Sustainable fabrication of PVAc-coated Nb–ZnO nanocomposites using Aegle marmelos L. extract for enhanced surface activity towards photocatalytic degradation of bisphenol A and bromothymol blue

Abstract

In this report, a sustainable and environmentally benign approach has been employed for the fabrication of niobium-doped zinc oxide nanoparticles (Nb/ZnO NPs) and their corresponding polyvinyl acetate coated nanocomposites (PVAc-Nb/ZnO NCs). The synthesis was carried out under ambient conditions using Aegle marmelos L. leaf extract as a green reducing and capping/stabilizing agent. Specifically, ZnO matrices doped with 5% and 10% Nb were successfully isolated and subsequently subjected to a facile PVAc surface-coating procedure to enhance their physicochemical stability and catalytic performance. All synthesized materials were comprehensively characterized using spectroscopic (UV-Vis and FT-IR), XRD, SEM, EDS, and BET analyses. XRD patterns confirmed the formation of single-phase crystalline ZnO without the emergence of secondary impurity peaks, whereas FT-IR spectra verified the presence of characteristic functional groups associated with both ZnO and the PVAc coating. SEM micrographs revealed distinct morphological features: a flower-petal for 5% Nb/ZnO and spherical agglomerates for 10% Nb/ZnO NPs. Notably, the PVAc-coated samples exhibited increased agglomeration due to polymer encapsulation. The average particle size was found to be 19.7 nm and 16.3 nm for 5% and 10% Nb/ZnO NPs. While, in the case of PVAc-5% and 10% Nb/ZnO NCs, the average particle size was observed as 23.9 nm and 22.05 nm, respectively. BET analysis demonstrated a significant enhancement in specific surface area following PVAc coating, increasing from 5 and 4 m² g⁻¹ (for 5% and 10% Nb/ZnO NPs, respectively) to 28 and 17 m² g⁻¹ for the corresponding PVAc-Nb/ZnO NCs. The photocatalytic efficiencies of all the synthesized materials were evaluated for the degradation of BPA and BTB under UV irradiation (9 W Hg lamp). The PVAc-Nb/ZnO NCs achieved remarkable degradation efficiencies, exceeding 92% for BPA and 90% for BTB within 50 minutes. Key operational parameters—including catalyst dosage, pollutant concentration, and irradiation time—were systematically optimized. The degradation kinetics for both pollutants followed a pseudo-first-order model. To elucidate the plausible degradation mechanism and identify intermediate species, radical-quenching experiments and LC–MS analyses were also conducted. Importantly, recyclability studies demonstrated superior structural integrity and catalytic stability of the PVAc-coated samples across six to eight cycles for BPA and seven to nine cycles for BTB. In a nutshell, the PVAc-Nb/ZnO NCs exhibit significantly enhanced photocatalytic performance, making them promising candidates for efficient removal of organic pollutants from contaminated water.