Characteristics and useful effects for human health of antioxidant carbon nanodots contained in microwave-assisted Opuntia humifusa extract (MA-OHE(CD)) were investigated in this work. MA-OHE(CD) was characterized using transmission electron microscopy, dynamic light scattering analysis, X-ray diffraction, UV–vis spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform-infrared spectroscopy. Besides, total phenolic content and antioxidant activity of MA-OHE(CD) were measured. It was revealed that the MA-OHE(CD) increases aquaporin-3 expression in human epidermal keratinocytes cell with hydrophilic characteristics. Moreover, the bio-active compound extraction efficacy and antioxidant activity of microwave-assisted extraction were great when compared to maceration.

The rapid synthesis techniques and interesting multidisciplinary applications make carbon nanodots (CNDs) stand out from semiconductor quantum dots. Moreover, CNDs derived from green precursors have gained more importance beyond chemically derived CNDs due to sustainable synthesis opportunities. However, the presence of molecular impurities or intermediates or fluorophores was neglected during the entire process. Herein, we illustrate the sustainable synthesis of CNDs from Hemigraphis alternata plant leaves with extended carbonization procedure (3 and 9 min) along with simultaneous ethylene glycol and diethyl ether solvent treatment method for the successful removal of interfering fluorophores. To unravel the distinction between purified CNDs (P-CNDs) and organic fluorescent carbon nanostructures (org-FCNs), we carried out photophysical, structural, and morphological studies. A quantum yield (QY) of 69 and 42% was observed for crude org-FCNs, and crude P-CNDs; however after purification, QY of 1% and absence of one component from the fluorescent decays curve suggest the removal of fluorophores. Further, HR-TEM and DLS studies showed the quasi-spherical amorphous particles having < 10 nm particle size for P-CNDs. Besides, in vitro biocompatibility investigation and cellular uptake assay (1–100 μg/mL) against the MDA-MB 468 cell lines proves the ≥ 95% cell viability and good internalization for both org-FCNs and P-CNDs. Hence, our study shows the presence of fluorophore impurities in plant-derived CNDs, the removal and resemblance in biocompatibility properties. Hence, this information can be considered during the synthesis and isolation of CNDs. Simple and effective removal of impurities to harvest pure carbon nanodots (CNDs) through solvent-based selective separation method, and revelation of the cocktail flourphores similar to biocompatible blue fluorescent CNDs were studied.

Due to their fascinating properties, there is a rise in the critical consideration of carbon-based nanomaterials in a plethora of applications. Carbon nanomaterials, such as nanotubes, graphene, fullerenes, and nanodiamonds, have broad applicability and potential research prospects. In the past few years, the developments and consumption of still smaller nanomaterials, namely graphene quantum dots and carbon nanodots or carbon dots (CDs) have been explored. Since carbon as a component exhibits insignificant cytotoxicity and remarkable biocompatibility, CDs have found a wide scope of potential applications. Owing to their fascinating aspects, such as small size, biocompatibility, low toxic nature, environment-friendliness, costeffectiveness, ease of chemical functionalization, derivatization and surface modification, and photoluminescence tenability, CDs have been widely acknowledged. CDs have found major prospects in the areas of catalysis, sensors, and optical and bio-related applications. CDs are generally synthesized by employing techniques of pyrolysis, laser ablation, arc discharge, electrochemical method; hydrothermal and solvothermal techniques; and microwave and ultrasonic irradiations. This review article presents a brief account of the major properties of CDs, and applications, with particular emphasis on the green and environment-friendly synthesis methodologies. An overview of the microwave and ultrasound irradiation-induced syntheses for the preparation of CDs is presented in the light of green chemistry principles. In addition, some of the green and environmentally benign precursors for the production of CDs are outlined. The most recent work on CDs is included in this review article.

Fluorescent nanostructures based on carbon, or carbon dots, are attracting much attention and interest because of their diverse properties which can be applied in several fields of knowledge, such as optics, biomedicine, environmental research, among others. Such properties are in part, derived from its intrinsic luminescence from tunable functional groups. In this work, we produced carbon nanodots (CND) using agro-industrial residues, such as Lolium perenne and malt bagasse. The methods used were conventional hydrothermal syntheses and microwave-assisted hydrothermal synthesis. To the best of our knowledge, this is the first time that carbon dots synthesized from this ryegrass type are reported. The synthesis methods were one step (no catalyst, base, or acid were added for passivation), and the functional groups responsible for the luminescence and high solubility in water were identified by infrared spectroscopy, being mainly C=O, C–OH, C–N, and N–H. According to our theoretical studies, the C=O group introduced a new energy level for electronic transitions that can affect the emission properties. Fluorescence images of osteoblasts using CNDs were acquired and their chelating property towards Pb2+ and Cr6+ detection was tested.

We report on the one-step synthesis of luminescent carbon nanodots (C-dots) via an electrical discharge between two graphite electrodes submerged into organic solvent (octane). This is a simple approach for the fabrication of C-dots with tunable photoluminescence (PL) that differs from the other preparation methods, as no post-passivation step is required. The synthesized carbon nanoparticles are of spherical shape and their size is distributed in the range of 2–5 nm and exhibit luminescence sensitive to excitation wavelength.