Rajesh Kumar

The ubiquitous presence of microplastics in the environment has raised serious environmental and health concerns. These tiny plastic particles can enter the food chain, posing a significant threat to human health. Researchers worldwide have focused their efforts on developing strategies to mitigate microplastic pollution. This review focuses on the potential of nano/microstructured metal oxide semiconductors as effective photocatalysts for microplastic degradation. The review is divided into two sections: static metal oxides and dynamic micromachines based on metal oxides. The modifications made to nano/microstructured metal oxides such as TiO₂, ZnO, bismuth oxyhalides (BiOX), NiO, Cu₂O/CuO, perovskite‐like Bi₂WO₆, Fe₃O₄, etc., to enhance their degradation efficiency are thoroughly discussed and reviewed. Additionally, the photocatalytic pathways for the conversion of microplastics into C₂ fuel and other value‐added products are also elaborated. The current developments in the realm of dynamic, self‐propelled, and controlled micromotors for the photodegradation of microplastics are also highlighted. The review concludes by proposing future perspectives and challenges to facilitate the remediation of microplastics in water and wastewater systems in a more effective, scalable, and environmentally friendly manner. Overall, the review emphasizes the potential of photocatalysis using nano/microstructured metal oxide semiconductors as an eco‐friendly and promising approach for microplastic degradation.

CdO-ZnO nanocomposites were synthesized using a simple solution approach, and several characterization approaches were used to examine the morphological, structural, phase, vibrational, optical, and compositional properties of these CdO-ZnO nanocomposites. The FESEM study revealed the development of aggregates ranging in size from 250 nm to 500 nm. These aggregates were composed of various CdO-ZnO nanoparticle shapes and sizes. XRD investigation revealed hexagonal wurtzite and cubic phases in ZnO and CdO, respectively. The crystal size was 28.06 nm. The band-gap energy of the produced nanocomposites was calculated using UV-Vis analysis and was determined to be 2.55 eV. The CdO-ZnO nanocomposites were employed as a promising material for the effective fluorescence detection of hydrazine and for the quicker photocatalytic degradation of Rhodamine B (RhB) dye. Within 120 min of UV light exposure, the RhB dye was 87.0% degraded in the presence of the CdO-ZnO nanocomposites and the degradation process followed zero-order and pseudo-first-order kinetics. Based on 3σ IUPAC criteria, the limit of detection for fluorescent hydrazine sensing was 28.01 µM. According to the results presented here, CdO-ZnO nanocomposites may function as both a photocatalyst for the breakdown of organic pollutants as well as an effective luminous sensor for the detection of harmful analytes.

Herein, a simple, economical and low temperature synthesis of leaf-shaped CuO nanosheets is reported. As-synthesized CuO was examined through different techniques including field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), fourier transform infrared spectroscopic (FTIR) and Raman spectroscopy to ascertain the purity, crystal phase, morphology, vibrational, optical and diffraction features. FESEM and TEM images revealed a thin leaf-like morphology for CuO nanosheets. An interplanar distance of ~0.25 nm corresponding to the (110) diffraction plane of the monoclinic phase of the CuO was revealed from the HRTEM images XRD analysis indicated a monoclinic tenorite crystalline phase of the synthesized CuO nanosheets. The average crystallite size for leaf-shaped CuO nanosheets was found to be 14.28 nm. Furthermore, a chemo-resistive-type gas sensor based on leaf-shaped CuO nanosheets was fabricated to effectively and selectively detect H₂S gas. The fabricated sensor showed maximum gas response at an optimized temperature of 300 °C towards 200 ppm H₂S gas. The corresponding response and recovery times were 97 s and 100 s, respectively. The leaf-shaped CuO nanosheets-based gas sensor also exhibited excellent selectivity towards H₂S gas as compared to other analyte gases including NH₃, CH₃OH, CH₃CH₂OH, CO and H₂. Finally, we have proposed a gas sensing mechanism based upon the formation of chemo-resistive CuO nanosheets.

Herein, we report a chemi-resistive sensing method for the detection of formaldehyde (HCHO) gas. For this, α-MnO₂ nanowires were synthesized hydrothermally and examined for ascertaining their chemical composition, crystal phase, morphology, purity, and vibrational properties. The XRD pattern confirmed the high crystallinity and purity of the α-MnO₂ nanowires. FESEM images confirmed a random orientation and smooth-surfaced wire-shaped morphologies for as-synthesized α-MnO₂ nanowires. Further, the synthesized nanowires with rounded tips had a uniform diameter throughout the length of the nanowires. The average diameter of the α-MnO₂ nanowires was found to be 62.18 nm and the average length was ~2.0 μm. Further, at an optimized temperature of 300 °C, the fabricated HCHO sensor based on α-MnO₂ nanowires demonstrated gas response, response, and recovery times of 19.37, 18, and 30 s, respectively.