Design/Synthesis

Sensing/Removal

Catalysis

Photonics

Research Interest

Research Experience

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.

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.

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 current acene-based MOF system will be useful in understanding the chromophore orientation, molecular motions and exciton dynamics affecting singlet fission for photonic applications.