No abstract

Understanding the transformation of graphitic carbon nitride (g-C3N4) is essential to assess nanomaterial robustness and environmental risks. Using an integrated experimental and simulation approach, our work has demonstrated that the photoinduced hole (h+) on g-C3N4 nanosheets significantly enhances nanomaterial decomposition under •OH attack. Two g-C3N4 nanosheet samples D and M2 were synthesized, among which M2 had more pores, defects, and edges, and they were subjected to treatments with •OH alone and both •OH and h+. Both D and M2 were oxidized and released nitrate and soluble organic fragments, and M2 was more susceptible to oxidation. Particularly, h+ increased the nitrate release rate by 3.37–6.33 times even though the steady-state concentration of •OH was similar. Molecular simulations highlighted that •OH only attacked a limited number of edge-site heptazines on g-C3N4 nanosheets and resulted in peripheral etching and slow degradation, whereas h+ decreased the activation energy barrier of C–N bond breaking between heptazines, shifted the degradation pathway to bulk fragmentation, and thus led to much faster degradation. This discovery not only sheds light on the unique environmental transformation of emerging photoreactive nanomaterials but also provides guidelines for designing robust nanomaterials for engineering applications.

No abstract

No abstract

The corrosion behavior of single-phase Mg-Al alloys has been examined using a combination of aqueous, atmospheric and ionic liquid based techniques. Our results show preferential rapid dissolution of Mg along with redistribution and enrichment of the effectively more "noble" Al component. During aqueous free corrosion experiments immediate pH increases were measured at the solid-liquid interface in aqueous chloride. Using inductively coupled plasma mass spectroscopy the oxide/hydroxide chemical dissolution rates were determined to be 0.222 per atomic site/s for Mg 2+ and 0.022 per atomic site/s for Al 3+ from the elemental alloy components. Atmospheric corrosion studies measured a 60 • contact angle decrease during 20 hour free corrosion corresponding to a small 0.04 Jm −2 reduction in the MgO/water interfacial free energy. Rotating disk electrode and ionic liquid dissolution techniques revealed mud cracking, platelet formation and nanowire morphologies that can result from selective dissolution of Mg in single-phase Mg-Al alloys. The evolution of these morphologies is described in terms of a step-flow dissolution mechanism.