Mechanism Of Phenol Adsorption Research Articles

Construction of coal fly ash-based spherical grain adsorbents and their adsorption characteristics on phenolic compounds

Addressing the significant emissions and severe pollution hazards posed by coal fly ash waste in the coal chemical industry, as well as the challenges in recovering phenolic substances from coal chemical wastewater, this study utilized coal fly ash as a raw material to construct two types of spherical grain adsorbents: coal fly ash and coal gangue spherical grain (CFAGsg) and coal fly ash and pyrite spherical grain (CFAPsg). The adsorption performance of CFAGsg and CFAPsg towards phenolic substances in coal chemical wastewater was investigated. The research results demonstrated that CFAGsg and CFAPsg exhibited adsorption capacities of 20.31 mg/L and 30.42 mg/L for phenol, respectively, and maintained stable adsorption performance even after multiple regeneration cycles. Further analysis using kinetic, isotherm, and thermodynamic models, along with various characterization techniques, revealed that the adsorption of phenol onto CFAGsg and CFAPsg was primarily governed by physical and chemical adsorption, involving an endothermic reaction. Moreover, the study on the adsorption mechanism of phenol revealed that the adsorption behavior of CFAGsg and CFAPsg was mainly driven by pore filling, π-π stacking, and hydrogen bonding. Additionally, hydrophobic interactions were involved in the adsorption of phenol onto CFAGsg, while surface complexation forces played a role in the adsorption of phenol onto CFAPsg. Overall, the research findings provide vital theoretical support and practical application prospects for the high-value utilization of coal fly ash and the clean production of the coal chemical industry.

Modeling the Kinetics, Equilibrium and Thermodynamics of Poly(acrylamide)/Sodium-Bentonite for Enhanced Phenol Removal from Aqueous Media

A composite based on polyacrylamide and Na-bentonite, designated as PAAm/Na-bentonite was prepared by in-situ radical polymerization using ammonium persulfate as an initiator and bis-acrylamide as a crosslinker. The structural and morphological features were examined by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunner − Emmet − Teller measurements. The results showed PAAm intercalation in the Na-bentonite layers. Equilibrium, thermodynamics, and kinetic studies were conducted by considering the effects of pH, initial phenol concentration, contact time and temperature. The zeta potential of the PAAm/Na-bentonite composite was calculated to understand the mechanism of phenol adsorption onto our product. The pollutant uptake behavior was determined by UV-Vis spectrophotometry. Adsorption results showed that PAAm/Na-bentonite composite showed a maximum adsorption of 160.3 mg.g−1 of 30 mg.L−1 phenol solution at pH 6 after 15 min of adsorption using 4 g.L−1 of the adsorbent. The presence of acrylamide modified the surface characteristics of the Na-bentonite and offered more adsorption sites as confirmed by XRD and SEM. Equilibrium modeling of the phenol removal process was carried out using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) adsorption isotherms. The equilibrium adsorption data were well fitted with the Langmuir model. In addition, the kinetics of adsorption were best described by a pseudo-second-order expression rather than a first-order model. The interactions between phenol molecules and adsorbent were explained by electrostatic as well as hydrogen bonding interactions, as confirmed by the pseudo-second-order kinetic model. A model for the interactions between the composite and the phenol molecules is proposed. The negative values of Gibb’s free energy (ΔG°) confirmed that the process was spontaneous. The positive value of change in entropy (ΔS° = 0.922 JK−1mol−1) suggests that the randomness was increased at the solution/solid interface. We suggest, the results indicate that PAAm/Na-bentonite presents a significant potential as an adsorbent material for phenol removal from aqueous solutions.

Interaction of phenolic compounds with functionalized TiO2: Enhanced catechol adsorption and cooperative phenol adsorption

A commercial TiO2 sample functionalized with 3-aminopropyltrimethoxysilane (APTMS) and 4-carboxyphenylboronic acid (CPBA), has been previously proposed as a suitable photocatalyst to perform selective photocatalytic degradation of pollutants in aqueous streams, while avoiding the oxidation of valuable catechol simultaneously present in the reacting medium. In the present study, we highlight the adsorption mechanisms underlying the higher affinity of catechol, compared to phenol, with the surface of modified TiO2, quantitatively justifying the photocatalytic selective degradation results previously obtained. Moreover, a cooperative adsorption mechanism of phenol onto the TiO2 sample modified with APTMS has been for the first time observed. The resulting sigmoidal adsorption isotherms, satisfactorily fitted with the Hill model, could be attributed to the enhanced surface hydrophobicity and, more importantly, to alterations of the folding of APTMS molecules on the TiO2 surface occurring upon increasing the concentration of the phenolic compounds.Photocatalytic tests revealed that the existence of boronate groups on the surface of TiO2 hinders the photocatalytic degradation of catechol and facilitates a swifter oxidation of phenol. These findings confirm the potential for selective photocatalytic degradation, in line with modern conceptions of innovative and environmentally sustainable wastewater treatments.

Preparation of acidity-sensitive N-isopropylacrylamide and methacrylic acid copolymer monolithic column for the pipette tip solid phase extraction of phenols

An acidity-sensitive poly(N-isopropylacrylamide-methyl acrylic acid-co-divinyl- benzene) monolith was prepared in situ in a pipette tip for solid phase extraction of phenol, m-cresol, o-nitrophenol, 2,4-dichlorophenol and p-tert-butylphenol. The monolith was characterized by FT-IR, BET (surface area = 266.56 m2/g) and thermogravimetric analysis (thermally stable up to 350 °C). The introduction of methyl acrylic acid enhanced the stability in the strong alkaline condition. The adsorption experiments and density function theory calculations indicated NIPAM was the main adsorption sites and the adsorption mechanism of phenol on the monolith was hydrophobic interaction, H-bond interaction, C − H···π interaction of isopropyl group of NIPAM with the phenyl group of phenols. Based on these features and under the optimal extraction conditions, a pipette tip solid phase extraction coupled to high-performance liquid chromatography with ultraviolet detection method was developed for the determination of 5 phenols in the diffusion of polycarbonate cups. Due to the usage of 0.1 M NaOH as the eluent, the method presented selectivity for phenols based on the acidity-sensitive of the monolith. Wide linear range (0.6–200 µg/L), low detection limits (0.2–0.3 µg/L), good reproducibility (%RSD less than 9.8%) and satisfactory recoveries (86.3–114.1%) were obtained. The proposed method was suitable for quantitative analysis of phenollic in water samples.

Comparison of Phenol Adsorption Property and Mechanism onto Different Moroccan Clays

This study focuses on the removal of phenol from aqueous media using Agouraï clay (Fes-Meknes-Morocco region) and Geulmima clay (Draa Tafilalet region). The characterization of the clay by Fourier Transform Infrared (FTIR) Spectroscopy, X-ray diffraction (XRD), N2 adsorption (BET), Scanning Electron Microscopy (SEM), and Thermogravimetric and differential thermal analysis (DTA/GTA) indicates that it is mainly composed of quartz, kaolinite, and illite. The results showed that raw Clay Agourai (RCA) and raw Clay Geulmima (RCG) adsorbed phenol very quickly and reached equilibrium after 30 min. Thermodynamic parameters reveal the physical nature of the adsorption, the spontaneity, and the sequence of the process. However, the structure and structural characterization of the solid before and after phenol adsorption indicated that the mechanism of the reaction was electrostatic and that hydrogen bonding played an important role in RCG, while kinetic modeling showed the pseudo-second-order model dynamics. The physics-statistics modeling was employed for describing the isotherm adsorption for both systems. It was found that the monolayer model with two different energy sites best describes adsorption irrespective of the system. The model indicates that the receptor density of each clay direct influences the adsorption capacity, demonstrating that the composition of the clay is the main source of the difference. Thermodynamic simulations have shown that the adsorption of phenol is spontaneous and endothermic, irrespective of the system. In addition, thermodynamic simulations show that the RCG could be adsorbed even further since the equilibrium was not achieved for any thermodynamic variable. The strength of this study lies in the determination of the adsorption mechanism of phenol on clay materials and the optimum values of temperature and pH.

Predictive Model Based on K-Nearest Neighbor Coupled with the Gray Wolf Optimizer Algorithm (KNN_GWO) for Estimating the Amount of Phenol Adsorption on Powdered Activated Carbon

In this work, the adsorption mechanism of phenol on activated carbon from aqueous solutions was investigated. Batch experiments were performed as a function of adsorbent rate, solution temperature, phenol initial concentration, stirring speed, and pH. The optimal operating condition of phenol adsorption were: mass/volume ratio of 0.6 g.L−1, temperature of 20 °C and stirring speed of 300 rpm. The equilibrium data for the adsorption of phenol were analyzed by Langmuir, Freundlich, and Temkin isotherm models. It was found that the Freundlich and Temkin isotherm models fitted well the phenol adsorption on the activated carbon and that the adsorption process is favorable. The Langmuir equilibrium isotherm provides a maximum adsorption of 156.26 mg.g−1 at 20 °C. The pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Boyd models were used to fit the kinetic data. The adsorption kinetics data were well described by the pseudo-second-order model. The kinetic was controlled by the external diffusion by macropore and mesopore, as well as by the micropore diffusion. The thermodynamic study revealed the exothermic and spontaneous nature of phenol adsorption on activated carbon with increased randomness at the solid-solution interface. On the other hand, a very large model based on the optimization parameters of phenol adsorption using k-nearest neighbor coupled with the gray wolf optimizer algorithm was launched to predict the amount of phenol adsorption. The KNN_GWO model showed an advantage in giving more precise values related to very high statistical coefficients (R = 0.9999, R2 = 0.9998 and R2adj = 0.9998) and very low statistical errors (RMSE = 0, 0070, MSE = 0.2347 and MAE = 0.2763). These advantages show the efficiency and performance of the model used.

Insight into the dynamic adsorption behavior of graphene oxide multichannel architecture toward contaminants

Graphene oxide (GO) channels exhibit unique mass transport behaviors due to their flexibility, controllable thinness and extraordinary physicochemical properties, enabling them to be widely used for adsorption and membrane separation. Nevertheless, the adsorption behavior of nanosized contaminants within the channels of GO membrane has not been fully discussed. In this study, we fabricated a GO membrane (PGn, where n represents the deposition cycles of GO) with multi channels via the cross-linking of GO and multibranched poly(ethyleneimine) (PEI). Phenol was used as molecular probe to determine the correlations between dynamic adsorption behavior and structural parameters of the multilevel GO/PEI membrane. PG8 shows higher adsorption capacities and affinity, which is predominantly attributed to the multichannel structure providing a large specific surface for phenol adsorption, enhancing the accessibility of active sites for phenol molecules and the transport of phenol. Density functional theory calculations demonstrate that the adsorption mechanism of phenol within GO channel is energetically oriented by hydrogen bonds, which is dominated by oxygen-containing groups compared to amino groups. Particularly, the interfaces which facilitate strong π-π interaction and hydrogen bonds maybe the most active regions. Moreover, the as-prepared PG8 membrane showed outstanding performance for other contaminants such as methyl orange and Cr(VI). It is anticipated that this study will have implications for design of GO-related environmental materials with enhanced efficiency.

Study of the biosorption of phenol by the cell walls of brewing yeast

Sorption capabilities of cell walls of yeast Saccharomyces cerevisiae with respect to phenol have been investigated. Elemental analysis established the composition of yeast cell walls: 47.8–48.6% C; 5.7-6.1% N and 6.86% H. The surface of the sorbent determined by BET, was 118.6 m2/g, ash content – 18-22%. Using FTIR-spectroscopy, it is shown that the prevailing mechanism of phenol adsorption is physical sorption, and not complexation. The adsorption abilities of yeast cell walls with respect to phenol were studied relative to pH, initial phenol concentration, sorbent dose and activation time. It is shown that the sorption efficiency increases in protonated solutions with pH<3. Experimental data were analyzed using Freundlich and Langmuir models. The model of the adsorption isotherm is more precisely described by the Langmuir equation with R2 0.9987. The calculated maximum capacity is 18.9 mg of phenol per 1 g of dry sorbent. The study showed that the cell walls of the yeast Saccharomyces cerevisiae can be used as a new adsorption material for eliminating phenol from aqueous solutions.

Unravelling the adsorption mechanism of phenol on zinc oxide at various coverages via statistical physics, artificial neural network modeling and ab initio molecular dynamics

A novel modeling approach based on ab initio molecular dynamics, artificial neural networks and statistical physics has been applied to analyze, characterize, and explain the phenol adsorption on zinc oxide. Phenol experimental adsorption studies were performed with zinc oxide synthesized via the precipitation method. Adsorption equilibrium data were obtained at 30 to 60 °C for the modeling analysis. Artificial neural networks and statistical physics calculations predicted a monolayer phenol adsorption process, which was endothermic and multimolecular. It was expected that hydrogen bonding and electrostatic forces were involved in the adsorption of this organic pollutant. Ab initio molecular dynamics confirmed these predictions thus concluding that phenol adsorption involved mixed vertical and tilted configurations depending on the adsorbent coverage. This study contributes with new theoretical findings to understand the adsorption of phenol molecules on zinc oxide surface.

Lignite-Based N-Doped Porous Carbon as an Efficient Adsorbent for Phenol Adsorption

The treatment of phenolic-containing wastewater has received increased attention in recent years. In this study, the N-doped porous carbons were prepared from lignite with tripolycyanamide as the N source, and their phenol adsorption behaviors were investigated. Results clearly showed that the addition of tripolycyanamide largely improved the surface area, micropore volume, N content and thus the phenol adsorption capacity of lignite-based carbons. The N-doped sample prepared at 700 °C showed a surface area of 1630 m2/g and a phenol adsorption capacity as high as 182.4 mg/g at 20 °C, which were 2.0 and 1.6 times that of the lignite-based carbon without N-doping. Pseudo-second order and Freundlich adsorption isotherm models could better explain the phenol adsorption behaviors over lignite-based N-doped porous carbon. Theoretical calculations demonstrated that phenol adsorption energies over graphitic-N (−72 kJ/mol) and pyrrolic-N (−74 kJ/mol) groups were slightly lower than that over the N-free graphite layer (−71 kJ/mol), supporting that these N-containing groups contribute to enhance the phenol adsorption capacity. The adsorption mechanism of phenol over porous carbon might be interpreted by the π–π dispersion interactions between aromatic-ring and carbon planes, which could be enhanced by N-doping through increasing π electron densities in the carbon plane.

A mussel-pearl side chain interaction in mercury(II) and phenol removal by sulfur-functionalized covalent organic frameworks: A DFT study

The covalent organic framework materials (COFs) with excellent chemical and physical characteristics have been rapidly developed as adsorbents in the application of environmental remediation. In the design of COFs, the selection of functional groups and side chains is of great significance. Herein, density function theory (DFT) method is used to illustrate the adsorption behavior and mechanism of three sulfur-functionalized COFs (S-COFs) for the adsorption of mercury(II) and phenol. According to the analysis of geometric configurations and electronic properties, it demonstrated that the side chains of S-COFs with high flexibility and concentrated sulfur-functional groups, acting like a closed mussel which tightly confined the contaminants, the highest adsorption was −24.32 kcal/mol. The adsorption mechanism of phenol and mercury(II) on S-COFs was elucidated. For phenol, hydrogen bonds and π-π stacking interaction played an important role in the adsorption process, while the coordination interaction was dominated for the adsorption of mercury(II). This research explains the importance of selecting appropriate functional groups and side chains for COFs in the removal of contaminants in the molecular scale, and reveals the great potential of COFs in environmental remediation applications.

Phenol adsorption mechanism on the zinc oxide surface: Experimental, cluster DFT calculations, and molecular dynamics simulations

Pollution by phenols is considered a major environmental issue. Therefore, their removal from wastewaters is of great practical significance and is directly related to human health. Herein, a porous zinc oxide (ZnO) was synthesized by a simple precipitation method and used as an adsorbent for the removal of phenol at different operating conditions. Besides experimental investigations, a comprehensive understanding of the mechanism of phenol adsorption on ZnO surface at the molecular level was achieved by using cluster Density Functional Theory (DFT) and molecular dynamics (MD) simulations. The prepared adsorbent was characterized using a variety of techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), as well as the Brunauer Emmett Teller (BET) method. The effects of different variables, such as pH, pHpzc (pH at the point of zero charge), initial concentration, and temperature, were investigated to optimize and understand the adsorption process. Possible controlling mechanism and the potential rate-limiting steps were analyzed using Lagergren's pseudo-first-order and pseudo-second-order models, and the data were found to follow the pseudo-second-order equation. The maximum removal of the phenol molecule was observed at pH = 4 with adsorption capacities of 3.61 and 4.51 mg/g at 30° and 50°, respectively. Furthermore, Cluster DFT calculations and molecular dynamics simulations were used to get deeper mechanistic insights on the adsorption behavior of the phenol molecule onto zinc oxide. DFT results confirmed the predominance of chemisorption while those from MD simulations indicated an increased interaction of ZnO with phenol in the presence of solvent due to water-bridged H-bonds.

Improved phenol sequestration from aqueous solution using silver nanoparticle modified Palm Kernel Shell Activated Carbon

Modified Palm Kernel Shell Activated Carbon (PKSAC) using silver nanoparticle (Ag-NPs-PKSAC) was investigated on phenol uptake from aqueous solution. Effects of temperature (500–700 °C), time (90–120 min), and alkaline concentration (0.1–0.5 M) were studied on the yield and methylene blue numbers for the synthesis. Effects of initial concentration (100–200 mg/L), agitation (150–250 rpm), contact time (30–120 min), and adsorbent dosage (0.15–0.25 g) were studied in a batch experiment on percentage removal of phenol. The PKS, char, PKSAC and Ag-NPs-PKSAC were characterized using BET, FTIR, SEM, and proximate analyses. The synthesis of PKSAC was optimum at 608 °C, 0.5 M KOH, and carbonization holding time of 60 min. The optimum phenol uptake was 85.64, 90.29 and 91.70% for PKSAC, Ag-NPs-PKSAC, and commercial adsorbent, respectively. The adsorption mechanism of phenol followed the Langmuir isotherm and best described as physio-sorption with pseudo-second-order kinetics. Phenol exhibits high affinity (ΔS° = 0.0079 kJ/mol K) for Ag-NPs-PKSAC with favorable adsorption (ΔG° = -1.551 kJ/mol) at high temperature due to endothermic (ΔH° = 1.072 kJ/mol) nature of the system. The result obtained in this study compared favorably with the literature.

Incorporation of humic acid into biomass derived carbon for enhanced adsorption of phenol

In the present work, the biomass derived carbon decorated with humic acid (HC), was synthesized through impregnation method for the adsorption of phenol from water environment. Humic acids contain more oxygen-containing functional groups and hydrogen bonds, which promotes the binding between HC and phenol molecules. The results indicated that the adsorption performance of HC to phenol was better than that of commercial activated carbon. Moreover, in addition to physical absorption, the chemical reaction between carboxylic groups on the carbon surface and hydroxyl in phenol also played an important role during the process. The adsorption behavior of HC was described by equilibrium and kinetics parameters. Pseudo-second order model can describe the adsorption process well. Langmuir model was more suitable for the equilibrium adsorption data fitting, indicating that the adsorption mechanism of phenol on carbon surface tends to be monolayer adsorption. Considering practical application, UV254, chemical oxygen demand (COD) and ammonia from raw wastewater were selected as target contaminants and the corresponding adsorption experiments were carried out. The results displayed that HC exhibited excellent adsorption performance, especially for UV254, indicating that as-prepared carbon material had potential application for the control of certain organic pollutants in actual wastewater.

Adsorption mechanism of phenol, p-chlorophenol, and p-nitrophenol on magnetite surface: A molecular dynamics study

Industrial wastewater organic pollutants like phenol can either be treated by a catalytic oxidation process or by adsorption on active surfaces. In this context, the understanding of the mechanism of adsorption on easily recoverable magnetic adsorbents is an important requirement for further progress in this area. The present study employs canonical ensemble molecular dynamics simulations to gain a better understanding of the adsorption mechanism of the organic pollutants phenol (Ph), p-chlorophenol (PCP) and p-nitrophenol (PNP) present in water on (111) magnetite surface. Systems with varying concentrations of these molecules in water were considered. Simulations generated equilibrium density profiles of adsorbed molecules on the (111) magnetite surface. The density profiles at various adsorbate concentrations were used to generate adsorption isotherms. It was found that data generated for all three organic molecules fitted best the non-linear Freundlich isotherm. Adsorption constant for PCP is found to be greater than those of PNP and Ph. The order of adsorption energies is in agreement with this. Functional groups involved in absorbate-adsorbent interaction have been identified by radial distribution function analysis.

Comparative study of the batch adsorption kinetics and mass transfer in phenol-sand and phenol-clay adsorption systems

This study was aimed at evaluating the kinetics and mass transfer of phenol adsorption onto sand and clay sediments. The adsorption studies were carried out in batch mode. The results showed that the time taken to attain equilibrium in the adsorption of phenol onto sand and clay sediments are 21 and 27 h, respectively. At an equal given time, clay sediments relatively had higher adsorption of phenol than sand sediments, which can be ascribed to its large surface area and higher porosity. The kinetic data adjusted well to the pseudo-first-order and Elovich kinetic models; however, Elovich kinetic model best describe the phenol adsorption kinetics. Mass transfer models were applied to the adsorption data to evaluate the rate-limiting step in the adsorption of phenol onto the sand and clay sediments. The values of the external mass transfer coefficient and diffusion coefficient were estimated from the models. Biot number was determined using the estimated internal mass transfer (intraparticle diffusion) coefficient and the external mass transfer coefficient. From the applied models and the calculated Biot number, the results revealed that the mechanism of phenol adsorption onto sand and clay sediments was not only by intraparticle diffusion but also by film diffusion.

Kinetic, isotherm and mechanism investigations of the removal of phenols from water by raw and calcined clays

In this work, the phenols removal of phenol from water by raw clay (RCG) and calcined one at 1000 °C (CCG) of Goulmima city (Morocco) was investigated. The kinetics and isotherms experiments were also studied at pH = 4. The results indicated that the phenol adsorption reached equilibrium within 3 h, and the removal of phenol was enhanced at the same temperature by CCG (2.932 mg/g) adsorbent, compared to RCG (1.640 mg/g) due to the removal of organic matter by heat treatment, and an increase in adsorption temperature, indicating the endothermic process. The adsorbents were characterized by means of X-ray fluorescence, FTIR, XRD, B.E.T, and TGA/DTA analysis and showed that the clay consists essentially of silica and alumina. The experimental data were examined by using linear and nonlinear forms of the kinetics and the isotherms models. Based on the errors of the calculated values of R2 (Coefficient of determination), χ2 (Chi-square) and standard deviation (Δq (%)), it was found that the nonlinear forms of second-order kinetic model and Freundlich and Redlich-Peterson (R–P) isotherm models are best fit the experimental data for both adsorbents. However, the enthalpy ΔH° is less than 20 kJ/mol and the free energy ΔG° has a negative value, which shows that the adsorption is done physically and spontaneously on heterogeneous sites. The interest of this study is the use of FTIR and XRD to determine the effect of calcination on the phenol adsorption mechanism. However, the analysis of both adsorbents, before and after adsorption of phenol, shows that the adsorption mechanism of phenol is provided by the hydrogen bonding of the water molecules.

Understanding the adsorption mechanism of phenol and 2-nitrophenol on a biopolymer-based biochar in single and binary systems via advanced modeling analysis

In this paper, the adsorption of phenol and 2-nitrophenol on a biopolymer-based biochar in single and binary systems was investigated at 298–328 K and pH 5. Experimental results indicated that the adsorption capacities of phenol were significantly reduced from single to binary systems compared to those obtained for 2-nitrophenol. This experimental evidence suggested an antagonistic effect between both adsorbates generating an inhibitive adsorption. In terms of modeling analysis, the single and binary adsorption isotherms were well reproduced by monolayer and competitive monolayer statistical physics models, respectively. These two models showed that phenol and 2-nitrophenol molecules have been mainly docked with an inclined and horizontal positions in single and binary systems, respectively. A detailed analysis of the number of captured phenol (n1) and 2-nitrophenol (n2) molecules per site in the binary systems demonstrated that its corresponding evolution varied with a completely inverse way thus corroborating the inhibition effect between phenol and 2-nitrophenol molecules. The monolayer and competitive monolayer models were used to estimate two adsorption energies to characterize the single and binary adsorption mechanisms. The analysis of the energetic parameters suggested that the adsorption process was a physisorption. The interpretation of all monolayer and competitive monolayer model parameters provided new insights that contributed to understand the single and binary adsorption mechanisms of phenol and 2-nitrophenol molecules on tested adsorbent.

A study on the preparation of pitch-based high-strength columnar activated carbon and mechanism of phenol adsorption from aqueous solution.

Coal tar pitch was ground into powder and hydroformed with high pressure. After pre-oxidation, the pitch was activated by CO2 at high temperature. The effects of different preparation conditions on the yield, pore structure and phenol adsorption capacity of activated carbon were investigated, and activated carbon prepared under suitable conditions had good adsorption performance. A pore volume of 1–10 nm is the main absorption structure according to the analysis of pore size distribution and phenol adsorption capacity. The activated carbon showed high mechanical strength through compressive strength tests. Graphite nanocrystals around 5 nm were observed in the TEM images, and it illustrates that grain refinement results in the high strength. These nanocrystal stacked structures are easier to make and enlarge pores by activation than graphite layer stacked structures. Surface functional groups are considered not to be the active sites of phenol adsorption as suggested by the results of FTIR and Boehm's titration, and acidic oxygen-containing functional groups are harmful to phenol adsorption, which happen to be removed in the reductive preparation atmosphere. The donor–acceptor complex mechanism can be ruled out, and the π–π interactions are considered the most likely mechanism. The Langmuir and Redlich–Peterson models are better fitted to the adsorption isotherms. Adsorption kinetics fit the intraparticle diffusion model best. Comparison of different activated carbons shows that suitable pore size is important for phenol adsorption. Thermodynamic parameters demonstrate that the adsorption process is spontaneous and exothermic, and the entropy increases. Pitch-based high-strength columnar activated carbon is an effective and low cost adsorbent for phenol wastewater treatment. This carbon nanocrystal material also provides a new direction for catalyst carriers.

Effects of calcination temperature on the structure and adsorption performance of Ce-Mn/AC materials

Activated carbon-supported bimetallic cerium-manganese (Ce-Mn/AC) materials were prepared by impregnation method to study the effect of calcination temperature on the structure and adsorption performance of absorbents. The obtained materials were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption-desorption isotherm, Fourier transformed infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). As the results showed, the diffraction peaks of CeO2 decreased and even disappeared; Mn species were transformed from Mn3O4 to Mn2O3 on the surface of Ce-Mn/AC; the BET specific surface area increased first and then decreased on the elevating calcination temperature; the number of acid functions of AC was reduced after being modified by cerium and manganese. All these changes were directly attributed to the synergistic effects between MnOx and CeO2. AC800 exhibited the best phenol adsorption capacity. The adsorption mechanism of phenol on Ce-Mn/AC was discussed with hydrophilic (hydrophobic) interaction and hard and soft acid-base theory.