Having porous structure, large surface area, and high carbon content of biochar facilitates interface bonding of polylactic acid (PLA) composites, but uneven dispersion by its irregular morphology is becoming a new challenge in damaging properties. Based on this, the novelty of this study is using carbon quantum dots (CQDs) to overcome the performance defects of caused PLA composites by biochar while the ultimate goal is to reveal the influence mechanism of CQDs on structure, characteristics, and properties of PLA composites based on disclosing the forming mechanism of CQDs. It was found that adding CQDs accelerated the degradation of PLA from the results of Phosphate Buffer Saline (PBS) degradation, hydrolysis, and soil degradation. PLA/CQDs composite films also showed better thermal properties due to the excellent thermal stability of CQDs, and nucleation effect of CQDs should be responsible for the improvement of PLA crystallization. Additionally, having good activity, regular morphology, and uniform size of CQDs facilitated uniform dispersion and good interface combination in PLA system and thereby improved the tensile strength, tensile modulus, and elongation at break simultaneously. As a comparison, the tensile strength, tensile modulus, and elongation at break of 1 wt% PLA/CQDs composite films are 55.00 MPa, 1.76 GPa, and 9.84 %, this provides a promising, sustainable, and eco-friendly solution for reinforcing PLA composites.

Lead (Pb) toxicity impairs the growth, yield, and biochemical traits of rice, making it essential to mitigate Pb stress in soil and restore its growth and production. This study investigated the potential of ascorbic acid-coated quantum dots (AsA-QDs) in alleviating Pb stress in two rice cultivars, Japonica (JP-5) and Indica (Super Basmati), grown in pots under Pb stress (50 mg/kg as lead chloride) with AsA-QD suspensions (50 ppm and 100 ppm) as treatments. The synthesized AsA-QDs were characterized by zeta potential (-14.4 mV), particle size (472.3 nm, PDI 0.745), UV-Vis absorption peak (240 nm), FT-IR analysis revealing functional groups (carboxylic acid and alkene), and TEM showing spherical morphology (average size 9.43 nm). Pb stress reduced key traits in JP-5, including tillers per plant (11.11 %), grain yield (18.22 %), kernel weight (18.22 %), protein (40.19 %), phenolic content (59.66 %), and antioxidant capacity (17.75 %), while 50 ppm AsA-QDs improved these by 33.33 %, 5.73 %, 2.03 %, and 13.19 %, respectively. Similarly, Pb stress reduced plant height, T/P, biomass yield (BY), GY, TKW, total sugars, reducing sugars, non-reducing sugars, starch, proteins, and TPC in Super Basmati by 19.76 %, 21.43 %, 11.01 %, 11.01 %, 7.52 %, 38.09 %, 7.24 %, 13.96 %, 11.97 %, and 40.39 %, respectively, while PbQD1 improved these traits by 14.29 %, 15.49 %, 9.25 %, 109.52 %, 8.31 %, 31.72 %, 25.91 %, and 7.075 %, respectively. The findings demonstrate that AsA-QDs effectively mitigate Pb toxicity by reducing oxidative stress, enhancing growth parameters, and restoring yield components, establishing them as a promising nanomaterial for sustainable crop resilience under Pb stress.

Mercury ion (Hg2+) is one of the most toxic pollutants that can exist throughout the environment and be diffused into water, soil, air, and eventually the food chain. Even a very low level of Hg2+ diffused in living organisms can hurt their DNA and cause the permanent damage of the central nervous system and a variety of consequential disorders. Hence, the development of a sensitive and specific method for the detection of Hg2+ at trace ranges is extremely important as well as challenging. Fluorometric detection assays based on graphene quantum dots (GQDs) and carbon quantum dots (CQDs) offer considerable potential for the determination and monitoring of heavy metals due to their fascinating properties. Although the quantum yield of GQDs and CQDs is sufficient for their use as fluorescent probes, doping with heteroatoms can significantly improve their optical properties and selectivity toward specific analytes. This review explores the primary advances of CQDs and GQDs in their great electronic, optical, and physical properties, their synthetic methods, and their use in Hg2+ fluorimetry detection.

Graphene quantum dots (GQDs) are useful nanomaterials of excellent water solubility, biocompatibility and optical stability for various applications. In this study, we achieved the nitrogen fixation activity enhancement of autogenous azotobacters (Azotobacter vinelandii) by GQDs and revealed its mechanism. GQDs (1-10 mg/L) accelerated the logarithmic growth phase of A. vinelandii, making bacteria enter the plateau earlier. Biocompatible GQDs did not cause cell death and oxidative damage of A. vinelandii. The expression levels of metabolism and nitrogen fixation related genes were significantly up-regulated by GQDs, thereby enhancing the activity of nitrogenase. The nitrogen fixation activity of A. vinelandii reached 471.7 % of the control upon the exposure to GQDs. The intracellular polyhydroxyalkanoate vesicles were consumed to provide energy for nitrogen fixation, which involved with a chain reaction of carbohydrate metabolism, lipid metabolism, and energy metabolism pathways accompanied by significant increases in electron transfer rate. The synergistic effect of GQDs on A. vinelandii further facilitated the augmentation of soil nitrogen content in Qinghai-Tibet Plateau. Our results provided an effective approach to enhance the biological nitrogen fixation by GQDs.