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Can a cheap and bench stable salt catalyse the hydrosulfonylation of unactivated alkenes? Yes it does! Just mix a diarylmethylium tetrafluoroborate salt with a sulfinate salt, wait for the formation of the adduct and turn purple light on it.

Microplastics are of rising health concerns because they have been detected even in remote and pristine environments, from the Artic snow to the Marianne Trench. The occurrence and impact of nanoplastics in ecosystems is almost unknown, in particular due to analytical limitations such as very small sizes that fall below detection limits of current techniques. Here we take advantage of a common interference in analytical flow cytometry to develop a method for the quantification of the number of plastic particles in the 0.6–15 µm size range. Plastic particles are stained with the lipophilic dye Nile-Red then detected by flow cytometry, a method regularly used in biology for rapid quantification of fluorescent cells. We found that sample analysis lasts 90 s, which is hundreds of times faster than the analysis of filter portions by micro-Raman and other spectroscopic techniques. Our method is highly efficient in detecting polyethylene, with staining efficiency higher than 70% and signal linearity with concentration. Staining efficiency up to 96% was observed for polyvinylchloride and for polystyrene.

In the present work a series of design rules are developed in order to tune the morphology of TiO2 nanoparticles through hydrothermal process. Through a careful experimental design, the influence of relevant process parameters on the synthesis outcome are studied, reaching to the develop predictive models by using Machine Learning methods. The models, after the validation and training, are able to predict with high accuracy the synthesis outcome in terms of nanoparticle size, polydispersity and aspect ratio. Furthermore, they are implemented by reverse engineering approach to do the inverse process, i.e. obtain the optimal synthesis parameters given a specific product characteristic. For the first time, it is presented a synthesis method that allows continuous and precise control of NPs morphology with the possibility to tune the aspect ratio over a large range from 1.4 (perfect truncated bipyramids) to 6 (elongated nanoparticles) and the length from 20 to 140 nm.

We demonstrated that controlled periodic illumination (CPI) is unable to increase the quantum yield (or photoefficiency) of the photocatalytic process. Nevertheless, choosing the appropriate experi...

Solid phase synthesis (SPS) of molecularly imprinted nanopolymers (nanoMIPs) represents an innovative method to prepare nanomaterials with tailor-made molecular recognition properties towards peptides and proteins. The synthesis of nanoMIPs by SPS usually involves a pre-polymerization formulation, where the cross-linker is invariably

Atmospheric plastic pollution is now a global problem. Microplastics (MP) have been detected in urban atmospheres as well as in remote and pristine environments, showing that suspension, deposition and aeolian transport of MP should be included and considered as a major transport pathway in the plastic life cycle. Due to the limitations in sampling and instrumental methodology, little is known about MP and nanoplastics (NP) with sizes lower than 50 µm, which is the current limit for FT-IR and Raman microscopy. In our recent work [Bianco et al. 2020], we describe how NP could be transported for longer distances than MP, making them globally present and potentially more concentrated than MP. We highlight that it is crucial to explore new methodologies to collect and analyse NP.Small MPs can be detected by fluorescence spectroscopy: for example, particles can be efficiently stained using Nile Red, as described by Erni-Cassola et al. [2017]. This hydrophobic dye shows fluorescence in green and yellow range of the electromagnetic spectrum and can be easily detected also at low concentration. We are developing a new method, based on this principle, to detect MPs in natural matrices. These are, for instance, surface and atmospheric waters, containing dissolved organic matter and suspended organic particles. Preliminary results on polyethylene, polystyrene and polyvinylchloride are promising for particles in the range 1-25 µm suspended in MilliQ water. We are currently testing the method on river water and snow. Bianco, A.; Passananti, M. Atmospheric Micro and Nanoplastics: An Enormous Microscopic Problem. Sustainability 2020, 12, 7327.Erni-Cassola, G.; Gibson, M.; Thompson, R.; Christie-Oleza, J. Lost, but Found with Nile Red: A Novel Method for Detecting and Quantifying Small Microplastics (1 mm to 20 μm) in Environmental Samples. Environ. Sci. Technol. 2017, 51, 23, 13641–13648

Efficient solar water photosplitting is plagued by large overpotentials of the HER and OER. Even with a noble metal catalyst, the hydrogen evolution reaction can be limited by the strong M-H bonding over some metals, such as Pt, Pd, and Rh, inhibiting hydrogen desorption. H absorption is regulated by the potential at the metal nanoparticles. Through controlled periodic illumination of a Pt/TiO2 suspension, we hypothesized a fast variation of the photopotential that induced catalytic surface resonance on the metal, resulting in more than a 50% increase of the efficiency at frequencies higher than 80 Hz.

The photocatalytic activity of graphitic carbon nitride (g-C3N4) is actually a hot topic in the field of photocatalysis, as more than one thousand papers have been published in 2019 regarding the photocatalytic properties of this material. Here, we critically evaluated the state-of-the-art focusing on (i) the photophysical and electrochemical properties of this organic semiconductor; (ii) the proposed methods of synthesis that affect dramatically its properties starting from the stoichiometry and the p- or n-type nature; (iii) the features of the heterojunctions in g-C3N4-based hybrid heterostructures (binary, ternary, or also of higher complexity); (iv) its photocatalytic and photochemical applications; and (v) its uses in processes and technologies beyond (photo)catalysis (e.g., analytical applications). The photocatalytic applications of g-C3N4 are reviewed in the light of its overall semiconducting properties and chemical reactivity, focusing on the water photosplitting, the artificial photosynthesis, and photocatalytic CO2 reduction, its use in advanced oxidation processes for the abatement of (bio)recalcitrant pollutants and for photocatalytic disinfection, and last, as photoactivated catalyst for the synthesis of value-added compounds in organic syntheses. Some conclusions regarding the properties of this material and its more promising applications are drawn, together with some general perspectives of this organic semiconductor in the field of photocatalysis.

Understanding the correlation between the morphological and functional properties of particulate materials is crucial across all fields of physical and natural sciences. This manuscript reports on the investigation of the effect of polyethylene glycol (PEG) employed as a capping agent in the synthesis of SrTiO3 crystals. The crucial influence of PEG on both the shape and size of the strontium titanate particles is revealed, highlighting the effect on the photocurrents measured under UV&ndash, Vis irradiation.

The large production of plastic material (PlasticsEurope, 2019), together with the mishandling of plastic waste, has resulted in ubiquitous plastic pollution, which now reaches even the most remote areas of the Earth (Allen et al., 2019; Bergmann et al., 2019). Plastics undergo a slow process of erosion in the environment that decreases their size: microplastics (MPs) and nanoplastics (NPs) have diameters between 1 µm and 5 mm and lower than 1 µm, respectively (Frias and Nash, 2019).The occurrence, transformation and fate of MPs and NPs in the environment are still unclear. Therefore, the objective of this work is to better understand the reactivity of NPs using an aqueous suspension of polystyrene NPs (PS-NPs) as a proxy, in the presence of sunlight and chemicals oxidants. The results obtained are relevant to both the atmospheric aqueous phase, such as cloud and fog droplets, and surface waters. We investigated the reactivity of PS-NPs with light and with two important oxidants in the environment: ozone (O3) and hydroxyl radicals (•OH). The adsorption of ozone (O3) on PS-NPs is investigated, showing a significant O3 uptake. Moreover, for the first time, a reactivity constant with •OH is determined. We found a linear correlation between the kinetic constants measured for three different sizes of PS-NPs and the surface exposed by the particles. Degradation products (short chain carboxylic acids and aromatic compounds), obtained by direct and •OH-mediated photolysis of PS-NPs suspensions, are identified by high-resolution mass spectrometry. Irradiation of a PS-NPs suspension under natural sunlight for 1 year has shown the formation of formic acid and organic compounds similar to those found in riverine and cloud dissolved organic matter.This work is crucial to assess the impact of NPs abiotic degradation in atmospheric and surface waters; indeed, the reactivity constant and the degradation products can be implemented in environmental models to estimate the contribution of NPs degradation to the natural dissolved organic matter in the aqueous phase. A preliminary simulation using APEX (Aqueous Photochemistry of Environmentally occurring Xenobiotics) (Bodrato and Vione, 2014) model shows that in NPs-polluted environments (109 particles mL-1) there is potential for NPs to significantly scavenge •OH, if the content of natural organic matter is not too high, as observed for surface and cloud water.Allen, S., et al., 2019. Nat. Geosci. 12, 339–344. https://doi.org/10.1038/s41561-019-0335-5Bergmann, et al., 2019. Sci. Adv. 5, eaax1157. https://doi.org/10.1126/sciadv.aax1157Bodrato, M., Vione, D., 2014. Environ. Sci.: Processes Impacts 16, 732–740. https://doi.org/10.1039/C3EM00541KFrias, J., Nash, R., 2019. Mar. Pollut. Bull. 138, 145–147. https://doi.org/10.1016/j.marpolbul.2018.11.022

International audience; Hydrogen production by the electrolysis of plastic-waste was recently suggested as an alternative approach to water electrolysis, owing to its favoured thermodynamics. However, the fundamental aspects of such electro-catalytic process were not studied in detail. Here we propose a new approach to understand the electrolysis of polymers, by the use of model molecules. Our target is to develop a technology for the electrolysis of poly(methyl methacrylate), PMMA, plastic waste. We used methyl pivalate (MP) as a model molecule, since it contains similar functional groups than PMMA. We performed electrolysis experiments in a Polymer Electrolyte Membrane reactor with Nafion® protonic membranes and Pt/C electrodes at low temperatures (

The light absorption and scattering play a prominent and often underrated role in the overall photocatalytic process and heavily affect the rate. This is particularly important for the choice of the catalyst in addition to other chemical and physical parameters usually considered for their catalytic role. Here we propose an approximated but easy-to-apply method to evaluate the light harvested by the photocatalyst slurry and its scattering/absorption coefficients, which does not require the use of complex spectrophotometric tools and the complicated radiative transport equation. The optical properties are obtained with the lamp and in the experimental setup employed in the photocatalytic batch tests. Among the four TiO2 specimens considered, we characterized Evonik P25 and Hombikat UV100. The obtained scattering and absorption coefficients helped in rationalizing the experimental results on the degradation of formic acid at low concentration. From the rate dependence on the catalyst concentration, this approach allowed further understanding of the role of catalyst-specific properties affecting the overall catalytic performance. This approach is proposed as a starting point for fixing conditions to compare different photocatalysts.

Microplastics (MPs) and nanoplastics (NPs) are ubiquitous and contaminate soil, surface waters, atmospheric aerosol, precipitations, indoor and outdoor environments. However, the occurrence, transformation and fate of NPs in the environment are still unclear. In this work, polystyrene nanoparticles (PS-NPs) are used as a proxy of NPs to study their reactivity and potential impact on atmospheric and surface waters. In particular, the reactivity with hydroxyl radicals (OH) in the aqueous phase is investigated. For the first time, a reactivity constant for the reaction of NPs with OH is measured, strongly dependent on the exposed particle surface area of NPs. Degradation products (short chain carboxylic acids and aromatic compounds), obtained by direct and OH-mediated photolysis of PS-NPs suspensions, are identified by mass spectrometry. Irradiation of a PS-NPs suspension under natural sunlight for 1 year has shown the formation of formic acid and organic compounds similar to those found in riverine and cloud dissolved organic matter, which could contribute significantly to the dissolved organic matter in the aqueous phase.

In this study, we demonstrated that BaCO3 and NH3SO3 can be conveniently used as BaSO4 precursors. BaSO4 is obtained by treating the precursor, BaCO3, with a sulfate-containing solution, owing to the lower solubility product constant of BaSO4 compared to that of BaCO3. Using this procedure, BaSO4 particles with pseudo-cubic/prismatic morphology are obtained. In this case, temperature and reaction time have little influence on morphology, which is mainly controlled by supersaturation and sulfate concentration. Sulfate counter ion also affects the morphology, but its effect is less pronounced. The hydrolysis of NH3SO3 in the presence of soluble barium salts produces BaSO4 particles, and different kinds of morphology can be obtained, encompassing rounded and nearly spherical particles, prismatic and pseudo-cubic, irregular shapes with flat and well-developed facets, and even hopper crystals. In these syntheses, temperature and pH are playing a major role in controlling sulfamic acid hydrolysis and, therefore, supersaturation, with remarkable consequences for crystal nucleation and growth. Considering that BaSO4 finds applications in many sectors and for different purposes, the variety of particle size and shape reported in this study can potentially improve the performance of the materials in which BaSO4 particles are employed.

We report the electrosynthesis of a water oxidation catalyst based on Ag oxides (AgCat). The deposited AgCat is composed of mixed valence crystalline Ag oxides with the presence of particle aggregates whose size is ∼1 μm. This catalyst, coupled with TiO2 and hematite, and under photoelectrochemical conditions, substantially increases photocurrents in a wide range of applied potentials compared with bare and Co-Pi-modified photocatalysts. AgCat can sustain current densities comparable with other water oxidation catalysts. Dark bulk electrolysis demonstrated that AgCat is stable and can sustain high turnover number in operative conditions. Oxygen evolution from water occurs in mild conditions: pH = 2–13, room temperature and pressure, and moderate overpotentials (600 mV) compatible with the coupling with semiconducting oxides as sensitizers. Using hematite in sustained electrolysis O2 production is significant, both in the dark and under irradiation, after an initial slow induction time in which modificatio...

Different amounts of graphene oxide were chemically reduced with hydrazine in the presence of nanometric TiO 2 and SiO 2 . The photocatalytic performance of the resulting hybrid materials was compared with pristine supports using phenol and methylene blue (MB) under two different irradiation conditions (UV–vis and Vis only light). MB is strongly adsorbed on the hybrid materials. Significant MB degradation rates were observed on pristine TiO 2 and hybrid TiO 2 -reduced graphene oxide (rGO) material under both irradiation conditions. In the presence of the hybrid catalyst, the degradation of MB under Vis is due to the dye-sensitized mechanism, while under UV–vis there is an additional semiconductor-based photocatalytic mechanism. Conversely, the presence of rGO reduces the rate of photocatalytic transformation for the poorly adsorbed phenol under UV irradiation, and a negligible degradation rate was observed under Vis. The UV–vis absorption spectra of aqueous suspensions of hybrid materials with different rGO loading indicate a strong interaction of the two materials and a reduction of the light absorption due to the presence of rGO. Among many mechanisms reported on the role of rGO, it is inferred that the working mechanism involves electron transfer from photoexcited states of rGO onto the titania, and holes migration from titania to rGO, where adsorbed substrates are oxidized. This oxidation is possible only if the substrate HOMO has higher energy (less positive standard redox potential) than the empty states of excited rGO, supposedly for MB and not for phenol. Then, reduced graphene is advantageous when substrates are adsorbed and when the charge separation is possible (coupled with a proper semiconductor like TiO 2 ). Alone, or coupled with low work function oxides like SiO 2 , rGO could be ineffective.

The electrochemical behavior of fac-[Mn(pdbpy)(CO)3 Br] (pdbpy=4-phenyl-6-(phenyl-2,6-diol)-2,2'-bipyridine) (1) in acetonitrile under Ar, and its catalytic performances for CO2 reduction with added water, 2,2,2-trifluoroethanol (TFE), and phenol are discussed in detail. Preparative-scale electrolysis experiments, carried out at -1.5 V versus the standard calomel electrode (SCE) in CO2 -saturated acetonitrile, reveal that the process selectivity is extremely sensitive to the acid strength, producing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV/Vis) study under Ar and CO2 atmospheres shows that 1 undergoes fast solvolysis; however, dimer formation in acetonitrile is suppressed, resulting in an atypical reduction mechanism in comparison with other reported MnI catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO2 reduction pathways. Furthermore, a comparative investigation performed on the new fac-[Mn(ptbpy)(CO)3 Br] (ptbpy=4-phenyl-6-(phenyl-3,4,5-triol)-2,2'-bipyridine) catalyst (2), bearing a bipyridyl derivative with OH groups in different positions to those in 1, provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO2 .

p-Type organic semiconductors are attractive to develop new photo- and photoelectro-catalytic systems, particularly if the conduction band is located at negative redox potentials. An easy synthetic route to produce carbon-doped carbon nitride (Cn>3N4) with a stable p-type semiconducting character was optimized. The precursors used were melamine and triaminopyrimidine. The p-type Cn>3N4 exhibited a remarkable photoactivity under visible light compared with pristine C3N4, which is a stable n-type organic semiconductor deeply studied as heterogeneous photocatalyst for many environmental applications. The photoelectrochemical features of the synthesized p-type materials and pristine C3N4 were deeply investigated with chronopotentiometry and cyclic voltammetry, in the dark and under different illumination conditions, and then compared with the photocatalytic activity using 2-fluorophenol as substrate and different radiation sources. The p-doping with carbon of C3N4 reduces the band gap, slightly moves the potential of the valence band, and increases the conduction band to more positive potentials, thus precluding the application of these materials when large negative redox potentials are needed.

Hydrogen production via formate photoreforming on TiO2 is characterized by marked dependence on the ratio between {101} and {001} surfaces for anatase nanoparticles. We observed higher rates of hyd...

It has been often reported that an efficient and green photocatalytic dissociation of water under irradiated semiconductors likely represents the most important goal for modern chemistry. Despite decades of intensive work on this topic, the efficiency of the water photolytic process under irradiated semiconductors is far from reaching significant photocatalytic efficiency. The use of a sacrificial agent as hole scavenger dramatically increases the hydrogen production rate and might represent the classic “kill two birds with one stone”: on the one hand, the production of hydrogen, then usable as energy carrier, on the other, the treatment of water for the abatement of pollutants used as sacrificial agents. Among metal oxides, TiO2 has a central role due to its versatility and inexpensiveness that allows an extended applicability in several scientific and technological fields. In this review we focus on the hydrogen production on irradiated TiO2 and its fundamental and environmental implications.

The photocatalytic performance of pristine and rare earth elements (La, Ce, Pr, Er, Yb) doped zinc oxide was tested toward the abatement of a model pollutant in MilliQ water and wastewater matrices. ZnO doped with Ce, Er and particularly with Yb exhibited photoactivity higher than bare zinc oxide and the benchmark TiO2 P25, especially in wastewater matrix. Several electrochemical investigations were performed via chronopotentiometry and cyclic voltammetry aimed to shed light on the reasons why the diverse materials behaved differently. From the overall data a complex picture emerged, where there is not a single property of the materials evidently outperforming the others. Nonetheless, from the analysis of whole data a limited role of doping emerged for La and Pr, doping with Er improved the photocurrent, doping with Yb favored a better accumulation of photoelectrons, and doping with Ce promoted a faster electron transfer.

The release in the environment of antibiotics develop microbial resistance. In this work we investigated the feasibility of the electrochemical degradation in synthetic urine of cefazolin (CFZ), an antibiotic used for the treatment of antibiotic-resistant infections, which could be carried out in hospital wards on source-separated urine. CFZ is primarily excreted in urine without modifications. The removal of CFZ from human wastes would contribute to slow down the diffusion of CFZ-resistant bacterial strains more efficiently, compared to the treatment of much larger volumes of wastewater. CFZ can be electrochemically degraded using relatively low current density (≥0.5 mA cm−2) and without important generation of toxic by-products such as chlorate (

The addition of graphene nanoplatelets (GNP) to TiO2 nanoparticles (NPs) has been recently considered as a method to improve the photocatalytic efficiency of TiO2 by favoring charge carrier separation. Here, we show that it is possible to improve the efficiency of GNP-TiO2 composites by controlling the shape, stability, and facets of TiO2 NPs grown on GNP functionalized with either COOH or NH2 groups, while adding ethylendiamine (EDA) and oleic acid (OA) during a hydrothermal synthesis. We studied the photocatalytic activity of all synthesized materials under UV-A light using phenol as a target molecule. GNP-TiO2 composites synthesized on COOH-functionalized GNP, exposing {101} facets, were more efficient at abating phenol than those synthesized on NH2-functionalized GNP, exposing {101} and {100} facets. However, neither of these composites was stable under irradiation. The addition of both OA and EDA stabilized the materials under irradiation; however, only the composite prepared on COOH-functionalized GNP in the presence of EDA showed a significant increase in phenol degradation rate, leading to results that were better than those obtained with TiO2 alone. This result can be attributed to Ti-OH complexation by EDA, which protects GNP from oxidation. The orientation of the most reducing {101} facets toward GNP and the most oxidizing {100} facets toward the solution induces faster phenol degradation owing to a better separation of the charge carriers.

This work reports the effect of doping zinc oxide with lanthanide ions on structural, EPR and UV visible properties. Bare and doped samples were synthesized using the simple and green hydrothermal process. Different rare earth ions (RE = La, Ce, Pr, Er and Yb) with 1% molar ratio RE/Zn were used. The samples have been studied using X Ray Diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and UV visible diffuse reflectance spectroscopy. Finally, electron paramagnetic resonance (EPR) spectroscopy, was used to assess the materials photoactivity under UV irradiation, both in solid state, to see the charge carriers’ generation and in solution, evaluating the OH• radical formation using the DMPO (5,5-Dimethyl-1-Pyrroline-N-Oxide) spin trapping technique. The results suggest that the synthesized materials could be interesting systems for the photocatalytic abatement of emerging organic persistent pollutants in wastewater treatment plants.

The photoreactivity of graphene oxide (GO) suspensions was investigated with a double aim: (i) to give insights into the previously reported photo-reduction process, which allows a partial elimination of the oxygen-containing groups from the 2D graphitic structure; (ii) to explore the possible use of GO as photo-activator able to promote the photo-transformation/abatement of organic molecules. To reach these goals and clarify some peculiar aspects of the photochemistry of GO till now obscure or confuse, we synthesized and characterized stable GO suspensions which were then subjected to UV–Vis irradiation for prolonged times. GO underwent partial photo-reduction with the release of gaseous molecules and soluble organic species (e.g., carboxylic acid). The mechanisms of photo-reduction occurring under air or N2 are different, as assessed by the release in solution of diverse soluble molecules. In the presence of oxygen, at long irradiation time, a complete solubilization of the graphenic structures was observed. No difference in the nature and amount of released gases (principally CO2 and CO) was observed in the oxic or anoxic conditions. The possible use of GO as photo-activator was evaluated using phenol as probe molecule. GO revealed a double role of photo-activator and reagent in phenol degradation, as competition was assessed between GO self-transformation/reduction and phenol degradation. At prolonged irradiation time, a marked reactivity of the photoformed species was observed and the complete degradation was achieved for both organic small molecules formed from GO and the phenol added as probe molecule.

Particle aggregation and agglomeration influence the optical properties of materials and therefore their ability to absorb and scatter the incoming radiation, also affecting their photocatalytic activity [1] , [2] , [3] , [4] , [5] , [6] , [7] . We have studied the correlation between aggregation and photocatalytic activity for titanium dioxide by means of experimental measurements of extinction and photocatalytic activity and calculations of their optical properties (extinction, absorption and scattering cross-sections). This approach can be adopted to quantitatively assess the quantum yields of the heterogeneous photocatalytic systems. The study was performed on TiO2 PC105 Cristal ACTiV™, made of aggregated (and agglomerated) primary particles of anatase. The size of the aggregates has been reduced with ultra-sonication. Aqueous suspensions of the obtained materials were characterized by measuring the optical properties (UV–vis extinction), the sizing properties (DLS) and the photocatalytic activity (degradation of phenol under standard conditions). The extinction and absorption spectra of the suspensions were derived from the calculated coefficients, considering also the size distributions measured with DLS, and revealed that light absorption is maximized when particle aggregation and agglomeration are avoided, while diffusion of the incoming radiation dominates when large aggregates and agglomerates are present. The present paper represents a valuable approach to the accurate and reproducible measurement of the photocatalytic activity of TiO2 nanoparticles suspensions, thus allowing a more reliable comparison of the properties of different materials.

The electrochemical behavior of fac-[Mn(pdbpy)(CO)

According to numerous previous reports, a Z-scheme with two photon absorbers is the most promising strategy to achieve artificial photosynthesis, but in addition to two efficient catalysts — one for oxygen evolution, the other for CO2 reduction — two different and complementary semiconducting sensitizers are required. Here we present the synthesis of two bipyridine-functionalized terthiophenes, which can be electropolymerized to give photoactive p-type semiconductors the capability to perform as photocathode in photoelectrochemical cells for water photosplitting or artificial photosynthesis. Indeed the bipyridine moiety in their structure allows the binding of transition metal carbonyl complexes employed in CO2 reduction, and their band-gap is suitable for the coupling with wide band-gap semiconductors, which have already found application as photoanodes. Finally, they are characterized by photogenerated charge carrier density between 1.1 and 1.4 × 1019 cm−3, with first-order recombination constant of 0.7–1.8 × 10−2 s−1. These figures are of the same order of magnitude of their inorganic counterparts and would therefore guarantee photoconductivity of the device and the activation of the organometallic catalysts with which they should be coupled to function as photocathodes for CO2 reduction.

The photoinduced transformation of 2,4,6-triamino-1,3,5-triazine (melamine) was studied by using different advanced oxidation technologies under a variety of experimental conditions. The systems involving homogeneous hydroxyl radicals, as generated by H2O2/hν, Fenton reagent, and sonocatalysis are ineffective. However, melamine is degraded under photocatalytic conditions or by SO4 − (S2O82−/hν). The time evolution of long-living intermediates, such as 2,4-diamino-6-hydroxy-1,3,5-triazine (ammeline) and 2-amino-4,6-dihydroxy-1,3,5-triazine (ammelide), has been followed, being 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid) the final stable product. During both photocatalytic and S2O82−/hν experiments, in the early steps, a fairly stable intermediate evolving to ammelide is observed in a large extent. This intermediate was identified as 2,4-diamino-6-nitro-1,3,5-triazine. This indicates that the primary photocatalytic event is the oxidation of the amino-group to nitro-group through several consecutive fast oxidation steps, and that a hydrolytic step leads to the release of nitrite in solution. To elucidate the nature of the oxidant species hole scavengers such as methanol and bromide ions were added to the irradiated TiO2. They completely stop the degradation, whereas chloride and fluoride ions decrease the degradation rate. The study of the photocatalytic degradation rate of melamine at increasing concentrations using two different commercial titanium dioxides, such as P25 and Merck TiO2, showed an intriguing behavior. A drastic abatement of the melamine transformation rate was observed when coagulation of the P25 slurry occurs due both to the pH change and melamine concentration effect that increase melamine adsorption. In the presence of TiO2 (Merck) the melamine initial degradation rates are significantly lower than those observed in the presence of P25 but are not depressed at larger concentrations. The experimental evidences (e.g., absence of melamine adsorption onto TiO2 surface at low concentrations or at acidic pH or due to the catalyst surface texture, and the lack of reactivity toward OH free and bound) suggest that the effective photocatalytic mechanism is based on an outer sphere direct hole transfer to the melamine. Its formal potential lies in the range 1.9–2.3 V vs NHE. Then, the photodegradation of melamine is an efficient tool to evaluate the direct hole transfer ability of a photocatalyst.

Red cubic and spherical hematite red cool pigments of different particle size were synthesized following two different methods. Cubic and spherical particles with larger particle sizes were obtained through a gel–sol method using chloride and nitrilotriacetate ions as shape controllers, and changing the starting temperature to control the final particles size. Smaller spherical particles were synthesized more rapidly following a catalytic phase transformation method in which the size control is obtained by varying the reagent concentration. Cool properties for the obtained particles were evaluated by calculating the solar reflectance for all hematite samples. The cool properties differ depending on the particle size and shape. By controlling the final size and morphology of pigment particles it is possible to obtain pigments with the desired cool properties. Pigment color properties were also evaluated using CIE XYZ and CIE xyY color spaces.

TiO2 inverse opals present increased photocatalytic production of H2. TiO2 inverse opals with different pore size and TiO2 macroporous structures with disordered arrangement of the pores have been tested in the photocatalytic production of hydrogen in aqueous solution with a formate buffer as hole scavenger. TiO2 inverse opals belong to the family of metamaterials and exhibit unique catalytic properties arising from their peculiar interaction with light. To discriminate the effects of slow photons the hydrogen photoproduction experiments were carried out at two different wavelengths, at 365 nm where the effect of slow photons is maximized, and at 254 nm where it is negligible. The resulting hydrogen production rates suggest a strong effect of the slow light and of the polymer template used in the synthesis of the TiO2 powders. The chemical properties of the polymeric sacrificial template determine the crystalline phase of the sample and as a consequence affect the catalytic performances of the resulting TiO2 structures.

The effects of the highly fluorescent 4-piperidinyl-1,8-naphthalimide (PNI) chromophore on the CO2 reduction catalytic properties of rhenium-based catalysts are investigated herein. In particular, the electro- and photocatalytic CO2 reduction features of [Re(CO)3(bpy)Cl] (bpy = 2,2′-bipyridine) are compared with the activity of [Re(CO)3(phen–PNI)Cl] (phen = 1,10-phenanthroline), which is known for its long excited-state lifetime. Moreover, another Re complex, namely [Re(CO)3(bpy–Ph–PNI)Cl], has been synthesized and tested as an electro- and photocatalyst. The catalytic properties of the selected compounds were studied by means of electrochemical (cyclic voltammetry and controlled-potential electrolysis) and photophysical measurements together with DFT calculations. [Re(CO)3(bpy–Ph–PNI)Cl] showed good electrocatalytic efficiency toward selective CO2 reduction to CO, as well as reduced electrocatalytic overpotential.

Tetracarbonyl complexes of low-valent Group VI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO)4(4,6-diphenyl-2,2′-bipyridine) (1), W(CO)4(6-(2,6-dimethoxyphenyl)-4-phenyl-2,2′-bipyridine) (2), Mo(CO)4(2,2′-dipyridylamine) (3), and W(CO)4(2,2′-dipyridylamine) (4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO2 in nonaqueous media. Cyclic voltammetry performed under a CO2 atmosphere, revealed that these complexes have significant catalytic activity in acetonitrile, and gas chromatographic measurements together with exhaustive electrolysis showed that CO is the major reduction product. Mechanistic insights were obtained by IR-spectroelectrochemical measurements. The substantially different electrocatalytic performances obtained for the two classes of catalysts are compared and discussed.