Quenching and enhancing of SERS of methyl orange after the addition of chlorine and nitrate anions

The influence of Cl⁻ and NO₃⁻ anions on surface enhanced Raman scattering (SERS) of methyl orange adsorbed on “chemical pure” silver colloids was studied. It was found that NO₃⁻ could give rise to a large enhancement of SERS of methyl orange, while Cl⁻ could obviously weaken the SERS intensity of this molecule. Both quenching and enhancing effects were discussed and compared with each other. It indicated the coadsorbed process of these adsorbed species, and different adsorption behaviors of the molecules on silver surface directly resulted in the difference. In addition, the results of TEM pictures and UV-visible spectral experiments have also confirmed the conclusion above.     

Structural, vibrational and dielectric properties of new potassium hydrogen sulfate arsenate: K4(SO4)(HSO4)2(H3AsO4)

A new compound, K₄(SO₄)(HSO₄)₂(H₃AsO₄) was synthesized from water solution of KHSO₄/K₃H(SO₄)₂/H₃AsO₄. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å³, Z=2 and ρ_cal=2.466 g cm⁻³. The refinement of 3760 observed reflections (I>2σ(I)) leads to R₁=0.0394 and wR₂=0.0755. The structure is characterized by SO₄²⁻, HSO₄⁻ and H₃AsO₄ tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O₄⁻?S(1)O₄²⁻ and H(12)S(2)O₄⁻?H₃AsO₄). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H₃AsO₄ group to build the chain S(1)O₄?H₃AsO₄ which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K₄(SO₄)(HSO₄)₂(H₃AsO₄) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature.     

Berberine as a natural source inhibitor for mild steel in 1 M H2SO4

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H₂SO₄ was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H₂SO₄. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10⁻⁴ M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H₂SO₄ containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory-Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.     

Phase transitions and molecular motions in [Zn(NH3)4](BF4)2 studied by nuclear magnetic resonance, infrared and Raman spectroscopy

Middle infrared absorption, Raman scattering and proton magnetic resonance relaxation measurements were performed for [Zn(NH₃)₄](BF₄) in order to establish relationship between the observed phase transitions and reorientational motions of the NH₃ ligands and BF₄⁻ anions. The temperature dependence of spin-lattice relaxation time (T₁(¹H)) and of the full width at half maximum (FWHM) of the bands connected with ρ_r(NH₃), ν₂(BF₄) and ν₄(BF₄) modes in the infrared and in the Raman spectra have shown that in the high temperature phase of [Zn(NH₃)₄](BF₄)₂ all molecular groups perform the following stochastic reorientational motions: fast (τ_R≈10⁻¹² s) 120° flips of NH₃ ligands about three-fold axis, fast isotropic reorientation of BF₄⁻ anions and slow (τ_R≈10⁻⁴ s) isotropic reorientation (“tumbling”) of the whole [Zn(NH₃)₄]²⁺ cation. Mean values of the activation energies for uniaxial reorientation of NH₃ and isotropic reorientation of BF₄⁻ at phases I and II are ca. 3 kJ mol⁻¹ and ca. 5 kJ mol⁻¹, respectively. At phases III and IV the activation energies values for uniaxial reorientation of both NH₃ and of BF₄⁻ equal to ca. 7 kJ mol⁻¹. Nearly the same values of the activation energies, as well as of the reorientational correlation times, at phases III and IV well explain existence of the coupling between reorientational motions of NH₃ and BF₄⁻. Splitting some of the infrared bands at T_C2=117 K suggests reducing of crystal symmetry at this phase transition. Sudden narrowing of the bands connected with ν₂(BF₄), ν₄(BF₄) and ρ_r(NH₃) modes at T_C3=101 K implies slowing down (τ_R?10⁻¹⁰ s) of the fast uniaxial reorientational motions of the BF₄⁻ anions and NH₃ ligands at this phase transition.     

A C2-symmetric ratiometric fluorescence and colorimetric anion sensor based on pyrrole derivative

A C₂-symmetric fluorescence and colorimetric anion sensor (1) based on pyrrole derivative was designed and synthesized according to binding site-signaling subunit approach. The compound 1 was easily prepared by reaction of pyrrole-2,5-dicarboxaldehyde with 4-nitrophenylhydrazine in ethanol (yield=78%). In DMSO, the sensor 1 exhibited a visible color change from red to brown upon exposure to anions such as AcO⁻ and F⁻; however, no obvious color changes were observed when the other tested anions (e. g. H₂PO₄⁻, Cl⁻, Br⁻ and I⁻) were added. There was a significant redshift (Δλ_max=160 nm) in UV-vis spectrum during UV-vis spectral titrations. In particular, the sensor 1 showed ratiometric fluorescence responses to anions.     

H nuclear magnetic resonance study of the ferroelastic and superionic phase transitions of (NH4)4LiH3(SO4)4 single crystals

We investigated the temperature dependences of the line shape, spin-lattice relaxation time, T₁, and spin-spin relaxation time, T₂, of the ¹H nuclei in (NH₄)₄LiH₃(SO₄)₄ single crystals. On the basis of the data obtained, we were able to distinguish the “ammonium” and “hydrogen-bond” protons in the crystals. For both the ammonium and hydrogen-bond protons in (NH₄)₄LiH₃(SO₄)₄, the curves of T₁ and T₂ versus temperature changed significantly near the ferroelastic and superionic phase transitions at T_C (=232 K) and T_S (=405 K), respectively. In particular, near T_S, the ¹H signal due to the hydrogen-bond protons abruptly narrowed and the T₂ value for these protons abruptly increased, indicating that these protons play an important role in this superionic phase transition. The marked increase in the T₂ of the hydrogen-bond protons above T_S indicates that the breaking of O-H?O bonds and the formation of new H-bonds with HSO₄^- contribute significantly to the high-temperature conductivity of (NH₄)₄LiH₃(SO₄)₄ crystals.     

Improved luminescent properties of red-emitting Ca0.54Sr0.16Eu0.08Gd0.12(MoO4)0.2(WO4)0.8 phosphor for LED application by charge compensation

The red-emitting Ca_0.54Sr_0.16Eu_0.08Gd_0.12(MoO₄)_0.2(WO₄)_0.8 phosphor is improved in the emission charateristics by charge compensation, of which chromaticity coordinates (CIE) are x=0.66 and y=0.33. Three approaches to charge compensation are investigated, namely (a) 3Ca²⁺/Sr²⁺→2Eu³⁺/Gd³⁺+vacancy, (b) 2Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+M⁺(M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ employed as a charge compensator) and (c) Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+N⁻ (N⁻ is a monovalent anion like F⁻, Cl⁻, Br⁻ and I⁻ employed as charge compensation ions). Through photoluminescent spectra analyzing the radiative and non-radiative relaxation mechanisms of luminescent system are obtained. Under 20 mA forward-bias current, one red-emitting LED is made by combining 390-405 nm-emitting LED chip and the phosphor. The red-emitting phosphor has broad prospects in LED application field.     

Near-infrared luminescence of OH and Cl doped Bi4Ge3O12 crystals

OH⁻ and Cl⁻ doped Bi₄Ge₃O₁₂ (BGO) single crystals had been grown by Vertical Bridgman (VB) method. The structure of these crystals was determined by XRD, the transmittance and emission spectra in near infrared region (NIR) were measured at room temperature. 5% OH⁻ doped BGO shows a significant emission band peaking around 1181 nm under 808 nm laser diodes (LDs) excitation, and the 5% Cl⁻ doped BGO exhibits a relatively weak emission band as well. 100% and 5% OH⁻ doped BGO show noticeable emission band centered at about 1346 nm under 980 nm LDs excitation.     

MO study of counter anions of TMTSF: Electronic structure of NO−3, BF−4, ClO−4 and FSO−3

The electronic structure and geometrical structure of NO^-₃, BF^-₄, ClO^-₄ and FSO^-₃ anions are studied by means of the ab initio molecular orbital method. According to the results obtained, the central atoms of these anions are all positively charged and the surrounding atoms negatively charged. The bonding nature of ClO^-₄ and FSO^-₃ is similar to that of XF^-₆ (X = P, As and Sb) previously studied, and has a coordination-like character. However, BF^-₄ and NO^-₃ show a covalent-like character. The ion radii of these anions are determined from the total density contour maps obtained by the calculation.     

Removal of organic dye by air and macroporous ZnO/MoO3/SiO2 hybrid under room conditions

A new macroporous ZnO/MoO₃/SiO₂ hybrid was synthesized by a method involving sol-gel technology and biomimetic synthesis. It was characterized by Elemental analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and scanning electron microscopy (SEM). Chemical degradation of 0.3 g/L Safranin T (ST) by air oxidation over macroporous ZnO/MoO₃/SiO₂ hybrid was studied. It was found that the decolorization efficiency and the chemical oxygen demand (COD) removal of ST reached above 95.3% and 93.2%, respectively, within 25 min at room temperature and atmospheric pressure. And the organic pollutant was mineralized to simple inorganic species such as HCO₃⁻, Cl⁻ and NO₃⁻, while the total organic carbon (TOC) decreased 95.4%. The structure and morphology of the catalyst were still stable after six cycling runs and the leaching test showed negligible leaching effect.     

Heats of solution/substitution in TlNO3 and CsNO3 crystals and in RbNO3 and CsNO3 crystals from heats of transition: the complete phase diagrams of TlNO3-CsNO3 and RbNO3-CsNO3 systems

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope ΔH_t/x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, ΔH_s^°, of Tl⁺ in CsNO₃ crystal and Cs⁺ in TlNO₃ crystal and Rb⁺ in CsNO₃ crystal and Cs⁺ in RbNO₃ crystal along with their recovered lattice energies, ΔH_L^°, are reported. ΔH_s^° of Tl⁺ and Rb⁺ in CsNO₃ crystal are each found to be negligible or zero representing an ideal solid solution, i.e. ΔH_mix=0. The complete phase diagrams of the TlNO₃-CsNO₃ and RbNO₃-CsNO₃ systems with details of the sub-solidus regions are included. The properties of Tl_(1−x)Cs_xNO₃ and Rb_(1−x)Cs_xNO₃ compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl_(1−x)Rb_xNO₃.     

High-pressure Raman spectroscopic studies on orthophosphates Ba3(PO4)2 and Sr3(PO4)2

By using diamond anvil cell (DAC), high-pressure Raman spectroscopic studies of orthophosphates Ba₃(PO₄)₂ and Sr₃(PO₄)₂ were carried out up to 30.7 and 30.1 GPa, respectively. No pressure-induced phase transition was found in the studies. A methanol:ethanol:water (16:3:1) mixture was used as pressure medium in DAC, which is expected to exhibit nearly hydrostatic behavior up to about 14.4 GPa at room temperature. The behaviors of the phosphate modes in Ba₃(PO₄)₂ and Sr₃(PO₄)₂ below 14.4 GPa were quantitatively analyzed. The Raman shift of all modes increased linearly and continuously with pressure in Ba₃(PO₄)₂ and Sr₃(PO₄)₂. The pressure coefficients of the phosphate modes in Ba₃(PO₄)₂ range from 2.8179 to 3.4186 cm⁻¹ GPa⁻¹ for ν₃, 2.9609 cm⁻¹ GPa⁻¹ for ν₁, from 0.9855 to 1.8085 cm⁻¹ GPa⁻¹ for ν₄, and 1.4330 cm⁻¹ GPa⁻¹ for ν₂, and the pressure coefficients of the phosphate modes in Sr₃(PO₄)₂ range from 3.4247 to 4.3765 cm⁻¹ GPa⁻¹ for ν₃, 3.7808 cm⁻¹ GPa⁻¹ for ν₁, from 1.1005 to 1.9244 cm⁻¹ GPa⁻¹ for ν₄, and 1.5647 cm⁻¹ GPa⁻¹ for ν₂.     

Electron paramagnetic resonance investigation of K3H(SO4)2 proton conductor doped with Cr ion

The proton arrangement around SO₄ units in K₃H(SO₄)₂ (KHS) was studied in detail by X-band CW EPR spectra of CrO₄³⁻ paramagnetic centre incorporated into KHS during the crystal growth process. The EPR data prove the theoretical model of coherent motion of protons and SO₄ units at the fast-proton conducting phase proposed by Ito and Kamimura.     

Template-free synthesis of MnO2 nanowires with secondary flower like structure: Characterization and supercapacitor behavior studies

Manganese dioxide (MnO₂) nanowires with diameter about 30-70 nm is achieved via a two-step process: first, template-free cathodic electrodeposition from aqueous solution of Mn(NO₃)₂ on steel substrate and followed by heat treatment. The temperature-annealed sample was studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) methods and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical performance of the MnO₂ sample was studied by cyclic voltammetry (CV) and chronopotentiometry in Na₂SO₄ solutions. The sample showed excellent supercapacitive behavior. The specific capacitance (SC) of 237 F g⁻¹ in a potential window of 0-0.9V was obtained at the scan rate of 2 mV s⁻¹. The SC calculated from the chronopotentiometry data is about 246 F g⁻¹. The SC was decreased by 16% after 1000 cycles.     

High-Resolution Infrared Studies of ν1, 2ν1, and 2ν4 Bands of CHCl3

The C-H stretching fundamental band ν₁ (3033 cm⁻¹) of chloroform CH³⁵Cl₃ has been investigated together with the first overtone 2ν₁ (5941 cm⁻¹) in order to determine the rotation vibration parameters. From the ν₁ band α₁^C=−0.025 46(41)×10⁻³ cm⁻¹ and α₁^B=−0.010 688(44)×10⁻³ cm⁻¹ were obtained. The hot bands connected to the low lying fundamentals ν₃ and ν₆ have been analyzed and anharmonicity constants have been derived. Both the parallel and the perpendicular component band of the C-H bending overtone 2ν₄ have also been studied. In the parallel band (2410 cm⁻¹) more than 900 lines were included in the fit. In the perpendicular band (2443 cm⁻¹) 2615 lines were fitted using a model with one resonance. Among other things the results C₀−C_v=0.025 262 (20)×10⁻³ cm⁻¹, B₀−B_v=0.134 883 (25)×10⁻³ cm⁻¹, and (Cζ)_v=−0.111 867 56 (30) cm⁻¹ were obtained.     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

High temperature and low current density synthesis of Mn3O4 porous nano spheres: Characterization and electrochemical properties

Uniform and single-crystalline Mn₃O₄ nano-spheres were synthesized by cathodic electrodeposition at high temperature (80 °C) and low current density (0.25 mA cm⁻¹) on steel electrode. Further the annealed samples were characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) studies. TEM and SEM images showed that particles have spherical shapes and the average diameter size was about 50 nm. Formation of Mn₃O₄ compound was confirmed from FTIR studies. The XRD pattern showed that the Mn₃O₄ exhibit tetragonal hausmannite structure. The results of N₂ adsorption-desorption analysis indicated that Mn₃O₄ nano-sphere has BET surface area of about 177.6 m² g⁻¹ and average pore diameters of 3 and 4 nm. The possible formation mechanism of Mn₃O₄ nanostructures has been discussed. The supercapacitive properties of Mn₃O₄ sample in 0.5 M Na₂SO₄ electrolyte showed maximum supercapacitance of 235.4 Fg⁻¹ at scan rate 10 mV s⁻¹. Coulumbic efficiency could be kept about 90% during 1000 cycles at 10 mV s⁻¹.     

High resolution fourier transform spectrum of PD3 in the region of the stretching overtone bands 2ν1 and ν1+ν3

The infrared spectrum of the PD₃ molecule has been measured in the region of the first stretching overtone bands on a Fourier transform spectrometer with a resolution of 0.0068 cm⁻¹ and analyzed for the first time. More than 800 transitions with J^max=15 have been assigned to the bands 2ν₁ and ν₁+ν₃. An effective Hamiltonian was used which takes into account both the presence of resonance interactions between the states (2 0 0 0) and (1 0 1 0), and interactions of these with the third stretching vibrational state of the v=2 polyad, (0 0 2 0). A set of 44 spectroscopic parameters is obtained from the fit. This reproduces the 305 initial “experimental” upper rovibrational energies with an rms=0.0015 cm⁻¹.     

Role of Cl ions in photooxidation of propylene on TiO2 surface

The effect of Cl⁻ ions on photooxidation of propylene on TiO₂ semiconductor was investigated. Cl⁻/TiO₂ catalysts were prepared by annealing Degussa P25 TiO₂ in the gas flow of N₂ and Cl₂ under 100-400 °C. The photocatalytic oxidation of propylene was carried out in a continuous flow system, with the chromatograph to analyze the products on line. The experimental results showed that the activity of Cl⁻/TiO₂ catalysts increased as heat-treated temperature decreased. The activity of the sample heat-treated at 100 °C was about two times higher than that of pure TiO₂. Moreover, as to TiO₂, the main product of the propylene photocatalytic oxidation was CO₂, but with Cl⁻/TiO₂ catalysts, not only CO₂ but also trace CO was determined. The adsorbed species on TiO₂ surface before and after reaction were analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric/differential thermal analyses (TG-DTA) coupled to a mass spectrometer (MS). XPS analysis showed that there was Cl⁻ absorbed on the Cl⁻/TiO₂ surface, and the absorption amount of Cl⁻ decreased after the photooxidation reaction of propylene. TG-DTA-MS analysis confirmed chlorine absorbed on the surface of TiO₂ in the form of Cl⁻ ion. These results illuminated that absorbed Cl⁻ on the surface of TiO₂ formed a weak physical absorption on TiO₂ at low temperature, and subsequently participated in the photooxidation of propylene, finally removed from TiO₂ surface.     

Preparation and characterization of cerium oxide doped TiO2 nanoparticles

A mixed oxide consisting of TiO₂ as the major phase and CeO_2−y (0<y<0.5) as the dopant phase was prepared via the sol-gel reaction of Ti(i-OC₃H₇)₃ in an aqueous solution of Ce(NO₃)₃. The resulting oxide powders with different CeO_2−y contents were all composed of nano-sized spheres. The CeO_2−y phase was identified to have retarding effect on the phase transition from anatase TiO₂ to rutile TiO₂ at calcinations temperature as high as 800 °C, which would otherwise be a thorough conversion. The CeO_2−y-TiO₂ powders could apparently shift the UV-absorption band of TiO₂ toward visible range, and there was an optimal CeO_2−y content in association with the maximum absorbance. This effect is interpreted as the existence of an n-type impurity band, due to the substitution of Ti⁴⁺ for Ce^3+/4+ at the interface between the two oxides, in the gap of TiO₂. According to X-ray photoelectron spectroscopy (XPS) investigation, the Ti element mainly existed as the chemical state of Ti⁴⁺ and the Ce oxide doping did not affect the peak position of Ti 2p. The Ce 3d spectrum of CeO_2−y-doped TiO₂ sample basically denotes a mixture of Ce^3+/4+ oxidation states giving rise to a myriad of peaks.