Effects of particle size and solution chemistry on Triclosan sorption on polystyrene microplastic

Fenton aging significantly affects the heavy metal adsorption capacity of polystyrene microplastics

Microplastics released into the environment undergo a variety of aging processes, however, information about the influence of aging on the adsorption behavior of microplastics is limited. In order to better understand the effect of aging polystyrene (PS) on the ability to adsorb heavy metal, H₂O₂ and Fenton reagent were used to investigate the aging properties of PS. Aging PS with these two different aging agents at pH = 4 and room temperature for the same time. Physical and chemical characterization indicated that aging caused oxidation of the surface of PS and the formation of surface micro-cracks. Based on the 2D-COS analysis, the aging process of PS functional groups could occur in the following sequence: 1375 (C-OH) > 1739 (C=O) > 1182 cm^-1 (C-O-C) > 1716 (O-C=O). The adsorption experiments for Cd²⁺ with two different concentrations were carried out by PS with different aging time at room temperature. The adsorption data showed that the adsorption capacity of Cd²⁺ was significantly enhanced after aging compared with pristine PS, and the adsorption capacity of PS after Fenton aging treatment is much stronger than that after H₂O₂ aging treatment. The kinetic analysis of the adsorption data indicates that the adsorption process is more consistent with the second-order kinetics than the first-order kinetics, and it is further concluded that the adsorption of Cd²⁺ by PS is a relatively complicated process. According to the fitting results of adsorption isotherms, the adsorption process of pristine PS mainly occurs on the surface, but with the continuous aging, more adsorption sites may be exposed on the surface of PS, so it can be concluded that the adsorption mechanism of Cd²⁺ by PS is the coexistence of physics and chemistry. This study indicates aging microplastics may have a significant impact on the destination and migration of metal contaminants, which deserves to be further concerned.

Adsorption of organic contaminants on biochar colloids: effects of pyrolysis temperature and particle size

Biochar (BC) colloids attract increasing interest due to their unique environmental behavior and potential risks. However, the interaction between BC colloids and organic contaminants that may affect their fates in the environment has not been substantially studied. Herein, adsorption and desorption of phenanthrene (PHN), atrazine (ATZ), and oxytetracycline (OTC) by a series of BC colloids derived from bulk rice straw BC samples with 6 pyrolysis temperatures (200-700 °C), and 3 particle sizes (250 nm, 500 nm, and 1 μm) were investigated. Regardless of pyrolysis temperature, BC colloids from a given sized bulk BC had a comparable size, being 30 ± 6, 70 ± 18, and 140 ± 15 nm corresponding to the three sized bulk BCs, respectively. The adsorption kinetics curves were well explained by the pseudo-second-order model, and pore diffusion was the primary rate-determining step. Both Freundlich and Langmuir models well fitted the adsorption isotherms. With increasing pyrolysis temperature or decreasing particle size of bulk BC, the specific surface area and pore volumes of the derived BC colloids increased, the kinetics model fitted adsorption rates (k₂) of the three organics by the BC colloids all largely decreased, and the Langmuir model fitted adsorption capacities (Q_max) increased. The highest Q_max was obtained by BC colloids from the smallest (250 nm) bulk BC with the highest pyrolysis temperature (700 °C), being 212 μmol g^-1 for PHN, 815 μmol g^-1 for ATZ, and 72.4 μmol g^-1 for OTC. The adsorption was reversible for PHN and ATZ, while significant desorption hysteresis was observed for OTC on BC colloids with middle pyrolysis temperatures (300-500 °C). The underlying mechanisms including hydrophobic interaction, π-π electron donor-acceptor interaction, molecular size effect, and irreversible reactions were discussed to explain the difference in the adsorption and desorption behaviors. The findings increased our understanding of the environmental fate and risk of BC.

Sorption of three common nonsteroidal anti-inflammatory drugs (NSAIDs) to microplastics

High disposability, high durability, and indiscriminate use have led to the accumulation of plastics at uncontrolled rates in the environment. However, plastics are not the only source of water pollution in the environment. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a group of pharmaceuticals widely and highly consumed in the market due to a low price and over-the-counter accessibility. NSAIDs are frequently detected in surface water environments at μg L^-1 concentrations. In the present study, the sorption behavior of three NSAIDs (ibuprofen, naproxen, diclofenac) was examined with four types of microplastics (polystyrene (PS), ultra-high molecular weight polyethylene (UHMWPE), average molecular weight medium density polyethylene (AMWPE), and polypropylene (PP)), under varying water conditions. Low sorption occurred between NSAIDs and microplastics under environmentally relevant conditions. The sorption process exhibited a pronounced pH dependency due to the effect of pH on the speciation of the compounds and the surface charge of the particles. Only under acidic conditions (pH: 2), NSAIDs were highly sorbed onto microplastics mainly ruled by hydrophobic interactions. Among NSAIDs tested, diclofenac exhibited the highest sorption coefficients to microplastics. Polyethylene particles exhibited the highest affinity for NSAIDs.

Sorption Behavior and Mechanisms of Organic Contaminants to Nano and Microplastics

Nano and microplastics (NPs/MPs) have received widespread attention in recent years. Because of their large specific surface area and hydrophobicity, NPs/MPs can adsorb various organic contaminants. This article gives a brief review of the sorption behavior of organic contaminants to NPs/MPs, summarizes the possible sorption mechanisms, and analyzes the influencing factors in the environment on the sorption behavior and mechanisms of NPs/MPs. The main mechanisms of sorption of organic contaminants to NPs/MPs are partitioning, surface sorption (hydrogen bonding, π-π interaction, electrostatic interaction, and van der Waals force), and pore filling. The sorption behavior of organic contaminants to NPs/MPs is not only affected by the properties of the NPs/MPs and the organic contaminants, but also by the solution chemistry, such as the pH, ionic strength, and dissolved organic matter.

Adsorption behavior and mechanism of 9-Nitroanthracene on typical microplastics in aqueous solutions

Microplastics and Nitropolycyclic aromatic hydrocarbons (NPAHs) are two types of emerging pollutants that are strong potential threats to aquatic ecosystems and organisms. The adsorption of NPAHs on microplastics may explain the fate and effects of NPAHs in natural environments. In this study, the adsorption behavior of 9-Nitroanthrene (9-NAnt) on polyethylene (PE), polypropylene (PP) and polystyrene (PS) was investigated. Kinetic experiments revealed that 9-NAnt was inclined to be adsorbed onto microplastics, especially PE, which had a large adsorption amount of 734 μg g^-1. A linear isothermal model better described the isothermal adsorption process for 9-NAnt, which indicated that a hydrophobic distribution may be the main adsorption mechanism in an aqueous solution. Water environment factors, such as the pH and ionic strength, had negligible effects on the adsorption for PE. In contrast, alkaline and high ionic strength conditions resulted in the inhibition of adsorption of PP and PS. In addition, the particle size of microplastics was negatively correlated with the log K_d of 9-NAnt, and the performance of transient aging treatments on microplastics reduced their affinity for 9-NAnt, due to the addition of oxygen-containing functional groups. Above all, hydrophobic and electrostatic processes were the main adsorption mechanisms between microplastics and 9-NAnt.

Sorption of antibiotics onto aged microplastics in freshwater and seawater

Microplastics in environments undergo aging processes and may sorb antibiotics from surrounding water. Understanding the interaction between aged microplastics and antibiotics is important to assess the impact of microplastics on environments. In this paper, the sorption of three typical antibiotics, i.e., sulfamethoxazole (SMX), sulfamethazine (SMT), and cephalosporin C (CEP-C) onto the naturally aged microplastics (polystyrene (PS) and polyethylene (PE)) derived from aged plastics samples from the coast of East China Sea and Yellow Sea, China in freshwater and simulated seawater systems were studied. The results indicated that the mixed order (MO) model provided good prediction for the kinetics data. The linear isotherm represented adequately the sorption equilibrium data in freshwater. The K_d values ranged from 0.0236 L·g^-1 to 0.0383 L·g^-1. In simulated seawater, only CEP-C could be sorbed onto the microplastics. The main sorption mechanisms are hydrophobic, van der Waals, and electrostatic interactions.

Effect of microplastic size on the adsorption behavior and mechanism of triclosan on polyvinyl chloride

Microplastics in water environment and its ability to load various environmental pollutants have attracted wide attention in recent years. However, effect of microplastic size on the adsorption behavior of environmental pollutants and interaction mechanism has not been thoroughly explored. In this study, triclosan (TCS) was selected as model pollutant, and polyvinyl chloride (PVC) with different particle sizes (small size (<1 μm) is recorded as PVC-S and PVC-L means large particle size of about 74 μm) were used as the typical microplastics, the adsorption behavior of TCS on PVC was investigated by studying kinetics, isotherms, and other influencing factors, such as pH and salinity. The results indicate PVC-S has greater distribution coefficient k_d values of TCS (1.35 L/g > 1.05 L/g) and stronger adsorption capacity (12.7 mg/g > 8.98 mg/g) compared with PVC-L, which may be due to higher specific surface area, stronger hydrophobicity and relatively small electronegative property of PVC-S. Moreover, the initial pH value and salinity of the solution played crucial role in the adsorption process. The distribution diffusion mechanisms (including liquid-film diffusion and intra-particle diffusion), hydrophobic interaction, electrostatic interaction, halogen bonding, and hydrogen bonding may be the important reasons for adsorption. These findings show that MPs with different particle sizes have vary adsorption behaviors and load capacities for environmental pollutants, which deserve our further concerned.