Abstract
In this paper, we present a comprehensive first-principles investigation of the electronic structure and optical properties of pristine CdS nanofilms and CdS@Co(OH) 2 nanocomposites, employing linear response time-dependent density functional theory. Our modeling reveals that two-dimensional, graphene-like CdS nanofilms exhibit a shortened Cd–S bond and a reduced band gap relative to bulk CdS, thereby extending their optical absorption into the visible region. Upon deposition of Co(OH) 2 , the band gap is further narrowed (redshifted), and new in-gap states emerge. Although these states may not favor overall water splitting, our calculations confirm that hydrogen evolution remains feasible in the presence of sacrificial agents. Notably, the formation of the CdS@Co(OH) 2 nanocomposite induces a transition from a direct to an indirect band gap, resulting in prolonged photoexcited electron lifetimes and suppressed recombination. The calculated optical response spectra are critically compared with available experimental data, providing a robust validation of our theoretical approach. By elucidating the interfacial electronic and optical behavior at the atomic scale, this work addresses a significant knowledge gap in the field and offers valuable guidance for the rational design of next-generation photocatalysts.