Electrochemical sensing has unique advantages in developing on-site and online detection technologies for heavy metal ions (HMIs) due to its fast response, simple operation, high sensitivity, and portable instruments. The vigorous development of modern micro/nanomaterial preparation technology has provided greater space for improving the performance of electrochemical sensing platforms. In this work, a novel hetero-shelled hollow structure metal-organic framework (MOF) hybrid material (denoted as HCZ@UN) was prepared by adopting the hollow carbonized ZIF-8 (HCZ) as the substrate for growing UiO-66(Zr)-NH2 (UN), and subsequently used for efficient electrochemical detection of lead ions (Pb2+). The grown UN crystal particles were anchored on the HCZ hollow cages and showed nanometer size. The unique shell structure and nanometer size of UN created large specific surface area and rich accessible adsorption sites, which promoted the preconcentration of Pb2+. While the hollow carbon polyhedron structure of HCZ improved the dispersibility of UN and electron transfer ability of the material. These factors synergistically improved the detection sensitivity and sensing performance for Pb2+ determination with a wide linear range of 0.100-500 nM, a low detection limit of 0.0492 & PLUSMN; 0.00523 nM as well as good selectivity, repeatability and long-term stability. This paper provides a simple and effective method for the preparation of electroactive MOF functional materials, which is expected to inspire more interest in building other MOF-based materials with unique structure, high-performance and extensive application value.

制备了NH2-UiO66和电化学还原氧化石墨烯(rGO)的混合材料NH2-UiO66/rGO,并将其成功地用于电化学同时检测镉离子(Cd2+)和铅离子(Pb2+).通过采用扫描电子显微镜(SEM)、X射线衍射和各种电化学技术对材料的形貌及其电化学性质进行了表征.结果表明:NH2-UiO66/rGO具有较NH2-UiO66明显改善的电化学性质.所构建的电化学传感平台在优化条件下可以实现对Cd2+和Pb2+的灵敏检测.此外,该传感器具有良好的选择性、重现性和稳定性,在实际样品检测中也具有广阔的应用前景.

It is a significant and challenging task to simultaneously detection of multiple heavy metal ions with convenience, sensitivity and reliability. Herein, a novel ratiometric electrochemical sensing method was established for the simultaneously detection of three main heavy metal ion pollutants (Cd2+, Pb2+ and Cu2+). The sensing platform was constructed by a composite of ferrocenecarboxylic acid functionalized metal-organic framework (MOF), Fc-NH2-UiO-66, and thermally reduced graphene oxide (trGNO), which was designated as trGNO/Fc-NH2-UiO-66. NH2-UiO-66 has porous structure and large specific surface area, which is beneficial to the adsorption and preconcentration of heavy metal ions. The introduction of trGNO and Fc improves the conductivity and electrochemical activity of the MOF material. Moreover, the signal of Fc can be used as internal reference to develop ratiometric detection, which greatly improves the reproducibility and reliability of electrochemical detection. Based on this ratiometric electrochemical sensing platform, the simultaneous, sensitive and reliable detection of Cd2+, Pb2+ and Cu2+ was realized. This work provides a new sensing platform for simultaneous detection of multiple heavy metal ions and greatly expands the application of UiO-66-type MOFs in electrochemical field.

采用酸刻蚀后处理制备了具有中空结构的UiO-66-NH2材料(P-UiO-66-NH2),并利用其构建电化学传感平台实现了对水溶液中铅离子(Pb2+)和铜离子(Cu2+)的同时电化学检测.采用扫描电子显微镜(SEM),透射电子显微镜(TEM)和各种电化学技术对材料的形貌及其电化学性质进行了表征.结果表明:P-UiO-66-NH2具有较UiO-66-NH2明显改善的电化学性质.基于P-UiO-66-NH2所构建的电化学传感平台,在优化条件下可实现对Pb2+和Cu2+的灵敏检测,检测限分别为0.020μmol·L-1(Pb2+)和0.030μmol·L-1(Cu2+).此外,该传感器还具有良好的选择性、重现性和稳定性,对实际样品中Pb2+和Cu2+的检测也表现出令人满意的结果.

Metal manic frameworks (MOFs) have unique advantages in adsorption and preconcentration of heavy metal ions due to their structure and composition characteristics, which make them show great potential in optical sensing of heavy metal ions. However, their applications in the field of electrochemical sensing is greatly limited because of their poor conductivity. In this work, a functionalized MOF composite, thermally reduced graphene oxide-Au nanoparticles-zeolitic imidazolate skeleton material (RGO-Au-ZIF-8), was fabricated. It exhibits much improved electrochemical properties compared with the pristine MOF. A novel electrochemical sensing platform was constructed based on it, and simultaneous detection of lead ions (Pb2+) and copper ions (Cu2+) in aqueous solution was realized. Specifically, the Au-ZIF-8 was prepared by adding polyvinylpyrrolidone (PVP)-stabilized Au nanoparticles (AuNPs) to the reaction solution of ZIF-8. The modification of AuNPs effectively improved the conductivity of the material. After compounding with RGO, the RGO-Au-ZIF-8 composite was prepared. The RGO was used as scaffold for the Au-ZIF-8 in the composite to increase the effective surface area of electrode and improve conductivity. The morphology and structure of the prepared materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible absorption spectroscopy (UV-Vis). The electrochemical properties of the modified electrodes were characterized by various electrochemical techniques. The experimental parameters, such as pH value of working solution, accumulation potential, accumulation time and composition ratio of Au-ZIF-8 to RGO were optimized. Under the optimized conditions, simultaneous and sensitive detection of Pb2+ and Cu2+ on the prepared electrochemical sensor was realized with the detection limits of 2.6 x 10(-9) and 7.8 x 10(-9) mol.L-1 for Pb2+ and Cu2+, respectively (S/N =3). The interference test showed that the electrochemical sensor has good selectivity for the detec tion of Pb2+ and Cu2+, and further electrochemical studies revealed that the designed sensor has excellent reproducibility and good stability. The result of recovery test indicated that the prepared electrochemical sensor has great potential in Pb2+ and Cu2+ detection in real water samples. This work provides a new platform for simultaneous, rapid and sensitive detection of heavy metal ions, and greatly expands the electrochemical applications of MOF materials.

The ratiometric method allows the measurement of ratio changes between two signals, which can reduce the detection signal fluctuations caused by distinct background conditions and greatly improve the reproducibility and reliability of detection. However, in contrast with the emerging dual excitation or dual emission dyes applied in ratiometric luminescence measurement, only a few internal reference probes have been exploited for ratiometric electrochemical detection. In this paper, a gold nanoparticles@carbonized resin nanospheres composite with thermally reduced graphene oxide as scaffold (AuNPs@CRS-TrGNO) has been fabricated, and the AuNPs embedded in the CRS were first used as an internal reference probe for ratiometric electrochemical detection. The detachment and aggregation of AuNPs is suppressed by embedding in the CRS, so its redox signal is very stable, which provides feasibility for ratiometric detection. Moreover, the embedment of AuNPs, carbonization of resin spheres, and hybridization with TrGNO all have played positive roles in improving the charge transfer rate, which leads to excellent electrochemical performance of the composite. Based on these characteristics of the AuNPs@CRS-TrGNO, a new ratiometric electrochemical detection platform was constructed, and copper ions (Cu2+) in simulated seawater were successfully detected. This ratiometric method has the advantages of simple design and convenient operation, and obviously it improves the reproducibility and reliability of the electrochemical sensor.

The lignin pyrolysis products generated by biomass combustion make an essential contribution to the formation of secondary organic aerosols (SOAs). The ozone-initiated oxidation of guaiacol, syringol and creosol, major constituents of biomass burning, were investigated theoretically by using the density functional theory (DFT) method at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. Six primary addition reaction pathways and further decomposition routes with corresponding thermodynamic values were proposed. The Criegee intermediates can be excited by small molecules, such as NOx, H2O in the atmosphere, and would further proceed via self-decomposition or isomerization. The most predominant product for ozonation of guaiacol is the monomethyl muconate (P1). At 295 K and atmospheric pressure, the rate constant is 1.10 × 10−19 cm3 molecule−1 s−1, which is lies a factor of 4 smaller than the previous experimental study. The branching ratios of the six channels are calculated based on corresponding rate coefficient. The present work mainly provides a more comprehensive and detailed theoretical research on the ozonation of methoxyphenol, which aspires to offer novel insights and reference for future experimental and theoretical work and control techniques of SOAs caused by lignin pyrolysis products.

以制浆中段废水为研究对象,首先采用正交实验研究了石墨烯促进Fenton氧化的各影响因素间的显著程度,然后通过单因素实验研究了废水pH值、 石墨烯加入量以及H2O2加入量对废水处理效果的影响.结果表明,石墨烯促进Fenton氧化的各影响因素间的显著程度为废水pH值>石墨烯加入量>H2O2加入量>n(Fe2+):n(H2O2);加入石墨烯后,Fenton反应的最佳pH值由4提高至6;石墨烯最佳加入量为3 mg/L;随着H2O2的不断加入,制浆中段废水降解效果先不断升高而后趋于平稳,H2O2的最佳加入量为7 mL/L.Fenton反应体系符合一级反应动力学方程,加入石墨烯的Fenton反应速率常数k为0.0632 min-1,比传统Fenton反应速率常数大,表明制浆中段废水的降解速率明显加快.