Hydrothermal synthesis of sustainable carbon dots from blended aquatic plant biomass: Structure–Property relationships and optical characterization

Carbon dots (CDs) are an emerging class of fluorescent carbon-based nanomaterials known for their superior photostability, biocompatibility, and environmentally friendly synthesis routes. In this work, CDs were synthesized via a green hydrothermal process using a mixed aquatic plant biomass composed of Eichhornia crassipes [EC] and Ipomoea aquatic [IA] in a 1:1 ratio. The use of mixed biomass precursors aims to exploit the synergistic interaction of different phytochemical compositions to enhance the optical and structural characteristics of the resulting CDs. The synthesis involved direct hydrothermal treatment of the blended plant material without addition of toxic passivation or doping agents, thereby maintaining the eco-friendly nature of the process. The prepared mixed biomass-derived CDs (Blend-CDs) were comprehensively characterized using UV–Visible (UV–Vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The UV-Visible spectra had distinct absorption bands corresponding to n-π* transitions in C O groups, in addition to a weak broad shoulder region in the visible region that corresponded to surface defect states. The photoluminescence (PL) spectra showed highly excitation-dependent emission, with peak emissions in the blue and cyan regions due to radiative recombination at surface defect sites and functional groups. The FTIR spectra indicated that there were hydrophilic functional groups present, including –OH, –CO, and –NH. The XRD pattern showed that the carbon nanoparticles had an amorphous structure, which was demonstrated by the presence of a broad peak at 2θ ~ 28º, alongside a few crystalline peaks that might have formed from the minerals left behind by the biomass. The findings showed that the use of a mixed aquatic plant precursor provided not only a sustainable method of CD fabrication but also gave the opportunity to tailor the properties of the CDs through the choice of the precursor used.