Visible light sensitization effect of polyaminobenzoate adsorbed on TiO2 nanocrystal surface

Poly-o-aminobenzoate (POA) was prepared by oxidizing o-aminobenzoic acid with (NH₄)₂S₂O₈ in an acidic solution. POA was adsorbed on TiO₂ nanocrystal surface to obtain a POA-TiO₂ nanocomposite. The polymerization reaction, structure, adsorption reaction on TiO₂ surface, and visible light sensitization effect of the polymer adsorbed on TiO₂ surface were studied by FT-IR and UV-visible spectra, cyclic voltammetry, and measurements of visible light photoelectrochemical and photocatalytic activities. Three kinds of POA with different long conjugate structures can be formed. These polymers have large absorbance in wide visible light region. POA molecules can be adsorbed on TiO₂ surface by anchoring their carboxylate groups to the TiO₂ surface with a multi-bridging chelating mode, which causes formation of the POA-TiO₂ nanocomposite with a high stability. POA adsorbed on the TiO₂ nanocrystal showed high visible light sensitization effect in the photocatalytic reaction.     

Surface modification of natural vein graphite for the anode application in Li-ion rechargeable batteries

Natural vein graphite with high purity and crystallinity is seldom used as anode material in lithium-ion rechargeable batteries (LIB) due to impurities and inherent surface structure. This study focuses on improving the surface properties of purified natural vein graphite surface by employing mild chemical oxidation. Needle-platy graphite sample with initial average carbon percentage of 99.83% was improved to 99.98% after treatment with 5 vol.% HCl. Surface modification of purified graphite was done by chemical oxidation with (NH₄)₂S₂O₈ and HNO₃. Fourier-transform infrared spectra of graphite after chemical indicating surface oxidation of graphite surface. X-ray diffraction and scanning electron microscopic studies show the improvement of graphite structure without modification of crystalline structure. Electrochemical performance of lithium-ion cell assembled with developed anode material shows noticeable improvement of the reversible capacity and coulombic efficiency in the first cycle and cycling behavior after surface modification.     

Metal/electrolyte surface chemistry: The adsorption of nitric acid and water on Ag(110)

The adsorption of HNO₃/H₂O mixtures on Ag(110) was investigated to learn more about the chemistry of the metal/electrolyte interface. The experiments were performed in ultrahigh vacuum (UHV) using thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED), and electron stimulated desorption ion angular distribution (ESDIAD) over temperatures of 80–650 K and coverages of 0–10 monolayers (ML). As this is the first known study of HNO₃ in UHV, the mass spectrometer cracking pattern for HNO₃ is here reported. HNO₃ adsorbs irreversibly on the clean surface at 80 K and loses its acidic proton to form an adsorbed surface nitrate (NO₃) below 150 K. The saturation amount of adsorbed NO₃ is 0.4 ± 0.1 ML for which adsorption occurs in either a normal or split c(2 × 2) structure. N03 is stable on the surface up to 450 K beyond which it decomposes directly to gaseous NO₂ and NO and adsorbed atomic oxygen. NO₃ decomposition is first order with an activation energy E_a = 151±4 kJ mol⁻¹ and a pre-exponential factor of A = 10^15.4±0.4s⁻¹. NO₃ stabilizes adsorbed H₂O by about 8 kJ mol⁻¹ and is hydrated by as many as three H₂O molecules. Multilayers of HNO₃/H₂O desorb at 150–220 K and show evidence of extensive hydrogen bonding and hydration interactions. No evidence for HNO₃-induced corrosion or other surface damage was detected in any of these experiments.     

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.     

Chalcogen based treatment of InAs with [(NH4)2S/(NH4)2SO4]

A sulphur based chemical, ([(NH₄)₂S/(NH₄)₂SO₄]) to which S has been added not previously reported for the treatment of (111)A InAs surfaces is introduced and benchmarked against the commonly used passivants Na₂S·9H₂O and ((NH₄)₂S + S), using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It has been found that the native oxide layer present on the InAs surface is more effectively removed when treated with ([(NH₄)₂S/(NH₄)₂SO₄] + S) than with ((NH₄)₂S + S) or Na₂S·9H₂O. AES depth profiles of the sulphurized layers revealed the formation of a thin (less than 8.5 nm) In–S surface layer for both ((NH₄)₂SO₄ + S) and ([(NH₄)₂S/(NH₄)₂SO₄] + S) treatments. No evidence for the formation of As―S bonds was found. Treatment with ([(NH₄)₂S/(NH₄)₂SO₄] + S) also affected a significant improvement compared to the more established sulphur treatments in the surface morphology of the otherwise poor as-received n-InAs (111)A surface.     

Surface modification of carbon nanotubes for enhancing BTEX adsorption from aqueous solutions

Carbon nanotubes (CNTs) were fabricated by the catalytic chemical vapor deposition method and oxidized by HCl, H₂SO₄, HNO₃ and NaOCl solutions for enhancing benzene, toluene, ethylbenzene and p-xylene (BTEX) adsorption in an aqueous solution. The surface nature of CNTs was changed after the H₂SO₄, HNO₃ and NaOCl oxidation, which makes CNTs that adsorb more BTEX. The NaOCl-oxidized CNTs show the greatest enhancement in BTEX adsorption, followed by the HNO₃-oxidized CNTs, and then the H₂SO₄-oxidized CNTs. The adsorption mechanism of BTEX via CNTs is mainly attributed to the π-π electron-donor-acceptor interaction between the aromatic ring of BTEX and the surface carboxylic groups of CNTs. The NaOCl-oxidized CNTs have superior adsorption performance of BTEX as compared to many types of carbon and silica adsorbents reported in the literature. This suggests that the NaOCl-oxidized CNTs are efficient BTEX adsorbents and that they possess good potential applications for BTEX removal in wastewater treatment.     

DRIFTS study of different gas adsorption for CO selective oxidation on Cu-Zr-Ce-O catalysts

The adsorptions of different gases (CO, H₂ and O₂) in the hydrogen-rich gas on the co-precipitated Cu-Zr-Ce-O catalyst were discussed and the active sites were ascertained with infrared spectroscopy technique. It was shown that the adsorption strength of CO was stronger than that of O₂ or H₂. Hydrogen and CO were competitive adsorption and the coexistence H₂ and CO on the surface accelerated the rate of CO desorption. Adsorbed H₂ could convert into geminal OH groups on the ceria surface at high temperatures in the absence of oxygen, while it was easy to form surface hydroxyl groups at low temperatures and condensed to physical water with increasing desorption temperature in the existence of oxygen. The adsorption of CO₂ was strong and it could transform into thermal stable carbonate species even in the reaction conditions. The active sites of the Cu-Zr-Ce-O catalyst were Cu²⁺ and Cu⁺, mainly the latter. The oxygen defect sites could be formed on the Cu-Zr-Ce-O catalyst surface through dehydration and decarboxylation.     

pH‐dependent surface‐enhanced Raman scattering observation of sulfanilamide on the silver surface

Monolayers of sulfanilamide on metallic surface can serve as an ideal model for understanding the interaction mechanism between the metal and the sulfanilamide molecule. In the present paper, the surface‐enhanced Raman scattering (SERS) technique was employed to obtain the SERS spectra of sulfanilamide monolayers formed on the silver surface under different pH values. Assignments of the spectra were carried out with the aid of density functional theory (DFT) calculations (BLYP/6‐311G). It can be found that the adsorption function of sulfanilamide on the silver surface was influenced by the pH value. The fully protonated sulfanilamide molecule adsorbed on the silver surface through N¹³H₂ group and the benzene ring anchored in a relatively perpendicular manner leading to N⁷H₂ and S¹⁰O₂ groups near the surface, while the completely deprotonated sulfanilamide molecule attached on the silver surface via N⁷H₂ and the benzene ring was perpendicular to, and the N¹³H₂ and S¹⁰O₂ groups were far from the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared Observation of the Effects of Aqueous Oxidizing Agents on the Functional Groups on Carbon Surfaces

FTIR photothermal beam deflection spectroscopy (PBDS) was used to record infrared spectra of medium-temperature carbons before and after they had been subjected to treatments with aqueous HNO₃ or H₂O₂ solution. Changes in the functional groups present on the carbon surfaces can be clearly observed.     

Adsorption behaviors of V2O5 nanowires on binary mixed self-assembled monolayers

The adsorption behaviors of V₂O₅ nanowires on binary mixed self-assembled monolayers (SAMs) were investigated with variation of the mixing ratio of two differently terminated thiolates on Au. Hydroxyl-covered V₂O₅ nanowires showed a preferential adsorption on amine (NH₂)-terminated thiolates over methyl (CH₃)-terminated ones. However, on the binary mixed SAM of NH₂- and CH₃-terminated thiols, the adsorption behavior did not follow a simple expectation based upon the electrostatic interaction. The total number of adsorbed V₂O₅ nanowires increased with the mole fraction of NH₂-terminated thiolates up to χNH₂∼0.5, then it decreased with further increase of χNH₂. The height distribution of adsorbed nanowires showed that the relative portion of the agglomerated wires thicker than 3.5 nm to individual wires thinner than 3.5 nm increased up to χNH₂∼0.75 and then it decreased with further increase of χNH₂. The dispersion of molecules with polar-functional groups as well as the molecular ordering of mixed SAMs is attributed to such adsorption behaviors of V₂O₅ nanowires.     

Adsorption of water and ammonia on TiO2-anatase cluster models

Density functional theory (DFT) calculations performed at B3LYP/6-31G^∗∗ level are employed to study water and ammonia adsorption and dissociation on (1 0 1) and (0 0 1) TiO₂ anatase surfaces both represented by totally fixed and partially relaxed Ti₂O₉H₁₀ cluster models. PM3 semiempirical calculations were also conducted both on Ti₂O₉H₁₀ and Ti₉O₃₃H₃₀ clusters in order to assess the effect of cluster size. Following dissociation, the adsorption of H₂O and NH₃ by H-bonding on previously H₂O and NH₃ dissociated systems, respectively are also considered. It is found that the adsorption energies and geometries of water and ammonia molecules on (1 0 1) and (0 0 1) anatase cluster models depend on surface relaxation. The vibration frequency values are also calculated for the optimized geometries. The adsorption energies and vibration frequency values computed are compared with the available theoretical and experimental literature.     

Oxidation of Activated Carbon in Liquid Phase. Study by FT-IR

Surface chemistry of a commercial activated carbon (AC) and of products oxidized in liquid phase using aqueous solutions of a series of oxidizing agents (H₂SO₄, HNO₃, HClO₄, H₂O₂, O₃, ClO₂, KlO₄ and KMnO₄) has been studied by FT-IR. Oxidation led to surface groups and structures which, and also the extend of formation, depended on the oxidizing agent and the pH and concentration of the solution used. Most oxidizing agents proved to be effective for the formation of surface C[dbnd]O groups. Variations in pH of solutions of H₂O₂, KlO₄ and KMnO₄ unequally affected the oxidation of AC. This was unfavourable with the increase in concentration of the solutions of HNO₃ and KMnO₄. The reverse was noted with KlO₄.     

Synthesis and characterization of superhydrophobic functionalized Cu(OH)2 nanotube arrays on copper foil

Superhydrophobic functionalized cupric hydroxide (Cu(OH)₂) nanotube arrays were prepared on copper foils via a facile alkali assistant surface oxidation technique. Thus nanotube arrays of Cu(OH)₂ were directly fabricated on the surface of copper foil by immersing in an aqueous solution of NaOH and (NH₄)₂S₂O₈. The wettability of the surface was changed from surperhydrophilicity to superhydrophobicity by chemical modification with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS). The morphologies, microstructures, crystal structure, chemical compositions and states, and hydrophobicity of the films on the copper foil substrates were analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. It was found that the rough structure of the surface helped to magnify the wettability. The static contact angle (CA) for water is larger than 160° and the contact angle hysteresis (CAH) is lower than 5° on the modified surface. The high roughness of the nanotube arrays along with the generated C-F chains by chemical modification contributed to the improved superhydrophobicity. The present research is expected to be significant in providing a new strategy for the preparation of novel multifunctional materials with potential industrial applications on copper substrates.     

Functionalization of carbon encapsulated iron nanoparticles

Carbon-encapsulated magnetic nanoparticles are a new class of materials where the core magnetic nanoparticle is protected from reactions with its environment by graphite shells. Having a structure similar to carbon nanotubes, these nanoparticles could be potentially functionalized using methods which are already applied to those structures. We present the effects of acidic treatments based on HCl, HNO₃, and H₂SO₄ on these nanoparticles highlighting the impact on their magnetic and surface properties. We show that acidic treatments based on HNO₃ can be successfully applied for the generation of carboxylic groups on the surface of the nanoparticles. Using methylamine as a model, we demonstrate that these functional groups can be used for further functionalization with amino-containing biomolecules via diimide-activated amidation.     

Synthesis of single crystalline (NH4)2V6O16·1.5H2O nest-like structures

Novel nest-like (NH₄)₂V₆O₁₆·1.5H₂O structures made of nanobelts have been synthesized by a facile hydrothermal approach. The powder X-ray diffraction pattern of the sample reveals the monoclinic crystalline phase of (NH₄)₂V₆O₁₆·1.5H₂O. The scanning electron microscopy images of the sample obtained at 130 °C for 3 days exhibit nest-like morphology. The transmission electron microscopy result reveals that the nanobelts have a smooth surface. The selected area electron diffraction pattern of the nanobelts indicates single crystalline nature. The two major weight losses occur in thermogravimetric analysis which correspond to the removal of water and ammonia molecules. Further, calcination of the (NH₄)₂V₆O₁₆·1.5H₂O product results in the formation of orthorhombic phase of shcherbianite V₂O₅.     

In situ 1H NMR Study of Nanoreactor Interaction NH3–H2O in Zeolite Nanopores

The interaction between ammonium NH₃ and H₂O molecules in zeolitic nanopores is studied by in situ ¹H nuclear magnetic resonance (NMR) method. The powder and single crystal samples of natural zeolites, heulandites Ca₄[Al₈Si₂₈O₇₂]·24H₂O and clinoptilolite (Na, K,Ca_1/2)₆[Al₆Si₃₀O₇₂], were used as the model system. It is shown that penetration of NH₃ into the zeolitic nanopores is accompanied by disordering of the hydrogen sublattice of zeolitic water and by the fast proton exchange NH₃ + H₂O ? [NH₄]⁺ + [OH]^? characterized by correlation frequency v _c = ~40 kHz. Another nanoreactor interactions are represented by interaction of [NH₄]⁺ ions with exchangeable Na⁺ and Ca²⁺ ions of the zeolitic structure. The slow ionic exchange [NH₄]⁺ → [Na,Ca_1/2]⁺ and binding of [NH₄]⁺ in cationic sites of the framework were visualized by NMR spectroscopy along with stepwise release of (Na,Ca_1/2)OH from zeolitic pores to the external surface of zeolite grains.     

Structural and electrical properties of core–shell structured GaP nanowires with outer Ga2O3 oxide layers

This paper presents a review of our current experimental research on GaP nanowires grown by a vapor deposition method. Their structural, electrical, opto-electric transport, and gas-adsorption properties are reviewed. Our structural studies showed that a GaP nanowire consisted of a core–shell structure with a single-crystalline GaP core and an outer Ga₂O₃ layer. The individual GaP nanowires exhibited n-type field effects. Their electron mobilities were in the range of about 6 to 22 cm²/V s at room temperature. When the nanowires were illuminated with an ultraviolet light source, an abrupt increase of conductance occurred resulting from carrier generation in the nanowire and de-adsorption of adsorbed OH^- or O₂ ^- ions on the Ga₂O₃ surface shell. Using an intrinsic Ga₂O₃ shell layer as a gate dielectric, top-gated GaP nanowire field-effect transistors were fabricated and characterized. Like other metal oxide nanowires, the carrier concentration and mobility of GaP nanowires were significantly affected by the surface molecular adsorption of OH or O₂. The GaP nanowire devices were fabricated as sensors for NO₂, NH₃, and H₂ gases by using a simple metal decoration technique. PACS 73.63.-b; 72.80.Ey; 85.35.-p     

Role of sticking coefficients on kinetic phase transitions in catalytic reactions

The kinetic model for irreversible COO₂ surface reaction proposed by Ziff et al. is extended to include the variable sticking coefficients of carbon-monoxide (S_CO) and oxygen (S_O). For all values of S_O and S_CO a steady reactive state (SRS) is ob unless one of them is zero. The same is true for the NOCO reaction. These results are easily understood in terms of the adsorption rates of the reacting agents.     

Application of crystalline silicon surface oxidation to silicon heterojunction solar cells

We study the effect of ultra-thin oxide (SiO_x) layers inserted at the interfaces of silicon heterojunction (SHJ) solar cells on their open-circuit voltage (V_OC). The SiO_x layers can be easily formed by dipping c-Si into oxidant such as hydrogen peroxide (H₂O₂) and nitric acid (HNO₃). We confirm the prevention of the undesirable epitaxial growth of Si layers during the deposition of a-Si films by the insertion of the ultra-thin SiO_x layers. The formation of the SiO_x layers by H₂O₂ leads to better effective minority carrier lifetime (τ_eff) and V_OC than the case of using HNO₃. c-Si with the ultra-thin SiO_x layers formed by H₂O₂ dipping, prior to deposition of a-Si passivation layers, can have high implied V_OC of up to ∼0.714 V.