Amount Of Carboxyl Groups Research Articles

Chemofunctionalization of knitted silk to improve interface connection in a nano/micro scaffold based on polycaprolactone-chitosan-multi-walled carbon nanotube/silk.

Nano/micro hybrid scaffolds in long-term healing tissue engineering can simultaneously offer both mechanical and biological properties. In this study, a hybrid scaffold was fabricated through electrospinning of polycaprolactone (PCL)-chitosan (Cs)/ multi-walled carbon nanotubes (MWCNTs) based nanofibers onto a chemically functionalized knitted silk substrate (F-Silk) and the scaffold were evaluated with regard to morphology, chemical and crystalline structure, hydrophilicity, mechanical properties, bioactivity, biodegradability, and cellular behavior. Chemical functionalization of silk using N-hydroxysuccinimide (NHS) and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) resulted in greater integrity in the formation of nanofibers onto the microfibers. The presence of MWCNTs significantly reduced the contact angle of the scaffolds from 79.72°±2.72 to 68.92°±5.63. Chemical functionalization of silk, the presence of nanofiber coating, and the presence of MWCNTs increased the ultimate tensile strength of the hybrid scaffolds by 18%, 20%, and 30% compared to raw silk fabric, respectively. The presence of MWCNTs and chemical functionalization of knitted silk increased the bioactivity and reduced the degradation rate of hybrid scaffolds. The increase in the amount of carboxyl groups as a result of adding 0.5wt% of MWCNTs significantly improved the adhesion, growth and proliferation of chondrocyte cells on the hybrid scaffolds as observed through cell morphology. According to the obtained results, hybrid scaffold based on PCL-Cs-MWCNTs/F-silk can be a suitable option for further research in cartilage tissue engineering.

Tri-monomer polyamide acid nanofiber separator for safe and high performance lithium-ion batteries

The separators play a crucial role in ensuring the safety of lithium batteries and greatly affect the electrochemical performance of the battery. However, the weak thermal stability and non-polar surface of commercial polyolefin separators severely restrict the development of the high-performance lithium batteries. In this work, we initially proposed polyamide acid (PAA) nanofiber separator with three monomers through a two-step synthesis method, which was prepared by electrospinning. By controlling different processing temperatures, PAA separators containing different amount of carboxyl groups were obtained. PAA separator had better wettability and thermal stability than PE separator. Meanwhile, the electrospinning method brings ultra-high porosity (95.3 %) to the membrane, resulting a much higher electrolyte absorption and retention rate of PAA (initially 3214 %, 240 % at 50 min) compared to PE separator. In particular, carboxyl groups serve as functional groups to provide an electronegative atmosphere, promoting the transport of lithium ion between the anode and cathode, and playing an important role in improving ionic conductivity. Consequently, batteries with PAA-SOH-50 separator showed the best rate charging/discharging performance, maintaining 87.7 % and 73.6 % of its initial capacity at 2.0 C. Moreover, cells with PAA separator exhibited much higher initial discharge capacity (164.3 mAh g−1) than that with PE separator (126.8 mAh g−1). After 100 cycles at 0.5 C, the PAA nanofiber separator achieved an ultralow attenuation rate of only 0.04 % per cycle, which was less than half of the commercial PE separator (0.10 % per cycle). This work provides a new vision for the development of separator materials, revealing the great influence of functional groups, such as carboxyl groups, on the performance of separators, which provides a strong basis for the further research of high-performance separators.

STUDY OF THE EFFECTIVENESS OF THE INFLUENCE OF PLASTICIZERS AND FUNCTIONAL ADDITIVES IN THE RECEIVING OF THERMOPLASTIC STARCH ON ITS FILM-FORMING AND DESTRUCTIVE PROPERTIES

A literature review on the production of thermoplastic starch (TPS) with various plasticizing additives as a component of biodegradable polymer compositions was conducted. Plasticizing additives with different functional groups, due to which starch modification occurs, were analyzed. In order to expand the spectrum of functional additives for the formation of TPS, the introduction of acids with different amounts of carboxyl groups: citric, oxalic, oleic, stearic was studied. The technological parameters of thermomechanical processing of starch compositions and the quantitative composition of the components are determined. Physical and mechanical tests of strength and elasticity of film samples of TPS compositions and compatible with synthetic polymer were carried out. In order to obtain the structural characteristics of TPS and TPS films with polyethylene, studies were carried out by IR-Fourier spectroscopy and mass spectrometry. Studies of the effect of UV irradiation on the degradability of TPS compositions after exposure in a climate chamber for 90 days were conducted. It was found that the loss of strength and elasticity of TPS and TPS+PE film samples is (82–90)%, elasticity (60–70)%, depending on plasticizing and structure-forming additives and their amounts.

New approaches for regulation of structure and adsorption properties of biochar based on freshwater sediments (sapropels)

Biochar based on sapropel have been synthesized and the effect of chemical modification on their textural characteristics, acid-base and adsorption properties has been studied. It was found that preliminary treatment of raw sapropel with a weakly concentrated solution of alkali increases the fraction of micropores: from 0.006 cm3 g−1 (for BС-N) to 0.021 cm3 g−1 (for КОН-BC), and additional treatment with hydrofluoric acid leads to an increase in the fraction of micropores up 0.047 cm3 g−1 (for КОН-BC-HF) and also of specific surface area up to 211 m2 g−1 at a considerable decrease in the fraction of mineral part due to leaching of silicon-containing phases. The proposed chemical modification makes it possible not only to change the ratio of mineral and carbon parts and the pore space, but also to vary the surface properties of biochar: рНPZC, concentration and features of oxygen-containing groups. It is shown that the total content of acidic groups increases in the series BС-N (0.3290 mmol g−1) < КОН-BC (0.5567 mmol g−1) < КОН-BC-HF (1.3046 mmol g−1). Simultaneously the type of treatment affects the nature of oxygen-containing groups: the maximum amount of phenolic groups (0.4845 mmol g−1) in sample КОН-BC, the surface acidity of КОН-BC-HF is contented by the presence of a considerable amount of carboxyl groups (0.9198 mmol g−1). The analysis of the data obtained shows that the total content of acidic groups increases in the series The adsorption of Cu(II) ions from an aqueous solution on the synthesized samples of biochar was studied for the first time. Biochar obtained using the sapropel pretreated with alkali showed the maximum adsorption capacity toward copper ions of 27.9 mg g−1. Conceptual model identifying the mechanisms of adsorption copper (II) ions on biosorbent from sapropels was shown. The experimentally obtained isotherms were approximated using the Freundlich and Langmuir models. It was found that the adsorption of copper on the tested samples can be described quite adequately by the Langmuir monomolecular adsorption model (R2 ≥0.98).

Effect of Coconut Fiber Biochar and Its Nitrate Modification on Pb Passivation in Paddy Soils

The effects of coconut fiber biochar (CFB) and nitrate-modified coconut fiber biochar (NCFB) on the passivation of exogenous lead (Pb) in paddy soils and their underlying mechanisms were investigated using soil incubation experiments combined with spectroscopic techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), synchrotron radiation X-ray fluorescence (SRXRF), and Fourier transform infrared absorption spectroscopy (FTIR). The effects of NCFB and CFB on the passivation of exogenous lead (Pb) in paddy soils and its underlying mechanisms were investigated. Compared with that of CFB, the inner wall of NCFB honeycomb pores was rougher, and the amount of alcohol-phenol-ether functional groups containing the C-O structure and the amount of carboxyl groups containing the C[FY=,1]O/O[FY=,1]C-O structure on the surface of CFB was significantly decreased after nitric acid modification. Compared with that in the control (without biochar) paddy soil after 150 d of incubation, the EDTA-extracted Pb content in the paddy soil with CFB and NCFB was reduced by 39.7% and 105.4%, respectively. The carbonate-bound and Fe-Mn oxide-bound Pb contents were significantly lower, and the organic-bound and residue Pb contents were significantly higher in the NCFB-added soil. The SRXRF scans showed that the exogenous Pb was enriched in the microregions of CFB particles rich in Ca and Cu elements and relatively less so in the microregions of soil aggregates rich in the Fe, Mn, and Ti elements. In addition, the characteristic peaks of carboxylates (1384 cm-1) in A-CFBPb and A-NCFBPb were significantly enhanced in the incubation experiment in the presence of exogenous Pb compared to A-CFB and A-NCFB in the absence of exogenous Pb. The addition of CFB or NCFB was more effective in passivating exogenous Pb in paddy soils and promoted the gradual transformation of Pb from unstable to more stable forms in paddy soils to achieve the effect of passivating Pb. The greater amount of carboxyl functional groups in NCFB participated in the passivation of exogenous Pb, which made NCFB more effective than CFB in passivating Pb. NCFB was more effective than CFB in passivating exogenous Pb in paddy soils due to its rougher inner walls of honeycomb pores and abundant carboxyl functional groups. In tropical areas such as Hainan, coconut fiber biochar and its modification can be considered as an environmentally friendly candidate method for the remediation of soil Pb contamination.

Multistage treatment of bamboo powder waste biomass: Highly efficient and selective isolation of lignin components

Bamboo pulp and papermaking produce a lot of bamboo powder waste, and its resource utilization is of great significance for biomass refining and environmental protection. Here, we propose an integrated approach involving mechanical activation, hydrothermal extraction, and deep eutectic solvents (DESs) multiple delignification for the efficient separation of bamboo powder. Among seven carboxylic acids based DESs, choline chloride (ChCl)-lactic acid (La) DES (1:1) is the most effective, with over 78.0% lignin removal and 88.9% cellulose retained after mechanical-hydrothermal (180 °C, 5 h)-DES (110 °C, 12 h) treatment. Notably, 84.7% of delignification is achieved after three times of ChCl-La DES treatment at 70, 90, and 110 °C respectively. The delignification rate is negatively correlated with the amount of carboxyl group in the DESs. The lower the pKa value, the higher the delignification rate. Additionally, the selectivity for lignin is improved with decreasing solvent polarity. DES treatment effectively degrades the guaiacyl unit lignin fractions and disrupts several β-aryl-ether bonds (e.g., β-O-4, β-β, and β-5). Furthermore, DESs exhibit good recyclability, with less than 10% reduction in delignification after three cycles. Theory calculations confirm that ChCl-carboxylic acid DESs could compete with lignin to break hydrogen bonds in lignocellulosic biomass by providing their chloride, hydroxyl, and carboxyl groups. Overall, this study demonstrates the practical significance of multistage treatment for the effective fractionation of biomass into its three components.

In-situ etching MOF nanoparticles for constructing enhanced interface in hybrid membranes for gas separation

Metal-organic frameworks (MOFs) based hybrid membranes have great potential for energy-efficient gas separation. However, the defective interface structure greatly depresses their separation performance. In this work, a distinctive interfacial design strategy via in-situ etching ZIF-8 nanoparticles is proposed to construct hybrid membranes with nearly defect-free interfaces. The nanoscale etching of ZIF-8 nanoparticles in polymer matrix with acid group (PI-COOHx) is well controlled by the amount of carboxyl group and reaction time. Owing to the strong coordination interaction between Zn2+ ions and –COOH groups, the residual ZIF-8 nanoparticles are tightly wrapped by polymer matrix. Molecular simulation was performed to study the in-situ etching ZIF-8 in PI-COOHx matrix in molecular level. The resulted hybrid membranes (PI-COOHx/E-ZIF-8) exhibit simultaneously enhanced permeability and selectivity with increasing filler loading content. Benefiting from the rational interfacial design, the effective loading content of ZIF-8 nanoparticles is up to 50 wt% for PI-COOH20/E-ZIF-8 membrane. The H2, CO2, and O2 permeability of the membrane are 3058.6, 1429.0, and 459.0 Barrer, increasing by 468.5%, 288.3% and 348.2%, respectively, of pristine PI-COOH20 membrane, and the gas selectivity for H2/N2, H2/CH4, O2/N2, and CO2/CH4 gas pairs are greatly improved from 20.3, 23.4, 3.9 and 16.0 of pristine PI-COOH20 membrane to 30.7, 37.6, 4.6 and 17.6. The comprehensive separation performance for H2/N2, H2/CH4, and O2/N2 gas pairs surpass the 2008 upper bound and approach the 2015 upper bound. Meanwhile, the CO2 plasticization resistance of PI-COOH20/E-ZIF-8 membrane also achieves significant improvement from 6 bar of PI-COOH20 membrane to 27 bar. This work provides an effective and robust strategy to effectively enhance the interfacial compatibility of hybrid membranes.

Competitive removal mechanism to simultaneously incarcerate bisphenol A, triclosan and 4-tert-octylphenol within beta-cyclodextrin crosslinked citric acid used for encapsulation in polypropylene membrane protected-micro-solid-phase extraction

Endocrine disrupting compounds (EDCs) are extensively found in the environment and severely impacting human health. In addressing this issue, the beta-cyclodextrin crosslinked citric acid (BCD-CA) had been previously employed in membrane-protected micro-solid phase extraction for sequestering EDCs from water medium; and the findings revealed that BCD-CA possessed a selectivity property. On that account, the potential of BCD-CA towards competitive adsorption of selected EDCs was investigated in terms of adsorption mechanism and selectivity property. Factors that affected the removal efficiencies such as sample pH, sorbent dosage, contact time and initial concentration were evaluated. The characterization results revealed that the carbon percentage of BCD-CA had increased by 2.04%, while the hydrogen percentage had reduced by 1.83%, signifying the successful crosslinking of BCD-CA. Besides, the amount of active BCD was calculated to be 3.2 × 10−7 mol, while the amount of carboxyl group was 2.48 × 10−5 mol per 4 mg of BCD-CA. Moreover, BCD-CA was stable in an aqueous medium with the zeta potential obtained at −36.5 mV and had a high-water retention capacity (∼150%). The competitive adsorption mechanism by BCD-CA with EDCs followed the pseudo-second-order kinetics and Freundlich isotherm, suggesting that the adsorption process was dominated by chemisorption on the heterogeneous surface of the adsorbent. Thermodynamic results revealed that adsorption of 4-tert-octylphenol had the most negative ΔG value, indicating most favorable to be adsorbed by BCD-CA as opposed to triclosan and bisphenol A, which was coherent with the apparent formation constant results. These unique properties manifested the practicality of BCD-CA as a selective adsorbent to detect and remove EDCs from the water medium.

New Membrane-Forming Aromatic Co-Poly(amide-imide)s: Influence of the Chemical Structure on the Morphological, Thermal and Transport Properties

Polymer film membranes are used to solve specific separation problems that dictate structural requirements. Structural and morphological parameters of film membranes based on glassy polyheteroarylenes can be controlled in the process of preparation from solutions that opens up prospects for obtaining structured membranes required for targeted separation. In the case of aromatic poly(amide-imide)s, the possibility of controlling film formation and structure virtually has not been studied. In the present work, a series of homologous co-poly(amide-imide)s differing in the number of repeating units with carboxyl-substituted aromatic fragments was synthesized by polycondensation. Comparative analysis of the processes of formation of membranes with different morphologies based on these polymers under equal conditions was performed. New information was obtained about the influence of the amounts of carboxyl groups and the residual solvent on structural properties of asymmetric membranes. The influence of these factors on transport properties of dense membranes under pervaporation conditions was studied. It was demonstrated that in the case of carboxyl-containing poly(amide-imide)s, the domains formed during film preparation had a significant effect on membrane properties.

How to improve the efficiency of biocatalysis in non-aqueous pure deep eutectic solvents: A case study on the lipase-catalyzed transesterification reaction

Non-aqueous biocatalysis has been expanding the application fields of biocatalysis and is playing an increasingly important role in industrial biocatalysis. Deep eutectic solvents (DESs) have been recognized as green reaction media of non-aqueous biocatalysis. To provide guidance for improving the catalytic performance of enzymes in pure DESs, Candida antarctica lipase B (CALB) catalyzed transesterification reaction was chosen as the model reaction to assess the catalytic efficiency in different series of pure DESs. The catalytic efficiency of CALB was strongly influenced by the properties of DESs. Hydrophobic DESs caused less inactivation of CALB than hydrophilic DESs. The highest yield in hydrophobic DESs reached 56.75% after 12 h. The amount of carboxyl group in hydrophobic DESs, the amount of hydroxyl group in hydrophilic DESs, and the length of carbon chain had positive impacts on the catalytic efficiency of CALB in DESs. Learning from the CALB behaviors in DESs, a preliminary attempt in rational design DESs for higher transesterification efficiency was provided. Except for reaction media, the catalytic activity of CALB in DESs was improved by medium engineering means and enzyme engineering measures, such as adding a trace amount of water, imprinting CALB with pH buffer or inorganic salt, and protecting CALB by lyoprotectants. Synergistic effect of multiple activation methods could also be observed in improving the catalytic efficiency. This study can provide insights into expanding the application of DESs in non-aqueous biocatalysis.

Titration of weak base fibrous anion exchangers in the presence of complex-forming divalent cations

Curves of potentiometric titration of fully protonized fibrous ion exchangers with potassium hydroxide against the background of 1 M KCl in the presence of chlorides of Ni2+, Со2+, Сu2+ and Ca2+ were obtained. The ion exchangers were synthesized by modifying of industrial polyacrylonitrile fiber with diethylenetriamine and triethylenetetraamine and predominantly contained functional groups R-CO-NH- (CH2CH2NH)nH (n = 2 or 3) and a small amount of carboxyl groups. The sorption of Ni2+, Со2+, Сu2+ и Ca2+by ion exchangers was calculated from the data obtained depending on the pH of the medium. It was found that the investigated ion exchangers with high selectivity sorb heavy metal ions in a wide range of acidity of solutions (pH 2–9) due to the formation of metal-polymer complexes with polyamine functional groups. The maximum sorption capacity is 1.5–2.7 and 4–5 meq/g for ion exchangers with n = 2 and 3, respectively.

Core-Shell Fe2O3@La1-xSrxFeO3-δ Material for Catalytic Oxidations: Coverage of Iron Oxide Core, Oxygen Storage Capacity and Reactivity of Surface Oxygens.

A series of Fe2O3@LSF (La0.8Sr0.2FeO3−δ perovskite) core-shell materials (CSM) was prepared by infiltration of LSF precursors gel containing various complexants and their mixtures to nanocrystalline aggregates of hematite followed by thermal treatment. The content of LSF phase and amount of carboxyl groups in complexant determine the percent coverage of iron oxide core with the LSF shell. The most conformal coating core-shell material was prepared with citric acid as the complexant, contained 60 wt% LSF with 98% core coverage. The morphology of the CSM was studied by HRTEM-EELS combined with SEM-FIB for particles cross-sections. The reactivity of surface oxygen species and their amounts were determined by H2-TPR, TGA-DTG, the oxidation state of surface oxygen ions by XPS. It was found that at complete core coverage with perovskite shell, the distribution of surface oxygen species according to redox reactivity in CSM resemble pure LSF, but its lattice oxygen storage capacity is 2–2.5 times higher. At partial coverage, the distribution of surface oxygen species according to redox reactivity resembles that in iron oxide.

Facile preparation of cellulose nanofibrils (CNFs) with a high yield and excellent dispersibility via succinic acid hydrolysis and NaClO2 oxidation

An efficient and low-cost approach to preparing CNFs with succinic acid hydrolysis and NaClO2 oxidation is explored. High-temperature-short-time hydrolysis can depolymerize the cellulose, whereas the dispersibility of the CNFs is hugely enhanced by NaClO2 oxidation under alkaline condition. The degradation of cellulose in succinic acid hydrolysis follows first-order reaction kinetics and is severely influenced by the hydrolysis temperature, moreover, the molecular chains of the cellulose are seriously cracked under the optimized condition. The NaClO2 oxidation greatly improves the zeta potential (−36.2 mV) and the dispersibility of the CNFs. The obtained CNFs have an ultimate yield of 94.6%, and the diameter distribution is mainly within 20–40 nm. In addition, some amount of carboxyl groups in the cellulose will be instead of the hydroxyl groups, and the crystallinity of the CNFs is significantly increased.

Carboxyl groups on g-C3N4 for boosting the photocatalytic U(VI) reduction in the presence of carbonates

The photocatalytic U(VI) reduction provides a promising strategy for extracting uranium from seawater. However, seawater contains ~2.75 mM carbonates, which would seriously inhibit the photocatalytic reduction of U(VI), restricting the practical application of this method. This study is devoted to realizing the photo-reduction of U(VI) in carbonates-containing system by developing a highly efficient photocatalyst. Carboxylated carbon nitride (CCN) catalysts with different amounts of carboxyl groups were prepared (CCN-5 and CCN-24) by oxidating bulk carbon nitride (BCN). Compared to BCN, the adsorption ability of CCN-24 for U(VI) increased by 30% and 9% in the presence of 2.0 mM and 10.0 mM NaHCO3, respectively. Moreover, the modification of electron-withdrawing carboxyl groups reduced the conduction band position and promoted the separation efficiency of electrons and holes, facilitating the photocatalytic performance for the reduction of U(VI). Under the illumination of visible-light, CCN exhibited high reactivity for the photocatalytic U(VI) reduction in carbonates-containing system. In the presence of 10.0 mM HCO3−, CCN-24 showed a U(VI) reduction rate of 0.0867 min−1, being ~33 times of that for BCN (0.0026 min−1). Electron spin resonance (ESR) and radical trapping investigation proved that •O2− was the main active reduction species for U(VI), and more •O2− and fewer oxidizing •OH radicals were generated on CCN than BCN. It was also verified that CCN could remain stable and keep high photocatalytic reactivity after at least 5 recycles. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) confirmed that U(VI) was finally reduced to U(IV) and UO2+x was finally formed on the photocatalyst surface. This work opens up the possibility of extracting uranium from carbonates-containing solutions via photocatalysis method, expending the application of this method in natural systems.

Hydrogels of Polysaccharide Carboxymethyl Hydroxypropyl Guar Crosslinked by Multivalent Metal Ions

Hydrogels of polysaccharide carboxymethyl hydroxypropyl guar crosslinked by chromium(III) ions are synthesized. The effect of crosslinker concentration on the mechanical behavior of the gels is studied, and the amount of chromium compounds able to interact with polymer chains and the amount of carboxyl groups of the polymer involved in crosslinking are compared. It is shown that the elastic modulus of the gels attains a constant value when not all but only about 10% functional groups interact with chromium compounds. At high concentrations, crosslinker molecules basically bind to one functional group; as a result, the gel recharges. This binding proceeds until all carboxyl groups are filled.

Optical Properties of Soil Dissolved Organic Matter Are Related to Acidic Functions of Its Components as Revealed by Fractionation, Selective Deuteromethylation, and Ultrahigh Resolution Mass Spectrometry.

The goal of this study was to establish a relationship between the optical properties of soil dissolved organic matter (DOM) and acidic functions carried out by its individual constituents. We obtained 12 fractions of DOM samples using sequential solid phase extraction on nonionic sorbent at steadily lowered pH values: 7, 5, 3, 2, which correspond to low bounds of pKa values of phenols, aliphatic, and aromatic carboxylic acids, and ketoacids. The structural studies were conducted with the use of NMR and selective deuteromethylation of isolated fractions coupled to ultrahigh resolution mass spectrometry. First, a gradual shift of molecular compositions was observed from reduced components to aromatic oxidized compounds isolated at pH 7 and 2, respectively. Changes in molecular compositions were accompanied by a red shift of fluorescence spectra. Further application of deuteromethylation enabled us to distinguish DOM constituents with different amounts of carboxylic groups. Moreover, identification of structural isomers in a single DOM sample was achieved. Statistical analysis revealed that red shift of fluorescence is facilitated by the increase of a contribution of aromatic poly(carboxylic acid)s with high conjugation lengths. Additionally, analysis of the labeled fractionated permafrost thaw DOM directly showed carboxyl-rich alicyclic molecules, while the same components from lower-latitude DOM were assigned to lignin-like species.

Simple Universal Strategy for Quantification of Carboxyl Groups on Carbon Nanomaterials: Carbon Dioxide Vapor Generation Coupled to Microplasma for Optical Emission Spectrometric Detection

The physicochemical properties and applications of carbon nanomaterials are remarkably dependent on the amount of carboxyl group on their surfaces. Unfortunately, it is challenging to determine the carboxyl group on carbon nanomaterials at an ultralow density not only due to the low sensitivities of conventional techniques, but also because there are no matrix-matched certified reference materials available. In this work, a novel strategy comprising coupling carbon dioxide vapor generation to a microplasma optical emission spectrometer was developed for the sensitive and accurate quantification of surface carboxyl groups on carbon nanomaterials. The carboxyl group on multiwall carbon nanotubes (MWCNTs), graphene (G), or its oxide (GO) was converted to carboxylic acid using concentrated hydrochloric acid prior to quantification. The generated carboxylic acid was purified and then reacted with sodium bicarbonate to generate CO2, which was swept into a miniaturized point discharge optical emission spectrometer (μPD-OES) for the detection of carbon atomic emission lines. Potassium hydrogen phthalate (KHP) served as a calibration standard for quantification of the carboxyl group on G/GO/MWCNTs, thus, overcoming the lack of CRMs. Owing to the high sensitivity of μPD-OES for the detection of CO2, a limit of detection of 0.1 μmol g-1 (1 nmol) was obtained for the carboxyl group based on a sample mass of 10 mg G/GO/MWCNTs, superior to that obtained using conventional methods. Moreover, the proposed method not only retains several unique advantages of good accuracy and elimination of the use of complicated, expensive, and high power-consumption instruments, but was also applicable to the quantification of the carboxyl group on other nanomaterials such as carboxylated magnetic microspheres.

Spectral study of humic substance extract from pressurized oxidizing slag of Carlin-typed gold deposit

Carbonaceous matters in Carlin-type gold deposit, especially the humic substance, which have a serious preg-robbing effect on the process of cyanidation. In this paper, the humic acid and fulvic acid were extracted from oxidizing slag via pre-activation alkaline-heat method, and using FTIR and UV-Vis spectra to study the molecular structure of humic acid extract and fulvic acid extract. The FITR spectrum demonstrated that hydroxyl, carboxyl and benzene rings characteristic stretching vibration peaks occurred in spectra of humic acid and fulvic acid, but humic acid extract had a finer molecular structure. The result of UV-Vis spectra analysis showed that the extract contained alkyl-substituted benzene ring structure, and the amount of carboxyl groups and hydroxyl groups in fulvic acid molecule was larger than that of humic acid. The fulvic acid extract contained more chromophores, while humic acid molecules have a higher degree of humification and a higher average molecular weight. Although there were some differences in the molecular structure of the both, they were both complex macromolecular organic compounds with a benzene ring as a basic unit.

Multifunctional Nanovectors Based on Polyamidoamine Polymers for Theranostic Application.

We present multifunctional, biocompatible and biodegradable magnetic nanovectors based on different polyamidoamine (PAA) polymers tailored with different diagnostic and therapeutic properties. Using maghemite nanoparticles with average size 15.5 ± 2.8 nm prepared by thermal decomposition, superparamagnetic nanovectors were obtained by coating the nanoparticles with synthetic polymers of PAA. These have a segmented copolymer structure, and bear PAA segments containing different amount of carboxyl groups per repeating units together with PEG segments. These copolymers are thought to combine the binding properties of the carboxylated PAA segments to inorganic nanoparticles, with the stealth properties of the PEG ones. The magnetic, hyperthermal and relaxometric properties of the synthesized samples were investigated. Magnetic measurements revealed that the samples are superparamagnetic at room temperature and the overall magnetic behavior is not affected by the functionalization process. Calorimetric measurements demonstrated a good heating efficiency at alternating magnetic field parameters below the human tolerability threshold (SAR of ca. 70 W/g at 260 Hz and 10.8 kA/m). 1H-NMR relaxivities were relevant compared to the values of the commercial contrast agents over the whole investigated frequency range.

Interactions of silicon nanoparticles with carboxymethyl cellulose and carboxylic acids in negative electrodes of lithium-ion batteries

Slurry preparation in a citric-acid-buffered aqueous solution at low pH has been established as a viable strategy for tackling the poor capacity retention of silicon electrodes. A number of studies ascribed the improved capacity retention to the formation of a silyl ester between the Si surface and carboxymethyl cellulose (CMC-Na). Most recent findings suggest that the citric acid itself interacts with the Si surface. Moreover, cross-linking reactions between the carboxylic acid and the binder can occur. In order to provide a comprehensive overview and to gain a better understanding of the reactions on the Si surface during slurry preparation, we review here previous results and interpretations and revisit earlier infrared (IR) studies, whose findings we link to our own IR studies of the impact of the slurry components, individually and combined. Specifically, we studied the interactions between the carboxylic acid, CMC-Na and Si particles, with the aim to clarify the effects of different amounts of carboxyl groups in carboxylic acids, namely glycolic, malic and citric acids with 1, 2 and 3 carboxyl groups, respectively. Furthermore, we demonstrate that the capacity retention of Si electrodes can be improved considerably with any of the acids studied.