Nitrogen-doped carbon dots: Recent developments in its fluorescent sensor applications.

Doped carbon dots have attracted great attention from researchers across disciplines because of their unique characteristics, such as their low toxicity, physiochemical stability, photostability, and outstanding biocompatibility. Nitrogen is one of the most commonly used elements for doping because of its sizeable atomic radius, strong electronegativity, abundance, and availability of electrons. This distinguishes them from other atoms and allows them to perform distinctive roles in various applications. Here, we have reviewed the most current breakthroughs in nitrogen-doped CDs (N-CDs) for fluorescent sensor applications in the last five years. The first section of the article addresses several synthetic and sustainable ways of making N-CDs. Next, we briefly reviewed the fluorescent features of N-CDs and their sensing mechanism. Furthermore, we have thoroughly reviewed their fluorescent sensor applications as sensors for cations, anions, small molecules, enzymes, antibiotics, pathogens, explosives, and pesticides. Finally, we have discussed the N-CDs' potential future as primary research and how that may be used. We hope that this study will contribute to a better understanding of the principles of N-CDs and the sensory applications that they can serve.

3D CoMoO4 nanoflake arrays decorated disposable pencil graphite electrode for selective and sensitive enzyme-less electrochemical glucose sensors.

Three-dimensional (3D) cobalt molybdate (CoMoO4) hierarchical nanoflake arrays on pencil graphite electrode (PGE) (CoMoO4/PGE) are actualized via one-pot hydrothermal technique. The morphological features comprehend that the CoMoO4 nanoflake arrays expose the 3D, open, porous, and interconnected network architectures on PGE. The formation and growth mechanisms of CoMoO4 nanostructures on PGE are supported with different structural and morphological characterizations. The constructed CoMoO4/PGE is operated as an electrocatalytic probe in enzyme-less electrochemical glucose sensor (ELEGS), confronting the impairments of cost- and time-obsessed conventional electrode polishing and catalyst amendment progressions and obliged the employment of a non-conducting binder. The wide-opened interior and exterior architectures of CoMoO4 nanoflake arrays escalate the glucose utilization efficacy, whilst the intertwined nanoflakes and graphitic carbon layers, respectively, of CoMoO4 and PGE articulate the continual electron mobility and catalytically active channels of CoMoO4/PGE. It jointly escalates the ELEGS concerts of CoMoO4/PGE including high sensitivity (1613 µA mM-1 cm-2), wide linear glucose range (0.0003-10 mM), and low detection limit (0.12 µM) at a working potential of 0.65 V (vs. Ag/AgCl) together with the good recovery in human serum. Thus, the fabricated CoMoO4/PGE extends exclusive virtues of modest electrode production, virtuous affinity, swift response, and excellent sensitivity and selectivity, exposing innovative prospects to reconnoitring the economically viable ELEGSs with binder-free, affordable cost, and expansible 3D electrocatalytic probes.

Exploring the Bioactive Potentials of C60-AgNPs Nano-Composites against Malignancies and Microbial Infections.

At present, the potential role of the AgNPs/endo-fullerene molecule metal nano-composite has been evaluated over the biosystems in-vitro. The intra-atomic configuration of the fullerene molecule (C60) has been studied in-vitro for the anti-proliferative activity of human breast adenocarcinoma (MDA-MB-231) cell lines and antimicrobial activity against a few human pathogens that have been augmented with the pristine surface plasmonic electrons and antibiotic activity of AgNPs. Furthermore, FTIR revealed the basic vibrational signatures at ~3300 cm-1, 1023 cm-1, 1400 cm-1 for O-H, C-O, and C-H groups, respectively, for the carbon and oxygen atoms of the C60 molecule. NMR studies exhibited the different footprints and magnetic moments at ~7.285 ppm, explaining the unique underlying electrochemical attributes of the fullerene molecule. Such unique electronic and physico-chemical properties of the caged carbon structure raise hope for applications into the drug delivery domain. The in-vitro dose-dependent application of C60 elicits a toxic response against both the breast adenocarcinoma cell lines and pathogenic microbes. That enables the use of AgNPs decorated C60 endo fullerene molecules to design an effective anti-cancerous drug delivery and antimicrobial agent in the future, bringing a revolutionary change in the perspective of a treatment regime.

NiMoO4 nanorods photocatalytic activity comparison under UV and visible light.

Waste water remediation is the ongoing hot research topic that can reduce the water scarcity all over the world. By reducing the pollutants in the waste water drawn from industries and other sources will be more useful for domestic purposes. To reduce the rate of pollutants in water may also help in improving the aquatic environment and decreases other side effects. Efficient and cost effective catalysts were in search for both dye degradation and water remediation treatment applications. NiMoO4 nanorods were prepared by employing co-precipitation method with different stirrer time (2 h, 4 h and 6 h). The formation of NiMoO4 was substantiated employing X-ray diffractometer analysis (XRD). Vibrational and rotational property of the samples was analyzed by FT-IR spectra and Raman spectra. The optical property was further confirmed by UV-vis spectral studies. Morphological analysis studies revealed growth of nanorods with 6 h stirrer time. The photocatalytic behavior of the obtained product was carried out under both UV light (364 nm) and visible light irradiation. The samples subjected to visible light environment showed better efficiency on degrading the methylene blue (MB) dye. The efficiency obtained under UV irradiation were 20%, 31%, 33%, 41% and efficiency obtained in visible light irradiation were 27%, 42%, 46%, 55% with respect to bare methylene blue (MB), MB with NiMoO4 (2 h), MB with NiMoO4 (4 h), MB with NiMoO4 (6 h) catalyst added. NiMoO4 sample with 6 h stirrer time and fine nanorods growth will be the good candidate for future use.

Investigation on (Zn) doping and anionic surfactant (SDS) effect on SnO2 nanostructures for enhanced photocatalytic RhB dye degradation.

Herein we reported the effect of doping and addition of surfactant on SnO2 nanostructures for enhanced photocatalytic activity. Pristine SnO2, Zn-SnO2 and SDS-(Zn-SnO2) was prepared via simple co-precipitation method and the product was annealed at 600 °C to obtain a clear phase. The structural, optical, vibrational, morphological characteristics of the synthesized SnO2, Zn-SnO2 and SDS-(Zn-SnO2) product were investigated. SnO2, Zn-SnO2 and SDS-(Zn-SnO2) possess crystallite size of 20 nm, 19 nm and 18 nm correspondingly with tetragonal structure and high purity. The metal oxygen vibrations were present in FT-IR spectra. The obtained bandgap energies of SnO2, Zn-SnO2 and SDS-(Zn-SnO2) were 3.58 eV, 3.51 eV and 2.81 eV due to the effect of dopant and surfactant. This narrowing of bandgap helped in the photocatalytic activity. The morphology of the pristine sample showed poor growth of nanostructures with high level of agglomeration which was effectively reduced for other two samples. Product photocatalytic action was tested beneath visible light of 300 W. SDS-(Zn-SnO2) nanostructure efficiency showed 90% degradation of RhB dye which is 2.5 times higher than pristine sample. Narrow bandgap, crystallite size, better growth of nanostructures paved the way for SDS-(Zn-SnO2) to degrade the toxic pollutant. The superior performance and individuality of SDS-(Zn-SnO2) will makes it a potential competitor on reducing toxic pollutants from wastewater in future research.

Wet chemical development of CuO/GO nanocomposites: its augmented antimicrobial, antioxidant, and anticancerous activity.

This study employed a bottom-up technique to synthesize copper oxide (CuO) nanoparticles over hydrophilic graphene oxide (GO) nanosheets. The CuO/GO nanocomposite has been prepared using two selected precursors of copper nitrate and citric acid with an intermittent mixing of GO solutions. The synthesized Nanocomposites were characterized using different biophysical techniques like FT-IR, NMR, FE-SEM, and HR-TEM analyses. FT-IR analyses confirm the nanocomposites' successful formation, which is evident from the functional groups of C=C, C-O, and Cu-C stretching vibrations. Morphological analyses reveal the depositions of CuO nanoparticles over the planar rough GO sheets, which has been elucidated from the FE-SEM and HR-TEM analyses supported by respective EDAX analyses. The antimicrobial activities have been evident from the surface roughness and damages seen from the FE-SEM analyses. The CuO/GO sheets were tested against Gram-positive (e.g., Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa). It is evident that the intrinsic antibacterial activity of CuO/GO sheets, when combined in equal proportions, elicited a robust antibacterial activity when tested over Gram -ve representative bacteria Escherichia coli. The antioxidant behaviour of synthesized CuO/GO nanocomposite was evaluated by scavenging the free radicals of DPPH and ABTS. Moreover, the cytotoxic activity was also studied against epidermoid carcinoma cell line A-431. A brief mathematical formulation has been proposed in this study to uncover the possibilities of using the nanocomposites as potential drug candidates in theranostic applications in disease treatment and diagnosis. This study would help uncover the electronic properties that play in the nano-scaled system at the material-bio interface, which would aid in designing a sensitive nano-electromechanical device bearing both the therapeutic and diagnostic attributes heralding a new horizon in the health care systems.

Waste paper derived three-dimensional carbon aerogel integrated with ceria/nitrogen-doped reduced graphene oxide as freestanding anode for high performance and durable microbial fuel cells.

Despite the green energy generation with low cost compared to conventional fuel cells, microbial fuel cells (MFCs) still suffer with anode related constraints including laborious pretreatment and modification process of conventional electrodes, limited bacterial loading capacity, and inferior extracellular electron transfer efficiency. Accordingly, this investigation explores the waste tissue paper derived three dimensional (3D) carbon aerogel (CA) integrated with cerium dioxide (CeO2) nanotubes decorated nitrogen-doped reduced graphene oxide nanosheets (NRGO) as a competent anode to address these technical complements. The direct growth of NRGO and CeO2 over CA in the form of freestanding and binder-free NRGO/CeO2(1:2)/CA alleviates the significant constrains of conventional anode fabrication. The 3D hierarchical architectures of CA with open porous structure provide easy access of bacteria, thus increases the bacterial colonies per unit volume. Furthermore, the hydrogen bonding between the interfacial oxygen atoms of CeO2 and lysine residues of the cytochrome c in bacteria yields excellent extracellular electron transfer efficiency. The electrostatic interaction between the NRGO and bacteria cells improves the bacterial adhesion and biofilm formation, leading to the compact biofilm formation for the improved direct electron transference. With the profits of above, the MFC with NRGO/CeO2(1:2)/CA demonstrates a maximum power output and good lifespan performances. The present exploration facts thus access advanced avenues to converting waste matters of tissue paper, human urine, and wastewater into profitable constituents for the development of efficient and durable power producing systems.

Photophysics of Dihydroquinazolinone Derivatives: Experimental and Theoretical Studies.

Herein, we report the synthesis of two dihydroquinazolinone derivative 2-(2-Hydroxy-naphthalen-1-yl)-2, 3-dihydro-1H-quinazolin-4-one (1) and 2-(3-Methyl-thiophen-2-yl)-2,3-dihydro-1H-quinazolin-4-one (2) by using 2-aminobenzamide, 2-hydroxybenzaldehyde and 3-methyl thiophene-2-carboxaldehyde. The synthesized compounds were characterized by 1H NMR, 13C NMR, FT-IR and its spectral, photophysical, intramolecular charge transfer characteristics were studied by absorption and emission spectroscopy. The synthesized compound exhibits significant changes in their photophysical properties depending on the solvent polarity. The observed bathochromic emission band and difference in Stokes shift on changing the polarity of the solvents clearly demonstrate the highly polar character of the excited state. The synthesized compounds were also studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT) to expose the reproducibility by computational means.

A Combined Experimental and Computational Investigation on Spectroscopic and Photophysical Properties of a Coumarinyl Chalcone.

Here, we synthesized a new coumarinyl chalcone derivative 3-[3-(3-Methyl-thiophen-2-yl)-acryloyl]-chromen-2-one (MTC) by simple and proficient method. A comprehensive study on the photophysics of a coumarinyl chalcone derivative having pi-conjugated potential chromophore system 3-[3-(3-Methyl-thiophen-2-yl)-acryloyl]-chromen-2-one (MTC) has been carried out spectroscopically. The electronic absorption and emission characteristic of MTC were studied in different protic and aprotic solvents using absorption and steady-state fluorescence techniques. The spectral behavior of this compound is found to be extremely sensitive to the polarity and hydrogen bonding nature of the solvent. The compound shows very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of the compound has been investigated in detail. The difference between the excited and ground state dipole moments (Δµ) were estimated from solvatochromic methods using Lippert-Mataga and Reichardt's correlations. The prepared compound was also studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results revealed that it could be easily reproduce by computational means.

Structural and photophysical properties of (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) in different media.

The spectral and photophysical properties of a new chalcone derivative (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) containing donor-acceptor group has been synthesized and characterized on the basis of the spectral (IR, (1)HNMR & (13)C NMR) and X- ray crystallographic data. The effect of solvents on photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of DPNP have been investigated comprehensively. Significant red shift was observed in the emission spectrum of DPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state. The difference between the excited and ground state dipole moments (Δµ) were obtained from Lippert-Mataga and Reichardts correlations by means of solvatochromic shift method. The effects of medium acidity on the electronic absorption and emission spectra of DPNP were studied. The interaction of DPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of DPNP by Ag NPs.

Spectroscopic investigation, effect of solvent polarity and fluorescence quenching of a new D-π-A type chalcone derivative.

A new chalcone derivative 3-(1-methyl-1H-pyrrol-2-yl)-1-naphthalen-2-yl propenone (MPNP) with electron donor-acceptor group has been synthesized and characterized by IR, (1)HNMR, (13)C NMR and X- ray crystallography. Electronic absorption and emission spectra of MPNP have been studied in solvents of different polarity. A remarkable red shift was observed in the emission spectrum of MPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state and the transition involved are π-π* with charge transfer character. Lippert-Mataga and Reichardts correlations were used to estimate the change in dipole moments (Δµ); suggest that the emissive state of MPNP is of strong ICT character. Fluorescence quantum yield (ϕf) of MPNP was correlated with empirical solvent polarity parameter ET(30), and it is observed that ϕf increases with increase in solvent polarity of polar aprotic solvents and decrease in alcoholic solvents. The interaction of MPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state emission measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of MPNP by Ag NPs.

Thermally stable strongly fluorescent multi-stimuli responsive carbazole zwitterionic fluorophores: Alkyl chain length dependent thermofluorochromism and latent fingerprinting.

Carbazole-picoline based π-conjugated zwitterionic fluorophores, (E)-3-(4-(4-(9H-carbazol-9-yl)styryl)pyridin-1-ium-1-yl)propane-1-sulfonate (Cz-PS) and (E)-4-(4-(4-(9H-carbazol-9-yl)styryl)pyridin-1-ium-1-yl)butane-1-sulfonate (Cz-BS) were synthesized and investigated the stimuli-responsive solid-state fluorescence properties. Cz-PS and Cz-BS displayed enhanced fluorescence in the solid-state (555 and 542 nm) with the quantum yield (Φf) of 32.9 and 28.5 %, respectively. Thermogravimetric analysis (TGA) indicated good thermal stability up to 300 °C for both Cz-PS and Cz-BS. Single crystal structural analysis of Cz-BS confirmed twisted molecular conformation and supramolecular interactions induced network structure, which lead to increase of solid-state fluorescence. Cz-BS showed mechanical stimuli-induced reversible/self-reversible fluorescence switching between two fluorescence states whereas Cz-PS did not show mechanofluorochromism. But both Cz-PS and Cz-BS showed acid/base dependent on-off reversible fluorescence switching in solution as well as solid-state. Further, both compounds also displayed reversible thermofluorochromism by heating and cooling. The yellow fluorescence of Cz-PS and Cz-BS was transformed to orange upon heating at 110 °C and cooling reversed the fluorescence to initial state. The good thermal stability and enhanced solid-state fluorescence of Cz-PS and Cz-BS were utilized for latent fingerprinting (LFP) application on various solid substrate. Particularly, LFP images of Cz-BS showed finger marks with well-defined features. Thus, integrating zwitterionic functionality produced strong solid-state fluorescence with multi-functional applications.

Propeller shaped triarylamine acid: An ultra-sensitive fluorescence probe for distinguishing propanol isomers and water sensing in organic solvents.

The photophysical properties of conformationally flexible (TPA-C) and partially rigidified (Cz-C) triarylamine acids were explored in solid as well as solution state and correlated with the structure. TPA-C and Cz-C exhibited moderate solid-state fluorescence (Φf = 6.2 % (TPA-C) and 5.6 % (Cz-C)) and self-reversible mechanofluorochromism. TPA-C produced fluorescent polymorphs (TPA-C-1 and TPA-C-2) with tunable fluorescence. TPA-C-1 showed unusual carboxylic acid intermolecular interactions whereas TPA-C-2 and Cz-C showed usual carboxylic acid dimer. TPA-C exhibited strong solvent polarity dependent tunable fluorescence (Φf = 0.01 to 0.11 compared to quinine sulphate standard) but Cz-C was non-emissive in the solution state. The dual emissive TPA-C showed highly sensitive fluorescence changes in organic solvents (CH3CN, THF, DMF, EtOH) when trace amount of water was added. In CH3CN, TPA-C showed weak fluorescence at 474 nm and addition of water (1 %) exhibited significant blue shift (λmax = 416 nm). The fluorescence intensity was gradually decreased with blue shifting in DMF, THF and EtOH with water addition. Importantly, TPA-C showed drastically different fluorescence in n-propanol (n-PA) and iso-propanol (IPA). TPA-C in n-PA showed fluorescence at 408 nm that was clearly red shifted to 438 nm with 0.1 % addition of IPA. The limit of detection (LOD) of water in CH3CN, DMF, THF and EtOH by TPA-C revealed 0.02, 0.7, 0.08 and 0.77 %, respectively. The LOD of IPA sensing in n-PA is 0.05 % and indicated the very efficient sensing and distinguishing propanol isomers. Thus, simple triphenylamine acid showed excellent water sensing and propanol isomers discrimination that could be attributed to the twisted intramolecular charge transfer (TICT) formation.

Deep blue emitting dual state fluorescent triphenylamine-dicyclohexylurea derivative: Multi-stimuli responsive fluorescence switching and methanol/water sensing.

A new deep blue emissive organic fluorophore (N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(diphenylamino)benzamide (NCDPB)) was designed and synthesized, which showed strong fluorescence both in solution and solid-state. Solid-state structural analysis of NCDPB revealed non-planar twisted molecular conformation with extended hydrogen bonding between the amide functionalities. The propeller shaped triphenylamine (TPA) and non-planar cyclohexyl unit prevented close π…π stacking and produced strong deep blue emission in the solid state (λmax = 400 nm, quantum yield (Φf) = 12.6 %). NCDPB also exhibited strong solvent polarity dependent tunable emission in solution (λmax = 402-462 nm, Φf = 1.15 (compared to quinine sulphate)). NCDPB showed reversible fluorescence switching between two fluorescence states upon mechanical crushing and heating/solvent exposure. Mechanical crushing caused red shifting of fluorescence from 400 to 447 nm and heating/solvent exposure reversed the fluorescence. Further, NCDPB also displayed off-on reversible/self-reversible fluorescence switching upon exposure to trifluoracetic acid (TFA) and NH3. The repeated fluorescence switching cycles indicated high reversibility without any significant change of fluorescence intensity. The drastically different fluorescence of NCDPB in CH3OH and EtOH was utilized to distinguish them and monitor CH3OH contamination in ethanol and benzene. It showed limit of detection (LOD) of methanol up to 0.25 % and 7 % in benzene and ethanol, respectively. The water sensitive fluorescence modulation of NCDPB in organic solvents was used to sensing water contamination in common organic solvents. Thus, integration of twisted TPA with H-bonding urea produced dual state emitting organic fluorophore with multi-responsive fluorescence switching and solvent sensing.

Water sensitive fluorescence tuning of V-shaped ESIPT fluorophores: Substituent effect and trace amount water sensing in DMSO.

Highly sensitive nature of excited state intramolecular proton transfer (ESIPT) functionality in organic fluorophores made them potential candidates for developing environmental sensors and bioimaging applications. Herein, we report the synthesis of V-shaped Dapsone based Schiff base ESIPT derivatives (1-3) and water sensitive wide fluorescence tuning from blue to red in DMSO. Solid-state structural analysis confirmed the V-shaped molecular structure with intramolecular H-bonding and substituent dependent molecular packing in the crystal lattice. 1 showed strong solid-state fluorescence (λmax = 554 nm, Φf = 21.2 %) whereas methoxy substitution (2 and 3) produced tunable but significantly reduced fluorescence (λmax = 547 (2) and 615 nm (3), Φf = 2.1 (2) and 6.5 % (3)). Interestingly, aggregation induced emission (AIE) studies in DMSO-water mixture revealed water sensitive fluorescence tuning. The trace amount of water (less than 1 %) in DMSO converted the non-emissive 1-3 into highly emissive state due to keto tautomer formation. Further increasing water percentage produced deprotonated state of 1-3 in DMSO and enhanced the fluorescence intensity with red shifting of emission peak. At higher water fraction, 1-3 in DMSO produced aggregates and red shifted the emission with reduction of fluorescence intensity. The concentration dependent fluorescence study revealed the very low detection limit of water in DMSO. The limit of detection (LOD) of 1, 2 and 3 were 0.14, 1.04 and 0.65 % of water in DMSO. Hence, simple Schiff bases of 1-3 showed water concentration dependent keto isomer, deprotonated and aggregated state tunable fluorescence in DMSO. Further, scanning electron microscopic (SEM) studies of 1-3 showed water concentration controlled self-assembly and tunable fluorescence.

Enhancing the oxygen evolution reaction of cobalt hydroxide by fabricating nanocomposites with fluorine-doped graphene oxide.

Fluorine and nitrogen codoped cobalt hydroxide-graphene oxide nanocomposites (N,F-Co(OH)2/GO) were synthesized by a simple hydrothermal method and demonstrated highly enhanced oxygen evolution activity in an alkaline medium. N,F-Co(OH)2/GO synthesized under optimized reaction conditions required an overpotential of 228 mV to produce the benchmark current density of 10 mA cm-2 (scan rate 1 mV s-1). In contrast, N,F-Co(OH)2 without GO and Co(OH)2/GO without fluorine required higher overpotentials (370 (N,F-Co(OH)2) and 325 mV (Co(OH)2/GO)) for producing the current density of 10 mA cm-2. The low Tafel slope (52.6 mV dec-1) and charge transfer resistance, and high electrochemical double layer capacitance of N,F-Co(OH)2/GO compared to N,F-Co(OH)2 indicate faster kinetics at the electrode-catalyst interface. The N,F-Co(OH)2/GO catalyst showed good stability over 30 h. High-resolution transmission electron microscope (HR-TEM) images showed good dispersion of polycrystalline Co(OH)2 nanoparticles in the GO matrix. X-ray photoelectron spectroscopic (XPS) analysis revealed the coexistence of Co2+/Co3+ and the doping of nitrogen and fluorine in N,F-Co(OH)2/GO. XPS further revealed the presence of F in its ionic state and being covalently attached to GO. The integration of highly electronegative F with GO stabilizes the Co2+ active centre along with improving the charge transfer and adsorption process that contributes to improved OER. Thus, the present work reports a facile method for preparing F-doped GO-Co(OH)2 electrocatalysts with enhanced OER activity under alkaline conditions.

Highly enhanced electrocatalytic OER activity of water-coordinated copper complexes: effect of lattice water and bridging ligand.

The use of metal-organic compounds as electrocatalysts for water splitting reactions has gained increased attention; however, a fundamental understanding of the structural requirement for effective catalytic activity is still limited. Herein, we synthesized water-coordinated mono and bimetallic copper complexes (CuPz-H2O·H2O, CuPz-H2O, CuBipy-H2O·H2O, and CuMorph-H2O) with varied intermetallic spacing (pyrazine/4,4'-bipyridine) and explored the structure-dependent oxygen evolution reaction (OER) activity in alkaline medium. Single crystal structural studies revealed water-coordinated monometallic complexes (CuMorph-H2O) and bimetallic complexes (CuPz-H2O·H2O, CuPz-H2O, CuBipy-H2O·H2O). Further, CuPz-H2O·H2O and CuBipy-H2O·H2O contained lattice water along with coordinated water. Interestingly, the bimetallic copper complex with lattice water and shorter interspacing between the metal centres (CuPz-H2O·H2O) showed strong OER activity and required an overpotential of 228 mV to produce a benchmark current density of 10 mA cm-2. Bimetallic copper complex (CuPz-H2O) without lattice water but the same intermetallic spacing and bimetallic complex with increased interspacing but with lattice water (CuBipy-H2O·H2O) exhibited relatively lower OER activity. CuPz-H2O and CuBipy-H2O·H2O required an overpotential of 236 and 256 mA cm-2, respectively. Monometallic CuMorph-H2O showed the lowest OER activity (overpotential 271 mV) compared to bimetallic complexes. The low Tafel slope and charge transfer resistance of CuPz-H2O·H2O facilitated faster charge transfer kinetics at the electrode surface and supported the enhanced OER activity. The chronoamperometric studies indicated good stability of the catalyst. Overall, the present structure-electrocatalytic activity studies of copper complexes might provide structural insight for designing new efficient electrocatalysts based on metal coordination compounds.

F and rare V4+ doped cobalt hydroxide hybrid nanostructures: excellent OER activity with ultralow overpotential.

Highly efficient and stable Earth abundant transition metal electrocatalysts are in great demand for the oxygen evolution reaction (OER), a bottleneck process involved in the water splitting reaction and metal-air batteries. Herein, we have demonstrated a single step direct fabrication of cobalt hydroxide (Co(OH)2) nanowires doped with vanadium(V) in a less stable +4 oxidation state and fluoride (F) ions (V-Co(OH)2) on a carbon cloth electrode that showed highly enhanced OER activity under alkaline conditions. V-Co(OH)2 nanowires synthesized under the optimized conditions produced excellent OER activity with an ultralow overpotential of 136 mV at 10 mA cm-2 (scan rate 1 mV s-1), a small Tafel slope (51.6 mV dec-1) and good stability over 72 h. To the best of our knowledge, this is the lowest overpotential reported for cobalt-based electrocatalysts to achieve a geometric current density of 10 mA cm-2. The controlled synthesis and HR-TEM studies revealed the formation of hybrid nanostructures (nanowires along with spherical assembly of nanoparticles) and codoping of V and F ions played an important role in enhancing the OER activity. The detailed chemical composition and oxidation state analysis by X-ray photoelectron spectroscopy (XPS) confirmed the doping of V4+ and ionic F in V-Co(OH)2 with mixed valence states of Co2+/Co3+ and a higher Co2+ ratio. The outstanding OER activity of V-Co(OH)2 is attributed to the formation of a spherical assembly of nanoparticles with nanowires, which provided a high number of catalytically active sites with enhanced charge transport, and doping of higher valence V4+ and strongly electronegative F in V-Co(OH)2 with a higher ratio of Co2+/Co3+ promoted OOH* intermediate generation and significantly boosted the OER activity. Overall, the present work highlights the possibility of achieving highly active Earth abundant OER electrocatalysts by controlling the mixed oxidation state of Co with a judicious choice of dopants along with maintaining optimal nanostructure morphologies.

A water coordinated Ni complex and a 2D Ni-MOF: topology dependent highly enhanced electrocatalytic OER activity.

Metal-organic frameworks (MOFs) with their tunable topology, functionality and coordination environment have been considered as potential materials for various applications including electrocatalysis. Herein, we have synthesised a water coordinated nickel based 2D metal-organic framework (Ni-MOF) and a coordination complex (Ni-C) and investigated their electrocatalytic OER activity. The Ni-MOF showed a 2D sheet structure with one water coordination whereas a four water molecule coordinated charged complex was formed in the Ni-C. Thermogravimetric analysis (TGA) confirmed their water coordination and good thermal stability. Interestingly, electrocatalytic OER studies showed strongly enhanced activity for the Ni-MOF and that it required a low overpotential (194 mV) to produce a geometric current density of 10 mA cm-2. The Ni-C required 225 mV to produce 10 mA cm-2. The post-catalytic analysis suggested that the Ni-MOF and Ni-C are converted to nickel hydroxides/oxyhydroxides during electrocatalysis and acted as the catalytic centre. The low Tafel slope and charge transfer resistance further supported the higher activity of Ni-MOF based nickel hydroxides/oxyhydroxides. Chronoamperometric studies revealed the excellent stability of the Ni-MOF based catalyst over 72 h. The present study revealed the potential of developing highly active electrocatalysts based on Ni-MOFs by optimizing the topology and coordination environment.

Advancements in COVID-19 Testing: An In-depth Overview.

COVID-19 rapidly evolved as a pandemic, killing and hospitalising millions of people, and creating unprecedented hurdles for communities and health care systems worldwide. The rapidly evolving pandemic prompted the head of the World Health Organisation to deliver a critical message: "test, test, test." The response from the diagnostic industry and researchers worldwide was overwhelming, resulting in more than a thousand commercial tests being available worldwide. Several sampling approaches and diagnostic techniques have been employed from the early stages of the pandemic, such as SARS-CoV-2 detection by targeting the viral RNA or protein indirectly via antibody testing, biochemical estimation, and various imaging techniques, and many are still in the various stages of development and yet to be marketed. Accurate testing techniques and appropriate sampling are the need of the hour to manage, diagnose and treat the pandemic, especially in the current crisis where SARS-CoV-2 undergoes constant mutation, evolving into various strains, which are pretty challenging. The article discusses various testing techniques as well as screening methods for detection, treatment, and management of COVID-19 transmissions, such as NAAT, PCR, isothermal detection including RT-LAMP, RPA, NASBA, RCA, SDA, NEAR, and TMA, CRISPR strategy, nanotechnology approach, metagenomic profiling, point of care tests, virus neutralization test, ELISA, biomarker estimation, utilization of imaging techniques such as CT, ultrasonography, brain MRI in COVID-19 complications, and other novel strategies including microarray methods, microfluidic methods and artificial intelligence with an emphasis on advancements in the testing strategies for the diagnosis, management, and prevention of COVID-19.