Carbonyl Index Research Articles

Accelerated aging behavior of degradable and non-degradable microplastics via advanced oxidation and their adsorption characteristics towards tetracycline

The increasing global utilization of biodegradable plastics due to stringent regulations on traditional plastics has caused a significant rise in microplastic (MPs) pollution in aquatic ecosystems from biodegradable products. However, the environmental behavior of biodegradable MPs remains inadequately elucidated. This study explored the aging processes of polylactic acid (PLA) and polystyrene (PS) under a heat-activated potassium persulfate (K2S2O8) system, as well as their adsorption characteristics towards tetracycline (TCs). In comparison to PS, the surface structure of PLA experienced more pronounced changes over aging, exhibiting evident pits, cracks, and fragmentation. The carbonyl index (CI) and oxygen/carbon ratio (O/C) of PS displayed exponential growth over time, whereas the values for PLA showed linear and exponential increases, respectively. The adsorption capacity of TCs by PS and PLA aged for 6 days increased from 0.312 mg‧g−1 and 0.457 mg‧g−1for original PS and PLA, respectively, to 0.372 mg‧g−1 and 0.649 mg‧g−1. Meanwhile, the adsorption rate (k2 values) for TCs decreased by 42.03 % for PS and 79.64 % for PLA compared to their initial values. The findings indicated that biodegradable PLA-MPs may exhibit higher tetracycline carrying capacities than PS, potentially increasing environmental and organismal risks, particularly in view of aging effects.

Effect of microwave and deodorant treatments on long-term aging characteristics of crumb rubber modified asphalt

This research examined and compared the effect of microwave and deodorant treatments on the rheological and microscopic characteristics of crumb rubber modified asphalt (CRMA) after long-term aging. Although the emissions from the asphalt modified by microwave treatment of crumb rubber (CR-micr) or high-alkane alcohol deodorant treatment of crumb rubber (CR-de) are reduced significantly compared with the ordinary CRMA, the research on their rheological and microscopic properties after aging is insufficient (especially for the CRMA with CR-de), which may pose a potential risk to their application in road engineering. To address this issue, this paper first used the rolling thin film oven and pressure aging vessel test to imitate the long-term aging of CRMAs. Then, the rheological properties of aged CRMA samples were evaluated using a dynamic shear rheometer and a bending beam rheometer. Meanwhile, the surface micromorphology, micromechanical characteristics and the chemical functional groups of CRMA samples before and after long-term aging were characterized by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the microwave treatment can enhance the fatigue life of the long-term aged CRMA by approximately 29 % under 8 % CR content and 3 % strain level, while effectively improve the resistance to low-temperature cracking. Meanwhile, after long-term aging, the carbonyl index of CRMA with CR-micr is 36 % lower than that of CRMA with CR-de and 50 % lower than that of ordinary CRMA. The micromechanical modulus of CRMA with CR-micr is also lower than that of CRMA with CR-de and ordinary CRMA. These findings manifest that the microwave treatment can improve the ability of CRMA to resist long-term aging, and the deodorant treatment does not have an adverse effect on this ability.

Adsorption and Desorption Behavior of PAEs Plasticizer on PVC and Rubber Particles After Natural Environment Aging

Microplastics （MPs） coexist with plasticizers in the aqueous environment to form composite pollution, but the adsorption and desorption behaviors of MPs and plasticizers under natural conditions are unknown. Polyvinyl chloride （PVC） and rubber were used as the target MPs to characterize the changes in their morphological features after aging for one anniversary in atmospheric exposure and lake sedimentary burial environments and to investigate the adsorption and desorption behavior of the MPs to the coexisting phthalate esters （PAEs） plasticizer before and after aging. The results showed that the surface of MPs was rougher after exposure to the atmospheric environment and burial in a depositional environment, showing the characteristics of porous polymers. The carbonyl index （CI） of PVC and rubber increased by 62.2% and 321.2%, respectively, in the atmospheric environment and increased by 51.1% and 223.1%, respectively, in the depositional environment. The atmospheric exposure was capable of accelerating the aging process of MPs. PAEs were adsorbed on the surface of MPs through hydrophobic interaction, and the amount of adsorption was significantly and positively correlated with their hydrophobic properties. The adsorption capacity and adsorption rate of PVC on PAEs were inhibited after aging. Aging promoted the adsorption of rubber on strongly hydrophobic PAEs plasticizers and inhibited the adsorption of weakly hydrophobic PAEs. The environmental aging process reduced the desorption of strongly hydrophobic PAEs from rubber, enhanced the reversibility of rubber adsorption of weakly hydrophobic PAEs, and increased the desorption rate of PAEs from PVC.

Isolation of seawater microplastics from biologically rich samples using an alkaline K2S2O8 method

In recent years, microplastics, especially marine microplastic pollution, have received global attention as a new type of environmental problem. The establishment of accurate and efficient methods for the detection of microplastics is the basis for in-depth research on the transport, transformation, fate, and ecotoxicological effects of microplastics in the environment. Microplastics in seawater frequently mix with biological tissues, resulting in challenges when identifying samples. However, commonly used pretreatment protocols for microplastics often suffer from long digestion times, inadequate digestion, and the risk of potentially damaging microplastics. This study compared the digestion efficiencies of five digestion reagents and provided further insights into two advanced oxidation methods involving Fenton’s reagent and an innovative alkaline K2S2O8 protocol based on sulfate and hydroxyl radicals. Using Raman spectroscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM−EDS), and carbonyl index (CI) analyses, the status of microplastics after pretreatment was evaluated. The results revealed that the alkaline K2S2O8 method could enhance the reaction efficiency while reducing the potential for functional group damage during microplastic pretreatment. Moreover, the proposed K2S2O8 method was applied to the pretreatment of field seawater samples, and field microplastics were effectively separated from biologically rich samples. Thus, a digestion protocol based on alkaline K2S2O8 provides an effective way to isolate seawater microplastics from biologically rich samples. This study contributes to the development of efficiently microplastic monitoring and provides valuable insights into access to reliable data for fate and inventory of oceanic microplastics.

Enhancing biodegradation efficiency of PLA/PBAT-ST20 bioplastic using thermophilic bacteria co-culture system: New insight from structural characterization, enzyme activity, and metabolic pathways

The rising utilization of PLA/PBAT-ST20 presents potential ecological risks stemming from its casual disposal and incomplete degradation. To solve this problem, this study investigated the degradation capabilities of PLA/PBAT-ST20 by a co-culture system comprising two thermophilic bacteria, Pseudomonas G1 and Kocuria G2, selected and identified from the thermophilic phase of compost. Structural characterization results revealed that the strains colonized the PLA/PBAT-ST20's surface, causing holes and cracks, with an increase in the carbonyl index (CI) and polydispersity index (PDI), indicating oxidative degradation. Enzyme activity results demonstrated that the co-culture system significantly enhanced the secretion and activity of proteases and lipases, promoting the breakdown of ester bonds. LC-QTOF-MS results showed that various intermediate products were obtained after degradation, ultimately participating in the TCA cycle (ko00020), further completely mineralized. Additionally, after 15-day compost, the co-culture system achieved a degradation rate of 72.14 ± 2.1 wt% for PBAT/PLA-ST20 films, with a decrease in the abundance of plastic fragments of all sizes, demonstrating efficient degradation of PLA/PBAT-ST20 films. This study highlights the potential of thermophilic bacteria to address plastic pollution through biodegradation and emphasizes that the co-culture system could serve as an ideal solution for the remediation of PLA/PBAT plastics.

Investigation and optimization of short-term aging test conditions for asphalt binders

The existing short-term aging test methods have disadvantages such as not being suitable for high viscosity modified asphalt, different aging degrees between them and poor testing convenience. Therefore, this paper investigated and optimized the aging test conditions of asphalt. The macroscopic rheology and microchemistry of aged asphalt prepared by different aging conditions were comprehensively evaluated. Finally, the most suitable aging test conditions for asphalt was determined by referring to the aging degree of loose asphalt mixture. The experiment results showed that after aging, the rutting factor, carbonyl index, asphaltene content, and creep stiffness of asphalt would increase. The aging degree of existing asphalt aging methods (TFOT and RTFOT) and the corresponding loose asphalt mixture was quite different, and the difference percentage could reach 86.6%. Based on the TFOT test, the asphalt aging conditions were optimized. The aging temperature was 163 ℃. For 70# and SBS modified asphalt, the recommended asphalt film thickness and aging time were 1.59 mm–85 min and 0.80 mm–85 min, respectively. The aging degree of high viscosity modified asphalt under the condition of 0.80 mm–85 min was close to the aging degree of loose asphalt mixture at 135 ℃, and the aging degree of 0.80 mm–100 min was close to the aging degree of loose asphalt mixture at 165 ℃. The proposed aging test conditions can not only accurately simulate the short-term aging behavior of asphalt, but also shorten aging time and save resources.

Microbial Allies in Plastic Degradation: Specific bacterial genera as universal plastic-degraders in various environments

Microbiological degradation of polymers offers a promising approach for mitigating environmental plastic pollution. This study (i) elucidated the diversity and structure of bacterial microbiomes from distinct environments (landfill soil, sewage sludge, and river water) characterized by specific physicochemical parameters, and (ii) utilized environment-derived microbial cultures enriched with microplastics (MPs) to investigate the degradation of polymers and identify culturable bacterial strains contributing to the plastisphere. We found that alpha diversity was notably higher in river water (∼20%) compared to landfill soil and sewage sludge. Dominant phyla included Pseudomonadota in sewage sludge (39.1%) and water (23.7%), while Actinomycetota prevailed in soil (38.5%). A multistage experiment, involving successive subcultures of environmental microbiomes exposed to polypropylene (PP), polyvinyl chloride (PVC), polycarbonate (PC), and polylactic acid (PLA), facilitated the assessment of MPs degradation processes. Analysis of carbonyl indices CIs and FTIR spectra revealed substantial structural changes in the treatment PVC-landfill soil, as well as in PLA- and PC-sludge enriched cultures. Further, using enriched cultures as a source of microorganisms, the study obtained 17 strains of plastic degraders from landfill soil, 14 from sewage sludge, and 6 from river water. Remarkably, similar bacterial genera were isolated across environmental microbiomes regardless of the MPs substrate used in enriched cultures. Among the 37 identified strains, Pseudomonadota predominated (64.86%) and were accompanied by Bacteroidota (16.22%), Actinomycetota (13.51%), and Bacillota (5.41%). This study highlights the complex relationship between microbiome diversity and the biodegradation efficiency of plastics, showing the potential for using microbial communities in the plastic pollution management.

Evaluation of the stabilizing effect and ageing time indicator properties of poly(flavonoids) in a cyclic olefin copolymer

Few studies are concerned with the stabilization of polymers using natural polymeric polyphenols. There are no literature reports on the use of poly(flavonoids) produced by bio-chemical polymerization as stabilizers. The aim of the research was to analyse the stabilizing potential (anti-ageing UV) of poly(catechin) and poly(naringenin) in polymer compositions based on the thermoplastic elastomer of ethylene-norbornene copolymer (TOPAS Elastomer E-140). Poly(flavonoids) were obtained in a polymerization reaction with a cross-linking compound and then introduced into cyclic olefin copolymer TOPAS. For comparison, materials with monomeric catechin and naringenin were also prepared. The scope of research included the thermal analysis of the polymer compositions (Oxidation induction time OIT, Thermogravimetry TG), determination of carbonyl indices and ageing coefficients K (based on changes in mechanical properties) after UV ageing (400 h). In addition, the colour change after ageing of the samples was investigated. Samples containing polymeric forms of catechin and naringenin were more susceptible to degradation than samples with monomeric flavonoids. Inferior stabilizing properties of poly(flavonoids) were associated with steric hindrances and limited availability of hydroxyl groups to provide the antioxidant activity of the polymeric compounds. The work extends the literature data by providing an analysis of the stabilizing effect of synthetic poly(flavonoids) in polymer compositions.

Characteristics and aging of microplastics in waste activated sludge under persulfate and hydrothermal co-treatment: Impact of solid content and temperature

Activated persulfate and hydrothermal treatment (HTT) are often employed to treat waste activated sludge, which can improve the efficiency of subsequent sludge treatment and change the distribution of pollutants in the sludge. However, the impact of sludge solid content and temperature on the occurrence and aging of microplastics (MPs) during HTT remains poorly understood. This study investigated the effects of persulfate-HTT (SPS-HTT) co-treatment on the migration, occurrence, and aging of MPs in sludge with different solid contents (2% and 5% solid content). The results indicated that SPS-HTT co-treatment triggers both the disruption of sludge flocs and the melting deformation of MPs at high temperatures, leading to variations in the increasing trend of MP concentration in the solid-liquid phase at different solid contents. 5% solid content sludge showed a weak release of MPs from the solid phase. The proportion of fiber MPs first increased and then decreased with increasing temperature, while no significant changes were observed in the color and type of MPs. Higher temperature and solid content induced the melting deformation of MPs, exacerbated the aging of polypropylene MPs, and resulted in rough surfaces, higher carbonyl index, and variations in crystallinity. Moreover, the correlation between the carbonyl index and aging indicators increased with increasing solid content. The MP-derived dissolved organic matter under HTT primarily comprised soluble microbial by-products and humic acid-like substances. These findings underscore the significance of sludge solid content in affecting the migration and aging of MPs during HTT, and offer novel insights into the application of HTT to MP management in sludge treatment.

Natural iron-containing minerals catalyze the degradation of polypropylene microplastics: a route to self-remediation learnt from the environment

Virgin and environmentally aged polypropylene (PP) micropowders (V-PP and E-PP, respectively) were used as reference microplastics (MPs) in comparative photo- and thermo-oxidative ageing experiments performed on their mixtures with a natural ferrous sand (NS) and with a metal-free silica sand (QS). The ferrous NS was found to catalyze the photo-oxidative degradation of V-PP after both UV and simulated solar light irradiation. The catalytic activity in the V-PP/NS mixture was highlighted by the comparatively higher fraction of photo-oxidized PP extracted in dichloromethane, and the higher carbonyl index of the bulk polymer extracted with boiling xylene, when compared with the V-PP/QS mixture. Similarly, NS showed a catalytic effect on the thermal degradation (at T = 60 °C) of E-PP. The results obtained indicate that, under suitable environmental conditions (in this case, an iron-containing sediment or soil matrix, combined with simulated solar irradiation), the degradation of some types of MPs could be much faster than anticipated. Given the widespread presence of iron minerals (including the magnetite and iron-rich serpentine found in NS) in both coastal and mainland soils and sediments, a higher than expected resilience of the environment to the contamination by this class of pollutants is anticipated, and possible routes to remediation of polluted natural environments by eco-compatible iron-based minerals are envisaged.Graphical abstract

Adsorption behaviors of perfluorooctanoic acid on aged microplastics.

The presence of perfluoroalkyl substances (PFAS) in the environment poses a significant threat to ecological safety and environmental health. Widespread microplastics (MPs) have been recognized as vectors for emerging contaminants due to human activities. However, the adsorption behaviors of PFAS on MPs, especially on aged MPs, have not been extensively investigated. This study aimed to investigate the adsorption behaviors of perfluorooctanoic acid (PFOA) on aged MPs (polystyrene, polyethylene, and polyethylene terephthalate) treated with UV irradiation and persulfate oxidation under salinity and dissolve organic matter (DOM) condition. Carbonyl index values of MPs increased after the aged treatment, indicating the production of oxygen-containing groups. The PFOA adsorption on aged MPs was impacted by the co-existence of Na+ ions and DOM. As PFOA adsorption onto aged MPs was mainly controlled by hydrophobic interaction, the electrostatic interaction also made a contribution, but there was no significant change in PFOA adsorption behavior between the pristine and aged MPs. While these findings provide insight into PFAS adsorption on aged MPs, further research is necessary to account for the complexity of the real environment. PRACTITIONER POINTS: Adsorption behaviors of perfluorooctanoic acid (PFOA) on aged microplastics were investigated. Hydrophobic interaction mainly controlled PFOA adsorption on aged microplastics (MPs). Co-existence dissolve organic matter and salinity influenced PFOA adsorption behaviors on aged MPs.

CuO/Bi2O3/g-C3N4 nanoparticles for sunlight-mediated degradation of polyethylene terephthalate microplastic films

A novel photodegradable CuO/Bi2O3/g-C3N4(copper oxide/bismuth oxide/graphitic carbon nitride) nanoparticle (NP) was synthesised using the sol-gel method and sunlight-mediated degradation of polyethylene terephthalate (PET) microplastics (MPs) films. The optical and structural properties of the sol-gel method were investigated using a variety of characterization methods, like UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier transform infrared (FT-IR), X-ray diffractometer (XRD) analysis, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis. Degradation study results suggest that the photocatalytic activity of CuO/Bi2O3/g-C3N4/PET nanocomposites (NCs) films was greater than that of pure PET, CuO/PET, Bi2O3/PET, g-C3N4/PET, CuO/g-C3N4, Bi2O3/g-C3N4, and CuO/Bi2O3/PET films. Because of their increased optical absorption and efficient suppression of photo-produced charge carriers’ recombination, the CuO/Bi2O3/g-C3N4/PET NCs films showed higher photocatalytic degradation than PET films. Thus, PET films with CuO/Bi2O3/g-C3N4 (5:5:2 % wt) NPs showed a degradation of around 41.60 % among pure PET, CuO/PET, Bi2O3/PET, g-C3N4/PET, CuO/g-C3N4/PET, Bi2O3/g-C3N4/PET, and CuO/Bi2O3/PET NCs films under visible light over a short period of 30 days (240 h). When compared to the original PET MPs, the CuO/Bi2O3/g-C3N4/PET NCs films showed a significant decrease in crystallinity and carbonyl indexes, as much as 29.2 % lower. The present research also suggests a photocatalytic mechanism, which may explain the increased photocatalytic activity.

The degradation of poly(1-butene) extrudates subjected to artificial and natural aging

In this work, we examined the degradation behavior of isotactic poly(1-butene) (PB-1) under artificial aging and natural weathering conditions. PB-1 samples underwent accelerated aging through UV irradiation and natural weathering. Chemical and structural changes in the degraded samples were characterized using Fourier-transform infrared–attenuated total reflectance (FTIR–ATR) spectroscopy, surface analysis, and wide-angle X-ray scattering (WAXS). The mechanical properties were evaluated via tensile testing. FTIR–ATR analysis revealed the presence of carbonyl groups in the degraded samples, indicating oxidative degradation. Surface observations employing scanning electron microscopy (SEM) revealed the formation of surface cracks in both samples, with differing crack initiation mechanisms. The two aging methods affected the mechanical properties of the samples: artificial aging induced a gradual reduction in both tensile modulus and strength, whereas natural weathering engendered a marginal increment in modulus alongside diminished strength. Additionally, elongation-at-break value witnessed a marked decrease in both sample sets during the preliminary stages of degradation. This work employed accelerated time equivalent, obtained by juxtaposition of the values of carbonyl index during both artificial aging and natural weathering and their interpolation to determine the degradation rate and adequately to correlate the final properties of the aged PB-1. It was observed that surface morphology and mechanical attributes of degraded samples were subject to additional influences such as temperature, humidity, and precipitation during natural weathering. This research work provided significant insights into PB-1 degradation mechanisms and effect of different aging conditions on its performance.Graphical abstract

Atmospheric cold plasma as a novel approach to remediating microplastics pollution in water

Microplastics (MPs) have become an environmental and health threat to aquatic species and humans because they are small and can easily reach water bodies for municipal and agricultural uses. MPs have been traced in food commodities and products derived from animals and even found in bottles of drinking water. Current treatment techniques for permanently destroying MPs require high energy inputs and thus are generally cost-inefficient. Atmospheric cold plasma (ACP) is a low-cost energy-efficient technology to produce highly reactive species that can induce physicochemical changes in plastic polymers. This study, for the first time, used ACP as a novel method for MPs treatment. Polypropylene (PP) and low-density polyethylene (LDPE) were used to prepare model MPs. The effects of plasma working gas (oxygen, nitrogen, or their mixture) and post-ACP treatment storage (24 h) on MPs were studied. ACP treatments for 30 min successfully degraded both MPs, by 1.4–11.3% in weight. PP MPs had larger weight reduction than LDPE and the ACP of mixture gas was most effective. PP MPs also showed increased carbonyl index after treatments, to up to 6.89, indicating hydrolytic degradation. For LDPE MPs, oxygen ACP caused more oxidation, but storage did not have an enhancing effect. The results of physicochemical analyses indicated that MPs degradation by ACP was possibly mainly through oxidative and hydrolytic reactions, but further characterizations are needed. This study proves that ACP is a promising strategy to remediate MPs pollution, and thus has great potential for addressing the severe challenges of MPs that the food and agriculture sectors are currently facing.

Cobalt catalyzed carbonyl functionalization to boost the biodegradation of polyethylene by Bacillus velezensis C5

Polyethylene plastics are widely used in daily life since known for their resistance to biodegradation, but posing a significant environmental challenge. The biodegradation of polyethylene can contribute to environmental protection and facilitate energy conservation, in comparison with physical or chemical methodologies. However, the stable and inert C–C bond structure of polyethylene limits biodegradation effectiveness, leading to a slow breakdown rate and extended life cycle. In this study, Co(acac)2 was used as a catalyst to generate free radicals that activated the interface of low-density polyethylene, resulting in the formation of oxygen-containing functional groups. Under the condition of Co(acac)2-mediated catalysis at 120 °C for 24 h, the carbonyl index of polyethylene rose from 0 to 2.99. The weight-average molecular weight of polyethylene was reduced by 8.77 % compared to the control, leading to the generation of small molecules. The density functional theory elucidated showed that the active oxygen substitution in the single electron transfer reaction was driven by the high-energy intermediate alkyl radical. The bond energy of the resulting carbonyl functional group (CO) is 76.4 % lower than that of the original C–C bond, making it more susceptible to cleavage and depolymerization. Following 90 d of biodegradation, the laccase activity showed a 25 % increase compared to the control, indicating an improved oxidase release by chemical oxidation. The weight loss of low-density polyethylene was 23.91 %, and the microbial degradation efficiency was 2.32 times higher. This strategy significantly improves the ability of microorganisms to degrade low-density polyethylene and is a novel approach to the design of pathways for the polyolefin degradation.

Anti-ageing and rheological performance of bitumen modified with polyaniline nanofibres

Asphalt pavements represent the great majority of roads worldwide. However, the bitumen physico-chemical properties change due to ageing processes during both the production and service life of the asphalt mixes. In recent years, a completely new trend has been observed in the road engineering industry oriented to extending the service life of roads, bringing direct economic, ecological and social benefits. This work presents the possibility of inhibiting ageing of road bitumen by using polyaniline nanofibers (PANI_NFs) as well as enhancing its rheological properties examined with Linear Amplitude Sweep (LAS) as well as Multiple Stress Creep and Recovery (MSCR) tests. These results show that the application of PANI_NFs maintains the primary penetration value of bitumen short-term and long-term aged road bitumen at 88 % and 52 %, respectively. Moreover, bitumen modification with PANI_NFs reduces the softening temperature increase by 33 % and 24 %, respectively, and the viscosity increase of road asphalt by 50 % and 25 %, respectively. PANI_NFs also stabilised the bitumen surface adhesion force, determined with AFM, consequently confirming the enhanced resistance to ageing processes. In addition, changes in the carbonyl index, sulphoxide index and aromaticity of bitumen demonstrated that PANI_NFs inhibit oxidation and aromatisation reactions of its components. The tests indicated a 4-fold decrease in the degree of bitumen component oxidation after short-term ageing and a 33 % decrease after long-term ageing. FTIR analysis also showed a reduction in the degree of bitumen component aromatisation process of 79 % and 76 % for short-term and long-term ageing, respectively. The LAS and MSCR test results also showed that PANI_NFs had a beneficial impact on the resistance of the bitumen to fatigue and rutting. Overall, the study results suggest that PANI_NFs consitute a promising modifier for bitumen in terms of ageing inhibition and performance characteristics.

Surface characteristics and adsorption properties of polypropylene microplastics by ultraviolet irradiation and natural aging

The vast application and deep integration of plastic commodity with our human lives raise a great concern about the ubiquitous microplastics (MPs) in nature, yet the environmental behavior of MPs remain unclear. As a main type and candidate of MPs, pristine polypropylene MPs (PP-MP-Pris), as well as the influence of ultraviolet (UV) irradiation on the degree of aging and surface characteristics, were characterized quantitatively by Fourier infrared spectroscopy, scanning electron microscopy, contact angle meter, automatic specific surface area and pore analyzer and laser particle analyzer, with natural aged PP-MPs (PP-MP-Age) as comparison. The carbonyl index (CI) of UV aged PP-MPs (PP-MP-U) was increased with extension of exposure time, while biofilm with abundant functional groups and the maximum CI value were the characteristics of PP-MP-Age. Moreover, the adsorption capacity of PP-MP-U for crystal violet (CV) was increased and reached the maximum after 30 days, while that of PP-MP-Age was weakened, probably due to the enhanced hydrophilicity and the shedding of calcium carbonate (CaCO3) during the natural aging process, which was demonstrated by hydrochloric acid treatment, indicating the vital involvement of CaCO3. Moreover, the better fitting to PSO kinetics and Freundlich isotherm models indicated that the multilayered and non-homogeneous surface adsorption was acted as the rate-controlling step. Furthermore, the positive values of ΔGθ, ΔHθ and ΔSθ indicated that the adsorption was a non-spontaneous, endothermic process with increased degree of the freedom on the interface of PP-MPs and CV solution. The presence of divalent salts inhibited CV adsorption, demonstrating that electrostatic attraction played a major role in CV capture. The hydrophobic interaction, micropore filling, hydrogen bonding, and π - π conjugation were possible involved. This study is of great significance for better understanding the complex pollution of MPs and its potential environmental risks in the future.

Joule heat assisting electrochemical degradation of polyethylene microplastics melted on anode

Polyethylene (PE) microplastics (MPs) in water was rapidly degraded using a “Joule heat assisting electrochemical degradation” strategy. In a tailor-made reactor, PE MPs were captured by anode, being softened or even melted by the interface Joule heat, enabling direct electron transfer and making the maximum use of short-lived active species. Within a few hours, above 99 % of PE MPs (∼ 1 g·L−1) vanished, and residual solid products with higher carbonyl index (CI) and O/C ratio inclined to combine, avoiding creating more harmful nanoplastics (NPs), just leaving a few low-threatening soluble products with unsaturated carbon chains. Compared with SO42- and S2O82-, the presence of Cl- water matrix could facilitate the chain-scission degradation and make solid products fusion more significant. After proposing a novel MPs degradation mechanism and verifying the universality of this novel strategy by degrading other five kinds of MPs. Subsequently, a techno-economic analysis was conducted.

Effects of Aging on Rheological Properties and Microstructural Evolution of SBS Modified Asphalt and Crumb Rubber Modified Asphalt Binders

Focusing on the comparison of aging resistance between styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) and crumb rubber modified asphalt binders (CRMA), the influences of aging on rheological properties and microstructural characteristics of different modified asphalts were investigated in this work. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were carried out, and the variations in rheological properties for different modified asphalts after the rotating thin film oven test (RTFOT) were analyzed with the rutting factor aging index (RAI) and creep rate aging index (CAI). By using Fluorescence microscopy (FM) and Fourier transform infrared (FTIR) spectroscopy, the evolutions of microstructure and chemical composition for two modified asphalts were analyzed with carbonyl index growth rate (CIR) and sulfoxide index growth rate (SIR). Then, The relationships between CIR/SIR and RAI/CAI were established to show the correlation between the deterioration of macroscopic performance and the evolution of micro-structure. The results indicated that the aging degree of asphalt increases with elevated temperatures, leading to decreasing low-temperature performance while improving high-temperature performance. Nevertheless, SBSMA exhibited strong sensitivity to aging temperature. Under thermo-oxidative aging, the RAI and CAI of SBSMA were lower than those of CRMA, whereas the regularities of CIR and SIR were opposite, indicating that CRMA was superior to SBSMA in terms of anti-aging properties due to the rupture of the cross-linked network structure of SBSMA. However, CRMA experienced aging accompanied by full swelling, and thus, relatively minor performance declined. The CIR and SIR exhibited a better correlation with the RAI and CAI, illustrating that both CIR and SIR could characterize the aging degree of modified asphalts well.

Aging and Small-sized Particles Release Characteristics of Tire Microplastics in Various Environmental Media

In recent years, research on microplastics has mostly focused on thermoplastic materials, and there is a lack of research on the pollution status and environmental behavior of tire microplastics, a type of rubber elastomers. In order to investigate the aging and small-sized particles release characteristics of tire microplastics in various environmental media, the aging process of two different tire microplastics, one for cars and the other for electric bicycles, was simulated in dry and aquatic environments under laboratory conditions. The results showed that the tire microplastics would be aged after 30 d of UV illumination, which was manifested by the roughness of the surface and the appearance of cracks and flaking. The Fourier infrared spectra showed that the carbonyl index of the surface also increased. In addition, tire microplastics released a large number of small sub-micron particles under the influence of UV illumination and hydrodynamic action, and the number of particles released from car tire microplastics in aquatic environments reached 694.8 million particles per milliliter of solution at 30 d of the UV light condition, among which 694.6 million particles with a particle size of less than 1 μm were released, which was approximately 100 times of that in the dark condition. The study showed that tire microplastics in aquatic environments were more susceptible to aging and released more small particles under light conditions and that car tire microplastics released more small particles than electric bicycle tire microplastics, posing ecological and environmental risks.