D. Alonso Cerrón-Infantes

Hydrothermal synthesis (HTS) designates the use of hot liquid water as medium for chemical reactions. The technique is very well established for generating crystalline inorganic materials. Recently it was shown that HTS can also be used to prepare organic compounds, which are all bearing a high content in aromatics and heterocyclics. The technique is environmentally friendly for using solely water as medium, especially in comparison to conventional syntheses of such compounds. Here we present HTS of organic compounds in a fashion that allows for implementing it in the classroom. First, we show how HTS can be used as an example to introduce the timely concepts of green chemistry and sustainable syntheses. Second, we review organic cyclocondensation reactions including reaction equilibrium and enthalpic/entropic driving forces as well as real-life examples of cyclocondensation products, as HTS is especially amenable to cyclocondensations. Third, as liquid high-temperature water is well suited to review the temperature-dependence of certain physicochemical features, we provide interactive plots for exploring these data. Fourth, we develop a classroom friendly HTS of a simple organic colorant, that can be performed simple in kitchen pressure cookers. Fifth, at the hand of this classroom experiment we show how measures for the green-ness of a chemical synthesis, such as the Ecoscale are used.

Hydrothermal synthesis (HTS) designates the use of hot liquid water as medium for chemical reactions. The technique is very well established for generating crystalline inorganic materials. Recently it was shown that HTS can also be used to prepare organic compounds, which are all bearing a high content in aromatics and heterocyclics. The technique is environmentally friendly for using solely water as medium, especially in comparison to conventional syntheses of such compounds. Here we present HTS of organic compounds in a fashion that allows for implementing it in the classroom. First, we show how HTS can be used as an example to introduce the timely concepts of green chemistry and sustainable syntheses. Second, we review organic cyclocondensation reactions including reaction equilibrium and enthalpic/entropic driving forces as well as real-life examples of cyclocondensation products, as HTS is especially amenable to cyclocondensations. Third, as liquid high-temperature water is well suited to review the temperature-dependence of certain physicochemical features, we provide interactive plots for exploring these data. Fourth, we develop a classroom friendly HTS of a simple organic colorant, that can be performed simple in kitchen pressure cookers. Fifth, at the hand of this classroom experiment we show how measures for the green-ness of a chemical synthesis, such as the Ecoscale are used.

We report a facile green hydrothermal synthesis (HTS) of monoliths of hydrogels decorated with noble metal nanoparticles (NPs). The one-pot approach requires solely water, a polysaccharide able to form a hydrogel, and a salt precursor (M^x+-containing) for the metal NPs. The polysaccharide fulfills three roles: (i) it acts as the reducing agent of M^x+ to M⁰ under hydrothermal conditions, (ii) it stabilizes NPs surfaces, and (iii) it forms a hydrogel scaffold in which the metal NPs are embedded. The NPs’ localization in the hydrogel can be controlled through the gelation mechanism. Specifically, the NPs can either be located on and slightly under the surface of the hydrogel monoliths or in the volume. The former is found when a hydrogel monolith is crosslinked prior to HTS. The latter is observed when the HTS reaction mixture contains a polysaccharide dissolved in H₂O, which forms a hydrogel upon cooling. Furthermore, we studied the influence of HTS conditions on NP shapes. To find significant levers towards morphological control, a set of HTS experiments featuring broad ranges of reaction conditions was performed. Subsequently, we employed statistical analyses with multivariate regression fits to evaluate synthesis parameter effects. Thereby, we can link the synthesis parameters of temperature, time, precursor concentration, heating rate, choice of metallic precursor, and type of biopolymer, to morphology descriptors such as diameter, circularity, and polydispersity index. The presented approach is in fine compatible with broad arrays of NPs and can in principle be modified for different chemistries, thereby providing a tool for quantitatively assessing morphological impacts of reaction parameters.

We report on the hydrothermal polymerization (HTP) of porous polyimide (PI) networks using the medium H₂O and the comonomers 1,3,5-tris(4-aminophenyl)benzene (TAPB) and pyromellitic acid (PMA).

In this work, a novel class of fully organic, lightweight composite materials was prepared by incorporating highly crystalline, hydrothermally synthesized poly(p-phenylene pyromellitimide) (PPPI) microparticles into a commercial epoxy matrix. Particle loadings of up to 15 vol% could be achieved. Microstructural, mechanical, and thermal properties of these composites were investigated by scanning electron microscopy, three-point bending and Vickers hardness testing, dynamic mechanical analysis, nanoindentation, and thermogravimetric analysis. The incorporation of the PPPI filler particles into the epoxy matrix was found to be homogeneous. Powder X-ray diffraction shows that PPPI's crystallinity is retained in the composites, and infrared spectroscopy indicates a covalent bonding of PPPI to the epoxy matrix. Flexural modulus and storage modulus were increased by the PPPI addition, while the flexural strain at break was reduced. In contrast to that, the flexural strength remained unaffected by the incorporation of PPPI filler particles. Raising the filler content also resulted in an improvement of hardness. Furthermore, a decrease in glass-transition temperature with increasing PPPI content was observed, as well as a pronounced increase in thermal stability of the composites in comparison to the unfilled cured epoxy resin. These results indicate the high potential of this new class of composites with prospective applicability e.g. in the fields of sports equipment, aerospace, and automotive technology.