The Hazardous Origin of Photocatalytic Activity of ZnCr2O4

The ZnCr₂O₄ catalysts are synthesized by thermal decomposition of (NH₄)₂[Zn(NH₃)₂(CrO₄)₂] and materials with high surface areas and particle sizes in the nano regime are obtained. A special structural feature of the materials are stacking faults with densities strongly depending on the synthesis temperature, i.e. the lower the temperature the larger the number of stacking faults. The catalyst prepared at the lowest decomposition temperature exhibiting the smallest particle size shows the highest catalytic activity in the photocatalytic degradation of y‐Eosin in a photo‐Fenton process. The results of different analytic methods demonstrate that the high catalytic activity is directly correlated with CrO₄^2– anions generated via photo‐oxidation of the catalyst. Therefore, ZnCr₂O₄ cannot be regarded as an environmental friendly catalyst for advanced photocatalytic oxidation processes.     

尖晶石型CoCr_2O_4催化剂上二氯甲烷高效催化燃烧

采用共沉淀法在不同焙烧温度下制备一系列尖晶石型CoCr_2O_4催化剂并测试其对CH_2Cl_2催化燃烧性能.制备的催化剂都具有高的反应活性,并发现其性能受到表面酸性和氧化还原性的协同作用.经600℃焙烧的CoCr_2O_4-6催化剂因其具有较高的表面酸量(0.46 mmol·gcat~(-1))和较高表面吸附氧浓度(O_(ads)/O_(lat)=0.55),因此活性最佳,其T_(50)为201℃,T_(90)为278℃.由XRD等结构表征可知该催化剂含CoCr_2O_4和Cr_2O_3两相,但CoCr_2O_4尖晶石是该催化剂的主要活性组分.     

Magnetic and electronic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by first-principles density functional calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d2) and Cr3+ 3d (d3) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 microB for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t2g (t2g3) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.     

CoCr2O4型催化剂上二氯甲烷的高效催化燃烧

采用共沉淀法在不同焙烧温度下制备一系列尖晶石型CoCr2 O4催化剂并测试其对CH2 Cl2催化燃烧性能．制备的催化剂都具有高的反应活性,并发现其性能受到表面酸性和氧化还原性的协同作用．经600℃焙烧的CoCr2 O4-6催化剂因其具有较高的表面酸量（0．46 mmol·gcat－1）和较高表面吸附氧浓度（Oads／Olat＝0．55）,因此活性最佳,其T50为201℃,T90为278℃．由XRD等结构表征可知该催化剂含CoCr2 O4和 Cr2 O3两相,但CoCr2 O4尖晶石是该催化剂的主要活性组分．     

Initial Studies on the Oxide System Cr2O3–Sb2O4

Differential thermal analysis (DTA) and X-ray diffraction (XRD) were utilized to study the phase equilibrium established in the subsolidus area of the system Cr₂ O₃ –Sb₂ O₄ . It was found that the components of the title system interact in ambient air to produce CrSbO₄ . The compound is stable up to ~1380°C, at which temperature it starts to decompose. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cr2O3-Co3O4／SiO2对十八醇氧化生成十八酸反应的催化性能

 制备了一系列不同Cr／Co比例的Cr2O3－Co3O4／SiO2催化剂，并用XRD，FT－IR和BET等手段对催化剂进行了表征；考察了催化剂对十八醇氧化生成十八酸反应的催化性能，及反应条件（反应温度和反应时间）对催化性能的影响，确定了最佳反应条件．结果表明，金属硝酸盐在773K焙烧后转变成相应的氧化物并负载于二氧化硅上．Cr2O3－Co3O4／SiO2催化剂对十八醇氧化反应有很高的催化活性，十八酸选择性最高可达99．93％，收率可达52．44％．Cr2O3－Co3O4／SiO2催化剂的活性明显高于单一的Cr2O3／SiO2或Co3O4／SiO2催化剂     

Preparation, characterization and gas-sensitive properties of nano-crystalline Cr2O3Fe2O3 mixed oxides

A series of Fe₂-_xCr_xO₃(x = 0, 0.4, 0.8, 1.2, 1.6, 2.0) mixed oxides have been prepared with the chemical coprecipitation method and characterized by specific surface area, transmission electron microscopy (TEM), powder X-ray diffraction (XRD), IR and Mössbauer spectroscopy. Single-phase Fe-Cr mixed oxide nano-crystalline powders with corundum structure are obtained, and the results of the five characterization methods are well accordant with each other. Furthermore, gas-sensitive properties of the sensors made of the oxide powders have been studied.     

Solubility in the systems KClO4-RbClO4-H2O,KBrO3-RbBrO3-H2O,KIO3-CsIO3-H2O,RbClO4-CsClO4-H2O,RbBrO3-CsBrO3-H2O,RbIO3-CsIO3-H2O at 25°

Conclusions The solubility in the systems KClO₄-RbClO₄-H₂O, KBrO₃-RbBrO₃-H₂O, KIO₃-CsIO₃-H₂O, RbClO₄-CsClO₄-H₂O, RbBrO₃-CsBrO₃-H₂O, RbIO₃-CsIO₃-H₂O was studied at 25°. In all cases the formation of continuous series of solid solutions was established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2631–2634, December, 1971.The authors would like to express their gratitude to A. I. Vulikh for his constant interest in this work and his valuable advice.     

Polymerization of aniline derivatives by K2Cr2O7 and production of Cr2O3 nanoparticles

Oxidative polymerization of aniline, anthranilic acid, and aniline‐co‐anthranilic acid by potassium dichromate Cr(VI) as an oxidant in acidic medium was investigated. In this study, the polymerization process of aniline, o‐anthranilic acid as well as aniline/o‐anthranlic acid using K₂Cr₂O₇ produced, coordinated Cr(III)/polyaniline (PANI), Cr(III)/polyanthranilic acid (PAA) and Cr(III)/poly aniline‐co‐anthranilic acid (PANAA). The mechanism of polymerization reaction in the presence of dichromate was hypothesized. The precursor chromium doped polymers were characterized by TGA, FT‐IR, UV‐visible, XRD analyses. Cr₂O₃ nanoparticles size were determined using TEM analysis. The calcinations process of synthesized chromium doped PANI, PAA and PANAA yields Cr₂O₃ nanoparticles 26%, 31%, and 34% wt. respectively. Rhombohedral phase of Cr₂O₃ particles in the range from 33 to 61 nm was produced from chromium/polyanthranilic acid (PAA) and chromium/poly(aniline‐co‐anthranilic acid) PANAA. UV‐ visible analysis showed that optical band gaps (E_g) of doped poly aniline and its derivatives are in the range from1.55 to 1.80 using Tacu's law. The band gap values reveal that the doped chromium emeraldine base can be used as semiconductor materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermodynamics of ionization of D2O and D2PO 4 −

The quotients for the ionization of D₂O and the neutralization of D₂PO ₄ ^– have been determined potentiometrically in 0.2m KCl from 50 to 300°C at the saturation pressure. By combination with the other data, analytical expressions for the dependence on temperature and ionic strength have been derived. Rounded values for the thermodynamic quantities for the ionization of D₂O and the neutralization of D₂PO ₄ ^– are given along with standard errors. The magnitude of the isotope effects is discussed in terms of the zero-point-energy approximation and the acid strength in light water.ORAU Summer Trainee Program 1973.     

Structural investigation of Cr2B3, Cr3B4, and CrB by single-crystal diffractometry

The crystal structures of Cr₂B₃, Cr₃B₄, and CrB, of which Cr₂B₃ is a new compound, were investigated by single-crystal X-ray diffractometry. Cr₂B₃ crystallizes in the orthorhombic space groupCmcm witha = 3.0264(5), b = 18.115(4), c = 2.9542(4)A˚, Z = 4. The intensity data were collected on a four-circle diffractometer with graphite-monochromatizedMoKα radiation. The structure was solved by the Patterson method and refined with a full-matrix least-squares program to anR value (= Σ|ΔF|Σ|F_o|) of 0.021 for 1310 reflections. The structures of Cr₃B₄ and CrB were refined starting from published data; theR values were 0.032 (Cr₃B₄) and 0.022 (CrB). The structure of Cr₂B₃ can be described by stacking sheets of the AlB₂ structure type in the same manner as in the cases of Cr₃B₄ and CrB. The fusion of two neighboring sheets is performed by a 5Cr tetragonal pyramid and a Cr-B direct bond at their boundary. The essential difference between the structures of these compounds is only in the widths of the sheets. The relations of the widths of the sheets to the bond distances and angles of boron atoms are discussed.     

Spin dimer analysis of the magnetic structures of Ba3Cr2O8, Ba3Mn2O8, Na4FeO4, and Ba2CoO4 with a three-dimensional network of isolated MO4 (M = Cr, Mn, Fe, Co) tetrahedra

The spin exchange interactions of the magnetic oxides Ba3Cr2O8, Ba3Mn2O8, Na4FeO4, and Ba2CoO4 with a three-dimensional network of isolated MO4 (M = Cr, Mn, Fe, Co) tetrahedra were examined by performing spin dimer analysis on the basis of tight-binding electronic structure calculations. Although the shortest O...O distances between adjacent MO4 tetrahedra are longer than the van der Waals distance, our analysis shows that the super-superexchange interactions between adjacent MO4 tetrahedra are substantial and determine the magnetic structures of these oxides. In agreement with experiment, our analysis predicts a weakly interacting isolated AFM dimer model for both Ba3Cr2O8 and Ba3Mn2O8, the (0.0, 0.5, 0.0) magnetic superstructure for Na4FeO4, the (0.5, 0.0, 0.5) magnetic superstructure for Ba2CoO4, and the presence of magnetic frustration in Ba2CoO4. The comparison of the intra- and interdimer spin exchange interactions of Ba3Cr2O8 and Ba3Mn2O8 indicates that orbital ordering should be present in Ba3Cr2O8.     

Synthesis of Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 nanoparticles and their electrocatalytic properties

Two important iron oxides:Fe3O4 and Fe2O3,as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure.The samples were confirmed and characterized by X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The morphology of the samples was observed by transmission electron microscopy(TEM).The results indicated Fe3O4,Fe2O3,Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes.The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated.The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode.Furthermore,p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.     

Synthesis and characterization of Al2O3/Cr2O3-based ceramic pigments

The synthesis and the characterization of Al₂O₃-based nanocrystalline inorganic pigments are reported. The pigments were synthesized by the polymeric precursor (Pechini method) using Cr₂O₃ as chromophore. XRD results only evidenced the corundum phase. The average particle size was about 34 nm. The samples were also characterized by differential scanning calorimetry (DSC) and thermogravimetry (TG), and CIE-L*a*b* calorimetry. The pigments obtained in this work presented different colors, ranging from green to rose. This revised version was published online in August 2006 with corrections to the Cover Date.     

ZnGa2O4∶Cr3+红色荧光粉的光致及电致发光性能

采用柠檬酸络合溶胶-凝胶法合成ZnGa2O4∶Cr3 红色荧光粉,在空气气氛中1000℃煅烧得到ZnGa2O4单相.对粉体进行X射线光电子能谱(XPS)和电子顺磁共振(EPR)测试,结果显示,在空气气氛中煅烧,铬离子以三价形式存在(Cr3 ),未出现高价铬离子(Cr5 ,Cr6 ).Cr3 取代Ga3 占据八面体格位,位于695nm的红光发射带属于Cr3 的2E-4A2跃迁.Cr3 的激发带与基质发射带间有大面积重叠,两者间存在有效的能量传递.利用丝网印刷方法制成电致发光器件,与硫化物电致发光器件相似,ZnGa2O4∶Cr3 电致发光器件的亮度与电压满足L=L0exp(-bV-1/2)关系,且亮度与频率成正比.器件的Q-V曲线为闭合回路,发光效率η约为13lm·W-1.     

Impedance-based total-NOx sensor using stabilized zirconia and ZnCr2O4 sensing electrode operating at high temperature

We report here a new-type zirconia-based sensor that can detect total NO_x content at high temperatures such as 700 °C. A closed-one-end yttria-stabilized zirconia (YSZ) tube was used as a base sensor material. An oxide sensing electrode (SE) and a Pt counter electrode (CE) were formed on the outer and inner surfaces of the YSZ tube, respectively. The complex impedance of the device using a ZnCr₂O₄-sensing electrode was measured with an impedance analyzer in the frequency and the temperature ranges 0.1 Hz–100 kHz and 600–700 °C, respectively. A large semicircular arc was observed in complex impedance plots (Cole–Cole plots) in the lower frequency range examined and it seemed to correspond to the electrolyte/electrode interface. The impedance value at 1 Hz of the present device was found to vary almost linearly with the concentration of NO (or NO₂) from 50 to 400 ppm in the sample gas at 600–700 °C. Furthermore, it is noted that the sensitivity of NO is almost equal to that of NO₂. This means that the present device can detect the total NO_x at higher temperatures.     

Solubility in the system Na2Cr2O7 + 2NH4Cl ⇆ (NH4)2Cr2O7 + 2NaCl-H2O

The solubility in the water-salt quaternary reciprocal system Na₂Cr₂O₇ + 2NH₄Cl ⇆ (NH₄)₂Cr₂O₇ + 2NaCl-H₂O has been investigated for the first time at 25, 50, and 75°C. Using a formal analytical model, the boundaries of the phase fields have been determined, and the univariant lines and invariant points have been calculated. The experimental data have been used to calculate the temperature and concentration parameters of the circular isohydric process of potassium dichromate preparation with the participation of ammonium salts as intermediates.     

Ab initio calculations of nitrogen oxide reactions: formation of N2O2, N2O3, N2O4, N2O5, and N4O2 from NO, NO2, NO3, and N2O

Ab initio computational methods were used to obtain Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) for the reactions 2 NO <=> N(2)O(2) (I), NO+NO(2) <=> N(2)O(3) (II), 2 NO(2) <=> N(2)O(4) (III), NO(2)+NO(3) <=> N(2)O(5) (IV), and 2 N(2)O <=> N(4)O(2) (V) at 298.15 K. Optimized geometries and frequencies were obtained at the CCSD(T) level for all molecules except for NO, NO(2), and NO(3), for which UCCSD(T) was used. In all cases the aug-cc-pVDZ (avdz) basis set was employed. The electronic energies of all species were obtained from complete basis set extrapolations (to aug-cc-pV5Z) using five different extrapolation methods. The [U]CCSD(T)/avdz geometries and frequencies of the N(x)O(y) compounds are compared with literature values, and problems associated with the values and assignments of low-frequency modes are discussed. The standard entropies are compared with values cited in the NIST/JANAF tables [NIST-JANAF Thermochemical Tables, J. Phys. Chem. Ref. Data Monograph No. 9, 4th ed. edited by M. W. Chase, Jr. (American Chemical Society and American Institute of Physics, Woodbury, NY, 1988)]. With the exception of I, in which the dimer is weakly bound, and V, for which thermodynamic data appears to be lacking, the calculated standard thermodynamic functions of reaction are in good agreement with literature values obtained both from statistical mechanical and various equilibrium methods. A multireference-configuration interaction calculation (MRCI+Q) for I provides a D(e) value that is consistent with previous calculations. The combined uncertainties of the NIST/JANAF values for Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) of II, III, and IV are discussed. The potential surface for the dissociation of N(2)O(4) was explored using multireference methods. No evidence of a barrier to dissociation was found.