Nanomaterials

Paper-supported noble metal catalysts represent an attractive platform for the development of reusable and easily recoverable heterogeneous catalytic systems. In this work, gold, palladium and platinum nanoparticles were directly grown onto cellulose filter paper through a simple one-step in situ deposition-reduction method. Metal ions were first adsorbed onto the paper fibers and subsequently reduced with sodium borohydride, yielding uniformly decorated catalytic papers. Transmission and scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the formation of metallic nanoparticles distributed across the cellulose network. Inductively coupled plasma analysis revealed that metal loading depends mainly on precursor concentration, whereas immersion time has a negligible influence on catalyst incorporation. The catalytic performance of the materials was evaluated using the model reduction in p-nitrophenol to p-aminophenol in the presence of sodium borohydride. All systems exhibited pseudo-first-order kinetics, and the reaction rate increased with the number of catalytic papers employed. Turnover frequency analysis demonstrated that palladium-based papers display the highest catalytic activity, followed by platinum and gold. The catalysts showed good stability and recyclability, remaining active after five consecutive reaction cycles, although a small decrease in catalytic performance was observed. In addition, the metal-decorated papers exhibited peroxidase-like nanozyme activity in the H₂O₂-mediated oxidation of tetramethylbenzidine, again following the activity order Pd > Pt > Au. The combination of simple preparation, efficient catalytic performance, reusability and enzyme-mimicking behavior highlights the potential of noble metal-decorated paper substrates as versatile platforms for heterogeneous catalysis, sensing and bioanalytical applications.

Nanoporous anodic aluminum oxide (AAO) photonic crystals (PhCs) offer a versatile platform for controlling light propagation, but precisely positioning their photonic band gap (PBG) when the pores are filled with a liquid remains a challenge. Anodizing with voltage modulated as a function of optical path length, U(L), enables control PBG position, yet its accuracy has been demonstrated only for air-filled pores. Extending this control to other pore-filling media is important for applications such as sensing and photocatalysis. Here, we determine the key model parameters experimentally, including the pore wall refractive index and its dependence on porosity, rather than relying on assumed literature values. We use this framework to adapt the U(L) method to anodizing in 2 M NaHSO₄ at 20 °C, providing a faster alternative to low-temperature anodizing in H₂SO₄. The resulting one-dimensional (1D) AAO PhCs exhibit PBG positions within 1% of the target values for both air- and water-filled pores. PBG tuning over 250–2000 nm is demonstrated for air-filled pores, while the synthesis time is reduced to 4 h, up to fourfold shorter than in the previously reported process. These results connect experimentally measured material properties with precise optical design for operation in different pore-filling media.

Ultrasound has become a pioneering, efficient, and economical technology for nanomaterial fabrication, revolutionizing materials nanoscience. Ultrasound enhances mass and heat transfer through acoustic cavitation and mechanical vibrations, enabling shorter synthesis times and diverse structures. As a nonthermal method, ultrasound preserves the physical and chemical properties of materials, making it a greener alternative to conventional processing. Surface-enhanced Raman scattering (SERS) has broad potential for environmental, materials, food, and biomedical analysis. SERS is highly sensitive and provides unique molecular fingerprints, enabling miniaturized, integrated, high-throughput sample control. Ultrasonication-assisted fabrication of gold- and/or silver-based hybrid SERS substrates leverages the self-assembly of plasmonic noble metals (Au and Ag), generating numerous “hot spots” in structural substrates; these channels are promising for enhancing detection sensitivity. Environmental pollutants (e.g., pesticides, micro- or nano-plastics) harm ecosystems and threaten human and wildlife health and life, so monitoring these hazardous chemicals is essential. This review comprehensively summarizes the latest updates on well-established Au- and/or Ag-based hybrid SERS substrates for monitoring hazardous chemicals and key progress in their development under ultrasonication-assisted synthesis. It also describes the challenges encountered and future directions for development. This detailed overview is designed to support scholars and professionals working toward breakthroughs in ultrasound-assisted SERS monitoring for environmental protection.