Attachment of cerium oxide nanoparticles of different surface charges to kaolinite: Molecular and atomic mechanisms

Recent Advances in Kaolinite Nanoclay as Drug Carrier for Bioapplications: A Review

Advanced functional two-dimensional (2D) nanomaterials offer unique advantages in drug delivery systems for disease treatment. Kaolinite (Kaol), a nanoclay mineral, is a natural 2D nanomaterial because of its layered silicate structure with nanoscale layer spacing. Recently, Kaol nanoclay is used as a carrier for controlled drug release and improved drug dissolution owing to its advantageous properties such as surface charge, strong biocompatibility, and naturally layered structure, making it an essential development direction for nanoclay-based drug carriers. This review outlines the main physicochemical characteristics of Kaol and the modification methods used for its application in biomedicine. The safety and biocompatibility of Kaol are addressed, and details of the application of Kaol as a drug delivery nanomaterial in antibacterial, anti-inflammatory, and anticancer treatment are discussed. Furthermore, the challenges and prospects of Kaol-based drug delivery nanomaterials in biomedicine are discussed. This review recommends directions for the further development of Kaol nanocarriers by improving their physicochemical properties and expanding the bioapplication range of Kaol.

Cerium oxide nanoparticles (nCeO2) exert minimal adverse effects on microbial communities in soils with and without biosolids amendment

Increased use of nano-cerium oxide (nCeO₂) in an array of industrial applications has raised environmental concerns due to potential increased loadings to the soil environment. This research investigated the potential adverse effects of nCeO₂ (10-30 nm) on the soil microbial community in two exposure scenarios: direct application to soil, and indirect application to soil through chemical spiking of biosolids, followed by mixing into soil. Total Ce in test soils without, and with biosolids amendment, ranged from 44 to 770, and 73 to 664 mg Ce kg^-1 soil, respectively. In order to help distinguish whether observed effects were elicited by the solid-phase colloids or the activity of dissolved Ce, a soluble Ce salt (Ce (NO₃)₃) treatment was included in select assays. A suite of tests was used to investigate effects on critical processes: microbial growth (heterotrophic plate count), microbial activity (organic matter (OM) decomposition, enzyme activity and, nitrification) and diversity (structural and functional). Although results showed significant inhibition on microbial growth in soil without biosolids amendment at ≥ 156 mg Ce kg^-1 soil by week 5, these results were inconsistent and non-significant thereafter. In general, nCeO₂ showed no evidence of consistent adverse effects on OM decomposition, nitrification, soil enzyme activities and functional diversity. Leucine aminopeptidase showed significant (p< 0.05) stimulatory effects over time at ≥ 44 mg Ce kg^-1 in soils without biosolids, which was not observed in soils with biosolids amendment. The lack of inhibitory effects of nCeO₂ may be attributed to its low solubility; Ce in soil extracts (0.01 M CaCl₂) were all below detection (< 0.003 mg kg^-1) in the nCeO₂-spiked soils, but detectable in the Ce (NO₃)₃ samples. In contrast, soluble Ce at 359 mg Ce kg^-1 showed a significant reduction in OM decomposition and effects on microbial genomic diversity based on the 16S rDNA data in soils with and without biosolids amendment (359 and 690 mg Ce kg^-1). The nCeO₂ behaviour and effects information described herein are expected to help fulfill data gaps for the characterization of this priority nanomaterial.

The aggregation of natural inorganic colloids in aqueous environment: A review

Natural inorganic colloids (NICs) are the most common and dominant existence in the ecosystem, with high concentration and wide variety. In spite of the low toxicity, they can alter activity and mobility of hazardous engineered nanoparticles (ENPs) through different interactions, which warrants the necessity to understand and predict the fate and transport of NICs in aquatic ecosystems. Here, this review summarized NICs properties and behaviors, interaction mechanisms and environmental factors at the first time. Various representative NICs and their physicochemical properties were introduced across the board. Then, the aggregation and sedimentation behaviors were discussed systematically, mainly concerning the heteroaggregation between NICs and ENPs. To speculate their fate and elucidate the corresponding mechanisms, the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (X-DLVO) theories were focused. Furthermore, a range of intrinsic and extrinsic factors was presented in different perspective. Last but not the least, this paper pointed out theoretical and analytical gaps in current researches, and put forward suggestions for further research, aiming to provide a more comprehensive and original perspective in the fields of natural occurring colloids.

Influence of extracellular polymeric substances on the heteroaggregation between CeO2 nanoparticles and soil mineral particles

Interaction with soil mineral particles (SMPs) and organic matters can significantly determine the fate of nanoparticles (NPs) in the environment such as waters, sediments, and soils. In this study, the heteroaggregation of CeO₂ NPs with different soil minerals (kaolinite, montmorillonite, goethite and hematite) and the influence of extracellular polymeric substance (EPS) were studied. The obvious heteroaggregation between CeO₂ NPs with different SMPs were demonstrated via co-settling and aggregation kinetics experiments. The variety in the heteroaggregation between CeO₂ NPs with different SMPs is mainly induced by the difference in their surface properties, such as surface charge, specific surface areas and surface complexation. The presence of EPS can result in great inhibition on the heteroaggregation between CeO₂ NPs with the positive charged goethite by enhancing the electrostatic repulsion between NPs and mineral colloids. However, the influence of EPS on the interaction between CeO₂ NPs with negative charged SMPs is more dependent on the steric stabilization. The presence of EPS may promote the migration of CeO₂ NPs in environment and then increase their risks to human health and ecosystems. These findings contribute to better understanding interactions between NPs and SMPs and have important implications on predicting the behaviors and risks of NPs in the natural environment.

Elucidating the impact of three metallic nanoagrichemicals and their bulk and ionic counterparts on the chemical properties of bulk and rhizosphere soils in rice paddies

Growing applications of nanoagrichemicals have resulted in their increasing accumulation in agricultural soils, which could modify soil properties and affect soil health. A greenhouse pot trial was conducted to determine the effects of three metallic nanoagrichemicals on several fundamental chemical properties of a rice paddy soil, including zinc oxide nanoparticles (ZnO NPs) and copper oxide nanoparticles (CuO NPs) at 100 mg/kg, and silicon oxide nanoparticles (SiO₂ NPs) at 500 mg/kg, as well as their bulk and ionic counterparts. The investigated soil amendments displayed significant and distinctive impact on the examined soil chemical properties relevant to agricultural production, including soil pH, redox potential, soil organic carbon (SOC), cation exchange capacity (CEC), and plant available As. For example, all amendments increased the bulk soil pH at day 47 to some extent, but the increase was substantially higher for SiO₃^2- (37.7%) than other amendments (5.8%-13.7%). Soil Eh was elevated markedly at day 47 after the addition of soil amendments in both the bulk soil (45.9%-74.4%) and rice rhizosphere soil (20.3%-68.9%). CuO NPs and Cu²⁺ generally exhibited greater impact on soil chemical properties than other agrichemicals. Significantly different responses to soil amendments were observed between bulk and rhizosphere soils, suggesting the essential role of plants in affecting soil properties and their responses to environmental disturbance. Overall, our results confirmed that the tested amendments could have remarkable impacts on the fundamental chemical properties of rice paddy soils.

Recent insights into the impact, fate and transport of cerium oxide nanoparticles in the plant-soil continuum

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture provided that the exposure and toxicity are adequately assessed and properly controlled. The global production and application of cerium oxide nanoparticles (CeO₂-NPs) in various industrial sectors have tremendously increased. Most of the nanoparticles end up in water and soil where they interact with soil microorganisms and plants. Investigating the uptake, translocation and accumulation of CeO₂-NPs is critical for its safe application in agriculture. Plant uptake of CeO₂-NPs may lead to their accumulation in different plant tissues and interference with key metabolic processes of plants. Soil microbes can also be affected by increasing CeO₂-NPs in soil, leading to changes in the physiology and enzymatic activity of soil microorganisms. The interactions between CeO₂-NPs, microbes and plants in the agricultural system need systemic research in ecologically relevant conditions. In the present review, The uptake pathways and in-planta translocation of CeO₂-NPs,and their impact on plant morphology, nutritional values, antioxidant enzymes and molecular determinants are presented. The role of CeO₂-NPs in modifying soil microbial community in plant rhizosphere is also discussed. Overall, the review aims to provide a comprehensive account on the behaviour of CeO₂-NPs in soil-plant systems and their potential impacts on the soil microbial community and plant health.

Composite materials based on heteroaggregated particles: Fundamentals and applications

Homoaggregation of dispersed particles, i.e., aggregation of particles of the same shape, charge, size, and composition, is a well-studied field and various theoretical and experimental approaches exist to understand the major phenomena involved in such processes. Besides, heteroaggregation of particles, i.e., aggregation of particles of different shape, charge, size, or composition, has attracted widespread interest due to its relevance in various biomedical, industrial, and environmental systems. For instance, heteroaggregation of plastic contaminant particles with naturally occurring solid materials in waters (e.g., clays, silica and organic polymers) plays an important role in the decontamination technologies. Moreover, nanofabrication processes involving heteroaggregation of particles to prepare novel composite materials are widely implemented in fundamental science and in more applied disciplines. In such procedures, stable particle dispersions are mixed and the desired structure forms owing to the presence of interparticle forces of various origins, which can be tuned by performing appropriate surface functionalization as well as altering the experimental conditions. These composites are widely used in different fields from sensing through catalysis to biomedical delivery. The present review summarizes the recent progresses in the field including new findings regarding the basic principles in particle heteroaggregation, preparation strategies of heteroaggregated structures of different morphology, and the application of the obtained hybrid composites. Such information will be very helpful to those involved in the design of novel composites consisting of different nano or colloidal particles.

Impact of nanoparticle surface charge and phosphate on the uptake of coexisting cerium oxide nanoparticles and cadmium by soybean (Glycine max. (L.) merr.)

Engineered nanoparticles (ENPs) often interact closely with coexisting environmental pollutants; however, the effect of their surface properties on such interactions in a plant system has not been examined. This study investigated the roles of ENP surface charge and growth media chemistry on the mutual effects of cerium oxide nanoparticles (CeO2NPs) and cadmium (Cd) on their plant uptake and accumulation in a hydroponic system. Soybean seedlings were exposed to five nanoparticle/Cd treatments including: 100 mg L-1 CeO2NPs(+); 100 mg L-1 CeO2NPs(-); 100 mg L-1 CeO2NPs(+) + 1 mg L-1 Cd; 100 mg L-1 CeO2NPs(-) + 1 mg L-1 Cd; and 1 mg L-1 Cd only, in the presence or absence of 15 mg L-1 phosphorous in the form of phosphate. After 4 days of exposure, concentrations of Cd and Ce in plant tissues were quantified by inductively coupled plasma-mass spectrometry. Roots exposed to CeO2NPs(+) contained 87% higher Ce than plants exposed to CeO2NPs(-). Phosphate significantly increased the root concentration of Ce by 61% and 66% exposed to CeO2NPs(+) and CeO2NPs(-), respectively. The mutual effect of CeO2NPs and Cd was also affected by phosphate, and the net effect of phosphate depended upon the surface charge of CeO2NPs.