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Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Metal nanoparticles have drawn great attention in heterogeneous catalysis. One challenge is that they are easily deactivated by migration-coalescence during the catalysis process because of their high surface energy. With the rapid development of nanoscience, encapsulating metal nanoparticles in nanoshells or nanopores becomes one of the most promising strategies to overcome the stability issue of the metal nanoparticles. Besides, the activity and selectivity could be simultaneously enhanced by taking advantage of the synergy between the metal nanoparticles and the encapsulating materials as well as the molecular sieving property of the encapsulating materials. In this review, we provide a comprehensive summary of the recent progress in the synthesis and catalytic properties of the encapsulated metal nanoparticles. This review begins with an introduction to the synthetic strategies for encapsulating metal nanoparticles with different architectures developed to date, including their encapsulation in nanoshells of inorganic oxides and carbon, porous materials (zeolites, metal-organic frameworks, and covalent organic frameworks), and organic capsules (dendrimers and organic cages). The advantages of the encapsulated metal nanoparticles are then discussed, such as enhanced stability and recyclability, improved selectivity, strong metal-support interactions, and the capability of enabling tandem catalysis, followed by the introduction of some representative applications of the encapsulated metal nanoparticles in thermo-, photo-, and electrocatalysis. At the end of this review, we discuss the remaining challenges associated with the encapsulated metal nanoparticles and provide our perspectives on the future development of the field.

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and reactors, optical properties and applications, magnetic properties, energy storage, catalysis, biomedical applications, environmental remediation, and sensors. Finally, we provide a perspective on future development in the research relevant to hollow micro-/nanostructures.