RESUMO
Transition metal borides (TMBs) are a class of important but less well-explored electrocatalytic materials for water splitting. The lack of an advanced methodology to synthesize complex nanostructured TMBs with tunable surface properties is a major obstacle to the exploration of the full potential of TMBs for electrocatalytic applications. Here, we report the facile fabrication of a cobalt foam (CF)-supported hierarchical nanostructured Co-Mo-B/CoMoO4-x composite using a hydrothermal method, followed by annealing and NaBH4 reduction treatments. Our study found that NaBH4 reduction of CoMoO4 resulted in the concurrent formation of amorphous Co-Mo-B and an O-vacancy-rich CoMoO4-x substrate, which cooperatively catalyzed the hydrogen evolution reaction (HER) in an alkaline electrolyte. The hierarchical nanoporous structure derived from the dehydration and partial reduction reactions of the CoMoO4·nH2O precursor could offer ample accessible active sites, as well as interconnected channels for rapid mass transfer. In addition, the in situ growth of electrically conductive Co-Mo-B nanoparticles on the defective structured CoMoO4-x substrate imparted the electrocatalyst with good electrical conductivity. As a result, the Co-Mo-B/CoMoO4-x/CF catalyst showed impressively high activity and outstanding stability for the alkaline HER, outperforming most reported TMB electrocatalysts. For instance, it required an overpotential of 55 mV to afford 10 mA·cm-2 and showed a fluctuation of only ±8 mV in a 100 h constant-current test at 100 mA·cm-2.
RESUMO
Catalytic decomposition of the hydrogen-rich hydrazine monohydrate (N2H4·H2O) represents a promising hydrogen storage/production technology. A rational design of advanced N2H4·H2O decomposition catalysts requires an overall consideration of intrinsic activity, number, and accessibility of active sites. We herein report the synthesis of a hierarchically nanostructured NiPt/N-doped carbon catalyst using a three-step method that can simultaneously address these issues. The chelation of metal precursors with polydopamine and thermolysis of the resulting complexes under reductive atmosphere resulted in a concurrent formation of N-doped carbon substrate and catalytically active NiPt alloy nanoparticles. Thanks to the usage of a silica nanosphere template and dopamine precursor, the N-doped carbon substrate possesses a hierarchical macroporous-mesoporous architecture. This, together with the uniform dispersion of tiny NiPt nanoparticles on the carbon substrate, offers opportunity for creating abundant and accessible active sites. Benefiting from these favorable attributes, the NiPt/N-doped carbon catalyst enables a complete and rapid hydrogen production from alkaline N2H4·H2O solution with a rate of 1602 h-1 at 50 °C, which outperforms most existing catalysts for N2H4·H2O decomposition.
RESUMO
A glycosylation strategy based on click chemistry was employed to develop a naphthalimide-based Fe3+ fluorescent probe with low cytotoxicity and good water-solubility. The selectivity and sensitivity to Fe3+ of three synthesized naphthalimide-based fluorescent probes follows a Nap-PZ < Nap-OH < Nap-Glc trend, because Nap-PZ was modified with a good water-soluble group. The cytotoxicity follows a Nap-PZ > Nap-OH > Nap-Glc trend, because the exposed toxic group of Nap-PZ was shielded by a good biocompatible group. The detection limit toward Fe3+ ion follows a Nap-PZ (7.40 × 10-6 M) > Nap-OH (2.73 × 10-7 M) > Nap-Glc (4.27 × 10-8 M) trend. Moreover, Nap-Glc could be used to detect Fe3+ in living cells. The fluorescent "off-on" response of Nap-Glc towards Fe3+ could be recognized by the naked eye, and the "off-on" fluorescent mechanism also was demonstrated by theoretical calculations. Therefore, Nap-Glc is a novel glucosyl naphthalimide fluorescent probe for environmental or biological detection of Fe3+ with low cytotoxicity and good water-solubility.
