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A set of four composite materials was prepared, consisting of a nanosponge matrix based on beta-cyclodextrin in which carbon nitride was dispersed. The materials were characterized by the presence of diverse cross-linker units joining the cyclodextrin moieties, in order to vary the absorption/release abilities of the matrix. The composites were characterized and used as photocatalysts in aqueous medium under UV, visible and natural solar irradiation for the photodegradation of 4-nitrophenol, and for the selective partial oxidation of 5-hydroxymethylfurfural and veratryl alcohol to the corresponding aldehydes. The nanosponge-C3N4 composites showed higher activity than the pristine semiconductor, which can probably be attributed to the synergic effect of the nanosponge, capable of increasing the substrate concentration near the surface of the photocatalyst.[GRAPHICS].

Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported on boron nitride (BN) and two types of carbon nitride (C3N4) in the gas-solid 2-propanol dehydration to propene has been studied. Apart from characterizing the materials by a set of conventional laboratory-scale structural and physical-chemical techniques, an insight into the variations of the local structure of supported HPAs is provided by means of X-ray absorption spectroscopy (XAS), and their influence on the supported HPAs (photo)catalytic activity is discussed. The irradiation with UV light increased the activity of both heteropolytungstates with respect to the catalytic experiments. The apparent activation energy calculated for the photo-assisted process resulted always lower with respect to that obtained for the catalytic one alone. Moreover, the materials that showed the highest apparent turnover frequency (TOF) were those in which the HPAs were impregnated on graphitic C3N4 or on BN and, in particular, the highest TOF values were observed at the highest temperature for the PW12/BN and P2W18/BN samples. Interestingly, the highest activity of HPAs supported on BN seems to be due to the stabilization of the W octahedral coordination, according to the XAS data., LFL is grateful to progetto di Ricerca ARS01_00637 Energie per l’Ambiente-TARANTO (PNR 2015-2020) for financial support. IK acknowledges support by Spanish MINECO (MAT2016-78155-C2-1-R), Gobierno del Principado de Asturias (GRUPIN-ID2018-170) and the Alexander von Humboldt Foundation through the Humboldt Research Fellowship. S.V.-R. and J.I.P. acknowledge financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU), the Spanish Agencia Estatal de Investigación and European Regional Development Fund (ERDF) through project RTI2018-100832B-I00, and partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF (project IDI/2018/000233). A.S acknowledges financial support from the MCIU through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52 and from the Comunidad de Madrid for an “Atracción de Talento Investigador” contract (No. 2017t2/IND5395). The European Synchrotron (ESRF), MCIU and Consejo Superior de Investigaciones Científicas (CSIC) are also acknowledged for the provision of synchrotron radiation facilities. We also thank the BM25-SpLine staff for the technical support beyond their duties.

A set of C3N4 samples has been prepared by using melamine, cyanuric acid and barbituric acid as the precursors. The materials were subjected both to physical and chemical characterization and were used as photocatalysts for the selective oxidation of aromatic alcohols in water suspension under UV and visible irradiation. The photoactivity of the materials versus the partial oxidation of four substituted benzyl alcohols was investigated. The type and position of the substituents in the aromatic molecule influenced conversion and selectivity to the corresponding aldehyde. The presence of barbituric and cyanuric acids in the preparation method has changed the graphitic-C3N4 structure, and therefore both the characteristics of the material and the ability of light to activate the surface of the photocatalyst. The most active material prepared in the presence of melamine and cyanuric acid showed a remarkable selectivity towards the aldehyde even under visible irradiation.

The most investigated materials used as heterogeneous photocatalysts for the formation of high-value chemicals under mild experimental conditions are presented in this survey. Only papers reporting reactions carried out in harmless solvents such as water, the green solvent par excellence, are reported. Metal oxides have been used often, but carbon-based materials such as carbon nitride and graphene, metal nanoparticles, sulphides and selenides also have received a great attention mainly due to their good performances both in partial oxidations and reductions. The results presented indicate that an appropriate choice of the photocatalytic material is the main problem to be faced to efficiently perform the desired photocatalytic synthesis. Moreover, the highly specific nature of the interaction between the surface of the photocatalyst and the molecules involved in the process must be carefully considered in order to maximize conversion and selectivity and to make these processes green and sustainable competitive alternatives to traditional synthetic methods. Many structural and physicochemical parameters can be tailored such as the initial pH in the case of liquid-solid systems, concentration of reagent(s), induction of defects in the photocatalyst, crystallinity, addition of loading or dopant species to tune the opto-electronic features of semiconductors, and specific surface area.

Background: The influence of the potassium metal cation on the graphitic carbon nitride (g-C3N4) photocatalyst has been studied in the partial oxidation of 5-hydroxymethyl-2-furfural (HMF) to 2,5-furandicarboxaldehyde (FDC). Objective: The aim of this study was to understand if the presence of K in C3N4 could increase the oxidative conversion of HMF to high added value species. Methods: Two sets of photocatalysts were prepared by following two different methodologies. In both series of the materials, the precursor of C3N4 was melamine with different types of the K containing species including KCl and KOH in one case and KNO3 alone in the other case. However, for both series of photocatalysts, materials were prepared with different amounts of potassium. Results: The results obtained by using materials prepared by the two different methodologies indicate that in both cases the presence of K was almost irrelevant at least for the lower amounts of potassium content. On the contrary, its presence was beneficial for the activity versus the photocatalytic partial oxidation reaction of the alcohol for the highest K content. Conclusion: Some of the prepared K containing g-C3N4 materials showed increased photocatalytic activity for the partial oxidation reaction of HMF in water, particularly by using natural solar light as the irradiation source.

Au nanoparticles supported on CeO2 have been prepared and investigated as photocatalysts for the photocatalytic selective oxidation of benzyl alcohol and 4-methoxybenzyl alcohol to the correspondent benzaldehydes, in aqueous suspensions and room conditions under UV, visible and natural solar light irradiation. Au nanoparticles have been supported by impregnation (1 and 3 wt.%) on two types of CeO2 (i.e., a commercial one and a home prepared oxide obtained in the presence of NaOH as precipitation agent). The Au impregnated samples showed strong visible radiation absorption at 565–570 nm associated to localized surface plasmon resonance (LSPR). The bare CeO2 samples are activated by UV light and resulted virtually inactive under visible irradiation, whereas the presence of Au improved both the conversion of the alcohols and the selectivity of the reaction towards the aldehyde, giving rise to good results, particularly under visible and natural solar light irradiation. The activity of the materials increased by increasing the Au content.

ZnO nanoparticles (NPs) were synthesized using zinc acetate dihydrate, ethanol, and oxalic acid as precursor, solvent, and complexing agent, respectively, and urea–hydrogen peroxide (UHP) as, simultaneously, nitrogen precursor and oxygen donor. The structural, morphological, textural, and optical properties of ZnO photocatalysts were investigated using different characterization methods such as XRD, SEM, BET, and UV-Vis-DRS. The XRD patterns showed that the products consisted of ZnO and revealed the presence of nitrogen. SEM images revealed the agglomeration and aggregation of NPs. The photocatalytic activity of ZnO samples was estimated based on the photo-oxidation of 2-propanol under UV irradiation, and ZnO doped with 5%UHP showed higher photocatalytic activity than bare ZnO.

Heterogeneous TiO2 photocatalysis is a promising technology based on the capability of the semiconducting material to generate charges upon irradiation of suitable energy. The photogenerated electrons and holes, in turn, induce redox reactions involving species adsorbed on the surface of the photocatalyst, giving rise to chemical transformations. The presence of highly oxidizing radicals, thus generated, has long led to consider TiO2 photocatalysis only a nonselective oxidation process. In fact, so far it is possible to find in the literature many examples of its use in the field of environmental remediation aimed at the degradation of harmful molecules, although the studies are almost all limited to the laboratory scale. However, selective synthetic reactions can also be carried out both in organic solvents and in water, carefully tuning the crystallinity and surface physicochemical properties of the photocatalyst. Oxidation, reduction, and coupling reactions, together with fuels production, for example, have been reported under mild experimental conditions, using both artificial and sunlight. The efficiency of TiO2 photocatalysis for production of fine chemicals can be further improved by tuning some parameters such as the setup configuration and the reactor geometry and by coupling photocatalysis with a membrane separation unit. The present chapter reports various examples of photocatalytic reactions in the presence of TiO2 photocatalyst, and among them oxidation of alcohols to aldehydes, hydroxylation of aromatic compounds, epoxidation of alkenes, hydrogenation of carbon–carbon multiple bonds, and some types of alkylation reactions will be presented.

The synthesis of photocatalytic materials is an important task for obtaining better results in terms of activity and/or selectivity in photocatalysis. This chapter reports an overview of the main methodologies using physical techniques to obtain bulky, supported powders or films and coatings to be used as heterogeneous photocatalysts. The classical chemical methodologies for the preparation of photocatalytic materials are presented in the previous chapter, so the information presented here complements the aforementioned one. Materials scientists and engineers have made significant progresses in the improvement of methods of synthesis of nanomaterial solids by developing different apparatuses supporting this aim. Various experts including physicists, chemists, material scientists, and mechanical and electrical engineers are involved in this research. New physical approaches, both for sample preparation and device fabrication, have aroused on account of the development of this nanoscience. The significant potential of the physical approach in material synthesis and their applications in photocatalysis, and other branches of catalysis and science, still needs to be explored offering numerous challenges to overcome. The understanding of these synthetic approaches would help in designing better materials. In this chapter, various methods for material preparation both bulk and supported as thin films or coatings are presented. All of them have in common the use of some apparatuses or equipments more or less sophisticated. The methodologies described include spray pyrolysis, flame synthesis, sonochemical and mechanochemical procedures, and use of microwaves as well as techniques to obtain thin films or coatings such as wet-coating synthesis methodologies, chemical and physical vapor deposition, and electrodeposition, among others, as examples of the physical approaches to prepare photocatalysts.

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water was performed in the presence of pristine Nb2O5 and composites containing Nb and Ti, Ce or Zr oxides. In all experiments, fructose was converted to HMF using water as the solvent. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, N2 physical adsorption, infrared and Raman spectroscopy and temperature-programmed desorption of NH3. Experimental parameters such as fructose initial concentration, volume of the reacting suspension, operation temperature, reaction time and amount of catalyst were tuned in order to optimize the catalytic reaction process. The highest selectivity to HMF was ca. 80% in the presence of 0.5 g·L−1 of bare Nb2O5, Nb2O5-TiO2 or Nb2O5-CeO2 with a maximum fructose conversion of ca. 70%. However, the best compromise between high conversion and high selectivity was reached by using 1 g·L−1 of pristine Nb2O5. Indeed, the best result was obtained in the presence of Nb2O5, with a fructose conversion of 76% and a selectivity to HMF of 75%, corresponding to the highest HMF yield (57%). This result was obtained at a temperature of 165° in an autoclave after three hours of reaction by using 6 mL of 1 M fructose suspension with a catalyst amount equal to 1 g·L−1.

Preface of the book "Heterogeneous Photocatalysis Relationships with Heterogeneous Catalysis and Perspectives"

A facile method to produce paper&ndash, TiO2 decorated with AgBr nanoparticles by a mild hydrothermal process at 140 &deg, C was reported. The synthesis method was based on the immersion of the paper in a ready-made suspension of TiO2/AgBr, comprising TiO2 sol solution prepared in acidic conditions and AgBr solution (10&minus, 4 M). A paper&ndash, TiO2 sample was prepared and used as reference. The formation of crystalline phases of titanium oxide (TiO2) and silver bromide (AgBr) was demonstrated by XRD, Raman and EDX analyses. The surface morphology of the TiO2&ndash, AgBr was investigated by Field Effect Scanning Electronic Microscopy (FE&ndash, SEM). The photocatalytic performances of the prepared material were evaluated in the degradation of 2-propanol in the gas phase, under simulated sunlight illumination. Its antibacterial properties against Escherichia coli (E. coli) were also assessed. The efficiency of photodegradation and the anti-bacterial properties of paper&ndash, TiO2&ndash, AgBr were attributed to an improvement in the absorption of visible light, the increased production of reactive oxygen species (ROS) and the low recombination of photogenerated charge carriers due to the synergistic effect between TiO2 and AgBr/Ag nanoparticles.

The photocatalytic oxidation of 5-hydroxymethyl-2-furfural (HMF) under natural solar irradiation was carried out in liquid– solid regime by using a batch reactor. Home prepared meso-tetra aryl substituted porphyrins (Pps) whether metal-free ( H2Pp) or containing Cu(II) or Zn(II) complexes (CuPp, ZnPp), opportunely functionalized with lipophilic [(3-n-pentadecylphenoxyethoxy)-] chains, were supported on graphitic (g-C3N4) or thermo-exfoliated carbon nitride ( C3N4-TE) to obtain a set of heterogeneous photocatalysts. The loading of the Pps on both carbon nitrides was 6 μmol per gram of support. During the experiments all the photocatalysts resulted active for the conversion of HMF, and in all cases its partial oxidation product, 2,5-furandicarboxyaldehyde (FDC), was selectively obtained in the aqueous suspension. Both carbon nitrides played the key role as photocatalysts whereas the presence of porphyrin improved the visible light absorption. The presence of the metalporphyrin in the composite slightly increased the selectivity to FDC. The best compromise between selectivity to FDC (36%) and conversion of HMF (73%) was obtained in the presence of the ZnPp-C3N4-TE photocatalyst at natural pH. Moreover, at pH 9 the CuPp-C3N4-TE sample showed the best performances, indicating that the pH can affect the photocatalytic activity of the samples towards the partial selective oxidation of HMF to FDC.

The Keggin heteropolyacid (HPA), H3PW12O40 (PW12) has been supported on commercial boron nitride (BN) and two types of home prepared carbon nitride (C3N4). The supported PW12 was used in the gas-solid (photo)catalytic 2-propanol dehydration reaction to give propene at atmospheric pressure and temperatures in the range 70-120°C and resulted more active than the pristine PW12. Reaction rate increased by increasing the temperature. Noticeably, the propene formation rate was higher by irradiating the catalytic system. The PW12/BN material resulted more active than PW12/C3N4. The acidity of the HPA cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction.

The Keggin heteropolyacid (HPA), H3PW12O40 (PW12) has been supported on commercial boron nitride (BN) and two types of home prepared carbon nitride (C3N4). The supported PW12 was used in the gas-solid (photo)catalytic 2-propanol dehydration reaction to give propene at atmospheric pressure and temperatures in the range 70–120 °C and resulted more active than the pristine PW12. Reaction rate increased by increasing the temperature. Noticeably, the propene formation rate was higher by irradiating the catalytic system. The PW12/BN material resulted more active than PW12/C3N4. The acidity of the HPA cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction.

Graphitic carbon nitride (g-C3N4) is a metal-free conjugated polymer which has become a new research hotspot in photocatalysis. It can be used for solar energy exploitation like in solar energy organic synthesis, one of the most new and appealing green applications of heterogeneous photocatalysis. This chapter resumes the state-of-the-art and progresses in the application of heterogeneous visible light photocatalysis in organic selective transformations by using C3N4 as photocatalyst.

Polymeric carbon nitride-hydrogen peroxide adduct (PCN-H2O2) has been prepared, thoroughly characterised and its application for selective photocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxaldehyde (FDC) in aqueous suspension has been studied. The PCN-H2O2 adduct is stable in aqueous suspension under UV and solar irradiation up to 100 °C. It is also stable up to 200 °C if heated in air, while at temperatures close to 300 °C its decomposition takes place. Based on the obtained characterisation data it has been proposed that H2O2 attaches to the non-polymerised carbon nitride species and to the heptazine nitrogen atoms, thus producing strong hydrogen bonding within the PCN-H2O2 adduct. The blockage of the surface amino-groups in PCN-H2O2 by H2O2 hinders the interaction of HMF with these sites, which are responsible for unselective substrate conversion. PCN-H2O2, although being less active, possesses a superior selectivity in natural solar light assisted oxidation of HMF to FDC reaching 80% with respect to its thermally etched PCN counterpart, which gives rise to a 40–50% selectivity. We believe that the exceptional performance of the applied photocatalyst in the selective photocatalytic conversion of HMF to a high added value FDC in a green solvent under natural illumination makes a significant contribution to the development of environmentally friendly technologies for biomass valorisation.

Two simple routes for the synthesis of a paper-TiO2 composite were tuned up and the efficiency of the resulting paper-TiO2 photocatalyst was investigated in the 2-propanol oxidation in gas phase. The first route involved the in-situ generation over the sheet of paper of a TiO2 layer starting from a solution of Ti (OBu)4 in tert-butanoliacetic acid, followed by hydrothermal treatment at 120 degrees C for 3 h. The sample was labelled as paper-TiO2 (H). The second approach was based on the adsorption on the paper of a ready-made suspension of titania nanoparticles (TiO2 sol), generated in autoclave at 140 degrees C and stable in acid medium at pH

A set of bare and P-doped graphitic carbon nitride (g-C3N4) photocatalysts has been prepared by thermal condensation of melamine, urea or thiourea. For the sake of comparison, a g-C3N4 sample obtained in the presence of cyanuric acid and thermally exfoliated C3N4 powders were also studied. The materials were physicochemically characterized and their photocatalytic activity was studied for the selective oxidation of benzyl alcohol (BA), 4-methoxy benzyl alcohol (4-MBA) and piperonyl alcohol (PA) in water suspension both under UV and visible light irradiation. The influence of the type and position of the substituents on conversion and selectivity to aldehyde was remarkable. The presence of P in the C3N4 material improved the selectivity of the reaction towards the aldehyde., University of Oviedo thanks for financial support Spanish MINECO (MAT2013-40950-R, CTQ2014-52956-C3-1-R and MAT2016-78155- C2-1-R) grants. I.K. is grateful for financial support of the Ministry of Education and Science of the Russian Federation (grant No 4.9722.2017/8.9)

Catalytic and photocatalytic 2-propanol dehydration to propene at atmospheric pressure and a temperature range of 60–120 °C were carried out in gas-solid regime by using bare and supported Keggin H 3 PW 12 O 40 (PW 12 ) and Wells-Dawson H 6 P 2 W 18 O 62 (P 2 W 18 ) heteropolyacids (HPAs). Binary materials were prepared by impregnation of the HPAs on commercial SiO 2 and TiO 2 . The Wells-Dawson was in any case more active than the Keggin heteropolyacid and the differences were enhanced when the supported samples were used. In particular, Wells-Dawson HPA supported on TiO 2 and under irradiation showed the highest activity. The HPA species played the key role both in the catalytic and photo-assisted reactions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction. The estimated apparent activation energy resulted always lower for the photocatalytic process than for the catalytic one.

[EN] Keggin [PW12O40]3– and Wells–Dawson [P2W18O62]6– heteropolyanions are nanosized transition-metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts due to their high Brønsted acidity, and their dispersion on solid supports favors the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells–Dawson HPAs and SiO2, TiO2, and ZrO2 have been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural changes of the HPAs due to the cluster–support interaction, which is different depending on preparation methodologies of the binary material. In the present work, the modes of interaction between the two types of HPA, Keggin and Wells–Dawson, and various supports have been studied by X-ray absorption spectroscopy. The obtained data have been compared to the characterization of the same materials reported before by using different bulk and surface physicochemical techniques. The characterization results were then used to correlate the interaction modes between the HPAs and the supports with the catalytic performances reported for 2-propanol dehydration to propene and for propene hydration to 2-propanol. The results reveal that the deposition of HPA by impregnation or solvothermal treatment may cause distortions in the H3PW12O40 cluster structure depending on the presence of stronger (TiO2 and ZrO2) or weaker (SiO2) basic sites in the support, respectively. Moreover, the type of preparation method affects the structure and acidic properties of the supported HPAs. In particular, during the preparation of TiO2 and ZrO2 with HPA by in situ solvothermal method, the reaction of the HPA with the products of metal alkoxides hydrolysis occurs with consequent destruction of the Keggin structure. Therefore, the catalytic activity of such materials is poor. These modifications, in addition to the bulk and surface features of the supported HPAs, affected the catalytic 2-propanol dehydration to a significant extent. On the contrary, the propene hydration was less influenced, probably, due to the propene nonpolar nature., I.K. acknowledges the financial support from Spanish MINECO (MAT2016-78155-C2-1-R), Gobierno del Principado de Asturias (GRUPIN-ID2018-170), and Ministry of Education and Science of the Russian Federation (grant No. 4.9722.2017/8.9). L.F.L. is grateful to progetto di Ricerca ARS01_00637 Energie per l′Ambiente-TARANTO (PNR 2015-2020) for financial support. The authors acknowledge The European Synchrotron (The ESRF), MINECO, and CSIC for the provision of measurements using the BM25-SpLine beamline. They also thank the BM25-SpLine staff for the technical support beyond their duties.

The C3N4 -based nanopowders prepared by thermal condensation of melamine (MCN) with subsequent thermal etching (MCN-TE) and H2O2 -treatment were investigated by Q- and X-band EPR spectroscopy in dark and upon in situ UVA or visible-light exposure. Lorentzian signal at g = 2.003, more pronounced in the case of the thermally etched material, dominates EPR spectra of MCN and MCN-TE. More complex spectra were found for H2O2 -treated photocatalysts revealing the presence of signals attributed to the radicals produced via H2O2 interaction with C/N sites in the C3N4 polymeric network. The X-band spectra monitored upon in situ irradiation of the C3N4 -based photocatalysts evidenced the intensity growth of the single line at g = 2.0033 indicating the photoinduced generation of electrons in localized paramagnetic states with the Curie dependence on temperature in the temperature range 100–180 K. The response towards UV or visible-light exposure was significantly limited in the case of H2O2 -treated photocatalysts. EPR spin trapping experiments performed in aqueous suspensions demonstrated the formation of HO2[rad] and HO [rad] spin-adducts, and the increased stability of the primary photogenerated O2 javax.xml.bind.JAXBElement@3a251187 – in aprotic media was well documented by the irradiation of the photocatalysts in the dimethylsulfoxide/water mixed solvent. The highest activities in the production of the non-persistent radical species spin-adducts were found for the thermally etched and pristine photocatalysts, confirming the negative effect of H2O2 -treatment.

Heterogeneous photocatalytic and thermal-catalytic reactions are here presented focusing the differences and similarities between the two processes. When possible, the comparison was made for the same chemical reaction in the presence of an inorganic material playing the role of both catalyst or/and photocatalyst. Several examples are presented where a catalytic reaction can occur at milder experimental conditions and, particularly, at lower temperature when the system is also irradiated by UV and/or visible light. The differences in mechanistic aspects, conversions, and selectivities between catalytic and photocatalytic reactions will be also considered because these occurrences are related to various reasons, and they can change due to the effects of the interaction of light with the solid surface or to the temperature that influences the adsorption–desorption of species involved in the (photo)reactions and to the activation energy consequently to the different pathways followed by the reactions.

We investigated CO2 photocatalytic reduction coupling, for the first time in literature, the assets offered by the continuous operating mode using C3N4-TiO2 photo-catalyst embedded in a dense Nafion matrix. The reactor performance was analyzed under UV–vis light in terms of productivity, selectivity and converted carbon. Reaction pressure was specifically investigated for its effect as a “driver” in determining reactor performance, modulating products removal from the reaction volume. In addition, the membrane reactor performance was explored as a function of H2O/CO2 feed molar ratio and contact time. The higher feed pressure (5 bar) led to a lesser MeOH production and a greater amount of HCHO, owing to a hindered desorption, which promoted partial oxidation reactions. Total converted carbon instead did not vary significantly with reaction pressure. Membrane reactor with C3N4-TiO2 photocatalyst resulted more performant than other photocatalytic membrane reactors in terms of carbon converted (61 μmol gcatalyst−1 h−1).

Insoluble rust waste from the scraping of rusted iron-containing materials represents a cheap, eco-friendly, and available source of iron. LaFeO3 perovskite-type powders were successfully prepared by solution combustion synthesis using rust waste from an electricity transmission tower manufacturer. Solution combustion synthesis enabled introduction of this insoluble iron precursor directly into the final product, bypassing complex extraction procedures. Catalytic activity in the propylene oxidation of the waste-derived LaFeO3 with stoichiometric Fe/La ratio was almost identical to the commercial iron nitrate-derived LaFeO3 , thus demonstrating the viability of this recycling solution. The amount of waste iron precursor was varied and its effect on the powder properties was investigated. A lesser stoichiometric amount of precursor produced a LaFeO3 -La2O3 binary system, whereas a higher stoichiometric amount led to a LaFeO3 -Fe2O3 binary system. Catalytic activity of iron-rich compositions in the propylene oxidation was only slightly lower than the stoichiometric one, whereas iron-poor compositions were much less active. This eco-friendly methodology can be easily extended to other iron perovskites with different chemical compositions and to other iron-containing compounds.

Differently shape-controlled anatase TiO2 materials were tested as photocatalysts under both simulated and natural solar irradiation. Their photocatalytic activity in 2-propanol and propene partial oxidation and in the complete mineralization of acetaldehyde appears to increase with decreasing the shape control of the TiO2 material. This insight seems to be related to the residual presence of the templating species (fluoride anions) employed during the preparation of the shape-controlled TiO2 materials. In fact, the calcination of the powders, leading to levelling of the fluoride ions content, but also to a remarkable surface area decrease, gave rise to an increase of photocatalytic activity per unit surface area of the materials. In these photocatalytic materials two opposing effects may concur in determining their photoactivity, i.e. the possibly beneficial effect of an increased extent of exposed {001} facets and the detrimental effect resulting from a larger amount of residual fluoride ions employed as capping agents during their synthesis.

In the present work we scrutinize the effect of substituents in the phenyl ring of the benzyl alcohol on its photo-oxidation to the corresponding benzaldehyde driven by polymeric carbon nitride photocatalyst in aqueous medium. It has been established that electron donating (ED) substituents in para- and ortho-position with respect to the CH2OH-group promote the reactivity of the substrate without compromising the selectivity towards benzaldehyde formation, maintaining it in the range of 84–98 %, if compared to the unsubstituted molecule. The same observation is true for meta-substituted benzyl alcohol with an electron withdrawing (EW) group. On the other hand, the presence of ED-group in meta-position or EW-group in para-position with respect to the CH2OH-group reduces the reactivity as well as the selectivity towards the aldehyde production, resulting in the values of selectivity ranging from 40 to 80 %. Quantum chemical calculations have allowed to establish that the reactivity correlates with the positive charge on the benzylic carbon in benzyl alcohol cation intermediate, while the selectivity, most probably, is conditioned by a negative charge on the carbon atoms in the phenyl ring being a target for an electrophile attack. The modification of the polymeric C3N4 photocatalyst with H2O2 reduces the unselective benzyl alcohol oxidation, thus favouring the higher selectivity towards benzaldehyde production.

Four different C 3 N 4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H 2 O 2 (MCN-H 2 O 2 ) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H 2 O 2 ). The principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions. Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of photoconductivity, whereas MCN-H 2 O 2 was defective and evidenced a poor mobility of carriers. EPR studies showed a maximum generation of reactive oxygen species irradiating the MCN-TE sample. The photocatalytic activity of these materials in the selective oxidation of three different alcohols to the corresponding aldehydes, both under UV and natural solar light, showed that the highest conversion was obtained in the presence of the MCN-TE sample, whereas the most selective one was MCN-TE-H 2 O 2 . Under solar light irradiation the performances of the powders were generally better than those under UV light. The characterization of the C 3 N 4 -based materials well justified their photocatalytic activity. The pristine C 3 N 4 materials were more active but less selective than those prepared in the presence of H 2 O 2 .