Composite aerogels with a metallic Ag phase and a semiconductor CeO2 phase are prepared using a conventional epoxide assistant sol–gel method and ethanol supercritical drying. In such an aerogel, CeO2 nanoparticles surround Ag nanoparticles to form a continuous network for mass and charge transfer. The photocatalytic CO2 reduction reaction is studied on the gas–solid interface of the composite aerogels. It is found that with the Ag additives, the activity of the composite aerogels is greatly improved compared with that of pristine CeO2, both under the full-spectrum light and visible light. A high CH4 yield up to 21.9 μmol/g/h and high selectivity can be simultaneously achieved in a composite aerogel containing ∼5 wt.% Ag. Such an enhancement is attributed to the surface plasmon resonance effect brought by Ag, which promotes charge generation and separation efficiency in the composite aerogel.

Metal oxide aerogels have emerged as a new class of photocatalysts. As a type of 3-dimensional (3D) porous structure, an aerogel owns the characteristics of high specific surface area, tunable pore size, and large pore volume, which can distinguish itself from conventional powder or film counterparts. Such merits allow aerogels to expose more active catalytic sites and support other active cocatalysts. Metal oxide aerogels in a monolithic form also overcome the recycling and separation issues that hinder the application of free-standing powder photocatalysts. This article reviews the typical synthesis methodologies of metal oxide aerogels, including alkoxide hydrolysis and condensation, epoxide assistant, and self-assembly. It also discusses the interfacial charge and mass transfer processes in metal oxide aerogels and correlations among the composition, microstructure, and photocatalytic activity. In addition, this article gives a summary of photocatalytic applications of aerogels in water purification and sterilization, solar water splitting, and gas-phase reactions such as CO 2 reduction and CO oxidation. It also discusses the strategies for enhancing the performance of aerogel photocatalysts. In particular, this paper highlights the recent development of plasmonic aerogel photocatalysts.

This work reports the synthesis of CuxSny alloy aerogels for electrochemical CO2 reduction catalysts. An in situ reduction and the subsequent freeze-drying process can successfully give CnxSny aerogels with tuneable Sn contents, and such aerogels are composed of three-dimensional architectures made from inter-connected fine nanoparticles with pores as the channels. Density functional theory (DFT) calculations show that the introduction of Sn in Cu aerogels inhibits H2 evolution reaction (HER) activity, while the accelerated CO desorption on the catalyst surface is found at the same time. The porous structure of aerogel also favors exposing more active sites. Counting these together, with the optimized composition of Cu95Sn5 aerogel, the high selectivity of CO can be achieved with a faradaic efficiency of over 90% in a wide potential range (−0.7 V to −1.0 V vs. RHE).

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In this paper, a series of Au–Ru–CeO2 aerogel-based photocatalysts are constructed for the nonoxidative methane coupling reaction. A modified epoxide-adding method is employed to incorporate Au and Au–Ru nanoparticles into the CeO2 aerogel framework. While the pristine CeO2 shows negligible activity, it is found that the incorporation of Au nanoparticles can greatly enhance the photoactivity, which is attributed to the improved charge separation efficiency and the surface plasmon resonance effect of Au. The nonoxidative methane coupling reaction then becomes feasible in the visible light region. The C2H6 yield rate on Au–CeO2 aerogel photocatalyst can reach 3.17 μmol/g/h under full-spectrum light and 0.48 μmol/g/h under visible light. Adding an appropriate amount of Ru to the above composite during the synthesis can further improve the activity. By screening several Au–Ru–CeO2 aerogel photocatalysts, an optimized Au-to-Ru ratio (10:1) is found. The C2H6 yield rate on Au10Ru1–CeO2 aerogel photocatalyst can be further increased to 7.09 and 1.55 μmol/g/h, under the full-spectrum light and visible light, respectively. Theoretical calculation shows that a small amount of Ru can lower the reaction barrier of H2 evolution and facilitate the overall reaction.