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A model of nitrogen biogeochemical cycling in agriculture soil at the field scale for assessing how crop management practices affect nitrogen fertilizer fate and transport. 

Graphitic carbon nitride (g-CN) catalyzes various energy and environmental applications. Evaluating physicochemical properties and sustainability metrics presents valuable insights into designing minimally impactful, high-performing g-CN materials. 

Managing drinking water-associated pathogens that can cause infections in immunocompromised individuals is a persistent challenge, particularly for healthcare facilities where occupant exposures carry a substantial health risk. 

The toxicity of graphene oxide (GO) has been documented for multiple species. However, GO has variable surface chemistry, and it is currently unclear whether changes in oxygen content impact GO-organism interactions the same way across species. In this study, a modified Hummer's GO (ARGO) was systematically reduced by thermal annealing at 200, 500, or 800 °C and toxicity towards bacteria ( Escherichia coli ), alga ( Scenedesmus obliquus ), cyanobacteria ( Microcystis aeruginosa ), and invertebrates ( Daphnia magna ) was assessed by measuring the effective concentrations inducing 50% inhibition (EC 50 ). The EC 50 –carbon/oxygen ratio relationships show similar trends for bacteria and invertebrates, where toxicity increases as the material is reduced. Conversely, cyanobacterial inhibition decreases as GO is reduced. Further testing supports differences in cell-GO interactions between bacteria and cyanobacteria. Cyanobacteria showed a decrease in metabolic activity, evidenced by a 69% reduction in esterase activity after ARGO exposure but no oxidative stress, measured by 2′,7′-dichlorodihydrofluorescein diacetate (H 2 DCFDA) fluorescence and catalase activity. In contrast, ARGO induced a 55% increase in H 2 DCFDA fluorescence and 342% increase in catalase activity in bacteria. These changes in cell–material interactions propose different mechanisms of action, a physical mechanism occurring in cyanobacteria, and a chemical mechanism in bacteria. The differences in GO toxicity observed in different organisms emphasize the need to differentiate the safe-by-design guidelines made for GO in relation to the potential organisms exposed. 

While nitrogen doping greatly broadens graphene applications, relatively little is known about the influence of this heteroatom on the biological activity of graphene. A set of systematically modified nitrogen-doped graphene (NG) materials was synthesized using the hydrothermal method in which the degree of N-doping and N-bonding type is manipulated using two nitrogen precursors (urea and uric acid) and different thermal annealing temperatures. The bioactivity of the NG samples was evaluated using the oxidation of the intracellular antioxidant glutathione (GSH) and bacterial viability (of Escherichia coli K12), and oxidative stress was identified as the predominant antibacterial mechanism. Two key energy-relevant electrochemical reactions, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), were used to characterize the influence of different N-types on the electronic properties of the NG materials. Electron-donating graphitic-N and electron-withdrawing pyridinic-N were identified as effective promoters for ORR and OER, respectively. The similar mechanisms between the GSH oxidation (indicative of oxidative stress) and ORR mechanisms reveal the role of graphitic-N as the active site in oxidative stress related bioactivity, independent of other consequential properties ( e.g. , defect density, surface area). This work advances a growing rational design paradigm for graphene family materials using chemical composition and further provides valuable insight into the performance-hazard tradeoffs of NG applications in related fields. 

It is increasingly realized that rational design is critical to advance potential applications and proactively preclude adverse consequences of carbon nanomaterials (CNMs). Central to this approach is the establishment of parametric relationships that correlate material properties to both their functional performance and inherent hazard. This work aims to decouple the causative mechanisms of material structure and surface chemistry as it relates to the electrochemical and biological activities of graphene oxide (GO). The results are evaluated in the context of established relationships between surface chemistry and oxygen functionalized multi-walled carbon nanotubes (O-MWCNTs), a carbon allotrope. Systematic manipulation of GO surface chemistry is achieved through thermal annealing (under inert conditions, 200–900 °C). To further elucidate the contribution of several properties, chemical reduction was also used as an approach to differentially modify the surface chemistry. Physicochemical properties of GO and reduced GO (rGO) samples were comprehensively characterized using multiple techniques (AFM, TGA, XPS, ATR-FTIR, Raman, and DLS). The results indicate that surface chemistry is a viable design handle to control both activities. Rather than a single direct property ( i.e. , relative presence of carbonyl-containing moieties), it is a balance of multiple consequential properties, (extent of dispersion, defect density, and electrical conductivity) in combination with the relative presence of carbonyl moieties that synergistically contribute to electrochemical and biological activities. The identification of these governing physicochemical properties aims to inform the establishment of design parameters to guide the rational and safe design of CNMs.