Nanoparticles In Aqueous System Research Articles

Colloidal phenomena and aggregation mechanisms of cerium oxide nanoparticles in aqueous systems: effects of monovalent and divalent cations, and Suwanee River humic and fulvic acids

Colloidal phenomena and aggregation mechanisms of cerium oxide nanoparticles in aqueous systems: effects of monovalent and divalent cations, and Suwanee River humic and fulvic acids

TiO2 Assisted Photocatalytic Decomposition of 2-Chloronaphthalene on Iron Nanoparticles in Aqueous Systems: Synergistic Effect and Intermediate Products

2-Chloronaphthalene (2-CN), used as an intermediate for organic synthesis, is a new type of persistent organic pollutant. In this work, the decomposition efficiency and decomposition mechanism of 2-CN by zero-valent iron (ZVI) assisted TiO2 photodecomposition were studied in aqueous medium. Under UV light intensity of 38 mW cm–2, the optimal conditions for photodecomposition at an initial concentration of 5 μmol L–1 of 2-CN were pH 3 and 0.04 g L–1 TiO2 and ZVI, as catalysts. Then, the decomposition efficiency of 2-CN reached 66 and 100% in the UV/TiO2 and UV/ZVI/TiO2 systems, respectively. Based on analysis of the primary intermediate products of 2-CN, the chlorine on 2-CN was first replaced by a hydroxyl group to form 2-hydroxynaphthalene, and then the naphthalene ring was opened and gradually demethylated to produce small molecules, such as water and carbon dioxide.

Efficient removal of graphene oxide by Fe3O4/MgAl-layered double hydroxide and oxide from aqueous solution

With widespread utilization of graphene oxides (GO) in industry, it is ineluctably discharged into environment and has been found to be toxic to cells and animals. Effective techniques and functional materials are necessary for the elimination of GO from wastewater. In this work, the GO was removed by the magnetic Fe3O4/MgAl-layered double hydroxide (MLDH) and its oxide (MLDO) from aqueous solution. The effects of dosage, time and solution pH on the removal capacity of the MLDH and MLDO was carried out in detail through batch experiments. The results showed that the MLDH and MLDO can remove GO from aqueous solution quickly and efficiently. The maximum adsorption capacities were 82.4 mg/g of MLDH and 86.7 mg/g of MLDO. The pseudo-second-order equation was well accorded with the adsorption kinetic data. The isothermal data followed the Langmuir and Freundlich models. The interaction mechanisms of GO were ascribed to the surface complexation and electrostatic attraction by using zeta potential determination and XRD spectra. Moreover, the MLDH and MLDO after adsorbing GO can be separated in 10 s by a magnet. The short adsorption time, excellent removal capacity and extremely fast solid-liquid separation indicated that the MLDH and MLDO were potential magnetic adsorbents to remove the GO nanoparticles in aqueous system.

Zn(II) porphyrin-based photocatalytic synthesis of Cu nanoparticles for electrochemical reduction of CO2

Copper nanoparticles frequently exhibit unique electrocatalytic activity for the electrochemical reduction of carbon dioxide. However, the synthesis of Cu nanoparticles in aqueous systems remains rare. Herein, we report the synthesis of copper nanoparticles by using a zinc(II) porphyrin-based photocatalytic method in the presence of polyacrylic acid sodium salt (PAA) in water under visible light irradiation, leading to a series of Cu nanoparticles with relatively small average sizes ranging from 69 to 97 nm. PAA molecules adsorbed on Cu nanoparticles were simply removed by washing with copious amount of water. The purified Cu nanoparticles show some activity toward the electrochemical reduction of carbon dioxide as evidenced by linear sweep voltammetry (LSV) and gas chromatography (GC).

Dilution destabilizes engineered ligand‐coated nanoparticles in aqueous suspensions

It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one because dilution reduces collision rates of the particles and therefore delays the formation of aggregates. However, this generalization does not apply for some engineered ligand-coated nanoparticles (NPs). We observed the opposite relationship between stability and concentration of NPs. We tested 4 different types of NPs: CdSe-11-mercaptoundecanoic acid, CdTe-polyelectrolytes, Ag-citrate, and Ag-polyvinylpyrrolidone. The results showed that dilution alone induced aggregation and subsequent sedimentation of the NPs that were originally monodispersed at very high concentrations. Increased dilution caused NPs to progressively become unstable in the suspensions. The extent of the dilution impact on the stability of NPs is different for different types of NPs. We hypothesize that the unavoidable decrease in free ligand concentration in the aqueous phase following dilution causes detachment of ligands from the suspended NP cores. The ligands attached to NP core surfaces must generally approach exchange equilibrium with free ligands in the aqueous phase; therefore, ligand detachment and destabilization are expected consequences of dilution. More studies are necessary to test this hypothesis. Because the stability of NPs determines their physicochemical and kinetic behavior including toxicity, dilution-induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated NPs in aqueous systems. Environ Toxicol Chem 2018;37:1301-1308. © 2018 SETAC.

Single-chain folding of amphiphilic copolymers in water via intramolecular hydrophobic interaction and unfolding triggered by cyclodextrin

Poly(ethylene glycol) methyl ether acrylate (PEGMEA) is copolymerized with 2-(ferrocenecarboxylate ethyl) methacrylate (EMA-Fc) and 4-(propoxy urethane ethyl acrylate) azobenzene (EMA-Azob), respectively. The nanoparticles can be obtained via the single-chain folding of these amphiphilic copolymers with hydrophilic poly(ethylene glycol) (PEG) side chains and hydrophobic ferrocene (or azobenzene) pendant groups in dilute aqueous solution via intramolecular hydrophobic interaction. After the addition of cyclodextrin, the inclusion complex can be formed between cyclodextrin and ferrocene (or azobenzene) pendant groups, which makes the amphiphilic copolymers hydrophilic and triggers the chain unfolding of the nanoparticles in aqueous system. Such kind of process has potential application in the fields of drug delivery systems and their controlled release, sensors, controllable catalysis, mimicry of biomacromolecules, as well as other fields.

Dynamics and Morphology of Nanoparticle-Linked Polymers Elucidated by Nuclear Magnetic Resonance.

Nanoparticles are frequently modified with polymer layers to control their physical and chemical properties, but little is understood about the morphology and dynamics of these polymer layers. We report here an NMR-based investigation of a model polymer-modified nanoparticle, using multiple NMR techniques including 1H NMR, diffusion-ordered spectroscopy (DOSY), total correlation spectroscopy (TOCSY), and T2 relaxometry to characterize the dynamics of the nanoparticle-polymer interface. Using 5 nm detonation nanodiamond covalently linked to poly(allylamine) hydrochloride as a model system, we demonstrate the use of NMR to distinguish between free and bound polymer and to characterize the degree to which the segments of the nanoparticle-wrapping polymer are mobile (loops and tails) versus immobile (trains). Our results show that the polymer-wrapped nanoparticle contains a large fraction of highly mobile polymer segments, implying that the polymer extends well into solution away from the nanoparticle surface. Flexible, distal polymer segments are likely to be more accessible to extended objects such as cell membranes, compared with polymer segments that are in close proximity to the nanoparticle surface. Thus, these flexible segments may be particularly important in controlling subsequent interactions of the nanoparticles. While reported here for a model system, the methodology used demonstrates how NMR methods can provide important insights into the structure and dynamics at nanoparticle-polymer interfaces, leading to new perspectives on the behavior and interactions of polymer-functionalized nanoparticles in aqueous systems.

Aggregation behavior of TiO2 nanoparticles in municipal effluent: Influence of ionic strengthen and organic compounds

The influence of ionic strengthen and dissolved organic matter (DOM) on the aggregation of TiO2 nanoparticles (NPs) in municipal effluent was investigated. The results demonstrated that DOM promoted the mobility of NPs in aquatic system by synergism between static repulsion and steric effect, while electrolytes were opposite by charge-neutralization. The physical-chemical characteristics of DOM played the major role on the mobility of NPs. Bovine serum albumin (BSA) showed the strongest enhancement on the mobility of TiO2 NPs. High adsorption of BSA introduced vast negative charges on the TiO2 NPs' surface, leading to static repulsion and neutralizing positive charges of electrolytes in surrounding as well. By contrast, another protein α-amylase retarded the aggregation rate of TiO2 NPs through steric repulsion of the long-chain construction. Humic substances (Fulvic acid and alginate) also reflected the combination of static repulsion and steric effect. However, in the high electrolytes concentration (especially Ca2+), the long-chain aliphatic compounds were prone to form calcium bridge which increased the hydrodynamic diameter of TiO2 aggregates consequently. Sodium dodecylbenzene sulfonate (SDBS) showed low adsorption capacity, while the unabsorbed SDBS retarded the aggregates caused by the changes of pH and electrolytes. These data indicated that decreasing of DOC concentration in aqueous system was important to reduce the mobility and potential risk of NPs in aqueous system.

The rapid coagulation of graphene oxide on La-doped layered double hydroxides

Since graphene oxide (GO) has been found to be one of the toxic graphene-based nanomaterials, the environmental behavior of GO has been studied extensively in aqueous solution systems. In this work, the large ionic radius lanthanum (La) was doped onto the layered double hydroxides (LDHs), which was conducive to remove the negatively charged GO. The results showed that the coagulation of GO on La-doped LDHs was dependent on pH and the types of electrolytes. After calcined at 400°C for 4h, the maximum GO removal capacities could reach 565.8mg/g on Mg/Al/La-CLDHs and 558.6mg/g on Ca/Al/La-CLDHs at GO initial concentration of 120mg/L and LDHs content of 0.2g/L. The short equilibrium time and high removal capacity suggested the huge advantage of LDHs in practical applications. More importantly, the La-doped LDHs could still exhibit high removal capacities after five cycles, indicating that the La-doped LDHs hold good reusability and could be used for GO pollution cleanup from water. The coagulation of GO on La-doped LDHs was mainly dominated by electrostatic attraction and hydrogen bond. These findings were useful to understand the environmental fate and transport of GO nanoparticles in aqueous systems.

Synthesis of SiO<sub>2</sub>-PCE Core-Shell Nanoparticles and its Modification Effects on Cement Hydration

NanoSiO2 was widely used to modify the property of cementitious materials, however, for nanoparticles used in cement-based materials, key problem is the effective dispersion. The surface modification technology can be introduced to promote dispersion of nanoparticles in aqueous system, especially in cement pore solution, which possess high concentration of ions. In this study, at first, NanoSiO2-polycarboxylate superplasticizer (SiO2-PCE) core-shell nanoparticle was synthesized from silanized polycarboxylate superplasticizer and colloidal nanoSiO2 by the “grafting to” method, then SiO2-PCE was testified by UV-Vis, FTIR, and TGA. Additionally, stability of SiO2-PCE and its effect on cement hydration were investigated. Results shows: SiO2-PCE possess higher stability in saturated calcium hydroxide solution compared to nanoSiO2, and heat development of cement hydration can be regulated by shell structure of SiO2-PCE. The research implied a new approach for nanoSiO2 to optimize cement-based composites.

Synthesis of nanoSiO2@PCE core-shell nanoparticles and its effect on cement hydration at early age

NanoSiO2 has been widely used to improve properties of cement-based composites, but effective dispersion of nanoparticles in cementitious materials remains to be a challenge for their practical applications. This paper introduces a surface modification technique that can enhance dispersion of nanoparticles in aqueous system, especially in the pore solution of cement paste. First, a series of nanoSiO2-polycarboxylate superplasticizer core-shell nanoparticles (nanoSiO2@PCE) were synthesized from silanized polycarboxylate superplasticizer and colloidal nanoSiO2 by the “grafting to” method, the prepared nanoSiO2@PCE were characterized by DLS, FTIR, and TGA. Then the investigation on the interaction between nanoSiO2@PCE and cement shows that nanoSiO2@PCE exhibits higher stability in saturated calcium hydroxide solution than pristine nanoSiO2, and the heat development during cement hydration can be regulated by shell structure of nanoSiO2@PCE. The research provides a new route for nanoSiO2 to optimizing cement-based composites.

Oleate coating of iron oxide nanoparticles in aqueous systems: the role of temperature and surfactant concentration

Coating magnetic nanoparticles (MNPs) with sodium oleate (SO) is known to be an excellent method to create biocompatible, stable colloids with a narrow size distribution. However, the mechanism of oleate adsorption on the MNP surface in aqueous systems, as well as its influence on colloidal stability, is not yet fully understood. In this context, we present here a physico-chemical study to provide a deeper understanding of surfactant interaction mechanisms with nanoparticles. We examined the effect of temperature and the SO/MNP ratio (w/w) on the adsorption process in water and observed the existence of a maximum for the adsorbed oleate amount at lower temperatures, whereas at higher temperatures, the isotherm can be adapted to the Langmuir model with constant capacity after saturation. The oleate load on the MNP surface was quantified using reversed-phase high-performance liquid chromatography measurements of samples in solution. The thermogravimetric analyses of the solid residues together with infrared spectroscopy analyses indicate a bilayer-similar structure at the MNP/water interface even for low oleate loads. The oleate interacts with the iron oxide surface through a bidentate coordination of the carboxyl group. Zeta potential measurements demonstrate the high stability of the coated system. The maximal oleate load per unit mass of MNPs reaches approximately 0.35 goleate g MNP −1 .

Manufactured Nanoparticle Behavior and Transformations in Aquatic Systems. Importance of Natural Organic Matter.

Major concerns to elucidate the fate of nanomaterials and manufactured nanoparticles in aquatic systems are related to the lack of data on nanoparticle transformations under relevant environmental conditions. The present article discusses some of the important physicochemical processes controlling the behavior of manufactured nanoparticles in aqueous systems by focusing on their interaction with natural organic matter, which is expected to play a crucial role when adsorbing at the nanoparticle surface. The precise knowledge and consequences of such adsorption processes are important not only to predict the nanoparticle stability and dispersion state but also to evaluate their chemical reactivity and ecotoxicology. Most importantly, findings indicate that the presence of natural organic matter, at typical environmental concentrations, can induce significant disagglomeration of large nanoparticle agglomerates into small fragments. Such a result constitutes an important outcome with regard to the risk associated with the possible transformation and redispersion of large assemblies containing manufactured nanoparticles.

Role of combinatorial environmental factors in the behavior and fate of ZnO nanoparticles in aqueous systems: A multiparametric analysis

To better understand the environmental behavior, fate, and exposure risks of engineered nanoparticles in aquatic systems, for the first time, combinatorial aqueous systems were established using three-level orthogonal array design (OAD), an OA27 (313) matrix, to assess the effects of six co-varying environmental factors (organic acid type, organic acid concentration, NP concentration, pH, salt content, and electrolyte type) on the aggregation of commercial zinc oxide nanoparticles (ZnO NPs, mean diameter ∼41nm). A separate set of OA27 (313) experiments including temperature was conducted for the dissolution of these NPs. The results showed that the organic acid concentration and the pH were the most significant factors (p<0.001) influencing aggregation and dissolution of ZnO NPs, respectively. The electrolyte type and the salt content were the next most important factors in both the aggregation and dissolution. Based on the kinetics study of the aggregation, a high rate of the NP aggregation resulted in decreased dissolution, such that observed in the presence of calcium chloride. Clear temperature-induced aggregation and reduced dissolution were further observed with increasing temperature. This approach demonstrates that the behavior of ZnO NP may vary substantially under combinatorial environmental conditions.

New heparin–indomethacin conjugate with an ester linkage: Synthesis, self aggregation and drug delivery behavior

New heparin–indomethacin conjugate with an ester linkage was prepared by the carbodiimide-mediated condensation reaction, and then characterized by FTIR and 1HNMR analyses. Due to its amphiphilic character, such a conjugate could self-aggregate into spherical nanoparticles in aqueous system, as confirmed by fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. By the in vitro drug release tests, the resultant conjugate nanoparticles were found to have a sustained and esterase-sensitive release behavior for conjugated indomethacin. In addition, the uptake of these conjugate nanoparticles into human nasopharyngeal carcinoma CNE1 cells was confirmed by fluorescence microscopy.

Processes improving the dispersibility of spray-dried zein nanoparticles using sodium caseinate

Zein has been studied as a versatile food biopolymer to fabricate nanoparticles for encapsulating a large variety of bioactive compounds. Being water-insoluble prolamines, dispersing zein nanoparticles in aqueous systems is a challenge. Recently, sodium caseinate (NaCas) was observed to have improved the dispersibility of freeze-dried zein nanoparticles but not for spray-dried samples. In this paper, three different approaches were studied to produce spray-dried zein nanoparticles precipitated by dispersing aqueous ethanol solutions of zein into the aqueous phase. The control (S2) was produced by dispersing zein solution into NaCas dispersion without pH adjustment. The other two approaches involved conditions dissociating NaCas: adjusting NaCas dispersion to pH 11.0 (S5) or dissolving NaCas in heated zein solution before dispersing to a pH 8.0 buffer (S4). After hydrating the spray-dried powder, dispersions demonstrated varying turbidity and precipitation stability during storage. Entire NaCas was observed to have adsorbed on S2 zein nanoparticles, corresponding to bigger particles, higher turbidity and lower stability of dispersions than those of S4 and S5. Conversely, only κ-casein was on zein nanoparticles of S4 and S5, corresponding to a higher zein:casein mass ratio and higher surface hydrophobicity than that of S2. The best dispersibility was observed for S4 at pH 7.0 and 0–300 mM NaCl, with the smallest hydrodynamic diameter (∼125 nm), lowest turbidity, and without precipitation during 15-day refrigerated storage. Compositional analyses suggested that κ-casein in S4 was a part of zein nanoparticle matrices and was not detached by increased ionic strength during storage. Conversely, caseins detached from zein nanoparticles of S2 and S5, causing particle aggregation and precipitation. Additionally, the approach in S4 utilized less ethanol (50% v/v vs. 80% in the other two approaches) to dissolve zein. Our work is significant in fabricating delivery systems of bioactive compounds utilizing zein as a carrier biopolymer.

Novel biosensing platform based on self-assembled supramolecular hydrogel

The supramolecular hydrogel self-assembled from α-cyclodextrin (α-CD) and an amphiphilic triblock copolymer was used for the first time as a biosensing platform by the in-situ incorporation of horseradish peroxidase and polyaniline (PANI) nanoparticles. It was found that the used triblock copolymer could disperse well PANI nanoparticles in aqueous system and then interact with α-CD in the presence of horseradish peroxidase for the formation of supramolecular hydrogel composite. The content of PANI nanoparticles was found to affect the gelation time and gel strength. The circular dichroism analyses showed that the entrapped horseradish peroxidase could retain its native conformation. By electrochemical experiments, the incorporated PANI nanoparticles were confirmed to improve the current response and enzymatic activity, and the fabricated biosensor was found to provide a fast amperometric response to hydrogen peroxide.

Surface-functionalization effects on uptake of fluorescent polystyrene nanoparticles by model biofilms

A study was conducted to investigate the role of nanoparticle (NP) surface functionalization/charge on their uptake by biofilms. Biofilms, bacterial colonies attached to surfaces via extracellular polymers, are effective at removing suspended nanomaterials from the aqueous phase. However, the mechanisms regulating particle uptake are unknown. Here, it was shown that the mechanism was strongly dependent on the nanoparticle surface ionization, and not the core composition of the NP. Uptake experiments were conducted using laboratory-cultured biofilms. The biofilms were incubated in the presence of fluorescent polystyrene NPs with either negatively-charged surfaces (i.e. functionalized with sulfated (SO(4) (-)-NP) or carboxylated (COO(-)-NP) groups) or positively-charged surfaces (functionalized with primary amines, Amine-P). Particles with negatively-charged sulfated surfaces associated most strongly to biofilms across all experimental conditions. Associations of positively-charged amine particles with biofilms were greatest at high ionic conditions resembling those of seawater, but were sensitive to changes in ionic strength. Sorption of COO(-)-NPs was lowest, relative to other particle types, and was not sensitive to ionic strength. The results of this study support an emerging precedent that biofilms may be an effective player in the binding and sequestration of nanoparticles in aqueous systems.

Radiation formation of Al–Ni bimetallic nanoparticles in aqueous system

This work concerns the study of Al–Ni bimetallic nanoparticles synthesized by gamma-radiolysis of aqueous solution containing aluminium chloride hexahydrate, nickel chloride hexahydrate, polyvinyl alcohol for capping colloidal nanoparticles, and isopropanol as radical scavenger. While the Al/Ni molar ratio is kept constant, size of the nanoparticles can be well controlled by varying the radiation dose. The products were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD). Observations of UV–vis absorption spectra and TEM images showed that as the radiation dose increases from 50 to 100 kGy the particle size decreases and the number particles distribution increases. It may be explained due to the competition between nucleation and aggregation processes in the formation of metallic nanoparticles under irradiation. The EDX and XRD analysis confirmed directly the formation of Al–Ni bimetallic nanoparticles in form of alloy nanoparticles.

Aggregation of ferrihydrite nanoparticles in aqueous systems

Crystal growth by non-classical mechanisms, such as oriented aggregation, frequently involves an aggregation step. The aggregation of nanoparticles is sensitive to solution variables like ionic strength and pH, as well as the presence and concentration of other chemical species. Aggregation is a critical first step during the early stages of oriented aggregation. Time-resolved, cryogenic transmission electron microscopy was employed to characterize the degree of aggregation, the reversibility of aggregation, and the influence of additives on aggregation in aqueous suspensions. In this work, freshly synthesized ferrihydrite nanoparticles in aqueous suspension were employed as the model system. These nanoparticles are largely aggregated even with a solution pH several pH units away from the point of zero net proton charge (PZNPC) and a very low ionic strength (<10−4 M). Reversibility of aggregation was observed to be time-dependent. Finally, chemical additives dramatically change the evolution of aggregation state with strongly coordinating ligands strongly suppressing aggregation, even after aging at an elevated temperature.