Design/Synthesis
Sensing/Removal
Catalysis
Photonics
Research Interest
Inorganic Chemistry
Metal-Organic Frameworks (MOFs)
Coordination Polymers (CPs)
Fluorescence Sensing
Heterogeneous Catalysis
Photo-Physical Chemistry
Mechanochemical Synthesis
Pollutant Sensing/Encapsulation
CO2 Capture and Conversion
Electrocatalysis (OER, HER)
Triplet-Fusion; Singlet-Fission
Quantum Information Science
Design and Fabrication of coordination polymers (CPs)/metal-organic frameworks (MOFs) and their composites.
Application of MOF-based Materials as an Environmental Remediation Probes towards Chemical Sensing and Adsorptive Removal of Hazardous Organic/Inorganic Pollutants.
Application of MOF-based Materials as Heterogeneous Catalysts towards CO2 Sequestration, Small Organic Transformation and Water Splitting.
Application of MOFs/CPs materials for Triplet Fusion (TTA), Singlet Fission (SF) and Quantum Information Science (QIS).
Research Experience
MOFs/CPs Chemistry: Design, synthesis and characterization of mixed-linker coordination polymers (metal-organic frameworks) and MOF-derived nanomaterials. Application of these materials towards chemical/fluorescence sensing, heterogeneous catalysis, pollutant encapsulation/degradation, gas adsorption, CO2 capture/conversion, electrocatalytic water splitting, and photonics for quantum information science.
Crystallization: Hydrothermal/Solvothermal, Diffusion techniques, and non-ambient crystallization.
Mechanochemistry: Mechanochemical (Neat grinding and LAG) synthesis of MOFs/CPs.
Instruments Operating Skills: Experience in handling Single Crystal X-ray Diffractometer (SXRD), Powder X-ray Diffractometer (PXRD), UV-Vis spectrophotometer, Fluorescence spectrophotometer with Time-resolved photoluminescence and lifetime, Circular Dichroism, Rotary evaporator, surface area and gas adsorption analyser and high-pressure gas reactors for catalysis. Basic handling knowledge and advanced data interpretation skills for thermal analytical techniques (TGA, DSC), CHN analyser, FT-IR, FT-NMR, FE-SEM, TEM, EDX, XPS, light/fluorescence microscopes, LC-MS, GC, ICP, zeta analyser instruments.
Research Summary
I am an “Experimental Inorganic Chemist,” working on the development of sustainable material systems to tackle environmental remediation. My research interests are focused on the design, synthesis and characterization of mixed-linker coordination polymers (CPs)/metal-organic Frameworks (MOFs) based materials and their functional aspects. Main aim of my research is a versatile synthesis of phase pure bulk MOFs or MOFs-based materials using sustainable synthetic protocols such as diffusion and mechanochemical methods via energy-efficient ways. The application of these materials is mainly divided as 1) fluorescence sensing or adsorptive removal of environmentally hazardous inorganic/organic pollutants (nitroaromatics, organic dyes, solvents, heavy metal anions/cations) in the aqueous phase, and 2) heterogeneous catalysis for CO2 sequestration, small organic transformations (C-C/C-H bond formation, desulfurization, biomass conversion) and electrocatalytic water splitting.
Thousands of structurally unique MOFs are reported in the literature, yet, most of them doesn’t qualify the criterion of functional material; primarily due to instability in the on-field conditions. The prime objective of my doctoral research was to develop new robust and luminescent MOFs (LMOFs) for real-world applications. Thus, in order to sustainably develop functional LMOFs, we have identified and sequentially categorize the obstacles in front of us which are also presented in Figure 1a. Our idea was to tackle these challenges one by one so as to systematically resolve the specific issues and to garner insights for re-designing processes. Eventually, we have chosen d10 metal nodes, Zn(II) and Cd(II) in combinations with polycarboxylate and azine based polypyridyl linkers depicted in Figure 1b. These judicious combinations have resulted in more than 50 robust LMOFs for each of which x-ray quality single crystals were harvested and their crystal structures were determined. Producing sufficient quantities of the phase pure end product for application purposes is an important issue which is scarcely discussed in the literature. Solvothermal or diffusion techniques are not only time-consuming but also often offer poor yields of MOFs, hence one has to repeat several experiments to obtain usable quantities of materials. We have optimized time-efficient thermal and mechanochemical methods for the rapid production of phase-pure MOFs in gram scales. Application-wise my doctoral research achievements can be classified into the following two categories:
1) MOFs for fluorescence sensing and encapsulation of hazardous organic/inorganic pollutants:
We have extensively worked on the practical utility of LMOFs towards sensing and adsorption of pollutants in aqueous solutions. Our expertise and comprehensive understanding of the field has resulted in a couple of perspective reviews (Inorg. Chem. Front., 2020, 7, 1082-1107; Dalton Trans., 2021, 50, 3083-3108) besides the original research. A few representative studies are bulleted hereunder:
Figure 1. (a) Challenges in developing new LMOFs; (b) Explored N-donors; (c) & (d) representative depictions of sensing and adsorption application of LMOFs.
One of our early contributions includes a 2D LMOF, [Cd(5-bromoisophthalate)(1,3,5-tris(imidazol-1-ylmethyl)benzene)]n which remains chemically stable for 60 days in the aqueous solution of TNP with good thermal stability up to 350 °C has been successfully implemented for the detection of ppb levels of TNP in aqueous solutions (Dalton Trans., 2016, 45, 7881-7892).Â
Another study resulted in 2D LMOF, {[Zn2(H-trimesate)2(L1)(water)2].solvent}n which could reversibly uptake as much as 60 to 97% of cationic dyes from their aqueous solutions. The practical applicability of this result for environmental remediation was further appreciated by the demonstrated dye removal using MOF packed columns (Dalton Trans., 2017, 47, 898-908).
Yet another important work involved the development of two pairs of robust Zn and Cd frameworks, {[M(isophthalate)(L2)]}n and {[M(2-aminoterephthalate)(L3)]}n those could detect ppm levels of chromates and ppb levels of 2,4,6-trinitrophenol and Fe3+/Pd2+ in aqueous solutions (Figure 1c). These results were achieved in the presence of interfering analytes and have been best at the time of publication (Inorg. Chem., 2017, 56, 2627-2638; Inorg. Chem., 2017, 56, 10939-10949).Â
Recently, we have also developed a multi-functional MOF, {[Zn(5-nitroisophthalate)(L2)2]}n, {[Zn(5-hydroxyisophthalate)(L2)2]}n, {[Cd(5-hydroxyisophthalate)(L2)2]}n which serves as a dye adsorbent (Figure 1d) and heterogeneous catalyst (Mater. Chem. Front., 2021, 5, 304-314; Inorg. Chem. 2021, 60, 9181-9191).
2) MOFs/CPs for heterogeneous catalysis (CO2 sequestration) and electrocatalysis (water splitting):
Leaching of heterogeneous catalysts in aqueous, non-aqueous or organic solvents has been a significant challenge before the material scientists for since long. Considering the thermal and chemical stability as well as the presence of supramolecular unsaturated sites on our prepared materials has motivated us to explore their utility as heterogeneous catalysts (Figure 2). A few important results are presented below:
Figure 2. One of the developed MOF as a representative heterogeneous catalyst and studied organic transformations.
CO2 sequestration has been achieved in solvent-free and ambient conditions by employing MOFs, {[Zn(terephthalate)(L3)]}n, {[M(1,4-cyclohexane dicarboxylate)(L3)]}n, {[Co(oxybis(benzoate))(L3)]}n, {[Co(terephthalate)(L3)]}n, {[Zn(5-nitroisophthalate)(L3)]}n as heterogeneous catalyst for cycloaddition reaction between organic epoxide and carbon dioxide (Figure 2; ChemCatChem, 2018, 10, 11, 2401-2408; Chem. Eur. J., 2018, 24, 15831-15839; J. Mater. Chem. A, 2019, 7, 2884-2894; Inorg. Chem., 2019, 58, 10084-10096; Appl. Catal. A: Gen., 2020, 590, 117375; Cryst. Growth Des. 2021, 21, 1833-1842).
Similarly, C-H activation, Knoevenagel condensation, Biginelli reaction and sulfoxidation reactions are heterogeneously catalyzed by MOFs, {[M(1,3-adamantanediacetate)(L3)]}n, {[Zn2(5-nitroisophthalate)2(L2)2]}n, {[Zn(2-aminoterephthalate)(L3)]}n, {[Cd(terephthalate or 2-aminoterephthalate)(L2)]}n (Inorg. Chem. Front., 2018, 5, 2630-2640; Mater. Chem. Front., 2021, 5, 304-314; Dalton Trans., 2018, 47, 8041-8051; Eur. J. Inorg. Chem., 2022, 2022, e202200410).
Additionally, a Co(II) containing MOF was pyrolyzed to obtain Co-nanoparticle encapsulated N-doped carbon nanomaterial which was utilized as electrocatalyst towards water splitting via oxygen / hydrogen evolution reaction (OER/HER) (Appl. Sur. Sci., 2020, 529, 147081; RSC Adv. 2021, 11, 21179-21188; Appl. Sur. Sci., 2023, 616, 156499). The electrocatalytic activity of these materials for OER outperformed the benchmark electrocatalyst such as RuO2 and IrO2 (Appl. Sur. Sci., 2020, 529, 147081).
3) MOFs/CPs for Photonics Applications: Singlet Fission, Triplet Fusion and Quantum Information Science (QIS): (Unpublished work)
Singlet Fission (SF) process is the splitting of one singlet exciton (S1; spin = 0) into two triplet excitons (T1; spin = 1). In organic semiconductors, acene (Tetracene (Tn)/Pentacene (Pn)) molecules are well-known to undergo exciton fission. The acene chromophore pair upon excitation generates an initial state as singlet exciton (S1) and a final state as two independent triplet excitons (T1 + T1) with almost half the energy of singlet exciton. This two-triplet exciton generates the exciton pair (T1T1) and the net spin of the exciton pair is classified as singlet 1(T1T1), triplet 3(T1T1) or quintet 5(T1T1) (Figure 3). Particularly the quintet 5(T1T1) pair is more interesting due to a total spin of 2, and higher energies than singlets or triplets. But in practical applications, generation/control of quintet pair and understanding its dynamics are challenging. In literature, chromophore pair-based dimers are dominant and major studies involving high magnetic fields or cryogenic temperatures limit practical application in photonics. Our main objectives are to generate quintet pair 5(TT) in solid-state SF-active materials applicable at mild temperatures and low magnetic fields for practical photonics applications in quantum sensing as well as quantum information science (QIS). Metal-organic Frameworks (MOFs) are well-known for their inherent tailorability, ordered structure, porosity, and guest accessibility.
Figure 3. Schematic representation of acene chromophore pairing in MOFs and upon photoexcitation these pair undergo singlet fission to generate triplet exciton pair.
The acene-based chromophores can be introduced as linkers in MOFs to generate well-ordered nets and dynamics control of chromophores to form a pair for SF generation. We have designed the diphenyl tetracene and diphenyl pentacene-based dicarboxylates (H2TDBA/H2PDBA) organic linkers and successfully utilized them to engineer two well-known MOFs topologies like, fcu (UiO-68 type) and pcu (IRMOF-16 type) (Figure 3).
The homo-linker, as well as hetero-linker MOFs containing acene (Tn/Pn) linkers, have successfully been synthesized via a solvothermal method, phase purity characterized by various analytical techniques and photophysical properties of these materials have been accessed by different spectroscopic analysis. The exciton generated by the SF process has been analysed by transient-EPR spectroscopy measurements at room temperature as well as cryogenic temperature.
The current acene-based MOF system will be useful in understanding the chromophore orientation, molecular motions and exciton dynamics affecting singlet fission for photonic applications.