Mechanisms of polystyrene nanoplastics adsorption onto activated carbon modified by ZnCl2

Enhanced flotation removal of polystyrene nanoplastics by chitosan modification: Performance and mechanism

Nanoplastics are difficult to remove from water using conventional flotation processes due to their stability and resistance to biodegradation. Here, polystyrene nanoplastics (PSNPs) were selected as the object of study. In addition, chitosan (CTS), an environmentally friendly natural cationic polymer, was selected to modify the air flotation process to improve the separation of PSNPs using air flotation. Adding chitosan effectively enhanced the removal of PSNPs using air flotation from 3.1 % to 96.7 %. The residual concentration decreased from 9.69 mg/L to 0.33 mg/L. Removal of PSNPs by CTS-modified air flotation was maintained at 92.8 % even when the air flotation time was significantly shortened. The zeta potential alterations demonstrated robust electrostatic attraction within the CTS-modified air flotation process. The contact angle measurements indicated that incorporating CTS could enhance the hydrophobic interaction between bubbles and PSNPs. PSNPs particles around 100 nm agglomerated to form floating flocs with a particle size of more than 4500 nm. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) images confirmed the presence of tight adhesion between PSNPs and CTS, indicating the presence of bridging adsorption during the process. The major PSNPs removal mechanisms included electrostatic attraction, enhancement of hydrophobicity, and bridging adsorption. Increasing the aeration volume could improve the removal rate, but this improvement was finite. Weakly acidic and low ionic strength conditions favored PSNPs removal. The CTS-modified air flotation process showed great potential for PSNPs removal from real water bodies.

Zanthoxylum bungeanum Waste-Derived High-Nitrogen Self-Doped Porous Carbons as Efficient Adsorbents for Methylene Blue

In this study, we prepared high-nitrogen self-doped porous carbons (NPC1 and NPC2) derived from the pruned branches and seeds of Zanthoxylum bungeanum using a simple one-step method. NPC1 and NPC2 exhibited elevated nitrogen contents of 3.56% and 4.22%, respectively, along with rich porous structures, high specific surface areas of 1492.9 and 1712.7 m2 g-1 and abundant surface groups. Notably, both NPC1 and NPC2 demonstrated remarkable adsorption abilities for the pollutant methylene blue (MB), with maximum monolayer adsorption capacities of 568.18 and 581.40 mg g-1, respectively. The adsorption kinetics followed the pseudo-second-order kinetics and the adsorption isotherms conformed to the Langmuir isotherm model. The adsorption mechanism primarily relied on the hierarchical pore structures of NPC1 and NPC2 and their diverse strong interactions with MB molecules. This study offers a new approach for the cost-effective design of nitrogen self-doped porous carbons, facilitating the efficient removal of MB from wastewater.

Lignin derived hydrophobic deep eutectic solvents for the extraction of nanoplastics from water

As a growing concern in aqueous systems, micro- and nano-plastics, especially nanoplastics (NPs), have been widely detected in the environment and organisms, posing a potential threat to ecosystems and human health. Hydrophobic deep eutectic solvents (HDESs) have emerged as environmentally friendly solvents that have shown promise for extracting pollutants from water, either for detection or removal purposes. Herein, we investigated the extraction of polystyrene (PS) and polyethylene terephthalate (PET) NPs from aqueous solution using lignin based HDESs as sustainable solvents. Rapid extraction of both PET and PS NPs was observed with the high extraction efficiency achieved (> 95%). The extraction capacities for PET and PS could reach up to 525.877 mg/mL and 183.520 mg/mL, respectively, by the Thymol-2,6-dimethoxyphenol 1:2 HDES. Moreover, the extraction mechanism was studied using various techniques including Fourier-transform infrared analysis, contact angle measurements, molecular dynamics simulation, kinetics, and isotherm studies. This work lays a foundational basis for the future development of innovative HDES-based technologies in the detection and remediation of NPs as part of the grand challenge of plastic pollution.

Nanomaterials and biochar mediated remediation of emerging contaminants

The unrestricted release of various toxic substances into the environment is a critical global issue, gaining increased attention in modern society. Many of these substances are pristine to various environmental compartments known as contaminants/emerging contaminants (ECs). Nanoparticles and emerging sorbents enhanced remediation is a compelling methodology exhibiting great potential in addressing EC-related issues and facilitating their elimination from the environment, particularly those compounds that demonstrate eco-toxicity and pose considerable challenges in terms of removal. It provides a novel technique enabling the secure and sustainable removal of various ECs, including persistent organic compounds, microplastics, phthalate, etc. This extensive review presents a critical perspective on the current advancements and potential outcomes of nano-enhanced remediation techniques such as photocatalysis, nano-sensing, nano-enhanced sorbents, bio/phyto-remediation, which are applied to clean-up the natural environment. In addition, when dealing with residual contaminants, special attention is paid to both health and environmental implications; therefore, an evaluation of the long-term sustainability of nano-enhanced remediation methods has been considered. The integrated mechanical approaches were thoroughly discussed and presented in graphical forms. Thus, the critical evaluation of the integrated use of most emerging remediation technologies will open a new dimension in environmental safety and clean-up program.

Adsorption Characteristics of Ball Milling-Modified Chinese Medicine Residue Biochar Toward Quercetin

Using traditional Chinese medicine residues as raw materials, different biochars (BC) were prepared through oxygen-limited pyrolysis at 300 °C, 500 °C, and 700 °C, and BC was ball-milled to produce ball-milled biochar (BMC). Using these adsorbents to adsorb the allelopathic autotoxic substance quercetin. The physical and chemical properties of various biochars derived from traditional Chinese medicine residues were characterized using the Brunauer-Emmett-Teller-N2 surface areas (BET), scanning electron microscopy (SEM), Fourier transform IR spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy (Raman). The study investigated the effects of the initial pH value, different humic acid concentrations, and multiple adsorption-desorption experiments on the removal of quercetin from the solution. The article discusses the adsorption mechanism of quercetin in solution by biochar from a traditional Chinese medicine residue, based on the results of adsorption kinetics and adsorption isotherm fitting. The findings indicate that increasing the pyrolysis temperature reduces the oxygen-containing functional groups of BC, enhances the aromaticity, and stabilizes the carbon structure. The pore structure of BMC becomes more complex after ball milling, which increases the number of oxygen-containing functional groups on the surface. Among the samples tested, BMC700 exhibits the best adsorption performance, with an adsorption capacity of 293.3 mg·g-1 at 318 K. The adsorption process of quercetin by BMC700 follows the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model. The process is primarily a form of multimolecular layer adsorption. Its mechanism involves the pore-filling effect, hydrogen-bonding interaction, electrostatic interaction, and π-π coexistence, as well as the yoke effect. Additionally, they are highly recyclable and show promise in addressing continuous cropping issues.

Synthesis of lignin nanoparticle‑manganese dioxide complex and its adsorption of methyl orange

Lignin nanoparticles (LNPs) were synthesized using an anti-solvent method and subsequently loaded with manganese dioxide (MnO2) via potassium permanganate treatment, resulting in the formation of MnO2@LNPs. An extensive investigation was conducted to elucidate the influence of MnO2@LNPs on the decolorization of methyl orange solution. The LNPs were successfully obtained by adjusting the preparation parameters, yielding particles exhibited average sizes ranging from 300 to 600 nm, and the synthesis process exhibited a high yield of up to 87.3% and excellent dispersion characteristics. Notably, LNPs size was reduced by decreasing initial concentration, increasing stirring rate, and adding water. In the acetone-water two-phase system, LNPs self-assembled into spherical particles driven by π-π interactions and hydrogen bond forces. Oxidation modification using potassium permanganate led to the formation of nanoscale MnO2, which effectively combined with LNPs. Remarkably, the resulting MnO2@LNPs demonstrated a two-fold increase in methyl orange adsorption capacity (227 mg/g) compared to unmodified LNPs. The process followed the Langmuir isotherm model and was exothermic.

Retention and Transport of Nanoplastics with Different Surface Functionalities in a Sand Filtration System

The efficiency of sand filtration was investigated in terms of the behavior of the nanoplastics (NPLs) with different surface functionalities. The initial condition concentrations of NPLs were varied, and their effects on retention and transport were investigated under a constant flow rate in saturated porous media. The behavior of NPLs in this porous system was discussed by considering Z- average size and zeta (ζ) potential measurements of each effluent. The retention efficiencies of NPLs were ranked as functionalized with amidine [A-PS]+ > with sulfate [S-PS]- > with surfactant-coated amidine [SDS-A-PS]-. The reversibility of the adsorption process was revealed by introducing surfactant into the sand filter system containing adsorbed [A-PS]+ at three different initial state concentration conditions. The deposition behavior on sand grain showed that positively charged NPLs were attached to the quartz surface, and negatively charged NPLs were attached to the edge of the clay minerals, which can be caused by electrical heterogeneities. The homoaggregates made of positively charged NPLs were more compact than those made of negatively charged NPLs and surfactant-coated NPLs. An anti-correlation was revealed, suggesting a connection between the fractal dimension (Df) of NPL aggregates and retention efficiencies. Increased Df values are associated with decreased retention efficiencies.The findings underscore the crucial influence of NPL surface properties in terms of retention efficiency and reversible adsorption in the presence of surfactants in sand filtration systems.