Two-Dimensional Heterospectral Correlation Analysis of X-ray Photoelectron Spectra and Infrared Spectra for Spin-Coated Films of Biodegradable Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Copolymers

Geographical discrimination and adulteration analysis for edible oils using two-dimensional correlation spectroscopy and convolutional neural networks (CNNs)

Geographical discrimination and adulteration analysis play significant roles in edible oil analysis. A novel method for discrimination and adulteration analysis of edible oils were proposed in this study. The two-dimensional correlation spectra of edible oils were obtained by solvents perturbation and the convolutional neural networks (CNNs) were constructed to analyze the synchronous and asynchronous correlation spectra of the edible oils. The differences for geographical origins of oils or oil types could be amplificated through the networks. For different networks, the layer sequences and the filter number of convolutional layers may affect the analysis results. A group of sesame oils from different geographical origins and a group of olive oils adulterated by other vegetable oils were adopted to evaluate the proposed method. The results show that the proposed method may provide an alternative method for edible oil discrimination and adulteration analysis in practical applications. For the two datasets, the prediction accuracy could be 97.3% and 88.5%, respectively.

Characterizing Properties and Environmental Behaviors of Dissolved Organic Matter Using Two-Dimensional Correlation Spectroscopic Analysis

Dissolved organic matter (DOM) exists ubiquitously in environments and plays critical roles in pollutant mitigation, transformation, and organic geochemical cycling. Understanding its properties and environmental behaviors is critically important to develop water treatment processes and environmental remediation strategies. Generalized two-dimensional correlation spectroscopy (2DCOS), which has numerous advantages, including enhancing spectral resolution and discerning specific order of structural change under an external perturbation, could be used as a powerful tool to interpret a wide range of spectroscopic signatures relating to DOM. A suite of spectroscopic signatures, such as UV-vis, fluorescence, infrared, and Raman spectra that can be analyzed by 2DCOS, is able to provide additional structural information hiding behind the conventional one-dimensional spectra. In this article, the most recent advances in 2DCOS applications for analyzing DOM-related environmental processes are reviewed, and the state-of-the-art novel spectroscopic techniques in 2DCOS are highlighted. Furthermore, the main limitations and requirements of current approaches for exploring DOM-related environmental processes and how these limitations and drawbacks can be addressed are explored. Finally, suggestions and new approaches are proposed to significantly advance the development of 2DCOS in analyzing the properties and behaviors of DOM in natural and engineered environments.

Diversity in the Mechanisms of Humin Formation during Composting with Different Materials

Humins (HMs) play a very important role in various environmental processes and are crucial for regulating global carbon and nitrogen cycles in various ecosystems. Composting is a controlled decomposition process accompanied by the stabilization of organic solid waste materials. During composting, active fractions of organic substances can be transformed into HMs containing stable and complex macromolecules. However, the structural heterogeneity and formation mechanisms of HMs during composting with various substrates have not been clarified. Here, the structure and composition of HMs extracted from livestock manure (LM) and straw (SW) during composting were investigated by excitation-emission matrices spectroscopy and Fourier transform infrared spectroscopy. The results showed that the stability and humification of LM-HM were lower than that of SW-HM. The parallel factor analysis components of the HM in LM composting contained the same fluorescent unit, and the intermediate of cellulose degradation affected the structure of the HM from SW composting. Structural equation modeling demonstrated that low-molecular-weight compounds were key factors in humification. On the basis of the structure and key factors impacting HM, we constructed two mechanisms for the formation of HM from different composting processes. The LM-HMs from different humification processes have multiple identical fluorescent structural units, and the high humification of SW is affected by its polysaccharide constituents, which contains a fluorescent component in their skeleton, providing a basis for studying HM in composting.

Studies on Chemical IR Images of Poly(hydroxybutyrate⁻co⁻hydroxyhexanoate)/Poly(ethylene glycol) Blends and Two-Dimensional Correlation Spectroscopy

Biodegradable poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoates] (PHBHx) have been widely studied for their applications in potentially replacing petroleum-based thermoplastics. In this study, the effect of the high molecular weight (Mn = 3400) poly(ethylene glycol) (PEG) blended in the films of PHBHx with different ratios of PEG was investigated using chemical FTIR imaging. Chemical IR images and FTIR spectra measured with increasing temperature revealed that PEG plays an important role in changing the kinetics of PHBHx crystallization. In addition, two-dimensional correlation spectra clearly showed that thermal properties of PHBHx/PEG blend film changed when the blending ratio of PHBHx/PEG were 60/40 and 50/50. Consequently, PEG leads to changes in the thermal behavior of PHBHx copolymers.

Surface Structure of Acrylate Polymer Adhesives

Total internal reflection infrared (IR) absorption and visible-IR sum-frequency spectroscopies were used to study the role of acrylic acid in the evolution of surface structure in a poly(butyl acrylate)-based pressure-sensitive adhesive during the drying process. By monitoring these spectral responses and calculating the heterospectral correlation coefficients, we established that acrylic acid alters the nature of the molecular interactions at the surface. In the absence of acrylic acid, butyl acrylate orientation is driven by the packing of the polymer as the water evaporates. When acrylic acid is present, a rapid ordering of the copolymer takes place as a result of favorable hydrogen-bonding interactions with the surface.

Two-dimensional correlation spectroscopy in polymer study

This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted.

FTIR and synchronous fluorescence heterospectral two-dimensional correlation analyses on the binding characteristics of copper onto dissolved organic matter

Dissolved organic matter (DOM) is known to form strong complexes with heavy metals and thus governs the distribution, toxicity, bioavailability, and ultimate fate of heavy metals in the environment. The relevant aspects of metal-organic interactions remain unclear because the metal binding functionalities in DOM are substantially nonuniform and the availability of the models is limited. In this work, two-dimensional correlation spectroscopy (2DCOS) integrated with synchronous fluorescence and infrared absorption spectroscopy was used to explore the binding process of copper to DOM. A series of heterogeneous binding sites in humic acid (HA), a representative DOM, and the subsequent subtle changes of these sites within the molecular interactions were elucidated by the 2DCOS method. The band assignments and the correspondence between the results obtained by two spectral probes (synchronous fluorescence and infrared absorption spectra) were verified by hetero-2DCOS. Our results showed that, during the copper binding process, the carboxyl and polysaccharide groups gave the fastest responses to copper binding. Then fluorescence quenching of fluorescent humic-like moieties occurred with a vibrational change of the related functionalities, i.e., phenolic and aryl carboxylic groups, which further induces the fluorescence quenching of fulvic-like fractions. Finally, small amounts of amide and aliphatic groups participated in the copper binding after the fluorescence of the protein-like fraction decreased. With these promising results, a comprehensive picture of structural changes of HA during the copper binding process was developed, highlighting the superior potential of 2D heterospectral correlation spectroscopy in studying complex interactions in the environment.