Two-dimensional Correlation Spectroscopy Research Articles

Revealing the Inner Changes of Component Composition Derived from DOM PARAFAC Based on Two-Dimensional Correlation Spectroscopy.

Plenty of humic acid components compositions are contained in dissolved organic matter (DOM) derived from composting. Fluorescence signals were employed to characterize the changes in DOM components in the component process. In the composting process, five individual DOM fluorescence parallel factor analysis (PARAFAC) components were identified. At the end of the composting, PARAFAC component C5, which represented high humification and complex structure compounds, was detected, but the simple structure DOM PARAFAC component C1 was absent. In this study, a technique combining EEM-PARAFAC with two-dimensional correlation spectroscopy (2DCOS) further supplied detailed information about the dynamics of DOM peaks in PARAFAC components. 2DCOS results showed that the variation of the peaks in PARAFAC components was different in the composting process. The formation of a complex DOM fluorescence substance was attributed to the residues from the simple fluorescence peak degradation. The evolution of the DOM fluorescence peaks in each PARAFAC component indicated that simple structure compounds helped the formation of the complex DOM fluorescence substance in the composting process. These results revealed that EEM/PARAFAC combined with 2DCOS could be used to track the evolution of DOM PARAFAC components during the composting process.

Two-directional two-dimensional fractional-order embedding canonical correlation analysis for multi-view dimensionality reduction and set-based video recognition

Set-based video recognition is an important application in practice, and many specialized approaches have been proposed. However, most of these methods either only use one kind of visual features for classification, or are sensitive to the noises and the number of training images when using several kinds of features, resulting in limited discrimination. To explore a possible solution to these issues, in this paper, a novel efficiently and effectively dimensionality reduction method, named two-directional two-dimensional fractional-order embedding canonical correlation analysis ((2D)2FECCA), is proposed. (2D)2FECCA borrows the idea of fractional-order embedding to correct the estimation of sample covariance matrices, which can significantly reduce the influence of noise disturbance and effectively utilizing the discriminative information from different view features. In addition, several set-based video recognition schemes are introduced to determine the labels of the test videos. Extensive experimental results on four familiar single image based databases and two video based benchmark databases demonstrate the effectiveness of the proposed method. These quantitative assessments reinforce the significance as well as the importance of embedding the proposed method in other intelligent systems application areas.

Study on the performance and mechanism of bio-electrochemical system to mitigate membrane fouling in bioreactors

To alleviate membrane fouling, a membrane of the membrane bioreactor was directly used as the anode of the bio-electrochemical system. On the 14th day, the control group had blocked, while the experimental group with a current of 0.44 mA, the increase in ΔTMP was only 2.2 kPa. The polysaccharide and protein concentrations in the open-circuit group were 4.2 and 2.9 times higher than those in the closed-circuit group, respectively. Three-dimensional fluorescence spectroscopy and gas chromatography mass spectrometry showed that most of the deposition in the control group contained high-molecular-weight compounds, especially long-chain ester derivatives, phenols, and complex hydrocarbons, whereas the experimental group was the opposite. Therefore, current (electrons) can change the composition of the cake layer. High-throughput sequencing indicated that a significantly higher abundance of electroactive microorganisms on the experimental than control group. Two-dimensional correlation spectroscopy showed that electrons promote the degradation of polysaccharides, thereby alleviating membrane fouling.

Insight into the Soil Dissolved Organic Matter Ligand-Phenanthrene-Binding Properties Based on Parallel Faction Analysis Combined with Two-Dimensional Correlation Spectroscopy.

Dissolved organic matter (DOM) can strongly bind to organic contaminants and control phenanthrene in soil. Herein, four individual parallel factor analysis (PARAFAC) components were found in soil DOM. Component C1 was the humic-like component ligand T, and component C2 was a combination of humic fluorophore ligands M1 and M2. Furthermore, components C3 and C4 were characterized as terrestrial and ubiquitous humic substances. Then, the modified Stern-Volmer complexation model was used to reveal soil DOM component-phenanthrene-binding properties. The overall binding characteristics of a PARAFAC component could not express the phenanthrene-binding properties. Therefore, two-dimensional correlation spectroscopy was used to reveal DOM ligand-phenanthrene-binding properties. After binding with phenanthrene, DOM ligands T, M2, A2, and C1 were quenched but DOM ligands M1, A1, and C2 were excited. The ligands with higher humification presented higher phenanthrene-binding ability. With these promising results, the DOM ligand-phenanthrene-binding characteristics offered theoretical support for soil pollution control.

New insights into the adsorption behavior of thiacloprid at the microfibers/water interface: Role of humic acid

Dissolved organic matter regulates the interaction between microplastics (MPs) and organic pollutants. Here, this paper investigated the effect and mechanism of humic acid (HA) on the adsorption behavior of thiacloprid at two microfibers (MFs)/water interface, and compared the differences in the performance of MFs and pure MPs. The results showed that 10 mg L−1 HA decreased the adsorption capacity and the partition coefficient KD of thiacloprid on MFs and pure MPs. Spectral analysis showed that HA could form hydrogen bonds and van der Waals forces with both MPs and thiacloprid, ultimately affecting the adsorption behavior of thiacloprid at MPs/water interface via competitive adsorption and bridging effect. Furthermore, two-dimensional correlation spectroscopy demonstrated that thiacloprid was preferentially adsorbed onto MPs compared with HA. Finally, density functional theory calculation demonstrated that phenolic-OH, –COOH, and alcoholic-OH played critical roles in competing adsorption and bridging effect. This study offers a theoretical foundation for a better comprehension of the adsorption behavior of organic pollutants at the MPs/water interface.

The molecular nature of the eliminating azeotropy of dimethyl carbonate–ethanol system by ionic liquid entrainer

Ionic liquids (ILs) have unique physicochemical features, such as insignificant vapour pressure, which make ILs excellent entrainers in extractive distillation to separate the azeotrope. For better utilization of the IL entrainer in extractive distillation, the microstructure properties of dimethyl carbonate (DMC)–ethanol azeotrope mixtures, before and after the separation breaking of the azeotrope by IL, were studied by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations with focus on the vibrational region of the ethanol hydroxyl group. Excess spectroscopy followed by two-dimensional correlation spectroscopy (2D-COS) was performed on the original IR spectra to extract the microstructural features of different mixtures step by step. Different sizes of ethanol self-aggregations, DMC–ethanol interaction complex and different IL–ethanol interaction complexes were identified in different mixtures. Specifically, the DMC–ethanol interaction complex existed in both the DMC–ethanol and IL–DMC–ethanol systems at lower IL concentrations (x(IL) < 0.125) while broken out by IL at higher IL concentrations (x(IL) > 0.125). The intrinsic cause of the azeotrope breaking by the 1-hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide ([HMIM][Tf2N]) entrainer was revealed to be the disappearance of the DMC–ethanol interaction complex by the IL at higher IL concentrations. The hydrogen-bonds between DMC/IL and ethanol were also identified and confirmed in the DMC–ethanol and different IL–ethanol interaction complexes. Both the oxygen atom and the hydrogen atom in the hydroxyl group of ethanol participated in the hydrogen-bond, which confirmed the sensitivity of the hydroxyl group vibrational region. The hydrogen-bonds are weak strength, closed shells and electrostatic dominant interactions.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low‐impact development facilities

Sulfadiazine (SD) is a common antibiotic administered to treat bacterial infections in livestock, and its fate and migration are greatly affected by dissolved organic matter (DOM). The soil infiltration system [a typical low-impact development (LID) facility] can significantly alter DOM properties during runoff pollution, thus affecting the complexation of SD with DOM. Here, the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques (excitation–emission matrices, parallel factor analysis, and synchronous fluorescence spectroscopy). Combined with the weakening of DOM fluorescence intensity and 78.63% reduction in mean SD concentration following treatment, synchronous degradation may have occurred. The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy. Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM. Moreover, hydrophobic protein-like substances exhibited higher log KM values than other fluorescent components, indicating that protein-like components play significant roles in SD complexation. The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances. Thus, SD–DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.

Separation of the overlapped humic acid and BGP characteristic peaks using two-dimensional correlation fluorescence-UV-vis spectroscopy

Fluorescence spectroscopy has been widely used to detect polycyclic aromatic hydrocarbons (PAHs) in the environment. However, the interference of coexisting humic acids (HA) in the environment poses a great challenge to the qualitative and quantitative detection of PAHs using fluorescence spectroscopy. In this study, the spectral properties of benzo [ghi] perylene (BGP) and HA were investigated based on fluorescence and UV–vis spectroscopy combined with two-dimensional (2D) correlation analysis. Under the external disturbance of HA concentration, the homo-2D (fluorescence, UV–visible) correlation and hetero-2D fluorescence-UV–visible correlation spectral characteristics of the mixed samples of HA and BGP were studied, and the effect of HA on the fluorescence of BGP was investigated. It can be inferred that the fluorescence peak at 478 nm come from BGP, and the fluorescence peaks at 442 nm and 533 nm, UV absorption peak at 233 nm come from HA. Meanwhile, asynchronous two-trace two-dimensional (2T2D) fluorescence correlation slice spectra at 533 nm were obtained. The slice spectral intensity at 478 nm was extracted to quantify the BGP concentration in mixture. The results showed that the slice spectral intensity and BGP concentration had a good linear relationship with the coefficient of determination R2 = 0.96. This research provides a way to further study the separation method of HA and PAHs or explore the correction method of the effect of HA on PAHs.

Two-Dimensional Clustering of Spectral Changes for the Interpretation of Raman Hyperspectra.

Two-dimensional correlation spectroscopy (2D-COS) is a technique that permits the examination of synchronous and asynchronous changes present in hyperspectral data. It produces two-dimensional correlation coefficient maps that represent the mutually correlated changes occurring at all Raman wavenumbers during an implemented perturbation. To focus our analysis on clusters of wavenumbers that tend to change together, we apply a k-means clustering to the wavenumber profiles in the perturbation domain decomposition of the two-dimensional correlation coefficient map. These profiles (or trends) reflect peak intensity changes as a function of the perturbation. We then plot the co-occurrences of cluster members two-dimensionally in a manner analogous to a two-dimensional correlation coefficient map. Because wavenumber profiles are clustered based on their similarity, two-dimensional cluster member spectra reveal which Raman peaks change in a similar manner, rather than how much they are correlated. Furthermore, clustering produces a discrete partitioning of the wavenumbers, thus a two-dimensional cluster member spectrum exhibits a discrete presentation of related Raman peaks as opposed to the more continuous representations in a two-dimensional correlation coefficient map. We demonstrate first the basic principles of the technique with the aid of synthetic data. We then apply it to Raman spectra obtained from a polystyrene perchlorate model system followed by Raman spectra from mammalian cells fixed with different percentages of methanol. Both data sets were designed to produce differential changes in sample components. In both cases, all the peaks pertaining to a given component should then change in a similar manner. We observed that component-based profile clustering did occur for polystyrene and perchlorate in the model system and lipids, nucleic acids, and proteins in the mammalian cell example. This confirmed that the method can translate to "real world" samples. We contrast these results with two-dimensional correlation spectroscopy results. To supplement interpretation, we present the cluster-segmented mean spectrum of the hyperspectral data. Overall, this technique is expected to be a valuable adjunct to two-dimensional correlation spectroscopy to further facilitate hyperspectral data interpretation and analysis.

Detection and visualization of soybean protein powder in ground beef using visible and near-infrared hyperspectral imaging

The undeclared addition of soybean proteins in meats is a serious problem due to health and economic reasons. This paper proposes a methodology for quantitative determination and rapid visualization of soybean protein powder (SPP) addition in ground beef using hyperspectral imaging (HSI). Hyperspectral images of a total of 256 samples with different SPP contents were acquired by HSI system in spectral range of 400–1000 nm. Regions of interest (ROIs) were identified to withstand interference of background and containers to extract spectra. Principal component analysis (PCA) of extracted spectra found that PC1 and PC2 were effective for grouping samples into different levels. Gray level co-occurrence matrix (GLCM) algorithm was thus applied on the corresponding first two PC score images to extract eight texture features. Partial least squares regression (PLSR) was used to establish quantitative models, yielding the optimal correlation coefficient in prediction (Rp) of 0.9979 and residual predictive deviation (RPD) of 14.48 using standard normal variate (SNV) followed by detrending preprocessed spectra. Deming and Passing-Bablok regression were also conducted, and HSI results revealed high model performance which can be interchanged with laboratory standard. Key wavelengths were selected using PC loadings, two-dimensional correlation spectroscopy (2D-COS) and regression coefficients (RC), respectively. After that, PLSR models were evaluated with various inputs, and results showed spectra played predominate role rather than texture. Consequently, simplified PLSR model based on six selected wavelengths from PC loadings was retained with Rp = 0.9933, RPD = 8.45 and limit of detection (LOD) of 0.74%. Colorful spatial distribution maps were successfully created to clearly observe SPP adulteration levels. Current study indicates that HSI has high potential for determining and visualizing SPP adulteration in ground beef.

The role of organic and inorganic substituents of roxarsone determines its binding behavior and mechanisms onto nano-ferrihydrite colloidal particles

The retention and fate of Roxarsone (ROX) onto typical reactive soil minerals were crucial for evaluating its potential environmental risk. However, the behavior and molecular-level reaction mechanism of ROX and its substituents with iron (hydr)oxides remains unclear. Herein, the binding behavior of ROX on ferrihydrite (Fh) was investigated through batch experiments and in-situ ATR-FTIR techniques. Our results demonstrated that Fh is an effective geo-sorbent for the retention of ROX. The pseudo-second-order kinetic and the Langmuir model successfully described the sorption process. The driving force for the binding of ROX on Fh was ascribed to the chemical adsorption, and the rate-limiting step is simultaneously dominated by intraparticle and film diffusion. Isotherms results revealed that the sorption of ROX onto Fh appeared in uniformly distributed monolayer adsorption sites. The two-dimensional correlation spectroscopy and XPS results implied that the nitro, hydroxyl, and arsenate moiety of ROX molecules have participated in binding ROX onto Fh, signifying that the predominated mechanisms were attributed to the hydrogen bonding and surface complexation. Our results can help to better understand the ROX-mineral interactions at the molecular level and lay the foundation for exploring the degradation, transformation, and remediation technologies of ROX and structural analog pollutants in the environment.

Active binding sites for ofloxacin resulted from adsorptive fractionation of humic acid on kaolinite

The adsorptive fractionation of humic acid (HA) at the interface between minerals and water can significantly affect the fate of pollutants in water-soil environment. However, the adsorptive fractionation behavior of HA on kaolinite and its effect on the migration of fluoroquinolones (FQs) have not been fully understood. In this study, fluorescence and infrared spectroscopy, combined with two-dimensional correlation analyses, were used to explore the adsorptive fractionation of humic acid (HA) and its effects on ofloxacin adsorption on kaolinite. The results indicated that humic-like, rather than reduced quinone-like and tyrosine-like, was the main adsorptive fractionation component and preferentially bound to the Al–O sites of kaolinite. The adsorption mechanisms of humic-like and tyrosine-like mainly include hydrogen bonds between acidic functional groups and the Si–O or Al–O groups of kaolinite, n-π electron donor-acceptor interaction and electrostatic attraction. At pH 7.0, with addition of 4.0 and 16.0 mg C/L HA in solution, the adsorptive fractionation of HA on kaolinite led to increases in ofloxacin (in zwitterionic form) adsorption capacity by 1.46 and 3.35 mg/g, respectively. The interactions between ofloxacin and the humic-like were mainly hydrogen bonds and electrostatic attraction. Therefore, the influence of adsorptive fractionation of dissolved organic matter on minerals should be considered in estimating FQs environmental behaviors.

Mechanism of cellulose regeneration from its ionic liquid solution as revealed by infrared spectroscopy

Dissolution followed by regeneration is a typical processing route to cellulose, which triggers much attention in the research of regeneration mechanism, especially for the new solvent ionic liquids (ILs). It has been known that H-bond (HB) interaction between IL and anti-solvent through double diffusion triggers the cellulose regeneration. The structural change including H-bonds transformation mainly during regeneration process is still unclear, however. In the present work, a device for in situ characterization of infrared spectroscopy was set up to monitor the cellulose regeneration from microcrystalline cellulose (MCC)/1-ethyl-3-methylimidazolium acetate ([Emim]Ac) solution. With the help of time-dependent infrared spectroscopy combined with two-dimensional spectral analysis, that is perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and generalized two-dimensional correlation spectroscopy (2DCOS), the mechanism of cellulose regeneration from MCC/[Emim]Ac solution as water diffusion was revealed. We proposed a two-stage model. The diffusion of the free [Emim]Ac and water contributes to the structural changes occurred at the former stage. Water interacts with free IL to form HB W-IL in one hand, and with non-H bonded hydroxyl groups on cellulose to form HB C-W in another hand. HB C-IL is destroyed as water diffusion further at the later stage. Continuous HB C-W is constructed, accompanied by more HB W-IL formation between released anion of [Emim]Ac and water. No crystallization or aggregation of cellulose other than improved regularity of the chain arrangement is revealed by infrared spectroscopy. This study provides a new testing technique for the characterization of H-bonds structures of cellulose on the one hand. On the other hand, it is conductive to the in-depth understanding of the regeneration mechanism of cellulose in ionic liquid systems. 1. A device for in situ characterization of infrared spectroscopy was set up for the research on the cellulose regeneration from MCC/[Emim]Ac solution. 2. Two dimensional spectral analysis including perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and generalized two-dimensional correlation spectroscopy (2DCOS) was used to monitor the H-bonds changes during regeneration process. 3. The characteristic bands located at 3128, 3190, 3367, and 3557 cm −1 was assigned to the H-bonds between water (W), ionic liquid (IL), and cellulose (C), that is HB W-W , HB W-IL , HB C-IL , and HB C-W successfully. 3. A two-stage model involving destruction and reconstruction of H-bonds was proposed for the cellulose regeneration mechanism. HB C-W and HB W-IL are formed on the basis of the destruction of HB C-IL and HB W-W .

Application of 2D-COS-FTIR spectroscopic analysis to milk powder adulteration: Detection of melamine

Milk and its products are important and widely traded food commodities, which made them the target for adulteration. Fourier Transform Infrared spectroscopy (FTIR) is one of the most widely used methods to identify chemical contaminations and determine their concentrations. In the present work, two-dimensional correlation spectroscopy (2D-COS) was applied to analyse FTIR spectra of milk powder having different concentration of melamine. With the help of sequential order analysis, the FTIR band at 815 cm −1 was determined as the most qualified FTIR band for carrying quantitative analysis. It is recommended to perform 2D-COS and determine the sequential order of intensity change among all peaks of the contamination. This is to establish the appropriate bands for quantitative analysis, and help to improve the values of analytical parameters. • FTIR spectrum of milk powder was examined for melamine adulteration. • 2D-COS-FTIR and the sequential analysis were used to determine a quantitative band. • The band at 815 cm −1 was the most qualified band for quantitative analysis. • The proposed method is particularly important when dealing with new adulterations. • FTIR combined with 2D-COS are powerful tools in milk powder adulteration.

A clear view of zeolite-catalyzed processes

Understanding the detailed mechanistic pathways of zeolite-catalyzed reactions enables high activity and product selectivity of desired transformations, crucial for the development of more sustainable and benign methods. However, gaining the knowledge required to delineate detailed mechanisms for these reactions is challenging because of difficulties associated with elucidating the nature of dynamically evolving products and transient intermediates. Approaches in which <i>in situ</i> techniques are combined with two-dimensional correlation analysis have now been developed that enable a clearer analysis of the mechanistic pathways for oxygenate-based zeolite-catalyzed reactions of C₁ molecules.

Insights on the Effect of Heavy Metals on Subcritical Hydrothermal Recycling of Heavy Metal-Contaminated Biomass and Its Derived Porous Carbon Properties Using Cu as a Case

Subcritical hydrothermal liquefaction (HTL) technique has shown great potential in recycling heavy-metal-contaminated biomass derived from phytoremediation and biosorption. However, the effect of heavy metals on the physicochemical characteristics of HTL products and their derivatives has not been elaborated so far. Herein, various Cu content-contaminated derived biomass was recycled by HTL. We found that over 99% of Cu was enriched in hydrochar at 300 °C, enabling us to obtain clean chemicals (e.g., levulinic acid and acetic acid). Furthermore, a large amount of Cu(0) was formed, especially at high temperatures, because HTL products acted as electron donors. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry analysis showed that Cu catalyzed the depolymerization and deoxygenation of macromolecular lignins/carboxylic-rich alicyclic molecule-like compounds, resulting in the production of more levulinic acid. Two-dimensional FTIR correlation spectroscopy analysis indicated that the intensity of C═C increased first, and the intensity of C–O–C decreased later as the Cu content increased. Notably, the low-risk hydrochar could be upgraded into porous carbon (PC) with excellent CO2 capture performance (up to 6.64 mmol/g), whereas Cu enhanced the CO2 capture capacity of PC by increasing its porosity. Undoubtedly, such findings have important implications for recycling heavy-metal-contaminated biomass into high value-added products.

An inevitable but underestimated photoaging behavior of plastic waste in the aquatic environment: Critical role of nitrate

Photoaging is an important reaction for waste plastics in the aquatic environment and plays a key role in the lifetime of plastics. Nevertheless, when natural photosensitive substances such as nitrate participate in this process, the physiochemical changes in plastics and the corresponding reaction mechanisms are not well-understood. In this work, the photochemical behavior of polyethylene terephthalate (PET) bottles in deionized water and nitrate solution was systematically investigated under ultraviolet (UV) irradiation. The analyses of the surface physicochemical properties of the photoaged PET bottles indicated that, after 20 days of photo-irradiation, the presence of nitrate reduced the contact angle from 69.8 ± 0.9° to 60.0 ± 0.3°, and increased the O/C ratio from 0.23 to 0.32, respectively. The leaching rate of dissolved organic carbon (DOC), which was 0.0193 mg g−1·day−1 in nitrate solution, was twice that of 0.00941 mg g−1·day−1 in deionized water. Furthermore, fluorescence spectroscopy revealed that the increasing DOC had aromatic rings with hydroxyl on the side-chain formed after UV irradiation. The positive effect of nitrate on the degradation of PET bottles was mainly through the generation of hydroxyl radicals that were produced through the photolysis of nitrate. In addition, two-dimensional correlation spectroscopy analysis showed that the chain scission of PET plastics could be initiated by nitrate-induced ·OH attacking the carbon-oxygen bonds instead of forming peroxides with oxygen. This work elucidates the mechanism of photodegradation of plastics that was induced by nitrate and highlights the important role of natural photosensitive substances in the photoaging process of plastics.

Maturity Stage Discrimination of Camellia oleifera Fruit Using Visible and Near-Infrared Hyperspectral Imaging.

The maturity of Camellia oleifera fruit is one of the most important indicators to optimize the harvest day, which, in turn, results in a high yield and good quality of the produced Camellia oil. A hyperspectral imaging (HSI) system in the range of visible and near-infrared (400–1000 nm) was employed to assess the maturity stages of Camellia oleifera fruit. Hyperspectral images of 1000 samples, which were collected at five different maturity stages, were acquired. The spectrum of each sample was extracted from the identified region of interest (ROI) in each hyperspectral image. Spectral principal component analysis (PCA) revealed that the first three PCs showed potential for discriminating samples at different maturity stages. Two classification models, including partial least-squares discriminant analysis (PLS-DA) and principal component analysis discriminant analysis (PCA-DA), based on the raw or pre-processed full spectra, were developed, and performances were compared. Using a PLS-DA model, based on second-order (2nd) derivative pre-processed spectra, achieved the highest results of correct classification rates (CCRs) of 99.2%, 98.4%, and 97.6% in the calibration, cross-validation, and prediction sets, respectively. Key wavelengths selected by PC loadings, two-dimensional correlation spectroscopy (2D-COS), and the uninformative variable elimination and successive projections algorithm (UVE+SPA) were applied as inputs of the PLS-DA model, while UVE-SPA-PLS-DA built the optimal model with the highest CCR of 81.2% in terms of the prediction set. In a confusion matrix of the optimal simplified model, satisfactory sensitivity, specificity, and precision were acquired. Misclassification was likely to occur between samples at maturity stages two, three, and four. Overall, an HSI with effective selected variables, coupled with PLS-DA, could provide an accurate method and a reference simple system by which to rapidly discriminate the maturity stages of Camellia oleifera fruit samples.

Aging of poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends under different conditions: Environmental concerns on biodegradable plastic

Biodegradable plastics (BPs) have been used to replace conventional plastics owing to their environmental harmless and ease of degradation. However, the aging processes of BPs in different environments remain unclear. In this study, we used poly (lactic acid)/poly (butylene adipate-co-terephthalate) (PLA/PBAT) films as model BPs and investigated the 30-d aging behavior of PLA/PBAT films under four conditions (i.e., air without ultraviolet (UV) irradiation, water without UV irradiation, air with UV irradiation, and water with UV irradiation). Our results showed that the aging of PLA/PBAT films was insignificant in all groups except the water with UV irradiation group. In the physical characterization, the PLA/PBAT films exhibited layered structures in water with UV irradiation condition, and the submicron- and nano-sized particles adhered to the bigger-sized fragments. In the chemical characterization, the carbonyl index (CI) of PLA/PBAT films in water with UV irradiation condition decreased from 3.84 to 1.36, and the oxygen-to-carbon (O/C) ratio reached a maximum of 1.78 at 20 d and declined to 0.49 at 30 d, indicating that the oxygen-containing functional groups underwent bond breaking and showed a rapid aging process. This is mainly attributed to the combined effect of hydrolysis and photolysis increases the contact area of PLA/PBAT films and accelerates the aging process. Furthermore, based on two-dimensional correlation spectroscopy (2D-COS) analysis, we suggest that free radicals generated in water with UV irradiation conditions also accelerate the aging process of PLA/PBAT films. This study explored the aging processes of PLA/PBAT films under different conditions, which could aid in clarifying the environmental behavior and provide further information to assess the potential risks of BPs.

Isothermal crystallization of polyhydroxyalkanoate (PHA) utilizing Raman spectroscopy to follow chain packing as well as molecular motion

Raman spectra of bioplastic poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx at 13.8 % Hx) were recorded between −250 cm−1 and 3200 cm−1 during isothermal crystallization at 25⁰C after quenching from the melt in liquid nitrogen. At room temperature the crystallization proceeds slowly, so spectra were recorded over a 14-hour period. While there are spectral changes throughout the spectrum, the focus was on interpretable bands known to be sensitive to crystalline form. These bands included the carbonyl band that sharpens and shifts, a pair of bands on the high energy side of the carbon-hydrogen stretch, and a low frequency band that we assign to the molecular phonon in the crystal unit cell. After appropriate pre-processing of the spectra, they were further analyzed by 2D-COS (two-dimensional correlation spectroscopy) that provides determination of the order in which the polymer functional regions assemble into the crystalline state. According to this analysis one of the methyl CH’s interacts with the carbonyl bond to produce a line at 3000 cm−1. Following that, multiple changes appear in the carbonyl region, the strong CH band at 2930 cm−1 of the crystalline phase grows, then the 80 cm−1 phonon band, and the splitting of the methyl CH only appears after the phonon. From this sequence one can derive a picture of how the polymer unit locks into the crystal form. This can be of interest to commercialization of the materials because mechanical properties are intimately controlled by the crystallinity of the material. By understanding how the crystallization process proceeds, it can be engineered to be “fit for purpose” for a polymer targeted for a specific use.