Comparison of adsorption capacity of p-Cresol & p-Nitrophenol by activated carbon in single and double solute

Adsorption of p-Cresol and p-Nitrophenol by untreated activated carbon in single and multisolute solutions was carried out at 301 K and at controlled pH conditions. In acidic conditions, well below the pK(a) of both solutes, it was observed that the adsorbate solubility and the electron density of aromatic rings influenced the extent of adsorption by affecting the extent of London dispersion forces. The fitted parameters obtained from single-solute Langmuir equation show that Q(max) and the adsorption affinity of carbon for the compound with low pK(a) decrease more significantly. In higher solution pH conditions, on the other hand, it was found that electrostatic forces played a significant role on the extent of adsorption. The presence of another compound decreases Q(max) and the adsorption affinity of carbon for the principal compound. The effect of pH, on the carbon surface and on the solute molecules, must be considered. Adsorption of the solute at higher pH values was found to be dependent on the concentration of anionic form of the solute. The isotherm data were fitted to the Langmuir isotherm equation for both single and double solute solutions.

Close packed transitions in slit-shaped pores: Density functional theory study of methane adsorption capacity in carbon

An important feature of improving lattice gas models and classical isotherms is the incorporation of a pore size dependent capacity, which has hitherto been overlooked. In this paper, we develop a model for predicting the temperature dependent variation in capacity with pore size. The model is based on the analysis of a lattice gas model using a density functional theory approach at the close packed limit. Fluid-fluid and solid-fluid interactions are modeled by the Lennard-Jones 12-6 potential and Steele's 10-4-3, potential respectively. The capacity of methane in a slit-shaped carbon pore is calculated from the characteristic parameters of the unit cell, which are extracted by minimizing the grand potential of the unit cell. The capacities predicted by the proposed model are in good agreement with those obtained from grand canonical Monte Carlo simulation, for pores that can accommodate up to three adsorbed layers. Single particle and pair distributions exhibit characteristic features that correspond to the sequence of buckling and rhombic transitions that occur as the slit pore width is increased. The model provides a useful tool to model continuous variation in the microstructure of an adsorbed phase, namely buckling and rhombic transitions, with increasing pore width. (C) 2002 American Institute of Physics.

High-pressure adsorption capacity and structure of CO2 in carbon slit pores: Theory and simulation

We present new simulation results for the packing of single-center and three-center models of carbon dioxide at high pressure in carbon slit pores. The former shows a series of packing transitions that are well described by our density functional theory model developed earlier. In contrast, these transitions are absent for the three-center model. Analysis of the simulation results shows that alternations of flat-lying molecules and rotated molecules can occur as the pore width is increased. The presence or absence of quadrupoles has negligible effect on these high-density structures.

Estimation of adsorption capacity for dissociating and non dissociating aromatic compounds on activated carbon with different models

The process of adsorption of two dissociating and two non-dissociating aromatic compounds from dilute aqueous solutions on an untreated commercially available activated carbon (B.D.H.) was investigated systematically. All adsorption experiments were carried out in pH controlled aqueous solutions. The experimental isotherms were fitted into four different models (Langmuir homogenous Models, Langmuir binary Model, Langmuir-Freundlich single model and Langmuir-Freundlich double model). Variation of the model parameters with the solution pH was studied and used to gain further insight into the adsorption process. The relationship between the model parameters and the solution pH and pK(a) was used to predict the adsorption capacity in molecular and ionic form of solutes in other solution. A relationship was sought to predict the effect of pH on the adsorption systems and for estimating the maximum adsorption capacity of carbon at any pH where the solute is ionized reasonably well. N-2 and CO2 adsorption were used to characterize the carbon. X-ray Photoelectron Spectroscopy (XPS) measurement was used for surface elemental analysis of the activated carbon.

Phosphorus nutrition of Caustis blakei grown with two phosphorus sources of different solubility in two soils of differing phosphorus adsorption capacity

A barrier to the domestication of the phosphorus (P) sensitive Australian species Caustis blakei (Cyperaceae) is the standard production systems used commercially which invariably result in problems associated either with P deficiency or P toxicity. This paper reports on the growth responses of Caustis blakei cv. M63 to applications of fertiliser P as either monocalcium phosphate (MCP) or granulated Guano Gold (R) rock phosphate (RP) in two soils with different capacities to adsorb P. The Caustis M63 plants grown in the two soils did not show P toxicity symptoms when fertilised with RP, but shoot dry weight was 30-60% lower than the control in both soils at the highest rate of MCP-P application (156 kg ha(-1), 184 g m(-3)) and this was associated with visible symptoms of drying of the tips of the ultimate branchlets, in the Mt Cotton soil only. The greatest shoot and root dry weights were achieved by plants grown in the higher P adsorbing Palmwoods soil fertilised with RP at P rates of 30-184 g m(-3). Caustis plants grown in the Palmwoods soil had 2.3 times greater root dry weights than plants grown in the Mt Cotton soil irrespective of the P fertiliser type used. Caustis plants growing in Mt Cotton soil which did not receive P showed significantly lower shoot and root dry weight when compared to plants in the Palmwoods soil, probably due to the low initial bicarbonate-extractable P and the high buffering capacity of the Mt Cotton soil. The P concentration in shoots of Caustis fertilised with MCP at 184 g m(-3) was higher when grown in Mt Cotton soil (0.22%) than in the Palmwoods soil (0.15%). The P concentration was lower in the terminal ultimate branchlets (TUB); 0.15% for the Mt Cotton soil and 0.10% for the Palmwoods soil, suggesting that shoots would provide a more useful indicator of P toxicity than the TUB. It is interesting to speculate as to why plants in the Palmwoods soil showed greater root growth and fewer symptoms of P toxicity. This could be because the Palmwoods soil had the greater P adsorption capacity. These results indicate in ground production of Caustis cut foliage will require careful management of P nutrition and understanding of the complex soil/plant interactions associated with the acquisition of P. (c) 2006 Elsevier B.V. All rights reserved.

Adsorption characteristics of carbonized bark for phenol and pentachlorophenol

The potential of using carbonized slash pine bark as a substitute for activated carbon was examined in this study. The bark was carbonized by slow heating in nitrogen for 6.5 h to 672 degrees C. The BET-N-2 surface area, average micropore and mesopore diameter, and micropore volume were 332 m(2) g(-1) 21.7 Angstrom, and 0.125 cm(3) g(-1), respectively. The adsorption capacities for phenol and pentachlorophenol (PCP) at pH 2 and pH 8 were evaluated. The Langmuir equation provided a slightly better fit than the Freundlich equation to two sets of phenol data. The calculated Freundlich constants, K = 0.41 - 0.58 mmol/g/(mmol dm(-3))(1/n) and 1/n = 0.30 - 0.41, were lower and higher, respectively, than literature values for activated carbons. The adsorption capacity of the carbonized bark was much lower for PCP than for phenol. The protonated and anionic PCP isotherms were Type II or III, respectively, in the Brunauer classification. The BET equation provided the best fit to protonated PCP isotherm data. The anionic PCP data were fitted to both the BET model and an equation used in the literature to represent phosphate adsorption on activated carbons. Nonlinear regression of the data for both phenol and PCP adsorption with the Freundlich, Langmuir and BET equations generally gave more accurate parameters, compared with the use of linearized equations to obtain the parameters. (C) 1998 SCI.

The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater

Adsorption of a basic dye, methylene blue, from aqueous solutions onto as-received activated carbons and acid-treated carbons was investigated. The physical and surface chemical properties of the activated carbons were characterized using BET-N-2 adsorption, X-ray photoelectron spectroscopy (XPS), and mass titration. It was found that acid treatment had little effect on carbon textural characteristics but significantly changed the surface chemical properties, resulting in an adverse effect on dye adsorption. The physical properties of activated carbon, such as surface area and pore volume, have little effect on dye adsorption, while the pore size distribution and the surface chemical characteristics play important roles in dye adsorption. The pH value of the solution also influences the adsorption capacity significantly. For methylene blue, a higher pH of solution favors the adsorption capacity. The kinetic adsorption of methylene blue on all carbons follows a pseudo-second-order equation. (c) 2004 Elsevier Inc. All rights reserved.

High-pressure adsorption of methane and carbon dioxide on coal

Adsorption isotherms of methane and carbon dioxide on two kinds of Australian coals have been measured at three temperatures up to pressures of 20 MPa. The adsorption behavior is described by three isotherm equations: extended three-parameter, Langmuir, and Toth. Among these, the Toth equation is found to be the most suitable, yielding the most realistic values of pore volume of the coals and the adsorbed phase density. Also, the surface area of coals obtained from CO2 adsorption at 273 K is found to be the meaningful parameter which captures the CO2 adsorption capacity. A maximum in the excess amount adsorbed of each gas appears at a lower pressure with a decrease in temperature. For carbon dioxide, after the appearance of the maximum, an inflection point in the excess amount adsorbed is observed close to the critical density at each temperature, indicating that the decrease in the gas-phase density change with pressure influences the behavior of the excess amount adsorbed. In the context of CO2 sequestration, it is found that CO2 injection pressures of lower than 10 MPa may be desirable for the CH4 recovery process and CO2-holding capacity.

Adsorption study for removal of basic red dye using bentonite

Colored wastewater poses a challenge to the conventional wastewater treatment techniques. Solid-liquid phase adsorption has been found to be effective for the removal of dyes from effluent. In this paper, the ability of bentonite as an adsorbent for the removal of a commercial dye, Basic Red 2 (BR2), from an aqueous solution has been investigated under various experimental conditions. The adsorption kinetics was shown to be pseudo-second-order. It was found that bentonite had high adsorption capacity for BR2 due to cation exchange. The adsorption equilibrium data can be fitted well by the Langmuir adsorption isotherm model. The effect of the experimental parameters, such as temperature, salt, and pH was investigated through a number of batch adsorption experiments. It was found that the removal of dye increased with the increase in solution pH. However, the change of temperature (15-45 degrees C) and the addition of sodium chloride were found to have little effect on the adsorption process. The results show that electrostatic interactions are not dominant in the interaction between BR2 and bentonite. It was found that the adsorption was a rapid process with 80-90% of the dye removed within the first 2-3 min. Bentonite as an adsorbent is promising for color removal from wastewater.

Effects of acidic treatments on the pore and surface properties of Ni catalyst supported on activated carbon

Activated carbon as catalyst support was treated with HCl, HNO3, and HF and the effects of acid treatments on the properties of the activated carbon support were studied by N-2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). Ni catalysts supported on untreated and treated activated carbons were prepared, characterized and tested for the reforming reaction of methane with carbon dioxide. It is found that acid treatment significantly changed the surface chemical properties and pore structure of the activated carbon. The surface area and pore volume of the carbon supports are generally enhanced upon acid treatment due to the removal of impurities present in the carbon. The adsorption capacity of Ni2+ on the carbon supports is also increased, and the increase can be closely correlated with the surface acidity. The impregnation of nickel salts decreases the surface area and pore volume of carbon supports both in micropores and mesopores. Acid treatment results in a more homogeneous distribution of the nickel salt in carbon. When the impregnated carbons are heated in inert atmosphere, there exists a redox reaction between nickel oxide and the carbon. Catalytic activity tests for methane reforming with carbon dioxide show that the activity of nickel catalysts based on the acid-treated carbon supports is closely related with the surface characteristics of catalysts. (C) 1998 Elsevier Science Ltd. All rights reserved.

Coalbed methane sorption related to coal composition

Gas sorption by coal is closely related to its physical and chemical properties, which are, in turn, governed by coal type and rank. The role of coal type (sensu maceral composition) is not fully established but it is clear that coal type may affect both adsorption capacity and desorption rate. Adsorption capacity is closely related to micropore (pores <2 nm) development, which is rank and maceral dependent. Adsorption isotherms indicate that in most cases bright (vitrinite-rich) coals have a greater adsorption capacity than their dull (often inertinite-rich) equivalents. However, no differences, or even the opposing trend, may be observed in relation to coal type. Desorption rate investigations have been performed using selected bright and dull coal samples in a high pressure microbalance. Interpretation of results using unipore spherical and bidisperse pore models indicate the importance of the pore structure. Bright, vitrinite-rich coals usually have the slowest desorption rates which is associated with their highly microporous structure. However, rapid desorption in bright coals may be related to development of extensive, unmineralised fracture systems. Both macro-and micro-pore systems are implicated in the more rapidly desorbing dull coals. Some dull, inertinite-rich coals may rapidly desorb due to a predominance of large, open cell lumina. Mineral matter is essentially nonadsorbent to coal gases and acts as a simple diluent. However, mineral-rich coals may be associated with more rapid desorption. Coal rank and type (maceral composition) per se do not appear to be the critical factors in controlling gas sorption, but rather the influence they exert over pore structure development. (C) 1998 Elsevier Science B.V.

A comparative study of carbon gasification with O-2 and CO2 by density functional theory calculations

A comparative study of carbon gasification with O-2 and CO2 was conducted by using density functional theory calculations. It was found that the activation energy and the number of active sites in carbon gasification reactions are significantly affected by both the capacity and manner of gas chemisorption. O-2 has a strong adsorption capacity and the dissociative chemisorption of O-2 is thermodynamically favorable on either bare carbon surface or even isolated edge sites. As a result, a large number of semiquinone and o-quinone oxygen can be formed indicating a significant increase in the number of active sites. Moreover, the weaker o-quinone C-C bonds can also drive the reaction forward at (ca. 30%) lower activation energy. Epoxy oxygen forms under relatively high O-2 pressure, and it can only increase the number of active sites, not further reduce the activation energy. CO2 has a lower adsorption capacity. Dissociative chemisorption of CO2 can only occur on two consecutive edge sites and o-quinone oxygen formed from CO2 chemisorption is negligible, let alone epoxy oxygen. Therefore, CO2-carbon reaction needs (ca 30%) higher activation energy. Furthermore, the effective active sites are also reduced by the manner Of CO2 chemisorption. A combination of the higher activation energy and the fewer active sites leads to the much lower reaction rate Of CO2-carbon.

Use of anion clay hydrotalcite to remove coloured organics from aqueous solutions

Anion clay hydrotalcite sorbents were prepared to investigate their adsorption capabilities in the removal of coloured organic substances from various aqueous systems. Anion clay hydrotalcite was found to be particularly effective at removing negatively charged species. Its excellent uptake levels of anionic species can be accounted for by its high surface area and anion exchange ability. That is, coloured substances can be adsorbed on the surface or enter the interlayer region of the clay by anion exchange. In the adsorption of Acid Blue 29 on the anion clay hydrotalcite, an equilibrium time of 1 h with dye removal exceeding 99% was obtained. The hydrotalcite was found to have an adsorption capacity marginally below that of commercial activated carbon. It should be noted that the spent sorbents can be regenerated easily by heating at 723 K to remove all adsorbed organics. The reused sorbents displayed greater adsorption capabilities than the newly prepared hydrotalcite. Hence, the anion clay hydrotalcite is easily recoverable and reusable such that it is a promising sorbent for environmental and purification purposes. (C) 2002 Elsevier Science B.V. All rights reserved.

Research on the BET surface area and packing of molecules on the activated carbon

Adsorption of different aromatic compounds (two of them are electrolytes) onto an untreated activated carbon (F100) is investigated. The experimental isotherms are fitted into Langmuir homogenous and heterogeneous Model. Theoretical maximum adsorption capacities that are based on the BET surface area of the adsorbent cannot be close to the real value. The affinity and the heterogeneity of the adsorption system observed to be related to the pK(a) of the solutes. The maximum adsorption capacity (Q(max)) of activated carbon for each solute dependent on the molecular area as well as the type of functional group attached on the aromatic compound and also pH of solution. The arrangement of the molecules on the carbon surface is not face down. Furthermore, it is illustrated that the packing arrangement is most likely edge to face (sorbate-sorbent) with various tilt angles. For characterization of the carbon, the N-2 and CO2 adsorption were used. X-ray Photoelectron Spectroscopy (XPS) measurement was used to surface elemental analysis of activated carbon.

Fractal effects on the measurement of the specific surface areas of single-walled carbon nanotubes

The specific surface area (SSA) of single-walled carbon nanotubes (SWNTs) has been measured by different groups. Fujiwara et al. measured the SSA of SWNT bundles by using nitrogen and oxygen as adsorbates, and found that the SSA from O2-adsorption was 6.6% larger than that from N2-adsorption for the same SWNT sample [1]. Also Wei et al. [2] measured the SSA of HiPco SWNTs by using O2, N2 and Ar, and found that, for the same samples, Vm(Ar) > Vm(O2) > Vm(N2), here Vm is the monolayer adsorption capacity at the standard conditions of temperature and pressure (STP). Those research results indicate that, for the same SWNT sample, its measured surface area depends on the employed adsorbate.