Photocatalytic Hydrogen Production: A Rift into the Future Energy Supply

Photocatalytic hydrogen (H2) production is a process that converts solar energy into chemical energy by means of a suitable photocatalyst. After the huge amount of systems that have been tested in the last forty years, the advent of nanotechnology and a careful design at molecular level, allow to obtain attractive activity, even using pure visible light. At the same time we are approaching reasonable photocatalyst stability in laboratory test, and the attention is paid to identify cost-effective photocatalysts that might find real applications. This Review provides a broad overview of the elementary steps of the heterogeneous photocatalytic H2 production, including an outline of the physico-chemical reactions occurring on semiconductors and cocatalysts. The use of different renewable oxygenates as sustainable sacrificial agent for the H2 production is outlined, in view of a transition from fossil fuels to pure water splitting. Finally, the recent advances in the development of photocatalyst are discussed focusing on the current progress in organic and hybrid organic/inorganic photocatalysts

Metal-free dual-phase full organic carbon nanotubes/g-C 3 N 4 heteroarchitectures for photocatalytic hydrogen production

Hydrogen generation from water using solar energy has grown into a promising approach for sustainable energy production. Over the last years, graphitic carbon nitrides (g-C3N4, CN), polymers based on the heptazine-group, have been widely applied as photocatalysts for H2 evolution. The poor charge separation efficiency of CN is considered the major drawback. Here, we investigated the effect of coupling CN with different types of carbon nanotubes on the charge transfer properties and the photocatalytic H2 evolution. We used carbon nanotubes (CNTs) of different wall number (single (SWCNTs), double (DWCNTs) and multi-walled (MWCNTs) CNTs) for the development of full-organic CN based composite photocatalysts. Photoactivity was drastically affected by the content but more importantly by the nature of the CNTs. The SWCNTs functionalized CN composites were the most active presenting approximately 2\u20135 times higher H2 evolution than the corresponding DWCNTs and MWCNTs functionalized CN under both solar and pure visible light irradiation. Photoactivity was primarily controlled by the improved electronic properties linked with the abundance and stability of photogenerated charges as evidenced by electron paramagnetic resonance spectroscopy. Transient absorption spectroscopy verified the transfer of reactive electrons from CN to CNTs. CNTs functioned as electron acceptors improving charge separation. The data suggest that charge transfer is inversely proportional to the wall number of the CNTs and that photoactivity is directly controlled by the size at the nanoscale of the CNTs used. In the CNTs/CN nanocomposites, photogenerated electrons are transferred more efficiently from CN when SWCNTs are used, providing more available electrons for H2 production

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Application of biomimetic catalysts on the removal of environmental pollutants

One of the most important issues of the oxidative degradation of organic pollutants is that they may be resistant and highly toxic to microorganisms. Chlorophenols are such substances. Chemical oxidative degradation is probably the most advantageous reaction type to overcome these problems. The aim of this PhD thesis was to evaluate iron based catalytic systems on the decomposition of pentachlorophenol. Specifically, the Fenton reaction and biomimetic Fe-porphyrin catalysts were studied. In both cases, spectroscopic techniques were used to study the catalytic mechanism. In the case of biomimetic oxidation, the reaction intermediate of metallo-porphyrins, responsible for the catalytic conversion of the organic substrate, was identified and studied using EPR spectroscopy and UV-Vis. Also, based on the products of PCP decomposition, a common mechanism for the oxidation of PCP was proposed for all the systems studied. Finally, the improvement of the catalysis was performed via: A. Immobilization on SiO₂. In this way the oxidative stability of metallo-porphyrins was increased. The heterogenized catalyst was also highly recyclable losing some of its catalytic efficiency after the third use. Moreover, the percent of dechlorination accomplished by the immobilized catalyst was the highest achieved in the literature of biomimetic oxidation of pentaclorophenol. B. Introduction of co-catalysts - Additives. The catalytic performance of the homogeneous catalysts was increased by the presence of imidazole, which acted as axial ligand to the iron of the complex. The presence of gallic acid and triethylamine under optimal catalytic conditions, led also to a great increase of PCP decomposition. In the case of the Fenton reaction, the effect of natural organic matter (humic acid) and of structural models of humic acid (gallic acid) was extensively studied. It was observed that the effect of the above mention substances was affect by the initial catalytic conditions, mostly by the concentration of iron. Based on the findings of EPR spectroscopy, a general mechanism was also proposed for the effect of such substances on the catalytic oxidation of PCP by the Fenton reaction. Finally, a system was developed for: 1. The control of an EPR spectrometer 2. To read, present and save the experimental data. This system was consisted of (i) software based on LabVIEW and (ii) hardware capable to read and transfer analog and digital signals.Ένα από τα σημαντικότερα προβλήματα που πρέπει να ξεπεραστούν στην οξειδωτική διάσπαση ρυπαντών είναι η ανθεκτικότητα που παρουσιάζουν ορισμένοι από αυτούς όπως και η υψηλή τοξικότητά τους στους μικροοργανισμούς. Στην κατηγορία αυτή ανήκουν οι χλωροφαινόλες. Για την αντιμετώπιση τέτοιων ουσιών, το ενδιαφέρον της επιστημονικής κοινότητας έχει στραφεί τα τελευταία χρόνια στη χρήση χημικών μεθόδων οξείδωσης. Στην παρούσα διδακτορική διατριβή χρησιμοποιήθηκαν καταλυτικά συστήματα σιδήρου στην οξείδωση της πενταχλωροφαινόλης. Συγκεκριμένα, μελετήθηκε η αντίδραση Fenton και βιομιμητικοί αιμικοί καταλύτες. Και στις δύο περιπτώσεις ιδιαίτερη έμφαση δόθηκε στην εύρεση του μηχανισμού οξείδωσης του υποστρώματος χρησιμοποιώντας φασματοσκοπία EPR. Στην περίπτωση των αιμικών καταλυτών το ενεργό ενδιάμεσο - υπεύθυνο για την οξείδωση του υποστρώματος - παγιδεύτηκε, ταυτοποιήθηκε και μελετήθηκε με φασματοσκοπία EPR και UV-Vis. Επίσης, βάση των προϊόντων της αντίδρασης προτάθηκε μηχανισμός αποικοδόμησης ο οποίος είναι ενιαίος για όλα τα καταλυτικά συστήματα που χρησιμοποιήθηκαν. Η αύξηση της απόδοσης των καταλυτικών συστημάτων πραγματοποιήθηκε μέσω δύο διαφορετικών οδών: Α. Πραγματοποιήθηκε ακινητοποίηση των καταλυτών σε SiO₂, οδηγώντας σε αύξηση της σταθερότητας του μεταλλικού συμπλόκου κάτω από τις ισχυρές οξειδωτικές συνθήκες των αντιδράσεων. Οι ετερογενοποιημένοι καταλύτες αποδείχθηκαν επαναχρησιμοποιήσιμοι χάνοντας ένα μικρό ποσοστό της καταλυτικής τους δράσης μετά την τρίτη χρήση τους. Επίσης, το ποσοστό αποχλωρίωσης του υποστρώματος έφτασε το 100%, κάτι που παρατηρήθηκε για πρώτη φορά στην βιβλιογραφία. Β. Πραγματοποιήθηκε προσθήκη διαφόρων πρόσθετων ουσιών παίζοντας το ρόλο του συγκαταλύτη. Συγκεκριμένα, η απόδοση των ομογενών καταλυτών αυξήθηκε με την παρουσία ιμιδαζολίου, το οποίο λειτούργησε ως αξονικός υποκαταστάτης του μετάλλου. Επίσης, εντυπωσιακή αύξηση παρατηρήθηκε παρουσία γαλλικού οξέος και τριαιθυλαμίνης κάτω από κατάλληλες συνθήκες. Στην αντίδραση Fenton μελετήθηκε αναλυτικά η επίδραση της διαλυμένης οργανικής ύλης (χουμικού οξέος) καθώς και μοντέλων αυτής (γαλλικό οξύ). Παρατηρήθηκε τόσο αύξηση όσο και μείωση της απόδοσης ανάλογα με τις αρχικές συνθήκες των αντιδράσεων. Ο παράγοντας που επηρέασε κυρίως ήταν η συγκέντρωση του σιδήρου. Με τη χρήση φασματοσκοπίας EPR προτάθηκε ένας ενιαίος μηχανισμός ικανός να ερμηνεύσει και τις δύο περιπτώσεις. Τέλος, στα πλαίσια της παρούσας διατριβής αναπτύχθηκε σύστημα αποτελούμενο από (α) λογισμικό και (β) κάρτες ανάγνωσης και μεταφοράς ψηφιακών και αναλογικών σημάτων, για τον έλεγχο οργάνου EPR και την ανάγνωση, παρουσίαση και αποθήκευση των πειραματικών δεδομένων

Covenant of Mayors initiative-Public perception issues and barriers in Greece

The Covenant of Mayors (COM) initiative invites cities to commit themselves to reduce voluntarily the greenhouse gas emissions within their territories. This manuscript presents the COM initiative and analyzes its mechanisms. In order to better quantify the penetration of the initiative, the authors introduce suitable "participation factors". Moreover, a study and a survey are presented concerning the COM initiative in Greece. Certain barriers are identified preventing the realization of the initiative's full potential in Greece. Results from the public survey indicate lack of proper information and communication about the COM initiative and the obligations arising from its signing towards the citizens itself. Nevertheless, once the citizens are informed properly, the public acceptance of the initiative and its commitments is considerable, to the extent that its success would influence the vote of a substantial percentage of citizens. The positive role of supporting structures is evaluated and may be demonstrated through the survey's results and discussion. Recommendations are provided for future or existing signatories based on the findings of this work.JRC.F.3-Energy securit

High Field Electron Paramagnetic Resonance Studies of Humic Acids & Related Compounds

Humic substances, the greater carbon pool of Earth, contain inside their molecules free stable radicals, which participate into significant biogeochemical environmental processes in soil and aqueous ecosystems. In this work we present the first worldwide spectrum of electron paramagnetic resonance spectroscopy (EPR) high field (285GHz) for humic acids from various geographical locations. All humic acids, no matter the location, are consisted by two types of free stable radicals, type I and type II with specific electron structure. Type I free radicals excel at pH 5 and are characterized by a g factor with values of gIx = 2.0032, gIy = 2.0032 and gIz = 2.0023. Free radicals type II excel at pH 12 and are characterized by a g factor with values of gIIx = 2.0057, gIIy = 2.0055 and gIIz = 2.0023. The phenomenon of obtaining two distinguished types of free radicals at different pH is reversible and independent of the humic acid source. Both centers of the two free radical types are consisted by pi type free radicals. They are present not only in humic acid solutions but also in humic acid in solid state (powder)

Probing Local pH in Hydrophobic Domains of Humic Acids: An EPR Based Method

Despite the focused efforts by many labs during the last 30 years, vital aspects of the structure and fundamental physicochemical aspects of Humic Acids (HA) are largely unknown. It is currently accepted that humic acids contain both hydrophilic as well as hydrophobic domains which are the locus of sequestration of xenobiotic molecules. However vital information on the detailed nature, the accessibility of the hydrophobic domains is lacking. On the other hand, HA behave as polyelectrolytes which bear variable charge modulated by pH. It is considered that this pH-dependent charge is modulated by the local pKa of the chargeable structural groups i.e. carboxylates and phenolics. Traditionally only the water accessible hydrophilic fraction of the chargeable groups can be probed by H-binding or metal binding studies. However the function of chargeable groups in hydrophobic domains, local pKa, and their geometrical location are largely unknown. In this context we have developed a novel methodology by using the Spin-Probe method with Electron Paramagnetic Resonance (EPR) spectroscopy. A series of specific spin-probes with varying hydrophobicity as well as pH sensitivity were used and studied with EPR spectroscopy. The experiments were carried out in well characterized HA samples of varying molecular weight providing information of the local environment of the spin-probes, their mobility, and local pKa values