Metallic Cu is a well-known electrocatalyst for nitrate reduction reaction (NO 3 RR), but it suffers from relatively low activity, poor stability, and inducing nitrite accumulation during the long-term operation. Herein, it is found that Cu catalysts minimized at the single-atom level can overcome the limitations of bulk materials in NO 3 RR. A metal-nitrogen-carbon (M-N-C) electrocatalyst composed of carbon nanosheets embedding isolated copper atoms coordinated with N, Cu-N-C-800, is synthesized by pyrolysis of a Cu-based metal-organic framework at 800 °C. In comparison with Cu nanoparticles and Cu plate-800, kinetic measurements show that the Cu-N-C-800 electrocatalyst is more active and stable and distinctly suppresses the release of nitrite intermediate into the solution. The combined results of experimental data and density functional theory calculations indicate that Cu bound with N (particularly Cu-N 2) is the key to favorable adsorption of NO 3 − and NO 2 −. This strong binding is responsible for the enhanced rate of nitrate conversion to the end products of ammonia and nitrogen. These findings highlight the promise of single-atom Cu electrocatalysts for nitrate reduction with desirable performance.

Introduction

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In this study, we proposed a new concept of utilizing the biological electrons produced from a microbial fuel cell (MFC) to power an E-Fenton process to treat wastewater at neutral pH as a bioelectro-Fenton (Bio-E-Fenton) process. This process can be achieved in a dual-chamber MFC from which electrons were generated via the catalyzation of Shewanella decolorationis S12 in its anaerobic anode chamber and transferred to its aerated cathode chamber equipped with a carbon nanotube (CNT)/gamma-FeOOH composite cathode. In the cathode chamber, the Fenton's reagents including hydrogen peroxide (H(2)O(2)) and ferrous irons (Fe(2+)) were in situ generated. This Bio-E-Fenton process led to the complete decolorization and mineralization of Orange II at pH 7.0 with the apparent first-order rate constants, k(app) = 0.212 h(-1) and k(TOC) = 0.0827 h(-1), respectively, and simultaneously produced a maximum power output of 230 mW m(-2) (normalized to the cathode surface area). The apparent mineralization current efficiency was calculated to be as high as 89%. The cathode composition was an important factor in governing system performance. When the ratio of CNT to gamma-FeOOH in the composite cathode was 1:1, the system demonstrated the fastest rate of Orange II degradation, corresponding to the highest amount of H(2)O(2) formed.

Notch (N) is a cell surface receptor that mediates an evolutionarily ancient signaling pathway to control an extraordinarily broad spectrum of cell fates and developmental processes. To gain insights into the functions of N signaling in the adult brain, we examined the involvement of N in Drosophila olfactory learning and memory. Long-term memory (LTM) was disrupted by blocking N signaling in conditional mutants or by acutely induced expression of a dominant-negative N transgene. In contrast, neither learning nor early memory were affected. Furthermore, induced overexpression of a wild-type (normal) N transgene specifically enhanced LTM formation. These experiments demonstrate that N signaling contributes to LTM formation in the Drosophila adult brain.A ctivation of Notch (N) receptors has been linked to the specification of many cell types in both vertebrates and invertebrates (1). Binding of ligands such as Delta (2) causes cleavage of the intracellular domain of the N protein (3-5). The cleaved cytoplasmic domain of N (Nintra) enters the nucleus, in which it regulates expression of target genes (1). Intercellular communication mediated by N signaling consists of two different modes: lateral inhibitory signaling and inductive signaling. A prototypic example of lateral inhibitory signaling is that loss of N function causes a cluster of equivalent proneural cells to all assume the default neuronal fate rather than an epidermal fate (6). Inductive N signaling, on the other hand, mediates interactions between cells that are nonequivalent before the signal initiates, such as induction of cone cells by photoreceptor cells and specification of midline cells in the embryo (7-9).In contrast to the extensive understanding of the vital role of N in development, the significance of N signaling in adult brains has yet to be revealed, although there is continuous presence of N protein and its ligands in the adult vertebrate nervous system (10). It has been reported that N signaling regulates neurite outgrowth in mammals (11), and chronic reduction of N activity in adult fruit flies also leads to progressive neurological syndromes (12). Processing of N requires ␥-secretase activity, whereas presenilin (PS) is a critical component of the ␥-secretase complex (13). Mutations in the PS genes are associated with the early onset of Alzheimer's disease (14). Conditional knockout of the PS1 gene in mice is also associated with reduced clearance of hippocampal memory traces (15). Although involvement of N in these PS mutant phenotypes remains to be determined, it has been shown that N plays a role in PS-mediated formation of neural projections in postmitotic neurons necessary for learned thermotaxis in Caenorhabditis elegans (16). In the present study, we examined the role of N signaling in learning and memory in Drosophila.A Pavlovian procedure that pairs odors with foot-shock (17) was used in this study to assess the effects of N signaling on adult behavioral plasticity. Genetic analyses have demonstrated that memory formation afte...