Suitability of bio-desiccants for energy wheels in HVAC applications

Government of the Saskatchewan (Ministry of Agriculture), Agricultural Development Fund: Project #20160266Peer ReviewedThis paper investigates the suitability of bio-desiccants for moisture recovery in energy wheels. Bio-desiccants are environment-friendly materials that have high water vapor adsorption capacities. The main contribution of this paper is that it reports the latent effectiveness of flax-fiber (bio-desiccant) coated energy wheels for a wide range of operating conditions and compares the effectiveness of the flax-fiber wheels with wheels that are coated with commercially available desiccants and other biomaterials. The moisture transfer performance of a flax-fiber coated exchanger is determined using a small-scale test facility and two different experimental methods: single step change tests and cyclic tests. The test results are used to verify the applicability of an effectiveness correlation from the literature. Using the energy wheel correlation and the sorption isotherms, the latent effectiveness of commercially available energy wheels coated with molecular sieve, ion exchange resin and silica gel desiccants are obtained and compared with that of bio-desiccants (flax fiber and starch particles). The highest latent effectiveness is obtained for silica gel followed by starch particles, ion exchange resin, flax-fiber and molecular sieve. The results from this study will be useful in research and development of bio-materials for energy recovery systems for building applications

Nano-Sized Cyclodextrin-Based Molecularly Imprinted Polymer Adsorbents for Perfluorinated Compounds—A Mini-Review

Recent efforts have been directed towards the design of efficient and contaminant selective remediation technology for the removal of perfluorinated compounds (PFCs) from soils, sediments, and aquatic environments. While there is a general consensus on adsorption-based processes as the most suitable methodology for the removal of PFCs from aquatic environments, challenges exist regarding the optimal materials design of sorbents for selective uptake of PFCs. This article reviews the sorptive uptake of PFCs using cyclodextrin (CD)-based polymer adsorbents with nano- to micron-sized structural attributes. The relationship between synthesis of adsorbent materials and their structure relate to the overall sorption properties. Hence, the adsorptive uptake properties of CD-based molecularly imprinted polymers (CD-MIPs) are reviewed and compared with conventional MIPs. Further comparison is made with non-imprinted polymers (NIPs) that are based on cross-linking of pre-polymer units such as chitosan with epichlorohydrin in the absence of a molecular template. In general, MIPs offer the advantage of selectivity, chemical tunability, high stability and mechanical strength, ease of regeneration, and overall lower cost compared to NIPs. In particular, CD-MIPs offer the added advantage of possessing multiple binding sites with unique physicochemical properties such as tunable surface properties and morphology that may vary considerably. This mini-review provides a rationale for the design of unique polymer adsorbent materials that employ an intrinsic porogen via incorporation of a macrocyclic compound in the polymer framework to afford adsorbent materials with tunable physicochemical properties and unique nanostructure properties

Physicochemical Properties and the Gelation Process of Supramolecular Hydrogels: A Review

Supramolecular polysaccharide-based hydrogels have attracted considerable research interest recently due to their high structural functionality, low toxicity, and potential applications in foods, cosmetics, catalysis, drug delivery, tissue engineering and the environment. Modulation of the stability of hydrogels is of paramount importance, especially in the case of stimuli-responsive systems. This review will update the recent progress related to the rational design of supramolecular hydrogels with the objective of understanding the gelation process and improving their physical gelation properties for tailored applications. Emphasis will be given to supramolecular host–guest systems with reference to conventional gels in describing general aspects of gel formation. A brief account of the structural characterization of various supramolecular hydrogels is also provided in order to gain a better understanding of the design of such materials relevant to the nature of the intermolecular interactions, thermodynamic properties of the gelation process, and the critical concentration values of the precursors and the solvent components. This mini-review contributes to greater knowledge of the rational design of supramolecular hydrogels with tailored applications in diverse fields ranging from the environment to biomedicine

A Review on the Design and Hydration Properties of Natural Polymer-Based Hydrogels

Hydrogels are hydrophilic 3D networks that are able to ingest large amounts of water or biological fluids, and are potential candidates for biosensors, drug delivery vectors, energy harvester devices, and carriers or matrices for cells in tissue engineering. Natural polymers, e.g., cellulose, chitosan and starch, have excellent properties that afford fabrication of advanced hydrogel materials for biomedical applications: biodegradability, biocompatibility, non-toxicity, hydrophilicity, thermal and chemical stability, and the high capacity for swelling induced by facile synthetic modification, among other physicochemical properties. Hydrogels require variable time to reach an equilibrium swelling due to the variable diffusion rates of water sorption, capillary action, and other modalities. In this study, the nature, transport kinetics, and the role of water in the formation and structural stability of various types of hydrogels comprised of natural polymers are reviewed. Since water is an integral part of hydrogels that constitute a substantive portion of its composition, there is a need to obtain an improved understanding of the role of hydration in the structure, degree of swelling and the mechanical stability of such biomaterial hydrogels. The capacity of the polymer chains to swell in an aqueous solvent can be expressed by the rubber elasticity theory and other thermodynamic contributions; whereas the rate of water diffusion can be driven either by concentration gradient or chemical potential. An overview of fabrication strategies for various types of hydrogels is presented as well as their responsiveness to external stimuli, along with their potential utility in diverse and novel applications. This review aims to shed light on the role of hydration to the structure and function of hydrogels. In turn, this review will further contribute to the development of advanced materials, such as “injectable hydrogels” and super-adsorbents for applications in the field of environmental science and biomedicine

A Spectroscopic Study of a Cyclodextrin-Based Polymer and the “Molecular Accordion” Effect

The formation of host-guest complexes was studied for two hosts; β-cyclodextrin (β-CD) and a cross-linked polymer containing an equimolar ratio of β-CD and hexamethylene diisocyanate (HDI), denoted as HDI-1. The thermodynamics of host-guest binding was studied with 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) using steady-state fluorescence spectroscopy in aqueous solution at variable temperature and ambient pH. The association of 1,8-ANS with β-CD and HDI-1, showed a fluorescence enhancement of ~4 and 12 units, respectively. Greater fluorescence enhancement for the polymer/dye system indicates the presence of multiple binding sites (inclusion vs. interstitial). By contrast, the β-CD/dye system adopt trends that indicate the formation of well-defined inclusion complexes. HDI-1 has inclusion sites (β-CD) and interstitial domains (HDI) that afford dual binding with variable binding affinity. Simplified binding models employed herein address the role of inclusion binding without an explicit account for higher order or secondary binding equilibria. The approximate 1:1 binding constant (K1:1) for CD/1,8-ANS is about two-fold greater over the HDI-1/1,8-ANS system, where HDI-1 displays cooperative effects among the polymer subunits, according to changes in relative fluorescence intensity related to structural transitions and binding site loci. The relative fluorescence intensities of the HDI-1/1,8-ANS system relate to a reversible temperature-driven structural transition (globular ⇌ extended) between 5 ºC and 60 °C of the polymer, in contrast to the β-CD/1,8-ANS complex. The temperature- and guest-driven structural transition, described as the “molecular accordion” effect is supported by new insight provided by complementary fluorescence and 1H NMR spectral results in aqueous solution.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Spectroscopic and Thermodynamic Study of Biopolymer Adsorption Phenomena in Heterogeneous Solid–Liquid Systems

Molecular selective adsorption processes at the solid surface of biopolymers in mixed solvent systems are poorly understood due to manifold interactions. However, the ability to achieve adsorptive fractionation of liquid mixtures is posited to relate to the role of specific solid–liquid interactions at the adsorbent interface. The hydration of solid biopolymers (amylose, amylopectin, cellulose) in binary aqueous systems is partly governed by the relative solvent binding affinities with the biopolymer surface sites, in accordance with the role of textural and surface chemical properties. While molecular models that account for the surface area and solvent effects provide reliable estimates of hydration energy and binding affinity parameters, spectroscopic and thermal methods offer a facile alternative experimental approach to account for detailed aspects of solvation phenomena at biopolymer interfaces that involve solid−liquid adsorption. In this report, thermal and spectroscopic methods were used to understand the interaction of starch- and cellulose-based materials in water–ethanol (W–E) binary mixtures. Batch adsorption studies in binary W–E mixtures reveal the selective solvent uptake properties by the biomaterials, in agreement with their solvent swelling in pure water or ethanol. The nature, stability of the bound water, and the thermodynamic properties of the biopolymers in variable hydration states were probed via differential scanning calorimetry and Raman spectroscopy. The trends in biopolymer–solvent interactions are corroborated by dye adsorption and scanning electron microscopy, indicating that biopolymer adsorption properties in W–E mixtures strongly depend on the surface area, pore structure, and accessibility of the polar surface groups of the biopolymer systems, in agreement with the solvent-selective uptake results reported herein

Preparation and Characterization of a Polymer-Based “Molecular Accordion”

A urethane-based polymer material, denoted HDI-1, was obtained from the addition reaction of β-cyclodextrin (β-CD) with 1,6-hexamethylene diisocyanate (HDI) at the 1:1 mole ratio. In aqueous solution and ambient temperature conditions, HDI-1 adopts a compact (coiled) morphology where the cross-linker units become coiled and are partially self-included in the annular hydroxyl (interstitial) region of β-CD. As the temperature is raised or as <i>p</i>-nitrophenol (PNP) was included within the β-CD cavity and the noninclusion sites of the polymer, an extended (uncoiled) morphology was adopted. The equilibrium distribution between the extended and the compact forms of HDI-1 is thermally and chemically switchable, in accordance with the hydration properties and host–guest chemistry of this responsive polymer system. The molecular structure of this water-soluble urethane polymer and its host–guest complexes with PNP were investigated using spectroscopic (Raman, ¹H NMR, induced circular dichroism), dynamic light scattering (DLS), and calorimetric (DSC) methods in aqueous solution at ambient pH, and compared with native β-CD. This study reports on the unique supramolecular properties of a polymer that resembles a thermally and chemically responsive “molecular accordion”

Renewable Starch Carriers with Switchable Adsorption Properties

This Research Article describes a systematic study on the structure and sorption properties of Carnation-based starch-particles (SPs) by various techniques. Structural characterization of the SPs utilized spectroscopy (¹H NMR and FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The sorption properties of the SPs were characterized by solvent swelling and uptake isotherms with cationic adsorbates at equilibrium and kinetic conditions. The surface area (SA; ∼3–588 m²/g) of the SPs was estimated using nitrogen gas and dye adsorption isotherm methods, where the range in SA was related to solvent swelling effects on the textural properties. The SPs contain lipid constituents according to results obtained by ¹H NMR spectroscopy, DSC, and confocal laser microscopy (CLM) with iodine staining. The unique solvent swelling properties of the SPs reveal greater swelling in water over ethanol. SPs display preferential equilibrium uptake of methylene blue (MB; <i>Q</i>_m ≈ 716 mg/g) over cetylpyridinium bromide (CPB; <i>Q</i>_m ≈ 292 mg/g). The uptake of MB was reduced by an order of magnitude (<i>Q</i>_m ≈ 67 mg/g) when the SPs were doped with CPB, further revealing the role of competitive adsorption and similar binding modes for MB and CPB. The doping of SPs with CPB provide a facile approach for alteration of the surface functional properties such as the hydrophile–lipophile character, surface charge, and hydration properties of the SPs. Evidence of monolayer and multilayer adsorption of CPB onto SPs lead to switchable adsorption properties where such amphiphile surface patterning can be harnessed to yield materials with unique controlled-release properties for diverse chemical systems according to tunable surface charge using self-assembly

Characterization and Dynamic Properties for the Solid Inclusion Complexes of β‑Cyclodextrin and Perfluorooctanoic Acid

The structural characterization and dynamic properties of solid-state inclusion complexes (ICs) formed between β-cyclodextrin (β-CD; host) and perfluorooctanoic acid (PFOA; guest) were investigated using ¹³C NMR spectroscopy. The 1:1 and 2:1 host/guest solid-state complexes were prepared using a modified <i>dissolution</i> method to obtain complexes with high phase purity. These complexes were further characterized using differential scanning calorimetry (DSC), FT-IR spectroscopy, powder X-ray diffraction (PXRD), ¹⁹F direct polarization (DP), and ¹³C cross-polarization (CP) with magic-angle spinning (MAS) NMR spectroscopy. The ¹⁹F → ¹³C CP results provided unequivocal support for the formation of well-defined inclusion compounds. The phase purity of the complexes formed between β-CD and PFOA were assessed using the ¹⁹F DP NMR technique at variable temperature (VT) and MAS at 20 kHz. The complexes were found to be of high phase purity when prepared in accordance with the modified dissolution method. The motional dynamics of the guest in the solid complexes were assessed using <i>T</i>₁/<i>T</i>₂/<i>T</i>_1ρ relaxation NMR methods at ambient and VT conditions. The relaxation data revealed reliable and variable guest dynamics for the 1:1 versus 2:1 complexes at the VTs investigated. The motional dynamics of the guest molecules involve an ensemble of axial motions of the whole chain and 120° rotational jumps of the methyl (CF₃) group at the termini of the perfluorocarbon chain. The axial and rotational dynamics of the guest in the 1:1 and 2:1 complexes differ in distribution and magnitude in accordance with the binding geometry of the guest within the host