Publications by authors named "John Vakros"

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied.

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Biochars, i.e. porous carbons obtained by pyrolysis of biomass, can act as electrocatalysts for oxygen evolution and oxygen reduction reaction.

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The current era has been defined as "The Plastic Era", considering that over the past 50 years the role and importance of polymeric materials in our economy has steadily grown, reaching a production of around a few hundred million tons per year which may even double in the next 20 years [...

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Today, sustainability represents the key factor for economic progress in compliance with social advancement and environmental protection, driving innovation in materials, processes and technologies [...

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Different species of microorganisms colonize the plastic surfaces and form biofilms depending on the aquatic environment. In the current investigation, characteristics of the plastic surface after exposure to three different aquatic environments based on visualization using scanning electron microscopy (SEM) and spectroscopic (diffuse reflectance (DR) and infrared (IR)) techniques were examined in laboratory bioreactors with time. For both materials, there were no differences observed in the ultraviolet (UV) region among the reactors and several peaks were observed with fluctuating intensities and without any trends.

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Biochar has been obtained by pyrolysis of spent malt rootlets under limited oxygen supply and further activated by mixing with KOH and pyrolyzed again at high temperature. The total specific surface area of such activated biochar was 1148 m g, while that of micropores was 690 m g. This biochar was used to make a functional electrode by deposition on carbon cloth and was combined with a photoelectrochemical cell.

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Mono-doped (Mo-TiO and W-TiO) and co-doped TiO (Co-Mo-TiO, Co-W-TiO, Cu-Mo-TiO, Cu-W-TiO, Zn-Mo-TiO, and Zn-W-TiO) catalysts were synthesized by simple impregnation methods and tested for the photocatalytic degradation of 4-tert-butylphenol in water under UV (365 nm) light irradiation. The catalysts were characterized with various analytical methods. X-ray diffraction (XRD), Raman, Diffuse reflectance (DR) spectroscopies, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Energy dispersive spectroscopy (EDS) were applied to investigate the structure, optical properties, morphology, and elemental composition of the prepared catalysts.

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Over the last few decades, nanotechnology has received a huge level of interest due to its extensive applications in various fields, including catalysis, electronics, optics, energy, and the environment [...

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A series of WO/TiO catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH. Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO and TiO and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO/TiO interface were quantified using variations in the system's electronic structure.

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Biochar from spent malt rootlets was employed as the template to synthesize hybrid biochar-ceria materials through a wet impregnation method. The materials were tested for the activation of persulfate (SPS) and subsequent degradation of sulfamethoxazole (SMX), a representative antibiotic, in various matrices. Different calcination temperatures in the range 300-500 °C were employed and the resulting materials were characterized by means of N adsorption and potentiometric mass titration as well as TGA, XRD, SEM, FTIR, DRS, and Raman spectroscopy.

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In this work, we evaluated the valorisation of agricultural waste materials by transforming coconut husks and shells, corncobs and rice straw into biochar for water treatment in aquaculture. We compared the biochars' suitability for removal of organic micropollutants (acetaminophen, oxytetracycline, tetracycline, enrofloxacin, atrazine, diuron and diclofenac) from surface water needed for aquaculture. The biochars were prepared by three methods ranging from inexpensive drum kilns (200 °C) to pyrolysis with biogasfication (350-750 °C).

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In the present study, biochar from spent coffee grounds was synthesized via pyrolysis at 850 °C for 1 h, characterized and employed as catalyst for the degradation of sulfamethoxazole (SMX) by persulfate activation. A variety of techniques, such as physisorption of N, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and potentiometric mass titration, were employed for biochar characterization. The biochar has a surface area of 492 m/g, its point of zero charge is 6.

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The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.

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Biofilm formation on plastic debris needs to be further investigated, because microorganisms attached to plastics are transferred in all three dimensions to new regions by ocean currents. The current study aims to investigate biofilm formation on plastic strips in aquatic ecosystems using a simple physicochemical method commonly used to characterize solid surfaces, namely, the diffuse reflectance UV-Vis spectroscopy (DRS) method. Using virgin polymers that have not being exposed to the environment as a reference, DRS peaks can be attributed to the microorganisms attached to the polymer surface with time.

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In the present work we studied, for the first time, the kinetics of adsorption of the Co(H(2)O)(6)(2+) species on the "electrolytic solution/gamma-Al(2)O(3)" interface at pH = 7 and 25 degrees C for a very broad range of Co(II) surface concentrations ranged from 0.03 to 6 theoretical Co(H(2)O)(6)(2+) surface layers. Moreover, we studied the surface dissolution of gamma-alumina in the presence of the Co(H(2)O)(6)(2+) ions in the impregnating solution, the contribution of the Co(II) desorption on the whole deposition process and the deposition isotherm.

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In the present work we studied the influence of the preparation method and the Co loading on the physicochemical properties and the catalytic activity of the cobalt oxide/gamma-alumina catalysts for the reduction of NO by propene under net oxidizing conditions. Two series of catalysts containing 1 and 5% w/w Co, respectively, were prepared using three preparation methods, namely, the equilibrium deposition filtration (EDF), the conventional incipient wetness impregnation (IWI) and the IWI adding nitrilotriacetic acid (nta) in the impregnating solution (IWInta). The catalysts were tested at various temperatures in the range 300-550 degrees C using a fixed-bed microreactor for the NO reduction by propene under lean burn conditions.

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Diffuse reflectance spectroscopy was used for the first time to investigate the adsorption of the [Co(H2O)6]2+ ions on the interface developed between the surface of the gamma-alumina particles and the electrolytic aqueous solutions used for the preparation of cobalt-supported gamma-alumina catalysts by equilibrium deposition filtration. The formation of inner-sphere Co(II) surface complexes in which Co(II) is in octahedral symmetry was confirmed. A deconvolution peak centered at approximately 585 nm was attributed to the exchange of one aqua ligand with one AlxOHy (x = 1, 2, or 3; y = 0 or 1) negatively charged surface group resulting in the formation of mononuclear monosubstituted inner-sphere Co(II) complexes at a Co(II) surface concentration equal to 0.

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In the present review article, we present the efforts done so far for elucidating the mechanism of adsorption of the Co(II) species, mainly Co(H(2)O)(6)(2+), on the interfacial region developed between metal oxide particles, used as catalytic supports, and aqueous electrolytic solutions. Specifically, we present: (i) the principal modes of deposition of the transition metal ionic species (TMIS) on the surface of oxidic supports related with the various methodologies used for the preparation of the supported catalysts; (ii) the state of the art concerning the general aspects of the adsorption mechanisms of the TMIS on the aforementioned interfacial region; and (iii) the works reported so far dealing with the adsorption of the Co(II) species on the surface of gamma-Al(2)O(3) (gamma-alumina), alpha-Al(2)O(3) (alpha-alumina), TiO(2) (rutile), and SiO(2) (silica). It was concluded that the mechanism of adsorption depends on two main factors: on the Co(II) surface concentration and on the nature of the support surface.

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A novel technique for determining the point of zero charge (pzc), called 'potentiometric mass titrations technique', has been developed and used for determining the pzc of several industrially used catalytic supports (SiO2, TiO2, gamma-Al2O3 and MgO).

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