Self-Optimizing Effect in Lithium Storage of GeO2 Induced by Heterointerface Regulation.

Herein, a heterostructural hexagonal@tetragonal GeO2 (HT-GeO2 ) composite has been designed based on density functional theory (DFT) calculations and synthesized via an acidic-heating route dealt with rapid cooling, where the inner hexagonal GeO2 (H-GeO2 ) phase is covered by a porous layer of tetragonal GeO2 (T-GeO2 ) owing to HF etching. Interestingly, the HT-GeO2 electrode has a self-optimizing effect in lithium storage induced by heterointerface regulation, where the porous T-GeO2 layer on the surface of HT-GeO2 can act as not only a Li+ /electron conducting layer, but also a buffer layer, while the inner H-GeO2 phase can react preferentially with Li ions owing to lower intercalation energy, which is confirmed by operando XRD measurement contributing to thorough lithiation for HT-GeO2 . Moreover, the heterointerface can enhance the pseudocapacitance effect, which can boost the Li storage and accelerate the discharge-charge process. As a result, a large capacity of 984 mAh g-1 after 500 cycles at 2 A g-1 and a capacity of 430 mAh g-1 at a high current density of 20 A g-1 are delivered. This work provides an easy and efficient way to improve the cycling stability of the GeO2 anode, and the T-GeO2 phase would be a novel anode material in energy storage devices.

In Situ Confined Co5Ge3 Alloy Nanoparticles in Nitrogen-Doped Carbon Nanotubes for Boosting Lithium Storage.

Ge-based materials have garnered much attention in lithium-ion batteries (LIBs) for their high theoretical capacity, but these materials suffer from huge volume changes and serious pulverization, which cause insufficient lithium storage performance. Herein, a composite composed of Co5Ge3- and nitrogen-doped carbon nanotube (Co5Ge3/N-CNT) was successfully synthesized using ZIF-67 and GeO2 as precursors. There are interactions between the Co5Ge3 alloy nanoparticles and carbon nanotubes in the growth process, in which the Co5Ge3 alloy nanoparticles were confined in situ in N-CNTs and the in situ growth of N-CNTs was boosted in the existence of the Co5Ge3 catalyst. Density functional theory calculations revealed that the electronic conductivity of the Co5Ge3 alloy is much higher than that of Ge and the Li+ interaction energy of the former is lower than that of the latter. In addition, the interconnected carbon nanotubes not only offer Li+ diffusion pathways and electronic networks but also increase electronic conductivity. Importantly, carbon nanotubes and Co metal have a synergistic effect of buffering volume charge of Ge in the process of Li+ intercalation/deintercalation. As expected, the Co5Ge3/N-CNT composite demonstrated a high reversible capacity of 853.7 mA h g-1 at 2 A g-1 after 1500 cycles and attractive rate performance of up to 10 A g-1.

Synthesis of yeast extract-stabilized Cu nanoclusters for sensitive fluorescent detection of sulfide ions in water.

In this work, we have presented a novel strategy to utilize as-synthesized yeast extract-stabilized Cu nanoclusters (Cu NCs) for sensitive and selective detection of S(2-). The fluorescence intensity of Cu NCs was enhanced significantly in the presence of both Na2S2O8 and S(2-). By virtue of this specific response, a Cu NC-based fluorescent turn-on sensor was developed, which allows the detection of S(2-) in the range of 0.02-0.8 µM with a detection limit of 10nM. The enhancing mechanism was also discussed based on fluorescence decay, transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies, indicating that S(2-) enhanced the Cu NCs emission mainly through sulfide-induced aggregation of Cu NCs. Furthermore, we demonstrated the usability of the present approach for the detection of S(2-) in water samples, which illustrates its great potential for the environmental monitoring and water quality inspection fields.