Study of phenol adsorption on modified forms of zeolite

Analcime samples were studied with the aim of cleaning air from phenol.     

Adsorption of phenol onto surfactants modified bentonite

Bentonite was modified with hexadecyltrimethylammonium bromide or bencylhexadecyldimethylammonium chloride. Phenol adsorption kinetic and isotherms experiments were performed; in both cases, phenol was determined in the aqueous solutions by UV–Vis spectroscopy. The results showed that the adsorption of phenol depends on the kind of surfactant, and pH of the solutions. The adsorption was higher for the clay modified with bencylcetyldimethylammonium chloride than hexadecyltrimethylammonium bromide.     

Adsorption of aniline,phenol, and chlorophenols on pure and modified bentonite

In the present study, pure bentonite and bentonite modified by HNO₃, EDTA, and HDTMA are adsorbents. The changes on the surfaces of bentonite samples are studied by IR spectroscopy. The adsorption of aniline, phenol, and phenol derivatives on these adsorbents is examined by means of gas chromatography. As the result of these examinations, it is seen that the adsorption capacities of clay-organic complexes (bentonite-EDTA and bentonite-HDTMA) are higher than those of bentonite-HNO₃ and pure bentonite.

     

Uranium and lead adsorption onto bentonite and zeolite modified with polyacrylamidoxime

Polyacrylonitrile (PAN) and bentonite (B)/zeolite (Z)-PAN composites were prepared by direct polymerization of acrylonitrile (AN) and AN adsorbed onto B and Z. PAN and the composites were subjected to amidoximation procedure to obtain polyacrylamidoxime (PAO), B-PAO and Z-PAO compositions. The structural features were evaluated by FT-IR, XRD and SEM analysis. The adsorption dependency of the materials on ion concentration, temperature and time were investigated for Pb²⁺ and UO₂ ²⁺. The adsorption capacities of B/Z-PAO composites were higher than those of pure PAO. The values of enthalpy and entropy changes were positive. The kinetics of the adsorption was well defined by the pseudo second order rate model. For the use of 1 M HCl as a regenerative effluent, the composites were reusable for five sequential treatments without any change in their structures whereas PAO completely gelled in the first use.     

Uranium adsorption from a liquid waste using thermally and chemically modified bentonite

In this work, uranium adsorption from aqueous (waste) solution onto thermal and chemical modified bentonite (TCMB) has been studied. The relevant factors affecting uranium adsorption onto our TCMB adsorbent were studied. These factors involved contact time, initial uranium concentrations, pH, adsorption temperature, foreign ion and the effect adsorbent (TCMB) amount using synthetic solution. The theoretical capacity of TCMB adsorbent is about 29 mg/g TCMB. The optimum adsorption conditions were choiced. Uranium elution from the loaded TCMB adsorbent has been carried out using CH₃COONa as an effective eluent. Uranium adsorption from Gattar liquid waste by TCMB adsorbent was carried out in columns. The low uranium adsorption efficiency (37.5 % of the theoretical capacity of TCMB) may be due to the adsorption competition between uranium and difference foreign ion present in the solution (as iron). More than 92 % of the loaded uranium amount on the TCMB adsorbent has been eluted using CH₃COONa as an efficient eluent.     

Thermodynamics of the adsorption of different dyes onto bentonite modified with hexadecyltrimethylammonium cation

Removal of two different dyes: Acid Orange 10 (AO10) and Reactive Black 5 (RB5) from their aqueous solutions using organobentonite as adsorbent was investigated. The experiments were carried out at different temperatures (298, 313, 323, and 333 K) in order to obtain thermodynamic parameters for adsorbate/adsorbent system i.e., activation energy, Gibbs free energy, enthalpy and entropy. The results of thermodynamic studies indicated that the adsorption of both dyes onto organobentonite is an endothermic process, while the values for activation energies (76 kJ mol^?1 for AO10 and 51 kJ mol^?1 for RB5) indicated that chemisorption occurred.     

Samarium (III) adsorption on bentonite modified with N-(2-hydroxyethyl) ethylenediamine

A new material has been synthesized using dry process to activate bentonite followed by N-(2-hydroxyethyl) ethylenediamine connecting chlorosilane coupling agent. The synthesized new material was characterized by elemental analysis, FT-IR and thermogravimetry which proved that bentonite was successfully modified. The most interesting trait of the new material was its selective adsorption for rare earth elements. A variety of conditions of the new material were investigated for adsorption. The optimal conditions were determined with respect to pH and shaking time. Samarium (Sm) was quantitatively adsorbed at pH 4 and shaking time of 2 min onto the new material. Under these conditions the maximum static adsorption capacity of Sm(III) was found to be 17.7 mg g⁻¹. The adsorbed Sm(III) ion were quantitatively eluted by 2.0 mL 0.1 mol L⁻¹ HCl and 5% CS (NH₂)₂ solution. According to IUPAC definition, the detection limit (3σ) of this method was 0.60 ng mL⁻¹. The relative standard deviation (RSD) under optimum conditions was less than 3% (n = 8). The new material also was applied for the preconcentration of trace Sm(III) in environmental samples with satisfactory results.     

Calorimetric evaluation of activated carbons modified for phenol and 2,4-dinitrophenol adsorption

Two commercial activated carbons with differences in their superficial chemistry, one granular and the other pelletised, were modified for use in phenol and 2,4-dinitrophenol adsorption. In this paper, changes to the activated carbon surface will be evaluated from their immersion calorimetry in water and benzene, and they will then be compared with Area BET, chemical parameters, micropore size distributions and hydrophobicity factors of the modified activated carbons. The activated carbons were modified using 60 % solutions of phosphoric acid (H₃PO₄), nitric acid (HNO₃), zinc chloride (ZnCl₂) and potassium hydroxide (KOH); the activated carbon/solution ratio was 1:3 and impregnation was conducted 291 K for a period of 72 h before samples were washed until a constant pH was obtained. Water immersion calorimetry showed that the best results were obtained from activated carbons modified with nitric acid, which increased from ?10.6 to ?29.8 J g^?1 for modified granular activated carbon, and ?30.9 to ?129.3 J g^?1 for pelletised activated carbon. Additionally, they showed the best results in phenol and 2.4-dititrophenol adsorption. Those results indicate that impregnation with nitric acid under the employed conditions could generate a greater presence of oxygenated groups on their surface, which favours hydrogen bond formation and the increased adsorption of polar compounds. It should also be noted that immersion enthalpy in benzene for modified activated carbon with nitric acid is the method with the lowest value, which is consistent with the increased presence of polar groups on its surface. Regarding hydrophobicity factors, it was observed that granular carbons modified with nitric acid and potassium hydroxide have the lowest ratios, indicating greater interaction with water.     

Understanding phenol adsorption mechanisms on activated carbons

The interactions between phenol molecules and activated carbons were investigated in order to understand the adsorption mechanism of this aromatic compound. A series of activated carbons with varied chemical composition but similar porous features were synthesized and submitted to phenol exposure from aqueous phase, followed by thermogravimetric analysis and identification of the desorbed species by temperature programmed desorption coupled with mass spectrometry. Based on these experiments, both physi- and chemisorption sites for phenol were identified on the activated carbons. Our results demonstrate that physisorption of phenol depends strictly on the porosity of the activated carbons, whereas chemisorption depends on the availability of the basal planes in the activated carbons. Thus, oxidation of the carbon can suppress the fraction of chemisorbed phenol since the surface functionalities incorporate to the edges of the basal planes; notwithstanding, hydrophilic carbons may present a small but not negligible contribution of chemisorbed phenol depending on the extent of the functionalization. Moreover, these adsorption sites (chemi-) are recovered by simply removal of the surface functionalities after thermal annealing.     

On the adsorption mechanism of copper ions on bentonite clay

Russian Chemical Bulletin - The adsorption of copper ions on bentonite clay was studied as a function of the pH of the medium, contact time, and temperature. A comparative study of the...     

Characteristics of phenol and chlorinated phenols sorption onto surfactant-modified bentonite

Surfactant-modified bentonite was synthesized by replacing adsorbed Na+ with long-chain alkyl quaternary ammonium cation, hexadecyltrimethylammonium bromide (HDTMAB). The sorption isotherms of phenol, p-chlorophenol, and 2,4-dichlorophenol were modeled according to the Langmuir and Freundlich equations. The Langmuir isotherm was found to describe the equilibrium adsorption data well. The mechanisms and characteristics of sorption of these ionizable organic contaminants onto surfactant-modified bentonite from water were investigated systematically and described quantitatively. The sorption properties are affected by the treatment conditions, such as amount of organobentonite, and the properties of organic compounds. Results indicated that adsorption of phenols from water was in proportion to their hydrophobicities, which increased with chlorine addition (phenol相似文献   

Equilibrium, FTIR, scanning electron microscopy and small wide angle X-ray scattering studies of chromates adsorption on modified bentonite

The study presents a discussion about the adsorption mechanism of chromate anions on bentonite modified by hexadecyltrimethylammonium bromide (HDTMA-Br). The formation of alkylammonium chromates: HDTMAHCrO₄, (HDTMA)₂Cr₂O₇ and to the lesser extent (HDTMA)₂CrO₄ at the water–bentonite interface is examined based on the Scanning Electron Microscopy and surface tension measurements. The histograms of HDTMA/Cr(VI) molar ratio on the bentonite surface, found from Scanning Electron Microscopy (SEM) measurements, show that for the majority of points of bentonite surface the value of this ratio is in 1–2 range. FTIR spectra of modified bentonite samples show the change from gauche to trans conformation in the surfactant arrangement in the clay interlayer accompanying its concentration increase.

In turn Small Wide Angle X-Ray Scattering (SWAXS) patterns evidently suggest incorporation of chromate anions into the interlamellar space of bentonite structure.     

Predicting solute adsorption on activated carbon: phenol

Activated carbon (AC), the most widely used adsorbent in water and in wastewater treatment, comprises a high surface area of very small, convoluted and interconnected pores. Despite the wide use of AC, there is little fundamental atomic-level understanding of its adsorption capacity and selectivity as well as its pore structure. The purpose of this work is to suggest the methodology for calculation of equilibrium adsorption capacity of common water organic pollutants and use it for phenol as a model. The effects of various functional groups, pore size, and coverage on thermodynamics of phenol adsorption from the gas phase and from water media are calculated using molecular mechanics (MM) and density functional theory (DFT) approaches.     

Methylation of phenol over modified pentasils

The reaction of phenol with methanol over pentasiltype zeolites has been studied. The most effective catalyst proves to be a manganese form of pentasil. Formation of its catalytic properties is shown to proceed as three stages: ion exchange, oxidation of introduced cations and zeolite treatment with the reaction mixture during the catalytic process.     

Competitive adsorption of phenol and 3-chlorophenol on purified MWCNTs

A commercial multiwall carbon nanotube and its carboxylated derivate (CNTC and COOHC, respectively) was used after purification to study the competitive adsorption of phenol (P) and m-chlorophenol (CP) from 0.1 M aqueous NaCl solutions without external pH control. The adsorption takes place practically exclusively on the external surface of the nanotubes. The uptake of P is suppressed in comparison to its single solute behaviour on both nanotubes, independently of the initial pollutant concentration. The uptake of CP however is more sensitive to the concentration and the surface chemistry of the nanotube. The measured co-adsorption isotherms were compared to the isotherms calculated from the competitive Langmuir model (CLM). Preferential adsorption of CP was observed in about 95% of the relative concentration range. The total adsorption may exceed the corresponding single component sorption capacity.     

苯酚及取代酚在碳纳米管上的吸附研究

本文研究了水溶液中碳纳米管(CNTs)吸附苯酚、对甲酚和对甲氧基苯酚的热力学特性,测定了不同温度下的吸附等温线,并探讨了其可能的吸附机理。结果表明:在稀溶液中碳纳米管对三种酚类物质的吸附均符合Freund lich和Langmu ir方程,吸附均为放热、熵增的自发过程,并且都具有物理吸附特征;碳纳米管与三种酚类物质分子之间的л—л共轭作用的强弱决定了碳纳米管对三种酚类物质的吸附能力,顺序依次为:对甲氧基苯酚>对甲酚>苯酚。     

On the mechanisms of phenol adsorption by carbons

The removal of phenol and related compounds from dilute aqueous solutions by activated carbons corresponds to the coating of the micropore walls and of the external surface by a monolayer. This process is described by an analog of the Dubinin—Radushkevich—Kaganer equation. On the other hand, as suggested by immersion calorimetry at 293 K, in the case of concentrated solutions, the mechanism corresponds to the volume filling of the micropores, as observed for the adsorption of phenol from the vapor phase. The equilibrium is described by the Dubinin—Astakhov equation. It follows that the removal of phenol from mixtures with water depends on the relative concentrations, and the limiting factor for adsorption is either the effective surface area of the carbon, or the micropore volume.     

Nonlinear isotherm and kinetics of adsorption of copper from aqueous solutions on bentonite

Bentonite is one of the most significant of clay minerals that has been studied extensively due to its potential applications in removal of various environmental pollutants. This ability is related to its high ionic exchange capacity and high specific surface area. Copper is one of the important elements of non-ferrous metals found in industrial waste waters. In the present work, the removal of copper from aqueous solutions with Iranian bentonite (from Birjand area, southeastern Iran) used without any chemical pretreatment, was studied. The experimental results were fitted by adsorption isotherms equations with two or three parameters, which include Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Redlich-Peterson, Khan, and Toth models. The best correlation coefficient (r²) is 0.9879 observed for Langmuir model, maximum adsorption capacity of bentonite was 55.71 mg/g. The first-order and pseudo-second-order kinetic equations were used to describe the kinetics of adsorption. The experimental data were well fitted by the pseudo-second-order kinetics.     

Role of surface chemistry in adsorption of phenol on activated carbons

Two samples of activated carbon of wood origin were oxidized using ammonium persulfate. The structural properties and surface chemistry of the samples and their oxidized counterparts were characterized using sorption of nitrogen and Boehm titration, respectively. Phenol adsorption from solution (at trace concentrations) was studied at temperatures close to ambient without maintaining a specific pH of the solution. The results showed, as expected, that the phenol uptake is dependent on both the porosity and surface chemistry of the carbons. Furthermore, phenol adsorption showed a strong dependence on the number of carboxylic groups due to two factors: (1) phenol reacts with carboxylic groups on the carbon surface, forming an ester bond, and (2) carboxylic groups on the carbon surface remove the pi-electron from the activated carbon aromatic ring matrix, causing a decrease in the strength of interactions between the benzene ring of phenol and the carbon's basal planes, which decreases the uptake of phenol.     

Isotherm analysis of phenol adsorption on polymeric adsorbents from nonaqueous solution

Macroporous poly(methyl methacrylate-co-divinylbenzene) (PMMA), interpenetrating polymer adsorbent based on poly(styrene-co-divinylbenzene) (PS) and poly(methyl methacrylate-co-divinylbenzene) (PMMA/PS), and macroporous cross-linked poly(N-p-vinylbenzyl acetylamide) (PVBA) were prepared for the adsorption of phenol from cyclohexane. The sorption isotherms of phenol on the three polymeric adsorbents were measured and fitted to Langmuir and Freundlich isotherms. It is shown that the Langmuir isotherm, which is based on a homogeneous surface model, is unsuitable to describe the sorption of phenol on the adsorbents from nonaqueous solution and the Freundlich equation fits the tested three adsorption systems well. The isosteric enthalpy was quantitatively correlated with the fractional loading for the sorption of phenol onto the three polymeric adsorbents. The surface energetic heterogeneity patterns of the adsorbents were described with functions of isosteric enthalpy. The results showed that the tested three polymeric adsorbents exhibited different surface energetic heterogeneity patterns. The initial isosteric enthalpy of phenol sorption on polymeric adsorbent has to do with the surface chemical composition and is free from the pore structure of the polymeric adsorbent matrix. Forming hydrogen bonds between phenol molecules and adsorbent is the main driving force of phenol sorption onto PVBA and PMMA adsorbent from nonaqueous solution. When phenol is adsorbed on PMMA/PS, pi-pi interaction resulting from the stacking of the benzene rings of the adsorbed phenol molecules and the pendant benzene ring of adsorbent is involved.