The effects of KBrO 3 modification on polyacrylonitrile (PAN) precursor fibers at different modification temperatures were studied. The mechanical properties, chemical structure, aggregation structure, morphological structure, and thermal behavior of PAN precursor fibers were analyzed. The mechanical properties of PAN precursor fibers are essentially unaltered after KBrO 3 modification, although oxygen-containing functional groups are introduced. KBrO 3 can ionize bromate ion in aqueous solution, which has good nucleophilicity and can attack the positively charged carbon atom in C≡N, so that the cyclization proceeds according to the ionic mechanism, allowing the transformation of C≡N to C = N in the PAN precursor fibers generated a cyclic trapezoidal structure containing primary aromatic amine, which reduced the peak temperature of the cyclization reaction from 284.5 °C to 275.1 °C and decreased the heat release. The sp3-hybridized carbon structure changes into a sp2 hybridized C = C structure with increasing aromatization, according to XRD and Raman data, and the KBrO 3 alteration accelerates the degradation of the original microcrystalline structure and transforms into a new polycyclic aromatic structure. The degree of conjugation and aromatization of the system rapidly increased with the rise in modification temperature. The stabilized fibers were discovered to have the lowest R-value, the highest aromatization, the smoothest surface, and the fewest flaws at impregnation temperature of 60 °C.
Semiconductor photocatalytic performances can be modulated through morphology modification. Herein porous hierarchical BiOBr microspheres (BiOBr-MS) of ~3 μm was firstly self-assembled without the assistance of a template via a facile solvothermal synthesis in triethylene glycol (TEG) at 150 °C for 3 h. KBrO3was exploited as a bromine source, which slowly provided bromide ions upon reduction in TEG and controlled the growth and self-assembly of primary BiOBr nanoplates. The addition of PVP during solvothermal synthesis of BiOBr-MS reduced the particle size by about three-fold to generate BiOBr sub-microspheres (BiOBr-sMS) of <1 μm. BiOBr-sMS exhibited significantly higher photocatalytic activity than BiOBr-MS for aerobic photooxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) under simulated sunlight irradiation (conversions of BzOH (50 mM) over BiOBr-sMS and BiOBr-MS were, respectively, 51.3% and 29.6% with 100% selectivity to BzH after Xenon illumination for 2 h at 25 °C). The photogenerated holes and ·O2−were found to be main reactive species for the BzOH oxidation over BiOBr spheres by scavenging tests and spin-trapping EPR spectra. The higher photocatalytic activity of BiOBr-sMS was attributed to its more open hierarchical structure, efficient charge separation, more negative conduction-band position and the generation of larger amounts of ·O2−.Keywords:BiOBr spheres;hierarchical nanostructures;photocatalysis;benzaldehyde
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