R. Sirera

Solidification/stabilization of toxic metals in calcium aluminate cement matrices.

The ability of calcium aluminate cement (CAC) to encapsulate toxic metals (Pb, Zn and Cu) was assessed under two curing conditions. Changes in the consistency and in the setting time were found upon the addition of the nitrates of the target metals. Both Pb and Cu caused a delay in CAC hydration, while Zn accelerated the stiffening of the mortar. Compressive strengths of the metal-doped mortars, when initially cured at 60 °C/100% RH, were comparable with that of the free-metal mortar. Three different pore size distribution patterns were identified and related to the compounds identified by XRD and SEM. Sorbent capacities of CAC for the toxic metals were excellent: a total uptake was achieved for up to 3 wt.% loading of the three metals. In this way, CAC mortars were perfectly able to encapsulate the toxic metals, allowing the use of CAC for waste management as proved by the leaching tests.

Metal complexes with N-methyldiethanolamine as new photosensitive precursors for the low-temperature preparation of ferroelectric thin films

New photosensitive precursors for the low-temperature preparation of ferroelectric PbTiO3 thin films are obtained by using a sol–gel synthetic route. The reaction of N-methyldiethanolamine (MDEA) with lead acetate and titanium bis(acetylacetonate) diisopropoxide reagents leads to the formation of metal-MDEA complexes with a significant ultraviolet (UV) absorption due to the chromophore groups arisen from the orbital splitting between the respective metal atom and the organic ligand. Processes of transference of charge between the nitrogen and the metallic centre are responsible for the UV absorption in the resulting sols: ligand to metal charge transfer (LMCT) in the case of the Ti(IV) complex, d0 element, and metal to ligand charge transfer (MLCT) in the case of the Pb(II) one, d10 element. The enhanced photosensitivity of the precursor solutions provided by these complexes is exploited for the fabrication of ferroelectric PbTiO3 films at temperatures compatible with silicon microelectronics (400 °C).

Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi 2 O 3 polymorph

The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi2O3 polymorph. The pure β-Bi2O3 phase is thermodynamically stable at high temperature (450–667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a –Bi–O–Bi– continuous network in the deposited layers and the further conversion into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.

A UV-absorber bismuth(III)-N-methyldiethanolamine complex as a low-temperature precursor for bismuth-based oxide thin films

Novel synthetic methods in solution that reduce the formation temperature of bismuth-based electronic oxides are essential for their successful integration with substrates of low thermal stability within micro- and flexible-electronic devices. This has become crucial for these oxides, since they appear as promising low-toxic functional materials alternative to other electronic oxides containing heavy metals. However, this is a challenge, since the crystallization of bismuth oxides occurs at high temperatures. To overcome these problems, we synthesize here a UV-absorber charge transfer metal complex in solution between the Bi(III) ion and an alkanolamine, N-methyldiethanolamine (Bi(III)–mdea). We take advantage of the photoreactivity of this complex to prepare bismuth-based oxide thin films at low temperature, which cannot be achieved by traditional thermal processing methods. Room temperature stable oxide thin films of the high-temperature δ-Bi2O3 phase are prepared from these solutions by UV-irradiation and annealing at 350 °C. The efficiency of this synthetic strategy is additionally proven for the low temperature preparation of thin films of much more complex bismuth based functional oxides: the multiferroic bismuth ferrite, BiFeO3, and the relaxor-ferroelectric perovskite of bismuth, sodium and barium titanate, (Bi0.5Na0.5)0.945Ba0.055TiO3.

Treatment of toxic metal aqueous solutions: encapsulation in a phosphate-calcium aluminate matrix.

Polyphosphate-modified calcium aluminate cement matrices were prepared by using aqueous solutions polluted with toxic metals as mixing water to obtain waste-containing solid blocks with improved management and disposal. Synthetically contaminated waters containing either Pb or Cu or Zn were incorporated into phosphoaluminate cement mortars and the effects of the metals presence on setting time and mechanical performance were assessed. Sorption and leaching tests were also executed and both retention and release patterns were investigated. For all three metals, high uptake capacities as well as percentages of retention larger than 99.9% were measured. Both Pb and Cu were seen to be largely compatible with this cementitious matrix, rendering the obtained blocks suitable for landfilling or for building purposes. However, Zn spoilt the compressive strength values because of its reaction with hydrogen phosphate anions, hindering the development of the binding matrix.

Solution processing and crystallization of ferroelectric samarium modified lead titanate thin films

Samarium-doped lead titanate thin films have been prepared by a sol–gel technique. The processing of precursor solutions through two different synthetic routes and containing differing excesses of PbO is described. The films deposited from these solutions are crystallized by thermal treatments at temperatures higher than 550 °C. The crystalline structure, composition and microstructure of the resulting films are studied by grazing incidence X-ray diffraction analysis, energy dispersive spectroscopy, quantitative scanning electron microscopy and transmission electron microscopy. It is observed that the film microstructure and the development of non-ferroelectric phases in these films are influenced by both the solution chemistry and the lead oxide stoichiometry. Preliminary results concerning the ferroelectric behaviour of these films are also given.

Influence of Two Polymer-Based Superplasticizers (Poly-naphthalene Sulfonate, PNS, and Lignosulfonate, LS) on Compressive and Flexural Strength, Freeze-Thaw, and Sulphate Attack Resistance of Lime-Metakaolin Grouts

A new range of grouts prepared by air lime and metakaolin (MK) as a pozzolanic admixture has been obtained by using as dispersing agents two polymers, namely poly-naphthalene sulfonate (PNS) and lignosulfonate (LS), with the aim of improving the fluidity of the fresh grouts. Fluidity and setting times of the grouts were assessed. Differences in the molecular architecture and in the anionic charge density explained the different adsorption of the polymers and the different performance. The higher anionic charge of PNS and its linear shape explained its better adsorption and effectiveness. The pozzolanic reaction was favoured in grouts with PNS, achieving the highest values of compressive strength (4.8 MPa after 182 curing days). The addition of PNS on lime grouts slightly decreased the frost resistance of the grouts (from 24 freeze-thaw cycles for the polymer-free samples to 19 or 20 cycles with 0.5 or 1 wt % of PNS). After the magnesium sulphate attack, grouts were altered by decalcification of hydrated phases and by formation of hexahydrite and gypsum. A protective role of portlandite against magnesium sulphate attack was clearly identified. Accordingly, the polymer LS, which preserves a significant amount of Ca(OH)2, could be an alternative for the obtaining of grouts requiring high sulphate attack resistance.

Photochemical solution deposition of β-Bi2O3 thin films

The non-equilibrium β-Bi2O3 polymorph is stabilized in thin films by a photochemical synthesis method. A strong ultraviolet-absorbing bismuth(III)-N-methyldiethanolamine complex is synthesized in solution as an ideal precursor for the β-Bi2O3 phase. Ultraviolet-light induces the formation of an amorphous —Bi—O—Bi— continuous network in the films deposited from the former solution that easily converts into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The room temperature stabilization of the β-Bi2O3 phase is confirmed by their structural characterization using four-circle X-ray diffractometry. This study unequivocally identified the tetragonal crystal structure of the β-Bi2O3 polymorph in the films. The high phase purity of these β-Bi2O3 films is responsible for their exceptional visible-light photocatalytic activity, thus enabling the applications of the films of this metastable phase at room-temperature conditions.Graphical AbstractPhotosensitive precursor solutions containing a photosensitive Bi(III)-N-methyldiethanolamine complex lead to the stabilization of the high-temperature β-Bi2O3polymorph in films on Pt-coated silicon substrates prepared at a low temperature of 250 °C using UV-irradiation.

A safer disposal of hazardous phosphate coating sludge by formation of an amorphous calcium phosphate matrix.

Phosphate coating hazardous wastes originated from the automotive industry were efficiently encapsulated by an acid-base reaction between phosphates present in the sludge and calcium aluminate cement, yielding very inert and stable monolithic blocks of amorphous calcium phosphate (ACP). Two different compositions of industrial sludge were characterized and loaded in ratios ranging from 10 to 50 wt.%. Setting times and compressive strengths were recorded to establish the feasibility of this method to achieve a good handling and a safe landfilling of these samples. Short solidification periods were found and leaching tests showed an excellent retention for toxic metals (Zn, Ni, Cu, Cr and Mn) and for organic matter. Retentions over 99.9% for Zn and Mn were observed even for loadings as high as 50 wt.% of the wastes. The formation of ACP phase of low porosity and high stability accounted for the effective immobilization of the hazardous components of the wastes.

A study of the defect formation during the preparation of 2D-colloidal crystals by electrophoresis

Summary form only given, as follows. The preparation of structured materials with a controlled density of defects is becoming important for their applications as photonic crystals. 2D-colloidal crystals have been prepared through the assembly of charged colloidal particles by application of electric fields. The domain size of such structures has been determined by studying the influence of relevant experimental parameters.