No abstract

Heat treatment of metal–organic frameworks (MOFs) has provided a wide variety of functional carbons coordinated with metal compounds. In this study, two kinds of zinc‐based MOF (ZMOF), C16H10O4Zn (ZMOF1) and C8H4O4Zn (ZMOF2), were prepared. ZMOF1 and ZMOF2 were carbonized at 1000 °C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (SBET) of CZMOF2 was ~2700 m2 g−1, much higher than that of CZMOF1 (~1300 m2 g−1). A supercapacitor electrode based on CZMOF2 achieved specific capacitances of 360, 278, and 221 F g−1 at 50, 250, and 1000 mA g−1 in an aqueous electrolyte (H2SO4), respectively, the highest values reported to date for ZMOF‐derived electrodes under identical conditions. The practical applicability of the CZMOF‐based supercapacitor was verified in non‐aqueous electrolytes. The initial capacitance retention was 78% after 100 000 charge/discharge cycles at 10 A g−1. Crucially, the high capacitance of CZMOF2 arises from pore generation during carbonization. Below 1000 °C, pore generation is dominated by the Zn/C ratio of ZMOFs, as carbon atoms reduce the zinc oxides formed during carbonization. Above 1000 °C, a high O/C ratio becomes essential for pore generation because the oxygen functional groups are pyrolyzed. These findings will provide insightful information for other metal‐based MOF‐derived multifunctional carbons.

The inactivation ability of SARS-CoV-2 (COVID-19) was examined using two types of transparent Cu2O thin films with different crystallinities on a Na-free glass substrate. The low-crystallinity Cu2O thin film, which was fabricated by irradiating 254 nm ultraviolet (UV)-light with an intensity of 6.72 mW cm[Formula: see text] onto a spin-coated precursor film involving Cu[Formula: see text] complexes at room temperature, exhibited an outstanding COVID-19 inactivation ability to reduce 99.999% of the virus after 1 h of incubation. The X-ray diffraction results of the UV-irradiated thin film indicated a cubic Cu2O lattice with a small crystallite size of 2 ± 1 nm. Conversely, the high-crystallinity Cu2O thin film with a crystallite size of 16 ± 3 nm, obtained by heating a spin-coated precursor film containing another Cu[Formula: see text] complex, showed a negligibly low inactivation activity at the same level as the Na-free glass substrate. The eluted concentrations of Cu ions from both Cu2O thin films were analyzed after immersion in Dulbecco’s modified Eagle’s medium (DMEM) for 0.25–2 h. The eluted Cu–ion concentration of 1.16 ppm was observed for the UV-irradiated thin film by DMEM immersion after 1 h, but that of 0.04 ppm was observed for the heat-treated thin film. This indicated that an important factor of virus inactivation on Cu2O thin films is highly related to the elution of Cu ions that occurred from the surface in the medium.

A Cu film with the ability to rapidly inactivate the COVID-19 virus was easily fabricated at approximately 23[Formula: see text]C on a Na-free glass substrate. The well-adhered Cu films with thickness of approximately 16 [Formula: see text]m and surface area of 8.71 10[Formula: see text] m2 g[Formula: see text] were obtained by immersion of the glass substrate into an aqueous solution with dissolved Cu (II) complex of ammonia and ascorbic acid. The interface bonded between the film and glass substrate was very strong, such that the film did not peel off even when it was exposed to an ultrasonic wave of 100 mW (42 kHz) in water. The anti-COVID-19 activity in Dulbecco’s modified Eagle’s medium (DMEM) is effective within 2 h and is faster than that of commercial copper plates. The changes in the relative abundance of Cu2O and CuO crystallines on the Cu film due to DMEM treatment and those in surface morphology were examined by X-ray diffraction peak analysis and field emission-scanning electron microscopy, respectively. The flame atomic absorption analyses of the recovered solutions after DMEM treatment indicated that the Cu ions from the Cu film with DMEM treatment for 1 hour at a concentration of 0.64 ± 0.03 ppm were eluted 2.3 times faster than those from the Cu plate. The rapid elution of Cu ions from Cu2O crystallines on the film in the early stage is the primary factor in the inactivation of the COVID-19 virus, as elucidated from the time dependence of eluted Cu ions by DMEM treatment. Results from thermogravimetric and differential thermal analysis (TG-DTA) of the powder scratched from the Cu film suggested that a trace amount of organic residues remaining in the Cu film was important in the rapid activity.