Two-dimensional FTIR Correlation Spectroscopy Research Articles

Effect of hydration on the H-bond dynamics of adsorbed water in cellulose/polyethyleneimine nano-sponges probed by 2D-COS and PCMW2D two-dimensional FTIR correlation spectroscopy

Effect of hydration on the H-bond dynamics of adsorbed water in cellulose/polyethyleneimine nano-sponges probed by 2D-COS and PCMW2D two-dimensional FTIR correlation spectroscopy

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.

Remediation potential of magnetic biochar in lead smelting sites: Insight from the complexation of dissolved organic matter with potentially toxic elements

Magnetic biochar has been widely used in potentially toxic elements (PTEs) polluted soils due to its magnetic separation capability and synchronous immobilization for multiple metals. However, the contribution of magnetic biochar to soil dissolve organic material (SDOM) and its binding behavior with PTEs needs to be further clarified prior to its remediation application on lead smelting sites. In this study, multi-spectral techniques of excitation-emission matrix (EEM) fluorescence spectroscopy and two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) were used to explore the evolution characteristics of SDOM in the lead smelting site under the remediation of magnetic biochar, and to further analyze its affinity and binding behavior with Pb and As. Results showed that magnetic biochar significantly increased SDOM content and decreased Pb and As available content. EEM and parallel factor analysis (EEM-PARAFAC) and Self-Organizing map analysis showed that humus-like and aromatic DOM increased and microbial-derived SDOM decreased after magnetic biochar cultivation. Furthermore, 2D-FTIR-COS correlation spectroscopy analysis indicated that BDOM had a stronger binding affinity to Pb, while SDOM has a stronger binding affinity to As. The binding sequences of different DOMs to PTEs varied greatly, the carboxyl and amide groups of SDOM and BDOM showed a remarkable and rapid response. Our results enhance the insights of magnetic biochar on soil function and PTEs remediation potential, providing novel information for its environmental remediation application.

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.

Temperature-Dependent Dynamical Evolution in Coum/SBE-β-CD Inclusion Complexes Revealed by Two-Dimensional FTIR Correlation Spectroscopy (2D-COS).

A combination of Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) and 2D correlation analysis (2D-COS) was applied here for the first time in order to investigate the temperature-dependent dynamical evolution occurring in a particular type of inclusion complex, based on sulfobutylether-β-cyclodextrin (SBE-β-CD) as hosting agent and Coumestrol (7,12-dihydorxcoumestane, Coum), a poorly-soluble active compound known for its anti-viral and anti-oxidant activity. For this purpose, synchronous and asynchronous 2D spectra were calculated in three different wavenumber regions (960–1320 cm−1, 1580–1760 cm−1 and 2780–3750 cm−1) and over a temperature range between 250 K and 340 K. The resolution enhancement provided by the 2D-COS offers the possibility to extract the sequential order of events tracked by specific functional groups of the system, and allows, at the same time, the overcoming of some of the limits associated with conventional 1D FTIR-ATR analysis. Acquired information could be used, in principle, for the definition of an optimized procedure capable to provide high-performance T-sensitive drug carrier systems for different applications.

Alkali lignin and sodium lignosulfonate additives promote the formation of humic substances during paper mill sludge composting

Alkali lignin (AL) and sodium lignosulfonate (SLS) are by-products of the papermaking industry and could influence composting processes due to their rich aromatic structures. In this study, the roles of AL and SLS additives in the formation of humic substances (HS) during paper mill sludge composting were investigated. Results showed that HS content and degree of polymerization of the final products in AL (44.42 mg·g−1 and 0.70, respectively) and SLS (45.87 mg·g−1 and 1.14, respectively) treatments were appreciably higher than those of the control sample (34.36 mg·g−1 and 0.67). Excitation-emission matrix-parallel factor coupled with two-dimensional FT-IR correlation spectroscopy analysis suggested that AL and SLS additives could speed the transformation of quinone-like substances by increasing the amounts of low molecular weight lignin depolymerized products, which led to higher HS concentrations. This work provided a way of promoting HS formation and the comprehensive utilization of papermaking wastes.

XPS and two-dimensional FTIR correlation analysis on the binding characteristics of humic acid onto kaolinite surface

The stabilization and preservation of soil organic matter have been attributed to the strong reactive sites of mineral surfaces that cause physical isolation and chemical stabilization due to the organic-mineral interface. However, much of the micro-scale knowledge about interactions between organic ligands and minerals largely remains at the qualitative level, and neglects the heterogeneity of functional groups of organic matter. Here, we report the use of molecular-scale technologies of two-dimensional FTIR Correlation Spectroscopy (2D-FTIR-CoS) and X-ray Photoelectron Spectroscopy (XPS) to directly measure the binding processes of humic acid (JGHA) groups onto kaolinite surface. The spectroscopy results showed that the carboxylate groups, aliphatic OH and aromatic structure participate in the binding of JGHA on kaolinite surface. The carboxylic and phenolic hydroxyl interact with kaolinite surface through the interfacial COAl/Si bonds. Kaolinite prefers to adsorb C-groups at pH 4.0 and O-groups at pH 8.0. The interaction of COO– group at 1566 cm−1 of JGHA leads to the formation of inner-sphere complex first and then outer-sphere complex with increasing contact time. The interaction of COOH group at 1261 cm−1 with the AlOH2+ of kaolinite was could be ascribed to ligand exchange and/or electrostatic attraction, whose contribution was evaluated to be 13.90%, 7.65% and 0% at pH 4.0, 6.0 and 8.0, respectively. These results of molecular binding provide quantitative mechanistic insights into organic-mineral interactions and expound the effect of functional groups of HA on binding mechanisms, and thus bring important clues for better understanding the mobility and transformation of land‑carbon including mineral-bound carbon.

Hyperthermophilic composting of sewage sludge accelerates humic acid formation: Elemental and spectroscopic evidence

Application of thermophilic composting (TC) is limited due to poor efficiency and long composting period. Hyperthermophilic composting (HTC) could effectively overcome this defect. Here, the transformation of humic acid (HA) in both HTC and TC was characterized and compared to investigate the roles of HTC toward accelerating the formation of HA. In HTC, the highest temperature was 96.6 °C, and the hyperthermophilic and thermophilic phases exceed 18 days. The degree of polymerization (DP) in HTC increased to 1.27 on day 27, while it only increased to 1.15 at the end of TC. The elemental composition of the HA in HTC showed higher O atomic content (36.3%) and lower C/N atomic ratio (6.5) compared with TC. These changes indicated that HTC could significantly accelerate oxidized and polycondensed reactions for HA formation, which resulted in the shortening of composting period to 27 days. The maximum fluorescence intensity (Fmax) of humic-like components were achieved faster in HTC (Fmax = 1649.9) than in TC (Fmax = 1316.9), implying that HTC promoted the polycondensation of small molecular components to form HA with larger molecular weight and higher degree of aromatization. Two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) analysis demonstrated that HTC prevented the HA precursor from condensing before it was deeply oxidized, and increased the content of small molecules rich in carboxyl moieties. Based on the evolution of the molecular structure of HA, the level of oxidation of HA precursors was a key factor to determine the degree of polymerization and the degree of HA humification.

Effects of humic acid on the biodegradation of di-n-butyl phthalate in mollisol

Soil phthalic contamination has received more and more attention due to the widespread use of plastic mulching films. Humic acid (HA) is a natural antidote. The effects of HA on the biodegradation of dibutyl phthalate (DBP) in mollisol was investigated in this study. Through the calculation by bi-exponential model, the half-life of DBP was effectively shortened after adding HA, from 11.65 days to 3.36 days, and soil bulk density decreased. The enhancement mechanism for DBP removal by HA was analyzed by fluorescence spectrometry, two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) and PLFA analysis. Two major functional groups (aryl C–O and alkyl ester CO) were found at the binding site between DBP and HA. By mediating the transportation of DBP, HA could provide more time for soil microorganisms to degrade DBP. Meanwhile, HA effectively stabilized the mollisol microbial community composition and promote the growth of aerobic bacteria, which contributes to the degradation of DBP. The results are valuable for relieving DBP pollution caused by agricultural production and promoting sustainable use of mollisol.

Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process

Microplastics (MPs) as new pollutants of environmental concern have been widely detected in sewage sludge, and may act as significant vectors for metal pollutants due to their adsorption property. Our findings show that Cd, Pb, and Co, but not Ni, contents in sewage sludge are lower than that of corresponding metal irons adsorbed on sludge-based MPs, indicating that the MPs accumulate such metal pollutants as Cd in the sludge samples. In contrast to virgin MPs, sludge-based MPs are one order of magnitude higher adsorption capacity for Cd, which reaches up to 2.523 mg g−1, implying that there is a considerable enhancement in adsorption potential of the MPs for metals after the wastewater treatment process. SEM analysis shows that sludge-based MPs have rougher and more porous surface than virgin MPs, and FTIR spectra reveal that functional groups such as CO and OH are found on sludge-based MPs. Further, two-dimensional FTIR correlation spectroscopy indicates that CO and NH functional groups play a vital role in the process that sludge-based MPs adsorb Cd, which are not found in virgin MPs. The results imply that increased adsorption potentials of the sludge-based MPs to Cd are attributed to changes in the MP physicochemical properties during wastewater treatment process. In addition, such factors as pH value, and sludge inorganic and organic components also have an effect on the MP adsorption to Cd. Principal component analysis shows that the MPs could be divided into three categories, i.e. polyamide, rubbery MPs (polyethylene and polypropylene) and glassy MPs (polyvinyl chloride and polystyrene). Their adsorption potentials to Cd follow the decreasing order: polyamide > rubbery MPs > glassy MPs. In summary, these findings indicate that MPs may exert an important influence on fate and transport of metal pollutants during sewage sludge treatment process, which deserves to be further concerned.

Preliminary study of experimental parameters for projection moving-window two-dimensional correlation FTIR spectroscopy

Our group proposed the projection moving-window two-dimensional (Proj-MW2D) correlation FTIR spectroscopy in 2015. In this study, the influence of three important experimental parameters on the quality and accuracy of Proj-MW2D was investigated, including the number of scans, the spectral resolution, and the heating rate. By changing parameters, a total of 36 in situ FTIR experiments of isotactic polypropylene (iPP) upon heating from 30 °C to 210 °C were performed. Proj-MW2D and conventional MW2D FTIR spectra were then calculated. It was confirmed that the quality and accuracy of Proj-MW2D were actually predominated by the number of spectra collected (codetermined by above three parameters). Importantly, a big problem of Proj-MW2D spectroscopy was found that the number of spectra used to calculate Proj-MW2D spectra cannot be too few, otherwise the results will lead to an error. It was also confirmed that the heating rate itself has a negative impact on Proj-MW2D in the temperature axis when a very fast rate was used (15 °C/min). This study summarized the optimal experimental parameters: 1) 2−4 cm−1 (the spectral resolution); 2) 10–30 scans (the number of scans); 3) 2–10 °C/min (the heating rate). Moreover, please ensure the number of spectra is ≥ 72 at least. More accurately, when using a linear heating, there should contain 0.4 spectrum per 1 °C at least. These findings are also applicable to other types of two-dimensional (2D) correlation FTIR spectroscopy based on the moving-window. People can follow the recommendations to avoid unnecessary mistakes.

Two-dimensional correlation spectroscopic analysis on the interaction between humic acids and aluminum coagulant

In this study, two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy was employed to investigate the interaction between humic acids and aluminum coagulant at slightly acidic and neutral pH. Higher fluorescence quenching was produced for fulvic-like and humic-like fractions at pH5. At pH5, the humic-like fractions originating from the carboxylic acid, carboxyl and polysaccharide compounds were bound to aluminum first, followed by the fulvic-like fractions originating from the carboxyl and polysaccharide compounds. This finding also demonstrated that the activated functional groups of HA were involved in forming the Al-HA complex, which was accompanied by the removal of other groups by co-precipitation. Meanwhile, at pH7, almost no fluorescence quenching occurred, and surface complexation was observed to occur, in which the activated functional groups were absorbed on the amorphous Al(OH)3. Two-dimensional FT-IR correlation spectroscopy indicated the sequence of HA structural change during coagulation with aluminum, with IR bands affected in the order of COOH>COO−>NH deformation of amide II>aliphatic hydroxyl COH at pH5, and COO−>aliphatic hydroxyl COH at pH7. This study provides a promising pathway for analysis and insight into the priority of functional groups in the interaction between organic matters and metal coagulants.

Interaction between bacterial cell membranes and nano-TiO2 revealed by two-dimensional FTIR correlation spectroscopy using bacterial ghost as a model cell envelope

The interaction between microorganisms and nanoparticles is a crucial step towards understanding the subsequent biological effect. In this study, the interaction between TiO2 nanoparticles and bacterial cell membrane was investigated by Two-dimensional Correlation Fourier Transformation Infrared spectroscopy (2D-FTIR-COS) using bacterial ghosts (BGs), which are non-living bacterial cell envelopes devoid of cytoplasm. The synchronous map of 2D-FTIR-COS results indicated that the functionalities in proteins of BGs preferentially interacted with TiO2 nanoparticles; whereas the interaction of TiO2 nanoparticles with characteristic functionality in polysaccharides (COH) and phospholipids (PO) were very weak or insensitive. This conclusion was further corroborated by settling of TiO2 nanoparticles in the presence of pure protein, polysaccharide and phospholipid represented by bovine serum albumin (BSA), alginate and phosphatidylethanolamine (PE). Additionally, the asynchronous map of 2D-FTIR-COS indicated a sequential order of functionalities bonded to TiO2 nanoparticles with the order of: COO− > aromatic CC stretching > NH, amide II > CO, ketone. These findings contribute to deeper understanding of the interaction between TiO2 nanoparticles and bacterial cell membrane in aquatic systems.

New understanding on the reaction pathways of the polyacrylonitrile copolymer fiber pre-oxidation: online tracking by two-dimensional correlation FTIR spectroscopy

FTIR spectroscopy in combination with scaling-MW2D and 2D correlation analysis is used to study the reaction pathways of polyacrylonitrile copolymer fibers pre-oxidation.

Investigation on structural changes of isotactic polypropylene mesophase in the heating process by using two-dimensional infrared correlation spectroscopy

Two-dimensional FT-IR correlation spectroscopy was used to reveal the structural changes of isotactic polypropylene (iPP) mesophase during the heating process. The co-relationship among the regular helical bands of iPP was discussed according to synchronous spectrum. The results show that the segments with different length-helixes were found to undergo a disordered process in the temperature range of 25–60 °C.

Two-dimensional FTIR correlation spectroscopy reveals chemical changes in dissolved organic matter during the biodrying process of raw sludge and anaerobically digested sludge

2D FTIR COS analysis is a feasible technique to explore the degradation characteristics of sludge organic matter, and supplies the first evidence for the complementarities of anaerobic and aerobic process in sludge organic compound degradation.

New insight into chemical changes of dissolved organic matter during anaerobic digestion of dewatered sewage sludge using EEM-PARAFAC and two-dimensional FTIR correlation spectroscopy

Dissolved organic matter (DOM) is a key component in reaction network of anaerobic digestion. In this study, fluorescent excitation-emission matrix-parallel factor (EEM-PARAFAC) analysis and two-dimensional (2D) FTIR correlation spectroscopy were firstly used to explore chemical changes of soluble intermediates in high-solid biogas reactor. EEM-PARAFAC showed that fluorescent components (tyrosine-like, tryptophan-like and humic-like groups) in DOM over time increased gradually, implying that these groups were reluctant to biodegrade (acidogenesis). The resistance to biodegradation presented the following order: humic-like group>tyrosine-like group>tryptophan-like group. 2D FTIR correlation spectroscopy indicated that the DOM change sequence with time followed the order: protein-like groups>structural carbohydrates and carboxylic acids>polysaccharides-like groups. Fluorescence intensities from EEM-PARAFAC and main bands of FTIR spectra correlated significantly with other chemical parameters, e.g. biogas production and dissolved organic carbon content. These findings supply novel realization for degradation degree and order of individual DOMs during anaerobic digestion for dewatered sewage sludge.

Binding of Organic Ligands with Al(III) in Dissolved Organic Matter from Soil: Implications for Soil Organic Carbon Storage

The binding characteristics of organic ligands with Al(III) in soil dissolved organic matter (DOM) is essential to understand soil organic carbon (SOC) storage. In this study, two-dimensional (2D) FTIR correlation spectroscopy was developed as a novel tool to explore the binding of organic ligands with Al(III) in DOM present in soils as part of a long-term (21-year) fertilization experiment. The results showed that while it is a popular method for characterizing the binding of organic ligands and metals, fluorescence excitation-emission matrix-parallel factor analysis can only characterize the binding characteristics of fluorescent substances (i.e., protein-, humic-, and fulvic-like substances) with Al(III). However, 2D FTIR correlation spectroscopy can characterize the binding characteristics of both fluorescent and nonfluorescent (i.e., polysaccharides, lipids, and lignin) substances with Al(III). Meanwhile, 2D FTIR correlation spectroscopy demonstrated that the sequencing/ordering of organics binding with Al(III) could be modified by the use of long-term fertilization strategies. Furthermore, 2D FTIR correlation spectroscopy revealed that the high SOC content in the chemical plus manure (NPKM) treatment in the long term fertilization experiment can be attributed to the formation of noncrystalline microparticles (i.e., allophane and imogolite). In summary, 2D FTIR correlation spectroscopy is a promising approach for the characterization of metal-organic complexes.

Polymer chain organization in tensile-stretched poly(ethylene oxide)-based polymer electrolytes

Polymer chain orientation in tensile-stretched poly(ethylene oxide)–lithium trifluoromethanesulfonate polymer electrolytes are investigated with polarized infrared spectroscopy as a function of the degree of strain and salt composition (ether oxygen atom to lithium ion ratios of 20:1, 15:1, and 10:1). The 1359 and 1352 cm −1 bands are used to probe the crystalline PEO and P(EO) 3LiCF 3SO 3 domains, respectively, allowing a direct comparison of chain orientation for the two phases. Two-dimensional correlation FT-IR spectroscopy indicates that the two crystalline domains align at the same rate as the polymer electrolytes are stretched. Quantitative measurements of polymer chain orientation obtained through dichroic infrared spectroscopy show that chain orientation predominantly occurs between strain values of 150% and 250%, regardless of salt composition investigated. There are few changes in chain orientation for either phase when the films are further elongated to a strain of 300%; however, the PEO domains are slightly more oriented at the high strain values. The spectroscopic data are consistent with stretching-induced melt-recrystallization of the unoriented crystalline domains in the solution-cast polymer films. Stretching the films pulls polymer chains from the crystalline domains, which subsequently recrystallize with the polymer helices parallel to the stretch direction. If lithium ion conduction in crystalline polymer electrolytes is viewed as consisting of two major components (facile intra-chain lithium ion conduction and slow helix-to-helix inter-grain hopping), then alignment of the polymer helices will affect the ion conduction pathways for these materials by reducing the number of inter-grain hops required to migrate through the polymer electrolyte.

Mechanism of PEO–PPO–PEO micellization in aqueous solutions studied by two-dimensional correlation FTIR spectroscopy

The micellization mechanism of PEO–PPO–PEO block copolymer in aqueous solutions was studied by two-dimensional correlation FTIR spectroscopy. The 1400–1000 cm −1 region was investigated, involving the stretching vibrations of ether band, C–H wagging vibrations of EO methylene groups and C–H symmetric deformation vibrations of PO methyl groups. In the 2D correlated spectra, the hydrous and anhydrous state of the ether band, PO methyl groups, and the two conformations of EO methylene groups were observed. Molecules with different PO lengths and increasing molecular weight were investigated to determine the sequence of association of the separate groups. During temperature-induced micellization, the following changes were detected: firstly, EO methylene groups changed from a gauche state to a trans state; secondly, conformational transitions led to the dehydration of hydrated methyl groups; next, the hydrogen bonding between C–O band and water diminished; and finally, dehydrated groups approached to form hydrophobic cores, resulting in micelle formation. From this variation in the sequence of group associations, it is concluded that aggregates of unimers first formed, then hydrophobic cores formed through the hydrophobic interaction from dehydrated PPO blocks, and proper micelles eventually evolved. The temperature-induced conformational changes are suggested the reason for micellization.