Spectroscopic characterization of chain-to-ring structural evolution in platinum carbide clusters

Metal carbides play an important role in catalysis and functional materials.However,the structural characterization of metal carbide clusters has been proven to be a challenging experimental target due to the difficulty in size selection.Here we use the size-specific photoelectron velocity-map imaging spectroscopy to study the structures and properties of platinum carbide clusters.Quantum chemical calculations are carried out to identify the structures and to assign the experimental spectra.The results indicate that the cluster size of the chain-to-ring structural evolution for the PtC_(n)^(-)anions occurs at n=14,whereas that for the PtC_(n) neutrals at n=10,revealing a significant effect of charge on the structures of metal carbides.The greatest importance of these building blocks is the strong preference of the Pt atom to expose in the outer side of the chain or ring,exhibiting the active sites for catalyzing potential reactions.These findings provide unique spectroscopic snapshots for the formation and growth of platinum carbide clusters and have important implications in the development of related single-atom catalysts with isolated metal atoms dispersed on supports.

Biological soil crust distribution in Artemisia ordosica communities along a grazing pressure gradient in Mu Us Sandy Land, Northern China

This study investigated the distribution pattern of biological soil crust （BSC） in Artemisia ordosica communities in Mu Us Sandy Land. Three experimental sites were selected according to grazing pressure gradient. In each experimental site, the total vegetation cover, A. ordosica cover, BSC cover, litter-fall cover, BSC degree of fragmentation, BSC thickness and soil properties were investigated in both fixed and semi-fixed sand dunes and simultaneously analyzed in the laboratory. The results showed that at the same grazing pressure, BSC cover and composition were significantly affected by the fixation degree of sand dunes. In addition, BSC cover in the fixed sand dunes was 83.74% on average, whereas it is proportionally dominated by 28% mosses, 21% lichens, and 51% algae. Meanwhile, BSC cover in the semi-fixed sand dunes was 23.54% on average, which is proportionally domi- nated by 6.3% mosses, 2.5% lichens, and 91.2% algae. Fine sand, organic matter, and total nitrogen （N） contents in the fixed sand dunes were all significantly higher than those in the semi-fixed sand dunes. Litter-fall cover de- creased along the grazing pressure gradient, whereas BSC fragmentation degree increased. Fine sand content decreased along with the increase of grazing pressure, whereas medium sand content increased in both fixed and semi-fixed dunes. The organic matter and total N contents in the no grazing site were significantly higher than those in light and normal grazing sites. However, there were no significant differences between the light and normal grazing sites. In addition, there were also no significant differences in BSC thickness between the light and normal grazing sites in the fixed sand dunes. However, a significant decrease was observed in both BSC cover and thick- ness in the normal grazing site. The BSC in the semi-fixed dunes was more sensitive to disturbance.

Recent development in electronic structure tuning of graphitic carbon nitride for highly efficient photocatalysis

The utilization of solar energy to drive energy conversion and simultaneously realize pollutant degradation via pho-tocatalysis is one of most promising strategies to resolve the global energy and environment issues.During the past decade,graphite carbon nitride(g-C3N4)has attracted dramatically growing attention for solar energy conversion due to its excellent physicochemical properties as a photocatalyst.However,its practical application is still impeded by several limitations and short-comings,such as high recombination rate of charge carriers,low visible-light absorption,etc.As an effective solution,the elec-tronic structure tuning of g-C_(3)N_(4)has been widely adopted.In this context,firstly,the paper critically focuses on the different strategies of electronic structure tuning of g-C_(3)N_(4)like vacancy modification,doping,crystallinity modulation and synthesis of a new molecular structure.And the recent progress is reviewed.Finally,the challenges and future trends are summarized.

High performance optical sensor based on double compound symmetric gratings

A high performance optical sensor based on a double compound symmetric gratings(DCSGs) structure is designed. The reflection spectrum of the DCSG is investigated by utilizing a method that combines a theoretical model with the eigenmode information of the grating structure. The theoretical results, which are observed to agree well with those acquired by rigorous coupled-wave analysis, show that the linewidth of the reflection spectrum decreases upon the increasing distance between the grating strips. This research work will lay a foundation for studying high performance integrated optical sensors in miniature nanostructures.