Department of Physics

Permanent URI for this community

http://ssm.ndl.gov.in/handle/123456789/1180

Browse

Browsing Department of Physics by Title

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    A density functional study of type I to type II crossover in g-C3N4/CoN4 heterostructure in presence of external perturbation
    (International Journal of Hydrogen Energy, 2024) V.N. D.;Sen S.;Chattopadhyaya M.
    Herein, we report the impact of external perturbation on the photocatalytic performance of g-C3N4/CoN4 heterojunction and concomitant transition from type-I to type-II. The state-of-the-art theoretical modeling presented here is the first study on dynamic role of strain and electric field on g-C3N4/CoN4 heterojunction and its potential application as a solar-driven water splitting reaction. Utilizing the density functional theory (DFT) calculation, V. N. et al. recently reported the photocatalytic activity of g-C3N4/MN4 (M = Mn, Fe and Co) heterojunction [J. Comput. Chem. 2024, 45, 2518-2529, https://doi.org/10.1002/jcc.2746412] and subsequently established g-C3N4/CoN4 as a type I heterojunction for photocatalytic water splitting reaction [Phys. Chem. Chem. Phys. 2024, 26, 21117–21133]. In the present study, we applied external perturbation in the form of mechanical strain, electric field and evaluated the electronic structure properties of the system along with the detailed examination of concomitant optical and magnetic properties of g-C3N4/CoN4 heterojunction. The switching of photocatalytic feature from type I to type II originates due to the crossover between valence band maxima (VBM) of g-C3N4 and CoN4 in presence of external perturbation. Notably, the resulting system acts as a type II photocatalyst for water splitting reaction while applying compressive (negative) strain of −2 to −6% and an electric field of −0.5 and +0.5 V/Å, respectively. Accumulation of photogenerated electrons and holes separately in g-C3N4 and CoN4 units confirms the perceptible separation of charge carriers and thereby reduces the recombination compared to un-perturbed system. A red-shifted absorption maximum (689 nm), superior charge transfer (0.9e), and clear separation of photogenerated electrons and holes are the origin of enhanced photocatalytic efficiency of g-C3N4/CoN4 heterojunction in the presence of external perturbation. We believe that our work will provide enough evidence to the experimentalists to achieve such a system in practice leading to human-friendly applications.
  • No Thumbnail Available
    Item
    Comparative study of the photocatalytic activity of g-C3N4/MN4 (M = Mn, Fe, Co) for water splitting reaction: A theoretical study
    (Journal of Computational Chemistry, 2024) Dhilshada. V.N.;Sen S.;Chattopadhyaya M.
    In this study, nanocomposites of g-C3N4/MN4 (where M is Mn, Fe and Co) have been designed using advanced density functional theory (DFT) calculations. A comprehensive analysis was conducted on the geometry, electronic, optical properties, work function, charge transfer interaction and adhesion energy of the g-C3N4/MN4 heterostructures and concluded that g-C3N4/FeN4 and g-C3N4/CoN4 heterojunctions exhibit higher photocatalytic performance than individual units. The better photocatalytic activity can be attributed mainly by two facts; (i) the visible light absorption of both g-C3N4/FeN4 and g-C3N4/CoN4 interfaces are higher compared to its isolated analogs and (ii) a significant enhancement of band gap energy in g-C3N4/FeN4 and g-C3N4/CoN4 heterostructures limited the electron–hole recombination significantly. The potential of the g-C3N4/MN4 heterojunctions as a photocatalyst for the water splitting reaction was assessed by examining its band alignment for water splitting reaction. Importantly, while the electronic and magnetic properties of MN4 systems were studied, this is the first example of inclusion of MN4 on graphene-based material (g-C3N4) for studying the photocatalytic activity. The state of the art DFT calculations emphasis that g-C3N4/FeN4 and g-C3N4/CoN4 heterojunctions are half metallic photocatalysts, which is limited till date.
  • No Thumbnail Available
    Item
    Density functional theory-based modeling of the half-metallic g-C3N4/CoN4 heterojunction for photocatalytic water splitting reaction
    (Physical Chemistry Chemical Physics, 2024) Dhilshada V.N.;Chandran A.;Sen S.;Chattopadhyaya M.
    Using density functional theory (DFT), we have investigated the structural, optical, electronic and magnetic properties of a graphitic carbon nitride (g-C3N4) and CoN4 composite to explore the effect of the heterojunction on the photocatalytic performance of g-C3N4. The structure of g-C3N4 is modified while complexing with CoN4 and the corresponding stabilization is confirmed through adhesion energy calculation. The phonon spectra analysis furthermore guaranteed the lattice-dynamic stability of the CoN4 bulk and the CoN4 slab. Pristine g-C3N4 is a wide band gap semiconductor, which becomes half metallic upon CoN4 inclusion. The metallicity in the g-C3N4/CoN4 composite originates from the spin down channel, keeping the spin up channel in a semiconducting state. The charge density analysis and work function calculation suggest a substantial amount of charge transfer from g-C3N4 to the CoN4 unit in the g-C3N4/CoN4 heterojunction. The model heterojunction of the g-C3N4/CoN4 composite can enhance the utilization ratio of visible light for the g-C3N4 photocatalyst. In g-C3N4/CoN4, the valence band maximum (VBM) has a more positive potential compared to O2/H2O (+1.23 V) on the normal hydrogen electrode (NHE) scale. However, the conduction band minimum (CBM) displays a more negative potential compared to H+/H2 (0 V) on the NHE scale. The details of the band structure, density of states and band edge position determining calculations confirm that the g-C3N4/CoN4 composite forms a type 1 heterojunction, making it a suitable photocatalyst for water splitting reaction. The practical application of the g-C3N4/CoN4 heterostructure as a photocatalyst was substantiated in the presence of polar solvent (water) by calculating the band gap, charge transfer interaction and charge density difference. There is a significant decrease of charge transfer and thereby charge density difference in the g-C3N4/CoN4 heterojunction in the presence of water; however, it still holds potential for use as a photocatalyst for water splitting reaction. The state-of-the-art theoretical modeling of the g-C3N4/CoN4 heterojunction is the first theoretical study incorporating the CoN4 crystal.
  • No Thumbnail Available
    Item
    Evidence of half metal to insulator transition and subsequent photocatalytic action in g-C4N3@Lin =1 to 4: A systematic theoretical analysis
    (Solid State Communications, 2024) Biswas A.;Prasad Mitra S.;Bhowmick R.;Adak D.;Chattopadhyaya M.;Sen S.
    We report herein, emergence of photocatalytic action in Li doped two-dimensional nanosheet of graphitic carbon nitride [g-C4N3@Lin = 0-4]. Doping concentration varied from 3.57 % to 14.28 %. Pristine graphitic carbon nitride is half metallic and at the highest level of doping (14.28 %) it transforms into an insulating system. Observed results have been examined through the estimation of coupling between magnetic centers and the overall magnetic moment of the system. The exchange coupling (JAB) within Heisenberg–Dirac–van Vleck Hamiltonian being negative indicates antiferromagnetic coupling in presence of Li, doping. Related optical spectrum quite clearly illustrates that only at the doping level [14.28 %] the absorption peak is in the optical region. Band structure obtained illustrates a band gap of 1.92 eV and 1.93 eV in both spin channels and both oxidation and reduction potential falls within the band gap. The presence of reduction potential below the conduction band and oxidation potential above the valence band clearly illustrates the possibility of photocatalytic action.