Suresh Kumar Megarajan

Solar-driven evaporation based on photothermal membrane has been proved to be promising in the field of fresh water generation, and it is considered as an emerging strategy both in laboratory and in industrial scales. However, further research efforts have to be made on light harvesting and thermal management to improve water evaporation. In this study, an extensive research was carried out to develop a bio-inspired 3D photothermal cone for high-efficiency solar-driven evaporation with minimum light reflection and heat loss to bulk water. The artificial photothermal cone with a polypyrrole (PPy) coating layer was facilely fabricated via chemical vapor deposition polymerization (CVDP). The present 3D cone with a rationally designed conical structure exhibited satisfactory absorbance around 99.2% in the entire solar spectrum, which is comparable with the performances of super-black materials. Additionally, the heat loss has been minimized by elevating the photothermal cone to narrow the contact area between water and the PPy-based cone with good wettability, thus achieving a highly efficient interface heating. The solar conversion efficiency up to 93.8% for evaporation was achieved for the photothermal cone under one sun illumination, which is about 1.7 times as high as the result obtained for a plane film. Based on our results, controlling the 3D morphology can be considered as an important strategy for designing a novel high-efficiency photothermal membrane and also, it provides new opportunities in practical application.

Solar-driven water evaporation assisted by photothermal membranes is considered as one of the sustainable and cost-effective strategies for pure water generation and wastewater treatment. Herein, we report a facile but effective approach to improve the photothermal performance by combining 2D reduced graphene oxide (rGO) and 1D multi-walled carbon nanotubes (MWCNTs), which have different nanomorphologies. The photothermal layer can be easily deposited on different substrate materials via simple vacuum assistance. Such a composite photothermal layer shows a rough surface with a controllable nano-structure, which can thus optimize solar light harvesting. On the other hand, the formation of a loose internal porous structure and suitable wettability ensure water transport inside the photothermal layer during evaporation. The surface temperature reaches as high as 78 °C even under one sun irradiation (1 kW m⁻²), which is 10 °C higher than the result of pure rGO membranes. When loaded on a PVDF substrate, the rGO–MWCNT based membrane is flexible and shows an obvious improvement in the evaporation rate, about 79.0% and 8.9% higher than those of pure rGO and MWCNT membranes, respectively. The solar thermal conversion efficiency can reach up to 80.4% without any extra accessory for thermal management. Based on our results, the nanocomposite strategy is facile and effective for the development of novel photothermal membranes for high-efficiency evaporation, and contributes to the widespread application in the fields of desalination and wastewater treatment.

Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N2O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications.

A novel and simple hydrothermal synthesis method using metal cyano complex precursors was demonstrated to synthesize nano-sized PrCoO₃ and PrFeO₃ perovskites. It was possible to achieve significantly improved catalytic properties, but more importantly with thermal stability and purity of perovskite phases in their nanoparticle form. These materials were characterized by means of X-ray powder diffraction, FE-SEM, HR-TEM as well as H₂-TPR analysis, and evaluated for their catalytic activity towards CO oxidation reaction. Both the nanoperovskites were able to retain their morphology achieved through hydrothermal treatment, even after high temperature calcination. The catalytic activity of these materials was also compared with conventionally synthesised materials using a solid state method, as well as those reported in the literature. The superior catalytic activity of the PrCoO₃ catalyst for CO oxidation over the PrFeO₃ catalyst is mainly because of its better redox properties and may also be due to preferential adsorption of CO on PrCoO₃ perovskite at low temperature. However, the marked improvement in catalytic activity for both nanoperovskites was primarily due to their improved surface area and better reducibility, which can be attributed to their nanoform. It appears possible to control the particle size as well as the shape of perovskites using this improved synthesis method, while more importantly, it was possible to reduce sintering and agglomeration of perovskites. While the method has potential to apply for synthesis of several other mixed oxide materials in nanoform, it will be important to investigate other physical properties of such thermally stable nanoperovskites.