Development of perovskite in Fe-substituted Pb(Zn1/3Ta2/3)O3 and dielectric characteristics

Pb(Zn_1/3Ta_2/3)O₃ ceramics, compositionally modified by the incorporation of Fe to the octahedral lattice sites, were prepared and characterized in terms of perovskite development, dielectric properties, as well as microstructure evolution. The powders of the B-site precursor compositions were synthesized separately and reacted with PbO to form Pb[(Zn_1/3Ta_2/3),(Fe_1/2Ta_1/2)]O₃. The perovskite contents increased continuously with the Fe concentration. The maximum dielectric constant values of the ceramics increased tremendously with the fraction of Fe, whereas the dielectric maximum temperatures were rather insensitive to the compositional change.     

Enhanced photocatalytic activity of sulfur doped TiO2 for the decomposition of phenol: A new insight into the bulk and surface modification

Sulfur ion (S⁶⁺) was doped into the anatase TiO₂ prepared by sol–gel method (SG-TiO₂) using sulfur powder as a sulfur source (S-TiO₂) and its photoreactivity was probed for the degradation of phenol under UV/solar light illumination. The S-TiO₂ and SG-TiO₂ were characterized by PXRD, UV–vis DRS, FTIR, SEM, XPS, BET and PL techniques. It was observed that S⁶⁺ ion was incorporated into the TiO₂ crystal lattice at Ti⁴⁺ lattice site and the sulfur on the surface gets modified to ₄SO²⁻${{\text{SO}}_4}^{2-}$ due to the heat treatment under atmospheric conditions. The high photocatalytic activity of S-TiO₂ compared to SG-TiO₂ is attributed to the surface modification of sulfur as sulfate which plays a crucial role in trapping electrons. S-TiO₂ shows significant increase in the surface area, reduced crystallite size, increased surface acidity, visible light absorption and prolonged lifetime of the photogenerated charge carriers. Hole scavengers like potassium iodide and tertiary butanol suggested the surface degradation mechanism rather than the bulk degradation pathway. Addition of oxidizing agents to the degradation reaction did not show any enhancement in the degradation rates since the presence of ₄SO²⁻${{\text{SO}}_4}^{2-}$ on the TiO₂ surface itself acts as the efficient electron trapping centers. Both trapping and detrapping of the electron takes place more efficiently at ₄SO²⁻${{\text{SO}}_4}^{2-}$ centers. The enhanced activity of S-TiO₂ is attributed to the synergistic effect between S⁶⁺ dopant with surface modified ₄SO²⁻${{\text{SO}}_4}^{2-}$.     

Characterization and enhanced field emission properties of carbon nanotube bundle arrays coated with N-doped nanocrystalline anatase TiO2

Anatase TiO₂ nanocrystals (NCs) were deposited onto patterned carbon nanotube (CNT) bundle arrays to form a TiO₂/CNT composite using metal organic chemical vapor deposition (MOCVD) using titanium-tetraisopropoxide (Ti(OC₃H₇)₄) as a source reagent. The N-doped TiO₂/CNT composite was then fabricated using nitrogen plasma treatment. The structural and spectroscopic properties of TiO₂/CNT composites were characterized by field-emission scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The combined geometrical structure and low electron affinity effects of N-doped TiO₂ led to a low turn-on field of 1.0 V μm⁻¹ at a current density of 10 μA cm⁻², a low threshold field of 1.9 V μm⁻¹ at a current density of 1 mA cm⁻², a high field enhancement factor of 3.0 × 10³, and long-term stability for the N-doped TiO₂/CNT composite. The results revealed that the N-doped TiO₂/CNT composite can be a potential candidate for field emission devices.     

Synthesis of MnO2/short multi-walled carbon nanotube nanocomposite for supercapacitors

Multi-walled carbon nanotubes (MWNTs) were selectively etched in molten nitrate to produce short MWNTs (s-MWNTs). MnO₂/s-MWNT nanocomposite was synthesized by a reduction of potassium permanganate under microwave irradiation. For comparative purpose, MnO₂/MWNT nanocomposite was also synthesized and investigated for its physical and electrochemical performance. Uniform and conformal MnO₂ coatings were more easily formed on the surfaces of individual s-MWNTs. MnO₂/s-MWNT nanocomposite estimated by cyclic voltammetry (CV) in 0.5 M Na₂SO₄ aqueous solution had the specific capacitance as high as 392.1 F g⁻¹ at 2 mV s⁻¹. This value was more than 48.9% larger than MnO₂/s-MWNT nanocomposite. In addition, MnO₂/s-MWNT nanocomposite was also examined by repeating the CV test at a scan rate of 50 mV s⁻¹, exhibiting an excellent cycling stability along with 99.2% specific capacitance retained after 1000 cycles. Therefore, MnO₂/s-MWNT nanocomposite is a promising electrode material in the supercapacitors.     

Synthesis of micro-sized hierarchical TiO2 particles of nano-scale effectiveness and their photocatalytic activities at various surface hydroxyl concentrations

The 3-dimensional hierarchical TiO₂ particles of micro-sized diameter were synthesized through modified sol–gel process with polyethylene glycol (PEG) as a structure-controlling agent. The anatase crystal structure was obtained after calcination at 450 °C. The size and specific surface area of particles were 1.0–1.8 μm and 96.85 m² g⁻¹, respectively. The specific surface area of the TiO₂ particles corresponded to that of the spherical nanoparticles with average size of 15.9 nm. Although the size of synthesized TiO₂ was micro-scale, they had the specific surface area similar to that of nano-scale particles due to the effect of PEG on the formation of particles. Subsequently, the surface modification with various concentration of ammonia solution was carried out for the preparation of hydroxyl-rich TiO₂ particles at surfaces. As the concentration of ammonia solution was increased, the amount of chemically adsorbed hydroxyl groups on the TiO₂ surface was increased. As an application of prepared TiO₂ for water treatment, their catalytic performances for the degradation of methylene blue (MB) were examined by using UV–Vis spectrophotometer with the assistance of UV lamp. After hydroxylation treatment, the micro-sized TiO₂ particles showed the higher performance of MB degradation than that of nano-sized P25 particles because of their large specific surface area and hydroxyl-rich surface.     

Unusual broadening of the NIR luminescence of Er-doped Nb2O5 nanocrystals embedded in silica host: Preparation and their structural and spectroscopic study for photonics applications

This paper reports on the preparation of novel sol-gel erbium-doped SiO₂-based nanocomposites embedded with Nb₂O₅ nanocrystals fabricated using a bottom-up method and describes their structural, morphological, and luminescence characterization. To prepare the glass ceramics, we synthesized xerogels containing Si/Nb molar ratios of 90:10 up to 50:50 at room temperature, followed by annealing at 900, 1000, or 1100 °C for 10 h. We identified crystallization accompanying host densification in all the nanocomposites with orthorhombic (T-phase) or monoclinic (M-phase) Nb₂O₅ nanocrystals dispersed in the amorphous SiO₂ phase, depending on the niobium content and annealing temperature. A high-intensity broadband emission in the near-infrared region assigned to the ⁴I_13/2 → ⁴I_15/2 transition of the Er³⁺ ions was registered for all the nanocomposites. The shape and the bandwidth changed with the Nb₂O₅ crystalline phase, with values achieving up to 81 nm. Er³⁺ ions were located mainly in Nb₂O₅-rich regions, and the complex structure of the different Nb₂O₅ polymorphs accounted for the broadening in the emission spectra. The materials containing the T-phase, displayed higher luminescence intensity, longer ⁴I_13/2 lifetime and broader bandwidth. In conclusion, these nanostructured materials are potential candidates for photonic applications like optical amplifiers and WDM devices operating in the S, C, and L telecommunication bands.     

The bonding of heavy metals on nitric acid-etched coal fly ashes functionalized with 2-mercaptoethanol or thioglycolic acid

Coal fly ash is a waste by-product of the coal fire industry, which generates many environmental problems. Alternative uses of this material would provide efficient solutions for this by-product. In this work, nitric acid-etched coal fly ash labelled with 2-mercaptoethanol or thioglycolic acid was assessed for retention of Al(III), As(III), Cu(II), Cd(II), Fe(III), Mn(II), Hg(II), Ni(II), Pb(II) and Zn(II) ions. The bonding characteristics between the organic compounds with the solid support, as well as with the metal ions, were evaluated using various surface analytical techniques. Visualization of the organically-functionalized coal fly ash particle was possible using scanning electron microscopy (SEM), while the elemental composition of the functionalized material, before and after retention of the metal ions, was obtained by energy dispersive (ED)-X ray spectrometry (XRS) and electrothermal atomic absorption spectrometry (ETAAS). Fourier transform infrared (FT-IR) spectrometry and Raman spectrometry were used to obtain information about the functional groups. It was found that some metal(oid) ions (As, Ni, Pb, Zn) were coordinated through the mercaptan group, while other metal(oid)s (Al, Cd, Cu, Fe, Hg, Mn) were apparently bonded to oxygen atoms. A low-cost and effective solid phase retention system for extraction of heavy metals from aqueous solutions was thus developed.     

Structural,spectroscopic and biological investigation of copper oxides nanoparticles with various capping agents

Powder composed of copper oxides nanoparticles with various capping agents has been synthesized and characterized with the use of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Polyvinyl alcohol (PVA), glycol propylene, glycerin and glycerin plus ammonia were used as capping agents. The scanning electron microscopy (SEM) studies showed that nanoparticles form agglomerates with the size from 80 to 120 nm while particles size determined from the XRD experiment was in the range from 7 to 21 nm. XPS and XRD experiments revealed that depending on capping and reducing agents used in the synthesis nanoparticles are composed of Cu₂O, CuO or a mixture of them. The biological activity test performed for a selected sample where the capping agent was glycerin plus ammonia has shown promising killing/inhibiting behavior, very effective especially for Gram negatives bacteria.     

Single and multilayered a-SiOx:H (x < 1) thin film samples analyzed by optical absorption and small-angle X-ray scattering

Hydrogenated amorphous silicon oxygen alloy thin films (a-SiO_x:H) were prepared on glass and crystalline silicon substrates, with two different oxygen contents: x = 0.15 and x = 0.32. The deposition was realized in an RF-PECVD reactor by using the plasma of the gas mixture SiH₄ and CO₂ with tunable flow rates. The optical characterization data of the single layers were received from the optical transmittance experiments. Multilayered samples were designed upon the results of the single layers. In depositing the multilayers the repetition of the a-SiO_0.15:H/a-SiO_0.32:H kernel-pair was used. The samples were prepared as 25-pair of λ/4 layers, 3-pair of λ/4 layers and 3-pair of λ/2 layers. The inner morphologies and nanostructural contents of the films were investigated by Small-Angle X-ray Scattering (SAXS) method.     

Tetra-anionic porphyrin loading onto ZnO nanoneedles: A hybrid covalent/non covalent approach

A stepwise surface functionalization procedure, based on hybrid covalent and non-covalent approach is herein proposed to anchor tetra-anionic meso-tetrakis(4-sulfonatophenyl)porphyrin on ZnO nanorods. Carboxyalkylphosphonic acids have been proven effective to form stable self-assembled monolayers through the surface grafting of –PO₃H₂ headgroups. The exposed carboxylic functionalities are suitable for the successful grafting of cationic poly-l-lysine that drives, in water, the non-covalent anchoring of the anionic porphyrin. A stepwise surface characterization, provided by X-ray photoelectron spectroscopy, elucidates the multilayers deposition and surface composition after each process step, thus, giving interesting insights on the chemical speciation of the exposed functionalities. UV–vis spectroscopy confirms the role of ZnO morphology to increase the porphyrin loading onto the investigated surfaces. The proposed approach is effective to achieve deposition of anionic porphyrins on ZnO nanostructures and combines the robustness of covalent functionalization with the versatility and full reversibility of the non-covalent strategies.