Boosting Hydrogen Photogeneration via Controlled CdS Nucleation on PEI-Modified Graphene Surfaces

The performance of CdS-based photocatalysts can be enhanced by incorporating graphene co-catalysts in close contact with the photoactive phase. However, assembling these distinct components remains a bottleneck, as their differing chemical natures often limit effective interfacial interaction when they are synthesized separately. In this work, we present an adaptable PEI-mediated interfacial assembly strategy for promoting the nucleation and growth of nanocrystalline CdS phases on different graphene-based supports within a common, yet support-adapted, approach. Specifically, by functionalizing the surface of various graphene materials with hyperbranched polyethyleneimine (PEI) as a multifunctional interlayer mediator, we achieve controlled CdS formation. This strategy provides a common chemical framework for producing CdS nanocrystals closely associated with the carbon surface, regardless of the substrate. Diverse materials, including low-defect graphene sheets (G-Sheets), graphene nanoplatelets (GNPs), and graphene oxide (GO), were integrated using tailored architectures: noncovalent PDI-anchoring for GNP and G-Sheets and direct covalent functionalization for GO. In the latter case, PEI acts simultaneously as a mild reducing agent, yielding a covalently grafted reduced graphene oxide hybrid (rGO-PEI). XRD patterns confirm comparable CdS crystallinity across all hybrids, while photocatalytic hydrogen evolution measurements reveal a strong dependence on the nature of the graphene support. rGO-PEI@CdS exhibits the highest hydrogen evolution rate (0.44 mmol g^-1 h^-1) without any noble-metal cocatalyst, highlighting the role of surface defects and oxygen functionalities in interfacial charge transfer. Thermal treatment of rGO-PEI@CdS enhances activity (average 1.20 mmol g^-1 h^-1) but leads to partial deactivation over time. Overall, this study provides an adaptable PEI-mediated framework for integrating diverse graphene-type materials as co-catalysts within CdS-based photocatalytic materials and investigates structure-function relationships in graphene@CdS systems.