Robert C Pullar | Università Ca' Foscari Venezia (original) (raw)

Papers by Robert C Pullar

Synthetic Metals, 2024

This research article describes the synthesis of composite materials by combining T-type hexagona... more This research article describes the synthesis of composite materials by combining T-type hexagonal ferrite and reduced Graphene Oxide using the standard ceramic process. The Calcium-based T-type hexagonal ferrite was synthesized by using the sol-gel auto-combustion method while the reduced graphene oxide by adopting the Hummer method. The crystallite size varied in the range of 23.38 -39.16 nm as calculated from the X-ray diffraction (XRD) data. Consequently, the lattice parameters 'a' and 'c' decreased from 5.9 to 5.1 Å and from 29.92 to 28.32 Å, respectively. The use of atomic force microscopy (AFM) revealed a range of particle sizes at the surface, varying from 1.70 nm to 3.85 nm. Moreover, the saturation and remanence magnetization values demonstrated an increasing trend with T-type hexaferrites concentration whereas the coercivity decreased. The UV–vis near-infrared spectra exhibited substantial light absorption, characterized by a wide absorption range in the visible and near-infrared (NIR) region (700–1100 nm) which indicates its use in Photothermal therapy (PTT). The Calcium T- type hexaferrite exhibited clear peaks in the blue, green, violet, and yellow spectra in its photoluminescence (PL) properties. These peaks are believed to be caused by oxygen vacancies and defects. The synthesized samples displayed a lossy behavior in the polarization-electric field (P-E) loop, with saturation polarization levels exceeding remnant polarization, which is an amenable condition for lossy behavior. Most importantly, the synthesized materials had significant thermal responses when exposed to an alternation (AC) magnetic field, indicating their potential use in magnetic hyperthermia applications.
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Elsevier Sustainable Chemistry and Pharmacy, 2024

In this study, the effect of salinity in wastewater on the adsorption capacity of a bone char mat... more In this study, the effect of salinity in wastewater on the adsorption capacity of a bone char material prepared through pyrolysis of tuna bones at 1000 °C was investigated for two pharmaceuticals, tramadol (TRA) and venlafaxine (VNF), both contaminants of emerging concern. This is the first time that the adsorption efficiency of a bone char-type material was tested in such conditions.

The Tuna Bone Char (TBC) was composed of calcium phosphate (hydroxyapatite), and graphitic carbon. The TBC is a nanostructured material (particle size 30–60 nm), with a surface area of 100.67 m2/g (higher than other waste-derived type materials), and a total pore volume of 575.2 mm3/g.

TBC capacity to adsorb TRA and VNF, individually or combined, was evaluated in batch experiments using different aqueous matrices: water, non-saline wastewater, and wastewaters with different salinity levels (7.5 and 12 g/L).

For individual pharmaceuticals, the TBC had a higher affinity for TRA than VNF. The presence of salts in wastewaters led to a decrease in the TBC adsorption capacity but it was still effective for pharmaceuticals adsorption. Indeed, for the individual pharmaceuticals, the TBC adsorption capacity (qt) was 0.72–2.14 and 0.77–1.70 mg/g for TRA and VNF respectively, depending on the aqueous matrix. With both pharmaceuticals present, lower qt values were experimentally obtained for TRA and VNF.

The potential of the TBC, a material derived from a by-product of the fish industry, to be used for environmental remediation in different environments, such as saline wastewaters was demonstrated, widening the range of its potential applications.

Journal of Materials Chemistry C, 2023

Polycrystalline X-type hexagonal ferrites are investigated regarding phase formation at different... more Polycrystalline X-type hexagonal ferrites are investigated regarding phase formation at different temperatures and the effect of partial substitution of Ga3+ for Fe3+ ions in the octahedral and tetrahedral sites of the unit cell. The system of Sr2Co2GaxFe28−xO46 (x ranges from 0.0 to 2.0 in steps of 0.4) was synthesised by the sol–gel auto-combustion technique and calcined between 1200–1300 °C with a temperature of 1300 °C required to be able to obtain a pure X-phase. Lattice parameter a did not alter with partial substitution, suggesting minimum crystal distortion, while the unit cell volume shrank from 2488 to 2465 Å3 due to smaller size of Ga3+. Denser and more agglomerated grains were observed in the samples heated to 1300 °C. Soft magnetic behaviour was seen in all samples and the saturation magnetisation was 63–69 A m2 kg−1 for pure X-ferrites, with low coercivity between 8.5–9.5 kA m−1 (106–119 Oe). Reasonably high Ha and K1 values were observed due to a cone of magnetisation partially aligned along the c-axis, and lower HC, Ha and K1 values were seen for pure X-ferrites, decreasing monotonously with increasing gallium substitution. dM/dH curves for pure X-ferrites indicated one magnetic domain type with restricted domain dispersion, and superior exchange coupling with more gallium substitution. Mössbauer spectroscopy of samples heated to 1300 °C reveals Fe3+ ions in high spin state and probable occupancy of Ga3+ in the octahedral site a = a1+a2. Room temperature (RT) dielectric studies show a significant rise in dielectric constant at low frequencies <50 Hz and in ac conductivity with increasing gallium.

Materials Research Bulletin, 2024

Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 emerged as one of the most technologically important lead-fr... more Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 emerged as one of the most technologically important lead-free piezoelectric compositions, and has undoubtedly shown remarkable advancements with regards to applied research. This article outlines the technological relevance of the Ba(Zr,Ti)O3-(Ba,Ca)TiO3 based piezoelectric system, and summarizes the developments made in various traditional and emerging potential application areas. The outstanding piezoelectric properties with d33 ∼600 pC/N in BZT-50BCT laid the foundations for its applicability in mechanical energy harvesters. In recent years, its utility in energy storage and electrocaloric cooling applications have propelled its prominence in addressing the challenges associated with sustainable energy solutions. Strikingly, the characteristic ability to autonomously generate electric surface potentials with low cytotoxicity also renders the BCZT system a promising candidate for biomedical applications. Other applications explored include magnetoelectrics, photoluminescence and photocatalysis.

Lastly, the future perspectives of the BCZT system are outlined based on the current research status and the existing scientific challenges.

Nanoscale, 2023

Cork is a renewable and sustainable material, highly porous and lightweight. We valorised waste c... more Cork is a renewable and sustainable material, highly porous and lightweight. We valorised waste cork and recycled wine stoppers to make pyrolysed/carbonised solid cork, for use as economic and sustainable microwave (MW) absorbers at the microwave X-band (8-12 GHz), without binder or additives. Although cork is already a very lightweight material (0.16 g cm −3), the pyrolysed cork is five-times less dense at 0.031 g cm −3 , was amorphous graphitic carbon, and had an excellent shielding effectiveness (SE T) of −18 to −38 dB, depending on thickness, with attenuation of the electromagnetic energy through internal reflection within the cellular cork structure. Furthermore, this ultra-lightweight material has an extremely high MW specific shielding effectiveness or efficiency (SSE), between −640 to −1235 dB g −1 cm 3 over the entire X-band range, depending on thickness (3.0-8.6 mm), one of the highest reported for any pure carbon material, this upper value being more than twice that of any previously reported graphite-based foams.

Ceramics International, 2023

The hexagonal Z-type ferrite Sr3Co2Fe24O41 (SrZ) was first synthesised in 2001 and reported as be... more The hexagonal Z-type ferrite Sr3Co2Fe24O41 (SrZ) was first synthesised in 2001 and reported as being a room temperature multiferroic material in 2010, with subsequent investigations into its multiferroic properties, but little into high frequency and microwave properties, and ferromagnetic resonance frequency (FMR), which determines its ability as an electromagnetic (EM) absorber and radar absorbing (RAM) stealth material. It was shown that SrZ existed as a majority or single phase after heating in a narrow temperature range between 1170 and 1190 °C using X-ray diffraction (XRD) and measurement of magnetic hysteresis loops, with the sample appearing to be single phase SrZ at 1190 °C. We measured complex permeability and permittivity of a single phase polycrystalline ceramic sample of SrZ between 500 MHz and 8 GHz (X-band). The sample had a relatively high permittivity >17 over this entire frequency range, and it showed a strong ferromagnetic resonance (FMR) at 2.3 GHz. This FMR could also be tuned by the effect of an external magnetic field, by moving a simple bar magnet progressively closer to a toroidal sample. This incurred a very slight shift in the peak up to 2.48 GHz at distances of 2.5–10 cm from the sample – a tuning of ∼5–6% with applied magnetic fields estimated to be 0.11–0.23 T, which is not insignificant. At a close distance of 0.5 mm we got a high degree of tuning of FMR to 3.4 GHz, a large change of 1.07 GHz (= 46% increase) with an applied magnetic field estimated to be 0.40 T. Despite this, the applied field had no significant effect on permittivity over 0.5–8 GHz. Such results have never been reported before, and are significant, as this would enable tuning of the FMR via simple physical/mechanical movement of a bulk alloy magnet, effectively creating a tuneable microwave filter or absorber.

Materials Chemistry and Physics, 2023

DOWNLOAD FREE FOR 50 DAYS AT: https://authors.elsevier.com/c/1g3Afvn2L-mfu Indium subst... more DOWNLOAD FREE FOR 50 DAYS AT: https://authors.elsevier.com/c/1g3Afvn2L-mfu
Indium substituted X-type Ba2Zn2InxFe28-xO46 (0<x<2.0) ferrites were synthesised by a citrate-gel aqueous combustion technique, and heated at 1300 °C. XRD, FTIR, SEM with EDX, magnetic hysteresis, Mössbauer spectroscopy, UV–visible spectroscopy, and dielectric measurements up to 20 GHz have been carried out to study the modification of the structural, morphological, magnetic, optical and frequency dependant dielectric properties when indium is introduced, replacing iron in the lattice of X-type hexaferrites. XRD analysis reveals formation of a major X-type phase in all compositions. The systematic rise in lattice constants (a, c) along with cell volume (V) confirm the replacement of iron by indium. Magnetic hysteresis loops reveal a soft ferrite nature with low Mr/MS values, suggesting a multidomain structure in all samples. The HC values decrease from 22.22 kA m-1 to 12.18 kA m−1 (279 Oe to 153 Oe) with increasing indium, while magnetisation remained high between 56 A m2 /kg and 62 A m2/kg for all samples. Room temperature Mӧssbauer spectra of all samples were fitted with six Zeeman sextets of five different magnetic sublattices. It was ascertained that In-substitution reduces the Fe population in the k (spin up) sublattice, resulting in a reduction in magnetisation. The average hyperfine magnetic field is also reported to decrease with Indium substitution for all samples. The value of the isomer shift (δ) confirmed that the iron-ions are in high spin Fe3+ state. The complex impedance and electric modulus plots reveal non-Debye type relaxation in all samples at 100 Hz to 2 MHz.

Water, Air & Soil Pollution, 2022

This paper presents a study on orange II sodium salt (OII) degradation based on iron nanoparticle... more This paper presents a study on orange II sodium salt (OII) degradation based on iron nanoparticles supported by kaolinite clays. The effects of nanoscale iron and initial dye concentration, as well as hydrogen peroxide dosage in a Fenton process, on the degradation of OII were studied. These nanoparticles were synthesized by green methods using coffee bean extract as a natural antioxidant for this process. Aqueous iron chloride was mixed with coffee extract, which is rich in antioxidants, and these antioxidants are responsible for the reduction of metal compounds into nanoparticles. The composite iron nanoparticle-kaolinite composite was synthesized from an aqueous FeCl3 and kaolinite solution with the added coffee bean extract. The results showed that OII removal efficiency increased with the amount of iron nanoparticles (n-Fe) alone and with the amount iron-supported-kaolinite composite. By increasing the amount of composite, the adsorptive surface area increases as well as the number of active sites, which determine the higher removal efficiency. Regarding H2O2 dosage, dye removal was more efficient at lower quantities: 62% removal efficiency with addition of 10 mL H2O2, while for the test conducted with 20 mL H2O2, removal efficiency was 47%. A possible reason for this behavior can be the n-Fe/ H2O2 ratio, which influences the production of degradation products and hinders the degradation.

Energy Advances, 2022

A pure TiO2 thin film (100–120 nm) was made from a green aqueous sol–gel precursor on FTO glass a... more A pure TiO2 thin film (100–120 nm) was made from a green aqueous sol–gel precursor on FTO glass and calcined at 430 °C. It was a mix of amorphous, anatase, rutile and brookite TiO2 phases, and exhibited very good electrochromic properties over visible and NIR wavelengths with an applied bias of +0.1 V to −1.5 V. It was highly transparent showing excellent coloration with applied voltage, with transmittance modulation (ΔT) = 69.7% at 550 nm, 86% at 700 nm and an overall ΔT between 400–1650 nm of 60%, giving a very large change in optical density (ΔOD) of 1.4 at 550 nm and 2.4 at 700 nm. Cyclic voltammograms had typical peaks for TiO2 at −1.3 V for colouration and −0.9 V for bleaching, with a high separation of 0.37 V between peaks, and a charge density after charging for 25 min of Qc = 50 mC cm−2. After only 60 s and 120 s at −1.5 V, inserted charge values of 17.6 and 22 mC cm−2 were observed, leading to a high colouration efficiency (CE) of 55.9 cm2 C−1 at 550 nm. These ΔOD, ΔT, Qc and CE values are superior to any previously reported for crystalline sol–gel TiO2 films. They also possessed rapid switching times for bleaching and colouring of τb90% = 10 s and τc90% = 55 s, comparable to the best previously reported sol–gel anatase-based TiO2 films. This makes this nanomaterial an excellent candidate for smart windows and other electrochromic devices and applications.

Nanoscale, 2022

We report the first ever robocast (additive manufacturing/3D printing) sintered ceria scaffolds, ... more We report the first ever robocast (additive manufacturing/3D printing) sintered ceria scaffolds, and explore their use for the production of renewable fuels via solar thermochemical fuel production (STFP, water and carbon dioxide splitting using concentrated solar energy). CeO2 catalyst scaffolds were fabricated as 50 mm diameter discs (struts and voids ∼500 μm), sintered at 1450 °C, with specific surface area of 1.58 m2 g−1. These scaffolds have hierarchical porosity, consisting of the macroporous scaffold structure combined with nanoscale porosity within the ceria struts, with mesopores <75 Å and an average pore size of ∼4 nm, and microporosity <2 nm with a microporous surface area of 0.29 m2 g−1. The ceria grains were ≤500 nm in diameter after sintering. STFP testing was carried out via thermogravimetric analysis (TGA) with reduction between 1050–1400 °C under argon, and oxidation at 1050 °C with 50% CO2, gave rapid CO production during oxidation, with high peak CO production rates (0.436 μmol g−1 s−1, 0.586 ml g−1 min−1), for total CO yield of 78 μmol g−1 (1.747 ml g−1). 90% CO was obtained after just 10 min of oxidation, comparing well to reticulated ceria foams, this CO production rate being an order of magnitude greater than that for ceria powders when tested at similar temperatures.

Materials Chemistry and Physics, 2022

50 days' free access: https://authors.elsevier.com/c/1eh8Mvn2L-k8U Ba2Zn2Fe28O46 hexaferrite ... more 50 days' free access: https://authors.elsevier.com/c/1eh8Mvn2L-k8U Ba2Zn2Fe28O46 hexaferrite was prepared using green synthesis with different quantities of ginger root extract (obtained from 0.0, 17.5, 35, 52.5 and 70 g of ginger root) as a natural antioxidant reducing agent. The dried precipitates were preheated at 550 °C/4 h and finally heated at 1200 °C/5 h. The effect of ginger root extract on structural, phase purity, magnetic, Mӧssbauer and low frequency (10 Hz–2 MHz) dielectric properties were investigated. XRD analysis of samples prepared with extracts from 35, 52.5, and 70 g of ginger depicted pure X-phase, while the other samples (0.0, 17.5 g) showed the secondary phase of M-type (BaM, BaFe12O19) along with hematite (12% α-Fe2O3). Hence, samples with greater amounts of ginger extract formed single-phase X-type hexaferrite. Saturation magnetization (MS) varied from 40.8 A m2/kg without ginger extract to 69.8 A m2/kg with extract from 52.5 g ginger, and was <65 A m2/kg for all samples made with the ginger extract. All synthesized samples were relatively soft ferrites, and coercivity increased with amount of ginger extract used. The Mӧssbauer spectra explored six sextets of five magnetic sub-lattices, and the presence of Fe3+ (99.4–97.3 %) and Fe2+ (0.6–2.7 %) ions, with more Fe2+ present in the extract-derived samples. The variations in MS based on hysteresis loops were in agreement by Mössbauer spectroscopy. The use of the extract also significantly reduced the grain size, from 3.3 μm without ginger extract to 0.7–1.7 μm with the extract, with a corresponding increase in coercivity from 16 to 40–80 kA/m. The samples prepared with extracts from 35 g to 52.5 g ginger root possessed considerable real dielectric constant compared to the others, but the extract also increased conductivity in the high-frequency region. Complex impedance displayed low values in the high-frequency region, and Cole-Cole plots revealed that the main contribution to conductivity in extract-based samples was from the grains. The reducing action of the green extract not only produced single phase X ferrite, but it also reduced grain size to ∿1–2 μm and greatly increased MS.

Open Ceramics, 2022

Environmentally conscious biomorphic ceramics (Ecoceramics) are a new class of material manufactu... more Environmentally conscious biomorphic ceramics (Ecoceramics) are a new class of material manufactured from renewable resources and wastes. Sustainable cork wastes were pyrolysed, and this activated carbon template infiltrated with a sol-gel precursor (from aqueous green-chemistry) to form TiO 2 on heating in air, with the honeycomb microstructure of cork. Physical and optical band gap properties were characterised by XRD, SEM and Raman and UV-vis spectroscopy, and differences between alkaline and acidic activation of the carbon template also studied. With activation by HCl, HNO 3 or H 2 SO 4 , a mixture of anatase and rutile formed. NaOH activation resulted in pure anatase, but a large amount of Na was retained. At 1000 • C acid activated ecoceramics formed pure rutile, but the NaOH activated one formed Na 2 Ti 6 O 13 (sodium hexatitanate) as the major phase, coexisting with anatase, brookite and rutile. This material is worth further investigation, as Na 2 Ti 6 O 13 is reported as a photocatalyst in its own right.

Materials, 2022

In this work, alkali-activated fly ash-derived foams were produced at room temperature by direct ... more In this work, alkali-activated fly ash-derived foams were produced at room temperature by direct foaming using aluminum powder. The 1 cm 3 foams (cubes) were then evaluated as adsorbents to extract heavy metals from aqueous solutions. The foams' selectivity towards lead, cadmium, zinc, and copper ions was evaluated in single, binary, and multicomponent ionic solutions. In the single ion assays, the foams showed much higher affinity towards lead, compared to the other heavy metals; at 10 ppm, the removal efficiency reached 91.9% for lead, 83.2% for cadmium, 74.6% for copper, and 64.6% for zinc. The greater selectivity for lead was also seen in the binary tests. The results showed that the presence of zinc is detrimental to cadmium and copper sorption, while for lead it mainly affects the sorption rate, but not the ultimate removal efficiency. In the multicomponent assays, the removal efficiency for all the heavy metals was lower than the values seen in the single ion tests. However, the superior affinity for lead was preserved. This study decreases the existing knowledge gap regarding the potential of alkali-activated materials to act as heavy metals adsorbents under different scenarios.

Silicon, 2022

The present study concerns the elimination by retention of the anionic dye orange II (OII) from a... more The present study concerns the elimination by retention of the anionic dye orange II (OII) from aqueous solutions was studied using a silica gel prepared from Tunisian silica sands (Barremian age). These Sidi Aich sands were collected in central Tunisia. The collected raw silica sand from the Jebel Meloussi (central Tunisia) was characterised by different techniques, such as X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). X-ray diffraction showed a predominance of quartz and potassic feldspars and lower amounts of kaolinite and calcite. The N2 adsorption isotherms show that these are mesoporous materials with high chemi-physical adsorption capabilities, and indicated a multilayer process for N2 absorption. They had pore diameters between 60 and 118 Å (mesoporous) and specific surface areas up to 183 m2/g, close to those reported for commercial silica gel materials. Maximum retention rates of the anionic dye orange II (OII, up to 89.73 % after 180 min contact time) were achieved with products prepared in acidic medium (pH 3). The adsorption is mechanism was well described with both Langmuir and Freundlich models, allowing for a multilayer coverage process of OII molecules on the gel surface, and the pseudo-second-order model is the most reliable for determining the order of absorption kinetics of OII by silica gel. The values of the adsorption capacities at equilibrium calculated (Qe = 242 mg / g) by the pseudo-second-order model are very close to the Qe determined experimentally (224 mg / g), and to those of an industrial silica gel (234 mg / g).

Materials Chemistry Frontiers, 2021

Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is the major mineral component of human bone, but has a wide... more Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is the major mineral component of human bone, but has a wide range of interesting and useful properties, and many applications beyond biomedicine. Here we produce HA-based materials from a naturally templated precursor which can have a variety of tailored microstructures and hierarchical porosities, and we investigate their use as designed functional materials for several applications. HA-based materials with different stoichiometries of Ca/P = 1.67 (HA) and 1.5 (Ca-deficient HA) were successfully synthesised from a previously prepared and reported cork-derived CaCO3. The CaCO3 was reacted with a phosphorus containing precursor solution at 60 °C, and also successively recalcined at 700 °C. The samples prepared at 60 °C maintained the 3D honeycomb structure of ∼20 μm hexagonal cells typical of cork, and showed high specific surface areas (SSA > 85 m2 g−1) and a high mesoporosity (average mesopores ∼10–15 nm). These features made them suitable for environmental remediation applications such as heavy metals (i.e. lead) removal from water, with calcium-deficient HA (higher degree of mesoporosity) adsorbing >99% of Pb(II) ions from solutions containing up to 1.5 g of lead per L. Recalcined samples (SSA = 29 m2 g−1), on the other hand, had very low cytotoxicity towards MG-63 osteoblasts, showing them to be biocompatible for biomaterials. All had cell viabilities of over 70% against a control, and the calcium-deficient HA proved to be even less cytotoxic than the control (>100% viability after 24 and 48 h). Therefore, cork was shown to be an excellent template agent for the design of HA materials with varied properties, tailored for different applications in the environmental and biomedical fields.

Journal of Alloys and Compounds, 2021

FREE ONLINE FOR 50 DAYS AT: https://authors.elsevier.com/c/1dJ-b3IWkc2zfB Polycrystalline lead... more FREE ONLINE FOR 50 DAYS AT: https://authors.elsevier.com/c/1dJ-b3IWkc2zfB
Polycrystalline lead-free (1-x)BaFe12O19–x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis routes, comparisons were made between uniaxial pressing and cold isostatic pressing of the samples prior to sintering at 1200 °C/2 h. Formation of separate magnetic hexaferrite BaFe12O19 (BaM) and ferroelectric (K0.5Na0.5)NbO3 (KNN) phases in the composites was confirmed using x-ray diffraction. The microstructural features revealed distribution of BaM and KNN grains in all the composite systems. Piezoresponse (PFM) and magnetic force (MFM) modes of scanning probe microscopy (SPM) were utilised to assess responses from piezoelectric and magnetic grains. Localised piezoelectric hysteresis loops were measured on KNN grains in composites made by all four methods. Typical hard magnetic hysteresis loops for BaM were observed exhibiting high coercivity values (up to 281 kA m−1 or 3530 Oe), and those composites made using solid state reaction and citrate combustion methods, which contained no impurity phases, had close to maximum magnetisation values (equivalent to ~70 A m2 kg−1 for the BaM phase). SEM, MFM and magnetisation measurements all suggested that the grain size of the BaM in the composites made using solid state reaction, co-precipitation and citrate combustion methods was around 1 µm, and consisting of single magnetic domains. As a result, it is likely that these samples will exhibit a high degree of magnetoelectric coupling.

Arabian Journal of Geosciences , 2021

In this paper, we use Tunisian clay materials as alternative low-cost adsorbents, as well as subs... more In this paper, we use Tunisian clay materials as alternative low-cost adsorbents, as well as substrates to immobilise TiO2 for the decolouration of methylene blue (MB) dye solutions. The collected raw clay from the mine of Tamra was characterised by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF). XRD patterns of the raw clay showed halloysite as the main phase (61%), with a lower content of kaolinite (39%). For MB adsorption, the experimental data were fitted by Langmuir and Freundlich adsorption equations. It was found that the studied clays alone were not very efficient at adsorbing MB dye molecules. The decolouration of MB was improved by adding a photocatalytic function to the clay, by adding various amounts of TiO2 nanopowder (20–80 wt%) to the clay, imbuing it with photocatalytic capabilities. These combined effects of the phenomena of adsorption and photocatalysis for MB removal by the TiO2-doped clay resulted in a very satisfactory performance, even with the relatively low quantity of 20 wt% added TiO2 photocatalyst. This gave 48.6% removal after only 30-min adsorption in the dark, increasing to 84.1% removal after a further 3 h under UV light, through combined chemo-physical adsorption and photocatalytic decolouration phenomena.

Ceramics International, 2021

FREE ONLINE FOR 50 DAYS AT: https://authors.elsevier.com/c/1c3sJ\~2-F173U Gallium substituted Z... more FREE ONLINE FOR 50 DAYS AT: https://authors.elsevier.com/c/1c3sJ~2-F173U Gallium substituted Z-type Sr3GaxCo2-xFe24O41 (x = 0.0–2.0 in steps of 0.4) hexaferrites were synthesised by the sol-gel auto-combustion process, and sintered at 1150 °C. The structural, morphology, magnetic, Mössbauer, dielectric and microwave absorption properties were examined. XRD results of x = 0.0, 0.4, 0.8, and 1.2 samples show the formation of a single Z-type hexagonal phase. The samples x = 1.6 and 2.0 show the formation of Z and M phases. Hysteresis loops analysis suggest that samples x < 1.6 possess a soft magnetic nature, while the samples x = 1.6 and 2.0 show a hard ferrite characteristics. All samples possess multi-domain microstructures. The composition x = 0.4 [maximum MS = 97.94 Am2kg−1] was fitted with seven sextets (Fe3+) and a paramagnetic doublet-A (Fe3+), while beyond x ≥ 0.8 two more doublets (Fe2+) were observed along with seven sextets in Mössbauer spectra. The maximum values of Fe2+ ions (1.26%) and relative area of paramagnetic doublets (1.91%) were observed for x = 1.6 composition, which is also responsible for the lowest value of MS (69.99 Am2kg−1) for this composition. The average hyperfine magnetic field was found to decrease, whereas average quadrupole splitting was found to increase, with Ga-substitution. The substitution of Ga ions enhanced permeability, dielectric constant, magnetic loss and dielectric loss, in a non-linear fashion. The reflection loss was maximum at lower frequencies for samples x = 0.0 and 0.8, and decreases with frequency. Sample x = 0.8 has maximum reflection loss of −12.44 dB at 8 GHz, a measured thickness of 3 mm, and a bandwidth of −10 dB at 1.18 GHz. The observed absorption has been discussed with the help of the input impedance matching mechanism and quarter wavelength mechanism. The observed coercivity in different samples also influenced microwave absorption which demonstrated potential in microwave absorber applications.

Nanotechnology, 2021

Nanostructured thin films are widely investigated for application in multifunctional devices than... more Nanostructured thin films are widely investigated for application in multifunctional devices thanks to their peculiar optoelectronic properties. In this work anatase TiO2 nanoparticles (average diameter 10 nm) synthesised by a green aqueous sol-gel route are exploited to fabricate optically active electrodes for pseudocapacitive-electrochromic devices. In our approach, highly transparent and homogeneous thin films having a good electronic coupling between nanoparticles are prepared. These electrodes present a spongy-like nanostructure in which the dimension of native nanoparticles is preserved, resulting in a huge surface area. Cyclic voltammetry studies reveal that there are significant contributions to the total stored charge from both intercalation capacitance and pseudocapacitance, with a remarkable 50% of the total charge deriving from this second effect. Fast and reversible colouration occurs, with an optical modulation of ~60% in the range of 315–1660 nm, and a colouration efficiency of 25.1 cm2 C−1 at 550 nm. This combination of pseudocapacitance and electrochromism makes the sol-gel derived titania thin films promising candidates for multifunctional 'smart windows'.

Journal of Physics D: Applied Physics, 2020

Many modern technologies require permanent magnets with combinations of properties that cannot be... more Many modern technologies require permanent magnets with combinations of properties that cannot be met by conventional metallic or ceramic magnets. Ferrite/polymer composite magnets are a type of rare-earth free magnet with a wide range of magnetic and material property combinations. The uncertainty surrounding the supply and pricing of rare-earth elements, along with environmental issues of using these elements, have motivated many researchers to develop high-performance ferrite-based magnets via an exchange spring method. The present study explores magnetite coated M-type ferrite nanocomposites synthesised via a hydrothermal and coprecipitation method, and investigates the mechanical and magnetic properties of warm compressed high-performance exchange-coupled nanocomposites in an epoxy matrix. We show how the powder-to-resin ratio and preparation conditions lead to optimised mechanical properties, and enhancement in the maximum energy product of the composite magnet by up to 120% compared to a commercial SrM bonded plasto-ferrite magnet. These high performance composite magnets can lower the final cost of ferrite based bonded magnets without reducing the permanent magnetic properties or can be used in applications that a ferrite magnet has inadequate performances.

Synthetic Metals, 2024

Elsevier Sustainable Chemistry and Pharmacy, 2024

Journal of Materials Chemistry C, 2023

Materials Research Bulletin, 2024

Lastly, the future perspectives of the BCZT system are outlined based on the current research status and the existing scientific challenges.

Nanoscale, 2023

Ceramics International, 2023

Materials Chemistry and Physics, 2023

Water, Air & Soil Pollution, 2022

Energy Advances, 2022

Nanoscale, 2022

Materials Chemistry and Physics, 2022

Open Ceramics, 2022

Materials, 2022

Silicon, 2022

Materials Chemistry Frontiers, 2021

Journal of Alloys and Compounds, 2021

Arabian Journal of Geosciences , 2021

Ceramics International, 2021

Nanotechnology, 2021

Journal of Physics D: Applied Physics, 2020

The CICMT (Ceramic Interconnects and Ceramic Microsystems Technology) 2018 Conference is in Aveir... more The CICMT (Ceramic Interconnects and Ceramic Microsystems Technology) 2018 Conference is in Aveiro from the 18th - 20th April http://www.imaps.org/ceramics/ CICMT 2018 Special Session Topics to include: Additive manufacturing / 3D printing, Emerging Technologies (4G/ 5G/ Car-Car Comms/ Automatic cars (ADAS)), Ferrites, Ferroics (ferroelectrics / piezoelectrics / multiferoics), Flexible Electronics, Low Temperature Sintering Processes / ULTCC, MHz, GHz and THz for Communications, Sensors and Devices, Microfluidics and Lab-on-a-chip, Processing and Fabrication / LTCC

Magnetic Nanoparticles for Biomedical Applications, 2023

This chapter compares the electromagnetic behavior of CoFe2O4 with and without addition of Nb2O5 ... more This chapter compares the electromagnetic behavior of CoFe2O4 with and without addition of Nb2O5 in order to find biomedical applications of these compositions. Taking into account that their electromagnetic behavior is affected by their morphological structure, a structural analysis of samples prepared with different stoichiometries and sintered at different temperatures was performed. The formation of a new phase and the presence of lamellar veins crystallographically oriented by their magnetic domains were identified. In addition, complex measurements of electrical permittivity and magnetic permeability allowed us to infer that maximum absorption frequency increases with the addition of niobium pentoxide, while hysteresis cycles indicated a decrease in saturation magnetization and an increase in coercive force.

Magnetic Nanoparticles for Biomedical Applications, 2023

Magnetic oxide nanoparticles (NPs) are probably the most common nanomaterials in everyday biomedi... more Magnetic oxide nanoparticles (NPs) are probably the most common nanomaterials in everyday biomedicine, and have been in use since the 1990’s. They are usually magnetic iron oxide NPs, made of magnetite (Fe3O4) or maghemite (gamma-Fe2O3), or a mixture of the two. Both of these have the spinel structure, and other spinel ferrites such as ZnFe2O4, CoFe2O4 and NiFe2O4 are also used. For applications in magnetic hyperthermia these NPs must be below the magnetic domain size, making them superparamagnetic, which means that their magnetisation can be “switched on” by the application of an external magnetic field. Magnetic hyperthermia treatment is a form of thermotherapy which is used to kill tumour cells with thermal energy (heat) in a very localised manner, by causing magnetic oxide NPs to heat up near tumour cells. Under an applied AC magnetic field the magnetic spin of the NPs switches rapidly in direction, transforming the magnetic energy into thermal energy. Temperatures of 41-46 °C are sufficient, this localised heating elevating the temperature of tumour cells, inhibiting growth, killing them, or inducing tumour cell apoptosis. Magnetic NPs were first used in tumour thermotherapy in 1996, and since then there has been a great deal of research in this field. The treatment can be applied alone, or used in combination with other therapies such as surgery, radiotherapy and chemotherapy, and it has shown excellent synergistic effects in combination with anticancer drugs (chemotherapeutics).

Chemical Valorization of Carbon Dioxide, 2023

With increasing demand for renewable energy and fuels there much interest in solar thermochemical... more With increasing demand for renewable energy and fuels there much interest in solar thermochemical fuel production (STFP), the use of concentrated solar power (CSP) to power the splitting of water and carbon dioxide into H2 and CO for sustainable fuels. This is usually a two-step process: the reduction of a catalyst at high temperatures followed by oxidation at lower temperatures utilising CSP to provide the high reaction temperatures (up to 1500 °C). Since it was first explored as a solar-driven redox catalyst to split CO2 in 2010, there has been an increasing interest in cerium oxide as the catalyst for the solar-driven production of CO from CO2. This chapter looks at pure CeO2, and especially the effects of its stoichiometry on the redox process, as ceria will partially reduce from Ce4+ to Ce3+ to create CeO2-d with oxygen deficiencies (d). It also looks at the extensive work on the doping or substitution of ceria, which has been explored with a wide range of transition metal and rare earth ions, with particularly interesting results for tetravalent Hf4+ and Zr4+.

Ch 1 in "Magnetic Oxides and Composites" Magnetoelectric composite ceramics were prepared to stu... more Ch 1 in "Magnetic Oxides and Composites"

Magnetoelectric composite ceramics were prepared to study their phase compatibility, magnetic and piezoelectric/ferroelectric properties, and coupling between magnetic and ferroelectric properties. The synthesis of various BaFe12O19 and SrFe12O19 hexaferrites was undertaken with different sintering temperatures, and exploring four different methods: solid state reaction, coprecipitation, sol-gel and citrate (Pechini) routes. Ceramic composites of BaM and SrM with BaTiO3 (BT) as a ferroelectric/piezoelectric phase, were prepared with both uniaxial and isostatic pressing, and then sintered. The composites were characterised by XRD, SEM and VSM. Results showed that BaM and BT did not react in the composites, while SrM-BT composites possess SrM, BT and SrTiO3 phases.