Faculty Publications
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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 Unprecedented Electroreduction of CO2over Metal Organic Framework-Derived Intermetallic Nano-Alloy Cu0.85Ni0.15/C(American Chemical Society, 2022) Payra, S.; Devaraj, N.; Tarafder, K.; Roy, S.Designing suitable catalysts for efficient and selective electrocatalytic reduction of CO2 is a need of the hour, and in this regard, the well-defined, highly dispersed active metal centers can be a trendsetting research endeavor toward CO2 electroreduction due to the maximum atom utilization and unique electronic structure. This study describes the synthesis and electrocatalytic CO2 reduction activity of atomistically dispersed Cu/C and Ni/C and the intermetallic nano-alloy Cu0.85 Ni0.15 /C. The catalysts were synthesized from the corresponding MOF precursors. The successful synthesis of the monometallic and intermetallic nano-alloys was established from structural, surface morphological, and electronic properties. Cu0.85 Ni0.15 /C exhibited an unprecedented electrocatalytic reduction of CO2 with a high selectivity and high faradaic efficiency toward CH3 OH. The kinetic studies and the first-principles calculations elucidated the intricate mechanism and the superior activity of electrocatalytic reduction of CO2 over the intermetallic Cu0.85 Ni0.15 /C catalyst. © 2022 American Chemical Society. All rights reserved.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