Nitrogen and sulfur co-doped carbon quantum dots as "on-off-on" fluorescence probes to detect Hg2+ and MnO4- and improving the photostability of Rhodamine B.

BACKGROUND: Carbon quantum dot (CQDs) are zero-dimensional carbon nanomaterials with a size of less than 10 nm CQDs are widely used in the field of ion detection by virtue of their fluorescence characteristics such as strong fluorescence intensity, good optical stability and tunable emission wavelength. Although the traditional atomic absorption method, electrochemical method and other metal ion detection methods are highly sensitive, the operation is complex, expensive and limited by the site. Therefore, we prepared the N, S-CQDs capable of detecting Hg2+ and MnO4- in water with the advantages of simple operation, low cost, and direct visual signal. RESULTS: N, S-CQDs with high-quantum yield (77.68%), uniform particle size (0.4 nm-2.6 nm) and green fluorescence were created utilizing a one-pot hydrothermal process with the precursors ASDA-Na4 and m-phenylenediamine. N, S-CQDs has good optical properties such as high fluorescence intensity, wavelength independence, up-conversion luminescence and fluorescence stability. We examined 27 common ions in water and found that the fluorescence of N, S-CQDs could be selectively quenched by Hg2+ and MnO4-, and the detection limits are 0.41 µM and 1.2 µM, respectively. The mechanism of quenching is further investigated. The fluorescence of N, S-CQDs-Hg2+ system can be restored by halogen ions (Cl-, Br-, I-), while the fluorescence of N, S-CQDs-MnO4- system can be partially restored by Fe2+. This forms an "on-off-on" mode of fluorescent probes. In addition, we also studied that trace amounts of N, S-CQDs can improve the photostability of RhB. SIGNIFICANCE: The N, S-CQDs are fluorescent probes in an "on-off-on" mode. N, S-CQDs with green fluorescence (on) can be quenched by Hg2+ and MnO4- (off). The fluorescence quenched by Hg2+ can be restored by halogen ions again, while the fluorescence quenched by MnO4- can partially be restored (on). This ion detection method can be used to visually detect the two ions in the field, with the advantages of low cost, simple operation and visual intuition.

The construction of molecularly imprinted electrochemical biosensor for selective glucose sensing based on the synergistic enzyme-enzyme mimic catalytic system.

It is generally accepted that glucose oxidase (GOx) shows unique specificity in ß-d-glucose catalysis. However, it has been found that GOx can catalyze diverse monosaccharides. Therefore, the sensing accuracy for glucose biosensors using GOx as probes will be largely compromised by the presence of other monosaccharides. Herein, multifunctional bi-nanospheres (Fe3O4@Au NCs), which show both peroxidase-like and catalase-like catalytic activities in different working conditions, are successfully constructed and served as desirable platform with huge surface area for the immobilization of large amount of GOx probes. In acidic environment, hydroxyl radicals could be generated via the cascaded catalysis of ß-d-glucose by Fe3O4@Au-GOx, and then employed to initiate the polymerization of boric acid derivative to prepare molecularly imprinted polymers (MIPs) on the surface of GOx using ß-d-glucose as template. Then, the molecularly imprinted GOx are immobilized on the surface of highly oriented pyrolytic graphite (HOPG) electrode and an electrochemical biosensor (Fe3O4@Au-GOx-HOPG) for glucose sensing is successfully obtained. Interestingly, the as-prepared biosensors could selectively detect glucose in the range of 10.0 µM - 5.0 mM with a LOD = 5.0 µM with the help of MIPs, which is comparable or better than other glucose sensors reported recently.

A Pyrene Fluorescent Probe for Rapid Detection of Ferric Ions.

The 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSA) is a pyrene derivative with high fluorescence characteristics and is widely used in fluorescence tracer. This study aims at investigating a simple and fast fluorescence detection method for determining the concentration of ferric ion by using PTSA, which the principle is that the fluorescence quenching of PTSA by ferric ions. Theoretical and experimental methods were adopted to deeply analyze its detection performance and characteristics. The fluorescence quenching phenomena under different pH conditions and the effect of the different interfering metal ions on PTSA/Fe3+ system was studied. The results showed that the PTSA was quite promising for the fluorescence detection of trace ferric ions, and the limit of detection is 9 µg/L. This study is envisioned to provide inspirational insights on trace detection of iron ions, opening new routes for water monitoring use fluorescence properties.

Three-dimensional self-floating foam composite impregnated with porous carbon and polyaniline for solar steam generation.

A promising approach to resolving insufficient freshwater resources is utilizing solar energy for steam generation. Although various types of photothermal conversion materials have been developed, there are still some obstacles, such as complicated system structure fabrication and low energy utilization, that severely hinder their practical application. Herein, we designed and produced a self-floating porous carbon/polyaniline foam (PCPF) evaporator via impregnating melamine foam with porous carbon generated following the bottom-up pyrolytic method and polyaniline, followed by thermal treatment, for efficient solar steam generation. The PCPF obtained with a porous carbon (PC) to polyaniline (PAN) mass ratio of 3:5 (PCPF-3) exhibited a rich pore structure, good hydrophilicity, low thermal conductivity (0.0413 W m-1 K-1), and excellent light absorption (96.1%). Our results show that, without additional thermal insulators, the evaporation rate of PCPF-3 reached 1.496 kg m-2 h-1, and the photothermal conversion efficiency reached 87.3% under one sun irradiation. Furthermore, it also exhibited good durability and desalination performance. This type of environmentally friendly, low-cost, and stable photothermal conversion material could be used in water treatment and seawater desalination.

Degradation of fluorescent dye-Solvent Green 7 (HPTS) in wastewater by advanced oxidation process.

Solvent Green 7 (HPTS) is a widely used fluorescent dye. As a kind of polycyclic aromatic hydrocarbon (PAHs) derivative, HPTS would cause pollution when it is discharged into the environment. This study adopted advanced oxidation processes (UV/H2O2) to degrade the HPTS in aqueous solution and investigated the effects of various factors on the degradation. The results showed that: the initial concentration and the fluorescence characteristics of HPTS reduced the degradation efficiency. When the oxidant concentration of H2O2 was 3 mg/L, the degradation efficiency and cost of HPTS (20 mg/L) were the most appropriate; when there were various inorganic anions in the solution, the degradations were not affected, but when the solution was strong acid and there existed a lot of chloride ions, the degradation of HPTS was inhibited. The degradation pathways indicated HPTS degraded into naphthalene derivatives, benzene derivatives through oxidation and decarboxylation reactions, finally into water and carbon dioxide. Further research for substances similar to HPTS structure will make progress in understanding the degradation process of PAHs.