Characterization of chemically modified carbon black for sorption application

A commercial grade carbon black was chemically modified using mineral acids (either with HNO₃ or H₂SO₄ or mixture) and the sorption performance of the virgin and modified forms were investigated. Chemical modification resulted in the creation of surface acidic functional groups (COOH, SO₂OH) and was verified by FTIR spectra. This was further verified by TGA analysis revealing higher weight loss characteristics of the modified carbons in comparison to virgin carbon black. Morphological changes were observed from BET surface area measurements and SEM analysis. XRD study revealed the change of graphitic crystallite size as a result of modification. The suspension pH of the materials in deionized water and the point of zero charge (pH_pzc) in inert electrolyte were determined. The measured values of suspension pH and pH_pzc for all the carbons were found to be acidic with more acidic character in the modified carbons. These materials were used as sorbents for the removal of arsenic from aqueous medium and showed excellent adsorption performance.     

Preparation and ozone-surface modification of activated carbon. Thermal stability of oxygen surface groups

The control of the surface chemistry of activated carbon by ozone and heat treatment is investigated. Using cherry stones, activated carbons were prepared by carbonization at 900 °C and activation in CO₂ or steam at 850 °C. The obtained products were ozone-treated at room temperature. After their thermogravimetric analysis, the samples were heat-treated to 300, 500, 700 or 900 °C. The textural characterization was carried out by N₂ adsorption at 77 K, mercury porosimetry, and density measurements. The surface analysis was performed by the Bohem method and pH of the point of zero charge (pH_pzc). It has been found that the treatment of activated carbon with ozone combined with heat treatment enables one to control the acidic-basic character and strength of the carbon surface. Whereas the treatment with ozone yields acidic carbons, carbon dioxide and steam activations of the carbonized product and the heat treatment of the ozone-treated products result in basic carbons; the strength of a base which increases with the increasing heat treatment temperature. pH_pzc ranges between 3.6 and 10.3.     

Water vapor adsorption onto activated carbons prepared from cattle manure compost (CMC)

Activated carbons were prepared from cattle manure compost (CMC) using zinc chloride activation. The structural and surface chemical characteristics of CMC-based activated carbons were determined by N₂ adsorption-desorption and Boehm titration, respectively. The water vapor adsorption properties of the prepared activated carbons with various pore structure and surface nature were examined, and the mechanism of water adsorbed onto activated carbon was also discussed. The results show that the adsorption of water vapor on carbons begins at specific active sites at low relative humidity (RH), followed by micropore filling at medium RH through the formation of pentamer cluster of water molecules in the narrow micropores. The water vapor adsorption capacity of activated carbon is predominantly dependent on its pore volume and surface area. Although capillary condensation is not the mechanism for water adsorption onto activated carbon, water can adsorb on narrow mesopore to some extent.     

Surface modification of pitch-based spherical activated carbon by CVD of NH3 to improve its adsorption to uric acid

Surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by chemical vapor deposition of NH₃ (NH₃-CVD) to improve the adsorption properties of uric acid. The texture and surface chemistry of PSAC were studied by N₂ adsorption, pH_PZC (point of zero charge), acid-base titration and X-ray photoelectron spectroscopy (XPS). NH₃-CVD has a limited effect on carbon textural characteristics but it significantly changed the surface chemical properties, resulting in positive effects on uric acid adsorption. After modification by NH₃-CVD, large numbers of nitrogen-containing groups (especially valley-N and center-N) are introduced on the surface of PSAC, which is responsible for the increase of pH_PZC, surface basicity and uric acid adsorption capacity. Pseudo-second-order kinetic model can be used to describe the dynamic adsorption of uric acid on PSAC, and the thermodynamic parameters show that the adsorption of uric acid on PSAC is spontaneous, endothermic and irreversible process in nature.     

Carbon Modified Silica based Adsorbent for Potential Application

The carbon modified silica adsorbents were prepared by synthesizing and modifying zeolite Y type with activated carbon. This paper reports on effects of activated carbon loadings on the methane and nitrogen adsorption, structure and properties of carbon modified zeolite Y. With the increase in activated carbon loadings, the surface area, pore size and pore volume of the activated carbon loaded zeolite Y adsorbent decreased. The intensity of the diffraction patterns of zeolite Y decreased after the activated carbon was loaded. With increasing activated carbon loadings, the intensity of diffraction peaks decreased. Adsorption capacity of nitrogen (N₂) was smaller than adsorption capacity of methane (CH₄) by using activated carbon modified silica. When activated carbon loadings 30% wt.%, adsorption capacity of methane and nitrogen was 12.9317 wt.% and 12.6115 wt.%, these were caused by difference in molecular weight. The molecular weight of nitrogen is bigger than molecular weight of methane.     

Removal of organic contaminants from aqueous solution by cattle manure compost (CMC) derived activated carbons

The activated carbons (ACs) prepared from cattle manure compost (CMC) with various pore structure and surface chemistry were used to remove phenol and methylene blue (MB) from aqueous solutions. The adsorption equilibrium and kinetics of two organic contaminants onto the ACs were investigated and the schematic models for the adsorptive processes were proposed. The result shows that the removal of functional groups from ACs surface leads to decreasing both rate constants for phenol and MB adsorption. It also causes the decrement of MB adsorption capacity. However, the decrease of surface functional groups was found to result in the increase of phenol adsorption capacity. In our schematic model for adsorptive processes, the presence of acidic functional groups on the surface of carbon is assumed to act as channels for diffusion of adsorbate molecules onto small pores, therefore, promotes the adsorption rate of both phenol and MB. In phenol solution, water molecules firstly adsorb on surface oxygen groups by H-bonding and subsequently form water clusters, which cause partial blockage of the micropores, deduce electrons from the π-electron system of the carbon basal planes, hence, impede or prevent phenol adsorption. On the contrary, in MB solution, the oxygen groups prefer to combine with MB⁺ cations than water molecules, which lead to the increase of MB adsorption capacity.     

Preparation of activated carbons previously treated with hydrogen peroxide: Study of their porous texture

Cedar wood was used as raw material for the preparation of activated carbons by treatment with hydrogen peroxide of different concentrations. The samples were next carbonised and activated under CO₂ atmosphere. The activated carbons were characterised by means of the adsorption isotherms of N₂ at 77 K, as well as by applying the Density Functional Theory (DFT) method and mercury porosimetry. The experimental results corresponding to the activated samples indicate a more remarkable porous development as a consequence of the treatment with hydrogen peroxide, probably due to the elimination of surface complexes produced during the activation step. The DFT diagrams point out that the activating treatment favours the development of medium and narrow-size micropores whereas the carbonisation process leads to the development of wide micropores of size close to that corresponding to mesopores.     

Cobalt-nickel mixed oxide surface: A promising adsorbent for the removal of PR dye from water

A mixed oxide of cobalt (Co) and nickel (Ni) with an approximate composition of Co_0.4Ni_0.4O_0.2 was prepared chemically by precipitating from the corresponding metal carbonates and heating the mixture of carbonates at 650 °C under ambient atmosphere. The mixed (Co-Ni) oxide thus prepared was characterized by IR, SEM and XRD methods. The composition of the mixed metal oxide was obtained by EDX analysis. The surface behavior of the Co-Ni mixed oxide matrix was tested by adsorption studies and pH_pzc measurement. The Co-Ni mixed oxide matrix behaves as a charged adsorbent at the pH media higher and lower than its pH_pzc value (9.50) and thus found to be capable of anchoring the oppositely charged species onto its surface. Removal of cationic and anionic dyestuffs, viz., methylene blue (MB) and procion red (PR), respectively, was attempted using the mixed oxide surface as adsorbent. Although both the dyes can be removed by the mixed oxide, the extent of PR removal (∼70%) seems to be much higher than that of MB (∼20%) demonstrating the superior performance of the Co-Ni mixed oxide for its use as adsorbent in removing the anionic PR dyestuff from water.     

p-Chlorophenol adsorption on activated carbons with basic surface properties

The adsorption of p-chlorophenol (PCP) from aqueous solution on activated carbons (ACs) with basic surface properties has been studied. The ACs were prepared by two methods. The first method was based on the modification of a commercial CWZ AC by high temperature treatment in an atmosphere of ammonia, nitrogen and hydrogen. The second approach comprised the carbonization followed by activation of N-enriched polymers and coal tar pitch using CO₂ and steam as activation agent. The resultant ACs were characterized in terms of porous structure, elemental composition and surface chemistry (pH_PZC, acid/base titration, XPS). The adsorption of PCP was carried out from an aqueous solution in static conditions. Equilibrium adsorption isotherm was of L2 type for polymer-based ACs, whereas L3-type isotherm was observed for CWZ ACs series. The Langmuir monolayer adsorption capacity was related to the porous structure and the amount of basic sites. A good correlation was found between the adsorption capacity and the volume of micropores with a width < 1.4 nm for polymer-based ACs. Higher nitrogen content, including that in basic form, did not correspond to the enhanced adsorption of PCP from aqueous solution. The competitive effect of water molecule adsorption on the PCP uptake is discussed.     

Effect of combined activation on the preparation of high porous active carbons from granulated post-consumer polyethyleneterephthalate

Activated carbons were prepared from granulated post-consumer PET by combined activation including heat treatment with sulphuric acid (chemical activation) followed by steam activation. The effect of activation time, temperature, impregnation coefficient in the activation process was studied in order to optimize those reception parameters. One of the most important parameter in combined activation of crushed PET was found to be impregnation coefficient. It was defined that the optimal impregnation coefficient is equal 28%. Activation temperature is another variability which has a significant effect on the pore volume evolution. The increasing of activation temperature enhances the surface area and pore volumes of active carbons. The yield of final product which composes of nearly 15% is the factor limited the activation temperature above 800 °C. Textural characteristics of the samples were carried out by performing N₂ adsorption isotherm at −196 °C. The obtained active carbons were mainly micro- and mesoporous and with BET apparent surface areas of up to 1030 m²/g. The adsorption capacity on methylene blue reaches 1.0 mmol/g, the sorption activity on iodine comes to 77%.     

Adsorption of octadecyltrichlorosilane on mesoporous SBA-15

Adsorption of octadecyltrichlorosilane (OTS) on mesoporous SBA-15 has been studied by using Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermo-gravimetric analysis (TGA) techniques. BET surface area analysis shows decrease of surface area from 930 to 416 m²/g after OTS adsorption. SEM pictures show close attachment of SBA-15 particles. EDAX measurements show increase of carbon weight percentage and decrease of oxygen and silicon weight percentage. XPS results closely support EDAX analysis. FTIR spectra shows presence of methyl (-CH₃) and methylene (-CH₂) bands and oriented OTS monolayer on SBA-15. Thermo-gravimetric analysis shows that the OTS adsorbed on SBA-15 are stable up to a temperature of 230 °C and that the OTS monolayers decompose between 230 and 400 °C.     

Chemisorption of hydrogen sulphide on zinc oxide modified aluminum-substituted SBA-15

Aluminum silicate mesoporous material, ZnO/Al-SBA-15, was synthesized by post-synthesis and immobilization method via microwave-assisted route. Desulphurization tests from a gas mixture with low content H₂S were carried out as the probing reaction on these materials. Chemical effects and the nature of the ZnO additive and textural properties on desulphurization capacity were studied over this material. Material was characterized using N₂ adsorption, XRD, TEM, FTIR, XPS, ICP and other techniques. The analysis suggests that the as-synthesized material had well-ordered hexagonal mesopores and was abundant in micropores. ZnO nanoparticles dispersed well and anchored both in the channel and the wall of mesoporous silica. The material with 2.1 wt.% zinc loading presented the highest H₂S uptake capacity. Both micropores and mesopores are active sites for H₂S capture, especially micropores. The enhancement of H₂S removal capacity was attributed to the integration of the pore structure of mesoporous material and the promising desulphurization properties of ZnO nanoparticles. ZnO/Al-SBA-15 could be an effective alternative to remove H₂S from gaseous streams and it also extends the research of mesoporous material.     

Sonoprecipitation dispersion of ZnO nanoparticles over graphene oxide used in photocatalytic degradation of methylene blue in aqueous solution: Influence of irradiation time and power

In this paper, ZnO/Graphene Oxide (ZnO/GO) is synthesized via ultrasound assisted precipitation method and the effect of power and ultrasound time irradiation is studied on photocatalyst properties. The synthesized samples are used for methylene blue (MB) degradation as an organic water pollutant. Physicochemical properties of the samples are investigated by XRD, FESEM, EDX, BET-BJH, FTIR and DRS techniques. Moreover, pH_pzc of the sample with the best performance is calculated to study the effect of acidity on the photocatalyst efficiency in photocatalytic process. Ultrasound has a positive effect on photocatalyst performance that is because of its effect on distribution of particles and semiconductor band gap, but it has no effect on photostability of the nanocomposite. Sonication has modified distribution of particles by enhancing the active sites for oxidation process. Making structural gaps by ultrasound irradiation increases available surface area which has a similar effect on photocatalyst performance. Graphene oxide as electron collector and transporter prevents electron-hole recombination and it can be an acceptable reason for enhancement at photocatalyst performance. Finally, some of operational parameters such as pH, photocatalyst loading and dye concentration are investigated.     

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.     

Surface modification of a granular activated carbon by dielectric barrier discharge plasma and its effects on pentachlorophenol adsorption

The surface properties of a granular activated carbon (GAC) were modified by dielectric barrier discharge (DBD) plasma to enhance its adsorption capacity to pentachlorophenol (PCP). Surface characteristics and adsorption capacity of GAC before and after DBD plasma modification were investigated. Results showed that the surface of GAC after plasma modification, especially N₂ plasma, became smoother and the particulates on virgin GAC's surface were eliminated due to deposit effect of plasma. The N₂ plasma modification reduced the specific surface area and surface oxygen-containing functional groups of GAC. In contrast, O₂ plasma modification increased the specific surface area and introduced oxygen-containing groups.     

Effects of textural and surface characteristics of microporous activated carbons on the methane adsorption capacity at high pressures

The objective of this study is to relate textural and surface characteristics of selected microporous activated carbons to their methane storage capacity. In this work, a magnetic suspension balance (Rubotherm, Germany) was used to measure methane adsorption isotherms of several activated carbon samples. Textural characteristics were assessed by nitrogen adsorption on a regular surface area analyzer (Autosorb-MP, by Quantachrome, USA). N₂ adsorption was analysed by conventional models (BET, DR, HK) and by Monte Carlo molecular simulations. Elemental and surface analyses were performed by X-ray photoelectronic spectroscopy (XPS) for the selected samples. A comparative analysis was then carried out with the purpose of defining some correlation among the variables under study. For the system under study, pore size distribution and micropore volume seem to be a determining factor as long as the solid surface is perfectly hydrophobic. It was concluded that the textural parameters per se do not unequivocally determine natural gas storage capacities. Surface chemistry and methane adsorption equilibria must be taken into account in the decision-making process of choosing an adsorbent for gas storage.     

Modification of polystyrene-based activated carbon spheres to improve adsorption of dibenzothiophene

Polystyrene-based activated carbon spheres (PACS) were modified with either air, HNO₃, (NH₄)₂S₂O₈, H₂O₂ or H₂ to improve their adsorption properties of dibenzothiophene (DBT). The texture and surface chemistry of PACS were characterized by N₂ adsorption, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), acid-base titration and elemental analysis. The results showed that HNO₃ and (NH₄)₂S₂O₈ treatments introduced large amount of acidic groups such as carboxylic, lactones and anhydride groups, while air and H₂O₂ had relatively mild effects and introduced a small quantity of phenol, carbonyl and ether groups. In the HNO₃ treatment, the acidic groups might be fixed on the internal and external surface of PACS, which may act as active sites of adsorption, resulting in increase of the adsorption amount by 45%. Whereas H₂O₂ and (NH₄)₂S₂O₈ treatments might fix more oxygen-containing groups on the external surface, which may hinder DBT molecule enter into micropores, leading to rather lower adsorption capacity with the extent of oxidation. So, the concentration, distribution and types of the acidic functional groups are responsible for the removal of DBT.     

Hydrothermal synthesis of graphene oxide/multiwalled carbon nanotube/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> ternary nanocomposite for removal of Cu (II) and methylene blue

In this work, highly activated graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite adsorbent was prepared from a simple hydrothermal route by using ferrous sulfate as precursor. For this purpose, the graphene oxide/multiwalled carbon nanotube architectures were formed through the π-π attractions between them, followed by attaching Fe₃O₄ nanoparticles onto their surface. The structure and composition of as-prepared ternary nanocomposite were characterized by XRD, FTIR, XPS, SEM, TEM, Raman, TGA, and BET. It was found that the resultant porous graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite with large surface area could effectively prevent the π-π stacking interactions between graphene oxide nanosheets and greatly improve sorption sites on the surfaces. Thus, owing to the unique ternary nanocomposite architecture and synergistic effect among various components, as-prepared ternary nanocomposite exhibited high separation efficiency when they were used to remove the Cu (II) and methylene blue from aqueous solutions. Furthermore, the adsorption isotherms of ternary nanocomposite structures for Cu (II) and methylene blue removal fitted the Langmuir isotherm model. This work demonstrated that the graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite was promising as an efficient adsorbent for heavy metal ions and organic dye removal from wastewater in low concentration.     

BET surface area of carbonaceous adsorbents—Verification using geometric considerations and GCMC simulations on virtual porous carbon models

The applicability of BET model for calculation of surface area of activated carbons is checked by using molecular simulations. By calculation of geometric surface areas for the simple model carbon slit-like pore with the increasing width, and by comparison of the obtained values with those for the same systems from the VEGA ZZ package (adsorbate-accessible molecular surface), it is shown that the latter methods provide correct values. For the system where a monolayer inside a pore is created the ASA approach (GCMC, Ar, T = 87 K) underestimates the value of surface area for micropores (especially, where only one layer is observed and/or two layers of adsorbed Ar are formed). Therefore, we propose the modification of this method based on searching the relationship between the pore diameter and the number of layers in a pore. Finally BET; original and modified ASA; and A, B and C-point surface areas are calculated for a series of virtual porous carbons using simulated Ar adsorption isotherms (GCMC and T = 87 K). The comparison of results shows that the BET method underestimates and not, as it was usually postulated, overestimates the surface areas of microporous carbons.