Alessandro Ciccone

Lead-free halide nanocrystals have emerged as a sustainable alternative to lead halide perovskites materials; owing to their strong light absorption, low-toxicity and optimal bandgap for visible light driven applications. Herein, we aim to broaden the application of benzoyl bromide as Br-source in a modified hot-injection protocol for the synthesis of colloidal Cs3Bi2Br9 nanocrystals (cCBB NCs). Moreover, for comparative purposes CBB NCs incorporated into the mesoporous silica SBA-15 were prepared. The photocatalytic performance of both systems was evaluated using the degradation of cationic organic dyes, such as methylene blue (MB) and rhodamine B (RhB), as model reactions. Notably, complete dye degradation was achieved at very short irradiation times, ca. 300 s for RhB in both colloidal and supported systems, the fastest rate reported up to now, mediated predominantly by anion superoxide as selective oxidizing agent. However, in the case of MB, its strong binding to CBB surface and incorporation into the SBA-15 pores limit the photodegradation process, which is proposed to occur via direct charge transfer and anion superoxide formation. This work highlights the importance of the CBB synthetic procedure and the dye adsorption behavior on the NCs surface or into the silica pores in determining the photocatalytic activity of bismuth halide NCs.

Carbon-based nanomaterials have attracted tremendous interest as metal-free fluorophores and photocatalysts due to their unique optoelectronic properties and (photo)stability. Herein, we report the ultrarapid (75 s) microwave-assisted synthesis of two distinct carbon-based materials using benzoic acid (BA) as the sole precursor. Comprehensive structural and spectroscopic characterization allowed the identification of graphene quantum dots (GQDs) and turbostratic carbon (TC) formed simultaneously. The GQDs (average size of 6.5 nm) exhibit excitation-independent green emission with a photoluminescence quantum yield of 11%, show excellent cytocompatibility toward HaCaT cells at concentrations up to 10 μg·mL−1, and potential selective toxicity toward skin cancer cells. In contrast, the TC demonstrates efficient visible-light photocatalytic activity for the photoreduction of methyl viologen (MV2+) to MV•+, maintaining activity over at least four consecutive cycles, thus evidencing its performance as a robust carbon-based photocatalyst for electron−transfer reactions. Overall, this work presents an eco-friendly and fast synthetic strategy to obtain two structurally and functionally distinct carbon nanomaterials with potential for biological and visible-light photocatalytic applications, respectively.