Two-dimensional Correlation Spectroscopy Research Articles

Exploring the influence of sludge dewatering agents on Microplastic aging under hydrothermal treatment: Insights from Polylactic Acid microplastics

In this research, we examined the combined effects of hydrothermal treatment and different dewatering agents on the morphological, molecular, and functional properties of Polylactic Acid Microplastics (PLA-MPs). Under hydrothermal treatments, the presence of dewatering agents leads to pronounced alterations in PLA-MPs as evidenced by SEM, showing the compound effects of both treatments. In detail, PFS (polyferric sulfate) results in an enhanced porosity on the surface, PAC (polyaluminum chloride) imparts a distinct roughness, while Fe/PMS (iron/peroxymonosulfate) leads to surface deterioration with the emergence of larger pores. Fe/PMS exhibits the most significant difference in its impact on microplastics in both water and sludge, significantly reducing molecular weight in water, while its effect becomes minimal in sludge. The carbonyl index (CI) predominantly increases across agents in water treatments, with PAC standing out with a CI of 17.50. Conversely, in sludge environments, the CI displays a decreasing trend, especially with Fe/PMS which shows a CI of 15.00. Additionally, employing FTIR and XPS analyses, this study validates the rise in oxygen-centric functional groups on PLA-MPs post hydrothermal treatments, particularly a marked enhancement in C=O and C–O groups due to Fe/PMS. Two-dimensional correlation spectroscopy revealed a distinct sequence of spectral changes in PLA-MPs. The hydrothermal samples in water showed the earliest structural alterations, whereas the presence of iron and persulfate in sludge led to the most pronounced molecular transitions, emphasizing the intricate interactions of the microplastics with different chemicals. This study highlights the impact of hydrothermal treatment and dewatering agents on the properties of the microplastics.

Co-combustion performances of biomass pyrolysis semi-coke and rapeseed cake: PCA, 2D-COS and full range prediction of M-DAEM via machine learning

Biomass pyrolysis semi-coke (PC) is a refractory byproduct of biomass refinery system, and its efficient downstream disposal is of significance to improve the bioenergy utilization efficiency. Herein, we proposed an environmentally friendly co-combustion strategy to explore the synergistic conversion of PC with agricultural waste rapeseed cake (RC). The co-combustion interaction, kinetics, prediction and emission responses were determined through principal component analysis (PCA), multiple distributed activation energy model (M-DAEM), artificial neural network (ANN) and two-dimensional correlation spectroscopy (2D-COS) analysis. The results indicated that the P/R (mixed) ratio in 1:1 strengthened the reaction rate for main incineration stage, whereas lower P/R ratio advanced the peak temperature and cooperated with temperature range in 730–790 K to facilitate co-combustion synergies. The prediction of the kinetic distribution under all mixed ratios was successfully conducted (R2 = 0.999863) through M-DAEM coupling with ANN, from which the activation energy distribution centers E0 and standard deviation σ were in the ranges of 115.23–270.84 kJ/mol and 2.89–42.11 kJ/mol, respectively. Co-combustion resulted in centralized activation energy distribution, and successfully lowered the reaction energy barriers while augmenting the instantaneous energy release. Meanwhile, the temperature dependency responses of flue gas were varied significantly as a function of mixed ratios and temperatures.

Insights into the morphology-dependent adsorption of aged polystyrene nanoplastics on manganese oxides

Limited research has been conducted on the adsorption behavior of nanoplastics onto manganese oxides with varying morphologies. In this study, four different morphologies of manganese oxides (γ/α/β/ε-phase MnO2) were prepared to explore the relationship between the morphology of manganese oxides and the adsorption efficiency of polystyrene nanoplastics (PSNP) aged by xenon lamp irradiation. The exceptional adsorption capacity exhibited by minerals towards aged PSNP may be attributed to electrostatic attraction. The order in which materials exhibit adsorption capacities is as follows: γ-MnO2 > α-MnO2 > β-MnO2 > ε-MnO2. Fourier transform infrared spectroscopy and two-dimensional correlation spectroscopy reveal a correlation between changes in oxygen-containing functional groups and the sequence in which aged PSNP are adsorbed onto minerals. This study provides valuable insights for further development of manganese oxides with diverse morphologies and an objective assessment of the ecological impact posed by nanoplastics.

Study on removal of oxytetracycline by KOH-modified chestnut shell biochar: Based on two-dimensional spectroscopy and molecular density functional theory

The adsorption type and mode of biochar have been extensive research. However, as an indispensable link to reveal the adsorption mechanism, the study of the adsorption sequence is greatly lacking, especially for different pollutants, the way of adsorption is different. In this study, the observation of the adsorption sequence was amplified by KOH modification and optimization of experimental conditions. Persistent radicals (PFRs) combined with liquid mass spectrometry (LC-MS) eliminated interference from oxidation-reduction. Notability, two-dimensional correlation spectroscopy (2D-COS), Raman and Fourier-transform infrared (FTIR) spectroscopy reveals that the vibration amplitude and velocity of the hydroxyl group are better than those of the carboxyl group, methyl group, and methylene group under time interference. Electrostatic adsorption (EA), H-bood (HB), and π-π* contribute 63.5 %, 35.3 %, and 1.2 %, respectively, to the adsorption of oxytetracycline (OTC). The density functional calculation shows that the nucleophilic and electrophilic reactions of OTC are easy to occur near oxygen atoms and nitrogen atoms. The Fukui function proves that the free radical weight of the N atom is 0.096, which is further confirmed the theoretical predictions by liquid chromatography and four-stage electrostatic field orbital trap mass spectrometry. Finally, this study provides a deeper insight into the biochar adsorption OTC.

An integrated chemical characterization based on FT-NIR, and GC–MS for the comparative metabolite profiling of 3 species of the genus Amomum

BackgroundThe fruits and seeds of genus Amomum are well-known as medicinal plants and edible spices, and are used in countries such as China, India and Vietnam to treat malaria, gastrointestinal disorders and indigestion. The morphological differences between different species are relatively small, and technical characterization and identification techniques are needed. ResultsFourier transform near infrared spectroscopy (FT-NIR) and gas chromatography-mass spectrometry (GC-MS), combined with principal component analysis and two-dimensional correlation analysis were used to characterize the chemical differences of Amomum tsao-ko, Amomum koenigii, and Amomum paratsaoko. The targets and pathways for the treatment of diabetes mellitus in three species were predicted using network pharmacology and screened for the corresponding pharmacodynamic components as potential quality markers. The results of “component-target-pathway” network showed that (+)-Nerolidol, 2-Nonanol, α-Terpineol, α-Pinene, 2-Nonanone had high degree values and may be the main active components. Partial least squares-discriminant analysis (PLS-DA) was further used to select for differential metabolites and was identified as a potential quality marker, 11 in total. PLS-DA and residual network (ResNet) classification models were developed for the identification of 3 species of the genus Amomum, ResNet model is more suitable for the identification study of large volume samples. SignificanceThis study characterizes the differences between the three species in a visual way and also provides a reliable technique for their identification, while demonstrating the ability of FT-NIR spectroscopy for fast, easy and accurate species identification. The results of this study lay the foundation for quality evaluation studies of genus Amomum and provide new ideas for the development of new drugs for the treatment of diabetes mellitus.

Molecular insights into complexation between protein and silica: Spectroscopic and simulation investigations

The synergistic effect of protein-silica complexation leads to exacerbated membrane fouling in the membrane desalination process, exceeding the individual impacts of silica scaling or protein fouling. However, the molecular-level dynamics of silica binding to proteins and the resulting structural changes in both proteins and silica remain poorly understood. This study investigates the complexation process between silica and proteins—negatively charged bovine serum albumin (BSA) and positively charged lysozyme (LYZ) at neutral pH—using infrared spectroscopy (IR), in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and multiple computational simulations. The findings reveal that both protein and silica structures undergo changes during the complexation process, with calcium ions in the solution significantly exacerbating these alterations. In particular, in situ ATR-FTIR combined with two-dimensional correlation spectroscopy analysis shows that BSA experiences more pronounced unfolding, providing additional binding sites for silica adsorption compared to LYZ. The adsorbed proteins promote silica polymerization from lower-polymerized to higher-polymerized species. Furthermore, molecular dynamics simulations demonstrate greater conformational variation in BSA through root-mean-square-deviation analysis and the bridging role of calcium ions via mean square displacement analysis. Molecular docking and density functional theory calculations identify the binding sites and energy of silica on proteins. In summary, this research offers a comprehensive understanding of the protein-silica complexation process, contributing to the knowledge of synergistic behaviors of inorganic scaling and organic fouling on membrane surfaces. The integrated approach used here may also be applicable for exploring other complex complexation processes in various environments.

Origin of rate dispersion in translational diffusion: Distinguishing heterogeneous from homogeneous using 2D correlation analysis

Rate dispersion is commonly observed when measuring relaxation in complex media such as solution of a protein. Its origin is often associated to molecular heterogeneity in the system. However, interpretation of rate dispersion is not straightforward, and it can be exhibited by both heterogeneous (all molecules are different) and homogeneous (all molecules are identical) systems. Here, we report two-dimensional (2D) correlation analysis of intensity fluctuations originating from translational diffusion-lead fluctuations in number of particles simulated in an observation volume resembling fluorescence correlation spectroscopy experiment. Translational diffusion of particles representing a protein having two different conformations are simulated. Homogeneous and heterogeneous systems are simulated to have similar one-dimensional (1D) autocorrelation curves with comparable extent of rate dispersion, α ∼ 0.8. Time slices of 2D autocorrelation curves and rate-rate spectra obtained from them clearly demonstrate that similar extent of rate dispersion observed in 1D autocorrelation can originate from both heterogeneous and homogeneous systems. We establish that one-dimensional analysis only reports on the extent of rate dispersion. Two-dimensional analysis reports on the origin of rate dispersion and distinguishes heterogeneous from homogeneous.

Interactions between cellulose and lignin during pyrolysis: Evolutions of condensed-phase functional groups and gas-phase volatile fraction

Understanding cellulose-lignin interactions during biomass pyrolysis is important to improve the overall product distribution and quality. In the current study, the condensed-phase cellulose-lignin interactions during biomass pyrolysis from 100° to 600°C were systematically investigated with in-situ diffuse reflectance infrared Fourier transform spectroscopy and modified perturbation correlation moving-window two-dimensional correlation spectroscopy. It was found that compared to the individual component pyrolysis, the decomposition peak, evident by thermogravimetric analysis, of cellulose-lignin co-pyrolysis became wider and shifted to higher temperature range. The cellulose-lignin interactions further promoted the formations of char, and H2O, CH3/CH2, CO, aromatic-containing compounds. With simultaneous IR identification of gaseous products and condensed-phase remaining, the detailed interaction mechanism was elucidated as: 1) hydrogen donation from cellulose hydroxyl to lignin Cα could promote the lignin rearrangement at low temperature range through quinone methide structure; 2) the reactive species from homolytic cracking of lignin could abstract hydrogen from CH/CH2 groups of cellulose to generate phenolic compounds; 3) dehydration reactions of cellulose was therefore enhanced to promote char formation.

The effect and spectral response mechanism of dissolved organic matter (DOM) in Pb(II) adsorption onto biochar

This study investigated the interaction of biochar-derived dissolved organic matter (DOM) and metal pollutant Pb(II) during adsorption. Research data showed that the adsorption capacity of biochar and residual biochar (after removal of DOM) was 277.62 and 204.47 mg g−1, respectively, indicating that DOM played a significant role in enhancing the adsorption efficiency of Pb(II). The results indicated that the adsorption process of Pb(II) on biochar and residual biochar followed the pseudo-second-order kinetic equation (R2 > 0.99), and the adsorption isotherm was much closer Freundlich model. A combination of three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence, Fourier transform infrared spectroscopy (FT-IR), and two-dimensional correlation spectroscopy (2D-COS) was employed to investigate the interaction between DOM and Pb(II). 3D-EEM indicated the presence of four major components of DOM, namely two protein-like substances, one humic acid-like substance, and one fulvic acid-like substance. The synchronous fluorescence revealed a gradual quenching of the fluorescence of the DOM sample with an increase in Pb(II) concentration, indicating a static quenching mechanism between DOM and Pb(II). FTIR-2D-COS analysis showed a specific sequence of DOM binding with Pb(II) is as follows: 1500 > 1010 > 880 > 1390 > 1260 cm−1. This findings have significant implications for the role of DOM in environmental science and have potential applications in various fields.

Raman identification of adulteration in poly-alpha-olefin synthetic lubricant using principal component analysis and two-dimensional correlation spectroscopy

Poly-alpha-olefin (PAO) synthetic lubricating oil provides significant advantages over mineral oil. Highly discerning methods of PAO adulteration with inexpensive mineral oil is crucial to promote energy conservation and emission reduction and safeguard the rights of consumers. In this research, conventional principal component analysis (PCA), modified principal component analysis (MPCA) and two-dimensional correlation spectroscopy (2D-COS) with temperature as perturbation factor were used for Raman identification of PAO adulteration with 5 %, 20 % and 50 % mineral oil (150 N). The influence of spectrum normalization on identification was also studied. When using maximum intensity normalization, the modified principal component analysis is more efficient than the conventional PCA and can distinguish the adulterated oil from the authentic PAO even when the adulteration ratio decreases to 5 %. Comparably, the conventional PCA can distinguish the adulteration with 5 % mineral oil by using peak area normalization. These results suggest that the area normalization is prior to the maximum intensity normalization for PCA identification, as attributed to that the maximum intensity normalization might weaken the intensity difference of strongest peak among different samples. By either peak area or maximum intensity normalization, the difference between the authentic and the adulterated PAO can be detected by synchronous 2D-COS, in which both the autocorrelation peak at 2843 cm−1 and the negative cross correlation peak at (2843, 2935 cm−1) become weakened along with the increase of adulteration ratio. This work can provide important technical support to ensure the safe operation of equipment and crack down on the illegal trade of counterfeit synthetic lubricants.

Photochemical behavior of dissolved organic matter derived from Alternanthera philoxeroides hydrochar: Insights from molecular transformation and photochemically reactive intermediates

Hydrochar-derived dissolved organic matter (HDOM) enters aquatic ecosystems through soil leaching and surface runoff following the application of hydrochar. However, the photochemical behavior of HDOM remains unclear. The photo-transformation of HDOM was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), multiple spectroscopy methods, high-performance liquid chromatography, and combining synchronous fluorescence and Fourier-transform infrared spectroscopy with two-dimensional correlation spectroscopy. The results showed that with the increase of carbonization temperature, amide II in protein-like substances were observed to be preferentially photolyzed, and the protein-like substances were more sensitive to low irradiation time, while the duration time of the photochemical behavior of amide II and aliphatic C−H were more persistent. FT-ICR MS results showed that N and S-containing molecules, including lignins and lipids were more sensitive to ultraviolet irradiation. Furthermore, the photo-transformation of HDOMs was accompanied by the generation of triple excited state dissolved organic matter and singlet oxygen. Our findings will be beneficial for understanding the mechanisms of photo-transformation of HDOM and for predicting the possible behaviors of hydrochar produced at different temperatures before large-scale application.

Highly efficient and targeted adsorption of Congo Red in a novel cationic copper-organic framework with three-dimensional cages

Metal-organic frameworks (MOFs) with a three-dimensional (3D) caged structure and charged networks are promising adsorbents for separation and purification applications. However, it is a challenge to synthesize the MOFs in crystalline structures with a targeted ability of efficiently removing and reutilizing the individual diazo dye from sewage. Here, we report the synthesis of a novel copper-organic framework (Cu-MOF) with a 3D caged stucture and cationic networks using CuCl2 and a triazole ligand (methyl-1H-1,2,4-triazole-3-carboxylate MTC). The novel Cu-MOF exhibited highly efficient and targeted adsorption, separation and recovery characteristics for Congo Red (CR). Specifically, the maximal adsorption capacity was 119.76 mg·g−1, and the adsorbed CR can be efficiently released in NaCl-DMF solution with a recovery rate of almost 100%. After suffered from three adsorption–desorption cycles, the Cu-MOF could still reach a adsorption rate of >85% and maintain an intact skeleton structure. The batch-equilibrium experiment combined with density functional theory calculation further revealed that the adsorption process was spontaneous and exothermic, following the pseudo-second-order kinetic equation with monolayer diffusion. The specific adsorption of Cu-MOF for CR was precisely generated through electronic interaction with the –NH2 and -SO3 groups, exhibiting the adsorption energies of −2.16 eV and −2.04 eV, respectively. The two-dimensional correlation spectroscopy analysis comfirmed that the energy distribution in CR adsorption was dominated by electrostatic interactions, followed by π-π stacking and van der Waals interactions. In summary, our work not only presents a promising strategy for the targeted separation and purification of CR from wastewater, but also contributes to the design of highly efficient MOF-adsorbents for other organic pollutants.

Characterizing dissolved organic matter and bacterial community interactions in a river network under anthropogenic landcover

Anthropogenic landcover could rise nutrient concentrations and impact the characteristics and bioavailability of dissolved organic matter (DOM) in a river network. Exploring the interactions between DOM and microbials might be conducive to revealing biogeochemistry behaviors of organic matter. In this study, synchronous fluorescence spectra (SFS) with Gaussian band fitting and two-dimensional correlation spectroscopy (2D-COS) were employed to identify DOM fractions and reveal their interactions with bacterial communities. DOM was extracted from a river network under eco-agricultural rural (RUR), eco-residential urban (URB), eco-economical town (TOW), and eco-industrial park (IND) regions in Jiashan Plain of eastern China. The overlapping peaks observed in the SFS were successfully separated into four fractions using Gaussian band fitting, i.e., tyrosine-like fluorescence (TYLF), tryptophan-like fluorescence (TRLF), microbial humic-like fluorescence (MHLF), and fulvic-like fluorescence (FLF) materials. Across all four regions, TRLF (44.79% ± 7.74%) and TYLF (48.09% ± 8.85%) were the dominant components. Based on 2D-COS, variations of TYLF and TRLF were extremely larger than those of FLF in RUR-TOW. However, in URB-IND, the former exhibited lower variations compared to the latter. These suggested that FLF be likely derived continuously from lignin and other residue of terrestrial plant origin along the river network, and TYLF and TRLF be originated discontinuously from domestic wastewater in RUR-TOW. By high-throughput sequenced OTUs, the number of organisms in RUR-TOW could be higher than those in URB-IND, while genes associated with carbohydrate metabolism were lower in former than those in the latter. According to co-occurrence networks, microbes could promote the production of TYLF and TRLF in RUR-TOW. In contrast, microbial communities in URB-IND might contribute to decompose FLF. The obtained results could not only reveal interactions between DOM fractions and bacterial communities in the river network, but this methodology may be applied to other water bodies from different landscapes.

Adsorption Mechanisms of Glyphosate on Ferrihydrite: Effects of Al Substitution and Aggregation State.

Ferrihydrite is one of the most reactive iron (Fe) (oxyhydr)oxides in soils, but the adsorption mechanisms of glyphosate, the most widely used herbicide, on ferrihydrite remain unknown. Here, we determined the adsorption mechanisms of glyphosate on pristine and Al-substituted ferrihydrites with aggregated and dispersed states using macroscopic adsorption experiments, zeta potential, phosphorus K-edge X-ray absorption near-edge structure spectroscopy, in situ attenuated total reflectance Fourier transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy, and multivariate curve resolution analyses. Aggregation of ferrihydrite decreases the glyphosate adsorption capacity. The partial substitution of Al in ferrihydrite inhibits glyphosate adsorption on aggregated ferrihydrite due to the decrease of external specific surface area, while it promotes glyphosate adsorption on dispersed ferrihydrite, which is ascribed to the increase of surface positive charge. Glyphosate predominately forms protonated and deprotonated, depending on the sorption pH, monodentate-mononuclear complexes (MMH1/MMH0, 77-90%) on ferrihydrites, besides minor deprotonated bidentate-binuclear complexes (BBH0, 23-10%). Both Al incorporation and a low pH favor the formation of the BB complex. The adsorbed glyphosate preferentially forms the MM complex on ferrihydrite and preferentially bonds with the Al-OH sites on Al-substituted ferrihydrite. These new insights are expected to be useful in predicting the environmental fate of glyphosate in ferrihydrite-rich environments.

Applying fluorescence spectroscopy and DNA pyrosequencing with 2D-COS and co-occurrence network to deconstruct dynamical DOM degradation of air-land-water sources in an urban river

In an urban river, comprehending the interplay between dissolved organic matter (DOM) and atmospheric, terrestrial, and aquatic sources is crucial. This encompassed investigating temporal variations in DOM and its association with the bacterioplankton community to gain profound insights into the biogeochemical dynamics and biodegradability of DOM. DOM was extracted from PM2.5, soil, sediment, bait, and terrestrial/aquatic plant residuals collected along the Wenyuhe River in Beijing, China - a region predominantly supplied with reclaimed water. Subsequently, mixed microbial communities from the river were introduced into DOM samples originating from each source and incubated for 10 days. Principal component analysis (PCA) applied to reassembled excitation-emission matrix (EEM) data revealed two distinct clusters: cluster 1 comprising soil, sediment, and PM2.5 samples; and cluster 2 consisting of bait as well as terrestrial/aquatic plant residuals. According to parallel factor analysis, C1 (microbial humic-like) and C2-C3 (fulvic-like) dominated the DOM from soil, sediment, and PM2.5. These components were continuously degraded during incubation, except for PM2.5. DOM from bait and terrestrial/aquatic plants contained representative components of C6 (phenolic-like) and C7 (tryptophan-like), which underwent extensive decomposition. Interestingly, DOM in PM2.5 contained aliphatic compounds and polycyclic aromatic hydrocarbons (PAHs) but exhibited weak degradation with the complete disappearance of C6 and C7. Rhodococcus was a unique species capable of degrading PAHs, which might be particularly important considering the specificity of PM2.5 pollution. Based on two-dimensional correlation spectroscopy (2D-COS), variations in DOM components such as C6, and C7 were significantly larger compared to those of C1, C2, C3, and C5 (terrestrial humic-like) from bait samples, sediments, and residual terrestrial plants. MW-2D-COS analysis revealed that DOM from bait samples and terrestrial/aquatic plants experienced substantial degradation by the second day while DOM from soil or sediment decomposed mainly on the fourth day. Notably, the decomposition of DOM fractions in PM2.5 occurred throughout the entire four-day period. Co-occurrence network analysis classified sources of DOM into two clusters similar to PCA results: cluster 1 showed significant microbial degradation of fulvic-like compounds while cluster 2 demonstrated deep microbial decomposition of tyrosine-like and phenolic compounds. Therefore, the artificial loading of DOM into rivers not only expands the chemical diversity within DOM but also perturbs bacterioplankton diversities.

Reinterpret the heterogeneous reaction of α-Fe2O3 and NO2 with 2D-COS: The role of SDS, UV and SO2

Heterogeneous reaction of mineral aerosols and atmospheric polluting gases play an important role in atmospheric chemistry. In this study, the reactions of NO2 with or without SO2 mixture gas on the surface of α-Fe2O3 particles under dry conditions were studied. The effects of sodium dodecyl sulfate (SDS) and the heterogeneous reaction under both dark and UV irradiation conditions were investigated. The infrared spectrum analyzed by the two-dimensional correlation spectroscopy (2D-COS) was used to obtain the products formation sequences. The results showed that UV irradiation can promote the production of nitrate. The 2D-COS analysis indicated SDS changed the sequence order of nitrate and nitrite species during reactions. In oxidation conditions, the final product of heterogeneous reaction of NO2 and α-Fe2O3 was monodentate nitrate. Only the heterogenous reaction of NO2 and α-Fe2O3 containing SDS (FOS) without UV light, the final product was bidentate nitrate. SDS was the catalysis agent supply and photoresist to the system. With surface active compounds, the environmental lifetime of heterogeneous reactions between trace gases and aerosols extends. Surfactants, ultraviolet light, and the types of gases involved in the reaction all have complex effects on the aerosol aging process. This study provided a reference for subsequent heterogeneous reaction studies and the formation of aerosols.

Simultaneous enhancement on lignocellulose degradation and humic acid formation using the electric field coupled with an iron anode in the co-composting of food waste and agricultural waste

The co-composting of food waste and agricultural waste presents a promising biotechnology for mitigating the challenges of organic solid waste treatment. However, the low degradation rate of lignocellulosic content hindered its application. This study explored a novel approach that employs an electric field coupled with an Fe anode to accelerate crude fiber decomposition and humic acid formation in a composting system. The results demonstrated that the group subjected to direct current exposure matched Fe anode (EF) exhibited the lowest crude fiber content, supported by observed loose cellulose structures using a confocal laser scanning microscope. The humic acid content in EF was also superior, exceeding both the control group without direct current exposure (CK) and with direct current exposure matched carbon anode (EA) by 72.5% and 29.3%, respectively. Two-dimensional FTIR correlation spectroscopy analysis revealed that this technology leveraged the intermediate products of lignocellulose degradation to provide a stable core structure for humic acid formation, promoting the highest humification degree. Microbial community analysis indicated that the enriched dominant phylum Firmicutes in EF was responsible for crude fiber degradation. Metagenomics analysis further suggested that the upregulations of carbohydrate-active enzymes with the signal peptide and reactive oxygen species formation triggered by microorganisms contributed to the crude fiber decomposition. This study demonstrates an efficient technology for improving composting quality.

2D gradient and correlation FTIR analyses for optimizing thermal curing process of commercial-grade polyurethane coatings for automotive interior parts

Soft-feel coatings for automotive interior parts are a crucial factor in consumer purchase preferences owing to the growing awareness of human sensibility ergonomics. Herein, the thermal curing of commercial-grade polyurethane (PU) coatings was optimized using advanced spectroscopic tools. Conventional FTIR spectra were collected at various curing temperatures and times, and analyzed using two-dimensional (2D) gradient maps and 2D correlation spectroscopy (2D COS); while the former demonstrates the spectral variation trend with curing time, the latter provides whole spectral sequences that inform the cure reaction mechanism. The thermal curing continued for 50 min at 60 and 70 °C, and was halted after 30 min above 80 °C. According to the 2D COS and kinetic model fitting, the cure reaction was initiated by solvent evaporation and followed nucleation and growth mechanisms. PUs cured at lower temperatures were ductile owing to incomplete reactions, whereas PUs cured above 80 °C exhibited brittle features. Consequently, the optimal curing process was determined to be at 80 °C for 30 min. The 2D FTIR analytic tools can be useful in the development of high-quality soft-feel coatings for automotive interior parts.

Effects of photochlorination on the physicochemical transformation of polystyrene nanoplastics: Mechanism and environmental fate.

With the increasingly severe plastic pollution, the environmental behavior and effects of nanoplastics (NPs) have attracted much attention. The transformation of NPs in natural and engineered environments (e.g., photooxidation, disinfection) can significantly alter the physicochemical properties and thus affect the fate and toxicity of NPs. However, how solar irradiation with free chlorine, an inevitable process once NPs enter the environment from wastewater treatment plants, affects the physicochemical properties of NPs is still unclear. In this study, the behavior and mechanism of polystyrene (PS) NPs transformation in the solar/chlorine process were evaluated. The results demonstrated that solar irradiation significantly enhanced the physicochemical transformation of PS NPs during chlorination, including chain scission, surface oxidation, and organic release. In addition, two-dimensional correlation spectroscopy analysis using Fourier transform infrared spectroscopy and reactive species quenching experiments showed that chain scission and surface oxidation of PS NPs were primarily caused by direct oxidation of hydroxyl radicals and ozone, while reactive chlorine species played an indirect role. Moreover, photochlorination-induced changes in the properties of PS NPs enhanced the colloidal stability in synthetic wastewater solution and toxicity to Caenorhabditis elegans. These findings reveal an important transformation behavior of nanoplastics in the environment and emphasize the importance of accounting for photochlorination to accurately assess the ecological risk of nanoplastics.

Evolutions of dissolved organic matter and disinfection by-products formation in source water during UV-LED (275 nm)/chlorine process.

Ultraviolet light-emitting diode (UV-LED) is a promising option for the traditional low-pressure UV lamp, but the evolutions of DOM composition, the formation of disinfection by-products (DBPs) and their toxicity need further study in raw water during UV-LED/chlorine process. In UV-LED (275nm)/chlorine process, two-dimensional correlation spectroscopy (2DCOS) analysis on synchronous fluorescence and UV-vis spectra indicated the protein-like fractions responded faster than the humic-like components, the reactive sequence of peaks for DOM followed the order: 340 nm→240 nm→410 nm→205 nm→290nm. Compared to chlorination for 30 mins, the UV-LED/chlorine process enhanced the degradation efficiency of three fluorescent components (humic-like, tryptophan-like, tyrosine-like) by 5.1%-46.1%, and the formation of carbonaceous DBPs (C-DBPs) significantly reduced by 43.8% while the formation of nitrogenous DBPs (N-DBPs) increased by 27.3%. The concentrations of C-DBPs increased by 17.8% whereas that of N-DBPs reduced by 30.4% in 24h post-chlorination. The concentrations of brominated DBPs increased by 17.2% during UV-LED/chlorine process, and further increased by 18.5% in 24h post-chlorination. According to the results of principal component analysis, the non-fluorescent components of DOM might be important precursors in the formation of haloketones, haloacetonitriles and halonitromethanes during UV-LED/chlorine process. Unlike chlorine treatment, the reaction of DOM in UV-LED/chlorine treatment generated fewer unknown DBPs. Compared with chlorination, the cytotoxicity of C-DBPs reduced but the cytotoxicity of both N-DBPs and Br-DBPs increased during UV-LED/chlorine process. Dichloroacetonitrile had the highest cytotoxicity, followed by monobromoacetic acid, bromochloroacetonitrile and trichloroacetic acid during 30 mins of UV-LED/chlorine process. Therefore, besides N-DBPs, the more toxic Br-DBPs formation in bromide-containing water is also not negligible in the practical applications of UV-LED (275nm)/chlorine process.