Contribution Of Functional Groups Research Articles

Green synthesis of multifunctional carbon quantum dots: An approach in cancer theranostics.

Carbon quantum dots (CQDs) have gained significant growing attention in the recent past due to their peculiar characteristics including smaller size, high surface area, photoluminescence, chemical stability, facile synthesis and functionalization possibilities. They are carbon nanostructures having less than 10nm size with fluorescent properties. In recent years, the scientific community is curiously adopting biomass precursors for the preparation of CQDs over the chemical compounds. These biomass sources are sustainable, eco-friendly, inexpensive, widely available and convert waste into valuable materials. Hence in our work the fundamental understating of diverse fabrication methodologies of CQDs, and the types of raw materials employed in recent times, are all examined and correlated comprehensively. Their unique combination of remarkable properties, together with the ease with which they can be fabricated, makes CQDs as promising materials for applications in diverse biomedical fields, in particular for bio-imaging, targeted drug delivery and phototherapy for cancer treatment. The mechanism for luminescence is of considerable significance for leading the synthesis of CQDs with tunable fluorescence emission. Therefore, it is aimed to explore and provide an updated review on (i) the recent progress on the different synthesis methods of biomass-derived CQDs, (ii) the contribution of surface states or functional groups on the luminescence origin and (iii) its potential application for cancer theranostics, concentrating on their fluorescence properties. Finally, we explored the challenges in modification for the synthesis of CQDs from biomass derivatives and the future scope of CQDs in phototherapy for cancer theranostics.

Single and combined toxicity of polystyrene nanoplastics and copper on Platymonas helgolandica var. tsingtaoensis: Perspectives from growth inhibition, chlorophyll content and oxidative stress

The combined toxic effects of nanoplastics and heavy metals on aquatic organisms have attracted widespread attention; however, the results are inconsistent and the mechanisms remain unclear. In this study, the single and combined toxicity effects of Cu and two types of polystyrene nanoplastics (PS-NPs; 50 nm PS and 55 nm PS-COOH) on Platymonas helgolandica var. tsingtaoensis were investigated, including growth inhibition, chlorophyll content, and oxidative stress. An adverse dose-response relationship on growth inhibition was found in the Cu treatment groups, which was related to the decrease in chlorophyll content and damage to cell membranes. The growth inhibitory effect of PS-NPs on microalgae increased with exposure time and concentration, and no significant difference was found in the two types of PS-NPs because of the negligible contribution of functional groups. A more significant increase in chlorophyll content was found in PS treatments than in PS-COOH treatments at 96 h because of the microscale aggregates formed by PS. Higher concentrations (≥ 50 mg/L) of PS-NPs caused membrane lipid peroxidation, which might be responsible for growth inhibition. In the combined exposure experiments, a synergistic effect on the growth inhibition rate was obtained using the independent action model and Abbott model. Combined exposure triggered more severe oxidative damage to the microalgae. Adsorption experiment results showed that there was no adsorption between PS-NPs and Cu, while the interaction of Cu and algal cells could be promoted due to the presence of the PS-NPs, which explained the increasing combined toxicity. This study could improve our understanding of the combined toxicity of nanoplastics and heavy metals and could provide a new explanation for the mechanism of combined toxicity.

Contribution of legume and non-legume trees to litter dynamics and C-N-P inputs in a secondary seasonally dry tropical forest

Many studies have investigated nutrient cycling in seasonally dry tropical forests, but few have assessed the contribution of different functional groups to these processes. Here, we investigated general litter dynamics patterns and the contribution of legume and non-legume trees to litter dynamics and carbon (C), nitrogen (N), and phosphorus (P) inputs in a fragment of secondary seasonally dry tropical forest after half a century of forest succession in the Atlantic Forest biome in Brazil. Between 2016 and 2017, we quantified litterfall production, canopy cover, forest floor, and soil C and N storage in 11 permanent plots distributed in the fragment. Vegetation identity and structure had been previously assessed. We quantified the seasonal inputs of leaf litter and C, N, and P separately for each functional group (legume and non-legume tree species). We also analyzed the correlations between the variables measured for each functional group with the variables measured at the plot level. Litter dynamics and nutrient input were affected by climate and functional group. Litterfall production during the two driest months was three times higher than during the other periods of the year, suggesting that species synchronicity is likely to minimize drought-related damage on trees. Legume trees had twice the basal area attained by non-legume trees, but while legumes were larger, non-legumes were more abundant and dominant in the smaller diameter class. Legumes deposited twice as much N during the driest period of the year as non-legumes. Although leaf litter, C, and P inputs by legumes were generally higher than those of non-legumes, these differences during the dry season were not statistically significant. We also found that the legume variables correlated better with the plot-level variables, compared to the non-legume functional group. Our results also indicated potential effects of the leaf litter and nutrient inputs by the legume functional group on the decomposition constant and, consequently, on the time of forest floor decomposition. Further studies should assess the role of different functional groups in litter dynamics and nutrient inputs in seasonally dry tropical forests.

Screening for New Efficient and Sustainable-by-Design Solvents to Assist the Extractive Fermentation of Glucose to Bioethanol Fuels

The production of bioethanol fuels using extractive fermentation increases the efficiency of the bioconversion reaction by reducing the toxic product inhibition. The choice of appropriate solvents to remove the bioethanol product without inhibiting the fermentation is important to enable industrial scale application. This work applies computer-aided molecular design technologies to systematically screen a wide variety of candidate solvents to enhance the separation, also considering the microorganisms that perform the fermentation. The performance of the candidates was evaluated using a rigorous process simulator for extractive fermentation, assisted by functional group-contribution (QSPR/QSAR) models for the prediction of various solvent properties, including toxicity and life cycle impacts. The solvent designs generated through this approach can provide powerful insights on the kind of molecular structures and functionalities that satisfy the process objectives and constraints, as well the desired sustainability features.

A study on the utilization of rice husk as a biosorbent material for Cr (VI) removal from industrial effluent


 
 
 
 Purpose: To study Cr (VI) removal from waste water using chromium-resistant bacterial strains in combination with rice husk.
 Methods: Two strains of Exiguobacterium sp. resistant to chromium (VI) were applied in the present work. Rice husk (RH) was used as an agricultural waste for Cr (VI) removal. The elimination of Cr from the husk was chemically facilitated using hydrochloric, sulphuric and citric acids, as well as formaldehyde and potassium dihydrogen phosphate Investigation of optimum physical factors such as pH, temperature, shaking speed and biomass concentration on Cr (VI) removal was carried out using citric acid-processed rice husk alone, and in combination of bacterial strains. Fourier transform infra-red (FTIR) spectroscopy was performed to determine the contributions of different functional groups involved in Cr (VI) binding. Scanning electron microscopy (SEM) of treated and untreated RH was also performed.
 Results: Citric acid-processed RH was most effective in the removal of chromate (97.3 %). The two bacterial strains combined with rice husk proved highly efficient in Cr (VI) removal from sterile and non-sterile industrial effluents. FTIR spectra showed the involvement of esters, amines and aliphatic functional groups in Cr (VI) binding, while SEM displayed the damaging effects of Cr (VI) on the surface of RH; however, bacterial inoculation minimized the damage.
 Conclusion: Exopolysaccharides from Exiguobacterium strains and citric acid-processed rice husk demonstrated high efficiency for Cr (VI) removal. Hence, RH with these bacterial strains are potential biosorbents for control of heavy metal contamination arising from industrial effluents.
 
 
 

Electronic properties and reactivity of oxidized graphene nanoribbons and their interaction with phenol.

The effect of the oxidized functional groups on the structural, electronic, and reactivity properties of armchair graphene nanoribbons has been investigated in the framework of the density functional theory. The presence of functional groups near the edges stabilizes the oxidized graphene nanoribbons (OGNRs) more than substituting near the center. Overall, we found slight differences in the electronic properties of OGNRs concerning the pristine ones. The oxygen contribution of functional groups to the DOS is found in the conducting energy bands far from the Fermi level. Consequently, the semiconducting behavior is maintained after doping. Based on the reactivity of OGNRs, the most promising nanostructures were proposed as adsorbents studying the interaction and complexation with phenol, a critical pollutant removed mainly by hydrotreating processes (HDO) to produce bio-oil. Parallel and perpendicular phenol conformations were found towards the OGNRs in the optimized complexes driven by a physisorption process. These results provide significant insights for catalytic processes that use biomass derivatives containing phenolic compounds. The physisorption of streams containing pollutants on OGNRs could be adapted to new technological applications for the remotion of aromatic compounds under environmentally friendly operational conditions.

QSPR Models for the Molar Refraction, Polarizability and Refractive Index of Aliphatic Carboxylic Acids Using the ZEP Topological Index

The molar refraction, polarizability, and refractive index for a series of monocarboxylic, dicarboxylic, and unsaturated monocarboxylic acids, having a symmetric or asymmetric structure, were investigated by the application of quantitative structure property relationship (QSPR) technique. We used a linear regression method and a single molecular descriptor, the ZEP topological index, calculated in a simple manner, with the help of weighted electronic distances, and also calculated on the basis of the chemical structure of the molecules. The high-quality performance and predictive ability of the QSPR models obtained were validated by means of specific validation techniques: y-randomization test, the leave-one-out cross validation procedure, and external validation. The investigated properties are well modeled (with r2 > 0.99) by the ZEP index, using the regression analysis as a statistical tool for developing reliable QSPR models. Our approach provides an alternative technique to the existing additive methods for predicting the molar refraction and polarizability of carboxylic acids, which is essentially based on the summation of atom and/or functional group contributions or bond contributions, and of some correction increments.

Porous Carbon Nanofibers with Heteroatoms Doped by Electrospinning Exhibit Excellent Acetone and Carbon Dioxide Adsorption Performance: The Contributions of Pore Structure and Functional Groups.

Rich chemical properties and a well-developed pore structure are the key factors of porous materials for gas storage. Herein, rich heteroatom-doped porous carbon nanofibers (U1K2-X) with a large surface area were prepared by electrospinning followed by potassium hydroxide (KOH) activation. Low-cost urea was chosen as the nitrogen source and structural guiding agent. U1K2-X have a high specific surface area (628–2688 m2 g–1), excellent pore volume (0.468–1.571 cm3 g–1), and abundant nitrogen (2.5–12.8 atom %) and oxygen (4.5–12.5 atom %) contents. Acetone and carbon dioxide were used as target adsorbents to evaluate the adsorption properties of U1K2-X by experiments. These U1K2-X exhibit excellent adsorption performance (260.03–955.74 mg g–1, 25 °C, 18 kPa) and multilayer adsorption (the adsorption layer number n > 2) for acetone, which is mainly attributed to the large specific surface area and pore volume. Besides this, the carbon dioxide uptake reached 2.73–3.34 mmol g–1 at 25 °C. This was attributed to the combination of high nitrogen–oxygen contents and microporous structure. Furthermore, U1K2-X show the desirable repeatability. This study provides a new direction for the preparation of heteroatom-doped porous carbon nanofibers, which will be a promising material for gas adsorption.

Theoretical Insights into the Cooperative Catalytic Mechanism of a PW-Containing Keggin Heteropolyacid Anion and Ethanol toward Conversion of Fructose into 5-Ethoxymethylfurfural in Ethanol Solution

Toward the conversion of fructose and ethanol into 5-ethoxymethylfurfural (EMF), the catalytic contribution of typical functional groups in PW-containing Keggin polyoxometalates has been theoretically studied at the M06/LANL2DZ,6-31++G(d,p) level in ethanol solution. The [HPW12O40]2– anion is regarded as the model catalyst for the PW-containing polyoxometalates of both homogeneous and heterogeneous catalysts in ethanol solution, as it possesses basic functional groups, that is, [W–OcH–W], [W═OdH], and [W═Od]. The [HPW12O40]2– anion displays good catalytic activity, which originates from the contained proton H+, that is, both [W–OcH–W] and [W═OdH] catalytically active sites. Herein, over both [W–OcH–W] and [W═OdH], the rate-controlling steps are associated with both C2–OH and C1–H bond cleavages in fructose moiety, respectively. A mechanism of proton-induced C–H bond cleavage is proposed, in which the [HPW12O40]2– anion is responsible for both the C–OH bond cleavage and C–O–C ether–oxygen bond formation, while the ethanol solvent answers for the C–H activation of the protonated intermediates. The appropriate protonation capacity of a protic solvent plays an important role in the conversion of fructose and ethanol into EMF. Alternatively, the [HPW12O40]2– anion displays almost no catalytic activity toward the O–H bond cleavage through [2 + 2] addition, which comes from the very strong Lewis acidity of the W-site.

Effects of environmental aging on the adsorption behavior of antibiotics from aqueous solutions in microplastic-graphene coexisting systems

The extensive use of nanofillers, such as graphene oxide (GO) and reduced graphene oxide (rGO), as plastic additives has led to the coexistence of microplastics (MPs) and nanomaterials in aquatic environments. However, there is a lack of studies on the adsorption behavior of MPs when coexisting with GO. Moreover, MPs and GO are prone to undergoing aging processes in real environments under conditions such as sunlight exposure, which changes their physicochemical properties and affects their adsorption behavior. In this study, the aging processes of MPs and GO in a real environment were simulated by ultraviolet (UV) irradiation and thermal treatments, respectively. The adsorption behavior of ciprofloxacin (CIP) on three types of MPs (polypropylene (PP), polyamide (PA), and polystyrene (PS)) before and after aging was explored. The MPs are ordered in terms of CIP adsorption capacity as aged-PA > aged-PS > aged-PP > PA > PP > PS, and the adsorption capacity of aged MPs was approximately twofold higher than that of pristine MPs. This paper also studied the adsorption performance of antibiotics in a coexisting system of aged MPs and GO/rGO, and the tetracycline (TC) adsorption capacity was increased by ~336% in aged PP-GO and ~100% in an aged PP-rGO coexisting system. GO/rGO with high degree of oxidation and concentration in an aged- PP-GO/rGO coexisting system are more conducive to the TC adsorption, due to the contribution of oxygen-containing functional groups. Surface and partition adsorption co-occurred during the TC adsorption process. The TC adsorption behavior in the MPs-GO/rGO coexisting system was strongly dependent on the solution pH, which was more favorable under acidic (pH = 3) or alkaline (pH = 11) conditions. This study improves the understanding of the environmental behavior of MPs, graphene, and antibiotics and guides research on strategies for preventing the migration of antibiotics in MPs-GO/rGO coexisting systems.

Enhanced removal of Cr(VI) by nitrogen-doped hydrochar prepared from bamboo and ammonium chloride

N-doped biochar can effectively eliminate toxic Cr(VI). Here, N-doped hydrochar (NHC) was successfully synthesized by one-pot hydrothermal carbonization (HTC) of NH4Cl and bamboo, and employed to adsorb Cr(VI). The specific surface area, pore volume, and carbon and nitrogen contents of NHC all increase compared with the undoped hydrochar (HC). NH4Cl acts as a cheap nitrogen source to enhance the nitrogen content of hydrochar and as an acid catalyst to accelerate hydrochar carbonization. Adsorption experiments show NHC has higher adsorption capacity than HC for Cr(VI). XPS and FTIR imply the dominant mechanisms of adsorbing Cr(VI) onto two hydrochars are electrostatic attraction, reduction and complexation, but the contributions of surface functional groups in two hydrochars for elimination of Cr(VI) differ. The doped nitrogen in NHC is pivotal in adsorbing and reducing Cr(VI). Hence, NHC prepared from bamboo and NH4Cl by one-step HTC is a cheap and efficient adsorbent to eliminate aqueous Cr(VI).

Optimize the co-solvent for methanol in diesel with group of oxygen-containing reagents: Molecular structure and intermolecular forces analysis

Oxygen-containing fuels or additives used to reduce the pollutant emissions from diesel combustion have the potential as a co-solvent to prepare methanol/diesel blends, however their performance has less been evaluated, especially how their molecular structure affects the solubility of methanol in diesel. In this work, the abilities of higher alcohols, long-chain ethers and esters to improve the solubility of methanol in diesel were investigated, and intermolecular forces were also analyzed according to the solubility parameters. Results show that different performance for oxygen-containing chemicals as a co-solvent to prepare methanol/diesel blends originates from different contribution of various functional groups to their Hansen solubility parameters (HSPs) and the fraction of HSPs. And dispersion solubility parameter larger than 15.9 and its fraction in the range of 0.45–0.64 were proposed as a reference for choosing a suitable co-solvent to prepare methanol/diesel blends. Besides, it was found that 1-Octanol exhibits excellent performance as a co-solvent to prepare stable methanol/diesel blends, and can substantially reduce the PODE or methyl palmitate usage when they being used in preparing methanol/diesel mixtures.

Synthesis, characterization and theoretical exploration of pyrene based Schiff base molecules as corrosion inhibitor

Synthesis of highly efficient organic molecules to be used for corrosion inhibition is the prime importance to minimize the degradation of metal substrates from the corrosive solutions. In this regards, the theoretical exploration of the corrosion inhibitor before its application is very important. Herein, pyrene based two novel Schiff bases, viz., 4-((pyren-3-yl)methyleneamino)phenol (PMP) and 2-(2,4-dinitrophenyl)-1-((pyren-3-yl)methylene)hydrazine (DPH) were synthesized and characterized. The incorporation of pyrene unit (fused aromatic rings) and contribution of hydroxyl or nitro functional groups in the Schiff base skeleton might make these molecules work as efficient corrosion inhibitors. The atomic-level insight of the electronic properties, the presence of local reactive sites and the adsorption behaviours of these molecules were investigated meticulously. Subsequently, it's probable use as corrosion inhibiting molecule was predicted based on computational outcomes obtained from density functional theory (DFT), Fukui indices (FIs) analysis and molecular dynamics (MD) simulation approaches, simultaneously. The optimization of the geometries of molecules, analysis of electron density distribution within frontier molecular orbitals obtained from DFT outcomes; and FIs analysis of each atom of these synthesized molecules were carried out to investigate the plausible mode of interactions of these designed molecules with metal's atoms. Furthermore, the crystal morphology study was performed using “Morphology” module in Material Studio software to explore the growth characteristics as well as to find out the exceptionally stable surface present in α-Fe crystal. In doing so, the Wulff construction plot was used to analyse α-Fe crystal morphology. Afterwards, the MD simulation technique was employed to envisage interaction spontaneity and adsorption of the synthesized molecules with equilibrium configuration onto the metal surface atoms imitating the actual corrosion inhibiting processes that occurs in actual corrosive environments.

Quantifying organic matter and functional groups in particulate matter filter samples from the southeastern United States – Part 2: Spatiotemporal trends

Abstract. Organic species within atmospheric particles vary widely in molecular structure. The variety of molecules that comprise the aerosol make it rich in information about its sources and chemical life cycle but also make particulate organic matter (OM) difficult to characterize and quantify. In Part 1 of this pair of papers, we described a direct method for measuring the composition and concentrations of OM in aerosol samples that is compatible with routine monitoring of air quality. This method uses Fourier transform infrared (FT-IR) spectrometry of filter-based aerosol samples to quantify bonds, or functional groups, that represent the majority of organic composition. Summation of these functional groups gives OM. In this paper, functional group and OM concentrations are directly measured in 8 years of aerosol samples collected at two rural and two urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. FT-IR spectrometry with a multivariate calibration is used to quantify the concentrations of aliphatic C−H (aCH), carboxylic acid (COOH), oxalate (oxOCO; representing carboxylates), non-acid and non-oxalate carbonyl (naCO), and alcohol O−H (aCOH) in approximately 3500 filter samples collected every third day from 2009 through 2016. In addition, measurements are made on samples from all days in 2016. To the best of our knowledge, this is the longest time period over which this type of analysis has been applied, and this work also demonstrates the application of a more chemically complete and less destructive method than in prior work using alternate techniques. A decline in the total OM is observed from 2011 to 2016 due to a decrease in the more oxygenated functional groups (carboxylic acid and oxalate) and is attributed to anthropogenic SO2 and/or volatile organic compound (VOC) emissions reductions. The trend in OM composition is consistent with those observed using more time- and labor-intensive analytical techniques. Concurrently, the fractional contributions of aCOH and naCO to OM increased, which might be linked to monoterpene-derived secondary OM, with plausible influences from decreasing NOx and/or increasing O3 concentrations. In addition, this work demonstrates that OM to organic carbon (OM/OC) ratios in the southeastern US (SE US) did not appreciably change over the study time period as a result of these competing functional group contributions to OM. Monthly observations support the sources suggested by these overall trends, including evidence of strong biogenic and photo-oxidation influences. Daily samples from 2016 further elucidate the consistent impact of meteorology and biomass burning events on shorter-term OM variability, including prescribed burning in the winter or spring and wildfires in the autumn, although these sources did not appear to be strong contributors to long-term OM or composition trends in the SE US. These shorter-term and spatial observations reinforce the results of the broader dataset and serve to evaluate the applicability of FT-IR spectrometry measurement to trends analysis on various timescales relevant to routine monitoring of aerosol composition.

Thermal neutron cross sections of amino acids from average contributions of functional groups

The experimental thermal neutron cross sections of the 20 proteinogenic amino acids have been measured over the incident-neutron energy range spanning from 1 meV to 10 keV and data have been interpreted using the multi-phonon expansion based on first-principles calculations. The scattering cross section, dominated by the incoherent inelastic contribution from the hydrogen atoms, can be rationalised in terms of the average contributions of different functional groups, thus neglecting their correlation. These results can be used for modelling the total neutron cross sections of complex organic systems like proteins, muscles, or human tissues from a limited number of starting input functions. This simplification is of crucial importance for fine-tuning of transport simulations used in medical applications, including boron neutron capture therapy as well as secondary neutrons-emission induced during proton therapy. Moreover, the parametrized neutron cross sections allow a better treatment of neutron scattering experiments, providing detailed sample self-attenuation corrections for a variety of biological and soft-matter systems.

Root influence on soil nitrogen availability and microbial community dynamics results in contrasting rhizosphere priming effects in pine and spruce soil

Abstract The rhizosphere priming effect (RPE) is increasingly considered an important regulator of below‐ground C and N cycling, with implications for terrestrial ecosystem feedback to global change. Even so, there is a lack of knowledge about the mechanisms underlying RPEs. We used novel stable isotope probing methods to investigate RPEs in an experiment with Scots pine and Norway spruce seedlings, two of the most common boreal forest species. We determined root exudation rates, RPEs on SOM decomposition and gross N mineralization, and the contribution of different microbial functional groups to the observed RPEs. Pine induced positive and spruce induced negative RPEs on SOM decomposition, while no RPE on gross N mineralization was observed. Negative RPEs in the spruce treatment were attributed to an opportunistic subset of the fungal community that was growing on root‐derived 13C while depleting available N, thus reducing the activity of microbial SOM decomposers. In the pine treatment, available N was likely sufficient to support the root‐induced decomposition activities of fungal decomposers, resulting in positive RPEs. The findings suggest that RPEs, promoted by root stimulation of distinct subsets of the microbial community, can either contribute to conserving the soil C stock or to depleting it, depending on plant species and soil N availability. A free Plain Language Summary can be found within the Supporting Information of this article.

Biomass-Derived Carbonaceous Materials to Achieve High-Energy-Density Supercapacitors

Biomass-derived carbonaceous materials are considered as one of the most perspective electrodes for symmetric supercapacitors working with alkaline-basic electrolytes. However, they still exhibit lower energy density. Herein, we demonstrate the capacitance performance of the commercial carbon product (YP-50F, “Kuraray Europe” GmbH), obtained from coconuts, in symmetric supercapacitors by using lithium and sodium organic electrolytes. It is found that YP-50F delivers higher energy density when lithium electrolyte containing LiBF4 salt is employed. The sodium electrolyte with NaPF6 salt is less aggressive toward YP-50F than that of LiPF6 salt, as a result of which a good capacitance performance is observed in the sodium electrolyte. The contributions of surface functional groups of YP-50F, as well as its compatibility with non-aqueous lithium and sodium electrolyte, are discussed on the basis of post-mortem scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) data analyses. The obtained correlations could be of significance in order to design sustainable supercapacitors with high energy density.

Annual Net Primary Productivity of Different Functional Groups as Affected by Different Intensities of Rainfall Reduction in the Semiarid Grasslands of the Gauteng Province in South Africa

Rainfall variability is expected to change the soil water regime thereby impacting negatively on rangeland species composition, productivity and ecosystem services. The aim of this study was to assess the impact of different intensities of rainfall reduction (RR) on vegetation annual net primary productivity (ANPP). Twenty 7 × 7 m experimental plots with different intensities of RR structures consisting of transparent acrylic bands were built on a natural grassland. The interspaces between acrylic bands varied in size to intercept different intensities of ambient rainfall (0, 15, 30 and 60%) as RR treatments, with each RR treatment replicated five times in a complete randomised block design. A fixed 1 m2 quadrat was marked at the centre of each plot and the ANPP within the quadrats was determined by harvesting the quadrant at the end of the growing season. Generally, as compared to the control (ambient rainfall intensity) the overall grass ANPP (P > 0.05) showed resilience to lower and moderate intensities of (15 and 30%) RR, but at a severe intensity of RR (60%) the ANPP was significantly reduced. Compared to the control the percentage contribution of grasses towards the overall ANPP increased at a lower intensity of RR (15%). In contrast, the percentage contribution of forbs towards the overall ANPP significantly reduced at lower intensity of RR. Within the grass species, however, those grasses that decrease when the veld is undergrazed or overgrazed (decreaser grass species) showed resilience at lower intensity (15 and 30%) of RR, while at a severe intensity of RR the ANPP of decreaser grasses were significantly reduced (1841 vs. 220 kg DM/ha). Those grasses that increase with undergrazing or overgrazing (increaser I or increaser II grass species) recorded a higher ANPP at moderate intensity of RR (30% RR) than at a higher intensity of RR, while the difference between 60% RR and 0% RR in terms of increaser grasses ANPP were not significant (P > 0.05) (650 kg DM/ha). Up to 88% reduction in ANPP were recorded for decreaser grass species at severe intensity of RR as compared to the control the corresponding reduction in ANPP noted for increaser grasses were relatively less (up to 56% reduction in ANPP at 60% RR vs. 0% RR). Generally, the overall ANPP yield of the semiarid grassland in Gauteng province showed resilience to a low intensity of RR (15% RR) and moderate intensity of RR (30% RR) partly due to a shift in the species composition of grasses from decreasers to increasers ecological groups, as well as due to a decrease and an increased contribution of forb functional groups at a lower and moderate intensity of RR, respectively.

Lignin dissolution model in formic acid–acetic acid–water systems based on lignin chemical structure

The separation of lignin from woody biomass and subsequent conversion into useful products requires a solution to the problem of its solubility. The expanded C9 formula of lignin, along with its atomic and functional groups, was determined by elemental analysis and NMRs spectroscopy. Based on the thus-obtained expanded C9 formula, the cohesion parameters of lignin dispersion (10.8–11.1 cal1/2·cm−3/2), polarity (4.15–4.31 cal1/2·cm−3/2), hydrogen bonding (6.30–7.38 cal1/2·cm−3/2), and solubility (13.2–14.0 cal1/2·cm−3/2) were respectively calculated using atomic and functional group contributions method. We established the relationship between lignin structure and lignin solubility parameters. The dissolution characteristics of wheat straw organic acid lignin, industrial eucalyptus kraft lignin, bamboo kraft lignin, and softwood kraft lignin in formic acid–H2O, acetic acid–H2O, and formic acid–acetic acid–H2O solvent systems were analyzed. The results indicate that the dissolution behavior of lignins follows the solubility parameters theory. We have developed a lignin dissolution model according to the lignin structure. This model obeys the solubility parameter theory, overcomes the limitations of the “like dissolves like” principle in organic acid–water systems, and provides a concise method for the selection of lignin solvent systems and the quantitative determination of their solvent composition.

Vapour-liquid phase equilibria and thermodynamic properties of solutions of the ethylbenzene and n-alkylbenzenes binary systems

The methods of theoretical description of the patterns of changes in thermodynamic properties depending on the composition and structure of solution components are a priority direction in the development of the theory of solutions. This article is devoted to the establishment of relationships between the thermodynamic properties, composition of solutions, and the structure of their components. The study of the thermodynamic properties of binary solutions formed by a common solvent (ethylbenzene) and substances of the homologous series of n-alkylbenzenes contributes to the establishment of the aforementioned relationships. In the production of ethylbenzene and its homologues, solutions based on n-alkylbenzenes are quite common. Alkylbenzenes are widely used in various fields of science and chemical technology as solvents, extractants, and plasticisers. Using the ebuliometric method, we measured the boiling points of solutions of four binary systems formed by ethylbenzene and n-alkylbenzenes under various pressure values. Compositions of equilibrium vapour phases of the binary systems were calculated using the obtained isotherms of saturated vapour pressure of the solutions. Using the Runge-Kutta method, the composition of the vapour phases of the solutions of the systems was calculated by the numerical integration of the Duhem–Margules equation on a computer. The obtained data on the vapour-liquid equilibrium became the basis for calculating the thermodynamic functions of the systems’ solutions. The Gibbs and Helmholtz energy values, the enthalpies of vaporisation and mixing, the internal energy, and entropy of solutions were calculated. The thermodynamic properties of the solutions were calculated using a comparison of the values baed on two standards: an ideal solution and an ideal gas. It was found that the values of the Helmholtz energy linearly depend on the molar mass of the substance (the number of –CH2– groups in a molecule) in the homologous series of n-alkylbenzenes. An increase in the Helmholtz energy values for n-alkylbenzenes in the homologous series is associated with a linear increase in the molar volume of liquid substances and an exponential decrease in the saturated vapour pressure of substances. For binary solutions of constant molar concentrations formed by ethylbenzene and n-alkylbenzenes, the Helmholtz energy linearly depends on the molar mass (number of –CH2– groups in the molecule) of n-alkylbenzene in the homologous series. We obtained an equation that makes it possible to predict the thermodynamic properties of solutions of binary systems with high accuracy. The equation accelerates the process of studying vapour-liquid phase equilibria and thermodynamic properties of solutions of binary systems by 300 times. The determined patterns confirm the hypothesis of the additive contribution of functional groups to the thermodynamic properties of solutions. This hypothesis underlies the statistical theory of group models of solutions. The thermodynamic patterns determined by this study can also be used to solve a wide range of technological issues in the chemical industry.