Aqueous solutions containing light-absorbing nanoparticles have recently been shown to produce steam at high efficiencies upon solar illumination, even when the temperature of the bulk fluid volume remains far below its boiling point. Here we show that this phenomenon is due to a collective effect mediated by multiple light scattering from the dispersed nanoparticles. Randomly positioned nanoparticles that both scatter and absorb light are able to concentrate light energy into mesoscale volumes near the illuminated surface of the liquid. The resulting light absorption creates intense localized heating and efficient vaporization of the surrounding liquid. Light trapping-induced localized heating provides the mechanism for low-temperature light-induced steam generation and is consistent with classical heat transfer.

The rational combination of plasmonic nanoantennas with active transition metal-based catalysts, known as ‘antenna-reactor’ nanostructures, holds promise to expand the scope of chemical reactions possible with plasmonic photocatalysis. Here, we report earth-abundant embedded aluminum in cuprous oxide antenna-reactor heterostructures that operate more effectively and selectively for the reverse water-gas shift reaction under milder illumination than in conventional thermal conditions. Through rigorous comparison of the spatial temperature profile, optical absorption, and integrated electric field enhancement of the catalyst, we have been able to distinguish between competing photothermal and hot-carrier driven mechanistic pathways. The antenna-reactor geometry efficiently harnesses the plasmon resonance of aluminum to supply energetic hot-carriers and increases optical absorption in cuprous oxide for selective carbon dioxide conversion to carbon monoxide with visible light. The transition from noble metals to aluminum based antenna-reactor heterostructures in plasmonic photocatalysis provides a sustainable route to high-value chemicals and reaffirms the practical potential of plasmon-mediated chemical transformations.

With more than a billion people lacking accessible drinking water, there is a critical need to convert nonpotable sources such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their operating costs, so alternative, lower energy approaches are equally critical. Membrane distillation (MD) has shown potential due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy intensive. Here, we demonstrate nanophotonicsenabled solar membrane distillation (NESMD), where highly localized photothermal heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising solution for household-or community-scale desalination.our billion people around the world face at least 1 month of water scarcity every year (1, 2). To meet increasing water demand, it has become necessary to exploit saline water, abundant in the ocean and in brackish aquifers, and convert it to potable water (3, 4). Presently, there are more than 18,000 water desalination plants operating in 150 countries, producing 86.8 × 10 6 m 3 of water per day, enough for 300 million people (5, 6). The annual energy consumed by these plants is nominally 75 TWh, accounting for 50% of their operating costs (7-9) and 0.4% of the world electric power consumption (10). The possibility of directly using renewable energy would reduce this highly demanding cost of operation and make affordable clean water more accessible around the world.Many of the current desalination techniques involve phase change, and thus are inherently energy intensive. Among these, membrane distillation (MD) has gained recent attention because it can distill water at lower temperatures than conventional distillation (i.e., boiling) and lower pressures than reverse osmosis (RO) (11-16). In the conventional direct-contact MD process, hot saline water (feed) and cold purified water (distillate) flow on opposite sides of a hydrophobic membrane (Fig. 1A). The temperature difference between the two flows produces a vapor pressure difference across the membrane, leading to (salt-free) water vapor transporting through the membrane from the warmer feed to the colder distillate, where it condenses. However, MD suffers from several inherent limitations. Heat transfer reduces the cross-membrane temperature difference, resulting in lower vapor flux across the membrane and thus lower efficiency. This temperature difference is further decreased along the length of the membrane module, resulting in a maximal usable length of a single module.When no recirculation or heat recovery is used, energy is also lost when hot feed water exits the membrane module. Heating the volume of feed wat...

Efficient photocatalysis requires multifunctional materials that absorb photons and generate energetic charge carriers at catalytic active sites to facilitate a desired chemical reaction.Antenna-reactor complexes are an emerging multifunctional photocatalytic structure where the strong, localized near field of the plasmonic metal nanoparticle (e.g. Ag) is coupled to the catalytic properties of the non-plasmonic metal nanoparticle (e.g. Pt) to enable chemical transformations. With an eye towards sustainable solar driven photocatalysis we investigate how the structure of antenna-reactor complexes governs their photocatalytic activity in the light- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 where the plasmonic nanoparticle is the antenna and the catalytic particle, which can be interchanged based on desired reactivity, is the reactor. In an antenna-reactor complex, the local field induced by the photoexcited antenna particle drives a "forced" plasmon in the nonplasmonic, catalytic nanoparticle: this forced plasmon can serve as a direct source of hot carriers in the catalytic particle to drive chemical processes without the need for charge transfer between the antenna and the reactor components of the nanocomplex. In the initial demonstrations of antenna-reactor coupling, however, the optimal geometric configuration of the constituent materials to maximize photocatalytic performance was not addressed. Furthermore, while it is relatively straightforward to conclude that localizing a plasmonic particle near a non-plasmonic catalytic particle will enhance light absorption in the non-plasmonic particle, it is not clear how this translates to enhanced photocatalysis in the light-limited regime, where all photons must be utilized in a 3-D packed bed of catalytic particles. Optimizing photocatalytic complexes for highest efficiency photon management in the light-limited regime is of critical importance for further development of this approach.In the work reported here, a series of antenna-reactor complexes consisting of core@shell/satellite (Ag@SiO 2 /Pt) heterostructures with varying Ag core diameter (12,25,50 and 100 nm) were synthesized and their photocatalytic properties for the kinetically well-defined CO oxidation reaction were quantitatively compared. Rigorous quantum yield measurements in the light-limited regime demonstrate that for heterostructures with Ag nanoparticles (Ag NPs) in an intermediate size range of 25 and 50 nm diameter, plasmon-enhanced photocatalytic performance was observed at rates more than four times larger than for either smaller (12 nm diameter) or larger (100 nm diameter) Ag particles. Using optical and Monte Carlo simulations, it was shown that if the Ag NPs were too large, the heterostructures scattered light out of the catalyst bed, reducing photocatalytic reactivity. If the Ag NPs were too small, l...

Nanoparticle-based platforms for gene therapy and drug delivery are gaining popularity for cancer treatment. To improve therapeutic selectivity, one important strategy is to remotely trigger the release of a therapeutic cargo from a specially designed gene- or drug-laden near-infrared (NIR) absorbing gold nanoparticle complex with NIR light. While there have been multiple demonstrations of NIR nanoparticle-based release platforms, our understanding of how light-triggered release works in such complexes is still limited. Here, we investigate the specific mechanisms of DNA release from plasmonic nanoparticle complexes using continuous wave (CW) and femtosecond pulsed lasers. We find that the characteristics of nanoparticle-based DNA release vary profoundly from the same nanoparticle complex, depending on the type of laser excitation. CW laser illumination drives the photothermal release of dehybridized single-stranded DNA, while pulsed-laser excitation results in double-stranded DNA release by cleavage of the Au-S bond, with negligible local heating. This dramatic difference in DNA release from the same DNA-nanoparticle complex has very important implications in the development of NIR-triggered gene or drug delivery nanocomplexes.