Nanostructured carbons for solid phase extraction

Nanostructured carbons have been obtained by the template method using zeolite NaY and silica gels (SG60, Fluka and ZK, POCh) as structure directing agents. Texture and porous structure of carbons were characterized by TEM, XRD and nitrogen adsorption. Surface chemistry was investigated by the potentiometric titration method. It has been shown that all carbons show developed and uniform porous structure with mean size in the micropore range (1.1 nm) for zeolite derived carbon and in the mesopore range (3.4 and 4.8 nm) for silica gel derived carbons. The BET surface area of silica gel derived carbons is in the range 1230-1280 m²/g whereas zeolite derived carbon possesses very high BET surface area, 3000 m²/g. Potentiometric titration showed that carbons obtained by the template method contain significant amount of acid surface groups (carboxylic, lactone/enol and phenolic) with the total amount 1.1-1.5 mmol/g. To study adsorption-desorption properties of nanostructured carbons towards phenol and chlorophenols the solid phase extraction method was used. High recoveries of chlorophenols were obtained (80-93%) at the breakthrough volumes 1700-3000 mL. The recoveries are much higher than that obtained with commercially available carbon ACC (Supelco).     

Surface and adsorptive properties of carbons prepared from biomass

A number of activated carbons were prepared from a locally available by-product, corncobs, under currently established activation schemes. Obtained carbons were characterized by N₂ adsorption at 77 K and the isotherms were analyzed by BET and α_s methods. Steam-activation at 900 °C produced a microporous carbon having the highest S^α of 788 m² g⁻¹, whereas activation with air at 350 °C produced a carbon of S^α = 321 m²/g and possess wider pores. KOH impregnation with char in ratio 1:1 (w/w) and impregnated in the same ratio with the raw material prior to pyrolysis at 700 °C for 1 h, gave CK700, K700 respectively. An additional sample was obtained by oxidizing part of K700 with conc. HNO₃. All three KOH carbons show pore structures much close to char itself which may be due to potassium salt left in pores and is not easily leached with repeated water washings. In addition, KOH is more effective on the precursor itself than on its char of already developed porosity. FT-IR spectra show an increase in oxygen functionalties on the carbon surface as a result of activation process and the bands become stronger in the spectra of the acid-treated sample. The oxidized carbon sample showed relatively higher uptake of Pb²⁺ and MB and its surface chemistry plays the key role in their adsorption, while sharp decrease was observed in the uptake of phenol and mono-nitrophenols from aqueous solutions. An SEM study showed that air activation produce obvious voids reflecting its erosive effect on the external carbon surface.     

X-ray photoelectron spectroscopic analysis of the surface chemistry of silica nanowires

A thorough analysis of the surface chemistry of silica nanowires has been performed by X-ray photoelectron spectroscopy to investigate unexpected surface changes. Examination of the Si 2p, O 1s, and C 1s core level states before and after exposure of the nanowires to various liquid media showed that silica nanowires are capable of much higher surface hydroxyl concentrations than planar native oxides. It is further demonstrated that the nanowire surface hydroxyl concentration corresponds to the pH of the aqueous media to which the nanowires are exposed. Spectral feature changes due to water exposure similar to those observed for fibronectin binding suggests that fibronectin binding is competitively inhibited by slow changes in surface chemistry resulting from water exposure.     

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.     

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.     

Structure evolution from nanocolumns to nanoporous of nitrogen doped amorphous carbon films deposited by magnetron sputtering

Different nitrogen doped amorphous carbon (CNx) films were obtained by magnetron sputtering of carbon target in argon and nitrogen atmosphere at the increasing negative bias voltages from 0 to 150 V. The films structures have experienced great change, from the novel column to nanoporous structure at the bias voltage of 0 V to the porous structure at 150 V. The proposed growth process was that the CNx nuclei grew at 0 V acted as the “seeds” for the growth of the nanocolumns, and ion etching effects at 150 V induced the formation of nanoporous structures. Furthermore, a comparison study showed that the field emission properties of the CNx films were related with the introduction of the nitrogen atoms, the size and concentration of sp² C clusters and the surface roughness. The films with rougher surface have lower threshold field.     

Adsorption of aromatic compounds from the biodegradation of azo dyes on activated carbon

The adsorption of three selected aromatic compounds (aniline, sulfanilic acid and benzenesulfonic acid) on activated carbons with different surface chemical properties was investigated at different solution pH. A fairly basic commercial activated carbon was modified by means of chemical treatment with HNO₃, yielding an acid activated carbon. The textural properties of this sample were not significantly changed after the oxidation treatment. Equilibrium isotherms of the selected compounds on the mentioned samples were obtained and the results were discussed in relation to their surface chemistry. The influence of electrostatic and dispersive interactions involved in the uptake of the compounds studied was evaluated. The Freundlich model was used to fit the experimental data. Higher uptakes are attained when the compounds are present in their molecular form. In general, adsorption was disfavoured by the introduction of oxygen-containing groups on the surface of the activated carbon.     

Surface energy and hybridization studies of amorphous carbon surfaces

Surface properties of a large number of amorphous carbon (a-C) films have been investigated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Dense a-C surfaces with variable sp³/(sp² + sp³) average hybridization were grown using sputtering or pulsed laser deposition (PLD) and were further chemically modified by thermal annealing, ion bombardment or covalent grafting of organic monolayers. The average carbon hybridization, impurity level and mass density, were deduced from XPS and photoelectron energy loss spectroscopy (PEELS). The depth sensitivity of the dispersive (Lifshitz–van der Waals) interaction, estimated at 1–2 nm from the dependence of γ^LW on the grafted perflorodecene molecule coverage, is much better than XPS which probes a 3–5 nm depth. The observation of a non-monotonic behavior in the correlation between surface hybridization and electron donor component of surface energy reveals that the average carbon hybridization alone does not describe the entire surface energy physics. The role of π bond clustering in the polar interactions is thus considered and some implications on surface reactivity and mutual interactions with molecular or biomolecular species are discussed.     

GaAs（100）表面氧化的XPS 研究

用X射线光电子能谱仪 (XPS)研究了砷化镓 (GaAs)晶片在空气中的热氧化和在紫外光 臭氧激发下的氧化反应 .分析了氧化层中的微观化学构成、表面化学计量比以及表面氧化层的厚度等 .研究表明 ,两种氧化方法的氧化过程不同 ,在砷化镓表面形成的氧化膜的厚度以及组成也不同 ,热氧化下氧化层主要由Ga2 O3、As2 O3、As2 O5 以及少量元素As组成 ,而且表面明显富镓 ;紫外光激发下生成的氧化物主要为Ga2 O3 和As2 O3 ,镓砷比与本体一致 .讨论了可能的反应机理 ,紫外光不仅将氧分子激发为激发态氧原子 ,增加了氧的反应活性 ;同时也激发了GaAs材料的价电子 ,使其更容易被氧化     

Ultrasonic-assisted preparation and characterization of hierarchical porous carbon derived from garlic peel for high-performance supercapacitors

Ultrasonic-assisted impregnation is used to synthesize physically modified garlic peel-based 3D hierarchical porous carbons (PCs), and the effect on PCs is investigated by changing ultrasonic time. The results show that ultrasonic waves can effectively peel off surface attachments of the carbonized product, so that activator has a better mass transfer process and create more active sites. The connectivity of 3D pore network is enhanced as well, so the structure and electrochemical properties of garlic peel-based porous carbon (GBPC) are improved. The ultrasonic disperser is used as an ultrasonic generator, specific conditions are as follows: ultrasonic frequency is 40 kHz, ultrasonic power is 500 W, and ultrasonic time is 0, 3, 6, and 9 min, respectively. With the increase of ultrasonic time, impurities again block the pore structure during dynamic movement, resulting in a decrease in electrochemical performance. Specifically, the performance of GBPC-6 is the most excellent, the specific surface area (SSA) increases from 2548 m² g⁻¹ to 3887 m² g⁻¹, the specific capacitance increases from 304 F g⁻¹ to 426 F g⁻¹ at a current density of 1 A g⁻¹ in a two-electrode test system. Energy density and cycle performance are also improved at the same time, which are attributed to rational structure. In addition, the effectiveness of the strategy of ultrasonic-assisted synthesis has been confirmed on another precursor material–scallion, meaning that this work proposes a new and simple modification method for improving the performance of biomass-based PCs.     

X-ray photoemission studies of the electronic structure of single-crystalline CdO(100)

The electronic structure of single-crystalline CdO is investigated using X-ray photoemission spectroscopy. The surface is prepared by in situ Ar⁺ ion bombardment and annealing (IBA). The core level spectra before and after the IBA are presented, and reveal a dramatic reduction in the surface contamination. The semi-core Cd 4d level and valence band region following the IBA are also shown. The surface Fermi level is pinned 1.3±0.10 eV above the valence band maximum.     

Factors affecting the adsorption of trichloroethylene onto activated carbons

In this work, an experimental study aimed at the assessment of the factors affecting the adsorption of trichloroethylene (TCE) from water solutions onto activated carbons is presented. The influence of sorbent properties, such as B.E.T. surface area, micropore volume, chemical composition and acid/basic surface functional groups on TCE adsorption capacity is experimentally assessed by testing a set of 12 sorbents. Moreover, the effect of the presence of other species in solution, such as sodium acetate and tetrachloroethylene (PCE), is studied through parametric TCE adsorption isotherms realization. The experimental results show that the TCE adsorption capacity is promoted by a high B.E.T. surface area, micropore volume and C content and it is significantly affected by the presence of a non-ionic compound of similar structure (PCE), however it does not depend on the presence of an organic salt (sodium acetate). These results confirm that neither TCE-carbon ionic interaction nor sorbent ionization phenomena are involved in the TCE adsorption, since its mechanism is based on dispersion forces (London-Van Der Walls interaction). A thorough analysis of the experimental data set suggests that, in consideration of the TCE adsorption mechanism, the maximization of basal plane extent (as the B.E.T. surface area) and its effective fraction (as the C content) is a valid criterion to select or synthesize a new suitable sorbent for TCE adsorption from waters.     

In situ gas-phase catalytic properties of TiC-supported size-selected gold nanoparticles synthesized by diblock copolymer encapsulation

TiC-supported size- and shape-selected Au nanoparticles with well defined interparticle distances were synthesized by diblock copolymer encapsulation. Atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) have been used to investigate the correlation between the nanocatalyst morphological/electronic structure and its chemical reactivity. Using the low-temperature oxidation of CO as a model reaction, our TPD results showed an enhancement of the catalytic activity with decreasing particle size. Two desorption features were observed and assigned to kinks/steps in the gold surface and the Au-TiC interface. The role of the interparticle distance on the activity is discussed. AFM measurements showed drastic morphological changes (Ostwald ripening) on the nanoparticles after CO oxidation when the initial interparticle distance was small (∼30 nm). However, no sintering was observed for Au nanoparticles more widely spaced (∼80 nm).     

Influence of temperature-pressure treatment on heavily hydrogenated silicon surface

Microstructure and related properties of hydrogenated silicon samples, Si:H, treated at high-temperature (HT) up to 1270 K under hydrostatic argon pressure (HP) up to 1.1 GPa are investigated. To prepare Si:H, Czochralski grown 0 0 1 oriented single crystalline Si wafer with 50 nm thick surface SiO₂ layer was heavily implanted with hydrogen using the immersion plasma source of hydrogen ions with energy 24 keV.The surface of HT-HP treated Si:H was characterised by scanning electron microscopy. Reflectivity pattern measurements in the wavelength range of 350-2000 nm have been performed to analyse their surface and bulk properties. The volume averaging method for a model of layer-like structure has been used to simulate the HT-HP treated Si:H. The analysis of Si:H samples suggests the multi-layer structure composed of Si, Si:H, SiO, SiO₂, and of porous Si layers in the sub-surface region. The porous Si:H samples model is in good consistency with experimental data from reflectance measurements.     

Improving the surface properties of multi-walled carbon nanotubes after irradiation with gamma rays

The effects of gamma-irradiation on the modification of the surface and structure of multi-walled carbon nanotubes were studied. Gamma-irradiation affected the graphitization properties of functional groups, and decreased the diameter of multi-walled carbon nanotubes. The irradiated multi-walled carbon nanotubes with the absorbed dose of 100 kGy exhibited a larger specific surface area and microporous volume as compared with the other samples. The Raman spectroscopy and X-ray photoelectron spectroscopy showed that the interaction between the gamma-irradiation and the multi-walled carbon nanotubes with the absorbed dose of 150 kGy destroyed the nanostructure of carbons, leading to the formation of diamond-like structures and carbon oxides. In addition, gamma-irradiation with the absorbed dose of 100 kGy improved multi-walled carbon nanotubes graphitization and surface properties while at higher absorbed dose (150 kGy), it induced damaged structures (sp³ bonds and oxygen compositions).     

Preparation and characterization of activated carbons from impregnation pitch by ZnCl2

Using an impregnation pitch from bituminous coal tar (OP) supplied by Industrias Químicas del Nalon Company as raw material, two phases (isotropic and anisotropic) have been obtained. The latter was used as precursor for the preparation of activated carbons. First, a chemical activation process was carried out with ZnCl₂ as activating agent. The process was conducted at different concentrations and temperatures and by means of impregnation with solid zinc chloride. Optimal values were obtained for samples prepared by using a ZnCl₂:pitch ratio equal to 3:1 (sample AZn3). Next, this sample was thermally treated at two different temperatures, i.e., 700 and 800 °C. A lose of specific surface area, microporosity and mesoporosity was observed with respect to sample AZn3, such a lose being more remarkable as temperature increased. Moreover, impregnation of the anisotropic phase of the original pitch with an aqueous solution of ZnCl₂ followed by thermal treatment resulted in a poorly developed surface area and porous texture, probably due to the presence of Zn complexes, which interfere with the activation process.     

Influence of surface structure of SiC nano-sized powder analyzed by X-ray photoelectron spectroscopy on basic powder characteristics

SiC nano-sized powder with high specific surface area is potentially of considerable interest to form fully dense SiC ceramics at lower sintering conditions (temperature/pressure). Surface structure of six kinds of commercially available SiC nano-sized powders produced by three different venders was analyzed in detail by X-ray photoelectron spectroscopy (XPS). The overall XPS spectra of all nano-sized powders detected O-based bond (O1s peak), C-based bond (C1s peak) and Si-based bond (Si2s and Si2p peak). Surface structure of nano-sized powders included one of three impurity phases: (1) free carbon, (2) silica and (3) silicon oxycarbide. Furthermore, the influences of surface structure by XPS were systematically investigated on basic powder characteristics, such as chemical composition, morphology, particle density and primary particle size. It was revealed that the basic powder characteristics had a close relationship to the surface structure of nano-sized powder each impurity.     

Characterization of plasma fluorinated zirconia for dental applications by X-ray photoelectron spectroscopy

This paper discusses fluorination of biomedical-grade yttria-stabilized zirconia (YSZ) by sulfur hexafluoride plasma treatment and characterization of near-surface chemistry products by X-ray photoelectron spectroscopy (XPS). Deconvolution of the Zr 3d and Y 3d XPS core level spectra revealed formation of both ZrF₄ and YF₃. In addition, seven-coordinate ZrO₂F₅ and/or ZrO₃F₄ phases were deconvolved, retaining similar atomic coordination as the parent oxide and believed to have formed by substitutional displacement of oxygen by fluorine. No additional components attributed to yttria oxyfluoride were deconvolved. Argon ion sputter depth profiling determined the overlayer to be ∼4.0 nm in thickness, and angle resolved XPS showed no angle dependence on component percentages likely due to fluorination extending into the grain boundaries of the polycrystalline substrates. Importantly, the conversion layer did not induce any apparent change in zirconia crystallinity by inspection of Zr-O 3d_5/2,3/2 peak positions and full-width-at-half-maximum values, important for retaining its desirable mechanical properties.     

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.