RESUMO
Novel materials of (E)-N'-(4-chlorobenzylidene)-4-hydroxybenzohydrazide (CBHB) and (E)-N'-(4-(diethylamino) benzylidene)-4-hydroxybenzohydrazide (DEABHB) were synthesized by condensation reaction process and solvent evaporation method was employed to grow CBHB and DEABHB single crystals at room temperature. Lattice parameters of CBHB and DEABHB compounds were recorded using single crystal X-ray diffraction method. The presence of functional groups of the synthesized CBHB and DEABHB compounds were confirmed by Fourier transform infrared and Fourier transform Raman spectral analyses. Various intermolecular interactions were studied using Hirshfeld surface analysis. Thermal stability of the hydrazone Schiff base compounds CBHB and DEABHB were studied by thermogravimetric and differential thermal analyses. Third order nonlinear optical properties of CBHB and DEABHB were measured using open aperature Z scan technique. Two photon absorption coefficient and optical limiting properties of the crystals were reported from the Z scan studies.
RESUMO
Lithium Borohydride (LiBH4), from the family of complex hydrides has received much attention as a potential hydrogen storage material due to its high hydrogen energy densities in terms of weight (18.5 wt%) and volume (121 kg H2 per mol). However, utilization of LiBH4 as a hydrogen carrier in off- or on-board applications is hindered by its unfavorable thermodynamics and low stability in air. In this study, we have synthesized an air stable SWCNT@LiBH4 composite using a facile ultrasonication assisted impregnation method followed by oxidation at 300 °C under ambient conditions (SWLiB-A). Further, part of the oxidized sample is treated at 500 °C under nitrogen atmosphere (SWLiB-N). Upon oxidation in air, the in situ formation of lithium borate hydroxide (LiB(OH)4) and lithium carbonate (Li2CO3) on the surface of the composite (SWLiB@LiBH4) is observed. But in the case of SWLiB-N, the surface hydroxyl groups [OH4]- completely vanished leaving porous LiBH4 with SWCNT, LiBO2 and Li2CO3 phases. Hydrogen adsorption/desorption experiments carried out at 100 °C under 5 bar H2 pressure showed the highest hydrogen adsorption capacity of 4.0 wt% for SWLiB-A and 4.3 wt% for SWLiB-N composites in the desorption temperature range of 153-368 °C and 108-433 °C respectively. The observed storage capacity of SWLiB-A is due to the H+ and H- coupling between in situ formed Li+[B(OH)4]-, Li2+[CO3]- and Li+[BH4]-. Whereas in SWLiB-N, the presence of positively charged Li and B atoms and LiBO2 acts as a catalyst which resulted in reduced de-hydrogenation temperature (108 °C) as compared to bulk LiBH4. Moreover, it is inferred that the formation of intermediate phases such as Li+[B(OH)4]-, Li2+[CO3]- (SWLiB-A) and Li+[BO2]- (SWLiB-N) on the surface of the composites not only stabilizes the composite under ambient conditions but also resulted in enhanced de- and re-hydrogenation kinetics through catalytic effects. Further, these intermediates also act as a barrier for the loss of boron and lithium through diborane release from the composites upon dehydrogenation. Furthermore, the role of in situ formed intermediates such as LiB(OH)4, Li2CO3 and LiBO2 on the stability of the composite under ambient conditions and the hydrogen storage properties of the SWCNT@LiBH4 composite are reported for the first time.
