Two-dimensional/two-dimensional Z-scheme photocatalyst of graphitic carbon nitride/bismuth vanadate for visible-light-driven photocatalytic synthesis of imines

As an environmentally friendly strategy, photocatalytic synthesis of imines via selective oxidation of amines has inspired numerous interests. In comparison to conventional type-II heterojunction, the photogenerated electrons and holes on a Z-scheme photocatalyst has strong redox ability. Herein, we prepared a two-dimensional/two-dimensional (2D/2D) Z-scheme photocatalyst of graphitic carbon nitride nanosheet/bismuth vanadate (CNNS/BVO) with a large two-phase interface, which is favorable for the transfer and separation of photoexcited charge carriers. For selective oxidation of benzylamine to N-benzylidenebenzylamine under oxygen atmosphere and visible light irradiation, the CNNS/BVO showed much higher activity than the single CNNS and BVO. The optimized nanocomposite photocatalyst with a 50% CNNS/BVO mass ratio presented a high conversion (~96%) and selectivity (~99%) in 6 h oxidative coupling reaction of benzylamine. More importantly, this 2D/2D CNNS/BVO photocatalyst has good cycling stability, as well as universality for different benzylamine derivatives. Based on the experimental results, a Z-scheme mechanism was determined, where photoinduced electrons were accumulated on the conduction band (CB) of CNNS that is higher than that of BVO and holes were collected on the valence band (VB) of BVO that is lower than that of CNNS. Further, superoxide radicals and photogenerated holes are examined to the mainly active species for selective oxidation of benzylamine, and a possible reaction pathway was therefore proposed. This study demonstrates that the Z-scheme 2D/2D CNNS/BVO with high redox ability is an efficient photocatalyst for the imine synthesis.     

Concentration Effect of Gd3+ on the Structural,Optical and Spectroscopic Properties of NdVO4 Nanoparticles

Abstract

Neodymium vanadate with concentration of gadolinium as 3% and 5% having general formulae Gd_xNd_1-xVO₄ where x?=?0.03 and 0.05 was prepared by chemical route technique. The effect of concentration of gadolinium on the structural, optical and spectroscopic properties was explained by various characterization techniques. Powder X-ray diffraction study suggests tetragonal zircon structure; various parameters such as crystallite size, volume and X-ray density were calculated. A change in morphology with the change in concentration of gadolinium was observed through scanning electron microscopy. Ultraviolet absorption spectroscopy shows various transitions from ground state to various excited state within 4f shell, and variation in the optical band gap calculated by Tauc plot is due to the incorporation of Gd³⁺ ions.     

Fabrication and negative thermal expansion properties of P-substituted ZrV2O7 sintered bodies

Calcined powders of ZrV_1.2P_0.8O₇ (ZVP) and ZrV₂O₇ (ZV) were synthesized by heating gels prepared from NH₄H₂PO₄, NH₄VO₃, and ZrOCl₂ solutions at 500 and 400 °C, respectively. Dense ZV-added ZVP sintered bodies were subsequently fabricated through heating at 850 °C for 20 h, with the addition of ZrV₂O₇ as a sintering additive. The resulting material had a relative density of ca. 92%, while the relative density of pure sintered ZVP was ca. 72%. NH₄H₂PO₄ (NHP) was also added to ZVP along with ZV to obtain a molar ratio of P in NHP for V in ZV = 1. Subsequently, a single phase (NHP, ZV)-added ZVP sintered body was obtained by heating at 850 °C. Thermomechanical analysis showed that the dense ZV-added ZVP sintered body exhibited a positive thermal expansion from 25 to 150 °C and a negative thermal expansion from 150 to 500 °C.     

Boosting carrier dynamics of BiVO4 photoanode via heterostructuring with ultrathin BiOI nanosheets for enhanced solar water splitting

Bismuth vanadate (BiVO4) has been one of the most promising candidates for solar water splitting while still suffers from poor bulk charge transport that limits its solar to hydrogen conversion efficiency.We demonstrate in this work an efficient strategy for boosting bulk charge transport of BiVO4 through the facile impregnation of as-prepared BiVO4 photoanode in the precursor solution of ultrathin BiOI nanosheets.Such impregnation creates increased oxygen vacancies in the bulk of BiVO4 through the reduction of V5+ to V4+ by I,which greatly improves bulk separation efficiency for BiVO4-BiOI up to 65.9％ at 1.23 VRHE from the original 51.9 ％ of pure BiVO4.Moreover,the decoration of the BiOI nanosheets on BiVO4 photoanode is also beneficial for addressing the carrier dynamics at surface due to the matched energy levels of BiOI nanosheets and BiVO4.The introduced plenty of oxygen vacancies in the bulk of BiVO4 and the built-in electric field in BiVO4-BiOI synergistically improve the photocurrent density at 1.23 VRHE up to 3.88 mA cm-2.We believe that such facile impregnation strategy will pave an alternative way to the development of highly efficient BiVO4 photoanode.     

树脂金刚石砂轮磨削钒酸钇晶体中磨削参数对力和磨削表面质量的影响

本文用树脂结合剂金刚石砂轮对钒酸钇晶体进行了平面磨削实验,研究了砂轮线速度、工件进给速度和磨削深度对磨削力和磨削表面粗糙度的影响。结果表明:磨削力和磨削表面粗糙度都是随着砂轮线速度的增加而减小,随进给速度和磨削深度的增加而增加,其中磨削深度对磨削力影响最大,砂轮线速度对磨削表面粗糙度影响最大。钒酸钇晶体的磨削表面主要由断裂区域和光滑区域组成,当砂轮线速度为30m/s时,磨削表面存在宽度约100μm的裂痕,而随着砂轮线速度的上升,裂痕宽度降低到50μm以下,同时光滑区域所占的比例增加,这可能与发生塑性变形的机率增大有关。     

Enhanced Photocatalytic Properties of Silver Oxide Loaded Bismuth Vanadate

In this work, BiVO4 powders were synthesized by a sol-gel method, and the BiVO4 gels with different calcination temperature were investigated by X-ray diffraction (XRD). Absorption range and band gap e...     

ZrV_2O_7的热膨胀和非简谐振动(英文)

因零膨胀材料在工程上的潜在应用,近10多年来,对材料的热膨胀特性得以深入了解.本文对ZrW2O8的负热膨胀现象的研究进展进行了简要回顾,并特别指出理解非简谐振动的重要性.讨论了ZrV2O7的声了特性和非简谐振动,其负热膨胀的高温相和具有正的热膨胀的低温相特征. 此外,还比较了ZrV2O7和ZrW2O8的热膨胀特性.     

微波还原法制备三氧化二钒的工艺研究

在不外加任何还原剂的条件下, 通过微波加热偏钒酸铵制备三氧化二钒, 并研究了微波加热条件下温度对NH₄VO₃的分解及还原的影响。用XRD分析生成物的相结构, 用SEM观察晶体形貌。结果表明: 在温度为800 ℃, 还原反应时间为30 min时, 偏钒酸铵可完全转化为三氧化二钒, 产物的全钒含量达到67%～68%。     

Synthesis of butterfly-like BiVO4/RGO nanocomposites and their photocatalytic activities

A simple and high efficient method was proposed for the synthesis of uniform three dimensional(3D) BiVO_4/reduced graphene oxide(RGO) nanocomposite photocatalyst by adopting the microwave assistant and using Bi(NO_3)_3·5H_2O, graphene oxide(GO) and NH_4VO_3 as precursor. The as-obtained composites were well characterized with the aid of various techniques to study the morphology, structure, composition, optimal and electrical property. In the as-obtained composites, the GO sheets were fully reduced into RGO, and monoclinic structure BiVO_4 crystallized completely into butterfly-like BiVO_4 lamellas and well bonded with the RGO lamellas. The length and the width of the butterfly-like BiVO_4 particle were about 1.5 μm, and the thickness of the flake was about 20 nm. Photocatalytic performances of BiVO_4/RGO composite and pure BiVO_4 particle have been evaluated by investigating the reduction of Cr(Ⅵ) ion-contained wastewater under simulated solar light irradiation, where the BiVO_4/RGO composite displayed enhanced photocatalytic activity. It is found that the pseudo-first-order rate constants(k) for the photocatalytic reduction of Cr(VI) by BiVO_4/RGO composite was about 4 times as high as that of the pure BiVO_4. The present work suggested that the combination of BiVO_4 and RGO displayed a remarkable synergistic effect, which led to enhanced photo-catalytic activity on Cr(Ⅵ) reduction.     

多钒酸铵的微波干燥特性研究

对高含水量的多钒酸铵干燥是其大部分工业应用的关键步骤。微波干燥由于独特的加热特性,可以作为传统干燥的替代品。在本试验中,通过微波干燥系统研究了不同微波功率、样品质量和初始含水率对微波干燥多钒酸铵性能的影响。研究发现,微波功率、样品质量及初始水分含量对微波干燥多钒酸铵有显著影响,都能促使物料吸收更多微波能加速水分的蒸发。且微波干燥过程中减少了粉尘的产生,是一种环保清洁、高效节能的技术。