RESUMO
It is well known that surface ligands are vital layers for ligand-protected Aun nanoclusters. Improving the knowledge of the relationship between ligands and catalytic properties is a forefront research topic for Aun nanoclusters. Enormous effort has been devoted to realizing the ligand effect in synthesis, including well-controlled sizes and shapes as well as structural transformation. However, the crucial function of surface ligands has not been addressed yet in catalytic reactions. Here, this review mainly aims to summarize the recent progress concerning the influence of surface ligand layers on catalytic activity and selectivity, based on the various types of ligand protected Aun nanoclusters. Besides, the potential challenges and opportunities of Aun nanoclusters are indicated, mainly in terms of surface ligands to guide the improvement of catalytic performances.
RESUMO
Coalfield fire area reburning is one of the serious disasters in fire prevention and safety production. In this study, a synchronous thermal analyzer was used to conduct isothermal pyrolysis of jet coal at different temperatures, and the reaction characteristic parameters of different pyrolysis residual structures were analyzed. FTIR was used to measure group contents in raw coal and different pyrolysis residues. Programmed oxidation thermogravimetric experiments were carried out on the residues to obtain their oxidation characteristic parameters. The results demonstrated that the reaction characteristic parameters of the residual structures changed at 450 °C. The pyrolysis reaction mainly affected the variation of hydroxyl, aliphatic hydrocarbon, and aromatic hydrocarbon groups. The increase in pyrolysis temperature resulted in the decline in hydroxyl and aliphatic hydrocarbon groups as well as the increase in the aromatic hydrocarbon group. After pyrolysis, the ignition point temperature of the coal sample decreased, which causes the coal more likely to spontaneously ignite. It indicated that the pyrolysis residue at 450 °C is most likely to reburn. Compared with raw coal, the maximum combustion intensity of the pyrolysis residue was greatly increased, which reached the peak at 500 °C.
RESUMO
The mixed-ligand strategy is one of the important methods for preparing new materials and regulating the properties of materials. In this work, by introducing different auxiliary ligands (ALs), we have obtained a series of mixed-ligand uranyl complexes (1-6) from a flexible biphenyltetracarboxylic acid (H4bptc) with an adjustable orthogonal conformation and studied the influence of different organic base molecules on the coordination and assembly of H4bptc with a uranyl cation. It is found that the coordinated ALs, including 4,4'-bipyridine-1,1'-dioxide and 1,10-phenanthroline, partially occupy the coordination sites of the uranyl center and directly affect the molecular conformations and uranyl coordination of flexible bptc linkers. On the other hand, noncoordinated ALs such as protonated 4,4'-bipyridine ([H2(4,4'-bpy)]2+) or dimethylammonium, which work as counterions in the form of encapsulated guests or hydrogen-bonded templates, also have a nonnegligible impact on the conformation and coordination of bptc linkers. Most interestingly, the AL-mediated evolution of uranyl coordination by the bptc linker and coordination geometry of the uranyl center is clearly observed, which suggests the adaptability of flexible bptc linkers to take suitable molecular configurations and uranyl coordination modes so as to adapt to the external regulator agents and varying environment. The physicochemical characterization of these uranyl compounds, especially photoluminescence, is addressed and discussed, and the results reveal that compound 5 has the potential to serve as a multifunctional radiation detection material for UV light and X-ray radiation.
