Thermoelectrics are energy harvesters that can directly convert waste heat into electrical energy and vice versa. Currently, thermoelectric (TE) devices display lower efficiency as the materials used for construction possess a very low figure of merit (ZT). Therefore, understanding the structural features of materials, finding new materials, and analyzing their chemistry and physics play a vital role in enhancing their energy conversion efficiency. Among the different classes of TE materials, some inorganic chalcogenides are perfect candidates for power generation as they possess excellent TE properties. The objective of this review is to provide insights into structural features and innovative methods to obtain enhanced thermoelectric properties of selected inorganic chalcogenides. The review covers recent advances in preparation methods, structural features, and thermoelectric properties of selected metal selenides (Bi2Se3, Ag2Se, SnSe, etc.) and metal tellurides (Bi2Te3, SnTe, PbTe, etc.). The review also discusses the critical parameters for designing and optimizing the TE materials to obtain the required electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (k). In addition, promising mechanistic approaches to be adopted for enhancing the efficiency of TE materials such as doping, alloying, and nanostructuring are discussed in detail. Finally, a summary that describes advancements in the materials design is provided with a prospect for future applications from these materials in the development of energy harvesting technology.

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The grape extract is a potential natural reducing agent because of its high phenolic content. The extracts of seeds, skin, and pulp of grape were prepared by digestion, grinding, and soxhlet methods and used for reducing graphene oxide (GO). The reduced GO made using the soxhlet extract of grape seed (GRGO) was hydrothermally treated with titanium dioxide (TiO 2 ) for the synthesis of GRGO–TiO 2 nanocomposite. The X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), UV–vis, photoluminescence, and Raman spectra studies further confirmed the formation of GRGO and the GRGO–TiO 2 hybrid. Scanning electron microscope and transmission electron microscope studies showed the decoration of spherical TiO 2 particles (<100 nm) on the few-layered GRGO sheets. The GRGO–TiO 2 hybrid was explored as a working electrode for supercapacitors and visible light photocatalyst for water decontamination. GRGO–TiO 2 showed higher specific capacitance (175 F g –1 ) than GRGO (150 F g –1 ) and TiO 2 (125 F g –1 ) in an aqueous electrolyte. GRGO–TiO 2 exhibited 83.6% capacitance retention even after 2000 cycles, indicating the good stability of the material. Further, under visible light irradiation (λ > 400 nm), GRGO–TiO 2 showed ∼30% higher photo-oxidation of the bromophenol blue (BPB) dye than TiO 2 . Also, GRGO–TiO 2 decreased the total organic carbon content of BPB from 92 to 18 ppm. Overall, the soxhlet extract of grape seed was found to be a cost-effective reducing agent for the preparation of GRGO, which is a suitable material to be used in supercapacitors and photocatalysis.

Two-dimensional nanostructures have gained tremendous interest in the field of biomedical applications and cancer activity in particular. Although sulfur is known for its wide range of biological activities, its potentiality in two-dimensional forms as an antitumor agent is hitherto unexplored. To address the current deficient knowledge on nano-sulfur as an antitumor agent, we report the synthesis of nano-sulfur sheets/particles and their cytotoxic, apoptotic activity against human carcinoma cell lines. In vitro cytotoxic effects of biogenic nanosheets (SNP-B) and chemogenic nanoparticles (SNP-C) were assessed against human lung carcinoma (A549), human epidermoid carcinoma (A431), human promyelocytic leukaemia (HL60) and human lung fibroblast (IMR90) cell lines. Cell cycle analysis, apoptotic study, and caspase-3 expression studies were carried out to understand the mechanism of cytotoxic activity of nano-sulfur. The MTT assay indicated a dose-dependent decrease in viability of all the cell lines treated with nano-sulfur, with SNP-B being more toxic compared to SNP-C. The apoptotic study and cell cycle analysis indicated cell cycle arrest followed by apoptosis-induced cell death. The caspase-3 expression study indicated that nano-sulfur induces apoptosis by the activation of caspase through the mitochondrial pathway. Apart from this, a lower cytotoxicity was observed in IMR90 cell lines treated with SNP-B , indicating a higher specificity of synthesized nanosheets towards cancer cells. Taken all together, this work highlights the potentiality of sulfur nanosheets in inducing cytotoxicity and apoptotic activity, and the impact of morphology as a critical determinant on the cytotoxic response on various cell lines.

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