Hydrogen dissociation is a critical step in many hydrogenation reactions central to industrial chemical production and pollutant removal. This step typically utilizes the favorable band structure of precious metal catalysts like platinum and palladium to achieve high efficiency under mild conditions. Here we demonstrate that aluminum nanocrystals (Al NCs), when illuminated, can be used as a photocatalyst for hydrogen dissociation at room temperature and atmospheric pressure, despite the high activation barrier toward hydrogen adsorption and dissociation. We show that hot electron transfer from Al NCs to the antibonding orbitals of hydrogen molecules facilitates their dissociation. Hot electrons generated from surface plasmon decay and from direct photoexcitation of the interband transitions of Al both contribute to this process. Our results pave the way for the use of aluminum, an earth-abundant, nonprecious metal, for photocatalysis.

Abstract:We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 nm to 220 nm diameter, with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support sizedependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.

Aluminum is an abundant and high-quality material for plasmonics with potential for large-area, low-cost photonic technologies. Here we examine aluminum nanoclusters with plasmonic Fano resonances that can be tuned from the near-UV into the visible region of the spectrum. These nanoclusters can be designed with specific chromaticities in the blue-green region of the spectrum and exhibit a remarkable spectral sensitivity to changes in the local dielectric environment. We show that such structures can be used quite generally for colorimetric localized surface plasmon resonance (LSPR) sensing, where the presence of analytes is detected by directly observable color changes rather than through photodetectors and spectral analyzers. To quantify our results and provide a metric for optimization of such structures for colorimetric LSPR sensing, we introduce a figure of merit based on the color perception ability of the human eye.

Synthetic ammonia has been the primary worldwide source of agricultural fertilizer over the last century and is a promising carbon-free energy carrier for sustainable transportation. Despite its global importance, synthetic ammonia produced with the Haber−Bosch process is extremely energy-and resource-intensive. Here we demonstrate a three-step chemical looping strategy to produce ammonia using only light, natural gas, nitrogen, and water. Titanium nitride nanoparticles were utilized as plasmonic antennas to assist the transformation of magnesium-based nanomaterials through oxide, metallic, and nitride phases under optical illumination. All reactions were performed and monitored in situ using frequencymodulated rotational spectroscopy, which allowed the experiments to take advantage of the rotational spectra's unique sensitivity to isotopic labeling to monitor and verify key reaction intermediates. This validation of a light-driven process for the synthesis of ammonia demonstrates an innovative route toward photosynthetic production of essential chemical commodities.