Liquid phase exfoliation of MoSe2: Effect of solvent on morphology, edge confinement, bandgap and number of layers study

In this study, a facile and scalable method for synthesizing MoSe2 nanomaterial via a sonication-assisted liquid-phase exfoliation method is proposed. This study shows the successful synthesis of few-layered MoSe2 in various solvents including DI water, ethanol, N-Methyl-2-pyrrolidone (NMP), Dimethylformamide (DMF) and Dimethylsulfoxide (DMSO). The exfoliated nanosheets have remarkably different properties than bulk MoSe2 which were studied using Field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and UV-Vis spectroscopy to investigate their morphology, functional groups, structure and optical properties, respectively. The mean values of the number of layers from an optical extinction spectrum based on the effect of edge and quantum confinement were also calculated. Moreover, the exfoliated material using this method has potential application in energy storage as demonstrated by the electrochemical performance of the bulk and exfoliated materials.•Successful synthesis of the few-layer MoSe2 from bulk MoSe2 using liquid phase exfoliation method in various solvents•The investigation of the effect of solvent on the number of layers and optical properties of MoSe2.

MoSe2-modified ZIF-8 novel nanocomposite for photocatalytic remediation of textile dye and antibiotic-contaminated wastewater

COVID-19-led antibiotic waste generated from hospitals and health centres may cause serious health issues and significantly impact the environment. In the coming decades, antibiotic resistance will be one of the most significant threats to global human health. Photocatalytic water remediation is an effective and promising environmental solution that can be utilized to address this issue, to convert antibiotic waste into non-toxic products by utilizing renewable and abundant solar energy. In the present study, a novel nanocomposite of zeolitic imidazolate frameworks (ZIF-8) and molybdenum diselenide (MoSe₂) was efficiently synthesized by the solvothermal method for the complete degradation of the antibiotics and textile waste from water. The morphology, crystallinity and band gap of the samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and UV-visible spectroscopy. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) provide the binding information of the sample. The photocatalytic activity was tested for degradation of the antibiotics (tetracycline hydrochloride (TC) and metronidazole (MNZ)) used in COVID-19 treatment and textile dye (malachite green). Time-resolved photoluminescence spectroscopy confirmed the enhanced charge separation in the MoSe₂@ZIF-8 nanocomposite with an average lifetime of 4.72 ns as compared to pristine samples. The nanocomposite showed ~ 100% removal efficiency with rate constants of 63 × 10^-3, 49 × 10^-3 and 42 × 10^-3 min^-1 for TC, MNZ and malachite green, respectively. The photocatalytic degradation of TC was carried out under different pH conditions (4, 7 and 9), and the degradation mechanism was explained on the basis of zeta potential measurements and active species trapping experiment. The by-products of the photocatalytic treatment of TC antibiotics were tested using liquid chromatography-mass spectroscopy (LC-MS), and they were found to be non-toxic for aquatic and human life. The regeneration property of the nanocomposite was confirmed by FESEM with regeneration efficiency of 88.7% in the 4th cycle. Thus, MoSe₂@ZIF-8-based photocatalysts have potential application in water remediation, especially in making the antibiotic waste less toxic.

A source and ground motion study of earthquakes in and near Delhi (the National Capital Region), India

We study source parameters of 10 local earthquakes (2.7 ≤  M w ≤ 4.5) that have occurred in the National Capital Region (NCR) since 2001 and the ground motions produced by these events. Moment rate spectra of the earthquakes retrieved from the recordings at hard sites after applying corrections for geometrical spreading (1/R, R ≤ 100 km), anelastic attenuation (Q = 253f ^0.8) and cutoff frequency (f _m = 35 Hz) are reasonably well fit by the Brune ω ²-source model with stress drop ranging between 0.9 and 13 MPa. Neglecting the outlier low-stress drop value, the average stress drop is 6 MPa. We apply a modified standard spectral ratio technique to estimate site effect at 38 soft sites in the NCR as well as the geometrical mean site effect with respect to a reference hard site. Application of the stochastic method, with source characterized by the Brune ω ²- model with stress drop of 6 MPa and the mean site effect for soft sites, yields peak horizontal ground acceleration and velocity curves that are in good agreement with the observed values. These results provide the parameters needed for the application of the stochastic method to predict ground motions at hard and soft sites in the NCR during postulated M w ≤ 5.5 earthquakes.

Nanosheets- and nanourchins-like nanostructures of MoSe2 for photocatalytic water purification: kinetics and reusability study

In this paper, we are reporting a simple hydrothermal technique for preparation of MoSe₂ nanostructures (nanourchins and nanosheets) using selenium and sodium molybdate as precursors. Samples are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, UV-Vis spectroscopy, Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS). The FESEM revealed that the morphology of materials was varying significantly by changing pH value during synthesis. Photocatalytic degradation of anionic dye (MO), cationic dye (MB), and reduction of Cr(VI) into Cr(III) were performed. Nanosheets and nanourchins showed higher photocatalytic activity, enhanced photocatalytic degradation efficiency is correlated with the higher ^•OH radical concentration, crystallinity of material, and large surface area as evident through XPS, XRD, and BET, respectively. Photocatalysis mechanism along with role of reactive species (^•OH and holes) were explained using trapping experiments. Identification of degraded products was carried out using high-performance liquid chromatography (HPLC). Reaction kinetics and reusability of materials were also studied; wherein, it was observed that the materials have reusable properties.

Biosorption potential of Gum ghatti-g-poly(acrylic acid) and susceptibility to biodegradation by B. subtilis

This article reports the biosorption potential of Gum ghatti (Gg)-grafted-acrylic acid (AA) polymer and its susceptibility to biodegradation by Bacillus subtilis (BS) in two different liquid media, i.e. phosphate buffered saline (PBS) and mineral salt medium (MSM). The progress of biodegradation was monitored after every 15 days using FT-IR and SEM techniques. The degradation of the polymer was further evidenced by a loss of weight of 23.2% and 27% in BS-MSM and BS-PBS, respectively, after 60 days. The AA-grafted polymer was then utilized for the removal of Pb(II) and Cu(II) from aqueous solution. The adsorption isotherm data were studied using Langmuir, Freundlich, Temkin, Flory-Huggins and Dubinin-Kaganer-Radushkevich isothermal models. High values of correlation coefficients confirmed the applicability of Langmuir isotherm model used to determine the adsorption capacity of the AA-grafted polymer. The maximum adsorption capacity was found to be 84.74 mg/g for Cu(II) and 310.55 mg/g for Pb(II). Kinetic data were evaluated using pseudo first order, pseudo second order, Elovich, intraparticle diffusion and liquid film diffusion models. The experimental kinetic data fitted well with the pseudo second order rate model.