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•PS were aged by air, pure water and seawater under UV irradiation.•Changes in chemical/physical properties of PS were examined by FTIR, XPS, XRD and SEM.•Aging mechanisms of PS in ...water environment is different from that in air.•Aging can significantly improve the adsorption of heavy metals by PS.
Microplastics are formed by the degradation of plastic wastes under the action of physicochemical mechanisms in environment, and they are becoming a new type of pollutant that is attractings global attention. However, research on the aging characteristics and mechanism of microplastics is limited. The aging mechanism of Polystyrene (PS) with UV irradiation under different conditions (air, pure water and seawater) and the effect of aging on heavy metal adsorption were studied. The results show that PS have different characteristics with UV irradiation under different conditions, and the aging of PS is the most obvious in air. Based on the 2D-COS analysis, different aging mechanisms were identified under different aging conditions, aging sequence of aged PS functional groups in air and water were clearly definited. An isothermal adsorption model shows that aging can significantly increase the adsorption of heavy metals by PS. The adsorption of heavy metals is also affected by different aging methods. Over all, a 2D-COS analysis was an effective method for understanding the aging process of PS. These results further clarify the aging mechanism of PS, and provides a theoretical basis for the assessment of environmental behavior and ecological risk when microplastics and heavy metals coexist.
The usage of biodegradable plastics is expanding annually due to worldwide plastic limits, resulting in a substantial number of microplastics (MPs) particles formed from biodegradable plastic ...products entering the aquatic environment. Until now, the environmental behaviors of these plastic product-derived MPs (PPDMPs) have remained unclear. In this work, commercially available polylactic acid (PLA) straws and PLA food bags were used to evaluate the dynamic aging process and environmental behavior of PLA PPDMPs under UV/H2O2 conditions. By combining scanning electron microscopy, two-dimensional (2D) Fourier transform infrared correlation spectroscopy (COS) and X-ray photoelectron spectroscopy, it was determined that the aging process of the PLA PPDMPs was slower than that of pure MPs. The 2D-COS analysis revealed that the response orders for the functional groups on the PLA MPs differed during the aging process. The results demonstrated that the oxygen-containing functional groups of the PLA PPDMPs were the first to react. Subsequently, the –C–H and –C–C− structural responses began, and the polymer backbone was ruptured by the aging process. However, the aging of the pure-PLA MPs started with a brief oxidation process and then breakage of the polymer backbones, followed by continuous oxidation. Moreover, compared to the PLA PPDMPs, the pure-PLA MPs exhibited a greater adsorption capacity, which was increased by 88% after aging, whereas those of the two PPDMPs only increased by 64% and 56%, respectively. This work provides new insights into the behaviors of biodegradable PLA MPs in aquatic environments, which is critical for assessing the environmental risks and management policies for degradable MPs.
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•The aging process of PLA plastic product-derived MPs was slower than pure-PLA MPs.•The UV/H2O2 aging process significantly increased the adsorption capacity of PLA MPs.•Product-derived MPs had lower adsorption capacity for pollutants compared to pure MPs.•2D-COS demonstrated the dynamic aging process of PLA product-derived MPs and pure-PLA MPs.
Noteworthy new progress in 2D correlation spectroscopy (2D-COS) and its versatile applications for the last two years are compiled in this comprehensive survey review. We report the new and ...significant concepts of 2D-COS, various 2D-COS software and useful display techniques, and numerous applications of 2D-COS in various external perturbations, analytical methods, and systems. Applications of 2D-COS in fluorescence spectroscopy have noticeably increased, as well as applications of 2D-COS to field closely related to daily life, such as environmental, medical, and food, are greatly increased. 2D-COS is continuously evolving and growing with new developments and successful applications in various scientific fields. Diverse studies using 2D-COS would surely open a new promising way for in-depth studies of various materials and systems in many applications.
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•Comprehensive survey on new progresses of 2D-COS for last two year.•Noteworthy new developments of 2D-COS and its versatile applications.•Journal articles, review articles, patents and publication trend.
Microplastics, as an emerging class of pollutants has become a global concern, and is receiving increasing attention. Interestingly, microplastics are always in their ageing process when they enter ...the real environment. Our study investigated the ageing properties of polystyrene (PS) plastics in air, pure water and seawater environments at 75 °C. A two-dimensional (2D) Fourier transform infrared (FTIR) correlation spectroscopy (COS) analysis was used to better understand the ageing mechanism of the PS plastics. Based on the 2D-COS analysis, different ageing mechanisms were identified under different ageing conditions, such as an ageing sequence of aged-PS particle functional groups in air: 1601(CC) > 1050(C–O)>1453(C–H)>1493(C–H)>1375(C–OH)>1666(CO). Among the functional group changes, O-functional groups (C–O, C–OH and CO) were introduced during the ageing process. Moreover, for pristine PS particles, hydrophobicity was a major factor for the interaction between the microplastics and organic pollutants. For aged-PS particles, their adsorption capacities were significantly enhanced as the degree of ageing increased. The ageing degree of PS was highly responsible for increasing of the specific surface area and the increase in oxygen-containing surface groups. Furthermore, there was a significant enhancement in the adsorption affinity for antibiotic contaminants than for polycyclic aromatic hydrocarbon contaminants. Aged PS particles had little adsorption of polycyclic aromatic hydrocarbons, because the presence of oxygen-containing surface groups on the aged PS plastics might allow the formation of hydrogen bonds with the surrounding water molecules. Overall, a 2D-COS analysis was an effective method for understanding the ageing process of microplastics under different environmental conditions at high temperature. These results also clearly demonstrated the characteristics and mechanisms of the interaction between aged-microplastics and organic pollutants, which could be useful for understanding the environmental behavior of co-existing pollutants.
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•Microplastics were aged by air, pure water and seawater on 75 °C.•The aging mechanism of PS were different under different aging conditions.•The adsorption capacities of PS were enhanced with the increase of aging degree.•The adsorption of PS on organic pollutants depend on its properties.
A biochar (KBC) enriched with O functional groups was prepared by torrefaction using lignin-rich kiwifruit branches (KBM) as a raw material, which was characterized, and then KBC was used to adsorb ...hexavalent chromium (Cr6+) from water. The results showed that KBC contained more functional groups compared to KBM. The maximum adsorption of Cr6+ by KBC could reach 143.64 mg·g−1 and also had better adsorption performance than other adsorbents reported in some other reports. Cr6+ absorption by KBC was mainly a mechanism of electrostatic interaction and adsorption-reduction coupling. FTIR and XPS revealed that -OH, -COOH, CO and CC on KBC participated in Cr6+ adsorption and new groups (C=O) were generated during the process of adsorption, which implied that a redox reaction occurred. 2D-COS and DFT calculations showed that the order of functional groups on KBC interacting with Cr6+ was -OCH3 > -COOH > -OH > phenolic hydroxyl, and the binding tightness of the different functional groups to Cr6+ was -OCH3 (the shortest displacement of both groups after the adsorption) > -COOH > -OH > phenolic hydroxyl. KBC has good regeneration performance, and it is a good adsorbent for Cr6+.
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•Biochar (KBC) rich in O functional groups was prepared from lignin-rich kiwifruit waste branches under torrefaction conditions.•The maximum adsorption capacity of KBC for Cr6+ in water was 143.64 mg·g-1.•The role of functional groups on KBC was revealed by 2D-COS and DFT calculations.•The adsorption mechanism of Cr6+ by KBC is mainly based on electrostatic interaction and adsorption-reduction coupling mechanism.•KBC has stable renewable performance and good application potential.
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In this study, a nano-sheet C3N4-WO3 composite (nsCW21) was applied as a visible-light active photocatalyst to degrade natural organic matter (NOM). The nsCW21 photocatalyst exhibited ...a higher removal efficiency for NOM than the bare host and other composite counterparts due to the effective separation of the charge carriers in the Z-scheme pathway. The addition of H2O2 resulted in the enhanced photocatalytic performance via the generation of hydroxyl radicals from the catalyst with an NOM removal rate of up to 71% for 5 h. The catalyst showed a considerable stability, which held a good NOM degradation efficiency during five cycle runs. The complex NOM removal behavior was unraveled by using a fluorescence excitation emission matrix-parallel factor analysis and a two-dimensional correlation spectroscopy (2D-COS) combined with Fourier-transform infrared spectroscopy (FT-IR). The large sized and the terrestrial humic-like component exhibited a high adsorption tendency toward the catalyst and was degraded primarily by h+, while a typical humic-like component, which is mainly removed by .OH, displayed a high degradation rate constant (k = 0.159 h−1). The 2D-COS revealed the sequence of the preferable removal among the different NOM functional groups in the nsCW21 system with H2O2 addition, which occurred in the order of open ring reaction > oxygenated functional groups > the transformation into aliphatic compounds/inorganic moieties. Meanwhile, the hybrid system that employed ultrafiltration as a post-treatment demonstrated synergetic effects on the improved effectiveness for NOM removal in the overall system, which was a total of 91%, of the residuals from the precedent photocatalysis as well as alleviating the membrane fouling.
A comprehensive survey review is compiled to showcase new progresses in 2D correlation spectroscopy (2D-COS) field for the last two years. It surveys most of the published journal articles, review ...articles, and patents on 2D-COS. Not only noteworthy new concepts of 2D-COS but also versatile applications of 2D-COS employing various analytical probes and perturbation methods are reviewed.
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•Comprehensive survey on new progresses of 2D-COS for last two years.•New and noteworthy developments and experimental practices in 2D-COS.•Journal articles, review articles, patents and publication trend.
The metal-binding characteristics of water-soluble organic matter (WSOM) emitted from biomass burning (BB, i.e., rice straw (RS) and corn straw (CS)) with Cu(II) under various pH conditions (i.e., 3, ...4.5, and 6) were comprehensively investigated. Two-dimensional correlation spectroscopy (2D-COS) and excitation–emission matrix (EEM) –PARAFAC analysis were applied to investigate the binding affinity and mechanism of BB WSOM. The results showed that pH was a sensitive factor affecting binding affinities of WSOM, and BB WSOMs were more susceptible to bind with Cu(II) at pH 6.0 than pH 4.5, followed by pH 3.0. Therefore, the Cu(II)-binding behaviors of BB WSOMs at pH 6.0 were then investigated in this study. The 2D-absorption-COS revealed that the preferential binding with Cu(II) was in the order short and long wavelengths (237–239 nm and 307–309 nm) > moderate wavelength (267–269 nm). The 2D-synchronous fluorescence-COS results suggested that protein-like substances generally exhibited a higher susceptibility and preferential interaction with Cu(II) than fulvic-like substances. EEM–PARAFAC analysis demonstrated that protein-like (C1) substances had a greater complexation ability than fulvic-like (C2) and humic-like (C3) substances for both BB WSOM. This indicated that protein-like substances within WSOM played dominant roles in the interaction with Cu(II). As a comparison, RS WSOM generally showed stronger complexation capacity than CS WSOM although they exhibited similar chemical properties and compositions. This suggested the occurrence of heterogeneous active metal-binding sites even within similar chromophores for different WSOM. The results enhanced our understanding of binding behaviors of BB WSOM with Cu(II) in relevant atmospheric environments.
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•Metal-binding characteristics of BB WSOM were comprehensively investigated.•WSOM bound with Cu(II) more strongly at high pH values than at low ones.•Protein-like substances in WSOM displayed a preferential interaction with Cu(II).•Tryptophan-like components exhibited higher binding capacity than humic-like ones.
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•Comprehensive survey review on versatile applications of 2D-COS for the last two years.•Dramatic increasing of 2D-COS applications for variations in concentration, pH, and relative ...compositions.•Significantly emerged 2D-COS applications in environments and natural products.
In this review, the comprehensive summary of two-dimensional correlation spectroscopy (2D-COS) for the last two years is covered. The remarkable applications of 2D-COS in diverse fields using many types of probes and perturbations for the last two years are highlighted. IR spectroscopy is still the most popular probe in 2D-COS during the last two years. Applications in fluorescence and Raman spectroscopy are also very popularly used. In the external perturbations applied in 2D-COS, variations in concentration, pH, and relative compositions are dramatically increased during the last two years. Temperature is still the most used effect, but it is slightly decreased compared to two years ago. 2D-COS has been applied to diverse systems, such as environments, natural products, polymers, food, proteins and peptides, solutions, mixtures, nano materials, pharmaceuticals, and others. Especially, biological and environmental applications have significantly emerged. This survey review paper shows that 2D-COS is an actively evolving and expanding field.
This study explored the interacting mechanism between pristine and aged polypropylene microplastics (PP-MPs) and extracellular polymeric substances (EPS) in the natural water environment. ...Three-dimensional excitation-emission matrix (3D-EEM) spectra displayed that the change in the fluorescence components of EPS were induced by high PP-MPs concentrations. Two-dimensional correlation spectroscopy (2D-COS) revealed that the order of EPS structural change was the phosphate groups, CO, COO–, C–O–C, CO and OH. From the scanning electron microscopy (SEM) images, it was observed that the surfaces of aged PP-MPs were rougher after interaction with EPS. The carbonyl index (CI) of FT-IR and the O/C ratio of X-ray photoelectron spectroscopy (XPS) showed that the addition of EPS increased the oxygen-containing groups and accelerated the surface oxidation of MPs. 2D-COS showed that CH in pristine PP-MPs and OH in aged PP-MPs were most affected by EPS, respectively. XPS further explained the oxidation mechanism of PP-MPs by EPS: the initial CC firstly formed CO bond, and was finally transformed into O–C=O. The aged PP-MPs interacted more strongly with EPS and there was a higher affinity between them. This work will contribute to better understand the interaction between MPs and EPS and to assess the ecological risks to MPs.
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•High concentrations of PP-MPs induced the changes in the fluorescent components of EPS.•Phosphate group of EPS was the most sensitive to changes of PP-MPs concentrations.•OH of alcohol in aged PP-MPs were most affected by EPS.•Aged PP-MPs surface roughness increased significantly after the interaction with EPS.•Oxygen-containing groups of aged PP-MPs increased after interaction with EPS.
