 mg/g at 25 °C and 8 bar. Additionally, to determine the adsorbent behavior, CO2 adsorption experimental data were fitted by isotherm and kinetic models. CO2 adsorption isotherm modeling was studied up to 8 bar at 25 °C, and kinetic modeling was investigated up to 85 °C at 6 bar. The results show that Hill isotherm model and Elovich kinetic models have a good agreement with the adsorption data. Finally, thermodynamic modeling was carried out for modified and unmodified adsorbents, and enthalpy, entropy, and Gibbs free energy changes of adsorption for piperazine-modified activated carbon at 25 °C and 6 bar obtained 17.078 kJ/mol, - 0.039 kJ/mol.K, and - 5.318 kJ/mol, respectively.

Mesoporous magnesia sorbent for removal of organic contaminant methyl tert -butyl ether (MTBE) from water

ABSTRACT Methyl tertiary butyl ether (MTBE) is used as a gasoline additive formed by the reaction of isobutylene and methanol. Due to its high water solubility and low soil adsorption coefficient, leakages from storage facilities cause immediate groundwater contamination. The aim is to use alternative adsorbent for the removal of MTBE that causes various environmental and health problems. Mesoporous magnesia (MgO) that was synthesized via template-free hydrothermal method and commercial adsorbent Sepabeads-207 (SP-207) were used in this study. MTBE adsorption experiments were carried out at room temperature with a fixed sorbent/liquid ratio (0.1 g sorbent/10 mL aqueous solution) and 100–500 mg/L MTBE initial concentrations. Batch adsorption experiments showed that MgO and SP-207 have high MTBE adsorption capacity with a maximum adsorption amount of 333 and 233 mg MTBE/g adsorbent. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models of adsorption isotherms were used to investigate the adsorption behavior and the Langmuir isotherm model showed a better fit. Adsorption kinetic studies were also performed, and the pseudo-second-order kinetics fitted well with experimental data. Gibbs free energy changes of adsorption were obtained as −48.4 and −60.3 kJ/mol for MgO and SP-207, respectively. Methanol was used to regenerate the used adsorbents, and the re-use of MgO demonstrated good performance.

Thermodynamic and Adsorption Study of the Corrosion Inhibition of Mild Steel by Aframomum chrysanthum Extract in 0.1 M Hydrochloric Acid Solution

The study reports the corrosion inhibition activity of methanol extract of Aframomum chrysanthum on mild steel in 0.1 M HCl, using gravimetry analysis. The weight loss of the mild steels was observed to increase with increasing immersion time. The inhibition efficiency (%IE) was also observed to have increased with increasing concentrations of the inhibitor but decreases with increasing immersion time. The effect of temperature change on the inhibition efficiency was also studied and it was observed that for every increase in temperature there was a corresponding increase in weight loss and decreased in the %IE. The highest values of %IE; 46.66, 56.66, 60.0, 80.0 & 93.33 was observed at temperature 303 K for 0.2, 0.4, 0.6, 0.8 & 1.0 g/L respectively. Activation energy (Ea) values and the enthalpy values reviews that the adsorption process followed a physisorption’s mechanism. Change in enthalpy (ΔH) and entropy change (ΔS) of the reaction was positive indicating the endothermic nature and the spontaneity of the reaction. Three adsorption isotherms were tried on the inhibition process and only the Temkin isotherm gave the best fit with R2 value of 0.903, describing the best adsorption mechanism. The adsorption equilibrium constants K­ads were positive, indicating the feasibility of the adsorption of the inhibitor to the metal surface. Gibb’s Free Energy change of adsorption, ΔGads are negative indicating that the adsorption of the extract of Aframomum chrysanthum on mild steel surface is spontaneous. The values of ΔGads shows physisorption mechanism. All confirming that Aframomumm chrysanthum extract is a good corrosion inhibitor on mild steel in 0.1 M HCl.

Corrosion Inhibition Efficiency, Adsorption and Thermodynamic Studies of Ocimum Gratissimum on Carbon Steel in 2 M Sodium Chloride Solution

The gravimetric method was applied to investigate the corrosion inhibition efficiency of ocimum gratissimum leaf extract on carbon steel, in 2 M NaCl solution. Concentration of the extract was varied from 0.5 to 3.0 g/L, using a step size of 0.5 g/L. The corrosion test was performed at temperature values of 308 K, 318 K, 328 K and 338 K for 3 h, 6 h and 9 h intervals. Six adsorption isotherm models were tested to study the mechanism of adsorption of the leaf extract onto the metal surface. Kinetic and thermodynamic parameters such as activation energy (Ea), enthalpy (∆H), entropy (∆S) and Gibb’s free energy change of adsorption (∆Gads) were also estimated. Results obtained revealed that inhibition efficiency increased with increase in concentration and time, but decreased with increased temperature. Maximum inhibition efficiency of 95.8%, was obtained at inhibition concentration of 3.0 g/L after a -9 h exposure period, at 308 K. The Langmuir model was found to have the best fit. While all the values of Ea were positive, the lower spectrum of Ea reflected the absence of ocimum gratissimum leaf extract. Also, ∆H values were positive and increased with increase in concentration and time. ∆S values were negative with decreasing magnitude as time and concentration increased. Similarly, ∆Gads values were shown to be negative and with magnitude less than 20 kJ/mol. These results obtained, show that ocimum gratissimum leaf extract can be a good corrosion inhibitor for carbon steel in 2 M NaCl solution and that its adsorption onto the metal surface is realistic, spontaneous and occurred by physisorption.

Thermodynamic Parameters and Adsorption Mechanism of Corrosion Inhibition in Mild Steel Using Jatropha Leaf Extract in Hydrochloric Acid

Corrosion inhibition performance, thermodynamic parameters and adsorption mechanism of jatropha leaf extract in 2 M HCl solution have been investigated. Inhibition efficiency and corrosion rate were evaluated using gravimetric method, based on ASTM G-31 standards. Activation energy, entropy and enthalpy changes were determined using relevant thermodynamic equations. The mechanism of adsorption was studied using six different adsorption isotherm models. Results obtained show that corrosion rate increased with increase in temperature and decreased with increase in concentration of jatropha leaf extract beyond a maximum dosage. The activation energy of the inhibited process was higher than that of the uninhibited process. The enthalpy and entropy changes obtained were positive and negative, respectively. While the constant of adsorption was positive, Gibb’s free energy change of adsorption was negative with values less than 20KJ/mol. Data obtained fit into Langmuir, Frumkim, El-Awady, Freundlich, Flory Huggins and Tempkin isotherm adsorption models. It was observed that Tempkin model had the best fit and as such was used to evaluate the adsorption constant and Gibb’s free energy change of adsorption. The study found that the adsorption of jatropha leaf extract, on the surface of mild steel, is feasible, spontaneous and follows physical adsorption mechanism.

Ultrasound-assisted adsorption of paraquat herbicide from aqueous solution by graphene oxide/ mesoporous silica

In the present study, the graphene oxide (GO) nanosheets /mesoporous SiO2 nanocomposites were prepared from graphene oxide without any surfactant. The obtained GO/SiO2 was synthesized through a simple two-step reaction, including modified Hummer's method and sol-gel route using a mixture of tetraethylorthosilane (TEOS). The as-synthesized GO/SiO2 composite was characterized by FE-SEM, EDS, XRD, FTIR, BET and element mapping. The as-synthesized GO/SiO2 composite used as an adsorbent to remove herbicide paraquat (PQ) from aqueous solution by ultrasound-assisted. To investigate the influence of various variables including initial concentration of PQ, pH and mass of adsorbent in batch experiments based on CCD. The equilibrium data were better explained by Langmuir isotherm model and adsorption capacity of GO/SiO2 from Langmuir model was 31.34 mg g−1. The exothermic enthalpy change of −48.791 kJ mol−1 and the results indicated the spontaneous nature based on negative Gibbs free energy change for adsorption of PQ by GO/SiO2. The presence 0.1 M of NaCl, Na2CO3 and KNO3 salt in aqueous solution have a significant effect on the adsorption of PQ.

Study of volumetric, viscometric, and aggregation properties of losartan potassium and its interaction with amino acids and cetyltrimethylammonium bromide in aqueous solution

AbstractThis manuscript reports volumetric, viscometric, and aggregation properties of losartan potassium (LP) in aqueous medium and its interaction with a cationic surfactant (cetyltrimethylammonium bromide [CTAB]). Densities of drug solutions were used to calculate apparent molar volumes while constants of Jones–Dole equation were calculated from viscosity measurements. By measuring surface tension, refractive index, and electrical conductivity of drug solutions, critical micelle concentration (CMC) of drug was determined, and calculation of surface excess concentration, free energy change of adsorption, free energy change, entropy change, and enthalpy change of micellization was carried out. UV/Visible spectroscopic data were used to get an understanding about the interaction of drug with cationic surfactant (CTAB). This interaction gives an idea about the interaction of drug with biomembrane as micelles of surfactant are similar to membranes in structure. The data were also used to calculate different important parameters for drug–surfactant interaction such as partition coefficient and binding constant. Moreover, two amino acids (glycine and l‐tryptophan) were used in solutions of drug separately to change its CMC. The results from volumetric and viscometric studies showed that the presence of drug in solution resulted in more organization of solvent molecules due to hydrophobic interaction. From the values of ∆G°ads and ∆G°m, it was concluded that the adsorption of drug molecules at solution–air interface and formation of micelles occurred spontaneously. A strong drug‐surfactant (LP–CTAB) interaction was observed by the attachment of drug molecules onto micellar surface of surfactant. The presence of amino acids in the solution of drug caused a decrease in the CMC of LP.

Thermodynamics and adsorption study of the corrosion inhibition of mild steel by Euphorbia heterophylla L. extract in 1.5 ​M HCl

This work investigates the thermodynamics parameters and adsorption mechanism of Euphorbia heterophylla L. extract as a corrosion inhibitor for mild steel in 1.5 ​M HCl. The gravimetric method was used to determine the inhibition efficiency and corrosion rate. Relevant thermodynamic equations were employed to determine the activation energy, enthalpy change and entropy change. The adsorption isotherms were used to evaluate the Gibbs free energy change. Observation from the results of the study showed that the activation energy of an inhibited process was higher when compared with the uninhibited process. Also, the enthalpy change was positive and less than 100 ​KJ/mol threshold. The adsorption study showed that the data fit into the Langmuir, Flory-Huggins, El-Awary’s and Temkin isotherms but Flory-Hugins gave the best fit. The Gibb’s free energy change of adsorption was negative and less than the −20 ​KJ/mol threshold. As concluded from the results, the adsorption of Euphorbia heterophylla L. on mild steel in 1.5 ​M HCl medium is feasible, spontaneous and it occurred by physical adsorption according to Flory-Hugins isotherm model.

Adsorption behavior of magnetic bentonite for removing Hg(ii) from aqueous solutions.

Bentonite is a porous clay material that shows good performance for adsorbing heavy metals and other pollutants for wastewater remediation. However, it is very difficult to separate the bentonite from water after adsorption as it forms a stable suspension. In this paper, we prepared magnetic bentonite (M-B) by loading Fe3O4 particles onto aluminum-pillared bentonite (Al-B) in order to facilitate its removal from water. The functional groups, skeleton structure, surface morphology and electrical changes of the prepared material were investigated by FT-IR, XRD, BET, SEM, VSM and zeta potential measurements. It was used as an adsorbent for Hg(ii) removal from aqueous solutions and the influence of various parameters on the adsorption performance was investigated. The adsorption kinetics were best fitted by the pseudo-second-order model, and also followed the intra-particle diffusion model up to 18 min. Moreover, adsorption data were successfully reproduced by the Langmuir isotherm, and the Hg(ii) adsorption saturation capacity was determined as 26.18 mg g−1. The average adsorption free energy change calculated by the D-R adsorption isotherm model was 11.89 kJ mol−1, which indicated the occurrence of ionic exchange. The adsorption thermodynamic parameter ΔH was calculated as 42.92 kJ mol−1, which indicated chemical adsorption. Overall, the thermodynamic parameters implied that Hg(ii) adsorption was endothermic and spontaneous.

Degradation and adsorption of tralkoxydim in Chinese soils and water-sediment environments.

Tralkoxydim is a cyclohexanedione herbicide primarily used for gramineous weed control in China. In this paper, we present results of a tralkoxydim laboratory environmental fate study characterizing its degradation, adsorption, and mobility behavior in three different soils and two water-sediment systems (river and lake) in China. Degradation half-life of tralkoxydim in soil under aerobic conditions was 5.1, 7.7, and 7.9days in Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Under anaerobic and flooding conditions, half-life values were 6.2, 15.1, and 19.8days for the same three soils, respectively. Soil pH was the major factor effecting tralkoxydim degradation. In the aerobic water-sediment experiments, tralkoxydim degraded faster in the river system (total system half-life 43.3days) than the lake system (total system half-life 99.0days). Correspondingly, its anaerobic degradation half-life values were 46.2 and 53.3days for the river and lake systems, respectively. Tralkoxydim adsorption in the three soils was found to follow the empirical Freundlich isotherm. The adsorption coefficient (K d ) was 8.60, 1.00, and 1.57 for Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Soil pH was the major factor effecting tralkoxydim adsorption. Adsorption free energy change was less than 40kJmol-1 in all three soils, indicating a physical mechanism in the process. Thin-layer chromatography (TLC) tests showed that relative to the solvent transport to 11.5cm, the travel distance of tralkoxydim was 8-10cm in the three soils, corresponding Rf values at 0.05, 0.35, and 0.75 for Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Results of this work suggest that under alkaline conditions, tralkoxydim adsorption becomes smaller; thus, assessments on its mobility and potential groundwater impact should focus on these soil types.

Optimization of process variables and mechanism of arsenic (V) adsorption onto cellulose nanocomposite

Optimization of process variables for arsenic (V) adsorption onto some novel adsorbent, the cerium loaded cellulose nanocomposite bead, was made using response surface methodology, a popular statistical design for chemical experiments. The adsorbent was characterized for its physicochemical, spectral, surface and thermal nature. The influence and significance of experimental variables viz. pH, initial arsenic (V) concentration, adsorbent dose, contact time and temperature on the adsorption capacity (response) was estimated from fractional factorial design (25–1). The interactive and combined effects of significant variables were evaluated from central composite design and subsequent analysis of variance (ANOVA). The guiding parameters such as F- (58.45) and P-value (<0.0001) indicate that the design is statistically significant. A second-order polynomial regression equation is developed to predict the response at the optimized condition. A high value of regression coefficient (R2=0.9832) implies the validity of the model. Kinetic study reveals that the adsorption follows first order pathway. Diffusion phenomenon, particularly film diffusion prevails over the mass transport in governing the overall rate having activation energy of 19.34kJmol−1. Desorption of arsenic was found effective with NaOH (10−2N) and 98% elution was achieved. The regenerated adsorbent bead can be reused for As(V) adsorption up to four successive cycles. The mechanism of As(V) adsorption is assessed to be electrostatic rather than ion exchange as evaluated from mean free energy change of adsorption using Dubinin Raduskevich model. The method has been successfully applied for removal and estimation via recovery of arsenic (V) from different water samples.

Empirical and mechanistic evaluation of sodium exchange isotherms on natural mineral and organic adsorbents and organically functionalized nanoparticles

This study was conducted to evaluate the efficiency of low-cost adsorbents including bentonite, kaolinite and zeolite saturated with calcium and potassium, potato and wheat residues, and three metal oxide nanoparticles functionalized with an acidic extract of potato residues in improving the quality of sodic waters. The optimization of factors such as pH, contact time, and adsorbent dosage was investigated using a solution containing sodium, calcium, magnesium, and potassium. The optimal pH and contact time were 7.0 and 24 h, respectively. The optimal dosage for using functionalized nanoparticles was 0.1 g and for using other adsorbents was 1.0 g. The sodium exchange isotherms were conducted in binary sodium–calcium and sodium–potassium and quaternary sodium–calcium–magnesium–potassium systems. Zeolite saturated with potassium was the most effective adsorbent in removing sodium from aqueous solutions with an average removal efficiency of 69.2 and 66.5 % in binary and quaternary systems, respectively. Freundlich and Langmuir equations fitted well to experimental data in both binary and quaternary systems. Cation selectivity coefficients calculated based on the Gaines–Thomas convention varied with changing pH and adsorbent dosage. Graphical and statistical evaluations confirmed that the mechanistic cation exchange model using average Gaines–Thomas selectivity coefficients in geochemical PHREEQC program was able to successfully simulate the sodium exchange on different adsorbents in both systems. The Gaines–Thomas selectivity coefficient values greater than unity and as a consequence, the negative values of the Gibbs free energy change of adsorption indicated that sodium exchange reactions in the presence of different adsorbents used is this study were exergonic and spontaneous.