Uptake Of Polycyclic Aromatic Hydrocarbons And Graphene Quantum Dots On Plant Surfaces

Polycyclic aromatic hydrocarbons (PAHs), one kind of typical persistent organic pollutants (POPs), have been continuously receiving research attention on their transport and transformation in the environment, biological effect and health risks. Derive from incomplete combustion of biomatter and mineral fuel, PAHs usually bound with burning accompanied nanoparticles and transport together in the environment. Interaction and uptake of PAHs on plant surfaces are of great importance in the understanding of their environmental hazardous effects. In this study, the current status of PAH pollution and the application induced emission of carbon nanomaterials (CNMs) were briefly introduced. The interactions between organic pollutants and CNMs, and their co-uptake by plant were mainly reviewed. It is recognized that there were still uncertainties and controversies in the understanding of process and mechanism of organic pollutant and CNM uptake and transport onto plant. Under such concerns, the concentration level of 16 PAHs in the selected plant leaves were investigated, the distribution of 16 PAHs on the plant surfaces and inner tissues, and those on the adaxial and abaxial surfaces were distinguished. The composition, morphology and epicuticular wax structures of selected plant surfaces were characterized through FTIR-ATR, SEM, (TP-) CLSM, MDSC, and elemental analysis.Accordingly, the role of morphology and micro-structures of surface lipid in controlling the uptake of organic pollutants was emphasized as the main reason of the interspecific varieties. The stratification of cuticular components and the distribution of a representative PAH, phenanthrene in the leaf cuticle were observed by in situ method, and polymeric lipid was identified to be the main reservoir for organic pollutant. An ultra-small graphene-based material, graphene quantum dots, was synthesized and characterized through FTIR-ATR, Raman spec ropy, XPS,ζ-potential, SEM, TEM. The adsorption of phenanthrene on the GQDs was investigated. Through the application of time resolved dynamic light scatter (TR-DLS) method, the aggregation behavior and stability of GQDs were studied in four mono- and di-valent cations throughout a wide range of pH. Complex roles of pH and cation valence were discovered and self-assembly involved aggregation mechanism was proposed. The GQDs uptake by rice was investigated and positive impact of GQDs on the root and shoot elongation of rice seedling were discovered. The distribution of GQDs and its generated ROS were observed. The main original conclusion of this work are drawn as follow:(1) The concentrations, distribution characteristics of 16 PAHs in leaves of six selected shrub plant species were investigated. The impact of plant surface morphology and micro-structures of epicuticular waxes on the PAH uptake were initially studied and the varieties between adaxial and abaxial surfaces were distinguished. The role of lipids has been redefined and differentiated into the stereo micro-structure of surface epicuticular wax and the content of lipid. Uptake and diffusion of PAHs into plant was a multi-factor regulated process, in which, beside physicochemical properties of pollutants, plant surface characteristics including lipid content, surface stereo structures and hydrophobicity were all contributed.(2) TPCLSM was applied as a direct and noninvasive probe to explore the in situ uptake of phenanthrene into the cuticular membrane of a hypostomatic plant, Photinia serrulata. Phenanthrene was found to diffuse via a channel-like pathway into the middle layer of the cuticle matrix, where it was identified to be composed of polymeric lipids. The strong affinity of phenanthrene for polymeric lipids is a major contributor of the fugacity gradient driving the diffusive uptake of phenanthrene in the cuticular membrane.the liquid-like state of polymeric lipids may promote mobility by enhancing the diffusion rate. The proposed "diffusive uptake and storage" function of polymeric lipids within the membrane characterizes the modality of accumulation of the hydrophobic contaminant at the interface between the plant and the environment. Assessing the capacity of fugacity of these constituents in detail will bring about knowledge of contaminant fate in superior plants with a higher level of accuracy.(3) One novel species of ultrasmall graphene-based nanomaterial, graphene quantum dots (GQDs), had been synthesize and characterized to have crystal nanoplates and highly oxidized edges. The aggregation behavior and stability of GQDs were investigated in four mono- and di-valent cations throughout a wide range of pH. Complex roles of pH and cation valence were discovered and self-assembly involved aggregation mechanism was proposed. The interplay of several secondary interactions lead to the different interaction mode under varied solution chemistry. The tuning of the pH and coexisted cations could lead to anomalous aggregation behavior ascribe to the self-recognition triggered aggregation and enhanced by the above mentioned adjustments. Moreover, extended interaction modes of GQD nanosheets should be taken into account due to the charge heterogeneity induced conformational changes. Besides, the understanding on the aggregates should be updated as there could be aggregates stable in the solution as well as aggregates that would precipitate out of the solution.(4) The uptake of GQDs by rice seedlings and the impact of GQDs on the root/shoot elongation were investigated and comparison was made between GQDs and G/GO. The impact of graphene-based material on the plant was size dependent, along the size increase, the uptake was suppressed but the toxic effect was amplified, while on the contrary, along the size decrease, the uptake was enhanced and there was positive effect on the growth of rice seedlings were discovered in the exposure of GQDs, which have ultra-small sizes.