Green synthesis of ZnO nanoparticles using <i>E. cardamomum</i> and zinc nitrate precursor: a dual-functional material for water purification and antibacterial applications

This study presents an eco-friendly, bio-engineered approach for synthesizing zinc oxide nanoparticles (ZnO NPs) using <i>Elettaria cardamomum</i> pod (<i>EC</i>-pod) extract, offering a sustainable alternative for environmental remediation and antimicrobial applications. X-ray diffraction (XRD) analysis confirms the wurtzite crystalline phase, with an average particle size of 20.87 nm. Ultraviolet-visible (UV-Vis) spectroscopy reveals a characteristic absorption peak at 372 nm, corresponding to an energy band gap of 3.33 eV. Fourier-transform infrared (FTIR) spectroscopy highlights the role of phytochemicals as capping and stabilizing agents. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) confirm multi-architectural morphologies, including hexagonal, spherical, rod-like, and pentagonal structures, with energy-dispersive X-ray (EDX) spectroscopy verifying elemental purity. The photocatalytic efficiency of <i>EC</i>-pod:ZnO in degrading malachite green (MG) dye under UV irradiation reaches 99.8% removal within 160 minutes, with a high quantum yield of 2.73 × 10^-3 molecules per photon and a space-time yield of 1.37 × 10^-5 molecules per photon per mg. Additionally, <i>EC</i>-pod:ZnO exhibits significant antibacterial activity against both Gram-positive (<i>Staphylococcus aureus</i>) and Gram-negative (<i>Pseudomonas aeruginosa</i>) bacteria, showcasing its dual functionality as a potential photocatalyst and antimicrobial agent. This nature-inspired ZnO nanomaterial offers an economical, scalable, and sustainable solution for environmental and biomedical applications, highlighting its potential in wastewater treatment and microbial control.