Efficient degradation of polystyrene microplastic pollutants in soil by dielectric barrier discharge plasma

In this study, the atmospheric dielectric barrier discharge (DBD) plasma was proposed for the degradation of polystyrene microplastics (PS-MPs) for the first time, due to its ability to generate reactive oxygen species (ROS). The local temperature in plasma was found to play a crucial role, as it enhanced the degradation reaction induced by ROS when it exceeded the melting temperature of PS-MPs. Factors including applied voltage, air flow rate, and PS-MPs concentration were investigated, and the degradation products were analyzed. High plasma energy and adequate supply of ROS were pivotal in promoting degradation. At 20.1 kV, the degradation efficiency of PS-MPs reached 98.7% after 60 min treatment, with gases (mainly COx, accounting for 96.4%) as the main degradation products. At a concentration of 1 wt%, the PS-MPs exhibited a remarkable conversion rate of 90.6% to COx, showcasing the degradation performance and oxidation degree of this technology. Finally, the degradation mechanism of PS-MPs combined with the detection results of ROS was suggested. This work demonstrates that DBD plasma is a promising strategy for PS-MPs degradation, with high energy efficiency (8.80 mg/kJ) and degradation performance (98.7% within 1 h), providing direct evidence for the rapid and comprehensive treatment of MP pollutants.

Application of traceable calibration for gaseous oxidized mercury in air

BACKGROUND

The current speciation methods for mercury (Hg) measurements are fraught with considerable uncertainty, from sample collection to calibration. High reactivity of gaseous oxidized Hg (GOM) species and their ultra-trace level presence makes them difficult to sample and calibrate. Given that improper calibration may lead to measurement biases, reliable and metrologically traceable calibration methods are required for accurately quantifying GOM in air. In the present study, we applied the recently developed calibration method based on non-thermal plasma oxidation of elemental Hg, to a commercially available Hg air speciation system for actual environmental measurements of GOM for the first time.

RESULTS

Hg species such as HgO, HgCl2, and HgBr2 were produced with trace amounts of reactant gases (oxygen and electrolytically produced chlorine and bromine) and the production was driven by plasma-assisted oxidation. The plasma oxidation efficiency of elemental Hg with oxygen was 98.5 ± 7.5 % (k = 2), while that for chlorine and bromine was 96.8 ± 6.9 % (k = 2) and 97.4 ± 9.6 % (k = 2), respectively. The calibration method was tested against the internal permeation (Hg0) source of the Tekran 2537B Hg analyzer on-field by loading HgO to different KCl-coated denuders using the plasma. GOM concentrations were measured using the Tekran speciation system. With internal calibration, concentrations were up to 9.1 % lower than those in plasma calibration, thereby emphasizing the importance of the calibration strategy. Measurement uncertainty (k = 2) further emphasizes this distinction. Internal calibration measurement uncertainty was 36.8 %, while plasma calibration boasted lower uncertainty at 13.8 %.

SIGNIFICANCE

The non-thermal plasma calibration strategy, as a unique and discrete calibration method traceable to the NIST SRM 3133 for ambient air GOM measurements, provide a higher level of confidence in the accuracy of GOM measurements with several advantages over other methods. Calibrations at extreme low concentrations (<100 pg) are possible with this method relevant to ambient air GOM concentrations.

Dielectric barrier discharge plasma for the remediation of microplastic-contaminated soil from landfill

The huge amount of plastic waste accumulated in landfills has caused serious microplastic (MP) pollution to the soil environment, which has become an urgent issue in recent years. It is challenging to deal with the non-biodegradable MP pollutants in actual soil from landfills. In this study, a coaxial dielectric barrier discharge (DBD) system was proposed to remediate actual MP-contaminated landfill soil due to its strong oxidation capacity. The influence of carrier gas type, applied voltage, and air flow rate was investigated, and the possible degradation pathways of MP pollutants were suggested. Results showed the landfill soil samples contained four common MP pollutants, including polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) with sizes ranging from 50 to 1500 μm. The MP pollutants in the soil were rapidly removed under the action of reactive oxygen species (ROS) generated by DBD plasma. Under the air flow rate of 1500 mL min^-1, the maximum remediation efficiency represented by mass loss reached 96.5% after 30 min treatment. Compared with nitrogen, when air was used as the carrier gas, the remediation efficiency increased from 41.4% to 81.6%. The increased applied voltage from 17.5 to 24.1 kV could also promote the removal of MP contaminants. Sufficient air supply was conducive to thorough removal. However, when the air flow rate reached 1500 mL min^-1 and continued to rise, the final remediation efficiency would be reduced due to the shortened residence time of ROS. The DBD plasma treatment proposed in this study showed high energy efficiency (19.03 mg kJ^-1) and remediation performance (96.5%). The results are instructive for solving MP pollution in the soil environment.

Effect of surface modification of Ti-6Al-4V alloy by electron cyclotron resonance plasma oxidation

Ti-6Al-4V alloy is used as biomaterials for dental and orthopedic implants because of their excellent biocompatibilities and mechanical properties. However, it is unclear that electron cyclotron resonance (ECR) plasma oxidation can create the oxide films on Ti-6Al-4V alloy surface, and this technique improves the ability of its osseointegration. The purpose of this study was to investigate the characteristics and calcification ability of the oxide films. X-ray diffraction (XRD) peaks of rutile phase were intensified with increasing the temperature. Scanning electron microscopy (SEM) images showed a crater-like structure, and bonding strengths between the substrate and oxide film reached a maximum at 400°C. Calcium phosphate (CaP) compounds after calcification process were identified as octacalcium phosphate (OCP) and precipitation amount was maximized at 400°C. The results suggested that the altered surface of Ti-6Al-4V alloy by ECR plasma oxidation might have the potential of accelerating the ability of its osseointegration through enhancement of OCP.

Combination of plasma oxidation process with microbial fuel cell for mineralizing methylene blue with high energy efficiency

Plasma advanced oxidation process (PAOP) has great ability to break recalcitrant pollutants into small molecular compounds but suffers from poor performance and low energy efficiency for mineralizing dyeing pollutants. Combining advanced oxidation process with biodegradation process is an effective strategy to improve mineralization performance and reduce cost. In this study, a combined process using PAOP as pre-treatment followed by microbial fuel cell (MFC) treatment was investigated to mineralize methylene blue (MB). The PAOP could degrade MB by 97.7%, but only mineralize MB by 23.2% under the discharge power of 35 W for 10 min. Besides, BOD₅/COD ratio of MB solution raised from 0.04 to 0.38 while inhibition on E. coli growth decreased from 85.5% to 28.3%. The following MFC process increased MB mineralization percentage to 63.0% with a maximum output power density of 519 mW m^-2. The combined process achieved a mineralization energy consumption of 0.143 KWh gTOC^-1 which was only 41.8% of that of PAOP. FT-IR, UV-vis and pH variation demonstrated that PAOP could break the aromatic and heterocyclic structures in MB molecule to form organic acids. Possible degradation pathways of MB were accordingly proposed based on LC-MS, GC-MS, and density functional theory calculation.

Non-thermal plasma oxidation of Cu(II)-EDTA and simultaneous Cu(II) elimination by chemical precipitation

Cu²⁺ readily complexes with ethylenediaminetetraacetic acid (EDTA) to form a heavy metal complex (Cu-EDTA) that is typical in the effluents from mining and electroplating industries. It was difficult for the classical alkaline precipitation method to eliminate the heavy metal complex due to the strong bonding ability between Cu(II) and EDTA. Cu(II) release and removal performance after Cu-EDTA decomplexation in a non-thermal plasma oxidation system was carried out in this study. The removal process was characterized by chemical oxygen demand, total organic carbon, atomic force microscopy, and electroconductivity analysis. The toxicity effect of the treated Cu-EDTA solution was also tested by photobacterium bioassay. The experimental results showed that 80.2% of Cu was released and removed within 60 min of the non-thermal plasma treatment/alkaline precipitation. Relatively higher energy input, lower Cu-EDTA concentration, and acidic conditions were necessary to obtain greater Cu release and removal performance, and there existed an appropriate air flow rate for high-efficient Cu release and removal. O₂^-, OH, ¹O₂, and O₃ were the main active substances leading to Cu²⁺ release. Its residual toxicity to P.phosphoreum sp.-T3 was significantly reduced after treatment.

Oxidizability assay of unfractionated plasma of patients' with different plasma profile: a methodological study

BACKGROUND

Present study describe the in vitro model of plasma oxidation of patients with different lipid profile, that can be correlated to their invivo plasma oxidizability in order to find the arterial diseases prone patient groups.

METHOD

The method applied here to measure the invitro plasma oxidizability, accounts a convenient way that can be well suited in any clinical laboratory settings. Un-fractionated plasma was exposed to CuSO4 (5.0 mmol/L), a pro-oxidant, and low frequency ultrasonic wave to induce oxidation, and finally oxidizability was calculated by TBARS and Conjugated Diene methods.

RESULT

In our study, plasma LDL greater than 150 mg/dL possess 1.75 times more risk to undergo oxidation (CI, 0.7774 to 3.94; p = 0.071) than the low LDL plasma, percent of oxidation increased from 38.3% to 67.1% for the LDL level upto 150 mg/dL and high. Lag phase, which is considered as the plasma antioxidative protection, was also influenced by the higher LDL concentration. The mean lag time was 65.27 ± 20.02 (p = 0.02 compared to healthy), where as for 94.71 ± 35.11 min for the normolipidemic subject. The plasma oxidizability was also changed drastically for total cholesterol level, oxidative susceptibility shown 35% and 55.02% for 200 mg/dL and high respectively, however it didn't appear as risk factor. Patient samples were also stratified according to their age, gender, and blood glucose level. Older persons (≥40 years) were 1.096 times (95% CL, 0.5607 to 2.141, p = 0.396) than younger (≤39 years age), males are 1.071 (95% CI, 0.5072- 2.264) times than the females, and diabetic patients are 1.091 (CI, 0.6153 to 1.934, p = 0.391) times in more risk than the non-diabetic counterpart.

CONCLUSION

This method addressing its easy applicability in biomedical research. And by this we were able to show that patients with high LDL (≥150 mg/dL) are in alarming condition besides diabetic and elderly (≥40 years age) males are considered to be susceptible and more prone to develop vascular diseases.

Plasma treatment of PDMS for applications of in vitro motility assays

In vitro motility assays are readily used to simplify the complex environments within the cell and in muscle tissue. These assays have afforded considerable insight into the fundamentals of their underlying biophysics, interactions with cargo, intracellular regulation, and motor cooperation/competition. Extension of the standard in vitro motility assay into a more automated and cost-effective fluidic design while providing availability to the scientific community without expertise in lithographic fabrication is critical for the continued advancement of the field. In this work, we utilized a standard plasma cleaner to oxidize the widely prevalent material polydimethylsiloxane (PDMS) to create flow cells that could be used for in vitro motility assays. Our analysis indicated that a 40 min pre-treatment of the PDMS with plasma exposure resulted in optimal bundle motility. This finding was attributed to the condition at which the least amount of oxygen permeates the PDMS slab, enters the motility buffer, and oxidizes the motor proteins. Based on these findings, we developed a method for constructing microfluidic devices from glass and plasma-treated PDMS molds in which motility could be observed.