Magnetic Nanoparticles Interaction with Humic Acid: In the Presence of Surfactants

Interaction of Pb(II) with microplastic-sediment complexes: Critical effect of surfactant

In this study, the impact of surfactants on the adsorption behavior of Pb(II) onto microplastics-sediment (MPs-S) complexes was investigated. Firstly, virgin polyamide (VPA) and polyethylene (VPE) were placed in Xiangjiang River sediment for six months to conduct in-situ aging. The results indicated that the biofilm-developed polyamide (BPA) and polyethylene (BPE) formed new oxygen-containing functional groups and different biofilm species. Furthermore, the adsorption capacity of Pb(II) in sediment (S) and MPs-S complexes was in the following order: S > BPA-S > VPE-S > VPA-S > BPE-S. The addition of sodium dodecyl benzenesulfonate (SDBS) promoted the adsorption of Pb(II), and the adsorption amount of Pb(II) increased with the higher concentration of SDBS, while adding cetyltrimethylammonium bromide (CTAB) showed the opposite result. The adsorption process of MPs-S complexes to Pb(II) was dominated by chemical adsorption, and the interaction between MPs-S complexes and Pb(II) was multilayer adsorption involving physical and chemical adsorption when the surfactants were added. Besides, the pH exerts a significant effect on Pb(II) adsorption in different MPs-S complexes, and the highest adsorption amount occurred at pH 6. Noteworthy, CTAB promoted the adsorption ability of Pb(II) when the exogenous FA was added. The binding characteristic of sediment endogenous DOM components and Pb(II) was influenced by the addition of MPs and surfactants. Finally, it confirmed that adsorption mechanisms mainly involve electrostatic and hydrophobic interaction. This study provides a new perspective to explore the environmental behaviors of Pb(II) by MPs and sediments with the addition of surfactants, which was conducive to evaluating the ecological risks of MPs and heavy metals in aquatic environments.

Understanding the Interactions of Nanoparticles and Dissolved Organic Matter at the Molecular Level by 1H 2D Multi-Exponential Transverse Relaxation NMR Spectroscopy

The interaction between humic acid (HA) and engineered nanoparticles (NPs) is critical in environmental sciences, especially for understanding the behavior of NPs in natural waters. This study employs 1H 2D Multi-Exponential Transverse Relaxation (METR) NMR spectroscopy to examine the molecular-level interactions between Pahokee Peat humic acid (HA) and carboxyl-functionalized iron oxide nanoparticles (NPCOs). First, 1H 2D METR NMR spectroscopy allowed not only the identification of HA in terms of its chemical composition but also the separation of molecules with the same chemical shift values but different rates of molecular tumbling. Then, using solutions with varying NPCO concentrations (0, 10, 40, and 100 μM), we observed significant changes in the T2 relaxation times of HA components, indicating interactions between HA and NPCO. Analysis showed the biggest effect on two chemical shift regions, corresponding to lipids and carbohydrates, revealing that smaller molecules within these regions exhibit the most significant changes in T2 values upon the addition of NPCO. This suggests that these molecules are the initial sites of interaction, with the entire HA system being affected at higher NPCO concentrations. These findings highlight the utility of METR NMR spectroscopy in studying complex environmental mixtures and provide insights into the behavior of HA and NPs, essential for understanding the fate of NPs in the environment.

Effects of Mixtures of Engineered Nanoparticles and Cocontaminants on Anaerobic Digestion

The widespread application of nanotechnology inevitably leads to an increased release of engineered nanoparticles (ENPs) into the environment. Due to their specific physicochemical properties, ENPs may interact with other contaminants and exert combined effects on the microbial community and metabolism of anaerobic digestion (AD), an important process for organic waste reduction, stabilization, and bioenergy recovery. However, the complicated interactions between ENPs and other contaminants as well as their combined effects on AD are often overlooked. This review therefore focuses on the co-occurrence of ENPs and cocontaminants in the AD process. The key interactions between ENPs and cocontaminants and their combined influences on AD are summarized from the available literature, including the critical mechanisms and influencing factors. Some sulfides, coagulants, and chelating agents have a dramatic "detoxification" effect on the inhibition effect of ENPs on AD. However, some antibiotics and surfactants increase the inhibition of ENPs on AD. The reasons for these differences may be related to the interactive effects between ENPs and cocontaminants, changes of key enzyme activities, adenosine triphosphate (ATP) levels, reactive oxygen species (ROS) production, and microbial communities. New scientific opportunities for a better understanding of the coexistence in real world situations are converging on the scale of nanoparticles.

Emerging iron-based mesoporous materials for adsorptive removal of pollutants: Mechanism, optimization, challenges, and future perspective

Iron-based materials (IBMs) have shown promise as adsorbents due to their unique physicochemical properties. This review provides an overview of the different types of IBMs, their synthesis methods, and their properties. Results found in the adsorption of emerging contaminants to a wide range of IBMs are discussed. The IBMs used were evaluated in terms of their maximum uptake capacity, with special consideration given to environmental conditions such as contact time, solution pH, initial pollutant concentration, etc. The adsorption mechanisms of pollutants are discussed taking into account the results of kinetic, isotherm, thermodynamic studies, surface complexation modelling (SCM), and available spectroscopic data. A current overview of molecular modeling and simulation studies related to density functional theory (DFT), surface response methodology (RSM), and artificial neural network (ANN) is presented. In addition, the reusability and suitability of IBMs in real wastewater treatment is shown. The review concludes with the strengths and weaknesses of current research and suggests ideas for future research that will improve our ability to remove contaminants from real wastewater streams.

Deposition behaviors of carboxyl-modified polystyrene nanoplastics with goethite in aquatic environment: Effects of solution chemistry and organic macromolecules

The ubiquitous nanoplastics (NPs) in the environment are emerging contaminants due to their risks to human health and ecosystems. The interaction between NPs and minerals determines the environmental and ecological risks of NPs. In this study, the deposition behaviors of carboxyl modified polystyrene nanoplastics (COOH-PSNPs) with goethite (α-FeOOH) were systematically investigated under various solution chemistry and organic macromolecules (OMs) conditions (i.e., pH, ionic type, humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA)). The study found that electrostatic interactions dominated the interaction between COOH-PSNPs and goethite. The deposition rates of COOH-PSNPs decreased with an increase in solution pH, due to the enhanced electrostatic repulsion by higher pH. Introducing cations or anions could compress the electrostatic double layers and compete for interaction sites on COOH-PSNPs and goethite, thereby reducing the deposition rates of COOH-PSNPs. The stabilization effects, which were positive with ions valence, followed the orders of NaCl ≈ KCl < CaCl2, NaNO3 ≈ NaCl < Na2SO4 < Na3PO4. Specific adsorption of SO42- or H2PO4- caused a potential reversal of goethite from positive to negative, leading to the electrostatic forces between COOH-PSNPs and goethite changed from attraction to repulsion, and thus significantly decreasing deposition of COOH-PSNPs. Organic macromolecules could markedly inhibit the deposition of COOH-PSNPs with goethite because of enhanced electrostatic repulsion, steric hindrance, and competition of surface binding sites. The ability for inhibiting the deposition of COOH-PSNPs followed the sequence of SA > HA > BSA, which was related to their structure (SA: linear, semi-flexible, HA: globular, semi-rigid, BSA: globular, with protein tertiary structure) and surface charge density (SA > HA > BSA). The results of this study highlight the complexity of the interactions between NPs and minerals under different environments and provide valuable insights in understanding transport mechanisms and environmental fate of nanoplastics in aquatic environments.

Impact of iron/aluminum (hydr)oxide and clay minerals on heteroaggregation and transport of nanoplastics in aquatic environment

Nanoplastics (NPs) are emerging contaminants in the environment, where the transport and fate of NPs would be greatly affected by interactions between NPs and minerals. In the present study, the interactions of two types of polystyrene nanoplastics (PSNPs), i.e., bare-PSNPs and carboxylated PSNPs-COOH, with iron (hydr)oxides (hematite, goethite, magnetite, and ferrihydrite), aluminum (hydr)oxides (boehmite and gibbsite), and clay minerals (kaolinite, montmorillonite, and illite) were investigated. The positively charged iron/aluminum (hydr)oxide minerals could form heteroaggregates with negatively charged PSNPs. Electrostatic and hydrophobic interaction dominate for the heteroaggregation of bare-PSNPs with iron/aluminum (hydr)oxide minerals, while ligand exchange and electrostatic interaction are involved in the heteroaggregation of PSNPs-COOH with iron/aluminum (hydr)oxides minerals. However, heteroaggregation between PSNPs and negatively charged clay minerals was negligible. Humic acid markedly suppressed such heteroaggregation between PSNPs and minerals due to enhanced electrostatic repulsion, steric hindrance, and competition of surface attachment sites. The heteroaggregation rates of both bare-PSNPs and PSNPs-COOH with hematite decreased with increasing solution pH. Increased ionic strength enhanced the heteroaggregation of PSNPs-COOH but inhibited that of bare-PSNPs. The results of the present study suggested that the heteroaggregation of PSNPs in environments could be strongly affected by minerals, solution pH, humic acid, and ionic strength.

Sesamol alleviates manganese-induced neuroinflammation and cognitive impairment via regulating the microglial cGAS-STING/NF-κB pathway

Toxic effects of excessive manganese (Mn) from occupational or environmental exposure cause harm to human health. Excessive Mn exposure is intimately associated with neurodegeneration and cognitive dysfunction. Inflammatory responses mediated by microglia are essential contributors to the pathogenesis of Mn-induced neurotoxicity. Inhibition of microglia-mediated inflammation has been shown to alleviate Mn-induced neurotoxicity. Sesamol, derived from sesame, has neuroprotective properties in various disease models, including neurological diseases. Whether sesamol protects against Mn-induced neurological injuries has not been determined. Here, both in vivo and in vitro Mn exposure models were established to address the beneficial effects of sesamol on Mn-induced neurotoxicity. We showed that administration of sesamol mitigated learning and memory deficits of mice treated by Mn. Furthermore, sesamol reduced Mn-induced microglial activation and the expression of proinflammatory mediators (TNF-α, iNOS, and Cxcl10), while exerting a marginal effect on anti-inflammation and microglial phagocytosis. Mn exposure activated the microglial cGAS-STING pathway and sesamol inhibited this pathway by reducing the phosphorylation of STING and NF-κB, concomitantly decreasing IFN-α and IFN-β synthesis. In summary, our novel results indicated that sesamol exerted its protective effects on Mn-induced neuroinflammation and cognitive impairment via the microglial cGAS-STING/NF-κB pathway, providing evidence that sesamol may serve as an effective therapeutic for preventing and treating Mn-induced neurotoxicity.

Adsorption of p-benzoquinone at low concentrations from aqueous media using biosolid-based activated carbon

The toxic oxidation intermediate p-benzoquinone exists in aqueous environments at dilute concentrations above the fish-toxicity limit of 0.045 mg/L, affecting aquatic life. The reduction of this compound to the concentrations required to achieve safe discharge limits is challenging. In this study, the adsorptive removal of p-benzoquinone by a biosolid-based activated carbon (SBAC) was systematically investigated in batch experiments. The adsorption rate was rapid, and the bulk of p-benzoquinone adsorption occurred within 30 min. The maximum adsorption capacity of SBAC was estimated at 19.6 mg/g using the Langmuir isotherm model. Its adsorptivity was independent of temperature from 6 to 40 °C. The presence of 6 g/L of chloride and 500 mg/L of sulphate did not affect the removal of 1 mg/L p-benzoquinone, whereas 15 mg/L of humic acid media slightly decreased the p-benzoquinone removal from 87.0% to 83.2%. Diffusion, hydrophilic, and electrostatic interactions (i.e., dipole-dipole) govern the adsorption of p-benzoquinone and are influenced by the SBAC surface chemistry. Biosolid-based activated carbon can lower the residual p-benzoquinone to below the fish-toxicity limit of 0.045 mg/L within 1 h of sequential adsorption. Thus, biosolid-based activated carbon can effectively remove p-benzoquinone from aqueous environments; this is a waste-to-resource approach that addresses sustainability (waste disposal) and environmental protection (pollutant removal).

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation

The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to-prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control.

Effect of Tube Diameters and Functional Groups on Adsorption and Suspension Behaviors of Carbon Nanotubes in Presence of Humic Acid

The adsorption and suspension behaviors of carbon nanotubes (CNTs) in the water environment determine the geochemical cycle and ecological risk of CNTs and the compounds attached to them. In this study, CNTs were selected as the research object, and the effect of tube diameters and functional groups (multiwall CNTs (MWNTs) and hydroxylated MWNTs (HMWNTs)) on the adsorption and suspension behaviors of the CNTs in the presence of humic acid (HA) was systematically analyzed. The results indicate that HA adsorption decreased with the increase in the solution pH, and the adsorption amount and rate were negatively correlated with the tube diameter of the CNTs. The surface hydroxylation of the CNTs prevented the adsorption of HA, and the maximum adsorption amounts on the MWNTs and HMWNTs were 195.95 and 74.74 mg g-1, respectively. HA had an important effect on the suspension of the CNTs, especially for the surface hydroxylation, and the suspension of the CNTs increased with the increase in the tube diameter. The characteristics of the CNTs prior to and after adsorbing HA were characterized by transmission electron microscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. The results indicate that surface hydroxylation of the CNTs increased the adsorption of aromatic compounds, and that the CNTs with a smaller diameter and a larger specific surface area had a disordered carbon accumulation microstructure and many defects, where the adsorption of part of the HA would cover the defects on the CNTs' surface. Density functional theory (DFT) calculations demonstrated that HA was more easily adsorbed on the CNTs without surface hydroxylation. This investigation is helpful in providing a theoretical basis for the scientific management of the production and application of CNTs, and the scientific assessment of their geochemical cycle and ecological risk.

The influence of environmental factor on the coagulation enhanced ultrafiltration of algae-laden water: Role of two anionic surfactants to the separation performance

With the acceleration of urbanization and the improvement of people's living standards, more chemicals that humans rely on are entering the city and surrounding water bodies. Anionic surfactants are one of the essential products for human beings. It is also one of the inducements that cause the eutrophication. The algae-laden water caused by eutrophication is a headache in the traditional water treatment process. To solve the problem, ultrafitration combined process was widely investigated to treat the algae-laden water. The presence of stimuli, low concentration anionic surfactant, probably interfere the performance of ultrafiltration process during algae-laden water treatment. In this study, the influence of two typical anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (LAS), on the performance of coagulation-enhanced ultrafiltration was investigated. The aluminum sulfate hydrate and iron sulfate hydrate were respectively employed as coagulant. Based on the residual turbidity and zeta potential, 4 mg/L Al and 8 mg/L Fe were determined as the optimal coagulant dosage. The floc morphology confirmed that Al-algae flocs with lower fractal dimension (D_f) were looser and more porous compared to Fe-algae flocs. More coagulant was depleted by LAS due to the better hydrophobicity of LAS. During the filtration process, LAS caused a larger flux reduction compared with SDS regardless of the coagulant that was used. More organic compounds penetrate into membrane pores and block the pores with the presence of LAS since algal cell aggregation was weakened. Finally, the rejection of organic compounds by the coagulation-enhanced ultrafiltration process was studied, and the co-existing surfactants can cause effluent deterioration. Therefore, the presence of surfactants has a negative effect to the ultrafiltration treatment of algae-laden water.

Effect of different molecular coatings on the heating properties of maghemite nanoparticles

In this work, the effect of different molecular coatings on the alternating magnetic field-induced heating properties of 15 nm maghemite nanoparticles (NPs) in water dispersions was studied at different frequencies (159-782 kHz) and field amplitudes (100-400 G). The original hydrophobic oleate coating was replaced with dimercaptosuccinic acid (DMSA) or polyethylene glycol trimethoxysilane (PEGTMS), while cetrimonium bromide (CTAB) or stearic acid-poloxamer 188 (SA-P188) was intercalated or encapsulated, respectively, to transfer the dispersions into water. Surface modification, based on intercalation processes, induced clustering phenomena with the formation of spherical-like assemblies (CTAB and SA-P188), while ligand-exchange strategies kept the particles isolated. The clustering phenomenon has detrimental effects on the heating performances compared with isolated systems, in line with the reduction of Brown relaxation times. Furthermore, broader comprehension of the heating phenomenon in this dynamic system is obtained by following the evolution of SPA and ILP with time and temperature beyond the initial stage.

Freeze-Thaw Cycle-Enhanced Transformation of Iodide to Organoiodine Compounds in the Presence of Natural Organic Matter and Fe(III)

The formation of organoiodine compounds (OICs) is of great interest in the natural iodine cycle as well as water treatment processes. Herein, we report a pathway of OIC formation that reactive iodine (RI) and OICs are produced from iodide oxidation in the presence of Fe(III) and natural organic matter (NOM) in frozen solution, whereas their production is insignificant in aqueous solution. Moreover, thawing the frozen solution induces the further production of OICs. A total of 352 OICs are detected by Fourier transform ion cyclotron resonance mass spectrometry in the freeze-thaw cycled reactions of Fe(III)/I^-/humic acid solution, which are five times as many as OICs in aqueous reactions. Using model organic compounds instead of NOM, aromatic compounds (e.g., phenol, aniline, o-cresol, and guaiacol) induce higher OIC formation yields (10.4-18.6%) in the freeze-thaw Fe(III)/I^- system than those in aqueous (1.1-2.1%) or frozen (2.7-7.6%) solutions. In the frozen solution, the formation of RI is enhanced, but its further reaction with NOM is hindered. Therefore, the freeze-thaw cycle in which RI is formed in the frozen media and the resulting RI is consumed by reaction with NOM in the subsequently thawed solution is more efficient in producing OICs than the continuous reaction in frozen solution.

Iron particle formation under chlorine disinfection considering effects of deoxidizers in drinking water

Iron oxidation inevitably occurs in drinking water distribution systems (DWDSs) and can cause water quality problems such as increased turbidity and discoloration of tap water. Considering that chlorine disinfection is also widely used in DWDSs, the role of disinfectant and disinfection byproducts (DBPs) in iron oxidation should not be neglected. Interestingly, here the well-known deoxidizer ascorbic acid (VC), which is also a food additive, could induce the formation of Fe₃O₄ besides FeOOH resulting in the color change from yellow to black in the presence of trichloroacetic acid (TCA, one of the most typical DBPs) and NaClO (disinfectant). The oxygen-containing functional groups in TCA and VC may bind Fe(II) to guide the crystal growth. Though the particles generated in the presence of TCA and NaClO together with VC had higher content Fe₃O₄ which would be more difficult to suspend, once disturbance happened, these particles could increase the turbidity and color of water into higher value than the particles formed without VC and those generated in the absence of TCA and NaClO. Therefore, the deoxidizer VC may control "yellow water" without disinfectant, but may deteriorate the water quality under disinfection conditions.

New applications of quinone redox mediators: Modifying nature-derived materials for anaerobic biotransformation process

Due to their wide-distribution, high-biocompatibility and low-cost, nature-derived quinone redox mediators (NDQRM) have shown great potential in bioremediation through mediating electron transfers between microorganisms and between microorganisms and contaminants in anaerobic biotransformation processes. It is obvious that their performance in bioremediation was limited by the availability of quinone-based groups in NDQRM. A sustainable solution is to enhance the electron transfer capacity and retention capacity by the modification of NDQRM. Therefore, this review comprehensively summarized the modification techniques of NDQRM according to their multiple roles in anaerobic biotransformation systems. In addition, their potential applications in greenhouse gas mitigation, contaminant degradation in anaerobic digestion, contaminant bioelectrochemical remediation and energy recovery were discussed. And the problems that need to be addressed in the future were pointed out. The obtained knowledge would promote the exploration of novel NDQRM, and provide suggestions for the design of anaerobic consortia in biotransformation systems.

Strong influence of surfactants on virgin hydrophobic microplastics adsorbing ionic organic pollutants

Microplastic (MP) pollution has become an area of increasing concern because MPs accumulate various types of pollutants. Many previous studies have explored the interactions between MPs and hydrophobic pollutants. However, little research has been conducted on hydrophilic pollutants, which are of much higher concentration and ubiquitous in environment. Surfactants cause hydrophobic MPs to become hydrophilic, which may significantly enhance their capacities to adsorb hydrophilic pollutants. This study explored the influence of co-existing surfactants on the adsorption of ionic organic pollutants by MPs, and found that the presence of an ionic surfactant could significantly enhance the capacity of polyvinyl chloride (PVC, 0.2 mm) MPs to adsorb pollutants with opposite charges. The Langmuir methylene blue adsorption capacity of PVC could be increased from 172 to 4417 ppm in the presence of a sodium dodecyl benzene sulfonate surfactant. Nonionic surfactants impeded the adsorption of both cationic and anionic pollutants due to the steric resistance of the hydrophilic polyethelene glycol chains. The electrostatic interaction mechanism dominated the interfacial behaviors of ionic pollutants on surfactant-adsorbed MP interfaces. The effects of the surfactants were further verified using four different model pollutants and six surfactants. The adsorption capacities of real environmental MPs, including PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS), increased by three to twenty-six times. The adsorption properties of MPs may be determined by the presence of co-existing surfactants, rather than their polymer species or additives.

Surfactant stealth effect of microplastics in traditional coagulation process observed via 3-D fluorescence imaging

Microplastics (MPs) have aroused rising social concerns. Although amounts of surfactants exist in wastewater and are expected to alter the surface properties of MPs significantly as they are designed to be adsorbed by hydrophobic particles. However, rare works have been done on the influence of surfactants on the coagulation removal process of MPs which was thought to be an effective way to remove MPs together with other natural particles, such as clay. We used 3-D fluorescence imaging to track the coagulation removal process of polystyrene MPs. Our results indicate that nonionic surfactant, tween 20 in ppm scale, could inhibit the coagulation removal of polystyrene MPs significantly. Residue MPs in the effluent is proportional with the surfactant concentration and increases up to tens of times, which will lead to a dramatic increase in their potential environmental risks. Apparent size effect exists in the coagulation in which smaller MPs can escape from the coagulation removal more easily. Mechanism study suggests that the steric resistance of the hydrophilic flexible polyethylene glycol (PEG) layer formed by tween 20 adsorbed on MP surface inhibits clay deposition and thus hinders subsequent agglomeration and precipitation. A surfactant stealth effect, which is used in the design of nanomedicine to avoid the human immune recognition and clearance of nano-drugs from blood circulation, also exists in the coagulation removal process of MPs. Our finding not only proves the strong influence of surfactants on MPs but also will stimulate related studies on other latent surfactant effects of MPs.

Microwave-Assisted Synthesis of Water-Dispersible Humate-Coated Magnetite Nanoparticles: Relation of Coating Process Parameters to the Properties of Nanoparticles

Nowadays, there is a demand in the production of nontoxic multifunctional magnetic materials possessing both high colloidal stability in water solutions and high magnetization. In this work, a series of water-dispersible natural humate-polyanion coated superparamagnetic magnetite nanoparticles has been synthesized via microwave-assisted synthesis without the use of inert atmosphere. An impact of a biocompatible humate-anion as a coating agent on the structural and physical properties of nanoparticles has been established. The injection of humate-polyanion at various synthesis stages leads to differences in the physical properties of the obtained nanomaterials. Depending on the synthesis protocol, nanoparticles are characterized by improved monodispersity, smaller crystallite and grain size (up to 8.2 nm), a shift in the point of zero charge (6.4 pH), enhanced colloidal stability in model solutions, and enhanced magnetization (80 emu g⁻¹).

Antagonistic effect of zinc oxide nanoparticle and surfactant on anaerobic digestion: Focusing on the microbial community changes and interactive mechanism

The objective of this study was to evaluate the antagonistic effect of emerging pollutants of zinc oxide nanoparticles (ZnO NPs) and sodium dodecyl sulfate (SDS) on anaerobic digestion and explore their potential mechanism. The results indicated that at a low inhibitory concentration of ZnO NPs (1.0 mM), the practical co-inhibition was decreased by 24% and 18% in co-existence of 50 mg/L SDS and 300 mg/L SDS, respectively. More importantly, the co-existence of 300 mg/L SDS greatly enhanced methanogenesis of organics in seriously inhibited case (2.0 mM of ZnO NPs). The microbial community analysis showed that co-existed SDS enhanced the growth of Methanothrix, Methanosarcina and Methanobacterium. The antagonistic enhancement could be attributed to the net charge reversal, partially agglomeration of ZnO NPs and/or reduction of Zn²⁺ release in the presence of SDS. These findings could provide useful information for evaluating the co-inhibition of SDS and ZnO NPs on biological processes.

Detection of humic acid in water using flat-sheet and folded-rod viscous alkaline glucose syrups

Interaction of the alkaline glucose solution with humic acid.

Effects of fulvic acid on aggregation, sedimentation, and adsorption of Fe3O4 magnetic nanoparticles

Environmental behavior, bioavailability, and risks posed by Fe₃O₄, magnetic nanoparticles (Fe₃O₄ NPs) in surface waters are affected by complex geochemistry, including pH and inorganic and organic matter. This work provides a systematic analysis of adsorption of fulvic acid (FA) on surfaces of Fe₃O₄ NPs with adsorption kinetics, adsorption thermodynamic, and adsorption isotherm. Adsorption of FA on surfaces of Fe₃O₄ NPs is consistent with assumptions of Langmuir and Freundlich adsorption isotherm models. The adsorption amount of FA was inversely proportional to solution pH, and the maximum amount is 128.6 mg g^-1. Adsorption of FA on surfaces of Fe₃O₄ NPs is a spontaneous endothermic process. FA plays an important role in aggregation and suspension/sedimentation behavior of Fe₃O₄ NPs in aquatic environmental. With continuous adsorption of FA, electrostatic repulsion between the particles and the steric hindrance of FA significantly decreased aggregation and increased suspension of Fe₃O₄ NPs. The results of FTIR and XPS indicated that FA was adsorbed on Fe₃O₄ NPs mainly through chemical reactions, and carbohydrates particularly play an important role in adsorption.

Regulation of engineered nanomaterials: current challenges, insights and future directions

Substantial production and wide applications of engineered nanomaterials (ENMs) have raised concerns over their potential influences on the environment and humans. However, regulations of products containing ENMs are scarce, even in countries with the greatest volume of ENMs produced, such as the United States and China. After a comprehensive review of life cycles of ENMs, five major challenges to regulators posed by ENMs are proposed in this review: (a) ENMs exhibit variable physicochemical characteristics, which makes them difficult for regulators to establish regulatory definition; (b) Due to diverse sources and transport pathways for ENMs, it is difficult to monitor or predict their fates in the environment; (c) There is a lack of reliable techniques for quantifying exposures to ENMs; (d) Because of diverse intrinsic properties of ENMs and dynamic environmental conditions, it is difficult to predict bioavailability of ENMs on wildlife and the environment; and (e) There are knowledge gaps in toxicity and toxic mechanisms of ENMs from which to predict their hazards. These challenges are all related to issues in conventional assessments of risks that regulators rely on. To address the fast-growing nanotechnology market with limited resources, four ENMs (nanoparticles of Ag, TiO₂, ZnO and Fe₂O₃) have been prioritized for research. Compulsory reporting schemes (registration and labelling) for commercial products containing ENMs should be adopted. Moreover, to accommodate their potential risks in time, an integrative use of quantitative structure-activity relationship and adverse outcome pathway (QSAR-AOP), together with qualitative alternatives to conventional risk assessment are proposed as tools for decision making of regulators.