Amir Sheikhi

Copper Removal Using Electrosterically Stabilized Nanocrystalline Cellulose

Removal of heavy metal ions such as copper using an efficient and low-cost method with low ecological footprint is a critical process in wastewater treatment, which can be achieved in a liquid phase using nanoadsorbents such as inorganic nanoparticles. Recently, attention has turned toward developing sustainable and environmentally friendly nanoadsorbents to remove heavy metal ions from aqueous media. Electrosterically stabilized nanocrystalline cellulose (ENCC), which can be prepared from wood fibers through periodate/chlorite oxidation, has been shown to have a high charge content and colloidal stability. Here, we show that ENCC scavenges copper ions by different mechanisms depending on the ion concentration. When the Cu(II) concentration is low (C0≲200 ppm), agglomerates of starlike ENCC particles appear, which are broken into individual starlike entities by shear and Brownian motion, as evidenced by photometric dispersion analysis, dynamic light scattering, and transmission electron microscopy. On the other hand, at higher copper concentrations, the aggregate morphology changes from starlike to raftlike, which is probably due to the collapse of protruding dicarboxylic cellulose (DCC) chains and ENCC charge neutralization by copper adsorption. Such raftlike structures result from head-to-head and lateral aggregation of neutralized ENCCs as confirmed by transmission electron microscopy. As opposed to starlike aggregates, the raftlike structures grow gradually and are prone to sedimentation at copper concentrations C0≳500 ppm, which eliminates a costly separation step in wastewater treatment processes. Moreover, a copper removal capacity of ∼185 mg g(-1) was achieved thanks to the highly charged DCC polyanions protruding from ENCC. These properties along with the biorenewability make ENCC a promising candidate for wastewater treatment, in which fast, facile, and low-cost removal of heavy metal ions is desired most.

Electroacoustic characterization of conventional and electrosterically stabilized nanocrystalline celluloses

Nanoparticles are widely used as drug carriers, texturizing agents, fat replacers, and reinforcing inclusions. Because of a growing interest in non-renewable materials, much research has focused on nanocellulose derivatives, which are biodegradable, biocompatible, and easily synthesized. Among nanocellulose derivatives, nanocrystalline cellulose (NCC) has been known for half a century, but its utility is limited because its colloidal stability is challenged by added salt. On the other hand, electrosterically stabilized nanocrystalline cellulose (ENCC) has recently been observed to have superior colloidal stability. Here, we use electrokinetic-sonic-amplitude (ESA) and acoustic attenuation spectroscopy to assess NCC and ENCC ζ-potentials and sizes over wide ranges of pH and ionic strength. The results attest to a soft, porous layer of dicarboxylic cellulose (DCC) polymers that expands and collapses with ionic strength, electrosterically stabilizing ENCC dispersions at ionic strengths up to at least 200mmol L(-1).

Highly Stable, Functional Hairy Nanoparticles and Biopolymers from Wood Fibers: Towards Sustainable Nanotechnology

Nanoparticles, as one of the key materials in nanotechnology and nanomedicine, have gained significant importance during the past decade. While metal-based nanoparticles are associated with synthetic and environmental hassles, cellulose introduces a green, sustainable alternative for nanoparticle synthesis. Here, we present the chemical synthesis and separation procedures to produce new classes of hairy nanoparticles (bearing both amorphous and crystalline regions) and biopolymers based on wood fibers. Through periodate oxidation of soft wood pulp, the glucose ring of cellulose is opened at the C2-C3 bond to form 2,3-dialdehyde groups. Further heating of the partially oxidized fibers (e.g., T = 80 °C) results in three products, namely fibrous oxidized cellulose, sterically stabilized nanocrystalline cellulose (SNCC), and dissolved dialdehyde modified cellulose (DAMC), which are well separated by intermittent centrifugation and co-solvent addition. The partially oxidized fibers (without heating) were used as a highly reactive intermediate to react with chlorite for converting almost all aldehyde to carboxyl groups. Co-solvent precipitation and centrifugation resulted in electrosterically stabilized nanocrystalline cellulose (ENCC) and dicarboxylated cellulose (DCC). The aldehyde content of SNCC and consequently surface charge of ENCC (carboxyl content) were precisely controlled by controlling the periodate oxidation reaction time, resulting in highly stable nanoparticles bearing more than 7 mmol functional groups per gram of nanoparticles (e.g., as compared to conventional NCC bearing << 1 mmol functional group/g). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) attested to the rod-like morphology. Conductometric titration, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), electrokinetic-sonic-amplitude (ESA) and acoustic attenuation spectroscopy shed light on the superior properties of these nanomaterials.

Macromolecule-based platforms for developing tailor-made formulations for scale inhibition

Inorganic crystallization, commonly referred to as mineral scale formation, has posed tremendous challenges and is one of the leading assurance problems in water-based industries. A detailed understanding of the mechanism and influencing factors for the initiation and build-up of deposited scale is not only highly relevant for many industries but has also catalyzed academic research in developing efficient antiscalants. Macromolecules that can stop nucleation and inhibit crystallization or interact with forming crystals and modify their morphology to retard further growth have been the focus of intense scientific endeavors. There has been immense activity in developing additives which can regulate unwanted inorganic crystallization and understanding the complexity of how they work in preventing scale deposits. In this review, after a summary of the controlling parameters that define mineral scale growth, we review opportunities generated by using macromolecules as a platform for developing inhibitors for the two most common scale deposits, i.e. calcium salts and silica, with a discussion on their efficiencies in controlling nucleation and changing growing crystal morphology.

Design and Synthesis of Dendrimers with Facile Surface Group Functionalization, and an Evaluation of Their Bactericidal Efficacy

We report a versatile divergent methodology to construct dendrimers from a tetrafunctional core, utilizing the robust copper(I) catalyzed alkyne-azide cycloaddition (CuAAC, “click”) reaction for both dendrimer synthesis and post-synthesis functionalization. Dendrimers of generations 1–3 with 8–32 protected or free OH and acetylene surface groups, were synthesized using building blocks that included acetylene- or azide-terminated molecules with carboxylic acid or diol end groups, respectively. The acetylene surface groups were subsequently used to covalently link cationic amino groups. A preliminary evaluation indicated that the generation one dendrimer with terminal NH3+ groups was the most effective bactericide, and it was more potent than several previously studied dendrimers. Our results suggest that size, functional end groups and hydrophilicity are important parameters to consider in designing efficient antimicrobial dendrimers.

Nanoengineering colloidal and polymeric celluloses for threshold scale inhibition: towards universal biomass-based crystal modification

The first family of threshold (ppm level) cellulose-based scale inhibitors and crystal modifiers has been developed through the chemical nanoengineering of cellulose fibrils, the building blocks of plant cell walls, overcoming the structural and chemical limitations of conventional nanocelluloses. Dicarboxylated hairy cellulose nanocrystals and biopolymers address one of the most tenacious challenges of water-based industries, i.e., the scaling of inorganic salts, providing a green, environmentally-friendly alternative to the current phosphonated macromolecules. This research may shape the future of biomass-based antiscalants and advance the field of organic–inorganic biomimetic nanocomposites based on the most abundant biopolymers in the world.

Biomimetic scale-resistant polymer nanocomposites: towards universal additive-free scale inhibition

Macromolecular additives have long been used as the gold standard for inorganic scale inhibition in water-based industries. Despite their noticeable success in regulating the precipitation of sparingly soluble salts, environmental footprints such as eutrophication and acidification associated with anionic P, N, and S functionalized macromolecules have raised significant concerns, demanding green alternatives. Here, we show that incorporating a newly emerged nanoengineered cellulose, named anionic hairy cellulose nanocrystals (AHCNs, also known as electrosterically stabilized nanocrystalline cellulose, ENCC), into polymer matrices, e.g., cellulose acetate, a model system for water treatment membranes, mitigates the scaling of calcium carbonate, increasing the membrane lifetime up to a factor of 300% under harsh electrochemical conditions at only 0.4 wt% nanocellulose doping in the membrane casting solution. This may help establish the foundations for additive-free scale management based on plant-derived green, sustainable nanomaterials.

Overcoming Interfacial Scaling Using Engineered Nanocelluloses: A QCM-D Study

Nucleation of sparingly soluble species, such as the inorganic salts of calcium, magnesium, and phosphorous, followed by their growth at solid-liquid interfaces has turned into a major concern in water-based industries. Increased resistance against heat, mass, and momentum transfer is the main drawback of the so-called scaling phenomenon. Although phosphorous-, nitrogen-, and sulfur-based antiscaling macromolecules offer adequate antiscaling performance, their potential negative environmental impacts render them less desirable. Despite recent efforts in developing green antiscalants, there has been no promising green solution based on biomass due to its chemical inertness. Here, we use quartz crystal microbalance with dissipation monitoring (QCM-D) to evaluate the real-time performance of an emerging family of nanoengineered anionic hairy cellulose crystals, bearing dicarboxylated amorphous cellulose chains, with a charge density of more than 5.5 mequiv per g, in preventing the nucleation and growth of calcium carbonate, the most common industrial scale. Remarkably, a CaCO3 mass deposition rate ∼0 (complete scale inhibition) is obtained when less than 10 ppm of the hairy nanocellulose is added to an already scaled surface under a harsh supersaturated condition at 50 °C. Motivated by their threshold antiscaling effect, we show that coating planar silica surfaces with hairy nanocelluloses may result in scale-resistant interfaces. This research envisions how engineered hairy nanocelluloses may have practical implications for developing scale-resistant interfaces based on the most abundant biopolymer in the world.

Colloidal nano-toolbox for molecularly regulated polymerization: chemorheology over 6 decades of viscoelasticity

A universal approach to gain control over molecular interactions among activated, ready-to-react monomers, e.g., ammonium zirconium carbonate, has been proposed in which the monomers bind to two families of nanoengineered celluloses, namely hairy and conventional nanocelluloses with various surface functionalities and steric and electrosteric moieties. Engineering the colloidal interactions, the polymerization reaction was tailored to yield a spectrum of ultrasoft (5 decades decrease in viscoelastic moduli) to highly-reinforced (4000% enhanced viscoelasticity) nanocomposites using only 0.5 wt% nanoparticles.