Microwave synthesis, characterization and perspectives of wood pencil-derived carbon

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil's graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70-75 mg/g within 24 h at 23 degrees C, pH = 3.Web of Science121art. no. 41

Synthesis and chaqracterization of hybrid porous materials for engineering applications

The present Ph.D. thesis presents the synthesis and characterization of novel hybrid porous materials. These materials are modified derivatives of two and three-dimensional configurations of synthetic structures of carbon (CMK-3 and carbon nanosheets) as well as layered double hydroxides structures (LDH). The synthesis of the CMK-3 hybrid materials comprised three directions: binding of organo-silicate compounds on the surface of CMK-3, in-situ development of Fe(III)-oxide magnetic nanoparticles on the pores of CMK-3 and dispersion of zero valent iron nanoparticles on the surface of CMK-3. The binding of the organo-silicate compounds was achieved through silanization (development of covalent bonds). The nanoparticles of iron oxides, formed in CMK-3, featured superparamagnetic properties. They had a small size because the matrix of CMK-3 limits their development. The properties of the newly synthesized hybrid materials of CMK-3/nanoparticles Fe0 confer them qualifications for further consideration in advanced environmentalapplications, such as purification of aqueous solutions from Cr6+-ions. Synthesis of mesoporous carbon materials was also successfully realized, whereby acetylene-dicarboxylic acid, as a precursor agent, and SBA-15, as a geometric model of the mesoporous matrix of silica were used, resulting in the development of mesoporous carbon with high specific area. This method enables the formation of active groups of carboxy and carbonyl groups on the walls of the pores with no need of extra chemical treatment, which might frustrate the initial mesoporous structure. The modification of carbon nanosheets was also successfully carried out with the development of organo-silicate nanoparticles on their surfaces, which contained NH2-groups or thiols at their organic end and they bound to carbon surface via covalent bonds. The synthetic method leads to the formation of newly formed radicals on the surface of graphene nano-layers. Meanwhile, there is negligible change of the dynamic and the electronic properties compared to the initial material. Meanwhile, the synthesis of a special type of layered hybrid materials was also attempted. Two different methods were tested to intercalate molecules of vitamin Β1 in the layered structure of LDH. The two synthesis methods were evaluated with regards to the ability of the final product to maintain the catalytic properties of vitamin Β1 and the capability of LDH to safely store vitamin Β1 in their structure.Στην παρούσα διατριβή συντέθηκαν και χαρακτηρίστηκαν νέα υβριδικά πορώδη υλικά αποτελούμενααπό τροποποιημένα παράγωγα τρισδιάστατων και δυσδιάστατων συνθετικών δομών του άνθρακα (CMK-3 και γραφιτικά νανοφυλλίδια) καθώς επίσης και των διπλών υδροξειδίων φυλλόμορφης δομής (LDH). Η έρευνα για τη σύνθεση υβριδικών υλικών με βάση το CMK-3, επικεντρώθηκε: στην δέσμευση στην επιφάνεια του CMK-3 οργανοπυριτικών ενώσεων, στην in-situ ανάπτυξη μαγνητικών νανοσωματιδίων οξειδίων σιδήρου στους πόρους του CMK-3 και στη διασπορά νανοσωματιδίων μεταλλικού σιδήρου στην επιφάνεια του. Η δέσμευση των οργανοπυριτικών ενώσεων έγινε με αντιδράσεις σιλανοποίησης (ανάπτυξη ομοιοπολικών δεσμών) στην επιφάνεια του CMK-3. Τα νανοσωματίδια οξειδίων του σιδήρου που σχηματίστηκαν στο CMK-3, έχουν μικρό μέγεθος που προκύπτει από τον περιορισμό της ανάπτυξής τους στη μήτρα του CMK-3 και παρουσιάζουν υπερπαραμαγνητικές ιδιότητες. Τα υβριδικά υλικά CMK-3/νανοσωματίδια Fe0 επέδειξαν βελτιωμένες ιδιότητες σε περιβαλλοντικές εφαρμογές για τον καθαρισμό υδατικών διαλυμάτων από το Cr6+. Παράλληλα πραγματοποιήθηκε η σύνθεση μεσοπορώδους άνθρακα με πρόδρομη ένωση το ακετυλενο-δικαρβοξυλικό οξύ χρησιμοποιώντας ως μήτρα-εκμαγείο το μεσοπορώδες πυριτικό υλικό SBA-15. Ο πολυμερισμός και η πυρόλυση της πρόδρομης ένωσης στο εσωτερικό των πόρων του SBA-15, οδήγησε στην ανάπτυξη νέου μεσοπορώδους άνθρακα με μεγάλη ειδική επιφάνεια και ενεργές καρβόξυ και καρβονυλομάδες, χωρίς να χρειάζεται η χημική επεξεργασία του με οξέα που μπορεί να οδηγεί σε καταστροφή της αρχικής δομής. Μια άλλη κατηγορία υβριδικών υλικών με βάση τον άνθρακα που μελετήθηκε, είναι αυτή που προκύπτει από την τροποποίηση νανοφυλλιδίων άνθρακα, αναπτύσσοντας στην επιφάνειά τους οργανοπυριτικά νανοσωματίδια, που περιέχουν αμινομάδες η θειόλες στο οργανικό τους μέρος, ενώ συνδέονται με την επιφάνεια του άνθρακα αναπτύσσοντας ομοιοπολικούς δεσμούς. Έτσι δημιουργήθηκαν νέες ρίζες στην επιφάνεια των γραφιτικών νανοφυλλιδίων ενώ ταυτόχρονα οι δυναμικές και ηλεκτρονιακές τους ιδιότητες είναι συγκρίσιμες με αυτές του αρχικού υλικού. Τέλος, στην παρούσα διατριβή μελετήθηκε και μια άλλη κατηγορία φυλλόμορφων υβριδικών υλικών, που προκύπτουν από την ένθεση της βιταμίνης Β1 στα συνθετικά διπλά υδροξείδια φυλλόμορφης δομής (LDH). Μελετήθηκε ο τρόπος ένθεσης των βιομορίων στα LDH, με δύο διαφορετικές συνθετικές μεθόδους, η διατήρηση των καταλυτικών τους ιδιοτήτων και η ικανότητα των LDH ως υλικά αποθήκευσης των μορίων της βιταμίνης Β1

Advanced Cr(VI) sorption properties of activated carbon produced via pyrolysis of the “Posidonia oceanica” seagrass

This research deals with the removal of Cr(VI), one of the most toxic heavy metal in biological systems, from wastewater by using activated carbon produced via pyrolysis and chemical activation of "Posidonia oceanica". That is the most important and well-studied seagrass species of the Mediterranean Sea. The as produced activated carbon exhibited high specific surface area up to 1563 m(2)/g and a cumulative pore volume of 0.74 cm(3)/g, allocated to 74% micro-pores and 26% to meso-macro- pores. The adsorption capacity of Cr(VI) into Posidonia oceanica activated carbon was studied via batch experiments considering the contact time, the initial concentration and the pH parameters. The results were interpreted using four different adsorption kinetic models. The activated carbon material seems to exhibit excellent sorption properties with rapid removal capability for Cr(VI). The estimated maximum uptake capacity at equilibrium stage was similar to 120 mg/g. Also, the initial adsorption rate r(i) was dependent on the initial Cr(VI) concentration in aqueous solution and it was from 77 mg/(g*h) to 264 mg/ (g*h). The best fitted kinetic model seems to be the Diffusion-Chemisorption model with the rate constant K-DC of the Cr(VI) ions transfer from liquid to solid particles extend from 52 to 78 mg/(g*h(0.5)).Web of Science405art. no. 12427

Effect of Copper and Titanium-Exchanged Montmorillonite Nanostructures on the Packaging Performance of Chitosan/Poly-Vinyl-Alcohol-Based Active Packaging Nanocomposite Films

In this study, CuMt and TiMt montmorillonites were produced via an ion-exchange process with Cu+ and Ti4+ ions. These nanostructured materials were characterized with X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) measurements and added as nanoreinforcements and active agents in chitosan (CS)/poly-vinyl-alcohol (PVOH)-based packaging films. The developed films were characterized by XRD and FTIR measurements. The antimicrobial, tensile, and oxygen/water-barrier measurements for the evaluation of the packaging performance were carried out to the obtained CS/PVOH/CuMt and CS/PVOH/TiMt films. The results of this study indicated that CS/PVOH/CuMt film is a stronger intercalated nanocomposite structure compared to the CS/PVOH/TiMt film. This fact reflected higher tensile strength and water/oxygen-barrier properties. The antibacterial activity of these films was tested against four food pathogenic bacteria: Escherichia coli, Staphylococcus aureus, Salmonella enterica and Listeria monocytogenes. Results showed that in most cases, the antibacterial activity was generated by the CuMt and TiMt nanostructures. Thus, both CS/PVOH/CuMt and CS/PVOH/TiMt films are nanocomposite candidates with very good perspectives for future applications on food edible active packaging

Hypergolic Synthesis of Inorganic Materials by the Reaction of Metallocene Dichlorides with Fuming Nitric Acid at Ambient Conditions: The Case of Photocatalytic Titania

Hypergolic materials synthesis is a new preparative technique in materials science that allows a wide range of carbon or inorganic solids with useful properties to be obtained. Previously we have demonstrated that metallocenes are versatile reagents in the hypergolic synthesis of inorganic materials, such as γ-Fe2O3, Cr2O3, Co, Ni and alloy CoNi. Here, we go one step further by using metallocene dichlorides as precursors for the hypergolic synthesis of additional inorganic phases, such as photocatalytic titania. Metallocene dichlorides are closely related to metallocenes, thus expanding the arsenal of organometallic compounds that can be used in hypergolic materials synthesis. In the present case, we show that hypergolic ignition of the titanocene dichloride–fuming nitric acid pair results in the fast and spontaneous formation of titania nanoparticles at ambient conditions in the form of anatase–rutile mixed phases. The obtained titania shows good photocatalytic activity towards Cr(VI) removal (100% within 9 h), with the latter being dramatically enhanced after calcination of the powder at 500 °C (100% within 3 h). Notably, this performance was found to be comparable to that of commercially available P25 TiO2 under identical conditions. The cases of zirconocene, hafnocene and molybdocene dichlorides are discussed in this work, which aims to show the wider applicability of metallocene dichlorides in the hypergolic synthesis of inorganic materials (ZrO2, HfO2, MoO2)

Hypergolic Synthesis of Inorganic Materials by the Reaction of Metallocene Dichlorides with Fuming Nitric Acid at Ambient Conditions: The Case of Photocatalytic Titania

Hypergolic materials synthesis is a new preparative technique in materials science that allows a wide range of carbon or inorganic solids with useful properties to be obtained. Previously we have demonstrated that metallocenes are versatile reagents in the hypergolic synthesis of inorganic materials, such as γ-Fe2O3, Cr2O3, Co, Ni and alloy CoNi. Here, we go one step further by using metallocene dichlorides as precursors for the hypergolic synthesis of additional inorganic phases, such as photocatalytic titania. Metallocene dichlorides are closely related to metallocenes, thus expanding the arsenal of organometallic compounds that can be used in hypergolic materials synthesis. In the present case, we show that hypergolic ignition of the titanocene dichloride–fuming nitric acid pair results in the fast and spontaneous formation of titania nanoparticles at ambient conditions in the form of anatase–rutile mixed phases. The obtained titania shows good photocatalytic activity towards Cr(VI) removal (100% within 9 h), with the latter being dramatically enhanced after calcination of the powder at 500 °C (100% within 3 h). Notably, this performance was found to be comparable to that of commercially available P25 TiO2 under identical conditions. The cases of zirconocene, hafnocene and molybdocene dichlorides are discussed in this work, which aims to show the wider applicability of metallocene dichlorides in the hypergolic synthesis of inorganic materials (ZrO2, HfO2, MoO2)

The use of activated bio-carbon derived from “Posidonia oceanica” sea-waste for Lithium-Sulfur batteries development

Lithium-Sulfur Batteries is promising energy storage systems due to their superior capacity and energy density. A promising solution for drawbacks such as low sulfur utilization and cycling stability is the use of porous carbon as sulfur carrier. On the other hand, cyclic economy and green ideas is of great importance nowadays. Carbon-sulfur cathodes from waste valorization, abundant, and low-cost precursors is an attractive approach. Herein, an activated carbon (AC-Poc) derived from "Posidonia oceanica" sea-waste, was studied as a matrix for the development of a novel carbon-sulfur composite cathode (AC-Poc/S) for the first time. AC-Poc can be used as an effective sulfur host, due to its high specific BET surface area (1264 m(2).g(-1)) hierarchical porous structure, and total pore volume 0.81 cm(3).g(-1). AC-Poc/S reveals an outstanding initial capacity of 1539 mAh.g(-1) as cathode material, combined with high reversible capacity at 0.2 C. Furthermore, the discharge capacity of 390 mAh/g at 2 C reveals good rate capability, even at increased C-rate. AC-Poc/S composite exhibits excellent sulfur utilization (92 %) alongside with sufficiently well electrochemical performance. These results combined with the easy synthesis method of the activated carbon from an abundant and low-cost precursor make AC-Poc/S a very promising material for LSBs applications.Web of Science53art. no. 10274

Synthesis of a Novel Chitosan/Basil Oil Blend and Development of Novel Low Density Poly Ethylene/Chitosan/Basil Oil Active Packaging Films Following a Melt-Extrusion Process for Enhancing Chicken Breast Fillets Shelf-Life

An innovative process for the adsorption of the hydrophobic Basil-Oil (BO) into the hydrophilic food byproduct chitosan (CS) and the development of an advanced low-density polyethylene/chitosan/basil-oil (LDPE/CS_BO) active packaging film was investigated in this work. The idea of this study was the use of the BO as both a bioactive agent and a compatibilizer. The CS was modified to a CS_BO hydrophobic blend via a green evaporation/adsorption process. This blend was incorporated directly in the LDPE to produce films with advanced properties. All the obtained composite films exhibited improved packaging properties. The film with 10% CS_BO content exhibited the best packaging properties, i.e., 33.0% higher tensile stress, 31.0% higher water barrier, 54.3% higher oxygen barrier, and 12.3% higher antioxidant activity values compared to the corresponding values of the LDPE films. The lipid oxidation values of chicken breast fillets which were packaged under vacuum using this film were measured after seven and after fourteen days of storage. These values were found to be lower by around 41% and 45%, respectively, compared with the corresponding lipid oxidation values of pure LDPE film

Nanoporous activated carbon derived via pyrolysis process of spent coffee: Structural characterization. Investigation of its use for hexavalent chromium removal

Featured Application This work deals with the development of an activated carbon adsorber via the exploitation of spent coffee waste. Economic and environmental benefits from such processes are extended. The application on hexavalent chromium removal was tested. Hexavalent chromium (Cr(VI)) is a heavy metal that is highly soluble and exhibits toxic effects on biological systems. Nevertheless, it is used in many industrial applications. The adsorption process of Cr(VI), using activated carbon (AC), is under investigation globally. On the other hand, around six million tons of spent coffee is sent to landfill annually. In the spirit of cyclic economy, this research investigated the production of AC from spent coffee for the removal of Cr(VI) from wastewater. The AC was produced via pyrolysis process under a nitrogen atmosphere. Chemical activation using potassium hydroxide (KOH) occurred simultaneously with the pyrolysis process. The produced AC was tested as an absorber of Cr(VI). The best fitted kinetic model was the diffusion-chemisorption model. A 24-h adsorption experiment was carried out using a solution with a pH of 3 and an initial Cr(VI) concentration of 54.14 ppm. This resulted in an experimental maximum capacity of 109 mg/g, while the theoretical prediction was 137 mg/g. It also resulted in an initial adsorption rate (r(i)) of 110 (mg/(g h)). The Brunauer-Emmett-Teller surface area (S-gBET) was 1372 m(2)/g, the Langmuir surface area (S-gLang.) was 1875 m(2)/g, and the corrugated pore structure model surface area (S-gCPSM) was 1869 m(2)/g. The micropore volume was 84.6%, exhibiting micropores at D-micro1 = 1.28 and D-micro2 = 1.6 nm. The tortuosity factor (tau) was 4.65.Web of Science1024art. no. 881

Preparation and Characterization of Polystyrene Hybrid Composites Reinforced with 2D and 3D Inorganic Fillers

Polystyrene (PS)/silicate composites were prepared with the addition of two organoclays (orgMMT and orgZenith) and two mesoporous silicas (SBA-15 and MCF) via (i) solution casting and (ii) melt compounding methods. X-ray diffraction (XRD) analysis evidenced an intercalated structure for PS/organoclay nanocomposites. Thermogravimetric analysis indicated improvement in the thermal stability of PS-nanocomposites compared to the pristine polymer. This enhancement was more prevalent for the nanocomposites prepared with a lab-made organoclay (orgZenith). Tensile measurement results indicated that elastic modulus increment was more prevalent (up to 50%) for microcomposites prepared using mesoporous silicas as filler. Organoclay addition led to a decrease in oxygen transmission rate (OTR) values. This decrement reached up to 50% for high organoclay content films in comparison to pristine PS film. Decrement above 80% was measured for microcomposites with mesoporous silicas and 5 wt% filler content obtained via melt compounding