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Multifunctional composites that couple high-capacity adsorbents with catalytic nanoparticles (NPs) offer a promising route toward the degradation of organophosphorus pollutants or chemical warfare agents (CWAs). We couple mesoporous TiO2aerogels with plasmonic Cu nanoparticles (Cu/TiO2) and characterize the degradation of the organophosphorus CWA sarin under both dark and illuminated conditions. Cu/TiO2aerogels combine high dark degradation rates, which are facilitated by hydrolytically active sites at the Cu||TiO2interface, with photoenhanced degradation courtesy of semiconducting TiO2and the surface plasmon resonance (SPR) of the Cu nanoparticles. The TiO2aerogel provides a high surface area for sarin binding (155 m2g–1), while the addition of Cu NPs increases the abundance of hydrolytically active OH sites. Degradation is accelerated on TiO2and Cu/TiO2aerogels with O2. Under broadband illumination, which excites the TiO2bandgap and the Cu SPR, sarin degradation accelerates, and the products are more fully mineralized compared to those of the dark reaction. With O2and broadband illumination, oxidation products are observed on the Cu/TiO2aerogels as the hydrolysis products subsequently oxidize. In contrast, the photodegradation of sarin on TiO2is limited by its slow initial hydrolysis, which limits the subsequent photooxidation. Accelerated hydrolysis occurs on Cu/TiO2aerogels under visible illumination (>480 nm) that excites the Cu SPR but not the TiO2bandgap, confirming that the Cu SPR excitation contributes to the broadband-driven activity. The high hydrolytic activity of the Cu/TiO2aerogels combined with the photoactivity upon TiO2bandgap excitation and Cu SPR excitation is a potent combination of hydrolysis and oxidation that enables the substantial chemical degradation of organophorphorus compounds.

We describe the opportunity to deploy aerogels—an ultraporous nanoarchitecture with co-continuous networks of meso/macropores and covalently bonded nanoparticulates—as a platform to address the nature of the electronic, ionic, and mass transport that underlies catalytic activity. As a test case, we fabricated Au||TiO2junctions in composite guest–host aerogels in which ∼5 nm Au nanoparticles are incorporated either directly into the anatase TiO2network (Au “in” TiO2, AuIN–TiO2aerogel) or deposited onto preformed TiO2aerogel (Au “on” TiO2, AuON/TiO2aerogel). The metal–meets–oxide nanoscale interphase as visualized by electron tomography feature extended three-dimensional (3D) interfaces, but AuIN–TiO2aerogels impose a greater degree of Au contact with TiO2particles than does the AuON/TiO2form. Both aerogel variants enable transport of electrons over micrometer-scale distances across the TiO2network to Au||TiO2junctions, as evidenced by electron paramagnetic resonance (EPR) and ultrafast visible pump–IR probe time-resolved absorption spectroscopy. The siting of gold nanoparticles in the TiO2network more effectively disperses trapped electrons. Density functional theory (DFT) calculations find that increased physical contact between Au and TiO2, induced by oxygen vacancies, produces increased hybridization of midgap states and quenches unpaired trapped electrons. We assign the apparent differences in electron-transport capabilities to a combination of the relatively better-wired Au||TiO2junctions in AuIN–TiO2aerogels, which have a greater capacity to dilute accumulated charge over a larger interfacial surface area, with an enhanced ability to discharge the accumulated electrons via catalytic reduction of adsorbed O2to O2–at the interface. Solid-state 1H nuclear magnetic resonance experiments show that proton spin-lattice relaxation times and possibly proton diffusion are strongly coupled to Au||TiO2interfacial design, likely through spin coupling of protons to unpaired electrons trapped at the TiO2network. Taken together, our results show that Au||TiO2interfacial design strongly impacts charge carrier (electron and proton) transport over mesoscale distances in catalytic aerogel architectures.

Using a solution-based, non−line-of sight synthesis, we electrolessly deposit ultrathin films of RuO2(“nanoskins”) on planar and 3D substrates and benchmark their activity and stability for oxygen-evolution reaction (OER) in acid electrolyte under device-relevant conditions. When an electrically contiguous ∼9 nm thick RuO2nanoskin is expressed on commercially available, insulating SiO2fiber paper, the RuO2@SiO2electrode exhibits high current density at low overpotential (10 mA cm–2@ η = 280 mV), courtesy of a catalyst amplified in 3D; however, the mass-normalized activity falls short of that achieved for films deposited on planar, metallic substrates (Ti foil). By wrapping the fibers with a <100 nm thick graphitic carbon layer prior to RuO2deposition (RuO2@C@SiO2), we retain the high mass activity of the RuO2(40–60 mA mg–1@ η = 330 mV) and preserve the desirable macroscale properties of the 3D scaffold: porous, lightweight, flexible, and inexpensive. The RuO2@C@SiO2anodes not only achieve the 10 mA cm–2figure of merit at a low overpotential (η = ∼270 mV), but more importantly they do so while (1) minimizing the mass of catalyst needed to achieve this metric, (2) incorporating the catalyst into a practical electrode design, and (3) improving the long-term stability of the catalyst. Our best-performing anodes achieve state-of-the-art or better performance on the basis of area and mass, and do so with a catalyst density 300–580× less than that of bulk RuO2. By limiting the oxidizing potential required to evolve O2at the electrode, even at 10 mA cm–2, we achieve stable activity for 100+ h.