Faculty Publications
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Item Structure-sensitive electrocatalytic reduction of co2 to methanol over carbon-supported intermetallic ptzn nano-alloys(American Chemical Society service@acs.org, 2020) Payra, S.; Shenoy, S.; Chakraborty, C.; Tarafder, K.; Roy, S.The electrochemical reduction of CO2 (CO2RR) to produce valuable synthetic fuel like CH3OH not only mitigates the accumulated greenhouse gas from the environment but is also a promising direction toward attenuating our continuous reliance on fossil fuels. However, CO2RR to yield CH3OH suffers because of large overpotential, competitive H2 evolution reaction (HER), and poor product selectivity. In this regard, intermetallic alloy catalysts open up a wide possibility of fine-tuning the electronic property and attain appropriate structures that facilitate selective CO2RR. Here, we report for the first time the CO2RR over carbon-supported PtZn nano-alloys and probed the crucial role of structures and interfaces as active sites. PtZn/C, Pt3Zn/C, and PtxZn/C (1 < x < 3) synthesized from the metal-organic framework material were characterized structurally and morphologically. The catalysts demonstrated structure dependency toward CH3OH selectivity, as the mixed-phase PtxZn/C outperformed the phase-pure PtZn/C and Pt3Zn/C. The structure-dependent reaction mechanism and the kinetics were elucidated over the synthesized catalysts with the help of detail experiments and associated density functional theory calculations. Results showed that in spite of low electrochemically active surface area, PtxZn could not only have facilitated the single electron transfer to adsorbed CO2 but also showed better binding of the intermediate CO2 •- over its surface. Moreover, the lower bond energy between the mixed-phase surface and -OCH3 compared to the phase-pure catalysts has enabled higher CH3OH selectivity over PtxZn. This work opens a wide possibility of studying the role of interfaces between phase-pure nano-alloys toward CO2RR. © 2020 American Chemical SocietyItem Pressure-driven structural and spin-state transition in a Hofmann clathrate coordination polymer(Elsevier B.V., 2021) Reddy, I.R.; Oppeneer, P.M.; Tarafder, K.Hofmann-type organometallic frameworks are well known for their porous crystal structure, exhibiting interesting electronic, optical, and magnetic properties, and are therefore considered as promising materials for various technological applications. Here, using density functional theory+U (DFT+U) calculations, we investigate the spin-state transition in a newly synthesized Hofmann clathrate, namely the Fe{OS(CH3)2}2{Ag(CN)2}2 complex, by applying hydrostatic pressure as an external perturbation. Our study reveals that under a relatively low isotropic hydrostatic pressure, the complex exhibits a reversible spin switching, whereas it undergoes a structural phase transition when the pressure is larger and anisotropic. The spin state of the Fe atom in the Hofmann clathrate complex transforms from high spin to intermediate spin state under anisotropic compression of the lattice parameters. The coordination polymer complex remains a magnetic semiconductor after the pressure-driven structural transformation. © 2020 Elsevier B.V.Item Photo- and Electrocatalytic Reduction of CO2 over Metal-Organic Frameworks and Their Derived Oxides: A Correlation of the Reaction Mechanism with the Electronic Structure(American Chemical Society, 2022) Payra, S.; Ray, S.; Sharma, R.; Tarafder, K.; Mohanty, P.; Roy, S.A Ce/Ti-based bimetallic 2-aminoterephthalate metal-organic framework (MOF) was synthesized and evaluated for photocatalytic reduction of CO2 in comparison with an isoreticular pristine monometallic Ce-terephthalate MOF. Owing to highly selective CO2 adsorption capability, optimized band gaps, higher flux of photogenerated electron-hole pairs, and a lower rate of recombination, this material exhibited better photocatalytic reduction of CO2 and lower hydrogen evolution compared to Ce-terephthalate. Thorough probing of the surface and electronic structure inferred that the reducibility of Ce4+ to Ce3+ was due to the introduction of an amine functional group into the linker, and low-lying Ti(3d) orbitals in Ce/Ti-2-aminoterephthalate facilitated the photoreduction reaction. Both the MOFs were calcined to their respective oxides of Ce1-xTixO2 and CeO2, and the electrocatalytic reduction of CO2 was performed over the oxidic materials. In contrast to the photocatalytic reaction mechanism, the lattice substitution of Ti in the CeO2 fluorite cubic structure showed a better hydrogen evolution reaction and consequently, poorer electroreduction of CO2 compared to pristine CeO2. Density functional theory calculations of the competitive hydrogen evolution reaction on the MOF and the oxide surfaces corroborated the experimental findings. © 2022 American Chemical Society.Item Distal Synergistic Effect in Bimetal-Organic Framework for Superior Catalytic Water Oxidation(American Chemical Society, 2023) Bhoi, U.; Ray, S.; Bhand, S.; Ninawe, P.; Roy, D.; Rana, S.; Tarafder, K.; Ballav, N.Metal-organic frameworks (MOFs) are emerging as promising electro-catalysts for the oxygen evolution reaction (OER). The bimetallic design strategy was further adopted in MOFs to elevate the OER performance by a synergistic effect. The proximal metal-oxygen-metal bonding configuration with typical 3dπ-2pπ-3dπ interaction was apparently essential for an effective electronic coupling between the metal centers. Here, we report an example of distal synergy in a bimetal-organic framework exhibiting a better OER activity than the monometallic counterparts, as well as the conventional proximal synergy. To achieve a current density of 10 mA·cm-2, our electrodeposited bimetallic MOF, Co-Ni(TCNQ)2(H2O)2 (TCNQ = 7,7,8,8-tetracyanoquinodimethane), on a glassy-carbon electrode required an overpotential value of 220 mV. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed distinctive electronic coupling between the Co(II)-3d7 and Ni(II)-3d8 centers, despite being 9 Å apart, leading to an overall charge delocalization in the structure via TCNQ. © 2023 American Chemical Society.Item Ag Nanoparticles-Induced Metallic Conductivity in Thin Films of 2D Metal-Organic Framework Cu3(HHTP)2(American Chemical Society, 2023) Saha, S.; Ananthram, K.S.; Hassan, N.; Ugale, A.; Tarafder, K.; Ballav, N.Two-dimensional (2D) metal-organic frameworks (MOFs) are usually associated with higher electrical conductivity and charge carrier mobility when compared with 3D MOFs. However, attaining metallic conduction in such systems through synthetic or postsynthetic modifications is extremely challenging. Herein, we present the fabrication of thin films of a 2D MOF, Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), decorated with silver nanoparticles (AgNPs) exhibiting significant conductivity enhancement at room temperature. Variable-temperature electrical transport measurements across the low-temperature (200 K) to high-temperature (373 K) regime evidenced metallic conduction. Interestingly, thin films of a 3D MOF, CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane), upon decoration with AgNPs, disclosed a converse trend. The origin of such distinctive observations on AgNPs@Cu3(HHTP)2 and AgNPs@CuTCNQ systems was comprehended by using first-principles density functional theory (DFT) calculations and attributed to an interfacial electronic effect. Our work sheds new light on rationally designing synthetic modifications in thin films of MOFs to tune the electrical transport property. © 2023 American Chemical Society.Item Thermally-driven conformational twist in organic azobenzene linker activates molecular doping effect in thin films of lanthanide MOFs(Royal Society of Chemistry, 2025) Bhoi, U.; Kalyani, M.; Ananthram, K.S.; Saha, S.; Acharya, A.; Hassan, N.; Raj, M.; Tarafder, K.; Ballav, N.Azobenzene-based photo-switchable molecules have shown significant potential in stimuli-responsive systems, especially when incorporated into metal–organic frameworks (MOFs). This study reports thin films of lanthanide-based metal–organic frameworks (Ln-MOFs) with 4,4?-azobenzene dicarboxylic acid (H2ADA) as the organic linker – Tb-ADA, Eu-ADA, and Gd-ADA – using an electrodeposition method. Upon heating to 400 K, a reversible structural transition was observed via variable temperature grazing-incidence X-ray diffraction (GIXRD) and Raman spectroscopy, not due to trans–cis isomerization but rather a thermally-induced conformational twist of the ADA linker. Density functional theory (DFT) combined with molecular dynamics (MD) simulations supports this interpretation, revealing high-energy atropisomeric states stabilized by MOF confinement. Molecular doping of these films with 7,7,8,8-tetracyanoquinodimethane (TCNQ) significantly enhanced their electrical conductivity, increasing by two orders of magnitude at 400 K. This enhancement is attributed to improved ?–? stacking and charge-transfer interactions facilitated by the conformational twist. Temperature-dependent X-ray photoelectron spectroscopy (XPS) confirmed redox activity in TCNQ@Tb-ADA films, showing reversible conversion between Tb(iii) and Tb(iv), with back electron transfer at 400 K restoring Tb(iii). These findings introduce a new mechanism of thermally-driven conformational switching in MOFs and open avenues for developing responsive electronic materials based on azobenzene linkers. This journal is © The Royal Society of Chemistry, 2025