Production Of Nanocrystals Research Articles

Thermally stable surfactant-free ceria nanocubes in silica aerogel

Surfactant-mediated chemical routes allow one to synthesize highly engineered shape- and size-controlled nanocrystals. However, the occurrence of capping agents on the surface of the nanocrystals is undesirable for selected applications. Here, a novel approach to the production of shape-controlled nanocrystals which exhibit high thermal stability is demonstrated. Ceria nanocubes obtained by surfactant-mediated synthesis are embedded inside a highly porous silica aerogel and thermally treated to remove the capping agent. Powder X-ray Diffraction and Scanning Transmission Electron Microscopy show the homogeneous dispersion of the nanocubes within the aerogel matrix. Remarkably, both the size and the shape of the ceria nanocubes are retained not only throughout the aerogel syntheses but also upon thermal treatments up to 900 °C, while avoiding their agglomeration. The reactivity of ceria is measured by in situ High-Energy Resolution Fluorescence Detected - X-ray Absorption Near Edge Spectroscopy at the Ce L3 edge, and shows the reversibility of redox cycles of ceria nanocubes when they are embedded in the aerogel. This demonstrates that the enhanced reactivity due to their prominent {100} crystal facets is preserved. In contrast, unsupported ceria nanocubes begin to agglomerate as soon as the capping agent decomposes, leading to a degradation of their reactivity already at 275 °C.

Multifactor-Regulated Fast Synthesis of α-Zirconium Phosphate Nanocrystals Towards Highly Efficient Adsorption of Pesticides

α-zirconium phosphate (α-ZrP) nanocrystals with surface active groups and layered structure have been widely used in radionuclide removal, proton conductors, chemical sensors, flame retardant and corrosion-resistant materials. The previous synthesis of α-ZrP nanocrystals is time-consuming and lack of controllability. Herein, a multifactor-regulated fast synthesis strategy in a microwave reactor is proposed to realize the fast and controllable production of the high-quality α-ZrP nanocrystals. Compared with the conventional hydrothermal synthesis, the reaction time has been reduced from 24 h to 15 min. The degree of crystallinity, the morphology, the lateral size and the thickness can be controlled by adjusting the reaction parameters. Results demonstrate that the obtained α-ZrP nanocrystals possess good crystallinity, disk morphology, abundant active functional groups, superior thermal stability and strippable layered structure. Furthermore, the α-ZrP nanocrystals synthesized by the microwave-assisted multifactor-regulated method as environmentally friendly carriers possess better pesticide adsorption efficiency than those synthesized by the conventional hydrothermal synthesis as the result of the smaller size and more exposed adsorption sites. It is envisioned that the multifactor-regulated synthesis in a microwave reactor provides a more efficient and energy-saving alternative to synthesize high-quality nanocrystals and broaden their application in chemical engineering.

Production of cellulose nanocrystals from pineapple crown fibers through alkaline pretreatment and acid hydrolysis under different conditions

In the growing search for sustainability, nanocellulose has stood out, since it is obtained from natural fibers, a renewable and biodegradable source, being able to promote the reuse of agricultural waste. Due to their high availability and low cost, residues from pineapple consumption become a viable alternative for the nanocellulose production process, which has not been explored so far. In this sense, the work aimed to produce nanocellulose from pineapple crowns, via acid hydrolysis, promoting the study of different process conditions, to define which methods obtained better results. The fibers were pretreated by mercerizing with sodium hydroxide and bleaching with hydrogen peroxide and sodium hydroxide. This was followed by hydrolysis with sulfuric acid to obtain the nanoparticles. Chemical characterization and scanning electron microscopy were performed on the crude and bleached fibers, and transmission electron microscopy on the produced nanocellulose. The treatments were effective in reducing lignin and hemicellulose in the fiber, and microscopy proved the production of cellulose nanoparticles, with an average width equal to 10.38nm. Therefore, the results confirmed the potential of the process used to obtain nanocellulose from the pineapple crowns.

Production of Cellulose Nanocrystals from Australian Wood Sources.

Two Australian native wooden sources (Acacia Mangium and Eucalyptus Globulus) derived pulps were explored as raw feed stocks to prepare the valuable nanomaterial of cellulose nanocrystals (CNC). After bleaching and acid hydrolysis, cellulose nanocrystals were successfully produced with high yields of approximately 60% for both kraft pulps. According to the characterization of SEM and AFM, the as prepared CNC had a rod like structure with the length and diameter in the range of 200~1000 nm and 10~100 nm, respectively based on the initial wooden source. XRD confirmed the crystalline structure of the resulting CNC. Further characterisation by TGA showed that the chemical treatment of the wood pulp had impact upon the thermal stability, evidenced by a lower onset temperature of the thermal decomposition of CNC.

Particle Size Distributions for Cellulose Nanocrystals Measured by Transmission Electron Microscopy: An Interlaboratory Comparison.

Particle size is a key parameter that must be measured to ensure reproducible production of cellulose nanocrystals (CNCs) and to achieve reliable performance metrics for specific CNC applications. Nevertheless, size measurements for CNCs are challenging due to their broad size distribution, irregular rod-shaped particles, and propensity to aggregate and agglomerate. We report an interlaboratory comparison (ILC) that tests transmission electron microscopy (TEM) protocols for image acquisition and analysis. Samples of CNCs were prepared on TEM grids in a single laboratory, and detailed data acquisition and analysis protocols were provided to participants. CNCs were imaged and the size of individual particles was analyzed in 10 participating laboratories that represent a cross section of academic, industrial, and government laboratories with varying levels of experience with imaging CNCs. The data for each laboratory were fit to a skew normal distribution that accommodates the variability in central location and distribution width and asymmetries for the various datasets. Consensus values were obtained by modeling the variation between laboratories using a skew normal distribution. This approach gave consensus distributions with values for mean, standard deviation, and shape factor of 95.8, 38.2, and 6.3 nm for length and 7.7, 2.2, and 2.9 nm for width, respectively. Comparison of the degree of overlap between distributions for individual laboratories indicates that differences in imaging resolution contribute to the variation in measured widths. We conclude that the selection of individual CNCs for analysis and the variability in CNC agglomeration and staining are the main factors that lead to variations in measured length and width between laboratories.

Preparation of nanocellulose by hydrolysis catalysedusing salts with different Fe valency

The production of cellulose nanocrystals (CNCs) from vegetable fibres and residues has been intensely investigated due to the properties of high crystallinity and specific surface area of these nanofillers. The most common method of obtaining CNCs is by acid hydrolysis with inorganic acids; however, this method can lead to uncontrolled depolymerisation of the cellulose. Thus, this article examines the use of Lewis acids (FeSO4, Fe2(SO4)3 and FeCl3) as co-catalysts in the acid hydrolysis process and compares their impact on the yield, reduction of particle size and crystallinity index of the CNCs. The results show that the presence of Fe2(SO4)3 and FeCl3 improved the yield (50 and 27%, respectively) and decreased the particle size (632 and 66 nm, respectively) of the CNCs obtained in the hydrolysis process. On the other hand, the crystallinity index values were similar to that of microcrystalline cellulose (MCC), which was probably due to the severe conditions of the hydrolysis process that was used. The scanning transmission microscopy (STEM) images showed a spherical morphology for the CNCs obtained by both inorganic acid and Lewis acids; once again, this was probably due to the severe hydrolysis conditions. Thus, the presence of Lewis acids in the hydrolysis process makes it more efficient because it increases the efficiency of the hydrolysis in a less corrosive environment and with less probability of depolymerisation of the cellulose.

Sonication-Assisted Production of Fosetyl-Al Nanocrystals: Investigation of Human Toxicity and In Vitro Antibacterial Efficacy against Xylella Fastidiosa.

Recently, there is a growing demand in sustainable phytopathogens control research. Nanotechnology provides several tools such as new pesticides formulations, antibacterial nanomaterials and smart delivery systems. Metal nano-oxides and different biopolymers have been exploited in order to develop nanopesticides which can offer a targeted solution minimizing side effects on environment and human health. This work proposed a nanotechnological approach to obtain a new formulation of systemic fungicide fosetyl-Al employing ultrasonication assisted production of water dispersible nanocrystals. Moreover, chitosan was applicated as a coating agent aiming a synergistic antimicrobial effect between biopolymer and fungicide. Fosetyl-Al nanocrystals have been characterized by morphological and physical-chemical analysis. Nanotoxicological investigation was carried out on human keratinocytes cells through cells viability test and ultrastructural analysis. In vitro planktonic growth, biofilm production and agar dilution assays have been conducted on two Xylella fastidiosa subspecies. Fosetyl-Al nanocrystals resulted very stable over time and less toxic respect to conventional formulation. Finally, chitosan-based fosetyl-Al nanocrystals showed an interesting antibacterial activity against Xylella fastidiosa subsp. pauca and Xylella fastidiosa subsp. fastidiosa.

Production of cellulose nanocrystals integrated into a biochemical sugar platform process via enzymatic hydrolysis at high solid loading

This work evaluated the viability of integrating the isolation of cellulose nanocrystals (CNCs) via enzymatic hydrolysis at a high solid loading into the biochemical platform process for the production of sugars from sugarcane bagasse (SCB). SCB was first processed at a biochemical conversion pilot plant and bleached to yield a cellulose-rich pulp, which was enzymatically hydrolyzed at high solid and low enzyme loadings. The resulting hydrolysate had high sugar concentration (>120 g/L glucose) and the CNCs (20 nm in diameter) isolated directly from the hydrolysis residue showed superior properties (higher thermal stability, higher crystallinity index, and higher particle diameter uniformity) than the CNCs prepared from commercial bleached eucalyptus Kraft pulp. These findings demonstrate the technical viability of the proposed integrated process that combined with the high CNCs yield (approximately50%) and the no need for the costly ultrasonic dispersion treatment step to obtain nanoparticles can further contribute for improving the economic and environmental viability of the proposed enzyme-mediated isolation process.

Efficient Hydrolysis of Chitin in a Deep Eutectic Solvent Synergism for Production of Chitin Nanocrystals.

A deep eutectic solvent (DES) derived from ferric chloride hexahydrate and betaine chloride (molar ratio of 1:1) was used as hydrolytic media for production of chitin nanocrystals (ChNCs) with a high yield (up to 88.5%). The synergistic effect of Lewis acid and released Brønsted acid from betaine hydrochloride enabled the efficient hydrolysis of chitin for production of ChNCs coupled with ultrasonication with low energy consumption. The obtained ChNCs were with an average diameter of 10 nm and length of 268 nm, and a crystallinity of 89.2% with optimal synthesis conditions (at 100 °C for 1 h with chitin-to-DES mass ratio of 1:20). The ChNCs were further investigated as efficient emulsion stabilizers, and they resulted in stable o/w emulsions even at a high oil content of 50% with a low ChNC dosage of 1 mg/g. Therefore, a potential approach based on a DES on the production of chitin-based nanoparticles as emulsifiers is introduced.

Enzymatic Hydrolysis of Bacterial Cellulose for the Production of Nanocrystals for the Food Packaging Industry.

Bacterial cellulose nanocrystals (BCNCs) obtained by enzymatic hydrolysis have been loaded in pullulan biopolymer for use as nanoparticles in the generation of high-oxygen barrier coatings intended for food packaging applications. Bacterial cellulose (BC) produced by Komagataeibacter sucrofermentans was hydrolyzed by two different enzymatic treatments, i.e., using endo-1,4-β-glucanases (EGs) from Thermobifida halotolerans and cellulase from Trichoderma reesei. The hydrolytic activity was compared by means of turbidity experiments over a period of 145 h, whereas BCNCs in their final state were compared, in terms of size and morphology, by atomic force microscopy (AFM) and dynamic light scattering (DLS). Though both treatments led to particles of similar size, a greater amount of nano-sized particles (≈250 nm) were observed in the system that also included cellulase enzymes. Unexpectedly, transmission electron microscopy (TEM) revealed that cellulose nanoparticles were round-shaped and made of 4–5 short (150–180 nm) piled whiskers. Pullulan/BCNCs nanocomposite coatings allowed an increase in the overall oxygen barrier performance, of more than two and one orders of magnitude (≈0.7 mL·m−2·24 h−1), of pure polyethylene terephthalate (PET) (≈120 mL·m−2·24 h−1) as well as pullulan/coated PET (≈6 mL·m−2·24 h−1), with no significant difference between treatments (hydrolysis mediated by EGs or with the addition of cellulase). BCNCs obtained by enzymatic hydrolysis have the potential to generate high oxygen barrier coatings for the food packaging industry.

Melt Processing of Cellulose Nanocrystal-Filled Composites: Toward Reinforcement and Foam Nucleation

Although the mass production of cellulose nanocrystals (CNC) shows the possibility of their use in scalable nanocomposite manufacturing, the low compatibility between the CNC-hydrophobic matrix and...

Highly Efficient Preparation of Functional and Thermostable Cellulose Nanocrystals via H2SO4 Intensified Acetic Acid Hydrolysis

A highly efficient and sustainable strategy for the production of functional and thermostable cellulose nanocrystals (CNCs) was developed in this work. In which, the acid hydrolysis system composed with small doses of H2SO4 (5-10%) and large amounts of easily recoverable acetic acid (70-90%) was used to hydrolyze cellulose pulp at 80 °C for several hours. The rod-like CNCs were obtained with the length of 150-500 nm and diameter of 5-20 nm in high yield (Ymax = 81%). The resulted CNCs showed high thermal stability and excellent dispersion stability in both aqueous and organic phases. The acetic acid in the hydrolysis system can be completely recovered by vacuum distillation, and the dosage of sulfuric acid can be reduced significantly compared with the traditional sulfuric acid hydrolysis. Thus, this approach is promising for the large-scale and sustainable preparation of CNCs with excellent water dispersibility and good thermal stability, with less environmental issues.

The isolation of halophilic urease-producing bacteria and the study of their nano-crystal production

The isolation of halophilic urease-producing bacteria and the study of their nano-crystal production

Maximizing production of cellulose nanocrystals and nanofibers from pre-extracted loblolly pine kraft pulp: a response surface approach

This study aims to optimize strong acid hydrolysis-based production of cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) from pre-extracted and fully bleached kraft pulp of loblolly pinewood, the most abundant and commercially significant softwood species in southeastern United States. The effect of four parameters, including acid concentration, temperature, duration and pulp particle size, on the yield and properties of CNCs was investigated using the central composite design (CCD) of response surface methodology (RSM) for process optimization. While CNC yield was significantly affected by acid concentration and hydrolysis temperature and was adequately explained by an empirical model, none of the characteristic properties of CNCs, including crystallinity index, surface charge and particle size, displayed any strong correlation to the process parameters within the experimental ranges tested. At different hydrolysis severities, we not only analyzed the waste streams to determine the extent of holocellulose degradation, but also evaluated the properties of leftover partially hydrolyzed pulp, called cellulosic solid residues (CSR), to gauge its potential for CNF production via mechanical fibrillation. Conditions that maximized CNC yields (60% w/w) were 60% acid concentration, 58 °C, 60 min and 40 mesh particle size. Twenty percent (w/w) of the pulp was degraded under these conditions. On the other hand, conditions that maximized CSR yields (60% w/w) were 54% acid, 45 °C, 90 min and 20 mesh particle size, which also produced 15% CNCs, caused minimal pulp degradation (< 5%) and imparted sufficient surface charge such that CSR was easily microfluidized into CNFs. Therefore, the strong acid hydrolysis process could be tuned to maximize the production of cellulose nanocrystals and nanofibers and obtain two products with different properties and applications through the process optimization.

Scaled-up production of gelatin-cellulose nanocrystal bionanocomposite films by continuous casting

In this study, continuous casting is proposed as a suitable approach to scale up the production of gelatin-cellulose nanocrystals (CNCs) bionanocomposites. The processing conditions and bionanocomposite properties were established based on the ζ-potential and gelatin content, and CNCs concentration, respectively. Gelatin film-forming solution at 20 wt% was required for proper continuous casting processing, leading to a productivity of 0.20 m2 film/min, which was at least 1000-fold higher than that of the classical bench casting. The gelatin-CNCs bionanocomposites displayed transparency, flexibility, and improved UV-barrier and thermal properties. Adding only 0.5 wt% of CNCs resulted in an increase of 77 % and 48 % in the tensile strength and Young’s modulus of gelatin, respectively. Comparison with previous nanocellulose-based nanocomposites pointed out the relatively superior performance of the gelatin-CNCs bionanocomposites obtained by continuous casting for various applications, including flexible food packaging.

Oxidative treatments for cellulose nanofibers production: a comparative study between TEMPO-mediated and ammonium persulfate oxidation

In the recent years, several methods for producing cellulose nanofibers (CNF) have appeared. Depending on the type of treatment and its conditions, the source of cellulose and the fibrillation method, different properties and characteristics can be obtained. TEMPO-mediated oxidation has been extensively used for CNF production and it is considered as one of the most suitable treatments to obtain high-performance CNF with superior properties and reduced size. However, the recovery of the catalyst and its cost is still a challenge. In the recent years, the oxidation by means of ammonium persulfate (APS) has appeared as a potential alternative, although it is commonly used for cellulose nanocrystals production. The present work aims at comparing the properties of CNF obtained by means of TEMPO-mediated oxidation (TOCNF) and ammonium persulfate oxidation (APSCNF). For this, a similar oxidation degree was selected, adjusting the treatment conditions of both oxidative methods. The obtained results exhibited that similar properties can be obtained with different production costs associated. In addition, the APSCNF exhibited a significantly lower degree of polymerization and slightly higher transmittance, indicating the presence of higher crystalline regions. Finally, both types of CNF were tested over a recycled paper substrate, revealing that both APSCNF and TOCNF significantly increased the mechanical properties of paper with low effect on pulp drainability, representing a great advantage for the paper industry.

The role of NaOH content, grinding time, and drying temperature in controlling the shape and size of nano ZnO synthesized by a green chemistry approach

Zinc oxide (ZnO) has been widely exploited in different technological applications in virtue of its unique physical and chemical qualities. This study was designed to prepare ZnO nanorods for diagnostic applications using a simple, low cost, and solvent-deficient method with clarifying the effect of different experimental parameters on the shape and the size of the ZnO product. Under different experimental conditions, the synthesis was performed via a solid-state reaction of zinc sulfate and sodium hydroxide using the grinding method. The purity of nano ZnO products was investigated by X-ray diffractometer (XRD) while the size and the shape were demonstrated by high- resolution transmission electron microscopy (HRTEM). The XRD results confirmed the production of pure ZnO nanocrystals. The HRTEM micrographs illustrated the preparation of a mixture of nanospheroids and nanorods particles, nanorods with minor nanospheroids particles, and long nanorods particles when the applied mole ratio of (ZnSO4.7H2O: NaOH) was (1:2), (1:4), and (1:8) respectively. Our findings confirmed the vital role of NaOH in controlling the shape and the particle size of nano ZnO. Since ZnO nanorods can be easily prepared under mild environmentally friendly conditions, it is proposed that the described experimental conditions can be adapted for large scale production.

Low-Cost RoHS Compliant Solution Processed Photovoltaics Enabled by Ambient Condition Synthesis of AgBiS2 Nanocrystals.

Two major challenges exist before colloidal nanocrystal solar cells can take their place in the market: So far, these devices are based on Pb/Cd-containing nanocrystals, and second, the synthesis of these nanocrystals takes place in an inert atmosphere at elevated temperatures due to the use of air-sensitive chemicals. In this report, a room-temperature, ambient-air synthesis for nontoxic AgBiS2 nanocrystals is presented. As this method utilizes stable precursors, the need for the use of a protective environment is eliminated, enabling the large-scale production of AgBiS2 nanocrystals. The production cost of AgBiS2 NCs at room temperature and under ambient conditions reduces by ∼60% compared to prior reports based on hot injection, and the solar cells made of these nanocrystals yield a promising power conversion efficiency (PCE) of 5.5%, the highest reported to date for a colloidal nanocrystal material free of Pb or Cd synthesized at room temperature and under ambient conditions.

Comparison of acidic deep eutectic solvents in production of chitin nanocrystals

Five different acidic deep eutectic solvents (DESs) composed of choline chloride and organic acids were applied to fabricate chitin nanocrystals (ChNCs). All DESs resulted in high transmittance and stable ChNCs suspensions with very high mass yield ranging from 78 % to 87.5 % under proper reaction conditions. The acidic DESs had a dual role in ChNCs fabrication, i.e. they promoted hydrolysis of chitin and acted as an acylation reagent. Physicochemical characterization of chitin revealed that the removal of amorphous area during DES treatments led to increased crystallinity of ChNCs and a dimension diversity correlated the DES used. The average diameter and length of individual ChNCs ranged from 42 nm to 49 nm and from 257 nm to 670 nm, respectively. The thermal stability of ChNCs was comparable to that of pristine chitin. Thus, acidic DESs showed to be non-toxic and environmentally benign solvents for production of functionalized chitin nanocrystals.

Continuous production of magnetic iron oxide nanocrystals by oxidative precipitation

Abstract Continuous processes are always preferred over batch ones when reproducible and scalable industrial procedures are needed. This work illustrates the production of magnetite nanoparticles by oxidative precipitation in aqueous media, following a continuous approach that offers additional advantages. Particularly, the developed reaction setup succeeds (i) the complete separation of the green rust’s precipitation from Fe3O4 nucleation, (ii) the achievement of constant concentrations in all ionic and solid forms throughout the production line when steady-state is reached, what means constant supersaturation from both the formation of green rust and Fe3O4, and (iii) the possibility to control critical parameters, such as OH− excess over the initial stoichiometric Fe(OH)2 precipitation, through on-line regulation of synthesis parameters such as the reactor’s pH and redox potential. Importantly, continuous flow synthesis of Fe3O4 nanoparticles enables high production capacities, low energy consumption and proportional scale-up at any volume. As a proof of concept, obtained nanoparticles were evaluated according to their magnetic response as potential magnetic hyperthermia agents indicating significant improvement of heating efficiency that goes up to 1.5–2 kW/gFe3O4 for both smaller (~40 nm) and larger (~200 nm) particles.