Photocatalytic Degradation Efficiency of ZnO‐CdO (75:25 wt%) Nanocatalyst: Lemon‐Capped and Uncapped Nanoparticles Synthesized via Ultrasonic‐Assisted Sonochemical Method

ABSTRACT In this study, ZnO‐CdO (75:25 wt%) nanocatalysts were successfully synthesized using an ultrasonic‐assisted sonochemical route, both with and without Lemon as a capping agent. X‐ray diffraction pattern confirmed the cubic rock‐salt structure of CdO (space group Fm3̄m) and hexagonal wurtzite structure of ZnO (space group P63mc), with reduced crystallite size from 33.97 nm uncapped to 12.83 nm capped. Phase identification revealed 68% ZnO and 32% CdO in uncapped samples, while capped samples showed 71% ZnO and 29% CdO, confirming the preservation of both phases with slight compositional adjustment due to capping effects. SEM and HRTEM analyses demonstrated improved morphology, reduced agglomeration, and dispersion in capped samples. FTIR spectra confirmed the presence of hydroxyl, carbonyl, and carboxylic groups, supporting successful capping. UV–visible absorption showed a red shift in the absorption edge and reduced bandgap from 3.12 to 2.83 eV for capped samples due to quantum confinement effects and the introduction of localized defect states at the nanoparticle surface by organic ligands. Photocatalytic degradation studies under 366 nm UV light showed variation in performance of capped nanocatalysts, achieving 96.2% ± 1.8% (methylene blue), 94.7% ± 2.1% (crystal violet), and 95.3% ± 1.6% (tetrazine) dye degradation efficiency, compared to 84.8% ± 2.3%, 85.2% ± 1.9%, and 84.5% ± 2.4% for uncapped counterparts ( n = 3, p < 0.05). The superior performance is attributed to variations in charge carrier separation due to surface passivation of defect states, increased surface area (from 45 to 78 m 2 g −1 ), and improved dye adsorption facilitated by functional groups from lemon. The lemon capping significantly affected the charge separation and transfer kinetics, offering a sustainable strategy for wastewater remediation using green‐engineered photocatalysts.