Preconcentration of phenols by adsorption on organo-clay followed by capillary electrophoretic determination

The organo-clay adsorbent used was prepared by modification of montmorillonite from Kurşunlu, Turkey with the cationic surfactant cetyltrimethlyammonium bromide. The modification process involves replacing the inorganic exchange cations of the clay by organic cations containing long chain alkyl groups. The retention of phenolic compounds from aqueous solution on the organo-clay was studied. The analytes are quantitatively retained on the proposed adsorbent at pH 7 and recovered by elution with ethanol. The determination of phenols was performed by capillary electrophoresis. Received: 28 July 1997 / Revised: 15 December 1997 / Accepted: 8 January 1998     

Selected adsorbent materials for oil-spill cleanup

Thermogravimetric analysis and differential scanning calorimetry have been applied to determine the adsorption of oil on selected adsorbates: sand, organo-clay and raw cotton. Thermal analysis provides evidence for the interaction and physical adsorption of the diesel oil on the adsorbates. Sand adsorbed diesel to around 33% by mass through weak physical interactions and appeared to fractionate the diesel components. The organo-clays more strongly adsorbed the diesel as evidenced by higher thermal decomposition temperatures. Differential scanning calorimetry (DSC) shows a strong interaction between the organo-clay and the diesel oil. Diesel is effectively adsorbed on organo-clay through adsorption and partitioning and is not removed from the organo-clay until significantly higher temperatures. Cotton displayed a very high adsorption/absorption capacity. A shift in the peak at 110°C (compared with pure diesel at 90°C) suggests an interaction between the diesel compounds and the cotton fibres as diesel is being retained at higher temperatures and more energy is required to evaporate the diesel. DSC was used to determine the strength of the diesel adsorption on the sand, organo-clay and cotton. The use of adsorbent materials to adsorb oil from oil spills is of great significance in modern society. One method of proving the effectiveness of an adsorbent material is through thermoanalytical techniques.     

Sorption of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Natural Biomaterial: Duck Feather

Feather fibers were modified by treatment with 5% tannic acid (TA) solution. Kinetics of the modification was investigated as a function of the reaction time. The maximum loading of TA on feather reached 8.3% after being treated by TA for 9 h. The adsorption of metal cations (Cu²⁺, Zn²⁺) by unmodified and TA-modified feather fibers was investigated as a function of fiber weight gain, temperature, and pH of the metal solution. The adsorption was enhanced at alkaline pH and ambient temperature and increased with the weight gain of TA. The maximum uptake of metal cations (Cu²⁺, 0.77 mmol/g; Zn²⁺, 0.95 mmol/g) was obtained by TA-modified feather at weight gain: 8.3%, pH 11, while at the acidic pH, the adsorption of metal cations by either unmodified or TA-modified feather was negligible. The influence of anions on the adsorption of metal cations was also studied. The uptake of Cu²⁺ from chloride was higher and faster than that from nitrate. Desorption of the metals was performed at acidic pH 2.5 for 48 h. The feather–TA–metal complexes exhibited higher stability for metal cations than the feather–metal complexes. All these experiments reveal that TA-modified feather fibers have good adsorption to metal cations and can be used as metal adsorbent in wastewater treatment.     

The selectivity of active carbons modified by fullerenes with respect to mixtures of metal cations in aqueous solutions

The separating ability of active carbons and active carbons modified with fullerenes with respect to mixtures of nonferrous metal cations was studied. The selectivity series for the extraction of cations from aqueous solutions was Ag⁺ > Cu²⁺ > Pb²⁺. The selectivity of adsorption by active carbon modified with fullerenes was higher than that characteristic of the initial adsorbent, especially for the extraction of silver ions from a mixture of silver and copper cations.     

Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

Enhanced Removal of Cu(II) Ions from Aqueous Solution by Poorly Crystalline Hydroxyapatite Nanoparticles

Poorly crystalline and well-dispersed hydroxyapatite (HAP) nanoparticles were synthesized and used as novel adsorbents for the removal of Cu(II) from aqueous solution. Various factors affecting the adsorption such as adsorbent crystallinity, pH, adsorbent dosage, contact time, temperature, competing cations, and the presence of humic acid were investigated in detail. Results showed that the HAP calcined at lower temperature was poorly crystalline and had better adsorption capacity for Cu(II) than those calcined at higher temperature. Cu(II) removal was increased with increases of pH, adsorbent dosage, temperature, and the presence of humic acid, but decreased as the existence of competing divalent cations. Kinetic studies showed that pseudo-second-order kinetic model better described the adsorption process. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity of poorly crystalline HAP was 41.80 mg/g at 313 K, displaying higher efficiency for Cu(II) removal than many previously reported adsorbents. Thermodynamics studied revealed that the adsorption of Cu(II) by poorly crystalline HAP was spontaneous, endothermic, and entropy-increasing in nature. This study showed that poorly crystalline HAP could be used as an efficient adsorbent material for the removal of Cu(II) from aqueous solution.     

Infrared study of the effects of thermal treatment on montmorillonite-benzidine complexes

Li-, Na-, K-, Rb- and Cs-montmorillonites were saturated with benzidine, these organo-clay complexes heated under vacuum to 200°C and IR spectra recorded at various temperatures. Benzidine is mostly bound to interlayer cations through water molecules, except in Cs-clay where bonding to hydrophobic water and to water molecules which are hydrogen bonded to the oxygen plane predominates. During the thermal treatment water is lost and alkali, cations coordinate directly with benzidine. In Cs-, and to some extent also in Rb- and K-montmorillonite, benzidine is oxidized to semiquinone and quinoidal cation during the thermal treatment.     

Enthalpy of fuel gas odorants on surrogate soil surfaces by gas chromatography

Heats of adsorption and heats of interaction for natural gas odorants on clay and organo-clay, respectively, were determined by means of wall-coated open-tubular (WCOT) column gas chromatography. The odorants studied are organic thiol and sulfide compounds. Clay stationary phases were created from the synthetic clay Laponite-RD. Subsequent coatings with octadecane created an organo-clay stationary phase. Experimental results show that, as a class, sulfide odorants have larger enthalpies on clay and organo-clay surfaces than thiol odorants. Therefore, we conclude that thiols are less likely to be sequestered on soil surfaces. The effect of hydrated clay surfaces on odorant enthalpies is also presented. Further, we demonstrate that Lewis acid-base chemistry on clay surfaces explains the significant difference in enthalpy magnitudes between the sulfide and thiol classes.     

Adsorption of uranium on adsorbents produced from used tires

The present investigation deals with the potential use of adsorbents produced from used tires for the removal of uranium from aqueous solutions. Two different adsorbents were used including char and activated carbon produced from used tires. The surface area was larger on activated carbon. Adsorption experiments were carried out as a function of time, adsorbent concentration, pH and initial concentration of uranium. The adsorption kinetics was found to follow the Lagergren equation. The rate constants of intraparticle diffusion and mass transfer coefficients were calculated. It was shown that the equilibrium data could be fitted by the Langmuir and Freundlich equations. The adsorption of uranium in the presence of diffferent cations were also studied and the results were correlated with the ionic potential of the cations. Results obtained in the study demonstrate that the activated carbon produced from used tires can be considered as an adsorbent that has a commercial potential for uranium removal.     

Effective removal of anionic dyes from aqueous solutions by novel polyethylenimine-ozone oxidized hydrochar (PEI-OzHC) adsorbent

The adsorption behavior of the anionic dyes Remazol Brilliant Blue R (RBBR) and Reactive Black 5 (RB5) from aqueous solutions by polyethylenimine ozone oxidized hydrochar (PEI-OzHC) was investigated. The adsorption capacities of both dyes increased with functionalization of PEI in the hydrochar adsorbent. The results of surface characterization (FTIR, BET, TGA, elemental analysis, and SEM) showed that PEI modification greatly enhanced the adsorbent surface chemistry with a slight improvement of adsorbent textural properties. In addition, the adsorption kinetics data showed an excellent adsorption efficiency as reflected in the high removal percentages of the anionic dyes. The Isotherm results indicated that RBBR and RB5 dye adsorption occurred via monolayer adsorption, and chemisorption was the rate-controlling step. The PEI-OzHC adsorbent possesses higher maximum Langmuir adsorption capacity towards RBBR (218.3 mg/g) than RB5 (182.7 mg/g). This increase in adsorption capacity is attributed to the higher number of functional groups in RBBR that interact with the adsorbent. This study reveals the potential use of adsorbents derived from pine wood hydrochar in municipal as well as industrial wastewater treatment. Furthermore, surface chemistry modification is proven as an effective strategy to enhance the performance of biomass-derived adsorbents.     

Thermally stable organically modified layered silicates based on alkyl imidazolium salts

A series of imidazolium salts having various substituents and functional groups were synthesized and characterized by FTIR and NMR spectroscopy. Organic modification of natural and synthetic layered silicates involving montmorillonite (MMT), laponite (lap), and synthetic mica (mica) was carried out by ion-exchange reaction. The obtained organo-clays were characterized by FTIR and powder X-ray diffraction techniques. Results indicate that these organically modified clays have much higher thermal stabilities compared to their corresponding imidazolium halides. It was also observed from TGA analysis that thermal stability does not depend on the functional group present at the 3-position of the imidazolium salts. These studies strongly supports premise that the removal of halide is necessary to improve the thermal stability of the organo-clay produced.     

Chemical modification of the surface of a sulfonated membrane by formation of a sulfonamide bond

This paper describes a novel approach for the surface modification of a cation-exchange membrane, bearing sulfonate groups, by a cationic layer. The modification procedure involved the chlorosulfonation of the sulfonate groups of the base membrane with thionyl chloride, followed by a reaction with a diamine to yield a sulfonamide bond and a terminal amine. The latter could be quaternized by reaction with methyl iodide or protonated by soaking in acidic media. The membranes were characterized in detail by attenuated total reflectance Fourier transform infrared and X-ray photoelectron spectroscopies as well as elemental analysis to confirm that the above reactions occurred. The selectivity of these membranes toward the electrochemically assisted transport of protons versus Zn2+ metallic cations was determined during an electrodialysis in a two-compartment electrochemical cell. The data indicate a significant decrease of the transport of the metallic cations following modification of the membrane with the cationic layer. The later allows for the transport of protons from the catholyte to the anolyte compartment with much improved selectivity since the divalent cations are excluded from the membrane due to the electrostatic barrier of the cationic layer.     

Biodegradable metal adsorbent synthesized by graft polymerization onto nonwoven cotton fabric

A fibrous adsorbent for Hg ions was synthesized by radiation-induced emulsion graft polymerization of glycidyl methacrylate (GMA) onto a nonwoven cotton fabric and subsequent chemical modification. The optimal pre-irradiation dose for initiation of the graft polymerization of GMA, which minimized the effects of radiation damage on the mechanical strength of the nonwoven cotton fabric, was found to be 10 kGy. The GMA-grafted nonwoven cotton fabric was subsequently modified with ethylenediamine (EDA) or diethylenetriamine (DETA) to obtain a Hg adsorbent. The resulting amine-type adsorbents were evaluated for batch and continuous adsorption of Hg. In batch adsorption, the distribution coefficients of Hg reached 1.9×10⁵ and 1.0×10⁵ for EDA- and DETA-type adsorbents, respectively. A column packed with EDA-type adsorbent removed Hg from 1.8 ppm Hg solution at a space velocity of 100 h^?1, which corresponds to 16,000 times the volume of the packed adsorbent. The adsorbed Hg on the EDA-type adsorbent could be completely eluted by 1 M HCl solution. A microbial oxidative degradation test revealed that the EDA-type adsorbent is biodegradable.     

Cation-modified silikalit-2 as a selective adsorbent for gas chromatography columns

A selective adsorbent was proposed on the basis of synthetic zeolite silikalit-2 modified with cadmium, tallium, and silver cations. It is intended for the gas chromatographic separation of some isomeric benzene derivatives. The adsorbent possesses pronounced retention properties to para isomers of aromatic compounds, which is due to the molecular sieve properties of the zeolite and the ability of benzene derivatives to form unstable complexes with cations entering the composition of the zeolite. Low selectivity to ortho and meta isomers is due to only the complexation effect.     

Preparation of Isotactic Polypropylene/Organoclay Nanocomposites by Solution Mixing Methodology: Structure and Properties Relationships

Isotactic Polypropylene (iPP) based nanocomposites filled with organo-clay nanoparticles were prepared and the relationships between their structure and properties were investigated. Modified C₁₆-C₁₈ smectite clay nanoparticles were used in order to promote matrix/filler compatibilization and to improve interfacial adhesion. X-Ray analysis performed on the nanocomposites demonstrated that at low organo-clay content (1 and 3% by weight) a nanostructure has been obtained, while in presence of 5% by weight of organoclay cluster regions have been formed. Mechanical tests showed that the elastic modulus increases of about 20% compared to the neat polymeric matrix value when 1 and 3% of nanofiller is added.     

Removal of uranium(VI) from aqueous solution by apricot shell activated carbon

Uranium is a toxic and radioactive heavy metal found in nuclear effluents and should be treated based on environmental considerations. The adsorption of uranyl cations (UO₂ ²⁺) by apricot shell activated carbon (ASAC) was investigated in a batch system. The effects of pH, contact time, temperature, adsorbent dosage on the adsorption kinetics and equilibrium adsorption isotherms of U(VI) were examined. The U(VI) uptake was fast within the first 60 min and reached an equilibrium state at 120 min. The adsorption process was highly pH dependent and the maximum adsorption was obtained at an initial solution pH of 6.0. Temperature over the range 25–45 °C had little effect on the U(VI) adsorption. The U(VI) removal efficiency increased concurrently with increasing ASAC dosage, whereas the U(VI) adsorption capacity decreased with increasing ASAC dosage. The adsorption process followed both Langmuir and Freundlich isotherms. On the basis of Langmuir model, the maximum adsorption capacity was found to be 59.17 mg U(VI)/g adsorbent. The adsorption kinetics can be very well defined by the pseudo-first-order rate model. The present results suggest that ASAC could be used as an adsorbent for an efficient removal of U(VI) from aqueous solution.     

Preparation of anion exchanger by amination of acrylic acid grafted polypropylene nonwoven fiber and its ion-exchange property

To develop the polymeric adsorbent that possess anionic exchangeable function, PP-g-AA-Am fibers were prepared by photoinduced grafting of acrylic acid (AA) onto polypropylene (PP) nonwoven fibers and subsequent conversion of carboxyl group in grafted AA to an amine (Am) group by reaction with diethylene triamine (DETA). The amination of grafted AA increased with increase in the degree of grafting, the reaction time and temperature of the chemical modification process. Catalytic effect of metal chlorides such as AlCl(3) and FeCl(3) on the amination of grafted AA was significant but not essential to lead the amination. FT-IR and solid (13)C NMR data indicate that amine group was introduced into PP-g-AA fiber through amide linkage between grafted AA and DETA. The anion exchange capacity of PP-g-AA-Am fiber increased with increase in the degree of amination, but reached maximum value at about 60% amination of 150% grafted AA. PP-g-AA-Am fiber showed much higher maximum capacity for PO(4)-P and a similar capacity for NO(3)-N compared to commercial anion resins. Furthermore, the PP-g-AA-Am fiber also has adsorption ability for cations because of unaminated residual carboxyl group.     

Synthesis and characterization of a new adsorbent for capture of metal from aqueous solutions

A new material containing a potential ligand for transition metals was prepared through the reaction of 3-aminopropyltrimethoxysilane and thioglycolic acid. The new adsorbent was characterized by elemental analyses, infrared spectroscopy, solid-state ¹³C nuclear magnetic resonance, thermogravimetric analysis, transmission electron microscopy, and specific surface area calculations. The formulated material was used in the removal of cobalt, copper, and nickel cations from aqueous solutions. Calorimetric titration was applied to study the interaction of these cations with the new adsorbent; the latter displayed a chelating moiety with basic centers containing nitrogen, oxygen, and several sulfur atoms, capable of capturing cations from aqueous solutions. This process of extraction was carried out by a batch method to yield the following order of maximum retention capacity: Ni > Co > Cu. The process of cation interactions showed exothermic enthalpies. The calculated ΔG values are in agreement with the spontaneity of the proposed reactions and conformed to the values found by applying the Langmuir model to these systems. The positive entropy and negative enthalpy values indicated that the reactions are favorable.     

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.     

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.