Cobalt single atoms supported on monolithic carbon with a hollow-on-hollow architecture for efficient transfer hydrogenations

Single-atom catalysts(SACs)have received considerable attention in hydrogenation of nitroaromatic compounds to aromatic amines.In order to enhance the exposure of single atoms and overcome the mass transfer limitation,construction of hierarchical porous supports for single atoms is highly desirable.Herein,we report a straightforward method to synthesize Co single-atoms supported on a hollow-on-hollow structured carbon monolith(Co_(1)/HOHC-M)by pyrolysis ofα-cellulose monolith loaded with PS-core@ZnCo-zeolite imidazolate frameworks-shell nanospheres(PS@Zn-ZIFs/α-cellulose).The hollow-on-hollow structure consists of a large hollow void with a diameter of~290 nm(derived from the decomposition of polystyrene(PS)nanospheres)and a thin shell with hollow spherical pores with a diameter of~10 nm(derived from the evaporation of ZnO nanoparticles that are in-situ formed during pyrolysis in the presence of CO_(2)fromα-cellulose decomposition).Benefitting from the hierarchically porous architecture,the Co_(1)/HOHC-M exhibits excellent catalytic performance(reaction rate of 421.6 mmol·gCo^(-1)·h^(−1))in the transfer hydrogenation of nitrobenzene to aniline,outperforming the powdered sample of Co_(1)/HCS without the hollow spherical mesopores(reaction rate of 353.8 mmol·gCo^(-1)·h^(−1)).It is expected that this strategy could be well extended in heterogeneous catalysis,given the wide applications of porous carbon-supported single-atom catalysts.

Preliminary assessment of heavy metal contamination in surface water and sediments from Honghu Lake, East Central China

Heavy metal concentrations in surface water and sediments collected from Honghu Lake in Hubei Province, China were analyzed, and ecological risks were evaluated according to the sediment quality guidelines. The results showed that the average concentrations of heavy metals in surface water were ranked as： As 〉 Zn 〉 Cu 〉 Cr 〉 Pb 〉 Ni 〉 Cd 〉 Hg. In comparison with results reported in other rivers and the background values, The Honghu Lake was polluted by As, Cr, Pb, Cu and Ni. Most of metals might be mainly from fertilizers, industrial effluent and domestic wastewater around the lake. Heavy metals concentrations were relatively higher in the inlet area than in other areas. Negative correlations were observed between most heavy metals and pH, while a significant positive correlation was present between Zn, Cd and Pb. In the sediment core, Cu, Zn, Cr and Ni showed a decreasing trend while Cd present an increasing trend. The decrease of As, Cu, Zn, Cr and Ni in the 1990s might due to the flood event in 1998. The analysis of ecological risk assessment based on sediment quality guidelines suggested that heavy metals in most sediments from the Honghu Lake had moderate toxicity, with Cr being the highest priority pollutant.