Preparation of activated carbon from a renewable bio-plant of Euphorbia rigida by H2SO4 activation and its adsorption behavior in aqueous solutions

The use of activated carbon obtained from Euphorbia rigida for the removal of a basic textile dye, which is methylene blue, from aqueous solutions at various contact times, pHs and temperatures was investigated. The plant material was chemically modified with H₂SO₄. The surface area of chemically modified activated carbon was 741.2 m² g⁻¹. The surface characterization of both plant- and activated carbon was undertaken using FTIR spectroscopic technique. The adsorption process attains equilibrium within 60 min. The experimental data indicated that the adsorption isotherms are well described by the Langmuir equilibrium isotherm equation and the calculated adsorption capacity of activated carbon was 114.45 mg g⁻¹ at 40° C. The adsorption kinetics of methylene blue obeys the pseudo-second-order kinetic model and also followed by the intraparticle diffusion model up to 60 min. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated to estimate the nature of adsorption. The activation energy of the system was calculated as 55.51 kJ mol⁻¹. According to these results, prepared activated carbon could be used as a low-cost adsorbent to compare with the commercial activated carbon for the removal textile dyes from textile wastewater processes.     

Preparation of activated carbon from cherry stones by chemical activation with ZnCl2

Cherry stones (CS), an industrial product generated abundantly in the Valle del Jerte (Cáceres province, Spain), were used as precursor in the preparation of activated carbon by chemical activation with ZnCl₂. The influence of process variables such as the carbonisation temperature and the ZnCl₂:CS ratio (impregnation ratio) on textural and chemical-surface properties of the products obtained was studied. Such products were characterised texturally by adsorption of N₂ at −196 °C, mercury porosimetry and density measurements. Information on the surface functional groups and structures of the carbons was provided by FT-IR spectroscopy. Activated carbon with a high development of surface area and porosity is prepared. When using the 4:1 impregnation ratio, the specific surface area (BET) of the resultant carbon is as high as 1971 m² g⁻¹. The effect of the increase in the impregnation ratio on the porous structure of activated carbon is stronger than that of the rise in the carbonisation temperature, whereas the opposite applies to the effect on the surface functional groups and structures.     

Interactions of xanthines with activated carbon: I. Kinetics of the adsorption process

Because of their pharmaceutical and industrial applications, we have studied the adsorption of xanthine derivates (caffeine and theophylline) by activated carbon. To this end, we examined kinetic, equilibrium and thermodynamic aspects of the process. This paper reports the kinetics results. The experimental results indicate that the process was first order in C and the overall process was assumed to involve a single, reversible adsorption-desorption process obeying a kinetic law postulated by us.     

Preparation of activated carbons previously treated with sulfuric acid: A study of their adsorption capacity in solution

In the present work, cedar wood has been used as raw material for the preparation of activated carbons. The influence of a previous treatment with sulfuric acid on the textural properties of the carbonized and activated samples has been investigated. Finally, the adsorption capacity of para-nitrophenol in aqueous solution has been studied and the corresponding adsorption isotherms have been fitted to Langmuir's equation. The experimental results indicate that the previous dehydration of the raw material with sulfuric acid gives rise to an improvement in the porous texture and adsorption capacity of the activated carbons.     

Grand canonical Monte Carlo simulations of hydrogen adsorption in carbon cones

The Monte Carlo method in its grand ensemble variant (GCMC) is used in order to study the hydrogen adsorption (77 K) characteristics of novel carbon structures, namely Carbon Cones (CCs). CCs are conical shaped curved graphitic sheets, with five different apex angles. CC structures with correct bonding topology were developed via atomistic-molecular simulations, while GCMC simulations of hydrogen adsorption were carried out on the five different apex angle structures. Emphasis has been given on the adsorption properties inside the cones and it was found that cone tips are characterized by enhanced adsorbability. The results were also compared with similar calculations on carbon nanotubes.     

Preparation of activated carbons from cherry stones by activation with potassium hydroxide

Using cherry stones, the preparation of activated carbon has been undertaken in the present study by chemical activation with potassium hydroxide. A series of KOH-activated products was prepared by varying the carbonisation temperature in the 400-900 °C range. Such products were characterised texturally by gas adsorption (N₂, −196 °C), mercury porosimetry, and helium and mercury density measurements. FT-IR spectroscopy was also applied. The carbons prepared as a rule are microporous and macroporous solids. The degree of development of surface area and porosity increases with increasing carbonisation temperature. For the carbon heated at 900 °C the specific surface area (BET) is 1624 m² g⁻¹, the micropore volume is 0.67 cm³ g⁻¹, the mesopore volume is 0.28 cm³ g⁻¹, and the macropore volume is 1.84 cm³ g⁻¹.     

Adsorption in cylindrical pores: Mixed lattice-site/off-site Monte Carlo simulations in pores with heterogeneous wall structure

We present results of grand canonical Monte Carlo simulations of adsorption in cylindrical pores with rough surface modeled by lattice-site approach. Each site is characterized by two parameters: structural and energetic, which locally modify the structure and energy properties of the surface. There are three types of sites, randomly distributed over the wall: attractive, neutral and repulsive with respect to the smooth pore model. The results presented here show how this model affects the mechanism of adsorption and how it changes the forms of adsorption isotherm. We compare our numerical results with the experimental data of adsorption of a simple fluid (CH₄, T = 77 K) in cylindrical silica pore of diameter d = 4 nm (MCM-41 material).     

Adsorption of nicotine and tar from the mainstream smoke of cigarettes by oxidized carbon nanotubes

The adsorption of nicotine and tar from the mainstream smoke (MS) by the filter tips filled respectively with oxidized carbon nanotubes (O-CNTs), activated carbon and zeolite (NaY) has been investigated. O-CNTs show exceptional removal efficiency and their adsorption mechanism is investigated. Capillary condensation of some ingredients from MS in the inner hole of O-CNTs is observed and may be the primary reason for their superior removal efficiency. The effect of O-CNTs mass on the removal efficiencies is also studied and the results show that about 20-30 mg O-CNTs per cigarette can effectively remove most of nicotine and tar.     

Comparative analysis of heterogeneous solid and soft materials by adsorption, NMR and thermally stimulated depolarisation current methods

Structural characterisation of such bio-objects as fibrinogen solution, yeast cells, wheat seeds and bone tissues has been done using two versions of cryoporometry based on the integral Gibbs-Thomson (IGT) equation for freezing point depression of pore liquids and the measurements by ¹H NMR spectroscopy (180-200 < T < 273 K) and the thermally stimulated depolarisation current (TSDC) method (90 < T < 273 K) of structured water. The IGT equation was solved using a self-consisting regularization procedure including the maximum entropy principle applied to the distribution function of pore size (PSD). Both methods give clear pictures of changes in the structural characteristics caused, e.g., by hydration and swelling of wheat seeds and yeast cells, coagulation and interaction of fibrinogen with solid nanoparticles in the aqueous media, and the human bone tissue disease.     

Preparation and recognition of surface molecularly imprinted core-shell microbeads for protein in aqueous solutions

In this paper, a surface molecular imprinting technique was reported for preparing core-shell microbeads of protein imprinting, and bovine hemoglobin or bovine serum albumin were used as model proteins for studying the imprinted core-shell microbeads. 3-Aminophenylboronic acid (APBA) was polymerized onto the surface of polystyrene microbead in the presence of the protein templates to create protein-imprinted core-shell microbeads. The various samples were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) methods. The effect of pH on rebinding of the template hemoglobin, the specific binding and selective recognition were studied for the imprinted microbeads. The results show that the bovine hemoglobin-imprinted core-shell microbeads were successfully created. The shell was a sort of imprinted thin films with porous structure and larger surface areas. The imprinted microbeads have good selectivity for templates and high stability. Due to the recognition sites locating at or closing to the surface, these imprinted microbeads have good property of mass-transport. Unfortunately, the imprint technology was not successfully applied to imprinting bovine serum albumin (BSA).     

Preparation and textural characterisation of activated carbon from vine shoots (Vitis vinifera) by H3PO4—Chemical activation

An abundant and low-cost agricultural waste as vine shoots (Vitis vinifera) (VS), which is generated by the annual pruning of vineyards, has been used as raw material in the preparation of powder activated carbon (AC) by the method of chemical activation with phosphoric acid. After size reduction, VS were impregnated for 2 h with 60 wt.% H₃PO₄ solution at room temperature, 50 and 85 °C. The three impregnated products were carbonised at 400 °C. The product impregnated at 50 °C was heated either first at 150-250 °C and then at 400 °C or simply at 350-550 °C in N₂ atmosphere. The time of isothermal treatment after each dynamic heating was 2 h. The carbons were texturally characterised by gas adsorption (N₂, −196 °C), mercury porosimetry, and density measurements. FT-IR spectroscopy was also applied. Better developments of surface area and microporosity are obtained when the impregnation of VS with the H₃PO₄ solution is effected at 50 °C and for the products heated isothermally at 200 and 450 °C. The mesopore volume is also usually higher for the products impregnated and heated at intermediate temperatures.     

Interactions of xanthines with activated carbon: II. The adsorption equilibrium

In the present work, we have studied the adsorption of xanthine derivatives by activated carbon sorbents in aqueous solutions. The study comprised both kinetic, equilibrium and thermodynamic aspects. The kinetic results were reported in a previous paper; the equilibrium-related results are discussed here. The two types of carbon used exhibit some differences but the equilibrium isotherms obtained are all of the H-3 type in the classification of Giles. This suggests a high affinity of the sorbents for the sorbates. We also found that the overall adsorption process comprises more than one individual adsorption-desorption process of which one leads to the formation of a “monolayer” and the other to the “precipitation” of the sorbate on the sorbent surface (multilayer adsorption); the amount of sorbate adsorbed in monolayer form was seemingly greater in C-A14.     

Characterization of nanoporous carbons by combining CO2 and H2 sorption data with the Monte Carlo simulations

The Monte Carlo method in its grand ensemble variant (GCMC) is used in combination with experimental data in order to characterize microporous carbons and obtain the optimal pore size distribution (PSD). In particular, the method is applied in the case of AX-21 carbon. Adsorption isotherms of CO₂ (253 and 298 K) and H₂ (77 K) up to 20 bar have been measured, while the computed isotherms resulted from the GCMC simulations for several pore widths up to 3.0 nm. For the case of H₂ at 77 K quantum corrections were introduced with the application of the Feynman-Hibbs (FH) effective potential. The adsorption isotherms were used either individually or in a combined manner in order to deduce PSDs and their reliability was examined by the ability to predict the experimental adsorption isotherms. The combined approach was found to be capable of reproducing more accurately all the available experimental isotherms.     

Structural and hydrophobic-hydrophilic properties of nanosilica/zirconia alone and with adsorbed PDMS

Two nanosilica A-300/zirconia (SZ) composites at zirconia content CZrO₂=5 and 20 wt.% were synthesized using a wet impregnation method with zirconium acetylacetonate as a precursor. The specific surface area of SZ is larger than that of A-300 because zirconia is composed of nanoparticles (crystallites of 4 nm in average size at CZrO₂=20 wt.%) smaller than those of the initial silica (d_av ≈ 11 nm). A-300 and SZ modified by polydimethylsiloxane (PDMS at molecular weight 1700 and 7960) in amounts of 5, 10, 15, 20 and 40 wt.% remained in the powder state with aggregates of primary particles smaller than those of A-300. SZ is more hydrophilic than silica but PDMS/SZ is more hydrophobic (maximum hydrophobic at C_PDMS 15-20 or 40 wt.%) than PDMS/A-300.     

Study of the pore size distribution and fractal dimension of HNO3-treated activated carbons

In the present work, the effect of the oxidizing treatment with nitric acid on three activated carbon samples has been studied. The influence of the acid treatment on the surface groups of the different samples has been investigated by means of FT-IR spectroscopy. The pore size distributions of the different samples were determined by means of the HK and DFT methods. The HK method points out a moderate increment of the microporosity due to the action of the nitric acid, whereas the DFT method shows an increase in the microporosity range above 17 Å. Finally, the values of the fractal dimension reveal that the treatment of the samples with nitric acid leads to chemical reactions of a limited extent.     

Melting mechanism of monolayers adsorbed in cylindrical pores: An influence of the pore wall roughness

We have analyzed the mechanism of melting of layers adsorbed in cylindrical pores of porous materials. The goal was to understand the melting mechanism of simple fluids adsorbed in pores with heterogeneous wall surface. The studied system was a monolayer of methane molecules adsorbed in MCM-41 pore of diameter d = 4 nm. Both experimental (neutron scattering) and simulation (Monte Carlo) results proved extremely strong influence of the wall roughness on the melting mechanism. The most striking difference between melting on smooth and rough surfaces was in the temperatures of the transition. The transformation between solid-like and liquid-like monolayer phases adsorbed on a rough surface was observed in a very large temperature range and the solid like properties were observed even above the bulk methane melting temperature.     

Liquid crystal deposition on poled, single crystalline lithium niobate

For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), ‘Z-cut’ along the (0 0 0 1) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4-n-octyl-4′-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur.     

Si cleaning method without surface morphology change by cyanide solutions

Hydrogen cyanide (HCN) aqueous solutions can remove copper contaminants from Si surfaces more effectively than hydrochloric acid/hydrogen peroxide mixture (HPM) and sulfuric acid/hydrogen peroxide mixture (SPM). When pH of the HCN solutions is adjusted at 9, Si surface morphology is not changed, while when pH exceeds 10, the Si surfaces are considerably roughed. AFM measurements show that Cu contaminants are present in the form of particles on the bare Si surfaces. XPS measurements show that the particles consist of metallic Cu. The Cu particle height decreases almost linearly with the cleaning time, and the Cu surface concentration decreases exponentially with it. It is concluded that Cu particles gradually dissolve into the HCN aqueous solutions by the direct reaction with cyanide ions at the surface of the Cu particles.     

Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions

The heterogeneity of activated carbons (ACs) prepared from different precursors is investigated on the basis of adsorption isotherms of aniline from dilute aqueous solutions at various pH values. The APET carbon prepared from polyethyleneterephthalate (PET), as well as, commercial ACP carbon prepared from peat were used. Besides, to investigate the influence of carbon surface chemistry, the adsorption was studied on modified carbons based on ACP carbon. Its various oxygen surface groups were changed by both nitric acid and thermal treatments. The Dubinin-Astakhov (DA) equation and Langmuir-Freundlich (LF) one have been used to model the phenomenon of aniline adsorption from aqueous solutions on heterogeneous carbon surfaces. Adsorption-energy distribution (AED) functions have been calculated by using an algorithm based on a regularization method. Analysis of these functions for activated carbons studied provides important comparative information about their surface heterogeneity.     

Monte Carlo simulation of hydrogen physisorption in K-doped single walled carbon nanotube array

Properties of hydrogen physisorption in K-doped single walled carbon nanotube array (SWCNTA) are investigated in detail by grand canonical Monte Carlo simulation. The optimization of hydrogen storage capacity at 293 K and 10 MPa as a function of K-doping schemes, K atoms’ doped-sites, and SWCNTA configuration is discussed.