Our collaborators
INTERFACIAL
MATERIALS
CHEMISTRY
What we know is a drop, what we don't know is an ocean.
- Isaac Newton
Physical and Inorganic Chemistry
Interfacial Materials Chemistry:
Fundamentals to Applications
Objectives: An interface is a boundary between two spatial regions either occupied by different matters or by a matter in different physical states, for example, solid-solid, solid-liquid and liquid-liquid interfaces. Chemical reactions involving oxidation and reduction processes at interfaces may vary from those in conventional liquid-phase reactions and could thus influence the overall outcome. In search of capturing interfacial effects, we are exploring solid-solid and solid-liquid interfaces which could bring novel properties in the materials. An elegant interfacial effect is the formation of two-dimensional (2D) electron gas and a smart class of interface-engineered materials is supramolecular solids. Our research platforms include coordination polymers, low-dimensional materials, conducting polymers, metal nanoparticles, metal oxides and sulphides, and magnetic materials.
Thin Films of Coordination Polymers:
We are studying metal-ligand coordination at solid-liquid interface vis-à-vis thin film formation via layer-by-layer (LbL) method. Electronic, magnetic, and electrochemical characteristics of these interface-engineered materials are being routinely evaluated, majorly, in thin film configurations. Also, prototypical micron-to-nanoscale thin film devices are getting fabricated in our laboratory by employing electron-beam and photo-lithography techniques. Notable observations include (i) Spontaneous reduction of Cu(II) to Cu(I) at solid-liquid interface leading to for-
mation of Cu-TCNQ and Cu(I)-HCF thin films; (ii) Thermally-driven resistive switching in thin films of Cu-TCNQ and Ag-TCNQ; and (iii) Current rectification ratio beyond 10^5 (similar to Si) across molecularly doped thin film of a Cu(II)-coordination polymer.
Representative Publications:
1. Nat. Commun. 2022, 13, 7665
2. J. Phys. Chem. C 2021, 125, 7728-7733
3. J. Phys. Chem. Lett. 2020, 11, 10548-10551
4. J. Phys. Chem. Lett. 2020, 11, 6242-6248
Graphene Supercapacitors:
Owing to its remarkable properties, graphene (single layer of graphite) – an allotrope of elemental Carbon and a two-dimensional material discovered in 2004 – has emerged as a promising active-electrode material for developing high-performance supercapacitors. However, obtaining single layers of graphene in large scale by bottom-up approach is extremely difficult. Thus, top-down approach whereby graphite is first chemically oxidized to graphene oxide (GO) and subsequently reduced to reduced graphene oxide (rGO) which exhibits phy-
sicochemical properties in close resemblance to pristine graphene has emerged. We have explored unconventional transition metal salts-based reducing agents in the chemical reduction of GO to rGO and used rGO as such (without further treatments) in the fabrication of all-solid-state supercapacitors. The overall electrochemical performance of our rGO was found to be much superior in comparison to rGO obtained by conventional reducing agents such as NaBH4, and N2H4. Our process of producing rGO by top-down chemical approach in large scale was realized to be highly economic and thereby promising for supercapacitor applications in industrial level – as recently highlighted by Department of Science and Technology (DST), Govt. of India.
Representative Publications:
Magnetic Semiconductors (Quantum Materials):
We are embedding various Cu(II)-based low-dimensional S=1/2 spin lattices onto semiconducting functionalized graphene – reduced graphene oxide (rGO) – via in-situ oxidation-reduction reaction involving Cu(I) salts and graphene oxide (GO) as primary precursors. The magnetic signatures of insulating Cu(II)-based S=1/2 spin lattices, explored here, were significantly influenced by the diamagnetic and semiconducting rGO in the respective nanocomposites, thereby generating a new class of magnetic semiconductors. Specifically, we were able to embed exotic S=1/2 spin lattices of Cu(II) namely, clinoatacamite, barlowite, paratacamite, herbertsmithite, and botallackite from the atacamite family of minerals onto rGO matrix. rGO-atacamite sy-
stems presented here can be explored further by studying magnetic field dependent electrical transport characteristic as well as electric field dependent magnetic response; also, as quantum materials!
Representative Publications:
1. Phys. Rev. B 2021, 104, L100418
2. AIP Conference Proceedings 2020, 2265, 030585
3. J. Phys. Chem. C 2020, 124, 19753-19759
4. Inorg. Chem. 2020, 59, 6214-6219
5. J. Phys. Chem. Lett. 2019, 10, 2663-2668
6. J. Phys. Chem. C 2017, 121, 12159-12167
Electrically Conducting MOFs:
We have established two new concepts to modulate electrical conductivity in MOFs and attributed as extrinsic and intrinsic approaches: (i) by filling-up the pores in MOFs with chains of organic conducting polymers like polyaniline, polypyrrole and polythiophene (extrinsic); and (ii) by introducing ‘heterometallic’ concept (intrinsic). The electrical conductivity values of MOFs could thus be significantly enhanced ranging from milli-fold up to billion-fold. While introducing chains of conducting polymers, we realized the porosity loss in MOFs. Recently, we have introduced the motif of rationally designing porous and semiconducting MOF with high-electrical conductivity and low-thermal co-
nductivity onto a single material platform upon filling some void space in MOF with chains of conducting polymer – so called MOF-Conducting Polymer Nanocomposites. The key behind our success was the bi-porosity enabling us to impart such multi-functionality.
Representative Publications:
Plasmonic Nanoparticles:
We have developed a new wet-chemical method for co-reduction procedure for producing citrate-stabilized ‘homogeneously-alloyed’ Au-Ag NPs of average size sub-10 nm at room-temperature upon overcoming the detrimental factor of ‘solubility product’ (more than 15 years!) by the simple use of Tollen’s reagent. To empower the seed-mediated growth method, we have also introduced Tannic Acid as the new mild-reducing agent, for synthesizing convex and concave cubic (ETHH and CCB) Au nanocrystals (NCs) enclosed with high-index facets at room-temperature, which are routinely explored for electro-catalytic applications. We are introducing a facile and robust synthetic protocol for the generation of a new one-
dimensional nanostructure, Au nano-earbud (NEB). Amazingly, this nanostructure exhibits three distinct plasmon resonance peaks, the origin of which has been duly studied and assigned on the basis of theoretical calculations. Additionally, we are successful in tuning the longitudinal surface plasmon resonance into the NIR-II region while keeping the length sub-100 nm (with aspect ratios beyond 12).
Representative Publications:
1. ACS Appl. Nano. Mater. 2021, 4, 9155-9166
2. ACS Appl. Nano. Mater. 2021, 4, 7426-7434
3. J. Phys. Chem. Lett. 2020, 11, 3211-3217
4. Langmuir 2019, 34, 9456-9463
Spinterface Science:
Tuning molecule-substrate spin-interface (spinterface) by chemical or physical stimuli is the heart of emerging organic-spintronics. The combination of on-surface supramolecular chemistry with coordination chemistry provides a facile and unique approach to manufacture extended supramolecular arrays with switchable spin states. Our approach of combining spectroscopy and microscopy (so called spectro-microscopy correlation), together with numerical simulations (DFT+U) provide an in-depth fundamental understanding of the complexity of on-surface magnetochemistry. Notably, this body of work contributes to gaining control of the magnetic exchange coupling across the molecule‐substrate spin‐interface which constitutes a key requirement for molecular spintronic applications.
Representative Publications:
1. Nat. Commun. 2017, 8, 15388
2. Angew. Chem. Int. Ed. 2013, 52, 4568 –4571
3. Adv. Mater. 2013, 25, 2404–2408
Funding Sources:
