Biphasic impacts of graphite-derived engineering carbon-based nanomaterials on plant performance:Effectiveness vs.nanotoxicity

Graphite-derived carbon-based nanomaterials(GCNMs)as an exciting class of engineering carbonmaterials have been extensively exploited in environment and agriculture for pollution restorer,environmental purifier,plant growth stimulant,and stress resistance inducer.With the increasing demand of production in past decades,GCNMs were inevitably released into the natural environment and became emerging pollutants.This review briefly summarized the recent progress on GCNMs-plant interaction with positive and negative sides,and discussed the biphasic(stimulatory-inhibitory)regulation of GCNMs on plant systems.The emphasis was placed on disseminating the latest scientific research,covering various effectiveness of GCNMs on plants and cells as well as nanotoxicity.Particularly,it is highlighted that fullerenes,carbon nanotubes,graphenes,and their functionalized forms as the representative zero-,one-,and two-dimensional GCNMs in optimum quantity have favorable efficacy on plants for seed germination,growth and development,fruit and productivity,and stress tolerance.On the contrary,GCNMs have possibly induced cytotoxicity and phytotoxicity on plant at anatomic,physiological,and genetic levels.The toxic mechanisms were mainly attributed to ion leakage from membrane,chloroplast damage,decreasing the levels of photosynthetic/nonphotosynthetic pigments and plant hormones,downregulating activities of metabolism and enzymatic/non-enzymatic antioxidant systems,or triggering ROS increase for inducing oxidative stress.This comprehensive review provides an in-depth insight of advanced progress made toward the utilization of GCNMs in plant science fields as well as current challenges.Future perspectives on a directional guide for further research in the emerging area of GCNMs-enabled phytonanotechnology are summarized at the end.This will possibly provide an important reference role for further study and rational application of GCNMs in agriculture.

Optimizing synthesis conditions of nanoscale zero-valent iron （nZVI） through aqueous reactivity assessment

Nanoscale iron particles （nZVI） is one of the most important engineered nanomaterials applied to environmental pollution control and abatement. Although a multitude of synthesis approaches have been proposed, a facile method to screen the reactivity of candidate nZVI materials produced using different methods or under varying synthesis conditions has yet been established. In this study, four reaction parameters were adjusted in the preparation of borohydride-reduced nZVI. The reductive properties of the resultant nanoparticles were assayed independently using two model aqueous contaminants, Cu （II） and nitrate. The results confirm that the reductive reactivity of nZVI is most sensitive to the initial concentration of iron precursor, borohydride feed rate, and the loading ratio of borohydride to ferric ion during particle synthesis. Solution mixing speed, in contrast, carries a relative small weight on the reactivity of nZVI. The two probing reactions （i.e., Cu（II） and nitrate reduction） are able to generate consistent and quantitative inference about the mass-normalized surface activity of nZVI. However, the nitrate assay is valid in dilute aqueous solutions only （50 mg.L~ or lower） due to accelerated deactivation of iron surface at elevated nitrate concentra- tions. Additional insights including the structural and chemical makeup of nZVI can be garnered from Cu（II） reduction assessments. The reactivity assays investigated in this study can facilitate screening of candidate materials or optimization of nZVI production parameters, which complement some of the more sophisticated but less chemically specific material characterization methods used in the nZVI research.