Ivano Alessandri

The transition toward sustainable energy systems requires advanced catalytic technologies capable of efficiently converting solar energy into chemical fuels. In this Perspective, we critically examine the emerging role of nanophotonics in overcoming the intrinsic limitations of conventional photocatalysis, particularly the trade-off between light absorption and redox efficiency that constrains solar-to-chemical conversion. We discuss four major photonic strategies: hot carrier generation, polaritonic chemistry, enhanced photonic structures (photonic crystals), and metasurfaces/metamaterials, highlighting their potential to manipulate light–matter interactions at the nanoscale and thereby influence reaction pathways, selectivity, and efficiency. While these approaches offer compelling opportunities, including non-thermal reaction control, modification of potential energy surfaces, and improved light harvesting, their practical implementation remains hindered by fundamental and technological challenges. These include short hot-carrier lifetimes, limited reproducibility and scalability of polaritonic systems, defect sensitivity in photonic structures, and fabrication complexity and stability issues in metasurfaces. We emphasize that improvements in photocatalytic performance must be evaluated within the broader framework of overall reaction efficiency, encompassing both quantum yield and light transport. Bridging the gap between proof-of-concept studies and scalable applications will require closer integration between photonics and catalysis, along with a realistic assessment of energy costs and system-level design. Ultimately, nanophotonics provides powerful tools, but its translation into sustainable photocatalytic technologies demands a balanced and application-driven approach.

The transition of adsorbent materials from laboratory synthesis to industrial application requires a rigorous assessment of their durability under high concentrations. This study evaluates composite alginate hydrogels incorporating mill scale-derived magnetite (Fe₃O₄), activated carbon, and L-ascorbic acid (Fe₃O₄/AC/VitC alginate hydrogels) for the detoxification of highly concentrated chromium effluents. We investigated the operational limits of these hydrogel bubbles through three distinct scenarios: (1) Single-Batch Adsorption–Regeneration Cycling in Fresh Cr(VI) Solutions, (2) Sequential Reuse of Single-Batch Hydrogel Bubbles in the Same Effluent for Complete Cr(VI) Removal, and (3) the Multi-Batch Treatment Capacity Test for highly concentrated Cr(VI) loads. The composite demonstrated exceptional robustness, maintaining >80% removal efficiency over five cycles for 100 mg/L Cr(VI) without chemical treatment. For higher loads (150–400 mg/L), a simple regeneration protocol effectively restored performance, reducing Cr(VI) levels to below stringent discharge limits (<0.25 mg/L). Furthermore, in “worst-case” scenarios involving synthetic solutions (2500 mg/L) and real electroplating wastewater (~2000 mg/L), a multi-batch approach achieved complete abatement within 8–9 cycles. Notably, the treatment simultaneously neutralized the effluent pH from ~1.0 to 7.0, confirming the potential of this waste-derived material as a resilient, multi-functional solution for complex industrial wastewater management. Beyond performance, a techno-economic analysis was conducted to evaluate the economic feasibility of industrial-scale production. The results indicate that by utilizing industrial-grade reagents and waste-derived precursors, the production cost of the dry adsorbent can be estimated at ~45 EUR/kg. These findings confirm the potential of this material as a cost-effective, multi-functional solution for SMEs struggling with high operational costs and stringent environmental regulations.

The widespread occurrence of pharmaceutical contaminants in aquatic environments requires the development of sustainable and efficient water treatment technologies capable of operating under realistic conditions. In this study, an integrated remediation system based on chitosan hydrogels embedding TiO ₂ nanoparticles is investigated, combining pollutant adsorption and photocatalytic degradation within a single, reusable system. The performance of the composite hydrogels was evaluated for the removal of sulfamethoxazole (SMX), selected as a model antibiotic, under simulated and real solar irradiation, using mineral water to reproduce environmentally relevant ionic strength conditions. Structural characterization confirms the effective immobilization of TiO ₂ within the hydrogel matrix, ensuring material stability and preventing nanoparticle release into water. The hybrid system exhibits high SMX removal efficiency (>85% for 10 ⁻⁵ m SMX solutions) due to the synergistic interplay between adsorption and sunlight‐driven photocatalysis, with TiO ₂ showing photocatalytic activity under solar irradiation. Moreover, the hydrogels show excellent structural integrity, resistance to microbial colonization and biofouling, and stable performance over multiple adsorption–photocatalysis cycles. These results demonstrate the robustness and practical applicability of TiO ₂ /chitosan‐based hydrogels for solar‐driven water remediation and provide a promising platform for the development of advanced multifunctional materials for the treatment of emerging contaminants.

The characterization of surface plasmon–polaritons (SPPs) involved in surface-enhanced Raman scattering (SERS) and plasmon-driven photochemical processes is commonly performed through auxiliary techniques such as optical-, electron energy loss- or scanning probe-spectroscopy that neither reproduce the actual excitation conditions of a microRaman setup nor provide a direct, in situ probe of light confinement in real experiments. Here, we demonstrate an alternative approach based on the intrinsic Raman response of TiO2 hollow-shell cavities coated with ultrathin gold layers (T-horex@Au). The Raman spectra of these hybrid core/shell structures exhibit an additional mode that cannot be assigned to bulk TiO2 phonons. Confocal microRaman analysis reveals a clear dependence of this mode’s intensity on the laser penetration depth, enabling its attribution to surface phonon modes activated at the Au/TiO2 interface. This plasmon-mediated activation takes advantage of interfacial symmetry lowering and efficient electromagnetic field confinement. The simultaneous observation of this mode together with conventional Raman signals provides a direct, non-perturbative diagnostic of SPP excitation quality under realistic experimental conditions. Exploiting this feature, we show that the Raman enhancement induced by identical gold layers is strongly substrate-dependent and that the intensity of the TiO2 surface mode can be used as an internal standard to optimize and tune SERS performance. This strategy offers a practical route for large-scale fabrication and rapid optimization of metal/TiO2-based SERS substrates, opening intriguing perspectives for real-time control and monitoring of plasmon-driven photocatalytic and photochemical reactions at solid interfaces.

This work presents an electrochemical interpretation of Alkaline Hydrothermal Vents (HTVs), geological structures considered plausible sites for the origin of life. At these vents, a life-like thermodynamic disequilibrium is generated by the interaction of two fluids with contrasting characteristics across opposite surfaces of a mineral membrane. On the ocean-facing side, an acidic, CO₂-rich fluid prevails, while on the vent side, an alkaline, reducing hydrothermal fluid containing H₂ with minor concentrations of hydrogen sulphides (HS— > H2S) flows. The redox potential difference between these environments can drive the formation of organic molecules by coupling CO₂ reduction with H₂ oxidation at two different pHs. In this study, we validate the robustness of this model through electrochemical experiments, treating the system analogously to a short-circuited fuel cell. Using an H-type electrochemical cell, we place two electrodes in separate compartments and measure the open-circuit potential (OCP) under varying pH and solution compositions. This allows us to determine the cell potential (Uc) generated when a proton motive force—i.e., a pH gradient—is present across the membrane. Uc reflects the redox disequilibrium between the two fluids and is influenced not only by their bulk properties but also by specific interfacial interactions between the electrolytes and electrode materials. Because the mineral material is a reasonable electronic conductor, short-circuiting the electrodes equalizes their potentials (relative to an external reference electrode). The system thus transitions from a purely thermodynamic to a kinetic regime, allowing current to flow and redox reactions to proceed. An Evans diagram is a valuable tool to visualize this: the intersection of the anodic and cathodic curves defines the mixed potential (Em) and the corresponding reaction current (Ir). We use mackinawite as the model mineral, both for its electrochemical properties and its premetamorphic abundance in Archean HTVs. Two mackinawite electrodes were placed in the H-cell, with one exposed to an alkaline, H₂-rich solution and the other to an acidic, CO₂-rich solution, separated by a cation-exchange membrane. Upon short-circuiting, the resulting mixed potential (Em) was measured and found to lie within a range where CO₂ reduction is feasible on mackinawite. Moreover, spontaneous current generation was observed only under far-from-equilibrium conditions. The direction of current confirmed that reduction occurs on the acidic side and oxidation on the alkaline side, as theoretically predicted. These findings were then compared with an Evans-style diagram constructed from linear sweep voltammetry performed on individual electrodes.

Tunable optical devices are of paramount importance in modern optical engineering, offering the flexibility to dynamically adjust key optical parameters, thus enhancing functionality and adaptability. In this study, a fresh approach is presented to achieve on‐demand, spatially tunable optical properties using organic mixed ion‐electron conductors, which can be produced using large‐scale, cost‐effective technologies. It is demonstrated how, by exploiting, the spatial modulation of the bulk electronic conductance of PEDOT:PSS through an organic electrochemical transistor configuration, we can create a spatially tunable broadband gradient index profile with multiple degrees of freedom. These findings introduce a new class of tunable graded index media, which hold potential for a wide range of applications that span from optical interconnections to multi‐focal optical devices.

Catalysis stands as an indispensable cornerstone of modern society, underpinning the production of over 80% of manufactured goods and driving over 90% of industrial chemical processes. As the demand for more efficient and sustainable processes grows, better catalysts are needed. Understanding the working principles of catalysts is key, and over the last 50 years, surface-enhanced Raman Spectroscopy (SERS) has become essential. Discovered in 1974, SERS has evolved into a mature and powerful analytical tool, transforming the way in which we detect molecules across disciplines. In catalysis, SERS has enabled insights into dynamic surface phenomena, facilitating the monitoring of the catalyst structure, adsorbate interactions, and reaction kinetics at very high spatial and temporal resolutions. This review explores the achievements as well as the future potential of SERS in the field of catalysis and energy conversion, thereby highlighting its role in advancing these critical areas of research.

Here we investigated the dynamics of OER activity of NiFe (90/10) catalysts over 1000 potential sweep cycles as a function of their mass loading. Over twenty different films with mass loading in the 10 ng/cm²–30 μg/cm² range were deposited by Supersonic Cluster Beam Deposition (SCBD), allowing to study the progress of OER in sub‐monolayer, monolayer and multilayer regimes. Upon prolonged potential sweeps the electrocatalytic performances of multilayers decreased, while those of monolayers were significantly improved. The best balance in terms of catalytic efficiency and stability in working conditions is found for mass loadings corresponding to a NiFe monolayer, corresponding to a mass loading around 1 μg/cm² and a thickness of about 3 nm.