Papers

F. Giannopoulos, N. Chronopoulou, J. Bai, H. Zhao, D.I. Pantelis, E.A. Pavlatou, A. Karantonis

Electrochimica Acta (2016), 207, 76–86

In this work, composite coatings were fabricated by electrolytic co-deposition of hybrid MWCNT-Al2O3 particles with Ni matrix from a Watts type bath, with and without the use of the sodium dodecyl sulfate additive, under both direct and pulse current conditions. The surface morphology and structural characteristics of the coatings were investigated for the different types of applied current mode, in the absence and presence of the additive. The mechanism of electrochemical co-deposition of Ni and hybrid particles was investigated by linear sweep voltammetry, electrochemical impedance spectroscopy and quartz crystal microbalance measurements in order to elucidate some aspects of the co-deposition mechanism. It was found that the presence of hybrid MWCNT-Al2O3 particles promotes direct proton discharge as well as hydrogen coverage, thus decreasing the deposition efficiency.

doi: 10.1016/j.electacta.2016.04.162

N. Lagopati, E. Tsilibary, P. Falaras, P. Papazafiri, E.A Pavlatou, E. Kotsopoulou, P. Kitsiou

International Journal of Nanomedicine (2014), 9 (1), 3219-3230

The use of nanoparticles has seen exponential growth in the area of health care, due to the unique physicochemical properties of nanomaterials that make them desirable for medical applications. The aim of this study was to examine the effects of crystal phase-nanostructured titanium dioxide particles on bioactivity/cytotoxicity in breast cancer epithelial cells. Cultured Michigan Cancer Foundation (MCF)-7 and human breast adenocarcinoma (MDA-MB-468) breast cancer epithelial cells were exposed to ultraviolet A light (wavelength 350nm) for 20 minutes in the presence of aqueous dispersions of two different nanostructured titanium dioxide (TiO2) crystal phases: anatase and an anatase–rutile mixture. Detailed characterization of each titanium dispersion was performed by dynamic light scattering. A 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) colorimetric assay was employed to estimate the percentage of viable cells after each treatment. Western blot analysis of protein expression and characterization, as well as a deoxyribonucleic acid (DNA)-laddering assay, were used to detect cell apoptosis. Our results documented that 100% anatase TiO2 nanoparticles (110–130nm) exhibited significantly higher cytotoxicity in the highly malignant MDA-MB-468 cancer cells than anatase–rutile mixtures (75%/25%) with the same size. On the contrary, MCF-7 cells (characterized by low invasive properties) were not considerably affected. Exposure of MDA-MB-468 cells to pure anatase nanoparticles or anatase–rutile mixtures for 48 hours resulted in increased proapoptotic Bax expression, caspase-mediated poly(adenosine diphosphate ribose) polymerase (PARP) cleavage, DNA fragmentation, and programmed cell death/apoptosis. The obtained results indicated that pure anatase TiO2 nanoparticles exhibit superior cytotoxic effects compared to anatase–rutile mixtures of the same size. The molecular mechanism of TiO2 nanoparticle cytotoxicity involved increased Bax expression and caspase-mediated PARP inactivation, thus resulting in DNA fragmentation and cell apoptosis.

doi: 10.2147/IJN.S62972

Α. Tzani, A. Douka, A. Papadopoulos, E.A. Pavlatou, E. Voutsas, A. Detsi

ACS Sustainable Chemistry and Engineering (2013), 1 (9), 1180-1185

In the frame of research that examines the use of task-specific ionic liquids (ILs) for developing green methodologies toward novel bioactive compounds, ethanolamine-derived ILs were synthesized and used as solvents and catalysts in a domino Knoevenagel–Michael reaction. After extended optimization studies regarding the most important reaction parameters such as reaction time, temperature, and molar ratio of reactants, it was ascertained that the reaction between 4-hydroxy-coumarin and various benzaldehydes in the synthesized ILs proceeded smoothly at 40°C in 3h, providing the desired biscoumarins in very satisfactory yields (up to 97%) and high purity after simple workup. The task-specific ILs were recycled and reused three times without a noticeable decrease in their catalytic activity. Moreover, the biodegradability potential of the synthesized ILs has been investigated by applying the biological oxygen demand (BOD-5) closed bottle test. The results indicated that organic carbon was biodegraded up to 59% within five days.

doi: 10.1021/sc4001093

A.V. Katsanaki, A.G., Kontos, T.Maggos, M. Pelaez, V .Likodimos, E.A. Pavlatou, D.D. Dionysiou, P. Falaras

Applied Catalysis B: Environmental (2013), 140-141, 619-625

Visible light activated nanostructured TiO2 with nitrogen and fluorine co-dopants were prepared by the surfactant assisted sol–gel method and immobilized on glass substrates by dip coating. The films were inserted inside a continuous flow photoreactor and examined for the photocatalytic oxidation of NO air pollutant with initial concentration of 200–800 ppbv. The modified catalysts exhibited significant photocatalytic activity under daylight illumination, with maximum percentage of NO removal equal to 24.2% and photooxidation rate up to 0.66 μgm−2s−1. The reaction rates increased proportionally to the incident light intensity whereas for the strongly absorbed UV light a deviation from linearity was observed. Mass balance during photooxidation was confirmed by determining the amount of NO3 product residues onto the photocatalyst surface.

doi: 10.1016/j.apcatb.2013.04.070

N. Kalogeropoulos, J. Tzigounakis, E.A. Pavlatou, A. Boudouvis

Computer Applications in Engineering Education (2013), 21, 671-683

In this study, the score equivalence of computer‐based assessment (CBA) and paper‐and‐pencil testing (PPT) in an undergraduate course of introductory computer programing at the National Technical University of Athens' School of Chemical Engineering, was examined. The research was carried out with 211 students participating, and was realized by a specially constructed CBA platform as well as the classical PPT. Both types of assessment included the same questions of multiple‐choice type, completing and correcting code in Fortran, as well as writing Fortran code from scratch. The results showed that, in general, students performed better and received higher scores under CBA compared to PPT. In particular, the very good students benefited from the advantages that the computer compiler offers in debugging code and completing code exercises and, thus, received relatively higher scores in these parts of the test. Moreover, switching answers and devoting more time‐on‐task was found to be beneficial for the students' performance. Overall, the findings of this study revealed that the actual programing abilities of the students are better evaluated using such CBA tests.

doi: 10.1002/cae.20512

S. Spanou, Α.Ι. Kontos, Α. Siokou, Α.G. Kontos, Ν. Vaenas, P. Falaras, E.A. Pavlatou

Electrochimica Acta (2013), 105, 324-332

Titanium dioxide (TiO2) nano-particles were immobilized in nickel matrix coatings using the direct current electrodeposition technique. The influence of nickel surface morphology and crystallographic orientation on the photocatalytic activity and photo-induced hydrophilicity of the composite coatings were investigated under UVA illumination. The overall self-cleaning character of the composites was improved following the titania codeposition, as both hydrophilic and photocatalytic effects are present. Simultaneous optimization of the two functionalities was possible via tuning the titania percentage, indicating that the corresponding properties of the composite coatings are associated also to the induced crystalline nickel orientation and the nickel grain size. In particular, the data indicate that both enhanced photocatalytic activity and photo-induced hydrophilicity are achieved by increasing amounts of titania nano-particles embedded in the Ni matrix in combination with reduced grain size of nickel crystallites that are oriented towards the [110] axis.

doi: 10.1016/j.electacta.2013.04.174

M. Giallousi, V. Gialamas, E.A. Pavlatou

Learning Environments Research (2013), 16 (3), 349-366

The present study was the first in Greece in which educational effectiveness theory constituted a knowledge base for investigating the impact of chemistry classroom environment in 10 Grade students’ enjoyment of class. An interpretive heuristic schema was developed and utilised in order to incorporate two factors of teacher behaviour at classroom level, namely, ‘content coverage’ and ‘cognitive teaching processes’, with the patterns of a typology of classroom environments. The latter was drawn from data collected in Attica (a region in Greece) using a new and valid instrument, the How Chemistry Class is Working, while the Enjoyment of Chemistry Lessons scale was used to measure students’ attitudes. A two-step cluster analysis revealed four patterns of the typology that were adaptable to the heuristic schema. The relationship between the patterns and students’ gender, as well the variation in the level of students’ enjoyment among the patterns, were explored. The traditional chemistry classroom environments were found to prevail and to be less enjoyable for the students, especially for the girls. It was found also that students enjoy chemistry lessons more when their goals are taken into account and they have an active role in learning process.

doi: 10.1007/s10984-013-9133-y

A. Thanos, E. Katsou, S. Malamis, K. Psarras, E.A. Pavlatou, K.J. Haralambous

Chemical Engineering Journal (2012), 211-212, 77-88

The removal of Cr(VI) from aqueous solutions was investigated using various minerals, such as zeolite (clinoptilolite), bentonite, exfoliated vermiculite and attapulgite. These minerals were modified using hexadecylammonium bromide (HDTMA-Br). The parameters under investigation were the HDTMA-Br concentration (0.36–8 gL−1), the pH (3–9) at which the modification process was conducted, the pH (3–9) of the adsorption solution, the modified mineral type and its concentration (1.5–10 gL−1), the mineral–metal contact time, the chromium initial concentration (10–500 mgL−1) and the system equilibrium time with respect to chromate adsorption. FTIR, SEM-EDX, XRD and electrokinetic zeta measurements were conducted for the natural and modified minerals which confirmed the modification of the minerals. The optimum pH for Cr(VI) adsorption was 4, in all the examined cases. The maximum adsorption capacity followed the order vermiculite (27 mgg−1)>bentonite (24 mgg−1)>attapulgite (15 mgg−1)>zeolite (13 mgg−1). Freundlich was the isotherm that provided the best fit to the experimental data when attapulgite was employed, while Langmuir was the most suitable one when the other three minerals were employed. Kinetics examination revealed a rapid adsorption of the metal during the initial stages. The pseudo-second-order equation fitted well to the experimental data.

doi: 10.1016/j.cej.2012.08.086

E.A. Pavlatou, P. Gyftou, S. Spanou

Transactions of the Institute of Metal Finishing (2012), 90 (5), 267-273

Nickel nanocrystalline electrodeposits were produced from a Watts type bath with the addition of cis-2-butene-1,4-diol and simultaneous application of either direct or pulse current conditions. The surface morphology, the preferred orientation, grain size and microhardness of Ni deposits were determined as functions of the concentration of the additive in bath, the type of imposed current and the frequency of imposed current pulses. The combined imposition of predefined pulse current conditions (pulse frequency) and specific additive concentration in the bath leads to specific textural modifications ([211] and [100] preferred crystal orientations) accompanied by considerable nanosized grain refinement of the coatings. The overall experimental data indicate that the production of hard and bright nanostructured deposits could be obtained under pulse current regime and reduced amounts of cis-2-butene-1,4-diol compared to direct plating.

doi: 10.1179/0020296712Z.00000000049

G. Korakakis, A. Boudouvis, J. Palyvos, E.A Pavlatou

Procedia - Social and Behavioral Sciences (2012), 31, 145-149

This study reports research findings on whether the use of 3D visualization types i.e. Interactive 3D Virtual Environment (I3DVE), 3D Animations Interface (3DAIF) and 3D Static Illustrations Interface (3DSIIF), combined with narration and text in multimedia applications, contributes to the learning process of 12th grade students in science. A total of 111 students participated in the research that utilized three different versions of an interactive multimedia application called "Atomic Orbitals". The research results provide convincing evidence that I3DVE have a greater contribution to the learning process than the other two types of visualization.

doi: 10.1016/j.sbspro.2011.12.032

K. Dalacosta, M. Paparrigopoulou-Kamariotaki, E.A. Pavlatou

Procedia - Social and Behavioral Sciences (2011), 15, 3272-3276

The present paper concerns the use of animated cartoons as an assessment tool in teaching science regarding students of elementary education. Different instructional strategies are presented whereas with the aid of two sets of questions with animated cartoons, the teacher is able to: (i) find out and evaluate what students already know about specific science concepts or (ii) evaluate students’ knowledge and understanding of science concepts which are normally difficult to comprehend and often cause misconceptions to them. Concepts that have been chosen to be studied were those of mass volume and density, as well as dissolving, melting, and disappearing.

doi: 10.1016/j.sbspro.2011.04.284

S. Spanou, E.A. Pavlatou

Zeitschrift fur Physikalische Chemie (2011), 225 (3), 313-324

Nanocomposite coatings were obtained by electrochemical codeposition of TiO2 nano-particles (mean diameter 21nm, Degussa P25) with nickel, from an additive-free Watts type bath. Pure Ni and composite Ni-TiO2 coatings were electrolytically deposited under both direct and pulse current conditions and an extended region of electrolysis conditions (pH, current density, TiO2 loading in the bath). Pure Ni deposits were produced under the same experimental conditions for comparison. The aim of this study was to correlate the observed structural characteristics of the coatings (crystallographic orientation and grain size of nickel matrix,) and incorporation percentage with the resulting microhardness values and tribological behavior. Overall, the data have demonstrated that when attributing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms, but also preferred crystalline orientation should be taken into consideration. The variation of the wear rate is directly associated with the microhardness variations and consequently, governed by the same parameters that determine the synergistic strengthening mechanism proposed. Pure and composite coatings with [110] crystalline orientation exhibited the highest microhardness values and wear resistance.

doi: 10.1524/zpch.2011.0052

A. Zoikis-Karathanasis, E.A. Pavlatou, N. Spyrellis

Journal of Alloys and Compounds (2010), 494, 396-403

Ni–P/SiC composite coatings were produced under both direct and extended pulse current conditions from an additive-free modified Watts type bath at various hydrodynamic conditions. Structural analysis revealed an amorphous phase of Ni–P matrix for the majority of coatings, except for those prepared under low duty cycle and high frequency pulses that exhibited mainly the crystalline Ni12P5 compound. The practice of pulse plating regime led to composite coatings with higher incorporation rate of SiC particles (up to 22wt.) and microhardness values (up to 7.2GPa) than those produced under direct current conditions. It has been revealed that increased micron-SiC codeposition percentage resulted in decrease of P content in the amorphous matrix and increase of the deposits’ hardness values. After annealing at 400°C the amorphous matrix was crystallized to phases of Ni, Ni2P, and Ni3P, the formation of which depends on the P content. As-plated deposits exhibiting Ni12P5 phase preserved this crystalline structure after thermal treatment. Annealed coatings exhibited almost double values of microhardness relative to those of the as-deposited coatings.

doi: 10.1016/j.jallcom.2010.01.057

S. Spanou, E.A. Pavlatou

Journal of Applied Electrochemistry (2010), 40, 1325-1336

Pure and composite nickel deposits containing nano-TiO2 particles (dm=21nm) were produced under direct-DC and pulse current-PC conditions. The influence of pulse frequency on the codeposition of TiO2 particles, preferred orientation of Ni crystallites and grain size, as well as microhardness of the composites, was investigated systematically. Composites prepared in PC regime displayed higher incorporation percentage than those obtained under DC conditions, and the highest incorporation rates were achieved at pulse frequencies ν>100Hz. The application of pulse frequency accompanied by the embedding of TiO2 nanoparticles in the nickel matrix resulted in a strong influence upon the crystalline orientation, the grain size and the corresponding microhardness. All composites exhibited higher microhardness values compared to the pure deposits, independent of the applied current conditions. Overall, when ascribing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms but also preferred crystalline orientation should be taken into consideration.

doi: 10.1007/s10800-010-0080-3

M. Giallousi, V. Gialamas, N. Spyrellis, E.Α. Pavlatou

International Journal of Science and Mathematics Education (2010), 8, 761-782

This study describes the development and validation of a Greek-language instrument that can be used to assess grade 10 students' perceptions of their chemistry classroom environment as a means of showing differences between chemistry learning environments in Greece (Attica) and Cyprus. The development of the instrument was based on available learning environment questionnaires. The questionnaire was administered to 1.394 students from 49 chemistry classes in Attica, and the resulting data were analyzed to explore the reliability and the validity of the new instrument. The validated questionnaire was administered to 225 students from 15 classes in urban areas of Cyprus. The data analyses supported the questionnaire's internal consistency, discriminant validity, and ability to differentiate between classrooms. Effect sizes and independent samples t test analyses revealed differences between the two samples. Cypriot students viewed their chemistry classroom environment more favorably than did the Attica students. A possible cause for this difference could be the knowledge-centered aspect of the grade 10 chemistry curriculum in Greece compared to the corresponding tool-instrumental knowledge curriculum in Cyprus.

doi: 10.1007/s10763-009-9184-9

X. Vamvakeros, E.A. Pavlatou and N. Spyrellis

Science and Education (2010), 19, 119-145

A survey exploring the views of scientists, chemists and chemical engineers, on current trends in Chemistry Education was conducted in Greece. Their opinions were investigated using a questionnaire focusing on curricula (the content and process of chemistry teaching and learning), as well as on the respondents’ general educational beliefs and their underlying epistemological views. The aim of this work was to investigate the respondents’ opinions and, if possible, to identify the areas where convergence or even consensus occurred. The results showed that some of the items on the research questionnaire produced a high degree of agreement with the respondents’ views, while a few others were exactly the opposite. These items are considered to be representative of more widespread views. In order to explore the diverging opinions, the items on the research questionnaire that showed great variance were analyzed to determine, whether or not there were significant inter-item correlations among subgroups of participants with different demographic characteristics. Postgraduate studies, professional occupation, age/experience, and career within or outside the wide educational sector were among the main factors that significantly influenced the research results. The study did not reveal any single belief framework underlying the opinions of the respondents. Nevertheless, three specific approach frameworks—ACADEMIC, CONSTRUCTIVIST and SCIENTIFIC REALISM—were analyzed to determine which had the highest degree of agreement. It was found that the SCIENTIFIC REALISM framework and the curriculum emphasis characteristic of the context-based CTSE (Chemistry, Technology, Society and Environment) prevailed, as they produced a significantly higher mean score. The ACADEMIC framework followed with a moderate mean score and the CONSTRUCTIVIST framework had a lower mean score.

doi: 10.1007/s11191-009-9196-4

I. Masavetas, A. Moutsatsou, E. Nikolaou, S.Spanou, A. Zoikis-Karathanasis, E.A. Pavlatou, N. Spyrellis

Global NEST Journal (2009), 11 (2), 241-247

During the last years, the waste electrical and electronic equipment (WEEE) are gathering attention, as a very special section of waste. In fact, they have been proven to be source for the recovery of metals. In the present study printed circuit boards (PCBs) were cut and treated thermally at 500°C for 1h in both air and nitrogen atmosphere. The obtained material was dissolved in three different acid media HNO3(aq), HCl(aq) and H2SO4(aq), in order to extract copper. The achieved Cu recovery percentages were 97.5, 65 and 76.5% respectively. Electrodeposition technique was applied in order to recover copper in powder form. More than 98% of copper was recovered achieved by application of high current density resulting to dendritic structure of copper. The applied process was characterised by a high current efficiency and led to the production of copper powder of 80μm mean diameter appropriate for powder metallurgy applications.

doi: 10.30955/gnj.000595

N. Spyrellis, E.A. Pavlatou, S. Spanou, A. Zoikis-Karathanasis

Transactions of Nonferrous Metals Society of China (2009), 19 (4) 800-804

Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO2, SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts' type bath. The influence of the variable electrolysis parameters (type of current, frequency of current pulses and current density) and the reinforcing particles properties (type, size and concentration in the bath) on the surface morphology and the structure of the deposits was examined. It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process. On the other hand, Ni-P amorphous matrix is not affected by the occlusion of the particles. Overall, the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime.

doi: 10.1016/S1003-6326(08)60353-2

G. Korakakis, E.A. Pavlatou, J.A. Palyvos, N. Spyrellis

Computers & Education (2009), 52, 390-401

This research aims to determine whether the use of specific types of visualization (3D illustration, 3D animation, and interactive 3D animation) combined with narration and text, contributes to the learning process of 13- and 14-years-old students in science courses. The study was carried out with 212 8th grade students in Greece. This exploratory study utilizes three different versions of an interactive multimedia application called “Methods of separation of mixtures”, each one differing from the other two in a type of visuals. The results indicate that multimedia applications with interactive 3D animations as well as with 3D animations do in fact increase the interest of students and make the material more appealing to them. The findings also suggest that the most obvious and essential benefit of static visuals (3D illustrations) is that they leave the time control of learning to the students and decrease the cognitive load.

doi: 10.1016/j.compedu.2008.09.011

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