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Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 &deg, C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 &deg, C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the &alpha, O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 &deg, C, which could be related to an optimum in morphological and compositional characteristics of the support.

To increase the recycling potential of concrete, Completely Recyclable Concrete (CRC) has been developed to be used as a raw material for cement clinker production. Sulfates may penetrate CRC structures in time and their presence could affect the clinkering process of the eventually obtained CRC rubble. Therefore, the effect of CaSO 4 additions on the final CRC clinker mineralogy has been investigated using XRD/Rietveld and SEM/EDX. An increasing sulfate content was found to stimulate the formation of sulfates that incorporate CaO, i.e. calcium langbeinite and anhydrite. Moreover, belite tends to be stabilized at the expense of alite with more SO 3 present.

Chemical solution deposition (CSD) of YBa2Cu3O7−δ (YBCO) nanocomposites from colloidal precursor solutions containing double metal oxide preformed nanocrystals is a promising, cost effective and reproducible approach to produce superconducting films with high critical current density (Jc) and enhanced pinning. Here, the influence of the preformed nanocrystal composition on the microstructure and superconducting properties of the YBCO nanocomposite films is studied, with a focus on establishing a simple and scalable process to grow nanocomposites that can be transferred to grow nano-added coated conductors. Colloidal stable BaZrO3, BaHfO3, BaTiO3 and SrZrO3 nanocrystals (3-6 nm in diameter) were synthesized and added to an environment-friendly low-fluorine YBCO precursor solution. High-quality superconducting layers were grown on LaAlO3 single-crystal substrates from these four nanocomposite precursor solutions in a single deposition process, without the need of a seed layer, yielding Jc of 4-5 MA/cm² at 77 K in self-field. The different YBCO microstructures produced by the four types of nanocrystals and the resulting microstrain of the films are compared and related with the magnetic-field and angular dependence of Jc. We demonstrate the BaHfO3-containing nanocomposite as the best-performing with a homogeneous distribution of nanoparticles with 7 nm in average diameter and a high density of stacking faults, which leads to some of the best superconducting properties ever achieved via low-fluorine CSD. The Jc exhibits a much smoother decay in applied magnetic fields and a much more isotropic behaviour for non-parallel magnetic fields, and the pinning force is increased by a factor of 3.5 at 77 K and 1 T with respect to the pristine film.

A new series of bimetallic COMOC-2(V)/DUT-5(Al) frameworks are developed and fully characterized. Electron paramagnetic resonance and transmission electron microscopy confirm the homogeneous dispersion of Al/V in the entire framework. The study of the flexibility by means of CO2 pressure dependent XRPD and high pressure sorption reveals the co-existence of two different large pore phases and a narrow pore phase in the entire pressure regime.

A method to obtain photocatalytically active thin films of anatase nanocrystals on polymer substrates was explored. Anatase nanocrystals were synthesized by a fast hydrolysis synthesis in an apolar solvent and characterized with regard to their crystallinity, size, and dispersibility and the stability of the resulting suspensions. The stable titania nanocrystal suspensions were further processed for their use in polar solvents using ligand exchange. Oleic acid was exchanged for 3-aminopropyltriethoxysilane (APTES), resulting in aqueous suspensions of charge-stabilized nanocrystals. These were adapted for use as coating suspensions for surface-treated PMMA substrates in order to obtain thin films containing anatase nanocrystals covalently coupled to the surface of the PMMA substrates. Thereby, the ligand exchange was beneficial for increasing the compatibility and durability of the inorganic/organic composite, by the formation of a covalent amide bond between the silane ligands on the nanocrystals and the carboxylic acid groups on the polymer substrate. The surface morphology, transparency, and photocatalytic activity toward the degradation of organic pollutants of the coatings, obtained through dip-coating, were evaluated.

In this work, we present preparation and stabilization methods for highly crystalline TiO2 nanoparticle suspensions for the successful deposition of transparent, photocatalytically active TiO2 thin films toward the degradation of organic pollutants by a low temperature deposition method. A proof-of-concept is provided wherein stable, aqueous TiO2 suspensions are deposited on glass substrates. Even if the processing temperature is lowered to 150-200 °C, the subsequent heat treatment provides transparent and photocatalytically active titania thin layers. Because all precursor solutions are water-based, this method provides an energy-efficient, sustainable, and environmentally friendly synthesis route. The high load in crystalline titania particles obtained after microwave heating opens up the possibility to produce thin coatings by low temperature processing, as a conventional crystallization procedure is in this case superfluous. The impact of the precursor chemistry in Ti(4+)-peroxo solutions, containing imino-diacetic acid as a complexing ligand and different bases to promote complexation was studied as a function of pH, reaction time and temperature. The nanocrystal formation was followed in terms of colloidal stability, crystallinity and particle size. Combined data from Raman and infrared spectroscopy, confirmed that stable titanium precursors could be obtained at pH levels ranging from 2 to 11. A maximum amount of 50.7% crystallinity was achieved, which is one of the highest reported amounts of anatase nanoparticles that are suspendable in stable aqueous titania suspensions. Decoloring of methylene blue solutions by precipitated nanosized powders from the TiO2 suspensions proves their photocatalytic properties toward degradation of organic materials, a key requisite for further processing. This synthesis method proves that the deposition of highly crystalline anatase suspensions is a valid route for the production of photocatalytically active, transparent films on heat-sensitive substrates such as polymers.

Nine compositional series of 15(Na2O, K2O)center dot 10(CaO, ZnO)center dot 75(ZrO2, SiO2) glass-forming melts were studied, all with the ZrO2 content of 0, 1, 3, 5 and 7 mol.%. The investigated glass compositions were obtained by equimolar substitutions ZrO2 / SiO2, ZnO / CaO and K2O / Na2O. Surface tension of studied glassforming melts was de-termined by the sessile and pendant drop profile numerical analysis in the temperature range (1250 1500) degrees C. The experimental values of melt density were used. The linear temperature dependence of surface tension was observed for all samples with only small differences between values obtained from sessile and pendant drop profiles. The Shakhmatkin and Vedishcheva thermodynamic model (TDM) was evaluated for each glass melt at temperature of 1400 degrees C. The total number of 36 components was considered in TDM. Only 26 components were present with non-negligible equilibrium amount. The surface tension was described by the multilinear function of equilibrium amounts of statistically independent non-negligible components of the TDM. The surface active components were identified by negative values of their coefficients. Such way the N3S8 and C2ZrS4 were identified as "strongly" surface active and NCS5 and KS4 as probably surface active. Regarding the oxide compositional point of view, the surface tension was mostly influenced by ZnO (increase with the addition of the oxide) and by K2O (decrease with the addition of the oxide).

A challenge for the photodegradation of (organic) micro-pollutants in waste water treatment is the mechanistic and kinetic understanding beyond the degradation of the initial (parent) harmful product, e.g. the phenylurea herbicide isoproturon (IPU). By combining liquid chromatography-mass spectrometry and kinetic Monte Carlo modeling, we demonstrate that upon optimizing the dip-coating conditions (0.34 mol L (-1) TiO2 solution at a coating speed of 160 mm min( -1)) for the functionalization of a superhydrophilic electrospun silica nanofibrous membrane (i) hydroxylation is a dominant reaction pathway and (ii) once IPU reacts on the surface of the TiO(2 )nanoparticles, further hydroxylation occurs sufficiently fast, with complete IPU removal under the detection limit (5-10 mg Lsolution(-1)) as a result of UV irradiation within 8 h. As hydroxylation is dominant, degradation intermediates with a higher water solubility are formed and therefore a decreased toxicity is obtained upon reintroducing the treated solution into the environment. This is confirmed by respirometry, with an increase in the oxygen uptake rate of an activated sludge from 5.9 mg O(2 )g(activated) ( -1)(sludge) h (-1 )for an untreated 10 mg L-1 IPU solution to 8.2 mg O-2 g(activated sludge) (-1) h( -1) for a solution irradiated for 8 h, in line with a blank solution.

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 &deg, C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (&epsilon, ) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings.

The formation of superconducting nanocomposites from preformed nanocrystals is still not well understood. Here, we examine the case of ZrO2 nanocrystals in a YBa2Cu3O7&minus, x matrix. First we analyzed the preformed ZrO2 nanocrystals via atomic pair distribution function analysis and found that the nanocrystals have a distorted tetragonal crystal structure. Second, we investigated the influence of various surface ligands attached to the ZrO2 nanocrystals on the distribution of metal ions in the pyrolyzed matrix via secondary ion mass spectroscopy technique. The choice of stabilizing ligand is crucial in order to obtain good superconducting nanocomposite films with vortex pinning. Short, carboxylate based ligands lead to poor superconducting properties due to the inhomogeneity of metal content in the pyrolyzed matrix. Counter-intuitively, a phosphonate ligand with long chains does not disturb the growth of YBa2Cu3O7&minus, x. Even more surprisingly, bisphosphonate polymeric ligands provide good colloidal stability in solution but do not prevent coagulation in the final film, resulting in poor pinning. These results thus shed light on the various stages of the superconducting nanocomposite formation.

The metastable titania phase, bronze, has great potential as photo-catalyst or as anode material in Li-ion batteries. Here, we report the first synthesis of colloidally stable, size-tunable TiO2-bronze (TiO2-B) nanocrystals, via a hydrothermal process. By employing Definitive Screening Design, the experimental parameters affecting the size and agglomeration of the nanocrystals are identified. The size is mostly determined by the reaction temperature, resulting in 3 – 8 nm NCs in the range of 130 °C – 180 °C. To avoid irreversible aggregation, short reaction times are desired and in this respect microwave heating proved essential due to its fast heating and cooling rates. The resulting nanocrystals are de-aggregated and stabilized in polar solvents using either positive or negative surface charges. In nonpolar solvents, steric stabilization is provided by long chain amines and carboxylic acids. Furthermore, we study this peculiar post-synthetic surface modification through solution 1H NMR and elemental analysis. Surprisingly, we find ion-pairs of alkylammonium carboxylates bound to the surface, contrasting with earlier reports on carboxylic acid stabilized metal oxide nanocrystals. To rationalize this, a general framework of acid/base chemistry with metal oxide nanocrystals is constructed and discussed.

In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at reduced temperatures. Transparent and photocatalytically active TiO2 coatings that degrade organic matter, have been widely applied to bestow self-cleaning properties onto surfaces. This low-temperature deposition method and its transition to polymers would open an entire array of possible self-cleaning applications. During this research, incorporation of a silica buffer layer was applied to improve the compatibility of the inorganic coating on a substrate, such as polymethylmethacrylate (PMMA) and polyphenylsulphone (PPSU). The photocatalytic activity of the obtained coating was analyzed for its photocatalytic abilities by evaluating the color removal of a dye solution (methylene blue, MB) under UV irradiation and compared with commercial Pilkington Activ® self-cleaning glass. Our results indicate that the titania-coated silica-polymer systems yield a higher photocatalytic activity towards the degradation of organic pollutants. This method proves that the deposition of highly crystalline anatase suspensions on silica buffer layers is a viable method to produce photocatalytic coatings on heat-sensitive substrates.

Nanofibrous materials produced through electrospinning are characterized by a high porosity, large specific surface area, and high pore interconnectivity and, therefore, show potential for, e.g., separation and filtration. The development of more inert nanofibers with higher thermal and chemical resistance extends the application field to high-end purification. Silica nanofibrous membranes produced by direct electrospinning of a sol–gel solution without a sacrificing carrier, starting from tetraethoxysilane, meet these challenging requirements. After electrospinning the membrane is highly hydrophobic. Storage under dry conditions preserves this property. Oppositely, a superhydrophilic membrane is obtained by storage under high humidity (month scale). This switch is caused by the reaction of ethoxy groups, present due to incomplete hydrolysis of the precursor, with moisture in the air, resulting in an increased amount of silanol groups. This transition can be accelerated to hour scale by applying a heat treatment, with the additional increase in cross-linking density for temperatures above 400 °C, enabling applications that make use of hydrophobic and hydrophilic membranes by tuning the functionalization. It is showcased that upon designing the water repellent or absorbing nature of the silica material, fast gravity-driven membrane separation of heterogeneous azeotropes can be achieved.

Aluminium doped zinc oxide is considered an interesting, earth abundant alternative to the transparent conductor indium tin oxide. In this respect, we synthesized Al-ZnO (AZO) thin films by a chemical solution deposition approach. Using water-based inks, the AZO thin films were printed in one single step on glass substrates in non-vacuum conditions. The drying process and the humidity of the atmosphere proved to be crucial during the thermal processing of the wet deposited thin films. To improve the understanding of the phenomena involved, the influence of these processing parameters on the final properties of the AZO thin films are investigated by FTIR, XRD, SEM, 1H and 27Al NMR and resistivity measurements. Optimal conditions were obtained by drying the wet thin film at 120 °C, followed by heating in a tube furnace until 500 °C under a 200 ppm O2/N2 atmosphere with a humidity controlled by bubbling the gas flow through 2 glass bottles containing water at 20 °C. AZO thin films with an resistivity of 2.54 × 10−2 Ω cm were obtained.

Titania has already proven its added value for air and water treatment. The higher the surface-to-volume area, the better the performance of the TiO 2 photocatalyst. These nanoparticles are typically applied in a slurry form. The use of titania nanoparticles in suspension has, however, multiple disadvantages such as a high turbidity and complex recovery of the photocatalyst after use. Therefore, immobilization of titania nanoparticles on a porous support such as a nanofibrous membrane, can be highly valuable for water treatment. These TiO 2 functionalized nanofibrous membranes may be used not only in a membrane separation reactor, but also in a contact reactor. In this study, TiO 2 nanoparticles were immobilized on both polymer (polyamide 6) and ceramic (silica) nanofibrous membranes. Polymer nanofibers are chosen as they are the state-of-the-art material, silica nanofibers on the contrary are less studied but show additional advantages due their excellent chemical and thermal stability and can thus offer a clear benefit for a wider range of applications. Two immobilization techniques were used, namely inline functionalization and dip-coating. Inline functionalization showed to be the preferred method for polyamide 6 nanofibrous membranes, dip-coating for silica nanofibrous membranes. Complete degradation of isoproturon, an actual concern in water treatment, is shown. Even the widely available commercial TiO 2 nanoparticles allowed for a complete isoproturon removal as the result of a correct immobilization process on nanofibrous materials. This clearly opens up the high value of TiO 2 functionalized nanofibrous membranes for organic (micro)pollutants removal.

In this work, aqueous chemical solution deposition route suited for inkjet printing is used for the synthesis of photocatalytically active TiO 2 coatings. Environmentally friendly precursor solutions with electromagnetic ink-jet printing, allows cheap and simple processing of TiO 2 films on glass. The hydrolysis reaction of water sensitive titanium alkoxide (Ti-alkoxide) precursor is controlled by adding complexing agents as citric acid and triethanolamine prior to water addition, and aqueous stable solutions are achieved. The pH of the solutions is brought to neutral to guarantee flexible processing, avoid damage to substrates and equipment. Solution parameters are adapted to obtain optimal gelation conditions and good jettability. The influence of processing parameters on the phase formation and surface morphology is studied by thermogravimetric analysis and differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The photocatalytic activity of the films is evaluated by the degradation of methyl orange.

In this article, Al-doped ZnO thin films deposited by a one single-layer approach are studied. An aqueous precursor solution was prepared for the deposition of Al-doped ZnO thin film via ink-jet printing. The physical properties of the ink were studied in detail by rheology measurement and drop visualization. The wetting of the ink with the substrate was studied by the use of wetting envelopes. A single layer of the ink was deposited on the substrate and fully processed. The thin films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements, and optical transmission measurements. The optimal dopant concentration was set at 3 at.%, which resulted in thin films with a resistivity of 2.54 cΩ cm and an optical transmission larger than 90% over the visible range of the electromagnetic spectrum.

Colorimetric sensors for monitoring and visual reporting of acidic environments both in water and air are highly valuable in various fields, such as safety and technical textiles. Until now sol-gel-based colorimetric sensors are usually nonflexible bulk glass or thin-film sensors. Large-area, flexible sensors usable in strong acidic environments are not available. Therefore, in this study organically modified silicon oxide nanofibrous membranes are produced by combining electrospinning and sol-gel technology. Two pH-indicator dyes are immobilized in the nanofibrous membranes: methyl yellow via doping, methyl red via both doping, and covalent bonding. This resulted in sensor materials with a fast response time and high sensitivity for pH-change in water. The covalent bond between dye and the sol-gel network showed to be essential to obtain a reusable pH-sensor in aqueous environment. Also a high sensitivity is obtained for sensing of HCl and NH3 vapors, including a memory function allowing visual read-out up to 20 min after exposure. These fast and reversible, large-area flexible nanofibrous colorimetric sensors are highly interesting for use in multiple applications such as protective clothing and equipment. Moreover, the sensitivity to biogenic amines is demonstrated, offering potential for control and monitoring of food quality.

The critical parameters determining the electrospinning of silica nanofibers starting from tetraethoxysilane sols are reported. By controlling the reaction conditions, the rheological properties of the sol allowed for electrospinning without needing the addition of an organic polymer. This allows the polymer removal step, which is deleterious to the fibers and an economic and ecological inconvenience, to be skipped. The effects on the electrospinning process of the viscosity of the sol, the concentration of ethanol, the degree of crosslinking and the size of the colloidal species were studied in depth with ATR-FTIR, Si-29 NMR, H-1 NMR and DLS. Moreover, to separate the contributions of the different parameters three different set-ups for sol preparation were used. An optimum amount of 9 mol L-1 ethanol for electrospinning was determined. In addition, the optimum degree of crosslinking and size of colloidal particles, approximately 3.5-7 nm, were obtained for stable electrospinning and for producing uniform, beadless nanofibers that were stable in time. The optimum viscosity range is in between 100 and 200 mPa s, which is in line with previous work. Using these optimum conditions, continuous electrospinning was carried out for 3 h, resulting in large flexible silica nanofibrous membranes.

Lanthanum zirconate (LZO) films from water-based precursors were deposited on Ni-5% W tape by chemical solution deposition. The buffer capacity of these layers includes the prevention of Ni oxidation of the substrate and Ni penetration towards the YBCO film which is detrimental for the superconducting properties. X-ray Photoelectron Spectroscopy depth profiling was used to study the barrier efficiency before and after an additional oxygen annealing step, which simulates the thermal treatment for YBCO thin film synthesis. Measurements revealed that the thermal treatment in presence of oxygen could severely increase Ni diffusion. Nonetheless it was shown that from the water-based precursors' buffer layers with sufficient barrier capacity towards Ni penetration could be synthesized if the layers meet a certain critical thickness and density.

Lanthanumcerium oxide (LCO) films were deposited on Ni-5%W substrates by chemical solution deposition (CSD) from water-based precursors. LCO films containing different ratios of lanthanum and cerium ions (from CeO2 to La2Ce2O7) were prepared. The composition of the layers was optimized towards the formation of LCO buffer layers, lattice-matched with the superconducting YBa2Cu3Oy layer, useful for the development of coated conductors. Single, crack-free LCO layers with a thickness of up to 140 nm could be obtained in a single deposition step. The crystallinity and microstructure of these lattice-matched LCO layers were studied by X-ray diffraction techniques, RHEED and SEM. We find that only layers with thickness below 100 nm show a crystalline top surface although both thick and thin layers show good biaxial texture in XRD. On the most promising layers, AFM and (S)TEM were performed to further evaluate their morphology. The overall surface roughness varies between 3.9 and 7.5 nm, while the layers appear much more dense than the frequently used La2Zr2O7 (LZO) systems, showing much smaller nanovoids (12 nm) than the latter system. Their effective buffer layer action was studied using XPS. The thin LCO layers supported the growth of superconducting YBCO deposited using PLD methods.

In this work, water-based precursor solutions suitable for dip-coating of thick La{sub 2}Zr{sub 2}O{sub 7} (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100-280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55{sup o}. TEM studies illustrated the presence of nanovoids, typical for CSD-LZO films annealed under Ar-5%H{sub 2} gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer. - Graphical abstract: Thick LZO buffer layers from water-based precursor solutions were synthesized and their crystallinity, microstructure and buffer layer action were studied. The buffer layer action of the LZO layer was substantial to restrict the Ni penetration within 30 nm of a 140 nm thickmore » film. Highlights: > LZO buffer layers with high thicknesses for use in coated conductors were prepared. > Prepared from water-based solutions. > Polymeric PVP increases the crack-free critical thickness of thick films. > Thick films showed good barrier action against Ni penetration. > Seed layers promote epitaxial growth of thick layers.« less

In this work, we investigate the chemistry for an aqueous acetate-triethanolamine-ammonia based YBa(2)Cu(3)O(7-δ) (YBCO) precursor system. These precursor solutions are suited for the chemical solution deposition of superconducting YBCO layers on top of single crystal SrTiO(3) or buffered NiW tapes. The development of this kind of precursor inks often involves trial-and-error experimenting and thus is very time-consuming. To reduce labwork to the minimum, the theoretical prediction of pH stability limits and the complexation behaviour of the different metal ions and complexants in the inks are very important. For this purpose, we simulated, based on literature values, the complexation behaviour of Cu(2+) in the aqueous precursor solutions as a function of pH. To validate the used model, we performed potentiometric pH titrations for solutions with similar composition and checked the correctness of fit between experiment and model. The generated complexometric results are coupled with X-band EPR spectra to further confirm the results. EPR spectra for fully prepared precursor solutions as well as for Cu(2+) reference solutions containing only one type of ligand (acetate, triethanolamine or ammonia) were investigated as a function of pH. We find that, in line with speciation simulation, only acetates are actively complexing the Cu(2+) ions at pH values below 7, while when reaching higher pH levels mainly triethanolamine complexes are formed. Over the entire pH range, no trace of free Cu(2+)or Cu(OH)(2), possibly creating precipitation during gelation and thus complicating further processing, could be found.