Structure–Property Control through Sulfur Incorporation into Multicomponent Core–Shell Superstructures for the Detection of 1-Hexanol and Nonanal

Incorporating sulfur into multicomponent core–shell superstructures (CSs) offers a powerful strategy for tailoring their chemical composition, defect structure, and interfacial charge-transfer behavior. Herein, we report sulfur-tuned CSs (CSs-1, 0.12 wt %; CSs-2, 0.24 wt %; CSs-3, 0.36 wt %) composed of nanoscale ZnO, ZnS, Ta2O5, and SiOx that form heterogeneous architectures enabling precise modulation of interfacial chemistry and charge transfer. Increasing the sulfur content promotes progressive ZnS formation, which enlarges the ZnO/ZnS nanoparticle domains from 20–30 nm to 37–52 nm. Upon exposure to volatile organic compounds (VOCs), the direction and magnitude of band bending depend on the donor/acceptor nature of the analyte and the local oxide–sulfide composition. At low sulfur content (0.12 wt %), the shell remains predominantly oxide-rich, with ZnO/Ta2O5 domains and limited sulfur states, resulting in a strong positive contact potential difference (CPD) response toward nonanal (+1100 mV) due to electron withdrawal from an electron-deficient surface. Increasing the sulfur content to 0.24 wt % enriches the shell with ZnS and sulfur-rich domains, altering the ZnO/ZnS and ZnS/Ta2O5 band alignments and generating electron-rich surface states. At 0.36 wt %, nonanal induces a negative CPD shift (−700 mV), indicating reversed charge-transfer behavior. In contrast, 1-hexanol consistently produces positive CPD responses (+445–450 mV) across all compositions, reflecting its weaker electron-withdrawing interaction. N-Decane exhibits weak CPD signals, with small positive shifts in CSs-1 and CSs-2 and a negative shift in CSs-3, consistent with weak van der Waals adsorption and sensitivity to surface polarity. These results demonstrate that sulfur-tuned surface chemistry governs VOC-specific sensing polarity under ambient conditions.