The relationship between SnII fraction and visible light activated photocatalytic activity of SnOx·SiO2 glass studied by Mössbauer spectroscopy

The relationship between local structure and visible-light photocatalytic ability of tin silicate glass prepared by sol–gel method was investigated. ¹¹⁹Sn Mössbauer spectrum of SnO_x·SiO₂ glass prepared from SnCl₂ showed a small peak of Sn^II component besides the major amount of Sn^IV. The smallest bandgap energy of 2.5 ± 0.5 eV was estimated from Tauc plot, and the largest first order rate constant (k) of (13.8 ± 0.1) 10⁻³ min⁻¹ was recorded from the methylene blue degradation test under visible-light irradiation. It is concluded that Sn^II shows remarkable photocatalytic ability when it is incorporated into silica glass matrix.

     

Meta-substituted Ru rigid rods for sensitization of TiO2

Ruthenium polypyridyl rigid-rod compounds with phenylene–ethynelene (OPE) spacers and an isophthalic acid (Ipa) binding group were synthesized and characterized for sensitization of nanocrystalline TiO₂ (anatase) thin films. Density functional theory predicted that the most stable structure oriented the isophthalic group about 45° from normal to the TiO₂ surface. Comparative experimental studies of meta- and para-isomers revealed small changes in the ground state absorption spectra and very similar excited state and redox properties. The excited state injection yields (inj = 0.15 ± 0.03) into nanocrystalline TiO₂ and the subsequent charge recombination rates were found to be insensitive to the isomer utilized. Meta-substitution enabled the synthesis of sensitizers with two Ru^II sensitizers that displayed enhanced sunlight absorption relative to the monomeric compound.     

Semiconducting and quartz microbalance (QCM) humidity sensor properties of TiO2 by sol gel calcination method

Titanium dioxide (TiO₂) material was synthesized using the sol gel calcination method. The structural properties of the TiO₂ semiconductor were investigated by atomic force microscopy. The electrical conductivity of the TiO₂ was measured as a function of temperature and TiO₂ exhibits a conductivity of 2.55 × 10⁻⁶ S/m at room temperature with activation energy of 104 meV. The electrical conductivity of the TiO₂ at room temperature is higher than that of nanocrystalline TiO₂ (3 × 10⁻⁷ S/m) and TiO₂ thin film in air (5 × 10⁻⁹ S/m) and in vacuum (8.8 × 10⁻¹⁰ S/m). It was found that the electrical transport mechanism of the TiO₂ is controlled by thermally activated mechanism. The optical band gap of the TiO₂ powder sample was determined to be 3.17 eV, which is good in agreement with the bulk TiO₂ (E_g = 3.2 eV). Up to our knowledge, there is no any reported data about the band gap of TiO₂ nanopowder based on the diffused reflectance calculation. Quartz crystal microbalance (QCM) TiO₂ humidity sensor was prepared. The sensor indicates a large frequency change with an interaction occurred between TiO₂ and humidity molecules. The sensor exhibits a good repeatability when it was exposed to the moist air of 65% RH.     

Synthesis of novel cation-ordered compounds with fluorite-related structure prepared by oxidation of Sn-Ta-O pyrochlore

Pyrochlore-type oxide, Sn^II_1.64(Ta_1.88Sn^IV_0.12)O_6.58 was oxidized for exploring novel metastable phases. Two novel Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 phases with a fluorite-related structure, which was obtained as a pure phase, and with a rutile-related structure appearing as an impurity for the fluorite-related phase were successfully obtained similar to the previous Sn-Nb-O system. The ordered arrangement of respective cations of Sn and (0.94Ta+0.06Sn) in the precursor Sn^II_1.64(Ta_1.88Sn^IV_0.12)O_6.58 was left in the both oxidized Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 phases. In contrast to the previous Sn-Nb-O system, the cation-ordered α-PbO₂-related Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 could not be obtained in the present conditions. Such a difference between the Sn-Ta-O and Sn-Nb-O systems was interpreted by larger energy barrier of the transformation from the fluorite-related phase to α-PbO₂-related phase in Sn-Ta-O system than in Sn-Nb-O system.     

Synthesis,Structures, and Properties of Crystalline Salts with Radical Anions of Metal‐Containing and Metal‐Free Phthalocyanines

Radical anion salts of metal‐containing and metal‐free phthalocyanines [MPc(3?)]^.?, where M=Cu^II, Ni^II, H₂, Sn^II, Pb^II, Ti^IVO, and V^IVO ( 1 – 10 ) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C?N_imine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1 – 10 show new bands at 833–1041 nm in the NIR range, whereas the Q‐ and Soret bands are blue‐shifted by 0.13–0.25 eV (38‐92 nm) and 0.04–0.07 eV (4–13 nm), respectively. Radical anions with Ni^II, Sn^II, Pb^II, and Ti^IVO have S=1/2 spin state, whereas [Cu^IIPc(3?)]^.? and [V^IVOPc(3?)]^.? containing paramagnetic Cu^II and V^IVO have two S=1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal‐free phthalocyanine radical anions [H₂Pc(3?)]^.? (linewidth of 0.08–0.24 mT), broad EPR signals are manifested (linewidth of 2–70 mT) with g‐factors and linewidths that are strongly temperature‐dependent. Salt 11 containing the [Na^IPc(2?)]^? anions as well as previously studied [Fe^IPc(2?)]^? and [Co^IPc(2?)]^? anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3?)]^.? in 1 – 10 .     

Coordinatively Unsaturated Polynuclear Mixed-Valent Sn<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> and Cu<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> Oxo-Centered Carboxylates

The tetranuclear mixed-valent oxo-cluster [Sn^IISn^IVO(O₂CCF₃)₄]₂ (1) has been prepared by reacting SnCl₂ with AgO₂CCF₃ in a sealed ampoule at 90 °C. Alternatively, 1 was obtained by acidolysis of Ph₃SnSnPh₃ with trifluoroacetic acid in solution. The X-ray diffraction study of 1 revealed the presence of a Sn^IIOSn₂^IVOSn^II core comprised of the penta-coordinated divalent and six-coordinated tetravalent tin atoms. The ¹¹⁹Sn NMR studies confirmed the stability of the cluster in solution and the presence of two different oxidation states of tin. An acidolysis of Ph₃SnSnPh₃ in the presence of [Cu₂^II(O₂CCF₃)₄] followed by sublimation of the resulting product at 90 °C afforded the first trinuclear mixed metal Sn–Cu cluster [(C₆H₅)₂Sn₂^IVCu^IIO(O₂CCF₃)₆] (2). The X-ray diffraction analysis of 2 revealed the presence of two phenyl groups attached to the six-coordinated tin(IV) atoms and the tetragonal pyramidal environment of the copper(II) atom. Both complexes have been obtained free of exogenous ligands.     

不同浓度Sn4+离子掺杂TiO2的结构、性质和光催化活性

采用溶胶-凝胶法制备出纯TiO₂和不同浓度Sn⁴⁺离子掺杂的TiO₂光催化剂(TiO₂-Snx%, x%代表Sn⁴⁺离子掺杂的TiO₂样品中Sn⁴⁺离子摩尔分数). 利用X 射线衍射(XRD)、X 射线光电子能谱(XPS)和表面光电压谱(SPS)确定了TiO₂-Snx%催化剂的晶相结构和能带结构, 结果表明: 当Sn⁴⁺离子浓度较低时, Sn⁴⁺离子进入TiO₂晶格, 取代并占据Ti⁴⁺离子的位置, 形成取代式掺杂结构(Ti_1-xSn_xO₂), 其掺杂能级在导带下0.38 eV处; 当Sn⁴⁺离子浓度较高时, 掺入的Sn⁴⁺离子在TiO₂表面生成金红石SnO₂, 形成TiO₂和SnO₂复合结构(TiO₂/SnO₂), SnO₂的导带位于TiO₂导带下0.33 eV处. 利用瞬态光电压谱和荧光光谱研究了TiO₂-Snx%催化剂光生载流子的分离和复合的动力学过程, 结果表明, Sn⁴⁺离子掺杂能级和表面SnO₂能带存在促进光生载流子的分离, 有效地抑制了光生电子与空穴的复合; 然而, Sn⁴⁺离子掺杂能级能更有效地增加光生电子的分离寿命, 提高了光生载流子的分离效率, 从而揭示了TiO₂-Snx%催化剂的光催化机理.     

Visible LED light photoelectrochemical sensor for detection of L-Dopa based on oxygen reduction on TiO2 sensitized with iron phthalocyanine

The present work describes the development of a new strategy to photoelectrochemical detection of L-Dopa at low potential based on oxygen reduction on TiO₂ sensitized with iron phthalocyanine (FePc/TiO₂). The FePc/TiO₂ composite shows a photocurrent 10-fold higher than that of pure TiO₂ nanoparticles and it was 4-fold higher than that of FePc exploiting visible light. The band gaps of pure TiO₂ nanoparticles, FePc and FePc/TiO₂, calculated according to the Kubelka–Munk equation, were 3.22 eV, 3.11 eV and 2.82 eV, respectively. The FePc/TiO₂ composite showed a low charge transfer resistance in comparison to the photoelectrode modified with FePc or TiO₂. Under optimized conditions, the photoelectrochemical sensor shows a linear response range from 20 up to 190 μmol L^− 1 with a sensitivity of 31.8 μA L mmol^− 1 and limit of detection of 1.5 μmol L^− 1 for the detection of L-Dopa.     

SnIV Porphyrin Scaffolds for Axially Bonded Multiporphyrin Arrays: Synthesis and Structure Elucidation by NMR Studies

A simple, one‐step, supramolecular strategy was adopted to synthesize Sn^IV‐porphyrin‐based axially bonded triads and higher oligomers by using meso‐pyridyl Sn^IV porphyrin, meso‐hydroxyphenyl‐21,23‐dithiaporphyrin, and Ru^II porphyrin as building blocks and employing complementary and non‐interfering Sn^IV?O and Ru^II ??? N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. ¹H, ¹H–¹H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn^IV‐porphyrin‐based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady‐state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn^IV porphyrin to the axial 21,23‐dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru^II porphyrin unit(s), which quench the fluorescence of the Sn^IV porphyrin and 21,23‐dithiaporphyrin units.     

Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6 A. Phasenübergänge

Structure and Bonding in Transitition Metal Fluorides M^IIMe^IVF₆ A. Phase Transitions A summary outline of the structure types of all compounds M^IIMe^IVF₆ known so far is given. Compounds with a 3d transition metal ion in the M^II site crystallize in the cubic ordered ReO₃ lattice and the hexagonal LiSbF₆ structure. For cations with a Jahn- Teller unstable E_g ground state we have found a symmetry reduction to tetragonal and triclinic variants of those two lattice types in addition. Phase transitions between the different structures could be observed by Guinier techniques in the temperature range 80 K < T < 800 K in many cases. The relative stability of the hexagonal low temperature phases in comparison to the cubic high temperature modifications is extensively discussed on the basis of geometric parameters and the electronic properties of the Me^IV and M^II ions. Quite a number of compounds M^IIMe^IVF₆ was prepared and characterized for the first time. The results of the spectroscopic investigation will be published later.     

Nanocomposite of a chromium Prussian blue with TiO2. Redox reactions and the synthesis of Prussian blue molecule-based magnets

The reaction of [NEt₄]₃[Cr(CN)₆] with titanium(III) p-toluenesulfonate at a pH of 2 affords a gray solid whose metal content and spectroscopic and magnetic properties are fully consistent with it being a Prussian blue material of stoichiometry “Ti^III[Cr^III(CN)₆] · H₂O”. The carbon, nitrogen, and hydrogen content, however, are not consistent with this stoichiometry, and further investigation showed that the gray material has a powder X-ray diffraction profile, infrared spectrum, and magnetic properties very similar to those of the “all-chromium” Prussian blue Cr^II[Cr^III(CN)₆]_0.67 · 6H₂O. All data, including the C, H, and N weight percentages, are consistent with the conclusion that the material isolated is a nanocomposite of Cr^II[Cr^III(CN)₆]_0.67 · xH₂O and TiO₂ in the ratio of 1–1.6. These results suggest that Ti^III reduces some of the [Cr^III(CN)₆]³⁻ ions to generate Ti^IV and Cr^II; the former hydrolyzes to amorphous TiO₂ · 2H₂O, the latter loses its bound CN ligands and reacts with unreacted [Cr^III(CN)₆]³⁻ ions to generate the crystalline all-chromium PB species. The electrochemical potentials suggest that the [Cr^III(CN)₆]³⁻ ion should not be reduced by Ti^III; evidently, this unfavorable reaction is driven by the insolubility of the reaction products. The results constitute a cautionary tale in two respects: first, that the characterization of Prussian blue materials must be conducted with care and, second, that the insolubility of Prussian blue analogues can sometimes drive reactions that in solution are thermodynamically unfavorable.     

Synthesis of Zn doped black TiO2 nanoparticles for degradation of 2, 4, 6 tri-chloro-phenol under visible light

A modified sol-gel method was used for synthesis of zinc doped black TiO₂ nanoparticles. The modified sol-gel synthesised catalyst was utilised for degradation of 2, 4, 6 tri-chloro-phenol under visible light irradiation. The catalyst was characterized using XRD, SEM, TEM, BET and DRS analysis. The nanoparticles were crystalline in nature and in anatase phase. The size of zinc doped black TiO₂ nanoparticles was 5 nm. The synthesised nanoparticles were mesoporous in nature and the specific surface area was found to be 34.15 m²/g. The band gap energy of zinc black TiO₂ nanoparticles was found to be 2.73 eV. The point of zero charge of zinc doped black TiO₂ nanoparticles was 6.7. The maximum degradation of 2, 4, 6 tri-chloro-phenol using 2 mol% zinc doped black TiO₂ was found to be 95%.     

Successful location of tin dopant cations on surface sites of anatase-type TiO2 crystallites evidenced by 119Sn Mössbauer spectroscopic probe and XPS techniques

The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. ¹¹⁹Sn Mössbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn⁴⁺-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift δ and quadrupole splitting ΔE_Q values (δ_I = 3.25 mm s⁻¹, ΔE_QI = 1.75 mm s⁻¹; and δ_II = 2.85 mm s⁻¹, ΔE_QII = 1.71 mm s⁻¹). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mössbauer spectra of Sn^4+←2+ daughter ions, formed upon contact with air of Sn²⁺, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift (<δ> = 0.07 mm s⁻¹) and quadrupole splitting (<ΔE_Q> = 0.50 mm s⁻¹), as compared to the δ and ΔE_Q values for the bulk-located Sn⁴⁺. However, considerable broadening of Sn^4+←2+ doublet components (Γ = 0.97 mm s⁻¹) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn²⁺ precursors. The occurrence of Sn^4+←2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3–5 nm thick surface layers.     

The structure of nitratotriphenylstannyltin(II): A compound with a tin(IV)tin(II) bond

A compound of formula [Sn^II(NO₃) [(C₆H₅)₃ Sn^IV], containing a tin(IV)tin(II) bond, has been prepared, and its crystal structure is determined.     

Photocatalytic decomposition of 4-chlorophenol over an efficient N-doped TiO2 under sunlight irradiation

Using a new nitrogen precursor of a mixture of ammonia and hydrazine hydrate, N-doped TiO₂ photocatalyst with a high efficiency under visible light was synthesized by a precipitation method. The analysis of X-ray photoelectron spectroscopy (XPS) suggested that the doping concentration of nitrogen was 0.45 at%, while it was 0.21 at% or 0.24 at% using single ammonia or hydrazine hydrate as nitrogen precursor. The patterns of the electron paramagnetic resonance spectroscopy (EPR) indicated that the paramagnetic species of NO₂^2?, NO and Ti³⁺ existed as the proposed active species. The ultraviolet–visible (UV–vis) spectra revealed that the band-gap of the N-doped TiO₂ was 3.12 eV, which was slightly lower than 3.15 eV of pure TiO₂. The N-doped TiO₂ showed higher efficiency under both ultraviolet (UV) and visible light irradiations. Moreover, the degradation grade of 4-chlorophenol (4-CP) using the as-synthesized N-doped TiO₂ under sunlight irradiation for 6 h was 82.0%, which was higher than 66.2% of the pure TiO₂, 60.1% or 65.2% of the N-doped TiO₂ using single ammonia or hydrazine hydrate as precursor. Density functional theory (DFT) calculations were performed to investigate the visible light response of the N-doped TiO₂. Our study demonstrated that the visible activities vary well with the concentrations of NO₂^2? species incorporated by N–TiO₂ series photocatalysts and the higher activity of the as-prepared N-doped TiO₂ was attributed to the enhancement of the concentration of NO₂^2? species.     

Distannabarrelenes with Three Coordinated SnII Atoms

Crystalline 1,4-distannabarrelene compounds [(ADC^Ar)₃Sn₂]SnCl₃ ( 3 - Ar ) (ADC^Ar={ArC(NDipp)₂CC}; Dipp=2,6-iPr₂C₆H₃, Ar=Ph or DMP; DMP=4-Me₂NC₆H₄) derived from anionic dicarbenes Li(ADC^Ar) ( 2 - Ar ) (Ar=Ph or DMP) have been reported. The cationic moiety of 3 - Ar features a barrelene framework with three coordinated Sn^II atoms at the 1,4-positions, whereas the anionic unit SnCl₃ is formally derived from SnCl₂ and chloride ion. The all carbon substituted bis-stannylenes 3 - Ar have been characterized by NMR spectroscopy and X-ray diffraction. DFT calculations reveal that the HOMO of 3 - Ph (ϵ=−6.40 eV) is mainly the lone-pair orbital at the Sn^II atoms of the barrelene unit. 3 - Ar readily react with sulfur and selenium to afford the mixed-valence Sn^II/Sn^IV compounds [(ADC^Ar)₃SnSn(E)](SnCl₆)_0.5 (E=S 4 - Ar , Ar=Ph or DMP; E=Se 5 - Ph ).     

Dye degradation studies of Mo‐doped TiO2 thin films developed by reactive sputtering

TiO₂ thin films with various Mo concentrations have been deposited on glass and n‐type silicon (100) substrates by this radio‐frequency (RF) reactive magnetron sputtering at 400°C substrate temperature. The crystal structure, surface morphology, composition, and elemental oxidation states of the films have been analyzed by using X‐ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy, respectively. Ultraviolet‐visible spectroscopy has been used to investigate the degradation, transmittance, and absorption properties of doped and undoped TiO₂ films. The photocatalytic degradation activity of the films was evaluated by using methylene blue under a light intensity of 100 mW cm⁻². The X‐ray diffraction patterns show the presence of anatase phase of TiO₂ in the developed films. X‐ray photoelectron spectroscopy studies have confirmed that Mo is present only as Mo⁶⁺ ions in all films. The Mo/TiO₂ band gap decreases from ~3.3 to 3.1 eV with increasing Mo dopant concentrations. Dye degradation of ~60% is observed in Mo/TiO₂ samples, which is much higher than that of pure TiO₂.     

Sol-gel powder synthesis in the TiO2-TeO2-ZnO system: Structural characterization and properties

The present study deals with the gel formation tendency in the ternary TeO₂-TiO₂-ZnO system. Depending on the TiO₂ amount, the gelation occurred at different times and subsequently several gel formation regions have been determined. Homogeneous, transparent and monolithic gels were obtained using combination of organic and inorganic precursors during the synthesis. Using XRD analysis it was established that upon the heating composites were obtained which contain an amorphous phase and different crystalline phases: TiO₂ (anatase), TiO₂ (rutile), α-TeO₂ and ZnTeO₃, depending on composition. The IR results showed that the short range order of the amorphous phases which are part of the composite materials consist of TiO₆, ZnO₄ and TeO₄ structural units. Using UV–Vis spectroscopy it was established that the absorption edge of the gels varied from 330 nm to 364 mm and the increase in TiO₂ content caused a red shifting of the cut-off. The calculated Eg values are in the range 3.41–3.75 eV higher than that of pure TiO₂, TeO₂ and ZnO oxides. The XPS results showed that the Te atoms in the surface layers of the samples studied exist in several chemical states as Te²⁺, Te⁰, but Te⁶⁺ dominates. Octahedrally coordinated Ti⁴⁺ ions are observed in the gels and in the samples annealed at 200 °C but a small amount of tetrahedrally coordinated Ti⁴⁺ is also detected, which indicates the incomplete polymerization of TiO₆ units.     

Complexes of organometallic compounds : XXXVII. Mössbauer and other studies on adducts of organotin(IV) chlorides with N,N′-ethylenebis(salicylideneiminato)-nickel(II)

Novel 1/1 adducts have been obtained from the complex N,N′-ethylenebis(salicylideneiminato)nickel(II) (NiSalen) with di- and mono-organotin(IV) chlorides, and their solid state configuration investigated by Mössbauer , IR and electronic spectroscopy and magnetic measurements. In coordinated NiSalen the square planar structure is maintained around Ni^II, and the coordination to tin involves three-coordinate phenolic oxygens. The environment of Sn^IV is judged to be octahedral in both types of compounds. A trans-R₂, cis-Cl₂ configuration is advanced for R₂SnCl₂NiSalen.     

Surface properties and photoactivity of TiO2 treated with electron beam

The improvement of the TiO₂-photoactivitiy by electron beam treatment (1 MeV) as a function of the absorbed radiation dose (MGy) is reported. The radiation-induced effects in the TiO₂ crystal structure, e.g. change of the Ti³⁺/Ti⁴⁺ ratio, increase of the photoactivity, etc. were investigated. Three methods were implemented in this respect: for the change of the TiO₂ crystal structure X-ray photoelectron spectroscopy and photoluminescence spectroscopy were applied. The photocatalytic activity of the EB-treated TiO₂ was tested by taking the degree of methylene blue photodegradation as a measure of the achieved effect. The obtained experimental data of all testing methods showed that in TiO₂ at an absorbed dose of 0.5 MGy optimum changes in crystal structure of the catalyst occur, resulting in the highest photocatalytic efficiencies.