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Biomass reforming by harvesting solar energy can provide green hydrogen. Current biomass photoreforming provides H2 erratically and in limited yield although efficiently, owing to intermittent features of solar light and incomplete degradation of biomass C-C bonds. Here, we detour the flaws by prioritizing conversion of carbohydrates to liquid hydrogen carriers (LHCs, consisting of HCOOH and HCHO), appropriate for transportation. Subsequently, the LHCs are fully decomposed, releasing only H-2 and CO2. This stepwise process enables complete scission of carbohydrate C-C bonds, affording 44 g of H-2 per kg of glucose thereof. Intermittent solar light provides the photoenergy and heat to split glucose car-bons to produce LHCs (2.5 mmol h(-1)) in a flow apparatus. This work demonstrates hydrogen production and storage by empha-sizing the complete scission of biomass C-C bonds.

A more sustainable and efficient protocol for the photocatalytic α-amino arylation promoted by fac-Ir(ppy)3 was developed. Three noteworthy results were achieved: i) the replacement of toxic medium DMA with the greener solvents NBP and NHP, and the concurrent improvement of the process efficiency by lowering both the amine and the base amount; ii) the development of a recycling protocol for both the sustainable solvent NHP and the commercially available costly photocatalyst fac-Ir(ppy)3, achieving environmental and economic benefits. This approach to the photocatalyst recovery avoids very demanding catalyst structural modifications; iii) the protocol in green solvents proved to be scalable up to 10 mmol of limiting reagent, maintaining excellent performance also lowering the photocatalyst loading down to 0.05 mol%. This is the first example of photocatalytic α-arylation of amines promoted by such a low amount of catalyst. Lastly, the versatility of this approach was demonstrated by extending the use of the green solvent NBP to another photoredox process.

The use of glassceramics in photocatalysis is an attractive option for the realization of smart optical fibers and self-cleaning windows. Here we present the photocatalytic activity of germanosilicate glasses embedding Ga2O3 nanocrystals prepared by batch melting and glass heat treatment. The powdered material is used for UV-assisted degradation of rhodamine in water. The kinetics show changes after repeated experiments. In the first cycle, the apparent rate is governed by a second-order reaction with a Gaussian-like shape, whereas the second cycle follows a first-order reaction. The modification appears to be correlated with perturbations in the defect population. Photoluminescence has been used to monitor the evolution of such defects. Kinetic data on photoreactions and defect formation have been modelled in a combined frame in which the defect concentration determines the photocatalytic activity. The results prove the photocatalytic ability of the studied glassceramics. Moreover, the general validity of the kinetic model can be of interest for other systems in which the photocatalytic response depends on photoreactive species concentration.

A dehydrogenative functionalization of styryl carbon-carbon double bonds with triflamide is described via dual visible-light photoredox/cobaloxime catalysis. A range of allylic triflamides (20 examples) were isolated in moderate to good yields (up to 88%) under stoichiometric acceptorless conditions. Dedicated labelling, as well as spectroscopic experiments, enabled to shed light on the concatenated photo- and chemo-catalytic cycles. (Figure presented.).

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 H2 generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H2 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 H2 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 H2 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 H2 evolution.

We investigate the interface between carbon nitride (C3N4) and phosphorene nanosheets (P-ene) by means of Density Functional Theory (DFT) calculations. C3N4/P-ene composites have been recently obtained experimentally showing excellent photoactivity. Our results indicate that the formation of the interface is a favorable process driven by Van der Waals forces. The thickness of P-ene nanosheets determines the band edges offsets and the charge carriers’ separation. The system is predicted to pass from a nearly type-II to a type-I junction when the thickness of P-ene increases, and the conduction band offset is particularly sensitive. Last, we apply the Transfer Matrix Method to estimate the efficiency for charge carriers’ migration as a function of the P-ene thickness.

A photoredox catalytic synthesis of functionalized 2-aminofurans is proposed starting from α-halo carbonyl substrates and N-allenamides. The protocol proves to be efficient and sustainable thanks to: i) the use of visible light as green energy source, ii) the redox-neutral nature of the transformation, allowing to avoid additives and strong oxidants, iii) the mild reaction conditions and the functional groups tolerance, iv) the low photocatalyst loading and the absence of excess reagents, v) the one-pot formation of three new bonds in a domino sequence. According to our mechanistic hypothesis, the transformation is configured as a double radical-polar crossover reaction, in which the photocatalyst is excited, oxidized and reduced twice for each molecule of 2-aminofuran produced. The novelty of the designed synthetic approach also lies in the use of N-allenamides as substrates, which, after the addition of the first electrophilic radical, preserve a further reactive π-system, making possible the addition of a second α-keto radical and enabling the installation of a keto functionality at a remote position. The good yields, the broad scope, and the possibility to further synthetically elaborate the obtained furans make this protocol particularly promising for the construction of useful products. (Figure presented.).

In recent years, the issue of coral bleaching has led to restrictions in some tropical locations (i.e., Palau, Hawaii, etc.) on the use of some organic UV sunscreen filters, such as oxybenzone and ethyl hexyl methoxycinnamate. In contrast, ZnO is considered safe for marine environments and thus is often used without considering its photocatalytic and oxidative activities related to the generation of O2•− and HO•. Moreover, ZnO needs to be used in combination with other filters to reach higher protection factors. Thus, the study of its interaction with formulations and with organic filters is important in sunscreen technology for the development of safer by-design products. In this work, the photocatalytic activity of zinc oxides with different surface areas (30, 25 and 9 m2/g) and their interaction with selected organic sunscreen filters were investigated. In particular, the ZnO photocatalytic kinetics were studied following the photodegradation of Acid Blue 9 (AB9) observing a first-order reaction with a chemical regime. Our evaluations of the selective inhibitions by hvb+ and HO• demonstrated a substantial predominance of the hydroxide radicals in the expression of the photocatalysis, a trend that was also confirmed by the irradiation of ZnO in an ethanolic solution. Indeed, the formulations containing both ZnO and organic filters defined as “safe” for coral reefs (i.e., Diethylamino Hydroxybenzoyl Hexyl Benzoate, DHHB, and Ethylhexyl Triazone, EHT) showed a non-negligible photocatalytic oxidation and thus the combination was underlined as safe to use.

Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water. Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach.

Boron-dipyrromethene complexes (BODIPYs) are attracting a growing interest for their notable photophysical properties. Specifically, their application in organic photocatalysis is receiving particular attention thanks to their ability to undergo both electron and energy transfer processes, thus acting as promising photoredox catalysts and photosensitizers. Although the number of examples employing these organic dyes is constantly increasing, there are not so many studies that correlate their chemical composition to their photocatalytic activity. In this work, a rationally designed structure-activity relationship study was performed by selecting a synthetically relevant atom transfer radical addition (ATRA) reaction as a benchmark. We demonstrated how the presence of heavy atoms in the chromophore’s core turned out to be essential for achieving high reactivity levels. On the contrary, electron-withdrawing groups in position 8 (meso) undermined the catalytic performances, in agreement with the proposed reaction mechanism.

La ricerca di una nuova fonte di energia pulita è l'obiettivo per la comunità scientifica che dovrebbe essere raggiunto nei prossimi decenni. L'idrogeno ha guadagnato molta attenzione nella comunità scientifica come vettore di energia rinnovabile. Tuttavia, ora, l'obiettivo principale in campo energetico è quello di passare dalla produzione di idrogeno grigio (ottenuto da fonti fossili con successiva emissione di anidride carbonica) a quella di idrogeno verde (prodotto con zero carbon footprint). Durante il mio dottorato di ricerca, mi sono concentrata su diverse tematiche riguardanti l'uso dei coloranti organici per migliorare la cattura della radiazione solare in dispositivi per la produzione di combustibili solari. Ho studiato due diverse applicazioni, una fotocatalitica e una fotoelettrochimica. Per queste applicazioni, ho considerato approcci covalenti e non covalenti. In fotocatalisi, ho studiato solo un approccio non covalente tra il colorante e il donatore di elettroni sacrificali (SED). Ho deciso di non indagare su un'interazione covalente, perché, siccome il SED non può essere rigenerato dal sistema, porterebbe alla conseguente perdita di anche il colorante. In ogni caso, l'instaurazione dell'interazione supramolecolare ha favorito l'attività fotocatalitica confermando il successo del nuovo design proposto. Riguardo alle celle fotoelettrochimiche, ho invece investigato entrambi gli approcci. Presento il primo esempio di coloranti a base di calix[4]arene impiegati nei fotoanodi di celle fotoelettrochimiche per sfruttare le loro capacità host-guest. Tuttavia, le prove di una corretta interazione host-guest benefica o infruttuosa tra i coloranti e il catalizzatore sono ancora in fase di studio. Il secondo approccio non covalente investigato è l'interazione π-π tra un colorante funzionalizzato con grafene e un catalizzatore propriamente funzionalizzato. Sono tutt'ora in corso le ulteriori caratterizzazioni e gli studi in applicazioni fotoelettrochimiche. Riguardo all'approccio covalente, questo dovrebbe risultare più stabile e con l'immobilizzazione del catalizzatore a una distanza fissa dalla superficie del semiconduttore, è possibile evitare l'instaurarsi di interazioni dannose con il semiconduttore. Ho presentato il primo esempio di diadi a base di coloranti organici per l'applicazione di fotoanodi. Queste molecole hanno mostrato un'eccellente efficienza nell'evoluzione dell'ossigeno essendo la più alta rispetto allo stato attuale dell'arte per sistemi simili. L'altro disegno covalente proposto è stato ottenuto durante il mio periodo all'estero a Yale University. Questo design innovativo ha fallito nell’uso in celle fotoelettrochimiche, ma questa molecola ha mostrato ottime prestazioni come semplice catalizzatore in celle elettrochimiche. Significa che questo catalizzatore possiede il giusto potenziale per ossidare l'acqua e può essere utilizzato in combinazione con una fonte di energia esterna, come i pannelli solari. Tuttavia, sono necessarie ulteriori indagini nella porzione di colorante per ottenere un migliore trasferimento di carica per le applicazioni PEC. The pursuit of a clean energy source is a goal for the scientific community that should be achieved in the following decades. In recent years, hydrogen has gained much attention in the scientific community as a renewable energy carrier. However, the main goal in the energetic field is to move from the production of grey hydrogen (obtained using fossil sources with the subsequent emission of carbon dioxide) to the evolution of green hydrogen (produced with zero carbon footprint). During my Ph. D., I have focused on different topics regarding the use of organic dyes as visible light photosensitizers in devices for the production of solar fuels through efficient light harvesting. I investigated both photocatalytic (PC) and photoelectrochemical (PEC) applications. For these applications, I considered both covalent and non-covalent approaches. In the PC application, I investigated only a non-covalent approach between the dye and the sacrificial electron donor (SED). I decided not to investigate a covalent interaction because since the system cannot regenerate the SED, it would have led to the loss of the dye as well. Regardless, the establishment of supramolecular interactions that favored the photocatalytic activity confirmed the success of the new proposed design. In the PEC application, I investigated both approaches. I present the first example of calix[4]arene-based dyes employed in photoanodes of PEC cells to exploit their host-guest capabilities. However, the evidence of the establishment of either beneficial or fruitless host-guest interaction between the dyes and the water oxidation catalyst (WOC) is still under investigation. The second non-covalent approach investigated is the π-π interaction between a graphene-functionalized dye and a suitable modified WOC. All the further characterization and PEC applications are in progress. On the other hand, the covalent approach should be the most stable, and with the immobilization of the WOC at a fixed distance from the semiconductor surface, it is possible to avoid the establishment of a detrimental interaction with the semiconductor. We presented the first example of organic-dye-based dyads for photoanode application. These molecules showed excellent efficiencies in oxygen evolution being the highest concerning the actual state of the art for similar systems. The other covalent design proposed has been obtained during my Ph. D. period abroad at Yale University. This innovative design failed in the PEC application, but this molecule exhibited very good performances as simple WOC in electrochemical cells. This means that this WOC has the right potential to oxidize water and can be used in combination with an external source of energy, such as solar panels. However further investigation in the dye portion is required to achieve a better charge transfer for the PEC applications.

La presente tesi è centrata sul trattamento computazionale di ossidi di metalli di transizione e semiconduttori classici. L'interesse per questi materiali è dovuto alle loro proprietà elettroniche, ottiche e magnetiche e alla loro vasta gamma di applicazioni nella catalisi, nei dispositivi elettronici e nella foto ed elettrocatalisi. Una delle proprietà fondamentali di questi materiali è il gap di banda, che determina le proprietà ottiche, elettriche e chimiche. Da un punto di vista teorico, la metodologia più utilizzata per descrivere il gap di banda di questi materiali è la teoria funzionale della densità (DFT). La stima del gap di banda mediante DFT con l'approccio GGA o funzionali ibridi è giustificata per materiali non altamente correlati come semiconduttori TiO2, ZnO, V2O5, III-V, ecc. Tuttavia, quando si tratta di materiali altamente correlati, si è necessario introdurre metodi che includano effetti a molti corpi (saltellamento di elettroni), come il GW, e la teoria dinamica del campo medio (DMFT). Per risolvere il problema della descrizione di materiali altamente correlati, abbiamo iniziato questa tesi con lo studio degli ossidi di metalli di transizione con carattere di Mott Hubbard utilizzando l'approccio Charge Transition Level (CTL). Da questa ricerca, è emerso che l'approccio CTL fornisce una migliore descrizione del gap di banda di materiali altamente correlati rispetto a quelli ottenuti con funzionali ibridi e metodi teorici di alto livello come GW e DMFT, in cui i valori calcolati vengono confrontati con misurazioni sperimentali. Successivamente, è stata studiata la descrizione e la razionalizzazione del ruolo del confinamento quantistico sui semiconduttori III-V attraverso la considerazione di (110) superfici con spessori diversi. I risultati del confinamento quantistico indicano che esistono due gruppi di semiconduttori, il primo corrisponde ai semiconduttori meno colpiti come il gruppo Al-V e il secondo ai semiconduttori fortemente interessati come il gruppo In-V. Poi siamo passati al trattamento computazionale dei materiali compositi per applicazioni fotocatalitiche come le eterogiunzioni. In un capitolo dedicato sono stati forniti alcuni aspetti metodologici che devono essere considerati nella progettazione di eterogiunzioni binarie e ternarie. In particolare, viene fornita la descrizione delle eterogiunzioni di tipo II poiché questi tipi di interfacce sono le più interessanti per le applicazioni di fotocatalisi. In questo ultimo capitolo della tesi vengono descritti due casi di co-catalizzatori, entrambi basati su catalizzatori ad atomi singoli (SAC) per la reazione di evoluzione dell'idrogeno (HER). In primo luogo, viene discusso l'effetto delle diverse dimensioni delle nanoparticelle d'oro (atomi singoli, nanocluster e nanoparticelle) supportate sul grafene drogato con azoto. In secondo luogo, viene descritta la formazione di due intermedi (MH e HMH) in metalli di transizione adsorbiti su diversi supporti di grafene drogati con azoto e bisolfuro di molibdeno (MoS2). The present thesis is focused on the computational treatment of transition metal oxides and classical semiconductors. The interest in these materials is due to their electronic, optical, and magnetic properties, and their wide range of applications in catalysis, electronic devices, and photo-and electro-catalysis. One of the fundamental properties of these materials is the band gap, which determines the optical, electrical, and chemical properties. From a theoretical perspective, the most widely employed methodology to describe the band gap of these materials is the Density Functional Theory (DFT). The estimation of the band gap by DFT with the GGA approach or hybrid functionals is justified for materials that are not highly correlated such as TiO2, ZnO, V2O5, III-V semiconductors, etc. However, when one deals with highly correlated materials, it is necessary to introduce methods that include many-body effects (electron hopping), such as the GW, and the dynamical mean-field theory (DMFT). In order to solve the problem of the description of highly correlated materials, we started this thesis with the study of transition metal oxides with Mott Hubbard character by using the Charge Transition Level approach (CTLs). From this research, it was found that CTLs approach provides a better description of the band gap of highly correlated materials than those obtained with hybrid functionals and high level of theory methods such as GW and DMFT, where the computed values are compared with experimental measurements. Next, the description and rationalization of the role of quantum confinement on III-V semiconductors through the consideration of (110) surfaces with different thicknesses was studied. The results from quantum confinement indicate that there are two groups of semiconductors, the first one corresponds to semiconductors that are less affected such as the Al-V group, and the second one to semiconductors that are strongly affected such as the In-V group. Then we moved to the computational treatment of composite materials for photocatalytic applications such as the heterojunctions. In a dedicated chapter, some methodological aspects that need to be considered in the design of binary and ternary heterojunctions were provided. In particular, the description of type-II heterojunctions is given since these kinds of interfaces are the most interesting for photocatalysis applications. In this last chapter of the thesis two cases of co-catalysts are described, both based on single atoms catalysts (SACs) for the hydrogen evolution reaction (HER). First, the effect of different gold nanoparticles size (Single atoms, Nanoclusters, and Nanoparticles) supported on nitrogen-doped graphene is discussed. Second, the formation of two intermediates (MH and HMH) in transition metal oxides adsorbed on different nitrogen-doped graphene supports and molybdenum disulfide (MoS2) is described.

The shape-controlled synthesis of cuprous oxide (Cu$_2$O) photocatalysts with both low or high index crystal planes has received increasing attention due to their unique facet-dependent properties. Since they are cheap and earth abundant, these well-defined Cu$_2$O nanostructures are extensively used for different photocatalytic reactions, also because of their strong visible light absorption capability. However, further development will be still needed to enhance the efficiency and photostability of Cu$_2$O, which still limits its industrial application. We start this review by summarizing the synthetic advancement in the facet engineering of Cu$_2$O and other associated hybrid Cu$_2$O-based heterostructures with a special emphasis put on their growth mechanism. We then discuss different facet-dependent properties, which are relevant to photocatalysis. In the subsequent section, we present a critical discussion on the photocatalytic performance of faceted Cu$_2$O nanostructures during organic synthesis, hydrogen production, and carbon dioxide photoreduction. The relation between photocatalytic efficiency and product selectivity with exposed crystal facets or with different composition of hybrid nanostructures is also discussed. Finally, important strategies are proposed to overcome the photostability issue, while outlining the course of future development to further boost the technological readiness of well-defined Cu$_2$O-based photocatalysts.

One of the efficient strategies to enhance light harvesting capability of metal oxides nanoparticles (NPs) is to deposit low band gap metal sulfides on them via pseudo-successive ionic layer adsorption and reaction (p-SILAR). Resultant oxide-sulfide nanocomposites have a variety of applications, however there is still a need to increase the deposition of metal sulfide in the form of quantum-dots (QDs). In this work, we have successfully enhanced the deposition of QDs on TiO2 NPs using a modernized H2S-treatment strategy. A rotary reactor was employed for H2S-treatment of TiO2 NPs, ensuing higher deposition of PbS (in TiO2–PbS) and CdS (in TiO2–CdS) via p-SILAR. Resultantly, dye degradation of Rhodamine B increased from 63% to 75% and 72%–84%, respectively. X-ray photoelectron spectroscopy revealed the efficacy of modernized H2S-treatment while intensive electrochemical characterization affirmed reduction in charge carrier transfer resistances due to superior deposition of PbS and CdS QDs on TiO2 NPs.

We report the photocatalytic properties of ZnO and Cu2O thin films deposited on glass substrates at room temperature by DC sputtering and pulsed laser deposition. The photoactivity of the films was investigated through the degradation of rhodamine B (RhB) and methyl orange (MO) under solar light. In order to select the most suitable film of ZnO for the of RhB and MO degradation, the relationship between the characteristics (e.g. energy levels and defects concentration) of ZnO films and their effectiveness in the photocatalytic yield of RhB and MO been studied, where several films were deposited by using different oxygen partial pressures (PO2: 0.05–1.3mbar), while Cu2O films were grown under a pressure of 0.01mbar. The XRD patterns show that all ZnO films have (002) preferential orientation, and crystallite size increases from 73 to 122nm raising PO2. The gap Eg of ZnO (3.26 and 4.15eV) depends on PO2, and the films present photoluminescence emission in the UV–Vis-near IR region. On the basis of structural, optical and electrical characterizations of both films, a comparative study was carried out on the dyes degradation. Cu2O films exhibit a high photoactivity with MO (81.69%) under solar light (6h), whilst for RhB the best elimination rate (60.85%) was achieved with ZnO films deposited at 0.1mbar, which were also the ones exhibiting the highest PL peak intensity at the characteristic absorption wavelength of RhB (553nm).

Photocatalysis plays a key role in CO preferential oxidation (CO-PROX) in H2-rich streams thanks to the great performance this reaction can achieve when it is light driven, at atmospheric pressure and room temperature, with negligible hydrogen loss. This short review is an attempt to summarize the most recent advances in photo-PROX focused mainly on the most popular strategies to improve TiO2 photocatalytic activity, as well as on the active phases used, paying special attention to the synthesis and deposition of noble metal nanoparticles because of their outstanding properties. In this work, we critically review these results with the aim of finding general indications about the main characteristics of the catalysts and the optimal operating conditions of photo-assisted CO-PROX reaction.

Silver is extensively used in electronics, industrial catalysis, and biomedical sector owing to its enhanced physicochemical properties. E-waste recycling may contribute significantly to enhance silver recovery in the view of a circular economy and limit the depletion of mineral sources. In this scenario, hydrometallurgical routes represent the most widely used techniques for silver extraction/recovery and require strong acidic solutions, high temperatures, and multiple operating units. An alternative sustainable route for silver recovery from leaching solutions used for silver extraction in industrial applications is herein proposed for the first time. The novel green process of silver recovery is based on the UV/vis light-driven photocatalytic deposition of pure metallic silver over low-cost and non-toxic ZnO photocatalyst. In the second step, ZnO is dissolved by slight acidification and pure metallic silver is easily recovered. Low environmental impact, mild operating conditions, and economic viability are among the major perks of the new silver recovery process developed. In the view of a full-scale implementation, several operating conditions of the recovery process (i.e., photocatalyst load, starting silver concentration, type of hole scavenger and irradiation) were thoroughly investigated. A mathematical model capable of describing the system behaviour under different operating conditions was also developed and allowed to estimate unknown kinetic parameters for the Ag-photodeposition process.

Solar light can be used by semiconductor nanocrystals as a free and largely available source of energy to transform air pollutants into non-volatile less harmful chemicals. The efficiency of this process can be enhanced by doping the semiconductor with carbon-based materials, such as graphene. Nevertheless, such an increased activity has been reported (i) for nanocomposite photocatalysts produced on the research laboratory scale, (ii) analyzing their performance as self-standing photocatalysts and not after incorporation into “real” matrixes (e.g. building materials) and (iii) typically using model target pollutants instead of “real” hazardous ones. Here we describe the large-scale preparation of two series of carbon based photocatalysts starting from commercial materials and we demonstrate their superior photocatalytic activity in degrading important air pollutants as nitrogen oxides, compared to undoped photocatalysts. The photocatalytic activity was evaluated by NOx abatement adopting the continuous flow procedure and the apparatus reported in the Italian standard UNI 11,247. Best performing materials were incorporated into two different inorganic matrixes (cement and lime). In both cases, the superior photocatalytic performances were maintained. An improvement up to 42±7% of the photocatalytic activity was measured in the case of a cement sample for a carbon-doped photocatalyst with respect to bare TiO2 . The materials were characterized by UV-Vis spectroscopy, high resolution powder X-ray diffraction (HR-PXRD), high-resolution scanning electron microscopy (HR-SEM) energy-dispersive X-ray spectroscopy (EDS) and micro-Raman.

The photocatalytic and electrocatalytic conversion of CO2 has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO2 to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed.

Carbon nitride (CN) is a heterogeneous photocatalyst that combines good structural properties and a broad scope. The photocatalytic efficiency of CN is associated with the presence of defective and radical species. An accurate description of defective states—both at a local and extended level—is key to develop a thorough mechanistic understanding of the photophysics of CN. In turn, this will maximise the generation and usage of photogenerated charge carriers and minimise wasteful charge recombination. Here the influence of morphology and light-excitation on the number and chemical nature of radical defects is assessed. By exploiting the magnetic dipole-dipole coupling, the spatial distribution of native radicals in CN is derived with high precision. From the analysis an average distance in the range 1.99–2.34 nm is determined, which corresponds to pairs of radicals located approximately four tri-s-triazine units apart.

Photogeneration of Reactive Oxygen Species (ROS) finds applications in fields as different as nanomedicine, art preservation, air and water depollution and surface decontamination. Here we present photocatalytic nanoparticles (NP) that are active only at acidic pH while they do not show relevant ROS photo-generation at neutral pH. This dual responsivity (to light and pH) is achieved by stabilizing the surface of TiO2 NP with a specific organic shell during the synthesis and it is peculiar of the achieved core shell-structure, as demonstrated by comparison with commercial photocatalytic TiO2 NP. For the investigation of the photocatalytic activity, we developed two methods that allow real time detection of the process preventing any kind of artifact arising from post-treatments and delayed analysis. The reversibility of the pH response was also demonstrated as well as the selective photo-killing of cancer cells at acidic pH.

Photocatalytic chemical transformations in the presence of irradiated TiO2 are generally considered in terms of interfacial electron transfer. However, more elusive energy-transfer-driven reactions have been also hypothesized to occur, mainly on the basis of the indirect evidence of detected reaction products whose existence could not be justified simply by electron transfer. Unlike in homogeneous and colloidal systems, where energy transfer mechanisms have been investigated deeply for several organic syntheses, understanding of similar processes in heterogeneous systems is at only a nascent level. However, this gap of knowledge can be filled by considering the important achievements of synthetic heterogeneous photocatalysis, which bring the field closer to industrial exploitation. The present manuscript summarizes the main findings of previous literature reports and, also on the basis of some novel experimental evidences, tentatively proposes that the energy transfer in TiO2 photocatalysis could possess a Förster-like nature.

Carbon-based materials are widely employed as metal-free catalysts or supports in catalysis, energy, and ecological applications because of their interesting properties. Generally, their high surface areas, size, shape, porosity, and the possibility of incorporating additional moieties through chemical functional designs are believed to be essential for enriching the catalytic activity of carbon-containing materials. Lately, the new field of single-atom catalysts (SACs) has emerged as the finest alternative for not only homogeneous but also heterogeneous catalysts used in various kinds of catalytic applications. Among a variety of SACs, carbon-based SACs are widely investigated catalysts because of their extraordinary features such as tunable morphologies, ordered porosity, and effortless immobilization through various metals (noble and non-noble), making them highly efficient single-atom catalysts for numerous important catalytic applications. Herein, we intend to report on the progress achieved in researching carbon-based single-atom catalysts, including primarily metals such as Co, Cu, Zn, Pd, Ni, Pt, among others, embedded in carbon matrices and applied to applications in organic catalysis, photocatalysis, and electrocatalysis. It is important to point out that the main focus of this Review is directed to the activity and applications of single-atom catalysts, which are discussed in detail; thus, characterization and rationalization are excluded. Finally, we provide a future perspective on the development and progress made on a carbon-based single metal atom for catalysis.

A long-term test at a laboratory scale with a closed system (a coral reef aquarium) has been carried out to study the potentialities of photocatalytic ozonation and photocatalysis for the removal of noxious organic compounds in recirculating systems (aquaria and recirculating aquaculture systems) working with a minimum make up of new water. Attention has been focused not only on the depuration capabilities but also on possible negative phenomena, some of which could become apparent only at long times. After having tuned the system by setting appropriate operating conditions and procedures, positive results were obtained. In particular, it was observed that the alternation of photocatalytic ozonation with photocatalysis with definite cycle allowed to severely limit the presence of the organic compounds, which otherwise could accumulate in the system, and at the same time to control the formation of bromate, the ozonation side-product of main concern. In addition, the values of other parameters, which are important for water quality, remained at satisfactory values. It was also verified that the prepared photocatalytic films maintained a good photocatalytic activity even after several months of utilization in seawater. These results demonstrate that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of sustainable aquaculture.

The topic of production of useful chemical compounds with the help of solar light has been debated at a recent meeting organized in Rome on October 18 and 19, 2018, by the Accademia Nazionale dei Lincei. Some of the contributions presented at this event are collected in this special issue of the Rendiconti Lincei. Scienze fisiche e Naturali. In this paper, we briefly discuss some recent results concerning the use of solar energy by artificial photochemical reactions for four important applications: (i) conversion of solar energy into fuels or (ii) conversion of sunlight into electrical energy, (iii) use of solar energy to perform organic synthesis that cannot be obtained by conventional chemistry, and (iv) photochemical reactions to reduce pollution.

Photocatalytic hydrogen production from biomass is a promising alternative to water splitting thanks to the oxidation half-reaction being more facile and its ability to simultaneously produce solar fuels and value-added chemicals. Here, we demonstrate the coproduction of H2 and diesel fuel precursors from lignocellulose-derived methylfurans via acceptorless dehydrogenative C−C coupling, using a Ru-doped ZnIn2S4 catalyst and driven by visible light. With this chemistry, up to 1.04 g gcatalyst−1 h−1 of diesel fuel precursors (~41% of which are precursors of branched-chain alkanes) are produced with selectivity higher than 96%, together with 6.0 mmol gcatalyst−1 h−1 of H2. Subsequent hydrodeoxygenation reactions yield the desired diesel fuels comprising straight- and branched-chain alkanes. We suggest that Ru dopants, substituted in the position of indium ions in the ZnIn2S4 matrix, improve charge separation efficiency, thereby accelerating C−H activation for the coproduction of H2 and diesel fuel precursors. Biomass can be used to scavenge photogenerated holes in photocatalytic hydrogen production, but the oxidized molecules that form are not always useful products. Here, the authors use Ru-ZnIn2S4 to photocatalyse the dehydrogenative C−C coupling of lignocellulose-derived methylfurans, forming both hydrogen and diesel fuel precursors.

This study investigated the treatment of a shipboard slop containing commercial gasoline in a pilot plant scale consisting of a membrane biological reactor (MBR) and photocatalytic reactor (PCR) acting in series. The MBR contributed for approximately 70% to the overall slop purification. More precisely, the biological process was able to remove approximately 40%, on average, of the organic pollution in the slop. Nevertheless, the membrane was capable to retain a large amount of organic molecules within the system, amounting for a further 30% of the influent total organic content removal. However, this affected the membrane fouling, thus resulting in the increase of the pore blocking mechanism that accounted for approximately 20% to the total resistance to filtration (2.85∙10 13 m −1 ), even if a significant restoration of the original membrane permeability was obtained after chemical cleanings. On the other hand, the biological treatment produced a clear solution for the photocatalytic system, thereby optimizing the light penetration and generation of highly oxidizing active oxygen species that enabled the degradation of bio-recalcitrant compounds. Indeed, low total organic carbon (TOC) values (

Pseudo-successive ionic layer adsorption and reaction (p-SILAR) process was opted for deposition of PbS/CdS and CdS/PbS quantum-dots (QDs) on TiO2 to combine light absorbing tendency of PbS and CdS QDs which evolved significant photocatalytic behavior in TiO2 under visible light irradiation. It was shown that the resultant TiO2/PbS/CdS hierarchical nanocomposite exhibited better photo-electrochemical behavior than TiO2/CdS/PbS, ensuing ∼42% higher degradation of acid orange-56 than the latter and ∼65% higher than pristine TiO2. In addition, both nanocomposites resulted promising antibacterial activity against Escherichia coli (E. coli). Particularly TiO2/PbS/CdS showed much greater inhibition zone (∼14 mm) than TiO2 (∼8 mm).

The influence of BiVO4 and CuO on the chemico-physical properties of TiO2-based systems is reported. The performances of these systems were investigated in the photocatalytic H2 production both under UV and solar light irradiation. The characterization data pointed out that the obtained TiO2 samples have highly porous inverse opal structures with interconnected macropores. Inverse opal TiO2 exhibited higher activity in the H2 production than the commercial TiO2 due to the peculiar porosity that allows photons to enter inside the photocatalyst. A further improvement in terms of photoactivity was verified by addition of increasing amounts of BiVO4. On the contrary a small CuO content was found to be the optimal one for the inverse opal TiO2-CuO composites. In fact, due to surface segregation effects, a higher amount of CuO can partially keep the light radiation away from the TiO2 surface active sites, thus decreasing drastically the absorption of photons. The combination of the benefits of the highly ordered porous TiO2 structure and the presence of BiVO4 or small amounts of CuO can represent a promising strategy towards efficient photocatalytic H2 production.

Electronic structure calculations provide a useful complement to experimental characterization tools in the atomic‐scale design of semiconductor heterojunctions for photocatalysis. The band alignment of the heterojunction is of fundamental importance to achieve an efficient charge carrier separation, so as to reduce electron/hole recombination and improve photoactivity. The accurate prediction of the offsets of valence and conduction bands in the constituent units is thus of key importance but poses several methodological and practical problems. In this Minireview we address some of these problems by considering selected examples of binary and ternary semiconductor heterojunctions and how these are determined at the level of density functional theory (DFT). The atomically precise description of the interface, the consequent charge polarization, the role of quantum confinement, the possibility to use facet engineering to determine a specific band alignment, are among the effects discussed, with particular attention to pros and cons of each one of these aspects. This analysis shows the increasingly important role of accurate electronic structure calculations to drive the design and the preparation of new interfaces with desired properties., The nature, structure and electronic properties of some example of binary and ternary heterostructure relevant in photocatalysis experiments is reported in this work, focusing on important computational aspects such as the band gap problem, quantum size effects, band edges alignment, surface termination and on the insights that simulation can provide when designing new materials.

Photocatalysis exploits light to perform important processes as solar fuel production by water splitting, and CO2 reduction or water and air decontamination. Therefore, photocatalysis contributes to the satisfaction of the increasing needs for clean energy, environmental remediation and, most recently, sanification. Most of the efficient semiconductor nanoparticles (NP), developed as photocatalysts, work in the ultraviolet (UV) spectral region and they are not able to exploit either visible (Vis) or near infrared (NIR) radiation. This limitation makes them unable to fully exploit the broad band solar radiaton or to be applied in indoor conditions. Recently, different approaches have been developed to extend the spectral activity of semiconductor NP, like for example band-gap engineering, integration with upconversion NP and plasmonic enhancement involving also hot-electron injection. Nevertheless, the use of organic molecules and metal complexes, for enhancing the photoactivity in the Vis and NIR, was one of the first strategies proposed for sensitization and it is still one of the most efficient. In this minireview we highlight and critically discuss the most recent and relevant achievements in the field of photocatalysis obtained by exploiting dye sensitization either via dynamic or static quenching.

This project focus on a electron transfer reaction and its integration in a liquid-liquid interface. To do so we studied the synthesis of different dyes such as the Perylene, Perixanthene xanthene and the Naphthalimides. We then aplied these dyes in an interface between two liquids, either the complex emulsion of hexane/fluorohexane/water or a water/micellar interface. We finished with a study of a electron transfer model reaction in the interface using the dyes as photocatalysts.

In the last decades, the interest to adopt new sustainable industrial processes and to find new eco-friendly ways to convert and store energy with a lower impact on the environment is growing due to the devastating consequences of our actions. In this Ph.D. project are investigated new sustainable catalysts based on carbon nanostructures for photocatalytic and electrocatalytic applications. In the first part of this thesis, 3 electrocatalyst for the oxygen reduction reaction (ORR) are proposed: Raspberry-like FeOx nanoparticles were covered with graphitized polydopamine (SNC@PDA500). Subsequently the inorganic core was removed in order to form an hollow N,O co-doped carbon nanoshell (g-PDA500). The elimination of the inorganic core leaves low doses of Fe that migrates on the surface of the carbon nanoshell and form ultrasmall FeOx nanoparticles when g-PDA500 is treated at 700 °C (g-PDA700), following an ex-solution process. SNC@PDA500 and g-PDA500 are active for the O2-to-H2O process (that finds application in fuel cells) while g-PDA700 is active for the O2-to-H2O2 process (that could be relevant as a sustainable alternative to the traditional H2O2 industrial production). In the second part graphitic carbon-based nanomaterials are explored for light-mediated perfluoroalkylation reaction. In particular, the structure/activity relationship was studied in order to determine relevant mechanistic aspects. Graphitic carbon nitride (g-CN) was prepared by conventional thermal polymerization of melamine. Subsequently, post-synthetic structural modifications of g-CN were performed applying 3 different protocols to obtain amorphous carbon nitride (am-CN), reduced carbon nitride (red-CN) and oxidized carbon nitride (ox-CN). am-CN revealed high performance for the perfluorobutylation of 1,3,5 trimethoxy-benzene (model reaction) and showed high performances for 2 classes of reactions: homolytic aromatic substitution (HAS) and atom transfer radical addition (ATRA). Subsequently, the amorphization treatment was investigated: 4 superamorphed carbon nitrides (SACNs) were proposed: 4h-SACN, 6h-SACN, d-SACN and t-SACN. Similarly, the oxidation treatment was explored preparing 3 different oxidized carbon nitrides (OCNs): 2M-OCN, 8M-OCN and OW-OCN. In the last part, 3 different CN-based nanomaterials are prepared: 1) mesoporous graphitic carbon nitride (mpg-CN) using an eco-friendly protocol that involves CaCO3 as hard template, 2) poly heptazine imides (PHIs). The proposed PHIs are prepared following 2 approaches: using a eutectic mixture of LiCl and KCl (PHIK) and using both NaOH and KOH (PHIK-Na).

Photocatalysis based technologies have a key role in addressing important challenges of the ecological transition, such as environment remediation and conversion of renewable energies. Photocatalysts can in fact be used in hydrogen (H2) production (e.g., via water splitting or photo-reforming of organic substrates), CO2 reduction, pollution mitigation and water or air remediation via oxidation (photodegradation) of pollutants. Titanium dioxide (TiO2) is a “benchmark” photocatalyst, thanks to many favorable characteristics. We here review the basic knowledge on the charge carrier processes that define the optical and photophysical properties of intrinsic TiO2. We describe the main characteristics and advantages of TiO2 as photocatalyst, followed by a summary of historical facts about its application. Next, the dynamics of photogenerated electrons and holes is reviewed, including energy levels and trapping states, charge separation and charge recombination. A section on optical absorption and optical properties follows, including a discussion on TiO2 photoluminescence and on the effect of molecular oxygen (O2) on radiative recombination. We next summarize the elementary photocatalytic processes in aqueous solution, including the photogeneration of reactive oxygen species (ROS) and the hydrogen evolution reaction. We pinpoint the TiO2 limitations and possible ways to overcome them by discussing some of the “hottest” research trends toward solar hydrogen production, which are classified in two categories: (1) approaches based on the use of engineered TiO2 without any cocatalysts. Discussed topics are highly-reduced “black TiO2”, grey and colored TiO2, surface-engineered anatase nanocrystals; (2) strategies based on heterojunction photocatalysts, where TiO2 is electronically coupled with a different material acting as cocatalyst or as sensitizer. Examples discussed include TiO2 composites or heterostructures with metals (e.g., Pt-TiO2, Au-TiO2), with other metal oxides (e.g., Cu2O, NiO, etc.), direct Z-scheme heterojunctions with g-C3N4 (graphitic carbon nitride) and dye-sensitized TiO2.