Facile Synthesis of Nonprecious Bimetallic Zeolitic Imidazolate Framework-Based Hierarchical Nanocomposites as Efficient Electrocatalysts for Oxygen Reduction Reaction

Conversion of designer metal–organic frameworks (MOFs) into hybrid nanocomposites (HNCs) consisting of transition metal/metal oxides interfaced with carbon (C) matrices has emerged as a promising and economical alternative for the synthesis of oxygen reduction reaction (ORR) electrocatalysts, owing to their superior conductivity and high porosity. To that end, optimizing the performance of this class of material by tailoring its composition, structure, size, and morphology through an efficient synthesis route has become an active area of research. Specifically, this study employs Laser Ablation Synthesis in Solution in tandem with Galvanic Replacement Reaction (LASiS-GRR) technique as an environmentally friendly, facile, and rapid route for the design and synthesis of core–shell bimetallic zeolitic imidazolate framework (ZIF) heterostructures as bi-MOFs, and then uses pyrolytic postprocessing to yield hierarchical metal oxide/MOF-based functional HNCs as highly active ORR electrocatalysts. The LASiS-GRR technique employs high-energy laser plasma reactions as the rate-controlling step for initiating solution-phase galvanic reactions. The one-pot, two-step process introduced in this study enables tailoring of the composition, structure, size, and morphology of composite bi-MOFs comprising Co-based MOFs encapsulated in Zn-based porous crystals (Co/ZIF-67@Zn/ZIF-8). Pyrolytic postprocessing of these core–shell bi-MOF crystals leads to the creation of hierarchical ZnO@ZIF/C HNCs with superior ORR electrocatalytic performances under alkaline conditions. Overall, these findings not only elucidate the process by which LASiS-GRR protocols are optimized to tailor the morphology, structure, and composition of complex MOF structures but also demonstrate the superior performance and stability of the ensuing postpyrolyzed ZnO@ZIF/C HNCs as nonprecious metal-based ORR electrocatalysts, when compared to commonly used Pt- and Pt-group metal (PGM)-based electrocatalysts

Induction of systemic resistance and defense-related enzymes in tomato plants using Pseudomonas fluorescens CHAO and salicylic acid against root-knot nematode Meloidogyne javanica

Root-knot nematodes (Meloidogyne spp.) are the most economically important group of plant parasitic nematodes on many crops worldwide. Resistance-based management is considered as one of the most sound and effective strategies against these pathogens. Plant-mediated systemic resistance against the M. javanica in tomato cv. CALJN3 was triggered using salicylic acid (SA) and Pseudomonas fluorescens CHAO as elicitors. The effect of each elicitor was assayed by (1) the calculation of nematode indices including the number of nematode galls, egg masses and eggs/egg mass; (2) the analysis of changes in the concentration of reactive oxygen species (ROS); and (3) monitoring the activities of their scavenging enzymes viz. superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT). The results indicated that SA/bacterial elicitors induced the removal of high concentrations of the toxic ROS via an increase in the activity of their scavenging antioxidant enzymes, especially that of catalase. Moreover, pre- or post-treatment application of the elicitors significantly reduced the number of galls, egg masses or eggs of M. javanica in infected tomato plants as compared to the control. The results of the present study support the involvement of the elicitor-induced ROS and related scavenging enzymes for stimulating plant defense reactions in a moderately resistant tomato challenged with M. javanica