The versatility of perovskite crystal structure has become the great advantage of lead halide perovskite nanocrystals (NCs) during their functional applications. Here we report an effective solvothermal method for the controllable synthesis of CsPbBr3 nanoplatelets (NPLs) and their transformation to Cs4PbBr6 NCs. Through solvothermal reaction of a mixture of Cs-oleate and PbBr2 precursors, CsPbBr3 NPLs can be synthesized in mass production. The lateral sizes of CsPbBr3 NPLs can be precisely tuned by varying the solvothermal reaction temperatures and times, while the thickness of NPLs remains constant at ∼4.2 nm, which is in the quantum confinement regime. The fine-tuning of lateral NPL sizes results in precise modulation of their photoluminescence emission. Moreover, an interesting phase transformation from cubic CsPbBr3 NPLs to rhombohedral Cs4PbBr6 NCs, and the reversible transformation from Cs4PbBr6 NCs to CsPbBr3 NPLs can be readily achieved by changing the solvothermal reaction sources. The present solvothermal approach is simple, convenient, controllable, and can be easily extended to preparation of other perovskite NCs with different halide compositions.

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As a kind of macroscopic boron nitride (BN) architectures, ultralight BN cellular materials with high porosity and great resilience would have a broad range of applications in energy and environment areas. However, creating such BN cellular materials in large sizes has still been proven challenging. Here, we report on the unique self-assembly of one-dimensional porous BN microfibers into an integral three-dimensional BN foam with open-cell cellular architectures. An ultrasonic-assisted self-assembly, freeze-drying, and high-temperature pyrolysis process has been developed for the preparation of cellular BN foam with a large size and desired shape. The developed BN foam has low density, high porosity (∼99.3%), great resilience, and excellent hydrophobic-lipophilic nature. The foam also exhibits excellent absorption capacities for a wide range of organic solvents and oils (wt % of ∼5130-7820%), as well as a high recovery efficiency (∼94%). Moreover, the unique hierarchical porous structure enables the foam to demonstrate a very low thermal conductivity (∼0.035 W/K/m). The excellent thermal insulation performance, superior mechanical property, and superb chemical and thermal stability enable the developed BN foam as an integrating multifunctional material in a broad range of high-end applications.

It is very challenging to effectively exfoliate and functionalize hexagonal boron nitride (h-BN). Here, an efficient exfoliation and functionalization of bulk h-BN was carried out by a ball-milling method using boric acid (BA) as a lubricant and modifier. A series of boric-acid-functionalized boron nitride nanosheets (BNNSs) was successfully produced using this approach. The obtained BNNS thermostable suspension can be easily condensed into a jelly-like dispersion with ultra-high concentration, up to 90 mg ml −1 . The eco-friendly BA was readily and easily recyclable and remarkably reusable during the BNNS exfoliation. Interestingly, by means of a differential-centrifugation technique, the BNNSs could be easily separated and screened with different sizes and thicknesses. These screened BNNS samples also exhibited different levels of functionalization. As a result, filtration membranes made of various well-screened BNNSs exhibited an obviously different rejection rate for pollutant in water. In addition, the different screened BNNS products show a variable ability to dielectric behavior due to their different-level functionalization. We believe that our created boric-acidfunctionalized BNNSs, combined with the smartly screened separation by differential centrifugation, can broaden the future practical applications of BNNS materials.

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