ABSTRACT
Here, we present an experimental investigation on the nonlinear optical (NLO) and optical limiting properties of metalloporphyrin compounds (Cu-1-OH, Zn-1-OH, Cu-1-E and Zn-1-E) using spatial self-phase modulation (SSPM) method in the visible range. It is found that all of the samples show a large self-defocusing effect at 532 nm, which is attributed to the thermal nonlinear optical effects with negative nonlinear refractive index coefficient n2 due to the relatively high absorption at 532 nm. In contrast, at 780 nm where absorption is weak for both Zn- and Cu-porphyrins, Zn-porphyrins still exhibit visible self-defocusing while Cu-porphyrins do not show any nonlinear diffraction pattern. Such a phenomenon can be explained by the Kerr effect of Cu-porphyrins at 780 nm. As the thermal nonlinear optical effects (of negative n2) at 780 nm are reduced due to the low absorption, the Kerr effect with positive n2 becomes comparable and the overall nonlinearity is reduced. The Kerr effect of Cu-porphyrins is stronger than that of Zn-porphyrins because of the enhanced π-electron delocalization effect as Cu(II) has a variable number of valence electrons and incompletely filled d atomic orbitals. Finally, the optical limiting performance of Zn-porphyrins is demonstrated as a representative and its dependence on sample position is examined. This work not only enriches the understanding of the physical mechanism of optical limiting in porphyrin materials, but also provides a significant reference to improve the third-order NLO coefficient by adjusting the structure of compounds.
ABSTRACT
Actual high saline wastewater containing concentrated organics and sodium chloride is a bioenergy and renewable resource. This study compared two different bipolar membrane electrodialysis membranes from two companies' stacks to recover HCl and NaOH from sodium chloride solution and actual chemical wastewater. The results demonstrated that the electrolysis rates were around 1.5 kg/m2h, the HCl and NaOH production rates were about 0.9 kg/m2h, energy consumption was in the range of 1.05-1.27 kWh/kg, and the economic benefits were above 1 yuan/h in BMED systems. From analyzing the performance of seven different BMED membrane stacks, the B2 stack was chosen for electrolyzing actual high salt wastewater to observe the effect of chemical oxygen demand on BMED systems, where electrolytic salt performance, HCl-NaOH alkali production rates, and energy consumption show linear dependence on time for 5000 mg/L chemical oxygen demand wastewater. It illustrated chemical oxygen demand can enhance energy consumption and reduce electrolytic salt performance and the acid and alkali production rates, due to improving the membrane area resistance. In this study, the effect of high COD saline wastewater on the performance of a BMED membrane stack was clarified and the mechanism was analyzed for its practical application in treating chemical high salt wastewater.
