Department of Chemistry

The GRAPES-3 experiment is designed to perform precision studies of gamma-ray sources in the TeV-PeV energy region. It consists of 400 plastic scintillator detectors spanning an effective area of 25000 m2 and a large area (560 m2) muon telescope which records ∼ 4 x 109 muons every day. With the recent installation of an improved triggerless data acquisition (DAQ) system, the information related to every muon is recorded with a timing resolution of 10 ns. The angular resolution and pointing accuracy of the upgraded muon telescope has been validated by characterizing the shadow of the moon among recorded muons. Here, the details of the analysis and results, as well as the simulation studies to account for the deflection of the particles in the Earth’s magnetic field will be presented.

The GRAPES-3 experiment located in Ooty consists of an array of 400 plastic scintillator detectors spread over an area of 25000m2 and a large area (560 m2) muon telescope. Every day, the array records about 3 million showers induced by the interaction of primary cosmic rays in the atmosphere. One of the primary objectives of the experiment is to measure the energy spectrum and composition of the cosmic rays in the TeV-PeV energy range. However, some of the detected showers have cores outside the array. This fraction increases with energy due to the higher lateral spread of shower particles at higher energies. Identifying these events is thus crucial for accurate measurement of the cosmic ray energy spectrum. This work will describe simple cut based as well as machine learning based strategies for identifying and excluding such events and their impact on the cosmic ray energy spectrum as measured by the Bayesian unfolding technique.

The GRAPES-3 experiment located in Ooty consists of a dense array of 400 plastic scintillator detectors spread over an area of 25,000 m2 and a large area (560 m2) tracking muon telescope. Everyday, the array records about 3 million showers in the energy range of 1 TeV - 10 PeV induced by the interaction of primary cosmic rays in the atmosphere. These showers are reconstructed in order to find several shower parameters such as shower core, size, and age. High-energy showers landing far away from the array often trigger the array and are found to have their reconstructed cores within the array even though their true cores lie outside, due to reconstruction of partial information. These showers contaminate and lead to an inaccurate measurement of energy spectrum and composition. Such showers are removed by applying quality cuts on various shower parameters, manually as well as with machine learning approach. This work describes the improvements achieved in removal of such contaminated showers with the help of machine learning.

For detecting skin cancer, a silicon nitride based ring resonator refractive index sensor is modelled using coupled mode theory. This device has a high sensitivity of 249nm/RIU and Q factor of 1310.

Humidity sensors have gained immense importance as non-invasive, wearable healthcare devices for personal care as well as disease diagnostics. However, non-specificity, poor stability at extreme conditions, and low sensitivity of the humidity sensor inhibit its usage as a health monitoring device. In the present study, N−F containing organic molecule, SelectfluorTM (F-TEDA) based humidity sensors with ∼1–2 mm long needle-shaped crystals is fabricated on interdigitated electrodes resulting in excellent performance. The unidirectional growth of crystals led to the formation of a conduction pathway for water molecules across the crystal, which otherwise are non-conducting. The as-fabricated humidity sensor at an operational voltage of 0.8 V displays a sensitivity of six orders in magnitude, best reported so far. The sensor does not exhibit any response upon exposure to various volatile organic compounds and reactive gases, indicating remarkable specificity. The sensor is tolerant to high moisture of 95 % for prolonged hours followed by monitoring over several days and degrades to 50 % of its original sensitivity only after continuous exposure for several days. Electrochemical impedance spectroscopy (EIS) shows reversal from resistive to capacitive behavior with increasing humidity levels. The fabricated humidity sensor acts as a healthcare device for breath rate monitoring and touch-free examination of skin moisture.

Metal oxide-carbon nanocomposites offer an interesting platform for electrochemical sensing due to the synergistic effect of a highly active semiconducting surface and conducting carbon as the supporting backbone. In this work, the in situ synthesis of SnO2 with reduced graphene oxide (rGO) led to the formation of small, uniform SnO2 nanoparticles, measuring 10-20 nm in size, whereas the inclusion of multiwalled carbon nanotubes (MWCNT) resulted in the formation of (200) oriented SnO2 nanoplatelets of ∼200 nm. X-ray photoelectron spectroscopy (XPS) demonstrates a chemical interaction between Sn and C rather than physical adherence. The cyclic voltammograms (CVs) of SnO2-rGO and SnO2-MWCNT display high peak current density and small ΔE in comparison to SnO2, signifying fast electron transfer, reversibility, and enhanced electrochemically active sites. Under optimized experimental conditions of square wave anodic stripping voltammetry (SWASV), the nanocomposites demonstrate high sensitivity (3.9, 9.9, 45.5, and 25.4 mA cm-1 ppb-1) and a low detection limit (in ppb) toward Cd2+, Pb2+, Cu2+, and Hg2+, respectively. The high selectivity of SnO2-rGO for Cd2+ and Pb2+ ions and SnO2-MWCNT for Hg2+ and Cu2+ in a complex metal ion environment is encouraging and is probed by using density functional theory (DFT). Additionally, an artificial neural network (ANN)-based model justifies the sensor’s accuracy and precision for real-time, on-site detection of heavy metal ions directly in tap water.

Analysis of the interaction of pesticides and their metabolites with the cellular proteins has drawn considerable attention in past several years to understand the effect of pesticides on environment and mankind. In this study, we have investigated the binding interaction of Bovine Serum Albumin (BSA) with a widely used organophosphorous insecticide chlorpyrifos (CPF), and its stable metabolite, 3,5,6-trichloro-2-pyridinol (TCPy) to provide a comparative analysis of the two molecules by employing various spectroscopic techniques viz., UV–vis absorption, Circular Dichroism (CD), and Fluorescence spectroscopy. The fluorescence quenching studies of BSA emission in two different solvents viz., water and methanol in presence of CPF and TCPy have led to the revelation of several interesting facts about the pesticide-protein interaction. It has been found that both the molecules cause static quenching of BSA emission as seen from the Stern-Volmer constant (Ksv) irrespective of the solvent used for the analysis. While TCPy is a stronger quencher in water, it exhibits comparable quenching capacity with CPF in methanol. The solvent dependent differential binding interaction of the two molecules finally indicates possibility of diverse bio-distribution of the pesticides within human body. The UV–vis and CD spectra of BSA in presence of the test molecules have unravelled that the molecules formed ground state complex that are highly reversible in nature and have minimal effect on the protein secondary structure. Furthermore it is also understood that structural changes of BSA in presence of CPF is significantly higher compared to that in presence of TCPY.

A large area (560 m2) muon telescope in the GRAPES-3 experiment at Ooty, India records muon intensity at high cutoff rigidities (Rc) varies from 14–32 GV along 169 independent directions spanning a field of view of 2.3 sr. The threshold energy of the recorded muons is sec(θ) GeV along a direction with a zenith angle (θ) and with the average angular accuracy of ∼4σ. The directional capabilities of the muon telescope are exploited for studying the effect of atmospheric pressure on the muon flux as a function of Rc. It is observed that the barometric coefficients relationship with logarithmic Rc can be well described by second-order polynomial function with a high Spearman Rank correlation coefficient of 0.99.

The emerging class of MAX phases and corresponding MXenes offers a unique advantage of tunable surface functionalities, such as -O, -OH, and -F, which endow them with excellent electrochemical activity. This study focuses on the fluorination of the MAX phases and corresponding MXenes using an electrophilic fluorinating agent, Selectfluor (SF). The fluorination process was carried out to selectively fluorinate the MAX phase while minimizing etching effects, showcasing the distinct role of the electrophilic fluorine precursor over the conventional nucleophilic fluorinating agents. Intriguingly, the fluorinated MAX phase, with a fluorine content of 3.21 at%, demonstrated significantly enhanced electrochemical performance, exhibiting a two-fold increase in the specific capacitance compared to pristine MAX. Moreover, selective fluorination is further extended to MXene derivatives prepared through the conventional route. Using SF, we facilitated electrolyte-ion transport through the functionalized surface, resulting in an enhancement of ∼1400% in energy storage capacity after the fluorination of MXene. The observed improvement in the electrochemical performance can be attributed to the formation of electrochemically active Ti-F and C-F moieties at the surface as opposed to surface hydroxyls and oxidized MXene. The high electronegativity of fluorine atoms contributes to fast ion diffusion at the electrode surface, enhancing wettability and leading to superior electrochemical performance. As a result, our work introduces a novel and simple solution-based methodology for selectively fluorinating MAX phases and their MXene derivatives, unlocking their potential for enhanced electrochemical applications. This methodology can be extended to various MAX phases and their derivatives, offering precise control over the surface moieties in electrochemical systems where fine-tuning is essential for optimal performance. Overall, this study significantly contributes to advancing the understanding and utilization of fluorinated MAX and MXene materials in electrochemical energy storage and beyond.

Indolyl thioethers and indolin-2-one motifs are extremely common in pharmaceuticals and organic materials, therefore developing a method to create these scaffolds is considered to be a vital endeavour in the chemical sciences. Here we have reported a unified strategy developed by the fine-tuning of catalyst-solvent combination [SOCl2 /AlCl3 in CHCl3 and SOCl2/DMSO (1 : 1) in CHCl3 at 25 °C] towards selective functionalization of Indole to synthesize 2,2′-thiobisindoles and 3-chloro-3-alkyl substituted oxindoles selectively in one-pot manner with good to satisfactory yield (52-86 %; 26 Examples). In application, reactions of 3-subsituted indole and isatin derivatives produced the 1-(chloromethyl) indoline-2,3-diones by just changing the reaction condition (60 °C), which shows the synthetic utility of the developed method.