Surface modified silver/magnetite nanocomposite activating hydrogen peroxide for efficient degradation of chlorophenols.

The mixed-valent magnetite (Fe3O4) played a critical role in H2O2-based Fenton-like system for the removal of chlorophenols, but high activity and cycle stability of the Fe3O4-based catalysts are still a huge challenge. Herein, a series of surface hydroxyl- and carboxyl-modified Ag0/Fe3O4 nanocomposite catalysts were prepared and used to activate H2O2 for degradation chlorophenols pollutants. Under the optimized condition, nearly 100% degradation ratio were achieved within 2-30 min for 2,4-dichlorophenol, 2,3-dichlorophenol, 3,4-dichlorophenol, 2,4,6-trichlorophenol, p-nitrophenol, and 98% degradation ratio for 2,5-dichlorophenol, 2,6-dichlorophenol and 3,5-dichlorophenol,. Moreover, wide pH applicability was obtained for the Ag0/Fe3O4-H2O2 system, where 95% degradation ratio of 2,4-dichlorophenol was still obtained at pH 6.0. The excellent activity of Ag0/Fe3O4 catalyst can be ascribed to the incorporation of Ag0 nanoparticles that accelerated the Fe(III)/Fe(II) transformation with the assistance of surface hydroxyl and carboxyl groups. Detailed mechanism study indicated a pseudo-second-order kinetic model, where the oxidative degradation and reductive degradation pathways coexisted in the system. The surface-modified Ag0/Fe3O4-H2O2 provide a practical catalyst system for the removal of phenol contaminants with high reaction rate, wide pH adaptability, and validity for a series of chlorophenols.

3-Aminobenzeneboronic Acid Functionalized MoS2 Quantum Dot as Fluorescent Nanoprobe for the Determination of o-Dihydroxybenzene.

In this work, by functionalizing MoS2 quantum dot with 3-aminobenzeneboronic acid, a novel multifunctional quantum dot (denoted as B-MoS2 QD) was obtained and used successfully for a fluorescence nanoprobe for detecting o-dihydroxybenzene (o-DHB). Transmission electron microscopy, fluorescence spectrum, UV-vis spectrum and fluorescence lifetime were used to investigate the prepared nanoprobe. The results show that the B-MoS2 QD nanoprobe can exhibit strong fluorescence and excellent light fastness owing to the coupled effect from the MoS2 QDs and boronic acid; interestingly, the vicinal diols structure from its surface can bridge covalently with o-DHB, resulting in the fluorescence quenching of B-MoS2 QDs and selective recognition toward o-DHB. With the increasing of o-DHB concentration, the nanoprobe fluorescence would gradually decrease. By measuring the fluorescence intensity of B-MoS2 QDs, a wide linear range from 0.1 to 200.0 µM with a low detection limit of 0.025 µM was obtained for o-DHB analysis; meanwhile, this fluorescence nanoprobe possesses excellent selectivity for the selective detection of o-DHB from its analogues.

Highly sensitive and selective "off-on" fluorescent sensing platform for ClO- in water based on silicon quantum dots coupled with nanosilver.

We present a new "off-on" fluorescence probe for detecting hypochlorite (ClO-) based on silicon quantum dots coupled with silver nanoparticles (SiQDs/AgNPs) as nanocomplexes. Via introducing N-[3-(trimethoxysilyl)propyl]ethylenediamine and catechol as initial reactants, silicon quantum dots (SiQDs) with excellent properties were synthesized through a simple hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The fluorescence of SiQDs could be quenched by the silver nanoparticles (AgNPs) by surface plasmon-enhanced energy transfer (SPEET) from SiQDs (donor) to AgNPs (acceptor). The AgNPs could be etched by adding ClO-, thus freeing the SiQDs from the AgNP surfaces and restoring the SiQDs' fluorescence. The sensing system exhibits many advantages, such as wide linear response range, high sensitivity, and excellent selectivity. Under optimized conditions, wide linear ranges (from 0.1 to 100.0 µM) and low detection limits (0.08 µM) were obtained for ClO-. Graphical Abstract.

Silicon quantum dot-coated onto gold nanoparticles as an optical probe for colorimetric and fluorometric determination of cysteine.

Silicon quantum dots (SiQDs) were synthesized from N-[3-(trimethoxysilyl)propyl]-ethylenediamine and catechol by a hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The SiQDs were then placed on gold nanoparticles (AuNPs). When Cys is added to this solution, Cys will penetrate the SiQDs "shell" of the SiQDs/AuNP composite. This is due to the interaction and conformational differences of Cys and other substance with AuNPs and leads to the dispersion of the aggregated SiQD/AuNPs. A color change from purple to red can be visually observed, and the (green) fluorescence of SiQDs (with excitation/emission peaks at 430/520 nm) is restored. This dual-readout nanoprobe was successfully applied to the selective and sensitive detection of cysteine (Cys) in (spiked) serum and urine samples. The detection limit is 3.5 nmol·L-1 (at an S/N ratio of 3), and the method works on the 0.01 to 2 µM Cys concentration range. Graphical abstract Schematic illustration of a method for synthesizing silicon quantum dots (SiQDs) and coating them on gold nanoparticles (AuNPs) as an optical probe for colorimetric and fluorometric determination of cysteine.