4-Aminothiophenol Photodimerization Without Plasmons

The photodimerization of 4-aminothiophenol (PATP) into 4,4’-dimercaptobenzene (DMAB) has been extensively utilized as a paradigm reaction to probe the role of surface plasmons in nanoparticle-mediated light-driven processes. Over the past 25 years, a lively debate about the reaction mechanism involved several research groups. Plasmon-mediated generation of energetic (hot) electrons and holes has been invoked as the main driving-force, although plasmonic heating has recently gained attention. However, either model and their combinations are not sufficient to explain some experimental observations and appear, in some cases, contradictory. No matter the differences, there is a general, firm consensus about the presence of plasmonic nanoparticles (Ag or Au), which has always been considered mandatory for triggering the photoconversion. Here I report the first observation of the PATP-to-DMAB photoreaction in the absence of any plasmonic mediators. In particular, neither plasmonic heating nor charge transfer from hot carriers were exploited. The reaction was observed to occur with different kinetics on plasmon-free TiO2 nanoparticles, as well as on self-standing droplets. Confocal microRaman spectroscopy enabled to investigate the reaction progress in different plasmon-free contexts, either aerobic or anaerobic, suggesting a new interpretation of the photodimerization process, based on direct laser-induced activation of singlet oxygen species. These results provide new insights in light-driven redox processes, elucidating the role of sample morphology, light and oxygen.

Plasmonic Heating-Promoted Photothermal Synthesis of α-Cyanoacrylonitriles Over Au/h-BN Catalysts

Plasmonic nanoparticle-involved materials play an essential role in the field of photothermal conversion. Herein, we report the application of photothermal heterogeneous catalysts consisting of gold nanoparticles decorated on defect-rich h-BN sheets (Au/h-BN) for the photocatalytic synthesis of α-cyanoacrylonitriles under mild conditions. It has been demonstrated the–NH2 groups present in the defect-rich h-BN act as the catalytically active sites, while plasmonic heating from the gold nanoparticles can drive the reaction by providing local heat. Au/h-BN catalyst can work for a broad substrate scope in the synthesis of α-cyanoacrylonitriles, and a plausible –NH2 group-involved reaction mechanism has been proposed. This work may open up new avenues in photothermal catalysis by combining plasmonic materials and catalytic sites in one system.

Periodic bouncing of a plasmonic bubble in a binary liquid by competing solutal and thermal Marangoni forces

The physicochemical hydrodynamics of bubbles and droplets out of equilibrium, in particular with phase transitions, display surprisingly rich and often counterintuitive phenomena. Here we experimentally and theoretically study the nucleation and early evolution of plasmonic bubbles in a binary liquid consisting of water and ethanol. Remarkably, the submillimeter plasmonic bubble is found to be periodically attracted to and repelled from the nanoparticle-decorated substrate, with frequencies of around a few kilohertz. We identify the competition between solutal and thermal Marangoni forces as the origin of the periodic bouncing. The former arises due to the selective vaporization of ethanol at the substrate’s side of the bubble, leading to a solutal Marangoni flow toward the hot substrate, which pushes the bubble away. The latter arises due to the temperature gradient across the bubble, leading to a thermal Marangoni flow away from the substrate, which sucks the bubble toward it. We study the dependence of the frequency of the bouncing phenomenon from the control parameters of the system, namely the ethanol fraction and the laser power for the plasmonic heating. Our findings can be generalized to boiling and electrolytically or catalytically generated bubbles in multicomponent liquids.

Real-Time Temperature Detection Via Quantum Dots for Photothermal Cellular Actuation

Plasmonic heating finds multiple applications in cell manipulation and stimulation, where heat generated by metal nanoparticles can be used to modify cell adhesion, control membrane currents, and suppress neuronal action potentials among others. Metal nanoparticles can also be easily integrated in artificial extracellular matrices to provide tunable, thermal cueing functionalities with nanometer spatial resolution. In this contribution, we present a platform enabling the combination of plasmonic heating with localized temperature sensing using quantum dots (QDs). Specifically, a functional nanocomposite material was designed with gold nanorods (AuNRs) and QDs incorporated in a cell-permissive hydrogel (e.g., collagen) as well as an optical set-up combining optical heating and temperature imaging, respectively. Specific area stimulation/readout can be realized through structured illumination using digital micromirror device (DMD) projection.