Dr Tianyi Liu

ABSTRACT In confined mesoscopic spaces, the unraveling of a catalytic mechanism with complex mass transfer and adsorption processes such as reactant enrichment is a great challenge. In this study, a hollow nanoarchitecture of MnOx-encapsulated Pt nanoparticles was designed as a nanoreactor to investigate the reactant enrichment in a mesoscopic hollow void. By employing advanced characterization techniques, we found that the reactant-enrichment behavior is derived from directional diffusion of the reactant driven through the local concentration gradient and this increased the amount of reactant. Combining experimental results with density functional theory calculations, the superior cinnamyl alcohol (COL) selectivity originates from the selective adsorption of cinnamaldehyde (CAL) and the rapid formation and desorption of COL in the MnOx shell. The superb performance of 95% CAL conversion and 95% COL selectivity is obtained at only 0.5 MPa H2 and 40 min. Our findings showcase that a rationally designed nanoreactor could boost catalytic performance in chemoselective hydrogenation, which can be of great aid and potential in various application scenarios.

Gas-involving electrocatalytic reactions are of critical importance in the development of carbon-neutral energy technologies. However, the catalytic performance is always limited by the unsatisfactory diffusion properties of reactants as well as products. In spite of significant advances in catalyst design, the development of mesoscale mass diffusion and process intensification is still challenging due to the lack of material platforms, synthesis methods, and mechanism understanding. In this work, as a proof of concept, we demonstrated achieving these two critical factors in one system by designing a mesoporous carbon bowl (MCB) nanoreactor with both abundant highly active sites and enhanced diffusion properties. The catalysts with controlled opening morphology and mesoporous channels were carefully synthesized via a hydrogen-bonding uneven self-assembling followed by pyrolysis. Taking the two-electron oxygen reduction reaction (ORR) for the H2O2 production as a model, which is a strong diffusion-limiting reaction, the optimal MCB samples achieved a high H2O2 selectivity (>90%) across a wide potential window of 0.6 V, and a large cathodic current density of −2.7 mA cm–2 (at 0.1 V vs RHE). The electrochemical evaluation and finite-element simulation study for a series of MCBs revealed that the similar active sites intrinsically determined the H2O2 selectivity, while the well-designed mesoporous bowl configuration with different window sizes boosted the ORR activity by significantly accelerating the local mass diffusion. This work sheds new insights into the engineering of intrinsic active sites and local mass diffusion properties for electrocatalysts, which bridges the research of electrocatalysis from fundamental atomic-scale and practical macroscale devices.

Inspired by natural mobile microorganisms, researchers have developed micro/nanomotors (MNMs) that can autonomously move by transducing different kinds of energies into kinetic energy. The rapid development of MNMs has created tremendous opportunities for biomedical fields including diagnostics, therapeutics, and theranostics. Although the great progress has been made in MNM research, at a fundamental level, the accepted propulsion mechanisms are still a controversial matter. In practical applications such as precision nanomedicine, the precise control of the motion, including the speed and directionality, of MNMs is also important, which makes advanced motion manipulation desirable. Very recently, diverse MNMs with different propulsion strategies, morphologies, sizes, porosities and chemical structures have been fabricated and applied for various uses. Herein, we thoroughly summarize the physical principles behind propulsion strategies, as well as the recent advances in motion manipulation methods and relevant biomedical applications of these MNMs. The current challenges in MNM research are also discussed. We hope this review can provide a bird's eye overview of the MNM research and inspire researchers to create novel and more powerful MNMs.

Mechanism-switchable nanomotors are expected to exhibit high adaptability and wide applicability. Herein, for the first time, we report a flask-shaped carbon@Pt@fatty-acid nanomotor with a light-induced switch between nonionic self-diffusiophoresis and bubble propulsion. This nanomotor is fabricated through superassembly of platinum nanoparticles on the surface of carbon nanobottles, and fatty acids are infused into the cavity of carbon nanobottles to serve as a light-sensitive switch. Such a nanomotor can be propelled via catalytic decomposition of H O by platinum nanoparticles, exhibiting self-diffusiophoresis with opening-forward migration. Upon 980 nm laser irradiation, the fatty acids melt due to the photothermal effect and are released from the cavity, switching the dominant operational mechanism to bubble propulsion with bottom-forward migration. Compared with self-diffusiophoresis, bubble propulsion shows higher mobility and better directionality due to the hindered self-rotation. Simulation results further reveal that the confinement effect of the cavity, which facilitates the nucleation of nanobubbles, leads to the switch to bubble propulsion. This study offers an insight into the relationship between nanostructures, fundamental nanomotor operational mechanisms, and apparent propulsion performance, as well as provides a novel strategy for the regulation of movement, which is instructive for both the design and applications of nanomotors.