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Ultrasmall metal–organic frameworks (MOFs) may generate unique properties to expand the scope of applications. However, the synthesis is still a great challenge. Herein, we propose a strategy to synthesize ultrasmall MOFs by high gravity technology. With the aid of tremendous intensification of molecular mixing and mass transfer in high‐gravity field, six typical MOFs were obtained instantaneously in a continuous way. These samples are monodispersed with sub‐5 nm in size, smaller than the previously reported values and even close to the length of one crystal unit cell. As a proof‐of‐concept, catalytic activity for Knoevenagel reaction can be significantly enhanced using ultrasmall ZIF‐8. Conversion time of benzaldehyde was decreased by 94 % or 75 % compared to those using conventional or hierarchically porous ZIF‐8. More importantly, this approach is readily scalable with the highest space‐time yield for nano‐MOFs, which may promote the convenient synthesis and practical applications of ultrasmall MOFs in large‐scale. [ABSTRACT FROM AUTHOR]

• Ultrasmall molybdenum carbide α − MoC 1 − x nanoparticles (1.6 nm) and a hybrid material composed of α − MoC 1 − x and reduced graphene oxide (rGO/ α − MoC 1 − x ) were synthesized by a one-pot oleylamine-mediated at a low temperature. • The materials were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in the acid medium, evidencing quite large activity for the HER. • The synthesis route is simple with low cost and energy consumption, showing a high potential to develop efficient and inexpensive catalysts for HER. Ultrasmall molybdenum carbide α − MoC 1 − x nanoparticles (1.6 nm) and the hybrid material rGO/ α − MoC 1 − x supported in reduced graphene oxide (rGO) were synthesized by a one-pot oleylamine-mediated route at low-temperature (613 K). They were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in the acid medium after surface cleaning with an ethanol-acetic acid solution. The electrocatalysts were also thermal treated (N 2 flow, 773 K/30 min) and compared with untreated ones. Quite large HER activity was observed for the α − MoC 1 − x compared with the rGO/ α − MoC 1 − x and rGO/ α − MoC 1 − x − 773. In addition, after cycling, all catalysts showed considerable performance improvement assigned to removing residual oleylamine molecules from the electrocatalyst's surface. Compared to the unsupported sample, the lower catalytic activity in the supported materials was attributed to the ultrasmall carbide nanoparticles oxidation increases. The route is simple, with low costs and energy consumption, showing a high potential to develop efficient electrocatalysts for HER. [Display omitted] [ABSTRACT FROM AUTHOR]

• The highly stable dispersions of ultrasmall ZnO nanocrystals were prepared. • They were used as pseudohomogeneous catalyst for chemical depolymerization of PET. • ZnO nanodispersions displayed an excellent catalytic activity at 170 °C. • The methanolysis had shorter reaction time and higher activity than the glycolysis. Chemical depolymerization and recycling of polyethylene terephthalate (PET) is a sustainable way to preserve the resources and protect the environment. In this work, methanol and ethylene glycol dispersions of ultrasmall ZnO nanoparticles are firstly adopted as pseudohomogeneous catalysts for alcoholysis of PET. The as-prepared ZnO nanoparticles have a uniform size of 4 nm and can be stable in dispersions for 6 months. In the methanolysis process of PET, the effects of various parameters on the conversion of PET and the yield of dimethyl terephthalate (DMT) were investigated. The results show that higher temperature (170 °C) was beneficial to the conversion of PET and the yield of DMT, which can reach about 97% and 95% after 15 min, respectively. The excellent activity of 553 g PET h−1 (g ZnO)−1 was achieved. Furthermore, the methanolysis of PET have shorter reaction time (1/4) and higher activity (4.7 times) than the glycolysis of PET. [ABSTRACT FROM AUTHOR]