Concentration Of Acid Groups Research Articles

Effect of Electron Beam and Heat Treatment on the Reactivity of Aggregates and Mineral Additives towards Alkali-Silica Reaction in Portland Cement Compositions

Electron beam (EB) and heat treatment of silica-containing aggregates and mineral additives for Portland cement mortars is shown to affect their activity in alkali-silica reaction (ASR) damaging concrete structures. In the case of ordinary mortar based on the sand free of alkali-reactive inclusions, both heating to 900°C and EB processing result in a significant increase of reactivity growing with the absorbed dose in the range from 100 to 600 kGy and correlating with the increase in the content of acidic hydroxyl groups on the surface. For sand with reactive chalcedony inclusions, EB treatment results in the growth of their reactivity while heating provides its significant decrease. In case of mineral additives such as silica fume and metakaolin known as very effective ASR-inhibitors, similar processing leads to the increase of their activity in mitigation of ASR. The observed effect is promising for simulation of expansion processes caused by ASR and enhancement of concrete structure resistance to alkali destruction during exploration.

Effect of different carboxylic acid group contents on microstructure and properties of waterborne polyurethane dispersions

The waterborne polyurethane (WPU) with different carboxylic acid group contents were prepared by a prepolymer method, adopting polycarbonate diol (PCDL) as soft segments and isophorone diisocyanate (IPDI) as hard segments. The different amounts of 2,2-dimethylolbutyric acid (DMPA) as hydrophilic chain extender were introduced into polyurethane molecular for studying the effect on microstructure and properties. The solid content, pH value and viscosity measurement were used to characterize the performance of WPU emulsion. The fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water contact angle tester and mechanical testing machine were utilized to measure the structure, crystallization performance, thermal stability, low temperature flexibility, wetting performance and mechanical properties of WPU films, respectively. The test value of impact, adhesive, flexibility and pencil hardness on tinplate of WPU coatings were obtained for observing film properties. The results indicated that the emulsification effect increase with the increased DMPA contents. The decomposition temperature of WPU films perform a slight decrease and the WPU films have excellence low temperature flexibility with the increased DMPA contents. The hydrophilic property of WPU films mainly are about 80°and the tensile strength value of 7 wt% WPU reaches 45 MPa and elongation at break at 420%.

Kinetic and thermodynamic study of n-pentane adsorption on activated carbons modified by either carbonization or impregnation with ammonium hydroxide

Abstract This study investigates the n-pentane adsorption performances on different activated carbons both as raw and modified by means of either chemical (amination with ammonium hydroxide) or thermal (carbonization at 1273 K) treatments. The raw, chemically and physically modified activated carbons were tested for n-pentane adsorption at 261 K in a volumetric apparatus. Maximum adsorption capacity values of 13, 11.7 and 9.1 μmol g−1 were obtained for the thermally, chemically and raw activated carbons, respectively, thus testifying the effectiveness of the treatment methods in improving the n-pentane adsorption capacity of the parent sorbent, due to an increase in the content of both acidic and basic functional groups. On the other hand, at low n-pentane partial pressures the volume of ultramicropores appears the ruling faction in determining a higher sorbent capture capacity. Kinetic adsorption data were successfully modelled according to the fractal-like Vermeulen model, and the outcomes suggested a more marked time-dependence of the intraparticle diffusivity for the chemically treated sample, likely related to a greater surface heterogeneity of this sample. Immersion enthalpy data also suggested that weaker adsorbate-adsorbent interactions promote a faster diffusion process.

SYNTHETIC FULVIC ACIDS FROM POMEGRANATE PEEL

It is known that fulvic acids (FA) have a whole complex of therapeutic properties, but their widespread introduction into medical practice is limited by the dependence of the properties of the final product on the source of their extraction. In this regard, research aimed at developing experimental approaches for the production of synthetic substances that are similar in structure, physical, chemical and therapeutic properties to natural FA, but characterized by standardized and controlled parameters, is of interest. The purpose of the work was to develop a method of obtaining synthetic FA using as a precursor ellagitannins and lignin extracted from pomegranate peels and comprehensive study of their properties. As a result of the experiment and the analysis of the results it was found that the elagotanins and lignin contained in the peel of pomegranate can be used as a precursor to obtain synthetic FA. Comparative analysis of the elemental composition and spectral characteristics of synthetic FA with the literature data for natural FA allowed to ascertain the uniformity of their chemical structure. X-ray diffraction analysis of synthetic FA indicates their amorphous nature, which is typical of natural FA as well. The content of basic acid groups in the structure of synthetic FAs and their recovery capacity are calculated. In particular, the content of carboxyl groups is 2.7 ± 0.2 mmol/g, and the phenolic groups - 6.0 ± 0.1 mmol/g; the recovery capacity is 5.2 ± 0.3 mmol/g. The SEM images of the dried synthetic FA preparations show the uniformity of the powder particles obtained. However, unlike natural FA, synthetic analogues obtained by the developed method are characterized by controlled and reproducible properties, which greatly expands their use in medicine.

Chemical characterization of mountain forest soils: impact of long-term atmospheric deposition loadings (Czech-Polish-German border region).

The composition of lipids in soil offers clues to soil degradation processes due their persistency and selectivity in soil, and close relation to long-term processes in the ecosystem, thanks to their role in cell membranes of organisms. Organic solvent-extractable compounds were recovered from soils collected at two sites differing in the degree of forest damage. Gas chromatography/mass spectroscopy and Fourier transform infrared spectroscopy were applied in order to characterize solvent-extractable lipids. Raman spectroscopy was also applied as it provides distinct advantages for determining the structural order of carbonaceous materials. The organic matter measurement techniques were combined with an established simultaneous multi-element measurement technique. Variations in individual soil horizons from the sites were reflected in the crystallinity of epicuticular waxes, presence of long-chain aliphatic hydrocarbons, concentrations of n-alkanes, saturated and unsaturated fatty acids, dicarboxylic acids, and in the content of aromatic structures, hydroxyl, ester, and carboxylic acid groups. The results are explained by differently transformed organic matter. The concentrations of elements in the soils were also affected by atmospheric depositions, including higher accumulations of arsenic and antimony, and lower contents of natural nutrients. These data have potential to be used as sensitive biogenic indicators of ecosystem damage by long-term atmospheric depositions.

Synergistic Extraction and Characterization of Fulvic Acid by Microwave and Hydrogen Peroxide-Glacial Acetic Acid to Oxidize Low-Rank Lignite.

Fulvic acid (FA) has important properties and is used widely in agriculture, industry, medicine, and other fields. However, there is a lack of environmentally friendly and efficient extraction methods for coal-based FA and its molecular structural characterization. In this study, FA was extracted cleanly and efficiently from low-rank lignite via the innovative method of microwave combined with hydrogen peroxide and glacial acetic acid, followed by purification by the sulfuric acid–acetone method. The molecular structures of FA were precisely characterized by UV–vis spectroscopy, infrared (IR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography–mass spectrometry (GC–MS). The results showed that the microwave combined with hydrogen peroxide–glacial acetic acid method had stronger oxidative degradation ability compared with the conventional method. Under optimized conditions, the yield of FA reached 60.97%. During the oxidation process, the macromolecular network structure of coal was destroyed, resulting in the production of many oxygen-containing functional groups. According to the IR and UV–vis spectra, there were abundant oxygen-containing functional groups such as hydroxyl, carboxyl, carbonyl, and quinone groups in the molecular structure of FA. Determination of the total acid group content in the oxygen-containing functional groups of FA showed that the content of carboxyl groups was much higher than that of phenolic hydroxyl groups. The 1H NMR showed that there were hydrogen atoms present as part of carboxyl, aromatic, phenolic hydroxyl, and aliphatic groups in FA. The (GC–MS) results suggested that FA is a mixture of dozens of complex compounds, including alkanes, alcohols, esters, etc.

Extraction, purification and characterization of sulphated polysaccharide from Bellamya quadrata and its stabilization roles on atherosclerotic plaque

The aim of this paper was to investigate the extraction, purification and characterization of sulphated polysaccharide (BQPS) from Bellamya quadrata and its stabilization roles on atherosclerotic plaque. Firstly, crude polysaccharide (CBQP) from Bellamya quadrata was extracted by protease enzyme assisted extraction. Moreover, its optimal parameters were obtained by the response surface method as follows: the ratio of water to raw material of 24:1, enzyme dosage of 285 U/g, enzymolysis pH value of 4.7 and temperature of 67 °C. Secondly, CBQP was further purified to obtain the target polysaccharide BQPS by Q Sepharose Fast Flow and Sephacryl S-400 gel column chromatography. Then, the characterization of BQPS revealed that it possessed a total polysaccharide content of 91.88 ± 1.23%, sulfuric acid group content of 9.12 ± 1.59% and molecular weight of 91.1 kDa. BQPS was only consisted of glucose without any proteins. Finally, BQPS was confirmed to have a significant stabilizing effect on atherosclerotic plaque and its mechanism was related to the selective promotion of autophagy with the precisely right strength.

Effects of hypertension and FAAH inhibitor treatment of rats with primary and secondary hypertension considering the physicochemical properties of erythrocytes

Hypertension is one of the most common cardiovascular diseases in the world and is associated with oxidative stress. The aim of this study was to examine the effect of the chronic administration of the fatty-acid amide hydrolase inhibitor (URB597-[3-(3-carbamoylphenyl)phenyl]N-cyclohexylcarbamate) to rats with primary (SHRs – spontaneously hypertensive rats) and secondary (DOCA-salt – 11-desoxycorticosterone acetate-salt-induced hypertension) hypertension on the composition and physicochemical properties of erythrocytes membrane. Because changes in membrane composition lead to modifications of electrical charge what may affect cell functions, the levels of following components were determined: four classes of membrane phospholipids (by HPLC – high-performance liquid chromatograph), sialic acid (by resorcinol method), lipid peroxidation product – malondialdehyde (by GCMS – gas chromatography-mass spectrometry). The reduced levels of phospholipids and sialic acid, as well as the increased levels of malonodialdehyde observed in the erythrocyte membrane of rats with primary and secondary hypertension led to a decrease in the negative electrical charge of the membrane. Long-term administration of URB597 to SHRs and DOCA-salt-treated rats partially prevented changes caused by hypertension. Using theoretical equations and the dependence of cell surface charge density as a function of pH, total surface concentrations of acid and base groups and their association constants have been determined. Considering the changes in physicochemical parameters of erythrocyte membranes, URB597 can be considered a potential protective factor for erythrocytes in situations of metabolic changes associated with oxidative stress.

Milk metabolites as noninvasive indicators of nutritional status of mid-lactation Holstein and Montbéliarde cows

The objective was to investigate the effects of feed restriction on concentrations of selected milk metabolites in mid-lactation Holstein and Montbéliarde cows and to explore their correlations with energy balance and classic plasma and milk indicators of nutritional status. Eight Holstein and 10 Montbéliarde cows (165 ± 21 d in milk) underwent 6 d of feed restriction during which feed allowance was reduced to meet 50% of their net energy for lactation (NEL) requirements. The experiment was divided in 4 periods: control (CON; d -3 to -1), restriction (RES; d 1 to 6), wk 1 (W1; d 7 to 13), and wk 2 (W2; d 14 to 18) after refeeding at ad libitum intake. Intake, milk production, energy balance and plasma metabolites were used to validate the feed restriction model. Concentrations of 7 milk metabolites: β-hydroxybutyrate (BHB), glucose, glucose-6-phosphate, isocitrate, glutamate, uric acid, and free amino groups were measured in morning milk samples, and fatty acids were measured in pooled p.m. and a.m. samples. Feed restriction induced a negative energy balance (-42.5 ± 4.4 MJ/d), increased plasma nonesterified fatty acids and BHB, and decreased plasma glucose concentrations. Feed restriction increased milk glucose-6-phosphate and isocitrate (+38% and +39%, respectively) and decreased milk BHB, glucose, glutamate, uric acid and free amino group concentrations (-20%, -57%, -65%, -42%, and -14%, respectively), compared with pre- restriction. Milk concentrations of medium-chain fatty acids (e.g., sum of C10 to C15) decreased and those of long chain (e.g., 18:0, cis-9 18:1) increased during restriction. Breed differences were not detected for the majority of variables. All studied milk metabolites were significantly correlated with energy balance (Spearman correlation = 0.48, 0.63, -0.31, -0.45, and 0.61 for BHB, glucose, glucose-6-phosphate, isocitrate, and glutamate, respectively). Milk glucose and glutamate showed the strongest correlations with plasma metabolites and milk FA associated with lipomobilization. These results suggest that milk metabolites may be used as noninvasive indicators of negative energy balance and metabolic status of dairy cows.

A novel environmentally friendly process for depolymerization of hydrolysis lignin using Kraft cooking liquor: chemicals recoverable by the Kraft recovery cycle

AbstractHydrolysis lignin (HL) refers to a lignin‐rich residue obtained after the enzymatic hydrolysis of biomass. It is recalcitrant, heterogeneous, insoluble in most common solvents, and less reactive than other lignins. To enhance the reactivity of HL, a novel environmentally friendly depolymerization approach was demonstrated to produce depolymerized hydrolysis lignin (DHL) using Kraft cooking liquor, white liquor (WL) – recoverable by the Kraft recovery cycle. The effects of various process parameters such as reaction time, WL/HL ratio, and reaction temperature on lignin depolymerization were investigated using a 2 L Parr reactor under N2. The DHLs obtained were then characterized by Gel permeation chromatography (GPC)‐Ultraviolet Detector (GPC‐UV), 31P Nuclear Magnetic Resonance (NMR) spectroscopy, and ultraviolet visible (UV–visible) spectroscopy, while the filtrates were characterized by high‐performance liquid chromatography (HPLC) for saccharinic acids. The DHL yield reached 45–70% from the treatments at 150–190 °C for 1 h at a WL/HL mass ratio of 1:4 ~ 2:1. The weight‐average molecular weight (Mw) value of the DHL obtained at 190 °C after treatment for 1 h at a WL/HL ratio of 2:1 (w/w) was 2600 Da. Moreover, a significant increase in non‐condensed phenolic hydroxyl and carboxylic acid group content was observed with decreasing Mw. Compared with various existing lignin modification approaches, the approach reported here is less expensive and more environmentally friendly if integrated into Kraft pulp mill operations with the residual WL from the lignin depolymerization process being recycled to the mill chemical recovery cycle. Process scale‐up was also demonstrated using a 20 L circulating reactor. In this case, the Mw of the DHL produced after treatment at 170 °C for 2 h was 2400 Da. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Sustainable hydrocarbon fuels via “one-pot” catalytic deoxygenation of waste cooking oil using inexpensive, unsupported metal oxide catalysts

The present work explores the potential to upgrade waste cooking oil (WCO) via deoxygenation using inexpensive, unsupported metal oxide catalysts (CaO, TiO2, Mn(IV)O, and ZnO) in the absence of a hydrogen feedstock. WCO was mixed with 5 wt% catalyst material in a stainless steel reactor and heated to 300 °C for 60 min. The relative concentration of fatty acids increased upon heating in the absence of any catalyst, from ~15% of the total identifiable compounds for WCO to 64% for the Organic Liquid Products as a result of the nearly complete conversion of aldehyde and ester groups to organic acids, alkanes and aromatics. The inorganic catalysts shifted the product distributions significantly. CaO and ZnO slightly increased the concentration of acidic groups (versus WCO) but produced less acids than OLP alone, while Mn(IV)O and TiO2 resulted in overall decreases of free fatty acids. Mn(IV)O showed a slight preference for alkene formation, whereas TiO2 was selective toward alkanes. All catalysts – and uncatalyzed heating – showed significant deoxygenation in terms of ridding the WCO of C-O groups. Thermal treatment of WCO (with and without catalysts) resulted in a 25% increase in higher heating values, in line with those of commercial jet fuels. While the “one-pot” catalytic upgrading of WCO would not result in a direct substitute for aviation fuel, this work demonstrated the potential to significantly upgrade WCO using an inexpensive catalyst without relying on copious amounts of hydrogen gas to affect a hydrodeoxygenation reaction.

Nitrogen Fertilization Effects on the Composition of Foliar Amino Acids of Russet Burbank Potato

Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an important pest of potato crops. Potato foliar amino acids play essential roles in CPB growth. In this study, amino acids were classified into four groups according to their different roles in promoting CPB growth. Then, nitrogen (N) rate effects on the concentrations of amino acid groups were investigated under field conditions. Experiments were carried out with five N rates of 0, 60, 120, 180, and 240 kg N ha−1 in a randomized complete block design. Twenty leaves were collected at 40, 54, 68, and 82 days after planting (DAP) for amino acids analysis. Results showed that N rate had no significant effect on concentrations of each amino acid group at 40 DAP. However, their concentrations linearly increased as N rate increased at 54, 68, and 82 DAP, suggesting that higher N rates could potentially favor CPB growth after potato enters tuber initiation stage.

Facile Synthesis of Carboxylated Activated Carbon Using Green Approach for Water Treatment

A chemical treatment by using oxidizing agents is the most common methodology to modify or create functional groups on activated carbon. The modified activated carbon obtained from chemical oxidation needs further treatment and produced waste, therefore a new approach is needed. A facile green approach is reported. In this approach the activated carbon was oxidized using air without additional chemical treatment to increase the content of acidic surface functional groups, especially carboxyl groups. The formation of carboxyl groups was confirmed by Temperature Programmed Decomposition, Boehm titration, and Infra-red spectroscopy results. The Boehm titration result showed higher contents of carboxyl groups by three-fold. The carboxylated activated carbon synthesized by green approach showed excellent performance for water treatment.

PolyHIPEs for Water Treatment

PolyHIPEs (polymers synthesized within high internal phase emulsions) are porous materials with high specific surface area which suggests their use in ion exchange applications. We have successfully synthesized and functionalized such materials to make then hydrophilic by mixing an oil phase and an aqueous phase containing deionized water and sulphuric acid. The PolyHIPE samples were also subjected to a further microwave-assisted post-sulphonation process to increase hydrophilicity and water uptake. Post sulphonation results in a higher concentration of benzenesulphonic acid groups which are necessary for ion exchange. PolyHIPE beads processed in this manner were able to remove low concentrations (∼20mg/l) of nickel and copper ions from solution with high removal efficiency (80-95%) depending on the initial pH of the water. However, recovery of the metal through regeneration at different pH levels was less successful.

Development of microporous-activated carbons derived from two renewable precursors for CO2 capture

Wood sawdust from an invasive arboreal species, Parkinsonia aculeata, and seeds from a tropical fruit of massive consumption, Pouteria sapota, were used as precursors for the development of activated carbons (ACs) directed to CO2 adsorption. Chemical activation employing KOH as activating agent and pre-established experimental conditions was applied. Main physicochemical properties of the ACs in relation to their CO2 adsorption performance were examined. The ACs developed from the wood sawdust and the seeds presented specific surfaces areas of 770 and 1000 m2 g−1, respectively, with their porosity development resulting essentially microporous (< 2 nm). They also showed a similar content of acidic surface groups, but basic functionalities of the former duplicated those of the latter. Maximum CO2 adsorbed at equilibrium (273 K and 100 kPa) was 5.0 mmol g−1 and 4.4 mmol g−1 for the samples derived from the sawdust and the seeds, respectively. On the other hand, CO2 adsorption capacities mimicking post-combustion conditions, as evaluated from thermogravimetric assays and breakthrough curves obtained in a packed-bed column, were approximately 1 mmol g−1, indicating a good CO2 adsorption performance for both ACs. Nevertheless, those derived from the wood sawdust with a notorious preeminence of micropores (~ 93%), narrower pore size distribution centered around 1 nm, and a higher content of basic functionalities than the ACs obtained from the seeds showed a relatively better performance. The CO2 removal capacity of the activated carbons was not noticeably affected after five CO2 adsorption–desorption cycles, with both samples almost keeping their initial CO2 adsorption capacity.

On the cycling stability of biomass-derived carbons as electrodes in supercapacitors

The present work provides new insight into the long-term cycling stability of biomass-derived activated carbons as electrodes in symmetric supercapacitors on the basis of ex-situ and post-mortem spectroscopic and microscopic analyses. The physicochemical characterization of activated carbons is carried out by DTA/TG, XPS spectroscopy, SEM, AFM and BET analyses. The surface functional groups and pore size distribution are determined by Böhm titration method and Barett-Joyner-Halenda analysis, respectively. The supercapacitor performance of the composite electrodes is tested by charge/discharge galvanostatic experiments. To go inside into surface and bulk electrode changes during electrode cycling, the post-mortem XPS, SEM/EDS and AFM experiments are undertaken. It is found that activated carbon having higher content of acidic groups and narrow pore size distribution displays an impressive cycling stability in alkaline electrolyte solution. The observed changes in electrode morphology during cycling are discussed on the basis of electrode-electrolyte interaction.

Simultaneous desulfurization and denitrogenation of model fuels by polyethylene glycol-modified resorcinol/formaldehyde resin-derived carbon spheres

A series of resorcinol/formaldehyde (RF) resin-derived carbon spheres modified by polyethylene glycol (PEG) were prepared. The effects of PEG addition time during hydrothermal treatment and molecular weight on the pore structure, surface acidic groups, particle size, and adsorption performances of the obtained spherical activated carbons were investigated. Two types of model fuel containing indole, quinoline, and dibenzothiophene (DBT) as target adsorbates were prepared to evaluate the adsorption performances of the spheres, which increased in the order of DBT<quinoline<indole. Hydrogen bonding may be critical in the removal of indole. Both the surface area and oxygen-containing functional groups influenced the adsorption capacity, with the latter significantly influenced by PEG addition time. PEG addition during the RF resin cross-linking stage sharply reduced the total concentration of acidic groups on the carbon sphere surfaces. The adsorption thermodynamics and kinetics of nitrogen and sulfur compounds were also investigated. The adsorption isotherms of all S/N species were of the Freundlich type at 25 oC. The pseudo-second-order rate equation well described the adsorption kinetics. Both external diffusion and intra-particle diffusion controlled the rate of adsorption.

Biofilm microbial composition changes due to different surface chemical modifications of activated carbon cloths in the biotransformation of 4-nitrophenol

Activated carbon cloths (ACCs) were used as biofilms supports in the anaerobic biotransformation of 4-nitrophenol (4NP). As received ACC material (AW) was oxidized with HNO3 (OX) and then functionalized with anthraquinone-2,6-disulfonate (AQ). The three ACCs were packed in hybrid UASB reactors and seeded with anaerobic granular sludge for biotransformation experiments. The results indicated that ACC-packed bioreactors improved the biotransformation of 4NP by twofold as compared to the control reactor without support materials. However, the biotransformation effciency of AW, OX and AQ was very similar (59%), indicating the role of ACC as biofilm support and not as redox mediator. After 4NP biotransformation several physicochemical and biological changes were observed like (1) the point of zero charge (pHPZC) shift from acidic values (AW = 5.0, OX = 3.4, AQ = 3.1) to neutral values (pHPZC = 7.6 on average), (2) increase in the concentration of acidic and basic surface functional groups over ACC materials and the amount of supported biomass on ACCs due to biofilm formation, and (3) enrichment of exoelectrogenic microorganisms belonging to the genera Geobacter over carbonyl-rich ACC surface as revealed by 16S rRNA amplicon sequencing. Overall, the results suggest that chemical modifications of ACCs changed the microbial composition of the biofilm, but the higher concentration of carbonyl groups on ACC did not affect the biotransformation of 4NP.

Insight into the interaction mechanism of iron ions with soil humic acids. The effect of the pH and chemical properties of humic acids.

The main aim of this work was to study the mechanisms of interaction between iron(II) ions and humic acids as a function of pH, iron concentration and various humic acids chemical properties, including the degree of humification, elemental composition, aromaticity and content of acidic functional groups. The results indicated that iron was bound by humic acids at pH 7 in amounts ∼2 times higher than at pH 5 (averaged capacities: 117 and 57 cmol/kg, respectively). Iron binding at pH 7 increased with increasing the total carboxylic and phenolic groups content and the degree of humification of humic acids (R-coefficients: 0.99 and 0.95, respectively). The stability of humic acid-iron complexes at pH 7 were only slightly lower than at pH 5 due to iron hydroxides formed at pH > 5 (averaged stability constants: 5.18 and 5.26, respectively). Iron coordination mode varied depending on pH: at pH 5, the bidentate (chelate) mode dominated, whereas at pH 7 the bridging mode appeared prevalent. The total amount of bound iron was much smaller than the content of the carboxylic and phenolic groups in humic acids, on average by ∼80 (pH 7) and ∼90.1% (pH 5) indicating the occurrence of steric effects in humic acid structure i.e. the reduction of the complexation capacity of free functional groups by adjacent groups occupied by iron and/or the formation of intramolecular aggregates with iron hindering the access of further metal ions. At pH 5 the complexes were soluble in the iron concentration range positively correlated to carboxylic and phenolic groups content, showing the protective nature of negatively charged functional groups on the stability of the solution. At this pH, the destabilization of the system was governed by the neutralization of humic acid charged structures by metal cations and the compression of the double electric layer. At pH 7 the stability of the humic acid-iron solution was largely determined by the form of iron, mainly by the precipitation of metal hydroxides acting as a flocculant destabilizing the solution by co-precipitation of humic acid-iron complexes.

Changes in the physicochemical characteristics of peanut straw biochar after freeze-thaw and dry-wet aging treatments of the biomass

Effects of aging after pyrolysis were tested relative to the physicochemical characteristics of peanut straw biochar. Biochar was prepared at pyrolysis temperatures of 350 °C, 500 °C, and 650 °C; then, it was freeze-thawed and dry-wet aged. The physicochemical characteristics of the fresh and aged biochar were analyzed. The results showed that the pyrolysis temperature, ambient temperature, and humidity affected the physicochemical characteristics of the biochar. With the increase of pyrolysis temperature, the yield and surface acidic functional groups of the fresh biochar decreased, whereas the ash content, C content, pH, specific surface area, and mesoporous volume of the fresh biochar increased. The aging treatment increased the acidic functional groups content in the biochar and reduced the aromatic functional groups content, which decreased the pH value of the biochar. The aging treatment increased the specific surface area and pore volume of the biochar, and the effect of freeze-thaw aging was greater than that of dry-wet aging. The aging treatment also destroyed the complete shape of the fresh biochar, and reduced its stability. After the aging treatment, the C content of the biochar decreased, whereas the O content increased, due to oxidation of the biochar.