Content Of Phenolic Groups Research Articles

Laccase modified fulvic acid-like substance from paper spent cooking liquor: Chemical structure optimization, functional group reconstruction and bioactivity improvement

Identifying a recovery technology for paper spent cooking liquor and converting it into useful material is important for the sustainable development of paper industry. Previous research reported that paper spent cooking liquor-derived fulvic acid-like substances (molecular weight < 5 kDa, PFA) promotes rice growth under salt stress but not as well as natural fulvic acid, which restricts its application as a fertilizer synergist. The ability of PFA to promote rice growth was positively associated with functional groups content. Laccase was used to modify the chemical structure of PFA to further improve its bioactivity. Results showed that laccase modification increased carboxyl and phenolic group contents through oxidation and demethylation with 60 min as optimal reaction time. Under this condition, carboxyl and phenolic group content were increased by 33 %-68.9 % and 19.1 %-208.4 %, respectively. In addition, laccase lowered the molecular weight of PFA (the fraction of molecular weight < 1 kDa increased by 21 %-35.76 %), promoted the degradation of lignin, and increased the relative abundance of tannins (containing phenolic compounds) by 42.89 %-89.41 %. Moreover, laccase-modified PFA (PFA-Ms) promoted rice growth under salt stress than that of PFA. Correlation analysis verified that the promoting effect of PFA-Ms on the elongation of rice roots was associated with carboxylic-C and tannin contents. The antioxidant and root growth-promoting functions of the phenolic and carboxyl groups were confirmed by experiments using phenol and acetic acid, respectively. This study provides an attractive perspective for the sustainable utilization of paper spent cooking liquor as a fertilizer synergist in agriculture.

Silk acid-tyramine hydrogels with rapid gelation properties for 3D cell culture

Silk fibroin (SF) can be enzymatically crosslinked through tyrosine residues to fabricate hydrogels with good biocompatibility and tunable mechanical properties. Using tyramine substitution can increase the phenolic group content to facilitate the gelation kinetics and mechanical properties. In this study, a two-step chemical modification method is demonstrated to synthesize silk acid-tyramine (SA-TA) conjugates with a high phenolic group content (>7 mol%). The SA-TA shows rapid enzyme-catalyzed gelation property where the sol–gel transition takes less than 10 s at 37 °C, allowing cell encapsulation with uniform distribution while maintaining high cell viability (>90 %). Furthermore, the enzyme-catalyzed SA-TA hydrogels show enhanced storage modulus than enzyme-catalyzed SF hydrogels, long-term stability, and good cytocompatibility, indicating their great potential in 3D cell culture. The in vivo implantation study demonstrates that the SA-TA hydrogels are biodegradable with a mild immune response. This implies that SA-TA hydrogels can be applied in various medical applications, such as tissue engineering, cell delivery, and 3D bioprinting. Statement of significanceIn this study, a two-step chemical modification method is demonstrated to synthesize silk acid-tyramine (SA-TA) conjugates with a high phenolic group content (>7 mol%). Owing to the increased content of the phenolic group, the SA-TA shows rapid enzyme-catalyzed gelation property where the sol–gel transition takes less than 10 s at 37 °C, allowing cell encapsulation with uniform distribution while maintaining high cell viability (>90 %). Furthermore, the enzyme-catalyzed SA-TA hydrogels show enhanced storage modulus than enzyme-catalyzed SF hydrogels, long-term stability, and good cytocompatibility, indicating their great potential in 3D cell culture. The in vivo implantation study demonstrates that the SA-TA hydrogels are biodegradable with a mild immune response. This implies that SA-TA hydrogels can be applied in various medical applications, such as tissue engineering, cell delivery, and 3D bioprinting.

Understanding Zinc Transport in Estuarine Environments: Insights from Sediment Composition

Sediments are sources and sinks of heavy metals in water, and estuaries are heavily influenced by human production and life. Therefore, it is of great significance to study the composition of estuarine sediments and the relationship between their components to understand the transport and transformation pathways of heavy metals in the environment. In this research, we investigated the characteristics and patterns of Zn adsorption by organic–inorganic composites, organic–clay mineral composites, and iron oxide–clay mineral composites in eight estuarine sediment samples from Dianchi Lake. The results show that both Langmuir and Freundlich isothermal models can describe the adsorption behaviour of the adsorbent better. The order of the adsorption capacity of the three groups of samples for zinc was organic–inorganic composites &gt; organic–clay mineral composites &gt; iron oxide–clay mineral composites. Through FTIR and XRD analyses, the adsorption of Zn2+ on the three groups of samples was dominated by electrostatic attraction and coordination adsorption, accompanied by the occurrence of ion exchange and co-precipitation. After FTIR semi-quantitative analysis, it was found that the source of the differences in the high and low Zn adsorption of the three types of samples may be mainly due to the content of phenolic functional groups in the organic matter. This may be related to the low redox site of the phenolic hydroxyl group, which, as an electron donor, is susceptible to electrostatic attraction and complexation with heavy metal cations. The organic–inorganic composite has a higher adsorption capacity for Zn when the ratio of the active fraction of organic matter to the free iron oxide content is 0.65–0.70. In this range, the organic matter can provide enough negative charge without making the sample surface too dense. Iron oxides can also activate the sample by providing sufficient contact between the clay minerals and the organic matter. When this ratio is too high or too low, it will be unfavourable for Zn adsorption.

Assessment of Lignin Residues from Bioethanol Production of Olive Stones as Green Chemical Thickener of Epoxidized Linseed Oil

This work focused on the characterization of lignin residues from bioethanol production of olive stones (OS) and the use of these residues to chemically thicken epoxidized linseed oil (ELO). OS were processed by an acid/steam explosion pretreatment, followed by pre-saccharification, using different enzyme dosages, and simultaneous saccharification and fermentation. The chemical composition of the OS lignin residues was analysed, revealing a high lignin content (66.6–69.5%), and lower quantities of glucan (17.4–19.3%) and xylan (2.8–2.9%). Whereas, the structural properties of OS lignin residues were characterized by Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), thermogravimetric analysis and size exclusion chromatography (SEC). OS lignin residues displayed the main inter-unit linkages (β–β′ resinol (51.0–59.0%), followed by β-O-4′ alkyl aryl ethers (27.0–35.2%) and β-5′ phenylcoumaran (11.4–13.2%) substructures), high molecular weights (22,000–25900 Da), low S/G ratios (1.2–1.5) and phenolic groups content (48–55 mg GAE/g lignin). Moreover, OS lignin residues were dispersed in ELO to obtain thickened formulations, which were characterized by FTIR and NMR. Oil thickening was achieved by promoting the chemical crosslinking between lignocellulose hydroxyl groups and ELO epoxy groups, enabling the compatibilization of both components. Up to tenfold viscosity increment of the resulting thickened formulations in relation to ELO’s viscosity was observed. Besides, thickened formulations exhibited viscoelastic properties, evincing oil structuration to some extent.Graphical

Dissolved carbon in biochar: Exploring its chemistry, iron complexing capability, toxicity in natural redox environment

Dissolved black carbon (DBC) plays a crucial role in the migration and bioavailability of iron in water. However, the properties of DBC releasing under diverse pyrolysis conditions and dissolving processes have not been systematically studied. Here, the compositions of DBC released from biochar through redox processes dominated by bacteria and light were thoroughly studied. It was found that the DBC released from straw biochar possess more oxygen-containing functional groups and aromatic substances. The content of phenolic and carboxylic groups in DBC was increased under influence of microorganisms and light, respectively. The concentration of phenolic hydroxyl groups increased from 10.0∼57.5 mmol/gC to 6.6 ∼65.2 mmol/gC, and the concentration of carboxyl groups increased from 49.7∼97.5 mmol/gC to 62.1 ∼113.3 mmol/gC. Then the impacts of DBC on pyrite dissolution and microalgae growth were also investigated. The complexing Fe3+ was proved to play a predominant role in the dissolution of ferrous mineral in DBC solution. Due to complexing between iron ion and DBC, the amount of dissolved Fe in aquatic water may rise as a result of elevated number of aromatic components with oxygen containing groups and low molecular weight generated under light conditions. Fe-DBC complexations in solution significantly promoted microalga growth, which might be attributed to the stimulating effect of dissolved Fe on the chlorophyll synthesis. The results of study will deepen our understanding of the behavior and ultimate destiny of DBC released into an iron-rich environment under redox conditions.

The Effect of Sample Preparation Techniques on Lignin Fourier Transform Infrared Spectroscopy.

The characterization and quantification of functional groups in technical lignins are among the chief obstacles of the utilization of this highly abundant biopolymer. Although several techniques were developed for this purpose, there is still a need for quick, cost-efficient, and reliable quantification methods for lignin. In this paper, three sampling techniques for fourier transform infrared (FTIR) spectroscopy were assessed both qualitatively and quantitatively, delineating how these affected the resultant spectra. The attenuated total reflectance (ATR) of neat powders and DMSO-d6 solutions, as well as transmission FTIR using the KBr pelleting method (0.5 wt%), were investigated and compared for eight lignin samples. The ATR of neat lignins provided a quick and easy method, but the signal-to-noise ratios in the afforded spectra were limited. The ATR of the DMSO-d6 solutions was highly concentration dependent, but at a 30 wt%, acceptable signal-to-noise ratios were obtained, allowing for the lignins to be studied in the dissolved state. The KBr pelleting method gave a significant improvement in the smoothness and resolution of the resultant spectra compared to the ATR techniques. Subsequently, the content of phenolic OH groups was calculated from each FTIR mode, and the best correlation was seen between the transmission mode using KBr pellets and the ATR of the neat samples (R2 = 0.9995). Using the titration measurements, the total OH and the phenolic OH group content of the lignin samples were determined as well. These results were then compared to the FTIR results, which revealed an under-estimation of the phenolic OH groups from the non-aqueous potentiometric titration, which was likely due to the differences in the pKa between the lignin and the calibration standard 4-hydroxybenzoic acid. Further, a clear correlation was found between the lower Mn and the increased phenolic OH group content via SEC analyses. The work outlined in this paper give complementary views on the characterization and quantification of technical lignin samples via FTIR.

Key properties identification of biochar material in anaerobic digestion of sewage sludge for enhancement of methane production

Owing to the intricate physicochemical characteristics of biochar material, a comprehensive understanding of their effects and mechanisms involved in anaerobic digestion still needs to be explored. In this study, the methane yield of sludge hydrolysate was inhibited by 13.3% after the addition of granular activated carbon (GAC), which was due to the predominance of non-selective adsorption by GAC. Whereas the shortened lag phase time (38.2%), the improved methane production rate (16.6%), and the increased methane yield (7.6%) were achieved after the algal biochar (ABC) addition. The methanogenic improvements by ABC were attributed to its redox capacity other than pH buffering capacity. Quantitative results showed that the content of phenolic and lactonic groups were 4.8 and 2.3 times higher than that of GAC, respectively, which endowed ABC with a stronger redox capacity, especially electron-donating capacity. Surface oxygen-containing functional groups like phenolic and lactonic groups of biochar material should be valued for the improvement of anaerobic digestion. The findings of this study provided a comprehensive insight into the connection between mechanisms and related biochar properties during the anaerobic digestion of sewage sludge, which also provided an important clue to selecting, even harnessing desirable biochar material for a given biotechnological process.

Effects of thermal and physical modification on functional properties of organosolv lignin from sugarcane bagasse and its application in cosmeceutical products

Organosolv lignin is an emerging bio-additive for creating functional properties in various products with its advantages in high-purity, sulfur-free, biocompatibility, and solubility in green solvents. In this study, effects of thermal and physical modification on alterations of functional properties and particle size distribution of isolated organosolv lignin from sugarcane bagasse (OLB) were studied. Thermal treatment of OLB at increasing temperatures from 170 to 230°C in 70%w/w aqueous ethanol led to alteration of phenolic hydroxyl content, while ultrasonication resulted in homogeneous size distribution of the modified OLB according to laser diffraction and scanning electron micrograph. The highest ultraviolet light absorbance and antioxidant activities were obtained at 190°C treatment which were correlated to the highest phenolic group content. Application of the modified OLB at 3% w/w in a base cream formulation resulted in enhancement of the anti-UV activity to exceed SPF 50 with increasing antioxidant activity in the product. The work provides basis on modification of organosolv lignin for application as a potent functional additive in cosmeceutical products.

Organosolv Lignin as a Green Sizing Agent for Thermoformed Pulp Products.

The purpose of this study was to investigate the use of organosolv lignin as a sizing agent for thermoformed pulp products as a sustainable material with improved water resistance. For this purpose, an in-house-produced organosolv lignin from softwood (Norway Spruce) was mixed with bleached and unbleached chemi-thermomechanical pulp fibers. In addition, the isolated organosolv lignin was characterized by ATR-FTIR spectroscopy, size-exclusion chromatography, and thermogravimetric analysis. The analysis showed that organosolv lignin was of a high purity and practically ash-free, exhibiting low molecular weight, a glass transition temperature below the thermoforming temperature, and a high content of phenolic OH groups. The mechanical properties and water resistance of the organosolv lignin-sized thermoformed pulp materials were measured. A small decrease in strength and an increase in stiffness and density were observed for the lignin-sized thermoformed materials compared to the reference, that is, unsized materials. The addition of organosolv lignin decreased the wettability and swelling of the thermoformed product. These results are due to the distribution of organosolv lignin on the surface, filling in the pores and cavities, and providing a tighter fit within the thermoformed materials. In conclusion, the results from our study encourage the use of organosolv lignin as a sizing additive to thermoformed products, which can improve the water resistance to use it in sustainable packaging applications.

Acid-based organosolv lignin extraction from wheat straw: Kinetic and structural analysis

Optimizing the pretreatment of lignocellulosic biomass is essential to obtain high purity fractions, and particularly a lignin polymer which can be easily used for further high-value applications. To better understand the changes in the chemical structure of lignin during its extraction and its kinetics, wheat straw was pretreated at mild conditions (105 °C, atmospheric pressure) in an organic acid-based organosolv medium. Lignin, collected for extraction times 0 to 3h30, was analyzed by different techniques (GPC, GC-FID and 31 P NMR) to determine its chemical structure and to quantify the modifications which could occur during the organosolv pretreatment (phenolic and total hydroxyl groups content, molecular weight, fragments condensation, esterification). The kinetics of lignin extraction was successfully assessed with the potential degree of delignification model. • Pretreatment of wheat straw in an acetic and formic acid based organosolv medium. • Providing new insights of organosolv lignin extraction mechanisms at atmospheric pressure. • Chemical characterization of lignin fragments over time. • Successful application of potential degree of delignification kinetic model.

Acacia Wood Fractionation Using Deep Eutectic Solvents: Extraction, Recovery, and Characterization of the Different Fractions.

The selective extraction and recovery of different lignocellulosic molecules of interest from forestry residues is increasing every day not only to satisfy the needs of driving a society toward more sustainable approaches and materials (rethinking waste as a valuable resource) but also because lignocellulosic molecules have several applications. For this purpose, the development of new sustainable and ecologically benign extraction approaches has grown significantly. Deep eutectic solvents (DESs) appear as a promising alternative for the processing and manipulation of biomass. In the present study, a DES formed using choline chloride and levulinic acid (ChCl:LA) was studied to fractionate lignocellulosic residues of acacia wood (Acacia dealbata Link), an invasive species in Portugal. Different parameters, such as temperature and extraction time, were optimized to enhance the yield and purity of recovered cellulose and lignin fractions. DESs containing LA were found to be promising solvent systems, as the hydrogen bond donor was considered relevant in relation to lignin extraction and cellulose concentration. On the other hand, the increase in temperature and extraction time increases the amount of extracted material from biomass but affects the purity of lignin. The most promising DES system, ChCl:LA in a ratio of 1:3, was found to not significantly depolymerize the extracted lignin, which presented a similar molecular weight to a kraft lignin. Additionally, the 31P NMR results revealed that the extracted lignin has a high content of phenolic OH groups, which favor its reactivity. A mixture of ChCl:LA may be considered a fully renewable solvent, and the formed DES presents good potential to fractionate wood residues.

Contributions of Various Cd(II) Adsorption Mechanisms by Phragmites australis-Activated Carbon Modified with Mannitol.

Due to its high toxicity, persistence, and bioaccumulation in the food chain, controlling cadmium (Cd) pollution in wastewater is urgent. Activated carbon is a popular material for removing Cd. To improve the Cd(II) adsorption efficiency by increasing the number of oxygen-containing functional groups, Phragmites australis-activated carbon (PAAC) was modified with mannitol at a low temperature (150 °C). The textural and chemical characteristics of PAAC and modified PAAC (M-PAAC) were analyzed by surface area analysis, elemental analysis, Boehm’s titration, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Batch adsorption experiments were conducted to investigate the influence of Cd(II) concentration, contact time, ionic strength, and pH on Cd(II) adsorption. The main adsorption mechanisms of Cd(II) on activated carbon were quantitatively calculated. The results showed that mannitol modification slightly decreased the SBET (5.30% of PAAC) and increased the content of carboxyl, lactone, and phenolic groups (total increase of 43.96% with PAAC), which enhanced the adsorption capacity of PAAC by 58.59%. The adsorption isotherms of PAAC and M-PAAC were described well using the Temkin model, while the intraparticle diffusion model fitted the Cd(II) adsorption kinetics best. Precipitation with minerals was a crucial factor for Cd(II) adsorption on activated carbon (50.40% for PAAC and 40.41% for M-PAAC). Meanwhile, the Cd(II) adsorption by M-PAAC was also dominated by complexation with oxygen-containing functional groups (33.60%). This research provides a method for recovering wetland plant biomass to prepare activated carbon and efficiently treat Cd-containing wastewater.

Composition and Structure of Ethanol-Lignins of Coniferous and Deciduous Wood and Products of their Catalytic Telomerization with 1,3-Butadiene

The composition and structure of ethanol-lignins of coniferous (abies, pine) and deciduous (aspen, birch) wood and products of their catalytic telomerization with 1,3-butadiene has been studied with use of the methods 31P-NMR, gel-permeation chromatography, scanning electron microscopy and elemental analysis. Data on the nature and content of hydroxyl groups in ethanol-lignins were obtained using phosphorylation of lignins with 2-chloro‑4,4,5,5,-tetramethyl‑1,3,2-dioxaphospholane.The studied lignins differ from each other in the content of aliphatic, phenolic and carboxyl groups. The total content of hydroxyl groups increases in the series of ethanol-lignins: birch &lt; aspen &lt; pine &lt; abies. For the modification of ethanol-lignins, the reaction of catalytic telomerization with 1,3-butadiene was used at 70 °C and 90 °C in the presence of a complex of palladium (II) diacetate with the sodium salt of triphenylphosphine trisulfate. By comparing the number of aliphatic, phenolic and carboxyl OH- groups in the initial and telomerized ethanol-lignins, it was found that only aliphatic and phenolic hydroxyl groups participate in the telomerization reaction. Telomerization of ethanol-lignins with 1,3-butadiene increases their average molecular weight and reduces polydispersity. The morphology of telomerized and initial samples of ethanol-lignins varies significantly

Composition and Biological Activity of Vitis vinifera Winter Cane Extract on Candida Biofilm.

Vitis vinifera canes are waste material of grapevine pruning and thus represent cheap source of high-value polyphenols. In view of the fact that resistance of many pathogenic microorganisms to antibiotics is a growing problem, the antimicrobial activity of plant polyphenols is studied as one of the possible approaches. We have investigated the total phenolic content, composition, antioxidant activity, and antifungal activity against Candida biofilm of an extract from winter canes and a commercially available extract from blue grapes. Light microscopy and confocal microscopy imaging as well as crystal violet staining were used to quantify and visualize the biofilm. We found a decrease in cell adhesion to the surface depending on the concentration of resveratrol in the cane extract. The biofilm formation was observed as metabolic activity of Candida albicans, Candida parapsilosis and Candida krusei biofilm cells and the minimum biofilm inhibitory concentrations were determined. The highest inhibition of metabolic activity was observed in Candida albicans biofilm after treatment with the cane extract (30 mg/L) and blue grape extract (50 mg/L). The composition of cane extract was analyzed and found to be comparatively different from blue grape extract. In addition, the content of total phenolic groups in cane extract was three-times higher (12.75 gGA/L). The results showed that cane extract was more effective in preventing biofilm formation than blue grape extract and winter canes have proven to be a potential source of polyphenols for antimicrobial and antibiofilm treatment.

Unveiling the structural properties of water-soluble lignin from gramineous biomass by autohydrolysis and its functionality as a bioactivator (anti-inflammatory and antioxidative)

Due to its low molecular weight and abundant functional groups, water-soluble lignin (WSL) is considered as a more potent antioxidant than traditional industrial lignin in biofields. However, few studies have been conducted to evaluate its intracellular and endogenous reactive oxygen species (ROS)-scavenging ability, especially for the intervention of ROS-related disease in vivo. In this work, WSL in bamboo autohydrolysate (WSL-BM) and wheat stalk autohydrolysate (WSL-WS) were isolated and characterized to comparably analyze their bioactivities. The composition analysis and NMR characterization showed that both WSL-BM and WSL-WS contained relatively similar components and substructures, but WSL-BM contained higher contents of phenolic OH groups. Both WSL samples exhibited excellent biocompatibility with the concentration below 50 μg/mL, while WSL-BM exhibited superior ROS-scavenging ability and ROS-related ulcerative colitis treatment potential at same concentration. In addition, WSL-BM also showed better performance in ameliorating inflammation and oxidative stress in RAW 264.7 cells and colitis mice by activating Nrf2 and suppressing NFκB signaling, resulting in an overall improvement in both macroscopic and histological parameters. Overall, these results implied that WSL from gramineous biomass can be used as a novel anti-inflammatory and antioxidative agent in the biomedical field.

Efek Penambahan Minyak Zaitun pada Perekat Alami Berbahan Dasar Tepung Tapioka

The development of the quality of bioadhesive is an interesting subject to be studied. This study aims to improve the quality of starch-based bioadhesive using olive oil. The high content of phenolic functional groups makes an opportunity for olive oil to be used as an additive for adhesive. The bioadhesive was made by hydrolysis, oxidation, polymerization, and olive oil addition. The viscosity measurement, solid content measurement, dry and wet shear strength analysis were carried out to determine the quality of bioadhesive. The result showed that the viscosity of PA25% has increased compared to the viscosity of PA0%. The solid content and dry shear strength of the adhesive decreased along with the increase of olive oil. Polymerization reaction between MMA monomer and cassava starch as well as olive oil addition did not provide satisfactory adhesion strength.

Efek Penambahan Minyak Zaitun pada Perekat Alami Berbahan Dasar Tepung Tapioka

The development of the quality of bioadhesive is an interesting subject to be studied. This study aims to improve the quality of starch-based bioadhesive using olive oil. The high content of phenolic functional groups makes an opportunity for olive oil to be used as an additive for adhesive. The bioadhesive was made by hydrolysis, oxidation, polymerization, and olive oil addition. The viscosity measurement, solid content measurement, dry and wet shear strength analysis were carried out to determine the quality of bioadhesive. The result showed that the viscosity of PA25% has increased compared to the viscosity of PA0%. The solid content and dry shear strength of the adhesive decreased along with the increase of olive oil. Polymerization reaction between MMA monomer and cassava starch as well as olive oil addition did not provide satisfactory adhesion strength.

Formation of pure nanoparticles with solvent-fractionated lignin polymers and evaluation of their biocompatibility

This study aimed to determine the effects of lignin characteristics (mainly molecular weight, functional groups, and internal linkages) on nanoparticle formation. First, five different lignin fractions (Mw 1460–12,900) were obtained from commercial kraft lignin (KL) by sequential solvent extraction. Functional groups and internal linkages were determined in lignin fractions, each fraction consisting of different levels and ratios. Second, spherical lignin nanoparticles (i.d. 193–1039 nm) were synthesized by nanoprecipitation at different pre-dialysis concentrations (1, 2, 4, and 6 mg mL−1 THF) with the different fractions (F1, F2, F3, F4, and F5). The study revealed that larger particles consisted of lignin fractions of lower molecular weight and higher phenolic group content (KL-F1 and F2), while smaller but non-uniform particles were produced from fractions of higher molecular weight and lower phenolic group content (KLF4 and F5). Every zeta potential value of the particle exceeded −35 mV. The nanoparticles from raw kraft lignin exhibited no significant cytotoxicity, hemotoxicity, and hypersensitivity. This study revealed that molecular weight and hydroxyl group content in the lignin highly correlated with nanoparticle properties. The present kraft lignin nanoparticles have potential for use in various polymer-based nanotechnology.

Photo-oxidation of arsenite in acidic waters containing Suwannee River fulvic acid: roles of 3SRFA* and hydroxyl radical.

The photo-oxidation of arsenite (As(III)) in solution containing Suwannee River fulvic acid (SRFA) under the ultraviolet A (UVA) irradiation (λmax = 365 nm) was studied. In a solution containing 100.0 μg·L-1 As(III) and 10.0 mg·L-1 SRFA at pH 3.0, SRFA induced As(III) photo-oxidation by producing the triplet excited state of SRFA (3SRFA*) and hydroxyl radical(HO˙). Approximately 82% of As(III) oxidation was attributed to HO˙ which depended strongly on HO2˙/O2˙-. The remaining 18% of As(III) oxidation was attributed to the direct reaction between As(III) and 3SRFA*. The photo-oxidation of As(III) was significantly affected by solution pH. Excess SRFA inhibited As(III) photo-oxidation. The addition of a low concentration of ferric ions retarded the photo-oxidation of As(III) due to the poor photo-activity of Fe(III)-SRFA complexes. In contrast, the addition of ferric ions at high concentration greatly accelerated As(III) photo-oxidation because of the high photo-activity of Fe(III)-OH complexes. The fractions of SRFA with different molecular weight showed different oxidizing capacities under UV irradiation which was possibly related to the different contents of phenolic OH groups. The findings have important environmental implications for the photo-transformation behavior of As(III) in natural surface waters containing dissolved organic matter, especially acidic waters.

The C/N ratio and phenolic groups of exogenous dissolved organic matter together as an indicator for evaluating the stability of mineral-organic associations in red soil

Mineral-organic associations (MOAs) are the basic structural units of soil aggregates and are important reservoirs of nutrients for plants and soil microorganisms, determining the soil structure and fertility. However, the influence of exogenous dissolved organic matter (DOM) chemistry on the stability of MOAs is rarely reported. We first characterized different exogenous DOM through elemental analysis and spectroscopy analysis technologies. Then, a chamber incubation experiment was conducted with DOM addition concentration at 3 g C kg−1 red soil. Principal component analysis, redundancy analysis, and the partial least squares path model were used to better understand the effect of exogenous DOM chemistry on the stability of MOAs. The addition of DOM into the red soil significantly increased not only the organic carbon both in the bulk soil and the soil heavy fraction, but also the soil combined humus and the soil mineral-organic compound quantity. Moreover, the rice straw-derived DOM had the best effect on improving the soil mineral-organic compound quantity/degree (additional), followed by the animal-derived DOM, while the fulvic acid increased it the least. The ratios of elements (C/N ratio, O/C ratio, and H/C ratio), aromaticity (SUVA254), and phenolic C content of exogenous DOM had positively significant contributions to the stability of MOAs. The rice straw-derived DOM had the greatest enhancement on the stability of the MOAs for its higher C/N ratio and phenolic groups content, so the exogenous DOM characteristics could be as an indicator in predicting the stability of the MOAs and evaluating the soil fertility.