TMB+-mediated etching of urchin-like gold nanostructures for colorimetric sensing.

The morphology-dependent localized surface plasmon resonance of gold nanostructures has been widely utilized for designing sensors. One method relies on the color change of gold nanoparticles upon etching. In previous work, TMB2+oxidized from 3,3',5,5'-tetramethylbenzidine (TMB) was found to etch gold nanorods (AuNRs), leading to a spectrum of different colors. However, the preparation of TMB2+needs the addition of a strong acid and other harsh conditions. Herein, a new colorimetric biosensing platform was developed using urchin-like gold nanoparticles (AuNUs). Compared with AuNRs, the etching of AuNUs can happen under mild conditions by TMB+at pH 6, protecting enzymes and proteins from denaturation. The role of CTAB surfactant was dissected, and its bromide ions were found to be involved in the etching process. Based on these observations, a one-step colorimetric detection of H2O2was realized by using horseradish peroxidase and H2O2to oxidize TMB. Within 30 min, this system achieved a detection limit of 80 nM H2O2. This work offered fundamental insights into the etching of anisotropic gold nanostructures and optimized the etching conditions. These advancements hold promise for broader applications in biosensing and analytical chemistry.

Size-Tunable Fe3O4 Spherical Nanoclusters Through a One-Pot Hydrothermal Synthesis.

A new method is presented for the synthesis of monodisperse, size-tunable Fe3O4 spherical nanocluster particles through a simple, one-step hydrothermal reaction, according to a kinetics-controlled self-assembly process of smaller nanocrystals into hierarchical mesoporous aggregates. The mean diameter of the particles can be controlled over a broad range up to ~230 nm by simply varying the concentration of the precipitating reagent (urea or ammonia). The particles can be easily dispersed in water with excellent colloidal stability, exhibit a high surface area of ~ 60 m2 g(-1), and demonstrate size-dependent magnetic separation kinetics, where the larger nanoclusters exhibit rapid magnetophoresis, and the smaller nanoclusters remain inseparable. Thus particle size control is essential for improving magnetic separation processes.

Mesoporous magnetically recyclable photocatalysts for water treatment.

Photocatalysis over titanium dioxide is a promising technology for water purification and degradation of emerging contaminants, however, catalyst efficiency and recovery after the photocatalytic reaction are key challenges that have limited the practical deployment of TiO2 in water treatment applications. Herein we report the synthesis of core-shell, superparamagnetic gamma-Fe2O3@SiO2@TiO2 colloidal nanospheres with a mesoporous TiO2 shell, their characterization, and application in photocatalysis. The final surface area of the particles was - 100 m2 g(-1), and their photocatalytic efficiency matched that of P25 TiO2.

Photocatalytic activity of hydrogenated TiO2.

Photocatalysis is a promising advanced water treatment technology, and recently the possibility of using hydrogenation to improve the photocatalytic efficiency of titanium dioxide has generated much research interest. Herein we report that the use of high-temperature hydrogenation to prepare black TiO2 primarily results in the formation of bulk defects in the material without affecting its electronic band structure. The hydrogenated TiO2 exhibited significantly worse photocatalytic activity under simulated sunlight compared to the unhydrogenated control, and thus we propose that high-temperature hydrogenation can be counterproductive to improving the photocatalytic activity of TiO2, because of its propensity to form bulk vacancy defects.