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.

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.