This study investigates the influence of the chemical nature of nitrogen sources on the optical properties of Carbon Quantum Dots (CQDs) and evaluates their suitability for various industrial applications through a series of stability tests. Four nitrogen sources, —diethanolamine, diethylamine, ethylenediamine, and 1,2-phenylenediamine— were used to synthesize surface-active CQDs via a one-step microwave-assisted carbonization method. All CQDs exhibited a negative surface charge, ranging from −24.1 to −26.2 mV, indicating excellent colloidal stability at the working pH of 7. Nitrogen was successfully incorporated in all cases; however, CQDs synthesized with ethylenediamine and phenylenediamine showed significantly higher nitrogen contents. This increased incorporation was directly correlated with higher fluorescence quantum yields (QYs), reaching 20.44% with ethylenediamine and 22.61% with phenylenediamine, representing an improvement of up to 220% compared to those synthesized with other nitrogen sources. In addition to the nitrogen content, the carbon structure also influences the QY. Higher proportions of CC bonds contribute to more extensive sp²-conjugated domains, promoting electron delocalization and enhancing both electronic transitions and fluorescence efficiency. However, physical properties, such as particle size and thermal stability, remained unaffected by the choice of the nitrogen precursor. The CQDs demonstrated excellent thermal stability, ionic strength resistance, and long-term fluorescence retention, maintaining up to 90% of their initial fluorescence intensity under various storage conditions, making them suitable for use in harsh environments. However, an extremely acidic pH had the most detrimental effect, causing fluorescence intensity losses of up to 80% in CQD-phenylenediamine and CQD-diethylamine. These findings highlight the important role of nitrogen in enhancing the optoelectronic properties of the CQDs. Appropriate selection of the nitrogen source can significantly improve the fluorescence performance and optimize the response for practical applications.

In this work, the antioxidant properties of methanolic extract of Larrea tridentata were assessed through the free radical scavenging method, ferric reducing antioxidant power and oxygen radical absorbance capacity. The phenolic acids content in the extract was quantified by high-performance liquid chromatography (HPLC) and the total phenol content by the Folin–Ciocalteu method. The extract was used as an antioxidant in biodiesel from canola oil composed mostly by fatty acid methyl esters identified and quantified by gas chromatography-mass spectrophotometry (GC-MS). The performance of the extract as an antioxidant was assessed by the oxidative stability index (OSI) with a Rancimat equipment at 100, 110, 120 and 130 °C. Additionally, the change of the peroxide value (PV) and the higher heating value under conditions of oxidative stress at 100 °C and air injection were measured. The antioxidant capacity of the extract reached 50,000 TAEC (micromole of Trolox antioxidant equivalent capacity per gram). The biodiesel was constituted by more than 70% of unsaturated fatty acid methyl esters (FAME), mainly methyl oleate. The time needed to reach a PV of 100 meqO₂/kg was almost four times longer with an antioxidant concentration of 250 mg/L than the blank. The biodiesel showed an OSI time of 1.25 h at 110 °C, while it increased to 8.8, 15.89 and 32.27 h with the antioxidant at concentrations of 250, 500 and 1000 mg/L, respectively. The methanolic Larrea tridentata extract proved to have an antioxidant capacity and it is a green antioxidant in biodiesel to increase its oxidative stability. According to the results obtained, the L. tridentata methanolic extract is an alternative to the commercial synthetic antioxidants used in biodiesel nowadays.

This study aimed to develop and implement a nanotechnology-based alternative to traditional tracers used in the oil and gas industry for assessing interwell connectivity. A simple and rapid hydrothermal protocol for synthesizing carbon quantum dots (CQDs) using agroindustry waste was implemented. Three commercial CQDs were employed (CQDblue, CQDgreen, and CQDred); the fourth was synthesized from orange peel (CQDop). The CQDs from waste and other commercials with spherical morphology, nanometric sizes less than 11 nm in diameter, and surface roughness less than 3.1 nm were used. These tracers demonstrated high colloidal stability with a negative zeta potential, containing carbonyl-type chemical groups and unsaturations in aromatic structures that influenced their optical behavior. All materials presented high colloidal stability with negative values of charge z potential between −17.8 and −49.1. Additionally, individual quantification of these tracers is feasible even in scenarios where multiple CQDs are present in the effluent with a maximum percentage of interference of 15.5% for CQDop in the presence of the other three nanotracers. The CQDs were injected into the field once the technology was insured under laboratory conditions. Monitoring the effluents allowed the determination of connectivity for five first-line producer wells. This study enables the application of CQDs in the industry, particularly in fields where the arrangement of injector and producer wells is intricate, requiring the use of multiple tracers for a comprehensive description of the system.

The immobilization of bacteria cells has shown to be an efficient technology to improve cell viability. This study used lyophilized and pulverized coffee pulp (LPC) and LPC functionalized with theobromine at two concentrations, 3.1 w/w and 2.4 w/w named as LPF1 and LPF2, respectively, to immobilize Lactobacillus rhamnosus ATCC 53103 cells (biomaterials) and increase the viability of the cell at storage and gastrointestinal conditions. To characterize the biomaterials, SEM, Dynamic Light Scattering, TGA, , FTIR and Isoeletrc Point measurements (or zeta potential measurements) were carried out. To evaluate the effectiveness of immobilization, cell viability as a function of storage time and under simulated gastrointestinal conditions was evaluated. Regarding the characterization of the materials, the particle sizes were 21.7 to 334.4 nm and they experienced mass losses of less than 10% at 100 °C. The FTIR indicated the presence of functional groups related to caffeine, chlorogenic acid, sucrose, arabinogalactans, carbohydrates, and proteins in all biomaterials. The sorption kinetic parameters showed an adsorptive capacity between 3.0 × 10⁹ and 8.0 × 10⁹ CFU/g, being LPF1 the best materials to immobilize the cells, associated with LPF1 surface properties. The viability was higher for immobilized cells than for free cells, when left in storage and under simulated gastric conditions. Finally, the biomaterials could be used in the preparation of probiotic diets based on lactobacilli. To the best of our knowledge, this is the first study regarding the use of waste from coffee agribusiness to develop probiotic biocarriers which opens up possibilities for future developments.

This research involved a comprehensive multisystemic evaluation of the biotoxicity of three tracers (carbon quantum dots synthesized from citric acid and ethylenediamine “N-CQD”, commercial cadmium-tellurium quantum dots “CdTe-QD”, and a conventional tracer based on fluorinated benzoic acid derivatives “SB-tracer”). Biotoxicity was assessed at three organizational levels: DNA, cellular, and multicellular eukaryotic system, using the comet assay and chromosomal aberration tests, cytotoxicity assays, and plant growth profiling, respectively. The results revealed significant DNA damage induced by CdTe-QD and SB-tracer, with olive tail moment (a measure of DNA degradation) values up to 15 times higher than those observed for N-CQD in the comet assay. Cytotoxicity revealed an half maximal inhibitory concentration (IC₅₀) > 1000 mg L⁻¹ for N-CQD, 7.35 mg L⁻¹ for CdTe-QD, and 600.06 mg L⁻¹ for SB-tracer, classifying the samples as non-cytotoxic, cytotoxic, and moderately cytotoxic, respectively. However, the chromosomal aberration results for SB-tracer revealed its lethality by inhibiting the lymphocyte proliferation required for the test. Melon and sunflower seed sprouts were employed as multicellular eukaryotic models for toxicity evaluation at higher organizational levels, and it was observed that SB-tracer has a deleterious effect on germination, while N-CQD increased sprout biomass by up to 19 times compared to water irrigation, a result attributed to their positive effect on photosynthetic mechanisms. Finally, the non-toxic and protective effects of N-CQD can be attributed to their high ORAC (oxygen radical absorbance capacity) value considered in this research, which is associated with the prevention of damage to key biomolecules such as DNA and the promotion of cell growth. These results highlight the feasibility and potential use of CQDs as a safe alternative for both the environment and health, with the potential to substitute substances conventionally employed by different industries as multipurpose tracers. To the best of our knowledge, this is the first study to comprehensively evaluate the biotoxicity of QDs at multiple biological organization levels.