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ZIF-8@GO electrochemical sensor is fabricated via wrapping graphene oxide with ZIF-8 for the determination of Pb2+. The N2 adsorption data shows the pore size of ZIF-8@GO with 8.72 nm, which is larger than that of ZIF-8 and GO. The CV curve shows that the logarithm of the peak current value is linearly related to the logarithm of the scan rate, indicating that the reaction of Pb2+ on the electrode surface is controlled by both diffusion and adsorption process. Due to the synergy of ZIF-8 and GO, the modified electrode shows high selectivity toward Pb2+. And it has a low detection limit of 1.076 µM (S/N = 3) and a recovery between 90.6% and 100.3% in the actual sample detection, indicating that the sensor has good potential to detect Pb2+. [ABSTRACT FROM AUTHOR]

Catechol, which has a high toxicity and low degradability, poses significant risks to both human health and the environment. Tracking of catechol residues is essential to protect human health and to assess the safety of the environment. We constructed sensing platforms to detect catechol based on the conductive metal–organic frameworks [Ni3(HITP)2] and their nanosilver composites. The reduction process of catechol at the Ni3(HITP)2/AgNP electrode is chemically irreversible as a result of the difference in compatibility of the oxidation stability and conductivity between the Ni3(HITP)2/AgNS and Ni3(HITP)2/AgNP electrodes. The electrochemical results show that the Ni3(HITP)2/AgNS electrode presents a lower detection limit of 0.053 μM and better sensitivity, reproducibility and repeatability than the Ni3(HITP)2/AgNP electrode. The kinetic mechanism of the catechol electrooxidation at the surface of the electrode is controlled by diffusion through a 2H+/2e− process. The transfer coefficient is the key factor used to illustrate this process. During the electrochemical conversion of phenol to ketone, more than half of ΔG is used to change the activation energy. We also studied the stability, anti-interference and reproducibility of these electrode systems. [ABSTRACT FROM AUTHOR]

Hollow MoS2 cubes and spheres were synthesized by a one-step hydrothermal method with the hard template method. The structure and morphology were characterized, and their electrochemical properties were studied. It is concluded that the specific capacitance of the hollow MoS2 cubes (335.7 F g−1) is higher than that of the hollow MoS2 spheres (256.1 F g−1). The symmetrical supercapacitors were assembled, and the results indicate that the specific capacitance of the device composed of hollow MoS2 spheres (32.9 F g−1) is slightly lower than that of the hollow MoS2 cube (37.4 F g−1) device. Furthermore, the symmetrical supercapacitor (MoS2-cube//MoS2-cube) provides a maximum energy density of 4.93 W h kg−1, which is greater than that of the symmetrical capacitor (MoS2-sphere//MoS2-sphere, 3.65 W h kg−1). This may indicate that hollow molybdenum disulfide cubes with substructures have more efficient charge transfer capabilities and better capacitance characteristics than hollow spheres. After 8000 cycles, the coulombic efficiency of the two symmetrical capacitors is close to 100%. The capacity retention of the MoS2 sphere device (95.2%) is slightly higher than that of the MoS2 cube device (90.1%). These results show that the pore structure, specific surface, and active site of MoS2 with different hollow structures have a greater impact on its electrochemical properties. [ABSTRACT FROM AUTHOR]

Mixed anatase/rutile TiO2 exhibits high photocatalytic activity; however, the mechanism underlying the high performance of the mixed phases is not fully understood. We have performed time-domain ab initio calculations to study the exited state dynamics in mixed phase TiO2 and to investigate the impact of an oxygen vacancy on the dynamics. The anatase(100)/rutile(001) heterostructures with and without an oxygen vacancy used in this work exhibit type II band alignment with the conduction band of rutile residing above that of anatase. The oxygen vacancy introduces a hole trap state inside the bandgap. Owing to a strong coupling between the donor and acceptor states, the electron and hole transfers across the anatase/rutile interface occur on an ultrafast 100 fs timescale in both systems. The decoupling of electron and hole favors a long-lived charge separated state. The electron–hole recombination across the pristine anatase/rutile interface takes 6.6 ns and is significantly slower than that in the pure anatase and rutile phases, showing good agreement with experiments. The electron transfer dynamics is independent of the oxygen vacancy, which has some influence on the hole transfer and a strong effect on carrier recombination. By creating a hole trap state, the vacancy accelerates carrier losses by over an order of magnitude. The fast charge separation and the long lifetime of the charge separated state rationalize the enhanced photocatalytic performance of mixed phase TiO2 compared to the pure phases. [ABSTRACT FROM AUTHOR]