Publications of Rudi Cloots
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See detailExperimental design helps to optimize spray drying processes
Dellicour, Aline ULg; Cloots, Rudi ULg; Boschini, Frédéric ULg

Poster (2017, June)

Experimental design is necessary to identify major experimental parameters linked to a process in order to optimize it and reduce costs. It also helps to reduce the number of experiments and analyze data ... [more ▼]

Experimental design is necessary to identify major experimental parameters linked to a process in order to optimize it and reduce costs. It also helps to reduce the number of experiments and analyze data statistically. This work aims to present some possibilities of how experimental design may be applied in the field of pharmaceutical powders production by spray drying. Depending on the application, powders need particular size, morphology, purity, crystallinity or polymorphism. All these characteristics may be influenced by process parameters and should be controlled to reach pharmaceutical requirements. [less ▲]

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See detailStraightforward prediction of the Ni1−xO layers stoichiometry by using optical and electrochemical measurements
Manceriu, Laura ULg; Colson, Pierre ULg; Maho, Anthony ULg et al

in Journal of Physics : D Applied Physics (2017), 50

In this study, we propose a straightforward method for x determination in sub-stoichiometric nickel oxide (Ni1−xO) films prepared by ultrasonic spray pyrolysis on fluor-tin oxide (FTO) substrates by ... [more ▼]

In this study, we propose a straightforward method for x determination in sub-stoichiometric nickel oxide (Ni1−xO) films prepared by ultrasonic spray pyrolysis on fluor-tin oxide (FTO) substrates by varying the post-deposition thermal treatment. The Ni3+ concentration, the flat band potential (Φfb) and the open circuit potential (Voc) were determined by electrochemical impedance analysis in aqueous media and correlated to the transmission of Ni1−xO films. An x-ray photoelectron spectroscopy study was also performed to quantify the amount of Ni3+ in the films and compare it with the one determined by electrochemical analysis. The electrochromic behavior of the Ni1−xO films in non-aqueous electrolyte was investigated as well. With increasing Ni3+ concentration the films became more brownish and more conductive, both Voc and Φfb values increased. Calibration curves of transmission at 550 nm or open circuit potential versus carrier concentration were plotted and allowed the prediction of x in an unknown Ni1−xO sample. The Ni1−xO films characterized by the highest Ni3+ concentration have a darker colored state but lower transmission modulation, due to their reduced specific surface and increased crystallinity. [less ▲]

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See detailSpray Drying-­Assisted Synthesis of Na2FePO4F/CB and Na2FePO4F/CNT Composite Cathodes for Lithium Ion Battery
Mahmoud, Abdelfattah ULg; Brisbois; Caes, sebastien et al

Conference (2017, May 08)

Fluorophosphates are considered among the most interesting series of cathode materials for Li/Na-ion batteries. Na2FePO4F, with layered structure and two-dimensional pathways for facile Na+/Li+ transport ... [more ▼]

Fluorophosphates are considered among the most interesting series of cathode materials for Li/Na-ion batteries. Na2FePO4F, with layered structure and two-dimensional pathways for facile Na+/Li+ transport [1], exhibits minimal structural changes (3.7%) upon reduction/oxidation. The average working voltage is 3.3 V versus Li+/Li. However, one of the key drawbacks of Na2FePO4F electrodes is their low intrinsic electronic conductivity. In this work, we report on the synthesis of Na2FePO4F by spray-drying, a technique which is easily scaled-up from the lab- to the industrial-scale and ensures a good homogeneity of all precursors. We are investigating the replacement of the grinding step by the addition of conductive carbon (carbon black and carbon nanotubes) to the solution containing the inorganic precursors of the Na2FePO4F phase in order to prepare Na2FePO4F/CB and Na2FePO4F/CNT with different ratios of CB and CNT (10 and 20%) and enhanced conductivity. The electrochemical performance shows that the addition of CNT improves remarkably the capacity of the NFPF electrode material thanks to better CNT dispersion inside and at the surface of the NFPF particles which enhances the electronic conductivity. Acknowledgements: The authors thank the Walloon Region for support under the “PE Plan Marshall 2.vert” program (BATWAL -1318146). A. Mahmoud is grateful to the Walloon region for a Beware Fellowship Academia 2015-1, RESIBAT n° 1510399. References [1] M. Brisbois, S. Caes, M-T. Sougrati, B. Vertruyen, A. Schrijnemakers, R. Cloots, N. Eshraghi, R-P. Hermann, A. Mahmoud, F. Boschini, Solar Energy Materials & Solar Cells 148 (2015) 11-19. [less ▲]

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See detailInverse opal photoanodes: preparation and optical properties
Dewalque, Jennifer ULg; Spronck, Gilles ULg; Baron, Damien ULg et al

Conference (2017, March 01)

Perovskite compounds, used either in mesoscopic or planar solar cells, have allowed preparing highly efficient solid-state devices (>20%). In this study, we propose to design photoanodes with photonic ... [more ▼]

Perovskite compounds, used either in mesoscopic or planar solar cells, have allowed preparing highly efficient solid-state devices (>20%). In this study, we propose to design photoanodes with photonic structure in order to modulate light interaction. The periodic structure of porosity could add specific optical properties likely to increase light harvesting and reduce reflexion losses. Besides, current efficiencies reported for mesoscopic perovskite solar cells using an inorganic porous scaffold are slightly lower than those reported for planar perovskite cells mainly due to issues in perovskite infiltration. The control of the porous network architecture in terms of pore organization, size and connectivity could overcome this limitation. TiO2/perovskite and perovskite-only photoanodes with an inverse opal porous structure are prepared from templating techniques, using polystyrene beads as structuring agent. The photoanode microstructure is further characterized by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). In parallel, light interaction is modeled in order to find the best compromise in terms of photonic architecture (pore size, organization, thickness…). [less ▲]

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See detailUltrasonic spray pyrolysis as a processing route for templated electrochromic tungsten oxide films
Chatzikyriakou, Dafni ULg; Maho, Anthony ULg; Cloots, Rudi ULg et al

in Microporous and Mesoporous Materials (2017), 240

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See detailSodium vanadium (III) fluorophosphate/carbon nanotubes composite (NVPF/CNT) prepared by spray-drying: good electrochemical performance thanks to well-dispersed CNT network within NVPF particles
Eshraghi, Nicolas ULg; Caes, Sebastien; Mahmoud, Abdelfattah ULg et al

in Electrochimica Acta (2017), 228

We successfully prepared NASICON-type Na3V2(PO4)2F3 (NVPF) and a Na3V2(PO4)2F3/carbon nanotubes (CNT) composite by spray-drying followed by heat treatment in argon for 2 hours at 600 °C. The addition of ... [more ▼]

We successfully prepared NASICON-type Na3V2(PO4)2F3 (NVPF) and a Na3V2(PO4)2F3/carbon nanotubes (CNT) composite by spray-drying followed by heat treatment in argon for 2 hours at 600 °C. The addition of CNT in the spray-drying solution creates a CNT network within the NVPF particles. After grinding, the smaller NVPF particles remain linked by CNT. Thanks to this conducting network, the composite powder displays competitive electrochemical performance when cycled against lithium in hybrid-ion batteries (2–4.6 V vs. Li+/Li) with specific capacities of 125 mAh.g−1 at C/10, 103 mAh.g−1 at 1C and 91 mAh.g−1 at 4C, together with 97.5% capacity retention at 1C over 100 cycles with coulombic efficiency of 99.4%. These results demonstrate that sodium vanadium (III) fluorophosphate electrode material can be obtained in a time-efficient way using the easily up-scalable spray-drying method. [less ▲]

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See detailComparison of Indium Tin Oxide and Indium Tungsten Oxide as Transparent Conductive Substrates for WO3-Based Electrochromic Devices
Maho, Anthony ULg; Nicolay, Sylvain; Manceriu, Laura ULg et al

in Journal of the Electrochemical Society (2017), 164(2), 25-31

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See detailHydrothermal synthesis of tailored new  promising phosphate particles for lithium and sodium ion batteries
Karegeya, Claude ULg; Mahmoud, Abdelfattah ULg; Sougrati Tahar, Moulay et al

Conference (2016, December 16)

The rechargeable Li-ion batteries dominate the currently used storage systems due to their unrivalled electrochemical properties. However, this technology needs more improvements to meet coast, high ... [more ▼]

The rechargeable Li-ion batteries dominate the currently used storage systems due to their unrivalled electrochemical properties. However, this technology needs more improvements to meet coast, high capacity, safety and environmental requirements. Current researches on Li-ion batteries are focusing on the development of safe and cheap electrode compounds with good electrochemical performance. Iron phosphate-based electrodes have attracted increasing interest due to their environmental compatibility, low cost and its promising electrochemical performance as positive electrode materials in LIB. In this work, we report the electrochemical properties of Fex(PO4)(OH)y.zH2O) cathode material obtained by one-pot hydrothermal synthesis route, a technique which produces the particles with suitable properties for electrode application. We show that the addition of a conducting carbon (carbon black or carbon nanotubes) into the solution has a strong influence on reducing the size and tailoring morphology of material particles. These are among the main factors to enhance the electrochemical performance of the material. Combined with electrochemical and XRD studies, operando Mössbauer analysis shows that Fex(PO4)(OH)y.zH2O) undergoes a reversible reduction/oxidation during lithium intercalation/ deintercalation processes. Acknowledgments This work was supported by the Walloon Region through the BATWAL project [PE Plan Marshall 2.vert]; and the Beware Fellowship Academia [2015-1, RESIBAT n° 1510399]. [less ▲]

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See detailSurfactant-assisted USP deposition of WO3 electrochromic thin films on various TCO-glass substrates
Maho, Anthony ULg; Nicolay, Sylvain; Manceriu, Laura ULg et al

Conference (2016, August 31)

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See detailEffect of DOPA and dopamine coupling on protein loading of hydroxyapatite
Ozhukil Kollath, Vinayaraj ULg; Mullens, Steven; Luyten, Jan et al

in Materials Technology: Advanced Performance Materials (2016)

Hydroxyapatite (HA) is a promising carrier material for oral delivery of biomolecules such as proteins and drugs. Ways to increase the loading of such molecules on HA will lead to better nanomedicine ... [more ▼]

Hydroxyapatite (HA) is a promising carrier material for oral delivery of biomolecules such as proteins and drugs. Ways to increase the loading of such molecules on HA will lead to better nanomedicine. This study reports the surface functionalisation of HA particles using the mussel inspired molecules dopamine (DA) and 3,4-dihydroxy-L-phenylalanine (DOPA), in order to increase protein loading. The adsorption mechanisms are discussed based on the adsorption isotherms, zeta potential, thermal analysis and theoretical models. Results show that DA functionalisation enhanced the loading, while DOPA functionalisation was ineffective. [less ▲]

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See detailRadio-frequency magnetron sputtering: a versatile tool for CdSe quantum dots depositions with controlled properties
Dahi, Abdellatif; Colson, Pierre ULg; Jamin, Claire et al

in Journal of Material and Environmental Sciences (2016), 7(7), 2277-2287

CdSe nanoparticles are of great interest for many applications. However, their size, shape, and aggregation are still difficult to control by the conventional synthesis methods. Here, we report on the ... [more ▼]

CdSe nanoparticles are of great interest for many applications. However, their size, shape, and aggregation are still difficult to control by the conventional synthesis methods. Here, we report on the synthesis of CdSe quantum dots (QDs), with an average diameter less than 10 nm, using radio-frequency magnetron sputtering (RFMS) on glass and silicon substrates at 25 °C. First, results show that a target-substrate distance of 13.5 cm and a chamber pressure of 2.2 .10-1 mbar were required to deposit a CdSe QDs layer on the substrates. The morphology and optical properties of CdSe QDs were then studied as a function of RF power and deposition time. The size of CdSe QDs increases with increasing both the RF power and the deposition time. UV-visible spectroscopy shows that the CdSe QDs layer deposited on the glass-substrate by RFMS has almost the same optical properties as the one obtained from commercial CdSe QDs solutions. In both cases, a shift of the characteristic absorption band of CdSe QDs towards the higher wavenumbers is observed with the QDs size increase. AFM confirms the success of CdSe QDs layer deposition by RFMS: CdSe QDs with a mean diameter of 7.5 ± 2 nm were observed for a RF power of 14 W, a chamber pressure of 2.2 .10-1 mbar, a target-substrate distance of 13.5 cm and a deposition time of 7.5 min (optimal values). With these parameters, the coverage of the substrate by the nano-objects is estimated at 25-30 % of the overall surface. [less ▲]

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See detailElectrophoretic deposition of hydroxyapatite and hydroxyapatite– alginate on rapid prototyped 3D Ti6Al4V scaffolds
Ozhukil Kollath, Vinayaraj; Chen, Qiang; Mullens, Steven et al

in Journal of Materials Science (2016), 51

The advantage of using bioceramic particles coated on porous three-dimensional structures is still unexplored in the purpose of improving the osteoinduction of hybrid metallic scaffold implants in vivo ... [more ▼]

The advantage of using bioceramic particles coated on porous three-dimensional structures is still unexplored in the purpose of improving the osteoinduction of hybrid metallic scaffold implants in vivo. In this study, we evaluate electrophoretic deposition (EPD) to coat porous Ti6Al4V scaffolds with hydroxyapatite (HA). Scaffolds were shaped in different open structures with a horizontal shift in fiber stacking. They were produced using three-dimensional fiber deposition method and were coated by EPD with HA powder (d10 = 1.7, d50 = 5.7 and d90 = 18 lm) suspended in ethanol or butanol at different concentration, DC voltage, and time. A composite HA–alginate was also used to coat the scaffolds. Alginate was used as a binder, and the coating properties (homogeneity, thickness, cracks, continuity, etc.) were compared to coatings obtained from pure HA suspensions. Voltage and time of deposition effects were studied between 10 and 140 V and 10 and 120 s, respectively. Coating thickness and density with respect to the depth of the porous structure were studied by observing cross sections using scanning electron microscopy and image processing analysis. HA–alginate combination resulted in a homogeneous and deeper dense layer of HA. This work also points to the characteristics of HA–alginate composite as a superior alternative to pure HA coating which needs an appropriate thermal treatment for adequate substrate adhesion. [less ▲]

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See detailNa2FePO4F/multi-walled carbon nanotubes for lithium-ion batteries: Operando Mössbauer study of spray-dried composites
Brisbois, Magali; Caes, Sébastien ULg; Sougrati, M.T. et al

in Solar Energy Materials & Solar Cells (2016), 148

In order to favor electronic conductivity in sodium iron fluorophosphate electrodes for lithium- or sodium-ion batteries, composites of Na2FePO4F with multi-walled carbon nanotubes (CNTs) were prepared by ... [more ▼]

In order to favor electronic conductivity in sodium iron fluorophosphate electrodes for lithium- or sodium-ion batteries, composites of Na2FePO4F with multi-walled carbon nanotubes (CNTs) were prepared by pilot-scale spray drying. Addition of multi-walled CNTs in the solution results in an excellent dispersion of the CNTs within the volume of Na2FePO4F and not only at the surface of the particles. Following a heat treatment at 600°C in argon in order to reach crystallization, X-ray diffraction and ex situ Mössbauer spectroscopy revealed the presence of significant amounts of Fe(III) and maghemite (γ-Fe2O3) in the powder. However, Na2FePO4F/CNTs composites exhibit good electrochemical performance when cycling against lithium, with a discharge capacity of 104mAhg-1 at C/10 rate and 90mAhg-1 at 1C rate. Therefore, operando 57Fe transmission Mössbauer spectroscopy analyses were carried out in order to investigate the evolution of the iron oxidation state during cycling. During the first discharge, all the Fe(III) is reduced to Fe(II), explaining the good electrochemical performance. [less ▲]

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See detailSurfactant-assisted ultrasonic spray pyrolysis of hematite mesoporous thin films
Henrist, Catherine ULg; Toussaint, Caroline ULg; De Vroede, Jordan et al

in Microporous and Mesoporous Materials (2016), 221

Mesoporous crystalline hematite is a material difficult to prepare by soft-templating with conventional techniques, because of its high crystallization temperature associated to the crystal-to-crystal ... [more ▼]

Mesoporous crystalline hematite is a material difficult to prepare by soft-templating with conventional techniques, because of its high crystallization temperature associated to the crystal-to-crystal goethiteto-hematite phase transition. In a previous work, it has been reported that with very careful calcination steps, it is possible to prepare mesoporous hematite films with the spin-coating technique. However, with less conventional techniques such as surfactant-assisted ultrasonic spray pyrolysis, the deposition usually leads to non-porous oxide films or to films with interstitial porosity. In this work, we demonstrate for the first time the proof-of-concept of block-copolymer templating of hematite thin films by the ultrasonic spray pyrolysis technique. Despite the fast thermal decomposition during spray deposition, a regular, monodisperse packing of spherical pores is observed after deposition on pre-heated substrates (250 C) and after a careful post-annealing step at 470 C. Moreover, with the use of a silica scaffold, we successfully preserved porosity up to a temperature as high as 800 C. These films are highly crystalline and they are composed by randomly oriented nanocrystallites with sizes as small as 25 nm. Furthermore, we show that the crystallization evolution with temperature is influenced by the presence of the templating agent and also by the preparation technique. [less ▲]

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See detailInnovative semiconducting oxide materials reducing the energy footprint of buildings
Dewalque, Jennifer ULg; Maho, Anthony ULg; Spronck, Gilles ULg et al

Conference (2015, October 26)

In the current energy context, many efforts are devoted to the reduction of the energy footprint of buildings. To meet this challenge, the LCIS-GREENMAT laboratory developes a front edge research in the ... [more ▼]

In the current energy context, many efforts are devoted to the reduction of the energy footprint of buildings. To meet this challenge, the LCIS-GREENMAT laboratory developes a front edge research in the field of advanced materials associated to energy and environment, including structured materials for dye-sensitized solar cells (DSSCs) and electrochromic coatings. DSSCs have been reported by O’Regan and Grätzel in the early nineties as a very promising alternative to conventional photovoltaic silicon devices. Main benefits of these cells are their low cost as well as their mild manufacturing process. In most of the specific literature, DSSCs are made of TiO2 films prepared by doctor-blade or screen-printing of anatase nanoparticles paste. However, due to the random organization of the nanoparticles, pore accessibility by the dye and electrolyte could be incomplete. Moreover, some anatase crystallites could suffer from a lack of connectivity, leading to electron transfer issues. The strategy adopted by our group to improve photovoltaic efficiencies involves a templating-assisted process to prepare highly porous layers with well-ordered and accessible pores as well as improved crystallites connectivity. This talk especially focuses on the templating-assisted synthesis of TiO2 and ZnO semiconducting layers used as photoelectrode in DSSCs. Due to the surface area improvement as well as the perfect control of the pore organization and the pore size, the templating strategy is an effective solution to maximize the adsorption of active dye and the electrolyte infiltration inside the porous network. Besides, in the last few years, there has been increasing interest in electrochromic glazing due to its potential use as an energy-efficient component for buildings, as it could reduce considerably their CO2 emission by decreasing their energy consumption up to 30%. The crucial issues of such devices are the durability, the coloration efficiency and the reversibility upon coloration and bleaching of the electrochromic layers. In order to improve the performances of those electrochromic films, we have investigated a surfactant-assisted deposition process for WO3 layer and the insertion of lithium in the NiO layer. All films have been deposited on FTO glass substrates by ultrasonic spray pyrolysis (USP), which is a low-cost alternative to industrial vacuum processes for manufacturing high quality thin films. The presence of lithium ions in nickel oxide films has shown improved coloration efficiency compared to the undoped films. The higher active surface of surfactant-assisted tungsten oxide films has led to higher reversibility and coloration contrast. [less ▲]

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See detailA Modular Approach To Study Protein Adsorption on Surface Modified Hydroxyapatite
Ozhukil Kollath, Vinayaraj ULg; Van den Broeck, Freya; Fehér, Krisztina et al

in Chemistry : A European Journal (2015), 21(29), 10497-10505

Biocompatible inorganic nano- and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change ... [more ▼]

Biocompatible inorganic nano- and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change the protein adsorption capacity of hydroxyapatite (HA) powder. The adsorption capacity of bovine serum albumin as a model protein has been studied with respect to the surface modifications. The selected linker molecules (lysine, arginine, and phosphoserine) can influence the adsorption capacity by changing the electrostatic nature of the HA surface. Qualitative and quantitative analyses of linker-molecule interactions with the HA surface have been performed by using NMR spectroscopy, zeta-potential measurements, X-ray photoelectron spectroscopy, and thermogravimetric analyses. Additionally, correlations to theoretical isotherm models have been calculated with respect to Langmuir and Freundlich isotherms. Lysine and arginine increased the protein adsorption, whereas phosphoserine reduced the protein adsorption. The results show that the adsorption capacity can be controlled with different functionalization, depending on the protein–carrier selections under consideration. The scientific knowledge acquired from this study can be applied in various biotechnological applications that involve biomolecule–inorganic material interfaces. [less ▲]

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See detailLi4Ti5O12 powders by spray-drying: influence of the solution concentration and particle size on the electrochemical properties
Jamin, Claire; Brisbois, Magali; Caes, Sébastien ULg et al

Conference (2015, June 23)

Detailed reference viewed: 71 (13 ULg)