Developing generic strategies that are capable of driving multielectron processes are essential to realize important photocatalytic conversions. Here, we present the idea of introducing favorable catalyst–reactant interaction in achieving efficient photocatalytic regeneration of nicotinamide (NADH) cofactor by gold nanoparticles (AuNPs). The electrostatic attraction emanating from the ligands on the surface of NP increases the channeling and local concentration of NAD+ reactants around AuNP photocatalysts, thereby enhancing the probability of the electron transfer process. Detailed kinetics- and intensity-dependent studies confirm the involvement of multiple electron transfer from the AuNP photocatalyst to the NAD+ reactant. The photocatalytic performances of AuNPs presented here are comparable to or greater than most of the catalytic systems reported based on plasmonic NP, with the added advantage of being structurally less complex. The use of electrostatics mimics the underlying force involved in various enzyme catalysis, which can serve as a generic approach for other important artificial multielectron photocatalytic reactions as well.
Scheme 1. A schematic representation of the different classes of chemical transformations solely photocatalyzed by plasmonic NPs.
Doing chemistry with plasmons is rewarding but is often challenged by the competition between the intriguing relaxation processes in plasmonic materials. One of the currently debated and prominent examples of this is the interference of the thermalization process in bringing out different physicochemical transformations. We present here insights into the utilization and quantification of thermoplasmonic properties in configurable arrays of gold nanorods (AuNRs), which will help in accomplishing the desired outcome from the thermalization process. The plasmonic heat generated in AuNR arrays is used to perform versatile and useful photothermal processes, such as polymerization, solar-vapor generation, Diels−Alder reaction, and crystal-to-crystal transformation. The unprecedented use of thermochromism in quantifying the thermalization process shows that the surface of AuNR arrays can heat up to ∼250 °C within ∼15 min of irradiation, which is independently validated with standard infrared-based thermometric imaging studies. The plasmonic heat reported by the thermochromic studies is the lower limit corresponding to the phase change temperature of the thermochromic molecule, and the actual surface temperature of bundled AuNR arrays could be higher. The choice of reaction conditions is crucial for the effective utilization as well as dissipation of thermoplasmonic heat. The maximum impact of surface temperature was observed when substrates were adsorbed onto the AuNR arrays, whereas the influence of thermoplasmonic heat was minimum when the experiments were performed in a solution state. The insights provided here will have far-reaching implications in the emerging area of plasmonically powered processes, especially in plasmonic photocatalysis.
Plasmonic nanomaterials have the potential to convert light to heat energy in an efficient and localized fashion. Here, we report the use of plasmonic heat from gold nanoparticles (AuNPs) in performing an important chemical transformation of pyrone to pyridinone in water. The yield obtained using plasmonic heat (∼75%) is comparable to that obtained from normal heating at ∼90 °C. Further, this photothermally driven organic reaction is used as a tool to study the effect of NP size on the practical utilization of the plasmonic heat dissipated. AuNPs in the size regime of 10–24 nm are found to be most efficient in driving the pyrone to pyridinone conversion, which is attributed to the dependence of absorption cross‐section and heat capacity on the NP size. The results obtained are validated using conventional plasmonically driven solar‐vapor generation experiments. Our study proves the suitability of a thermally driven organic reaction for qualitatively comparing the effect of various NP parameters on the chemical effectiveness of the plasmonic heat, which can be crucial in our efforts to understand the role of thermalization process in different plasmonically powered processes.
Nanoparticles (NPs) offer their core as well as surface for manifesting various optoelectronic properties, making them one of the prominent class of materials in modern science. Here, we have used NPs as the building blocks to choreograph a multistimuli-responsive, dynamic solvent-mediated self-assembly process. Plasmonic NPs functionalized with hydrophobic thymine thiol (Thy-AuNPs) dispersed in dimethyl sulfoxide (DMSO) were our choice of NP building blocks. The hygroscopic nature of DMSO led to the autonomous dissolution of atmospheric moisture into the DMSO dispersion of Thy-AuNPs, thereby triggering the assembling step. This led to the formation of long-term stable (for weeks) controlled aggregates of Thy-AuNPs, wherein the inherent plasmonic properties of Thy-AuNPs were well preserved. This enabled the use of core-thermoplasmonic properties of Thy-AuNPs in realizing the disassembly step. The sunlight-triggered plasmonic heat dissipated from the Thy-AuNPs in controlled aggregates was used as the thermal energy source for the evaporation of water, which further triggered the disassembly step. In this way, sunlight was coupled as a fuel into the solvent-mediated dynamic self-assembly process of plasmonic NPs. Raman studies prove that the products of the self-assembly processcontrolled aggregates and densely packed plasmonic NP filmcan serve as effective surface-enhanced Raman scattering (SERS) substrates for analytical applications. The concept of light-coupled solvent-mediated dynamic self-assembly was extended to plasmonic NPs of different sizes and cores, proving the generality of our approach. The ability to retain the plasmonic properties of Thy-AuNPs in the aggregated state enabled the use of the core properties of NPs in achieving the disassembly step, which in turn led to the realization of dynamicity, multistimuli-responsiveness, and substantiality in the self-assembly process of NPs.
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