Adsorption of cellulose derivatives on flat gold surfaces and on spherical gold particles

Chitosan-coated different particles in spouted bed and their use in dye continuous adsorption system

In this work, three polymer suspensions were used for coating glass beads (GB), porcelain beads (PB), and polyethylene pellets (PP) in spouted bed. Subsequently, the continuous adsorption assays of the food dye Brilliant Blue FCF in a fixed bed column were performed, which was packed with the covered particles. Also, the static adsorption assays were carried out. The adsorption equilibrium isotherms were fitted by Freundlich, Langmuir, and Temkin models, being that the Temkin model was the most suitable to represent the equilibrium data. The particle coating in the spouted bed showed promising results due to the high efficiency of the process. The PB, GB, and PP obtained coating efficiency values in the range to 92-96% when using the suspension of chitosan and hydroxyethyl cellulose. However, only the polyethylene particles coated with the chitosan suspension maintained its coating efficiency (95%). The maximum adsorption capacities at equilibrium of the coated particles of PP and GB were achieved with the chitosan suspension, being the values of around 800 mg g^-1. Thus, the chitosan-coated polyethylene particles showed to be a promising adsorbent for fixed bed column. Graphical abstract.

Star-like Supramolecular Complexes of Reducing-End-Functionalized Cellulose Nanocrystals

In this work, we take advantage of the parallel organization of cellulose chains in cellulose I yielding an inherent chemical asymmetry of cellulose nanocrystals, i.e., reducing vs nonreducing end, to selectively modify only one end of these rigid rodlike crystals to be used as a linking point for the formation of supramolecular structures. We have prepared biotin-functionalized tunicate cellulose nanocrystals at the reducing end capable of forming new complex supramolecular hierarchies by the addition of the protein streptavidin. Biotin-streptavidin coupling was chosen because streptavidin has a multivalency of four and the biotin-streptavidin bond is known to be highly selective and stable. Hence, streptavidin molecules would link up to four cellulose nanocrystals through their biotin-modified reducing end. Two biotin derivatives were studied, consisting of an anchoring group, i.e., amine or hydrazine; the biotin moiety; and the linker between them. Results show that the length of the linker significantly affects the bond between the biotinylated cellulose nanocrystals and streptavidin, and a certain chain length is necessary for the supramolecular assembly of several cellulose nanocrystals by streptavidin.

Stability and Aggregation Kinetics of Titania Nanomaterials under Environmentally Realistic Conditions

Nanoparticle morphology is expected to play a significant role in the stability, aggregation behavior, and ultimate fate of engineered nanomaterials in natural aquatic environments. The aggregation kinetics of ellipsoidal and spherical titanium dioxide (TiO2) nanoparticles (NPs) under different surfactant loadings, pH values, and ionic strengths were investigated in this study. The stability results revealed that alteration of surface charge was the stability determining factor. Among five different surfactants investigated, sodium citrate and Suwannee river fulvic acid (SRFA) were the most effective stabilizers. It was observed that both types of NPs were more stable in monovalent salts (NaCl and NaNO3) as compared with divalent salts (Ca(NO3)2 and CaCl2). The aggregation of spherical TiO2 NPs demonstrated a strong dependency on the ionic strength regardless of the presence of mono or divalent salts; while the ellipsoids exhibited a lower dependency on the ionic strength but was more stable. This work acts as a benchmark study toward understanding the ultimate fate of stabilized NPs in natural environments that are rich in Ca(CO3)2, NaNO3, NaCl, and CaCl2 along with natural organic matters.

Directed assembly of bifunctional silica-iron oxide nanocomposite with open shell structure

The synthesis of nanocomposite with controlled surface morphology plays a key role for pollutant removal from aqueous environments. The influence of the molecular size of the polyelectrolyte in synthesizing silica-iron oxide core-shell nanocomposite with open shell structure was investigated by using dynamic light scattering, atomic force microscopy, and quartz crystal microbalance with dissipation (QCM-D). Here, poly(diallydimethylammonium chloride) (PDDA) was used to promote the attachment of iron oxide nanoparticles (IONPs) onto the silica surface to assemble a nanocomposite with magnetic and catalytic bifunctionality. High molecular weight PDDA tended to adsorb on silica colloid, forming a more extended conformation layer than low molecular weight PDDA. Subsequent attachment of IONPs onto this extended PDDA layer was more randomly distributed, forming isolated islands with open space between them. By taking amoxicillin, an antibiotic commonly found in pharmaceutical waste, as the model system, better removal was observed for silica-iron oxide nanocomposite with a more extended open shell structure.

Relative importance of the humic and fulvic fractions of natural organic matter in the aggregation and deposition of silver nanoparticles

As engineered nanoparticles (NPs) are increasingly used, their entry into the environment has become an important topic for water sustainability. Recent investigations point to the critical role of natural organic matter (NOM) in altering the persistence of NPs by complexing with their surfaces. The NP-NOM complex, in turn, is the new entity that may potentially influence subsequent fate of NPs. To understand the relative impact of humic (HA) and fulvic fraction of NOM on the stability and mobility of silver nanoparticles (AgNPs), a combination of dynamic light scattering and quartz crystal microgravimetry with dissipation monitoring was used. In the absence of unbound NOM, (1) surface modification on either AgNP or silica substrate by different NOM fractions could lead to substantial changes in the extent and kinetics of AgNP aggregation and deposition, and (2) HA has a greater capability to enhance the transport of AgNPs by reducing their aggregation and deposition. With unbound NOM, HA seems to compete more successfully for binding sites on the substrate under electrostatically favorable conditions and formed a steric layer to prevent subsequent deposition of AgNPs. These findings highlighted the importance of NOM fraction in the overall environmental partitioning of AgNPs.

A novel xyloglucan film-based biosensor for toxicity assessment of ricin in castor seed meal

Oil from the seed of the castor plant (Ricinus communis L.) is an important commodity for a number of industries, ranging from pharmaceuticals to renewable energy resources. However, the seed and subsequent seed meal contain ricin (RCA60), a potent cytotoxin, making it an unusable product for animal feed. In order to investigate the efficiency of reducing the toxicity of the seed meal, a biosensor is proposed by exploring the lectin-carbohydrate binding. A gold electrode was assembled with a film of Xyloglucan (XG) extracted from Hymenaea courbaril L. The analytical response to RCA60 was obtained using a polyclonal antibody against RCA60 conjugated to peroxidase. The current responses were generated by reaction with H2O2 and amplified with hydroquinone as chemical mediator. Voltammetric studies showed that the XG film was tightly bound to the gold electrode. This biosensor allows discriminate lectins in native and denatured forms. The limit of detection of native RCA60 was 2.1 μg mL(-1). This proposed biosensor showed to be a potential and accurate method for toxicity assessment of the ricin in castor seed meal by simple polysaccharide film-electrode strategy.

Adsorption of cationic hydroxyethylcellulose derivatives onto planar and curved gold surfaces

The adsorption of two positively charged hydroxyethylcellulose derivatives with 7 and 60 mol % positively charged groups and a cationic, hydrophobically modified hydroxyethylcellulose containing 1 mol % hydrophobic groups and 7 mol % charged groups onto flat and spherical citrate-coated gold surfaces of different sizes has been investigated. The planar surfaces were studied by means of the quartz crystal microbalance with dissipation monitoring, whereas nanoparticle suspensions were examined using dynamic light scattering and UV-vis spectroscopy. Two different driving forces for adsorption have been evaluated: the electrostatic interaction between the positive charges on the polymers and the negatively charged gold surfaces and the affinity of the polymers for gold due to hydrophobic interactions. The comparison between the data obtained from curved and planar surfaces suggests a strong correlation between surface curvature and adlayer conformation in the formation of the hybrid polymer-gold nanoparticles. The influence of particle size on the amount of adsorbed polymer has been evaluated for the different polymers. The impact of the ionic strength on polymer adsorption has been explored, and the adsorbed polymer layer has been found to protect the gold nanoparticles from aggregation when salt is added to the solution. The addition of salt to a mixture of gold particles and a charged polymer can induce a thicker adsorbed layer at low salinity, and desorption was found at high levels of salt addition.

Temperature-induced adsorption and optical properties of an amphiphilic diblock copolymer adsorbed onto flat and curved silver surfaces

Temperature-induced adsorption of a thermoresponsive amphiphilic copolymer, containing poly(N-isopropylacrylamide), on citrate-capped silver nanoparticles and planar silver surfaces has been studied with the aid of quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS). The results clearly show that both the amount of adsorbed copolymer and thickness of the adsorbed layer increase strongly at temperatures above the lower critical solution temperature (LCST). These findings are ascribed to enhanced hydrophobicity of the polymer and higher affinity for polymer adsorption at elevated temperatures and formation of intermicellar structures of the copolymer. The values of the layer thickness calculated from QCM-D data are practically identical to the values for the hydrodynamic thickness from DLS. This result suggests that the adsorbed layer is compact with few tails protruding out into the bulk. The surface plasmon peak for silver is observed at all temperatures, and the maximum is red-shifted with increasing temperature, which is attributed to an increase of the localized refractive index as more polymer chains are adsorbed onto the silver particles.