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Fe/N-doped carbon magnetic nanocubes (Fe/N-C MNCs) were feasibly fabricated through in situ thermal transformations of Prussian blue nanocubes (PB NCs) in an inert atmosphere, and the resultant composite employed as the heterogeneous noble-metal-free catalyst possessed satisfactory catalytic performance in hydrogen peroxide activation. By examining the properties of Fe/N-C MNCs, we demonstrate for the first time that the catalyst could act in synergy with ultrasonic irradiation and accelerate the selectivity of the degradation reaction of dyes. The degradation efficiency of the organic positively charged dye (methylene blue) is significantly increased after ultrasonic irradiation addition, probably owing to charge matching between a positively charged dye and the Fe/N-C MNCs. Interestingly, organic pollution degradation mainly follows a non-radical pathway. Furthermore, singlet oxygen ( 1 O 2 ) is predominantly produced by Fe/N-C MNCs on H 2 O 2 activation, and it is the contributor to catalytic degradation instead of hydroxyl and/or superoxide anion radicals. Moreover, the Fe/N-C MNCs exhibit excellent stability and reusability. These findings offer interesting insights into the potential application of functional noble-metal-free materials in catalysis and wastewater remediation under ultrasonic radiation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Iron-carbon (Fe/C) magnetic nanocubes were synthesized by direct pyrolysis of Prussian blue nanocubes under an inert gas atmosphere. They are shown to possess intrinsic peroxidase mimicking activity to catalyze the oxidation of peroxidase substrate N,N-diethyl-p-phenylenediamine sulfate salt to form a purple colored product in the presence of H 2 O 2 . The values for K m and V max are 74 μM and 46 nmol s -1 , respectively. Steady-state kinetic analysis also indicates that the catalysis reaction follows a ping-pong mechanism. Based on these findings, an ultrasensitive colorimetric H 2 O 2 assay was worked. Absorbance (best value measured at 550 nm) increases linearly in the 10 nM to 0.2 mM H 2 O 2 concentration range, and the limit of detection is 1.5 nM. The method was also applied to the quantification of glucose, which is oxidized by glucose oxidase in the coexistence of H 2 O 2 . The response covers the 0.1 to 500 μM glucose concentration range, and the limit of detection is 16 nM. The method was applied to the determination of H 2 O 2 in rainwater samples. The glucose assay was used to analyze serum samples, and satisfactory results were obtained. Other attractive features include good chemical activity, low cost, easy storage, and high catalytic efficiency. Graphical abstract Schematic presentation of converting Prussian blue nanoparticles into Fe/C magnetic nanocubes by a pyrolysis technique and the use of glucose oxidase and Fe/C magnetic nanocubes to establish a one-step spectrophotometric method for the determination of glucose and hydrogen peroxide.

Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe(3)O(4)/SiO(2) magnetic core-shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe(3)O(4)/SiO(2) nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able to activate hydrogen peroxide (H(2)O(2)), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H(2)O(2) concentrations ranging from 5.0 x 10(-9) to 1.0 x 10(-5) mol L(-1), with a detection limit of 2.1 x 10(-9) mol L(-1). By simultaneously using glucose oxidase and HRP-immobilized Fe(3)O(4)/SiO(2) nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0 x 10(-8) to 5.0 x 10(-5) mol L(-1) with a detection limit of 1.8 x 10(-8) mol L(-1). The proposed method was successfully applied for the determination of glucose in human serum sample.

Abstract: Electroactive TiO2 films were prepared by liquid-phase deposition (LPD) in the presence of sodium dodecylsulfonate. The doping of dodecylsulfonate (DS) converted the TiO2 film from a structure of globular nanoparticles to a structure of nano-flakes, which directly influenced the electrochemical behavior of the film. The DS-doped TiO2 film yields an enhanced reduction peak in the cyclic voltammograms, being attributed to the reduction of hydroxylated titanium(IV) species. The varied surface structure of the DS-doped TiO2 film provided a biocompatible platform for immobilizing hemoglobin (Hb), and the Hb-immobilized film electrode exhibited good electrocatalytic activity to the reduction of H2O2. As a sensor for the determination of H2O2, the Hb-immobilized film electrode yielded an excellently linear range from 0.003 to 1.5mM H2O2 in the correlation between reduction peak current and H2O2 concentration, with a low detection limit of 1.0μM. [Copyright &y& Elsevier]