Photocatalytic NADH Regeneration Employing Au–Pd Core–Shell Nanoparticles: Plasmonic Modulation of Underlying Reaction Kinetics

Abstract

Integrating catalytically active metals (Pt, Pd, Ru, etc.) with plasmonic metals (Au, Ag, Cu, etc.) allows to combine the merits of both and achieve efficient heterogeneous catalysis. Here, we have grown anisotropic Pd over Au nanocubes (NCs) using a seed-mediated method to engineer Au−Pd core−shell nanoparticles (Au−Pd CS NPs). The Au−Pd CS NPs showed a high conversion rate for nicotinamide adenine dinucleotide hydrogen (NADH) regeneration under visible light irradiation, while their activity in dark conditions remained limited. Moreover, only Au NCs or Pd seed nanoparticles under the same reaction conditions show no significant NADH regeneration, highlighting the synergistic effect of the plasmonic core and catalytic shell. To distinguish if the plasmonic enhancement with Au−Pd CS NPs resulted from hot charge carrier generation or plasmonic heating, we have (i) carried out the reaction under isothermal conditions and (ii) performed β-NAD + concentration-dependent kinetic studies to know the underlying mechanism in dark and light conditions, which should have been the same had the enhancement been a result of a heating effect. In β-NAD + concentration-dependent studies, it was discovered that the dark reaction rate reduced with increasing concentrations, while the light reaction rate became saturated. These observations follow the competitive and noncompetitive bimolecular Langmuir−Hinshelwood (L-H) model. The transition from competitive to non-competitive reaction kinetics has been explained by considering the energetic charge carrier generation on the catalyst surface with light illumination. Our study expands the current domain of catalysts involved in the β-NAD + reduction and provides a mechanistic insight for plasmondriven catalysis, which is necessary to improve catalytic efficiency.

Deciphering the Role of Light Excitation Attributes in Plasmonic Photocatalysis: The Case of Nicotinamide Cofactor Regeneration

“…[−] AuNRs were used as the sole photocatalyst in the presence of the [Cp*Rh­(bpy)­(H 2 O)] 2+ electron mediator, with triethanolamine (TEOA) as the hole scavenger, under continuous irradiation with a 450 nm CW diode laser for 12 h (light intensity measured at the test tube wall was ∼700 mW cm –2 , Figures a and S4). The photocatalytic conversion of NAD + to NADH by [−] AuNRs was monitored through UV–vis spectroscopy by following the absorption of NADH at ∼340 nm. ,− All photocatalytic experiments were performed by drop-casting [−] AuNRs on a paper substrate (see Section S1 in the Supporting Information for details) since the [−] AuNRs were losing their colloidal stability during the irradiation under our reaction conditions (Figure S5). The [−] AuNR-loaded paper substrate was characterized with UV–vis–NIR diffuse reflectance spectroscopy, where the presence of both transverse and longitudinal LSPR bands was observed (Figure S6).…”

“…The present work fills this gap by selecting the photoregeneration of the nicotinamide cofactor (NADH) as the reaction of choice, which occurs only in the presence of both the catalyst and light. The artificial regeneration of NADH from NAD + is a two-electron one-proton transfer (or hydride ion transfer) process that is being used as a model reaction to test several hypotheses in plasmonic photocatalysis. ,− Along with this, NADH is a key cofactor required by a majority (∼70%) of oxidoreductase enzymes to carry out various biocatalytic reactions, thereby justifying the choice of the reaction from an applied perspective as well. , …”

Sodium Alginate–CuS Nanostructures Synthesized at the Gel–Liquid Interface: An Efficient Photocatalyst for Redox Reaction and Water Remediation

“…The photographs of the aqueous dye (CV) solution turning transparent with time are shown in Figure S11. Further, the Langmuir–Hinshelwood (L–H) model was used to comprehend the kinetics of the degradation reactions using eq in order to assess the photocatalytic performance of SA-CuS. − r = prefix− normald C normald t = k ( KC 1 + KC ) where K is the Langmuir constant in L/mol, k is the pseudo-first-order rate constant (min –1 ), t is the photocatalytic activity time in min, r is the reaction rate in mol/(L min), and C is the equilibrium concentration of the constituent in mol/L. Assuming that the photodegradation of the pollutants follows a pseudo-first-order response, the steady state of the response was evaluated as the slope of the linear regression.…”

Metal‐semiconductor heterojunction accelerates the plasmonically powered photoregeneration of biological cofactors

“…Moreover, the regeneration of NADH has served as a model reaction to verify several hypotheses in plasmonic photocatalysis. [21][22][23][24][25][26] 'Sole' plasmonic photocatalysis with AuNPs has revealed the potential of plasmonic excitation in driving multielectron regeneration of NADH cofactors. 23 However, the yield of the NADH photoregeneration was poor.…”

“…[17][18][19][20] Additionally, the cofactor regeneration has served as a model reaction to test several hypotheses in photocatalysis in recent times. [21][22][23][24][25][26] Previous works from our group have already revealed the power of 'sole' plasmonic photocatalysis with gold nanoparticles (AuNPs) to regenerate NADH cofactor from NAD + in the presence of triethanolamine (TEOA) as a hole scavenger under visible-light irradiation. 23 With a focus on enhancing the yield of the photoregenerated NADH, n-type TiO 2 was incorporated into the AuNP-based plasmonic catalyst design.…”