Amino-functionalized highly crosslinked organic-inorganic hybrid polyphosphazene microspheres were prepared via a one-pot polycondensation method and served as a fluorescent sensor for the detection of Fe 3+ in solution. With the introduction of p-phenylenediamine unites, the polyphosphazene microspheres could be endowed with fluorescent property and abundant active amino groups on the surface. The microspheres were further used as the fluorescent sensor for the detection of Fe 3+ . Fluorescence study showed high sensing sensitivity and selectivity of the microspheres, and the limit of detection was determined as 0.076 μM for Fe 3+ . Active amino groups on the surface could efficiently improve the detection sensitivity of Fe 3+ . Moreover, highly crosslinked organic-inorganic hybrid structure was beneficial to the photostability and thermostability, enabled the microspheres to be possible for constructing practicable sensors. This work is expected to inspire the design of advanced polyphosphazene-based fluorescent sensors for applications in analytical detection.
The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron−hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, Cu 2 O@Cu 4 (SO 4 )-(OH) 6 •H 2 O core−shell polyhedral heterojunctions were fabricated via in situ etching Cu 2 O with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (Na 2 S 2 O 3 ). Cu 2 O@Cu 4 (SO 4 )(OH) 6 •H 2 O polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single Cu 2 O polyhedra and Cu 4 (SO 4 )(OH) 6 •H 2 O. When Cu 2 O with a different morphology contacts with Cu 4 (SO 4 )(OH) 6 •H 2 O, a built-in electric field is established at the interface due to the difference in Fermi level (E f ); meanwhile, the direction of band bending and the band alignment are determined. These lead to the different migration pathways of electrons and holes, and thereby, a type-II or S-scheme heterojunction is constructed. The results showed that octahedral o-Cu 2 O@ Cu 4 (SO 4 )(OH) 6 •H 2 O is an S-scheme heterojunction; however, cuboctahedral co-Cu 2 O@Cu 4 (SO 4 )(OH) 6 •H 2 O and cubic c-Cu 2 O@Cu 4 (SO 4 )(OH) 6 •H 2 O are type-II heterojunctions. By means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), diffuse reflectance spectra (DRS), and Mott−Schottky analyses, the band alignments, Fermi levels, and band offsets (ΔE CB , ΔE VB ) of Cu 2 O@Cu 4 (SO 4 )(OH) 6 •H 2 O polyhedral heterojunctions were estimated; the results indicated that the catalytic ability of the composite catalyst is determined by the type of heterojunction and the sizes of band offsets. Cubic c-Cu 2 O@Cu 4 (SO 4 )(OH) 6 •H 2 O has the strongest driving force (namely, biggest band offsets) to accelerate charge migration and effectively separate charge carriers, so it exhibits the strongest catalytic bactericidal and degrading abilities.
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