Functional Group Heterogeneity Research Articles

Carbon nanotube-based van der Waals heterojunction electrodes for high-performance intrinsically stretchable organic photoelectric transistors

Intrinsically stretchable organic field-effect transistors (STOFETs) that behave much like skin, have garnered widespread attention and demonstrated potential to more comfortable wearing electronics. Despite considerable efforts being exerted in stretchable hybrid polymeric semiconductors to achieve high-mobility and high-stretchability STOFETs, carbon nanotubes (CNTs) as ideal electrode materials, its interfacial quality seldom attracts research interests. Herein, we demonstrate a novel and general strategy on flexible CNT-based heterojunction electrodes by pentacene modification layer to enable high-performance and functional STOFETs. Pentacene transition layer can reduce the surface roughness and tune the heterogeneity of functional groups on the CNT thin film, as well as enhance the compatibility and van der Waals contact between CNT electrodes and organic semiconductors. The experimental results reveal that the carrier mobility of the resulting STOFETs increases by 2-3 times and the subthreshold slope decreases by 5 times compared with unmodified devices. The on-current/off-current ratio reaches nearly 107, which is approximately 1000 times as high as unmodified devices, and the highest value for stretchable organic transistors reported so far. Furthermore, STOFETs with heterojunction electrodes demonstrate better performance homogeneity and higher strain-independent capability. Noteworthy, these are the first intrinsically stretchable organic phototransistors (STOPTs) with superior photoswitching performances and high strain tolerance developed.

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.

Thermodynamic study of the complexation of humic acid by calorimetry

Although the thermodynamic quantities (Gibbs free energy, reaction enthalpy, and entropy) of the complexation of humic acid are necessary for the discussion of the reaction thermodynamics, their accurate determination, especially concerning dissolved humic acid in deep groundwater, has not been carried out. In this study, a combination of potentiometry and calorimetry was used for the determination of the thermodynamic values of complexation of typical humic acid and groundwater humic acid, which was isolated from deep groundwater at Horonobe, Hokkaido, Japan, with copper (II) ions and uranyl (VI) ions. The apparent complexation constant of Horonobe humic acid was independent of the pH of the bulk solution, whereas that of typical humic acid was dependent on the pH. This observation indicates that the polyelectrolyte effect of Horonobe humic acid is negligible because of its relatively small molecular size. In addition, the effect of the heterogeneity of Horonobe humic acid was not significant. Moreover, the complexation enthalpy of Horonobe humic acid was consistent with that of homogeneous poly(acrylic acid), which means the complexation of Horonobe humic acid was not affected by the functional group heterogeneity. Consequently, the unique complexation mechanism of Horonobe humic acid was revealed based on the determined thermodynamic quantities. The migration of radionuclides in the deep underground environment must be affected by these characteristics; thus, the accurate determination of thermodynamic quantities of in situ humic substances is very helpful for the safety assessment of geological disposal, when disposal sites for radioactive waste are chosen.

Interrogating Surface Functional Group Heterogeneity of Activated Thermoplastics Using Super-Resolution Fluorescence Microscopy.

We present a novel approach for characterizing surfaces utilizing super-resolution fluorescence microscopy with subdiffraction limit spatial resolution. Thermoplastic surfaces were activated by UV/O3 or O2 plasma treatment under various conditions to generate pendant surface-confined carboxylic acids (-COOH). These surface functional groups were then labeled with a photoswitchable dye and interrogated using single-molecule, localization-based, super-resolution fluorescence microscopy to elucidate the surface heterogeneity of these functional groups across the activated surface. Data indicated nonuniform distributions of these functional groups for both COC and PMMA thermoplastics with the degree of heterogeneity being dose dependent. In addition, COC demonstrated relative higher surface density of functional groups compared to PMMA for both UV/O3 and O2 plasma treatment. The spatial distribution of -COOH groups secured from super-resolution imaging were used to simulate nonuniform patterns of electroosmotic flow in thermoplastic nanochannels. Simulations were compared to single-particle tracking of fluorescent nanoparticles within thermoplastic nanoslits to demonstrate the effects of surface functional group heterogeneity on the electrokinetic transport process.

Interrogating Surface Functional Group Heterogeneity of Activated Thermoplastics Using Super-Resolution Fluorescence Microscopy

Interrogating Surface Functional Group Heterogeneity of Activated Thermoplastics Using Super-Resolution Fluorescence Microscopy

Carboxylic Content of Humic Acid Determined by Modeling, Calcium Acetate, and Precipitation Methods

The key to understanding proton equilibria and cation binding on the surface of humic acid is the quantification of the total carboxylic acid contents. Such quantification via titration alone is highly ambiguous and not straightforward due to the complexity and interference of noncarboxylic acids (phenolic acid, thiols, etc.). To gain a greater understanding of such analysis, potentiometric titration data was incorporated into modeling approaches, and they were compared with two other methods: conventional Ca(OAc)2 exchange and the precipitation titration method. Each of these three methods was used to analyze six different humic samples. The humic samples were collected from various sources, such as upland, paddy fields, sediments, and peat. The carboxylic acid contents ranged from 263 to 487 cmolc kg−1 Furthermore, the carboxylic acid content in the humic acid from the Namwon series showed significantly higher values. This was attributed to the relatively higher percentage of organic C in the mother material. Two modeling approaches using titration data were performed. The first was a simple electrostatic model with limited functional group heterogeneity (Model A). The second was our implemented version of Model V with four carboxylic acid group sites and four phenolic hydroxyl group sites. The relative difference in total carboxylic acid contents between the Ca(OAc)2 method and Model A prediction ranged from 0.21 to 7.43%, and that between the Ca(OAc)2 method and Model V prediction was 1.90 to 35.71%. The predicted carboxylic acid content from Model A was more comparable to the results of the Ca(OAc)2 method and the cetyltrimethylammonium method than the Model V prediction. The modeling approaches with the simple ligand model showed a better prediction of the total carboxylic acid content from the potentiometric titration data.

Differential Scanning Calorimetric Analysis of Composted Materials From Different Sources

Differential scanning calorimetry (DSC) was applied to the study of material composted from sawdust, used coffee, farmyard manure and the organic fraction of domestic solid waste. Composting trials were carried out in Morocco and samples were collected after different periods of composting. The results obtained provided evidence that sawdust substrate is not a suitable source for composting due to the high content of lignin; samples from used coffee are characterized by a degree of aromaticity that is lower and a functional group heterogeneity that is higher than those of organic wastes from manure and the organic fraction of domestic wastes. The latter organic waste substrates appear to be easily degraded and humified and to give DSC curves that at the end of composting are vary close to those of native soil humic acids.

Correlations between acidity and molecular size distributions of an aquatic fulvic acid

The overall acid-base properties of humic substances have been postulated to be affected by the functional group heterogeneity and heterogeneity in molecular size leading to an ionic strength effect. In this paper, the acidic properties of various molecular size fractions (500, 1000, 5000, 10 000 daltons as per ultrafiltration) of an aquatic fulvic acid (Rådsla FA) are determined and correlated to other physicochemical parameters such as UV, FTIR, and molecular weight determinations by gel-filtration chromatography. There was a positive correlation between the size cut-off as per ultrafiltration and the molecular weight determinations from the gel-filtration chromatography. The acid-base titrations of the filtrates and retentates corroborate the hypothesis that ionic strength effects are significantly larger for samples with higher molecular weight moieties.

Humic acid–proton equilibria: A comparison of two models and assessment of titration error

SummaryCharge development curves, obtained by potentiometric titration of ten soil–derived humic acids, are described using two modelling approaches: a simple electrostatic model with limited functional group heterogeneity (model A), and an implementation of an alternative from the literature, model V, incorporating up to 12 functional group types. Both models provide excellent descriptions of charge dependence on pH and ionic strength. However, for model A, 11 fitted parameters were required to describe the data across the full range of ionic strength (0.01–3.0), compared with seven for model V. Although model A required more parameters, it was conceptually simpler than model V, requiring only two functional group types, which may have advantages in describing the formation of metal complexes.Error in the determination of humic charge from titration data was shown to increase markedly for data obtained at pH<3. The apparently anomalous trends in humic charge at low pH reported in the literature are explained in terms of this error.Investigation of the kinetics of protonation and deprotonation reactions of humic acids suggested that titration hysteresis was the result of dis–equilibrium, especially at high pH. The use of a 7‐day batch titration technique, instead of continuous titration apparently eliminated hysteresis from the data.

Potentiometric Titrations of Humic Substances: Do Ionic Strength Effects Depend on the Molecular Weight?

That the solution chemistry of humic substances is perturbed by ionic strength effects and functional group heterogeneity is now widely accepted. Application of the two-phase approach employing concepts from the Donnan equilibrium and the electrochemical unit cell had earlier postulated the ionic strength effects to be due to the presence of higher molecular weight moieties in the fulvic acid assemblage. Potentiometric titrations of a number of aquatic fulvic and humic acids (isolated by an initial preconcentration on diethylaminoethyl (DEAE) cellulose prior to their adsorption on XAD-8 resins) are presented as a function of ionic strength and their molecular weight distributions. Even though an apparent correlation between molecular weight distribution and ionic strength effects was observed, for humic substances of similar molecular weight, ionic strength effects seem to increase with an increase in the polydispersity of the molecule.

The binding of strontium and europium by an aquatic fulvic acid—ion exchange distribution and ultrafiltration studies

The complexation of an aquatic fulvic acid, FA, with Sr 2+ and Eu 3+ was studied at 0.10 and O1.O1 M NaClO 4 using trace levels of metal ([Sr 2+] = 10 −9 M and [Eu 3+] = 10 −11 M) and a constant FA concentration (0.12 g/l) by an ultrafiltration technique (UF) and an ion exchange distribution method (IEDS). The overall complex formation function, β OV for the two metals was calculated and its dependence on pH, ionic strength and method was investigated. The absolute value of log β OV, the pH dependence and the influence of the ionic strength on the complexation differed depending on the metal ion and experimental technique employed. By considering the functional group heterogeneity of the FA molecule, it was possible to predict the most predominantly bound site (keto—enol) and resolve the complex formation function for this site and EU 3+ (IEDS: 9.43 ± 0.29 l/eq at 0.10 M and 10.58 ± 0.72 l/eq at 0.01 M; UF: 7.19 ± 1.51 l/eq at 0.01 M and 6.88 ± 0.91 l/eq at 0.01 M). The results are discussed in the light of possible intrinsic problems of the two experimental methods.

A combination of acid-base titrations and derivation for functional group determinations of an aquatic fulvic acid

Insight into the functional group heterogeneity of an aquatic fulvic acid has been gained via carefully designed acid-base titrations in aqueous and nonaqueous media and a newly developed derivatization technique. Results of the acid-base titrations in an aqueous medium and in the presence of heavy metals (eg. Cu(II) and La(III) indicate the presence of salicylic acid-like and catechol-like moieties in the fulvic acid molecule. The total acidic capacity can be separated into contributions from a weak acid of carboxylic functionality and a still weaker acid of -OH type by acid-base titrations in a nonaqueous medium in the presence of an internal reference standard. An organic derivatization technique in conjunction with high resolution gas chromatography has facilitated the determination of the total number of hydroxyl groups in the fulvic acid sample. The results obtained from the derivatization technique are compared with those obtained from the acid-base titrations in aqueous and nonaqueous systems.

A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid

Potentiometric studies of the neutralization of several fulvic acid sources with standard base in aqueous and nonaqueous media have been conducted. Analysis of the results with a recently developed unified physicochemical model has shown that the protonation behavior of these fulvic acid sources is a reflection of their polyelectrolyte nature and their heterogeneity. It has been possible to ascribe the polyelectrolyte properties observed to a rather inflexible fulvic acid molecule whose variably charged surface is impermeable to simple electrolyte. 42 references, 24 figures, 4 tables.