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Cobalt hydroxide Co(OH)2 is considered to be a potential material for electrocatalyst, especially for oxygen evolution reaction (OER), owing to the earth's abundance, environmentally benign nature, and redox-active properties of cobalt. Herein, we report the fabrication of pristine Co(OH)2 and AgNP-integrated Co(OH)2 (Ag–Co(OH)2) by simple wet chemical methods and explore the electrocatalytic OER activity in the alkaline medium. High-resolution transmission electro-microscopic (HR-TEM) analysis revealed featureless nanostructures for Co(OH)2 with coexisting amorphous and crystalline phases, as well as the inclusion of crystalline AgNPs in Ag–Co(OH)2. X-ray photoelectron spectroscopic (XPS) analysis confirmed the inclusion of metallic AgNPs and the presence of Co at a mixed oxidation state. Electrocatalytic OER studies indicated that pristine Co(OH)2 required the overpotential of 299 mV to achieve a geometric current density of 10 mA cm−2. The integration of AgNPs in Co(OH)2 (Ag–Co(OH)2) showed a gradual improvement in the OER activity. The optimized sample, Ag–Co(OH)2-5, required the overpotential of 253 mV to produce 10 mA cm−2 current density. Tafel slope analysis revealed a lower value upon AgNP integration and electrochemical impedance showed lower charge transfer resistance. The lower Tafel value and charge transfer resistance of Ag–Co(OH)2-5 indicated good chemical coupling and faster reaction kinetics at the electrode surface. AgNPs incorporation with Co(OH)2 also showed enhanced turn-over frequency, electrochemical active surface area, and double-layer capacitance. The fabricated hybrid Ag–Co(OH)2-5 catalyst also exhibited good stability over 60 h. Thus, the electrocatalytic activity of low-cost Co(OH)2 was improved by fabricating coexisting amorphous and crystalline phases and integrating noble silver nanoparticles. [ABSTRACT FROM AUTHOR]

The coordination environment and networks of metal–organic frameworks (MOFs) play a significant role in their functional properties, especially catalysis. In recent years, the use of MOFs for electrocatalytic water-splitting reactions to produce green hydrogen fuel has gained increasing attention. Herein, we report the preparation of Co-benzene dicarboxylic acid-based MOFs (Co-MOF-1 and Co-MOF-2) with different coordination environments and correlated their structure-controlled electrocatalytic OER activity in an alkaline medium. Both Co-MOF-1 and Co-MOF-2 showed 3D network structures with different coordination environments around the Co metal centre. In Co-MOF-1, the Co metal centre is coordinated with DMF and pyridine along with a benzene dicarboxylic acid (BDC) ligand, whereas the Co metal centre is coordinated only with BDC ligands in Co-MOF-2. The Co metal centres in Co-MOF-1 contain labile solvent coordination but have completely saturated coordination with the BDC ligand alone in Co-MOF-2. Interestingly, Co-MOF-1 showed relatively strong OER activity and required the overpotential (η) of 294 mV to produce 10 mA cm−2 current density. However, Co-MOF-2 required the overpotential of 343 mV to achieve the 10 mA cm−2 current density. Further Co-MOF-1 showed comparatively low Tafel slope and charge transfer resistance and high electrochemical surface area than Co-MOF-2 and supported the enhanced OER activity. XPS analysis of Co-MOF-1 before and after catalysis suggested the conversion of Co-MOF-1 to CoOOH during the electrocatalysis that boosted the OER activity. The presence of a labile coordination site in Co-MOF-1 might have facilitated the interaction of hydroxyl electrolyte with the metal centre and active site generation by forming CoOOH easily which enhanced the OER activity. Co-MOF-1 also showed excellent stability for over 48 h. Hence, the present work provides structural insight for designing new MOFs for electrocatalytic water-splitting reactions. [ABSTRACT FROM AUTHOR]

The current study demonstrates a facile one-pot pyrolysis route to develop photoluminescent graphitic carbon nitride nanosheets (g-C3N4) for the fluorescence detection of hydrazine. The morphological images show that MnO2 nanotubes are decorated over the surface of g-C3N4 nanosheets, and the addition of hydrazine completely topples the MnO2 nanotubes; this uncovers the g-C3N4 nanosheets. The turn-off fluorescence was achieved with the decoration of MnO2 nanostructures on the g-C3N4-nanosheets via the fluorescence resonance energy transfer mechanism. Morphological influences of MnO2 nanostructures on the dynamic quenching of the fluorescence behavior of g-C3N4 nanosheets were analyzed. The fluorescence energy transfer between g-C3N4 and MnO2 was restricted with the addition of hydrazine; this led to the recovery of the fluorescence behavior of g-C3N4. The proposed sensor exhibits high sensitivity, the wide linear range of 2–55 μM, and the low detection limit of 0.12 μM. The developed nanocomposite exhibits excellent selectivity towards hydrazine over common metal ions and molecules with analogous structures. Furthermore, the prepared nanocomposite exhibits good recovery in environmental water samples; this unveils its practical competence in real samples. Conspicuously, this study provides an excellent platform for the development of a competent fluorescent probe and dynamic opportunities for the effectual monitoring of hydrazine in environmental water samples. [ABSTRACT FROM AUTHOR]

Biochar (BC), prepared from the carbonization of neem wood, was modified with nickel ferrite (NiFe2O4) nanorod/poly(3,4-ethylenedioxythiophene) (PEDOT) composite and directly employed as a free-standing and binder-free anode in microbial fuel cells (MFCs). The morphological and X-ray diffraction analyses demonstrate that the cubic spinel-structured NiFe2O4 nanorods are homogeneously distributed over the sheet-like amorphous PEDOT. The bioelectrochemical activity of exoelectrogens is improved with PEDOT/NiFe2O4/BC as endorsed by the superior oxidation current in the voltammograms. Furthermore, the MFC with PEDOT/NiFe2O4/BC demonstrates a peak power of 1200 mW m−2 because of the unique catalytic nanoarchitectures, compact biofilm formation, continuous electron conduction paths, and elevated structural and chemical stabilities of PEDOT/NiFe2O4. The waste matter-derived electrode constituent, binder-free electrode modification, mediator-less electron transference, and considerable power generation associated with a proficient lifespan performance of PEDOT/NiFe2O4 open up a versatile avenue towards the development of cost-efficient, high-performance, and durable MFCs. [ABSTRACT FROM AUTHOR]