Removal of polystyrene nanoplastics from water by CuNi carbon material: The role of adsorption.

Nanoplastics have attracted wide attention worldwide as a new potentially threatening pollutant, and they can cause harm to the organisms and pose threat to the water environment. Therefore, efficient removal techniques for nanoplastics are urgently needed. In this study, CuNi carbon material (CuNi@C) was prepared by hydrothermal method for the removal of polystyrene (PS) nanoplastics from water. CuNi@C was effectively adsorbed on PS nanoplastics. When the CuNi@C dosage increased from 0.1 g/L to 0.3 g/L, the removal efficiency of PS nanoplastics (10 mg/L) elevated from 32.72% to 99.18%. The images of the scanning electron microscope (SEM) and the Fourier transform infrared spectroscopy (FTIR) spectra of CuNi@C confirmed the adsorption of PS nanoplastics on the CuNi@C. The fitting results of adsorption kinetic models and isotherms equations demonstrated that physical adsorption and monolayer coverage were the predominant mechanisms of the PS nanoplastics adsorption on CuNi@C. Thermodynamics analysis illustrated the adsorption of PS nanoplastics on CuNi@C was a spontaneous and endothermic process. The electrostatic attraction occurred in adsorption progress, and the removal efficiency of PS nanoplastics in the acidic system was generally higher than that in the alkaline system. CuNi@C can be recycled via washing and drying treatment and these CuNi@C comparable PS nanoplastics removal performance to the original ones. After four times cycles, CuNi@C can still remove ~75% of total PS nanoplastics from water. This study reveals that CuNi@C can be used as promising techniques for the removal of PS nanoplastics from the aqueous environment.

Oxygen functionalized g-C3N4 strengthen Fe(III)/H2O2 system by accelerating Fe(III)/Fe(II) cycles under natural solar light: A mutual-promoting configuration.

In response to the inherent restriction of low Fe(II) regeneration in the Fenton process, this study demonstrated a mutual-promoting configuration, where oxygen functionalized g-C3N4 (OCN) was applied in Fe(III)/H2O2 system to utilize mild natural solar light (SL) for persistent Fe(II) generation. The constructed OCN/Fe(III)/H2O2/SL system exhibited strong adaptability to various pollutants, and it well outperformed the g-C3N4 (GCN) modified system and the traditional Fenton system in pollutants degradation efficiency. Compared with GCN, OCN could significantly promote the Fe(II) generation under solar light (SL), leading to more efficient H2O2 activation. The characterization analyses revealed the larger surface area and enhanced charge separation of OCN, which were considered to take main responsibility for its enhanced photoactivity. The complexation of Fe(III) with the carboxyl groups of OCN also benefited the Fe(II) generation. ·OH was detected as the dominant radical responsible for metronidazole (MNZ) degradation, and its production in the OCN modified system was about twice that in the GCN modified system and the Fenton system. Moreover, the precipitation of FeOx on the OCN surface benefited the charge separation of the OCN, so that the improved OCN enabled a slight enhancement of MNZ degradation in the reuse experiments. The intermediates of MNZ degradation were analyzed based on the results of LC-MS, which provided insight into MNZ degradation pathways. This work highlighted the concept of self-improving photocatalyst, the ingenious combination of photocatalysis and Fenton-like system formed a mutual-promoting situation where the OCN and the Fenton-like system could both be improved, which endowed the configuration great potential for green and economical oxidation in environmental remediation.

Removal of polystyrene and polyethylene microplastics using PAC and FeCl3 coagulation: Performance and mechanism.

As a new type of potentially threatening pollutant, microplastics are widely distributed in water and may come into contact with the humans through tap water. The removal behaviors of microplastics in water treatment plants coagulation are not completely clear. In this paper, the removal performance and mechanism of polystyrene (PS) and polyethylene (PE) microplastics using PAC and FeCl3 coagulation were studied. Results showed that PAC was better than FeCl3 in removal efficiency of PS and PE microplastics. Charge neutralization occurred in the coagulation process. The figures of scanning electron microscope (SEM) illustrate that agglomeration adsorption occurred in PS system, and the Fourier transform infrared spectroscope (FTIR) spectra demonstrates that new bonds were formed during the interaction between PS microplastics and coagulants. In addition, the hydrolysis products of coagulants played a major role rather than the hydrolysis process in both PS system and PE system. The removal efficiency of microplastics in alkaline conditions was higher than that in acidic conditions. Cl- had little effect on the removal efficiency of microplastics, while SO42- and CO32- had inhibitory and promoting effects respectively. The increase of stirring speed could improve the removal efficiency of microplastics. This paper can provide a reference for the study of microplastics treated by coagulation.

Distribution and characteristics of microplastics in urban waters of seven cities in the Tuojiang River basin, China.

Microplastics pollution presents an increasing concern worldwide due to the large amount and potential risks. However, data on microplastics in the freshwater environment are still limited, especially in southwest China. This study investigated the microplastics distribution, characteristics and risks in urban water of different cities in the Tuojiang River basin in southwest China. Microplastics were found in all seven cities of the Tuojiang River basin and the concentrations varied from 911.57 ± 199.73 to 3395.27 ± 707.22 items/m3, among which Ziyang urban water had the highest microplastics concentration. Fiber (34.88-65.85%) was a typical and abundant microplastic type. The small size (0.5-1 mm) (27.27-66.67%) was predominant, and white (23.30-54.29%) was the dominant color among all samples. Polypropylene was identified as the main polymer type by Fourier transform infrared spectroscopy. The morphological analysis by scanning electron microscopy indicated that the surfaces of the microplastics had many cracks and a multitude of particles were adsorbed onto it. According to correlation analysis, there was a significant positive correlation between gross domestic product(P=0.015<0.05) and gross domestic product of the secondary industries(P=0.014<0.05) of cities in the Tuojiang River basin and microplastics concentrations, demonstrating impacts of the secondary industries on the microplastics pollution. In addition, water bodies with lower oxidation-reduction potential tended to have higher microplastics abundance. In the Tuojiang River basin, microplastics pollution was more serious in location where water quality was poor. The polymer risk index (H) was calculated to assess the environmental risk of microplastics in different cities, and the results showed that Fushun sites had the highest risk in regard to microplastics. This study provides a valuable reference for a better understanding of the microplastics level and source identification in southwest China.

Combined CASSCF and MR-CI study on photoinduced dissociation and isomerization of acryloyl chloride.

The potential energy surfaces of isomerization and dissociation reactions for CH2CHCOCl in the S0, T1, T2, and S1 states have been mapped with DFT, CASSCF, MP2, and MR-CI calculations. Rate constants for adiabatic and nonadiabatic processes have been calculated with the RRKM rate theory, in conjugation with the vibronic interaction method. Mechanistic photochemistry of CH2CHCOCl at 230-310 nm has been characterized through the computed potential energy surfaces and rate constants. Upon photoexcitation of CH2CHCOCl at 310 nm, the S1-->T1 intersystem crossing is the dominant primary process, which is followed by the 1,3-Cl migration along the T1 pathway. Meanwhile, the S1-->S0 internal conversion occurs with considerable probability and the subsequent trans-cis isomerization proceeds in the ground state. The C-Cl bond cleavage is an exclusive primary channel upon photoexcitation of gaseous CH2CHCOCl at 230 nm. The direct C-Cl bond cleavage is partially blocked by effects of the matrix, and the internal conversion from S1 to S0 becomes an important process for the excited molecule to deactivate in the condensed phase. The present calculations not only provide a reasonable explanation of the experimental findings, but also give new insight into the mechanistic photochemistry of CH2CHCOCl.