Nurul Illya Muhamad Fauzi, Yap Wing Fen, Mazliana Ahmad Kamarudin, Jaafar Abdullah, Muhammad Hakimi Mohd Khairul Anuar, Faten Bashar Kamal Eddin, Hazwani Suhaila Hashim, Muhammad Fahmi Anuar, Rahayu Emilia Mohamed Khaidir, Huda Abdullah, Ahmad Taufiq
Banana peels from Musa Acuminata species are often discarded as waste but possess high carbon content and hold considerable potential as sustainable precursors for nanomaterial synthesis. Herein, blue-emitting carbon quantum dots (CQDs) were synthesized via a green hydrothermal approach using banana peel as the sole carbon source. Although CQDs are widely recognized for their unique optical and structural properties, the effect of reaction time on these characteristics during green synthesis has received limited attention. To establish optimal conditions, thermogravimetric analysis (TGA) identified 200 °C as the most suitable reaction temperature. CQDs synthesized over 3–12 h were characterized using photoluminescence (PL), ultraviolet-visible (UV–Vis), Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). Prolonging reaction time induced a redshift in emission (449–460 nm), a band-gap reduction (3.985–3.942 eV), and particle growth from ~ 4 nm to 8 nm, with enhanced crystallinity (decreasing Iᴅ/Iɢ ratio) and carbon enrichment (87.4–96.3%). The 6-hour synthesis duration yielded CQDs with the most favorable optical and structural properties. To demonstrate practical utility, the optimized CQDs was employed as a fluorescence (FL) sensor for detecting methylparaben (MP), an environmental contaminant. The sensor exhibited a Stern–Volmer quenching constant (Ksv) of 0.10958 log10(nM)⁻¹ with R² = 0.97495 and a sensitivity of 1572.58 a.u./log₁₀(nM) with R² = 0.94425 across a broad linear range (1 nM–10 mM). Overall, the study provides a sustainable strategy for waste valorization and advances the development of green optical sensors for environmental monitoring. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2026.
Functional Nanotechnology Devices Laboratory, Institute of Nanoscience and Nanotechnology, Universiti Putra Malaysia, Selangor, Serdang, 43400 UPM, Malaysia; Department of Physics, Faculty of Science, Universiti Putra Malaysia, Selangor, Serdang, 43400 UPM, Malaysia; Centre for Optical and Electromagnetic Research, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310058, China; Faculty of Applied Sciences, Universiti Teknologi MARA, Sarawak, Cawangan Sarawak, Kota Samarahan, 94300, Malaysia; Department of Electrical, Electronic and System Engineering, Faculty of Engineering and Build Environment, Universiti Kebangsaan Malaysia, Selangor, Bangi, 43600 UKM, Malaysia; Department of Physics, Faculty of Mathematics and Natural Science, Universitas Negeri Malang, Jl. Semarang 5, Malang, 65145, Indonesia
