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Soon after realizing superbly important properties of few layer graphene and its derivatives, other layered materials have also received a great deal of interest in recent times, owing to their finite band gaps and layer-dependent optoelectronic responses. In this review, we discuss a variety of two-dimensional (2D) materials, highlighting fabrication routes already in practice and their technological relevance in a particular field, including photocatalysis, hydrogen evolution, sensing, actuation, and biomedical applications. Basically, layered materials processed via two widely accepted bottom-up and top-down approaches have been revisited. Because of large surface area, active reactive sites, tunable band gap etc., 2D systems are believed to deliberate their key performance in smart devices, from excellent electrodes to energy efficient candidates and from color switchable elements to high-precision biosensors. Given the importance of quality, reliability, and product cost realized in any commercial product, there exists ample scope to expand this frontier field of research for the benefit of society at large.

We report on the highly symmetric excitonic emission, manifested Raman active modes, and electrical properties of WSe2 and WS2 nanoflakes subjected to energetic β-particles. Raman spectra have revealed numerous mixed modes and a declining trend of the E12g-to-A1g intensity ratio with radiation dose (0–4.8 kGy). The nanoscale WSe2 exhibits a remarkable luminescence peak, located at ~ 675 nm and characterized by a combinatorial effect of both 2s and 2p excitons, whereas the nanoflakes of WS2 offered a testimony to charged excitons (trions) in the range ~ 624–630 nm. Moreover, a moderate (from ~ 2.29 to ~ 2.88 ns) and a nearly sevenfold enhancement in the slow life-time decay parameters have been observed for the irradiated WSe2 and WS2 nanoflakes, respectively. Furthermore, the rectifying nature of the I–V trends suggests formation of metal–semiconductor nanojunctions with transport characteristics described by parameters such as ideality factor (η) and barrier height (φb), both of which gave a declining trend with increasing β-dose. As substantiated by transport characteristics and first principle calculations, a semi-metallic behavior of WSe2 was also realized due to the introduction of excessive chalcogen defects at the highest radiation dose. The results would strengthen our insights prior to their deployment in next-generation nanodevices integrating nano-electronics and nano-photonics at large.

In the current research, we report on the synthesis of WO3/GQD system as a heterogeneous catalyst for the transesterification of waste cooking oil into biodiesel using methanol. The characterization of the prepared catalyst was done by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), energy-dispersive X-ray (EDX), Fourier transform-infrared spectroscopy (FT-IR) techniques, and Brunauer-Emmett-Teller surface area measurement. To study the effect of process variables such as methanol to oil ratio, reaction temperature, and time, we have employed response surface methodology (RSM) based on Box-Behnken design (BBD). The suitability of the predicted model was verified, and the average biodiesel yield of (96.8 ± 0.16%) was reported at optimal reaction condition of 1:6 oil to methanol ratio, 70 °C reaction temperature, 2 wt% catalyst loading, and 3.5 h reaction time. Biodiesel was characterized using proton nuclear magnetic resonance (1H NMR) and carbon nuclear magnetic resonance (13C NMR) techniques, and fatty acid methyl ester composition was determined using gas chromatography-mass spectrometry (GC-MS). Fuel properties of the biodiesel obtained comply with ASTMD6751 biodiesel standards. The kinetics of transesterification was studied and found to follow pseudo-first order. The results showed the rate constant ranging from 0.0028 to 0.007 min−1, activation energy (Ea) of 55.92 kJ mol−1, and frequency factor (A) of 1.72 × 106 min−1.

The effect of 80 keV Xe+ ion irradiation on the Raman spectra and electrical conductivity of 10B pencil-lead graphitic systems is being reported. The creation of localized nanoscale defects and a nearly five-fold improvement in the root mean square (RMS) roughness have been ascertained through atomic force microscopy (AFM) imaging studies. The introduction of defects is also substantiated by the appearance of the ∼1360 cm−1 peak (D-mode) along with the fundamental G-band (∼1600 cm−1) in the Raman spectra. With increasing fluence, the D-to-G band intensity ratio offered an increasing trend up to ∼0.44. Moreover, I–V characteristics indicated a significant drop in the conductivity of the irradiated graphitic systems. We ascribe it to substantial lowering of the mobility of the electrons owing to enhanced carrier-defect scattering events occurring in the irradiated systems. Mediated by defects introduced, a clear connection between the Raman characteristics and carrier transport phenomena is established.

This report describes a comparative study of dye degradation under 20-watt LED light using the perovskite photocatalyst Calcium Copper Titanate (CCTO) and its compositions (CaxCu3−xTi4O12) (x = 1, 1.5 and 2), synthesized by changing molar ratios of Ca2+ and Cu2+ ions. The 99.74% degradation of Rhodamine Blue (RhB) with composition (x = 1) within 6 h is reflected its better photocatalytic activity than the parent CCTO and other compositions. The band gap energy of the materials 2.18 eV (CCTO), 1.93 eV (x = 1), 2.40 eV (x = 1.5), and 2.55 eV (x = 2) are analysed with UV-Vis spectroscopy. The presences of Ca, Cu, Ti and O in the synthesized photocatalysts are confirmed with Elemental X-ray Dispersive (EDX) analysis. The cubic phases in the polyhedral shape of the materials are detected in X-ray diffraction and Scanning Electron Microscopy (SEM). This report further observes the defect density concentrations of the materials with Photoluminescence Spectroscopy (PL) and provides the approximate explanation of their dye degradation performance as photocatalysts. The rate constants are found in a first order reaction trend; where the composition (x = 1) shows about 1.683×10− 2 min− 1. The mechanistic understanding of the degradation process is also revisited and rationalized with different scavengers for the process.

We report on the collagenase activated progressive, yet spontaneous exfoliation of the stacked tungsten disulfide (WS2) system into a few-layer form via interface engineering and taking advantage of diffusion of hydronium ions (H3O+) through the interfaces. As evidenced from the Raman spectra, the apparent improvement of intensity ratio (E12g -to- A1g) from a value of 0.55 to 1.5, along with the evolution of (E12g+ LA), (A1g+ LA) modes have confirmed irreversible exfoliation of the stack of WS2 layers into its nano-dimensional form. Atomic force microscopy imaging confirms the exfoliation of WS2 system down to ten layers after eight days of continuous treatment with the super active biomolecules. The passage of H3O+ ions was believed to weaken the van der Waal forces between the WS2 layers and eventually cause impetuous exfoliation. The entropy change (ΔSt) during exfoliation and up to ten layers was predicted as, 1.83 ± 0.03 mJ m−2 K−1. The saturative trends of work accomplished and entropy change beyond six days of treatment indicate occurrence of complete exfoliation and with a high yield of nanoscale WS2. The scope of understanding the development of exfoliated layers linking diffraction, spectroscopic and imaging data is immensely beneficial for exploiting hybrid 2D nanostructures with suitable surface anchoring and designing miniaturized elements.

In this work, we report manifested optical, optoelectronic and spin–spin relaxation features of a few layered tungsten disulphide (WS2) nanosheets subjected to energetic γ-photons (∼1.3 MeV) emitted from a Co60 source. Upon intense irradiation (dose = 96 kGy), a slight departure from the pure hexagonal phase was realized with the introduction of the trigonal phase at large. Moreover, in the Raman spectra, as a consequence of the radiation-induced effect, an apparent improvement of the E-to-A mode intensity and a reduction in phonon lifetimes have been realized, with the latter being dependent on the linewidths. The emergence of the new peak (D) maxima observable at ∼406 cm−1 in the Raman spectra and ∼680 nm in the photoluminescence (PL) spectra can be attributed to the introduction of defect centres owing to realization of sulphur vacancies (V S) in the irradiated nanoscale WS2. Additionally, neutral exciton to charged exciton (trion) conversion is anticipated in the overall PL characteristics. The PL decay dynamics, while following bi-exponential trends, have revealed ample improvement in both the fast parameter (0.39 ± 0.01 ns to 1.88 ± 0.03 ns) and the slow parameter (2.36 ± 0.03 ns to 12.1 ± 0.4 ns) after γ-impact. We attribute this to the finite band gap expansion and the incorporation of new localized states within the gap, respectively. A declining exciton annihilation rate is also witnessed. The isotropic nature of the electron paramagnetic resonance spectra as a consequence of γ-exposure would essentially characterize a uniform distribution of the paramagnetic species in the system, while predicting a three-fold improvement of relative spin density at 96 kGy. Exploring defect dynamics and spin dynamics in 2D nanoscale systems does not only strengthen fundamental insight but can also offer ample scope for designing suitable components in the areas of miniaturized optoelectronic and spintronic devices.