Nano Au-Decorated 3D ZnO Tetrapods as Recyclable Sustainable Platform for Highly Efficient Natural Solar-Driven Photocatalysis and Ultrasensitive Surface-Enhanced Raman Scattering Detection

Materials development through sustainable approaches offers a promising route to address future challenges in the energy and environmental fields. The present work addresses such critical challenges in environmental monitoring through environmental sensing and remediation by developing a sustainable platform based on 3D nanomicro complex composite structures. It includes a facile synthesis of Au nanoparticles (NPs)-decorated 3D ZnO tetrapods (TPs) as an efficient solar-driven photocatalyst and ultrasensitive surface-enhanced Raman scattering (SERS) substrate. 3D TP nanoarchitectures with sharp arms provide efficient charge transport pathways, while Au NPs anchored on ZnO TPs enhance photocatalytic as well as SERS activity by introducing plasmonic features that intensify local electromagnetic field and facilitate stronger light–matter interactions. Various spectroscopic, microscopic, and electrochemical investigations confirm the successful deposition of Au NPs on ZnO TPs along with strong Au-ZnO interfacial coupling resulting in enhanced optoelectronic properties. The ZnO TPs exhibit a wide band gap of 3.11 eV, which is remarkably narrowed to 2.57 eV upon Au deposition, highlighting the profound influence of localized surface plasmon resonance in extending absorption into the visible region. The Au-ZnO 3D nanoarchitecture shows enhanced photocatalytic performance for methylene blue (MB) pollutant with a degradation efficiency of 96% within 60 min under natural sunlight, maintaining a stable recyclability of 88.3% after five cycles of photodegradation. Furthermore, 3D nanoarchitecture shows excellent SERS performance with a high enhancement factor of 1.38 × 105 and limit of detection of an extremely low concentration of 10–12 M for MB. Interestingly, such investigations have also been extended to other complex organic pollutants (i.e., ciprofloxacin, tetracycline hydrochloride, and phenol) including study of photodegradation byproducts and photocorrosion/stability of photocatalysts. The observed results are attributed to the synergy between plasmonic Au and 3D TP morphology, promoting charge separation, visible-light harvesting, and electromagnetic chemical enhancement, making it a versatile platform for environmental sensing and remediation.