Chungang Min

Removal of MercuryII from Aqueous Solutions by Adsorption on Poly1-amino-5-chloroanthraquinone Nanofibrils

Poly1-amino-5-chloroanthraquinone PACA nanofibrils were applied as novel nanoadsorbents for highly toxic mercury removal from aqueous solutions. A series of batch adsorption experiments were conducted to study the effect of adsorbent dose, pH, contact time, and metal concentration on HgII uptake by PACA nanofibrils. Kinetic data indicated that the adsorption process of PACA nanofibrils for HgII achieved equilibrium within 2 h following a pseudo-second-order rate equation. The adsorption mechanism of PACA nanofibrils for HgII was investigated by Fourier transform-infrared FT-IR spectra and X-ray photoelectron spectroscopy XPS analyses. The adsorption isotherm of HgII fitted well the Langmuir model, exhibiting superb adsorption capacity of 3.846 mmol of metal per gram of adsorbent. Lastly, we found out that the as-synthesized PACA nanofibrils are efficient in HgII removal from real wastewater. Furthermore, five consecutive adsorption-desorption cycles demonstrated that the PACA nanofibrils were suitable for repeated use without considerable changes in the adsorption capacity.

Intrinsically conducting polyaminoanthraquinone nanofibrils: interfacial synthesis, formation mechanism and lead adsorbents

Intrinsically conducting nanofibrils of poly(1-amino-5-chloroanthraquinone) (PACA) were successfully synthesized via the interfacial chemical oxidative polymerization of 1-amino-5-chloroanthraquinone (ACA) monomers in biphasic systems. The effects of the reaction parameters, including polymerization media and temperature, oxidant species, monomer concentrations, oxidant/monomer molar ratios, and acid concentrations, on the polymerization yield, bulk electrical conductivity, diameters and aspect ratio of the resulting PACA nanofibrils were systematically optimized. PACA nanofibrils exhibit the highest polymerization yield of 64.8%, aspect ratio of 67 (∼30 nm diameter, ∼2 μm length), and bulk electrical conductivity of 6.2 × 10−3 S cm−1, when the ACA monomers were oxidized by CrO3 in a combined medium consisting of nitrobenzene and 250 mmol L−1 HClO4 solution. PACA nanofibrils are highly water-dispersible and self-stable with no need to add any stabilizers. The formation mechanism of PACA nanofibrils was explored to understand what contributions are responsible for the functionalities. With a clean surface, high negatively charged density, and thermostability, as well as strong blue-light emitting fluorescence property, PACA nanofibrils are very promising materials for the fabrication of advanced iron sensors and lead adsorbents.

Theoretically obtained insight into the mechanism and dioxetanone species responsible for the singlet chemiexcitation of Coelenterazine

Coelenterazine is a widespread bioluminescent substrate for a diverse set of marine species. Moreover, its imidazopyrazinone core is present in eight phyla of bioluminescent organisms. Given their very attractive intrinsic properties, these bioluminescent systems have been used in bioimaging, photodynamic therapy of cancer, as gene reporter and in sensing applications, among others. While it is known that bioluminescence results from the thermolysis of high-energy dioxetanones, the mechanism and dioxetanone species responsible for the singlet chemiexcitation of Coelenterazine are not fully understood. The theoretical characterization of the reactions of model Coelenterazine dioxetanones showed that efficient chemiexcitation is caused by a neutral dioxetanone with limited electron and charge transfer, by accessing a region of the PES where ground and excited states are nearly-degenerated. This finding was supported by calculation of equilibrium constants, which showed that only neutral dioxetanone is present in conditions associated with bioluminescence. Moreover, while cationic amino-acids easily protonate amide dioxetanone, anionic ones cannot deprotonate the neutral species. These results indicate that, contrary to existent theories, efficient chemiexcitation can occur with significant electron and/or charge transfer. In fact, these processes can be prejudicial to chemiexcitation, as anionic dioxetanones showed a less efficient chemiexcitation despite the occurrence of significant electron and charge transfer.

TD-DFT accuracy in determining excited-state structures and fluorescence spectra of firefly emitter

We analyzed the excited-state structures and emission spectra of firefly emitter, the anionic keto form of firefly oxyluciferin(keto-1), determined by the time dependent-density functional theory(TD-DFT) approach. The analysis is based on a direct comparison with the highly correlated CASSCF(MS-CASPT2) ab initio approach. 49 DFT functionals were considered and applied to the study. Among the tested functionals, mPW3PBE, B3PW91 and B3P86 give the best performance for ground-state geometry, absorption spectrum, excite-state geometry and emission spectrum.