Dr. Dionisios Panagiotaras | Ionian University (original) (raw)

Papers by Dr. Dionisios Panagiotaras

Applied Sciences

This study was based on the reduction of the extraction of natural resources and, at the same tim... more This study was based on the reduction of the extraction of natural resources and, at the same time, was focused on the use of by-products and various wastes in construction applications by following the principles of circular economy. Sterile natural rocks (limestones, basalts), industrial by-products (slags), hotel construction wastes (bathroom wastes) and electronic wastes (e-wastes) were tested for pervious concrete aggregates. For this reason, ten concrete specimens were prepared and tested petrographically, structurally, and physically. The physical properties of the tested raw materials directly depended on their petrographic characteristics and played crucial role for the permeability of the produced concrete specimens, for their mechanical behavior, and for the freeze–thaw test results. Generally, from this study, strong encouraging results were achieved as concrete made by variable wastes and by-products can be compatible for concrete production as they show similar perform...

Analytical Methods, 2013

ABSTRACT This paper addresses issues of long-range memory and self-organisation in variations of ... more ABSTRACT This paper addresses issues of long-range memory and self-organisation in variations of radon in soil in Greece. The methods of rescaled-range, roughness-length, variogram, fractal dimension and block entropy were employed through lumping. Sliding was utilised with the wavelet spectral fractal technique. Antipersistent Hurst exponents in the range 0 < H < 0.5 were mainly identified. Persistent exponents (0.5 < H < 1) were also detected. Switching between persistency and antipersistency was observed and considered consistent with an underlying geo-environmental long-memory self-organisation. Fractal dimensions were in the range 1.2 < D < 2. The anomalous parts of the 2008 radon signal presented significantly lower fractal dimensions. Value ranges of Shannon, Shannon-per-letter, conditional, Tsallis and normalised Tsallis block entropies were 0.67 <= H(n) <= 2.73, 0.2 <= h((n)) <= 0.7, 0.2 <= h((n)) <= 0.6, 0.36 <= S-q <= 1.11, 0.50 <= (S) over cap (q) <= 9.55 respectively. The entropy values were affected by the block-size n. The entropic index values of the radon anomalies were significantly lower indicating long-memory underlying patterns. Underlying sources are discussed. The asperity-model is proposed.

Sol-gel method has been used to fabricate nanocomposite films on glass substrates compo... more Sol-gel method has been used to fabricate nanocomposite films on glass substrates composed halloysite clay mineral and nanocrystalline TiO2. The methodology for the synthesis involves a simple chemistry method utilized nonionic surfactant molecule as pore directing agent along with the acetic acid-based solgel route with the absence of water molecules. The thermal treatment of composite films at 450oC ensures elimination of organic material and lead to the formation of TiO2 nanoparticles onto the surface of the halloysite nanotubes. Microscopy techniques and porosimetry methods used in order to delineate the structural characteristics of the materials. The nanocomposite films produced have no cracks and active anatase crystal phase with small crystallite size were deposited on halloysite nanotubes. The photocatalytic properties for the new materials were ...

Progress in Organic Coatings, 2021

Abstract The design of antimicrobial polymers is a growing field, as they may replace conventiona... more Abstract The design of antimicrobial polymers is a growing field, as they may replace conventional antimicrobial agents leading to plenty of advantages in marine applications. Polymers with active functional groups may act as carriers for antimicrobial agents. The antimicrobial polymers P(SSAmC16-co-GMAx) and P(VBCHAM-co-AAx) bearing quaternary ammonium compounds, either electrostatically bound (cetyltrimethylammonium 4-styrene sulfonate, SSAmC16) or covalently attached (vinyl benzyl dimethylhexadecylammonium chloride, VBCHAM), were prepared in the present work. The cross-linking agent hexamethylene diamine (HMDA) was used for the reaction between copolymers’ reactive groups, epoxide groups of glycidyl methacrylate (GMA) or carboxylic groups of acrylic acid (AA), with the amine groups. Various blends of each reactive copolymer with hexamethylene diamine in different compositions were prepared and the cross-linking reaction was explored through solution casting after curing at room temperature (RT), 80 °C and 120 °C for 24 h in order to find the best conditions for the designing of a firm and strong coating. In a further step, specific blend combinations of the reactive antimicrobial copolymers combined with hexamethylene diamine were used to coat pre-weighed aquaculture nets which were cross-linked at 120 °C and used in laboratory accelerated conditions as well as in real conditions by immersion of the nets at an aquaculture unit in the Saronic Bay of Greece. The modified nets along with blank nets were tested in terms of antifouling efficacy for 35 days in accelerated conditions and 30 days in real conditions. The novel cross-linked antimicrobial coatings indicated high antifouling activity and high cleaning efficacy as the fouling microorganisms at the end of the test were easily removed from the coated net in contrast to the uncoated net after high pressure cleaning.

Water Environment Research, 2021

Raw palygorskite (Pal) samples went under acid (H-Pal), NaCl (Na-Pal), and CaCl2 treatment (Ca-Pa... more Raw palygorskite (Pal) samples went under acid (H-Pal), NaCl (Na-Pal), and CaCl2 treatment (Ca-Pal) in order to be examined as ammonium (NH4 + ) sorbents from aqueous solutions. The samples were characterized by XRD and FT-IR techniques to examine potential structural differences after modifications and batch kinetic experiment series were applied to determine the optimal conditions for NH4 + removal. According to thermodynamic analysis, the removal reaction for sodium and calcium treated samples was endothermic (ΔΗ0 > 0, 1.65 kJ/mol and 24.66 kJ/mol, respectively), in contrast with the exothermic reactions of raw and acidic-treated palygorskite samples (ΔΗ0 < 0, -37.18 kJ/mol and -27.56 kJ/mol respectively). Moreover, each sample presented a different order of sorbed ions preference, whereas the strong affinity for Ca2+ sorption was common in all cases since the NH4 + removal inhibited. Nevertheless, a similar pattern was followed for raw and modified samples at isotherm study, rendering the linear form of Freundlich isotherm to express better the NH4 + sorption on palygorskite sample, indicating that it is a heterogeneous procedure. In all cases, the NH4 + maximum uptake was within 15 minutes using 8 g/L of each sorbent, especially for the Na-Pal sample, which could reach almost 100 % removal of low concentration NH4 + .

Journal of Photochemistry and Photobiology A: Chemistry, 2021

Geosciences, 2019

In this study, soil and aquatic sediments were sampled in the Aetoliko Lagoon and its catchment a... more In this study, soil and aquatic sediments were sampled in the Aetoliko Lagoon and its catchment area, which is exclusively dominated by olive orchards. For the first time in Greece, soil as well as sediments samples of one coherent protected aquatic ecosystem were directly compared. In order to determine the influence that the usage of copper-based fungicides have on the lagoon sediments and on the soils of the surrounding area, twenty five (25) soil samples from different olive orchards that are bordering the water body and ten (10) sediment samples from the bottom of the lagoon were taken. The samples were analyzed for total copper content (total digestion) and extractable copper (diethylenetriaminepenta acetic acid, DTPA, extraction method). Furthermore, soil/sedimentological and geochemical analyses such as pH, grain size, total organic carbon, total sulfur, total nitrogen, and calcium carbonate content were carried out. The results show that the total copper in soils ranges fro...

Applied Clay Science, 2019

Abstract Un-exchanged and Zn or Cu ion exchanged samples of a newly discovered sepiolite clay fro... more Abstract Un-exchanged and Zn or Cu ion exchanged samples of a newly discovered sepiolite clay from Greece were combined with nanophase anatase titania for the synthesis of sepiolite based nanocomposites and tested for oxidation of NOx gases. The Zn or Cu ion exchanged clay was modified by replacing the exchangeable cations with Zn or Cu ions. Three separate single phase sepiolite samples were prepared, i.e., the sepiolite (S), the one modified with Zn (Zn-S) and the one modified with Cu (Cu-S). Additionally, three nanocomposites were synthesized combining the above three sepiolite samples with TiO2 in weight ratios of 30:70 and named S-TiO2, Zn-S-TiO2 and Cu-S-TiO2, respectively by depositing TiO2 (anatase) on the sepiolite surfaces using titanium isopropoxide as a precursor under hydrothermal treatment at 180 °C. The phase composition, particle morphology and physical properties of the sepiolite samples and the nanocomposites were characterized by XRD, ATR-FTIR, TEM, DRS-UV–Vis and N2-sorption/desorption analyses. The photocatalytic activity of all the clay mineral-titania nanocomposites was examined in the decomposition NOx gases. Sepiolite and especially Zn modified sepiolite based nanocomposites showed better photocatalytic activity for the oxidation of NOx gases compared to that of reference photocatalyst titania P25 under UV-light irradiation.

Materials Science in Semiconductor Processing, 2018

Two different nanoclay minerals were combined with nanophase anatase TiO 2 for the synthesis of c... more Two different nanoclay minerals were combined with nanophase anatase TiO 2 for the synthesis of clay-based nanocomposites for improved photocatalytic properties. A new Halloysite (Hal) + Sepiolite (S)-TiO 2 ternary nanocomposite was prepared using halloysite from Utah, USA and a recently discovered sepiolite from Greece. Three nanocomposites were synthesized with Hal-TiO 2 , S-TiO 2 and [Hal+S] to TiO 2. As a result, TiO 2 particles (anatase) were homogeneously deposited and dispersed on the clay surfaces. Phase composition, particle morphology and physical properties of these nanocomposites were characterized by XRD, ATR-FTIR, FE-SEM, DRS-UV-Vis and N 2-sorption/desorption isotherms at 77 K. The photocatalytic activity of the clay mineral-TiO 2 nanocomposites was examined in the decomposition of paracetamol and tetracycline antibiotics as well as dye Rhodamine-B. The nanocomposites exhibited higher photocatalytic activity under UV irradiation for the decomposition of the targeted pollutants than the benchmark in the field, i.e. TiO 2-P25 photocatalyst.

Bulletin of the Geological Society of Greece, 2013

The synthesis as well as the characterization of small-sized TiO2 particles supported on Halloysi... more The synthesis as well as the characterization of small-sized TiO2 particles supported on Halloysite are presented. Hallloysite from Utah, USA as well as from Limnos, island Greece, were used to synthesize two nanocomposites for each halloysite with TiO2 to halloysite weight ratios of 80: 20 and 60:40 and compare with published data of well formed nanocomposites of intermediate proportion (70-30) that were previously studied. All nanocomposites were prepared by deposition of anatase (TiO2) on the halloysite tubes using a sol–gel method under hydrothermal treatment at 180 °C. Phase composition, particle morphology and physical properties of these samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Attenuated Total Reflection using Fourier Transform Infrared spectroscopy (ATR-FTIR) and N2 surface area analysis by BET. Preparation of all halloysite–TiO2 nanocomposites led to the anticipated good dispersion of anatase particles on halloysite surf...

Materials Research Innovations, 2016

Halloysite nanotubes (HNTs) were used for the reduction of ammonium concentration in aqueous solu... more Halloysite nanotubes (HNTs) were used for the reduction of ammonium concentration in aqueous solutions under various experimental conditions. The results indicated that HNTs exhibit fast adsorption rates and high removal capacity for the NH 4 + ions at neutral pH. The removal efficiency of the treated halloysite depends on the mass/volume ratio and the initial concentration of NH 4 + ions. The adsorption capacity of the material was examined for different mass/volume ratios at initial concentration <40 mg/L and it was found that in some cases the material exhibit up to 30% removal efficiency. Halloysite clay removal efficiency was also examined in a 4-10 pH range and it was found that it is increasing continually upon increasing pH values. Additionally the adsorption efficiency is strongly and negatively related to temperature. Langmuir adsorption models were applied to describe the equilibrium isotherms. Estimation of thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°) and change in free energy (ΔG°) confirms that the process is spontaneous and exothermic. Adsorption experiments were also performed in aqueous NH 4 + solutions in the presence of other cations and it was found that the removal efficiency for NH 4 + follows the order Na > K > Zn > Cu > Mn > Ca > Fe > Mg. The above results indicate that halloysite clay mineral can be considered as a new material for use in large and/ or industrial-scale applications for water and wastewater purification purposes.

Fresenius Environmental Bulletin

The application of multivariate analyses on the hydrochemical data of the Trifilia karst aquifer ... more The application of multivariate analyses on the hydrochemical data of the Trifilia karst aquifer delineates the existing hydrogeochemical processes and their contribution to the configuration of the hydrochemical character of groundwater. The application of factor analysis on two different sets of data, discriminated factors with a common geochemical interpretation, such as the salinization and geothermal factors. Furthermore, the application of factor analysis on the trace element concentrations spotted the influence of hydrocarbons on the chemical composition of groundwater, since it classified the redox sensitive metals in two different factors. The discriminant analysis led to the conclusion that the most important hydrogeochemical process is the groundwater salinization, since the electrical conductivity plays the major role in the classification of samples into five hydrochemical zones.

Targeting energy savings in buildings, photovoltaics and other sectors, significant research acti... more Targeting energy savings in buildings, photovoltaics and other sectors, significant research activity is nowadays focused on the production of spectral selective nanocoatings. In the present study an ITO coating on glass substrate is prepared from ITO powder, characterized and analysed. The spectral transmittance and reflectance of the ITO coated glass and of two other commercially developed ITO coatings on glass substrate were measured and compared. Furthermore, a simulation algorithm was developed to determine the optical properties of the ITO coatings in the visible, solar and near infrared regions in order to assess the impact of the ITO coatings in the energy performance of buildings, and particularly the application in smart windows. In addition, the current density produced by a PV assuming each of the ITO coated glass served as a cover was computed, in order to assess their effect in PV performance. The preliminary ITO coating prepared and the two other coatings exhibit different optical properties and, thus, have different impact on energy performance. The analysis assists in a better understanding of the desired optical properties of nanocoatings for improved energy performance in PV and buildings.

Water Environment Research, 2013

ABSTRACT Limnos Island in Greece, which has been the subject of extensive hydrogeological researc... more ABSTRACT Limnos Island in Greece, which has been the subject of extensive hydrogeological research, contains confined volcanic aquifers that overlie impermeable flysch. Groundwater salinization is usually the effect of seawater intrusion, and results from a combination of factors such as low annual areal precipitation and exploitation of aquifers for civil, commercial, and agricultural purposes. Areas with intense agricultural activities have also increasingly observed these effects. A geochemical evaluation on the basis of multiple ion (Ca2+, Mg2+, Na+, K+, HCO3-, Cl-, SO4(2-), NO3-) concentrations and physicochemical parameters distribution revealed that ion exchange is the dominant hydrogeochemical process. However, the enrichment of groundwater in potassium and magnesium results from rock and mineral weathering and dissolution.

Journal of Hazardous Materials, 2012

Microfibrous palygorskite clay mineral and nanocrystalline TiO(2) are incorporating in the prepar... more Microfibrous palygorskite clay mineral and nanocrystalline TiO(2) are incorporating in the preparation of nanocomposite films on glass substrates via sol-gel route at 500°C. The synthesis involves a simple chemical method employing nonionic surfactant molecule as pore directing agent along with the acetic acid-based sol-gel route without direct addition of water molecules. Drying and thermal treatment of composite films lead to the elimination of organic material while ensure the formation of TiO(2) nanoparticles homogeneously distributed on the surface of the palygorskite microfibers. TiO(2) nanocomposite films without cracks consisted of small crystallites in size (12-16 nm) and anatase crystal phase was found to cover palygorskite microfibers. The composite films were characterized by microscopy techniques, UV-vis, IR spectroscopy, and porosimetry methods in order to examine their structural properties. Palygorskite/TiO(2) composite films with variable quantities of palygorskite (0-2 w/w ratio) were tested as new photocatalysts in the photo-discoloration of Basic Blue 41 azo-dye in water. These nanocomposite films proved to be very promising photocatalysts and highly effective to dye's discoloration in spite of the small amount of immobilized palygorskite/TiO(2) catalyst onto glass substrates. 3:2 palygorskite/TiO(2) weight ratio was finally the most efficient photocatalyst while reproducible discoloration results of the dye were obtained after three cycles with same catalyst. It was also found that palygorskite showed a positive synergistic effect to the TiO(2) photocatalysis.

Colloids and Surfaces B: Biointerfaces, 2011

Applied Clay Science, 2013

ABSTRACT In this paper we describe the synthesis and characterization of small-sized TiO2 particl... more ABSTRACT In this paper we describe the synthesis and characterization of small-sized TiO2 particles supported on palygorskite (Pal) with Pal to TiO2 mass ratios of 10:90, 20:80, 30:70,40:60 and 50:50. The above Pal-TiO2 nanocomposites were prepared by deposition of anatase form of TiO2 on the Pal surfaces using a sal-gel method with titanium isopropoxide as a precursor under hydrothermal treatment at 180 degrees C. Phase composition, particle morphology and physical properties of these samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and N-2 surface area analysis by BET. In order to investigate the absorption properties of the catalysts, UV-vis reflection spectra were measured. Preparation of Pal-TiO2 nanocomposites led to good dispersion of TiO2 on Pal surfaces. By increasing the amount of TiO2, the deposited 3-10 nm TiO2 particles were found to be aggregated on the surfaces of the Pal particles. However, by decreasing the amount of TiO2, the Pal particles were found to be aggregated. After treating with TiO2, Pal samples largely showed interparticle mesopores of about 5.8 nm. It was observed that the commercial titania P25 showed no absorption in visible light region. In contrast, the prepared Pal-TiO2 samples showed gray color and absorption in visible light region.

Applied Clay Science, 2013

Applied Sciences

Analytical Methods, 2013

Progress in Organic Coatings, 2021

Water Environment Research, 2021

Journal of Photochemistry and Photobiology A: Chemistry, 2021

Geosciences, 2019

Applied Clay Science, 2019

Materials Science in Semiconductor Processing, 2018

Bulletin of the Geological Society of Greece, 2013

Materials Research Innovations, 2016

Fresenius Environmental Bulletin

Water Environment Research, 2013

Journal of Hazardous Materials, 2012

Colloids and Surfaces B: Biointerfaces, 2011

Applied Clay Science, 2013