Rupali Nagar

Titanium dioxide (TiO2) is a commercially and widely used gas sensing material. Here, TiO2 nanoparticles (TNPs) are first synthesized using the sol-gel method (as-synthesized, T1). The samples are heated in an air environment at 400 °C and then allowed to cool (to room temperature, T2) or quenched to different final temperatures (ice @ -4 °C, T3 and liquid nitrogen i.e. LN2 @ -196 °C, T4) to initiate thermally induced microstructural changes. These thermally treated TNPs are then evaluated for their gas sensing performance by testing them against ethanol vapours (1-6 ppm). The response and recovery times are measured to be ~ 5.7 s and 7 s, respectively for 6 ppm ethanol under ambient conditions for LN2 quenched sample. However, the best response and recovery times are measured as 1.3 s and 3.7, s respectively for 4 ppm ethanol. Interestingly, while T1, T2, and T3 samples exhibited p-type behaviour upon ethanol exposure, T4 showed n-type behaviour. Crystallite size, porosity, oxygen vacancies, band gap changes and the presence of functional groups are understood to be important attributes influencing the sensor performance. This work demonstrates that cryogenic quenching can be a simple, effective strategy to control conduction type, charge carrier dynamics, and gas sensing performance offering a route for high-performance, selective and tunable ethanol sensors. A switch from p- to n–type conduction in the same material demonstrated here opens various avenues like dual-mode sensing, homojunction sensing and highly tunable sensor design.

Modern Internet of Things (IoT) and Intelligent Internet of Things (IIoT) may involve integrating optical photodetector-based sensing for their operation in future. In this work, iron oxide nanorods (IONRs) have been synthesized that exhibit photosensing in a broad (UV to visible) range discusses phototransients that can act as spurious signals. Results show that the nature of transients is wavelength dependent with distinct dynamics: visible (red and green) light yields faster response than UV, while green produces periodic modulations. A 5–10 s delay between UV and visible response exists. While UV photoresponse shows slower growth, visible light response shows a faster but decay-like behavior. The theoretical modeling of the photocurrent’s decay curve yields two different lifetimes (∼ ms and s) suggesting two different mechanisms. While visible photons can transport electrons via surface hydroxyl groups or surface states, UV photons facilitate ionic conduction through inverse spinel lattice of IONRs and green photons show fluctuating defect-mediated response. The electrochemical impedance spectroscopy (EIS) is used to validate the above results. EIS, Nyquist and Bode plots confirm different charge carrier types, transport behavior and time domains. The EIS study strengthens the mechanism that electron conduction via surface hydroxyl groups contributes to faster conduction process and the ionic movement (Fe ^+2/+3 ) within the inverse spinel lattice is slower of the two processes. The 5–10 s delay in UV/visible light irradiation points to a critical vulnerability-window which can compromise the sensor reliability by missing a red/ green trigger or misinterpreting a UV trigger. Thus, in-operando transient analysis is crucial for evaluating material response and designing robust, wavelength-selective photodetectors for emerging IoT and IIoT technologies.

This study investigates ethanol sensing properties of a hybrid sensing material prepared by mechano-mixing of tin oxide (SnO₂) quantum dots (SQDs) and template-free graphitic carbon nitride (g-C₃N₄) i.e. TGCN nanosheets (TNSs). Hybrid sensors comprising of various weight ratios of TNSs and SQDs ranging from 1:5 to 1:50 (T-SX where X denotes the proportion of SQDs) were prepared and tested for ethanol vapor sensing under ambient conditions. Structural, thermal, optical, and morphological properties of the hybrid samples were analyzed comprehensively using techniques such as x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and Raman microscopy. The results indicate that the SQDs crystallize in rutile crystal structure with an average diameter of ∼ 2.7 nm and are dispersed on the TNSs. The best response and recovery time were observed for T-S20 with a fast response time of 12 ± 3 s and recovery time of 20 ± 3 s under ambient conditions. The hybrid sensor showed a 48% faster response time, and 57% faster recovery time as compared to pure quantum dots. This improvement is attributed to dispersed SQDs on TNSs, optimum bond strength between SQDs and TNSs, surface plasmon states of SQDs, higher surface area of TNSs, catalytic activity of N-atoms and finally the heterojunction formed between SnO₂ quantum dots and TNSs which attracts bipolar hyroxyl group of ethanol vapors under ambient conditions and aids in their faster detection.

This review is focused on the topical developments in the synthesis of nanocomposites using the simplest top-down approach, mechanochemical milling, and the related aspects of the interfacial interactions. Milling constraints include time duration of milling, ball size, the ball-to-sample content proportion, rotation speed, and energy that took part in a vital part of the structure–property relationships and composite interactions. Milled nanocomposites are being used in different structural applications for their higher performance rate and throughput. The synthesis of different nanocomposites and the effect of various parameters on the mill-ability of nanocomposites are discussed. Moreover, some of the major advancements in the energy sector are discussed in the latter part of the review.