Lichun Zhang

Graphene sheets decorated with SnO2 nanoparticles: in situ synthesis and highly efficient materials for cataluminescence gas sensors

Graphene sheets decorated with SnO2 nanoparticles were prepared through a facile hydrothermal-assisted in situ synthesis route. According to the XPS, XRD, FESEM and TEM analysis, rutile SnO2 nanocrystals were exclusively deposited on graphene sheets with high density and high uniformity to form layered composite sheets. Propanal, a common volatile organic compound, was selected as a model to investigate the cataluminescence (CTL) sensing properties of the SnO2/graphene composite in this paper. It was found that the strong CTL emission could be generated due to the catalyzing oxidization of propanal on the surface of SnO2/graphene composite and this composite was an efficient sensing material for propanal. We further studied the analytical characteristics of the CTL sensor based on SnO2/graphene composite sensing material for propanal under the optimal experimental conditions. The linear range of the propanal gas sensor was 1.34–266.67 μg mL−1 (r = 0.9987), over two orders of magnitude, and the detection limit was 0.3 μg mL−1(S/N = 3).

Carbon Nitride Quantum Dots: A Novel Chemiluminescence System for Selective Detection of Free Chlorine in Water

A facile one-step microwave-assisted approach for the preparation of strong fluorescent carbon nitride quantum dots (g-CNQDs) by using guanidine hydrochloride and EDTA as the precursors was developed. Strong chemiluminescence (CL) emission was observed when NaClO was injected into the prepared g-CNQDs, and a novel CL system for direct detection of free chlorine was established. Free residual chlorine in water was sensitively detected with a detection limit of 0.01 μM and had a very wide detection range of 0.02 to 10 μM. On the basis of CL spectral, UV-visible absorption spectral, and electron spin resonance (ESR) spectral studies, as well as investigations on the effects of various free radical scavengers, a possible CL mechanism was proposed. It was suggested that the radiative recombination of oxidant-injected holes and electrons in the g-CNQDs accounted for the CL emission. Meanwhile, (1)O2 on the surface of g-CNQDs, generated from some reactive oxygen species in the g-CNQDs-NaClO system, could transfer energy to g-CNQDs and thus further enhance the CL emission. The CL system is highly sensitive and differentiable, opening a new field for the development of novel CL-emitting species, but also expanding the conventional optical utilizations of g-CNQDs.

SiO2/graphene composite for highly selective adsorption of Pb(II) ion

SiO(2)/graphene composite was prepared through a simple two-step reaction, including the preparation of SiO(2)/graphene oxide and the reduction of graphene oxide (GO). The composite was characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy, and what is more, the adsorption behavior of as-synthesized SiO(2)/graphene composite was investigated. It was interestingly found that the composite shows high efficiency and high selectivity toward Pb(II) ion. The maximum adsorption capacity of SiO(2)/graphene composite for Pb(II) ion was found to be 113.6 mg g(-1), which was much higher than that of bare SiO(2) nanoparticles. The results indicated that SiO(2)/graphene composite with high adsorption efficiency and fast adsorption equilibrium can be used as a practical adsorbent for Pb(II) ion.

Well-redispersed ceria nanoparticles: Promising peroxidase mimetics for H2O2 and glucose detection

Well-redispersed ceria nanoparticles (CeO2 NPs) were synthesized by a simple hydrothermal method. The prepared CeO2 NPs exhibited excellent catalytic activity towards classical peroxidase substrate 3,3,5,5-tetramethylbiphenyl dihydrochloride (TMB·2HCl) in the presence of H2O2, based on which a colorimetric method that is highly sensitive and selective was developed for glucose detection. The composition, structure, morphology and peroxidase-like catalytic activity of CeO2 NPs are investigated in detail by using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), thermal analysis (TG) and UV-vis absorption spectroscopy. According to this method, the detection of H2O2 and glucose are in linear range from 6.0 × 10−7 to 1.5 × 10−6 mol L−1 and 6.6 × 10−6 to 1.3 × 10−4 mol L−1, with the detection limit down to 5.0 × 10−7 mol L−1 H2O2 and 3.0 × 10−6 mol L−1 glucose, respectively. Further, this simple, cheap, highly sensitive and selective colorimetric method for glucose detection was successfully applied for the determination of glucose in human serum samples.

Luminescent ZnO quantum dots for sensitive and selective detection of dopamine

Water-soluble and luminescent ZnO quantum dots (QDs) capped by (3-aminopropyl) triethoxysilane (APTES) are environment-friendly with strong photoluminescence (max. wavelength: 530 nm). Interestingly, it was found that the fluorescence could be quenched by dopamine (DA) directly. On the basis of above, a novel ZnO QDs based fluorescent probe has been successfully designed to detect DA with high selectivity and sensitivity. Moreover, the possible fluorescence quenching mechanism was proposed, which showed that the quenching effect may be caused by the electron transfer from ZnO QDs to oxidized dopamine-quinone. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of DA within the range from 0.05 to 10 μM, with the detection limit down to 12 nM (n=3). Also, the selectivity experiment indicated the probe had a high selectivity for DA over a number of possible interfering species. Finally, this method was successfully used to detect DA in serum samples with quantitative recoveries (99-110%). With excellent selectivity and high sensitivity, it is believed that the ZnO QDs based fluorescent probe has a potential for the practical application in clinical analysis.

Colorimetric detection of glutathione in human blood serum based on the reduction of oxidized TMB

In this paper, a novel and simple colorimetric method for the determination of glutathione (GSH) was developed. The BSA–MnO2 NPs possess oxidase-like activity that can catalyze the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB), and the existence of GSH can cause reduction of oxidized TMB along with a visual color variation. A good linear relationship can be obtained from 0.26 to 26 μM with a limit of detection of 0.1 μM. Furthermore, the good recoveries for serum samples indicated that the present colorimetric methodology was feasible, simple and sensitive, with a promising application in routine analysis of biosamples.

A cataluminescence gas sensor for carbon tetrachloride based on nanosized ZnS

A novel and sensitive gas sensor was proposed for the determination of carbon tetrachloride based on its cataluminescence (CTL) by oxidation in the air on the surface of nanosized ZnS. The luminescence characteristics and the optimal conditions were investigated in detail. Under the optimized conditions, the linear range of the CTL intensity versus the concentration of carbon tetrachloride was 0.4-114microg mL(-1), with a correlation coefficient (R) of 0.9986 and a limit of detection (S/N=3) of 0.2microg mL(-1). The relative standard deviation (R.S.D.) for 5.9microg mL(-1) carbon tetrachloride was 2.9% (n=5). There was no or weak response to common foreign substances including methanol, ethanol, benzene, acetone, formaldehyde, acetaldehyde, dichloromethane, xylene, ammonia and trichloromethane. There was no significant change of the catalytic activity of the sensor for 40h over 4 days, with a R.S.D. of less than 5% by collecting the CTL intensity once an hour. The proposed method was simple and sensitive, with a potential of detecting carbon tetrachloride in environment and industry grounds. The possible mechanism was also discussed briefly.

A green solid-phase method for preparation of carbon nitride quantum dots and their applications in chemiluminescent dopamine sensing

A facile, green and one-step synthesis strategy towards highly fluorescent g-CNQDs via solid-phase pyrolyzing melamine and EDTA at low temperature was proposed. The obtained g-CNQDs can produce strong chemiluminescence (CL) in the presence of K3[Fe(CN)6]. The mechanism of the g-CNQDs–K3[Fe(CN)6] CL system was investigated by using CL, UV-Vis absorption, IR, fluorescence and electron spin resonance (ESR) spectrum. The CL emission was probably from the radiative recombination of oxidant-injected holes and the thermally excited electrons in g-CNQDs. The established new CL system was successfully applied to determinate dopamine in the range of 1 × 10−8 to 2 × 10−6 M with a detection limit of 4.7 nM (S/N = 3). The protocol was validated by analyzing serum samples with excellent sensitivity and good recoveries. The new CL system offered a valuable insight for the properties of luminescent g-CNQDs in CL field, and opened a new avenue for its practical applications.

One-step facile synthesis of coral-like Zn-doped SnO2 and its cataluminescence sensing of 2-butanone

Self-assembly of one-dimensional nanoscale building blocks into functional 2-D or 3-D complex superstructures is of great importance. In this work, we have developed a facile hydrothermal method to synthesize coral-like Zn-doped SnO2 hierarchical structures assembled from nanorods. XRD, SEM, TEM, XPS, FTIR and N2 adsorption–desorption were used to characterize the compositions and microstructures of the samples obtained. The growth mechanism was also explored by investigating the samples synthesized at different reaction times. As sensing materials for a cataluminescence (CTL) gas sensor, this coral-like Zn-doped SnO2 demonstrates excellent CTL behaviour (that is, high sensitivity, superior selectivity to 2-butanone compared with other fifteen kinds of common volatile organic compounds (VOCs) as well as a fast response and recovery). Three different Zn/Sn molar ratios of SnO2 samples were tested under the same conditions to prove the effect of Zn doping concentration on the sensing performance. We further studied the analytical characteristics of the CTL sensor based on 1 : 10 Zn-doped SnO2 sensing materials for 2-butanone under the optimal experimental conditions. The linear range of the gas sensor was 2.31–92.57 μg mL−1 (R = 0.9983), and the detection limit was 0.6 μg mL−1 (S/N = 3).

Sonochemical synthesis of Ag nanoclusters: electrogenerated chemiluminescence determination of dopamine.

We report a facile one-pot sonochemical approach to preparing highly water-soluble Ag nanoclusters (NCs) using bovine serum albumin as a stabilizing agent and reducing agent in aqueous solution. Intensive electrogenerated chemiluminescence (ECL) was observed from the as-prepared Ag (NCs) and successfully applied for the ECL detection of dopamine with high sensitivity and a wide detection range. A possible ECL mechanism is proposed for the preparation of Ag NCs. With this method, the dopamine concentration was determined in the range of 8.3 × 10(-9) to 8.3 × 10(-7) mol/L without the obvious interference of uric acid, ascorbic acid and some other neurotransmitters, such as serotonin, epinephrine and norepinephrine, and the detection limit was 9.2 × 10(-10) mol/L at a signal/noise ratio of 3.