SMART geopolymers, an ERA-MIN project

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Solar Photocatalytic Degradation of Bisphenol A on Immobilized ZnO or TiO2

The removal of bisphenol A (BPA) under simulated solar irradiation and in the presence of either TiO2 or ZnO catalysts immobilized onto glass plates was investigated. The effect of various operating conditions on degradation was assessed including the amount of the immobilized catalyst (36.1–150.7 mg/cm2 for TiO2 and 0.5–6.8 mg/cm2 for ZnO), initial BPA concentration (50–200 μg/L), treatment time (up to 90 min), water matrix (wastewater, drinking water, and pure water), the addition of H2O2 (25–100 mg/L), and the presence of other endocrine disruptors in the reaction mixture. Specifically, it was observed that increasing the amount of immobilized catalyst increases BPA conversion and so does the addition of H2O2 up to 100 mg/L. Moreover, BPA degradation follows first-order reaction kinetics indicating that the final removal is not practically affected by the initial BPA concentration. Degradation in wastewater is slower than that in pure water up to five times, implying the scavenging behavior of effluent’s constituents against hydroxyl radicals. Finally, the presence of other endocrine disruptors, such as 17α-ethynylestradiol, spiked in the reaction mixture at low concentrations usually found in environmental samples (i.e., 100 μg/L), neither affects BPA degradation nor alters its kinetics to a considerable extent

Solar light and metal-doped TiO₂ to eliminate water-transmitted bacterial pathogens:Photocatalyst characterization and disinfection performance

Summarization: The present study deals with the inactivation of Escherichia coli and Klebsiella pneumoniae in water by means of heterogeneous photocatalysis under simulated solar irradiation. For this purpose, novel Mn-, Co- and Mn/Co-doped TiO2 catalysts were prepared. A straightforward, simple and inexpensive process has been developed based on a co-precipitation method for the synthesis of metal-doped catalysts, which were subsequently assessed in terms of their disinfection efficiency. The effect of various operating conditions, such as metal dopant (Mn-, Co- and Mn/Co), dopant concentration (0.02–1 wt%), catalyst concentration (25–250 mg/L), bacterial concentration (102–108 CFU/mL), treatment time (up to 60 min), toxic effects on bacteria and photon flux (4.93–5.8 × 10−7 Einstein/(L s)), was examined under simulated solar irradiation. Metal-doped TiO2 samples were prepared reproducibly and doping shifted the optical absorption edge to the visible region. Their activity was superior to the respective of commercially available P25 titania. The reference strains of E. coli and K. pneumoniae proved to be readily inactivated during photocatalytic treatment of aqueous samples, since disinfection occurred rapidly (i.e. after only 10 min of irradiation) with the dopant concentration affecting the overall process to a certain extent. Disinfection follows a pseudo-first order kinetic rate in terms of both bacteria removal. Inactivation of the bacteria is attributed to the oxidative degradation of their cells and increase of their cell permeability and not to the potential toxicity of the metal-doped semiconductors, which did not exhibit any bactericidal properties. It has been shown that the improved activity of the Mn-, Co-, and binary Mn/Co doped TiO2 is accredited to the fact that they can be activated in the visible part of the spectrum, in the absence of UV light (i.e. >420 nm).Presented on: Applied Catalysis B: Environmenta

Solar photocatalytic decomposition of estrogens over immobilized zinc oxide

Summarization: The photocatalytic degradation of synthetic estrogen 17α-ethynylestradiol (EE2) in environmental samples was investigated. Zinc oxide immobilized onto a glass substrate was prepared and used as the photocatalyst, while radiation was provided by a solar simulator. EE2 in the range 50–200 μg/L was treated in various matrices, i.e. ultrapure water, wastewater and drinking water, and treatment efficiency was assessed as a function of photon flux, ZnO loading and addition of hydrogen peroxide. Degradation follows apparent first-order kinetics and increases with increasing photon flux (4.93·10−7–5.8·10−7 einstein/(L s)) and H2O2 concentration (up to 100 mg/L), while ZnO loading (1.2–16.3 mg) has a marginal effect. Reaction in ultrapure water is twice as fast as in wastewater (e.g. the respective apparent rate constants are 17.3·10−3 and 9.4·10−3 min−1 at maximum photon flux and 3.7 mg ZnO) due to the competition for oxidants between EE2 and the wastewater components (organic matter and ions). The catalyst retained most of its activity upon repeated use (i.e. 21 consecutive runs of 31.5 h duration) although it was partially dissolved in the liquid phase; leached zinc can trigger homogeneous reactions, thus contributing to the overall photocatalytic degradation.Presented on: Catalysis Toda

Novel nanoporous materials for adsorption and catalytic applications

The synthesis of new micro- and meso-porous solids is an important field of research worldwide. The diversity in their chemical and physical properties originating from the chemical composition of inorganic or inorganic-organic framework, structrure and porosity is responsible for their wide range of technologically important applications. In particular, catalysis and energy related applications are considered the most important. Catalysis, either homogeneous or heterogeneous, plays and important role to our modern society, because valuable products ranging from high value chemicals, to polymers and gasoline are accessible at an industrial scale through catalytic processes At the same time, energy consumption in our modern society is a real concern because conventional energy sources (petroleum, natural gas and coal) are directly associated with climate change including global warming among others. The present thesis, deals with the synthesis and characterization of new porous materials for application in heterogeneous catalysis (vanadium based catalysts) as well as in selective hydrogen and CO2 storage (organo-silicates and graphene-based materials). The thesis includes four (4) chapters and an annex with information on the techniques that were used. The first chapter includes the bibliographic review. In the second chapter, the synthesis and characterization of mesostructure and mesoporous vanadosilicates solid are reported, as well as a preliminary catalytic evaluation. Chapter three and four deals with the synthesis and characterization of nanoporous organosilica solids and carbon based materials, respectively. For these materials, extensive hydrogen, CO2 and CH4 sorption studies were conducted. All solids were fully characterized with a variety of experimental techniques, including powder X-ray diffraction (PXRD), specific surface area and distribution of porous, thermogravimetric analysis (TGA), elemental analysis (C, N, H), Raman and FT-IR spectroscopy, UVvis/near IR diffuse reflectance spectroscopy, scanning electron microscopy coupled with energy depressive spectroscopy (EDS) and transmission electron microscopy (TEM)Η σύνθεση νέων μίκρο- και μέσο-πορωδών στερεών αποτελεί ένα σημαντικό πεδίο έρευνας σε παγκόσμιο επίπεδο. Τα πορώδη στερεά λόγω της χημικής σύστασης του ανόργανου ή ανόργανου – οργανικού σκελετού, της δομής, του πορώδους, της ειδικής επιφάνειας και της κατανομής μεγέθους πόρων που διαθέτουν εμφανίζουν σημαντικές εφαρμογές σε ένα μεγάλο εύρος πεδίων. Ιδιαίτερα, η κατάλυση και οι ενεργειακές εφαρμογές αποτελούν ίσως δύο από τα σημαντικότερα πεδία στα οποία βρίσκουν χρήση τα πορώδη στερεά. Η κατάλυση κατέχει σήμερα κυρίαρχη θέση τόσο σε επίπεδο βασικής διεπιστημονικής έρευνας όσο και σε επίπεδο βιομηχανικών εφαρμογών παίζοντας ένα σημαντικό ρόλο στην καθημερινή μας ζωή. Ταυτόχρονα, η καθημερινή μας ζωή είναι άμεσα συνδεδεμένη με την κατανάλωση ενέργειας. Η κατανάλωση όμως ενέργειας, καθώς και συγκεκριμένες συμβατικές μέθοδοι παραγωγής της, έχουν οδηγήσει σε φαινόμενα όπως στην υπερθέρμανση της ατμόσφαιρας (φαινόμενο θερμοκηπίου) με τις γνωστές πλέον συνέπειες τόσο στο περιβάλλον όσο και στην υγεία του ανθρώπου (ρύπανση, έντονα και ακραία καιρικά φαινόμενα, κλπ). Στα πλαίσια αυτά και έχοντας σα κύριο στόχο την σύνθεση και τον χαρακτηρισμό νέων νανοπορωδών στερεών για προσροφητικές και καταλυτικές διεργασίες πραγματοποιήθηκε η παρούσα διατριβή. Η παρούσα διατριβή αποτελείται από 4 κεφάλαια και ένα παράρτημα με πληροφορίες για τις τεχνικές που χρησιμοποιήθηκαν. Το πρώτο κεφάλαιο περιλαμβάνει την βιβλιογραφική ανασκόπηση. Στο δεύτερο κεφάλαιο αναφέρεται η σύνθεση και ο χαρακτηρισμός μεσοδομημένων και μεσοπορωδών βαναδοπυριτικών στερεών και έχει κύριο στόχο την χρήση τους στο πεδίο της κατάλυσης. Στα πλαίσια της μείωσης των εκπομπών CO2 πραγματοποιήθηκε η μελέτη της αποθήκευσης υδρογόνου (πράσινος εναλλακτικός φορέας ενέργειας) καθώς επίσης και μελέτη της αποθήκευσης CO2 και της εκλεκτικότητας μεταξύ CO2 και CH4 σε δύο διαφορετικές οικογένειες νανο- υλικών (οργανοπυριτικά νανοπορώδη στερεά και υλικά βασισμένα σε άνθρακα). Έτσι λοιπόν, στο 3ο κεφάλαιο αναφέρεται η σύνθεση και ο χαρακτηρισμός νανοδομημένων υβριδικών οργανοπυριτικών στερεών (PNO) και πραγματοποιείται η μελέτη των προσροφητικών τους ιδιοτήτων. Τέλος στο τέταρτο κεφάλαιο αναφέρεται η σύνθεση, ο χαρακτηρισμός και η μελέτη των προσροφητικών ιδιοτήτων του άμορφου οξειδίου του γραφενίου. VIII Όλα τα στερεά χαρακτηρίστηκαν με πληθώρα τεχνικών συμπεριλαμβανομένων ακτίνων-Χ σε δείγματα σκόνης, μέτρηση ειδικής επιφάνειας και κατανομής των πόρων, θερμική ανάλυση (TGA/DSC), στοιχειακή ανάλυση (C,H,N), φασματοσκοπία υπερύθρου (FT-IR), Raman, ανακλαστικότητας ορατού–υπεριώδους-υπερύθρου (UVvis/ near IR), ηλεκτρονική μικροσκοπία διέλευσης (ΤΕΜ) και ηλεκτρονική μικροσκοπία σάρωσης (SEM)

Modified TiO2 based photocatalysts for improved air and health quality

Photocatalysis with modified titania is a promising approach to improve both air and health quality. Modified titania with novel photocatalytic properties under indoor light irradiation leads to smart coatings, which are benchmark materials suitable for their indoor applications. It is generally accepted that the photocatalytic activity is affected by the light absorption, charge creation/recombination rate and surface reactivity. In this contribution we focus on modified TiO2 as catalyst in heterogeneous photo-catalytic processes and address the efficiency of TiO2-based building and construction materials on the removal of environmental pollutants indoors and outdoors. We also present data on the presence of eventually formed, toxicologically relevant and harmful by-products as the result of the photo-induced degradation of pollutants in an effort for better evaluation of induced risks for human health from the application of TiO2 modified materials. Finally, we present recent results on the disinfection performance of these material and the inactivation of severe pathogens contained in water and indoor air environments

Photocatalytic oxidation of gaseous benzene, toluene and xylene under UV and visible irradiation over Mn-doped TiO2 nanoparticles

The photocatalytic oxidation of gaseous benzene, toluene and xylene (BTX) over un-doped, 0.1 and 1 wt% Mn-TiO2 nanoparticles under ultraviolet and visible irradiation was studied in atmosphere of synthetic air or inert gas. The photocatalytic decomposition efficiency and the oxidation products were determined using a Static Photochemical Reactor coupled with FTIR spectroscopy. BTX underwent efficient decomposition over Mn-TiO2 photocatalysts under UV irradiation, more with oxygen presence and less without oxygen. More important toluene and xylene went substantial decomposition over 0.1 mol% Mn-TiO2 under visible irradiation with oxygen presence. The main final oxidation products in the UV photocatalysis of BTX were CO2, CO and H2O, with CO2 and CO yields 4 and 2 respectively. The conversion percentage of benzene, toluene, and xylene to CO2 were 63.6%, 56.4%, 51.8%, and to CO 29%, 26.5%, 23.2%, respectively. In the visible photocatalysis of toluene and xylene the yields of CO were insignificant. Formation of carbon containing deposits on TiO2 surfaces was observed after extensive UV photocatalysis of toluene and xylene, and such by-products surface coverage may reduce the photocatalytic activity of TiO2 samples. Some aspects of the photocatalytic mechanism were examined. Keywords: Mn-doped TiO2, Visible, Light photocatalysis, Photodegradation of benzene, Toluene, Xylene, Indoors air pollutio

Design and Evaluation of Low-Power Co₃O₄ Gas Sensing Element as a Part of Cyber Physical Systems

Physical processes working in parallel with digital ones have transformed the way we view systems and have led to the creation of applications that boost the quality of people’s lives, increase security as well as decrease production costs of goods. Critical to this evolution is the cost decrease in the components of such systems, among which are gas sensors. In this work, a custom-made Co3O4 gas sensing element is presented, which can potentially be used as part of a cyber-physical system (CPS) for O3 monitoring. To investigate its performance, a CPS is developed using low-cost, low-power micro-controller units (MCUs) and comparisons both with the laboratory equipment and commercial off-the-shelf (COTS) ozone sensors are provided. The experiments show that the Co3O4 sensor works at room temperature with low input voltage and low power consumption when used with the proposed MCUs. Moreover, an enhanced gas sensing performance against ozone is observed under low-pressure conditions due to the detection of low ozone concentrations (85.90 ppb) and good sensor response (113.1%) towards 1100 ppb O3. However, the drawbacks that need improvement relate to the kinetics of the charge carriers, which affect the response time and recovery behavior. The effect of humidity needs to be clarified in further works

Study on the Ozone Gas Sensing Properties of rf-Sputtered Al-Doped NiO Films

Al-doped NiO (NiO:Al) has attracted the interest of researchers due to its excellent optical and electrical properties. In this work, NiO:Al films were deposited on glass substrates by the radio frequencies (rf) sputtering technique at room temperature and they were tested against ozone gas. The Oxygen content in (Ar-O2) plasma was varied from 2% to 4% in order to examine its effect on the gas sensing performance of the films. The thickness of the films was between 160.3 nm and 167.5 nm, while the Al content was found to be between 5.3 at% and 6.7 at%, depending on the oxygen content in plasma. It was found that NiO:Al films grown with 4% O2 in plasma were able to detect 60 ppb of ozone with a sensitivity of 3.18% at room temperature, while the detection limit was further decreased to 10 ppb, with a sensitivity of 2.54%, at 80 °C, which was the optimum operating temperature for these films. In addition, the films prepared in 4% O2 in plasma had lower response and recovery time compared to those grown with lower O2 content in plasma. Finally, the role of the operating temperature on the gas sensing properties of the NiO:Al films was investigated