Wei Chen,Jiayue Dong,Sihan Zhou,Chunyong Zhang,Degang Fu
1-naphthol (1-NAP) and 2-naphthol (2-NAP) are both hazardous pollutants which pose great threat to our living environment. In the current work, a comparative investigation on the electrochemical mineralization of 1-NAP and 2-NAP using boron-doped diamond (BDD) anode was presented. Experiments were carried out using synthetic 1-NAP or 2-NAP solutions containing Na 2 SO 4 as supporting electrolyte . A two-level factorial design methodology was adopted to optimize the mineralization process, six mathematical models were thus constructed and used to explore the structure-property relation involved. The results obtained suggested that 1-NAP was easier and faster to break down than 2-NPA under the same oxidation conditions, which were in line with the outcome obtained from cyclic voltammetry , HPLC and TOC measurements. To understand the destruction mechanism, the electron structures of 1-NAP and 2-NAP were further examined by the quantum chemistry calculations with density functional theory. It was also found that the results from frontier orbital analysis could well explain the differing mineralization performances recorded in BDD anode cell. Finally, with the aid of LC/MS analysis, the oxidation pathways of 1-NAP or 2-NAP on BDD anodes were proposed.
Degradation of phenols with different substituent groups (including –OCH 3 , –CHO, –NHCOCH 3 , –NO 2 , and −Cl) at boron-doped diamond (BDD) anodes has been studied previously based on the removal efficiency and •OH detection. Innovatively, formations of CO 2 gas and various inorganic ions were examined to probe the mineralization process combined with quantitative structure-activity relationship (QSAR) analysis. As results, all phenols were efficiently degraded within 8 h with high COD removal efficiency. Three primary intermediates (hydroquinone, 1,4-benzoquinone and catechol) were identified during electrochemical oxidation and degradation pathway was proposed. More importantly, CO 2 transformation efficiency ranked as: no N or Cl contained phenols ( p -CHO, p -OCH 3 and Ph) > N-contained phenols ( p -NHCOCH 3 and p -NO 2 ) > Cl-contained phenols ( p -Cl and o,p -Cl). Carbon mass balance study suggested formation of inorganic carbon (H 2 CO 3 , CO 3 2− and HCO 3 − ) and CO 2 after organic carbon elimination. Inorganic nitrogen species (NH 4 + , NO 3 − and NO 2 − ) and chlorine species (Cl − , ClO 3 − and ClO 4 − ) were also formed after N- and Cl-contained phenols mineralization, while no volatile nitrogen species were detected. The phenols with electron-withdrawing substituents were easier to be oxidized than those with electron-donating substituents. QSAR analysis indicated that the reaction rate constant ( k 1 ) for phenols degradation was highly related to Hammett constant (∑ σ o , m , p ) and energy gap ( E LUMO - E HOMO ) of the compound ( R 2 = 0.908), which were key parameters on evaluating the effect of structural moieties on electronic character and the chemical stability upon radical attack for a specific compound. This study presents clear evidence on mineralization mechanisms of phenols degradation at BDD anodes.
Amelogenin and its various derived peptides play important roles in promoting biomimetic mineralization of enamel. Previously, an amelogenin-derived peptide named QP5 was proved to be able to repair demineralized enamel. The objective here was to interpret the mechanism of QP5 by elucidating the specific function of each domain for further sequence and efficacy improvement. Peptide QP5 was separated into domains (QPX)5 and C-tail. (QPX)3 was also synthesized to investigate how QPX repeats affect the mineralization process. Circular dichroism spectroscopy showed that two (QPX) repeats adopted a β-sheet structure, while C-tail exhibited a disordered structure. (QPX)5 showed more absorption in confocal laser scanning microscopy observation and a higher K value in Langmuir adsorption isotherms compared to C-tail, while (QPX)3 with better hydropathy had greater adsorption capability than (QPX)5. Meanwhile, calcium consumption kinetics, transmission electron microscopy and selected area electron diffraction indicated that (QPX)5, C-tail and (QPX)3 had similar inhibitory effects on the spontaneous calcium consumption and the morphology of their nucleation products were alike, while QP5 had a greater inhibitory effect than them and induced elongated plate-like crystals. X-Ray diffraction further showed that both C-tail and (QPX)3 had greater potential in improving the apatite crystal orientation degree. In conclusion, (QPX)5 was the major adsorption region, both (QPX)5 and C-tail inhibited the nucleation, and C-tail contributed more to improve the HAP orientation degree, so QP5 could exert a significant remineralization effect. By reducing two repeats, (QPX)3 showed higher hydropathicity than (QPX)5 and achieved higher binding affinity, and it was more potential in improving the HAP orientation degree with lower economic cost.
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