Browsing by Author "Anjali Mishra"

Now showing 1 - 4 of 4

Axial ligand-induced high electrocatalytic hydrogen evolution activity of molecular cobaloximes in homo- and heterogeneous medium
(Royal Society of Chemistry, 2024) Jitendra Kumar Yadav; Baghendra Singh; Anjali Mishra; Sarvesh Kumar Pal; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Three new molecular cobaloxime complexes with the general formula [ClCo(dpgH)2L] (1-3), where L1 = N-(4-pyridylmethyl)-1,8-naphthalimide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalimide, L3 = 4-piperidin-N-(4-pyridylmethyl)-1,8-naphthalimide, have been synthesized and characterized by UV-Vis, multinuclear NMR, FT-IR and PXRD spectroscopic techniques. The crystal structures of all complexes have also been reported. The electrocatalytic activity of complexes is investigated under two catalysis conditions: (i) homogeneous conditions in acetonitrile using acetic acid (AcOH) as a proton source and (ii) heterogeneous conditions upon immobilization onto the surface of activated carbon cloth (CC). Complex 3 exhibited high electrocatalytic HER activity under both homogeneous and heterogeneous conditions. It catalyses proton reduction to molecular hydrogen in acetonitrile solution at a lower overpotential (640 mV) with a high turnover frequency (TOF) of 524.57 s−1 and demonstrates good stability in acidic conditions. Furthermore, catalytic (working) electrodes are prepared by immobilizing the complexes onto the surface of activated carbon cloth (CC) for electrocatalytic HER under heterogeneous conditions. An impressive HER performance was again obtained with catalytic electrode 3@CC in 1.0 M KOH, achieving a current density of −10 mA cm−2 at an overpotential of 262 mV. Chronoamperometric (CA) studies showed no significant decay of the initial current density for 10 h, indicating the excellent stability of 3@CC. Additionally, UV-Vis and NMR spectral studies of the recovered catalyst after electrocatalysis revealed no structural changes, demonstrating its robustness under reaction conditions. © 2024 The Royal Society of Chemistry.
Bioremediation Techniques of Microplastic Waste Management
(Springer Science+Business Media, 2025) Anjali Mishra; Rajak Preeti Phoolchandra; Shivam Yadav; Ekta Verma; Neelam Atri
Plastics’ unique physical and chemical properties have rendered them indispensable components of modern life and technology. Plastic waste does not easily break down in the environment, and the process of decomposition is slow. These plastics undergo fragmentation into microplastics (MPs) and nanoplastics (NPs). The slow degradation rate of MPs contributes to their pervasive contamination across various environmental ecosystems, including terrestrial and aquatic systems, posing detrimental effects on both ecosystems and human health. Among plastic pollutants, microplastics, which are plastic fragments smaller than 5 mm, have gained attention because of their potential harm to living organisms. This chapter explains different types of plastics, their properties, and factors that affect how they degrade. It discusses how organisms interact with microplastics and the harmful effects these particles have on living beings. To manage plastic waste, various disposal methods, such as incineration, landfilling, recycling, and transformation, have been globally implemented. However, due to their harmful effects, the utilization of bacterial, fungal, and microalgal strains for the elimination of environmental microplastics through eco-friendly bioremediation techniques has proven highly effective. Bioremediation and biodegradation are explicated herein. Additionally, new methods for biodegradation, like enzyme-based techniques, are being introduced. Certain types of fungi and bacteria, along with their enzymes, such as oxidoreductases and hydrolases, play a significant role in breaking down plastics. This chapter emphasizes diverse bioremediation techniques and their underlying mechanisms, as well as successful biotechnological strategies, including biostimulation, bioaugmentation, and enzymatic biodegradation, which are crucial for enhancing the efficacy of microplastics degradation in contaminated environments. The use of microbial communities and specially modified microorganisms with their enzymes are also effective ways to manage plastic pollution. © 2025 The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG.
Isonicotinate-Zn(ii)/Cd(ii) bridged dicobaloximes: synthesis, characterization and electrocatalytic proton reduction studies
(Royal Society of Chemistry, 2023) Jitendra Kumar Yadav; Anjali Mishra; Gaurav Kumar Mishra; Sarvesh Kumar Pal; Kedar Umakant Narvekar; Ahibur Rahaman; Nanhai Singh; Prem Lama; Kamlesh Kumar
Herein, we present the synthesis of two new dicobaloxime complexes, [{ClCo(dmgH)2(4-PyCOO)}2Zn(DMF)2] (1) and [{ClCo(dmgH)2(4-PyCOO)}2Cd(H2O)3(DMF)].4H2O (2) bridged by isonicotinate-Zn(ii) and Cd(ii) moieties. These complexes were synthesized upon reaction of a monomeric chlorocobaloxime [ClCo(dmgH)2(4-PyCOOH)] with Zn(NO3)2·6H2O and Cd(OAc)2·2H2O in a methanol/DMF solvent mixture. Both complexes are fully characterized by UV-Visible, FT-IR, and NMR (1H and 13C{1H}) spectral studies. The solid-state structures are also determined by single-crystal X-ray crystallography. In complex 1, Zn (ii) metal ions reside within a four coordinated distorted tetrahedral geometry (ZnO4) formed by two oxygen atoms of isonicotinate connected to cobaloxime units and two oxygen atoms of DMF molecules. In complex 2, the Cd(ii) metal ion exhibited distorted octahedral geometry (CdO6), with two oxygen atoms of isonicotinate that connect to cobaloxime units, one DMF, and three water molecules. The Co(iii) metal center of cobaloxime units in both complexes 1 and 2 displayed distorted octahedral geometry with two dmgH units in the equatorial plane whereas chloride ion (Cl−) and the nitrogen atom of isonicotinate occupy the axial coordination sites. The redox behaviour of both complexes was studied by cyclic voltammetry at variable scan rates in deoxygenated DMF/H2O (95 : 5) solution using 0.1 M TBAPF6 as the supporting electrolyte and a glassy carbon (GC) electrode as the working electrode. Both complexes exhibited similar redox properties and two redox couples CoIII/II and CoII/CoI are observed in the reductive scan. Furthermore, complexes are investigated as electrocatalysts for proton reduction in the presence of acetic acid (AcOH) and complex 1 exhibited impressive electrocatalytic activity compared to complex 2 and monomer. The stability study indicated the retention of molecular structural integrity during HER electrocatalytic experiments. © 2023 The Royal Society of Chemistry.
The rigidity and chelation effect of ligands on the hydrogen evolution reaction catalyzed by Ni(ii) complexes
(Royal Society of Chemistry, 2023) Anjali Mishra; Gaurav Kumar Mishra; None Anamika; Nanhai Singh; Rama Kant; Kamlesh Kumar
With increasing interest in nickel-based electrocatalysts, three heteroleptic Ni(ii) dithiolate complexes with the general formula [Ni(ii)L(L′)2] (1-3), L = 2-(methylene-1,1′-dithiolato)-5,5′-dimethylcyclohexane-1,3-dione and L′ = triphenylphosphine (1), 1,1′-bis(diphenylphosphino)ferrocene (DPPF) (2), and 1,2-bis(diphenylphosphino)ethane (DPPE) (3), have been synthesized and characterized by various spectroscopic techniques (UV-vis, IR, 1H, and 31P{1H} NMR) as well as the electrochemical method. The molecular structure of complex 2 has also been determined by single-crystal X-ray crystallography. The crystal structure of complex 2 reveals a distorted square planar geometry around the nickel metal ion with a NiP2S2 core. The cyclic voltammograms reveal a small difference in the redox properties of complexes (ΔE° = 130 mV) while the difference in the catalytic half-wave potential becomes substantial (ΔEcat/2 = 670 mV) in the presence of 15 mM CF3COOH. The common S^S-dithiolate ligand provides stability, while the rigidity effect of other ligands (DPPE (3) > DPPF (2) > PPh3 (1)) regulates the formation of the transition state, resulting in the NiIII-H intermediate in the order of 1 > 2 > 3. The foot-of-the-wave analysis supports the widely accepted ECEC mechanism for Ni-based complexes with the first protonation step as a rate-determining step. The electrocatalytic proton reduction activity follows in the order of complex 1 > 2 > 3. The comparatively lower overpotential and higher turnover frequency of complex 1 are attributed to the flexibility of the PPh3 ligand, which favours the easy formation of a transition state. © 2024 The Royal Society of Chemistry.