Tuning Redox Potential of Gold Nanoparticle Photocatalysts by Light

Abstract

Metallic nanoparticle-based photocatalysts have gained a lot of interest in catalyzing oxidation–reduction reactions. In previous studies, the poor performance of these catalysts is partly due to their operation that relies on picosecond-lifetime hot carriers. In this work, electrons that accumulate at a photostationary state, generated by photocharging the catalysts, have a much longer lifetime for catalysis. This approach makes it possible to determine and tune the photoredox potentials of the catalysts. As demonstrated in a model reaction, the photostationary state of the photocatalyzed oxidative etching of colloidal gold nanoparticles using FeCl3 was established under continuous irradiation of different wavelengths. The photoredox potentials of the nanoparticles were then calculated using the Nernst equation. The potentials can be tuned to a range of 1.28 to 1.40 V (vs SHE) under irradiation of different wavelengths in the range of 450 to 517 nm. The effects of particle size or optical power on the photoredox potentials are small compared to the wavelength effect. Control over the photoredox potential of the particles using different excitation wavelengths can potentially be used to tune the activities and selectivities of metallic nanoparticle photocatalysts.

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

“…The photothermal effect on the catalysis is neglectable in our experiment as local heating is minimal under continuous-wave irradiation and stirring (see more discussion in method details )( Mao et al., 2020 ; Nguyen et al., 2016 ). When considering the following processes after a colloidal metal nanoparticle in a stirring solution absorbs a single photon: (i) electron thermalization because of electron-electron and electron-phonon couplings (within few picoseconds ( Link and El-Sayed, 2000 ; Minutella et al., 2017 )), (ii) heat transfer from the particle to the local solvent (within 3 nanoseconds ( Nguyen et al., 2016 )), (iii) time gap for absorbing the second photon (about hundreds of nanoseconds), then it is obvious that the nanoparticle dissipates all the heat to the surrounding environment long before it absorbs the second photon.…”

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

“…The photothermal effect on the catalysis is neglectable in our experiment as local heating is minimal under continuous-wave irradiation and stirring (see detailed explanation in Supplementary Note 2). 52,53 When considering the following processes after a colloidal metal nanoparticle in a stirring solution absorbs a single photon: i) electron thermalization due to electron-electron and electron-phonon couplings (within few picoseconds 54,55 ), ii) heat transfer from the particle to the local solvent (within 3 nanoseconds 52 ), iii) time gap for absorbing the second photon (about hundreds of nanoseconds, see Supplementary Note 2), then it is obvious that the nanoparticle dissipates all the heat to the surrounding environment long before it absorbs the second photon. Since the hot carriers are well thermalized before the nanoparticle can transfer heat to the environment, it is reasonable to estimate the average temperature rise of the particle based on the energy of an absorbed photon, specific heat of Pd and the particle's mass.…”

“…50 In other words, deeper holes have much lower energy than Fermi level, and the lowest possible energy (as compared to vacuum level) is . 53,63 Thus, deeper holes lower the reduction potential of Pd(II)/Pd(0) and favor the oxidation of Pd on the nanoparticle catalyst. Thus, more R-Pd II -X intermediates are produced, and eventually the reaction yields and the quantum yields increase.…”

DNAzyme‐Functionalized Nanomaterials: Recent Preparation, Current Applications, and Future Challenges

“…Benefiting from their chemical stability, unique optical and electronic features, low‐/non‐cytotoxicity, high surface‐to‐volume ratio, and easy synthesis with different sizes and shapes, gold nanoparticles (AuNPs) show potential applications in nanoscience, [ 53,54 ] photocatalysts, [ 55 ] chemical and biological sensing, [ 56,57 ] and as theranostic platforms. [ 58–61 ] Recently, the roles of stabilizing agents, such as surfactants, polymers, silica, polyethylene glycol (PEG) ligands, and metal shells in colloidal suspensions of AuNPs, were reported.…”