Interaction between Al2O3 and different sizes of GO in aqueous environment

Silver nanoparticles exhibit in vitro anthelmintic and antimicrobial activities against Dactylogyrus minutus (Kulwieć, 1927), and Aeromonas hydrophila in Cyprinus carpio Koi

The study aimed to evaluate the in vitro anthelminthic and antimicrobial activity of silver nanoparticles (AgNPs) against Dactylogyrus minutus and Aeromonas hydrophila, pathogens of Cyprinus carpio Koi. Gill arches of the fish were removed and placed into six-well plates containing 10 mL of tank water with varying concentrations of AgNPs: 100, 400, 500, 600, and 800 mg/L, along with control groups using tank water and distilled water. Each group was tested in triplicate. Parasites were observed every 10 min for 300 min (5 h) using a stereomicroscope, and mortality rates were recorded. Anthelminthic efficacy was calculated at the end of the tests. For the in vitro antimicrobial test, the Minimum Inhibitory Concentration (MIC) of AgNPs was determined by adding 100 μL of Poor Broth (PB) culture medium to all 96 wells of a microplate. The first well was filled with 100 μL of AgNPs, followed by serial dilutions (1:2 ratio). Subsequently, 50 μL of A. hydrophila (1 × 107 CFU/mL) was added to all wells and incubated for 24 h at 28 °C. Results showed that 800 mg/L of AgNPs achieved 87% anthelminthic efficacy within 300 min, while 100 mg/L achieved 47% efficacy. The MIC showed bacterial growth inhibition at 125 mg/mL. Despite the 87% efficacy against parasites within 300 min, AgNPs did not reach 100% efficacy quickly, limiting their potential use in ornamental fish farming. Further studies are needed to assess the toxicity of AgNPs in fish.

A Meta-Analysis to Revisit the Property-Aggregation Relationships of Carbon Nanomaterials: Experimental Observations versus Predictions of the DLVO Theory

Contradicting relationships between physicochemical properties of nanomaterials (e.g., size and ζ-potential) and their aggregation behavior have been constantly reported in previous literature, and such contradictions deviate from the predictions of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. To resolve such controversies, in this work, we employed a meta-analytic approach to synthesize the data from 46 individual studies reporting the critical coagulation concentration (CCC) of two carbon nanomaterials, namely, graphene oxide (GO) and carbon nanotube (CNT). The correlations between CCC and material physicochemical properties (i.e., size, ζ-potential, and surface functionalities) were examined and compared to the theoretical predictions. Results showed that the CCC of electrostatically stabilized carbon nanomaterials increased with decreasing nanomaterial size when their hydrodynamic sizes were smaller than ca. 200 nm. This is qualitatively consistent with the prediction of the DLVO theory but with a smaller threshold size than the predicted 2 μm. Above the threshold size, the material ζ-potential can be correlated to CCC for nanomaterials with moderate/low surface charge, in agreement with the DLVO theory. The correlation was not observed for highly charged nanomaterials because of their underestimated surface potential by the ζ-potential. Furthermore, a correlation between the C/O ratio and CCC was observed, where a lower C/O ratio resulted in a higher CCC. Overall, our findings rationalized the inconsistency between experimental observation and theoretical prediction and provided essential insights into the aggregation behavior of nanomaterials in water, which could facilitate their rational design.

Size effect of graphene oxide from quantum dot to nanoflake on the mobility of nanoplastics in seawater-saturated sand

Marine sedimentary environment serves as an important sink of terrigenous nanoplastics (NP) and graphene oxides (GO). In this study, we discovered that GO of varying sizes exhibited distinct binding modes with 200 nm NP in 35 practical salinity unit (PSU) seawater, resulting in varying impacts on the mobility of NP in porous media. GO-8, with a size of 8±2 nm, firmly adhered to the surface of NP and formed stable primary heterogeneous aggregates, which promoted NP mobility and increased the mass recovery of effluent (Meff) from 24.74% to 31.08%. GO-250 (246±10 nm) partly enveloped NP and only slightly increased the volume of heteroaggregates, which had minimal effect on NP transport. Conversely, GO-850 (855±55 nm) wrapped numerous NP particles to form large secondary heteroaggregates that clung to sand surfaces, providing additional attachment sites for NP, resulting in complete inhibition of NP mobility in porous media (Meff = 0%). In brackish water with 3.5 PSU, all GO-8, GO-250 and GO-850 achieved enhanced mobility of NP, with Meff increasing from 50.35% to 85.62%, 69.45% and 75.41%, respectively. The results indicate that GO size effects on NP mobility are also salinity-dependent.

Study on the Adsorption Performance and Adsorption Mechanism of Graphene Oxide by Red Sandstone in Aqueous Solution

In order to deal with the increasingly serious pollution of graphene oxide (GO) to the environment. In this paper, the use of red sandstone to treat GO-contaminated aqueous solution is proposed for the first time, and the adsorption capacity and adsorption mechanism of red sandstone to GO are discussed. The controlled variable method was used to explore the optimal pH, concentration, and quality of red sandstone for GO aqueous solution. The adsorption isotherm, thermodynamics, and adsorption kinetics were fitted. Adsorption characterization tests were performed using XRD, AFM, XPS, FT-IR, SAP, TEM, SAP, laser particle size analyzer, and SEM. The results show that when $T=303\text{K}$ , the optimum adsorption condition of red sandstone for GO is $\text{pH}=4$ , the mass of the adsorbent is 40 mg, and when the concentration of GO is 80 mg/L, the adsorption capacity is 90 mg/g. The adsorption isotherm model fits the Langmuir model. The adsorption thermodynamic experiments and fitting results show that the reaction is endothermic. XRD and FT-IR tests showed that CaCO3 in red sandstone was involved in the adsorption of GO. SEM, TEM, and AFM microscopic results showed that GO was adsorbed on the surface of red sandstone particles. The XPS test showed that Ca2+ in red sandstone and C=O bond in GO undergo ionic or coordination reaction. The adsorption kinetics fit a pseudo-second-order kinetic model. This study will provide some references for the removal of GO in the environment and the interaction mechanism with natural minerals.

A critical review on the role of abiotic factors on the transformation, environmental identity and toxicity of engineered nanomaterials in aquatic environment

Engineered nanomaterials (ENMs) are at the forefront of many technological breakthroughs in science and engineering. The extensive use of ENMs in several consumer products has resulted in their release to the aquatic environment. ENMs entering the aquatic ecosystem undergo a dynamic transformation as they interact with organic and inorganic constituents present in aquatic environment, specifically abiotic factors such as NOM and clay minerals, and attain an environmental identity. Thus, a greater understanding of ENM-abiotic factors interactions is required for an improved risk assessment and sustainable management of ENMs contamination in the aquatic environment. This review integrates fundamental aspects of ENMs transformation in aquatic environment as impacted by abiotic factors, and delineates the recent advances in bioavailability and ecotoxicity of ENMs in relation to risk assessment for ENMs-contaminated aquatic ecosystem. It specifically discusses the mechanism of transformation of different ENMs (metals, metal oxides and carbon based nanomaterials) following their interaction with the two most common abiotic factors NOM and clay minerals present within the aquatic ecosystem. The review critically discusses the impact of these mechanisms on the altered ecotoxicity of ENMs including the impact of such transformation at the genomic level. Finally, it identifies the gaps in our current understanding of the role of abiotic factors on the transformation of ENMs and paves the way for the future research areas.

The detection and characterization techniques for the interaction between graphene oxide and natural colloids: A review

The high dispersibility of graphene oxide (GO) and the universality of natural colloids (clay minerals, (hydr)oxides of Al, Fe, silica, etc.) make them interact easily. Many kinds of analytical methods have been used to study the interaction between GO and natural colloids. This review provides a comprehensive overview of analytical methods for the detection and quantification of interaction process. We highlighted the influence of the most relevant environmental factors (ionic strength, pH, etc.) on batch experiment, quartz crystal microbalance with dissipation monitoring measurements, and column experiments. Besides, the benefits and drawbacks of spectroscopic, microscopic techniques, theoretical models, calculation and time-resolved dynamic light scattering methods also have discussed in this work. This review can give some guidance to researchers in their selection and combination of the technique for the research of the interaction between GO and natural colloids.

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.

Key principles and operational practices for improved nanotechnology environmental exposure assessment

Nanotechnology is identified as a key enabling technology due to its potential to contribute to economic growth and societal well-being across industrial sectors. Sustainable nanotechnology requires a scientifically based and proportionate risk governance structure to support innovation, including a robust framework for environmental risk assessment (ERA) that ideally builds on methods established for conventional chemicals to ensure alignment and avoid duplication. Exposure assessment developed as a tiered approach is equally beneficial to nano-specific ERA as for other classes of chemicals. Here we present the developing knowledge, practical considerations and key principles need to support exposure assessment for engineered nanomaterials for regulatory and research applications.

Crystalline phase-dependent toxicity of aluminum oxide nanoparticles toward Daphnia magna and ecological risk assessment

Aluminum oxide nanoparticles (Al₂O₃ NPs) can be found in different crystalline phases, and with the emergence of nanotechnology there has been a rapid increase in the demand for Al₂O₃ NPs in different engineering areas and for consumer products. However, a careful evaluation of the potential environmental and human health risks is required to assess the implications of the release of Al₂O₃ NPs into the environment. Thus, the objective of this study was to investigate the toxicity of two crystalline phases of Al₂O₃ NPs, alpha (α-Al₂O₃ NPs) and eta (η-Al₂O₃ NPs), toward Daphnia magna and evaluate the risk to the aquatic ecology of Al₂O₃ NPs with different crystalline phases, based on a probabilistic approach. Different techniques were used for the characterization of the Al₂O₃ NPs. The toxicity toward Daphnia magna was assessed based on multiple toxicological endpoints, and the probabilistic species sensitivity distribution (PSSD) was used to estimate the risk of Al₂O₃ NPs to the aquatic ecology. The results obtained verify the toxic potential of the NPs toward D. magna even in sublethal concentrations, with a more pronounced effect being observed for η-Al₂O₃ NPs. The toxicity is associated with an increase in the reactive oxygen species (ROS) content and deregulation of antioxidant enzymatic/non-enzymatic enzymes (CAT, SOD and GSH). In addition, changes in MDA levels were observed, indicating that D. magna was under oxidative stress. The most prominent chronic toxic effects were observed in the organisms exposed to η-Al₂O₃ NPs, since the lowest LOEC was 3.12 mg/L for all parameters, while for α-Al₂O₃ NPs the lowest LOEC was 6.25 mg/L for longevity, growth and reproduction. However, the risk assessment results indicate that, based on a probabilistic approach, Al₂O₃ NPs (alpha, gamma, delta, eta and theta) only a very limited risk to organisms in surface waters.

New insight into the aggregation of graphene oxide in synthetic surface water: Carbonate nanoparticle formation on graphene oxide

Graphene oxide (GO), used in a wide variety of applications, is increasingly being introduced into aquatic environments; this situation calls for research on GO aggregation and sedimentation to regulate the environmental behaviors and risks. Many studies have investigated the aggregation and the mechanism of GO in water with a single background salt (monosalt system); however, this may not reflect real water environments where multiple salts coexist (multisalt system). A typical synthetic surface water (soft water) with representative multisalts was therefore used to study the aggregation and sedimentation of GO. The GO concentration-dependent aggregation (low concentration aggregation, high concentration stability) was observed in the soft water, and this concentration-dependent aggregation is opposite to the aggregation in monosalt systems (NaCl or CaCl₂ solutions). The presence of GO sheets induced the formation of amorphous CaMg(CO₃)₂ nanoparticles on the GO surfaces in the soft water, and the formed nanoparticles promoted the aggregation and sedimentation of low concentrations of GO through bridging action. Neutral and alkaline conditions were favorable for the formation of CaMg(CO₃)₂ nanoparticles and the induced GO aggregation. These findings show a new mechanism of GO aggregation in environmentally relevant waters and help us to better evaluate the environmental fate of GO.

Is the interaction between graphene oxide and minerals reversible?

The increased applications and production of graphene oxide (GO) make the necessity to study information on the interaction of GO with minerals. In this work, adsorption and desorption were used to study the reversibility of interaction between GO and goethite/kaolinite. Result showed that the pH value, ionic strength, and temperature had significant effects on the adsorption and desorption behavior of GO. Interaction force was stronger between GO and goethite than that of kaolinite. The interaction may be attributed to the electrostatic, hydrogen-bonding, and Lewis acid base interactions. The irreversible interaction between GO and minerals may be a main mechanism for the observed desorption hysteresis. These results are important for evaluating the fate and health risk of GO in the environment.

Facile self-assembly synthesis of γ-Fe2O3 /graphene oxide for enhanced photo-Fenton reaction

A novel self-assembly method was developed to prepare a γ-Fe₂O₃/graphene oxide (GO) heterogeneous catalyst that showed excellent synergy between photocatalysis and Fenton-like reactions. The γ-Fe₂O₃/GO catalyst prepared on the iron plates demonstrated efficient and reproducible catalytic activities for water treatment. It takes only 80 min to degrade 50 mg L^-1 methylene (MB) completely, which is the main non-biodegradable dye in wastewater from the textile industry. The heterogeneous catalyst is stable over a wide range of pH (from 2.0 to 10.2) for MB degradation, and can be easily extracted from solution and repeatedly used with little loss of catalytic activity. The high activity and stability of the catalyst system can be attributed to charge separation between γ-Fe₂O₃ and GO, which could accelerate Fenton-like process and photocatalysis. In addition, the dominant reactive oxidant species responsible for the MB degradation, including the hydroxyl radicals (•OH) and holes (h⁺), were trapped on the surface of the γ-Fe₂O₃/GO composite, as proved by a free-radical quenching experiment. The γ-Fe₂O₃/GO heterogeneous catalyst could potentially provide a solution for removal of non-biodegradable dyes from wastewater in the textile industry.