Hydrazide- and Diazole-Linked Covalent Organic Frameworks and Their Water Harvesting Properties

We report a retrosynthetic strategy and its implementation to making covalent organic frameworks (COFs) with irreversible hydrazide and diazole (oxadiazole and thiadiozole) linkages. This involved the synthesis of a series of 2D and 3D hydrazine-linked frameworks, followed by their oxidation and dehydrative cyclization. Each linkage synthesis and functional group transformation—hydrazine, hydrazide, oxadiazole, and thiadia-zole—was evidenced by 15N multi-CP-MAS NMR. In addition, the isothermal water uptake profiles of these frameworks were studied, leading to the discovery that one hydrazide-linked COF is suitable for water harvest-ing from air in arid conditions. These COFs displayed characteristic S-shaped water sorption profiles, a steep pore-filling step below 18% relative humidity at 25 °C, and a total uptake capacity of 0.45 g g–1 at P/Psat = 0.95. In addition, a total of ten 2D and 3D structures with various such linkages were studies for their affinity to water. We found that even small changes made on the molecular level can lead to major differences in the water isotherm profiles and therefore pointing to the utility of water sorption analysis as a complementary analytical tool to study linkage transformations.

Analyzing the effects of thermal stress on insulator papers by solid-state 13C NMR spectroscopy

Million tons of cellulosic paper have been used for insulating coils in oil-filled electrical power transformers, thereby assuring the electricity supply for our societies. The high working temperatures in transformers constantly degrade paper insulators throughout their service life of up to 40 years. We approached the structural changes in oil-immersed cellulosic paper samples upon thermal stress in a study that compared unbleached softwood Kraft paper used as insulator paper with pure cotton cellulose paper. The model experiments used a thermal treatment in transformer oil at 170 °C for up to 14 days. The samples were characterized by means of 13C CP/MAS NMR spectroscopy, mainly based on deconvolution of the C4 resonance. An automated, fast, and reproducible C4 resonance deconvolution employing the “Peak Analyzer” tool of OriginPro 2020 (OriginLab Corporation, USA) was developed and used to exploit 13C CP/MAS NMR spectroscopy for the characterization of thermally stressed paper samples. Our results show that thermally induced structural changes depend heavily on the composition of paper, that hornification and coalescence of fibrils take place, and that the allomorph composition of cellulose crystallites is altered under the given conditions. Graphical abstract

N M R Studies of Coal

<p>Carbon-13 CP/MAS NMR was used to study a selection of fifty-seven New Zealand coals and ten Australian coals. The coal rank varied from lignite to semianthracite. A qualitative survey of the plant origins of NMR signals was followed by an EPR study of the unpaired spin-species in coal. The quantitative reliability of the NMR response of coal was analysed in relaxation and "visibility" studies. Different approaches to the problem of accounting for intensity in spinning-side-band (SSB) signals were assessed. The most successful approach was found to be the complete computer simulation of the spectrum from combinations of SSB intensity patterns broadened by a mixture of Lorentzian and Gaussian lineshapes. This method of analysis produced oxygen contents that showed a good correlation with oxygen contents (by difference) from Ultimate analysis. The resultant carbon, hydrogen and oxygen functional group analyses allowed considerable insight into the depositional influences on, and alteration of, the coal structure with increasing degree of coalification.</p>

N M R Studies of Coal

<p>Carbon-13 CP/MAS NMR was used to study a selection of fifty-seven New Zealand coals and ten Australian coals. The coal rank varied from lignite to semianthracite. A qualitative survey of the plant origins of NMR signals was followed by an EPR study of the unpaired spin-species in coal. The quantitative reliability of the NMR response of coal was analysed in relaxation and "visibility" studies. Different approaches to the problem of accounting for intensity in spinning-side-band (SSB) signals were assessed. The most successful approach was found to be the complete computer simulation of the spectrum from combinations of SSB intensity patterns broadened by a mixture of Lorentzian and Gaussian lineshapes. This method of analysis produced oxygen contents that showed a good correlation with oxygen contents (by difference) from Ultimate analysis. The resultant carbon, hydrogen and oxygen functional group analyses allowed considerable insight into the depositional influences on, and alteration of, the coal structure with increasing degree of coalification.</p>

N M R Studies of Coal

<p>Carbon-13 CP/MAS NMR was used to study a selection of fifty-seven New Zealand coals and ten Australian coals. The coal rank varied from lignite to semianthracite. A qualitative survey of the plant origins of NMR signals was followed by an EPR study of the unpaired spin-species in coal. The quantitative reliability of the NMR response of coal was analysed in relaxation and "visibility" studies. Different approaches to the problem of accounting for intensity in spinning-side-band (SSB) signals were assessed. The most successful approach was found to be the complete computer simulation of the spectrum from combinations of SSB intensity patterns broadened by a mixture of Lorentzian and Gaussian lineshapes. This method of analysis produced oxygen contents that showed a good correlation with oxygen contents (by difference) from Ultimate analysis. The resultant carbon, hydrogen and oxygen functional group analyses allowed considerable insight into the depositional influences on, and alteration of, the coal structure with increasing degree of coalification.</p>

N M R Studies of Coal

<p>Carbon-13 CP/MAS NMR was used to study a selection of fifty-seven New Zealand coals and ten Australian coals. The coal rank varied from lignite to semianthracite. A qualitative survey of the plant origins of NMR signals was followed by an EPR study of the unpaired spin-species in coal. The quantitative reliability of the NMR response of coal was analysed in relaxation and "visibility" studies. Different approaches to the problem of accounting for intensity in spinning-side-band (SSB) signals were assessed. The most successful approach was found to be the complete computer simulation of the spectrum from combinations of SSB intensity patterns broadened by a mixture of Lorentzian and Gaussian lineshapes. This method of analysis produced oxygen contents that showed a good correlation with oxygen contents (by difference) from Ultimate analysis. The resultant carbon, hydrogen and oxygen functional group analyses allowed considerable insight into the depositional influences on, and alteration of, the coal structure with increasing degree of coalification.</p>

Chitin Cryogels Prepared by Regeneration from Phosphoric Acid Solutions

Cryogelation is a developing technique for the production of polysaccharide materials for biomedical applications. The formation of a macroporous structure during the freeze-drying of polysaccharide solutions creates biomaterials suitable for tissue engineering. Due to its availability, biocompatibility, biodegradability, and non-toxicity, chitin is a promising natural polysaccharide for the production of porous materials for tissue engineering; however, its use is limited due to the difficulty of dissolving it. This work describes the preparation of cryogels using phosphoric acid as the solvent. Compared to typical chitin solvents phosphoric acid can be easily removed from the product and recovered. The effects of chitin dissolution conditions on the structure and properties of cryogels were studied. Lightweight (ρ 0.025–0.059 g/cm3), highly porous (96–98%) chitin cryogels with various heterogeneous morphology were produced at a dissolution temperature of 20 ± 3 °C, a chitin concentration of 3–15%, and a dissolution time of 6–25 h. The crystallinity of the chitin and chitin cryogels was evaluated by 13C CP-MAS NMR spectroscopy and X-ray diffractometry. Using FTIR spectroscopy, no phosphoric acid esters were found in the chitin cryogels. The cryogels had compressive modulus E values from 118–345 kPa and specific surface areas of 0.3–0.7 m2/g. The results indicate that chitin cryogels can be promising biomaterials for tissue engineering.

Effect of Dendritic Side Groups on the Mobility of Modified Poly(epichlorohydrin) Copolymers

The macromolecular dynamics of dendronized copolymer membranes (PECHs), obtained by chemical modification of poly(epichlorohydrin) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, was investigated. In response to a thermal treatment during membrane preparation, these copolymers show an ability to change their shape, achieve orientation, and slightly crystallize, which was also observed by CP-MAS NMR, XRD, and DSC. The phenomenon was deeply analyzed by dielectric thermal analysis. The dielectric spectra show the influence of several factors such as the number of dendritic side groups, the orientation, their self-assembling dendrons, and the molecular mobility. The dielectric spectra present a sub-Tg dielectric relaxation, labelled as γ, associated with the mobility of the benzyloxy substituent of the dendritic group. This mobility is not related to the percentage of these lateral chains but is somewhat hindered by the orientation of the dendritic groups. Unlike other less complex polymers, the crystallization was dismantled before the appearance of the glass transition (αTg). Only after that, clearing transition (αClear) can be observed. The PECHs were flexible and offered a high free volume, despite presenting a high degree of modifications. However, the molecular mobility is not independent in each phase and the self-assembling dendrons can be eventually fine-tuned according to the percentage of grafted groups.

Characterization of organic compost from urban pruning waste

Urban trees positively influence the quality of life in cities, but they need to be pruned regularly, generating a large amount of solid urban waste. This study aimed to compost urban pruning waste, evaluate its physical, chemical, structural characteristics, and determine its potential as a substrate to produce forest seedlings. The pruning residue was obtained from the Rio de Janeiro Municipal Cleaning Company (COMLURB) - Brazil. Twigs and leaves ≤ 8 cm in diameter were chopped and arranged on a trapezoidal windrow. Temperature, humidity, and aeration were controlled throughout the composting process. Irrigation and turning were carried out as needed. The composting process took 122 days. The compost was dried, processed, and evaluated for physical and chemical characteristics. The leachate was collected and characterized by 13C CP MAS NMR. The temperature patterns were consistent with the thermophilic, mesophilic, and maturation stages. Part of the chemical and physical characteristics of the compound was classified as adequate, according to the literature. The leachate contained large amounts of C alkyl and low amounts of C carbonyl at all times of composting. The characteristics determined indicated that the composting process was interrupted before complete maturation was achieved. However, the compound can be combined with other materials to produce a complete substrate.