Inorganic Functional Nanomaterials Laboratory
The research of our group is broadly and sequentially categorized into three aspects of nanoscale materials science. First of, we make the nanostructures through wet-chemistry. Then, we characterize them through an array of methods. Primary of which is electron microscopy - where we can "see" the materials, now even up to atomic scale! We focus a lot on interrogation of the nanoscale system through electron microscopy, and that is the primary expertise of our group. This helps us in understanding various aspects of nucleation and growth, which are two corner-stones of any nanomaterial synthesis. Once synthesized, we use the material for various applications, such as gas-phase catalysis, electrocatalysis, sensing. That's where we apply the materials. To know more, please visit our publications page. We also have very active collaborations to probe various areas of interest. For more details, please visit the page listing all our collaborators, and their webpages!
Recent Research Highlights
Anion-Exchange-Mediated Synthesis of Hollow 2D Layered Materials and Heterostructures: Mechanism and Room-Temperature Gas-Sensing Properties
The design of nanostructures with unique morphologies and enhanced functionalities is a cornerstone of modern materials science. Ion exchange reactions in inorganic crystals offer a versatile approach for precisely controlling the composition, morphology, and properties of the materials. We are exploring the anion-exchange-mediated conversion of 2D layered material SnSâ‚‚ into SnSeâ‚‚. To elucidate the anion-exchange mechanism, we conducted a comprehensive investigation using electron microscopy techniques, varying reaction parameters. Our findings revealed that the exchange process initiates at the edges of the template SnSâ‚‚ nanosheets and progresses inward. Cross-sectional electron microscopy of the interfaces uncovered numerous defects attributed to ion migration and lattice mismatch. The anion-exchange-derived SnSâ‚‚–SnSeâ‚‚ heterostructure and SnSeâ‚‚ exhibited exceptional selectivity and sensitivity toward NO2 gas (response >700%) at room temperature comparable to state-of-art sensors. This study underscores the potential of anion exchange as a powerful tool for designing novel nanomaterials with tailored properties and applications, particularly in the realm of gas sensing.
Defect-Mediated Growth of Layered Lateral Heterostructures
In-plane heterostructures of Biâ‚‚Te₃–Sbâ‚‚Te₃ have garnered significant interest owing to their topological properties and their applications as thermoelectric materials. While various solution-based approaches have been employed in the past for heterostructure formation, using multistep methods, achieving one-step synthesis has been challenging. We have explored the synthesis of BT–ST heterostructure using a one-pot solution-based synthetic strategy, where in situ generated Biâ‚‚Te₃ nanosheet acts as a template to grow Sbâ‚‚Te₃. Cross-section HAADF STEM imaging provide clues to a screw-dislocation-mediated growth mechanism. To gain insights into the screw-dislocation-driven growth, atomic-resolution imaging has been carried out. The screw dislocations are found to originate from pristine Biâ‚‚Te₃ and play a critical role in the overall growth process. Overall, this study demonstrates the versatility of a solution-based approach in designing multishell nanostructures and detailed analysis of interfaces, which provide insights into the atomic arrangement during the screw-dislocation-mediated growth mechanism.
Mutual Stabilization of Metastable Phases of Tin Oxide: Epitaxial Encapsulation of Tetragonal SnO Microcrystals by Orthorhombic SnOâ‚‚
Electron microscopy studies on α-SnO, a metastable t2D layered material, have revealed exciting aspects of the structure and phase stability in the Sn-O system. Electron diffraction from the sheets reveals a secondary metastable phase, namely, o-SnOâ‚‚, to be present coherently with the single-crystalline SnO. A detailed cross-sectional analysis of the sheets reveals that the SnO phase is completely encapsulated by a thin layer of the metastable orthorhombic phase. The metastable SnO phase is thus stabilized by the presence of the encapsulating o-SnOâ‚‚on its surface; the metastable o-SnOâ‚‚ phase itself is stabilized by the underlying SnO substrate. The present study clarifies several unexplained features of the reported microstructures in the SnO system and provides some new insights into the mutual stabilization of metastable phases in the oxides of Sn that could be applicable for other systems as well.
Designed synthesis of a hierarchical MoSeâ‚‚@WSeâ‚‚ hybrid nanostructure as a bifunctional electrocatalyst for total water-splitting
Owing to their anisotropic layered structure, LMDs can be synthesized as mono- or few-atomic layered nanosheets and as heterostructures with unique and diverse properties. The synthesis of LMDs via a wet-chemical method requires stringent control over the choice of metal and chalcogen precursors. Generally, a two-step synthesis route or substrate-based methods are followed to synthesize heterostructure or hierarchical nanostructures. Herein, exploiting the different reactivity of metal ion precursors towards chalcogens, we have explored a one-step wet-chemical reaction scheme to synthesize MoSeâ‚‚, WSeâ‚‚, and hierarchical MoSeâ‚‚@WSeâ‚‚ heterostructures. The as-synthesized nanostructures have a flower-like morphology, and the heterostructures are formed with a Mo-rich core and a W-rich petal. The as-synthesized nanostructures have been investigated for the electrochemical water-splitting reaction. The heterostructure shows better catalytic performance with MoSeâ‚‚@WSeâ‚‚having a Mo:W ratio of 1:1 being the best among them.
Shuttling Active Elements in and out of Ultrathin Nanowires: Toward Rational Design of Multicomponent Catalysts
One-dimensional nanostructures, with a high ratio of surface-bulk atoms, find applications as active catalysts. We have explored tunability in ultrathin single-crystalline AuPdPt nanowires by modifying synthesis conditions and postsynthetic treatment in a controlled ambient atmosphere. The surface microstructure modification of these nanostructures has been analyzed by integrating the results of three crucial techniques including Z-contrast HAADF-STEM imaging, X-ray photoelectron spectroscopy, and electrochemically active surface area from cyclic voltammograms.
Designing complex radial heterostructures of Te/Bi₂Te₃ and Te/Bi₂PbxTe₃ nanowires: fundamental mechanistic insights into nanowire growth and evolution
A good understanding of the reaction mechanism and critical observation of the evolution of the nanowire heterostructure during the course of reaction is essential to tune their properties. In this study single crystalline, anisotropic Te core/Biâ‚‚Te₃ shell nanowires have been synthesized by a facile template-based wet chemical synthesis method. The formation and evolution mechanism of the heterostructure has been elucidated by several control reactions, detailed TEM imaging and composition analysis using EDS in STEM mode of the products of the reactions. Fundamental understanding of the formation mechanism and time-dependent evolution of the core–shell structure in the nanowire have led to successful designing of higher order heterostructures involving Te/Biâ‚‚-xPbxTe₃. Through this study, interesting insights into the crystal structure evolution, crystal growth and miscibility of PbTe and Biâ‚‚Te₃ into each other is obtained.
Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires via Surface Segregation
The catalytic properties of the heterogeneous catalysts critically depends on the nature of the surface. Herein, we have controlled the composition in ultrathin bimetallic AuPd nanowires. AuPd wires with different amount of Pd was grown using Au nanowire templates; Further, segregation of Pd to the surface could be induced in alloyed nanowires by annealing under a controlled CO atmosphere. AuPd nanowires are assessed for the methanol oxidation reaction (MOR). The specific activity displays a typical volcano-type behavior. The CO-annealed nanowires show a lowering of potential owing to a higher Pd content on the surface while still maintaining the specific activity. . The experimental findings are well supported by the theoretical investigations using density functional theory (DFT) calculations.
Morphology Controlled SnSe2-graphene Hybrid for Photodetection
Photodetection with low band-gap semiconductor SnSeâ‚‚ suffers from low carrier mobility. This can be circumvented using graphene based hybrid device structure, which demands a flat 2D interface. Using solution chemistry, we have devised a way to control the growth of SnSeâ‚‚ with a flat 2D morphology. DFT simulations (with Thsim group, MRC) rationalize our synthesis strategy, and graphene-SnSeâ‚‚ hybrid device (with Nanoelectronics group, Physics) shows a photoresponse of ~1010 Jones, at par with state-of-the-art photodetectors.
Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires via Surface Segregation
Ultrathin single crystalline Au nanowire is a strained anisotropic morphology with interesting fundamental and applicative aspects. A disadvantage of the ultrathin morphology is the intrinsic fragility which makes it difficult to handle. Converting Au nanowires to its alloy counterpart maintaining the morphology and single crystalline nature is non-trivial due to its instability at higher temperature and polar solvents. An innovative and general reaction scheme of converting Au nanowire template to AuCu, AuPd and AuPt alloy nanowires at the liquid-liquid interface has been devised. The ultrathin alloy nanowires are found to have remarkable thermal and mechanical stability and are excellent electrocatalysts for methanol oxidation.
1-D Telluride Heterostructure with Controlled Morphology
Heterostructures of semiconductors with coherent interfaces and suitable morphology find applications in many fields. Here, we have been able to design beaded heterostructures of single crystalline nanowire of PbTe/Te using Te nanowires as templates. Control experiments show that the reduction of a Pb precursor to Pb on Te nanowire template, followed by interdiffusion of Pb into Te leads to the formation of a thin shell of PbTe on the wires. Further, controlled dewetting of the thin shell leads to the formation of cube-shaped PbTe, periodically arranged on the Te wires. The observations are consistent with surface energy minimisation argument. The inter-bead distance can also be controlled by the reaction conditions!