Groups Of Fulvic Acids Research Articles

Distribution characteristics of TiO2 NPs in Daihai lake and their stability regulated by abiotic factors

Accurate detection and stability analysis of titanium dioxide (TiO2 NPs) in surface water are critical for ecological risk assessment. Quantitative analysis of TiO2 NPs in water and sediment of Daihai Lake was performed and their occurrence forms was characterized by TEM, XRD and FTIR. Further investigation into the impact of pH, ionic strength (IS) and dissolved organic matter (DOM) on the stability of TiO2 NPs was carried out, along with a correlation analysis between abiotic factors and TiO2 NPs concentration. Results showed that TiO2 NPs in water and sediment are 1.01 × 105 and 5.66 × 105 particles/mL in July 2023, respectively. After transformed in water sample from Daihai Lake, the hydrodynamic particle (HDD) of TiO2 NPs reach 600–700 nm, with reduced crystallinity and observable characteristic peaks of NaCl, which is related to the high concentration of NaCl in Daihai Lake. Structural defects and changes in surface properties of TiO2 NPs are introduced due to the adsorption of organic matter, leading to higher aggregation and sedimentation rates. Specifically, Ca2+ promote the sedimentation of TiO2 NPs more than Na+. Conversely, A/A0 increased to 0.80–0.94 from 0.64 after humic acid (HA) and fulvic acid (FA) added. Hydroxyl and carboxyl groups of FA enhanced steric hindrance and inhibited TiO2 NPs sedimentation. While a strong promotion effect on the sedimentation of TiO2 NPs is detected when 10 mmol/L Ca2+ coexisted with 10 mg/L HA, with 70% of the TiO2 NPs settled within 120 min. Additionally, the concentration of TiO2 NPs in Daihai Lake is significantly positively correlated with dissolved organic carbon (DOC) and humification index, which might be relate to the enhancement of TiO2 NPs stability of aromatic organic matter. And the high concentration of DOC will also lead to the stable existence of TiO2 NPs in water and exacerbate aquatic toxicity.

A 44-year balanced fertilizer application affected rill erosion resistance by changing humus, aggregates, and polyvalent cation

Fertilizer application can affect the physicochemical properties of soil, such as the contents of large aggregates, humus, and exchangeable cations, thereby influencing soil erosion resistance. However, the rill erosion resistance and its key influencing factors of soil following long-term balanced fertilizer application remains unclear. This study aimed to analyze the change in rill erosion resistance following 44 years of balanced fertilizer application (No changes in the type of fertilizer) to non-calcareous soils and establish a Partial Least Squares Regression (PLSR) model of rill erodibility (kd) and soil critical shear stress (τc) to changes in the physical and chemical properties of the soil. Five treatments were designed: (1) CK (no fertilizer applied), (2) N (nitrogen), (3) NP (nitrogen plus phosphorus), (4) NK (nitrogen plus potassium), and (5) NPK (nitrogen, phosphorus, and potassium). Compared to CK, the N, NP, NK, and NPK application significantly increased τc by 49.6, 96.7, 73.6, and 36.2 %, respectively. Whereas, kd increased significantly only in the NPK treatment group. The optimal partial least squares regression model showed that mean weight diameter (MWD) had the greatest positive influence on soil critical shear stress, followed by fulvic acid (FA) content, whereas water-dissolved substances had a negative influence. Long-term balanced fertilizer application can increase MWD and τc by combining micro-aggregates and humus into large aggregates. Ca2+ content had the greatest positive effect on kd. Compared with that of CK, exchangeable Ca2+ content increased significantly with NP and NPK application (7.9 and 34.3 %, respectively). Ca2+ can increase kd by binding to the polar functional groups in FA to promote the shedding of hydration shells in large aggregates. Among all treatments, the NP treatment showed the best performance for reducing kd and increasing τc. This study could contribute to the understanding of the rill erosion process and modeling in non-calcareous soils and offer a reference for agricultural erosion control treatments.

Kinetics and molecular structure of the binding process between coal-based fulvic acid and zinc ions

The fulvic acid (FA) extracted by lignite oxygenolysis contains a variety of reactive functional groups that leading to trace element zinc (Zn) can be chelated at these sites, and has great potential in life science and environmental remediation. The interaction mechanism of FA with Zn ions (Zn(II)) was studied by reaction kinetics. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were applied in products characterization. The three-dimensional molecular structures of the zinc fulvate (FA-Zn) were explored by using quantum chemical calculations. The results show that the chelation reaction of FA with Zn(II) had pseudo-second-order reaction kinetics; the carboxyl, hydroxyl, carbonyl, amino and mercapto groups in FA act as monodentate or multidentate ligands to form chelates with Zn(II). The molecular structure formation of FA-Zn was related to its specific functional group binding sites and binding energy. when FA bound Zn(II) intramolecularly, the model was most stable when the ortho-dicarboxylic acid site was bound, the minimum energy of this model was −4095.9342 a.u. and the bond lengths were 1.87 Å and1.86 Å; when FA bound Zn(II) intermolecularly, among the models without water, the model with carbonyl and phenolic hydroxyl sites binding was the most stable, the minimum energy of this model was −6108.2298 a.u. and the bond lengths were 1.97 Å and1.89 Å; when Zn(II) was combined with two water molecules, the model with binding at the amino site was the most stable, the minimum energy of this model was −6261.0946 a.u. and the bond lengths were 1.93 Å and 2.04 Å.

Effect of Maillard reaction based on catechol polymerization on the conversion of food waste to humus

The pollution and harm of food waste (FW) are increasingly concerned, which has the dual attributes of pollutants and resources. This study aimed to improve the synthesis efficiency of FW humic substances (HS), and investigating the effect of catechol on the formation mechanism and structure of humic acid (HA) and fulvic acid (FA). Results indicated that catechol incorporation could enable to exhibit higher HS yield and more complex structure, especially the maximum particle size of FA reached 4800 nm. This was due to the combination of catechol with multiple nitrogenous compounds, which accelerated molecular condensation. Spectroscopic scans analysis revealed that Maillard reaction occurs first. Subsequently, Maillard reaction products and amino acids were combined with different sites of catechol, which leads to the difference of molecular structure of HS. The structure of FA is characterized by an abundance of carboxyl and hydroxyl groups, whereas HA is rich in benzene and heterocyclic structures. The structural difference was responsible for the disparity in the functional properties of FA and HA. Specifically, the presence of amino, hydroxyl, pyridine, and carboxyl groups in FA contributes significantly to its chelating activity. This research provides an efficient and sustainable unique solution for the high-value of FW conversion, and provides evidence for understanding the structural evolution of HA and FA.

Fulvic acid improves the degradation performance of Fe-Mn bimetallic in peroxymonosulfate based advanced oxidation process

The co-existing dissolved oxygen matters exhibited various influences on peroxymonosulfate (PMS) activation and organic contaminants degradation by the Fe/Mn based catalysts. This study has successfully constructed a Fe-Mn bimetallic catalyst (FMB)/PMS system to degrade aniline aerofloat (AAF). It was found the fulvic acid (FA) elevated the degradation efficiency of AAF (100 mg/L) from 73.54 % to 97.81 % within 10 min accompanied by the kinetic constant (kobs) increased from 0.237 min−1 to 0.638 min−1. The characterization and experimental results demonstrated that the FA-FMB exhibited a superior morphology and structure compared with FMB, contributing to a larger specific surface area (SSA). Meanwhile, FA introduced abundant oxygen vacancies (OV) into FA-FMB, facilitating the adsorption of PMS and the generation of abundant singlet oxygen (1O2) during the reaction process. While, the 1O2 played a dominant role in the AAF degradation. Furthermore, the active electron-donating groups in FA endow its enhanced reduction effect on Fe/Mn to promote the activation of PMS by Fe-Mn binary catalyst. This study has provided deep insights into the effect of FA on PMS activation by Fe-Mn bimetallic catalysts.

Adsorption behavior of soil fulvic acid on crystal faces of kaolinite and goethite: Described by CD-MUSIC model

The interaction between organic matter (OM) and minerals has significant impacts on the mineralization process and rate of OM, and can protect part of organic carbon in soils. In this study, the complex species of fulvic acid (FA) on the surface of minerals (kaolinite and goethite) and the corresponding thermodynamic characteristics were investigated with the CD-MUSIC model and isothermal titration calorimetry. With increasing pH, the adsorption of kaolinite for FA increased at pH < 5.5 and decreased at pH > 5.5, which might be due to the binding of carboxyl groups of FA onto the positively charged sites of O-face and edge-face. However, that of goethite consistently decreased with increasing pH from 3.5 to 9.0 due to an increase in electrostatic repulsion. The fraction of FA was mainly adsorbed on the edge-face and O-face to form inner sphere complexes on kaolinite and outer sphere complexes on goethite. Molar adsorption enthalpies indicated that FA was adsorbed through two site types on kaolinite, while that was one site type on goethite. In addition, the molar enthalpy was more closely associated with inner sphere complexation for kaolinite, while with outer sphere complexation for goethite. The findings shed new light on the adsorption behavior and complexation mechanism of OM on the crystal faces of mineral-water interface.

Effects of UV-irradiation on Cd[formula omitted] and Pb[formula omitted] binding to humic/fulvic acids: Methodological guidance to eliminating the interference of dissolved organic matter on SWASV detection of heavy metals in soil extracts

Humic acid (HA) and fulvic acid (FA) ubiquitous in the environment will interfere with the electrochemical signals of Cd2+ and Pb2+, thereby decreasing the detection accuracy of square-wave anodic stripping voltammetry (SWASV) for Cd2+ and Pb2+ in soil and sediment extracts. However, insight into the mechanism of HA and FA interference is lacking. This study investigated the interference mechanism of HA and FA on Cd2+ and Pb2+ SWASV currents from multiple perspectives and provided methodological guidance for eliminating the HA and FA interference. Our results indicated that the main interfering factor was the complexation of active functional groups in HA and FA, which converted free-state heavy metal (HM) ions into HA- and FA-complexed HMs (HA-HMs and FA-HMs) undetectable by SWASV. More O-containing groups in FA caused its more severe interference on Cd2+ and Pb2+ than HA. After 60 min of ultraviolet (UV) photolysis, the SWASV current recovery rates of Cd2+ and Pb2+ in HA-HMs almost reached 100%, while FA-HMs achieved the same goal after only 24 min of UV photolysis. The photo-degradation behaviors revealed that the mechanism of interference elimination was that UV photolysis destroyed the molecular structure and active groups of HA and FA, thereby releasing free-state Cd2+ and Pb2+ from HA-HMs and FA-HMs. This study also verified the above-obtained conclusions using real samples. The finding of this study is that advanced oxidation processes can eliminate the interference of HA and FA, thereby improving the detection accuracy of Cd2+ and Pb2+ in soil and sediment extracts by SWASV.

Binding of Cd(II) to birnessite and fulvic acid organo-mineral composites and controls on Cd(II) availability

Manganese oxide minerals (MnOs) are major controls on cadmium (Cd) mobility and fate in the environment. However, MnOs are commonly coated with natural organic matter (OM), and the role of this coating in the retention and availability of harmful metals remains unclear. Herein, organo-mineral composites were synthesized using birnessite (BS) and fulvic acid (FA), during coprecipitation with BS and adsorption to preformed BS with two organic carbon (OC) loadings. The performance and underlying mechanism of Cd(II) adsorption by resulting BS-FA composites were explored. Consequently, FA interactions with BS at environmentally representative (5 wt% OC) increase Cd(II) adsorption capacity by 15.05–37.39% (qm = 156.5–186.9 mg g−1), attributing to the enhanced dispersion of BS particles by coexisting FA led to significant increases in specific surface area (219.1–254.8 m2 g−1). Nevertheless, Cd(II) adsorption was notably inhibited at a high OC level (15 wt%). This might have derived from the supplementation of FA decreased pore diffusion rate and generated Mn(II/III) competition for vacancy sites. The dominant Cd(II) adsorption mechanism was precipitation with minerals (Cd(OH)2), and complexation with Mn–O groups and acid oxygen-containing functional groups of FA. In organic ligand extractions, the exchange Cd content decreased by 5.63–7.93% with low OC coating (5 wt%), but increased to 33.13–38.97% at a high OC level (15 wt%). These findings help better understand the environmental behavior of Cd under the interactions of OM and Mn minerals, and provide a theoretical basis for organo-mineral composite remediation of Cd-contaminated water and soil.

Hierarchical Nanoporous C/C Composite from Humic Fulvic Acid and Sulfonated Pitch for High‐Energy‐Density EDLC Electrodes

AbstractAs a new type of energy storage device, electric double layer capacitors (EDLCs) possess fast charge/discharge speed and good cycling stability. However, the low energy density and high production cost of EDLC electrodes are still big challenges. Herein, a hierarchical nanoporous C/C composite is synthesized by chemical recombination and subsequent activation strategy from low‐cost carbon resources, namely renewable humic fulvic acid (FA) and industrial sulfonated pitch (SP). Profiting from the abundant polycyclic aromatic hydrocarbons in SP and plentiful oxygen‐containing groups in FA, the resultant nanoporous C/C composite has both high e‐conductivity and high specific surface area (SSA). Thus, this porous C/C composite can be directly fabricated as EDLC electrode without any conductive agent. By fully exploiting the synergistic effect between high e‐conductivity and high SSA, it shows excellent electrochemical stability in EMIMBF4 ionic liquid electrolyte. Furthermore, it possesses a higher specific gravimetric capacitance (117 F g−1) than that of pure FA‐based porous carbon (92.5 F g−1) at a current density of 1 A g−1. More importantly, the maximum energy density can be as high as 55.4 Wh kg−1, largely better than commercial activated carbon.

بررسی همدمای جذب روی و مس بر سطح اسید هومیک استخراج شده از خاک

Introduction: Copper and zinc are two of the most important microelements affecting plant growth which can be influenced by many factors. The adsorption processes play a determinative role in solubility of copper and zinc elements in the soil solution and, therefore, their availability to plants. Organic matter is one of the most important factor that have an significant role on the absorption and desorption of elements in the soil. These materials are divided into humic and non-humic groups. Humic substances are divided into three groups of fulvic acid, humic acid and humic, based on their resistance and solubility in acid and base. Humic acid with a medium molecular weight and color is soluble into base and insoluble into acid, and has a medium resistance against the microbial attack. It forms the most important organic part of the soil and is capable to adsorb metals. The purposes of this study were to extract soil humic acid, study the adsorption of metals on the surface of humic acid and to determine the metals adsorption coefficients using adsorption isotherm models. Materials and Methods: Sampling was done from forest areas of northern Iran. Some physical and chemical properties of the studied soil were determined. Then, the humic acid of the soils was extracted by 0.1 M NaOH and 6 M HCl, and purified by 0.1M HCl+0.3M HF. Functional group, E4/E6 ratio (Optical density or absorption of dilute solutions at wavelengths of 465 and 665 nm), and humification index of the extracted humic acid were measured. Some other properties of the extracted humic acid have also been analyzed. To study the adsorption isotherms of Zn and Cu in the presence of humic acid, solutions with concentrations of 10, 20, 40, 60 and 80 mg/L of ZnCl2 (zinc adsorption testing) and CuSO4 (copper adsorption testing) were prepared, respectively in a 0.01M Ca(NO3)2 background solution, and added to 250 g of humic acid. The samples were shaken for 12 hours (based on the time of equilibrium) at pH=5 and 25 °C in incubator shaker, then the samples were centrifuged and the supernatant was passed through filter paper and measured using atomic adsorption spectrophotometer device. The difference between initial concentration and final concentration identified the amount of adsorbed element. Results and Discussion: The results of the acidic functional groups measurement in the humic acid samples revealed that the most of total acidity (60%) was due to the presence of phenolic groups while the carboxylic groups were responsible for the remaining (40%). Phenolic groups were abundant in the primary stages of the decomposition of humic materials. Since the soil used for extracting humic acid was covered with broad leaf trees and the continuous entry of organic matter into it (the fall of leaves) lasted for many years and due to the low temperature of the soil in part of the year, it can be said that a significant part of the soil organic matter is in the primary or middle stages of humification and the phenolic OH groups/carboxylic groups ratio in the humic acid extracted from them was high. The equilibrium time for adsorption of both metals occured at 12 h to achieve maximum adsorption level in the presence of humic acid. The obtained experimental data were fitted to three models of Langmuir, Freundlich, and Tampkin. The accuracy of mentioned models to fit data were estimated based on the detection coefficient (R2) and the roots of mean square error (RMSE). The results showed that the Freundlich model with higher detection coefficient and lower roots of mean squared error describes the adsorption of copper and zinc elements, well. To better compare the adsorption of the elements by humic acid, Langmuir's b parameter (Expresses maximum adsorption) can be used. The maximum adsorption of copper (23.04 mg/g) by humic acid was higher than zinc adsorption (13.8 mg/g). This trend is consistent with the Irving–Williams series of divalent elements: Mn < Fe < Zn < Co < Ni < Cu. It is generally believed that humic acid is a good complexing agent for many metal ions and its binding to metal ions can improve the adsorption. Significance differences were tested by a parametric 𝑡-test or 𝐹 statistics in ANOVA (analysis of variance). There was a significant correlation between the maximum adsorption of metals (b) and the properties of humic acid at a probability level of 5%.

Extraction of Fulvic Acid from Lignite and Characterization of Its Functional Groups.

Fulvic acid (FA) is a complex organic mixture composed of small molecules. The structure and composition of FA vary greatly because of the different raw materials used for preparing FA. In this work, FA was extracted from shallow low-rank lignite by hydrogen peroxide (H2O2) in a microwave field, and the functional groups of FA were characterized. The optimal extraction process was determined, with the H2O2 concentration being the key factor affecting the yield of FA. Thermogravimetric analysis showed that FA was mainly composed of low molecular weight and readily pyrolyzed compounds. As shown by Fourier transform infrared spectroscopy, in the process of FA extraction by H2O2 oxidation of lignite, the content of −COOH increased, long-chain aliphatic compounds decreased, stretching vibrations of aromatic ring skeletons disappeared, and aromatic ring substitution became mainly tri- or disubstitution. Fluorescence spectroscopy indicated that FA had a low degree of aromaticity. X-ray photoelectron spectroscopy qualitatively and quantitatively revealed that the main modes of carbon–oxygen bonding in FA were C–O–, COO–, and C=O. Thus, this study not only lays a foundation for studying the composition and structure of coal-based FA but also opens a new avenue for a clean and efficient utilization of lignite.

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.

The role of major functional groups: Multi-evidence from the binding experiments of heavy metals on natural fulvic acids extracted from lake sediments

Fulvic acid (FA) plays a key role in governing the environmental geochemistry behavior of heavy metals. In this work, the roles of major functional groups were investigated based on binding experiments of heavy metals on natural FA extracted from lake sediments. The results showed that the adsorption capacities were ranked as Cu2+ > Pb2+ >Cd2+. The differences of peak area at 3412, 1713, 617and 2430 cm−1 pre- and post-binding reactions in FTIR spectra suggested that phenolic, carboxyl and nitrogen-containing groups were the major functional groups providing sites binding heavy metals. Moreover, the results of bi-Langmuir model and the ionic strength effects jointly indicated that electrostatic attraction was the key mechanism during the adsorption process. The fitted results of Ligand-binding model suggested that the major functional groups in FA were classified into two types binding sites: weak (i.e. phenolic and carboxyl groups) and strong binding sites (i.e. nitrogen-containing groups). Additionally, there might be p-benzoquinone-like formed in FA which were then reduced to hydroquinone during the adsorption process, corresponding to the changing of peak area at 1614 and 830 cm−1 in FTIR spectra, the occurrence of Peak C in Fluorescence excitation-emission matrix (EEM) spectra and the ratios of H/C (<1) and O/C (≈1). The organic matter in sediments from Lake Wuliangsuhai presented similar characteristics with terrestrial plants due to the lake characterized by Phragmites australis and Potamogeton pectinatus L. being the dominant species, which shared large proportions of woody tissues as well as waxy hydrocarbons resembling that of terrestrial plants. This work is useful to insight the environmental effects of FA on heavy metals in environment.

Study on the extraction of fulvic acid from lignite by microwave-assisted hydrogen peroxide

Extraction of fulvic acid (FA) from Hulun Buir (HB) lignite were carried out under the conditions of hydrogen peroxide and microwave-assisted hydrogen peroxide. The results showed that the microwave can greatly improve reaction rate and observably shorten reaction time, while the extraction yield of FA increased around 4%. Purification technology of FA was studied by sulfuric acid-acetone aqueous solution, and then structure of purified FA was evaluated. All results demonstrated that under the assistance of microwave, the oxidative degradation ability of hydrogen peroxide is stronger, the solvent gets higher permeation ability and the oxygen content in FA is higher. Among the oxygenic functional groups of FA, carboxyl group has the highest content, followed by hydroxyl group and the ester content is the lowest. Trisubstituted benzene is the major component in the aromatic structure of FA. In aliphatic structure, content of methylene is the highest. [Received: March 4, 2017; Accepted: October 17, 2017]

Removal of Copper (II) by Biochar Mediated by Dissolved Organic Matter

The effects of humic acid (HA) and fulvic acid (FA) on Cu2+ adsorption on biochar were investigated, with mechanisms confirmed by excitation-emission matrix spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. HA loading enhanced Cu2+ adsorption on biochar, with the maximum enhancement of 55.0% occurring at an HA loading of 100 mg-C/L. The adsorbed HA introduced many additional functional groups to biochar, thus enhancing Cu2+ adsorption, which decreased at HA concentrations >100 mg-C/L due to self-association of HA at high loading concentrations. In contrast, FA loading caused no enhancement on Cu2+ adsorption on biochar. FA was adsorbed through H-bonding with the functional groups of biochar, which set up a competition with Cu2+ for adsorption on biochar. The functional groups occupied by adsorbed FA were offset by the newly introduced functional groups of FA, thus there was no net increase in the amount of Cu2+ adsorption upon FA loading. These findings imply that, because of the enhanced adsorption of HA-loaded biochar, the amount of Cu2+ immobilized would increase by 28.2% for mature compost and 31.9% for fresh compost if there exist interaction between biochar and HA compared with the amounts immobilized by non-interactive HA and biochar.

Composition and copper binding properties of aquatic fulvic acids in eutrophic Taihu Lake, China

Fulvic acid (FA) plays a significant role in biogenic-elemental cycling in aquatic ecosystems which is highly dependent on their organic composition. In this study, the aquatic FA contents and binding properties during bloom and non-bloom periods in Taihu Lake were investigated by two-dimensional correlation spectroscopy Fourier transform infrared spectroscopy (2D-COS-FTIR), nuclear magnetic resonance (NMR) and elemental analysis. Compared with non-bloom FA, bloom FA was of lower nitrogen content and higher C/N ratio. It contained more carboxylic and aliphatic groups while less amide groups. 2D-COS-FTIR spectra evidenced the carboxyl groups in bloom FA had the fastest response to Cu(II) binding. Also, polysaccharide in bloom FA was more susceptive to Cu(II) concentrations than that in non-bloom FA. While comparing with bloom FA, the N-rich organic compounds in non-bloom FA exhibited faster binding sequence with Cu(II). A comprehensive scheme about the interaction process of FA-Cu(II) showed that both nitrogenous and oxygenic groups in FAs were active in binding to Cu(II). The alteration in binding behaviors of organic groups in FAs to Cu(II) may have been driven by algal products and microbial community variety in Taihu Lake. Our results here have the potential to contribute significantly to future studies of dissolved organic matter dynamic biogeochemistry processes and trace metal cycling processes in eutrophic lakes.

Novel Process of Removal of Sulfur Dioxide by Aqueous Ammonia–Fulvic Acid Solution with Ammonia Escape Inhibition

A novel wet flue gas desulfurization process by aqueous ammonia–fulvic acid solution was proposed, in which fulvic acid (FA) could inhibit ammonia escape because carboxylic and phenolic groups in FA would interact with aqueous ammonia to form relatively stable ammonium fulvate. Experiments were conducted to research the effect of operating parameters such as initial pH value on the duration time of high efficiency (DTHE, time of above 95%) and absorption efficiency of SO2 in a bubbling reactor. Results indicate that SO2 absorption efficiency and DTHE increase with increasing initial pH value and that SO2 absorption capacity of aqueous ammonia can be improved by synergic action of FA. Concentration of FA has a slight effect on SO2 absorption efficiency (above 98.3%, pH0 8.5) but an obvious effect on DTHE. FA can successfully inhibit ammonia escape from absorption liquid during desulfurization. When the pH of aqueous ammonia–FA absorption liquid is above 4.1, absorption efficiency can be kept above 99.0% (f...

Treatment of NOM fractions of reservoir sediments: Effect of UV and chlorination on formation of DBPs

Abstract Humic acid (HA), fulvic acid (FA) and hydrophilic fraction of fulvic acid (FAHPI) were isolated from bottom sediments of a drinking water reservoir in North China. The effects of ultraviolet (UV) irradiation on the structure of the sedimentary natural organic matter (NOM) and subsequent disinfection by-products (DBPs) formation were investigated, with the comparison of commercial humic substances. HA sample mainly consisted of aromatic, methyl and guaiacyl lignin groups, which were reactive with chlorine to form trichloromethane (TCM). FA and FAHPI samples mainly contained ester, phenolic hydroxyl and aromatic ketone groups, among them, phenolic hydroxyl groups were highly reactive toward chlorine and primarily formed dichloroacetic acid (DCAA) during chlorination. UV irradiation decreased the hydrophobicity and increased the hydrophilicity of NOM. UV irradiation eliminated the aromatic, methyl and guaiacyl lignin groups of the HA sample, decreasing the formation of TCM, but increased the phenolic hydroxyl groups of FA and FAHPI samples, enhancing the formation of DCAA. In addition, UV irradiation promoted the trichloroacetic acid (TCAA) formation of the NOM samples from subsequent chlorination. Medium pressure (MP) UV irradiation had greater impacts on NOM fractions and DBPs formation during subsequent chlorination.

Poorly crystalline hydroxyapatite: A novel adsorbent for enhanced fulvic acid removal from aqueous solution

In this study, poorly crystalline hydroxyapatite (HAP) was developed as an efficient adsorbent for the removal of fulvic acid (FA) from aqueous solution. Surface functionality, crystallinity, and morphology of the synthetic adsorbent were studied by Fourier-transformation infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of various parameters such as crystallinity of adsorbent, contact time, adsorbent dosage, pH, initial adsorbate concentration, temperature, ionic strength and the presence of alkaline earth metal ions on FA adsorption were investigated. Results indicated that the nanosized HAP calcined at lower temperature was poorly crystalline (Xc=0.23) and had better adsorption capacity for FA than those (Xc=0.52, 0.86) calcined at higher temperature. FA removal was increased with increases of adsorbent dosage, temperature, ionic strength and the presence of alkali earth metal ions, but decreased as the pH increased. Kinetic studies showed that pseudo-second-order kinetic model better described the adsorption process. Equilibrium data were best described by Sips models, and the estimated maximum adsorption capacity of poorly crystalline HAP was 90.20mg/g at 318K, displaying higher efficiency for FA removal than previously reported adsorbents. FT-IR results revealed that FA adsorption over the adsorbent could be attributed to the surface complexation between the oxygen atom of functional groups of FA and calcium ions of HAP. Regeneration studies indicated that HAP could be recyclable for a long term. Findings of the present work highlight the potential for using poorly crystalline HAP nanoparticles as an effective and recyclable adsorbent for FA removal from aqueous solution.

Conformational changes of dissolved humic and fulvic superstructures with progressive iron complexation

Conformational changes of a humic acid (HA) and a fulvic acid (FA) induced by iron complexation were followed by high-performance size exclusion chromatography (HPSEC) with both UV–vis and refractive index (RI) detectors. Molecular size distribution was reduced for HA and increased for FA with progressive iron complexation. Since interactions of Fe with humic components are electrostatic, it is likely that the triple-charged Fe ions formed stronger complexes with the more acidic hydrophilic and hydrated FA than with the less acidic and more hydrophobic HA. The large content of ionized carboxyl groups in FA, thus favored the formation of intra- or intermolecular bridges between the negatively charged fulvic acid molecules, and led to more compact and larger size network than for HA. Conversely, iron complexation with HA disrupted the humic conformational arrangements stabilized by only weak hydrophobic bonds into smaller-size aggregates of greater conformational stability due to formation of strong metal complexes. These results confirmed that humic molecules in solution were organized in supramolecular associations of relatively small molecules loosely bound together by dispersive interactions and hydrogen bonds, and they specifically responded to chemical changes brought about by metal additions. The present study revealed the molecular changes occurring in superstructures of natural organic matter when in metal complexes and contributed to understand and predict the environmental behavior in waters and soil of metal complexes with natural organic matter.