Double Layer Compression Research Articles

Physical and chemical properties of aluminum tailings mud modified by metal ions

Aluminum tailings mud, a type of waste generated by bauxite washing during alumina production, is harmful. Owing to the isomorphism substitution of iron-aluminum symbiotic minerals, a large number of metal ions inevitably exist in the slurry, which causes the suspension to maintain dispersion and hinders the drainage of aluminum tailings mud. This study examined the effects of the pH and commonly associated metal ions, such as K+ and Fe3+, on the sedimentation characteristics of aluminum tailings mud. Zeta potential analyzer, X-ray fluorescence spectrum analysis, and electron scanning microscopy were used to study the effects of common metal ions in the tailings slurry on the sedimentation characteristics of aluminum tailings mud. The results showed that the sedimentation effect of the tailings slurry was superior after adding Fe3+ compared with K+. The mechanism analysis shows that at a certain pH range, the addition of metal ions can compress the thickness of the electric double layer on the surface. The high-valence ions (Fe3+) will have more electric double layer compression than monovalent ions (Na+), which is more conducive to the agglomeration of aluminum tailing mud particles. This conclusion provides guidance for efficient drainage of aluminum tailings mud.

Electrosorption approach removing PFOA from wastewater using a MXene-polyaniline film

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant found in various industrial effluents, posing significant environmental and health risks. Electrosorption of PFOA on MXene-polyaniline film from water was studied. The results of electrosorption kinetics showed that the functionalized MXene film with polyaniline resulting in an approximately 100 % increase in electrosorption capacitance for PFOA due to increasing of the MXene film's volumetric capacitance and modifying of surface chemistry of MXene. The maximum adsorption of PFOA on MXene and MXene-polyaniline films were 358.5 mg/g and 966.1 mg/g, respectively, at an initial concentration of 100 mg/L upon application of +1.0 V. Moreover, humic acid (HA) competing with the adsorption sites, sodium chloride through the double-layer compression effect, and pH affecting the amine or amide functional groups on MXene-polyaniline which inhibited PFOA adsorption onto MXene-polyaniline film were thoroughly examined. Lastly, the reversible adsorption–desorption cycles show that the MXene–polyaniline film possesses the potential to be used continuously. To address PFAS pollution in water sources, we think our approach can help build effective and long-lasting technology.

Aggregation of graphene oxide upon the stripping of oxidized debris: An experimental and molecular dynamics simulation study

The most recent structural study of graphene oxide (GO) indicates that the oxidized debris (ODs) adhered to as-prepared GO will strip in certain aquatic settings. The impact of ODs stripping on the characteristics of GO has been widely reported, but its effects on GO aggregation have received less attention. Here, the influence of OD stripping on the GO aggregation property was identified, and the aggregation of as-prepared GO and GO upon OD stripping was compared. Upon ODs stripping, the pKa values of GO shifted from 3.91, 6.25, and 9.84 to 4.54, 6.65, and 10.21, respectively. Further analysis indicated the removal of ODs reduced the net negative charge and improved the hydrophobicity of GO, hence promoting the aggregation of GO. The acceleration of GO-Ca2+-OD aggregate formation was facilitated by the collective effects of ODs stripping, functional group deprotonation, double layer compression, OD bridging, and charge neutralization. The metal ions and stripped ODs attach to GO edges and link GO, which perform like bridges and contribute to further aggregation. In general, the existence of ODs adds complexity to the constructions and characteristics of GO, and it is important to take this into account while evaluating the aggregation characteristic of GO-based materials.

Abstract 3384: Rapid and automated tumor cell phenotyping based on annexin-mediated enforce blebbing response

Abstract Introduction: Accumulating evidence supports the tight correlation between the physical characteristics of cells (including morphology, mechanical, and electrical properties) with the progression of cancer. Cellular blebbing, a distinctive feature observed during apoptosis and cell migration, has gained significant recognition. However, existing tools such as atomic force microscopy and optical tweezers have limitations in terms of throughput and complexity. Microfluidics has emerged as a promising technology to overcome these limitations. Methods: In this study, we developed a novel microfluidic device with a double-layer compression mechanism to induce controlled blebbing of cells. We implemented a convolution-based tracing program to enhance the accuracy and efficiency of cell area measurement. The device was used to examine the enforced blebbing response of two human breast cancer cell lines (MDA-MB-231 and MCF-7) and investigate the potential of blebbing as a marker for drug resistance using a human lung cancer cell line (HCC4006). Additionally, we elucidated the role of annexin-6 (A6) in enforced blebbing and its underlying mechanism. Results: Our microfluidic device successfully implemented a double-layered design that induced cell deformation through compression from the second pressurized polydimethylsiloxane layer. The findings revealed that highly invasive cell lines, such as MDA-MB-231 and osimertinib-resistant HCC4006, required significantly higher critical compression levels compared to their non-invasive counterparts (MCF-7 cell line) or osimertinib-sensitive cells. Moreover, the drug-resistant groups exhibited a greater compression strain requirement for blebbing compared to the control group, indicating their enhanced resilience against disruptive forces and superior survivability. Prior studies have demonstrated that A6 protein is recruited to the site of membrane injury and facilitates the formation of blebs, thereby contributing to cellular repair processes. Our further investigation into the role of A6 protein demonstrated its involvement in cell blebbing. Knockdown of A6 resulted in a notable 27% reduction in cellular volume, reflecting reduced intracellular pressure, and a corresponding 1.7-fold increase in the critical compressive strain necessary for inducing blebbing. Conclusion: Our microfluidic device allows for rapid and simultaneous testing and automated analysis of hundreds of cells, making it suitable for applications such as cell sorting, highly invasive and drug-resistant cancer cell detection, without the need for labeling. Furthermore, it serves as a powerful tool for fundamental studies of membrane and cytoskeleton dynamics. The label-free nature of the device, coupled with its high throughput capabilities, highlights its potential in future applications, including cancer monitoring and drug-resistance screening. Citation Format: Wei Huang, Zheng Wang, Dennis Wai-Yin Au, Bingxian Tang, Baiqian Qi, William C. Cho, Yuan Lin. Rapid and automated tumor cell phenotyping based on annexin-mediated enforce blebbing response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3384.

Rapid and automatic phenotyping of cells through their annexin-mediated enforced blebbing response

Cellular blebbing has been widely recognized as a hallmark of processes such as apoptosis and cell migration. Here, we developed a novel double-layer compression microfluidic device to trigger the enforced blebbing of cells in a programmable manner. It was found that the critical compression for inducing membrane bleb in highly invasive or drug-resistant breast and lung cancer cell lines could be several times higher than that of their non-invasive or drug-sensitive counterparts. Furthermore, we showed that knockdown of annexin-6, a protein known to be heavily involved in membrane and calcium dynamics in cells, led to a significantly reduced cellular volume, reflecting a lowered intracellular pressure, and an ∼twofold increase in the critical compressive strain for triggering blebbing. The fact that hundreds of cells can be tested and automatically analyzed in our device at the same time highlights the potential of this simple and label-free method in applications such as cell sorting and disease detection.

Flocculation of kaolin and anion dye by cationic cellulose-based flocculant: RSM-optimized synthesis and experimental study

An efficient cellulose-based flocculant, CMA, was synthesized using a free radical initiation method in a NaOH/Urea aqueous solution. The optimal synthesis conditions were determined through single-factor and RSM experiments: a molar ratio of MCC to AA of 1:3.6, MCC to CTA of 1:8.2, and a reaction temperature of 45.8 °C. CMA was characterized using FTIR, SEM, XRD, DLS, XPS, and TG and applied successfully to the flocculation treatments of kaolin, simulated dyes, and actual dye wastewater. It exhibited low pH sensitivity, achieving over 90% removal efficiency at pH 3–12, with a maximum of 98.3%. In simulated dye wastewater, the removal efficiency of various dyes was greater than 95%, with a maximum of 97%. After CMA flocculation and ozone aeration, 86.5% of COD and 93.6% of turbidity were removed from the actual dye wastewater. CMA carried out the flocculated dye removal process via charge neutralization, double layer compression, and bridging adsorption, as revealed by various instrument characterization and analysis. A polysaccharide-based flocculant, CMA exhibits environmentally friendly properties, low pH sensitivity, and high efficiency in removing wastewater pollutants, making it a promising flocculant for highly turbid wastewater and anionic dye wastewater.

Aggregation behavior of polystyrene nanoplastics: Role of surface functional groups and protein and electrolyte variation

Aggregation kinetics of plastics are affected by the surface functional groups and exposure orders (electrolyte and protein) with kinds of mechanisms in aquatic environment. This study investigates the aggregation of polystyrene nanoplastics (PSNPs) with varying surface functional groups in the presence of common electrolytes (NaCl, CaCl2, Na2SO4) and bovine serum albumin (BSA). It also examines the impact of different exposure orders, namely BSA + NaCl (adding them together), BSA → NaCl (adding BSA firstly and then NaCl), and NaCl → BSA (adding NaCl firstly and then BSA), on PSNPs aggregation. The presence of BSA decreased the critical coagulation concentration in NaCl (CCCNa+) of the non-modified PS-Bare from 222.17 to 142.81 mM (35.72%), but increased that of the carboxyl-modified PS-COOH from 157.34 to 160.03 mM (1.71%). This might be ascribed to the thicker absorbed layer of BSA onto the PS-Bare surface, known from Ohshima's soft particle theory. Their aggregation in CaCl2 was both increased because of Ca2+ bridging. Different from the monotonous effects of BSA on PS-Bare and PS-COOH, BSA initially facilitated PS-NH2 aggregation via patch-charge attraction, then inhibited it at higher salt levels through steric repulsion. Furthermore, exposure orders had no significant effect on PS-Bare and PS-COOH, but had a NaCl concentration-dependent impact on PS-NH2. At the low NaCl concentrations (10 and 100 mM), no obvious influence could be observed. While, at 300 mM NaCl, the high concentrations of BSA could not totally stabilize the salt-induced aggregates in NaCl → BSA, but could achieve it in the other two orders. These might be attributed to the electrical double layer compression by NaCl, “patch-charge” force and steric hindrance by BSA. These experimental findings shed light on the potential fate and transport of nanoparticles in aquatic environments.

Investigating the transport and colloidal behavior of Fe3O4 nanoparticles in aqueous and porous media under varying solution chemistry parameters.

The possible adverse effects of engineered iron oxide nanoparticles, especially magnetite (Fe3O4 NP), on human health and the environment, have raised concerns about their transport and behavior in soil and water systems. Accumulating these NPs in the environment can substantially affect soil and water quality and the well-being of aquatic and terrestrial organisms. Therefore, it is essential to examine the factors that affect Fe3O4 NP transportation and behavior in soil and water systems to determine their possible environmental fate. In this work, experiments were conducted in aqueous and porous media using an environmentally relevant range of pH (5, 7, 9), ionic strength (IS) (10, 50, 100 mM), and humic acid (HA) (0.1, 1, 10 mg L-1) concentrations. Fe3O4 NPs exhibited severe colloidal instability at pH 7 (⁓ = pHPZC) and showed an improvement in apparent colloidal stability at pH 5 and 9 in aquatic and terrestrial environments. HA in the background solutions promoted the overall transport of Fe3O4 NPs by enhancing the colloidal stability. The increased ionic strength in aqueous media hindered the transport by electron double-layer compression and electrostatic repulsion; however, in porous media, the transport was hindered by ionic compression. Furthermore, the transport behavior of Fe3O4 NPs was investigated in different natural waters such as rivers, lakes, taps, and groundwater. The interaction energy pattern in aquatic systems was estimated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This study showed the effects of various physical-chemical conditions on Fe3O4 NP transport in aqueous and porous (sand) media.

A comprehensive study on the performance and mechanism of microplastics removal by enhanced coagulation methods

Drinking water is probably the main route for microplastics (MPs) to enter the human body. However, due to factors such as density and volume, MPs are difficult to remove during coagulation. Accordingly, the purpose of this paper is to study the removal efficiency of MPs in water supply treatment. Parameter optimization during coagulation, as well as the pre-oxidation process and addition of coagulant aids were investigated to explore the sedimentation efficiency of polyethylene terephthalate (PET) and polystyrene (PS) MPs. The experimental results showed that the extension of stirring time, the increase of PAC dosage, and the addition of pre-oxidation could not significantly improve the removal of MPs, while the addition of cationic/anionic PAM can effectively improve the low removal rate of MPs (removal rates were PET: 60.5 %, PS: 40.5 %, and PET: 67.9 %, PS: 67.5 % when cationic PAM and anionic PAM were added respectively). Characterization results showed that pre-oxidation, coagulation, and the addition of cationic PAM mainly played the role of double-layer compression. The anionic PAM had a strong adsorption effect and the efficiency was further improved through enmeshment by a precipitate. In summary, coagulant aids may be an effective method for the removal of MPs and are worth further studying.

Dewatering behavior and regulation mechanism of montmorillonite nanosheet in aqueous solution

Two-dimensional montmorillonite nanosheet (MMTNS) is desirable building block for fabricating multifunctional materials as due to its extraordinary properties. In practical applications, however, the concentration of MMTNS prepared by exfoliation is normally too low to be used for material assembling. The general thermal-concentration method is effective, however, it can be time-consuming and require a lot of energy. In this case, the remarkable dispersion stability of MMTNS is worth noting. Herein, the extraordinary dispersion stability of MMTNS derived from electrostatic and hydration repulsion was firstly revealed by molecular dynamics (MD) simulation, which caused the poor dewatering of MMTNS. Further, based on the surface and structural chemistry of MMTNS, a series of strategies, involving charge and cross-linked structure regulation on the edge surface, as well as electrical double-layer modulation and calcification modification based on the electrolytes, were proposed to inhibit the dispersion and enhance the aggregation of MMTNS. Intriguingly, a novel chemical, Tetraethylenepentamine (TEPA) was applied in the dewatering of MMTNS. The TEPA not only act as a cross-linker to bond with MMTNS into an easy-to-dewatering 3D network structure, but also act as a switch for effortless viscosity tuning. Meanwhile, the dual function of electrolytes for electrical double layer compression and calcification modification of MMTNS was investigated by DLVO theory and structural analyses. This work offers explicit directions for improving the dewatering performance of MMTNS to meet the requirements of practical implementation.

The effect of salinity on the pressure susceptibility of the NF270 membrane

To avoid structural changes within nanofiltration membranes during operation, pre-compaction of filtration membranes is usually performed. However, even after pre-compaction, the NF270 membrane has previously been shown to display a level of pressure susceptibility in pure water systems, particularly evident at low pressures. For the first time, this study provides experimental evidence for the effect of salinity on the pressure susceptibility of the NF270 membrane. Permeability was shown to decrease with increasing salinity up to 189 mM MgSO4, with the largest reduction (22 %) observed at the lowest MgSO4 concentration (31.49 mM MgSO4). A significant reduction (35 %) in the membrane susceptibility was also observed following the introduction of MgSO4 to a concentration of 31.49 mM. A mathematical expression, developed for pure water systems, was modified to account for salinity effects and fitted the experimental data well for concentrations up to 0.2 M. These results are explained by compaction of the membrane polymer, due to either charge neutralisation at the membrane surface, or electric double layer compression, or both. However, further increases in salinity had no significant effect on membrane susceptibility, suggesting that salt induced membrane compaction occurs at very low concentrations.

Investigating the structure-to-property of thermo-thickening polymers capped by different structural side chains

This study investigates the structure and comparison of solution properties of a series of acrylamide-based polymers capped by different thermo-sensitive side chains such as N-vinyl caprolactam (NVCL), N,N-dimethylacrylamide (DEAM) and N-isopropylacrylamide (NIPAM) synthesized via continuous initiation free-radical polymerization. Techniques such as Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) afforded the chemical structure, X-ray diffraction (XRD) exhibit the tacticity and environmental scanning electron microscopy (ESEM) displayed the morphology. Turbidimetry, dynamic light scattering (DLS), and DSC techniques examined the responsiveness and hydrodynamic radii of the colloidal particles at their lower critical solution temperature (LCST). The thickening profiles were investigated via rheometric analysis and the relationship between viscoelastic properties and hydrodynamic radii synergistically explained the anomalous viscosity build-up among the different side chains. The polymers exhibited excellent thickening abilities at high temperatures (>70 °C) with relatively rough surface mixed intercalations attributed to the thermo-responsive moieties grafted on acrylamide methylpropane sulfonic acid (AMPS) as thermal resistance backbone. PAMPS/NVCL displayed particularly excellent responses owing to its partial conjugation effect, compared to PAMPS/DEAM and PAMPS/NIPAM in solution at 150 °C. The polymers also displayed strong anti-salt responses, with a drop in viscosity initially observed but quickly subdued due to hydrophobic side chain association, electrostatic shield, and double-layer compression of the hydrated shells. These polymer side chains grafted on acrylamide backbones promote excellent self-assembly properties at varying grafting ratios and are interesting as self-adaptive rheology modifiers and fluid immobilizers for enhanced oil and gas recovery in deep reservoirs.

Effects of biofilms on the retention and transport of PFOA in saturated porous media.

Understanding the fate and transport of perfluorooctanoic acid (PFOA) in soil and groundwater is essential to reliable assessments of its risks. This study investigated the impacts of Gram-positive Bacillus subtilis (BS), Gram-negative Pseudomonas aeruginosa (PA) and wild microbiota (WM) biofilm on the transport of PFOA in saturated sand columns at two ionic strengths (i.e., 1.0 and 20.0mM NaCl). The retention of PFOA in biofilm-coated sand columns was higher than that in uncoated sand columns, due to biofilm-induced reinforced hydrophobic interactions and surface roughness, and decreased zeta potential. However, the retention effects varied among biofilm bacterial species with PFOA retardation factors in PA, WM and BS columns of 1.29-1.38, 1.21-1.29 and 1.11-1.15, respectively. Notably, PA biofilm had the most pronounced effect on PFOA retention. While increasing ionic strength promoted the retention of PFOA in BS biofilm-coated sand, it had no significant impact on PFOA transport in PA and WM biofilm-coated sand. This could be attributed to the differences in biofilm composition, deviating the ionic strengths effects on electrostatic double layer compression. The advection dispersion equation coupled with two-site kinetic retention model well described the transport of PFOA in all saturated columns. Our findings reveal that biofilm plays important roles in PFOA transport in porous media, instructive for risk assessment and remediation of PFOA contamination.

Coaggregation of micro polystyrene particles and suspended minerals under concentrated salt solution: A perspective of terrestrial-to-ocean transfer of microplastics

This study evaluates the colloidal stability of polystyrene microplastics (PSMPs) in the presence of various mineral colloids. Although PSMPs were highly dispersive, they were found to be involved in the aggregation of each mineral colloid. The efficiency of mineral colloids to stimulate the coaggregation of PSMPs follows the order bentonite > kaolinitic soil clay > illitic soil clay > kaolinite > goethite > haematite. Surface charge density is likely a crucial factor that determines the efficiency of mineral colloids. In concentrated salt solution, PSMPs together with mineral colloids can be involved in various continuous and simultaneous electrochemical processes such as charge neutralization, double electric layer compression, van der Waals attraction stimulation and heteroaggregation. These processes may also occur in the estuary environments, where suspended mineral colloids may play an ultimate role in reducing the transport of microplastics into oceans while also intensifying microplastic enrichment in coastal sediments.

Role of Ca2+ and Mg2+ in changing biofilm structure and enhancing biofilm formation of P. stutzeri strain XL-2

The aim of this study was to elucidate the role of Ca2+/Mg2+ in changing biofilm structure and enhancing biofilm formation of P. stutzeri strain XL-2. It was found that Ca2+/Mg2+ stimulated the production of extracellular polymers substances (EPS). More specifically, Ca2+ mainly promoted the secretion of proteins in EPS, while Mg2+ promoted polysaccharides. The stimulation of EPS secretion was essential to promote the biofilm formation of strain XL-2. By the analysis of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, Ca2+ mainly interacted with the amide groups in proteins of EPS, and Mg2+ was able to interact with polysaccharides as well as proteins. This interaction between Ca2+/Mg2+ and specific functional groups in EPS acted as a bridge between the EPS matrix, which also promoted the biofilm formation and made the biofilm structure more compact. Besides, the charge neutralization and electric double layer compression caused by Ca2+/Mg2+ participated in the formation of biofilm to a certain extent.

Hypersaline produced water clarification by dissolved air flotation and sedimentation with ultrashort residence times

Treatment and reuse of some produced waters is made difficult due to their hypersalinity, high concentrations of myriad other dissolved and suspended components, specialized technology requirements (modularity, portability, and short residence times), and lack of existing information on their processing. In this work, produced water containing ∼100,000 mg/L total dissolved solids from the Permian Basin was coagulated with aluminum chlorohydrate (ACH) and flocculated with an anionic high molecular weight organic polymer prior to dissolved air flotation (DAF) and sedimentation to reduce turbidity to < 4 NTU and iron < 0.8 mg/L (>95% removal in both cases) with a total coagulation-flocculation-sedimentation/flotation residence time of only 5 min. Two advantages of DAF over sedimentation were noted: (i) DAF required only half the dosage of the pre-hydrolyzed ACH coagulant to remove ∼90% of turbidity and iron even without the organic polymeric flocculant and (ii) DAF even operated successfully without ACH coagulation (i.e., using only the organic polymeric flocculant) evidencing its lower chemical dosing needs. Further, DAF attained all water quality and operational goals at a recycle ratio of only 12% demonstrating that it outperformed sedimentation to generate clean brine at relatively reduced excess energies necessary for air saturation. Higher DAF recycle ratios reduced turbidity and iron removal possibly due to floc breakage. Colloids were effectively destabilized by double layer compression (due to high water salinity), charge neutralization (via adsorption of Al13 polycations), and enmeshment (precipitation of amorphous aluminum). They were flocculated via interparticle bridging (by the anionic organic polymeric flocculant) to create large, compact flocs facilitating ultrashort flotation/sedimentation times. Direct evidence for these individual coagulation and flocculation mechanisms were obtained using electrophoretic mobility measurements, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, optical microscopy, computational image and video analysis, and scanning electron microscopy – energy dispersive X-ray spectroscopy.

Removal of perfluorooctanoic acid via polyethyleneimine modified graphene oxide: Effects of water matrices and understanding mechanisms

This research aimed to evaluate the adsorption behaviors and mechanisms of perfluorooctanoic acid (PFOA) onto polyethyleneimine modified graphene oxide (GO-PEI) from aqueous solutions. The adsorption capacity was significantly improved by doping polyethyleneimine (PEI) onto graphene oxide (GO). The Brunauer-Emmett-Teller (BET) isotherm model was considered as the best isotherm model in describing the PFOA adsorption onto GO-PEI3 (wPEI/wGO = 3). GO-PEI3 exhibited high adsorption capacity (qe = 368.2 mg/g, calculated from BET isotherm model) and excellent stability. The maximum monolayer amount of PFOA adsorption onto GO-PEI3 (qm = 231.2 mg/g) was successfully evaluated. The calculated saturated concentration (Cs = 169.9 mg/L) of PFOA on GO-PEI3 closely agrees with its critical micelle concentration (CMC = 157.0 mg/L), suggesting the formation of multilayer hemi-micelles or micelles PFOA structures on the surface of GO-PEI3. PFOA adsorption onto GO-PEI3 was inhibited by several factors including: the presence of humic acid (HA) by competing with the adsorption sites, background salts through the double-layer compression effect, and the competition from soluble ions for the amine or amide functional groups on GO-PEI3. Finally, both the FT-IR and XPS results confirmed that the adsorption of PFOA onto GO-PEI3 was through electrostatic attraction and hydrophobic interaction (physical adsorption), but not chemical adsorption. This work provides fundamental knowledge both in understanding the adsorption behavior through the BET isotherm model and in developing a stable adsorbent for PFOA adsorption. In addition, the findings highlight the potential of PFOA remediation from wastewater systems using GO-PEI in engineering applications.

The fate of aggregated graphene oxide upon the increasing of pH: An experimental and molecular dynamic study

Given the possible ecological dangers of graphene oxide (GO), a thorough understanding of its aggregation behavior is essential. During industrial applications, GOs may be used as multi-layered, and there is some possibility that GOs are released into the water environment in the aggregated state. Thus, elucidating the fate of aggregated GO is valuable for evaluating their environmental fate. In this work, the effect of pH on the fate of aggregated graphene oxide (GO) was explored using experimental measurements and molecular dynamic simulations and promoted aggregation of GO upon the increase of pH was observed. Additional investigations show that the presence of oxidation debris (ODs) on GO served as the primary driver of the unanticipated trend in aggregation behavior. GO consists of lightly oxidized functionalized graphene sheets and highly oxidized ODs. Upon the increase of pH and the deprotonation of functional groups, ODs are stripped from GO due to electrostatic repulsions and steric hindrance of water molecules. The stripping of ODs decreased the zeta potential and increased the hydrophobicity of GO, thus accelerating the aggregation. Additionally, the stripped ODs may recombine to GO edges and bridged GOs, which also contribute to further aggregation. Functional group deprotonation, ODs stripping, OD bridging, double layer compression, and charge neutralization all worked together to promote aggregation, resulting in the formation of FG-water-OD aggregates. Overall, the presence of ODs complicates the structures and properties of GO and should be considered during the development of GO-related nanomaterials and the evaluation of their environmental impact.

Influence of protein configuration on aggregation kinetics of nanoplastics in aquatic environment

Aggregation kinetics of nanoplastics in aquatic environment are influenced by their interactions with proteins having different structures and properties. This study employed time-resolved dynamic light scattering (TR-DLS) to investigate the effects of 5 proteins (bovine hemoglobin (BHb), bovine (BSA) and human serum albumin (HSA), collagen type I (Col I), and bovine casein (CS)) on aggregation kinetics of polystyrene nanoplastics (PSNPs) under natural water conditions, which were simulated using various ionic strength (1-1000 mM NaCl and 0.01-100 mM CaCl2), pH (3-9), and protein concentration (1-5 mg/L of total organic carbon). The results indicated that the interactions between proteins and PSNPs strongly depended on electrostatic properties, protein structures, and solution chemistries, which induced distinct aggregation behaviors in NaCl and CaCl2 solutions. Electrostatic repulsion and steric hindrance dominated their interactions in NaCl solution by stabilizing PSNPs with the order of spherical BSA and disordered CS > heart-shaped HSA > fibrillar Col I; whereas positively charged BHb destabilized PSNPs with aggregation rate of 1.71 nm/s at 300 mM NaCl. In contrast, at CaCl2 concentration below 20 mM, proteins destabilized PSNPs following the sequence of HSA > BHb > Col I > BSA depending on counterbalance among double layer compression, cation bridging, and steric hindrance; whereas CS stabilized PSNPs by precipitating Ca2+ that inhibited charge screening effect. Both protein concentration and solution pH affected protein corona formation, surface charge, and protein structure that altered stability of PSNPs. Characterizations using fluorescence spectroscopy, circular dichroism, and two-dimensional correlation analysis spectroscopy showed fluorescence quenching and ellipticity reduction of proteins, indicating strong adsorption affinity between PSNPs and proteins. The study provides insight to how protein configuration and water chemistry affect fate and transport of nanoplastics in aquatic environment.

Reinterpretation of the mechanism of coagulation and its effects in waste activated sludge treatment

Previous studies suggest that the coagulation mechanisms in wastewater and sludge treatment are the same. However, this study found that changes of COD in wastewater and sludge supernatant after the addition of coagulants (Fe3+ and Al3+) were opposite, indicating that the mechanisms of coagulation in these two systems were not the same. The dose of coagulant efficiently reduced the pH of sludge, the higher the dosage, the lower the pH, indicating hydrolytic acidification exists in the sludge coagulation process. Coagulation proved superior to acid conditioning in reducing negative charge and improving the floc size of sludge, demonstrating that the mechanisms of double layer compression, charge neutralization, intraparticle bridging and colloid entrapment are suitable for sludge coagulation. Furthermore, the addition of Fe3+ and Al3+ promoted the exchange of Ca2+ and Mg2+ in extracellular polymeric substances (EPS), which weakened cross-linking between EPS and cells, and further accelerated the disintegration and release of EPS. Due to the mechanisms of hydrolytic acidification and ion exchange, the solid organic matter in sludge was dissolved and released as liquid, resulting in a significant increase of COD in the supernatant of sludge coagulation. In addition, changes in sludge extracellular substances do not reflect changes in intracellular substances well. This study contributes an improved understanding of the mechanism of coagulation in the sludge dewatering treatment.