The impact of nitrogen doping and reduced-niobium self-doping on the photocatalytic activity of ultra-thin Nb3O8- nanosheets.

Nitrogen doping via high-temperature ammonization is a frequently used strategy to extend the light harvesting capacity of wide-bandgap catalysts in the visible region. Under such a reductive atmosphere, the reduction of transition metals is supposed to occur, however, this has not been thoroughly studied yet. Here, by combining chemically-controlled doping and subsequent liquid exfoliation, ultra-thin [Nb3O8]- nanosheets with separate N doping, reduced-Nb doping and N/reduced-Nb codoping were fabricated for comparative studies on the doping effect for photocatalytic hydrogen evolution. Layered KNb3O8 was used as the starting material and the above-mentioned three doping conditions were achieved by high-temperature treatment with urea, hydrogen and ammonia, respectively. The morphology, crystal and electronic structures, and the catalytic activity of the products were characterized thoroughly by means of TEM, AFM, XRD, XPS, EPR, absorption spectroscopy and photocatalytic hydrogen evolution. Significantly, the black N/reduced-Nb co-doped monolayer [Nb3O8]- nanosheets exhibit the mostly enhanced photocatalytic hydrogen generation rate, indicating a synergistic doping effect of the multiple chemical-design strategy. The modified electronic structure of [Nb3O8]- nanosheets and the role of exotic dopants in bandgap narrowing are put forward for the rational design of better photocatalysts with reduced-metal self-doping.

A Multiple Structure-Design Strategy towards Ultrathin Niobate Perovskite Nanosheets with Thickness-Dependent Photocatalytic Hydrogen-Evolution Performance.

Hydrogen production by catalytic water splitting using sunlight holds great promise for clean and sustainable energy source. Despite the efforts made in the past decades, challenges still exist in pursuing solid catalysts with light-harvesting capacity, large surface areas and efficient utilities of the photogenerated carrier, at the same time. Here, a multiple structure design strategy leading to highly enhanced photocatalytic performance on hydrogen production from water splitting in Dion-Jacobson perovskites KCa2 Nan-3 Nbn O3n+1 is described. Specifically, chemical doping (N/Nb4+ ) of the parent oxides via ammoniation improved the ability of sunlight harvesting efficiently; subsequent liquid exfoliation of the doped perovskites yielded ultrathin [Ca2 Nan-3 Nbn O3n+1 ]- nanosheets with greatly increased surface areas. Significantly, the maximum hydrogen evolution appears in the n=4 nanosheets, which suggests the most favorable thickness for charge separation in such perovskite-type catalysts. The optimized black N/Nb4+ -[Ca2 NaNb4 O13 ]- nanosheets show greatly enhanced photocatalytic performance, as high as 973 µmol h-1 with Pt loading, on hydrogen evolution from water splitting. As a proof-of-concept, this work highlights the feasibility of combining various chemical strategies towards better catalysts and precise thickness control of two-dimensional materials.

Fluorescent N-Doped Carbon Dots as in Vitro and in Vivo Nanothermometer.

The fluorescent N-doped carbon dots (N-CDs) obtained from C3N4 emit strong blue fluorescence, which is stable with different ionic strengths and time. The fluorescence intensity of N-CDs decreases with the temperature increasing, while it can recover to the initial one with the temperature decreasing. It is an accurate linear response of fluorescence intensity to temperature, which may be attributed to the synergistic effect of abundant oxygen-containing functional groups and hydrogen bonds. Further experiments also demonstrate that N-CDs can serve as effective in vitro and in vivo fluorescence-based nanothermometer.

Visible-Light-Induced Effects of Au Nanoparticle on Laccase Catalytic Activity.

A deep understanding of the interaction between the nanoparticle and enzyme is important for biocatalyst design. Here, we report the in situ synthesis of laccase-Au NP (laccase-Au) hybrids and its catalytic activity modulation by visible light. In the present hybrid system, the activity of laccase was significantly improved (increased by 91.2% vs free laccase) by Au NPs. With a short time visible light illumination (λ > 420 nm, within 3 min), the activity of laccase-Au hybrids decreased by 8.1% (vs laccase-Au hybrid without light), which can be restored to its initial one when the illumination is removed. However, after a long time illumination (λ > 420 nm, over 10 min), the catalytic activity of laccase-Au hybrids consecutively decreases and is not reversible even after removing the illumination. Our experiments also suggested that the local surface plasma resonance effect of Au NPs causes the structure change of laccase and local high temperature near the Au NPs. Those changes eventually affect the transportation of electrons in laccase, which further results in the declined activity of laccase.

Non-metal single/dual doped carbon quantum dots: a general flame synthetic method and electro-catalytic properties.

A combustion flame method is developed for the convenient and scalable fabrication of single- and dual-doped carbon quantum dots (CQDs) (N-CQDs, B-CQDs, P-CQDs, and S-CQDs and dual-doped B,N-CQDs, P,N-CQDs, and S,N-CQDs), and the doping contents can be easily adjusted by simply changing the concentrations of precursors in ethanol. These single/dual-doped CQDs, especially B,N-CQDs, show high catalytic activities for the oxygen reduction reaction.

Size-dependent and real-time effect of SiO2 nanoparticles on a single living HeLa Cell's membrane permeability.

In this study, we provide the quantitative data on the membrane permeability of a HeLa cell in the presence of different sizes of SiO2 nanoparticles (NPs, 50, 100 and 200 nm). SiO2 NPs have low cytotoxicity, but 50 and 100 nm SiO2 NPs can increase the cell membrane permeability (a reversible effect) by 12.5% (0.02 mg mL-1, 4 min) and 9% (0.02 mg mL-1, 6 min), respectively. However, the 200 nm SiO2 NPs cannot affect the cell membrane permeability.

[Diagnosis boundary values of metabolic syndrome obesity index for children and adolescents].

OBJECTIVE: To determine the distribution characteristics of waist circumference (WC), waist height ratio (WHtR) of 6-18 years olds in Guangzhou, and to put forward the WC and WHtR appropriate boundary values for 6-18 years olds on the basis of cardiovascular disease (CVD) risk factor assessment. METHODS: We analyzed the height, weight, WC and its metabolic indication data (blood pressure, fasting blood glucose, and blood lipids) of 15 000 children in Guangzhou, aged 6-18, with the receiver-operating characteristic curve (ROC), and explored the best value point of WC and WHtR for the prediction of cardiovascular diseases. RESULTS: When the WC percent reached P85, and WHtR reached 0.48, the cardiovascular risk factors of fasting blood-glucose, blood pressure, and blood fat were significantly higher. CONCLUSION: The 85th percentile value of WC and 0.48 of WHtR are the appropriate boundary values in increasing the cardiovascular disease risk factors in Chinese children and teenagers. WC and WHtR as a relatively simple inspection method, can well predict cardiovascular diseases, and be used in the conventional measuring items among students.

Au nanoparticles in carbon nanotubes with high photocatalytic activity for hydrocarbon selective oxidation.

High-efficiency and high-selectivity catalytic oxidation of alkanes under mild conditions with air is a major aim of current catalytic chemistry and chemical production. Despite extensive development efforts on new catalysts for cyclohexane oxidation, current commercial processes still suffer from low conversion, poor selectivity, and excessive production of waste. Here, we present the design and synthesis of gold nanoparticle/carbon nanotube (CNT) composites for high-efficiency and high-selectivity photocatalyst systems for the green oxidation of cyclohexane. Remarkably, Au nanoparticles confined in carbon nanotubes (Au-in-CNTs) are photocatalytically active for the oxidation of cyclohexane with 14.64% conversion of cyclohexane and a high selectivity of 86.88% of cyclohexanol using air and visible light at room temperature. Given its diversity and versatility of structural and composition design, gold nanoparticle/CNT composites may provide a powerful pathway for the development of high-performance catalysts and production processes for green chemical industry.

Adsorption dominant catalytic activity of a carbon dots stabilized gold nanoparticles system.

Carbon dots (CDs) with abundant functional groups (-OH, -COOH, C=O) on their surface were specially designed to enhance the adsorption capacity and the catalytic activity of gold nanoparticles (AuNPs). The CDs stabilized gold nanoparticles (AuNPs-CDs) were greenly synthesized by a one-step reduction of HAuCl4 with CDs which were used as both the reductant and the stabilizer under visible light irradiation. The resulting AuNPs-CDs exhibit a high catalytic activity towards the reduction of 4-nitrophenol, with a good linear correlation of ln(C(i)/C0) versus time and a kinetic rate constant about 0.68 min(-1). Further detailed adsorption kinetics data indicated that the present adsorption system follows a predominantly second-order rate model, and the CDs capped on the surface of the AuNPs also enhanced the adsorption capacity and the catalytic activity of the AuNPs.

Quantitative and real-time effects of carbon quantum dots on single living HeLa cell membrane permeability.

The interaction between carbon quantum dots (CQDs) and a single living cell was explored in real time. Here, we provide the quantitative data on the permeability of the HeLa cell membrane in the presence of CQDs with different surface functional groups (CQDs terminated with -OH/-COOH (CQD-OH), -PEG (CQD-PEG), and -NH2 (CQD-NH2)). Although these CQDs have very low toxicity towards HeLa cells, they still increase the cell membrane permeability by 8%, 13%, and 19% for CQD-PEG, CQD-OH, and CQD-NH2, respectively, and this kind of permeability was irreversible. These observations are valuable for promoting the bio-applications of carbon nanostructures in living systems.

Carbon quantum dots with photo-generated proton property as efficient visible light controlled acid catalyst.

Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.

High-bright fluorescent carbon dots and their application in selective nucleoli staining.

Fluorescent carbon dots (FCDs) were synthesized by refluxing polyethylene glycol, which can emit bright and different fluorescent colours under various wavelengths as well as show stable fluorescence properties with different ionic strength, temperature and time. These FCDs exhibit good biocompatibility and very low toxicity for HeLa cells. Notably, these FCDs, as an efficient live cell fluorescence imaging probe, can selectively stain nucleoli, and the effect is similar to some commercially available dyes (such as Hoechst).

One-step catalase controllable degradation of C3N4 for N-doped carbon dot green fabrication and their bioimaging applications.

Water-soluble fluorescent N-doped carbon dots (N-C dots) obtained by enzyme catalyzed degradation of C3N4 show high stability, good biocompatibility, and can be promising candidates for bioimaging.

Convenient and sensitive detection of norfloxacin with fluorescent carbon dots.

Carbon dots (CDs) were synthesized by refluxing glucose, as efficient fluorescence probes, which show convenient and sensitive detection of norfloxacin (NOR) over a wide concentration range. It is worth noting that because of the hydrogen bond interactions between the CDs and NOR, the fluorescence intensity of CDs was remarkably enhanced in the presence of NOR, which indicates that CDs are capable of rapid, stable and sensitive determination of NOR. Compared with high-performance liquid chromatography, the fluorescence enhancement method is considerably simpler and faster, and will pave a new way for the determination of NOR.

Carbon dots for photoswitching enzyme catalytic activity.

Enzyme engineering for improved catalysis has wide implications. Here, we report the modulation of enzyme (porcine pancreatic lipase, PPL) catalytic activity in the presence of carbon quantum dots (CQDs) by visible light. Upon visible light irradiation, the activity of PPL/CQDs increased to 10% higher than that of free PPL, whereas without a light source, the activity of PPL/CQDs decreased to 30% lower than that of free PPL. Based on Michaelis-Menten kinetics, CQDs were confirmed to play an important role as a non-competitive inhibitor. Our results present a potential new method for developing hyper-catalytic hybrid enzymes for bio-catalytic applications.