RESUMEN
Semiconductor Cu2ZnSn(S x Se1-x )4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0-1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0-1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.
RESUMEN
g-C3N4 with π-delocalization was coordinated between urea and a small amount of 1,3,5-tris(4-aminophenyl)benzene (TAPB) (UCN-xTAPB) by a facile polymerization. Compared with pristine g-C3N4(UCN), the obtained materials, UCN-xTAPB, showed an extended delocalization with increased electrical conductivity, enhanced adsorption of visible light, and improved separation of photogenerated electron-hole pairs. The average H2 evolution rate of UCN-4TAPB is about 10.55 mmol h-1 g-1 under visible-light irradiation (λ > 420 nm), which is much higher than reported data. Furthermore, density-functional theory (DFT) calculation confirms that the proposed structure with the incorporation of TAPB into the CN network shows the extended delocalization. Moreover, different structures of aromatic rings (anthroic acid, naphthoic acid and benzoic acid) are applied to verify the role of the enhanced π-delocalization in g-C3N4. By adopting different precursors (thiourea, dicyandiamide) to polymerize with TAPB, we further confirm the extension of optical absorption under visible-light irradiation and the improvement of hydrogen evolution rate, indicating the universality of the current strategy. Therefore, we believe that our work provides an efficient strategy for constructing the delocalized structure of g-C3N4 as effective visible-light-responsive photocatalysts.
RESUMEN
Nitrogen-deficient graphitic carbon nitride (CN-HAc) was synthesized by thermal condensation of acetic acid-treated melamine as a precursor. The nitrogen vacancies play a remarkable role on controlling the electronic structure of g-C3N4, such as extending the optical absorption and enhancing the separation efficiency of photogenerated charge carriers, resulting in the improvement of photocatalytic activity. The photocatalytic activity of the catalysts was evaluated by splitting water and degradation of rhodamine B (RhB) under visible light irradiation (λ>420nm). The average H2 evolution rate on CN-HAc is 24µmolh-1, which is about 5 times of that on pristine g-C3N4. Meanwhile, CN-HAc exhibits superior photocatalytic mineralization of RhB. The possible formation mechanism of nitrogen-deficient in the framework of g-C3N4 is proposed.
RESUMEN
BiOBr/Na-montmorillonite composites (BiOBr-Mt) were prepared under laboratory ambient conditions by using the surfactant cetyltrimethylammonium bromide (CTAB) as the Br source and template, and the as-synthesized samples were characterized by XRD, FT-IR, FESEM, TEM equipped with EDS, BET and UV-vis DRS techniques. Interestingly, the particle size of BiOBr can be controlled by CTAB modified Na-montmorillonite. The photocatalytic activity of the as-prepared was further evaluated by decomposition of Rhodamine B (RhB) under visible light irradiation; the obtained results revealed that the BiOBr-Mt sample had strong photoabsorption in the visible light region. It has higher photocatalytic activity than pure BiOBr alone. There exists an efficient adsorption for RhB onto BiOBr-Mt contrast to that onto the pure BiOBr. The adsorption processes can be well described by pseudo-second-order kinetic model; meanwhile, the adsorption behaviors can be described by both Freundlich and Langmuir equations but the former was better. Additionally, the relevant adsorption and degradation mechanisms were explored and the possible mechanisms were presented. The photocatalytic activity has high effect both in acidic and basic conditions on the degradation reaction but in acidic condition is more favorable. After three recycles, BiOBr-Mt did not exhibit any significant loss of photocatalytic activity, confirming the photocatalyst was essentially stable.