LiXO2(X = Co, Rh, Ir) and solar light photocatalytic water splitting for hydrogen generation.

Alkali metal transition oxide LiCoO2 has been successfully commercialized as a lithium-ion battery material, and some attention is paid to its homologous derivatives LiRhO2 and LiIrO2. However, the photocatalytic properties have not been explored yet for these compounds. Using the first-principles calculations, we carry out investigations on the electronic properties, light absorption, and mobility to understand the feasibility of LiXO2(X = Co, Rh, Ir) for solar light photocatalytic hydrogen generation from water-splitting. The results show that the band edges of LiCoO2 and LiRhO2 meet the redox potential requirements of the water-splitting hydrogen evolution reaction. In addition, the enhanced absorptions of LiXO2(X = Co, Rh, Ir) in the visible light range imply that they could well respond to solar light, while the significant difference in the mobilities of electrons or holes can strengthen spatial charge separation of the photoexcited electron-hole pairs. The solar-energy-to-hydrogen conversion efficiencies of LiCoO2 and LiRhO2 can reach 11.2% and 15.5%, respectively. The results support LiCoO2 and LiRhO2 as promising candidates for visible-light photocatalytic hydrogen production from water-splitting.

[Characteristics of Spatial and Temporal Evolution and Investigation of Air Pollution in Guangdong-Hong Kong-Macao Greater Bay Area Based on Ground-Space Observation Data].

The temporal and spatial distribution characteristics, evolution trend and potential climatic effects of air pollution in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) were analyzed on different time scales and spatial spaces, based on ground environment observation data from June 2014 to December 2018 and satellite remote sensing inversion products from 2000 to 2018. The results show that:① From the in-situ observed daily average concentration of PM2.5, good or mild to moderate pollution occurred in January, February, October, November, and December every year, and the rest of the time was excellent. ② Based on the annual average PM2.5 concentration obtained by satellite for the past 20 years, the spatial characteristics showed that the external radiation is centered on Guangzhou and Foshan. The time evolution shows the characteristics of an Ω shape, which increases gradually from 2000 to 2009, is highest in 2008, and then gradually decreases. ③ The monthly average aerosol optical thickness (AOT) value from the Multi-angle Imaging Spectro Radiometer satellite reversion every 10 years for a period (2000-2009 for a period, 2010-2018 for a period) was used to see the monthly variation. The monthly average AOT value in the first period was larger than that in the second period of the same month, the maximum value was in March and April, and the minimum value was in November and December. It is envisaged to draw a line along the north-south direction of the Pearl River Port, which basically shows that the AOT value in the west is greater than that in the east. ④ According to the observed daily average concentration data of O3-8h, the main concentration level of O3-8h in the GBA is excellent. The cities with good ozone concentration were most numerous in 2014, with five cities, and least in 2018, with only one city. The highest ozone concentration was in September, followed by June and November, and then May and July. In the past 20 years, the spatial distribution of the average concentration of O3 monitored by satellite remote sensing showed a characteristic Ω shape, increasing initially and then decreasing. The maximum value was in May, and the north-south boundary line appeared in space. ⑤ There is a good linear relationship between the interannual variation of monthly mean temperature and radiation, whereas the relationship between AOT and radiation cannot be described by a simple linear relationship.

Photocatalytic water splitting for hydrogen generation driven by tetragonal, trigonal, hexagonal and cubic LiCoO2 and visible light.

The photocatalytic properties of LiCoO2 are not explored up to date although its cubic and trigonal structures are explored experimentally. Here, we investigate the feasibility of photocatalytic hydrogen production from water splitting driven by the tetragonal, trigonal, hexagonal and cubic LiCoO2 with the irradiation of the visible light. The band structure, density of state, optical absorption and mobility are calculated by the first-principles density functional theory. The results show that the band edges of all the four structures of LiCoO2 match to the conditions of the redox potentials of water splitting reaction and the enhanced optical absorption in the visible light range is observed. The obvious difference between the mobilities of the hole and electron are identified, especially for the cubic LiCoO2. All the obtained results suggest that the considered structures of LiCoO2 are promising candidates for the photocatalytic water splitting to produce hydrogen with the irradiation of the visible light.