Hydroxyl Content Research Articles

An oxidative depolymerized lignin treated by potassium ferrate and its use in preparation of epoxy resin

AbstractLignin, as an industrial by‐product, can be used as a phenolic substancen. In this study, enzymatic hydrolysis lignin (L) was treated with potassium ferrate and phenol respectively to obtain oxidized lignin (OL) and phenolated lignin (PL). Their phenolic hydroxyl content (PhOH) increased by 29.1% and 40.5%, respectively. Then four kinds of epoxy resins were prepared, namely lignin‐free epoxy resin (LFER), L epoxy resin (LER), PL epoxy resin (PLER), and OL epoxy resin (OLER). Gel permeation chromatography (GPC) and Fourier transform infrared analyses indicated that potassium ferrate oxidation could decline the molecular weight (Mw) and increase the PhOH of L. Mechanical properties test and dynamic mechanical analysis (DMA) results show that cured OLER (OLEN) has higher crosslinking density and better mechanical properties (shear strength increased by 14%, tensile strength increased by 15%) than cured LER (LEN). Thermogravimetric analysis results show that OLEN has better thermal stability than cured LFER (LFEN) and LEN. In addition, scanning electron microscopy images showed that the modified L had better compatibility. This study presents a novel approach for lignin oxidation.

Exploring the relationship between lignin structure and antioxidant property using lignin model compounds

Lignin has a natural polyphenol structure that is expected to replace chemically synthesized antioxidants as a native antioxidant with biodegradable and convenient source characteristics. However, the improvement of the antioxidant property of lignin and its application as an antioxidant are still somewhat limited due to the lack of understanding of the relationship between specific lignin structures and antioxidant property. Therefore, the study of the relationship between lignin structure and antioxidant property is crucial to realize the high-quality application of lignin. In this experiment, the scavenging ability of free 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radicals was determined for different grades of acetylated tannins, typical lignin model compounds and different structural units of milled wood lignin to investigate the relationship between lignin structure and antioxidant property. Based on the experimental results, some structure-activity relationships were proposed and the mechanism of the antioxidant property of lignin was discussed. The number of phenolic hydroxyl groups was linearly and positively correlated with antioxidant property, and the scavenging of DPPH radicals increased significantly with the increase in the number of methoxy groups in the model compounds. Moreover, aldehyde and carboxyl groups had a negative effect on the antioxidant property of lignin, while methoxy, alkyl and alcohol hydroxyl groups played a positive role. The guaiacyl (G) and syringyl (S) units favored the antioxidant property, so the difference in the content of structural units in lignin under certain conditions of phenolic hydroxyl content also affected the antioxidant property. Therefore, the antioxidant property of aspen milled lignin was higher than that of other milled lignin from different wood species. Finally, the mechanism of DPPH free radical scavenging by lignin was revealed to better understand the relationship between lignin structure and antioxidant property.

Skin rash related to the use of wood ash in wound healing, about a case

Abstarct Introduction: The ash of wood plants is part of the ancestral remedies because of its physical and chemical properties. It has detergent, fertilizing, and antiseptic properties, which justifies its many uses. Case report: We report the case of a woman aged 50 years who presented with a generalized rash all over the body with painful macules a burning sensation and a fever. Symptoms appeared after taking wood ash from plants, for three days. The reason for use was the healing of Zona's wound that she contracted and treated before admission. The patient’s general condition was preserved, and the drug treatment allowed a quick healing. Conclusion: Wood ash from plants with a high potassium hydroxyl content may be an irritant and partly explain the reaction observed. Traditional treatments should be used with great care to avoid adverse effects.

Achievement of biochar photocatalytic performance by synergistic oxidation of sulfuric acid/hydrogen peroxide: Towards revealing the mechanism of synergistic oxidation on photocatalytic performance

The oxygen-containing functional groups of biochar have great potential in tailoring photochemical properties, but the content of oxygen-containing functional groups of pristine biochar is insufficient to support photocatalytic reactions. In this study, a synergistic oxidation of H2SO4 and H2O2 was innovatively proposed to prepare biochar photocatalysts (OGPC400). The results showed that the synergistic oxidation of H2SO4 and H2O2 increased the contents of hydroxyl and carboxyl groups of biochar with the degree of oxidation, and the total concentration of acidic functional groups was about 4 mmol/g higher than that of the oxidation with H2SO4 or H2O2 alone, which was attributed to the synergistic oxidation to promote the conversion of CH and C-OH on the benzene ring. The achievement of electron exchange among hydroxyl and carboxyl groups and internal electron transfer within biochar by the benzene ring as a medium resulted in 100 % degradation of rhodamine b (RhB) and 25 times reaction rate constant higher than that of pristine biochar, as compared to only 45 % or 37 % degradation by oxidation with H2SO4 or H2O2 alone. The exciting results confirmed the positive availability of H2SO4 and H2O2 synergistic oxidation on biochar photocatalysts, which is expected to be applied in environmental remediation.

A Low-Hydroxyl Quartz Glass Prepared by Using a Plasma Heat Source as the Flame and High-Purity Quartz Sand as the Raw Material

In this paper, a quartz glass with low hydroxyl groups was prepared by combining the advantages of various processes, using a plasma heat source as the flame and high-purity quartz sand as the raw material. The purity of the quartz sand was 99.997%. The number of air bubbles in the quartz glass prepared using high-purity quartz sand was lower. The hardness and tensile strength of the quartz glass were 737.7–767.1 GPa and 6.88–9.64 MPa, respectively. The hydroxyl content of the sample was only 4.11 ppm, and the hydroxyl content of the homogenized quartz glass was reduced to 2.64 ppm, which was an improvement of about 35%. After homogenization, the fictive temperature (Tf) of the quartz glass was determined to be 1253 cm−1, and the variation of the Tf value along the radial direction was reduced, indicating a more homogeneous glass structure. The stress distribution in the quartz glass was significantly improved. These results indicate that the preparation of quartz glass from high-purity quartz sand using a plasma heat source as the flame opens up new avenues for optical applications.

Excellent facile fabrication of PVA and lignin nanoparticles from wheat straw after novel DES-THF pretreatment

The utilization of environmental friendly and renewable materials has received increasing attention recently. Lignin nanospheres (LNPs) prepared from recovered lignin and residual lignin after DESs and DESs-THF pretreatment were obtained by self-assembly in the present research. Then, films were prepared by incorporating them into polyvinyl alcohol (PVA) solution. The properties of various films were characterized and compared. Results showed that as the LNPs content increased, the UV blocking capacity of the films was gradually enhanced than PVA film. The DES-THF films showed better antioxidant properties up to 69 % due to higher phenolic hydroxyl content. The hydrophobicity of films incorporated with DESs-THF pretreated lignin was consistently better than that of DES pretreated. DES-THF-M films showed a higher Tmax than that of DES-M films, resulting in better thermal stability. Moreover, DES-THF-L films are lighter in color due to a lower degree of condensation, which is favorable to subsequent applications. The incorporation of LNPs improved mechanical and antioxidant properties, thermal stability, and UV shielding ability of PVA films, especially lignin after DES-THF pretreatment. In conclusion, the prepared PVA/LNPs composite films possessed good functional properties that make them potential for packaging materials.

Oxidative stability of chelated Sn(II)(aq) at neutral pH: The critical role of NO3- ions.

Tin(II) compounds are versatile materials with applications across fields such as catalysis, diagnostic imaging, and therapeutic drugs. However, oxidative stabilization of Sn(II) has remained an unresolved challenge as its reactivity with water and dioxygen results in loss of functionality, limiting technological advancement. Approaches to slow Sn(II) oxidation with chelating ligands or sacrificial electron donors have yielded only moderate improvements. We demonstrate here that the addition of nitrate to pyrophosphate-chelated Sn(II)(aq) suppresses Sn(II) oxidation in water across a broad pH range. Evidence of hydroxyl radical concentration reduction and detection of a radical nitrogen species that only forms in the presence of chelated Sn(II) point to a radical-based reaction mechanism. While this chemistry can be broadly applied, we present that this approach maintains Sn(II)'s antibacterial and anti-inflammatory efficacies as an example of sustained oral chemotherapeutic functionality.

Hydrogen enrichment in methanol SI engine at varying injection timing during compression stroke

This study investigates the effect of hydrogen enrichment in a direct-injected methanol-fuelled SI engine, with combustion and emission performance analysed by varying the methanol injection timing from 150° to 60° CA bTDC. A three-dimensional computational fluid dynamic model of the hydrogen-enriched methanol engine was developed to predict the engine performance, in-cylinder, and emission characteristics. The numerical model was solved using three-dimensional Reynolds-Averaged Navier Stokes, the RNG k-epsilon model for turbulence, the O'Rourke and Amsden sub-model for heat transfer, the extended Zeldovich mechanism for nitric oxide emissions, and the Hiroyasu-NSC model for soot emissions. The results indicated that retarding the injection timing resulted in a decrease in the indicated specific CO and soot emissions along with a rise in the indicated specific NOx emissions. Furthermore, hydrogen enrichment with methanol enhanced the hydroxyl radical concentration, reduced the combustion duration, reduced also the indicated specific CO and soot emissions while increasing the indicated specific NOx emissions. The study indicates that hydrogen enrichment could extend the late injection timing limit of methanol by enhancing fuel-air mixing, which improves and controls the combustion process more effectively.

Optimizing biosurfactant structure: Experimental and theoretical investigation of the influence of hydroxyl groups on sour corrosion mitigation

Oil and natural gas remain crucial for meeting global energy demands, but their extraction and processing face significant challenges due to sour corrosion. This study explores the influence of hydroxyl groups on the performance of biosurfactants, specifically sorbitol oleate (SOCI) and pentaerythritol oleate (POCI), in sour environments. This study reveals that the presence of more hydroxyl groups in inhibitor molecules significantly enhances their effectiveness against sour corrosion. A weight loss study showed that the corrosion rates dropped to 0.033 mm/y for POCI and 0.005 mm/y for SOCI from an initial rate of 0.490 mm/y in the blank solution, indicating the superior inhibition efficiency of SOCI (98.9 %) compared to POCI (93.3 %) at 24 × 10−4 M. Electrochemical measurements corroborated these findings, demonstrating increased corrosion resistance and reduced current densities in the presence of both inhibitors, with SOCI exhibiting better performance. The inhibition mechanism involves a combination of physical and chemical adsorption. Density functional theory calculations indicated the role of hydroxyl groups in enhancing adsorption and corrosion inhibition efficiency, with SOCI exhibiting a smaller energy gap, lower hardness, and higher softness compared to POCI. MD simulations confirmed the stable adsorption of both inhibitors on the Fe (110) surface, with SOCI showing a more favorable orientation and stronger interaction due to its higher number of hydroxyl groups. This facilitates stronger adsorption on the CS surface and the formation of a more robust protective film. The combined experimental and computational findings highlight the importance of molecular structure, film-forming ability, and hydroxyl content for the design and development of next-generation hydroxyl-rich biosurfactants for mitigating sour corrosion in the oil and gas industry.

A Nd-doped silica glass with high doping concentration, low hydroxyl content, and 900 nm fluorescence emission fabricated by laser additive manufacturing

The 900 nm wavelength laser is effective for atmospheric detection and various other applications.The frequency-doubled 450 nm deep blue laser can be used in maritime military, quantum optics, biomedicine, laser storage, laser display, and deep ultraviolet laser fields, among others. Although Nd3+ is considered the optimal medium for generating 900 nm lasers, competition with the 1060 nm emission wavelength must be addressed. In Nd-doped silica glass, without the introduction of aluminum, the emission intensity of the three-level transition is higher than that of the four-level transition. However, it can cause a concentration quenching between Nd3+, but co-doping with Al can effectively suppress it. As the Al/Nd ratio increases, the emission intensity at 1060 nm increases relative to that at 900 nm. By precisely adjusting the Al/Nd ratio, it is possible to suppress the 1060 nm emission while also inhibiting concentration quenching caused by Nd3+.

Designed synthesis of demethylated-hydroxymethylated lignin-based adsorbent for removal of Cr(VI) ions from wastewater

Lignin-based adsorbents for the removal of Cr(VI) ions have attracted intensive attention due to the advantages of renewability, biodegradablity, low cost and environmental friendliness. However, there are still a lot of challenges such as poor adsorption capacity, low lignin content in adsorbents, and harsh preparation conditions. Here, a tandem hydroxymethylation-demethylation method is proposed for preparing an excellent lignin-based Cr(VI) adsorbent (DHKL), which features with high lignin content (>85 wt%) and high hydroxyl content (up to 6.26 mmol/g) under milder conditions. The prepared DHKL exhibits an adsorption capacity reaching up to 1040.9 mg/g and can maintain this capacity even in the presence of other metal ions in the solution. Model analyses indicate that chemisorption occurring in a monolayer is the main process, which is spontaneous and endothermic. Structural changes of DHKL before and after adsorption indicated that Cr(VI) ions are mainly reduced to Cr(III) ions by hydroxyl groups with some of the absorbed Cr ions dispersed into the inner part of DHKL. Based on these results, the detailed possible adsorption mechanism is deduced, providing guidance for designing, producing and utilizing lignin-based adsorbents.

Correlation effect between the capillary flow and evaporation rate of water in a 2-D photothermal membrane

To shed light on the correlation effect between the capillary flow and phase transition of water in photothermal evaporation, the non-equilibrium molecular dynamics (NEMD) simulations were employed to investigate the evaporation of water in Multilayered graphene oxide membranes. It was initially found that water molecules need to overcome strong energy barriers to migrate upward by layers before evaporation, with the energy barrier increasing with the reduction in nanogap, hydroxyl content, or increase in layer spacing of graphene sheets. The strong energy barrier accordingly results in dramatic sensible heat conversion and high evaporation temperature. It was shown that the enhanced temperature and hydrophilicity both weaken the hydrogen bond strength of water molecules confined in 2-dimensional channels, contributing to the reduced evaporation enthalpy. The preferential pathways in graphene channels or the weakened hydrogen bonds in hydroxyl-functionalized graphene of water molecules were found to be important influences on capillary flow energy consumption, leading to differences in evaporation energy supply. In combination with these effects, the evaporation rate could be increased by up to 2 folds and an interfacial enthalpy of evaporation below 1500 kJ kg−1 could be achieved by properly tuning the configuration and chemical properties of the graphene membrane. Our findings lay a theoretical foundation for providing a strategy to improve the interfacial evaporation performance in desalination.

Insights into the Chemical Structure and Antioxidant Activity of Lignin Extracted from Bamboo by Acidic Deep Eutectic Solvents.

Deep eutectic solvents (DESs) composed of choline chloride as hydrogen bond acceptors (HBAs) and six organic acids as hydrogen bond donors (HBDs) were used to extract lignin from bamboo (Phyllostachys edulis (Carrière) J. Houz.). The structures of the DES-extracted lignin samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-vis), thermogravimetric analysis (TG), and gel permeation chromatography (GPC) to investigate the relationship between the chemical structure of lignin and its antioxidant activity. The results showed that DES treatment removed a large portion of the lignin (73.37-86.38%) from bamboo, and the chemical structure of lignin was changed due to the use of different types of HBDs. The extracted lignin exhibited good UV-vis light shielding properties, thermal stability, and antioxidant activity. Moreover, the total phenolic hydroxyl content of lignins was positively correlated with their antioxidant activity, while the molecular weight of lignins was negatively correlated with their antioxidant activity. Notably, lignin extracted with choline chloride-p-toluenesulfonic acid had the highest phenolic hydroxyl content and lower molecular weight, showing the strongest antioxidant activity (IC50DPPH = 417.69 μg/mL, IC50ABTS = 58.62 μg/mL). This study confirms the high thermal stability, excellent antioxidant activity, and UV shielding properties of lignin extracted with choline chloride-organic acid DESs, suggesting its potential application in the fields of antioxidants and material modifiers.

In situ activation of Sn(OH)4 catalyst for efficient CO2 electroreduction to formate

Electroreduction of CO2 into the highly valuable fuel formic acid (HCOOH) has been considered an ideal method for converting renewable energy and addressing environmental challenges. Herein, we present a straightforward and rapid method for preparing Sn(OH)4 catalysts specifically designed for electroreducing CO2 to formate. The Sn(OH)4 catalyst obtained through in-situ electrochemical reduction transforms from bulk morphology to nanoporous form, featuring numerous grain boundaries and a high hydroxyl content, enhancing its stability and availability of active sites.The resulting electrocatalyst demonstrates a remarkable formate faradaic efficiency (FEformate) exceeding 80 % across a broad potential range (−0.9 to −1.9 V). Notably, a peak FE value of 92 % is achieved for HCOOH production at −1.7 V vs RHE. This study presents a novel and effective method for developing high-performance Sn-based catalysts.

Ultralight activated carbon/polyimide foam with heterogeneous interfaces for improved thermal stability, mechanical properties, and microwave absorption

AbstractThe activated carbon (AC) has been widely used in the field of electromagnetic protection because of its porous, hollow microstructure and excellent electrical conductivity. In this paper, AC was prepared through KOH activation process. The ACs/polyimide foam (PIF) composite was prepared in situ during the synthesis of PI and the ACs. In this paper, AC was prepared using the potassium hydroxide (KOH) activation process. The AC/PIF composites were prepared by mixing ACs and pyromellitic dianhydride (PMDA) with methylene diphenyl diisocyanate (MDI). The pore structure and surface morphology of the ACs were observed using nitrogen adsorption–desorption isotherms and scanning electron microscopy (SEM). After KOH activation with KOH, the surface area and total pore volume of ACs significantly increased by 79.31% and 0.9539 cm3/g, respectively, mainly were the microporous structure. X‐ray photoelectron spectroscopy (XPS) results confirmed an increase in the oxygen content of ACs after KOH activation, indicating an increase in the relative hydroxyl content on the surface. The SEM resulting of the ACs/PIF composite has a well‐developed open cell structure. Thermal gravimetric analysis (TGA) revealed that ACs significantly improved the thermal stability of the ACs/PIF composite. The compressive strength of the ACs/PIF‐3 increased from 518 to 834 KPa, significantly enhancing its mechanical properties. Simultaneously, the microwave absorption performance can be controlled and regulated by optimizing the impedance gradient of the skeleton. Results showed that when ACs constituted 8 wt% of the PIF, the real permittivity (ɛ′) and imaginary permittivity (ɛ″) of ACs‐PIF‐5 were approximately 2.03 and 0.025, respectively.

Preparation and Characterization of Multi-Network Crosslinked Gels for Preventing Spontaneous Combustion of Coal

ABSTRACT In order to improve the inhibition performance of a retardant in various stages of coal spontaneous combustion, this study selected guar gum (guar) mixed with sodium tetraborate to form a multi-web gel. Then, polyethylene glycol (PEG) was added for the insertion and modification to improve the physical inhibition effect. Furthermore, we compounded the composite guar/PEG with the chemical retardant 2-hydroxyphosphonoacetic acid (HPAA) to prepare a composite retardant with the effect of full-stage inhibition. Multi-web gel composite inhibitor with a full-stage inhibition effect was prepared. Response surface analysis was used to determine the optimal solution. Scanning electron microscopy tests revealed that the surface folds of PEG/guar increased and the water retention capacity was greatly enhanced. The plugging wind experiment results show that the limiting air pressure of the gel material is 249 Pa, which can match the downhole plugging wind work. Using XRD experiments, the diffraction angle of PEG/guar was narrowed from 18.20° to 17.64°, the crystal layer spacing was increased from 4.8685 nm to 5.0218 nm, and PEG was successfully intercalated into the guar. Using Fourier-transform infrared spectroscopy, it was found that the content of free hydroxyl groups and aliphatic groups became lower, and the content of carbonyl groups and ether bonds increased, which greatly enhanced the antioxidant capacity of coal. Using thermogravimetric analysis, the characteristic temperature points of single and composite inhibitors were examined macroscopically. The results showed that the inhibition treatment could obviously chelate the transition metal ions in the coal samples, which greatly inhibited the process of coal oxidation and achieved the purpose of inhibiting the spontaneous combustion of coal.

Effect of PFDTS/TiO2 Coating on Microstructure and Wetting Behavior of Phosphogypsum.

Phosphogypsum (PG) constitutes a form of solid byproduct emanating from the manufacturing process of wet-process phosphoric acid. The fabrication of one metric ton of wet-process phosphoric acid entails the generation of approximately five tons of phosphogypsum, a highly prolific and economically viable waste stream. If we can effectively solve the problem of poor hydrophobicity of phosphogypsum, it is possible to replace cement and other traditional cementitious materials. In this way, we can not only improve the utilization rate of phosphogypsum but also obtain significant economic and environmental benefits. In the present investigation, hydrophobic surface coatings were synthesized and applied onto the surface of α-hemihydrate phosphogypsum (α-HPG) utilizing sol-gel processing and impregnation techniques. After hydroxylating α-HPG with alkaline solution (OH-α-HPG), titanium dioxide nanoparticles (TiO2) hybridized with perfluorodecyltriethoxysilane (PFDTS) were grafted on its surface. The assessment of the hydrophobic properties of the coatings was conducted through water contact angle measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) analyses. The contact angle remained above 124.2° after strong acidic and alkaline immersion and 50 tape adhesion experiments with good chemical stability and durability, and the mechanism of surface hydrophobicity modification was discussed. The experimental outcomes demonstrated a notable increase in the hydroxyl group concentration on the α-HPG surface following hydroxylation, significantly enhancing the attachment rate of PFDTS and TiO2 onto the HPG surface. PFDTS and TiO2 can undergo chemical interaction with hydroxyl groups, facilitating their robust adsorption onto the surface of OH-α-HPG through chemisorption mechanisms. After bonding the OH-α-HPG surface with PFDTS and TiO2 via hydrogen bonding, the otherwise hydrophilic α-HPG surface acquired excellent hydrophobicity (OH-α-HPG-PT, contact angle (CA) = 146.7°). The surface modification of α-HPG through hydroxylation and hydrophobicity enhancement significantly augmented the compatibility and interfacial interplay between α-HPG and PT. This research successfully enhanced the hydrophobic properties of α-HPG, profoundly showcasing its immense potential within the construction industry and the realm of comprehensive solid waste utilization.

Effect of Mono- and Polysaccharide on the Structure and Property of Soy Protein Isolate during Maillard Reaction.

As a protein extracted from soybeans, soy protein isolate (SPI) may undergo the Maillard reaction (MR) with co-existing saccharides during the processing of soy-containing foods, potentially altering its structural and functional properties. This work aimed to investigate the effect of mono- and polysaccharides on the structure and functional properties of SPI during MR. The study found that compared to oat β-glucan, the reaction rate between SPI and D-galactose was faster, leading to a higher degree of glycosylation in the SPI-galactose conjugate. D-galactose and oat β-glucan showed different influences on the secondary structure of SPI and the microenvironment of its hydrophobic amino acids. These structural variations subsequently impact a variety of the properties of the SPI conjugates. The SPI-galactose conjugate exhibited superior solubility, surface hydrophobicity, and viscosity. Meanwhile, the SPI-galactose conjugate possessed better emulsifying stability, capability to produce foam, and stability of foam than the SPI-β-glucan conjugate. Interestingly, the SPI-β-glucan conjugate, despite its lower viscosity, showed stronger hypoglycemic activity, potentially due to the inherent activity of oat β-glucan. The SPI-galactose conjugate exhibited superior antioxidant properties due to its higher content of hydroxyl groups on its molecules. These results showed that the type of saccharides had significant influences on the SPI during MR.

The superior adsorption capacity of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3 for five divalent heavy metal cations and the adsorption mechanism of biogenic α-Mn2O3: Experimental and DFT investigations

Manganese oxides play a crucial role in the adsorption of heavy metals in the environment. However, there is currently a lack of information regarding the comparative adsorption efficiency of heavy metals between biogenic and chemogenic manganese oxides. In this work, we compared the adsorption performance of biogenic and chemogenic α-Mn2O3 towards Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II). Mineral characterization analyses revealed that biogenic α-Mn2O3 exhibited a polycrystalline nature, whereas chemogenic α-Mn2O3 displayed a monocrystalline nature with a lower impurity content compared to biogenic α-Mn2O3. Under acidic conditions, biogenic α-Mn2O3 demonstrated a significantly higher adsorption capacity, ranging from 3 to 6 times greater than its chemogenic counterpart, within an initial heavy metal concentration range of 0.2–1.0 mM. This superiority can be attributed to the presence of more abundant functional groups and a greater content of hydroxyl O species on the surface of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3. During the adsorption process of biogenic α-Mn2O3, there were observed ionic exchanges between Mn(II) and these cations. More importantly, biogenic α-Mn2O3 bound with these cations probably through the formation of -O/OH/S complexes. The adsorption selectivity of biogenic α-Mn2O3 towards the five heavy metals was experimentally determined to follow the order of Ni(II) > Pb(II) > Cu(II) > Zn(II) > Cd(II). The electronic interaction between biogenic α-Mn2O3 and these cations indicated that Ni(II), Pb(II) and Cu(II) were more likely to share electrons with O atoms on the surface of biogenic α-Mn2O3 compared to Zn(II) and Cd(II).

The Enhancement Origin of Antioxidant Property of Carboxylated Lignin Isolated from Herbaceous Biomass Using the Maleic Acid Hydrotropic Fractionation.

Lignin is endowed with antioxidant activity due to its diverse chemical structure. It is necessary to explore the relationship between antioxidant activity and the chemical structure of the lignin to develop its high-value utilization. Herein, we employed maleic acid (MA) as a hydrotropic agent to preferably isolate the lignin from distinct herbaceous sources (wheat straw and switchgrass) under atmospheric pressure conditions. The resultant acid hydrotropic lignin (AHL) isolated from wheat straw exhibited high radical scavenging rates, up to 98% toward DPPH and 94% toward ABTS. Further investigations indicated that during the MA hydrotropic fractionation (MAHF) process, lignin was carboxylated by MA at γ-OH of the side-chain, providing additional antioxidant activity from the carboxy group. It was also found that the radical scavenging rate of AHL has a positive correlation with carboxyl, phenolic hydroxyl contents, and the S-G (syringyl-guaiacyl) ratio, which could be realized by increasing the MAHF severity. Overall, this work underlies the enhancement origin of the antioxidant property of lignin, which will facilitate its application in biological fields as an efficient, cheap, and renewable antioxidant additive.