Global consumption and discharge of palladium (Pd) have raised environmental concerns but also present an opportunity for the sustainable recovery and reuse of this precious metal. Adsorption has proven to be an efficient method for the selective recovery of Pd from industrial wastewater. This study investigated a hydrazone-linked covalent organic framework (Tfpa-Od COF) as a potential material for the high-affinity adsorption of Pd²⁺ ions from wastewater, achieving a K_d value of 3.62 × 10⁶ mL g^-1. The electron-rich backbone of the COF contributes to its excellent selective removal efficiency (up to 100%) and adsorption capacity of 372.59 mg g^-1. Furthermore, the Pd-adsorbed COF was evaluated as a sustainable catalyst for the Suzuki-Miyaura coupling reaction, demonstrating good catalytic conversion and recyclability. This work attempts to showcase a protocol for reusing waste palladium generated in water to fabricate heterogeneous catalysts and, thereby, promote the circular economy concept.

We report on a hydrothermal synthesis of hexagonal ultra-thin Bi₂Se₃ platelets, which was performed without any organic reactants. The synthesis resulted in the particles with a surface, clean of any organic adsorbents, which was confirmed with a high-resolution transmission electron microscopy, zeta-potential measurements and thermogravimetric measurements coupled with a mass spectroscopy. Due to the absence of the adsorbed organic layer on the Bi₂Se₃ platelet surface, we were able to measure their inherent surface and optical properties. So far this has not been possible as it has been believed that such hexagonal Bi₂Se₃ platelets can only be prepared by a solvothermal synthesis, for which it was unable to avoid the organic surface layer. Here we explain the mechanism behind the successful hydrothermal synthesis and show a striking difference in zeta potential behaviour and UV-vis absorption characteristics caused by the adsorbed layer. The surface of the hydrothermally synthesized Bi₂Se₃ platelets was so clean to enable the occurrence of the localized surface plasmon resonance due to the bulk and topological surface electronic states.

A sustainable nexus between renewable energy production and plastic abatement is imperative for overall sustainable development. In this regard, this study aims to develop a cheaper and environmentally friendly nexus between plastic waste management, wastewater treatment, and renewable hydrogen production. Fluorescent carbon (FCs) were synthesized from commonly used LDPE (low-density polyethylene) by a facile hydrothermal approach. Optical absorption study revealed an absorption edge around 300 nm and two emission bands at 430 and 470 nm. The morphological analysis showed two different patterns of FCs, a thin sheet with 2D morphology and elongated particles. The sheet-shaped particles are 0.5 μm in size, while as for elongated structures, the size varies from 0.5 to 1 μm. The as-synthesized FCs were used for the detection of metal ions (reference as Cu²⁺ ions) in water. The fluorescence intensity of FCs versus Cu²⁺ ions depicts its upright analytical ability with a limit of detection (LOD) reaching 86.5 nM, which is considerably lesser than earlier reported fluorescence probes derived from waste. After the sensing of Cu²⁺, the as-obtained FCs@Cu²⁺ was mixed with TiO₂ to form a ternary FCs@CuO@TiO₂ composite. This ternary composite was utilized for photocatalytic hydrogen production from water under 1.5 AM solar light irradiation. The H₂ evolution rate was found to be ~1800 μmolg⁻¹, which is many folds compared to the bare FCs. Moreover, the optimized FCs@CuO@TiO₂ ternary composite showed a photocurrent density of ~2.40 mA/cm² at 1 V vs. Ag/AgCl, in 1 M Na₂SO₄ solution under the illumination of simulated solar light. The achieved photocurrent density corresponds to the solar-to-hydrogen (STH) efficiency of ~0.95%. The efficiency is due to the fluorescence nature of FCs and the synergistic effect of CuO embedded in TiO₂, which enhances the optical absorption of the composite by reaching the bandgap of 2.44 eV, apparently reducing the recombination rate, which was confirmed by optoelectronic, structural, and spectroscopic characterizations.

Localized surface plasmon resonance (LSPR) is the cause of the photo-thermal effect observed in topological insulator (TI) bismuth selenide (Bi₂Se₃) nanoparticles. These plasmonic properties, which are thought to be caused by its particular topological surface state (TSS), make the material interesting for application in the field of medical diagnosis and therapy. However, to be applied, the nanoparticles have to be coated with a protective surface layer, which prevents agglomeration and dissolution in the physiological medium. In this work, we investigated the possibility of using silica as a biocompatible coating for Bi₂Se₃ nanoparticles, instead of the commonly used ethylene-glycol, which, as is presented in this work, is not biocompatible and alters/masks the optical properties of TI. We successfully prepared Bi₂Se₃ nanoparticles coated with different silica layer thicknesses. Such nanoparticles, except those with a thick, ≈200 nm silica layer, retained their optical properties. Compared to ethylene-glycol coated nanoparticles, these silica coated nanoparticles displayed an improved photo-thermal conversion, which increased with the increasing thickness of the silica layer. To reach the desired temperatures, a 10–100 times lower concentration of photo-thermal nanoparticles was needed. In vitro experiments on erythrocytes and HeLa cells showed that, unlike ethylene glycol coated nanoparticles, silica coated nanoparticles are biocompatible.

Glucose serves as a key biomarker of metabolic health, requiring continuous and reliable monitoring. Nonenzymatic impedimetric sensors have emerged as a promising alternative to enzymatic glucose sensors, which dominate current clinical practice. However, their sensitivity is limited by weak molecular recognition and inefficient charge transport at the sensing interface. In this study, we tuned the core flexibility and curvature of azine-linked covalent organic frameworks (COFs) by substituting the central triazine ring in the C₃ symmetric building unit with a nitrogen atom. This modification maximized glucose-framework interactions, thereby enhancing signal transduction and detection sensitivity. The results confirmed the sensitivity and selectivity of the COFs toward glucose, with a linear response over a wide concentration range [1 aM-5 mM], surpassing previously reported glucose sensors. The sensors achieved a subattomolar limit of detection (LOD), with excellent stability and reproducibility compared to traditional enzymatic sensors, offering a simpler and more practical alternative for integration into wearable and implantable devices. Experimental findings are supported by molecular simulations, which reveals the mechanism of sensing and charge transfer dynamics. This work establishes a versatile design strategy for enzyme-free designed-to-purpose transducers, opening new pathways for ultrasensitive and selective molecular detection.