Despite the growing use of organic or mixed solvents in zeolite processing, most studies focus only on aqueous suspension systems. We investigated the colloidal characteristics of submicron-sized zeolite NaA in mixed ethanol–water solvents. The effects of the mixing ratio of solvents and various additives on the dispersion of the zeolite powders were studied. The zeolite NaA particles were destabilized in solvent mixtures at a high ethanol-to-water ratio, a reduction in the zeta potential was observed, and the destabilization was rationalized by the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory. An improved stabilization of the zeolite NaA suspensions was achieved in ethanol-rich solvent mixtures using nonionic low molecular weight organic additives, but not with their ionic counterparts such as anionic, cationic surfactants or inorganic acids or bases. Polyethylene glycol (PEG)-400 was found to be a good dispersant for the submicron-sized zeolite NaA particles in the ethanol–water mixtures, which was attributed to its interaction with the zeolite surface, leading to an increased zeta potential. The PEG-stabilized zeolite suspensions led to low suspension viscosities as well as uniform and consistent spin-coated films. 

Nanocellulose (NC)-based materials constitute a new class of bio-based building blocks that are inspiring advances for the next generation of high-performance sustainable materials. However, NC exhibits important drawbacks which limit its applications, such as its inherent interaction with bacteria and proteins, low conductivity, poor thermal stability, high water absorption (leading to, among other things, loss of structural integrity), etc. An efficient strategy to improve this, besides the possibility of introducing further properties, is through mineralization by in situ growing inorganic subcomponents to form NC-based hybrids. Following the example of nature which has been mineralizing biopolymers from the beginning of life to create complex structures (forming protective shields or structural supports), mineralization can be adopted in different (2D/3D) configurations, for instance, membranes, scaffolds, sponges, and monoliths (as per requirements), by in situ growing multiple subcomponents such as metal oxides, silicates, and metal–organic frameworks. The components act synergistically complementing each other, thus providing new functionalities that the components individually do not possess. For instance, it is possible to introduce properties such as self-healing behavior, magnetic character, antimicrobial properties, electrical and thermal conductivity, etc., which opens a wide range of opportunities in a variety of fields (e.g., energy, printed electronics, biomedicine, water/gas purification, etc.) of current interest and requirements. The present review paper summarizes and discusses the advanced applications of thus-formed nanocellulose hybrids, along with a general overview of the synthesis protocol and advanced characterization tools used to analyze these complex materials.

Biomethane is a renewable fuel with a small environmental footprint. In its production, the removal of CO2 from the fermentation gas is critical. Pressure and vacuum swing adsorption (PSA and VSA) processes have certain advantages over other processes for the removal. Silicoaluminophosphate-56 (SAPO-56) has promising properties as an adsorbent for PSA- or VSA-based upgrading of raw biogas. It is typically synthesized by using N,N,N', N'-tetramethyl-1,6-hexanediamine (TMHD) as a structure directing agent (SDA). In this study, TMHD was partly replaced with three different low-cost templates: isopropylamine (IPA), dibutylamine, and tripropylamine. SAPO-56 was co-crystallized with mixtures of templating amines with up to a ratio of 30%:70% of TMHD:IPA. With using TMHD and IPA, small and defined crystals of SAPO-56 plus SAPO-47 formed instead of the large aggregates of SAPO-56 that formed when only TMHD was used. Solid-state 13C NMR spectroscopy was used to show that the IPA and TMHD had not been decomposed and that both molecules were included within the assynthesized crystals of SAPO-56. Synthetic composition diagrams were drawn with respect to the P2O5, SiO2, and Al2O3 compositions of the reaction mixtures and the formed crystalline SAPOs. In relation to these diagrams, the domains for stability of SAPO-56 were contrasted with those of SAPO-11, -17, -20, and -47. In particular, it was observed that SAPO-47 co-crystallized with SAPO-56 when a very large fraction of IPA was used under otherwise optimized conditions. As consistent with other studies, the SAPO-56 synthesized with dual SDAs had a very high uptake of CO2 at conditions relevant for PSA- or VSA-driven upgrading of raw biogas into methane.

Carbon dioxide must be removed from biogas or natural gas to obtain compressed or liquefied methane, and adsorption-driven isolation of CO2 could be improved by developing new adsorbents. Zeolite adsorbents can select CO2 over CH4, and the adsorption of CH4 on zeolite vertical bar Na12-xKx vertical bar-A is significantly lower for samples with a high K+ content, i.e., x > 2. Nevertheless, we show, using H-1 NMR experiments, that these zeolites adsorb CH4 after long equilibration times. Pulsed-field gradient NMR experiments indicated that in large crystals of zeolites vertical bar Na12-xKx vertical bar-A, the long-time diffusion coefficients of CH4 did not vary with x, and the upper limit of the mean-square displacement was about 1.5 mu m, irrespective of the diffusion time. Also for zeolite vertical bar Na-12 vertical bar-A samples of three different particle sizes (similar to 0.44, similar to 2.9, and similar to 10.6 mu m), the upper limit of the mean-square displacement of CH4 was 1.5 mu m and largely independent of the diffusion time. This similarity provided further evidence for an intracrystalline diffusion restriction for CH4 within the medium- and large-sized zeolite A crystals and possibly of clustering and close contact among the small zeolite A crystals. The upper limit of the long-time diffusion coefficient of adsorbed CH4 was (at 1 atm and 298 K) about 10(-10) m(2)/s irrespective of the size of the zeolite particle or the studied content of K+ in zeolites and vertical bar Na-12 vertical bar-A. The T-1 relaxation time for adsorbed CH4 on zeolites vertical bar Na12-xKx vertical bar-A with x > 2 was smaller than for those with x < 2, indicating that the short-time diffusion of CH4 was hindered.

Raw biogas is a renewable fuel that can be upgraded into biomethane using several technologies that include adsorption-driven processes. We evaluated two adsorbents using a lab-sized pressure-vacuum-swing adsorption (PVSA) unit. Pellets of nano-sized zeolite A (bla421-A and INa10K21-A) were prepared together with a clay-based binder and sintered for 1-3 h at 450-650 degrees C. The pellets were subsequently PVSA tested to record the steady-state conditions and breakthrough of CO2. Numerous cycles were recorded with pellets that had been activated at 200 C under dynamic vacuum. The working capacity for CO2 removal exceeded 1.2 mol/kg at a raw-biogas pressure of 4 bar, and the nano-lbla40K21-A adsorbent had a low CH4 slip. 

Microporous polymers (MPs) are studied for their intriguing chemistry and physics as well as their potential application in catalytic transformations, gas-separation processes, water purification and so on. Here, we critically review MPs with respect to the sustainability aspects of their synthesis as well as their applications that have sustainable character. Some MPs have been synthesized from monomers derived from biomass resources, but there is certainly a large potential for further developments. There are also opportunities to improve the sustainability of MP synthesis in terms of the use of solvents, catalysts, and related aspects. The applications of MPs in processes related to sustainability depend upon multiple properties. A rich and flexible chemistry is important to applications as catalysts for, among other useful reactions, the photoreduction of CO2 and selective oxidation. The (ultra) micropore volume of MPs are crucial in gas-separation applications such as CO2 capture, and the chemisorption of CO2 on MP-tethered alkylamines could offer a means to remove that gas from dilute mixtures. When it comes to the storage of H-2 and CH4 in MPs for onboard use in fuel cell or biogas cars, volumetric capacity is paramount, meaning that the density of the MPs must be considered. Finally, for use in separation and purifications from liquid mixtures (aqueous or hydrocarbon-based), crosslinked MPs are more limited than the solution-processable MPs that can be more easily processed into films and membranes.