CdS/ZnSe Quantum Dot Assembled Clusters vs. Dot‐on‐Rod: Charge Separation and Utilization for Efficient Photocatalytic NO ₃ ⁻ ‐to‐NH ₃ Conversion

Abstract

ABSTRACT Photocatalytic NO 3 − reduction with semiconductor nanocrystals has promising prospects for ammonia (NH 3 ) synthesis, which typically relies on broad light absorption, efficient charge separation, and high surface reactivity. Represented herein is, however, contrary to the widely accepted facts that long‐lived charge separation favors higher photocatalytic efficiency, i.e. ZnSe@CdS dot‐on‐rods with better charge separation unexpectedly yield NH 3 with much lower efficiency (4.10 mmol h −1 g cat. −1 ) than CdS/ZnSe assembled clusters (53.85 mmol h −1 g cat. −1 ). Mechanistic studies reveal that the intimate binding of ZnSe on CdS in dot‐on‐rods accelerates charge separation by 3 orders of magnitude, while the electron transfer from CdS to NO 3 − and the hole transfer from ZnSe to 1‐phenylethanol proceed at 10 8 s −1 . As a result, the comparable charge transfer rates in the assembled cluster of ZnSe and CdS quantum dots enable effective utilization of separated electrons and holes timely for photocatalytic NO 3 − ‐to‐NH 3 reaction, while the imbalance of fast charge separation and slow utilization of electrons and holes in dot‐on‐rods leads to inferior NH 3 yield. The kinetic balance for photocatalytic NO 3 − ‐to‐NH 3 reaction offers valuable guidance for orchestrating multi‐step photochemical events to realize elegant transformations.