Cadmium Sulfide Quantum Dot Sensitized Heptazine Photocatalysts for Visible-Light Hydrogen Evolution: Charge Transfer Kinetics, Quantum Yield Optimization, and Stability Under Prolonged Irradiation

This study investigates CdS quantum dot loading optimization on poly(heptazine imide) carbon nitride for visible-light photocatalytic H2 evolution, charge transfer kinetics by TRPL, and operational stability under 100-hour irradiation within the context of photochemistry and solar fuels materials chemistry, an area of growing scientific importance given its implications for solar-driven hydrogen production system scale-up, QD-sensitized carbon nitride photocatalyst design principles, and sacrificial system-free water splitting development. Using solvothermal CdS QD synthesis, electrostatic assembly on PHI, H2 evolution rate measurement under AM 1.5G illumination with optical filters, TRPL charge transfer kinetics, apparent quantum yield (AQY) at 420 nm, and 100-hour stability test, we examine photoexcited CdS QD injecting electrons into PHI conduction band with long-lived charge separation enabled by type-II heterojunction band alignment, driving proton reduction at PHI surface while TEOA scavenges valence band holes from CdS in 12 CdS loading compositions (0-8 wt%) with n=3 independent photocatalytic runs each, TRPL measured on 6 key compositions, 100-hour stability test for optimal composition drawn from photocatalysis reactor (300 W Xe lamp, AM 1.5G filter, lambda >420 nm cutoff) at Suncrest Chemical Institute with Bruker EPR, TRPL, and gas chromatography H2 quantification. Results indicate that 4 wt% CdS/PHI achieves optimal H2 rate 2,840 umol/hr/g (vs. 284 umol/hr/g pristine, 10x improvement) with AQY 8.4% at 420 nm; TRPL shows charge transfer lifetime 4.84 ns vs. 0.84 ns pristine; 100-hour stability with <8% activity loss (p < 0.001), with 10x H2 rate improvement; AQY 8.4%; <8% activity loss over 100 hours as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to photochemistry and solar fuels materials chemistry and carry actionable implications for the design of programs and policies targeting solar-driven hydrogen production system scale-up, QD-sensitized carbon nitride photocatalyst design principles, and sacrificial system-free water splitting development.