Synthesis and study of Bi2Ti2O7/TiO2 composites as efficient visible-light-active photocatalysts in the reduction of aqueous Cr(VI)

In this work, Bi_2Ti_2O_7/TiO_2 composites were synthesized and studied as potential visible-light-activated photocatalysts in the reduction of aqueous Cr(VI). Bi_2Ti_2O_7/TiO_2 composites with tunable compositions were synthesized via a solvothermal-calcination two-step method, simply by changing the molar ratios of Bi(NO_3)_3·5H_2O to tetrabutyl titanate in the reactants. The compositions, structures and optical properties of the as-synthesized Bi_2Ti_2O_7/TiO_2 composites were characterized by X-ray diffraction, field emission scanning electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized Bi_2Ti_2O_7/TiO_2 composites was tested in the reduction of aqueous Cr(VI)under visible-light(λ420 nm) irradiation, and compared with that of TiO_2 nanoparticles. It was observed that the as-synthesized Bi_2Ti_2O_7/TiO_2 composites exhibited much higher photocatalytic activity than TiO_2 nanoparticles, and the most efficient composite(300 mg) can achieve the complete reduction of Cr(VI) in 300 mL of 50 mg/L K_2Cr_2O_7 aqueous solution under visible-light(λ420 nm)irradiation in 90 min.     

Photocatalytic degradation of amoxicillin by carbon quantum dots modified K2Ti6O13 nanotubes: Effect of light wavelength

Novel carbon quantum dots modified potassium titanate nanotubes (CQDs/K₂Ti₆O₁₃) composite was synthesized and exhibited high photocatalytic activity for degradation of amoxicillin under UV and visible lights with nine wavelengths. Better amoxicillin removal was achieved at lower wavelength irradiation due to its higher photo energy.     

Synthesis of titania and titanate nanomaterials and their application in environmental analytical chemistry

TiO₂ nanoparticles and H₂Ti₂O₅·H₂O, Na₂Ti₂O₄(OH)₂ nanotubes were synthesized by solvothermal method and their applications in the degradation of active Brilliant-blue (KN-R) solution were investigated. The experimental results revealed that the synthesized TiO₂ nanoparticles had a good crystallinity and a narrow size distribution (about 4–5 nm); the obtained H₂Ti₂O₅·H₂O, Na₂Ti₂O₄(OH)₂ were tubelike products with an average diameter of 20–30 and 200–300 nm length. The three catalysts we synthesized had some hydroxyl groups and the maximum absorption boundaries of the samples were all red-shifted, which indicated the samples had a promising prospect in photocatalysis.

The results of the photocatalytic experiments indicated that the photocatalytic activity of the samples was: TiO₂ > H₂Ti₂O₅·H₂O > Na₂Ti₂O₄(OH)₂, which was in good accordance with the fact of FTIR and UV–vis absorption spectra. The formation mechanism of these nanostructures was also discussed.     

Evidence of lanthanum–chromium mixed oxides formed in CrOx/La2O3 model catalysts

CrO_x/La₂O₃ mixed oxides, prepared by impregnating La₂O₃ with appropriate aqueous solutions of (NH₄)₂CrO₄ and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La₂CrO₆, La(OH)CrO₄ and LaCrO₄ under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm⁻¹, as well as weak peaks at 136, 180, 354, 370, and 388 cm⁻¹ in the RS spectrum of CrO_x/La₂O₃ have been assigned to La₂CrO₆.     

Ion size dominated 1D and 2D Salen lanthanide coordination complexes and their luminescence

Lewis acid/base addition between Ln(NO₃)₃ · 6H₂O (Ln = Pr, Nd, Sm, Eu, Tb and Lu) and H₂salen [H₂salen = N,N′-ethylenebis(salicylideneimine)] gives rise to an array of coordination polymeric structures. Crystal structural analysis reveals that Salen effectively functions as a bridging ligand in these compounds. The size of the lanthanide ions controls the structures of these Salen lanthanide complexes. Two representative structures with one dimensional and two dimensional topologies, viz. [Pr(H₂salen)(NO₃)₃(CH₃OH)₂]_n (1) and [Ln(H₂salen)_1.5(NO₃)₃]_n [Ln = Pr (2), Nd (3), Sm (4), Eu (5), Tb (6) and Lu (7)] are reported. Luminescent spectra of complexes 4 and 5 exhibit characteristic metal-centered emission lines. However, the characteristic luminescence of the terbium(III) ion is not observed either in solution or in the solid state of complex 6.     

Photocatalytic degradation and kinetics of Orange G using nano-sized Sn(IV)/TiO2/AC photocatalyst

Sn(IV) doped and nano-sized TiO₂ immobilized on active carbon (AC) (Sn(IV)/TiO₂/AC) were prepared by the sol–gel and dip-calcination method. An azo dye, Orange G (OG), was used as a model compound to study its photocatalytic activity in a fluidized bed photoreactor. The addition of Sn(IV) on TiO₂ could greatly improve the activity of TiO₂, and the optimal amount of tin was 2.5 at.%. The effects of calcination temperature, pH value, the initial hydrogen peroxide concentration ([H₂O₂]₀), the catalyst amount ([TiO₂]), the initial OG concentration ([dye]₀) and co-existing negative ions on the photocatalytic activity of Sn(IV)/TiO₂/AC were studied. The optimal conditions were as follows: pH 2.00, [H₂O₂]₀ = 1.5mL/L, [dye]₀ = 50 mg/L, [TiO₂] = 12.5 g/L, when the 300 W high pressure mercury light was used as the light source. Under these conditions, the degradation efficiency of OG reached 99.1% after 60 min reaction. The kinetics of the OG degradation was also analyzed. The results showed that the kinetics of this reaction fit the Langmiur–Hinshelwood kinetics model well and the absorption of OG on the Sn(IV)/TiO₂/AC surface was the controlling step in the whole degradation process. In addition, the catalyst, liquid and gas were separated effectively, and the integrative process of reaction and separation was achieved during the experiment.     

A novel method for the preparation of Bi4Ti3O12 nanoparticles in w/o microemulsion

Nanometer-sized Bi₄Ti₃O₁₂ particles have been prepared by chemical reaction of bismuth nitrate pentahydrate, titanium sulfate and ammonia solution in a reverse microemulsion system consisting of water, OP (P-octyl polyethylene glycol phenylether, non-ionic surfactant), n-butanol (co-surfactant), and cyclohexane (oil). Precursor hydroxides precipitated in the droplets of water-in-oil (w/o) microemulsion were calcined at 800 °C for 4 h to form Bi₄Ti₃O₁₂ nanoparticles. The samples were investigated with X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectrophotometer (FT-IR) and ultraviolet visible spectrophotometer (UV–vis). It was found that the as-prepared Bi₄Ti₃O₁₂ nanoparticles had small particle sizes (35 nm), high crystallinity, narrow size distributions and strong light absorption properties not only in the ultraviolet light but also in the visible light region.     

光热效应增强的Au/RGO/Na2Ti3O7光催化加氢性能

将典型的光热等离激元石墨烯和纳米金简便地负载在钛酸钠(Na₂Ti₃O₇)载体上, 构建出具有较窄禁带宽度和较高光催化活性的Au/RGO/Na₂Ti₃O₇光热辅助光催化体系. 研究发现, 石墨烯片层与金纳米颗粒在光照下, 通过局域表面等离激元共振效应诱导产生大量的热电子, 以活化反应物并降低反应活化能, 其引发的光热效应还可精准提升光催化体系中反应位点附近的温度, 从而大幅提升光催化反应速率. 通过构建特殊微支结构, 进一步增强了Au/RGO/Na₂Ti₃O₇催化剂对光的捕获, 并限域锚定高表面能催化剂以增强体系的稳定性. 在光热、 光催化的高效协同增强下, Au/RGO/Na₂Ti₃O₇催化剂体系对对硝基苯酚和肉桂醛的加氢反应均表现出增强的光催化活性. 光热辅助下的Au/RGO/Na₂Ti₃O₇光催化剂在对硝基苯酚反应中的转换频率（TOF）值高达54.4 min^-1, 反应活化能显著降低至15.78 kJ/mol, 且其在长效测试中表现出良好的稳定性（4次循环催化后, 转化率的保持率近90%）.     

Electrochemical and gas-phase photocatalytic performance of nanostructured TiO2(B) prepared by novel synthetic route

Nanostructured phase pure TiO₂(B) with microfibrous morphology was synthesized by newly developed protocol employing amorphous TiO₂ as a precursor. Compared to traditional syntheses from K₂Ti₄O₉, the new product exhibited better electrochemical performance and stability. Cyclic voltammetry of Li-insertion into the TiO₂(B) evidences a pseudocapacitive faradaic process of Li accommodation which is basically different from the diffusion-controlled lithium storage in anatase or rutile. The presence of two pairs of peaks in cyclic voltammogram with formal potentials of ca. 1.5 and 1.6 V is specific for TiO₂(B). This enables to use cyclic voltammetry for identification of this phase in a broad palette of TiO₂ materials of various origin.

The photocatalytic activity of TiO₂(B) in a gas phase was evaluated using the total oxidation of propane with oxygen and the photocatalytic reduction of NO to N₂ in an oxygen rich gas mixture. For the total oxidation of propane in the gas mixture containing 300 ppm propane and 20% oxygen, the reaction rates per 1 m²/g of the BET surface area of the catalyst for TiO₂(B) prepared by our protocol and Hombifine N (anatase, S_BET = 300 m²/g) are comparable. For the photocatalytic NO reduction to N₂ in an atmosphere containing 20% oxygen the ratio of quantum yields for TiO₂(B) and Hombifine N was found to be 0.08, which is roughly equivalent to the ratio of their BET surface areas (0.09), despite different phase composition of both materials. In comparison with the standard catalyst our material exhibited higher selectivity in the reduction of NO to N₂.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

Neutron diffraction evidence for a cationic order in the REMn0.5Ni0.5O3 (RE = La, Nd) and YMn0.5Co0.5O3 perovskites

The REMn_0.5Ni_0.5O₃ (RE = La, Nd) and YMn_0.5Co_0.5O₃ compounds, prepared by solid-state reaction under air, were investigated by X-ray diffraction (XRD) and neutron powder diffraction (NPD). The La-compound contains some lanthanum vacancies decreasing the lattice parameters and increasing the crystal distortion. Nearly stoichiometric compositions were found for the other compounds prepared under similar conditions.

The NPD data of all compounds indicate some ordering of the mixed transition ions over the octahedral site, since the crystal structure is better described in monoclinic space group P2₁/n that accounts for two distinguishable octahedral sites, rather than in orthorhombic Pbnm. Such results contrast with those obtained from X-ray diffraction where the mixed ions appear to be randomly distributed over the only octahedral site of the Pbnm space group.

The low-temperature NPD patterns of YMn_0.5Co_0.5O₃ exhibit some magnetic peaks, below 70 K. The magnetic structure at 1.4 K consists of two collinear ferromagnetic sublayers with saturated magnetic moments of 3.26(2) μ_B and 2.14(2) μ_B per ion, at the 2c- and 2d-site, respectively. The low-temperature NPD patterns of LaMn_0.5Ni_0.5O₃ and NdMn_0.5Ni_0.5O₃ exhibit an obvious increase in intensity over the only nuclear peak, at 2θ  36.89° and 36.40°, respectively. Although such behavior indicates a ferromagnetic ordering, the magnetic structure could not be refined because of the faint magnetic properties, more likely due to the incomplete atomic ordering.     

Solid state synthesis and characterization of iron（Ⅱ） pyrophosphate Fe2P2O7

Offwhite pure Fe_2P_2O_7 was synthesized through solid phase reaction using Fe_2O_3 and NH_4H_2PO_4 in argon atmosphere.The reaction products of Fe_2O_3 and NH4_H_2PO_4 at a series of temperatures from 400 to 900℃were characterized by XRD.Comparison and analysis of XRD patterns of resultant products indicated well-crystallized Fe_2P_2O_7 could be obtained over 630℃and Fe_2P_2O_7 prepared at 700℃was triclinic in cell type.Comparison of the cell parameters proved that the as-prepared Fe_2P_2O_7 belonged toβ- Fe_2P_2O_7 in crystal phase and SEM showed its size distribution was 0.5-2μm.     

Large heteropolymetalate complexes formed from lanthanide (Y, Ce, Pr, Nd, Sm, Eu, Gd), nickel cations and cryptate [As4W40O140]: synthesis and structure characterization

A new family of heteropolytungstate complexes (NH₄)₂₁[Ln(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]·xH₂O(Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd) were prepared by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀]·60H₂O with NiCl₂·6H₂O and Ln(NO₃)₃·xH₂O at pH≈4.5. The crystal structures of (NH₄)₂₁[Gd(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]·51H₂O was determined by X-ray diffraction analysis and element analysis. The compound crystallizes in the monoclinic space group P2₁/n with a=19.754(3), b=24.298(4), c=39.350(6) Å, β=100.612(3)°, V=18564(5) ų, Z=2, R1(wR₂)=0.0544(0.0691). The central site S1 and two opposite sites S2 of the big cyclic ligand [As₄W₄₀O₁₄₀]²⁸⁻ are occupied by one Ln³⁺and two Ni²⁺, respectively, each site supply four O_d coordinating to metal ion, another one water molecule and other five water molecules coordinate, respectively, to Ni²⁺and Ln³⁺. Polyanion [Ln(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]²¹⁻ has C_2v symmetry. IR and UV–vis spectra of [NaAs₄W₄₀O₁₄₀]²⁷⁻ of the title compounds are discussed.     

La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)材料的制备及其上转换发光性质

采用高温固相法制备了La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)荧光粉。通过X射线衍射(XRD)和上转换发射光谱对样品进行了相结构和发光性质表征。XRD实验结果表明:合成的样品为面心立方萤石结构(Fm-3m)的La_(2.4)Mo_(1.6)O_8相。在980 nm红外光激发下,La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)荧光粉发出分别来自Er~(3+)离子的~2H1_(1/2)→~4I_(15/2)、~4S_(3/2)→~4I_(15/2)跃迁的绿光(主峰为548和529 nm)和~4F_(9/2)→~4I_(15/2)跃迁的红光(主峰为670 nm)。进一步地,对样品中可能的上转换发光机制进行了讨论。     

Ln2Zr2O7 compounds (Ln=La,Pr, Sm,Y) with varied rare earth A sites for low temperature oxidative coupling of methane

The replacement of Ln site with different rare earth cations alters the crystalline phases of Ln₂Zr₂O₇, which in turn influences the surface active oxygen and alkaline sites significantly. The abundance and the interaction of the two types of sites determine the OCM reaction performance.     

Hydrothermal synthesis, crystal structure and characterization of [Zn(H2O)4]2 [H2As6V15O42(H2O)]·2H2O

The compound [Zn(H₂O)₄]₂[H₂As₆V₁₅O₄₂(H₂O)]·2H₂O (1) has been synthesized and characterized by elemental analysis, IR, ESR, magnetic measurement, third-order nonlinear property study and single crystal X-ray diffraction analysis. The compound 1 crystallizes in trigonal space group R3, a=b=12.0601(17) Å, c=33.970(7) Å, γ=120°, V=4278.8(12) Å³, Z=3 and R1(wR2)=0.0512 (0.1171). The crystal structure is constructed from [H₂As₆V₁₅O₄₂(H₂O)]⁴⁻ anions and [Zn(H₂O)₄]²⁺ cations linked through hydrogen bonds into a network. The [H₂As₆V₁₅O₄₂(H₂O)]⁶⁻ cluster consists of 15 VO₅ square pyramids linked by three As₂O₅ handle-like units.     

Sn0.5Ti((0.5)O2固溶体的溶胶-凝胶法制备、表征及其热稳定性研究

采用溶胶-凝胶法制备了Sn_0.5Ti_0.5O₂固溶体.用X射线衍射(XRD)、差热分析(DTA)和红外(IR)技术对材料的结构和热稳定性进行了分析表征.固溶体的热稳定性与起始反应温度有关,在40℃水浴温度下制备的凝胶经1000℃烧结,发生了相分解,出现了富Sn和富Ti相,而在80℃水浴温度下制备的凝胶经1200℃烧结也不发生相分解,仍以Sn_0.5Ti_0.5O₂相存在,而且用差热分析也得到了同样的结论.     

Synthesis, characterization and thermal investigation of M[M(C2O4)3]·xH2O (x=4 for M=Cr(III); x=2 for M=Sb(III) and x=9 for M=La(III))

The complexes, M[M(C₂O₄)₃]·xH₂ O, where x=4 for M=Cr(III), x=2 for M=Sb(III) and x=9 for M=La(III) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR and electronic spectral data, conductivity measurement and powder X-ray diffraction (XRD) studies. The chromium(III)tris(oxalato)chromate(III)tetrahydrate (COT), Cr[Cr(C₂ O₄)₃]·4H₂O, released water in a stepwise fashion. Removal of the last trace of water was accompanied by a partial decomposition of the oxalate group. Thermal investigation using TG, DTG and DTA techniques in air produced Cr₂O₃ at 858°C through the intermediate formation of Cr₂O₃ and CrC₂O₄ at around 460°C. While DSC study in nitrogen up to 670°C produced a mixture of Cr₂O₃ and CrC₂O₄. In antimony(III)tris(oxalato)antimonate(III)dihydrate (AOD), Sb[Sb(C₂O₄)₃]·3H₂O the dehydration took place during the decomposition of precursor at 170–290°C and finally at ca. 610°C Sb₂ O₅ along with trace amounts of Sb₂O₄ were produced. Trace amount of Sb₂O₃ and Sb along with Sb₂O is proposed as the end product at 670°C of AOD in nitrogen. The oxide La₂O₃ is formed at 838°C from the study with TG, DTG and DTA in air of lanthanum(III)tris(oxalato)lanthanum(III)nonahydrate (LON), La[La(C₂O₄)₃]·9H₂O. Intermediate dioxycarbonate, La₂O₂CO₃ was generated at 526°C prior to its decomposition to lanthanum oxide in air; whereas in N₂ the formation of La₂(CO₃)₃ at 651°C was proposed. The thermal parameters have been evaluated for each step of the dehydration and decomposition of COT, AOD and LON using five non-mechanistic equations i.e. Flynn and Wall, Freeman and Carroll, Modified Freeman and Carroll, Coats–Redfern and MacCallum–Tanner equations. Kinetic parameters, such as, E^*, k_o, ΔH^*, ΔS^* etc. were also supplemented by DSC studies in nitrogen for all the three complexes. Some of the intermediate species have been identified by analytical and powder XRD studies. Tentative schemes has been proposed for the decomposition of all three compounds in air and nitrogen.     

Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium

Since H₂O₂ decomposition can result in selectivity/yield loss in the direct H₂O₂ synthesis process from H₂ and O₂ over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H₂O₂ decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H₂O₂ decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 °C. This study has shown that the H₂O₂ decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H₂O₂ decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid  acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H₂O₂ decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H₂O₂ decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H₂O₂ decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H₂O₂ decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H₂O₂. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H₂O₂ decomposition activity.     

La2O3助剂对Rh/SiO2催化CO加氢反应性能的影响

采用溶胶凝胶法制备了SiO_2和La_2O_3-SiO_2载体,再通过浸渍法分别引入Rh-La和Rh组分,研究考察了La引入方式对Rh/SiO_2催化CO加氢反应性能的影响。结果表明,La的添加有利于提高Rh的分散度,促进Rh+中心数的增加,有效地抑制产物中CO2的生成,提高含氧化合物选择性。此外,La的引入方式会影响La与Rh间的相互作用强弱,Rh和La共浸渍制得的2Rh-5La_2O_3/SiO_2催化剂中Rh-La相互作用较强,削弱的Rh-CO键有利于反应过程中CO的插入反应,使得产物以C_(2+)含氧化合物为主。而La以助剂形式掺入SiO_2制得的2Rh/5La_2O_3-SiO_2催化剂具有较弱的La-Rh相互作用,其产物则以甲醇、乙醇等低碳醇为主。