Co 3 O 4 is a well-known catalyst in the oxidation reaction. In such a catalyst, the geometric and electronic structures of tetrahedrally coordinated Co 2+ and octahedrally coordinated Co 3+ can be regulated by directional metal ion substitution strategy, accompanied by the modification of catalytic activity. Herein, normal and inverse cobalt-based spinel catalysts M x Co 3−x O 4 (M = Zn and Ni) with a threedimensionally ordered macroporous (3DOM) structure were successfully fabricated through the carboxy-modified colloidal crystal templating (CMCCT) method. The relationship between the dopant and activity during NO x -assisted soot oxidation was systematically studied by means of XPS, H 2 -TPR, soot-TPR, isothermal anaerobic titrations, NO-TPO, soot-TPO, and so on. The well-defined 3DOM structure for M x Co 3−x O 4 catalysts can improve the contact efficiency of soot and catalysts. 3DOM NiCo 2 O 4 exhibits high catalytic activity for soot oxidation under a loose contact mode between soot and catalyst. For instance, its T 50 and TOF values are 379 °C and 1.36 × 10 −3 s −1 , respectively. The doping of Ni to Co 3 O 4 will induce the structural distortion, improve the density of oxygen vacancies, and enhance lattice oxygen mobility. It leads to more surface-active oxygen species. A vacancy-mediated pathway of NO oxidation on the spinel catalyst is proposed according to the experimental results of in situ DRIFT spectra, in situ Raman spectra, and the theoretical knowledge of coordination chemistry of metal−NO. The catalytic performance of soot oxidation is highly related to the capacity of a catalyst in oxidizing NO to NO 2 . Therefore, indirect NO 2 -assisted mechanism is proposed for soot oxidation under an NO/O 2 /N 2 atmosphere.
This study demonstrates high contrast and sensitivity by designing a dual-emissive hydrogel particle system, whose two emissions respond to pH and temperature strongly and independently. It describes the photoluminescence (PL) response of poly(N-isopropylacrylamide) (PNIPAM)-based core/shell hydrogel nanoparticles with dual emission, which is obtained by emulsion polymerization with potassium persulfate, consisting of the thermo- and pH-responsive copolymers of PNIPAM and poly(acrylic acid) (PAA). A red-emission rare-earth complex and a blue-emission quaternary ammonium tetraphenylethylene derivative (d-TPE) with similar excitation wavelengths are inserted into the core and shell of the hydrogel nanoparticles, respectively. The PL intensities of the nanoparticles exhibit a linear temperature response in the range from 10 to 80 °C with a change as large as a factor of 5. In addition, the blue emission from the shell exhibits a linear pH response between pH 6.5 and 7.6 with a resolution of 0.1 unit, while the red emission from the core is pH-independent. These stimuli-responsive PL nanoparticles have potential applications in biology and chemistry, including bio- and chemosensors, biological imaging, cancer diagnosis, and externally activated release of anticancer drugs.
The authors describe strongly red-emitting carbon dots (CDs) which were obtained via microwave synthesis using phenylenediamine as the carbon source. The structural and optical properties of the resultant CDs are studied in some detail. The CDs possess (a) longwave emission (peaking at 620 nm under 470 nm excitation), (b) a quantum yield of ~15%, (c) a size of typically 3.8 nm; and (d) good photostability. The CDs have a pH-dependet response that covers the pH 5 to 10 range, and their fluorescence is quenched by ferric ions. The CDs can detect ferric ions in aqueous samples in the 0 to 30 μM concentration range with a lower detection limit of 15 nM. The CDs were also used to image pH values and ferric ions in E. coli bacteria. Graphical abstract The red-emitting carbon dots with high stability are synthesized which show dual response to pH-values and ferric ions in aqueous solution and biological media simultaneously.
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