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Bismuth Vanadate Based Nanostructured and Nanocomposite Photocatalyst Materials for Water Splitting Application
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
S. Moscow, K. Jothivenkatachalam
Recently, Bismuth Vanadate (BiVO4) has gained increasing attention for its use as a promising candidate under visible light irradiation among the bismuth metal oxide photocatalyst (Pilli et al. 2011, Moscow and Jothivenkatachalam 2016). The BiVO4 photocatalysts are highly promising for different applications such as renewable energy production systems (i.e., solar fuels production from water and sunlight) and to resolve environmental issues. Bismuth vanadate (BiVO4), which is an n-type semiconductor, has been identified as one of the most promising photocatalytic materials. As it is well known, BiVO4 exists in three polymorphs of monoclinic scheelite, tetragonal scheelite, and tetragonal zircon structures, with band gaps of 2.4, 2.34, and 2.9 eV, respectively. It is reported that BiVO4 mainly exists in three crystalline phases: monoclinic scheelite, tetragonal zircon and tetragonal scheelite structure (Lim et al. 1995, Bhattacharya et al. 1997, Luo et al. 2008) (Figure 2). Monoclinic scheelite BiVO4, (~ 2.3 eV band gap) shows both visible-light and UV absorption while tetragonal BiVO4 (~ 2.9 eV band gap) mainly possesses an UV absorption band. The UV absorption observed in both the tetragonal and monoclinic BiVO4 is associated with band transition from O2p to V3d, whereas visible light absorption is due to the transition from a valence band (VB) formed by Bi6s or a hybrid orbital of Bi6s and O2p to a conduction band (CB) of V3d (Ng et al. 2010). The scheelite structure can have a tetragonal crystal system (space group: I41/a with a = b = 5.1470 Å, c = 11.7216 Å) or a monoclinic crystal system (space group: I2/b with a = 5.1935 Å, b = 5.0898 Å, c = 11.6972 Å, and b = 90.3871), while the zircon-type structure has a tetragonal crystal system (space group: I41/a with a = b = 7.303 Å and c = 6.584 Å) (Park et al. 2013).
Cationic Cd(II) metal − organic framework based on tetrakis(1,2,4-triazol-1-yl)methane
Published in Journal of Coordination Chemistry, 2019
Ming Ze Wu, Zhi Long Ma, Jian Yun Shi, Xiu Juan Shi, Li Tian
Complex 1 crystallizes in the tetragonal crystal system with the space group P4/n (Table 1). As shown in Figure 2(a), each CdII has a distorted tetragonal pyramidal coordination sphere {CdN4O} by four triazole nitrogens from four different ttpm ligands and one oxygen from DMSO. The Cd–N bond lengths are 2.248(8) and 2.250(3) Å (Supplementary material Table S1), respectively. The Cd1–O1 bond distance is 2.363(12) Å, which is a little longer than the normal Cd–O bond. Each ttpm ligand bridging four Cd2+ cations constitutes a 2-D (4,4) network (Figure 2). In the 3-D stacking map, there exist 1-D channels to accommodate the charge-balancing NO3− anions, which are further confirmed by IR and elemental analysis. However, these anions are completely disordered and their position cannot be located in the electron density map. In addition, the ratio of the accessible porous volume (utilizable) in every unit cell is calculated as 24.1% with the help of PLATON [34].
Review: Downsizing effect on 2-D and 3-D spin crossover metal-organic frameworks
Published in Journal of Coordination Chemistry, 2019
Christina D. Polyzou, Vassilis Tangoulis
However, the detection of an incomplete bi-directional light-induced spin-transition at room temperature for the dehydrated form of polycrystalline 2c [49] raised questions regarding the authenticity of the photoinduced effect and created the necessity of its preparation in the form of single-crystals. The hurdles of poor crystallinity have been overcome by the research group of Bousseksou seven years later as they achieved the isolation of [Fe(pz)PtII(CN)4] (4) as single crystals (Figure 4) [50]. Complex 4 crystallizes in the tetragonal crystal system and P4/mmm space group independent of its FeII spin state reducing its volume from 293 to 223 K and presents for the first time a complete photoconversion between HS↔LS state.