Photothermal-driven micro/nanomotors: From structural design to potential applications.

Micro/nanomotors (MNMs) that accomplish autonomous movement by transforming external energy into mechanical work are attractive cargo delivery vehicles. Among various propulsion mechanisms of MNMs, photothermal propulsion has gained considerable attention because of their unique advantages, such as remote, flexible, accurate, biocompatible, short response time, etc. Moreover, besides as a propulsion source, the light has been extensively investigated as an excitation source in bioimaging, photothermal therapy (PTT), photodynamic therapy (PDT) and so on. Furthermore, the geometric topology and morphology of MNMs have a tremendous impact on improving their performance in motion behavior under NIR light propulsion, environmental suitability and functional versatility. Hence, this review article provides a comprehensive overview of structural design principles and construction strategies of photothermal-driven MNMs, and their emerging nanobiomedical applications. Finally, we further provide an outlook towards prospects and challenges during the development of photothermal-driven MNMs in the future. STATEMENT OF SIGNIFICANCE: Photothermal-driven micro/nanomotors (MNMs) that are regarded as functional cargo delivery tools have gained considerable attention because of unique advantages in propulsion mechanisms, such as remote, flexible, accurate and fully biocompatible light manipulation and extremely short light response time. The geometric topology and morphology of MNMs have a tremendous impact on improving their performance in motion behavior under NIR light propulsion, environmental suitability and functional versatility of MNMs. There are no reports about the review focusing on photothermal-driven MNMs up to now. Herein, we systematically review the latest progress of photothermal-driven MNMs including design principle, fabrication strategy of various MNMs with different structures and nanobiomedical applications. Moreover, the summary and outlook on the development prospects and challenges of photothermal-driven MNMs are proposed, hoping to provide new ideas for the future design of photothermal-driven MNMs with efficient propulsion, multiple functions and high biocompatibility.

Using Highly Electronegative Zn to Regulate the Superlattice Structure for the Na-Ion Layered Oxide Cathode with Superior Electrochemical Performance.

The introduction of a superlattice structure into layered oxide cathode materials is a novel strategy to improve the structural stability of sodium-ion batteries (SIBs). However, the superlattice structure gradually disappears during cycling, which shortens the long life of SIBs. Here, the highly electronegative Zn is introduced into a P2-type layered oxide to regulate the superlattice structure. The obtained P2-Na0.80Li0.13Ni0.20Zn0.03Mn0.64O2 exhibits excellent cycling performance (the capacity retention is 96.7% after 100 cycles at 0.5C) and rate capability (95.8 mAh g-1 at 5C). Zn effectively inhibits the Li migration and the Mn dissolution, which ensures the integrity of the Li/Mn superlattice structure during long cycling, thus achieving an ultralong cycling life of SIBs. The introduction of Zn dramatically increases the length of the c-axis, leading to a faster de-embedding rate of Na+ and a better diffusion kinetics. Meanwhile, the larger pristine volume can withstand more stress/strain due to the sharp increase in the level of O-O repulsion during the desodiation process. In addition, Raman test results show that Zn can inhibit the Na+/vacancy ordering transition and improve the structural stability. This study confirms the feasibility of a Zn-regulated superlattice structure. It provides inspiration for the construction of stable layered oxide cathode materials for SIBs.

Biomimetic submicromotor with NIR light triggered motion and cargo release inspired by cuttlefish.

Biomimetic design is very helpful and significant for the smart construction of micro/nanomotors with artificial intelligence. In this work, inspired by cuttlefish, who can rapidly eject poisonous ink and are also capable of fast movement to escape, we designed and fabricated a biomimetic submicromotor with the ability of simultaneous quick movement and a temperature threshold caused explosive cargo release triggered by near infra-red (NIR) light irradiation, which was approximately equivalent to the action of cuttlefish when encountering a predator. The yolk@shell structured polydopamine@mesoporous silica (PDA@MS60) with immovable and asymmetric yolk distribution was employed as a platform, and this was followed by the simultaneous encapsulation of phase change materials (PCM) and cargo molecules. The NIR light irradiation could not only propel the direct motion of the submicromotor, but also caused the explosive release of the cargo loaded in the submicromotor when the temperature exceeded the melting point of the PCM.

Superstructure Control of Anionic Redox Behavior in Manganese-Based Cathode Materials for Li-Ion Batteries.

Anionic charge compensation creates conditions for realizing high capacity and energy density of Li-ion batteries cathode materials. However, the issues of voltage hysteresis, capacity attenuation, and structure transformation caused by the labile anionic redox are still difficult to solve fundamentally. The superstructure formed by a Li-Mn ordered arrangement is the intrinsic reason to trigger the anionic charge compensation. In this work, manganese-based cathode materials with series of Li-Mn ordered superstructure types have been prepared by an ion exchange method, and superstructure control of the anionic redox behavior has been synthetically investigated. With the dispersion of a LiMn6 superstructure unit, the aggregation of Li vacancies in Mn slab is gradually inhibited, which eliminates the production of O-O dimers and improves the reversibility of oxygen redox. Therefore, the voltage hysteresis and capacity fading have been significantly improved. Meanwhile, the amount of reactive oxygen species and their capacity contribution is reduced, and the sluggish electrochemical reaction kinetics of anion requires a low current density to boost the high-capacity advantage. This paper provides effective ideas for the design of various superstructures and the rational utilization of anionic redox.

In Situ Preparation of MXenes in Ambient-Temperature Organic Ionic Liquid Aluminum Batteries with Ultrastable Cycle Performance.

A fluorine-free and water-free electrochemical preparation of MXenes is achieved in Lewis acidic molten salts at ambient temperature. In addition, the anode reaction of the MAX phase V2AlC is studied in the organic ionic liquid aluminum battery and the extraction voltages of the metal atoms Al and V in the MAX phase V2AlC are determined. This points out the direction for the constant-voltage electrochemical preparation of MXenes. Furthermore, the electrochemical performance of the etched V2AlC (E-V2AlC) in an aluminum battery is studied. The one-stop preparation-application process prevents the MXenes from contacting water and air, and the MXenes etched in the aluminum battery are more conducive to the intercalation/deintercalation of Al3+. Therefore, E-V2AlC exhibits excellent electrochemical performance in an aluminum battery. Under the conditions of a voltage window of 0.01-2.3 V (V vs Al/Al3+) and a current density of 500 mA g-1, the specific discharge capacity is about 100 mAh g-1 after 6500 cycles. In addition, the energy storage mechanism and Faraday energy storage method of E-V2AlC in an aluminum battery are studied. The diffusion coefficient D of Al3+ is determined by a galvanostatic intermittent titration technique. The reasons for its excellent electrochemical performance are clarified from the perspective of kinetics.