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Amino-alkylphosphonic acid-grafted TiO2 materials are of increasing interest in a variety of applications such as metal sorption, heterogeneous catalysis, CO2 capture, and enzyme immobilization. To date, systematic insights into the synthesis-properties-performance correlation are missing for such materials, albeit giving important know-how towards their applicability and limitations. In this work, the impact of the chain length and modification conditions (concentration and temperature) of amino-alkylphosphonic acid-grafted TiO2 on the surface properties and adsorption performance of palladium is studied. Via grafting with aminomethyl-, 3-aminopropyl-, and 6-aminohexylphosphonic acid, combined with the spectroscopic techniques (DRIFT, 31P NMR, XPS) and zeta potential measurements, differences in surface properties between the C1, C3, and C6 chains are revealed. The modification degree decreases with increasing chain length under the same synthesis conditions, indicative of folded grafted groups that sterically shield an increasing area of binding sites with increasing chain length. Next, all techniques confirm the different surface interactions of a C1 chain compared to a C3 or C6 chain. This is in line with palladium adsorption experiments, where only for a C1 chain, the adsorption efficiency is affected by the precursor concentration used for modification. The absence of a straightforward correlation between the number of free NH2 groups and the adsorption capacity for the different chain lengths indicates that other chain-length-specific surface interactions are controlling the adsorption performance. The increasing pH stability in the order of C1 < C3 < C6 can possibly be associated to a higher fraction of inaccessible hydrophilic sites due to the presence of folded structures. Lastly, the comparison of adsorption performance and pH stability with 3-aminopropyl(triethoxysilane)-grafted TiO2 reveals the applicability of both grafting methods depending on the envisaged pH during sorption. ispartof: ACS OMEGA vol:7 issue:49 pages:45409-45421 ispartof: location:United States status: published

Lithium−sulphur batteries attract increasing interest due to their high theoretical specific capacity, advantageous economy, and “eco-friendliness”. In this study, a metal-organic framework (MOF) GaTCPP containing a porphyrinic base ligand was used as a conductive additive for sulphur. GaTCPP was synthesized, characterized, and post-synthetically modified by the transition metal ions (Co2+/Ni2+). The doping of GaTCPP ensured an increase in the carbon dioxide adsorption capacities, which were measured under different conditions. Post-synthetic modification of GaTCPP with Co2+/Ni2+ ions has been shown to increase carbon dioxide storage capacity from 22.8 wt.% for unmodified material to 23.1 wt.% and 26.5 wt.% at 0 °C and 1 bar for Co2+ and Ni2+-doped analogues, respectively. As a conductive part of cathode material, MOFs displayed successful sulphur capture and encapsulation proven by stable charge/discharge cycle performances, high-capacity retention, and Coulombic efficiency. The electrodes with pristine GaTCPP showed a discharge capacity of 699 mAh g-1 at 0.2 C in the fiftieth cycle. However, the doping of GaTCPP by Ni2+ has a positive impact on the electrochemical properties, the capacity increased to 778 mAh g-1 in the fiftieth cycle at 0.2 C.

The rehydration behavior of metal oxides (LDOs) derived from calcination of Mg-Al layered double hydroxides (LDHs) at high temperatures of 600-900 °C was studied in the presence of deionized water under vapor or liquid conditions. XRD reflections showed that the LDO metal oxides obtained from thermally treated LDHs can rehydrate into LDHs at room temperature even after calcination as high as 900 °C, both in vapor and liquid conditions, although faster in the latter. Only when the calcination temperature was increased to 900 °C an additional spinel phase appeared, which remained in the particles under both vapor and liquid rehydration conditions. This is proven by 27Al MAS NMR showing the presence of a peak representing tetrahedral Al. Differences between the as-synthesized LDHs and rehydrated LDOs were observed via additional analysis with FTIR, SEM and nitrogen sorption. This illustrated that the process of the rehydration of the LDO into the LDH resulted in a new LDH rather than reconstructing it into the former LDH. Based on the results, it is suggested that even after high temperature calcination (600-900 °C), samples need to be stored carefully to avoid rehydration reactions to altered LDH materials, occurring at room temperature under ambient, moist containing atmosphere.

The Stöber method is one of the most important and fundamental processes for the synthesis of inorganic (nano)materials, but has the drawback of using a large amount of organic solvent. Herein, we used ethanol as an example to explore if the organic solvent in a typical Stöber method can be omitted. We found that ethanol increases the particle size of the obtained silica spheres and aids the formation of uniform silica particles rather than forming a gel. Nevertheless, the results indicated that an organic solvent in the initial synthesis mixture is not indispensable. We discovered, an initially immiscible synthesis method, which can replace the organic solvent based Stöber method to successfully synthesize silica particles with the same size ranges as the original Stöber process without addition of organic solvents. Moreover, this process can be of further value to be extended to synthesis processes of other materials based on the Stöber process.

The present research focuses on the development of porous MgAl-layered double hydroxide microspheres with high sphericity and uniform particle size distribution. This is based on the droplet coagulation technique using alginate biopolymer as a binder. To achieve this, the suspension formulation was systematically optimized based on zeta potential and rheology measurements. The structural, microtextural and porosity characteristics of the MgAl-LDH powder and the corresponding obtained microspheres were investigated by X-ray diffraction, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, optical and scanning electron microscopy, N-2 sorption and Hg intrusion characterization techniques. The combination of these techniques allowed us to highlight that this shaping process leads to the production of porous microspheres in which the LDH plate-like particles are held together in a calcium alginate network without altering their structural features. This research opens up new opportunities for the LDH-type materials towards packed bed applications, such as chemical reactors or sorption columns. (C) 2021 Published by Elsevier B.V.

Modification of metal oxides with organophosphonic acids (PAs) provides the ability to control and tailor the surface properties. The metal oxide phosphonic acid bond (M-O-P) is known to be stable under harsh conditions, making PAs a promising candidate for the recovery of metals from complex acidic leachates. The thiol functional group is an excellent regenerable scavenging group for these applications. However, the research on organophosphonic acid grafting with thiol groups is very limited. In this study, four different metal sorbent materials were designed with different thiol surface coverages. An aqueous-based grafting of 3-mercaptopropylphosphonic acid (3MPPA) on mesoporous TiO

The application of dielectric barrier discharge (DBD) plasma reactors is promising in various environmental and energy processes, but is limited by their low energy yield. In this study, we put a number of stainless steel rings over the inner electrode rod of the DBD reactor to change the local discharge gap and electric field, and we studied the dry reforming performance. At 50 W supplied power, the metal rings mostly have a negative impact on the performance, which we attribute to the non-uniform spatial distribution of the discharges caused by the rings. However, at 30 W supplied power, the energy yield is higher than at 50 W and the placement of the rings improves the performance of the reactor. More rings and with a larger cross-sectional diameter can further improve the performance. The reactor with 20 rings with a 3.2 mm cross-sectional diameter exhibits the best performance in this study. Compared to the reactor without rings, it increases the CO2 conversion from 7% to 16 %, the CH4 conversion from 12% to 23%, and the energy yield from 0.05 mmol/kJ supplied power to 0.1 mmol/kJ (0.19 mmol/kJ if calculated from the plasma power), respectively. The presence of the rings increases the local electric field, the displaced charge and the discharge fraction, and also makes the discharge more stable and with more uniform intensity. It also slightly improves the selectivity to syngas. The performance improvement observed by placing stainless steel rings in this study may also be applicable to other plasma-based processes.

The effect of pore size on plasma catalysis is crucial but still unclear. Studies have shown plasma cannot enter micropores and mesopores, so catalysts for traditional thermocatalysis may not fit plasma catalysis. Here, 3D porous Cu and CuO with different pore sizes were prepared using uniform silica particles (10–2000 nm) as templates, and compared in plasma-catalytic dry reforming. In most cases, the smaller the pore size, the higher the conversion of CH4 and CO2. Large pores reachable by more electrons did not improve the reaction efficiency. We attribute this to the small surface area and large crystallite size, as indicated by N2-sorption, mercury intrusion and XRD. While the smaller pores might not be reachable by electrons, due to the sheath formed in front of them, as predicted by modeling, they can still be reached by radicals formed in the plasma, and ions can even be attracted into these pores. An exception are the samples synthesized from 1 μm silica, which show better performance. We believe this is due to the electric field enhancement for pore sizes close to the Debye length. The performances of CuO and Cu with different pore sizes can provide references for future research on oxide supports and metal components of plasma catalysts.

The titanium dioxide nanocatalyst (TiO2:NC) was fabricated by chemical precipitation method and annealed at different temperatures. The texture parameters was estimated by Barrett–Joyner–Halenda (BJH) and Brunauer–Emmett–Teller (BET) utilizing nitrogen adsorption–desorption data. The crystal phase transition, enhanced crystallinity and increase in crystallite sizes with temperature were studied by using X-ray diffractograms (XRD). Coinciding with an increase in crystallite size supervising annealing temperatures, the surface area of the TiO2:NC decreases. The average grain size as calculated from scanning electron microscopy (SEM) initially decreases with increasing annealing temperature (300 °C), whereas further increase in annealing temperature (600 °C), is accompanied by the increase in grain size. A red shift was observed in the diffuse reflectance spectra (DRS) caused by a decrease in band gap energy with rising annealing temperatures. The chemical composition was examined by using Fourier transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopies. All the annealed TiO2:NC samples were used as photocatalysts for the degradation of rhodamine 6G (R6G) under simulated solar light source. The TiO2:NC annealed at 600 °C have a higher degradation rate constant than the other samples.

Modification of metal oxides with organophosphonic acids (PAs) provides the ability to control and tailor the surface properties. The metal oxide phosphonic acid bond (M-O-P) is known to be stable under harsh conditions, making PAs a promising candidate for the recovery of metals from complex acidic leachates. The thiol functional group is an excellent regenerable scavenging group for these applications. However, the research on organophosphonic acid grafting with thiol groups is very limited. In this study, four different metal sorbent materials were designed with different thiol surface coverages. An aqueous-based grafting of 3-mercaptopropylphosphonic acid (3MPPA) on mesoporous TiO2 was employed. Surface grafted thiol groups could be obtained in the range from 0.9 to 1.9 groups per nm(2). The different obtained surface properties were studied and correlated to the Pd adsorption performance. High Pd/S adsorption efficiencies were achieved, indicating the presence of readily available sorption sites. A large difference in their selectivity towards Pd removal from a spend automotive catalyst leachate was observed due to the co-adsorption of Fe on the titania support. The highest surface coverage showed the highest selectivity (K-d: 530 mL g(-1)) and adsorption capacity (Q(max): 0.32 mmol g(-1)) towards Pd, while strongly reducing the co-adsorption of Fe on remaining TiO2 sites. This work is supported by the Research Foundation Flanders (FWO) and Hasselt University via the Hercules project AUHL/15/ 2 – GOH3816N. Part of the presented work was executed within the PLATIRUS project, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 730224. This work reects only the author's views and the agency is not responsible for any use that may be made of the information it contains. The authors are grateful to all project partners for discussions and input, and in particular to Monolithos Ltd (Athens. Greece) for providing the spend automotive catalyst material used in this work. V. Meynen acknowledges the Research FoundationFlanders (FWO) for project K801621N. All calculations were performed using the Hopper HPC infrastructure at the CalcUA core facility of the University of Antwerp, a division of the Flemish Supercomputer Center VSC, funded by the Hercules Foundation, the Flemish Government (department EWI) and the University of Antwerp. Furthermore, the authors would like to acknowledge S. Defoss´e and K. Leyssens for the N2 sorption measurements, J. Lievens and A. Deibe Varela for the Pd sorption experiments, K. Duyssens and W. Brusten for the ICP measurements and M. Mertens for the XRD measurements.

Recently, interest has been directed towards the grafting of metal oxides with organophosphonic acids bearing terminal amine groups to extend the functionality and applicability of these materials. Previous reports mainly focus on the application perspective, while a detailed characterization of the surface properties at the molecular level and the correlation with the synthesis conditions are missing. In this work, mesoporous TiO2 powder is grafted with 3-aminopropylphosphonic acid (3APPA) under different concentrations (20, 75, 150 mM) and temperatures (50, 90 °C) and compared with propylphosphonic acid (3PPA) grafting to unambiguously reveal the impact of the amine group on the surface properties. A combination of complementary spectroscopic techniques and Density Functional Theory-Periodic Boundary Conditions (DFT/PBC) calculations are used. At 90 °C and high concentrations, lower modification degrees are obtained for 3APPA compared to 3PPA, due to amine-induced surface interactions. Both X-ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy reveal that both NH2 and NH3+ groups are present, with also contributions of NH2 groups involved in hydrogen bonding interactions. A similar ratio of NH2/NH3+ (65:35) is obtained irrespective of the modification conditions, suggesting similar relative contributions of different surface conformations. Calculated adsorption energies from DFT calculations on 3APPA adsorption on anatase (1 0 1) in relation to the water coverage reveals a coexistence of various structures with the amine group involved in intra-adsorbate, inter-adsorbate and adsorbate–surface interactions. Further validation is obtained from the strong overlap of different 31P environments represented by the broad band (35-12 ppm) in experimental 31P Nuclear Magnetic Resonance (NMR) spectra and calculated 31P chemical shifts of all modelled monodentate and bidentate structures. Structures related to the tridentate binding mode are not formed due to geometric restrictions of the anatase (1 0 1) facet applied as model support in the calculations. Nevertheless, they could be present in the experimental samples as they are composed of anatase (representing multiple crystal facets) and an amorphous titania fraction.

Plasma (catalysis) reactors are increasingly being used for gas-based chemical conversions, providing an alternative method of energy delivery to the molecules. In this work we explore whether classical concepts such as equilibrium constants, (overall) rate coefficients, and catalysis exist under plasma conditions. We specifically investigate the existence of a so-called partial chemical equilibrium (PCE), and how process parameters and packing properties influence this equilibrium, as well as the overall apparent rate coefficient, for CO2 splitting in a DBD plasma reactor. The results show that a PCE can be reached, and that the position of the equilibrium, in combination with the rate coefficient, greatly depends on the reactor parameters and operating conditions (i.e., power, pressure, and gap size). A higher power, higher pressure, or smaller gap size enhance both the equilibrium constant and the rate coefficient, although they cannot be independently tuned. Inserting a packing material (non-porous SiO2 and ZrO2 spheres) in the reactor reveals interesting gap/material effects, where the type of material dictates the position of the equilibrium and the rate (inhibition) independently. As a result, no apparent synergistic effect or plasma-catalytic behaviour was observed for the non-porous packing materials studied in this reaction. Within the investigated parameters, equilibrium conversions were obtained between 23 and 71%, while the rate coefficient varied between 0.027 s−1 and 0.17 s−1. This method of analysis can provide a more fundamental insight in the overall reaction kinetics of (catalytic) plasma-based gas conversion, in order to be able to distinguish plasma effects from true catalytic enhancement.

Hybrid titania phosphonate materials can demonstrate a high added value as tailored sorption materials. They combine high chemical stability with great structural versatility, given the wide diversity of functional groups that can be incorporated. Hereto, a fundamental understanding of the synthesis strategies influencing the material performance is required. Therefore three porous TiO2 phosphonate hybrid structures with different functional groups (octyl, propyl, and phenyl) were evaluated in a solid-phase extraction application aimed towards solvent separation. The synthesis was performed by mixing bridged diphosphonic acids (DPAs) with Ti(OBu)4 in a water-ethanol mixture at 30 °C, followed by a hydrothermal post-treatment at 120 °C. The materials were characterized by ICP-AES, 31P solid-state CP/MAS NMR, Raman and FTIR spectroscopy, X-ray diffraction, N2-sorption, and transmission electron microscopy. It is shown that the diphosphonic acids are quantitatively incorporated in the hybrid structures, leading to nanosized particles with a complex but uniquely functionalized surface. A study of the pore structure as a function of the incorporated DPA amount showed materials with a maximum BET surface area of 379 m2/g. The alkyl functionalized hybrid titania phosphonates demonstrated excellent and tunable sorption behavior.

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Titanium dioxide (TiO2) is a unique material for biosensing applications due to its capability of hosting enzymes. For the first time, we show that TiO2 can accumulate reactive oxygen species (ROS) under daylight irradiation and can support the catalytic cycle of horseradish peroxidase (HRP) without the need of H2O2 to be present in the solution. Phenolic compounds, such as hydroquinone (HQ) and 4-aminophenol (4-AP), were detected amperometrically in flow-injection analysis (FIA) mode via the use of an electrode modified with TiO2 impregnated with HRP. In contrast to the conventional detection scheme, no H2O2 was added to the analyte solution. Basically, the inherited ability of TiO2 to generate reactive oxygen species is used as a strategy to avoid adding H2O2 in the solution during the detection of phenolic compounds. Electron paramagnetic resonance (EPR) spectroscopy indicates the presence of ROS on titania which, in interaction with HRP, initiate the electrocatalysis toward phenolic compounds. The amperometric response to 4-AP was linear in the concentration range between 0.05 and 2 μM. The sensitivity was 0.51 A M–1 cm–2, and the limit of detection (LOD) 26 nM. The proposed sensor design opens new opportunities for the detection of phenolic traces by HRP-based electrochemical biosensors, yet in a more straightforward and sensitive way following green chemistry principles of avoiding the use of reactive and harmful chemical, such as H2O2.

The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity. ispartof: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY vol:142 issue:6 pages:3174-3183 ispartof: location:United States status: published

Organophosphonic acid surface modification is performed to alter the surface properties of titania or other ceramics. By changing the modification conditions the physicochemical properties of the surface can be controlled. While these changes have been studied on the macroscale for different functional groups, showing differences in sorption behavior and application, their local impact on the surface OH-groups and resulting interaction with water is still unclear. Hence, we report an in-depth in-situ IR investigation supported by quantum chemical calculations and focused on the states of adsorbed water and the surface OH-groups of organophosphonic acid modified P25. Infrared spectra are recorded from fully saturated to fully dehydrated state by systematic desorption in vacuum and in function of temperature. Interesting differences in water desorption/interaction behavior for propylphosphonic acid modified titania are revealed, in which not only the number of grafted groups but also their distribution influences (the strength of) the interaction with water. Furthermore, when modifying with phenylphosphonic acid, additional water interactions in between the aromatic rings, could be observed. Finally, an interesting difference in thermal behavior of surface hydroxyl condensation could be observed for the modified surfaces. In contrast to pristine P25, they still feature surface hydroxyl groups at 250 °C.

FeCO3 scaling is utilised in a system of closely packed wet Fe-particles (10 μm) to prepare blocks composed of unreacted Fe-cores connected by a ‘cementing matrix of FeCO3 scales’. Within four hours of carbonation at different temperatures (30 °C – 90 °C) and CO2-pressures (1 barg–20 barg), a compressive strength of up to 160 MPa, and a siderite (FeCO3) content of up to 28 % is observed. Typical rhombohedral and atypical needle-shaped FeCO3 crystal morphologies are observed. The dependence of phase composition/morphologies on reaction conditions/processes is discussed. This study is proposed as a prelude towards utilisation of Fe-rich industrial wastes for cementation.

Despite the intensive research on protein adsorption in mesoporous materials, the effect of (de)hydration and confinement on the adsorbed protein's stability and activity is poorly understood. In this paper, we study the effect of differences in structural features (pore size) and drying time on the adsorption and structural stability of horse heart myoglobin (hhMb) on mesoporous titanium dioxide. Infrared spectroscopy (DRIFT) and thermal analysis (TGA) coupled to a quadrupole mass spectrometer (TGA-MS) were used to evaluate the impact of the confinement in different pores and hydration on the myoglobin secondary structure. Electron paramagnetic spectroscopy (EPR) was applied to identify the changes in the heme and its close surrounding. The peroxidase-like activity of myoglobin toward 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) in the presence of hydrogen peroxide allowed us to detect changes in the protein activity after adsorption in pores with different sizes and drying for different periods of time. The results show a clear effect of the pore size and drying time on the secondary structure of hhMb, which is confirmed by differences induced in the catalytic activity of the adsorbed proteins. Therefore, we recommend evaluating the effect of both hydration and confinement in future applications involving biomolecule adsorption in porous matrices. We are grateful to Guy Reggers (University of Hasselt) for performing the TGA-MS analysis and to Nick Gys (VITO) for measuring the zeta potential of MT8 and MT17. This work was supported by the Research Foundation-Flanders (FWO) (Grant G.0687.13) and the University of Antwerp (GOA-BOF project 28312).

Selective oxidation of methane in a micro fixed-bed reactor by using aqueous H2O2 solution as oxidant was studied. Sub-micrometer sized crystals of HZSM-5 and silicalite-1 with Fe contents below 10 ppm were synthesized. Different methods were used to introduce iron to produce Fe/ZSM-5 zeolites with similar but defined Fe contents. Commercial ZSM-5 with trace amount (175 ppm) of Fe impurity showed considerable methane conversion while over the own nearly Fe-free HZSM-5 no conversion could be measured. Fe/ZSM-5 catalysts prepared by different methods starting from the own nearly Fe-free HZSM-5 showed similar methane conversions and catalysts based on Fe(II) as the precursor exhibited a better performance with regard to retarding over-oxidation. The productivities of oxygenates were enhanced more than two orders of magnitude while at the same time obtaining high turnover frequencies (TOFs) of 303 h−1. A methane conversion as high as 23.5% together with oxygenates selectivity of 90.1% was reached. In contrast to Fe/ZSM-5, Fe/silicalite-1, prepared from Fe-free silicalite-1 by activation via the same post-synthetic preparation methods that were also used to prepare Fe/ZSM-5 and having similar Fe contents, never led to an active catalyst.

Low to negative cost fine industrial metallic iron-rich waste powders are available in large amounts all over the world and are currently often landfilled. The goal of this paper is to investigate the applicability of such waste powders as raw materials for a recently developed hydrothermal hydrogen gas production method, optimised for pure metallic iron powder and operating at a mild hydrothermal temperature of 160 degrees C for 16 h. The influence of several metallic, oxide and salt compounds of elements (M) that are commonly present in metallic iron-rich powder wastes was systematically investigated for two concentration levels, (M:Fe)(low) and (M:Fe)(high). The kinetics of hydrogen gas formation was measured during reaction and the obtained solid residues were analysed. This work shows that the oxidation of metallic iron particles and the consequent H-2 gas production in the investigated hydrothermal reaction system were inhibited through three main effects by the here studied contaminants, namely passivation of the reaction surface, carbonate precipitation and/or redox effects. On the other side, Ni addition promotes the reaction kinetics and acts as a catalyst. However, an excess of Ni inhibits complete iron oxidation through fast precipitation of Fe3O4 on the metallic iron particle surface, forming a passivation layer. Finally, three industrial iron waste powders were treated according to the same hydrothermal treatment Hydrogen gas formation for an iron-rich foundry sand (IWP-A) was inhibited by the formation of a silicate deposit on the iron particles, while the hydrogen gas production from iron works' waste powders (IWP-B and IWP-C) increased with decreasing particle size of the metallic iron particles in the powder. (C) 2018 Elsevier Ltd. All rights reserved.

The impact of waste composition and morphology on the properties of the mullite microstructure were studied by reaction sintering two types of siliceous waste powders with calcined alum sludge. Stoichiometric mixtures of fly ash or rice husk ash with the alum sludge were shaped into mullite microspheres by droplet coagulation. The mullitization reaction was followed by HT-XRD with a distinct difference in onset temperature. The specific powder composition of fly ash (presence of primary mullite) shifted the onset temperature to higher values as compared to the rice husk ash mixture. After sintering at 1600 degrees C, the mullitization reaction resulted in the same yield for both samples. Although the mullite content in the microspheres was equal, distinct differences on the microstructure could be observed. Reaction sintering of the fly ash mixture resulted in lower total porosity with smaller pore sizes.

Carbonation-cementation and bulk reaction mechanisms are studied in systems containing closely packed mixes of particulate Fe (0) (~10 μm) and Ca(OH)2 (0%, 5%, 10% and 15% w/w of Ca(OH)2) subjected to elevated CO2-pressure (1, 5, 10, and 20 barg) and temperature (30 °C and 60 °C). Solid solutions of (CaxFe1-x)CO3 series minerals are observed through shifting and broadening of XRD-reflections with variations in Ca(OH)2 content, CO2-pressure and temperature. The product morphologies varied from rhombohedral in non-Ca(OH)2 systems, to distorted rhombohedral (at 60 °C) and scalenohedral (at 30 °C) in the systems containing Ca(OH)2. An X-ray diffraction-based interpolation method is developed to discern mixed and end-member carbonates for more accurate bulk phase quantification. Based on these observations, variations in cementation performances are explained. Exceptional formation of an Fe-LDH and a (Ca,Fe)-LDH has also been observed in some systems. Interestingly, these LDH phases were stable even after being exposed to ambient conditions for more than 75 days.

Anatase nanosheets with exposed {001} facets have gained increasing interest for photocatalytic applications. To fully understand the structure-to-activity relation, combined experimental and computational methods have been exploited. Anatase nanosheets were prepared under hydrothermal conditions in the presence of fluorine ions. High resolution scanning transmission electron microscopy was used to fully characterize the synthesized material, confirming the TiO2 nanosheet morphology. Moreover, the surface structure and composition of a single nanosheet could be determined by annular bright-field scanning transmission electron microscopy (ABF-STEM) and STEM electron energy loss spectroscopy (STEM-EELS). The photocatalytic activity was tested for the decomposition of organic dyes rhodamine 6G and methyl orange and compared to a reference TiO2 anatase sample. The anatase nanosheets with exposed {001} facets revealed a significantly lower photocatalytic activity compared to the reference. In order to understand the mechanism for the catalytic performance, and to investigate the role of the presence of F, light-induced electron paramagnetic resonance (EPR) experiments were performed. The EPR results are in agreement with TEM, proving the presence of Ti3+ species close to the surface of the sample and allowing the analysis of the photoinduced formation of paramagnetic species. Further, ab initio calculations of the anisotropic effective mass of electrons and electron holes in anatase show a very high effective mass of electrons in the [001] direction, having a negative impact on the mobility of electrons toward the {001} surface and thus the photocatalysis. Finally, motivated by the experimental results that indicate the presence of fluorine atoms at the surface, we performed ab initio calculations to determine the position of the band edges in anatase slabs with different terminations of the {001} surface. The presence of fluorine atoms near the surface is shown to strongly shift down the band edges, which indicates another reason why it can be expected that the prepared samples with a large amount of {001} surface, but with fluorine atoms near the surface, show only a low photocatalytic activity.

Selective oxidation of methane by using aqueous hydrogen peroxide solution as oxidant was investigated. Colloidal nanosized Cu-Fe-silicalite-1 was prepared and a micro reactor was used to intensify mass transport. It was found that the oxygenate productivity could be enhanced nearly three orders of magnitude while simultaneously ensuring high turn-over-frequencies of some 100h(-1). However, the main product in liquid phase was not methanol, but formic acid. At optimized reaction conditions, a selectivity to formic acid of 96.7% at a methane conversion of 10.3% could be achieved.

A DFT study on the adsorption of a series of phosphonic acids (PAs) on the TiO2 anatase (101) and (001) surfaces was performed. The adsorption energies and geometries of the most stable binding modes were compared to literature data and the effect of the inclusion of dispersion forces in the energy calculations was gauged. As the (101) surface is the most exposed surface of TiO2 anatase, the calculated chemical shifts and vibrational frequencies of PM adsorbed on this surface were compared to experimental 31P and 170 NMR and IR data in order to assign the two possible binding modes (mono- and bidentate) to peaks and bands in these spectra; due to the corrugated nature of anatase (101) tridentate binding is not possible on this surface. Analysis of the calculated and experimental 31P chemical shifts indicates that both monodentate and bidentate binding modes are present. For the reactive (001) surface, the results of the calculations indicate that both bi- and tridentate binding modes result in stable systems. Due to the particular sensitivity of 170 chemical shifts to hydrogen bonding and solvent effects, the model used is insufficient to assign these spectra at present. Comparison of calculated and experimental IR spectra leads to the conclusion that IR spectroscopy is not suitable for the characterization of the different binding modes of the adsorption complexes. All calculations were performed using the Hopper HPC infrastructure at the CalcUA core facility of the University of Antwerp, a division of the Flemish Supercomputer Center VSC, funded by the Hercules Foundation, the Flemish Government (department EWI) and the University of Antwerp. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation - Flanders (FWO) and the Flemish Government – department EWI. This research was financially supported by FWO (Fonds Wetenschappelijk Onderzoek) via project GO12712N.

Despite the numerous studies on the adsorption of different proteins onto mesoporous titanium dioxide and indications on the important role of buffer solutions in bioactivity, a systematic study on the impact of the buffer on the protein incorporation into porous substrates is still lacking. We here studied the interaction between a commercial mesoporous TiO2 and three of the most used buffers for protein incorporation, i.e. HEPES, Tris and phosphate buffer. In addition, this paper analyzes the adsorption of horse heart myoglobin (hhMb) onto commercial mesoporous TiO2 as a model system to test the influence of buffers on the protein incorporation behavior in mesoporous TiO2. N2 sorption analysis, FT-IR and TGA/DTG measurements were used to evaluate the interaction between the buffers and the TiO2 surface, and the effect of such an interaction on hhMb adsorption. Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) were used to detect changes in the microenvironment surrounding the heme. The three buffers show a completely different interaction with the TiO2 surface, which drastically affects the adsorption of myoglobin as well as its structure and electrochemical activity. Therefore, special attention is required while choosing the buffer medium to avoid misguided evaluation of protein adsorption on mesoporous TiO2.

Hybrid materials are being developed to add organic functionalities to inorganic materials. Here, titanium dioxide is modified with organophosphonic acids (PAs). In several applications, the surface properties of the material play a key role in their performance (e.g. separation, sorption, catalysis). Hence, the surface properties of these materials need to be specifically adjusted to meet the requirements of each application (e.g. in membrane separation or chromatography). As the synthesis conditions have an important influence on the obtained surface properties, it is necessary to understand the impact and differences introduced by altering synthesis conditions. Different solvents are being applied for modification, but a comparative study of the impact of this change in environments is missing in literature. Therefore, our aim is to study the impact of concentration, temperature and pH in water and toluene on the properties of TiO 2 modified with propylphosphonic acid (3PA). By combining complementary techniques (DRIFT, TGA and 31 P/CP MAS NMR), clear differences induced by the solvent can be found. Moreover, in toluene a lower concentration of 3PA is required to obtain closed packed monolayers than in water. Furthermore, both solvent and concentration are influencing the modification degree and binding type formed on the surface. Moreover, only in water, next to the concentration, also the temperature and pH have a strong impact on the binding type of 3PA. A clear difference in thermal stability of 70 °C was found between both binding types.

Titanium dioxide (TiO2) is a popular material as host matrix for enzymes. We now evidence that TiO2 can accumulate and retain reactive oxygen species after treatment by hydrogen peroxide (H2O2) and support redox cycling of a phenolic analyte between horseradish peroxidase (HRP) and an electrode. The proposed detection scheme is identical to that of second generation biosensors, but the measuring solution requires no dissolved H2O2. This significantly simplifies the analysis and overcomes issues related to H2O2 being present (or generated) in the solution. The modified electrodes showed rapid stabilization of the baseline, a low noise level, fast realization of a steady-state current response, and, in addition, improved sensitivity and limit of detection compared to the conventional approach, i.e. in the presence of H2O2 in the measuring solution. Hydroquinone, 4-aminophenol, and other phenolic compounds were successfully detected at sub-μM concentrations. Particularly, a linear response in the concentration range between 0.025 and 2 μM and LOD of 24 nM was demonstrated for 4-aminophenol. The proposed sensor design goes beyond the traditional concept with three sensors’ generations offering a new possibility for the development of enzymatic sensors based on peroxidases and the formation of ROS on titania after treatment with H2O2.

The paper reports the observation that siderite (FeCO3 mineral) cementation occurs when compacted Fe-powder (10 µm in this study) is subjected to aqueous carbonation. It is further shown that the siderite contents of the reaction products vary based on the temperature and the CO2-pressure conditions under which they are carbonated. Using SEM-SE observations, two different types of morphologies of siderite crystals are observed based on the temperature are which the aqueous carbonation of iron is performed. The XRD-Rietveld observations and the SEM-SE observations are combined to infer that dendritic Fe-oxide crystals are formed away from the Fe surfaces, and that the siderite crystals grow as scales at the carbonating Fe surfaces. The concurrence of the variation in the siderite content and compressive strength is observed based on XRD-Rietveld analysis. The results of XRD-Rietveld analysis and MIP are combined to show that pore filling and refinement may not be a suitable indicator of compressive strength in such systems.

We studied the influence of dense, spherical packing materials, with different chemical compositions, on the dry reforming of methane (DRM) in a dielectric barrier discharge (DBD) reactor. Although not catalytically activated, a vast effect on the conversion and product selectivity could already be observed, an influence which is often neglected when catalytically activated plasma packing materials are being studied. The &alpha, Al2O3 packing material of 2.0&ndash, 2.24 mm size yields the highest total conversion (28%), as well as CO2 (23%) and CH4 (33%) conversion and a high product fraction towards CO (~70%) and ethane (~14%), together with an enhanced CO/H2 ratio of 9 in a 4.5 mm gap DBD at 60 W and 23 kHz. &gamma, Al2O3 is only slightly less active in total conversion (22%) but is even more selective in products formed than &alpha, Al2O3. BaTiO3 produces substantially more oxygenated products than the other packing materials but is the least selective in product fractions and has a clear negative impact on CO2 conversion upon addition of CH4. Interestingly, when comparing to pure CO2 splitting and when evaluating differences in products formed, significantly different trends are obtained for the packing materials, indicating a complex impact of the presence of CH4 and the specific nature of the packing materials on the DRM process.

Plasma catalysis, a promising technology for conversion of CO2 into value-added chemicals near room temperature, is gaining increasing interest. A dielectric barrier discharge (DBD) plasma has attracted attention due to its simple design and operation at near ambient conditions, ease to implement catalysts in the plasma zone and upscaling ability to industrial applications. To improve its main drawbacks, being relatively low conversion and energy efficiency, a packing material is used in the plasma discharge zone of the reactor, sometimes decorated by a catalytic material. Nevertheless, the extent to which different properties of the packing material influence plasma performance is still largely unexplored and unknown. In this study, the particular effect of synthesis induced differences in the morphology of a TiO2 shell covering a SiO2 core packing material on the plasma conversion of CO2 is studied. TiO2 has been successfully deposited around 1.6–1.8 mm sized SiO2 spheres by means of spray coating, starting from aqueous citratoperoxotitanate(IV) precursors. Parameters such as concentration of the Ti(IV) precursor solutions and addition of a binder were found to affect the shells’ properties and surface morphology and to have a major impact on the CO2 conversion in a packed bed DBD plasma reactor. Core-shell SiO2@TiO2 obtained from 0.25 M citratoperoxotitante(IV) precursors with the addition of a LUDOX binder showed the highest CO2 conversion 37.7% (at a space time of 70 s corresponding to an energy efficiency of 2%) and the highest energy efficiency of 4.8% (at a space time of 2.5 s corresponding to a conversion of 3%).

Plasma reactors are interesting for gas-based chemical conversion but the fundamental relation between the plasma chemistry and selected conditions remains poorly understood. Apparent kinetic parameters for the loss and formation processes of individual components of gas conversion processes, can however be extracted by performing experiments in an extended residence time range (2–75 s) and fitting the gas composition to a first-order kinetic model of the evolution towards partial chemical equilibrium (PCE). We specifically investigated the differences in kinetic characteristics and PCE state of the CO2 dissociation and CH4 reforming reactions in a dielectric barrier discharge reactor (DBD), how these are mutually affected when combining both gases in the dry reforming of methane (DRM) reaction, and how they change when a packing material (non-porous SiO2) is added to the reactor. We find that CO2 dissociation is characterized by a comparatively high reaction rate of 0.120 s−1 compared to CH4 reforming at 0.041 s−1; whereas CH4 reforming reaches higher equilibrium conversions, 82% compared to 53.6% for CO2 dissociation. Combining both feed gases makes the DRM reaction to proceed at a relatively high rate (0.088 s−1), and high conversion (75.4%) compared to CO2 dissociation, through accessing new chemical pathways between the products of CO2 and CH4. The addition of the packing material can also distinctly influence the conversion rate and position of the equilibrium, but its precise effect depends strongly on the gas composition. Comparing different CO2:CH4 ratios reveals the delicate balance of the combined chemistry. CO2 drives the loss reactions in DRM, whereas CH4 in the mixture suppresses back reactions. As a result, our methodology provides some of the insight necessary to systematically tune the conversion process.

Amphiphilic Grignard modified ceramic nanofiltration membranes have been demonstrated to perform well for a wide range of solvents in organic solvent nanofiltration (OSN). The purpose of this study is to obtain a better understanding of the influence of the solvent-membrane-solute interactions governing the OSN membrane performance. This was achieved by performing an extensive retention study on two types of Grignard functionalised membranes, in many different solvents with a wide variety of polarity, and choosing three PEG molecules and polystyrene as solutes, all with almost the same size but different polarities. To unravel the transport mechanism properly, also the pressure effect on flux and retentions was thoroughly investigated. The retention results showed in general a very different behavior in different ranges of solvent polarity: at low solvent polarity, retentions are relatively low, varying with pressure and solvent polarity; at high solvent polarity, retentions are relatively high, and independent of pressure and solvent polarity. The Spiegler-Kedem theory, taking into account both diffusion and convection transport mechanisms, appears to be a very good basis for a fundamental explanation of all results. This knowledge shows also how membrane-solvent-solute interactions can be manipulated to enhance the membrane performance.

Immobilization of redox proteins on electrode surfaces is of special interest for mechanistic studies and applications, because of the well-controlled redox state of protein molecules at a polarized electrode and fast electron-transfer kinetics that are free from diffusion limitation. Here, bis-organosilane [1,2-bis(trimethoxysilyl)ethane] was used as a fresh solution in a pH 7 phosphate buffer without the use of any organic solvent, sol-gel, or mesoporous bulk matrix. A short aging period of 30 min before deposition on the electrodes was optimal for the immobilization of proteins. Three redox proteins (cytochrome c, neuroglobin, and GLB-12) were confined to the gold surface of electrodes with high coverages and stabilities, indicating that the suggested technique is simple, efficient, and generic in nature.

Exploitation of engineered nanomaterials with unique properties has been dynamically growing in numerous fields, including the agricultural sector. Due to the increasing resistance of phytopathogenic microbes, human control over various plant pathogens in crop production is a big challenge and requires the development of novel antimicrobial materials. Photocatalytic active nanomaterials could offer an alternative solution to suppress the plant pathogens. In this work, titanium dioxide nanoparticles (TiO2 NPs) with high photocatalytic activity were synthesized by hydrothermal post-treatment of amorphous titania at different temperatures (250 &deg, C or 310 &deg, C) without using any additives or doping agents. The obtained samples were investigated through X-ray diffraction, N2-sorption measurements, diffuse reflectance UV-Vis spectroscopy, transmission electron microscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The applied hydrothermal treatment led to the formation of TiO2 nanocrystallites with a predominant anatase crystal phase, with increasing crystallinity and crystallite size by prolonging treatment time. The photocatalytic activity of the TiO2 NPs was tested for the photo-degradation of phenol and applied for the inactivation of various plant pathogens such as Erwinia amylovora, Xanthomonas arboricola pv. juglandis, Pseudomonas syringae pv. tomato and Allorhizobium vitis. The studied bacteria showed different susceptibilities, their living cell numbers were quickly and remarkably reduced by UV-A-irradiated TiO2 NPs. The effectiveness of the most active sample prepared at 310 &deg, C was much higher than that of commercial P25 TiO2. We found that fine-tuning of the structural properties by modulating the time and temperature of the hydrothermal treatment influenced the photocatalytic properties of the TiO2 NPs considerably. This work provides valuable information to the development of TiO2-based antimicrobial photocatalysts.