The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

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Present and Future of Surface-Enhanced Raman Scattering

Metal–organic frameworks (MOFs), also known as porous coordination polymers (PCPs), synthesized by assembling metal ions with organic ligands have recently emerged as a new class of crystalline porous materials. The amenability to design as well as fine-tunable and uniform pore structures makes them promising materials for a variety of applications. Controllable integration of MOFs and functional materials is leading to the creation of new multifunctional composites/hybrids, which exhibit new properties that are superior to those of the individual components through the collective behavior of the functional units. This is a rapidly developing interdisciplinary research area. This review provides an overview of the significant advances in the development of diverse MOF composites reported till now with special emphases on the synergistic effects and applications of the composites. The most widely used and successful strategies for composite synthesis are also presented.

Metal–organic framework composites

Metal–organic frameworks (MOFs), established as a relatively new class of crystalline porous materials with high surface area, structural diversity, and tailorability, attract extensive interest and exhibit a variety of applications, especially in catalysis. Their permanent porosity enables their inherent superiority in confining guest species, particularly small metal nanoparticles (MNPs), for improved catalytic performance and/or the expansion of reaction scope. This is a rapidly developing interdisciplinary research field. In this review, we provide an overview of significant progress in the development of MNP/MOF composites, including various preparation strategies and characterization methods as well as catalytic applications. Special emphasis is placed on synergistic effects between the two components that result in an enhanced performance in heterogeneous catalysis. Finally, the prospects of MNP/MOF composites in catalysis and remaining issues in this field have been indicated.

Metal–organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis

Metal–organic frameworks (MOFs) have received a lot of attention because of their diverse structures, tunable properties and multiple applications such as gas storage, catalysis and magnetism. Recently, there has been a rapidly growing interest in developing MOF-based materials for electrochemical energy storage. MOFs have proved to be particularly suitable for electrochemical applications because of their tunable chemical composition that can be designed at the molecular level and their highly porous framework in which fast mass transportation of the related species is favorable. In this review, the recent progress in fabricating MOFs and MOF-derived nanostructures for electrochemical applications is presented. The review starts with an introduction of the principles and strategies for designing targeted MOFs followed by a discussion of some novel MOF-derived structures and their potential applications in electrochemical energy storage and conversion. Finally, major challenges in electrochemical energy storage are highlighted and prospective solutions from current progress in MOF-based nanostructure research are given.

Metal–organic frameworks and their derived nanostructures for electrochemical energy storage and conversion

The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

Of cores! Core–shell Au@metal-organic-framework-5 (MOF-5) nanoparticles (NPs), in which a single Au NP core is coated with a uniform MOF-5 shell, were prepared by a facile one-pot method. The diameter of the Au NP core and the thickness of the MOF-5 shell are easily tuned by controlling the reaction conditions. These nanoparticles are selective sensors of CO2 in gas mixtures.

Core–Shell Noble‐Metal@Metal‐Organic‐Framework Nanoparticles with Highly Selective Sensing Property

Disproportionated SiOx/C composite anode materials for lithium-ion batteries

Silicon (Si) anodes are expected to be employed in future for lithium-ion batteries (LIBs), due to their high capacity. However, the main challenge is to assemble Si with conductive materials to increase the conductivity and stability of Si anodes. In this work, we optimized a method to prepare Si nanoparticles (NP)/MXene anode materials for LIBs via electrostatic assembly of positively charged Si nanospheres, coated with poly-diallyl dimethyl ammonium chloride, and negatively charged MXene nanosheets, which increase the number of active sites for strong Si NP attachment and minimize both restacking of MXene nanosheets and Si NP aggregation. The Si NP/MXene anodes have a capacity of 1917.9 mA h g–1 after 300 charge/discharge cycles at 0.5 A g–1. The electrochemical characterization of Si NP/MXene nanocomposite shows high energy storage, cycle stability, and rate performance. Optimization of Si/MXene composites can improve their performance as anode materials for high energy density LIBs. 

Jingzhu Liu

Papers

Core–Shell Noble‐Metal@Metal‐Organic‐Framework Nanoparticles with Highly Selective Sensing Property

Disproportionated SiOx/C composite anode materials for lithium-ion batteries

Silicon Nanospheres Supported on Conductive MXene Nanosheets as Anodes for Lithium-Ion Batteries