Neutron collimator optimization for 14.1 MeV DT neutrons using Monte Carlo and Genetic algorithms.

The fast neutrons generated by Deuterium-Tritium (DT) fusion reaction have been widely applied in prompt gamma ray neutron activation analysis measurements. In this study, a multi-layer neutron collimator for DT neutron generator was developed. Genetic algorithm combined with Monte Carlo simulation was used to design a collimator made of iron, lead, graphite, and borated polyethene. Copper foil activations were conducted to determine the fast neutron flux ratios between the beam port and its nearby area and agreed well with those predicted by the simulations. The results demonstrated that a narrower beam was obtained. The fast neutron beam flux was 568 ± 14 s-1 cm-2. The neutron flux ratio of the collimator was improved by a factor of 2.36, which could provide a better neutron beam.

[Determination of seven organophosphorus insecticides in fruits and vegetables by ultra-high performance liquid chromatography-tandem mass spectrometry based on magnetic conjugated microporous polymers].

A method was developed for the determination of seven organophosphorus insecticides in fruits and vegetables by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) based on magnetic conjugated microporous polymers (CMPs). Fe3O4 nanoparticles modified by phenylene and ethynylene were cross-linked with 1,3,5-tribromobenzene and 1,3,5-trialkynylbenzene to obtain magnetic CMPs. This material with a three-dimensional network structure and covalently built-in Fe3O4 nanoparticles could effectively enrich organophosphorus insecticides with a conjugated structure, thus allowing for convenient magnetic separation in an external magnetic field. Under the optimized conditions, the seven organophosphorus pesticides were extracted by using the magnetic CMPs as magnetic solid phase extraction adsorbents. The limits of detection (LODs) of the seven target analytes were in the range of 0.12-5.0 ng/kg. The recoveries were between 80.8% and 125%, and the relative standard deviations (RSDs, n=5) were less than 6%. The organophosphorus insecticides were detected in fruits and vegetables at concentrations in the range of 1.1-500.0 ng/kg. The method is sensitive, accurate and reliable, and it shows good application potential for the determination of the organophosphorus pesticides in fruits and vegetables.

Magnetic poly(phenylene ethynylene) conjugated microporous polymer microspheres for bactericides enrichment and analysis by ultra-high performance liquid chromatography-tandem mass spectrometry.

The novel multifunction materials for bactericides residue enrichment is attractive. Few materials used in bactericides analysis could simultaneously achieve convenient separation, recycling and trace enrichment. Therefore, a magnetic poly (phenylene ethynylene) conjugated microporous polymer (CMP) microspheres with three-dimensional network structure and covalently built-in Fe3O4 nanoparticles was reported. The structure of dense poly (phenylene ethynylene) frameworks would enhance its conjugation system, which could adsorb bactericides with phenyl structure through π-π stacking. The material could be separated from sample matrix conveniently and recycled due to the super paramagnetism from embedded Fe3O4 nanoparticles. After response surface optimization on extraction and desorption conditions, a method for trace analysis of six bactericides determination was developed by collaborative use of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The detection limits were in the range of 0.27-3.1 ng / L, and bactericides had been found in vegetables and fruits at concentration among 0.038-0.62 µg/kg. Finally, the method was further applied to analyze the regression equations of bactericide dissipation under natural condition. Effects of different treatment during cleaning process of vegetables and fruits were investigated to seek for the optimal cleaning method. The results revealed that the analytical method based on magnetic CMP which could achieve convenient separation, recycling and trace enrichment, having a great potential for trace analysis of more phenyl pesticides from real samples.

Rational synthesis of Ni3(HCOO)6/CNT ellipsoids with enhanced lithium storage performance: inspired by the time evolution of the growth process of a nickel formate framework.

Metal-organic frameworks (MOFs) as novel electrode materials have attracted intensive attention; however, low electronic conductivity hinders their practical application in lithium ion batteries (LIBs). This work reports the synthesis of conductive MOF/CNT composites with enhanced electrochemical reactivity. The growth mechanism of the pristine MOF and the correlations of two components are investigated from the viewpoint of crystal engineering. The time dependent morphology evolution experiment reveals that [Ni3(HCOO)6] undergoes an 'aggregation-based nucleation-growth' mechanism. As a result, [Ni3(HCOO)6]/CNT microsized ellipsoidal particles are controllably synthesized by tuning the reaction time and the reagent concentration, where CNTs penetrate the entire particles thoroughly. The obtained [Ni3(HCOO)6]/CNT composites exhibit significantly enhanced electrochemical activity in comparison with the as-synthesized pristine [Ni3(HCOO)6]. This is ascribed to the effective 3D conductive network constructed by CNTs. Our results provide an effective synthetic strategy to construct conductive MOF/CNT composites, which pave the way for developing other conductive MOFs for electrode materials.