Correction: Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions.

Correction for 'Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions' by Thomas Degabriel, Elodie Colaço et al., Phys. Chem. Chem. Phys., 2018, 20, 12898-12907, https://doi.org/10.1039/C7CP08054A.

Hierarchical Collagen-Hydroxyapatite Nanostructures Designed through Layer-by-Layer Assembly of Crystal-Decorated Fibrils.

A comprehensive understanding of the mechanism by which type I collagen (Col) interacts with hydroxyapatite nanoparticles (Hap NPs) in aqueous solutions is a pivotal step for guiding the design of biologically relevant nanocomposites with controlled hierarchical structure. In this paper we use a variety of Hap NPs differing by their shape (rod vs platelet) and their size (∼30 vs ∼130 nm) and investigate their mechanism(s) of interaction with collagen. The addition of collagen to the Hap suspensions induces different effects that strongly depend on the nanoparticle type. Interestingly, the use of small rods, typically with ∼30 nm of length (R30), leads to the formation of assembled collagen fibrils decorated with Hap nanocrystals which, in turn, self-assemble progressively to form larger fibrillar Hap-Col composite. The crystals decorating collagen provide "intrinsic" negative charges to the fibrillar objects that allow their incorporation in three-dimensional structure using layer-by-layer (LbL) assembly. This offers a straightforward way to construct a collagen-based hybrid material with well-defined hierarchy under near-physiological conditions. In situ, QCM-D monitoring revealed the buildup of soft and highly hydrated hybrid (PAH/R30-Col)n multilayers for which the mechanism of growth was very different from that observed for polyelectrolytes and nanoparticles without collagen (PAH/R30). The LbL assembly of crystal-decorated collagen yields a hierarchical nanostructured film whose thickness and roughness can be modulated by the addition of salt and incorporate fibrillar objects of about 400 nm in width and few micrometers in length, as probed by AFM. The approach described in this work provides a relevant way to better control the (supra)molecular assembly of Col and Hap NPs with the perspective of developing hierarchical Hap-Col nanocomposites with tuned properties for various biomedical applications.

Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions.

We investigate the characteristics, fate and photocatalytic activity of spheroid- and rod-shaped TiO2 nano-crystals in aqueous solutions to better understand their behaviour in media of biological and environmental interest. For this purpose, the potential of a solvothermal method in synthesizing highly crystalline nanoparticles and tuning their sizes/shapes is explored. Spheroid- and rod-shaped nanoparticles are successfully obtained with different aspect ratios, while keeping their structures as well as their cross-sectional areas identical. The aggregation/agglomeration of these nanostructures in aqueous solutions shows an obvious shape effect, revealing critical coagulation concentrations (CCCs) significantly lower for the rods compared to the spheroids (aspect ratio ∼ 2-3). This trend is observed in both NaCl and CaCl2 electrolytes at pH values above and below the pHPZC of TiO2 nanoparticles. The photocatalytic activity of the spheroids is unexpectedly superior to that of the rods at NaCl and CaCl2 concentrations over a range of 2 to 100 and 1 to 50 mM, respectively. Our results show that an increase in the chloride concentration leads to an inhibition of the photocatalytic activity rate, with a more pronounced impact for the rods. In contrast, the size of aggregates/agglomerates has only a little effect on the photocatalytic properties of both nano-crystals.

AGNES at vibrated gold microwire electrode for the direct quantification of free copper concentrations.

The free metal ion concentration and the dynamic features of the metal species are recognized as key to predict metal bioavailability and toxicity to aquatic organisms. Quantification of the former is, however, still challenging. In this paper, it is shown for the first time that the concentration of free copper (Cu(2+)) can be quantified by applying AGNES (Absence of Gradients and Nernstian equilibrium stripping) at a solid gold electrode. It was found that: i) the amount of deposited Cu follows a Nernstian relationship with the applied deposition potential, and ii) the stripping signal is linearly related with the free metal ion concentration. The performance of AGNES at the vibrating gold microwire electrode (VGME) was assessed for two labile systems: Cu-malonic acid and Cu-iminodiacetic acid at ionic strength 0.01 M and a range of pH values from 4.0 to 6.0. The free Cu concentrations and conditional stability constants obtained by AGNES were in good agreement with stripping scanned voltammetry and thermodynamic theoretical predictions obtained by Visual MinteQ. This work highlights the suitability of gold electrodes for the quantification of free metal ion concentrations by AGNES. It also strongly suggests that other solid electrodes may be well appropriate for such task. This new application of AGNES is a first step towards a range of applications for a number of metals in speciation, toxicological and environmental studies for the direct determination of the key parameter that is the free metal ion concentration.

Polymer functionalized nanocomposites for metals removal from water and wastewater: An overview.

Pollution by metal and metalloid ions is one of the most widespread environmental concerns. They are non-biodegradable, and, generally, present high water solubility facilitating their environmental mobilisation interacting with abiotic and biotic components such as adsorption onto natural colloids or even accumulation by living organisms, thus, threatening human health and ecosystems. Therefore, there is a high demand for effective removal treatments of heavy metals, making the application of adsorption materials such as polymer-functionalized nanocomposites (PFNCs), increasingly attractive. PFNCs retain the inherent remarkable surface properties of nanoparticles, while the polymeric support materials provide high stability and processability. These nanoparticle-matrix materials are of great interest for metals and metalloids removal thanks to the functional groups of the polymeric matrixes that provide specific bindings to target pollutants. This review discusses PFNCs synthesis, characterization and performance in adsorption processes as well as the potential environmental risks and perspectives.

Manufactured nanoparticles in the aquatic environment-biochemical responses on freshwater organisms: A critical overview.

The enormous investments in nanotechnology have led to an exponential increase of new manufactured nano-enabled materials whose impact in the aquatic systems is still largely unknown. Ecotoxicity and nanosafety studies mostly resulted in contradictory results and generally failed to clearly identify biological patterns that could be related specifically to nanotoxicity. Generation of reactive oxygen species (ROS) is one of the most discussed nanotoxicity mechanism in literature. ROS can induce oxidative stress (OS), resulting in cyto- and genotoxicity. The ROS overproduction can trigger the induction of anti-oxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidases (GPx), which are used as biomarkers of response. A critical overview of the biochemical responses induced by the presence of NPs on freshwater organisms is performed with a strong interest on indicators of ROS and general stress. A special focus will be given to the NPs transformations, including aggregation, and dissolution, in the exposure media and the produced biochemical endpoints.

The role of charged polymer coatings of nanoparticles on the speciation and fate of metal ions in the environment.

Determining the environmental risk of metals requires an in-depth understanding of the environmental matrices composition, which currently also includes the presence of manufactured metallic nanoparticles (NPs) usually, stabilized by a polymer surface coating. As a consequence, is necessary to take into account effects of the NP core, the polymer surface coating and their mutual interaction as well as with other environmental components. The release of metal ions from metallic NPs is a well-known outcome, however, the effect of the presence of the NP polymer coating in the NPs solubilization mechanism is not well understood. In this study the dynamic speciation of Cd and Pb in presence of a polyacrylic acid (PAA)-stabilized CdTe/CdS NP was quantified by scanned stripping chronopotentiometry (SSCP). It was found that although the NP solubility was 5.8× larger at pH 8.5 than at pH 6.0, the amount of free Cd ions was much smaller (2.4 % at pH 8.5 vs. 57 % at pH 6.0). The concentration of free Cd and Pb ions in solution was larger in presence of the PAA-shells than when in presence of the same amount of polymer but when this is at the surface of the NP. This effect is attributed to the metal ions interaction with the particle itself. The effect is notably larger for Pb ions and might results from the exchange of Cd by Pb ions at the particle surface since PbS is less soluble than CdS.

Bioavailability of cadmium and biochemical responses on the freshwater bivalve Corbicula fluminea--the role of TiO2 nanoparticles.

The increasing and widespread applications of TiO2 engineered nanoparticles (nTiO2) led to the release of these materials into aquatic environments and consequently a change on the assessment of the environmental risk of trace metals. In this work, the role of two commercial nTiO2 with distinct crystalline phases and sizes (nTiO2-P25: 80% anatase+20% rutile, d=20nm; nTiO2-NA: 100% anatase, d=5 nm; 0.1 and 1.0 mg L(-1)) on Cd (112 µg L(-1)) speciation, biouptake and toxicity for the freshwater bivalve Corbicula fluminea was evaluated. The electroanalytical technique 'absence of gradients and Nernstian equilibrium stripping (AGNES)' was used to quantify the free Cd concentrations in the exposure medium in presence of both particles. Despite ca. 30-40% decrease of free Cd in the medium in presence of nTiO2, Cd uptake by C. fluminea was similar in the absence and presence of either of the particles. Superoxide dismutase and glutathione-S-transferase activities remained unchanged for Cd in absence and presence of nTiO2, whereas a significant increase of the catalase activity was obtained at the third day for Cd in presence of both nTiO2. Despite lipid peroxidation data shows that the presence of both nTiO2 seems to exert cells damage, a more quantitative description is not possible with the obtained data. The lack of clear-cut responses by the studied biomarkers, even when only in presence of Cd, do not allow insights into the effect of the presence of nTiO2 on the Cd toxicity to the bivalves. Notwithstanding, morphological changes in the digestive gland were clearly obtained in the presence of Cd, nTiO2 and Cd+nTiO2 indicating an inflammatory response.

The effects of different coatings on zinc oxide nanoparticles and their influence on dissolution and bioaccumulation by the green alga, C. reinhardtii.

Determining the environmental risk of nanoparticles (NPs) requires an in-depth understanding of the NP core, the particle surface coatings and the interactions of the two with environmental matrices. Non-coated ZnO NPs (nZnO) are known to release ionic Zn, contributing directly to the toxicity of these particles. On the other hand, relatively less data are available for particles that have coatings designed to increase particle stability. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Zn salt or nZnO with different stabilizers: (i) bare nZnO, (ii) polyacrylic acid-stabilized, nZnO-PAA, or a (iii) sodium hexametaphosphate-stabilized, nZnO-HMP. Multiple techniques were used to quantify particle agglomeration and dissolution. The dissolution of the NPs depended on the stabilizer, with the largest dissolution obtained for the bare nZnO (near total dissolution), followed by the nZnO-PAA. When exposed to the bare and PAA-stabilized nZnOs, bioaccumulation was largely accounted for by free Zn. On the other hand, the bioaccumulation of nZnO-HMP was greater than could be attributed to the release of free Zn from the particles. The increased Zn bioaccumulation was hypothesized to have resulted from the biological stimulation of C. reinhardtii due to phosphate from the particle coating.

Transcriptome sequencing (RNA-seq) analysis of the effects of metal nanoparticle exposure on the transcriptome of Chlamydomonas reinhardtii.

The widespread use of nanoparticles (NPs) raises concern over their potential toxicological effects in humans and ecosystems. Here we used transcriptome sequencing (RNA-seq) to evaluate the effects of exposure to four different metal-based NPs, nano-Ag (nAg), nano-TiO2 (nTiO2), nano-ZnO (nZnO), and CdTe/CdS quantum dots (QDs), in the eukaryotic green alga Chlamydomonas reinhardtii. The transcriptome was characterized before and after exposure to each NP type. Specific toxicological effects were inferred from the functions of genes whose transcripts either increased or decreased. Data analysis resulted in important differences and also similarities among the NPs. Elevated levels of transcripts of several marker genes for stress were observed, suggesting that only nZnO caused nonspecific global stress to the cells under environmentally relevant conditions. Genes with photosynthesis-related functions were decreased drastically during exposure to nTiO2 and slightly during exposures to the other NP types. This pattern suggests either toxicological effects in the chloroplast or effects that mimic a transition from low to high light. nAg exposure dramatically elevated the levels of transcripts encoding known or predicted components of the cell wall and the flagella, suggesting that it damages structures exposed to the external milieu. Exposures to nTiO2, nZnO, and QDs elevated the levels of transcripts encoding subunits of the proteasome, suggesting proteasome inhibition, a phenomenon believed to underlie the development and progression of several major diseases, including Alzheimer's disease, and used in chemotherapy against multiple myeloma.

Stability of core/shell quantum dots--role of pH and small organic ligands.

The improvement of knowledge about the toxicity and even processability, and stability of quantum dots (QD) requires the understanding of the relationship between the QD binding head group, surface structure, and interligand interaction. The scanned stripping chronopotentiometry and absence of gradients and Nernstian equilibrium stripping techniques were used to determine the concentration of Cd dissolved from a polyacrylate-stabilized CdTe/CdS QD. The effects of various concentrations of small organic ligands such as citric acid, glycine, and histidine and the roles of pH (4.5-8.5) and exposure time (0-48 h) were evaluated. The highest QD dissolution was obtained at the more acidic pH in absence of the ligands (52%) a result of the CdS shell solubility. At pH 8.5 the largest PAA ability to complex the dissolved Cd leads to a further QD solubility until the equilibrium is reached (24% of dissolved Cd vs. 4% at pH 6.0). The citric acid presence resulted in greater QD dissolution, whereas glycine, an amino acid, acts against QD dissolution. Surprisingly, the presence of histidine, an amino acid with an imidazole functional group, leads to the formation of much strong Cd complexes over time, which may be non-labile, inducing variations in the local environment of the QD surface.

Bioaccumulation and effects of CdTe/CdS quantum dots on Chlamydomonas reinhardtii - nanoparticles or the free ions?

In order to properly assess the environmental risk of engineered nanoparticles (ENP), it is necessary to determine their fate (including dissolution, aggregation, and bioaccumulation) under representative environmental conditions. CdTe/CdS quantum dots (QD), such as those used in medical imaging, are known to release Cd(2+) due (mainly) to the dissolution of their outer shell. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Cd salt or QD at similar concentrations of total Cd. Free Cd concentrations were measured using the Absence of Gradients and Nernstian Equilibrium Stripping technique. QD dissolution increased with decreasing pH and with increasing QD concentration. When exposed to QD, bioaccumulation was largely accounted for by dissolved Cd. Nonetheless, QD were shown to be taken up by the cells and to provoke unique biological effects. Whole transcriptome screening using RNA-Seq analysis showed that the free Cd and the QD had distinctly different biological effects.

Characterizing manufactured nanoparticles in the environment: multimethod determination of particle sizes.

Sizes of stabilized (24 h) nanoparticle suspensions were determined using several state-of-the-art analytical techniques (transmission electron microscopy; atomic force microscopy; dynamic light scattering; fluorescence correlation spectroscopy; nanoparticle tracking analysis; flow field flow fractionation). Theoretical and analytical considerations were evaluated, results were compared, and the advantages and limitations of the techniques were discussed. No "ideal" technique was found for characterizing manufactured nanoparticles in an environmental context as each technique had its own advantages and limitations.

Deposition of TiO2 nanoparticles onto silica measured using a quartz crystal microbalance with dissipation monitoring.

Titanium dioxide (TiO2) nanoparticles introduced into subsurface environments may lead to contamination of drinking water supplies and can act as colloidal carriers for sorbed contaminants. A model laboratory system was used to examine the influence of water chemistry on the physicochemical properties of TiO2 nanoparticles and their deposition. Deposition rates of TiO2 particles onto a silica surface were measured over a broad range of solution conditions (pH and ionic strength) using a quartz crystal microbalance with energy dissipation monitoring (QCM-D). Higher particle deposition rates were observed under favorable interaction conditions (i.e., in the presence of attractive electrostatic interactions) in comparison to unfavorable deposition conditions where electrostatic repulsion dominates particle-surface interactions. Nanoparticle sizes were characterized by fluorescence correlation spectroscopy (FCS), dynamic light scattering (DLS), and atomic force microscopy (AFM). These analyses confirmed the nanoscale of the system under study as well as the presence of TiO2 aggregates in some cases. TiO2 deposition behavior onto silica measured using QCM-D was generally found to be in qualitative agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability.

Aggregation of titanium dioxide nanoparticles: role of a fulvic acid.

The increasing use of nanomaterials in consumer products has led to increased concerns abouttheir potential environmental and health impacts. To better understand the transport, fate, and behavior of nanoparticles in aquatic systems, it is essential to understand their interactions with different components of natural waters including natural organic matter over a broad range of physicochemical conditions. Fluorescence correlation spectroscopy was used to determine the diffusion coefficients of TiO2 nanoparticles having a nominal size of 5 nm. The effects of a various concentrations of the Suwannee River Fulvic Acid (SRFA) and the roles of pH and ionic strength were evaluated. Aggregation of the bare TiO2 nanoparticles increased for pH values near the zero point of charge. At any given pH, an increase in ionic strength generally resulted in increased aggregation. Furthermore, conditions which favored adsorption of the SRFA resulted in less aggregation of the TiO2 nanoparticles, presumably due to increased steric repulsion. Under the conditions studied here, nanoparticle dispersions were often stable for environmentally relevant conditions of SRFA, pH, and ionic strength, suggesting that in the natural environment, TiO2 dispersion might occur to a greater extent than expected.

Copper removal by algal biomass: biosorbents characterization and equilibrium modelling.

The general principles of Cu(II) binding to algal waste from agar extraction, composite material and algae Gelidium, and different modelling approaches, are discussed. FTIR analyses provided a detailed description of the possible binding groups present in the biosorbents, as carboxylic groups (D-glucuronic and pyruvic acids), hydroxyl groups (cellulose, agar and floridean starch) and sulfonate groups (sulphated galactans). Potentiometric acid-base titrations showed a heterogeneous distribution of two major binding groups, carboxyl and hydroxyl, following the quasi-Gaussian affinity constant distribution suggested by Sips, which permitted to estimate the maximum amount of acid functional groups (0.36, 0.25 and 0.1 mmol g(-1)) and proton binding parameters (pK(H)=5.0, 5.3 and 4.4; m(H)=0.43, 0.37, 0.33), respectively for algae Gelidium, algal waste and composite material. A non-ideal, semi-empirical, thermodynamically consistent (NICCA) isotherm fitted better the experimental ion binding data for different pH values and copper concentrations, considering only the acid functional groups, than the discrete model. Values of pK(M) (3.2; 3.6 and 3.3), n(M) (0.98, 0.91, 1.0) and p (0.67, 0.53 and 0.43) were obtained, respectively for algae Gelidium, algal waste and composite material. NICCA model reflects the complex macromolecular systems that take part in biosorption considering the heterogeneity of the biosorbent, the competition between protons and metals ions to the binding sites and the stoichiometry for different ions.

Application of permeation liquid membrane and scanned stripping chronopotentiometry to metal speciation analysis of colloidal complexes.

The potential of permeation liquid membrane (PLM) to obtain dynamic metal speciation information for colloidal complexes is evaluated by measurements of lead(II) and copper(II) complexation by carboxyl modified latex nanospheres of different radii (15, 35, 40 and 65 nm). The results are compared with those obtained by a well characterized technique: stripping chronopotentiometry at scanned deposition potential (SSCP). Under the PLM conditions employed, and for large particles or macromolecular ligands, membrane diffusion is the rate-limiting step. That is, the flux is proportional to the free metal ion concentration with only a small contribution from labile complexes. In the absence of ligand aggregation in the PLM channels, good agreement was obtained between the stability constants determined by PLM and SSCP for both metals.