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.     

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.     

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.     

Adsorption of ammonia on vanadium-antimony mixed oxides

We analyzed the adsorption of ammonia (NH₃) on the VSbO₄(1 1 0) catalyst surface using density functional theory (DFT) calculations. We followed the evolution of the chemical bonds between different atoms of the resulting NH₃/VSbO₄ system and the changes in the electronic structure of the catalyst. NH₃ preferential adsorption geometries were analyzed through the crystal orbital overlap population (COOP) concept and the density of states (DOS) curves. The VSbO₄(1 1 0) surface exhibits Lewis and Brønsted acid sites on which the ammonia molecule can interact. On the Lewis acid site, NH₃ adsorption resulted in the interaction between the N and a surface V-isolated cation. On Brønsted acid site, N interacted with a surface H coming from the chemical dissociation of water. The COOP analysis indicate that NH₃ interaction on the VSbO₄(1 1 0) surface is weak. In addition, the DOS curves show more developed electronic interactions for NH₃ adsorption on Lewis acid site than over Brønsted acid site.     

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.     

Surface modification of indium tin oxide films by amino ion implantation for the attachment of multi-wall carbon nanotubes

Amino ion implantation was carried out at the energy of 80 keV with fluence of 5 × 10¹⁵ ions cm⁻² for indium tin oxide film (ITO) coated glass, and the existence of amino group on the ITO surface was verified by X-ray photoelectron spectroscopy analysis and Fourier transform infrared spectra. Scanning electron microscopy images show that multi-wall carbon nanotubes (MWCNTs) directly attached to the amino ion implanted ITO (NH₂/ITO) surface homogeneously and stably. The resulting MWCNTs-attached NH₂/ITO (MWCNTs/NH₂/ITO) substrate can be used as electrode material. Cyclic voltammetry results indicate that the MWCNTs/NH₂/ITO electrode shows excellent electrochemical properties and obvious electrocatalytic activity towards uric acid, thus this material is expected to have potential in electrochemical analysis and biosensors.     

Adsorption of biodegradable chelating compounds on inorganic oxides

The Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) method to characterize the interactions between selected aminopolycarboxylic acids and inorganic oxides surfaces is reviewed. In this work, the adsorption of four aminopolycarboxylates (biodegradable and with augmented biodegradability; all in the form of sodium salts), viz. ethylenediaminedisuccinic (EDDS), diethylenetriaminepentaacetic (DTPA), N-(hydroxyethyl)ethylenediaminetriacetic (HEDTA) and methylglycinediacetic (MGDA) acids on: zirconia, titania and alumina was carried out. The obtained results differ depending on the kind of aminopolycarboxylic acid used and the type of oxide support adsorbent characterized by its pH_PZC value.     

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.     

Tuning properties of NC3H quantum dot by adsorption of ammonia and carbon dioxide

Transport properties of NC₃H quantum dot by adsorption of ammonia and carbon dioxide are investigated with an ab initio method combined with a non-equilibrium Green function method. The effects of different configurations of ammonia, size of NC₃H surface and position where ammonia and carbon dioxide had been adsorbed onto NC₃H quantum dot on transport properties are revealed. In comparison with NC₃H quantum dot device, results show that the adsorption of ammonia molecule on NC₃H quantum dot in one configuration enhances the conductance of device, while adsorption in another configuration reduces the conductance. The size of NC₃H significantly altered the transport properties in both NC₃H–NH₃ and NC₃H–CO₂ system. The position of adsorption of ammonia displays obvious change on transport properties while the effects of position of carbon dioxide on transport properties are negligible.     

Computational study of adsorption, diffusion, and dissociation of precursor species on the GaN (0 0 0 1) surface during GaN MOCVD

The adsorption, diffusion, and dissociation of precursor species, MMGa (monomethylgallium) and NH₃, on the GaN (0 0 0 1) surface have been investigated using the DFT (density functional theory) calculation combined with a GaN (0 0 0 1) surface cluster model. The energetics of NH₃(ad) dissociation on the surface proposed of NH₃(ad) via NH₂(ad) to NH(ad) was facile with small activation barriers. A combined analysis with surface diffusion of adatoms demonstrated Ga(ad) and NH(ad) become primary reactant species for 2D film growth, and N(ad) develops into a nucleation center. Our studies suggest the control of NH₃(ad) dissociation are essential to improve epitaxial film quality as well as Ga-rich condition. In addition, the adsorbability of H(ad)s resulted from NH₃(ad) dissociation were found to influence on the surface chemistry during film growth.     

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.     

Comparative study of NH4OH and HCl etching behaviours on AlGaN surfaces

A controlled AlGaN surface preparation method avails to improve the performance of GaN-based HEMT devices. A comparative investigation of chemical treatments by (1:10) NH₄OH:H₂O and (1:10) HCl:H₂O solutions for AlGaN surface preparation by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) is reported. The XPS data clearly reveal that the native oxide on AlGaN was composed of Al₂O₃, Ga₂O₃ and NO compounds. These compounds were etched off partially or completely by both the chemical treatments, namely NH₄OH or HCl solutions, independently. The HCl treatment etches out Al₂O₃ completely from native oxide unlike NH₄OH treatment. The HCl treatment results in larger amount of carbon segregation on AlGaN surfaces, however it removes all oxides’ compounds faster than NH₄OH treatment. The AFM results reveal the improvement of surface morphology by both the chemical treatments leading to the surface roughness RMS values of 0.24 nm and 0.21 nm for NH₄OH and HCl treated AlGaN layers, respectively.     

Modeling of CN-functionalized silica as vehicle for delivery of the chemotherapeutic agent: cisplatin

The adsorption of cisplatin and its complexes, cis-[PtCl(NH₃)₂]⁺ and cis-[Pt(NH₃)₂]²⁺, on a CN-functionalized SiO₂(111) surface has been studied by the atom superposition and electron delocalization method. The adiabatic energy curves for the adsorption of the drug and its complexes on the delivery system were considered. Electronic structure and bonding analyses were also performed. The molecules are adsorbed on the functionalized surface resulting in a major absorption of the cis-[Pt(NH₃)₂]²⁺ complex. The molecule?Csurface interactions are strengthened due to the incorporation of the CN silane group. The most important bonds occur through Pt?CC, Pt?CN and Pt?CSi interactions. Despite the new interactions, the functionalized carrier maintains its matrix properties after adsorption. The remarkable properties may be attributed to the small electronic structure changes in the Si?CCN groups caused by the interaction with neighboring cisplatin molecules and the enhancement in Pt-bonding interactions due to the surface incorporation of the CN silane groups.     

Ca掺杂的氧化铍纳米管吸附H2O和NH3的选择传感特

通过密度泛函计算, 借助NH₃和H₂O分子对未掺杂以及钙掺杂的BeO碳纳米管的结构和电传导性进行了研究. 结果发现,NH₃和H₂O分子可以吸附在纳米管侧壁的Be原子上,吸附能分别为约36.1和39.0 kcal/mol. 态密度分析显示BeO纳米管的电传导性在吸附后稍有变化. 对于NH₃和H₂O分子,纳米管表面的钙原子替换Be原子可使吸附能分别增加约7.4和14.7 kcal/mol. 与未掺杂纳米管不同的是,钙掺杂BeONT吸附NH₃和H₂O分子的电传导性更加敏感,且H₂O分子比NH₃分子更敏感.     

Influence of SiNx:H film properties according to gas mixture ratios for crystalline silicon solar cells

The Hydrogenated silicon nitride (SiN_x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the SiN_x:H film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. For optimizing surface layer in crystalline silicon solar cells, by varying gas mixture ratios (SiH₄ + NH₃ + N₂, SiH₄ + NH₃, SiH₄ + N₂), the hydrogenated silicon nitride films were analyzed for its antireflection and surface passivation (electrical and chemical) properties. The film deposited with the gas mixture of SiH₄ + NH₃ + N₂ showed the best properties in before and after firing process conditions.The single crystalline silicon solar cells fabricated according to optimized gas mixture condition (SiH₄ + NH₃ + N₂) on large area substrate of size 156 mm × 156 mm (Pseudo square) was found to have the conversion efficiency as high as 17.2%. The reason for the high efficiency using SiH₄ + NH₃ + N₂ is because of the good optical transmittance and passivation properties. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.     

Decomposition of NH3 on Ir(110): A first-principle study

The adsorption and dehydrogenation of NH₃ on Ir(110) have been investigated using periodic density functional calculations. The adsorption sites, the adsorption energies, the predominant adsorption configurations and the transition states of the stepwise dehydrogenation of NH₃ were identified. The results show that the NH₃ prefers the top site with inclining 68.6° of N―Ir bond relative to the surface, while NH₂, NH, N and H favor the short bridge position. The NH decomposition to N and H or recombination with H to form NH₂ shares the similar and relatively high reaction energy barrier, implying that NH will be the main surface species in the NH₃ dehydrogenation processes. N―N bond formation possesses the highest energy barrier of 1.75 eV, indicating that it is the rate-limiting step for NH₃ decomposition. Barrier decomposition analysis reveals that the deformation and the binding to the surface of the reactants and the interaction among binding species in transition states will increase the activation energy while the bonding to the surface of the species in transition state will decrease the energy barrier.     

DFT study of NH3 adsorption on pristine,Ni- and Si-doped graphynes

The electronic sensitivity of pristine, Ni- and Si-doped graphynes to ammonia (NH₃) molecule was investigated using density functional theory, including dispersion correction. It was found that NH₃ is weakly adsorbed on the sheet, releasing energy of 2.9–4.4 kcal/mol, and the electronic properties of the sheet are not significantly changed. Although both Ni-doping and Si-doping make the sheet more reactive and sensitive to NH₃, Si-doping seems to be a better strategy to manufacture NH₃ chemical sensors because of higher sensitivity. Our calculations show that the HOMO/LUMO gap of the Si-doped sheet is significantly decreased from 2.13 to 1.46 eV after the adsorption of NH₃, which may increase the electrical conductance of the sheet. Therefore, the doped sheet might convert the presence of NH₃ molecules to electrical signals. Moreover, the shorter recovery time of the Si-doped sheet is because of the middle adsorption energy of 39.3 kcal/mol in comparison with 55.1 kcal/mol for the Ni-doped sheet.     

Theoretical and experimental investigations on the structures of purified clay and acid-activated clay

The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH₃-TPD, molecular NH₃ desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na⁺ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH₃ on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al³⁺ for tetrahedral Si will be favorable to NH₃ adsorption.     

Surface chemistry: from vibrational spectroscopy to photoemission spectromicroscopy

Vibrational spectroscopy and core-level photoelectron spectroscopy are two of the most powerful tools for surface chemical analysis. We have used both techniques in conjunction with others to study hydrocarbon radical interactions with metal and semiconductor surfaces as well as thin film deposition processes. These include the investigations of CH₂ and CH₃ reactions on Cu by high resolution electron energy loss spectroscopy (HREELS), and GaN formation from Ga(CH₃)₃ and NH₃ on SiC by SR-PES. The vibrational analysis has revealed rich surface chemistry of the radicals while the photoemission study has led us to develop new approach for probing ultrafine structures. The effort involves the construction of a scanning photoemission spectromicroscope (SPEM) coupled to a synchrotron radiation light source. Recent results are presented in this brief report.