Vanillin, one of the most widely used and appreciated flavoring agents worldwide, is the main constituent of vanilla bean extract, obtained from the seed pods of various members belonging to the Orchidaceae family. Due to the great demand in the food confectionery industry, as well as in the perfume industry, medicine, and more, the majority of vanillin used today is produced synthetically, and only less than one percent of the world's vanilla avoring market comes directly from the traditional natural sources. The increasing global demand for vanillin requires alternative and overall sustainable new production methods, and the recovery from biobased polymers, like lignin, is an environmentally friendly alternative to chemical synthesis. The present review provides rstly an overview of the different types of vanillin, followed by a description of the main differences between natural and synthetic vanillin, their preparation, the market of interest, and the authentication issues and the related analytical techniques. Then, the review explores the real potentialities of lignin for vanillin production, presenting rstly the well-assessed classical methods and moving towards the most recent promising approaches through chemical, biotechnological and photocatalytic methodologies, together with the challenges and the principal issues associated with each technique.

Volatile organic compounds (VOCs) are molecules present in our everyday life, and they can be positive, such as in the formation of odour and food flavour, or harmful to the environment and humans, and research is focusing on limiting their emissions. Various methods have been used to achieve this purpose. Firstly, we review three main degradation methods: activated carbon, photocatalysis and a synergetic system. We provide a general overview of the operative conditions and report the possibility of VOC abatement during cooking. Within the literature, none of these systems has ever been tested in the presence of complex matrices, such as during cooking processes. The aim of this study is to compare the three methods in order to understand the behaviour of filter systems in the case of realistically complex gas mixtures. Proton transfer reaction-mass spectrometry (PTR-MS) has been used in the real-time monitoring of volatilome. Due to the fact that VOC emissions are highly dependent on the composition of the food cooked, we evaluated the degradation capacity of the three systems for different burger types (meat, greens, and fish). We demonstrate the pros and cons of photocatalysis and adsorption and how a combined approach can mitigate the drawbacks of photocatalysis.

Light-powered micro- and nanomotors based on photocatalytic semiconductors convert light into mechanical energy, allowing self-propulsion and various functions. Despite recent progress, the ongoing quest to enhance their speed remains crucial, as it holds the potential for further accelerating mass transfer-limited chemical reactions and physical processes. This study focuses on multilayered MXene-derived metal-TiO2 micromotors with different metal materials to investigate the impact of electronic properties of the metal-semiconductor junction, such as energy band bending and built-in electric field, on self-propulsion. By asymmetrically depositing Au or Ag layers on thermally annealed Ti3C2Tx MXene microparticles using sputtering, Janus structures are formed with Schottky junctions at the metal-semiconductor interface. Under UV light irradiation, Au-TiO2 micromotors show higher self-propulsion velocities due to the stronger built-in electric field, enabling efficient photogenerated charge carrier separation within the semiconductor and higher hole accumulation beneath the Au layer. On the contrary, in 0.1 wt % H2O2, Ag-TiO2 micromotors reach higher velocities both in the presence and absence of UV light irradiation, owing to the superior catalytic properties of Ag in H2O2 decomposition. Due to the widespread use of plastics and polymers, and the consequent occurrence of nano/microplastics and polymeric waste in water, Au-TiO2 micromotors were applied in water remediation to break down polyethylene glycol (PEG) chains, which were used as a model for polymeric pollutants in water. These findings reveal the interplay between electronic properties and catalytic activity in metal-semiconductor junctions, offering insights into the future design of powerful light-driven micro- and nanomotors with promising implications for water treatment and photocatalysis applications.

Lead halide perovskite nanocrystals (NCs) are particularly suitable for light-emitting and photocatalysis applications, where their potential can be maximized by controlling the surface composition of their organic shell. In this study, the preparation of CsPbClBr NCs at room temperature in toluene is described. Three differently structured surfactants are utilized for the synthesis, each with a specific function, namely, the solubilization of the lead precursor (n-HeptNBr), the surface passivation with halide modification (dimethyldioctadecylammonium chloride), and the protection of the surface-active sites (octanoic acid) for photocatalysis. Under these conditions, nearly monodispersed blue-emitting nanocubes are selectively obtained in a one-pot synthesis by combining specific amounts of the perovskite precursors. As supported by thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy investigations, the organic shell of the obtained NCs is composed of electrostatically bound dimethyldioctadecylammonium ions, granting robustness to the corresponding NCs, and octanoic acid molecules, interacting with the nanoparticle surface through weaker secondary bonds. The obtained NCs exhibit a high photoluminescence quantum yield (PLQY = 72 ± 3%) notwithstanding multiexponential recombination dynamics of the excited state, resulting from the different passivation modes at the NC surface. Moreover, the NCs show a remarkable optical stability after exposure to high temperatures and to water contact due to the high surface density of the multifunctional organic ligands. The introduction of 4-tert-butylphenyl thiol promotes a charge transfer process at the NC/thiol interface formed upon removal of the labile ligands (octanoic acid) at the NC surface. In these conditions, the NCs are prone to the photoinduced conversion of the aromatic thiol into the corresponding disulfide without varying the optical properties of the perovskite photocatalyst upon the substrate conversion. Therefore, the obtained results cast light on the versatility of the surface engineering of lead halide perovskite NCs for efficient blue emission and photocatalysis with improved stability.

Among semiconductor metal oxides, that are an important class of sensing materials, titanium dioxide (TiO2) thin films are widely employed as sensors because of their high chemical and mechanical stability in harsh environments, non-toxicity, eco-compatibility, and photocatalytic properties. TiO2-based chemical oxygen demand (COD) sensors exploit the photocatalytic properties of TiO2 in inducing the oxidation of organic compounds to CO2. In this work, we discuss nanostructured TiO2 thin films grown via low-pressure metal organic chemical vapor deposition (MOCVD) on metallic AISI 316 mesh. To increase the surface sensing area, different inorganic acid-based chemical etching protocols have been developed, determining the optimal experimental conditions for adequate substrate roughness. Both chemically etched pristine meshes and the MOCVD-coated ones have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) microanalysis, and X-ray photoelectron spectroscopy (XPS). We demonstrate that etching by HCl/H2SO4 at 55 °C provides the most suitable surface morphology. To investigate the behavior of the developed high surface area TiO2 thin films as COD sensors, photocatalytic degradation of functional model pollutants based on ISO 10678:2010 has been tested, showing for the best performing acid-etched mesh coated with polycrystalline TiO2 an increase of 60% in activity, and degrading 66 µmol of MB per square meter per hour.

SiO2@TiO2 core-shell nanoparticles were successfully synthesized via a simple, reproducible, and low-cost method and tested for methylene blue adsorption and UV photodegradation, with a view to their application in wastewater treatment. The monodisperse SiO2 core was obtained by the classical Stober method and then coated with a thin layer of TiO2, followed by calcination or hydrothermal treatments. The properties of SiO2@TiO2 core-shell NPs resulted from the synergy between the photocatalytic properties of TiO2 and the adsorptive properties of SiO2. The synthesized NPs were characterized using FT-IR spectroscopy, HR-TEM, FE-SEM, and EDS. Zeta potential, specific surface area, and porosity were also determined. The results show that the synthesized SiO2@TiO2 NPs that are hydrothermally treated have similar behaviors and properties regardless of the hydrothermal treatment type and synthesis scale and better performance compared to the SiO2@TiO2 calcined and TiO2 reference samples. The generation of reactive species was determined by EPR, and the photocatalytic activity was evaluated by the methylene blue (MB) removal in aqueous solution under UV light. Hydrothermally treated SiO2@TiO2 showed the highest adsorption capacity and photocatalytic removal of almost 100% of MB after 15 min in UV light, 55 and 89% higher compared to SiO2 and TiO2 reference samples, respectively, while the SiO2@TiO2 calcined sample showed 80%. It was also observed that the SiO2-containing samples showed a considerable adsorption capacity compared to the TiO2 reference sample, which improved the MB removal. These results demonstrate the efficient synergy effect between SiO2 and TiO2, which enhances both the adsorption and photocatalytic properties of the nanomaterial. A possible photocatalytic mechanism was also proposed. Also noteworthy is that the performance of the upscaled HT1 sample was similar to one of the lab-scale synthesized samples, demonstrating the potentiality of this synthesis methodology in producing candidate nanomaterials for the removal of contaminants from wastewater.

The existing literature survey reports rare and conflicting studies on the effect of the preparation method of metal-based semiconductor photocatalysts on structural/morphological features, electronic properties, and kinetics regulating the photocatalytic H-2 generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H-2 generation synthesized via distinct methods (i.e., photodeposition and impregnation). Our study aims to establish a stringent correlation between physicochemical/electronic properties and photocatalytic performances for H-2 generation based on material characterization and kinetic modeling of the experimental outcomes. Estimating unknown kinetic parameters, such as charge recombination rate and quantum yield, suggests a mechanism regulating charge carrier lifetime depending on copper distribution on the TiO2 surface. We demonstrate that H-2 generation photoefficiency recorded over impregnated CuxOy/TiO2 is related to an even distribution of Cu(0)/Cu(I) on TiO2, and the formation of an Ohmic junction concertedly extended charge carrier lifetime and separation. The outcomes of the kinetic analysis and the related modeling investigation underpin photocatalyst physicochemical and electronic properties. Overall, the present study lays the groundwork for the future design of metal-based semiconductor photocatalysts with high photoefficiencies for H-2 evolution.

Perovskite-type compounds have found application in environmental remediation and in clean energy production, fundamental sectors for sustainable development. A challenge for these materials is the fine-tuning of their chemical composition and their chemical-physical characteristics, for example, microstructure, morphology and ability to form oxygen vacancies, through the introduction of dopant elements. In this work, we studied the effect of Cu doping at the B-site of a Ce, Co-doped strontium ferrate perovskite with chemical composition Sr0.85Ce0.15Fe0.67Co0.33O3-?. Indeed, Sr0.85Ce0.15Fe0.67Co0.23Cu0.10O3-? and Sr0.85Ce0.15Fe0.67Co0.13Cu0.20O3-? powders, where the B-site was codoped with both cobalt and copper, were synthesised by solution combustion synthesis and characterised for their physical-chemical properties by a multi-analytical approach, to assess their behaviour when subjected to different activation methods. The two codoped perovskites were tested 1) as catalysts in the oxidation of soot after activation at high temperatures, 2) as antibacterial agents in ambient conditions or activated by both UV exposure and low-temperature excitation to induce the generation of reactive species. Results demonstrated that these compounds react differently to various stimuli and that the increasing amount of copper, together with the presence of segregated ceria phase, influenced the materials' features and performances. The knowledge gained on the structure-properties relationships of these materials can inspire other research studies on perovskite oxides application as multifunctional materials for the benefit of the environment, society and economy.

In this work, we have fabricated an aryl amino-substituted graphitic carbon nitride (g-C3N4) catalyst with atomically dispersed Mn capable of generating hydrogen peroxide (H2O2) directly from seawater. This new catalyst exhibited excellent reactivity, obtaining up to 2230 ?M H2O2 in 7 h from alkaline water and up to 1800 ?M from seawater under identical conditions. More importantly, the catalyst was quickly recovered for subsequent reuse without appreciable loss in performance. Interestingly, unlike the usual two-electron oxygen reduction reaction pathway, the generation of H2O2 was through a less common two-electron water oxidation reaction (WOR) process in which both the direct and indirect WOR processes occurred; namely, photoinduced h+ directly oxidized H2O to H2O2 via a one-step 2e- WOR, and photoinduced h+ first oxidized a hydroxide (OH-) ion to generate a hydroxy radical (oOH), and H2O2 was formed indirectly by the combination of two oOH. We have characterized the material, at the catalytic sites, at the atomic level using electron paramagnetic resonance, X-ray absorption near edge structure, extended X-ray absorption fine structure, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, magic-angle spinning solid-state NMR spectroscopy, and multiscale molecular modeling, combining classical reactive molecular dynamics simulations and quantum chemistry calculations.

Photocatalysts which are stable to photocorrosion and noble metal-free, are highly desirable to achieve a light-driven hydrogen production which satisfies at the same time the criteria of low production cost and environmental sustainability. Herein, a new heterostructure TiO2/BP/CoP has been developed, where BP nanosheets by interacting strongly with TiO2 and CoP, can speed up the transfer of photogenerated electrons and thus increases the H2 production. Once BP is added to TiO2 (P25) as only 1% wt., the H2 evolution rate increases up to 3 times reaching a value of 830 ?mol/g?h under UV-Vis light irradiation. Integrating CoP nanoparticles as a cocatalyst up to 2% wt., the H2 production is furtherly promoted going to 7400 ?mol/g?h, 37 times higher than pristine TiO2. Photoluminescence and electrochemical impedance measurements showed that this heterostructure achieves a much more efficient charge separation and reduction of the internal resistance in comparison to pristine TiO2. Combining these data with UV-Vis Diffuse Reflectance and Mott-Schottky, a plausible mechanism was proposed.

Halide perovskite nanocrystals (PNCs) have demonstrated their wide potential to fabricate efficient optoelectronic devices and to prepare promising photocatalysts for solar-driven photo(electro)chemical reactions. However, their use in most of the practical applications is limited due to the instability of PNCs in polar environments. Here, the preparation of non-encapsulated CsPbX3 nanocrystals dispersed in fully alcohol environments, with outstanding stability through surface defect passivation strategy is reported. By using didodecyldimethylammonium bromide (DDAB) during material post-treatment, highly luminescent CsPbBr3 PNCs with remarkable stability in methanol/butanol medium up to 7 months with near-unity photoluminescence quantum yield are achieved. This approach is extrapolated to stabilize iodine-based CsPbBr3-xIx and CsPbI3 PNCs, showing an improvement of their photoluminescence features and stability in these high polar alcohols up to 6 h. DDAB mediates the defect suppression through ligand exchange and avoids the full permeation of alcohol to be in contact with the PNCs. In this context, DDAB induces ionization of alcohol molecules to strengthen the surface passivation. The findings open the door to the development of long-term stable CsPbX3 PNCs with high optical performance to be used in polar environments.

Hydrogen (H2), as an indispensable clean energy vector, has been well demonstrated to be produced via biomass photoreforming powered by solar light. For future biomass refining, biomass photoreforming deserves a high decomposition extent of biomass to maximize H2 production, as the greenhouse gas emissions from biomass acquisition and pretreatment will minimize per mass of H2. The main obstacle to high H2 yield is the far insufficient C-C bond breaking to convert biomass carbons into CO2 with maximization of H2 production. Here, we emphasize C-C bond breaking instead of direct H2 production. Such a "C-C bond first" strategy realizes conversion of carbohydrates into C1 liquid hydrogen carriers (LHCs, consisting of HCOOH and HCHO) over Ta-CeO2 photocatalyst and is demonstrated in a flow apparatus powered solely by solar energy. The LHCs can release H2 on-site where needed by either photocatalysis or thermocatalysis. This work provides a new perspective for H2 production by photocatalysis.

Dye-sensitized solar cell (DSSC) is an emerging photovoltaic (PV) technology allowing solar light harvesting even through colored semitransparent devices, such properties better meet the architectonical requirements for the exploitation in the urban context. The core component of a DSSC is the molecular dye; new organic dyes are generally developed following the D-A-?-A structural design. Some compounds have reached outstanding PV performances at the cost of low devices transparency and complex synthesis of non-symmetric structures obtained with metalorganic cross-couplings. We recently explored new structural designs for symmetrical organic photosensitizers that can be obtained with short synthetic strategies based on Palladium-catalyzed direct arylation reactions on a thienopyrazine core. The obtained dyes feature divergent optical properties ranging from pitch dark coloration to high transparency and uncommon colorations like green tones were also obtained. In order to enhance the divergent optical properties of the dyes, the PV devices were assembled using dedicated electrolyte compositions with no effect on the coloration and thin layers of supporting semiconductors allowing for high transparency. Among the resulting DSSC full devices, some have shown a composition of the transmitted light that fits well the human eye sensitivity spectrum, satisfying the requirements of perceived transparency for Building-Integrated PV.

Semiconductors such as TiO2 nanoparticles can be functionalized with metals like Pt to create catalytic sites for hydrogen evolution reaction (HER) from a protic sacrificial electron donor (SED) once light shines on the system. Unfortunately, most semiconductors have a wide bandgap requiring photoexcitation with UV light, which reduces the system efficiency under solar irradiation. By functionalizing of the nanocomposite with organic molecules, we improved visible-light-driven H2 generation. The dye affected both the spectral response toward the visible region and the possibility to use a wide range of compounds as SED. In our work, we developed three-component heterogeneous photocatalysts by sensitizing Pt/TiO2 nanoparticles with organic dyes inspired by the ones used in the dye-sensitized solar cells (DSSC) photovoltaics. The modular design D-?-A was employed to systematically alternate features like steric bulk, hydrophobicity, and hydrophilicity in different parts of the molecules to accommodate for the aqueous environment of the HER. The choice of SED and reaction conditions largely altered the overall hydrogen production efficiency. Best results were found with ascorbic acid and promising ones with EtOH, paving the way for using biomass-derivative as SED. Presently, we are reversing the technology transfer exploiting the insights in dyes compatible with the water environment to develop DSSC with aqueous electrolytes.

Titanium dioxide is a technologically interesting material in many applicative fields that, however, exhibits critical aspects in terms of phase purity and synthesis/ growth conditions. The presented work deals with the deposition, in vacuum, of single-phase rutile and anatase titania films by excimer laser ablation (? = 248 nm) of anatase and rutile targets. Post-deposition thermal treatment at 450 oC in air was applied to drive the crystalline evolution of the as-deposited films, limit oxygen desorption and avoid changes in the polymorph phase. Unlike the typical use of oxygen as a background gas and Ti target in pulsed laser deposition of TiO2, our setting vacuum background atmosphere not only allows to relate the final phase of the film directly to the target phase but also to rule out phase transitions and mixed-phase, by the interplay between post-growth temperature and limited oxygen desorption. Herein, we study and discuss how the ablation process impacts on and determines film composition and morphology. The discussed influence of the target phase on the optical, morphological and photocatalysis properties of the titania films points out good performances of our samples and the importance to tune deposition to obtain the titania polymorph phase more suitable for specific applications.

Heterogeneous photocatalysis is considered as one of the most appealing options for the treatment of organic pollutants in water. However, its definitive translation into industrial practice is still very limited because of both the complexity of large-scale production of catalysts and the problems involved in handling the powder-based photocatalysts in the industrial plants. Here, we demonstrate that the MOCVD approach can be successfully used to prepare large-scale supported catalysts with a good photocatalytic activity towards dye degradation. The photocatalyst consisted of nanostructured TiO2 thin film deposited on a stainless steel mesh substrate. The film thickness, the morphological features, and the crystallographic properties of the different portions of the sample were correlated to the position in the reactor chamber and the reaction conditions. The photocatalytic activity was evaluated according to the international standard test ISO 10678:2010 based on methylene blue degradation. The photocatalytic activity is essentially constant (PMB over 40 µmol·m-2·h-1) throughout the film, except for the portion of sample placed at the very end of the reactor chamber, where the TiO2 film is too thin to react properly. It was assessed that a minimum film thickness of 250-300 nm is necessary to reach the maximum photocatalytic performance.

The adverse effects of NOx (NO + NO2) gases on the environment and human health have triggered the development of sustainable photocatalysts for their efficient removal (De-NOx). In this regard, the present work focuses on supported Co3O4-based nanomaterials fabricated via chemical vapor deposition (CVD), assessed for the first time as photocatalysts for sunlight-activated NO oxidation. A proofof- principle investigation on the possibility of tailoring material performances by heterostructure formation is explored through deposition of SnO2 or Fe2O3 onto Co3O4 by radio frequency (RF) sputtering. A comprehensive characterization by complementary analytical tools evidences the formation of high-purity columnar Co3O4 arrays with faceted pyramidal tips, conformally covered by very thin SnO2 and Fe2O3 overlayers. Photocatalytic functional tests highlight an appreciable activity for bare Co3O4 systems, accompanied by a high selectivity in NOx conversion to harmless nitrate species. A preliminary evaluation of De-NOx performances for functionalized systems revealed a direct dependence of the system behavior on the chemical composition, SnO2/Fe2O3 overlayer morphology, and charge transfer events between the single oxide constituents. Taken together, the present results can provide valuable guidelines for the eventual implementation of improved photocatalysts for air purification.

Heterocyclic compounds have found extensive application as active components in optoelectronic and photovoltaic devices, either as light-harvesting or charge carrier-transporting materials. In recent years, our research group focused on the design and synthesis of donor-acceptor, conjugated organic compounds endowed with a wide array of heterocyclic moieties, and investigated their use in various solar energy conversion technologies, such as dye-sensitized and perovskite solar cells, photocatalytic systems for hydrogen production and luminescent solar concentrators. In this communication, we will present some selected examples of our activity, illustrating the logic behind the rational design of the compounds and describing the synthetic strategies followed for their preparation, mostly based on the assembly of molecular "jigsaw pieces" by cross-coupling reactions and direct arylation procedures. Finally, we will discuss the relationship between the compounds spectroscopic and electrochemical properties and the performances of the corresponding solar-powered devices.

A literature selection of the properties and performances of perovskite-type LaFeO3 prepared by solution combustion synthesis from different fuels is proposed in relation with their photocatalytic activity, particularly for the abatement of wastewater organic pollutants. In solution combustion synthesis, the fuel has the triple role of reducer, complexing agent and microstructural template, influencing both chemical-physical and photocatalytic properties of the perovskite powder. A specific dissertation is dedicated to LaFeO3 prepared by citric acid or by soluble bio-based substances extracted from urban waste, which are examined for the degradation of some phenolic derivatives and cationic dyes. Critical aspects related to the synthetic protocol are evidenced and LaFeO3 stability is also studied, considering the role of released substances, which can simultaneously initiate a photocatalytic process. It is highlighted that the fuel affects the reproducibility of LaFeO3 performance in the abatement of organic pollutants.

Cellulose nanomaterials have been widely investigated in the last decade, unveiling attractive properties for emerging applications. The ability of sulfated cellulose nanocrystals (CNCs) to guide the supramolecular organization of amphiphilic fullerene derivatives at the air/water interface has been recently highlighted. Here, we further investigated the assembly of Langmuir hybrid films that are based on the electrostatic interaction between cationic fulleropyrrolidines deposited at the air/water interface and anionic CNCs dispersed in the subphase, assessing the influence of additional negatively charged species that are dissolved in the water phase. By means of isotherm acquisition and spectroscopic measurements, we demonstrated that a tetra-sulfonated porphyrin, which was introduced in the subphase as anionic competitor, strongly inhibited the binding of CNCs to the floating fullerene layer. Nevertheless, despite the strong inhibition by anionic molecules, the mutual interaction between fulleropyrrolidines at the interface and the CNCs led to the assembly of robust hybrid films, which could be efficiently transferred onto solid substrates. Interestingly, ITO-electrodes that were modified with five-layer hybrid films exhibited enhanced electrical capacitance and produced anodic photocurrents at 0.4 V vs Ag/AgCl, whose intensity (230 nA/cm) proved to be four times higher than the one that was observed with the sole fullerene derivative (60 nA/cm).