Adsorption of phenol by oil-palm-shell activated carbons

Steam activated carbons from oil-palm shells were prepared and used in the adsorption of phenol. The activated carbon had a well-developed mesopore structure which accounted for 45% of the total pore volume. The BET surface area of the activated carbon was 1183 m²/g and a total pore volume of 0.69 cm³/g using N₂ adsorption at 77 K. The adsorption capacity of the activated carbon for phenol was 319 mg/g of adsorbent at 298 K. The adsorption isotherms could be described by both the Langmuir-Freundlich and the Langmuir equations. The adsorption kinetics consisted of a rapid initial uptake phase, followed by a slow approach to equilibrium. A new multipore model is proposed that takes into account of a concentration dependent surface diffusion coefficient within the particle. This model is an improvement to the traditional branched pore model. The theoretical concentration versus time curve generated by the proposed model fitted the experimental data for phenol adsorption reasonably well. Phenol adsorption tests were also carried out on a commercial activated carbon known as Calgon OLC Plus 12×30 and the agreement between these adsorption data and the proposed model was equally good.     

Adsorption of phenol in flow systems by a monolithic carbon cryogel with a microhoneycomb structure

Adsorption of phenol from an aqueous solution in batch and continuous flow systems using carbon gels with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) was studied. The obtained monolithic CMHs had fairly straight channels, 25–45 μm in diameter, and the thickness of the walls which form the channels was around 5 μm. The CMHs showed 370 times lower hydraulic resistance when compared with a column packed with particles having the same diffusion path length as it. The obtained CMHs have a hierarchical micro-meso porous structure giving BET surface area in the range of 513–1070 m²·g^?1.When used for phenol adsorption from an aqueous solution, the CMHs quickly adsorbed phenol at first, and then, the uptake gradually increased, which indicates that the adsorption mechanism is based on not only simple physisorption. The phenol adsorption capacity increased with the increase in carbonization temperature of the CMH and the decrease in its hydrophilicity. CMHs carbonized at temperatures higher than 1073 K showed the highest phenol adsorption capacity which was around 160 mg·g^?1. The CMHs could continuously adsorb phenol from aqueous solutions, and their length of unused bed (LUB) values depended on operation conditions but were in the range of 0.3–0.7 cm. The experimental results indicated that carbon cryogels with a microhoneycomb structure have a high potential to be used for effective separation of phenol.     

Adsorptive removal of phenol by bagasse fly ash and activated carbon: Equilibrium,kinetics and thermodynamics

Present study deals with the adsorption of phenol on carbon rich bagasse fly ash (BFA) and activated carbon-commercial grade (ACC) and laboratory grade (ACL). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse-fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH₀), contact time, adsorbent dose and initial concentration (C₀) on the removal of phenol. C₀ varied from 75 to 300 mg/l for the adsorption isotherm studies and the effect of temperature on adsorption. Optimum conditions for phenol removal were found to be pH₀ ≈ 6.5, adsorbent dose ≈10 g/l of solution and equilibrium time ≈5 h. Adsorption of phenol followed pseudo-second order kinetics with the initial sorption rate for adsorption on ACL being the highest followed by those on BFA and ACC. The effective diffusion coefficient of phenol is of the order of 10⁻¹⁰ m²/s. Equilibrium isotherms for the adsorption of phenol on BFA, ACC and ACL were analysed by Freundlich, Langmuir, Temkin, Redlich–Peterson, Radke–Prausnitz and Toth isotherm models using non-linear regression technique. Redlich–Peterson isotherm was found to best represent the data for phenol adsorption on all the adsorbents. The change in entropy (ΔS°) and heat of adsorption (ΔH°) for phenol adsorption on BFA were estimated as 1.8 MJ/kg K and 0.5 MJ/kg, respectively. The high negative value of change in Gibbs free energy (ΔG°) indicates the feasible and spontaneous adsorption of phenol on BFA. The values of isosteric heat of adsorption varied with the surface loading of phenol.     

Equilibrium,kinetics and thermodynamics study of phenols adsorption onto activated carbon obtained from lignocellulosic material (<Emphasis Type="Italic">Eucalyptus Globulus labill</Emphasis> seed)

Activated carbon was prepared from lignocellulosic material (Eucalyptus Globulus labill seed) by chemical activation with ZnCl₂ at two different concentrations (10 and 25 % m/v) named ACS25 and ACS10. The textural characteristics of the activated carbons (ACs) were determined by N₂ adsorption isotherms; these exhibit B.E.T. surface areas of 250 and 300 m² g^?1 for ACS25 and ACS10, respectively, with micropore volume contents of 0.140 and 0.125 cm³ g^?1 in the same order. In addition, the FTIR and Boehm methods were conducted for the chemical characterisation of ACs, where many groups with basic character were found, which favours the adsorption of phenols. The prepared carbonaceous adsorbents were used in the adsorption of wide pollutants monosubstituted phenol derivatives: phenol, 4-nitrophenol and 4-chlorophenol. The effect of temperature on the thermodynamics, kinetic and equilibrium of phenols adsorption on ACs was thoroughly examined. The adsorption kinetics adjusted properly for a pseudo-second-order kinetic model. However, the Elovich model (chemisorption) confirms that phenols adsorption did not occur via the sharing of electrons between the phenolic ring and basal plane of ACs because is not properly adjusted, so the process is given by physisorption. The thermodynamic parameters [i.e. Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°)] were also evaluated. The overall adsorption process was exothermic and spontaneous in nature. The values found in the thermodynamic study, confirm that the adsorption process corresponds to a clearly physical process.     

Magnetic porous polymer microspheres: Synthesis,characterization and adsorption performance for the removal of phenol

The magnetic poly(ethylene glycol dimethacrylate-n-vinylimidazole) (Fe₃O₄@poly (EGDMA@VIM)) microspheres were prepared by suspension polymerization method using magnetite Fe₃O₄ nano-powder and the porosity, morphology, chemical composition and structure of the magnetic polymer microspheres were characterized. The specific surface area and swelling ratio of the Fe₃O₄@poly(EGDMA@VIM) microspheres were found to be 278.6?m²·g^–1 and 48%, respectively. The Fe₃O₄@poly(EGDMA@VIM) microspheres were used as an adsorbent for phenol removal. The effects of the parameters such as adsorbent dosage, temperature, pH and initial concentration of phenol solutions on the adsorption were investigated. The experimental adsorption equilibrium data obtained were fitted with Langmuir, Freundlich and Dubinin-Radushkevich isotherms and the pseudo-first-order, pseudo-second-order and intra–particle diffusion kinetic models. The adsorption equilibrium data agreed well with the Freundlich isotherm and the pseudo-second-order kinetic model. The maximum capacity of the Fe₃O₄@poly(EGDMA@VIM) microspheres was calculated to be 33.83?mg·g^–1 at 298?K and natural pH from Langmuir isotherm. The Fe₃O₄@poly(EGDMA@VIM) microspheres were found to be reusable for removal of phenol after desorption for several times. The result indicated that the Fe₃O₄@poly(EGDMA@VIM) microspheres are potential candidate for removal of phenol in wastewaters.     

Adsorption of Phenolic Compounds from Water on Activated Carbon: Prediction of Multicomponent Equilibrium Isotherms using Single-Component Data

Batch-type experiments were carried out to obtain equilibrium isotherms for the adsorption of phenol and m-cresol in aqueous solutions on activated carbon. Single solute systems, at 20 and 40^∘C, were tested for Langmuir, Freundlich and Sips adsorption isotherms in the range of concentrations up to 200 mg/L. Equilibrium data were more closely followed by the Freundlich and Sips equations for all cases. Adsorption isotherms for bisolute systems at 20^∘C, with two different initial concentrations of phenol and m-cresol, were predicted solely on the basis of single solute equilibrium parameters by using the equations of Butler and Ockrent and the IAS theory. The best agreement with the experimental loading values was afforded with the IAS theory based on Sips isotherm for pure compounds. However, this theory is found to be not able to predict with success the binary isotherms in this work where significant displacement of one solute by the other is observed. Chemical interactions in the adsorbed phase, estimated by a modified Butler–Ockrent model, can be responsible for this lack of success of the conventional IAS theory. The predictions based on the IAS theory are compared with the results of some empirical models.     

On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

At concentrations higher than 2?10^?4 M , and below pH 3, the cyclic voltammograms of picloram (=4‐amino‐3,5,6‐trichloropyridine‐2‐carboxylic acid) on Hg electrodes show two prepeak systems (named I and II attending to the proximity to the main reductions peak), which can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface. The system II is due to the uncharged form of picloram, and system I to the picloram protonated at the pyridine N‐atom. Small amounts of the surfactant Triton X‐100 (=α‐[4‐(1,1,3,3‐tetramethylbutyl)phenyl]‐ω‐hydroxypoly(oxyethane‐1,2‐diyl)) cause the disappearance of system I, the shift of system II, and also affect the intensities and widths of anodic and cathodic peaks but not the charge passed in each peak. Thus, the adsorption process responsible for the appearance of system I is inhibited by the presence of Triton; by contrast, the process corresponding to system II is only modified by the surfactant, becoming an electrochemical process occurring at the potentials corresponding to system II, which is more reversible than that observed in the absence of Triton. The addition of Triton permitted the analysis of the main reduction process. Convolution voltammetry of the main reduction peak is consistent with the loss of a Cl‐atom in equilibrium which occurs after a reversible electron transfer and is followed by the reductions of both species present in the equilibrium (Scheme 2). This is also the reduction mechanism on a glassy carbon electrode but the electron transfer on the carbon electrode increases with respect to the mercury electrodes; in addition, the loss of the Cl‐atom does not take place on the electrode surface. From the recording of differential capacity–potential curves, it was concluded that picloram is adsorbed on the carbon electrode; but this adsorption is too weak to induce the appearance of prepeak systems.     

Lanthanum ion–impregnated granular activated carbon for the removal of phenol from aqueous solution: Equilibrium and kinetic study

The current study discusses application of the lanthanum ions (La³⁺) as an activating agent incorporated /immobilized into coconut shell–based granular activated carbon (GAC) for porosity development; subsequently, the carbon material is used for the adsorption of phenol from aqueous solutions. The new carbons were characterized using FTIR, XRD, CHNO, burn off, and carbon yield. The surface functional groups were determined by Boehm titration. The Brunauer–Emmett–Teller (BET) surface area of the carbons is 953 m² g⁻¹ (GACLa1073), 997 m² g⁻¹ (GAC383), and 973 m² g⁻¹ (GACO383). Langmuir, Freundlich, Dubinin–Radushkevich, and John–Sivanandan Achari (J-SA) isotherm models on the equilibrium isotherm data were examined for the new carbon-phenol system. It is found that the Langmuir isotherm fits better with a monolayer adsorption capacity, highest for GACLa1073 (387.59 mg g⁻¹) followed by GAC383 (303.03 mg g⁻¹) and GACO383 (197.62 mg g⁻¹). Kinetic studies reveal that the adsorption system follows the pseudo–second-order kinetic model. Isotherm analysis by the phase change method of John-Sivanandan Achari (J-SA) isotherm gives a better insight into adsorption phenomena, which is accompanied by regeneration studies of carbon with >75% for GACLa1073 after three cycles.     

The adsorption of resorcinol from water using multi-walled carbon nanotubes

Adsorption of resorcinol and other phenolic derivatives on pristine multi-walled carbon nanotubes (MWCNTs) and HNO₃ treated MWCNTs has been investigated in attempt to explore the possibility to use MWCNTs as efficient adsorbents for pollutants. MWCNTs showed higher adsorption ability in a rather wide pH range of 4–8 for resorcinol, while decreased uptake capacity was found for acid-treated MWCNTs. Other phenolic derivatives such as phenol, catechol, hydroquinone and pyrogallol were employed to study the influence of the number and position of hydroxyl groups on the adsorption capacity. The amounts adsorbed by MWCNTs increased with the increasing number of hydroxyl. The substitution of phenol with a hydroxyl in meta-position leads to a much higher absorption ability than substitution in ortho- or para-position, which suggested that MWCNTs possess a great potential in removal of resorcinol from water, as well as the other phenolic derivatives.     

介孔碳CMK-3对苯酚的吸附动力学和热力学研究

研究了介孔碳CMK-3对苯酚的吸附性能, 与传统商用活性碳(CAC)进行了比较, 结果表明, CMK-3比CAC的吸附量大、吸附速率快、达到平衡时间短, 是一种较好的吸附剂. 同时探讨了介孔碳CMK-3对苯酚的吸附热力学和动力学特征. CMK-3对苯酚的吸附行为可用Langmuir和Freundlich等温式进行描述, 相关性都较好, 但更符合Freundlich经验公式. 分别采用模拟一阶反应和二阶反应模型考察了吸附动力学, 并计算了这些动力学模型的速率常数. 模拟二级反应模型和实验数据之间有较好的相关性. 分别计算了热力学参数ΔG0, ΔS0和ΔH0, 结果表明, CMK-3对苯酚的吸附过程是吸热和自发的.     

Adsorption and redox processes at carbon nanofiber electrodes grown onto a ceramic fiber backbone

The adsorption of aromatic compounds onto activated carbons and carbon nanofibers is of considerable technical importance and beneficial in electroanalytical procedures. Here, effects due to the strong adsorption of hydroquinone, benzoquinone, and phenol onto carbon nanofiber electrodes immersed in aqueous media are reported. Carbon nanofiber materials (fiber diameter approximately 100 nm) are grown onto ceramic fiber substrates by employing an ambient pressure chemical vapour deposition process. The resulting composite electrode material is sufficiently electrically conducting due to the high carbon content and mechanically robust due to the ceramic backbone. It is shown that the voltammetric signal obtained for the one electron reduction of Ru(NH₃)₆³⁺ is dominated by solution trapped in the three-dimensional electrode structure. In contrast, for the hydroquinone/benzoquinone redox system in aqueous phosphate buffer (pH 7) strong adsorption onto the carbon nanofiber material is observed. In the presence of phenol also strong adsorption is detected. In the course of the chemically irreversible oxidation of phenol in aqueous phosphate buffer (pH 7), the formation of multi-electron oxidation products related to benzoquinone is observed. The pathway for the oxidation process is attributed to (i) the high surface area of the carbon nanofiber electrode and (ii) the adsorption of intermediates.     

Adsorption heats of phenol on activated carbon using adapted method of immersion calorimetry

Simple adaptation of the technique of immersion calorimetry enables determining both integral and differential adsorption heats as well as the course of the adsorption isotherm of phenol on activated carbon. The innovative aspect of the applied procedure consists in bringing the phenol aqueous solution to contact with the suspension of carbon with water. Thus, the “interfering” heat effect of carbon interaction with water is eliminated, and only the net adsorption heat of phenol is monitored. The value of −52.5 kJ mol⁻¹ was ascertained as the molar differential adsorption heat at the low surface coverage (cca 0.2 mmol g⁻¹) of the sample of microporous carbon. As the adsorption process continues, for adsorption uptakes exceeding the value of about 1 mmol g⁻¹, molar differential adsorption heats appear to be established at a level of about −20 + 5 kJ mol⁻¹.     

Kinetic,isothermal and thermodynamic studies on Th(IV) adsorption by different modified activated carbons

In this study, the performance of modified adsorbents obtained from activated carbon for the adsorption of thorium(IV) ions from aqueous media was investigated. The analytical and spectroscopic methods such as FT-IR, BET, SEM and UV–Vis were used to examine the properties of the modified materials. According to the analysis results, the both adsorbents had large surface areas after modification. Then, temperature, pH, mixing time and solution concentration parameters were observed to determine optimum thorium adsorption conditions on modified materials. The obtained results from the experiments were applied different three kinetic models and adsorption isotherms and thermodynamic parameters were calculated and then all of the results were interpreted. The adsorption process for both adsorption systems was observed to be compatible with the pseudo-second-order kinetic model. The adsorption equilibrium data were best described by the Langmuir model for modified adsorbent with KMnO₄ and by the Freundlich model for modified adsorbent with NaOH. Furthermore, the calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the both adsorption processes were endothermic and spontaneous. The data show that modified adsorbents can be used as influential and low-cost adsorbents to remove thorium ion. Modified new adsorbents were highly selective for thorium ion in competitive adsorption studies.

     

Removal of Phenol from Wastewater Using Date Seed Carbon

The adsorption of phenol on Date Seed Carbon (DSC) was investigated to assess its possible use as an adsorbent for the processing of phenolic wastewater. The influence of various factors such as initial concentration, agitation speed, amount of adsorbent and temperature on the adsorption capacity has been studied. The percentage removal of phenol was observed to increase with increase an initial concentration of phenol. The adsorption of phenol decrease with an increase in temperature indicated the exothermic nature of the reaction. The Langmuir and Freundlich equations interpret adsorption isothermal data. Kinetic data was obtained by using a pseudo‐second‐order equation to understand the reaction mechanism. Thermodynamic parameters such as ΔG, ΔH and ΔS for the adsorption process were calculated.     

Carbon‐Dot‐Sensitized,Nitrogen‐Doped TiO2 in Mesoporous Silica for Water Decontamination through Nonhydrophobic Enrichment–Degradation Mode

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO₂ through an impregnation–hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO₂ nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6mm symmetry, a high specific surface area (446.27 m² g^?1), large pore volume (0.57 cm³ g^?1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO₂ nanocrystals are anchored to the carbon dot through Ti?O?N and Ti?O?C bonds, as revealed by X‐ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO₂ is also verified by the formation of the Ti?N bond. This composite shows excellent adsorption capabilities for 2,4‐dichlorophenol and acid orange 7, with an electron‐deficient aromatic ring, through electron donor–acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible‐light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible‐light activity of TiO₂. The adsorption capacity does not suffer any clear losses after being recycled three times.     

Alternative Synthesis of 5-(1H-Pyrazol-4-yl)-2-{6-[(2,2,6,6-tetramethylpiperidin-4-yl)oxy]pyridazin-3-yl}phenol

A scalable and environmentally benign route to the free base of branaplam, a small molecule splicing modulator, was identified and developed. This alternative approach circumvented the inherent risk of dioxin formation associated with ortho-halo phenol derivatives present in the previous route. A Friedel–Crafts approach provided a reliable access to the key intermediate, subsequently followed by a Suzuki–Miyaura cross-coupling. Multiple process aspects of the synthetic approach were evaluated, and a robust process for its large-scale synthesis was developed and successfully demonstrated.     

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.     

Adsorption of Some Nitrogen-Containing Compounds and Benzene Derivatives from Aqueous Solutions on Active Carbons

The adsorption from aqueous solutions of benzene derivatives (phenol, benzoic acid, and newly synthesized benzoic acid derivatives containing imidazole heterocycles: hydrazide of 4-(1H-imidazole-1-ylmethyl) benzoic acid and methyl ester of 4-(1H-imidazole-1-ylmethyl)benzoic acid), as well as of imidazole and triazole, on active carbons with various microporous structures is studied. The effect of the nature of adsorbate molecules and the pore sizes of active carbons on the sorption character is analyzed. It is shown that the adsorption from aqueous solutions of the organic derivatives of benzene is determined, on the one hand, by the size of a molecule, and, on the other hand, by its hydration energy.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 416–420.Original Russian Text Copyright © 2005 by Kharitonova, Krasil’nikova, Vartapetyan, Bulanova.     

An NMR study of phenol self-association

This paper presents a study of the chemical shift of the phenol hydroxyl group as a function of concentration and temperature in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. The chemical shift of monomeric phenol has been found. For these solutions monomertrimer equilibrium is observed within the entire temperature range and within a wide concentration range. At low phenol concentrations, from 1 to 3 mole-%, the monomer-dimer equilibrium is observed in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. Chemical shift of the hydroxyl group of trimeric phenol is temperature-dependent. From the experimental data the association constants and thermodynamic functions of the systems under study have been determined. The association constants differ for the above systems at the same temperatures. Association entropy ΔS changes from one system to another, while ΔH is the same for all systems.     

Adsorption of Methylene Blue from Aqueous Solution on High Lime Fly Ash: Kinetic,Equilibrium, and Thermodynamic Studies

Kinetic, equilibrium, and thermodynamic studies were performed for the batch adsorption of methylene blue (MB) on the high lime fly ash as a low cost adsorbent material. The studied operating variables were adsorbent amount, contact time, dye concentration, and temperature. The kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic models and the adsorption kinetic was followed well by the pseudo-second order kinetic model. The equilibrium data were fitted with the Freundlich, Langmuir, and Dubinin Radushkevich (D–R) isotherms and the equilibrium data were found to be well represented by the Freundlich and D–R isotherms. Based on these two isotherms MB is taken by chemical ion exchange and active sites on the high lime fly ash have different affinities to MB molecules. Various thermodynamic parameters such as enthalpy of adsorption (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were investigated. The positive value of ΔH° and negative value of ΔG° indicate that the adsorption is endothermic and spontaneous. The positive value of ΔS° shows the increased randomness at the solid–liquid interface during the adsorption. A single-stage batch adsorber was also designed based on the Freundlich isotherm for the removal of MB by the high lime fly ash.