Synergistic Enhancement of Visible-Light Photocatalysis Through Controlled CdS Quantum Dot Deposition on Hierarchical TiO2

Hierarchical titanium dioxide (TiO2) has emerged as a promising photocatalytic material owing to its excellent chemical stability, environmental benignity, low cost, and high density of surface-active sites. Nevertheless, its practical application is constrained by rapid photogenerated charge-carrier recombination and poor visible-light utilization resulting from its wide bandgap. In the present study, a hierarchical TiO2/CdS quantum dot (QD) nanocomposite was engineered through a facile and cost-effective pseudo-successive ionic layer adsorption and reaction (p-SILAR) technique with controlled CdS QD deposition. The structural, morphological, optical, and electrochemical properties of the synthesized photocatalysts were systematically investigated using SEM, TEM, XRD, XPS, UV-Vis spectroscopy, photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The results confirmed the successful deposition of highly dispersed CdS QDs onto the hierarchical TiO2 framework without altering its morphology or crystal structure. The formation of the heterojunction significantly enhanced visible-light absorption and reduced the optical bandgap from 3.19 eV for pristine TiO2 to 2.37 eV for the TiO2/CdS QD nanocomposite. Furthermore, PL and EIS analyses demonstrated suppressed electron–hole recombination and improved interfacial charge-transfer characteristics, respectively. Owing to these synergistic effects, the optimized TiO2/CdS QD photocatalyst achieved 85.3% degradation of methylene blue under visible-light irradiation within 120 min, exhibiting substantially superior performance to pristine hierarchical TiO2. Radical scavenging experiments revealed that superoxide radicals ●O2− and photogenerated holes (h+) were the dominant reactive species governing the degradation process. The enhanced photocatalytic activity is attributed to the combined effects of efficient visible-light harvesting, accelerated charge separation, and effective interfacial charge migration across the TiO2/CdS QD nanocomposite. These findings highlight the potential of hierarchically structured TiO2/CdS QD nanocomposites as efficient and economically viable photocatalysts for environmental remediation and wastewater treatment applications.