Effect of humic acids on physicochemical property and Cd(II) sorption of multiwalled carbon nanotubes

Arsenic Stress Mitigation Using a Novel Plant Growth-Promoting Bacterial Strain Bacillus mycoides NR5 in Spinach Plant (Spinacia oleracea L.)

Present study aimed to identify arsenic (As)-resistant bacterial strains that can be used to mitigate arsenic stress. A bacterium Bacillus mycoides NR5 having As tolerance limit of 1100 mg L-1 was isolated from Nag River, Maharashtra, India. It was also equipped with plant growth-promoting (PGP) attributes like phosphate solubilization, siderophores, ammonia, and nitrate reduction, with added antibiotic tolerance. Furthermore, scanning electron microscopy (SEM) and transmission electron micrograph (TEM) suggested biosorption as possible mechanisms of arsenic tolerance. A strong peak in FTIR spectra at 3379.0 corresponding to amine in As-treated NR5 also indicated metal interaction with cell surface protein. Amplification of arsenic reductase gene in NR5 further suggested intracellular transformation of As speciation. Moreover, As tolerance capability of NR5 was shown in spinach plants in which the bacterium effectively mitigated 25 ppm As by producing defense-related proline molecules. Evidence from SEM, TEM, and FTIR, concluded biosorption possibly the primary mechanism of As tolerance in NR5 along with the transformation of arsenic. B. mycoides NR5 with PGP attributes, high As tolerance, and antibiotic resistance mediated enhanced As tolerance in spinach plants advocated that the strain can be a better choice for As bioremediation in contaminated agricultural soil and water.

Developing In2S3 upon modified MgTiO3 anchored on nitrogen-doped CNT for sustainable sensing and removal of toxic insecticide clothianidin

Herein, the study introduces a novel bifunctional In2S3/MgTiO3/TiO2@N-CNT (IMTNC) nanocomposite, which is poised to revolutionize the detection and removal of clothianidin (CLD) from aquatic environments by synergistic adsorption and photodegradation. Confirmation of the material's synthesis was done using structural, optical, morphological, and chemical characterizations. An outstanding sensitivity of 2.168 μA/nM.cm2 with a linear range of 4-100 nM and a LOD of 0.04 nM, along with an exceptional elimination efficiency of 98.06 ± 0.84% for about 10 ppm CLD within 18 min was demonstrated by the IMTNC nanocomposite. Extensive studies were carried out to appraise the material's effectiveness in the presence of various interfering species, such as cations, anions, organic compounds, and different water matrices, and a comprehensive assessment of its stability throughout several cycles was made. Response Surface Methodology (RSM) study was used to determine the ideal removal conditions for improved performance. In addition, the catalytic performance in removing various other pollutants was also analyzed. Adding In2S3 and developing N-doped Carbon Nanotubes (N-CNT) increased conductivity and higher electrochemical sensing skills, improving charge transfer and increasing photocatalytic activity. This research underscores the potential of the IMTNC nanocomposite as a promising candidate for advanced environmental sensing and remediation applications.

Aggregation, solubility and cadmium-adsorption capacity of CuO nanoparticles in aquatic environments: Effects of pH, natural organic matter and component addition sequence

Nanoparticles (NPs), heavy metals and natural organic matter may co-exist in the water bodies. Currently, knowledge on their interaction effects on the behaviors and fates of NPs and heavy metal ions is rather limited, which is critical to comprehensively understand their environmental risk. In this study, the aggregation, solubility and Cd-adsorption of CuO NPs co-existing with humic acid (HA) and Cd²⁺ upon different solution pH and contact sequences were determined. In the ternary systems of CuO NPs, HA and Cd²⁺, pH was more important than the contact sequence of the components in affecting the NP aggregation, while the contact sequence was a predominant factor in determining the NP solubility. Pre-equilibration of CuO NPs and HA before addition of Cd²⁺ resulted in the highest solubility and lowest aggregation of the NPs, relative to other sequences of addition of the components. The adsorption capacity of CuO NPs for Cd-ions increased with an increasing pH value from 5 to 9. HA significantly enhanced the Cd-adsorption capacity of CuO NPs at pH 7 and 9, while at pH 5 a non-significant effect was observed. The results are helpful to better estimate the behaviors and fates of CuO NPs and Cd²⁺ when they coexisting in natural waters.

Effect of insect feces (Hermetia illucens) on rice growth and heavy metal migration from polluted soil to rice plant

Insect feces are a new kind of biological organic fertilizer. Little is known about the influences of insect feces on rice growth and heavy metal migration from soil to rice plant. In this study, the effects of different amounts (CK (0%), T1 (2%), T2 (4%), T3 (6%), and T4 (8%)) of black soldier fly larvae (BSFL) feces on the rice growth and the migration/accumulation of heavy metals (Cd and Pb) were investigated by pot experiments within 2 years. The application of insect feces remarkably increased the contents of soil pH, organic matter, ammonium nitrogen, available phosphorus, and potassium. Meanwhile, the insect feces application reduced the weak acid-soluble contents of soil Cd and Pb by 8.3-56.8%, but increased those in the oxidizable (by 22.4-165.7%) and residual (by 1.8-225.6%) states. Except for the T4 treatment in the first year, all fertilization treatments increased the rice yield (up to 43.7% and 195.5% higher than those of CK within 2 years). Moreover, the insect feces application reduced the contents of Cd (8.3-66.7%) and Pb (6.4-61.8%) in different parts of rice. Under the same treatment, the metal contents in each part of rice in the second year were lower than those in the first year. The insect feces application decreased the absorption coefficients (24.4-57.5%) and secondary transport coefficients (3.6-44.1%) of Cd and Pb by rice plant. The findings implied that the insect feces might act as effective organic fertilizers for rice plants as well as reducing heavy metal accumulation in rice plants growing in polluted soil.

Immobilization properties and adsorption mechanism of nickel(II) in soil by biochar combined with humic acid-wood vinegar

Biochar (BC) combined with humic acid (HA) and wood vinegar (WV) was designed and prepared as an inexpensive, effective, and environmentally friendly immobilization material (BHW) for metal-polluted soil. The influences of the wood vinegar and humic acid on the immobilization properties and adsorption mechanism of this new material were also investigated. The remediation performance was evaluated using a laboratory-made, nickel-contaminated soil with a Ni²⁺ concentration of 200 mg per kg surface soil (top 20 cm from agricultural land). The results indicated that the immobilization ratio sequence of nickel (II) in the soil was BC< BH< BHW. The maximum adsorption capacity increased in the same order: BC< BH< BHW. All three adsorption isotherms were better fitted by the Freundlich model, which were consistent with the surface heterogeneity of the remediation materials. The cause of this surface heterogeneous migration may be due to the increase in oxygen-containing groups in the BC introduced by the HA and WV. The WV can increase the number of the oxygen-containing groups in the BC combined with HA, which enhanced the adsorption and immobilization of Ni²⁺ ions. The results suggested that BHW is recommended for the remediation of metal-contaminated soils, because of its high efficacy, economic feasibility, environmental and food safety.

Characterization of dissolved organic matter for understanding the adsorption on nanomaterials in aquatic environment: A review

Nanomaterials (NMs) have received tremendous attention as emerging adsorbents for environmental applications. The ever-increasing release into aquatic systems and the potential use in water treatment processes heighten the likelihood of the interactions of NMs with aquatic dissolved organic matter (DOM). Once DOM is adsorbed on NMs, it substantially modifies the surface properties, thus altering the fate and transport of NMs, as well as their toxic effects on (micro)organisms in natural and engineered systems. The environmental consequences of DOM-NMs interaction have been widely studied in the literature. In contrast, a comprehensive understanding of DOM-NM complexes, particularly regarding the controlling factors, is still lacking, and its significance has been largely overlooked. This gap in the knowledge mainly arises from the complex and heterogeneous structures of the DOM, which prompts the urgent need to further characterize the DOM properties to deepen the understanding associated with the adsorption processes on NMs. This review aims to provide in-depth insights into the complex DOM adsorption behavior onto NMs, whether they are metal- or carbon-based materials. First, we summarize the up-to-date analytical methods to characterize the DOM to unravel the underlying adsorption mechanisms. Second, the key DOM characteristics governing the adsorption processes are discussed. Next, the environmental factors, such as the nature of adsorbents and solution chemistry, affecting the DOM-NM interactions, are identified and discussed. Finally, future studies are recommended to fully understand the chemical traits of DOM upon its adsorption onto NMs.

Wood vinegar enhances humic acid-based remediation material to solidify Pb(II) for metal-contaminated soil

Heavy metal lead is a typical widespread potentially toxic element (PET) contamination due to their extensive and wide applications in industrial processes. The development of cost-effective methods for preventing potentially toxic element lead residues from soil into food is thus highly desirable. A new type of humic acid-based remediation material (HA/WV) incorporating humic acid salt (HA), biochar powder (BC), and wood vinegar (WV), which is a cheap and environmentally friendly industrial by-product from charcoal processing, was prepared and evaluated. The results showed that 0.10 g remediation material HA/WV with a mass ratio of 1:1 was added to 1 kg surface soil of 0-20 cm from agricultural land contaminated by 300 mg Pb²⁺, the reduction ratio of available Pb in soil can reach 61.4%. Especially, wood vinegar can enhance the reduction ratio of available Pb by at least 14.7% over without wood vinegar. Furthermore, according to the analysis of adsorption interaction and the electrostatic attraction between Pb(II) and oxygen-containing functional groups on HA/WV are the dominant mechanisms responsible for Pb(II) sorption. The wood vinegar liquid can improve the oxygen-containing group in HA/WV, which can enhance the complexation of remediation materials and Pb(II) ion.

Metal sorption onto nanoscale plastic debris and trojan horse effects in Daphnia magna: Role of dissolved organic matter

There is a debate on whether the Trojan horse principle is occurring for nanoscale plastic debris (NPD < 1 µm). It is realized that NPD have a high capacity to sorb environmental contaminants such as metals from the surrounding environment compared to their microplastic counterparts, which influences the sorbed contaminants' uptake. Herein, we studied the influence of dissolved organic matter (DOM) on the time-resolved sorption of ionic silver (Ag⁺) onto polymeric nanomaterials, as models of NPD, as a function of particle size (300 and 600 nm) and chemical composition [polystyrene (PS) and polyethylene (PE)]. Subsequently, the toxicity of NPD and their co-occurring (adsorbed and absorbed) Ag⁺ on Daphnia magna was determined. Silver nitrate was mixed with 1.2 × 10⁵ NPD particles/mL for 6 days. The extent of Ag⁺ sorption onto NPD after 6 days was as follows: 600 nm PS-NPD > 300 nm PS-NPD > 300 nm PE-NPD. The presence of DOM in the system increased the sorption of Ag⁺ onto 300 nm PS-NPD and PE-NPD, whereas DOM decreased the sorption onto 600 nm PS-NPD. Exposure to 1 mg/L NPD or 1 µg/L Ag⁺ was not toxic to daphnids. However, the mixture of these concentrations of PS-NPD and Ag⁺ induced toxicity for both sizes (300 and 600 nm). The addition of DOM (1, 10 and 50 mg/L) to the system inhibited the combined toxicity of Ag⁺ and NPD regardless of the size and chemical composition. Taken together, in natural conditions where the concentration of DOM is high e.g. in freshwater ecosystems, the sorption of metals onto NPD depends on the size and chemical composition of the NPD. Nevertheless, under realistic field conditions where the concentration of DOM is high, the uptake of contaminants in D. magna that is influenced by the Trojan horse principles could be negligible.

Ultrasound-assisted sorption of Pb(ii) on multi-walled carbon nanotube in presence of natural organic matter: an insight into main and interaction effects using modelling approaches of RSM and BRT

In real-scale applications, where NPs are injected into the aqueous environment for remediation, they may interact with natural organic matter (NOM). This interaction can alter nanoparticles' (NPs) physicochemical properties, sorption behavior, and even ecological effects. This study aimed to investigate sorption of Pb(ii) onto multi-walled carbon nanotube (MWCNT) in presence of NOM. The predominant behavior of the process was examined comparatively using response surface methodology (RSM) and boosted regression tree (BRT)-based models. The influence of four main effective parameters, namely Pb(ii) and humic acid (HA) concentrations (mg L⁻¹), pH, and time (min) on Pb removal (%) was evaluated by contributing factor importance rankings (BRT) and analysis of variance (RSM). The applicability of the BRT and RSM models for description of the predominant behavior in the design space was checked and compared using statistics of absolute average deviation (AAD), mean absolute error (MAE), root mean square error (RMSE), and multiple correlation coefficient (R²). The results showed that although both approaches exhibited good performance, the BRT model was more precise, indicating that it could be a powerful method for the modeling of NOM-presence studies. Importance rankings of BRT displayed that the effectiveness order of the studied parameters is pH > time > Pb(ii) concentration > HA concentration. Although HA concentration showed the least effect in comparison with three other studied parameters theoretically, the experimental results revealed that Pb(ii) removal is enhanced in presence of HA (73% vs. 81.77%), which was confirmed by SEM/EDX analyses. Hence, maximum removal (R% = 81.77) was attained at an initial Pb(ii) concentration of 9.91 mg L⁻¹, HA concentration of 0.3 mg L⁻¹, pH of 4.9, and time of 55.2 min.

The proposed mechanism for effect of HA on Pb(ii) removal using MWCNTs.

Effects of functionalized multi-walled carbon nanotubes on toxicity and bioaccumulation of lead in Daphnia magna

Increased production of carbon nanotubes (CNTs) and their widespread application in industrial and consumer products have led to a rise in the release of CNTs into the aquatic environment. CNTs have a very strong adsorption affinity for various environmental contaminants; therefore, they may also influence the toxic effects of other pollutants, such as toxic metals. In this study, the effect of two different functionalized carbon nanotubes, carboxylate and polyethyleneimine modified multi-walled carbon nanotubes (C-MWCNTs and N-MWCNT, respectively) on lead toxicity and bioaccumulation was investigated with a freshwater zooplankton Daphnia magna. The acute toxicity results indicate that the different surface properties of the two types of MWCNTs have different effects on lead toxicity to D. magna. The negatively charged C-MWCNT showed a notable decrease in lead toxicity (LC₅₀ value increased from 0.15 mg L^-1 to 1.08 mg L^-1 in the presence of 10 mg L^-1 C-MWCNT), whereas the positively charged N-MWCNT had only a slight effect on lead toxicity (LC₅₀ value increased from 0.15 mg L^-1 to 0.16 mg L^-1 in the presence of 10 mg L^-1 N-MWCNT). The decrease of lead toxicity was related with the reduced bioavailability of free metal form (Pb²⁺) caused by greater adsorption of lead onto the MWCNTs. The present study suggests that there is a need to consider carefully the complex interaction of CNTs with toxic metals in future ecotoxicological studies.

Biosorption performance evaluation of heavy metal onto aerobic granular sludge-derived biochar in the presence of effluent organic matter via batch and fluorescence approaches

In present study, the biosorption process of Cu(II) onto aerobic granular sludge-derived biochar was evaluated in the absence and presence of effluent organic matter (EfOM) by using batch and fluorescence approaches. It was found that EfOM gave rise to enhancement of Cu(II) removal efficiency onto biochar, and the sorption data were better fitted with pseudo-second order model and Freundlich equation, in despite of the absence and presence of EfOM. According to excitation-emission matrix (EEM), EfOM was mainly comprised by humic-like substances and fulvic-like substances and their intensities were reduced in the addition of biochar and Cu(II) from batch biosorption process. Synchronous fluorescence spectra coupled to two-dimensional correlation spectroscopy (2D-COS) further implied that a successive fluorescence quenching was observed in various EfOM fractions with the increasing Cu(II) concentration. Moreover, fulvic-like fraction was more susceptibility than other fractions for fluorescence quenching of EfOM.

Role of graphene oxide in mitigated toxicity of heavy metal ions on Daphnia magna

Graphene oxide (GO) is increasingly used and inevitably released into aquatic environments, facilitating its interaction with traditional pollutants such as heavy metal ions. However, the potential effect of GO on the toxicity of heavy metal ions to aquatic animals is unknown. This work aims to assess the toxicity of heavy metal ions (Cu(ii), Cd(ii), and Zn(ii)) on Daphnia magna (D. magna) in the presence of GO. GO nanoparticles remarkably reduced the concentrations of heavy metal ions by adsorption and decreased the metal accumulation in D. magna. The maximum desorption rate of heavy metal ions from metal-adsorbed GO was below 5%. At pH 7.8, with addition of 2 mg L⁻¹ GO, the 72 h median lethal concentration (LC₅₀) values of Cu(ii), Cd(ii), and Zn(ii) were increased from 14.3, 38, and 780 μg L⁻¹ to 36.6, 72, and 1010 μg L⁻¹, respectively. The analyses of oxidative stress indicators suggested that the oxidative damage to D. magna by heavy metal ions was reduced after addition of GO at pH 7.8. Moreover, a higher pH level in the growing range (6.5 to 8.5) of D. magna led to weaker toxicity of metal ions with GO addition due to more adsorption and less bioaccumulation. The results revealed the role of GO nanoparticles in the mitigated toxicity of heavy metal ions in the aquatic environment.

Graphene oxide nanoparticles mitigates the biotoxicity of heavy metal ions (Cu(ii), Cd(ii), and Zn(ii)) on aquatic animals (Daphnia magna).

Coating carbon nanotubes with humic acid using an eco-friendly mechanochemical method: Application for Cu(II) ions removal from water and aquatic ecotoxicity

In this work, industrial grade multi-walled carbon nanotubes (MWCNT) were coated with humic acid (HA) for the first time by means of a milling process, which can be considered an eco-friendly mechanochemical method to prepare materials and composites. The HA-MWCNT hybrid material was characterized by atomic force microscopy (AFM), scanning electron microscopies (SEM and STEM), X-ray photoelectron spectroscopy (XPS), termogravimetric analysis (TGA), and Raman spectroscopy. STEM and AFM images demonstrated that the MWCNTs were efficiently coated by the humic acid, thus leading to an increase of 20% in the oxygen content at the nanotube surface as observed by the XPS data. After the milling process, the carbon nanotubes were shortened as unveiled by SEM images and the values of ID/IG intensity ratio increased due to shortening of the nanotubes and increasing in the number defects at the graphitic structure of carbon nanotubes walls. The analysis of TGA data showed that the quantity of the organic matter of HA on the nanotube surface was 25%. The HA coating was responsible to favor the dispersion of MWCNTs in ultrapure water (i.e. -42mV, zeta-potential value) and to improve their capacity for copper removal. HA-MWCNTs hybrid material adsorbed 2.5 times more Cu(II) ions than oxidized MWCNTs with HNO₃, thus evidencing that it is a very efficient adsorbent material for removing copper ions from reconstituted water. The HA-MWCNTs hybrid material did not show acute ecotoxicity to the tested aquatic model organisms (Hydra attenuata, Daphnia magna, and Danio rerio embryos) up to the highest concentration evaluated (10mgL^-1). The results allowed concluding that the mechanochemical method is effective to coat carbon nanotubes with humic acid, thus generating a functional hybrid material with low aquatic toxicity and great potential to be applied in environmental nanotechnologies such as the removal of heavy metal ions from water.

Quantitative relationships between the adsorptivity of carbonaceous materials in soil for Pb(II) and soil organic matter content

Strong adsorptivity of manufactured carbonaceous materials (MCMs) mediates the behavior of heavy metals in soil. Laboratory-reported adsorptivity of MCMs often deviates from their actual abilities in soil, because soil organic matter (SOM) can change the adsorptive abilities of MCMs by coating dissolved organic matter (DOM) on the surface of the MCMs. It was considered that the influence of SOM on the adsorptivity of MCMs in soil follows a sequential pathway of SOM releasing DOM in soil solution and subsequent DOM binding onto MCMs, thereby altering MCM surface acidity and hence changing MCM adsorptivity for heavy metals. In this study, we first extracted DOM from ten topsoils collected over a broad region of China with a wide range of SOM. The DOM solutions were then used to load DOM onto four MCMs including activated carbon (AC), multiwalled carbon nanotube (MWCNT), and two biochars (BC400 and BC700), respectively, obtaining a total of 44 MCM-DOM complex samples with known amounts of bound DOM. These MCM-DOM complex samples were then determined for their surface acidities and adsorptive abilities for Pb(II). We found that there were significant correlations between DOM concentration and SOM content, between DOM binding onto MCMs and DOM concentration, between surface acidity of MCM-DOM complexes and DOM binding onto MCMs, as well as between Pb(II) adsorption on MCM-DOM complexes and surface acidity of MCM-DOM complexes. With understanding of these individual linear correlations, linear relationships between the Pb(II) adsorption and SOM content were established by combining individual correlations and by directly plotting the former against the latter. These relationships may be used to accurately predict the adsorptive abilities of MCMs for heavy metals in soils via simply determining SOM.

The interactions of UV and/or H2O2 treated CNTOH and CNTCOOH with environmental fulvic acids

The fate of carbon nanotubes (CNT) in the environment will be governed by the presence of natural dissolved organic matter (DOM). Many studies indicate that CNT create stabilized suspensions in the presence of DOM. Easier transport in the environment may indicate their greater hazard. However these studies describe the interactions of DOM with as produced CNT. In the present studies the interactions of UV and/or H2O2 treated wastewater containing CNTOH or CNTCOOH with the naturally occurred fulvic acids (FA) were presented. FA sorption, both kinetics and mechanism, were described using batch regime. The sorption of FA followed a pseudo-second order kinetics and was described with the highest accuracy by Langmuir or Dubinin-Radushkevich model for CNTOHs and Langmuir, Temkin or Dubinin-Radushkevich - for CNTCOOHs. The mechanism of FA sorption onto CNTOHs was ascribed to π-π, heterogeneous and electrostatic interactions. The π-π and electrostatic interactions can the mostly defined FA adsorption onto CNTCOOHs. The parameters affecting FA sorption were combination of porosity and dispersity.

Effects of single- and multi-organic acid ligands on adsorption of copper by Fe3O4/graphene oxide-supported DCTA

The Fe3O4/graphene oxide-supported 1,2-diaminocyclohexanetetraacetic acid composite (Fe3O4/GO/DCTA) was used as an adsorbent for Cu(II) removal. The effects of six organic acid ligands (formate, acetate, benzoate, oxalate, tartrate, and edetate) on the adsorption process were investigated in single- and multi-ligand systems. The results demonstrated that the adsorption processes were affected by solution pH and ionic strength. The experimental data of kinetics and isotherm followed the pseudo-second-order model and the Langmuir model, respectively. In the single-ligand systems, the presence of formate, acetate, and benzoate slightly altered the Cu(II) adsorption property, while the adsorption processes were significantly affected by the oxalate, tartrate, and edetate ligands. In the multi-ligand systems, the Cu(II) adsorption was influenced by the type and concentration of organic acid ligands. The sequence of the main effect was found to be: edetate>oxalate>benzoate>formate>tartrate>acetate, and the sequence of the two-factor interaction effect was found to be: AE (formate×tartrate)>BF (acetate×edetate)>AF (formate×edetate)>BD (acetate×oxalate)>AC (formate×benzoate)>AD (formate×oxalate)>AB (formate×acetate).

Sorption of diclofenac and naproxen onto MWCNT in model wastewater treated by H2O2 and/or UV

The application of oxidation processes such as UV and/or H2O2 will change the physicochemical properties of carbon nanotubes (CNT). It may affect the sorption affinity of CNT to different contaminants and then affect their fate in the environment. In the present study the adsorption of two very common used pharmaceuticals (diclofenac and naproxen) onto CNT treated by UV, H2O2 or UV/H2O2 was investigated. Four different adsorption models (Freundlich, Langmuir, Temkin, Dubinin-Radushkevich) were tested. The best fitting of experimental data was observed for Freundlich or Langmuir model. The significant relationships between Q calculated from Langmuir model with O% and dispersity were observed. Kinetics of diclofenac and naproxen followed mainly pseudo-second order indicating for chemisorption limiting step of adsorption. The data showed that the mechanism of sorption was physical or chemical depending on the type of CNT modification.

The sorption of the nonsteroidal anti-inflammatory drugs diclofenac and naproxen onto UV and/or H2O2 treated MWCNT-COOH and MWCNT-OH

The kinetics and mechanism of diclofenac and naproxen sorption onto UV and/or H₂O₂ treated functionalized CNTOHs and CNTCOOHs were studied.

Colloidal stability and ecotoxicity of multiwalled carbon nanotubes: Influence of select organic matters

In the last few years, the release of multiwalled carbon nanotubes (MWCNTs) into the environment has raised serious concerns regarding their fate and potential impacts. Aquatic organisms constitute an important pathway for their entrance and transfer throughout the food web, and the current demand for standardization of methodologies to analyze the interactions of MWCNTs with them requires aquatic media that represent natural systems. However, the inherent hydrophobicity of MWCNTs and the substances present in natural waters may greatly affect their stability and bioavailability. The present study analyzes the influence of the most referenced synthetic and natural organic matters (Sigma-Aldrich humic acid and Suwannee River natural organic matter) in the agglomeration kinetics and ecotoxicity of MWCNTs, with the aim of determining their suitability to fulfill the current standardization requirements. Natural organic matter provides increased colloidal stability to the MWCNTs' dispersions, which results in higher adverse effects on the key invertebrate organism Daphnia magna. Furthermore, the results obtained with this type of organic matter allow for observation of the important role of the outer diameter and content impurities of MWCNTs in their stability and ecotoxicity on daphnids. Sigma-Aldrich humic acid appeared to alter the response of the organisms to carbon nanotubes compared with that observed in the presence of natural organic matter.

Effect of humic acid on the sulfamethazine adsorption by functionalized multi-walled carbon nanotubes in aqueous solution: mechanistic study

The presence of humic acid (HA) inhibited sulfamethazine (SMZ) adsorption by three types of multi-walled carbon nanotubesviacompetitive interactions, molecular sieving, and pore blockage in solution (pH < 9).

Interactions of carbon nanotubes with aqueous/aquatic media containing organic/inorganic contaminants and selected organisms of aquatic ecosystems--A review

Due to their unique molecular architecture translating into numerous every-day applications, carbon nanotubes (CNTs) will be ultimately an increasingly significant environmental contaminant. This work reviews qualitative/quantitative analyses of interactions of various types of CNTs and their chemically modified analogues with aqueous/aquatic media containing organic and inorganic contaminants and selected organisms of aquatic ecosystems. A special emphasis was placed on physicochemical interactions between CNTs as adsorbents of heavy metal cations and aromatic compounds (dyes) with its environmental consequences. The studies revealed CNTs as more powerful adsorbents of aromatic compounds (an order of magnitude higher adsorption capacity) than metal cations. Depending on the presence of natural organic matter (NOM) and/or co-contaminants, CNTs may act as Trojan horse while passing through biological membranes (in the absence of NOM coordinating metal ions). Nanotubes, depending on flow conditions and their morphology/surface chemistry, may travel with natural waters or sediment with immobilized PAHs or metals and/or increase cyto- and ecotoxicity of PAHs/metal ions by their release via competitive complexation, or cause synergic ecotoxicity while adsorbing nutrients. Additionally, toxicity of CNTs against exemplary aquatic microorganisms was reviewed. It was found for Daphnia magna that longer exposures to CNTs led to higher ecotoxicity with a prolonged CNTs excretion. SWCNTs were more toxic than MWCNTs, while hydrophilization of CNTs via oxidation or anchoring thereto polar/positively charged polymer chains enhanced stability of nanotubes dispersion in aqueous media. On the other hand, bioavailability of functionalized CNTs was improved leading to more complex both mechanisms of uptake and cytotoxic effects.

Removal of cadmium ion from wastewater by carbon-based nanosorbents: a review

A green environment and a healthy life are dream projects of today's science and technology to save the world. Heavy metal ions in water affect both environment and human health. Cadmium has been identified as one of the heavy metals that causes acute or chronic toxic effects if ingested. Increasing use of cadmium in different technological fields has raised concern about its presence and removal from water/wastewater. Researchers have made many systematic efforts to remove heavy metals from water to reduce their impact on human beings and the environment. Adsorption is one of the best methods to remove heavy metals from water among the different proposed methods. This study explores carbon-based nanosorbents which have been proved as effective adsorbents for removal of cadmium ions from water. The adsorption efficiency of carbon-based nanosorbents is the main criterion to rank and select them for removal of cadmium ions from water. Toxicity, reusability and environmentally friendly characteristics of sorbents are also taken considered while ranking the suitable carbon-based nanosorbents for removal of cadmium ions from water.

Identification and avoidance of potential artifacts and misinterpretations in nanomaterial ecotoxicity measurements

Novel physicochemistries of engineered nanomaterials (ENMs) offer considerable commercial potential for new products and processes, but also the possibility of unforeseen and negative consequences upon ENM release into the environment. Investigations of ENM ecotoxicity have revealed that the unique properties of ENMs and a lack of appropriate test methods can lead to results that are inaccurate or not reproducible. The occurrence of spurious results or misinterpretations of results from ENM toxicity tests that are unique to investigations of ENMs (as opposed to traditional toxicants) have been reported, but have not yet been systemically reviewed. Our objective in this manuscript is to highlight artifacts and misinterpretations that can occur at each step of ecotoxicity testing: procurement or synthesis of the ENMs and assessment of potential toxic impurities such as metals or endotoxins, ENM storage, dispersion of the ENMs in the test medium, direct interference with assay reagents and unacknowledged indirect effects such as nutrient depletion during the assay, and assessment of the ENM biodistribution in organisms. We recommend thorough characterization of initial ENMs including measurement of impurities, implementation of steps to minimize changes to the ENMs during storage, inclusion of a set of experimental controls (e.g., to assess impacts of nutrient depletion, ENM specific effects, impurities in ENM formulation, desorbed surface coatings, the dispersion process, and direct interference of ENM with toxicity assays), and use of orthogonal measurement methods when available to assess ENMs fate and distribution in organisms.

Long-term colloidal stability and metal leaching of single wall carbon nanotubes: effect of temperature and extracellular polymeric substances

Long term (90 day) stability, aggregation kinetics in the presence and absence of natural organic materials (NOM), and metal leaching of five commercial single wall carbon nanotubes (SWCNTs) in waters (e.g. freshwater, seawater, stormwater, wastewater, and groundwater) were studied, as well as the effect of temperature on SWCNT stability and metal leaching. Zeta (ζ) potential of SWCNT decreased in magnitude with increase in temperature. In wastewater, SWCNT sedimented from the water column to below detectable levels after 30 days when kept at 40 °C, but at 20 °C 19% suspension was still observed after the same exposure time. Addition of 0.1 mg-C L(-1) EPS shifted the critical coagulation concentration (CCC) of SRNOM-stabilized SWCNT from 15 mM to 54 mM NaCl via additional electrostatic and possibly steric stabilization. Attachment efficiencies (α) of SWCNT in waters ranged from ∼0.001 in DI with 10 mg L(-1) SRNOM to 1 in seawater. However, sedimentation of SWCNT in seawater (and other high ionic strength conditions) was not as fast as expected due to improved buoyancy and/or drag. Purified forms of SWCNTs exhibited better dispersibility and stability in most waters, but as expected, the total metal leached out was higher in the raw variants. Metal leaching from CNT in these studies was controlled by metal and water chemistries, CNT pretreatment, leachable metal fraction, exposure time, and presence of NOM.

Impact of humic/fulvic acid on the removal of heavy metals from aqueous solutions using nanomaterials: a review

Nowadays nanomaterials have been widely used to remove heavy metals from water/wastewater due to their large surface area and high reactivity. Humic acid (HA) and fulvic acid (FA) exist ubiquitously in aquatic environments and have a variety of functional groups which allow them to complex with metal ions and interact with nanomaterials. These interactions can not only alter the environmental behavior of nanomaterials, but also influence the removal and transportation of heavy metals by nanomaterials. Thus, the interactions and the underlying mechanisms involved warrant specific investigations. This review outlined the effects of HA/FA on the removal of heavy metals from aqueous solutions by various nanomaterials, mainly including carbon-based nanomaterials, iron-based nanomaterials and photocatalytic nanomaterials. Moreover, mechanisms involved in the interactions were discussed and potential environmental implications of HA/FA to nanomaterials and heavy metals were evaluated.

Are engineered nanomaterials superior adsorbents for removal and pre-concentration of heavy metal cations from water?

We observed that the removal of metal ions with engineered nanomaterials could be largely attributed to precipitation by forming metal hydroxyl precipitates rather than adsorption, implying that ENMs cannot be superior adsorbents.