Calcination-driven phase evolution and morphology development in Buddleja paniculata-mediated ZnO-rich structures

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Abstract
Plant-mediated synthesis offers a low-toxicity route for preparing zinc oxide-based structures; however, the extent of ZnO formation depends strongly on precursor chemistry, phytochemical composition, and post-synthesis heat treatment. In this study, a stem-rich aqueous extract of Buddleja paniculata was used to precipitate a zinc-based precursor from ZnSO4·7H2O under alkaline conditions. The oven-dried precursor was coded as GB-Sample, and portions were calcined at 350 °C for 1 h and 450 °C for 2 h to produce GB-ZnO-350 and GB-ZnO-450, respectively. The materials were examined by XRD, FT-IR, and FESEM-EDX to track calcination-driven phase evolution, bonding changes, and morphology development. The XRD patterns show a progressive transition from a poorly ordered precursor to more ZnO-like calcined products, with GB-ZnO-450 exhibiting the strongest ZnO-related reflections, whereas GB-ZnO-350 already demonstrates credible ZnO-rich development under milder conditions. FT-IR spectra show suppression of precursor-associated hydroxylated/organic bands after calcination together with the emergence of Zn-O-region vibrations, although residual sulfate- and carbon-containing species remain. The FESEM images of GB-ZnO-350 reveal compact micrometre-scale secondary agglomerates assembled from anisotropic rod-/plate-like subunits, and image analysis gives a broad apparent diameter distribution of approximately 90-400 nm. Spot EDX shows Zn and O as the dominant elements with minor S and C, consistent with a ZnO-rich calcined product. The study demonstrates a coherent precursor-to-calcined transformation and shows that 350 °C for 1 h is sufficient to obtain a scientifically credible ZnO-rich material, whereas 450 °C for 2 h produces the more ZnO-like product under the present processing route.

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