Ferrocene-Decorated Nanocrystalline Cellulose with Charge Carrier Mobility

Ferrocene-decorated cellulose nanowhiskers were prepared by the grafting of ethynylferrocene onto azide functionalized cotton-derived cellulose nanowhiskers using azide–alkyne cycloaddition. Successful surface modification and retention of the crystalline morphology of the nanocrystals was confirmed by elemental analysis, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The coverage with ferrocenyl is high (approximately 1.14 × 10^–3 mol g^–1 or 4.6 × 10¹³ mol cm^–2 corresponding to a specific area of 61 Ų per ferrocene). Cyclic voltammetry measurements of films formed by deposition of ferrocene-decorated nanowhiskers showed that this small spacing of redox centers along the nanowhisker surface allowed conduction hopping of electrons. The apparent diffusion coefficient for electron (or hole) hopping via Fe­(III/II) surface sites is estimated as <i>D</i>_app = 10^–19 m²s^–1 via impedance methods, a value significantly less than nonsolvated ferrocene polymers, which would be expected as the 1,2,3-triazole ring forms a rigid linker tethering the ferrocene to the nanowhisker surface. In part, this is believed to be also due to “bottleneck” diffusion of charges across contact points where individual cellulose nanowhiskers contact each other. However, the charge-communication across the nanocrystal surface opens up the potential for use of cellulose nanocrystals as a charge percolation template for the preparation of conducting films via covalent surface modification (with applications similar to those using adsorbed conducting polymers), for use in bioelectrochemical devices to gently transfer and remove electrons without the need for a solution-soluble redox mediator, or for the fabrication of three-dimensional self-assembled conducting networks

Thermodynamic Study of Ion-Driven Aggregation of Cellulose Nanocrystals

The thermodynamics of interactions between cations of the second group of the periodic table and differently negatively charged cellulose nanocrystals was investigated using isothermal titration calorimetry (ITC). The interaction of cations with the negatively charged CNCs was found to be endothermic and driven by an increase in entropy upon adsorption of the ions, due to an increase in degrees of freedom gained by the surface bound water upon ion adsorption. The effect was pH-dependent, showing an increase in enthalpy for cellulose suspensions at near-neutral pH (6.5) when compared to acidic pH (2). Sulfated cellulose nanoparticles were found to readily interact with divalent ions at both pH levels. The adsorption on carboxylate nanocrystals was found to be pH dependent, showing that the carboxylic group needs to be in the deprotonated form to interact with divalent ions. For the combined system (sulfate and carboxylate present at the same time), at neutral pH, the adsorption enthalpy was higher than the value obtained from cellulose nanocrystals containing a single functional group, while the association constant was higher due to an increased favorable entropic contribution. The higher entropic contribution indicates a more restricted surface-bound water layer when multiple functionalities are present. The stoichiometric number n was nearly constant for all systems, showing that the adsorption depends almost completely on the ion valency and on the amount of ionic groups on the CNC surface, independent of the type of functional group on the CNC surface as long as it is deprotonated. In addition, we showed that the reduction in Gibbs free energy drives the ionotropic gelation of nanocellulose suspensions, and we show that ITC is able to detect gel formation at the same time as determining the critical association concentration

Metal Catalyst-Dependent Poisoning Effect of Organic Sulfur Species for the Hydroconversion of 5‑Hydroxymethylfurfural

The transformation of 5-hydroxymethylfurfural (HMF) into ring-saturated furanics is a vital step in carbohydrate valorization. In this work, we report on the remarkable catalyst poisoning effect of numerous sulfur species for HMF hydroconversion. The presence of minor amounts of dimethyl sulfoxide (DMSO) affects ring-saturated product selectivity for the metal-catalyzed reactions using molecular hydrogen, whereas it fully deactivates catalytic transfer hydrogenation (CTH) in 2-propanol. The degree of poisoning correlates with the thermodynamic favorability of the metal sulfide formation. Reduced sulfur species (sulfide or thiol) are the ultimate metal poisoning agent. Their easy formation from more oxidized sulfur compounds explains the observed poisoning effect for such species. Here, the metal’s oxophilicity determines the catalysts’ behavior in the presence of oxidized sulfur species by forming (or not) poisoning sulfur–metal interactions. To overcome the sulfur poisoning, we propose DMSO removal with organic solvent extraction and catalyst oxidation post-treatment. These findings pinpoint the crucial, though overlooked, role of the biobased HMF purity for reductive catalytic studies. We provide a deeper understanding of the noble metal poisoning by sulfur from different origins and oxidation states that may be present during HMF hydroconversion

Synthesis of Novel Renewable Polyesters and Polyamides with Olefin Metathesis

Unsaturated and hydroxyl-functionalized C6-dicarboxylic acids were successfully synthesized via olefin metathesis from methyl vinyl glycolate (MVG), a renewable α-hydroxy C4-ester product from Lewis-acid carbohydrate conversion. Addition of a second-generation Hoveyda–Grubbs catalyst to neat MVG leads to a near quantitative yield of dimethyl-2,5-dihydroxy-3-hexene­dioate (DMDHHD). Additional hydrolysis and hydrogenation steps form interesting polymer building blocks like 2,5-dihydroxy-3-hexenedioic acid (DHHDA) and 2,5-dihydroxy­adipic acid (DHAA). Their use in polyester and polyamide synthesis is demonstrated after determination of their physical and spectroscopic characteristics. Copolymerization of DHHDA with l-lactic acid for instance produces a cross-linked poly­(l-lactic acid-co-DHHDA) polyester. Proof of cross-links is ascertained by NMR and FTIR. Substantial impact on the melting, thermal, and polar properties of PLA are observed already at low amounts of DHHDA (0.1 mol %) in accord with the presence of cross-links in the polymer. Biobased polyamides were also synthesized by equimolar reaction of DHHDA with hexamethylenediamine, producing a renewable polyamide analogue of the petroleum-based nylon-6,6. Interestingly, the as-synthesized polyamide (α-bishydroxylated unsaturated polyamide, HUPA) possesses similar thermal stability as nylon-6,6 but shows different chemical properties as a result of the double bond and α-hydroxy functionality

Colloidal Stability and Aggregation Mechanism in Aqueous Suspensions of TiO₂ Nanoparticles Prepared by Sol–Gel Synthesis

Understanding the colloidal stability and aggregation behavior of TiO2 nanoparticles in aqueous suspension is a prerequisite to tune supracolloidal structure formation. While the aggregation mechanism for dried TiO2 nanopowders is well documented, there is still work to be done to understand TiO2 nanoparticle aggregation in suspension. Therefore, this work focuses on the colloidal stability and aggregation mechanism of TiO2 nanoparticle aqueous suspensions prepared using a straightforward one-step sol–gel-based approach over a concentration range of 0.5–5 wt %. Fully crystalline nanoparticles consisting primarily of anatase were obtained. After assessing the colloidal stability of the as-prepared suspensions, small-angle X-ray scattering coupled with fractal analysis was carried out. This analysis showed, for the first time, how the TiO2 nanoparticle aggregation mechanismpredicted by the diffusion limited cluster–cluster aggregation (DLCA) and diffusion limited particle–cluster aggregation (DLA) theoriesdepends directly on the starting concentration in the aqueous suspensions. We found that concentrated suspensions favored DLA, while dilute suspensions tend to follow the DLCA mechanism. The effect of the aggregation mechanism on the aggregate shape is also discussed

Effect of Source on the Properties and Behavior of Cellulose Nanocrystal Suspensions

Sulfuric acid hydrolysis of native cellulose fibers results in colloidally stable suspensions of cellulose nanocrystals (CNCs). We have investigated the effect of the cellulose source on the suspension properties of CNCs extracted from cotton and wood sources using a comparable preparation strategy. The structural properties were revealed to be similar within the given standard deviation and prevalent polydispersity, whereas other properties such as liquid crystalline phase behavior, viscosity, diffusion coefficients, and surface tension were found to differ significantly. This study shows that ostensibly similar suspensions may exhibit rather differing behaviors and attempts to interpret this phenomenon. This finding shows that full characterization and a detailed description of the preparation of the nanocrystals used in publications are extremely important and should be reported in detail in all instances

Metal Ion and Guest-Mediated Spontaneous Resolution and Solvent-Induced Chiral Symmetry Breaking in Guanine-Based Metallosupramolecular Networks

Two-dimensional (2D) chirality has been actively studied in view of numerous applications of chiral surfaces such as in chiral resolutions and enantioselective catalysis. Here, we report on the expression and amplification of chirality in hybrid 2D metallosupramolecular networks formed by a nucleobase derivative. Self-assembly of a guanine derivative appended with a pyridyl node was studied at the solution-graphite interface in the presence and absence of coordinating metal ions. In the absence of coordinating metal ions, a monolayer that is representative of a racemic compound was obtained. This system underwent spontaneous resolution upon addition of a coordinating ion and led to the formation of a racemic conglomerate. The spontaneous resolution could also be achieved upon addition of a suitable guest molecule. The mirror symmetry observed in the formation of the metallosupramolecular networks could be broken via the use of an enantiopure solvent, which led to the formation of a globally homochiral surface

Chlorine-Resistant Epoxide-Based Membranes for Sustainable Water Desalination

The hypersensitivity of state-of-the-art polyamide-based membranes to chlorine is a major source of premature membrane failure and module replacement in water desalination plants. This problem can currently only be solved by implementing pre- and post-treatment processes involving additional chemical use and energy input, thus increasing environmental, capital, and operational costs. Herein, we report a chlorine-, acid-, and base-resistant desalination membrane comprising a cross-linked epoxide-based polymer-selective layer with permanent positive charges. These novel membranes exhibit high mono- and divalent salt rejection (81% NaCl, 87% CaCl2, 89% MgCl2) and a water permeance of ∼2 L m–2 h–1 bar–1, i.e., desalination performance comparable to that of commercially available nanofiltration membranes. Unlike conventional polyamide-based membranes, this new generation of epoxide-based membranes takes advantage of the intrinsic chemical stability of ether bonds while achieving the polymer and charge density needed for desalination. In doing so, the stability of these membranes opens new horizons for sustainable water purification and many other separations in harsh media in a variety of applications (e.g., solvent recovery, gas separations, redox flow batteries)