Solid-state 13C NMR Spectra Research Articles

Mechanochemical Synthesis of the Catechol-Theophylline Cocrystal: Spectroscopic Characterization and Molecular Structure

Pharmaceutical cocrystallization offers the possibility to modify the physicochemical and biopharmaceutical properties of active pharmaceutical ingredients. The mechanochemical synthesis and spectroscopic characterization of the catechol-theophylline (CAT-TEO) cocrystal is reported. The cocrystal was prepared by the solvent-assisted grinding method. The ATR-IR spectroscopy study allowed to determine the formation of the cocrystal because the O-H and C=O stretching bands in the CAT-TEO cocrystal were shifted with respect to the starting materials, suggesting the formation of the C=O···H-O hydrogen bond interaction. Infrared spectroscopy also allowed to discard hydration of the cocrystal, and polymorphic transitions of the starting products as a consequence of the mechanochemical grinding. The X-ray powder diffraction and thermal studies confirmed the formation of a new solid phase. In the solid state 13C NMR spectra of the cocrystal, the signals were shifted with respect to the starting products. The 13C NMR chemical shifts of the CAT-TEO cocrystal were simulated by using the gauge including the atomic orbital (GIAO) method. These results showed a good correlation between the experimental and calculated 13C NMR results. Theoretical calculations and natural bonding orbital analysis (NBO) at a B3LYP/6-31G(d,p) level of theory were performed to obtain structural information of the cocrystal.

DFT computation, Hirshfeld surfaces analysis, non-linear optical and spectroscopic investigations of a novel non-centrosymmetric organic –inorganic hybrid material [(CH3CH2)4N]HSeO4(H2SeO4)2

The new hybrid compound, tetraethylammonium monohydrogenselenate bis selenic acid [(C2H5)4N]HSeO4(H2SeO4)2 is synthesized by slow evaporation at room temperature of a solution containing (C2H5)4NOH and H2SeO4. It is crystallized in the monoclinic space group Cc (Z ​= ​2), with the unit cell parameters: a ​= ​19.705 (1) Å, b ​= ​7.542 (3) Å, c ​= ​19.199 (1) Å, β ​= ​115°. The 3D Hirshfeld surface and 2D fingerprint plots analyses showed the predominance contribution of O–H⋯O bonding in the crystal structure crystal packing. The contributions importance of the different contacts in crystal packing of this compound are compared to that observed in the [(C3H7)4N]HSeO4(H2SeO4)2 crystal. The solid-state 13C NMR spectrum shows two signals corresponding to two different carbon environments in CH2 and CH3 groups. The IR and Raman spectra were recorded in the range 400–3600 ​cm−1 and 50-3500 ​cm−1, respectively. The observed bands are assigned and discussed based on the theoretical analyses and computational calculated frequencies. The theoretical bond lengths, angles, and frequencies computed from the optimized molecular geometry through DFT method using B3LYP function and the 6-31G(d) basis set, are discussed and compared to the experimental results, which reveals a good agreement between the observed and calculated parameters. The nonlinear optical properties of [(C2H5)4N]HSeO4(H2SeO4)2 were studied using the DFT method, the calculated values of the electric dipole μ, the polarizability α, and the hyperpolarizability β. The calculations showed that the selenate-based compound exhibits a non-zero b value, revealing NLO behavior which could be used in potential and functional applications including optical switching and optical disk data storage.

SYNTHESIS AND PROPERTIES OF NANOCELLULOSE-DYE CONJUGATES

Synthesis of conjugates of cellulose nanocrystals (CNC) with chlortriazine reactive dyes (RD) has been developed. The obtained CNC-RD conjugates were characterized using a complex of modern methods: UV-Vis, IR and 13C solid state NMR spectroscopy, thermogravimetric and elemental analysis, particle size and zeta potential analysis, scanning electron and polarization optical microscopy. IR spectra of CNC-RD films show absorption bands typical of cellulose. The formation of a covalent cellulose-dye bond is confirmed by the presence of characteristic absorption bands of the resulting ether bond in the region of 1000-1300 cm-1. Based on the analysis of solid-state 13C NMR spectra, it was concluded that the degree of crystallinity of the CNC-RD conjugates does not change compared to the CNC, i.e. the RD covalently bind to the surface of the CNC particles and do not affect the crystal structure of the CNC. Using a simple model of CNC with square cross-section, and based on the elemental analysis data, the amount of covalently bound dye on the surface of CNC particles was estimated. The results obtained allow us to conclude that covalent bound of RD occurs selectively at one of the ends of the cellulose nanocrystal (the so-called reducing end of the cellulose polymer chain). Successful CNC surface modification is confirmed by UV-Vis spectroscopy. It was found that aqueous suspensions of CNC-RD conjugates have indicator properties. The sizes and charges of the particles of CNC-RD conjugates in dilute aqueous suspensions were determined. High colloidal stability of the CNC-RD aqueous suspensions was confirmed. It has been shown that CNC-RD colloidal suspensions possess liquid crystalline properties, which is clearly demonstrated by their iridescent color in polarized light with stirring. CNC films modified with RD also possess birefringence properties and exhibit an iridescent color in polarized light. The morphology of CNC-RD particles was studied using scanning electron microscopy. The thermal stability of the CNC-RD conjugates was studied.

Oxabicyclic Guest Compounds as sII Promoters: Spectroscopic Investigation and Equilibrium Measurements.

In this study, we investigate three oxabicyclic compounds, 3,6-dioxabicyclo[3. 1.0]hexane (C4H6O2, ETHF), 7-oxabicyclo[2.2.1]heptane (C6H10O, 14ECH), and 7-oxabicyclo[4.1.0]heptane (C6H10O, 12ECH) as novel promoters for gas hydrates. According to the outcomes of powder X-ray diffraction (PXRD) and synchrotron high-resolution powder diffraction (HRPD), all CH4 hydrates formed with ETHF, 14ECH, and 12ECH were identified to be sII (Fd-3m) hydrates with corresponding lattice parameters of 17.195, 17.330, and 17.382 Å, respectively. It was also clearly demonstrated that CH4 molecules are accommodated in the sII-S cages through solid-state 13C NMR and Raman spectra. Consequently, we clarified that the three compounds observed are large guest molecules (LGMs) that occupy the sII-L cages. Moreover, the thermodynamic stability of each LGM + CH4 (and N2) hydrate system was remarkably improved compared to that of the simple CH4 (and N2) hydrate. In particular, 14ECH manifested several unique features compared to the other two promoters. First, the 14ECH + CH4 hydrate did not dissociate up to room temperature (298 K), even at a moderate pressure of approximately 60 bar. At a given pressure, 14ECH increased the dissociation temperature of the CH4 hydrate by ~18 K, indicating that its promotion capability is as strong as that of tetrahydrofuran (THF), currently considered to be the most powerful promoter. Second, more interestingly, it was revealed by further PXRD, NMR, and Raman analyses that 14ECH forms a simple sII hydrate in the absence of help gases. According to differential scanning calorimetry (DSC) outcomes, we revealed that the simple 14ECH hydrate dissociates at 270~278 K under ambient pressure. In addition to the thermodynamic stability, we also note that the 14ECH + CH4 hydrate presented a sufficiently high temperature of formation, requiring little additional cooling. Given these promising features, we expect that the 14ECH hydrate system can be adopted to realize hydrate-based technologies. We also believe that the LGMs introduced here have considerable potential to serve as alternates to conventional promoters and that they can be widely utilized in both engineering and scientific research fields.

Gas Adsorption of Mixed-Valence Trinuclear Oxothiomolybdenum Glycolates.

Trinuclear oxothiomolybdenum(IV) glycolates (H2glyc, glycolic acid) with 2-methylimidazole (2-mim), 4-methylimidazole (4-mim), and sulfite, Na2[MoIV3(μ3-S)(μ2-O)3(glyc)3(2-mim)3]·1.5H2O (1), (4-Hmim)6[MoIV3(μ3-S)(μ2-O)3(glyc)3(4-mim)3]2[MoVIO2(glyc)2] (2), and Na3(4-Hmim)[MoIV3(μ3-S)(μ2-O)3(SO3)(glyc)3(4-mim)]·8H2O (3), have been isolated in reduced media, where 4-methylimidazole trinuclear oxothiomolybdenum(IV) glycolates in 2 coprecipitate with dioxomolybdenum(VI) glycolate, exhibiting unusual mixed valences of 4+ and 6+. Large downfield shifts of glycolates have been observed in solid-state and solution 13C (1H) NMR spectra with coordination to Mo, indicating obvious dissociation of soluble 1 and 3 in solution. Investigations of the coordination modes and conversions among the three complexes give insight into the reactivities of trinuclear oxothiomolybdenum(IV) complexes. Channels with 3.1 × 7.0 Å2 diameters exist in 2, showing reversible O2 absorption of 65.03 mg at 29.9 bar compared with little or no adsorption of N2, H2, CO2, and CH4 at room temperature, respectively. Moreover, trinuclear 2- or 4-methylimidazole oxothiomolybdenum(IV) glycolates 1 and 3 show only a few adsorptions for O2 under the same conditions.

Structural changes in α-chitin through nanofibrillation by high-pressure homogenization in water

Chitin nanofiber was prepared from purified crab shell chitin by repeated high-pressure homogenization in water. The chitin nanofiber/water dispersion thus prepared was viscous and translucent, and maintained a stable dispersion at room temperature for several months. AFM images showed that the chitin nanofibers had heterogeneous network structures with widths ranging from several nanometers to several tens of nanometers. Some kinks and twisted structures were also observed in the AFM images. X-ray diffraction patterns showed that both the crystallinity index and crystal width of the original alpha-chitin decreased with nanofibrillation. Solid-state 13C-NMR spectra showed that the chemical shifts of all carbons were unchanged before and after nanofibrillation, and that all C6–OH groups had the gauche-gauche conformation irrespective of the crystalline fibril surfaces and insides. The degree of N-acetylation increased from 0.83 to 0.98, which was probably due to C2–NH2 groups present in the original chitin being partially removed during high-pressure homogenization in water. The original chitin and chitin nanofiber were dissolved in 8% LiCl/DMAc, and the solutions after dilution to 1% LiCl/DMAc were subjected to size-exclusion chromatography combined with multi-angle laser-light scattering to determine their molar masses and molar mass distributions. The weight-average molar mass (Mw) value of the original chitin was 271,200 (degree of polymerization [DP] ~1340). The Mw value of the chitin nanofiber was 165,500 (DP 820), showing that the DP of the original chitin decreased by 40% through the nanofibrillation in water to form the chitin nanofiber. Chitin nanofibers were prepared from purified crab-shell chitin particles by repeated high-pressure homogenization in water. AFM images showed that the chitin nanofibers had heterogeneous network structures. X-ray diffraction patterns showed that both the crystallinity index and crystal width of the original α-chitin decreased by nanofibrillation. Solid-state 13C-NMR spectra showed that all C6–OH groups had the gauche–gauche conformation. The degree of N-acetylation increased from 0.83 to 0.98 by nanofibrillation, while the weight-average molar masses of the original chitin and chitin nanofibers were 271,200 and 165,500, respectively.

Molecular structure characterization of low-medium rank coals via XRD, solid state 13C NMR and FTIR spectroscopy

In-depth understanding of coal molecular structures is crucial to the clean and efficient coal conversion, as they are the dominant factors determining the reactivity and reaction behaviors of coals in thermal conversions such as combustion, pyrolysis, gasification and liquefaction. However, the molecular structures of coals are still far from clear due to the intrinsic complexity and heterogeneity of coals. This work probes the molecular structures of eight coals of various metamorphic grades with combined spectral techniques of X-ray diffraction (XRD), solid state 13C NMR and FTIR spectra. The structural parameters were correlated with the coalification indicator Ro to investigate the structural evolutions during coal metamorphism. Consistent results concerning the structural evolution during coalification were obtained with different techniques. From the parameters of proximate and ultimate analysis, the increasing aromaticity and decreasing aliphatic fractions with rising coalification degree are observed. XRD patterns show the ubiquitous presence of amorphous carbon, the gradually condensing aromatic layers, and the size-growing but graphitizing crystallites during coalification. 13C NMR spectra reveal different types of carbons presented, the increasing aromatic and decreasing aliphatic components, the growing size and weight but reducing number of side-chains of the aromatic clusters. FTIR spectra indicate shortening and reducing of aliphatic chains, as well as enhancing aromaticity with the deepening metamorphism. These findings shed light on the structure features of coals and are potentially useful to the clean and efficient coal utilization.

How do earthworms affect organic matter decomposition in the presence of clay-sized minerals?

Clay-sized soil minerals are known to protect organic carbon (OC) from mineralisation by formation of organo-mineral associations limiting its availability to microorganisms. The impact of soil fauna on these processes is poorly known. The aim of this study was to investigate the effect of earthworms on organic matter (OM) decomposition and association with minerals during a laboratory experiment. We used a model system consisting of fresh OM incubated with and without epigeic earthworms (Eisenia andrei and foetida) in presence of different types and amounts of phyllosilicates (kaolinite, montmorillonite) and an iron oxide (goethite) and combinations of these minerals. Our experimental setup included a high OM:mineral ratio to represent the soil-litter interphase. We monitored OC mineralisation during 196 days. Additionally, we investigated physicochemical parameters and chemical OM characteristics of decomposition products by determination of water-soluble OC (WSOC) and acquisition of solid-state 13C NMR spectra. We also analysed microscale organisation of the organo-mineral associations produced with and without earthworms by transmission electron microscopy (TEM).Earthworms enhanced OC mineralisation in all treatments. They also led to greater reductions of OC emissions in the presence of minerals as compared to the mineral-free control, depending on the type and amount of minerals added. The presence of earthworms affected microbial biomass, the concentration of WSOC and increased the contribution of aromatic compounds to OM decomposition products. Microscale analyses by TEM showed that earthworms favoured association of minerals with partly degraded OM along with completely degraded material, while in absence of earthworms only completely degraded OM was associated with minerals. We conclude that earthworms impact OM decomposition through (1) their effect on microbial biomass and the physicochemical parameters of microbial habitat and (2) the formation of OM associations by changing the OM types associated to minerals and possibly by creating closer association of partly degraded OM and iron oxides. The stability of these associations remains to be investigated.

Porous organic polymer derived metal-free carbon composite as an electrocatalyst for CO2 reduction and water splitting

Abstract A hybrid porous organic polymer (POP) comprising of phenylenediamine, phloroglucinol and triazine was synthesized, carbonized at different temperatures and characterized. Solid state 13C and 15N CP-MAS NMR spectra of the POP showed evidences for the presence of the three moieties in varying composition. Raman analysis of the carbonized samples exhibited varying degrees of graphitization and powder X-ray diffraction (PXRD) analysis showed patterns corresponding to N-doped amorphous carbon. Surface morphological characteristics obtained from SEM and TEM analysis confirm different morphologies with slight variations in the particle size and porosity. Further, the electrocatalytic activities of the prepared metal-free catalysts were evaluated. Sample carbonized at 700 °C (PPT-700) showed excellent catalytic activity towards electrocarboxylation of 4-bromoacetophenone in 0.1 M TBABF4/DMF and OER in 1 M KOH as indicated by their onset potential and current density, whereas the sample calcined at 900 °C (PPT-900) exhibited excellent HER activity in 1 M H2SO4. The catalytic activity of PPT-700 towards electrocarboxylation and OER activity is ascribed to the presence of pyridinic, pyrrolic and quaternary nitrogen's, whereas the presence of pyridinic and pyrrolic nitrogen's are responsible for the enhanced HER activity of PPT-900 sample as evident from XPS.

Two copolymer-grafted silica stationary phases prepared by surface thiol-ene click reaction in deep eutectic solvents for hydrophilic interaction chromatography

Two new copolymer-grafted silica stationary phases were prepared and employed in hydrophilic interaction chromatography (HILIC). 2-(Dimethylamino)ethyl methacrylate (DMAEMA) are copolymerized with itaconic acid (IA) and acrylic acid (AA) respectively, via thiol-ene click reaction on silica surface with deep eutectic solvents (DES) as new solvents. The obtained poly(DMAEMA-co-itaconic acid)-grafted silica (Sil-PDM-PIA) and poly(DMAEMA-co-acrylic acid)-grafted silica (Sil-PDM-PAA) were characterized by Fourier transform infrared spectroscopy, elemental analysis and solid-state 13C NMR spectra. Their hydrophilic interaction performances were evaluated by separating nucleosides, nucleobases, saccharides, and amino acids. Compared with previous reported poly(itaconic acid)-grafted silica (Sil-PIA) and poly(acrylic acid)-grafted silica (Sil-PAA) stationary phases, these two new copolymer-grafted silica performed higher selectivity and better separation for polar analytes in HILIC.

Mechanisms on the impacts of humic acids on persulfate/Fe2+-based groundwater remediation

Persulfate (PS) has been increasingly applied for in situ chemical oxidation of organic contaminants in groundwater, while the impacts of humic acids (HAs) on the efficiency of persulfate/Fe2+-based remediation are not well understood. This study examined the effects of HAs originating from different places, including three commercial HAs and two soil HAs, on 2,4-dinitrotoluene (DNT) degraded by PS/Fe2+. DNT degradation by PS/Fe2+ was dependent on the types and concentrations of HAs and pH in solution. The positive correlation between the first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs and the conditional stability constant (KM) indicates that the complexation of HAs with Fe3+ was beneficial to the degradation of DNT. The first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs correlated well with their absorbance intensity of HAs at 465 or 665 nm. High positive correlation coefficients indicated that π-electrons of HAs strongly influenced DNT degradation, which was consistent with the results provided by solid-state 13C NMR spectra. Two-dimensional correlation spectroscopy (2DCOS) analysis confirmed that the fulvic-like fraction of HAs is prior to the humic-like fraction complexed with Fe3+.

NMR chemical shifts of urea loaded copper benzoate. A joint solid-state NMR and DFT study

We report solid-state 13C NMR spectra of urea-loaded copper benzoate, Cu2(C6H5CO2)4·2(urea), a simplified model for copper paddlewheel-based metal-organic frameworks (MOFs), along with first-principles density functional theory (DFT) computation of the paramagnetic NMR (pNMR) chemical shifts. Assuming a Boltzmann distribution between a diamagnetic open-shell singlet ground state (in a broken-symmetry Kohn-Sham DFT description) and an excited triplet state, the observed δ(13C) values are reproduced reasonably well at the PBE0-⅓/IGLO-II//PBE0-D3/AE1 level. Using the proposed assignments of the signals, the mean absolute deviation between computed and observed 13C chemical shifts is below 30 ppm over a range of more than 1100 ppm.

Novel porous β-cyclodextrin/pillar[5]arene copolymer for rapid removal of organic pollutants from water

A novel porous β‐cyclodextrin/pillar[5]arene copolymer was prepared using tetrafluoroterephthalonitrile as cross-linker for rapid removal of variety of organic pollutants. The copolymer was characterized by water contact angle, scanning electron microscope, FT-IR spectrum, solid-state 13C NMR spectrum, thermo-gravimetric analysis, nitrogen adsorption-desorption isotherms, and elemental analysis. Results showed that the co-polymer had good water immersibility, co-existing micro-/meso-pores, and a large specific surface area (BET) of 479 m2/g. The copolymer presented high adsorption capacity with the maximum adsorption capacity of 258 mg/g for bisphenol A and good reusability and reproducibility. It also showed fast binding kinetics with the apparent second-order rate constants of 0.109−0.179 g/mg·min and simultaneously rapid removal ability with removal efficiencies of 74–90% within 30 s for variety of organic pollutants. The new copolymer can be potentially used as adsorbent for rapidly removing a wide range of organic pollutants in wastewater.

2,2′-Bipyridine or 1,10-phenanthroline chelated oxomolybdenum(V) complexes with glycolate, lactate and malate in acidic media

A series of dimeric oxomolybdenum(V) 2,2′-bipyridine or 1,10-phenanthroline α-hydroxycarboxylates trans-[(MoO)2O(glyc)2(bpy)2]·3H2O (1), trans-[(MoO)2O(lact)2(bpy)2]·3H2O (2), trans-[(MoO)2O(Hmal)2(bpy)2] (3), trans-[(MoO)2O(lact)2(phen)2]·4H2O (4) and trans-[(MoO)2O(Hmal)2(phen)2]·4H2O (5) have been synthesized in acidic media for comparisons, where glycolate, lactate and malate in 1–5 chelate to molybdenum(V) with bidentate α-alkoxy and α-carboxy groups respectively. Unlike the molybdenum(IV) lactate in low valence [1], no protonation was observed for α-alkoxy groups even under acidic condition. The two molybdenum atoms in 1 and 3 are paramagnetic independently as examples by EPR spectroscopies. Solid state 13C NMR spectra of 1 and 3 show large downfield shifts for the coordinated glycolate and malate (δα-alkoxy 75.4, 82.8 ppm, Δδ 13.4 ppm). Moreover, a monomeric mixed ligand oxomolybdenum(VI) complex MoO2(glyc)(bpy) (6) was isolated.

Comprehensive understanding of the non-productive adsorption of cellulolytic enzymes onto lignins isolated from furfural residues

Effective enzymatic hydrolysis of lignocellulosic materials to produce fermentable sugars requires close cooperation between cellulase components. However, lignin remaining in the pre-treated substrate plays an inhibitory role in the synergistic action of enzymes through irreversible adsorption. In this study, the effect of cellulolytic enzyme lignin (CEL) isolated from pre-treated furfural residues and dissolved lignins (DLs) precipitated from black liquor on cellulase and cellobiase adsorption behavior was investigated. Green liquor (GL) combined with H2O2 (GL-H2O2) or ethanol (GL-ethanol) pre-treatments markedly decreased the adsorption capacity of CELs. However, the DLs had the strongest binding ability, which was approximately two to three times higher than that of CELs. According to SDS–PAGE analyses, only CBHII and EGII in cellulase and enzymes of 245 kDa and 55 kDa molecular weight in cellobiase were easily bound onto CELs and DLs. Solid-state 13C NMR spectra and FT-IR analysis indicated that pre-treatments reduced the hydrophobic structure of aromatic rings, β-O-4, and carbonyl, and increased the number of hydrophilic carboxyl groups in CELs. For this reason, the hydrophobicity of CELs was decreased, thus reducing their adsorption capacity. Compared with GL-H2O2 pre-treatment, GL-ethanol pre-treatment had a stronger effect on decreasing enzyme adsorption of lignin due to its high hydrophilicity. Heavy damage to aromatic structures, low molecular weight, and the large number of aliphatic portions in DLs caused their strong affinity for enzymes, although their BET surface area and hydrophobicity were low.

A comparison of the NaOH-HCl and HCl-HF methods of extracting kerogen from two different marine oil shales

The organic matter (kerogen, defined as including the organic material soluble and insoluble in organic solvents at room temperature) from two marine oil shales, El-Lajjun (Jordan) and Julia Creek (Queensland, Australia), has been extracted by the commonly used HCl-HF method and the resulting products compared with those obtained using the NaOH-HCl method, i.e. with initial strong alkali extraction. The elemental analyses on a dry ash-free basis of the solids obtained by the two methods were similar to each other and to that of the original oil shale. The pyrolysis-gas chromatography–total ion chromatograms were also similar for the kerogens obtained by the two methods and for the original oil shale, showing regular n-alkene/alkane series, as would be expected from the high atomic H/C ratio, and series of alkyl substituted thiophenes and benzothiophenes. The solid state 13C NMR spectra showed similar trends. The Fe contents of the solids obtained by the HCl-HF treatment were much higher than for the solids from NaOH-HCl treatment, which could have implications for reactivity studies. XPS showed depletion of the sulfur and oxidation near the surface and confirmed that some aliphatic sulfur was present. However, in general, both methods gave organic products with similar characteristics, allowing isolation of organic matter by a method not involving HF, whose use is restricted in many countries.

Influence of Acid on the Curing Process of Tannin-sucrose Adhesives

Tannin and sucrose (TS) can be used in a biomaterial-based wood adhesive that requires a higher hot pressing temperature and longer time than traditional resins. To solve these problems, hydrochloric acid and citric acid were utilized as a catalyst during the curing process to decrease energy costs (forming TSH and TSC adhesives, respectively). Thermal analysis revealed that the addition of hydrochloric acid and citric acid resulted in decreases to the thermal thresholds associated with degradation and curing. The resultant insoluble matter ratio verified that the polymerization reaction happened at a lower temperature than the adhesive without acidic conditions. The FT-IR and solid state 13C NMR spectra showed that the addition of acid compounds acted catalytically and increased the generation of 5-HMF in uncured adhesives. The dimethylene-ether bridges and methylene bridge were formed during the heat treatment. The water resistance of the particleboards manufactured by TSC and TSH adhesives were notably enhanced when the hot-pressing temperature was 180 °C. However, an increased hot pressing temperature did not improve the mechanical properties of the particleboard bonded by TSH, which was due to cellulose and hemicellulose decomposition under strong acidity conditions.

Effects of Sulfuric Acid on the Curing Behavior and Bonding Performance of Tannin⁻Sucrose Adhesive.

The development of biomaterials-based adhesives is one of the main research directions for the wood-based material industry. In previous research, tannin and sucrose were used as adhesive to manufacture particleboard. However, the reaction conditions need to be optimized. In this study, sulfuric acid was added to the tannin–sucrose adhesive as a catalyst to improve the curing process. Thermal analysis, insoluble mass proportion, FT-IR, and solid state 13C NMR were used to investigate the effects of sulfuric acid on the curing behavior of tannin and sucrose. Thermal analysis showed weight loss and endotherm temperature reduced from 205 and 215 to 136 and 138 °C, respectively, by adding sulfuric acid. In case of the adhesive with pH = 1.0, the insoluble mass proportion achieved 81% at 160 °C, which was higher than the reference at 220 °C. FT-IR analysis of the uncured adhesives showed that adding sulfuric acid leads to hydrolysis of sucrose; then, glucose and fructose converted to 5-hydroxymehthylfurfural (HMF) and levulinic acid. Dimethylene ether bridges were observed by FT-IR analysis of the cured adhesives. The results of solid state 13C NMR spectrum indicated that 5-HMF participated in the curing process and formed methylene bridges with the C8 position of the resorcinol A-rings of tannin, whereas dimethylene ether bridges were detected as a major chemical chain of the polymer. Lab particleboards were produced using 20 wt % resin content at 180 °C and 10 min press time; the tannin–sucrose adhesive modified with sulfuric acid to pH = 1.0 exhibited better performance than the unmodified tannin–sucrose adhesive; the properties of the boards fulfilled the requirement of Japanese Industrial Standard (JIS) A5908 type 15.

Green and facile surface modification of cellulose nanocrystal as the route to produce poly(lactic acid) nanocomposites with improved properties

In this study, lactic acid monomer or dimer is grafted onto CNC by a simple esterification reaction. The quantitative solid-state 13C NMR spectrum suggests that more than 87% of all the available OH groups on the surface of CNC are substituted by lactic acid. Such modified CNC (CNC-g-LA) exhibits excellent thermostability and nano-sized dispersion in chloroform. Benefit from this character, fully biobased PLLA/CNC-g-LA nanocomposite could be prepared simply by a solution-casting method. The crystallization behavior of obtained nanocomposites has been systematically investigated by differential scanning calorimetry (DSC). The results show that the crystallization rate of PLLA is distinctly enhanced. Moreover, the mechanical properties of nanocomposites are also improved remarkably by the addition of CNC-g-LA because of its excellent dispersion and compatibility with PLLA matrix. This study provides a green and facile way to modify CNC for fabricating bio-nanocomposites with fast crystallization rate and improved mechanical properties.

Remarkably enhanced H2 evolution activity of oxidized graphitic carbon nitride by an extremely facile K2CO3-activation approach

The photocatalytic activity enhancement of graphitic carbon nitride (g-C3N4) in water splitting were commonly achieved by introducing various functional groups onto/into its planar structure. Herein, oxidized g-C3N4 (CNO) was prepared via an extremely facile K2CO3 activation approach. The high-resolution XPS spectra and solid-state 13C NMR spectra confirmed the successful introduction of O-containing groups and O atoms were inherited the original molecular framework of g-C3N4, but exhibited effectively enlarged bonded with C atoms rather than N atoms in the tri-s-triazine structure of g-C3N4. CNO inherited the original molecular framework of g-C3N4, but exhibited effectively enlarged surface area and enhanced visible light absorption, and more attrractively, the band structure of g-C3N4 could be well-tuned with the introduction of oxygen species. Importantly, the surface O-containing moieties could strongly interact with cocatalyst Pt and thus remarkably promote interfacial electron transfer and consequent photo-generated charge carrier separation. Consequently, the as-obtained CNO exhibited the remarkably enhanced photocatalytic performance with a H2 evolution rate of 199.7 μmol h−1, which is 9 times that of g-C3N4 (22.2 μmol h−1).