Williamson-Hall analysis of lattice strain in green-synthesized ZnO nanoparticles using Mitragyna speciosa extract: microstructural insights and antibacterial application

• Green synthesis of ZnO NPs was achieved using Mitragyna speciosa leaf extract as a phytochemical reducing and stabilizing agent. • The Williamson–Hall analysis using UDM, USDM, and UDEDM models was applied to compare microstructural interpretations of ZnO NPs. • The synthesized ZnO NPs exhibited crystallite sizes of 39.1–42.6 nm with microstrain values on the order of 10⁻ 3 . • Tauc plot analysis revealed an optical band gap of approximately 3.03 eV, confirming the preservation of ZnO semiconductor characteristics. • Preliminary antibacterial evaluation demonstrated different responses toward Gram-positive and Gram-negative bacteria under ASTM E2149-13a test conditions. Green synthesis is a sustainable method for producing ZnO NPs. However, detailed microstructural interpretation remains limited. In this study, ZnO NPs were synthesized using Mitragyna speciosa leaf extract and systematically analyzed with emphasis on lattice characteristics. Structural and morphological analysis using UV–vis, FTIR, FESEM-EDS, and XRD techniques confirmed the formation of highly crystalline ZnO with a hexagonal wurtzite structure. Williamson-Hall (W-H) analysis was applied using three deformation models: UDM, USDM, and UDEDM to separate crystallite size and lattice strain components of the crystal structure. The results revealed relatively large crystallite sizes (∼39–43 nm) with low microstrain (2.09–2.30 × 10⁻ 3 ) and low deformation energy density (3.1 × 10⁻ 4 J m⁻ 3 ), suggesting comparatively low lattice strain characteristics. The optical band gap obtained from the Tauc plot analysis is approximately 3.03 eV, consistent with the properties of the ZnO semiconductor. Antibacterial activity was evaluated as a preliminary functional assessment, showing typical Gram-dependent behavior. This work highlights the applicability of W–H analysis for detailed microstructural evaluation in green-synthesized ZnO NPs.