Adsorption/Desorption of Pesticidal Carboxylate Esters by Switching Liquid Phases on Humic‐Fraction‐Modified Silica Gel Matrix

A humic‐fraction‐modified silica gel is prepared and used as the adsorbent for various pesticidal carboxylate esters in hexane. The percentage of adsorption, calculated on the basis of the difference in peak areas for most carboxylate esters in hexane, reaches more than 90% in 1 h. The FTIR (Fourier Transform Infrared) Spectroscopy results show that the interaction force leading to the adsorption observed in hexane is dipole‐dipole oriented and is affected negatively both by the steric hindrance created due to the presence of the group near the carbonyl center of esters and the bulky alkyl group attached to an ether linkage. The hydrogen bonding (i.e. strong dipole‐dipole interaction) and π‐π stacking complexation are either absent or the minor force responsible for the adsorption of carboxylate esters in hexane in most cases. Other factors that cause the variation in the percentage of adsorption include the type of liquid phase (e.g. ethyl ether or acetonitrile vs. hexane) and the additive of acidic or basic origin present in the matrix, which renders the desorption approach for analyte adsorbed.     

Fluorescence quenching study of humic‐fraction‐modified silica gel in a solid state after association with a variety of pesticidal analytes in hexane and acetonitrile

In this paper, we investigate the fluorescence quenching of acidic humic‐fraction‐modified silica gel in the solid state after association with a variety of pesticidal analytes in hexane and acetonitrile. The percentage of fluorescence quenching is found to be dependent on the contact time and linearly on the number of moles of analyte involved in the association process. However, any π–π complexation interaction arising from the acidic aromatic ring on the analyte due to the derivatization of a bulky electron‐withdrawing group is not observed. Also, any mechanism leading to adsorption or any quenching process occurring as a result of the steric hindrance obtained by a theoretical interaction simulation is not observed. The Fourier transform infrared (FTIR) data and simulation results, instead, suggest that electron‐rich atoms on the analyte, such as oxygen, sulfur, nitrogen, and phosphorus, are responsible for fluorescence quenching, following dipole–dipole interaction with the humic‐fraction‐modified adsorbent.     

Large‐scale Enrichment of Sulfur‐containing Acid in Acetonitrile Using Triazine Analog as the Derivatizing Reagent for Desorption from Humic‐fraction‐modified Silica Gel

The analog of triazine is used as the derivatizing reagent for enriching large‐scale acid (e.g. amino acid) containing a sulfur atom on the humic‐fraction‐modified silica gel in acetonitrile and desorbing from the adsorbent in hexane, respectively. The percent yield of the chemical derivatization under alkaline conditions, ranging from about 8 to almost 100 %, is pH dependent, and varies significantly among these examined analytes, believed to be due to the structure of the analyte, not the derivatizing reagent. The percentage of enrichment, not reproducible under an aqueous environment and independent of the type of triazine analogs, reaches almost 100 % in all cases. The force leading to the adsorption is the complexation between carboxyl groups on analyte and a humic‐fraction‐modified adsorbent based on the adsorption equilibrium results. Consequently, these results are not reproducible under ethyl ether or methanol environments due to the competition for binding sites from solvent molecules.     

Adsorption of three selected flavonoids with humic fraction-modified silica gel in hexane: A mechanism study

Three selected flavonoids, commonly found in spices, red-purple fruits, and vegetables, were adsorbed on humic fraction-modified silica gel in hexane. The percentage of adsorption in hexane for all examined analytes was nearly 100% after 1 hr, as a result of the strong dipole–dipole interaction. The increasing amount of adsorbent involved in the process improved the percentage of adsorption, which in turn shortened the time needed to reach the maximum by providing more binding sites. However, adsorption was not observed in other liquid phases under the same conditions, such as acetonitrile and ethyl ether. The mechanism leading to the adsorption was explored chromatographically, as well as by fourier transform infrared spectroscopy (FTIR) and theoretical simulations.     

Heavy Metallic and Organometallic Ions Scavenging Using Silica‐Based Adsorbent Functionalized with Ligands Containing Sulfur and Nitrogen Elements

A variety of silica‐based solid phases, whose surfaces are functionalized with ligands containing sulfur and nitrogen elements, are used as self‐supporting adsorbents for environmental remediation evaluation and potential separation application. Each adsorbent is tested for its ability to scavenge five metallic ions: Hg²⁺, Cu²⁺, Cd²⁺, Mn²⁺, Pb²⁺, and two organometallic ions: ethylmercury and phenylmercury, from independent homoionic solutions at both neutral and acidic pH values. The results indicate that the percentage of these ions scavenged by a given adsorbent varies, and is found to be highly related to the structural environment in the vicinity of the sulfur and nitrogen elements on the ligand. It is believed that the scavenging of metallic ions is a result of the complexation formation between the metallic ions and the ligands containing sulfur and nitrogen elements, and is not due to the irreversible association chemistry with the sulfur or nitrogen element itself. In the case of organometallic ions, a π‐π interaction is thought to be involved in the adsorption with ligands containing an aromatic moiety in addition to the aforementioned forces. The time needed to reach the maximum percent of adsorption decreases as the amount of adsorbent increases. The longer the adsorption time, the higher percent of ion is removed. Other factors, such as the temperature and the acidity in the liquid phase of the matrix affect the percentage of ions scavenged as well.     

Comparative study of acid yellow 119 adsorption onto activated carbon prepared from lemon wood and ZnO nanoparticles loaded on activated carbon

Activated carbon from lemon wood (AC) and ZnO nanoparticles loaded on activated carbon (ZnO‐NP‐AC) were prepared and their efficiency for effective acid yellow 199 (AY 199) removal under various operational conditions was investigated. The dependence of removal efficiency on variables such as AY 199 concentration, amount of adsorbent and contact time was optimized using response surface methodology and Design‐Expert. ZnO nanoparticles and ZnO‐NP‐AC were studied using various techniques such as scanning electron microscopy, X‐ray diffraction and energy‐dispersive X‐ray analysis. The optimum pH was studied using one‐at‐a‐time method to achieve maximum dye removal percentage. Small amounts of the proposed adsorbents (0.025 and 0.025 g) were sufficient for successful removal of AY 199 in short times (4.0 and 4.0 min) with high adsorption capacity (85.51 and 116.29 mg g^?1 for AC and ZnO‐NPs‐AC, respectively). Fitting the empirical equilibrium data to several conventional isotherm models at optimum conditions indicated the appropriateness of the Langmuir model with high correlation coefficient (0.999 and 0.978 for AC and ZnO‐NPs‐AC, respectively) for representation and explanation of experimental data. Kinetics evaluation of experiments at various time intervals revealed that adsorption processes can be well predicted and fitted by pseudo‐second‐order and Elovich models. This study revealed that the combination of ZnO nanoparticles and AC following simple loading led to significant improvement in the removal process in short adsorption time which was enhanced by mixing the media via sonication.     

Kinetics of solid-phase extraction and solid-phase microextraction in thin adsorbent layer with saturation sorption isotherm

The effects of sorbent saturation in thin adsorbent layers have been much overlooked in earlier research and should be taken into account in both the theory and practice of solid-phase extraction (SPE) and solid-phase microextraction (SPME). The adsorption kinetics of a single analyte into a thin adsorptive layer was modeled for several cases of agitation conditions in the analyzed volume. The extraction process in the adsorbent layer was modeled using a Langmuir isotherm approximated by the linear isotherm at low concentrations and by a saturation plateau at concentrations exceeding the critical saturation concentration. Laplace transformations were used to estimate the equilibration time and adsorbed analyte concentration profile for no agitation, practical and perfect agitation in the analyzed volume. The equilibration time may be significantly reduced at high degrees of oversaturation and/or agitation in the analyzed volume. The resulting models indicated that the adsorbent layer becomes saturated at some critical value of the oversaturation degree parameter. The critical value of the oversaturation parameter is affected by both the concentration of the analyte in the analyzed volume and the sorbent characteristics. It was also shown that the adsorption process is carried out via the propagation of the saturation adsorption boundary toward the inner boundary of the adsorbent layer. These new adsorption models should serve as "stepping stones" for the development of competitive adsorption kinetic models for both SPE and SPME, particularly in cases where fast sampling is used.     

Theoretical Assessment of Binding and Mass‐Transport Effects in Electrochemical Affinity Biosensors That Utilize Nanoparticle Labels for Signal Amplification

This paper presents a theoretical study of electrochemical affinity biosensors for the detection of DNA/protein that utilize nanoparticle labels for signal amplification. This study analyzes the effects of binding and mass transport of the analytes on biosensor performance by using numerical simulations. Four cases were considered: 1) nanoparticles used to increase the loading of an electroactive species, or used as catalysts under pseudo‐first‐order conditions; 2) nanoparticles used as ultramicroelectrode arrays for the electrolysis of large concentrations of substrate; 3) nanoparticles used as seeds to deposit electrochemically detectable species; and 4) nanoparticles used to mediate the deposition of electrocatalysts. By using nanoparticle labels, high sensitivity is possible under all conditions considered. However, theoretical findings suggested that nonspecific adsorption could be more problematic in cases 2–4 due to the mismatch between the chemistry of surface binding and the principle of signal amplification that originates from the effect of mass transport. Under these conditions, any given signal would plateau at a much lower analyte concentration, well before the analyte binding had actually reached a plateau. Views on possible solutions to the above limitations are also presented.     

Synthesis of calcium alginate nanoparticles for removal of lead ions from aqueous solutions

Calcium alginate nanoparticles (CANPs) were synthesized to remove lead ion [Pb(??)] as pollutant of environment from aqueous solutions. The produced CANPs were characterized by Fourier transform infrared spectroscopy (FTIR), particle size analysis (PSA) and scanning electron microscope (SEM). Various factors, which affected adsorption efficiency of lead ions by CANPs, such as pH (pH from 1 to 8), initial ions concentration (in the range of 25 to 125 mg L^–1), contact time (varying from 5 to 120 min), and adsorbent dose (50 to 500 mg L^–1), were investigated for determination of optimum experimental conditions. The result of tests showed that the investigated factors had significant effects on adsorption of Pb(??) ions and the maximum adsorption percentage of lead at pH = 6~7, 25 mg L^–1 initial ions concentration, contact time of more than 140 min. and for adsorbent dose at 500 mg L^–1. Also these results demonstrated the effective adsorption of Pb²⁺ ions by synthesized CANPs that occurred due to a high surface area of CANPs and the presence of anionic carboxylate functional groups and allowed effective absorbing and removing Pb(??) ions from aqueous solutions. Thus, these nanoparticles were able to remove over 99% of lead ions from solution.     

Functionalized silica nanoparticles for trapping Pb2+ ions via diazo‐azomethine scaffolds

Diazo‐azomethine coated silica sorbent for the adsorption of Pb²⁺ ions has been fabricated. The sorbent was obtained by one‐pot synthesis of silica nanoparticles in the presence of diazo‐azomethine molecules possessing silatranyl side chains for grafting via covalent bond formation. The functionalized silica nanoparticles exhibited characteristic physicochemical properties of diazo‐azomethine scaffolds as determined using Fourier transform infrared spectroscopy, scanning and transmission electron microscopies and thermogravimetric analysis. Various adsorption parameters such as pH, weight of adsorbent, time taken for equilibration and recovery of lead ions were optimized using a batch method. The sorbent showed high adsorption capacity for lead ions of 460.4 mg g^?1 at pH = 4. The effect of various competing ions on the adsorption of lead ions was studied and interference was removed by using a masking agent. The sorbent can be regenerated and reused, and is compatible for the adsorption of Pb²⁺ ions from green leafy vegetables. Copyright © 2016 John Wiley & Sons, Ltd.     

Facile Synthesis of Prussian Blue Derivate‐Modified Mesoporous Material via Photoinitiated Thiol–Ene Click Reaction for Cesium Adsorption

A novel strategy to synthesize a functional mesoporous material for efficient removal of cesium is reported. Specifically, Prussian blue derivate‐modified SBA‐15 (SBA‐15@FC) was prepared by photoinitiated thiol–ene reaction between thiol‐modified SBA‐15 and pentacyano(4‐vinyl pyridine)ferrate complex. The effects of weight percentage of the Prussian blue derivate, pH, adsorbent dose, co‐existing ions, and initial concentration were evaluated on the adsorption of cesium ions. The adsorption kinetically follows a pseudo‐second‐order model and reaches equilibrium within 2 h with a high adsorption capacity of about 13.90 mg Cs g^?1, which indicates that SBA‐15@FC is a promising adsorbent to effectively remove cesium from aqueous solutions.     

Magnetic hydroxyapatite nanoparticles: An efficient adsorbent for the separation and removal of nitrate and nitrite ions from environmental samples

A novel type of magnetic nanosorbent, hydroxyapatite‐coated Fe₂O₃ nanoparticles was synthesized and used for the adsorption and removal of nitrite and nitrate ions from environmental samples. The properties of synthesized magnetic nanoparticles were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray powder diffraction. After the adsorption process, the separation of γ‐Fe₂O₃@hydroxyapatite nanoparticles from the aqueous solution was simply achieved by applying an external magnetic field. The effects of different variables on the adsorption efficiency were studied simultaneously using an experimental design. The variables of interest were amount of magnetic hydroxyapatite nanoparticles, sample volume, pH, stirring rate, adsorption time, and temperature. The experimental parameters were optimized using a Box–Behnken design and response surface methodology after a Plackett–Burman screening design. Under the optimum conditions, the adsorption efficiencies of magnetic hydroxyapatite nanoparticles adsorbents toward NO₃^? and NO₂^? ions (100 mg/L) were in the range of 93–101%. The results revealed that the magnetic hydroxyapatite nanoparticles adsorbent could be used as a simple, efficient, and cost‐effective material for the removal of nitrate and nitrite ions from environmental water and soil samples.     

酚醛型吸附树脂在非水体系中对吡啶和N,N-二甲基苯胺的吸附性能研究

研究了酚醛型吸附树脂JDW 2在非水体系中对吡啶和N ,N 二甲基苯胺的静态吸附 .由实验结果推论正己烷中树脂对吡啶和N ,N 二甲基苯胺的吸附是以氢键吸附机理为主进行的 ,JDW 2酚醛型吸附树脂在正己烷中 ,等温吸附吡啶和N ,N 二甲基苯胺的平衡吸附数据符合Langmuir方程 ,相关系数在 0 99以上 ,因此 ,酚醛型吸附树脂在正己烷中吸附吡啶和N ,N 二甲基苯胺属单分子层吸附 ;同时对非水体系中乙醇或乙酸乙酯的含量对树脂吸附吡啶和N ,N 二甲基苯胺的影响进行了研究     

Isocratic Separation of Dansylated Biogenic Amines on a C8‐Bonded Silica Column under the LC Elution of Methanol‐Based Mobile Phase

Under the elution of methanol‐based mobile phase, the isocratic resolution of 12 biogenic amines, including 1 aromatic, 2 heterocyclic and 9 aliphatic amines, as the dansylated derivatives has been accomplished in less than 25 minutes on a 15 cm C₈‐bonded column. The resolution can not be reproduced on other examined alkyl‐bonded phases (e.g., C₄ and C₁₈) under the same chromatographic conditions, or in the reversed‐phase mode. The retention, mainly as a result of hydrophobic interaction between analyte and stationary phase, can be adjusted by varying the percentage of methanol in the mobile phase. Also, incorporating acetic acid as additive to the mobile phase to protonate the analyte and silanol groups that are little shielding on the surface of silica gel reduces the dipole‐dipole interaction, and thus the retention scale, which in turn deteriorates the resolution. Furthermore, the elution reversal is plausible for some of analytes as a greater percent of acetic acid is used in the elution. Values of correlation coefficients (R²) range between 0.9995 and 0.9996, indicating good linearity.     

An electrokinetic study on a synthetic adsorbent of crystalline calcium silicate hydrate and its mechanism of endotoxin removal

A synthetic, disposable adsorbent of crystalline calcium silicate hydrate, LRA product by Advanced Minerals Corp., has been found highly effective for endotoxin removal from aqueous solutions. Endotoxin removal by this adsorbent is greatly enhanced by the addition of an electrolyte, such as NaCl or Tris-HCl. The electrophoretic method has been used to study the mechanism of endotoxin adsorption. In many cases, adding the electrolyte increases the magnitude of negative zeta potential of the adsorbent in water, while endotoxin adsorption reduces the magnitude. It is hypothesized that ion-exchange between monovalent cations from the aqueous phase and Ca2+ ions near the surface of the adsorbent shift zeta potential of the adsorbent to the more negative direction. It is further hypothesized that endotoxins form cationic species through binding between its phosphate groups and Ca2+ ions dissolved from the adsorbent. The adsorption of endotoxins in the form of cationic species is enhanced by the increased negative zeta potential of the adsorbent when an electrolyte is added.     

Synthesis of propyl aminopyridine modified magnetite nanoparticles for cadmium (II) adsorption in aqueous solutions

In this study, 2‐aminopyridine functionalized magnetite nanoparticles were chemically synthesized and used for removing Cd²⁺ ions from aqueous solutions. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X‐rays (EDX), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The SEM results showed the synthesized magnetite nanoparticles have particle size around 26 nm. The effects of several variables including solution pH and volume, adsorbent mass, ionic strength and contact time on the Cd²⁺ adsorption were studied in batch experiments and finally the optimum conditions for adsorption were obtained. The kinetic data were investigated by pseudo‐ first‐order, pseudo‐ second‐order, intraparticle diffusion and Elovich kinetic models and data were described reasonably by pseudo‐ second‐order model (R² = 0.9996) with q_e = 2.31 mg g^?1. Adsorption data were analyzed using Langmuir, Freundlich and Temkin isotherm models. The results indicated that the data were well fitted to the Freundlich isotherm model (R² = 0.9907). After study the possible interference effect of foreign ions on Cd²⁺ removal, the applicability of the proposed nanoparticles for adsorption from real samples confirmed the successfully removal of Cd²⁺ ions with removal efficiency higher than 92%. The obtained results showed that the synthesized nanoparticles as a reusable adsorbent can act as a good choice for Cd²⁺ removal with an easy procedure.     

Fast Removal and Recovery of Methylene Blue by Activated Carbon Modified with Magnetic Iron Oxide Nanoparticles

A magnetic adsorbent was synthesized by modification of activated carbons with magnetic iron oxide nanoparticles (AC‐MIONs). The preparation method is fast and could be carried out in an ordinary condition. The AC‐MIONs were used as quite efficient adsorbents for separation of methylene blue (MB) from aqueous solution in a batch process. The effect of different parameters such as pH, temperature, electrolyte concentration, contact time and interfering ions on the removal of MB were studied. The adsorption data were analyzed by Langmuir and Freundlich isotherm models and a maximum adsorption amount of 47.62 mg g^‐1 and a langmuir adsorption equilibrium constant of 3.0 L mg^‐1 were obtained. The obtained results revealed that AC‐MIONs were effective adsorbents for fast removal of MB from different aqueous solutions. This adsorbent was successfully used for removal of MB from Karoon River water.     

Oxygen Selectivity on Partially K Exchanged Na-A Type Zeolite at Low Temperature

In previous work by the authors on Na-A zeolite (Izumi et al., Japan Patent Toku-Kou-Shou 63-058614, 1988), it was shown that the combination of high-temperature calcination and operation of the adsorption step at low temperatures improved the selectivity for oxygen over nitrogen from air (Izumi et al., CATS J Meeting Abstracts, 31(2A), 10, 1989; Izumi and Suzuki, Adsorption, 6, 2000). Berlin discloses in his U.S. Patent 3282028 (1966) that the partial exchange of potassium ions for sodium ions in the Na-A type zeolite also improved selectivity for oxygen by reducing the uptake rate of nitrogen. It was therefore expected that the oxygen selectivity of Na-K-A with high-temperature calcination and low-temperature adsorption might be enhanced. For the confirmation of optimum conditions for the appearance of oxygen selectivity on Na-K-A, samples were prepared with a K exchange ratio varied from 0–20 mol% (0–2.4 K ions/unit cell), and a calcination temperature varied from 923 to 1073 K, and an experiment concerning oxygen and nitrogen adsorption on Na-K-A was undertaken with a small adsorbent column under pressure swing adsorption (PSA) conditions at adsorption temperatures from room temperature to 213 K. It was found that (a) the K exchange ratio of 7 mol% (0.84 K ions/unit cell), and (b) the calcination temperature of 993 K, resulted in a remarkable increase in oxygen selectivity. Under optimum conditions for Na-K-A, the oxygen separation factor was about 8. Na-K-A has the potential to effectively separate oxygen and nitrogen from air by means of PSA.     

Speciation of ultra-trace amounts of inorganic arsenic in water and rice samples by electrothermal atomic absorption spectrometry after solid-phase extraction with modified Fe3O4 nanoparticles

A new magnetic adsorbent, 3-mercaptopropionic acid coated 3-aminopropyl triethoxysilane modified Fe₃O₄ nanoparticle, was synthesised and used for the extraction and preconcentration of arsenic ions in aqueous solutions followed by electrothermal atomic absorption spectrometric determination. The adsorbent was characterised by TEM, SEM, XRD and FT-IR techniques and the method used the unique properties of magnetic nanoparticles, namely, high surface area and superparamagnetism which gave it the advantages of high extraction capacity, fast separation and low adsorbent consumption. Different parameters affecting extraction efficiency of the analyte including pH value, sample volume, adsorbent amount, extraction time and desorption conditions were investigated and optimised. Under the optimum conditions, wide linear range of 30–25,000 ng L^?1 and low detection limit of 10 ng L^?1 were obtained. The interday and intraday precisions (as RSD%) for five replicates determination of 50 and 25,000 ng L^?1 of arsenic ions were in the range of 2.3–3.2%. Furthermore, no significant interference was observed in the presence of coexisting ions and high preconcentration factor of 198 was obtained. The adsorption isotherm followed Langmuir model and its kinetic was second-order. The accuracy of the method was validated by analysing certi?ed reference materials for water and rice with satisfactory recoveries. Finally, the proposed method was successfully applied for the determination of ultra-trace amounts of arsenic in rice and water samples.