Effect of Drying Temperature on Synthesised Zinc Oxide Microparticles from Mango Seed Extract

Zinc oxide (ZnO) is known for its antimicrobial activity, UV protection, and applications in environmental fields. However, the green synthesis of ZnO is often affected by processing conditions, especially drying temperature. This study investigates the effect of drying temperatures at 60, 70, and 80 °C on ZnO synthesis using mango seed extract (MSE) as a natural reducing agent. Zinc acetate dihydrate (ZA) and zinc nitrate hexahydrate (ZN) were used as precursors to supply Zn²⁺ ions during synthesis. ZA samples produced higher extraction yields, with a maximum of 37.80% at 60 °C. All ZN samples powders appeared finer and brighter in colour. SEM images showed that ZA samples formed larger rod-like agglomerates, while ZN samples produced more uniform and less clustered particles with spherical or flower-like shapes. EDX confirmed the presence of only zinc and oxygen, with ZN samples showing more consistent Zn to O ratios across all temperatures. Zeta potential analysis indicated that ZN samples had more stable negative surface charges ranging from −22 to −25 mV. In contrast, ZA sample showed fluctuating values with a strong positive charge at 80 °C. Particle size analysis showed that ZN sample at 70 °C had the smallest and most uniform size of 1.454 µm, while ZA sample at 70 °C showed the largest particles. XRD confirmed that all samples followed the wurtzite crystal structure. Crystallite size increased with temperature in ZA samples but decreased slightly in ZN samples. FTIR analysis confirmed Zn–O stretching and showed fewer organic residues in ZN samples. UV-Vis results indicated that ZA had consistent absorption peaks and band gap values between 4.53 and 4.61 eV. ZN showed a strong band gap of 4.54 eV at 60 °C but dropped significantly at higher temperatures. Overall, ZN at 70 °C produced ZnO with the best morphology and surface stability, while ZA at 70 °C showed better optical performance and consistent band gap behaviour.