Structural Investigations of (Ni,Cu) Co-Doped ZnO Nanocrystals by X-ray Absorption Spectroscopy

Preparation and Application of Nanostructured ZnO in Radiation Detection

In order to adapt to the rapid development of high-speed imaging technology in recent years, it is very important to develop scintillators with an ultrafast time response. Because of its radiation-induced ultrafast decay time, ZnO has become an important material for radiation detection and dosimetry. According to different detection sources and application scenarios, ZnO is used in various radiation detectors in different structures, including nanoarrays and nanocomposites. In this paper, the synthesis methods and research status of various nanostructured ZnO-based materials and their applications in the detection of high-energy rays (X-rays, γ-rays) and high-energy particles (α, β and neutron) are reviewed. The performance discussion mainly includes spatial resolution, decay time and detection efficiency.

Bioinspired Cu(II) Defect Sites in ZIF-8 for Selective Methane Oxidation

Activating the C-H bonds of alkanes without further oxidation to more thermodynamically stable products, CO and CO2, is a long-sought goal of catalytic chemistry. Inspired by the monocopper active site of methane monooxygenase, we synthesized a Cu-doped ZIF-8 metal-organic framework with 25% Cu and 75% Zn in the nodes and activated it by heating to 200 °C and dosing in a stepwise fashion with O2, methane, and steam. We found that it does oxidize methane to methanol and formaldehyde. The catalysis persists through at least five cycles, and beyond the third cycle, the selectivity improves to the extent that no CO2 can be detected. Experimental characterization and analysis were carried out by PXRD, DRUV-vis, SEM, and XAS (XANES and EXAFS). The reaction is postulated to proceed at open-coordination copper sites generated by defects, and the mechanism of methanol production was explicated by density functional calculations with the revMO6-L exchange-correlation functional. The calculations reveal a catalytic cycle of oxygen-activated CuI involving the conversion of two molecules of CH4 to two molecules of CH3OH by a sequence of hydrogen atom transfer reactions and rebound steps. For most steps in the cycle, the reaction is more favored by singlet species than by triplets.

Plasmonic Ag nanoparticles arbitrated enhanced photodetection in p-NiO/n-rGO heterojunction for future self-powered UV photodetectors

We report on the low cost and low temperature chemical synthesis of p-type nickel oxide (NiO) and n-type reduced graphene oxide (rGO) and their integration onto ITO/glass substrate to form p-NiO/n-rGO heterojunction for possible self-powered ultraviolet (UV) photodetector applications. Different spectroscopies and microscopes were employed to study their microstructural and surface properties. Whereas, the electrical characterizations have been performed on the devices to ascertain the responsivity, detectivity, external quantum efficiency and temporal responses under dark and UV illumination. It is noteworthy that rGO has not only been used as an n-type semiconductor, but also acted as an electron transport layer, which satisfactorily separates out the electrons from the generated carrier pairs, leading to enhanced photoresponse. Furthermore, efforts were also consecrated to synthesize Ag nanoparticles (NPs) of ∼5 nm radius. The integration of Ag NPs on the conventional NiO/rGO heterojunction facilitates an improved UV light absorption property. It was understood that the performance improvement was owed to the local surface plasmon resonance of Ag NPs within the active layer of NiO. Surprisingly, both the devices (with and without Ag NPs) exhibit photovoltaic behavior which shows its potential for self-powered device application. When the Ag NPs embedded device is concerned, it showed better on/off ratio (6.3 × 10³), high responsivity (72 mAW^-1), large detectivity (3.95 × 10¹² Jones), and high efficiency (24.46%) as compared to the conventional NiO/rGO heterojunction one (without Ag NPs). The variation in the photoresponse and improved charge transport was explained through a band-diagram, which also showcases a comprehensive understanding on the operational principle of the fabricated self-powered devices. Thus, this self-powered photodetector driven by built in electric field is operated independently and can be attached with any other electronic gadgets for internet of things applications.