Two-dimensional MXenes are promising for various energy-related applications such as energy storage devices and electrocatalysis of water-splitting. MXenes prepared from hydrofluoric (HF) acid etching have been widely reported. Nonetheless, the acute toxicity of HF acid impedes the large-scale fabrication of MXenes and their wide utilization in energy-related applications. It is thus greatly encouraging to explore a more innocuous protocol for MXenes synthesis. Thereby, a universal strategy based on thermal-assisted electrochemical etching route is developed to synthesize MXenes (e.g., Ti2CT x , Cr2CT x , and V2CT x ). Furthermore, the cobalt ion doped MXenes show an exceptionally enhanced capability of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity, demonstrating their multifunctionalities, which is comparable to the commercialized catalysts. Moreover, we successfully exploited our MXenes as cathodes for the novel aqueous rechargeable battery, with proficient retention and excellent electrical output performance. This work paves a nontoxic and HF-free route to prepare various MXenes and demonstrates practical applications of the materials.

Upconversion luminescence (UCL) refers to nonlinear optical processes, which can convert near-infrared photons to short-wavelength emission. Recent advances in nanotechnology have contributed to the development of photon upconversion materials as promising new generation candidates of fluorescent bioprobes and spectral converters for biomedical and optoelectronic applications. Apart from the remarkable photoluminescence of the materials under photon excitation, some UCL materials may exhibit intrinsic magnetic, ferroelectric, X-ray absorption properties, and so on. These interesting characteristics provide an opportunity for us to couple a single stimulus or multiple stimuli (electric field, magnetic field, X-ray, electron beam, temperature and pH, etc.) to various types of UCL materials. In this review, we will primarily focus on the stimuli responsive properties of UCL materials beyond light-matter interaction, which can aid both fundamental research and widespread applications of the materials. The mechanisms of the response to various stimuli in the UCL materials are discussed. This article will also highlight recent advances in the development of these materials in response to various stimuli and their applications in multimodal bioimaging, drug delivery and release, electro-optical devices, magnetic, temperature and pH sensors and multiple anti-counterfeiting inks. Lastly, we will present potential directions of future research and challenging issues which arise in expanding the applications of stimuli responsive UCL materials.

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Luminescent ions doped materials have been widely applied in many areas, both scientifi c research and practical fi elds. Recently, incorporating luminescent ions and advanced materials into versatile and multifunctional systems seems to be a tendency, motivated by the stimulating desires of fundamental studies and technological applications. This feature article provides a general overview of the myriad of luminescent ions-based advanced composite materials recently investigated. It is demonstrated that the improved or additional properties may be achieved via implementing a strategy of incorporating luminescent ions (lanthanide, transition and main group metal ions) into various types of materials, such as fl exible polymers, two-dimensional atomically thin layers, porous materials, and so on. We outline the design principles, synthesis and processing of various systems joined by luminescent ions doped phosphors. A number of recent works indicate that those novel composite materials allow one to conceive and develop multifunctional applications in a broad area, including optoelectronics, photonics, clean energy, biomedicine, and new types of sensors. Lastly, some challenging issues are discussed and potential directions are suggested for further developing advanced composite materials incorporated with luminescent ions.