Photocatalytic-photothermal evaporators are emerging as promising water purification technologies capable of removing both inorganic and organic pollutants while offering low-cost and low-energy desalination. Despite their potential, the interplay between photocatalysis and photothermal evaporation remains poorly understood. Here, we investigate the sequential application of the two processes and demonstrate, for the first time, the existence of synergistic effects that are independent of the specific materials used. We show that pollutant rejection by evaporation is very effective on the aromatic intermediates formed via hydroxyl-radical attack - an insight of general relevance to advanced oxidation processes. However, we also identify p-benzoquinone as a critical volatile intermediate whose concentration remains significant in the distillate after conventional liquidphase photocatalysis combined with evaporation. By examining the role of the water matrix, including common inorganic electrolytes and non-volatile organic compounds, we further reveal conditions under which the combined process becomes practically ineffective - an issue not previously recognized for photocatalytic-photothermal systems. Building on these findings, we propose an improved treatment sequence in which the evaporation step is brought forward, mitigating the inhibitory effects of non-volatile species and enabling robust synergistic coupling. This work highlights the overlooked importance of gas-phase photocatalysis and provides a rational framework for the future design and optimization of photocatalyticphotothermal evaporators.

Magnetite-based nanoparticles (MNPs) are widely investigated for biomedical applications including hyperthermia, drug delivery and magnetic resonance imaging (MRI). Precise control of their morphology is essential and typically achieved via thermal decomposition, though more scalable and energy-efficient approaches are needed, especially for ultrasmall (<5 nm) MNPs. Here, well-controlled MNPs were synthesized by optimizing a coprecipitation process conducted at low temperature and in air, without polymeric stabilizers or templates. The combined use of tetramethylammonium hydroxide (TMAOH) as a base, citric acid to quench growth, and controlled reaction temperature (from room temperature to 0 °C), enabled the reproducible formation of monodisperse, highly crystalline MNPs with core size tunable from 6.6 to 4.0 nm, as confirmed by (HR)TEM. The TMAOH could be readily replaced by citrate as biocompatible stabilizer, forming a 1 nm-thick shell (AFM) and ensuring long-term stability, even under magnetic fields. NMRD measurements (0.01-57 MHz) showed superparamagnetic behaviour and a size-dependent transition from T2-to T1-type relaxation, with r2/r1 ratio at 1.34 T decreasing from 3.3, 2.9, and 1.8 for 6.6, 5.3, and 4.0 nm particles, respectively. MRI at 3 T confirmed that the smaller MNPs exhibit significant T1 contrast. Finally, MNP@citrate were stable in cell culture medium, well tolerated at all tested concentrations (Cmax = 140 μg/mL) on Human Embryonic Kidney 293 (HEK) cells, and accumulated in the cytoplasm within 24 h incubation, as shown by reflectance confocal microscopy.

Photocatalysis is proposed as an environmentally friendly technology that exploits solar light for environmental purification. While its effect on treated effluent quality is indeed positive, studies on its overall environmental profitability generally disregard the fact that photocatalytic materials may themselves generate pollution in their production, use, and end‐of‐life phases. This work addresses two distinct methods for titanium dioxide (TiO 2 ) photocatalytic coatings preparation, that is, chemical –sol–gel, associated with spray coating– and electrochemical –anodic oxidation, which generates the oxide directly from a titanium substrate. Oxides are tested in the photocatalytic decomposition of tetracycline, an antibiotic commonly found in water. Both distilled and tap water are used as matrices. Coatings are tested multiple times to simulate real operating conditions, until photocatalytic activity is compromised. Life Cycle Assessment (LCA) is then used to quantify and compare the potential environmental impacts associated with the two different TiO 2 production strategies. Eventually, the assessment is completed by considering full photocatalyst regeneration: while for Sol–Gel this only implies cleaning and re‐deposition, anodizing required oxide detachment, and subsequent re‐anodization. The process of oxide removal and re‐anodizing, although invasive and titanium consuming, is repeated 20 times without significant loss of photocatalytic efficiency, indicating robustness and suitability for technology transfer.

Water scarcity is a growing global challenge, intensified by climate change, seawater intrusion, and pollution. While conventional desalination methods are energy-intensive, solar-driven interfacial evaporators offer a promising low-energy solution by leveraging solar energy for water evaporation, with the resulting steam condensed into purified water. Despite advancements, challenges persist, particularly in addressing volatile contaminants and biofouling, which can compromise long-term performance. The integration of photocatalysts into solar-driven interfacial evaporators has been proposed as a solution, enabling pollutant degradation and microbial inactivation while enhancing water transport and self-cleaning properties. This review critically assesses testing methodologies for solar-driven interfacial evaporators incorporating both photothermal and photocatalytic functions. While previous studies have examined materials and system design, the added complexity of photocatalysis necessitates new testing approaches. First, solar still setups are analyzed, particularly concentrating on the selection of materials and geometry for the transparent cover and water-collecting surfaces. Then, performance evaluation tests are discussed, with focus on the types of tested pollutants and analytical techniques. Finally, key challenges are presented, providing insights for future advancements in sustainable water purification.

In situ-functionalized Pickering emulsions can exhibit phase inversion by changing the concentration of surface modifiers. Here, we demonstrate that these systems are far more versatile as multiple stimuli can be harnessed to achieve their phase inversion. Oil-in-water Pickering emulsions were prepared using food-grade vegetable oil and stabilized solely by in situ-functionalized ZnO particles. ZnO was selected for its semiconductor and amphoteric properties, which enable the controlled switching/destabilization activated by multiple stimuli: acidification by mineral and organic acids, UV and sunlight irradiation, addition of multivalent cations and CO2 bubbling. Depending on the stimulus, the switching kinetics and reversibility can be tailored. Switching by acidification, light irradiation or CO2 bubbling is fully reversible upon either pH increase, N2 bubbling or storage in the dark. Even after consecutive cycles, stable oil-in-water Pickering emulsions could be reobtained. Irreversible destabilization can instead be triggered by excess addition of acids and multivalent cations. The switching kinetics can be modulated achieving either an on-off behavior or a controlled destabilization over several hours. The oil phase of the emulsion can be loaded with active substances, such as volatile and unstable essential oils. Emulsions containing cinnamaldehyde (up to 1500 ppm) were prepared and destabilized after accelerated aging: the molecule was stored and released in the aqueous phase without undergoing any degradation, with concentrations in a range suitable to avoid proliferation of bacteria and fungi. Up to four consecutive release cycles were successfully conducted by two different procedures, proving the system's applicability as a continuous source of the active molecule.

The interest in titanium and its oxides keeps growing on account of their peculiar engineered properties, which find applications in several fields, from architecture to bioengineering, from automotive to photovoltaic cells and photocatalytic devices. There are several methods that allow to grow titanium oxides, among which anodic oxidation has the nice advantage of growing TiO2 nanostructures directly immobilized on a substrate, avoiding the issue of nanostructure recovery from the medium [1]. Yet, these systems also present a drawback, i.e., the immobilization on a metallic, non-transparente and non-permeable substrate. For this reason, different methods have been developed to detach the nanotubes layer and use it as a self-standing membrane [2]. In this work, we address this specific challenge and present the obtaining and characterization of self-standing TiO2 nanotubes membranes. The application envisioned requires their mandatory detachment, as the membranes will be used inside a solar evaporator device to improve the quality of evaporating water, by removing also volatile compounds that may evaporate together with water, reducing the purification extent. Membranes are produced by anodizing commercially pure titanium sheets in ethylene glycol solutions containing different amounts of water, ammonium fluoride and lactic acid. Anodizing time was varied between 30 min and 90 min, and voltage was varied between 30 V and 60 V. Double anodizing was performed to ensure better nanotubes uniformity; then annealing was performed at 500°C for 2 h to allow for oxide crystallization to anatase form. Afterwards, a third, brief anodizing step (10 min) was needed to facilitate nanotubes detachment, which then was carried out chemically, by immersion in HCl. An example of SEM image of detached membrane is shown in Figure 1, indicating that membranes can indeed be obtained and have sufficient mechanical stability to allow for handling and testing. SEM and XRD results indicate a thickness ranging from few micrometers to tens of micrometers, and their crystal structure is mainly anatase, although small quantities of rutile may form in the base of the oxide. Preliminary photocatalysis tests were conducted on the degradation of organic dyes, showing promising photoactivity. Several decoration methods were also considered, with different aims: silver nanoparticles for antifouling, and quantum dots for improved photoactivity. Silver nanoparticles did not enhance photoactivity, and in some cases decreased it slightly; yet, their scope was different, i.e., exploiting the antibacterial and antifouling characteristics of silver on the membrane layer, therefore the formulation leading to unaltered photocatalytic activity was selected for the prosecution of this work, which envisions antibacterial and antifouling testing procedures. Acknowledgements: We acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 1409 published on 14.9.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Project Title COPE - COmposite nanomaterials coupling Photothermal Evaporation and photocatalysis for durable water purification systems – CUP G53D23006660001 - Grant Assignment Decree No. 1384 adopted on 01.09.2023 by the Italian Ministry of Ministry of University and Research (MUR). References Lee, K.; Mazare, A.; Schmuki, P. (2014) One-dimensional titanium dioxide nanomaterials: Nanotubes. Chem. Rev., 114, 9385–9454. So, S.; Hwang, I.; Riboni, F.; Yoo, J.; Schmuki, P. (2016) Robust free standing flow-through TiO2 nanotube membranes of pure anatase. Electrochem. Commun., 71, 73–78. Figure 1: Morphology of nanotubular membrane. Figure 1

Finding innovative and highly performing approaches for NOx degradation represents a key challenge to enhance the air quality of our environment. In this study, the high efficiency of PANI/TiO2 nanostructures in the NO2 abatement both in the dark and under light irradiation is demonstrated for the first time. Heterostructures were synthesized by a "green" method and their composition, structure, morphology and oxidation state were investigated by a combination of characterization techniques. The results show that the unique PANI structure promotes two mechanisms for the NO2 abatement in the dark (adsorption on the polymeric chains and chemical reduction to NO), whereas the photocatalytic behavior prevails under light irradiation, leading to the complete NOx degradation. The best-performing materials were subjected to recycling tests, thereby showing high stability without any significant activity loss. Overall, the presented material can represent an innovative and efficient night-and-day solution for NOx abatement.

Nanostructured oxide semiconductors are widely used in energy conversion, catalysis, sensing and environmental applications, due to their high stability, commercial availability, efficiency and low cost. Despite its crucial importance for the design of more efficient materials, the interplay between intrinsic and extrinsic defects is yet to be clarified. For example, oxygen vacancies (VO's) can be either beneficial or detrimental to the desired performances, depending on a variety of factors. Here, we synthesize TiO2-x samples by the addition of three different N chemical sources (NH3, triethylamine, urea). X-ray absorption spectroscopy, confocal microscopy, UV-vis absorbance and fluorescence, are employed to explore the occurrence and location of VO's both in real and energy spaces. High-grade bulk DFT simulations complement the experimental picture. Synergy between theory and experiment, on the one hand, estimates the relative VO's content in the different samples from local structural information. On the other hand, a sharp optical transition at & AP;2.7 eV serves an unequivocal spectral signature of bulk VO's, allowing a semi-quantitative analysis by confocal microscopy. Surface oxygen vacancies do not display fluorescence features under UV pumping, possibly due to the reaction of surface defects with atmospheric O2. Thus, the comparison between local structure and confocal microscopy can discriminate surface-localized and bulk VO's. Concurrently, UV-induced photochromism and visible light photodegradation shed light on the most effective reactive defects. Eventually, surface-localized oxygen vacancies are predominant where actual N substitutional doping occurs, leading to materials exhibiting visible-light activity and characteristic photochromic behaviour. Implications on strategies for concomitant VO engineering and extrinsic doping are discussed.

Wastewaters from precious metal industries contain high amounts of noble metals, but their efficient recycling is hindered by the wastewater complex composition. Here, we propose an innovative approach for the efficient recovery of noble metals contained in these metal-enriched wastewaters as precursors for the synthesis of noble metal nanoparticles (NPs) and supported metal catalysts. Silver NPs were synthesized from Ag-enriched wastewater and then deposited on TiO2 to prepare photocatalysts. Then, further promotion of the photocatalytic activity of Ag-modified TiO2 was achieved by the addition of as little as 0.5 wt.% of Au. STEM-EDS analyses proved that Au NPs were located on Ag or AgOx nanoparticles. The contact between the two metal-containing NPs results in charge transfer effects, appreciable both in terms of oxidation states determined by XPS and of optical properties. In particular, the plasmon band of Au NPs shows photochromic effects: under UV light irradiation, bimetallic samples exhibit a blue-shift of the plasmon band, which is reversible under dark storage. The activity of the materials was tested towards ethanol photodegradation under UV light. Adding 0.5 wt.% Au NPs resulted in a promoted activity compared to Ag-TiO2, thus showing synergistic effects between Au and Ag. Ethanol was completely converted already after 1 h of UV irradiation, acetaldehyde was formed as the main oxidation product and fully degraded in less than 180 min. Notably, bimetallic samples showed ethylene formation by a parallel dehydration mechanism.

Hypothesis: Oxide-stabilized emulsions generally require a surface functionalization step to tune the oxide wettability, often involving hazardous hydrophobizing agents. Here, we propose the in situ functionalization of ZnO in vegetable oils without the addition of any modifier, resulting in the one-step formation of highly stable Pickering emulsions. Experiments: The role of ZnO surface features was studied by modifying the particles' wettability through surface functionalization and by comparing different oil phases. The emulsion stability was assessed through aging tests, multiple hot-and-cold cycles, centrifugation, and addition of multiple electrolytes. Findings: While the wetting features of the functionalized oxide play a crucial role when the oil phase is methyl octanoate, emulsions based on vegetable oils form also using hydrophilic ZnO. During the emulsification, an in situ functionalization of bare ZnO particles takes place due to the fatty acids present in vegetable oil. These in situ-generated systems lead to stable emulsions showing < 2 mu m-diameter oil droplets. The resulting emulsions display excellent stability over time (over seven months) and against temperature variations, mechanical stress and increased ionic strength. Finally, we demonstrate that this approach can be extended to a variety of vegetable oils and oxides with different morphologies. (C) 2022 Elsevier Inc. All rights reserved.

Adsorption and photocatalysis are water remediation techniques with unique advantages and limitations that can make them complementary: while adsorption is a cheap and fast process that simply transfers the pollutant to another phase, photocatalysis is a slow and costly procedure that however can degrade recalcitrant pollutants. Here, we propose a sequential treatment based on reversible and selective adsorption, followed by heterogeneous photocatalysis. In particular, the reversible and selective adsorption of dye molecules was achieved by polyaniline (PANI)-based hybrid adsorbents. The role of the dye content, adsorbent dose, solution pH and electrolyte composition was investigated. By tuning the adsorption pH, an effective regeneration of the spent adsorbent could be achieved by the triggered release of the adsorbate in an aqueous solution and under mild conditions. Moreover, the separation of multi-dye mixtures (methyl orange and methylene blue) was proven, also in consecutive cycles. The selective recovery of one of the components could enable dye recycling. An ensuing photocatalytic step using a commercial photocatalyst could be adopted to either degrade the leftover solution or the regeneration solution. The release of a single pollutant in aqueous solvent, with controlled composition and tunable concentration, allows performing photocatalysis more efficiently. This combined approach enables a fast and effective treatment of the effluent and an easy regeneration of the spent adsorbent with ensuing treatment of the regeneration solution for a zero-waste strategy.

We here propose a simple and fast hands-on activity requiring limited equipment, to introduce students of various levels (bachelor's or high school) and backgrounds (from science to arts) to the chemistry of color. The different colors of stained glass are replicated through the deposition, on ordinary glass slides, of silica coatings colored by addition of metal ions and nanoparticles. A silica sol is used as a matrix to embed metal ions, followed by an in situ reduction activated by thermal treatment on a hot plate. The formation of metal nanoparticles by this procedure induces plasmonic colors in the glass coating, thus "mimicking" the ancient procedure of stained-glass fabrication through a simple and quick method. Characterization of the colored glass by optical spectroscopy is also presented. This easily reproducible activity demonstrates basic concepts of redox reactions, chemistry of color, and plasmonic nanoparticles. Thanks to its interdisciplinary character and immediate and tangible results, this activity is well-suited for teaching laboratories for bachelor's and high school students as well as for public engagement activities.

The photocatalytic oxidation of volatile organic compounds (VOCs) has been extensively investigated. With respect to water treatment, photocatalytic degradation of air pollutants is still less understood, but this has not prevented photocatalytic building materials and air purifiers to reach the market. Here, we provide a selective overview of the current understanding on VOC photocatalytic oxidation, focusing on ethanol, acetaldehyde, and acetic acid. Among the main indoor pollutants, these molecules are also oxidation intermediates of numerous VOCs. Their adsorption at the photocatalyst surface is first presented, based on theoretical and experimental evidence. Reaction intermediates are discussed, comparing proposed reaction mechanisms. The role of the photocatalyst features in directing adsorption and oxidation phenomena is highlighted, encompassing both TiO2 and emerging photocatalysts. We then critically discuss gaps in our knowledge, such as the effect of air humidity, multi-pollutant interactions and deactivation pathways. Finally, attempts to model VOC degradation in realistic conditions are reviewed.

In recent years, solar-driven steam materials and systems for water desalination and decontamination have received increasing attention from the scientific community. Notwithstanding the fundamental scientific achievements reached on this topic, numerous technological concerns still remain to be addressed, including heat loss, radiation reflection, low degree of purification of condensed water, biofouling, and salt accumulation on the surface. In this report, we critically reviewed the most recent advances in the engineering of solar-driven steam materials and the main technology challenges which may limit their large-scale application. First, different classes of materials, e.g., inorganic semiconductors, carbonaceous materials, polymers, and surface plasmon resonance metals, are compared in terms of the mechanistic pathways to generate steam vapor and condensed to freshwater on their surface. Then, the main approaches to tackle the technology shortcomings of solar-driven steam systems are discussed in depth. For instance, in terms of salt accumulation, several strategies were proposed such as solar-driven surfaces with ion exchange or/and salt dissolving, an inversion system to remove the salt from the active surface, and salt rejection surfaces. To enhance the photothermal process and limit the reflection of light, thermal insulators, reflective layers, and 3D/pyramidal photoabsorbers were proved to be excellent strategies. The review addresses as well the recent research regarding hybrid systems by incorporating photocatalysis effect in solar-driven water evaporators. Photocatalyst addition endows the surface of evaporators with unique properties, such as the radical oxidation of organic pollutants and microbial inactivation, resulting in reduced fast biofouling and condensed waters with higher purity. Finally, the remaining challenges and prospects for future developments are critically discussed.

The recent impressive growth of Li-ion batteries (LIBs) production infrastructures is related to the surge of electric automotive industry. However, the current performance of LIBs is limited by the intrinsic capacity of graphite anodes, the use of organic solvents and by the limited wettability of the separator. In this review, we aim at demonstrating the grade of advance that can be expected for the performances of Li-ion batteries in the short term (roughly, 5-10 years) thanks to introduction of smart materials and interfaces. This temporal limit reflects the need of maintaining the current production chain of LIBs and optimizing the relative investments. In particular, we analyze and discuss the most recent scientific findings on: (i) the solvent, focusing our attention on deep eutectic solvents and ionic liquids (ILs) as an alternative to the currently adopted organic solvents; (ii) tuning the wettability of the separator, thanks to the optimization of the material, its porosity and its surface features; (iii) the anodic materials, according to the different proposed mechanism for Li storage and classifying them into different categories (i.e. carbon-based, Si, perovskites). Finally, we must recognize that, among the so-called "post LIBs" batteries, Li metal batteries can also play a key role in the near future: this type of battery is currently under production for primary cells but requires a smart cathode|electrolyte interface to avoid Li dendrite growth during charge/discharge cycles in their future as secondary systems.

Sonication induces physical and chemical effects, such as promoting the mass transfer and active radical formation, that can be harnessed for process intensification in numerous fields, including photocatalysis. In this perspective, we discuss recent advances in the main domains where photocatalysis and ultrasound technology overlap, namely ultrasound-assisted synthesis of photocatalysts with controlled structural and morphological features and hybrid technologies combining ultrasound and light irradiation (sonophotocatalysis and piezo-enhanced photocatalysis). The latter, an external field-enhanced photocatalytic technology, is a relatively new approach that promises to boost photocatalytic efficiency (with enhancements up to 400%), even though significant challenges remain to be addressed. Finally, we offer some perspectives on the future of ultrasound-assisted photocatalysis, discussing current gaps in knowledge, economics, and scale-up issues.

In recent years, nanoparticles have come under close scrutiny for their possible health and environmental issues, making them less attractive for photocatalytic applications in air or water purification. Replacing free nano-powders with active and stable films is thus a fundamental step towards developing effective photocatalytic devices. Aluminum represents a cheap and technologically-relevant substrate, but its photocatalytic applications have been hampered by adhesion issues and metal ion diffusion within the photocatalytic layer. In this work, the use of silica interlayers is investigated as a strategy to promote adhesion, efficiency and reusability of TiO2films deposited on aluminum plates. Films were prepared from stable titania sols to avoid the use of nano-powders. Aluminum substrates with different surface morphology were investigated and the role of the silica interlayer thickness was studied. Films were extensively characterized, studying their structure, morphology, optical properties, adhesion and hardness. Self-cleaning properties were studied with respect to their superhydrophilicity and ability to resist fouling via alkylsilanes. Photocatalytic degradation tests were carried out using both volatile organic compounds and NOx, also in recycle tests. The presence of the silica interlayer proved crucial to promote the film robustness and photocatalytic activity. The substrate morphology determined the optimal interlayer thickness, especially in terms of the film reusability.