Fabrication of Tantalum Oxyfluoride and Oxynitride Thin Films via Ammonolysis of Sol-Gel Processed Tetraethoxo (β-diketonato) Tantalum (V) Precursors for Enhanced Photocatalytic Activity

In the present report, the generation of Tantalum oxyfluoride and oxynitride upon ammonolysis of the gel obtained from modified tantalum-alkoxo complexes is reported. To the best of our knowledge, this is first report of the formation of tantalum oxyfluoride thin films via ammonolysis of the β-diketone modified tantalum-alkoxo complex [Ta(OEt)4(CF3COCH2COCH3)]m. The integration of nitrogen and fluorine in lattice sites of metal oxides leads to significant reduction in the band gap, resulting in their activation under visible light. Moreover, in this report the effect of the modified alkoxide precursors and ammonolysis on the photo-physical properties of Ta2O5 thin films have also been investigated and compared with the results obtained from films fabricated from unmodified tantalum (V) ethoxide. 1H NMR, 13C NMR and elemental analyses confirmed successful modification of tantalum (V) ethoxide to [Ta(OCH2CH3)4(CH3COCHClCOCH3)]m (1), [Ta(OCH2CH3)4(CF3COCH2COCH3]m (2) and [Ta(OCH2CH3)4 (CH3COC(CH3)2COCH3))]m (3). The fabrication of Ta2O5 thin films involved the spin casting of the gels of modified tantalum alkoxo complexes (processed by sol-gel method) on to glass substrate. X-ray photoelectron spectroscopy results show that nitrogen was incorporated into the ammonolyzed films fabricated from complex precursors (1) and (3), while the presence of fluorine as tantalum oxyfluoride was confirmed in the ammonolyzed film fabricated from complex (2) precursor. The optical characterization insinuate band gap narrowing from 3.55 eV for undoped film prepared from tantalum (V) ethoxide to 3.47 eV for undoped film prepared from [Ta(OEt)4(CF3COCH2COCH3)]m and 3.05 eV for ammonolyzed film obtained from [Ta(OEt)4(CF3COCH2COCH3)]m precursor. Furthermore, enhanced photocatalytic efficiency of the films is demonstrated by degradation of methylene blue dye.

Band Gap Narrowing and Electrical Properties of (1-x)BaTiO3-xSrFe0.5Nb0.5O3 Lead-Free Ceramics

The composite materials in the form of (1-x)BaTiO3-xSrFe0.5Nb0.5O3((1-x)BT-xSFN) are synthesized via the solid-state reaction route. Structure, optical behaviors and electrical properties of (1-x)BT-xSFN are studied. It can be noted that the structure of the synthesized solid solution changes from the tetragonal phase to the cubic phase with increase of x-value. Due to the increase in content of double perovskite SFN, the optical band gaps of doped BT decrease to a minimum of 2.66 eV, which is smaller than that of pure BT (3.21 eV). However, the ferroelectric property deteriorates with the addition of dopants, which result from the lattice distortion caused by the substitution of Sr2+ and Fe3+/Nb5+ for Ba2+ and Ti4+, respectively. These results provide new insights into the control of the structure, optical behaviors and ferroelectric properties in BT-based oxides.

Boosting of photocatalytic hydrogen evolution via chlorine doping of polymeric carbon nitride

Chemical doping is an effective strategy for modifying the electrochemical properties of polymeric carbon nitride and tuning its visible-light photocatalytic activity. In this study, chlorine-doped polymeric carbon nitride (Cl-PCN) has been synthesized by the polycondensation method. Among a series of samples, 200Cl-PCN exhibited the best photocatalytic activities for the hydrogen evolution from water splitting. Main aspects were revealed: (i) unique location of Cl atoms at the interlayers of PCN instead of on its π-conjugated planes, (ii) slight band gap narrowing, (iii) lower recombination rate of the electron-hole pairs, and (iv) improved photogenerated charge transport and separation. The above factors affected the 4.4-fold enhancement of photocatalytic efficiency in hydrogen evolution in comparison to the pristine catalyst.