Nanoparticle Mass Research Articles

Techno-economic analysis of nitrogen-doped graphene/water nanofluid in various heat exchangers (A unified analysis)

Nitrogen-doped graphene (NDG)/water nanofluid is one of the emerging working fluids toward achieving high heating rates in heat transfer devices. In the present study, thermal performance improvement and techno-economic analysis of a double pipe, shell and tube, and plate heat exchangers are presented while incorporating NDG/water nanofluid as a working fluid. The variable properties of NDG nanofluid are incorporated and the influence of nanoparticle concentrations and mass flow rates on the device thermal performance and related costs are evaluated. The findings demonstrate that device heat transfer area and costs are adversely affected by using NDG/water nanofluid in all types of heat exchanging devices considered. An increase in heat transfer area is associated with the decrease of the specific heat capacity of the working fluid. The increase of heat transfer area can be as high as 58.5%, 45.1%, and 67.0% for double pipe, shell and tube, and plate heat exchangers, respectively. In addition, area increase becomes persistent with other types of nanoparticles used in the carrier fluid.

Recent progress in Arrhenius activation energy for radiative heat transport of cross nanofluid over a melting wedge

A theoretical numerical communication is demonstrated to analyze the impact of Arrhenius activation energy and melting phenomena on chemically reactive Falkner-Skan flow of cross nanofluid over a moving wedge with viscous dissipation and nonlinear radiation impacts. The basic partial differential equations for nanoparticle concentration, energy, momentum and mass conservation are reduced to nonlinear ordinary differential equations with the help of appropriate transforming variables and then solved numerically via bvp4c Matlab solver. It is interesting to notice that nanoparticle concentration and concentration boundary layer thickness are uplifted for enhancing values of activation energy parameter. Additionally, magnitude of heat transfer rate is a growing function of the Eckert number.

The experimental comparison between the effect of copper oxide and graphene nanoparticles on rheological behavior and thermal properties of engine oil

The low thermal conductivity and viscosity index of conventional lubricants limit their performance. Therefore, it is crucial to achieving a nano-lubricant with suitable thermophysical properties as an alternative for the base-oil. Some investigations have been carried out in the past decade on the anti-frictional and thermal properties of nano-lubricants containing different nanoparticles. Meanwhile, studies on copper oxide nanoparticles are mostly concerned with their effect on thermal conductivity, and only a small number of studies have been carried out on graphene, which is focused on its effect on viscosity. However, rarely investigations have been performed on the simultaneous effect of these nanoparticles on the rheological behavior and thermal properties of engine oil. Also, there are only a few published articles on deriving the thermo-physical properties of nano-lubricants containing these nano-additives from experimental and theoretical approaches. Therefore, current work aims to compare the thermophysical features (dynamic viscosity, shear stress, thermal conductivity, flash point, and pour point) of the engine oil using copper oxide and graphene nano-additives under the influence of the effective variables includes shear rate, temperature, and nanoparticles mass fraction. Also, some correlations are proposed based on the experimental data to predict the rheological behavior and thermal conductivity of the nanofluids.

Influences of Zero Mass Flux and Active Conditions on the Predictions of Double Dispersion and Double Diffusive Boundary Layer in Darcy/Non Darcy Nanofluid Flow

Free convective of nanofluid inside dispersive porous medium adjacent to a vertical plate under the effects of the zero mass nanoparticles flux condition and the thermal and solutal dispersions is studied. Buongiorno's model revised is used considering Darcy and non Darcy laminar flows, and isothermal or convective flux outer the wall. Dimensionless governing equations formulated using velocity, temperature, concentration and nanoparticle volume fraction have been solved by finite difference method that implements the 3-stage Lobatto collocation formula. The numerical data obtained with semi or full dispersions cases are compared to predictions made using the non dispersive porous medium. Taking into account the dispersions, the influence of the zero mass nanoparticles flux condition is examined to test the validity of the control active nanoparticle assumption. It is found mainly that the thermal transfers can reach more than 100% in connection with the case where of a semi-dispersion of the porous medium is applied. Realistic condition, i.e. zero mass flux should be addressed for the heat transfer rate rather than the mass transfer rate, discovered markedly different to the active condition. This signifies the importance of considering the zero nanoparticles mass flux and dispersions in the performance characterization of nanofluid flow in porous media.

Starch engineered with Moringa oleifera seeds protein crosslinked Fe3O4: A synthesis and flocculation studies

This study aimed to utilize cationic protein extracted from the Moringa oleifera seed in the fabrication of cationic starch crosslinked with magnetic nanoparticles (MagCS). Important synthesis parameters include starch to cationic protein volume ratio, magnetic nanoparticles mass fraction, reaction and crosslinking time, reaction and crosslinking temperature and crosslinker concentration. At optimum synthesis conditions, MagCS yield a 38.55% amide content, 2.46 degree of substitution, 1.1 mmol/g charge density and 78.6% crosslinking, which are much higher compared to other starch derivatives. A series of characterization analyses such as Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, elemental analysis and vibrating sample magnetometer concluded that MagCS was embedded with amide group, has high crystallinity structure, is thermally stable and shows a promising magnetic characteristic. Based on the synthesis parameters and characterization studies, the synthesis mechanism of MagCS was also postulated. The flocculation performance of MagCS was successfully assessed for the treatment of palm oil mill effluent. At optimum dosage, initial pH and settling time of 1.0 g/L, 9.0 and 15 min, the MagCS flocculant was able to remove 90.48, 83.95 and 58.19% of turbidity, color and chemical oxygen demand, respectively. This study provides an alternative eco-friendly materials in the wastewater treatment application.

Flow of aqueous Fe2O3–CuO hybrid nanofluid over a permeable stretching/shrinking wedge: A development on Falkner–Skan problem

Here, continuous two-dimensional boundary layer flow of a Fe2O3CuO/water hybrid nanofluid over a porous stretching/shrinking wedge with radiation and MHD effects has been investigated semi–analytically. The dual solutions of the problem and also its stability analysis are taken into account. Moreover, the mass-based procedure for hybrid nanofluid modeling has been used. According to this procedure, the volume fraction of first and second nanoparticles is written in terms of both nanoparticles as well as base fluid masses. The Tiwari-Das model joined with mass-based hybrid nanofluid procedure is applied to find the governing partial differential equations which are then transferred to a set of dimensionless ordinary differential equations with help of the similarity transform method. The numerical method of solution has been chosen based on a famous finite difference scheme (bvp4c) from MATLAB software. The results demonstrate that dual solutions exist for a certain domain of the wedge stretching/shrinking parameter. Also it is observed that always the first solutions have thinner boundary layer thickness than the second ones. Moreover, the critical value in which the solution is in existence increase with the enhancement of magnetic parameter and suction parameter. The magnetic parameter and the mass suction at the wedge's surface also leads to the increase in the local Nusselt number. Further, it is inferred that the second nanoparticle's mass enhancement results in the amplification of the skin friction coefficient and the local Nusselt number for the first solutions. In addition, the rise in radiation parameter tends to enhance the thermal boundary layer thickness.

Characteristics and Extent of Particulate Matter Emissions of a Ropeway Public Mobility System in the City Center of Perugia (Central Italy)

Minimetrò (MM) is a ropeway public mobility system that has been in operation in the city of Perugia for about ten years to integrate with urban mobility and lighten vehicular traffic in the historic city center. The purpose of this work was to evaluate the impact of MM as a source of pollutants in the urban context, and the exposure of people in the cabins and the platforms along the MM line. These topics have been investigated by means of intensive measurement and sampling campaigns performed in February and June 2015 on three specific sites of the MM line representative of different sources and levels of urban pollution. Stationary and dynamic measurements of particle size distribution, nanoparticle and black carbon aerosol number and mass concentrations measurements were performed by means of different bench and portable instruments. Aerosol sampling was carried out using low volume and high-volume aerosol samplers, and the samples nalysed by off-line methods. Results show that MM is a considerable source of atmospheric particulate matter having characteristics very similar to those of the common urban road dust in Perugia. In the lack of clear indications on road dust effect, the contribution of MM to the aerosol in Perugia cannot be neglected.

RETRACTED: Aqueous aluminium–copper hybrid nanofluid flow past a sinusoidal cylinder considering three-dimensional magnetic field and slip boundary condition

We analyzed the problem of the steady general three-dimensional magnetohydrodynamics stagnation-point boundary layer flow past an impermeable wavy circular cylinder considering aluminium–copper/water hybrid nanofluid as the working fluid and velocity slip as well as temperature jump boundary conditions. The induced magnetic field effect was also taken into account. The analytical procedure is based on the model that implements the nanoparticles and base fluid masses to formulate the equivalent volume fraction, equivalent density, and equivalent specific heat at constant pressure which is then substituted in the chosen single-phase thermophysical properties. Then, the foregoing relations were used in basic governing PDEs (partial differential equations), according to Tiwari–Das nanofluid scheme. It is worth mentioning that the bvp4c code from MATLAB software that is a famous finite-difference method has been exploited for solving the final similarity ODEs (ordinary differential equations). Results demonstrate that the developed mass-based model can be successfully employed with great confidence to study the flow and heat transfer of hybrid nanofluid in other similar problems. Moreover, it is proved that the nodal stagnation points possess higher values of skin friction coefficients and local Nusselt numbers relative to those for the saddle stagnation points. Besides, enhancing the second nanoparticle's mass leads to increase in all parameters of engineering interest including skin friction coefficients along x and y directions as well as local Nusselt number.

Influence of solid surface, temperature and concentration on contact angle of water-FeC nanofluid

Current study presents experimental results concerning dynamic contact angle of water-FeC nanofluid on three solid surfaces what are frequently used in practical applications involving heat transfer, namely aluminum, copper and stainless steel. Hence, measurement of both advancing and receding contact angles were carried out by the Wilhelmy plate procedure for each surface within a range of temperatures values from 20 °C to 50 °C, and three nanoparticles mass concentrations (0.1%, 0.5% and 1.0%). Results reveal the dynamic contact angles decrease with the temperature, the reduction in the average contact angle of aluminum–FeC nanofluid being more significant than of copper-FeC nanofluid and stainless steel–FeC nanofluid, showing that aluminum–FeC nanofluid exhibits better wettability. In addition, it was noticed a reduction of the average contact angle with the nanofluid concentration. The results contribute to a better comprehension of the nanoparticles influence in the surfaces wettability.

Degradation of Remazol Black dye from Aqueous Solution by Heterogeneous NH3(MoO3)3/H2O2 System

Aims: The pollution of the environment by organic dyes in water is a matter of great concern. Wastewater containing dyes is difficult to treat by conventional wastewater treatment methods such as coagulation, ozonation, biological treatment, etc. This is why the implementation of an effective method by not generating pollutants secondary is necessary.
 The objective of this work is to study the degradation of remazol black, an azo dye, by the coupling of hydrogen peroxide - molybdenum oxide nanoparticle. The nanoparticles were synthesized by the aqueous sol-gel method using a reflux assembly.
 Study Design: Random design.
 Methodology: The nanoparticles were synthesized by the aqueous sol-gel method using a reflux assembly and then characterized by X-ray diffraction and using software origin to determine the particles size by Scherrer's formula. The influence of hydrogen peroxide, molybdenum oxide and hydrogen peroxide / molybdenum oxide coupling, and the degradation kinetics of remazol black were studied. We also studied the influence of the pH of the solution, the mass of molybdenum nanoparticles and the concentration of remazol black on the dye degradation process.
 Results: The results showed that the synthesized oxide is ammonium molybdenum trioxide NH3(MoO3)3) with a hexagonal structure and size 22.79 nm. The study of the catalytic effect revealed a degradation rate of 17%, 0.83% and 42% respectively for H2O2, NH3(MoO3)3 and the coupling NH3(MoO3)3/H2O2. The study also showed that the degradation of remazol black by the couple NH3(MoO3)3 /H2O2 is better at pH = 4 and for a mass of nanoparticles of 400 mg. This degradation kinetics are pseudo 1st order. In addition, the degradation rate decreases when the concentration of remazol black increases. The efficiency of the coupling (NH3(MoO3)3 / H2O2 showed at ambient temperature, that it was possible to remove about 60% of the initial color of remazol black from the water in a batch reaction.
 Conclusion: The reflux method makes it possible to synthesize molybdenum nanoparticles. The molybdenum oxide hetero-Fenton process is effective in removing remazol black dye from water.

Electrochemical Impedance Spectroscopy of Zinc Oxide Nanoparticles After Deposition on Screen Printed Electrode.

A small aliquot (10-14 μL) of ZnO nanoparticles dispersed in deionized water was deposited by evaporation to produce a dry residue on the working area of a screen-printed electrode. An electrochemical test solution containing K₃Fe(CN)6 and KCl was added to the electrode surface for analysis by electrochemical impendence spectroscopy (EIS). Using this deposition analysis technique, a new relationship between the charge transfer resistance (Rct) and the amount of ZnO nanoparticles has been explored. Based on the trend of increasing Rct value with an increase of ZnO nanoparticles, a quantitative analysis method can be established to determine the mass of nanoparticles (0.01-1.00 μg) deposited from an unknown dispersion. To study the matrix effect, addition of Nafion solution to the aqueous dispersion resulted in a change of the linear range to 0.3-0.5 μg nanoparticles. Addition of methanol (10% by volume) to the aqueous dispersion changes the analysis range to 0.2-0.6 μg nanoparticles, while additional methanol (50% by volume) changes the analysis range to 0.06-1.00 μg nanoparticles. The analytical sensitivity, as indicated by the slope of each standard calibration curve, ranked as: aqueous dispersion > Nafion/aqueous dispersion > 10% methanol/aqueous dispersion > 50% methanol/aqueous dispersion. Altogether these results verify that deionized water is the best dispersion medium for EIS analysis of ZnO nanoparticles.

Dual similarity solutions because of mixed convective flow of a double-nanoparticles hybrid nanofluid: critical points and stability analysis

Purpose The purpose of this article is to study the steady laminar magnetohydrodynamics mixed convection stagnation-point flow of an alumina-graphene/water hybrid nanofluid with spherical nanoparticles over a vertical permeable plate with focus on dual similarity solutions. Design/methodology/approach The single-phase hybrid nanofluid modeling is based on nanoparticles and base fluid masses instead of volume fraction of first and second nanoparticles as inputs. After substituting pertinent similarity variables into the basic partial differential equations governing on the problem, the authors obtain a complicated system of nondimensional ordinary differential equations, which has non-unique solution in a certain range of the buoyancy parameter. It is worth mentioning that, the stability analysis of the solutions is also presented and it is shown that always the first solutions are stable and physically realizable. Findings It is proved that the magnetic parameter and the wall permeability parameter widen the range of the buoyancy parameter for which the solution exists; however, the opposite trend is valid for second nanoparticle mass. Besides, mass suction at the surface of the plate as well as magnetic parameter leads to reduce both hydrodynamic and thermal boundary layer thicknesses. Moreover, the assisting flow regime always has higher values of similarity skin friction and Nusselt number relative to opposing flow regime. Originality/value A novel mass-based model of the hybridity in nanofluids has been used to study the foregoing problem with focus on dual similarity solutions. The results of this paper are completely original and, to the best of the authors’ knowledge, the numerical results of the present paper were never published by any researcher.

Determination of Silver in Metal Plating Wastewater by Slotted Quartz Tube Flame Atomic Absorption Spectrometry (SQT-FAAS) after Preconcentration with Stearic Acid-Coated Magnetite Nanoparticle-Based Solid-Phase Microextraction (SA-MNP-SPME)

Here is reported the determination of silver at ultratrace levels by slotted quartz tube-flame atomic absorption spectrometry (SQT-FAAS) following stearic acid coated magnetic nanoparticle based solid phase microextraction (SA-MNP-SPME). The parameters affecting silver extraction were optimized to obtain high efficiency. In addition to the magnetic property of iron oxide (Fe3O4) nanoparticles, they were coated with stearic acid to increase the surface area and the capacity for the analyte. An external magnetic field was used to separate the silver from the liquid phase. To obtain the highest efficiency, the mass of magnetic nanoparticles, pH and volume of buffer solution, mixing type and period, volume of eluent and volume of sample were optimized univariately. Under the optimum conditions, the limits of detection and quantitation were determined to be 40 and 130 ng L−1, respectively. Recovery experiments were performed to investigate matrix effects on the developed method by spiking real samples. Recoveries were between 96.3 and 105.1% with low standard deviations by the matrix matching calibration. The developed MNP-SPME-SQT-FAAS method achieved 305-fold improvement in detection power. These results demonstrated the method’s applicability for the determination of trace silver in complex samples with good accuracy and precision.

Marangoni convection in layers of water-based nanofluids under the effect of rotation

Abstract A linear stability analysis is performed for the onset of Marangoni convection in a horizontal layer of a nanofluid heated from below and affected by rotation. The top boundary of the layer is assumed to be impenetrable to nanoparticles with their distribution being determined from a conservation condition while the bottom boundary is assumed to be a rigid surface with fixed temperature. The motion of the nanoparticles is characterized by the effects of thermophoresis and Brownian diffusion. A modification model is used in which the effects of Brownian diffusion and thermophoresis are taken into consideration by new expressions in the nanoparticle mass flux. Also, material properties of the nanofluid are modelled by non-constant constitutive expressions depending on nanoparticle volume fraction. The steady-state solution is shown to be well approximated by an exponential distribution of the nanoparticle volume fraction. The Chebyshev-Tau method is used to obtain the critical thermal and nanoparticle Marangoni numbers. Different stability boundaries are obtained using the modified model and the rotation.

Mixed convection of a nanofluid past an inclined wavy surface in the presence of gyrotactic microorganisms

AbstractThe mixed convection of a nanofluid flow past an inclined wavy surface in the existence of gyrotactic microbes is considered. To convert the wavy surface to a plane surface, a transformation of coordinates is applied. The governing equations that are nonlinear and the accompanying boundary conditions are converted into a dimensionless form using pseudo‐similarity variables. Using a local linearization process, the system of nonlinear partial differential equations is linearized. The resulting system is solved using the Bivariate Chebyshev pseudo‐spectral collocation method. The influence of different physical and geometrical factors on the parameters of engineering importance of the flow is analyzed and illustrated graphically. It is observed that the skin friction, the density of motile microorganisms, and nanoparticle mass transfer rate are increasing with an increase in the bioconvection Peclet and Schmidt numbers whereas these quantities are decreasing with an increase in Rayleigh number. The local Nusselt number, nanoparticle Sherwood number, and density number of microbes increases with an increase in the Brownian motion and thermophoresis parameter. These physical quantities are increasing when the surface changes from horizontal to vertical.

A neural network approach to estimate non-Newtonian behavior of nanofluid phase change material containing mesoporous silica particles

Neural networks are powerful tools for evaluating the thermophysical characteristics of nanofluids to reduce the cost and time of experiments. Dynamic viscosity is an important property in nanofluids that usually needs to be accurately computed in heat transfer and nanofluid flow problems. In this paper, the rheological properties of nanofluid phase change material containing mesoporous silica nanoparticles are predicted by the artificial neural networks (ANNs) method based on the experimental database reported in literature. Experimental inputs include nanoparticle mass fractions (0-5 wt.%), temperatures (35-55℃), and shear rates (10-200 s-1), and targets include dynamic viscosities and shear stresses. A multilayer perceptron feedforward neural network with Levenberg-Marquardt back-propagation training algorithm is utilized to predict rheological properties. The optimal network architecture consists of 22 neurons in the hidden layer based on the minimum mean square error (MSE). The results showed that the developed ANN has an MSE of 6.67×10-4 and 6.55×10-3 for the training and test dataset, respectively. The predicted dynamic viscosity and shear stress also have the maximum relative error of 6.26% and 0.418%, respectively.

Hybrid nanoparticles-laden fluid based spiral solar collector: A proof-of-concept experimental study

Over-reliance on limited fossil resources to meet the ever-increasing energy demand has several consequences such as high prices, unpredictable supply, and adverse environmental and ecological impact. It is the need of the current time to explore sustainable renewable energy sources in order to mitigate the environmental consequences and match the increasing demand economically. Out of various sustainable renewable energy sources, solar energy stands out as one of the exemplary candidates. It is a clean energy source with no greenhouse gas (GHG) emissions and is available in abundance at many parts of the world. Prevailing studies corroborate the merit of nanofluids in harnessing solar energy. In this experimental study, thermal analysis of a novel spiral-shaped collector is conducted with both hybrid nanofluid-based volumetric absorption system (VAS) and surface-based absorption system (SAS). In the case of hybrid VAS, homogenous mixture of Al2O3 and Co3O4 with de-ionized water as base fluid is employed. The experimental results reveal that the maximum temperature rise and thermal efficiency of 9.8 °C and 50%, respectively, is obtained at nanoparticle mass fraction of 100 mg/L Al2O3 +100 mg/L Co3O4 which is the optimum mass fraction. Whereas, in the case of SAS, volumetric flow rate of 100 mL/h is the optimum volumetric flow rate at which the maximum temperature rise of 8.5 °C is achieved. Further, the effect of variation in volumetric flow rate and the incident flux on the thermal performance of both VAS and SAS is also presented. On comparing the performance of VAS with SAS under a similar condition a temperature rise and thermal efficiency of about 15.3% and 15%, higher is achieved in VAS than SAS (at optimum volumetric flow rate).

Nanoparticle diffusion in polymer melts in the presence of weak nanoparticle-monomer attractive interactions: A mode-coupling theory study.

Mode-coupling theory is developed and employed to compute the nanoparticle diffusion coefficient in polymer solutions. Theoretical results are compared with molecular dynamics simulation data for a similar model. The theory properly reproduces the simulated effects of the nanoparticle size, mass, and concentration on the nanoparticle diffusion coefficient. Within the mode-coupling theory framework, a microscopic interpretation of the nonmonotonic dependence of the diffusion coefficient on the nanoparticle concentration is given in terms of structural and dynamic effects. Both the size dependence and mass dependence of the diffusion coefficient indicate a pronounced breakdown of the Stokes-Einstein relation for the present model.

Influence of bionanoparticles to treat a slaughterhouse wastewater

ABSTRACT Treatment of effluents from animal slaughterhouse industries is indispensable, standing out coagulation/flocculation/sedimentation processes. Bionanoparticles (BioNPs) (nanoparticles (NPs) functionalized with Moringa extracts (MO)) were studied as an alternative natural coagulant that would contribute to the microbial load reduction, without increasing the treated effluent toxicity. MO extracts were prepared with different salts, and then, in a kinetics study, different NPs mass and coagulant dosages were evaluated. In the best-defined conditions, microbial load, toxicity tests for the bioindicator Lactuca sativa, and NPs reuse evaluation were performed. Removals of 96.14% turbidity and 43.63% UV254nm were achieved when using 500 mg L−1 of BioNPs containing 60 mg of NPs for every 20 mL of MO extract prepared with 0.1 M CaCl2. The BioNPs with an external magnetic field also decreased the sedimentation time from 140 to 10 min compared to MO, and the process efficiency did not expressively decrease after reusing the recovered NPs. Through toxicity tests, BioNPs were not considered to leave residuals toxic to the Lactuca sativa in the treated effluent. Besides, the microbial load reduction was 97.33% for heterotrophic microorganisms and total mesophiles and 99.25% for moulds/yeasts. Therefore, a satisfactory primary treatment was achieved, contributing to the sustainability of industries.

Transfer of Cobalt Nanoparticles in a Simplified Food Web: From Algae to Zooplankton to Fish

Cobalt (Co) nanoparticles (NPs) may be diffusely dispersed into natural ecosystems from various anthropogenic sources such as traffic settings and eventually end up in aquatic systems. As environmentally dispersed Co NPs may be transferred through an aquatic food web, this study investigated this transfer from algae (Scendesmus sp.) to zooplankton (Daphnia magna) to fish (Crucian carp, Carassius carassius). Effects of interactions between naturally excreted biomolecules from D. magna and Co NPs were investigated from an environmental fate perspective. ATR-FTIR measurements showed the adsorption of both algae constituents and excreted biomolecules onto the Co NPs. Less than 5% of the Co NPs formed heteroagglomerates with algae, partly an effect of both agglomeration and settling of the Co NPs. The presence of excreted biomolecules in the solution did not affect the extent of heteroagglomeration. Despite the low extent of heteroagglomeration between Co NPs and algae, the Co NPs were transferred to the next trophic level (D. magna). The Co uptake in D. magna was 300 times larger than the control samples (without Co NP), which were not influenced by the addition of excreted biomolecules to the solution. Significant uptake of Co was observed in the intestine of the fish feeding on D. magna containing Co NPs. No bioaccumulation of Co was observed in the fish. Moreover, 10–20% of the transferred Co NP mass was dissolved after 24 h in the simulated gut solution of the zooplankton (pH 7), and 50–60% was dissolved in the simulated gut solution of the fish (pH 4). The results elucidate that Co NPs gain different properties upon trophic transfer in the food web. Risk assessments should hence be conducted on transformed and weathered NPs rather than on pristine particles.