Langmuir-type Adsorption Research Articles

Application of Date Palm Tree Branch-Based Activated Carbon for Aqueous Toxicity Reduction

The Kingdom of Saudi Arabia (KSA) has millions of date palm trees for commercial scale date-fruit production. The respective industry also generates agricultural waste including date palm tree branches. This rich bio-resource can be used for several beneficial applications. The present study therefore investigated the application of granular activated carbon (GAC) produced using date palm tree branches to successfully remove phenol, p-cresol, and copper from synthetic wastewater. The respective adsorption equilibrium results fitted well to the Langmuir-type adsorption isotherm. Furthermore, the pH-dependent adsorption results both for phenol and p-cresol appeared to follow an anionic-type adsorption behavior (i.e., decreasing adsorption with an increase in aqueous phase equilibrium pH). However, the pH-dependent adsorption finding for copper showed a cationic-type adsorption behavior. These adsorption trends were explained employing the pH-dependent speciation of the respective pollutants. In general, findings from the present work indicate that a high-specific-surface-area (SSABET) GAC material from the date palm tree branches can be successfully employed for aqueous phase pollution control.

Unraveling Ammonia and Trimethylamine Uptake on Conductive Doped Polyaniline.

Polyaniline (PAni)-based sensors are a promising solution for ammonia (NH3) detection at the ppb level. However, the nature of the NH3-PAni interaction and underlying drivers remain unclear. This paper proposes to characterize the interaction between doped PAni (dPAni) sensing material and NH3 by using a Knudsen cell. First, to characterize the dPAni interface, the probe-gas method, i.e., titration of surface sites with a gas of specific properties, is deployed. The dPAni interface is found to be homogeneous with more than 96% of surface sites of acid nature or with hydroxyl functional groups. This result highlights that basic gases such as amines might act as interfering gases for NH3 detection by polyaniline-based sensors. Second, the adsorption isotherms of NH3 and trimethylamine (TMA) on dPAni are reported at ambient temperature conditions, 293 K. The uptake of NH3 and TMA on dPAni follows a Langmuir-type behavior. This approach allows for the first time to quantify the uptake of NH3 and TMA on gas-sensor materials and determine typical Langmuir adsorption parameters, i.e., the partitioning coefficient, KLang, and the maximum surface coverage, Nmax. The corresponding values obtained for NH3 and TMA are Klang (NH3) = 19.7 × 10-15 cm3 molecules-1 Nmax (NH3) = 11.6 × 1014 molecules cm-2, KLang (TMA) = 7.0 × 10-15 cm3 molecules-1 Nmax (TMA) = 5.0 × 1014 molecules cm-2. KLang and Nmax values of NH3 are higher than those of TMA, suggesting that NH3 is more efficiently taken up than TMA on dPAni. The results of this work suggest that strong hydrogen bonding drives the performance of a polyaniline-based gas sensor for NH3 and amines. In conclusion, the Knudsen cell approach allows reconsidering the fundamentals of NH3 interactions with dPAni and provides new insights on drivers to enhance sensing properties.

Hydrogen Sulfide Adsorption Mechanism and Breakthrough Curves of Highly Stable Na-, Na-H-, Ca- and K-Mordenites.

Hydrogen sulfide (H2S) is a hazardous gas found in natural gas and biogas, lethal over 100 ppm. When released into the atmosphere, it can turn into sulfur dioxide. One option to remove H2S is using porous materials such as zeolites. Among them, mordenite stands out due to its channel structure, wide availability, and low cost. In this work, we evaluated the H2S adsorption capacity of mordenite using a volumetric static method. The results show the adsorption capacity of H2S in mordenite varies with the exchanged cation. The highest was measured in Na-mordenite (~4.08 mmol H2S/g mordenite). The experimental breakthrough curves for this zeolite confirmed Langmuir-type adsorption and strong affinity between Na+ cations and H2S. Despite this interaction, the XRD diffractograms of Na-mordenite show that the material retained its crystalline structure. More information about the differences in the amount of H2S adsorbed in the zeolites caused by the change in exchanged cation was obtained by H2S adsorption followed by FTIR spectroscopy. The spectra show differences in the position of the peaks related to the different adsorption modes of H2S caused by a change in the polarizing power of the cations due to their charge and position inside the zeolite pores.

An eco-friendly composite hydrogel based on covalently crosslinked cellulose/poly (glycerol citrate) for thallium (Ι) removal from aqueous solutions

Cellulose/poly (glycerol citrate) reinforced with thiol-rich polyhedral oligomeric silsesquioxane and apple peel (POSS-SH@CAG-CEL/AP) was synthesized using gelation method in the presence of glutaraldehyde as a crosslinker agent and used as an efficient composite hydrogel for elimination of Tl(Ι) from aqueous solutions. This composite hydrogel and synthesized thiol-rich polyhedral oligomeric silsesquioxane were characterized by elemental analysis, FT-IR, NMR, TGA, and FE-SEM techniques. The effects of synthetic and environmental parameters on the adsorption capacity of the composite hydrogel were investigated and it was found that thiol-rich polyhedral oligomeric silsesquioxane has improved the hydrogel properties including the Tl(Ι) uptake and the thermal stability. The maximum adsorption capacity of 352.3 mg g−1 was obtained within 30 min under optimum reaction conditions. A typical Langmuir adsorption isotherm with was observed for adsorption of Tl(I) onto POSS-SH@CAG-CEL/AP and pseudo-second-order kinetic model provided the best correlation between experimental data. Thermodynamic studies showed that the Tl(I) adsorption was spontaneous process and exothermic. Also, the reusability tests confirmed that the POSS-SH@CAG-CEL/AP can be reused for four times without any remarkable change in its adsorption capacity. Thus, this reusable biobased composite hydrogel can be an ideal candidate for elimination of Tl(I) from aqueous solutions.

Synthesis of hybrid layered double hydroxides (HLDH) and application as adsorbent for removal of direct sky-blue dye

Hybrid Layered Double Hydroxides (HLDH) are promising adsorption materials for water treatment due to their excellent anion exchange capacities, abundance of active sites, and eco-friendliness. HLDH was synthesized utilizing the co-precipitation technique in this work to demonstrate its applicability for the removal of direct sky-blue dye via an adsorption procedure. The effects of pH, dose, contact time, initial dye concentration, and temperature on the direct sky-blue dye adsorption efficiency were thoroughly investigated. The adsorbents were analyzed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), energy dispersive X-ray (EDX), and Brunauer–Emmett–Teller (BET). Under the best conditions, the maximum adsorption capacity has been achieved for Mg–Cr–Cl (42.95 mg/g) > Zn–Al–CO3 (39.76 mg/g) > Mg–Fe–Cl (38.08 mg/g). The adsorption of dyes on Mg–Cr–Cl, Zn–Al–CO3, and Mg–Fe–Cl followed a pseudo-second-order kinetic model and exhibited Langmuir-type monolayer adsorption. The influence of temperature was studied to determine the thermodynamic parameters. The estimated results showed spontaneous and exothermic adsorption processes. Electrolyte enhances the adsorption capacity to some extent, while surfactants block the sites, thus reducing the adsorption capacity. The maximum desorption of dye was influenced by the sodium hydroxide solution. The research described here might be utilized to create novel adsorbents with improved adsorption capacities for preserving the aquatic environment.

Investigation of adsorption performance of calcium oxide particles upon various treatments.

This study describes the improvements of adsorption capacities for raw calcium oxide (CaO) particles subjected to ultrasonication, activation with nitric acid and thermal treatments. The influence of acids and bases on CaO particle surface was assessed with respect to several variables including treatment methods, adsorption contact times, particle size and specific surface area characteristics, concentration and temperature along with various thermodynamic parameters. Structural analyses and physical characteristics of CaO particles were evaluated using FT-IR and SEM methods. SEM micrographs of samples revealed uniform distributions of CaO particles of average diameter 0.5-2.0µm. The CaO surfaces showed CH3COOH as having the greatest amounts of adsorbate and modeling of the experimental adsorption isotherm data agreed well with the Freundlich adsorption isotherm. Enhancements in adsorption performance of untreated CaO particles were noted with the ultrasonication, activation with HNO3 and thermal treatment processes. The Langmuir-type adsorption demonstrated that single layer adsorption capacities of adsorbate CH3COOH at 25oC on sonicated CaO (386.6mg/g), with nitric acid and thermal activation (354.9 and 320.8mg/g, respectively) were greater than that of the unsonicated CaO (296.3mg/g) particles. Adsorption spontaneities of the processes were confirmed by the decreases in adsorption free energy values, ΔGads0, changing from -16.1 to -17.1kJmol-1 with temperature range 283-338K.

MID-FTIR-PLS Chemometric Analysis of Cr(VI) from Aqueous Solutions Using a Polymer Inclusion Membrane-Based Sensor.

A partial least squares (PLS) quantitative chemometric method based on the analysis of the mid-Fourier transform infrared spectroscopy (MID-FTIR) spectrum of polymer inclusion membranes (PIMs) used for the extraction of Cr(VI) from aqueous media is developed. The system previously optimized considering the variables membrane composition, extraction time, and pH, is characterized in terms of its adsorption isotherm, distribution coefficient, extraction percent, and enrichment factor. A Langmuir-type adsorption behavior with KL = 2199 cm3/mmol, qmax = 0.188 mmol/g, and 0 < RL < 1 indicates that metal adsorption is favorable. The characterization of the extraction reaction is performed as well, showing a 1:1 Cr(VI):Aliquat 336 ratio, in agreement with solvent extraction data. The principal component analysis (PCA) of the PIMs reveals a complex pattern, which is satisfactorily simplified and related to Cr(VI) concentrations through the use of a variable selection method (iPLS) in which the bands in the ranges 3451-3500 cm-1 and 3751-3800 cm-1 are chosen. The final PLS model, including the 100 wavelengths selected by iPLS and 10 latent variables, shows excellent parameter values with root mean square error of calibration (RMSEC) of 3.73115, root mean square error of cross-validation (RMSECV) of 6.82685, bias of -1.91847 × 10-13, cross-validation (CV) bias of 0.185947, R2 Cal of 0.98145, R2 CV of 0.940902, recovery% of 104.02 ± 4.12 (α = 0.05), sensitivity% of 0.001547 ppb, analytical sensitivity (γ) of 3.8 ppb, γ-1: 0.6 ppb-1, selectivity of 0.0155, linear range of 5.8-100 ppb, limit of detection (LD) of 1.9 ppb, and limit of quantitation (LQ) of 5.8 ppb. The developed PIM sensor is easy to implement as it requires few manipulations and a reduced number of chemical compounds in comparison to other similar reported systems.

Investigation of copper underpotential deposition on polycrystalline gold electrodes

A combination of cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry techniques has been used to study the underpotential deposition (UPD) of copper on polycrystalline gold (pc Au) electrodes. The experiments were conducted in an electrolyte composed of CuSO4 (5 mM) and H2SO4 (0.5 M). The results revealed that the concentration of copper (II) ions and the applied voltage exerted a synergistic effect on the position, shape, and range of spanning of the curves describing the redox potential and current density. The charge transfer resistance (Rct) corresponding to the UPD of Cu decreased monotonically with a decrease in the applied voltage, and the phase angle shifted toward high-frequency regions with a negative shift in the potential. The process of UPD of Cu on pc Au can be divided into three stages: Langmuir-type adsorption, growth of Cu monolayers on pc Au following the process of two-dimensional instantaneous nucleation, and the continuous two-dimensional nucleation of grains on the Cu layer. UPD on single crystal substrates and the single-layer and multi-layer structures associated with UPD have been extensively studied worldwide. However, the UPD of polycrystalline electrodes with various crystal faces, grain boundaries, and defects is complex, and the associated mechanism has rarely been studied. In recent years, the process of UPD has been widely used in various fields, such as fields associated with electrochemical sensing, fabrication of fuel cells, electrochemical CO2 reduction, and fabrication of solar cells.

Protein Adsorption on Carboxy-Functionalized Microparticles Revealed by Zeta Potential and Absorption Spectroscopy Measurements

Abstract Addition of micro/nanoparticles to a protein solution leads to the formation of a protein layer on the particle surface, called a protein corona. We investigate here the adsorption behavior of myoglobin, hemoglobin, cytochrome-c, and lysozyme on carboxy-functionalized polystyrene microparticles using zeta potential and absorption spectroscopy measurements. The observed adsorption behavior differs according to the method of detection: monolayer for zeta potential and multilayer for absorption spectroscopy. Langmuir-type monolayer adsorption is observed with zeta potential measurements, because zeta potential (ζ) responds only to the charge density at the outermost protein layer. Multilayer adsorption is observed by absorption spectroscopy. Spectroscopic results were analyzed by the Guggenheim-Anderson-de Boer (GAB) model, which comprises a hard corona formed by strong interaction between the protein and the particle surface and a soft corona formed by weak interaction between adsorbed and bulk-solution proteins. The extent of hard and soft corona formation depends on pH. When a protein monolayer is prepared by covalent modification of the particle surface, the number of layers in the protein corona decreases relative to the case of protein adsorption on bare particles. This result demonstrates that electrostatic interactions between the protein and particle surface play a key role in the formation of a protein corona.

THE ACTIVATION OF ANIONIC DYE ADSORPTION AFTER UV IRRADIATION OF INDIVIDUAL AND BINARY XEROGELS OF ALUMINUM AND ZIRCONIUM OXIDES

Mesoporous xerogels of hydrated individual and binary oxides of aluminum (A) and zirconium (Z) were obtained by hydrolysis sol-gel method after drying at 180 °C of a hydrogel synthesized from aluminum nitrate and zirconium oxychloride in the presence of polyvinylpyrrolidone. The samples were examined by IR spectroscopy, SEM, XRD, BET/BJH. It was found that the xerogels are X-ray amorphous. The particles have a hierarchical structure, the specific surface in a series (number and mol.%) of samples A (1) &lt; 65AZ (2) &lt; 35AZ (3) &lt; Z (4) increases exponentially from 21 to 298 m2/g. The pore diameter is 4-6 nm. Photoactive aluminum oxohydroxide (δAlOOH = 1070 cm-1) is registered only in samples 1 and 2. Adsorption from an aqueous solution using the example of anionic dye methyl orange was determined by spectrophotometer for long-time (24 h) and dynamic (10 min) regime. In both cases, Gibbs adsorption of Гm (μmol/g) increases in a number of samples 1 &lt; 2 &lt; 3 &lt; 4. The value of ГS (μmol/m2) in the same series decreases sharply. Therefore, the adsorption centers of Al+3 and Zr+4 have different activity. It is shown that only in the case of AZ samples a photo activated adsorption rise after UV irradiation of sorbents with a mercury lamp for 10 min of duration. Kinetic adsorption curves for samples without and with UV treatment correspond to the pseudo-second-order equation with Langmuir-type two-fold adsorption model. The parameters of this equation Гmax (monolayer capacity) and W0 (initial adsorption rate) increase in a series of non-irradiated samples 1 &lt; 2 &lt; 3 &lt; 4. The effect of UV activation, as the ratio of Гmax and W0 after and before irradiation, augments in the sequence Z &lt; A &lt; 35AZ &lt; 65AZ (for 65AZ sample the growth of Гmax and W0 is 2.4 and 1.8 times, while the adsorption rate constant k2 decreases tenfold). Comparison of adsorption after 24 h with Гmax showed a linear decrease in the ratio Г24/Гmax for unirradiated sorbents A (2.9) &gt; 65AZ (2.2) &gt; 35AZ (1.6) &gt; I(1.0). This result is explained by adsorption-induced deformation of the xerogel framework, which is greatest in Al2O3 and absent in ZrO2. For citation: Vakhrushev N.E., MIkhalenko I.I., Podzorova L.I. The activation of anionic dye adsorption after UV irradiation of individual and binary xerogels of aluminum and zirconium oxides. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 61-68. DOI: 10.6060/ivkkt.20236606.6744.

Crucial role of alkali metal ions and Si/Al ratio in selective adsorption of 1-octene using faujasite zeolites

Linear α-olefins (LAOs) are conventionally purified from paraffins via energy-intensive superfractionation. Adsorptive separation with zeolite-based adsorbents is a promising alternative to distillation for olefin/paraffin purification. However, very few zeolites with different Si/Al ratios and metal ion types have been tested to separate LAOs in the liquid phase. In this study, we investigated the ability of various alkali metal ion-exchanged faujasites with different Si/Al ratios to separate 1-octene/n-octane mixtures. We prepared low-silica X (LSX), X, and Y zeolites loaded with Li+, Na+, K+, and Rb+ via ion exchange in an aqueous solution. The 1-octene adsorption capacities and selectivities were analyzed via liquid-phase batch adsorption experiments. Among LSX, X, and Y exchanged with the Na+ and Li+, LSX which had the lowest Si/Al ratios exhibited the highest selectivity. The 1-octene selectivities for LSX were in the following order: Rb+ ≈ K+ < Na+ < Li+. LiLSX demonstrated the greatest separation efficiency among the zeolites owing to the presence of the largest number of cation sites and the highest charge density of Li+. The affinity constants calculated from the Langmuir-type adsorption isotherms and enthalpies of adsorption suggest that cation–π interactions between the C = C bond in olefins and metal ions influence selective adsorption. Density functional theory calculations support this theory of intermolecular interactions. Furthermore, a series of adsorption and desorption breakthrough experiments using a column packed with LiLSX validated its applicability for separating 1-octene and n-octane. We believe these adsorbents can be modified further and widely applied in the purification of higher olefins from chemical and biochemical products.

Complete defluorination of perfluorooctanoic acid (PFOA) by ultrasonic pyrolysis towards zero fluoro-pollution

Advanced oxidation/reduction of PFAS is challenged and concerned by the formation of toxic, short-chain intermediates during water treatments. In this study, we investigated the complete defluorination of PFOA by ultrasound/persulfate (US/PS) with harmless end-products of CO2, H2O, and F‒ ions. We observed 100% defluorination after 4 h of US treatment alone with a power input of 900 W. PS addition, however, suppressed defluorination. We demonstrated by kinetics-fitted Langmuir-type adsorption modeling, the added PS increased competition with PFOA for adsorption sites on the bubble-water interface where radical oxidation and pyrolysis may occur. Providing sulfate (SO4•–) and hydroxyl (•OH) radicals by means other than US did not defluorinate PFOA, indicating that pyrolysis likely contributes to the high defluorination performance. Bond dissociation energies for CC and CF were independent of pressure but decreased at elevated temperatures within cavitation bubbles (i.e., 5000 K) favoring the pyrolysis reactions. Furthermore, bond length calculations indicated that PFOA cleavage only begins to occur at temperatures in excess of those generated at the bubble interface (i.e., >1500 K) at the femtosecond level. This suggests that PFOA vaporizes or injects by nanodrops upon attachment to the cavitation bubble, enters the bubble, and is then cleaved within the bubble by pyrolysis. Our research in low-frequency ultrasonic horn system challenges the previous founding that defluorination of PFOA initiates and occurs at the bubble-water interface. We describe here that supplementing US-based processes with complementary treatments may have undesired effects on the efficacy of US. The mechanistic insights will further promote the implementation of US technology for PFAS treatment in achieving the zero fluoro-pollution goal.

Adsorption of PFOS onto graphite intercalated compound and analysis of degradation by-products during electro-chemical oxidation

Perfluorooctane sulfonate (PFOS) is a highly recalcitrant perfluoro chemical belonging to the family of per- and polyfluoroalkyl substances (PFAS). Its adsorption and degradation was demonstrated in a novel PFAS remediation process involving the adsorption onto graphite intercalated compounds (GIC) and the electrochemical oxidation. The Langmuir type of adsorption was characterized by a loading capacity of 53.9 μg PFOS g−1 GIC and a second order kinetics (0.021 g μg−1 min−1). Up to 99% of PFOS was degraded in the process with a half-life of 15 min. The breakdown by-products included short chain perfluoroalkane sulfonates such as Perfluoroheptanesulfonate (PFHpS), Perfluorohexanesulfonate (PFHxS), Perfluoropentanesulfonate (PFPeS) and Perfluorobutanesulfonate (PFBS), but also short chain perfluoro carboxylic acids such as perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA) indicating different degradation pathways. These by-products could also be broken down but the shorter the chain the slower the degradation rate. This novel combined adsorption and electrochemical process offers an alternative treatment for PFAS contaminated waters.

Investigation into the adsorption and inhibition properties of sodium octanoate against CO2 corrosion of C1018 carbon steel under static and hydrodynamic conditions

Sodium octanoate (Na-oct), a simple, naturally-abundant, cheap and low-toxic organic molecule has been investigated for its adsorption and inhibition properties against the CO2 corrosion of C1018 carbon steel in 3.5 % NaCl under static (0 rpm) and hydrodynamic conditions (1000 rpm). At open circuit potential (OCP) under static condition, a Langmuir-type adsorption of Na-oct modified the dielectric property of the steel-solution interface by lowering double layer capacitance and increasing resistance to charge transfer, based on electrochemical impedance spectroscopy (EIS) analysis. Under this condition, potentiodynamic polarization (PDP) analysis showed that Na-oct adsorbed more preferentially on anodic sites of steel surface and impacted ∼96 % inhibition efficiency. Hydrodynamic condition at 1000 rpm caused a Langmuir and Temkin adsorption mechanism and diminished the Na-oct efficiency to ∼86 %. FTIR characterization revealed that the inhibitor adsorption was enabled by its COO– functional group. Computational modeling, using DFT and MDS, confirmed the experimental findings.

Novel Barite Crystallization and Inhibition Model Based on Surface Adsorption

Summary Inorganic mineral crystallization is a critical process for numerous industrial and geoengineering processes, including oil and gas production and transportation, geothermal energy exploitation, membrane filtration, cooling tower, heat exchanger, to mention a few. Its unexpected formation can cause significant engineering, economic, and safety issues. Scale inhibitors have been widely used in various geoengineering projects as one of the most efficient and economic methods for mineral scale control. However, after decades of research, the inhibition mechanisms still remain unknown. This study applied a newly developed mechanistic mineral crystallization and inhibition model to barite, one of the most difficult mineral scales to be remediated. This new model assumes that inhibitors prolong the crystallization induction time by adsorbing onto the nucleus surface following a Langmuir-type adsorption isotherm and increasing the surface tension. The new model accurately predicts the barite crystallization induction time without or with 10 commonly used scale inhibitors. More importantly, the adsorption affinity constants (i.e., KL) fitted with the new model from the barite crystallization induction time matched well with those fitted from the direct inhibitor adsorption testing and from measuring barite crystal growth rate changes due to various inhibitors. A good correlation was also observed between the KL values of various inhibitors with barite from this study and those with other minerals (i.e., hydroxyapatite and calcite) from the literature. Such good agreements and correlations validated the adsorption mechanism adopted in the new mechanistic model. This study will deepen the understanding of mineral crystallization and inhibition mechanisms and improve scale management in various industrial and geoengineering processes.

Morphology controlled nitrogen-doped mesoporous carbon vehicles for sustained release of paracetamol

The design of smart nanoporous vehicles for efficient and pH-dependent drug delivery is substantial. Due to their adjusted properties, they can release drugs in a controlled manner and maintain their optimum concentrations in the specific sites of the body. As a consequence, the bioavailability and therapeutic efficacy of pharmaceutics can be improved. In this work, novel nitrogen-doped mesoporous carbons have been attained as platforms for paracetamol - the antipyretic and analgesic drug. The carbon carriers were synthesized via an aqueous cooperative assembly route. Using l-arginine and l-lysine as polymerization catalysts, along with 3-aminophenol/resorcinol as nitrogen/carbon sources enabled enriching carbon materials with different nitrogen content (0.22–7.73%). The molar ratio of resorcinol and 3-aminophenol affected the structure ordering, morphology, and textural parameters of carriers. N-doped carbon materials revealed Langmuir-type adsorption of paracetamol (up to ∼ 148 mg g−1). The drug release from carbon surfaces occurred in a pH-dependent manner within 2 or 24 h. The controlled paracetamol liberation was observed mainly in an acidic medium. Providing an environment mimicking saliva and gastric fluid altered the percentage of paracetamol release from ∼40% to 100%. As the nitrogen content in the carbon structure increased, more paracetamol was released.

Meso- and Macroporous Polymer Gels for Efficient Adsorption of Block Copolymer Surfactants.

An understanding of surfactant adsorption at solid-liquid interfaces is important for solving many technological problems. This work evaluates surfactant adsorption abilities of high surface area (200-600 m2/g), high porosity (>90%), hierarchically structured open pore polymer gels. Specifically, the interactions of a nonionic block copolymer surfactant, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO), with three polymer gels, namely, syndiotactic polystyrene (sPS), polyimide (PI), and polyurea (PUA) offering different surface energy values, are evaluated at surfactant concentrations below and well above the critical micelle concentration (CMC). Two distinct surfactant adsorption behaviors are identified from the surface tension and nuclear magnetic resonance data. At concentrations below CMC, the surfactant molecules adsorb as a monolayer on polymer strands, inferred from the Langmuir-type adsorption isotherm, with the adsorbed amount increasing with the specific surface area of the polymer gel. The study reports for the first time that the gels show a strong surfactant adsorption above CMC, with the effective surfactant concentration in the gel reaching several folds of the CMC values. The effective surfactant concentration in the gel is analyzed using surfactant micelle size, polymer surface energy, and pore size of the gel. The findings of this study may have strong implications in liquid-liquid separation problems and in the removal of small dye molecules, heavy metal ions, and living organisms from aqueous streams.

Physicochemical Behavior of Superfine Wool Powder Dyed with Reactive Dye

ABSTRACT Superfine wool powder is obtained from waste wool fiber by physical grinding. Its physicochemical properties are different from those of wool fiber, and it is widely used in industry. In order to clarify the dyeing behavior of wool powder, C. I. Reactive Yellow 145 dye was used to dye wool powder, and the adsorption kinetics and thermodynamics were systematically studied in this work. The adsorption kinetics of reactive dye on wool powder was found to adhere to a pseudo-second-order kinetic model. At 60, 80 and 95°C, the half-dyeing time (t 1/2) and diffusion coefficient were 2.37, 1.56 and 1.00 min, and 0.2045, 0.1611 and 0.1368 cm2·min−1, respectively. And the diffusion activation energy was −11.82 kJ·mol−1. A Langmuir-type adsorption isotherm was obtained. At 60, 80 and 95°C, the standard affinity was 18.17, 20.06 and 20.82 kJ·mol−1, respectively. And the dyeing enthalpy change and dyeing entropy change were 7.27 kJ·mol−1 and 0.077 kJ·mol−1·K−1, respectively. In addition, the specific surface area, morphology and dyeing properties of wool fiber were compared. Through the study on the dyeing physicochemical properties of wool powder, it provides a theoretical basis for people to understand and use wool powder.

Gypsum scale formation and inhibition kinetics with implications in membrane system

Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25–90 °C), SI (0.04–0.96), and background NaCl concentration (0–6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system.

Adsorption of cytosine on prebiotic siliceous clay surface induced with metal dications: Relevance to origin of life

Adsorption of protobiomolecules on primigenial mineral surfaces transacts a very specific and selective role in prebiotic chemical evolution. Cytosine (CYN) is a core constituent of genetic macromolecules i.e., DNA and RNA. A prebiotic simulation experiment following adsorption behaviour of a nucleic acid base CYN, as a function of pH, concentration, time and temperature on the surface of Montmorillonite (MMT), a prominent siliceous clay of smectite group having specific surface area, was studied systematically and methodically using UV, FTIR, SEM and XRD. Biologically significant metal dication [M2+ = Mg2+, Ca2+, Fe2+ and Cu2+] embeded surfaces of MMT (MMT-M2+) were prepared separately by cation-exchange approach. Results observed through UV spectral data reveal a very significant role of metal ions on the quantity of CYN adsorbed on different solid surfaces. The adsorption behaviour fitted well with Langmuir isotherm model and the adsorption isotherm shows monolayer formation of CYN (as adsorbate) on the surface of MMT and MMT-M2+(as adsorbent) showing Langmuir type adsorption. The calculated Langmuir adsorption parameters (KL& Xm) delineate appreciable interaction of CYN on MMT-Fe2+ surface following MMT-Cu2+ as compared to MMT alone and to other metal induced MMTs.In terms of % binding and Xm data, the effectiveness of various adsorbents in adsorption of CYN on MMT/MMT-M2+ at pH 6.6 and temperature 298K was found in the order; MMT-Fe2+> MMT-Cu2+> MMT > MMT-Ca2+> MMT-Mg2+. The results were further confirmed by SEM, XRD and FTIR which also support the outcomes. The present work throws light on the affinity of MMT clay (having multifarious applications in biological systems) with and without biogenic metal diions towards the surface interaction of nucleic acid base mimicking primeval sea shore/sea bed or hydrothermal vent conditions deciphering the phenomena that how biomonomers could have been protected from extreme hazardous conditions of primitive Earth and stabilized during chemical evolution and availed them for consecutive molecular evolution. Results further embark better adsorption capability of transition metal ion incorporated MMTs than the clay without metal ion and exchanged with alkaline Earth dications.