Polyurea-crosslinked biopolymer aerogel beads

Polyurea-crosslinked calcium alginate (X-Ca-alginate) and chitosan (X-chitosan) aerogel beads have been prepared via reaction of an aliphatic triisocyanate (Desmodur N3300) with the -OH groups of calcium alginate or the -NH2 groups of chitosan preformed wet gels, forming surface urethane or urea groups, respectively, and the subsequent formation of a polyurea conformal coating of the network via reaction of the triisocyanate with adsorbed water retained on the inner surfaces of the wet gels. That conformal coating is evident by SEM, which showed that all aerogels, native and crosslinked, were fibrous and their micromorphology did not change after crosslinking. The chemical identity of the new materials was confirmed with ATR-FTIR spectroscopy and solid-state 13C and 15N CPMAS NMR spectroscopy. The percent uptake of polyurea in X-Ca-alginate aerogels (43-66%) and X-chitosan aerogels (31-51%) was calculated from skeletal density data. This work expands the methodology for polymer-crosslinked alginate aerogels from monoliths to beads, and from alginates to chitosan, establishing its generality for all biopolymer aerogels. Possible applications of these materials include environmental remediation and conversion to carbon aerogels. This journal is © The Royal Society of Chemistry

New insight into sorption cycling stability of three Al-based MOF materials in water vapour

Three porous aluminium benzene-1,3,5-tricarboxylates MIL-96(Al), MIL-100(Al) and MIL-110(Al) materials were studied for their hydrothermal stability. The 40-cycles water vapour sorption experiments for the three samples were performed by varying the temperature between 40 and 140 °C at 75% relative humidity to simulate working conditions for materials used in water sorption-based low-T heat storage and reallocation applications. The materials were characterized by powder X-ray diffraction, N(2) physisorption, and Nuclear Magnetic Resonance and Infrared spectroscopies before and after the cycling tests. The results showed that the structure of MIL-110(Al) lost its crystallinity and porosity under the tested conditions, while MIL-96(Al) and MIL-100(Al) exhibited excellent hydrothermal stability. The selection of structures, which comprise the same type of metal and ligand, enabled us to attribute the differences in stability primarily to the known variances in secondary building units and the shielding of potential water coordination sites due to the differences in pore accessibility for water molecules. Additionally, our results revealed that water adsorption and desorption at tested conditions (T, RH) is very slow for all three materials, being most pronounced for the MIL-100(Al) structure

Mechanically Strong Polyurea/Polyurethane-Cross-Linked Alginate Aerogels

Two types of preformed alginate wet gels, one with a low (30-35%) and the other with a high (65-75%) content of glucuronic acid, were reacted with an aliphatic triisocyanate that was priorly allowed to diffuse in the pores. This reaction formed urethane groups on the surface of the alginate framework and also formed a polyurea (PUA) network connecting these urethane groups via respective reactions of the triisocyanate with alginate surface -OH groups or with gelation water remaining adsorbed on the inner surfaces of the wet gels. These processes formed a conformal nanothin film of PUA around the alginate network. After drying the wet gels with the supercritical fluid CO2, we obtained PUA/polyurethane-cross-linked alginate (X-alginate) aerogels. Although X-alginate aerogels are essentially copolymers, unlike all copolymers mentioned in previous literature reports, the relative topology of the alginate and the cross-linker is defined at the nanoscopic scale rather than at the molecular level. For the systematic study of X-alginate aerogels as a function of synthetic conditions, the experimental protocol was designed according to the central circumscribed rotatory design model using the alginate and the triisocyanate concentration as independent variables. Empirical models were derived for all relevant material properties by fitting experimental data to the two independent variables. The chemical identity of all samples was confirmed with attenuated total reflectance-Fourier transform infrared spectroscopy and solid-state C-13 and N-15 cross-polarization magic angle spinning NMR spectroscopy. The percentage of PUA uptake in X-alginate aerogels (58-98%) was calculated from skeletal density data. Scanning electron microscopy showed that all samples were nanofibrous, indicating that PUA coated conformally the skeletal network of both alginates, and the micromorphology remained the same as in the native (non-cross-linked) samples. X-alginate aerogels are mechanically strong materials, in contrast to their native counterparts, which are extremely weak mechanically. Compared to various organic aerogels from the literature, X-alginate aerogels can be as stiff as many other polymeric aerogels with 2 or 3 times higher densities. In addition, X-alginate aerogels are good candidates for sound insulation applications, as the speed of sound in most samples was estimated to be significantly lower than the speed of sound in dry air

Impact of the Zn source on the RSN-type zeolite formation

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Study of Hydrothermal Stability and Water Sorption Characteristics of 3-Dimensional Zn-Based Trimesate

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