Wettability modification of pitch-based spherical activated carbon by air oxidation and its effects on phenol adsorption

The surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by air oxidation to enhance its wettability as well as adsorption properties. Changes of PSAC after modification in texture, surface chemistry and wettability were studied by different techniques including N₂ adsorption, X-ray photoelectron spectroscopy (XPS) and dynamic contact angle analyzer (DCA). Phenol adsorption characteristics in different solvents on PSAC were also investigated. When PSAC was modified under an atmosphere with 20 vol.% oxygen at 400 and 450 °C for 5 h, surface acidic groups increased from 0.11 to 1.22 and 1.60 meq/g, while basic groups decreased from 0.52 to 0.03 and 0.02 meq/g, respectively. After PSAC was modified, the increase of the oxygen-containing groups, especially carboxylic and phenolic ones, is responsible for the increasing of the surface acidity and the significant improvement of the wettability of PSAC. PSAC with a relatively high oxygen content provided a low adsorption capacity to phenol in aqueous solution, and the adsorption isotherms change from Langmuir class (L) to the S-shaped curve; while the solvent is changed into cyclohexane, all adsorption isotherms are type L, and the adsorption capacity to phenol increases with increasing oxygen-containing groups. Possible reasons, including the solvent effect, π-π dispersion and donor-acceptor interactions are discussed.     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

Surface modification of activated carbons for CO2 capture

The reduction of anthropogenic CO₂ emissions to address the consequences of climate change is a matter of concern for all developed countries. In the short term, one of the most viable options for reducing carbon emissions is to capture and store CO₂ at large stationary sources. Adsorption with solid sorbents is one of the most promising options. In this work, two series of materials were prepared from two commercial activated carbons, C and R, by heat treatment with gaseous ammonia at temperatures in the 200-800 °C range. The aim was to improve the selectivity and capacity of the sorbents to capture CO₂, by introducing basic nitrogen-functionalities into the carbons. The sorbents were characterised in terms of texture and chemical composition. Their surface chemistry was studied through temperature-programmed desorption tests and X-ray photoelectron spectroscopy. The capture performance of the carbons was evaluated by using a thermogravimetric analyser to record mass uptakes by the samples when exposed to a CO₂ atmosphere.     

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.     

SO2 adsorption capacity of K2CO3-impregnated activated carbon as a function of K2CO3 content loaded by soaking and incipient wetness

The SO₂ adsorption capacity of K₂CO₃-impregnated activated carbons, prepared by soaking carbon in large volumes of K₂CO₃ in solution of various concentrations, varies linearly with respect to the loading of K₂CO₃ on the carbon up to about 12% K₂CO₃ by weight. Above 12%, the capacity for SO₂ levels out and then decreases. This suggests that at high loadings the K₂CO₃ either aggregates and/or blocks pores of the activated carbon. In contrast, the adsorption capacity of carbons prepared by repeatedly (maximum of three times total) loading K₂CO₃ via incipient wetness is much larger than that of the soaked samples, up to 70% more, when the loading of K₂CO₃ is greater than 12%. Static and dynamic adsorption, DSC, SEM, EDX and incipient wetness studies of the samples show that the impregnant aggregates but does not block carbon pores.     

Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO₂) adsorbent. In general, CO₂ adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO₂ adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N₂ adsorption/desorption at −196 °C. CO₂ capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO₂ adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO₂ uptake at higher temperatures.     

Pore size control of Pitch-based activated carbon fibers by pyrolytic deposition of propylene

In this paper, we attempted to narrow the pore size of Pitch-based activated carbon fiber (Pitch-ACF) by chemical vapor deposition (CVD) of propylene at 700 °C. The BET equation was used to estimate the specific surface areas. The micropore volumes were determined using DR equation, t-plot and _s-plot, and mesopore surface areas were determined by t-plot and _s-plot. The pore size distribution (PSD) of micropores and mesopore was investigated by micropore analysis method (MP method) and MK method, respectively. The relation between the graphite-like crystal interlayer distance and pore size was analyzed by X-ray diffraction (XRD). The results showed that the pore size of Pitch-ACF was gradually narrowed with increasing deposition time. The catalytic activation of Ni was attempted when Pitch-ACF was modified simultaneously by pyrolysis of propylene. The results obtained from the analysis of PSD of micropores, mesopores and macropores in Ni–P-ACF by density function theory (DFT) showed that the pore structure and surface chemistry were greatly changed due to introducing nickel catalyst.     

Deposition and characterization of carbon nitride films from hexamethylenetetramine/N2 by microwave plasma-enhanced chemical vapor deposition

Carbon nitride thin films were deposited on Si(1 0 0) substrate by microwave plasma-enhanced chemical vapor deposition (PECVD). Hexamethylenetetramine (HMTA) was used as carbon and nitrogen source while N₂ gas was used as both nitrogen source and carrier gas. The sp³-bonded C---N structure in HMTA was considered significantly in the precursor selection. X-ray diffraction analysis indicated that the film was a mixture of crystalline - and β-C₃N₄ as well as graphitic-C₃N₄ and β-Si₃N₄ which were not easily distinguished. Raman spectroscopy also suggested the existence of - and β-C₃N₄ in the films. X-ray photoelectron spectroscopy study indicated the presence of sp²- and sp³-bonded C---N structures in the films while sp³C---N bonding structure predominated to the sp² C---N bonding structure in the bulk composition of the films. N was also found to be bound to Si atoms in the films. The product was, therefore, described as CN_x:Si, where x depends on the film depth, with some evidences of crystalline C₃N₄ formation.     

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.     

Texture structure and ablation behavior of TaC coating on carbon/carbon composites

TaC coatings with hybrid, (2 0 0) and (2 2 0) texture structure were prepared on carbon/carbon (C/C) composites by isothermal chemical vapor deposition with TaCl₅-Ar-C₃H₆ system. The residual stress, hardness and ablation behaviors of the different coatings were characterized by Raman spectra, nano-indentation and oxyacetylene flame ablation machine respectively. Results shown tensile stress exists in the TaC coatings and increases when texture orientation turns from hybrid to (2 2 0) and (2 0 0), while nano-indentation hardness of the coatings also obeys the same trend. The deposited coatings could improve the ablation-resistance properties of C/C composites effectively. The texture structure also had great effects on the ablation properties and ablation morphologies of the coatings. The mass ablation rate obviously decreases when the texture structure changes from hybrid orientation to (2 0 0) and (2 2 0) orientations. The hybrid orientation and (2 0 0) texture coatings exhibit coarse oxide morphologies with crater or some breakage existed; while the (2 2 0) texture coating shows dense, molten oxide morphology. The main ablation behaviors of the hybrid, (2 0 0) and (2 2 0) texture TaC coatings are oxidation and particle denudation and block denudation, oxidation and block denudation, oxidation and mechanical erosion and block denudation, respectively.     

化学溶液法制备的Pb(Mg1/3Nb2/3)O3-PbTiO3薄膜的光学性能

用化学溶液方法在宝石衬底及有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备了92%Pb(Mg_1/3Nb_2/3)O₃-8%PbTiO₃(PMNT)薄膜，X射线衍射测试结果表明：在有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备的PMNT薄膜几乎是纯钙钛矿相，且薄膜 关键词： PMNT薄膜 光学性能 化学溶液法     

Surface photoelectric and photodegradation activities of AgNbO3 synthesized by solvothermal method

Silver niobate (AgNbO₃) with different morphologies is obtained by annealing the precursors prepared at different temperatures by solvothermal method at 800 °C. Scanning electron microscope images of the samples show the formation process of the morphologies. The weakest photovoltaic and the highest photocatalytic properties of the sample obtained from the precursors prepared at 190 °C are possibly caused by the synergetic effects between several kinds of particles, and between AgNbO₃ and Nb₂O₅. Both the temperature and the amount of Nb₂O₅ are crucial for the morphologies, the photoelectric and photocatalytic properties of the samples.     

Influence of TaCl5 partial pressure on texture structure of TaC coating deposited by chemical vapor deposition

TaC was deposited on graphite substrate with different TaCl₅ partial pressure at 800 °C and 1200 °C by chemical vapor deposition. Microstructures and texture structures of the prepared coatings were researched with X-ray diffraction and scanning electronic microscopy. When the coating deposition process is controlled by surface reaction kinetics (800 °C), TaCl₅ partial pressure had little influence on the microstructure and texture structure of the coating. When the coating formation process is controlled by diffusion kinetics (1200 °C), the microstructure, texture structure of the prepared TaC grains vary greatly with TaCl₅ partial pressure. In the diffusion controlled process, the increasing of TaCl₅ partial pressure will result in the changing of gas supersaturation, and then the occurrence of secondary nucleation, which is the main reason for the changing of coating morphology and texture structure. With the help of competitive growth in (1 0 0) and (1 1 1) directions, the formation mechanism of the different texture coatings are discussed in detail. In addition, a diffusion model of deposition species around step-edge-corner was also proposed to explain the growth mechanism of the texture coatings.     

The study of dehumidifying of carbon monoxide and ammonia adsorption by Iranian natural clinoptilolite zeolite

The natural zeolite (clinoptilolite type) was obtained from the Neibagh region of Mianeh, the city in the west of Iran. The raw zeolite was tested for quality and quantity measurements including surface area and volumetric characteristics as well as thermogravimetry analysis. The acid activation process was used to increase the adsorption rate of zeolite and in order to obtain the optimum conditions: the effect of acid concentration, reaction time and the temperature were studied. A surface area measurement test was performed in each stage to get the best results. Thus, efficient condition was selected according to the produced highest surface area. The reaction was first obtained with hydrochloric acid, and then a comparison was made using the sulfuric acid. The hydrochloric reaction proved to be better. The result of activation was 2.5 times the increase in the surface area in relation to the raw sample. The result of elemental analysis conducted once again on the activated sample showed an increase in the ratio of Si/Al (approximately 0.6). Then, using CO, NH₃ and steam, the gas adsorption capacity of both the raw and activated samples was measured and compared. Since CO was not adsorbed at ambient temperature, but steam was adsorbed relatively well, the natural clinoptilolite zeolite of Iran was suggested as a suitable material for adsorbing humidity form carbon monoxide as well as synthesis gas (H₂ and CO mixture).     

Surface modification of multi-walled carbon nanotubes by O2 plasma

The surface modification of multi-walled carbon nanotubes (MWCNTs) by O₂ plasma was carried out in this study. In order to achieve a relatively homogeneous treatment of MWCNTs powder, a rotating barrel fixed between the two discharge electrodes was used. The effect of plasma treatment parameters, such as power, time, and positions of samples (inside and outside the barrel), on the morphology and structure of MWCNTs surface was systematically analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the direct discharge (outside the barrel) could result in not only a quick grafting of polar functional groups but also an easy damage of MWCNTs after longer time, particularly under intensive power. It was found that the surface of MWCNTs powder might be changed in three steps—expansion (loosed structure formed), peel off and oxidization with increasing of treatment time during the irradiation. In this way, a complete purification of MWCNTs powder could be finished within 30 min via plasma treatment. Our work suggested that plasma treatment could be a simple and nonpolluting method for a large scale purification of MWCNTs.     

Optimization of nickel adsorption from aqueous solution by using activated carbon prepared from waste apricot by chemical activation

Waste apricot supplied by Malatya apricot plant (Turkey) was activated by using chemical activation method and K₂CO₃ was chosen for this purpose. Activation temperature was varied over the temperature range of 400-900 °C and N₂ atmosphere was used with 10 °C/min heat rate. The maximum surface area (1214 m²/g) and micropore volume (0.355 cm³/g) were obtained at 900 °C, but activated carbon was predominantly microporous at 700 °C. The resulting activated carbons were used for removal of Ni(II) ions from aqueous solution and adsorption properties have been investigated under various conditions such as pH, activation temperature, adsorbent dosage and nickel concentration. Adsorption parameters were determined by using Langmuir model. Optimal condition was determined as; pH 5, 0.7 g/10 ml adsorbent dosage, 10 mg/l Ni(II) concentration and 60 min contact time. The results indicate that the effective uptake of Ni(II) ions was obtained by activating the carbon at 900 °C.     

Adsorption of CO, NH3 and O2 on Fe site of La0.875Sr0.125FeO3 (0 1 0) surface by density function theory calculation

The adsorption of CO, NH₃ and O₂ gas molecules on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface has been investigated based on the density functional theory (DFT) with the spin polarized generalized gradient approximation (GGA). The optimal adsorption orientations as well as the adsorption energies for these molecules adsorption on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface are derived. Results show that adsorption configurations with C-down for CO, N-down for NH₃ are stable. For the O₂ molecule adsorption, the mode with an angle about 120° between the oxygen molecule and La_0.875Sr_0.125FeO₃ (0 1 0) surface is stable.     

Preparation and characterization of activated carbon produced from pomegranate seeds by ZnCl2 activation

In this study, pomegranate seeds, a by-product of fruit juice industry, were used as precursor for the preparation of activated carbon by chemical activation with ZnCl₂. The influence of process variables such as the carbonization temperature and the impregnation ratio on textural and chemical-surface properties of the activated carbons was studied. When using the 2.0 impregnation ratio at the carbonization temperature of 600 °C, the specific surface area of the resultant carbon is as high as 978.8 m² g⁻¹. The results showed that the surface area and total pore volume of the activated carbons at the lowest impregnation ratio and the carbonization temperature were achieved as high as 709.4 m² g⁻¹ and 0.329 cm³ g⁻¹. The surface area was strongly influenced by the impregnation ratio of activation reagent and the subsequent carbonization temperature.     

Surface roughening by anisotropic adatom kinetics in epitaxial growth of La0.67Ca0.33MnO3

The growth mechanisms and surface morphology of colossal magnetoresistance (CMR) La_0.67Ca_0.33MnO₃ films deposited by rf magnetron sputtering on SrTiO₃(0 0 1) substrates are investigated. The films are epitaxial, coherently strained and ferromagnetic. It is found that at early growth stages, in nanometric films, a layer-by-layer mechanism dominates, which results in step and terrace surface morphology. Upon further growth, the flat surface becomes unstable when large two-dimensional (2D) islands form. The Erlich-Schwoebel step-edge energy barrier induces an anisotropic adatom kinetics that favors 2D nucleation on top of the islands as it reduces downhill adatom current. As a result, there is an evolution with growth to mound-like structures of increasing height. Critical thickness for mound formation and average mound separation can be tuned by substrate miscut angle and growth temperature. These results provide a detailed understanding of the roughening process in manganites and are relevant for the controlled fabrication of CMR films, in particular for its use in epitaxial heterostructures.     

The effects of activated carbon supports on the structure and properties of TiO2 nanoparticles prepared by a sol-gel method

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.