Atomic Aerogel Materials (or Single‐Atom Aerogels): An Interesting New Paradigm in Materials Science and Catalysis Science

Abstract

metal catalyst not only has a relatively low metal loading but also greatly improves the utilization efficiency of metal atoms. It can change the adsorption/desorption selectivity of the active components on the catalyst to different molecules, thus affecting the reaction kinetics. [4][5][6] With the development of advanced characterization technologies (synchrotron-radiation X-ray absorption fine structure (XAFS), including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS); special aberration-corrected transmission electron microscopy (AC-TEM), such as high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), etc.), it has become a reality to elucidate the structure-activity relationship of SACs at the angstroms atomic scale, which also provides an opportunity to link heterogeneous catalysis with homogeneous catalysis. [7,8] In particular, SACs provide a perfect operational platform for the study of molecular level catalytic reaction mechanism. The applications of SACs also become more and more wide, including the versatile heterogeneous catalytic fields (thermocatalysis, electrocatalysis, and photocatalysis) or noncatalytic fields (energy storage battery, electromagnetic wave absorption, and so on).Aerogel is a form of solid matter, one of the least dense solids in the world. The most common aerogel is made of silica; but there are also aerogels made of graphene, metal oxides, polymers, and so on. [9] The lightest silica aerogel is only 3 mg cm −3 , which is 3 times heavier than air, so it is also called "frozen smoke" or "solid smoke." Traditional aerogel material refers to a kind of porous solid material of nanometer or micrometer level formed by the sol-gel method, using certain drying methods (such as freeze drying) to make gas replace liquid phase in gel. [10] Aerogels are highly porous materials (more than 90% porosity), whose internal structure is formed by a network of interconnected basic units (nanosheets, nanofibers, or nanoparticles) separated by open pores. The combination of small basic units, high surface area, and open structure makes aerogels have many unique properties in thermal, mechanical, optical, electrical, and acoustic aspects, which can be used as excellent adsorbents, catalysts, heat insulation materials, and soundThe concept of "single-atom catalysis" is first proposed by Tao Zhang, Jun Li, and Jingyue Liu in 2011. Single-atom catalysts (SACs) have a very high catalytic activity and greatly improved atom utilization ratio. At present, SACs have become frontier materials in the field of catalysis. Aerogels are highly porous materials with extremely low density and extremely high porosity. These pores play a key role in determining their surface reactivity and mechanical stability. The alliance of SACs and aerogels can fully reflect their structural advantages and lead to new enhancement effects. Herein, a general concept of "atomic aerogel materials" (AAMs) (or single-atom aerogels (SAAs)) is proposed to descr...

Single-atom catalysts: promotors of highly sensitive and selective sensors

“…Recently, ultra-high density (5–15 atoms per square nanometer) SACs have attracted great attention due to their dense site synergy and corresponding electronic effect. 121,122 Wang's group proposed a synthesis method by freeze-drying interweaved graphene quantum dots (GQDs) as an aerogel substrate. 106 The result shows surprisingly high Ir loading up to 41.6 wt% (3.84 at%) without aggregation.…”

Single-atom nanozymes as promising catalysts for biosensing and biomedical applications

“…The optimal reaction conditions are similar to those for HRP, and the high activity can be retained within a wide range of pH and temperature. Xu et al 119 synthesized Mo/Zn dual-atom nanozymes supported on a macroscopic amphiphilic aerogel by pyrolysis of poly(vinyl alcohol) (PVA) and supramolecular coordination complexes. 120 The macroscopic dimension of the PVA substrate not only greatly enhanced the metal atom loading, but also stabilized the metal atoms.…”

Precise control of the catalyst interface at the atomic level

“…TiO 2 , IrO 2 , RuO 2 , and other minerals are frequently used to create mixed metal oxides, so these materials have also been chosen in recent research. 87,88 With 3-30 ALD cycles of TiO 2 , a RuO 2based catalyst showed high specific activities, together with the potentials of zero charge. Hence, TiO 2 with low cycle numbers could be used to adjust the surface electron densities of the catalyst.…”