Adsorption of phenol onto activated carbons having different textural and surface properties

Adsorption of phenol in aqueous phase onto activated carbons (ACs) having different textural and surface properties has been considered. Six types of ACs were used: three were commercial, and three were obtained from Kraft lignin chemically activated with sodium hydroxide, potassium hydroxide or ortho-phosphoric acid. The apparent surface areas of the commercial ACs varied from 620 to 1320 m²/g, while ACs made from lignin presented surface areas as high as 1300 m²/g and 2900 m²/g when prepared with H₃PO₄ and alkaline hydroxides, respectively; moreover, the highest proportion of microporosity was found for ACs derived from lignin. A kinetic study was carried out, showing that the phenol adsorption data may be correctly adjusted, for all the ACs tested, by an equation corresponding to a pseudo second-order chemical reaction. Freundlich, Langmuir and Tempkin equations were tested for modelling the adsorption isotherms at equilibrium, and it was concluded that Langmuir model fitted adequately the experimental data. However, Tempkin model fitted even better the adsorption data obtained with ACs derived from lignin activated with alkaline hydroxides, which are characterized by the highest number of surface groups. Remarkably high phenol adsorption capacities were found for the ACs prepared by activation of Kraft lignin with NaOH and KOH: 238 and 213 mg/g of AC, respectively. Finally, the adsorption of phenol was found to depend not only on the micropore volume, but also on the total amount of carbonyl and basic groups and on the ratio of acid to basic groups.     

Adsorption of ionic liquids from aqueous effluents by activated carbon

The separation of imidazolium-based ionic liquids (ILs) from aqueous solution by adsorption has been investigated using a commercial activated carbon (AC) as adsorbent. Equilibrium experiments were carried out for obtaining the adsorption isotherms of ILs on AC at different temperatures. The influence of both cation and anion was analyzed by studying 17 different ILs. The role of the surface chemistry of the adsorbent was also examined using ACs modified by oxidative and thermal treatments. The incorporation of IL on the AC surface was studied by N₂ adsorption-desorption measurements and elemental analysis. In addition to this, a COSMO-RS computational approach was developed to estimate molecular and thermodynamic properties of the solvent-adsorbate-adsorbent system, which allowed us to analyze the adsorption mechanism from a molecular point of view. The results of this work indicate that the adsorption with AC is an affordable environmental application to remove hydrophobic ILs from water streams, proposing the use of acetone for adsorbent regeneration. It has also been demonstrated that the adsorption of refractory hydrophilic ILs can be improved by modifying the amount and nature of oxygen groups on the AC surface, particularly by including hydroxyl groups to promote hydrogen-bonding interactions with the basic groups of hydrophilic ILs.     

Adsorption of polluting substances on activated carbons prepared from rice husk and sugarcane bagasse

Rice husk and sugarcane bagasse were chemically impregnated with ZnCl₂ and carbonized at 700 °C in a large-scale rotary furnace. The activated carbons (ACs) obtained had BET surface area of 811 and 864 m²/g, respectively, and were essentially microporous. The adsorption of arsenic, humic acid, phenol and a municipal solid waste landfill leachate was examined. Both ACs showed the best adsorption behaviour towards phenol, removing around 80% at the equilibrium time of 4 h. The adsorption isotherms for arsenic and humic acid were also favourable, although the maximum loadings achieved were lower than that of phenol. Finally, the rice husk AC showed 60% and 70% removal efficiency for colour and COD, respectively, when tested on a landfill leachate.     

The role of adsorbent pore size distribution in multicomponent adsorption on activated carbon

The impact of adsorbent pore size distribution (PSD) on adsorption mechanism for the multi solute system was evaluated in this study. Anoxic and oxic adsorption equilibrium for the single solute (phenol), binary solute (phenol/2-methylphenol) and ternary solute (phenol/2-methylphenol/2-ethylphenol) systems on one granular activated carbon (GAC) F400 and two types of activated carbon fibers (ACFs), namely, ACC-10 and ACC-15, were determined. F400 has a wide PSD, while ACC-10 and ACC-15 have narrow PSD and their critical pore diameters are 8.0 Å and 12.8 Å, respectively. In single solute adsorption, the increase of adsorptive capacity under oxic conditions as compared to anoxic ones was related to the PSD of the adsorbent. Binary solute adsorption on ACC-10 and ternary solute adsorption on ACC-15 indicated no impact of the presence of molecular oxygen on the adsorptive capacity and the adsorption isotherms were well predicted by the ideal adsorbed solution theory (IAST). Significant differences between oxic and anoxic isotherms were noticed for other multicomponent adsorption systems. The narrow PSD of ACFs was effective in hampering the oligomerization of phenolic compounds under oxic conditions. Such a phenomenon will provide accurate predictions of fixed bed adsorbers in water treatment systems.     

Effect of surface properties of activated carbons on surfactant adsorption kinetics

This research investigates the adsorption properties of three activated carbons (AC) derived from coconut, coal, and wood origin. A linear relationship exists between the number of water molecules adsorbed onto each AC and the oxygen content determined elemental analysis and XPS. An inverse linear relationship exists between the plateau amount of dodecanoic acid anionic surfactant and the oxygen content on the surface of ACs. The surface charge on each AC’s surface had a linear relationship with the plateau amount of dodecanoic acid. A plug-flow heterogeneous surface diffusion model (PFHSDM) for a fixed-bed adsorption process was developed to describe the adsorption kinetics in a fixed-bed column. The model represents axially dispersed plug-flow, external mass transfer, adsorption equilibrium on the fluid-particle interface, and intraparticle diffusion. The larger molecular dimension of the dodecanoic acid as a more hydrophobic entity than octanoic acid led to a faster external mass transfer rate but a slower surface diffusion rate as estimated from the PFHSDM. The interaction between the organic moiety of surfactant and the AC surface chemistry such as surface oxygen content and surface charge contributes to the adsorption performance in both to the adsorption equilibrium and kinetics.     

Preparation of powdered activated carbon from rice husk and its methane adsorption properties

Success of adsorbed natural gas (ANG) storage process is mainly based on the characteristics of the adsorbent, so various synthesized adsorbents were analyzed for methane adsorption on a thermodynamic basis. Activated carbon from rice husk (AC-RH) was synthesized and its methane adsorption capacities were compared with phenol based activated carbons (AC-PH₂O and AC-PKOH). The adsorption experiments were conducted by volumetric method under various constant temperatures (293.15, 303.15, 313.15 and 323.15 K) and pressure up to 3.5MPa. Maximum methane adsorption was observed in AC-RH as its surface area is higher than the other two adsorbents. The experimental data were correlated well with Langmuir-Fruendlich isotherms. In addition, isosteric heat of adsorption was calculated by using Clausius-Clapeyron equation.     

Surface‐Treated Activated Carbon for Removal of Aromatic Compounds from Water

Modifications of commercial activated carbons by chemical treatment with HNO₃ or HCl and HF and the adsorption behavior of simple aromatic compounds (aniline, pyridine, phenol, and benzene) on activated carbon and modified activated carbon were investigated. The results show that the textural properties change a little after these modifications, but the surface acidity (mainly oxygen‐containing groups) of activated carbon modified with HNO₃ increases greatly. The effect of ash of activated carbon on adsorption of the organic compounds mentioned above is insignificant. However, addition of surface acidity (mainly surface oxygen‐containing groups) decreases the adsorption capacity of compounds significantly. The adsorption uptake of compounds on activated carbon with oxidation of HNO₃ is low possibly due to dispersive interaction, water cluster blocking, or competition between water and compounds adsorbed on activated carbon's surface because of hydrophilic increase of the activated carbon surface. The solubility of aromatic compounds in water has an important effect on the adsorption capacity of activated carbon. q_m and K_L (Langmuir adsorption parameters) for the aromatic compounds vary similarly.     

Modification of the adsorption properties of high surface area graphites by oxygen functional groups

The role of the concentration of oxygen functional groups on the surface of commercial high surface area graphite has been studied in this work. For this purpose, two samples of the parent HSAG have been both oxidized with aqueous HNO₃ solution and pyrolysed at 900 °C under an He flow, in order to remove surface oxygen groups. TPD results, in agreement with XPS experiments, reveal the existence of oxygen groups on the surface of the parent HSAG, whose concentration increases substantially after the oxidative treatment, whereas they disappear after the thermal treatment. The adsorption of different alkanes, aromatics and chlorohydrocarbons on the three samples were compared. Adsorption capacities were derived from the adsorption isotherms, whereas thermodynamic properties have been determined from chromatographic retention data. Both the capacity and the strength of adsorption decrease after the oxidative treatment of the graphites. For n-alkanes and cyclic compounds, it was demonstrated that the presence of oxygen surface groups affects their interaction in lower extension. In the adsorption of aromatics and double-bonded compounds, the influence of surface functionalization is more pronounced, since the removal of electrons from the π-electron system of the basal planes, weaken these forces.     

The adsorption kinetics of sodium dodecylbenzenesulfonate on activated carbon. Branched-pore diffusional model revisited and comparison with other diffusional models

Abstract

The adsorption rate of sodium dodecylbenzenesulfonate (SDBS) on three commercial activated carbons (ACs) and an AC synthesized from almond shells was investigated in this study. The mechanisms controlling the overall adsorption rate of SDBS on ACs were found out by using the pore volume and surface diffusion model (PVSDM). The PVSDM showed that the intraparticle diffusion of SDBS in all ACs was mainly attributed to pore volume diffusion and surface diffusion. The surface diffusion coefficient, D_s, in all samples of ACs are influenced by the amount of surfactant adsorbed at equilibrium, q_e, as well as the mean micropore width, L₀. The contribution of surface diffusion to the overall intraparticle diffusion ranged from 45 to 70%, depending on the properties of AC. Moreover, the branched-pore diffusional model was revisited (BPDMR) assuming that the Fick diffusion is the only diffusion mechanism in the macropores and the diffusion in the micropores was represented by the micropore rate coefficient, K_C. Besides, it was proposed that the parameter f representing the mass fraction of SDBS adsorbed on macropores, can be estimated from the textural properties of ACs. Three new strategies were proposed to analyze the experimental data using BPDMR model, and it was demonstrated that the macropore diffusivity in BPDMR is close to the molecular diffusivity of SDBS in water solution. The micropore rate constant, K_C, ranged from 3.90?×?10^?6 to 10.6?×?10^?6 s^?1 and was affected by textural characteristics of ACs. Both models predicted the global adsorption rate of SDBS on ACs satisfactorily.     

The influence of porosity and surface oxygen groups of peat-based activated carbons on benzene adsorption from dry and humid air

Activated carbons (ACs) prepared from peat were used for benzene adsorption (5 ppmv) from dry and humid (relative humidity (RH) 70%) air streams. Benzene uptake by the ACs was lower in the presence of water vapor due to competition between benzene and water molecules for the adsorption sites. Adsorption of benzene from dry and humid air on the ACs with low content of surface oxygen groups was attributed to the presence of narrow micropores (size <0.7 nm). A linear correlation between the amount of adsorbed benzene and micropore volume calculated from CO₂ adsorption isotherms was found. The coefficients of determination R² were 0.87 for benzene adsorption in the absence of water vapor and 0.83 for adsorption at relative humidity 70%. It was shown that the presence of surface groups in the ACs reduces benzene uptake more profoundly in the presence of moisture than in the dry conditions.     

A new approach to obtain mesoporous-activated carbon via hydrothermal carbonization of Brazilian Cerrado biomass combined with physical activation for bisphenol-A removal

Abstract

The worrying hydric crisis and the increasing water contamination by emerging pollutants around the world stimulate the development of activated carbons (AC) for the removal of endocrine disruptors, including bisphenol-A (BPA). For this reason, a new approach for the synthesis of AC from hydrochar produced through hydrothermal carbonization (HTC) of Brazilian Cerrado biomass (Magonia pubescens–Sapindaceae) and physical activation using water vapor is highlighted. Compared to the traditional method of physical activation after pyrolysis, HTC was found to be better option to develop the specific surface area, porosity, and yield of the ACs, which presented mesoporous structure and carbon content higher than 80%. The BPA adsorption was evaluated by varying the contact time, BPA concentration, and pH. The Langmuir, Freundlich, and Redlich–Peterson isotherms were used to model the adsorption behavior. In the preliminary test to verify the adsorption efficiency, the AC obtained from hydrochar treated at 180?°C presented better results compared to commercial AC. The BPA adsorption data of the best treated hydrochar correlated well with the pseudo first-order model and the Langmuir isotherm (Q_max = 21.26?mg g^?1). The results of the studies indicated the combination of HTC and physical activation with steam to be an efficient way to prepare an ecologically sound adsorbent for removal of Bisphenol-A from water with lower temperature and without chemical reagents. The ACs obtained can also be potential materials for other applications, such as in the field of catalysis and environmental remediation.     

Desorption‐ and Decomposition‐Based Techniques for the Regeneration of Activated Carbon

Activated carbon (AC) is an adsorbent used in most adsorption processes related to micro removal of pollutants from the water phase, but the application is limited due to high costs and environmental issues related to the disposal after saturation. Different regeneration techniques, reducing costs and minimizing environmental impact, are reported for the reuse of saturated AC. These techniques can be performed via two separate strands: regeneration based only on desorption of adsorbed compounds in AC, or based on the decomposition of pollutants adsorbed on AC. Literature on the regeneration of saturated ACs is reviewed and promising techniques are highlighted. One of the most challenging bottlenecks preventing the commercial application of regeneration technologies is the difficulty of scaling‐up.     

On the interactions of phenol, aniline and p-nitrophenol on activated carbon surfaces as detected by TPD

The interactions of phenol, aniline and p-nitrophenol, adsorbed from aqueous solutions, with the surface of two activated carbons (with and without oxygen surface groups) were followed by temperature programmed desorption, thermogravimetry and analysis by mass spectrometry. The results reveal that on bare surface the three molecules can be presented as physisorbed and chemisorbed species. When oxygen surface groups are introduced on the carbon surface, there is a change in the adsorption/desorption behaviour; in such a way that the phenol chemisorption is inhibited and that decomposition of aniline and nitrophenol are originated.     

Phenol adsorption on porous and non-porous carbons

Phenol physisorption on a series of porous and non-porous amorphous carbons was studied at 298 K. Grand Canonical Monte Carlo computer simulations were performed to simulate phenol adsorption from the gas phase. Phenol is adsorbed in a solid-like state within the pores and there is no well-developed multilayer regime. The ‘t’ plot method was adapted to phenol adsorption and the results obtained are in agreement with the model solids employed. The simulated adsorption isotherms were compared with experimental results obtained for adsorption from aqueous solutions of phenol. BET surface areas were calculated. Other characteristics of the adsorption system analyzed were: adsorption energy distribution functions, density profiles, distribution of molecules according to gas-solid energy, and local isotherms.     

Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution

The objective of this research was to develop activated carbon selection criteria that assure the effective removal of trace organic contaminants from aqueous solution and to base the selection criteria on physical and chemical adsorbent characteristics. To systematically evaluate pore structure and surface chemistry effects, a matrix of activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels was prepared and characterized. In addition, three granular activated carbons (GACs) were studied. Two common drinking water contaminants, relatively polar methyl tertiary-butyl ether (MTBE) and relatively nonpolar trichloroethene (TCE), served as adsorbate probes. TCE adsorbed primarily in micropores in the 7-10 Å width range while MTBE adsorbed primarily in micropores in the 8-11 Å width range. These results suggest that effective adsorbents should exhibit a large volume of micropores with widths that are about 1.3 to 1.8 times larger than the kinetic diameter of the target adsorbate. Hydrophobic adsorbents more effectively removed both TCE and MTBE from aqueous solution than hydrophilic adsorbents, a result that was explained by enhanced water adsorption on hydrophilic surfaces. To assure sufficient adsorbent hydrophobicity, the oxygen and nitrogen contents of an activated carbon should therefore sum to no more than about 2 to 3 mmol/g.     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.     

Enhanced adsorption of phenol from aqueous solution by carbonized trace ZIF-8-decorated activated carbon pellets

Trace zeolitic imidazolate framework-8(ZIF-8)-decorated activated carbon(AC) pellets were synthesized by a facile wet impregnation technique. After pyrolysis of the above composite material, the obtained carbon had a large surface area and pore volume, with traces of Zn on its surface. Subsequently, the capacity of the ZIF8/AC samples to adsorb and remove phenol from aqueous media was evaluated in both batch and column experimental setups. The equilibrium adsorption capacity reached 155.24 mg·g~(-1), which was 2.3 times greater than that of the pure AC(46.24 mg·g~(-1)). In addition, adsorption kinetics were examined by pseudofirst and pseudosecond order models, and adsorption isotherms were fitted into Langmuir and Freundlich equations. The adsorbent could be easily filtered from the solution and washed with methanol and water, while maintaining an efficiency N 90% after 4 cycles. The above results make it a potentially reusable candidate for water purification.     

ADSORPTION ISOTHERMS AND HEATS OF IMMERSION IN THE ADSORPTION OF BINARY MIXTURES ON ACTIVATED CARBON

The surface excess and the heat of immersion in the adsorption from binary mixtures on the active carbon surface were calculated in terms of the concentrations of adsorbed phase, the adsorption capacity ratios and the heats of immersion of pure compounds. The surface concentrations of binary mixtures were obtained from the thermodynamic model incorporating the intermolecular interactions between the surface and bulk molecules, and a model for surface activity coefficient considering the orientational states of adsorbed molecules, and the UNIQUAC equation. The calculated adsorption isotherms and heats of immersion were fair agreement with experiments of various binary isotherms.     

活性炭吸附法脱除废水中的苯酚及吸附剂再生的研究

对活性炭对废水中苯酚的吸附平衡以及活性炭的再生进行了试验性研究和理论性探讨。结果发现,温度对活性炭的吸附能力有显著的影响,低温地吸附有利,吸附平衡可用Ｌａｒｇｍｕｉｒ方程描述;ＰＨ值对活性炭对苯酚捐附也有较强的影响,酸性的水溶液对吸附有利,强碱性水溶液对再生有利。分别采用乙醇、丙酮、ＮａＯＨ溶液、ＮａＯＨ溶液＋乙醇的混合液对吸附剂活性炭进行再生,再生率均能达到８５％以上,基本满足工业要求。     

Anomalies in standard gas adsorption isotherms of N2 and Ar on graphite at 77 K

Pronounced hysteresis due to pores, and a distinct step near a relative pressure of 0.4, appeared in the adsorption-desorption isotherms of N₂ and Ar at 77 K for both natural graphite and natural graphite subjected to various treatments. The step stems from the adsorption of a second layer. By applying the same method as that used to determine Point B, the amount of gas adsorbed up to the completion of a second layer was read from the isotherm and the relationship between the surface area of pores and the amount of surface oxygen was investigated.