Valorization of Tectona grandis Leaf Waste Into Cellulose Nanocrystals, Nanofibers, and S/N-Doped Carbon Dots

Abstract

This study presents an integrated, waste-based route to produce chemically purified cellulose (CPC), cellulose nanofibers (CNF), cellulose nanocrystals (CNCs), and carbon dots (CDs) from Tectona grandis (teak) leaves. CPC was obtained by sequential dewaxing, chlorite bleaching, sulfite treatment, and alkaline extraction. CNFs were prepared by high-shear processing and sonication, while CNCs were produced by controlled sulfuric-acid hydrolysis. CDs, including sulfur- and nitrogen-doped variants, were synthesized via hydrothermal carbonization of leaf powder. Materials were characterized by proximate/ultimate (elemental) analysis, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), atomic force microscopy, UV–vis/fluorescence spectroscopy, dynamic light scattering/zeta potential (ζ), and thermogravimetric analysis (TGA). Proximate/ultimate analysis indicates the leaves are a suitable feedstock (C ≈ 40.42 wt%, holocellulose ≈ 42.19 wt%, α-cellulose ≈ 18.18 wt%). XRD analysis yields a CNC crystallinity index of ≈63.19%. Microscopy confirms rod-like CNC morphology and nanoscale CDs. TGA shows thermal behavior consistent with a stable cellulose fraction, and preliminary antibacterial testing (Escherichia coli) was performed using the pour-plate method. The presented water-based procedures convert a combustible forest residue into value-added nanomaterials.