Time-resolved fluorescence measurements of graphene oxide in water show multiexponential decay kinetics ranging from 1 ps to 2 ns. Electron-hole recombination from the bottom of the conduction band and nearby localized states to wide-range valance band is suggested as origin of the fluorescence. Excitation wavelength dependence of the fluorescence was caused by relative intensity changes of few emission species. By introducing the molecular orbital concept, the dominant fluorescence was found to originate from the electronic transitions among/between the non-oxidized carbon regions and the boundary of oxidized carbon atom regions, where all three kinds of functionalized groups C-O, C = O and O = C-OH were participating. In the visible spectral range, the ultrafast fluorescence of graphene oxide was observed for the first time.

Future development of mini consumer electronics or large electric vehicles/power grids requires Li-ion batteries (LIBs) with not only an outstanding energy-storage performance but also a minimum cost, and the foremost sustainability. Herein, we put forward a smart strategy to convert used disposable bamboo chopsticks into uniform carbon fibers for anodes of LIBs. Bamboo chopsticks waste is recycled and simply treated by a controllable hydrothermal process performed in alkaline solutions, wherein abundant natural cellulose fibers in bamboo in situ get separated and dispersed spontaneously. After carbonization, the evolved carbon fibers exhibit superior anodic performance to the bulky bamboo carbons counterpart, and competitive electrochemical behavior and cost with commercial graphite. The performance of carbon fibers can be further upgraded by growing nanostructured metal oxides (like MnO₂) firmly on each fiber scaffold to form a synergetic core–shell electrode architecture. A high reversible capacity of ∼710 mA h g⁻¹ is maintained without decay up to 300 cycles. Our strategy presents a scalable route to transform chopsticks waste into carbon fibers, offering a very promising way to make sustainable anodes for LIBs and economical multi-functional carbon-based hybrids available for other practical applications.

Elemental sulfur cathodes for lithium/sulfur cells are still in the stage of intensive research due to their unsatisfactory capacity retention and cyclability. The undesired capacity degradation upon cycling originates from gradual diffusion of lithium polysulfides out of the cathode region. To prevent losses of certain intermediate soluble species and extend lifespan of cells, the effective encapsulation of sulfur plays a critical role. Here we report an applicable way, by using thin-layered nickel-based hydroxide as a feasible and effective encapsulation material. In addition to being a durable physical barrier, such hydroxide thin films can irreversibly react with lithium to generate protective layers that combine good ionic permeability and abundant functional polar/hydrophilic groups, leading to drastic improvements in cell behaviours (almost 100% coulombic efficiency and negligible capacity decay within total 500 cycles). Our present encapsulation strategy and understanding of hydroxide working mechanisms may advance progress on the development of lithium/sulfur cells for practical use.