Dissipation,residue, and distribution of pyraclostrobin in banana and soil under field conditions in South China

Two independent field trials were conducted in Guangdong and Guangxi, South China, in 2013, to study the dissipation, residue levels, and distribution of pyraclostrobin in banana and soil under field conditions. Pyraclostrobin residues were determined through a quick and effective method of high-performance liquid chromatography. Results showed that the average recoveries ranged from 80.55% to 98.08%, with relative standard deviations of 3.18–7.81% at three different spiking levels for each different matrix. The quantification limit of the proposed method was 0.006 mg/kg for both banana and soil. The half-lives of pyraclostrobin in bananas were 9.09 days in Guangdong and 8.26 days in Guangxi, and both bananas exhibited a dissipation rate of 90% after 28 days. The half-lives of pyraclostrobin in soil were 11.61 days in Guangdong and 10.60 days in Guangxi, with a dissipation rate of 90% after 35 days. Although several positive banana samples (i.e., pyraclostrobin exceeding the maximum residue limits (MRL) were found, the terminal residues in banana pulp were not detectable. All the terminal residues in banana pulp were below the MRL of 0.02 mg/kg, set by the Chinese Ministry of Agriculture, indicating a negligible risk associated with the exposure to pyraclostrobin via the consumption of banana. The distribution of pyraclostrobin in soil was also investigated in two experimental sites. The pyraclostrobin in different layer soil was time dependent and did not vary between the two sites. The result also showed that pyraclostrobin could be easily transported from the top soil to the subsoil. However, the highest quantity ratio did not exceed 10% in the bottom layer (20–30 cm). The distribution assessment also revealed that no significant potential environment risk was induced by pyraclostrobin in bananas.     

新型手性杀虫剂唑虫酯异构体拆分及其在蔬菜中的分析方法建立

以全新手性杀虫剂唑虫酯为研究对象,通过筛选手性色谱柱和优化流动相比例,建立了唑虫酯及其氧化代谢物异构体的拆分方法,在此基础上开发利用高效液相色谱-串联质谱(HPLC-MS/MS)同时测定小白菜和蕹菜中唑虫酯及其氧化产物手性异构体的分析方法。以纤维素-三(3,5-二氯苯基氨基甲酸酯)共价键合手性柱(Chiral INC)(250 mm×4.6 mm, 5 μm)为分析柱,乙腈和2 mmol/L甲酸铵水溶液作为流动相进行梯度洗脱分离,在多反应监测负离子模式下进行检测,唑虫酯4个异构体分离度分别为1.63、2.83和1.74,唑虫酯氧化产物异构体分离度为5.82。通过衍生化的方法进一步确定出峰顺序为RS-唑虫酯、SS-唑虫酯、RR-唑虫酯、SR-唑虫酯、S-唑虫酯氧化产物和R-唑虫酯氧化产物。唑虫酯和其氧化产物的手性异构体分别在1.25~1250 μg/L和2.5~2500 μg/L范围内具有良好的线性关系,相关系数(R²)大于0.99。在蕹菜和小白菜样品中同时添加唑虫酯和唑虫酯氧化产物消旋体进行添加回收试验,添加水平为1、20、400 μg/kg(即唑虫酯异构体为0.25、5、100 μg/kg;唑虫酯氧化代谢产物异构体为0.5、10、200 μg/kg),回收率为72.6%~110.6%,相对标准偏差(RSD)均在9.4%以下,其中日内重复性的RSD在0.5%~9.4%之间;日间重复性的RSD在1.0%~8.6%之间,表明该方法具有良好的回收率和精密度。该研究可为唑虫酯这一新型手性农药的环境行为研究及后续质量控制、药效评价等提供相应的分析技术,为新农药开发应用提供有力的技术支撑。     

A three-dimensional simulation of the effects of obstacle blockage ratio on the explosion wave in a tunnel

Journal of Thermal Analysis and Calorimetry - In this paper, a three-dimensional simulation has been performed to investigate the potential consequences of flammable vapor explosion in a tunnel...     

Enriched Surface Oxygen Vacancies of Photoanodes by Photoetching with Enhanced Charge Separation

A facile photoetching approach is described that alleviates the negative effects from bulk defects by confining the oxygen vacancy (O_vac) at the surface of BiVO₄ photoanode, by 10‐minute photoetching. This strategy could induce enriched O_vac at the surface of BiVO₄, which avoids the formation of excessive bulk defects. A mechanism is proposed to explain the enhanced charge separation at the BiVO₄ /electrolyte interface, which is supported by density functional theory (DFT) calculations. The optimized BiVO₄ with enriched surface O_vac presents the highest photocurrent among undoped BiVO₄ photoanodes. Upon loading FeOOH/NiOOH cocatalysts, photoetched BiVO₄ photoanode reaches a considerable water oxidation photocurrent of 3.0 mA cm^?2 at 0.6 V vs. reversible hydrogen electrode. An unbiased solar‐to‐hydrogen conversion efficiency of 3.5 % is realized by this BiVO₄ photoanode and a Si photocathode under 1 sun illumination.     

pH/temperature dual stimuli-responsive microcapsules with interpenetrating polymer network structure

The microcapsules with interpenetrating polymer network (IPN) structure based on crosslinked poly (N-isopropylacrylamide) (PNIPAM) and crosslinked poly (acrylic acid) (PAA) were fabricated in a three-step process. Firstly, silica/PNIPAM core/shell composite particles were synthesized by thermo-initiated seed precipitation polymerization using 3-(trimethoxysilyl)propyl methacrylate modified silica colloidal particles as seeds and N-isopropylacrylamide and N,N′-methylenebisacrylamide (MBA) as monomer and crosslinker, respectively. Secondly, PAA network was incorporated into the shell of the composite particles by redox-initiated polymerization of acrylic acid and MBA entrapped in the PNIPAM network. Finally, the silica core of the composite particles was removed using hydrofluoric acid under certain condition to produce the microcapsules. The chemical compositions, their mass ratio, and particle sizes of the particles formed in each step were determined by Fourier transformation infrared spectroscopy, thermogravimetry, and dynamic laser light scattering (DLLS), respectively. The IPN structure of the microcapsules was identified by transmission electron microscopy (TEM) using uranyl acetate staining method, and their hollow structure was evidenced by TEM and scanning electron microscopy. Their temperature- or pH-dependent hydrodynamic diameters were measured by DLLS, and the results showed that the microcapules had both pH- and temperature-responsive properties, and the temperature-responsive component and the pH-responsive component inside the microcapsule shell had little interference with each other.     

Carbon nanotube@ZIF–derived Fe-N-doped carbon electrocatalysts for oxygen reduction and evolution reactions

Journal of Solid State Electrochemistry - Iron-nitrogen co-doped hierarchical porous carbon (Fe-N-HPC) was synthesized through the carbonization of carbon nanotube@ZIF composite. It was found that...     

Theory assisted design of N-doped tin oxides for enhanced electrochemical CO2 activation and reduction

Clearly understanding the structure-function relationship and rational design of efficient CO_2 electrocatalysts are still the challenges.This article describes the molecular origin of high selectivity of formic acid on N-doped SnO_2 nanoparticles,which obtained via thermal treatment of g-C_3N_4 and SnCl_2·2H_2O precursor.Combined with density functional theory(DFT)calculations,we discover that N-doping effectively introduces oxygen vacancies and increases the charge density of Sn sites,which plays a positive role in CO_2 activation.In addition,N-doping further regulates the adsorption energy of*OCHO,*COOH,*H and promotes HCOOH generation.Benefited from above modulation,the obtained N-doped SnO_2 catalysts with oxygen vacancies(Ov-N-SnO_2)exhibit faradaic efficiency of 93% for C_1 formation,88% for HCOOH production and well-suppression of H_2 evolution over a wide range of potentials.     

特殊IC板引脚焊点缺陷检测中景深的研究

检测具有特殊空间结构的IC板引脚焊点缺陷时,相机镜头相对于引脚平面会有一定的倾斜角度,在特定的范围内获取图像清晰,超过此范围图像出现离焦模糊。针对此问题进行了研究,建立了景深的数学模型,推导出合理拍摄角度的公式,并通过实验进行了分析和验证。     

SpaceWire冗余网络故障检测恢复技术实现

为提高SapceWire网络可靠性,基于SpaceWire-D提出了一种应用于SpaceWire冗余网络的故障检测恢复技术。网络节点通过比较主、备份端口收到的时间码来判断链路故障状态,在确认主链路发生故障后,节点自动启用备份端口工作。通过引入时间码抖动容限参数,提高了节点对故障判断的准确性,避免了故障误判。测试结果表明,即使故障链路未与节点直接连接,节点也能够在一个时间槽长度内检测到链路故障并自动切换至备份链路。此技术保证了网络故障情况下的数据正确传输,提高了SpaceWire网络的可靠性,是一种稳定可靠的故障检测恢复技术。     

Reply to the ‘Comment on “Uncommon structural and bonding properties in Ag16B4O10” by A. Lobato,Miguel Á. Salvadó, and J. Manuel Recio,Chem. Sci., 2021, 12, DOI: 10.1039/D1SC02152D

Where are the excess electrons in Ag₁₆B₄O₁₀?

Ag₁₆B₄O₁₀ features an exotic scheme of chemical bonding and extends the growing family of subvalent silver oxides. These findings constitute a new general and intrinsic facet of the chemistry of silver, which has not been fully understood, yet, and definitely deserves to be analysed from different perspectives. Against this background, we distinctly appreciate the efforts made by A. Lobato, Miguel Á. Salvadó, and J. Manuel Recio (LSR) in studying these phenomena at the example of the title compound.¹ While the computational results presented in the Comment article well comply with those published in our original paper,² the interpretations follow different routes. Whereas LSR focus on the analogy of pattern of the Electron Localization Function (ELF) in position space in the title compound with those found in elemental silver, we interpreted the electronic structure of Ag₁₆B₄O₁₀, both in position and reciprocal space, also considering the interactions between cationic and anionic partial structures.