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Mesoporous phosphates are a group of nanostructured materials with promising applications, particularly in biomedicine and catalysis. However, their controlled synthesis via conventional template-based routes presents a number of challenges and limitations. Here, we show how to synthesize a mesoporous magnesium phosphate with a high surface area and a well-defined pore structure through thermal decomposition of a crystalline struvite (MgNH4PO4·6H2O) precursor. In a first step, struvite crystals with various morphologies and sizes, ranging from a few micrometers to several millimeters, had been synthesized from supersaturated aqueous solutions (saturation index (SI) between 0.5 and 4) at ambient pressure and temperature conditions. Afterwards, the crystals were thermally treated at 70-250 °C leading to the release of structurally bound water (H2O) and ammonia (NH3). By combining thermogravimetric analyses (TGA), scanning and transmission electron microscopy (SEM, TEM), N2 sorption analyses and small- and wide-angle X-ray scattering (SAXS/WAXS) we show that this decomposition process results in a pseudomorphic transformation of the original struvite into an amorphous Mg-phosphate. Of particular importance is the fact that the final material is characterized by a very uniform mesoporous structure with 2-5 nm wide pore channels, a large specific surface area of up to 300 m2 g-1 and a total pore volume of up to 0.28 cm3 g-1. Our struvite decomposition method is well controllable and reproducible and can be easily extended to the synthesis of other mesoporous phosphates. In addition, the so produced mesoporous material is a prime candidate for use in biomedical applications considering that magnesium phosphate is a widely used, non-toxic substance that has already shown excellent biocompatibility and biodegradability.

The controlled crystallisation of struvite (MgNH4PO4∙6H2O) is a viable means for the recovery and recycling of phosphorus (P) from municipal and industrial wastewaters. However, an efficient implementation of this recovery method in water treatment systems requires a fundamental understanding of struvite crystallisation mechanisms, including the behavior and effect of metal contaminants during struvite precipitation. Here, we studied the crystallisation pathways of struvite from aqueous solutions using a combination of ex situ and in situ time-resolved synthesis and characterization techniques, including synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) and cryogenic transmission electron microscopy (cryo-TEM). Struvite syntheses were performed both in the pure Mg-NH4-PO4 system as well as in the presence of cobalt (Co), which, among other metals, is typically present in waste streams targeted for P-recovery. Our results show that in the pure system and at Co concentrations &lt, 0.5 mM, struvite crystals nucleate and grow directly from solution, much in accordance with the classical notion of crystal formation. In contrast, at Co concentrations &ge, 1 mM, crystallisation was preceded by the transient formation of an amorphous nanoparticulate phosphate phase. Depending on the aqueous Co/P ratio, this amorphous precursor was found to transform into either (i) Co-bearing struvite (at Co/P &lt, 0.3) or (ii) cobalt phosphate octahydrate (at Co/P &gt, 0.3). These amorphous-to-crystalline transformations were accompanied by a marked colour change from blue to pink, indicating a change in Co2+ coordination in the formed solid from tetrahedral to octahedral. Our findings have implications for the recovery of nutrients and metals during struvite crystallisation and contribute to the ongoing general discussion about the mechanisms of crystal formation.

This chapter focuses on time-resolved studies of nanostructure development in sol-gel liquids, that is, diluted sols, wet gels, and drying thin fffilms. The most commonly investigated classes of sol-gel materials are silica, organically modified silica, template-directed mesostructured silica, titania and titania-based materials, zirconia and zirconia-based materials, and few others. After a brief overview of small-angle X-ray scattering (SAXS) theory and some experimental details, the chapter discusses separately each of these classes of sol-gel materials. Nearly all time-resolved SAXS studies on silica have been carried out starting with alkoxysilanes. The chapter discusses studies of systems with a single precursor under acidic and basic conditions, respectively, and reviews combinations of alkoxysilanes with other metal precursors and mixed organic-inorganic systems.

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Although clays are crucial mineral phases in Earth's weathering engine, it is unclear how they form in surface environments under (near-)ambient pressures and temperature. Most synthesis routes, attempting to give insights into the plausible mechanisms, rely on hydrothermal conditions, yet many geological studies showed that clays may actually form at moderate temperatures (< 100 deg. C) in most terrestrial settings. Here, we present the mechanism of the low-temperature (25-95 deg. C) crystallization of a synthetic Mg-clay, saponite. We describe the pathway at the various sub-stages of the reaction, as we derived from high-energy X-ray diffraction, infrared spectroscopy and transmission electron microscopy data. Our results reveal that saponite crystallizes via a two stage process: 1) a rapid (several minutes) co-precipitation where ~20% of the available magnesium becomes incorporated into an aluminosilicate network followed by 2) a much slower crystallization mechanism (many hours to days) where the remaining magnesium becomes gradually incorporated into the growing saponite sheet structure., manuscript + supporting information

By capillary electrophoresis (CE) in miniaturized lab-on-a-chip devices, integrated DNA sequencing and genetic diagnostics have become feasible. We introduce a principle of parallel optical processing to significantly enhance analysis capabilities. In a commercial microfluidic chip, a plug of DNA molecules was injected and the DNA molecules were CE-separated with a high relative sizing accuracy of >99%. Through an optical waveguide inscribed by femtosecond-laser writing a laser was launched perpendicularly into the microfluidic channel. A photomultiplier collected the fluorescence signals from a small detection window with a limit of detection of ~8 DNA molecules. In our approach, different sets of exclusively end-labeled DNA fragments are unambiguously identified by simultaneously launching several continuous-wave lasers, each modulated with a different frequency, detection of the frequency-encoded signals at different fluorescence wavelengths by a single ultrasensitive, albeit color-blind photomultiplier, and Fourier-domain frequency decoding. As a proof of principle, fragments from independent human genomic segments, associated with genetic predispositions to breast cancer and anemia, are simultaneously analyzed in a single flow experiment. This novel method of modulation-frequency-encoded fluorescence excitation opens new opportunities in genetic diagnostics. It enables the identification of end-labeled DNA samples of different genetic origin during their electrophoretic separation, opening perspectives for intrinsic size calibration, malign / healthy sample comparison, and exploitation of multiplex ligation-dependent probe amplification.

The formation of crystalline calcium sulfate (CaSO4*xH2O) polymorphs from aqueous solutions is assumed to occur via a single-step process following the classical nucleation paradigm. However, although recent research contradicts this classical picture and indicates that CaSO4*2H2O forms at room temperature through multiple steps at different length and time-scales, these steps have so far not been quantified. By using in situ and fast time-resolved small angle X-ray scattering (SAXS), we demonstrate that the nucleation and growth of CaSO4*2H2O involves at the very initial stages the formation of well-defined, primary species of < 3 nm in length (stage I). Stage II of the reaction is characterized by the arrangement of these primary species into domains, while in stage III these domains condense into larger aggregates. Based on volume fractions and electron density considerations we propose that the fast forming primary species from supersaturated aqueous CaSO4 solutions are composed of anhydrous Ca-SO4-cores. The first three stages of nucleation and aggregation of the primary species are followed by a final stage (stage IV), where the primary species grow within the aggregates, and eventually transform into gypsum (CaSO4*2H2O). This final stage was also confirmed through simultaneously collected wide-angle scattering (diffraction, WAXS) data, which clearly show the growth of gypsum during stage IV only. Our results demonstrate that CaSO4 formation is driven by the nucleation and aggregation of well-defined anhydrous Ca-SO4-cores that transform through hydration into gypsum through a complex nucleation and growth pathway., 41 pages of unformatted text, 5 main figures, 4 supporting figures