Transient Absorption Microscopy Explores the Effect of Pt Deposition on Charge Carrier Dynamics in Individual Carbon Nitride Particles

Abstract

This study aims to spatially understand the effect of Pt deposition on slow (μs-s) carrier dynamics in carbon nitride (CN_x) photocatalysts, using a homebuilt microsecond diffuse reflectance transient absorption microscopy setup. It is found that Pt deposition lengthens the overall charge half-lives about threefold, while having a spatial preference for binding with respect to defects that induce charge trapping in the μs-s timescale. The initial trapped charge population shows a slight decrease after Pt deposition, suggesting that the more reactive and mobile charges are extracted by Pt sites, leaving behind deeply trapped and long-lived charges. The results emphasize that spatial heterogeneity of surface cocatalysts likely plays a major role in controlling the charge carrier dynamics and activity of photocatalysts.

Keywords: carbon nitrides; charge transfers; heterojunctions; photocatalysis; transient absorptions.

Figure 1

a) Schematic demonstrating the μs‐DR‐TAM setup used for our experiments using a laser diode light source (820 nm). b) TA signal from a single CN _x particle measured and fitted to a power law decay. c) Typical TAM map performed on a single particle (scale bar‐5 μm). Abbreviations: THG, third‐harmonic generator; OF, optical filter; off‐axis PM, off‐axis parabolic mirror; mono., monochromator; PD, photodetector; Refl. Obj, reflective objective.

Figure 2

CN _x single‐particle TAM map examples revealing a general shift in pixel colors across different particles and conditions because of altered half‐lives (t _50% values). a) Particle B before Pt deposition, b) Particle A before Pt deposition, and c) Particle A after 60 min of Pt deposition.

Figure 3

Histograms depicting the frequency distributions of the parameters from the TA decay data for particles before and after 60 min of Pt deposition. Particle A results for a) the absorptance(t ₀) and b) the t _50% parameters. Particle B results for c) the absorptance(t ₀) and d) the t _50% parameters. Results across all particles (all spots) for e) the absorptance(t ₀) and f) the t _50% parameters. The dashed lines represent the baseline values (orange) and the predicted outcome (gray) from the GLMM fit results before and after Pt treatment, respectively.

Figure 4

Schematic showing the effect of Pt deposition on reactive and nonreactive charges (toward HER) in a single CN _x particle.