Water pollution, significantly influenced by the discharge of synthetic dyes from industries, such as textiles, poses a persistent global threat to human health. Among these dyes, methylene blue, particularly prevalent in the textile sector, exacerbates this issue. This study introduces an innovative approach to mitigate water pollution through the synthesis of nanomaterials using biomass-derived carbon quantum dots (CQDs) from grape pomace and watermelon peel. Utilizing the hydrothermal method at temperatures between 80 and 160 °C over periods ranging from 1 to 24 h, CQDs were successfully synthesized. A comprehensive characterization of the CQDs was performed using UV–visible spectroscopy, Fourier-transform infrared spectroscopy, dynamic light scattering, Raman spectroscopy, and luminescence spectroscopy, confirming their high quality. The photocatalytic activity of the CQDs in degrading methylene blue was evaluated under both sunlight and incandescent light irradiation, with measurements taken at 20 min intervals over a 2 h period. The CQDs, with sizes ranging from 1–10 nm, demonstrated notable optical properties, including upconversion and down-conversion luminescence. The results revealed effective photocatalytic degradation of methylene blue under sunlight, highlighting the potential for scalable production of these cost-effective catalytic nanomaterials for synthetic dye degradation.

In this study, luminescent upconversion nanoparticles (UCNPs) Y₂O₃ and Gd₂O₃ co-doped with Yb³⁺ and Er³⁺ were prepared by the sol-gel method (SG). These NPs are able to absorb near infrared photons and upconvert them into visible radiation with a direct application in bioimaging, as an important tool to diagnose and visualize cancer cells. The UCNPs were coated with a thin silica shell and functionalized with amino groups for further folic acid conjugation to allow their interaction with folate ligands on the cell surface. Their physical properties were analysed by Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) measurements. The PL results revealed excellent luminescence properties on all core-shell UCNPs. Cytotoxicity experiments with concentrations of bare and aminosilane coated/functionalized UCNPs between 0.001 μg/mL to 1 μg/mL were tested on two different cell lines from human cervix carcinoma (HeLa) and human colorectal adenocarcinoma (DLD-1) with a colorimetric assay based on the reduction of MTT reagent (methy-134-thiazolyltetrazolium). The assays show that some concentrations of bare UCNPs were cytotoxic for cervical adenocarcinoma cells (HeLa); however, for human colorectal adenocarcinoma all UCNPs are non-cytotoxic. After UCNPs functionalization with silica-aminosilane (APTES/TEOS), all of the nanoparticles tested were found to be non-cytotoxic for both cell lines. The UCNPs functionalized in this work can be further conjugated with specific ligands and used as biolabels for detection of cancer cells.

Upconversion nanoparticles (UCNs) find application in nanomedicine as biolabels to identify cancer cells. In this work, Y₂O₃: Er³⁺/Yb³⁺ and Gd₂O₃: Er³⁺/Yb³⁺ systems were fabricated by combustion synthesis (CS) and sol-gel (SG) methods to obtain nanoparticles with different shapes and sizes after post-annealing treatments. The crystallinity and morphology were analysed by x-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively, and the luminescent properties by spectrofluorescence measurements. The luminescence varied depending on the doping level. In this study, for the host Y₂O₃, with Er³⁺/Yb³⁺ (1%/1% mol), the green emission was more strongly attributed to the ²H _11/2→⁴I _15/2, ⁴S_3/2→⁴I _15/2 transitions of Er³⁺ ions. Red emission was present in Yb³⁺ (5%/10% mol) due to the ⁴F_9/2→⁴I_15/2 transition for both hosts. For the host Gd₂O₃, green emission was present in Er³⁺ (2% mol) and Yb³⁺ (3% mol). The surface of some UCNs was coated with a thin silica layer and analysed in order to compare the luminescence with the uncoated UCNs. The purpose of the coating was to prepare the samples for further functionalization for biolabel use. Results show that the emission intensity of all samples strongly depends on the synthesis method. SG was more reliable than CS synthesis in producing UCNs with better morphology and luminescent properties.