Search

Fabricating catalysts with dual active sites is an effective approach for boosting the catalytic activities. In this work, a highly active catalyst with Co nanoparticles decorating on interconnected N-doped carbon nanotube clusters (Co@NCNTS) was synthesized by directly heating the ZIF-67 precursor in H2/Ar atmosphere. The Co nanoparticles exhibited small particle sizes (7–11 nm) and high dispersions, which will prevent the particles from coalescence and agglomeration. In addition, the intertwined NCNTS network could also provide a long-term conductivity, which will facilitate the transfer of charge carriers and effectively enhance the catalytic performance. After that, the catalytic reduction performance of the catalysts to 4-nitrophenol in the presence of NaBH4 solution was also investigated. As expected, the as-synthesized Co@NCNTS catalyst exhibited a superior catalytic reduction ability to 4-nitrophenol in the presence of NaBH4 solution with an almost 100% conversion ratio and a high apparent kinetic rate constant k of 0.37 min−1. Furthermore, the pristine NCNTS also exhibited well catalytic reduction performance to 4-nitrophenol with a k constant of 0.09. The synergetic effect between Co nanoparticles and NCNTS could effectively boost the catalytic reduction performance. Thus, the excellent catalytic performance could own to the confinement effect of ZIF-67 precursors, high conductivity and synergetic effect between Co nanoparticles and NCNTS.

Surface oxygen vacancy defects (OV) are regarded to be beneficial to the gas sensing behavior by significantly improving the carrier density and providing more oxygen adsorption sites. In this work, Ce-doped α-Fe2O3 composites with abundant OV defects were synthesized using an oil bath method assisted with annealing treatment. Morphological characterization results indicate that the lamellar architecture of α-Fe2O3 is transformed to nanospheres composed of massive nanoparticles with small sizes (7–9 nm) after introducing Ce elements. Gas sensing results show that the FeCe10 (Fe/Ce = 10:1) sensors exhibit enhanced acetone sensing response of 26.3–100 ppm gas at the operating temperature of 220 °C toward that of pure α-Fe2O3. Most importantly, X-ray photoelectron spectroscopy and electron spin resonance spectroscopy results confirm that the sensing responses of Ce-doped α-Fe2O3 sensors are directly related to the OV defects, that is, the larger the quantity of the OV defects, the higher the sensing response. The unpaired electrons trapped in OV defects can provide more active sites for adsorption of oxygen and acetone molecules, resulting in a thicker depletion layer and a higher potential barrier. Our work highlights the decisive role of OV defects in gas sensors, which can also provide a rational approach to boost the sensing performance.