Degree Of Aromaticity Research Articles

Enhancing humic acids production from cornstalk under fast hydrothermal conditions: Insights into new pathways of skeleton self-polymerization and branch growth

Hydrochar, a sustainable fertilizer rich in humic substances, is made from lignocellulose through hydrothermal conversion. However, hydrothermal humification (HTH) is challenged by low yields and limited selectivity in the resulting hydrochar. This study proved humic-like acids production can be enhanced under fast non-catalytic conditions (260 ∼ 280 °C, 0 ∼ 1 h). A higher yield (by 14.1 %) and selectivity (by 40.2 %) in hydrochar of humic-like acids than conventional HTH (＜250 °C) were achieved. Meanwhile, decreased lignin derivatives, carbonyl and quinone groups, as well as increased sp2-C structures in the humic-like acids were observed. The synthesized humic-like acids exhibited a lower degree of aromatization and a higher molecular weight than commercial variants. Two pathways of humic-like acids formation of self-polymerization and the development of branched sidechains were hypothesized based on mass mitigation, carbon flow and aqueous phase compositions. This research contributes a novel approach to producing humic-like acids rich hydrochar for environmentally friendly fertilizer production.

Synergetic effects during co-pyrolysis of waste textiles and Ca/Fe-rich industrial sewage sludge: Reaction kinetics and product distribution

Co-pyrolysis is a promising technology for industrial organic waste to utilize their unique resource and energy properties for efficient conversion into valuable products. This study was the first time to characterize the co-pyrolysis of waste textiles with Ca-rich industrial sludge and Fe-rich industrial sludge on a laboratory-scale fixed bed. The properties, mechanisms, gas, oil and carbon production were investigated as a function of temperature and mixing type. Co-pyrolysis increased the total weight loss from 50.05 % to 69.81 % for Ca-rich industrial sludge mixed with 50 % waste textiles and from 49.13 % to 70.01 % for Fe-rich industrial sludge mixed with 50 % waste textiles. The activation energy of co-pyrolysis was approximately 50 % lower compared to the pyrolysis of waste textiles alone. The optimal reaction model for the different reaction stages for all samples was three diffusion (D3). Co-pyrolysis resulted in lower CO and CO2 emission temperatures of about 25–110 °C and produced more short-chain organic compounds (C < 10). Co-pyrolysis produced more aldehydes and ketones organics. Moreover, co-pyrolysis char exhibited an elevated level of fatty alkyl side chains and bridge branching, as well as higher degrees of aromatization and stability. This study offers valuable insights into the potential application of pyrolysis for the management of Ca/Fe-rich industrial sludge and waste textiles, thereby serving as a basis for future utilization endeavors.

High-Resolution Mass Spectrometry Combined with Reactive Oxygen Species Reveals Differences in Photoreactivity of Dissolved Organic Matter from Microplastic Sources in Aqueous Environments.

Microplastics (MPs)-derived dissolved organic matter (MPs-DOM) is becoming a non-negligible source of DOM pools in aquatic systems, but there is limited understanding about the photoreactivity of different MPs-DOM. Herein, MPs-DOM from polystyrene (PS), polyethylene terephthalate (PET), poly(butylene adipate-co-terephthalate) (PBAT), PE, and polypropylene (PP), representing aromatic, biodegradable, and aliphatic plastics, were prepared to examine their photoreactivity. Spectral and high-resolution mass spectrometry analyses revealed that PS/PET/PBAT-DOM contained more unsaturated aromatic components, whereas PE/PP-DOM was richer in saturated aliphatic components. Photodegradation experiments observed that unsaturated aromatic molecules were prone to be degraded compared to saturated aliphatic molecules, leading to a higher degradation of PS/PET/PBAT-DOM than PE/PP-DOM. PS/PET/PBAT-DOM was mainly degraded by hydroxyl (•OH) via attacking unsaturated aromatic structures, whereas PE/PP-DOM by singlet oxygen (1O2) through oxidizing aliphatic side chains. The [•OH]ss was 1.21-1.60 × 10-4 M in PS/PET/PBAT-DOM and 0.97-1.14 × 10-4 M in PE/PP-DOM, while the [1O2]ss was 0.90-1.35 × 10-12 and 0.33-0.44 × 10-12 M, respectively. This contributes to the stronger photoreactivity of PS/PET/PBAT-DOM with a higher unsaturated aromatic degree than PE/PP-DOM. The photodegradation of MPs-DOM reflected a decreasing tendency from aromatic-unsaturated molecules to aliphatic-saturated molecules. Special attention should be paid to the photoreactivity and environmental impacts associated with MPs-DOM containing highly unsaturated aromatic compounds.

Revealing mechanism of phenol-amine reaction to form humus in compost based on high-resolution liquid chromatography mass spectrometry and spectroscopy

Humus is the stable form of carbon storage in straw compost. The phenol-amine reaction is a pathway for humus formation in straw compost. In this study, two reaction systems, GP group (pyrogallol and glycine) and GCP group (catechol, pyrogallol, and glycine), were constructed in a simulated composting environment and revealed the molecular binding mechanism of the phenol-amine reaction through spectroscopy and mass spectrometry. The results showed that phenolic self-polymerization was faster than phenol-amine reaction. Therefore, the aromatization degree of GP was 27.14 % higher than that of GCP. The phenol-amine reaction first produced fulvic acid, and then formed humus units rich in active functional group structures (i.e., phenolic hydroxyl and carboxyl groups). These units further captured small molecule compounds to form humic acid eventually. This study would provide theoretical support for exploring the humus formation process and the promotion of straw humification by adding phenol or amino acids to compost.

Deactivation of nickel/biochar catalyst through metal-volatiles interaction in pyrolysis of poplar sawdust loaded with nickel salt

Metal/biochar is an important category of catalyst that can be prepared via direct impregnation of metal salt to a biomass feedstock. However, during pyrolysis of metal salt@biomass for catalyst preparation, metal-volatiles interaction might affect exposure or dispersion of metal species. To verify this, loading of nickel acetate to poplar sawdust directly and to the sawdust-derived biochar was conducted to prepare Ni/biochar and biochar/Ni at 500 or 750 °C, aiming to understand the effect of metal-volatiles interaction on exposure of nickel species in resulting Ni/biochar. The results indicated Ni species catalyzed cracking, dehydrogenation, and reforming reactions in sawdust pyrolysis, producing more bio-oil/gases at the expense of biochar and also making biochar of higher aromatic degree with improved thermal stability. The in-situ IR characterizations also evidenced high activity of Ni towards dehydration and cracking of carbonyls for enhancing aromatization of biochar. In biochar/Ni catalysts prepared via loading nickel to biochar, little metal-volatiles interaction existed and nickel species weakly interacted with the biochar, resulting in remarkable migration and agglomeration of nickel, forming nickel size of 2–3 times larger than that in Ni/biochar. However, biochar/Ni possessed higher capability for adsorption/activation of H2, thus exhibiting superior catalytic activity than Ni/biochar for hydrogenation of phenolics.

Insight into the molecular transformation pathways of humic acid in the co-composting of bagasse and cow manure after adding compound microorganisms

The inoculation of compound microorganisms effectively processes lignocellulosic biomass and promotes the formation of humic acid (HA). However, the basic mechanism of HA formation in compost remains unclear. In this study, we comprehensively characterized the transformation of HA molecules during co-composting. The addition of compound microorganisms enhanced the degradation of proteinoids and lignocellulose in the dissolved organic matter (OM), thereby accelerating the humification of bagasse cow dung co-compost. Elemental and UV–Vis spectral analyses showed that inoculation with the compound microorganisms enhanced the oxidation level and aromatization of the HA structure. Furthermore, two-dimensional Fourier-transform infrared spectroscopy correlation analysis suggested that the addition of compound microorganisms accelerated the decomposition and oxidation of OM. Accordingly, premature aggregation of HA was avoided, and the side chains bonded to HA were more abundant, promoting the evolution of HA to higher-order structures. By influencing the degree of aromaticity, molecular weight, and the C2 fluorescence peak of HA, the inoculation of compound microorganisms promoted HA synthesis during bagasse composting. These results provide an important basis for revealing the mechanism by which compound microorganisms are inoculated to promote HA formation at the molecular level and serve as a reference for the production of high-quality and high-maturity compost.

Effect of dilute acid on fulvic acid extracted from lignite

ABSTRACT To explore the effect of dilute acid on the extraction of fulvic acid by lignite using an alkali-soluble acid precipitation method, lignite was acid-precipitated by H2SO4, HNO3, HCl, and H3PO4, and the content, extraction rate, and structural characteristics of fulvic acid were analyzed. The results showed that the highest content of humic acid extracted by HNO3 is 0.3383 mg/mL, and the lowest content of humic acid extracted by sulfuric acid is 0.0817 mg/mL. The highest extraction rate of humic acid derived from lignite extracted by hydrochloric acid is 3.84%, and the lowest extraction rate of humic acid extracted by sulfuric acid is 0.89%. Fulvic acid extracted from lignite contained functional groups such as benzyl, carbonyl, methyl, and hydroxyl, but their contents varied; the benzene ring structure in fulvic acid precipitated by HNO3 was the most pronounced, but the aromatization degree was the lowest. By contrast, the aromatization degree of fulvic acid precipitated by H2SO4 was the highest. This indicates that the functional group contents in humic acid extracted from different dilute acids vary, although the types of functional groups are similar.

COMPATIBILITY STUDY OF HYDROCARBON RESINS WITH RUBBER COMPOUNDS FOR TIRE APPLICATIONS

ABSTRACT The addition of hydrocarbon resins to rubber compounds has a significant impact on their properties such as wet grip and rolling resistance. These performance characteristics have a strong correlation with the compatibility of the resin with the rubber matrix. Incompatible resins can cause excessive broadening of the damping curve, which results in poor rolling resistance. Compatibility, however, allows maximization of wet grip while minimizing the effect on rolling resistance. Compatibility is promoted by lower resin molecular weight and structural similarity to the polymers being blended. In this study, a method based on the Fox equation has been developed to quantitatively characterize the compatibility between resin and natural rubber (NR), a binary system. The dynamic shear rheometer (DSR), a tool new to the tire industry, is used to investigate the interaction between resin and two rubbers (i.e., a ternary system of NR–butadiene rubber [BR]–resin and solution polymerized styrene–butadiene rubber [SSBR]–butadiene rubber [BR]–resin), with a specific emphasis on resin partitioning among rubber blends. In addition, the DSR is applied to assess the Tg shift and tangent delta peak height, providing insight into the compatibility between rubbers and resin. A curve-fitting model was developed for the SSBR–BR–resin system to depict the relationship between these two parameters and the physical and chemical properties of resins, with the selection of resins featuring different degrees of aromaticity, Tg, and molecular weight. The findings indicated that higher Tg increased aromaticity and that lower molecular weight of the resin resulted in an elevated Tg shift in the blend, while lower molecular weight led to an increase in the tangent delta peak height. Our findings supply insight into the performance of rubber–resin blends and introduce a new screening tool for characterizing these blends in their green state.

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Photochemical evolution of the molecular composition of dissolved organic carbon and dissolved brown carbon from wood smoldering

Recently, extreme wildfires occur frequently around the world and emit substantial brown carbon (BrC) into the atmosphere, whereas the molecular compositions and photochemical evolution of BrC remain poorly understood. In this work, primary smoke aerosols were generated from wood smoldering, and secondary smoke aerosols were formed by the OH radical photooxidation in an oxidation flow reactor, where both primary and secondary smoke samples were collected on filters. After solvent extraction of filter samples, the molecular composition of dissolved organic carbon (DOC) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). The molecular composition of dissolved BrC was obtained based on the constraints of DOC formulae. The proportion of dissolved BrC fractions accounted for approximately 1/3–1/2 molecular formulae of DOC. The molecular characteristics of dissolved BrC showed higher levels of carbon oxidation state, double bond equivalents, and modified aromaticity index than those of DOC, indicating that dissolved BrC fractions were a class of organic structures with relatively higher oxidation state, unsaturated and aromatic degree in DOC fractions. The comparative analysis suggested that aliphatic and olefinic structures dominated DOC fractions (contributing to 70.1%-76.9%), while olefinic, aromatic, and condensed aromatic structures dominated dissolved BrC fractions (contributing to 97.5%-99.9%). It is worth noting that dissolved BrC fractions only contained carboxylic-rich alicyclic molecules (CRAMs)-like structures, unsaturated hydrocarbons, aromatic structures, and highly oxygenated compounds. CRAMs-like structures were the most abundant species in both DOC and dissolved BrC fractions. Nevertheless, the specific molecular characteristics for DOC and dissolved BrC fractions varied with subgroups after aging. The results highlight the similarities and differences in the molecular compositions and characteristics of DOC and dissolved BrC fractions with aging. This work will provide insights into understanding the molecular composition of DOC and dissolved BrC in smoke.

Varied directions of heat flow and emission of volatiles impact evolution of products in pyrolysis of wet and dry pine needles

In pyrolysis of biomass via furnace heating, directions for travel of volatiles and heat flow are opposite. This is drastically different from simultaneously heating surface/inner core of a biomass particle with microwave heating. Changing direction of heat flow and volatiles affects volatiles-char interactions and evolution of pyrolytic products. This was investigated herein by pyrolysis of wet and dry pine needles via furnace or microwave heating at 600 °C. The results indicated that microwave heating induced intensive cracking of outer/inner structures of pine needles. This promoted gasification, decreased production of biochar/bio-oil, diminished formation of both light and heavy organics in bio-oil. Microwave heating also accelerated aromatization, forming biochar of higher C/O and C/H ratios and thermal stability. Additionally, formation of “hot spot” in pyrolysis of wet pine needles via microwave heating was evidenced by the phenomenon of decomposition of CaCO3 to CaO in pyrolysis, which also contributed to enhanced aromatic degree of biochar. Besides, pyrolysis of wet pine needles via microwave heating also generated developed pore structures in biochar (151.4 m2 g−1), as the inherent water and carbonaceous organics were heated simultaneously. Hydrogen bonding from inherent water was largely cracked only above 500 °C. Prolonged retention time of H2O reacted with carbonaceous intermediates, generating more aliphatic structures. Additionally, microwave heating also induced formation of unique morphology like massive thorn-like particulate matters on biochar.

Oxidative pyrolysis of poplar sawdust: Probing the influence of oxidation reactions on property of biochar

Partial oxidation of some organics is desirable in some scenarios for compensation of the heat required for pyrolysis, which, however, impacts not only composition of bio-oil but also possibly property of biochar. This was investigated herein by oxidative pyrolysis of poplar sawdust from 300 to 600 °C and further analysis of the pyrolytic products, especially biochar. The results showed that O2 could oxidize some organics on surface of biochar, forming more volatiles below 400 °C. Above this temperature the excessive oxidation of the light and heavy organics with π-conjugated structures in bio-oil dominated, producing more gases. Weight loss of biochar from oxidation of organics on its surface was only remarkable at 300 °C, while some weight gain was observed from introduction of additional oxygen-containing functionalities from the oxidation. The removal of aromatic structures on biochar at 500 or 600 °C via oxidation was rather difficult. However, the oxidation reactions did make the biochar oxygen-rich but hydrogen-deficient, which, in overall, improved thermal stability and comprehensive combustion performance of the biochar. Additionally, oxygen presence enhanced aromatic degree of biochar by increasing regularity of (100) facet of carbon crystals while narrowing interplanar spacing of (002) facets. The oxygen-rich nature also made the biochar from the oxidative pyrolysis more hydrophilic while the removal of some organics via oxidation promoted development of the pore structures.

Distribution, chemical, and molecular composition of high and low molecular weight humic-like substances in ambient aerosols

Abstract. Humic-like substances (HULIS) encompass a continuum of molecular weight (MW) ranges, yet our understanding of how HULIS characteristics vary with MW is still limited and not well established. In this study, a combination of ultrafiltration and solid-phase extraction protocols was employed to fractionate the high MW (HMW; &gt; 1 kDa) and low MW (LMW; &lt; 1 kDa) HULIS fractions from ambient aerosols collected during summer and winter at a rural site. Subsequently, comprehensive characterization using total organic carbon, high-performance size exclusion chromatography (HPSEC), UV-visible (UV-vis) and fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and negative electrospray ionization high-resolution mass spectrometry (ESI–HRMS) were conducted. The results revealed that HMW HULIS were dominated by larger-sized chromophores, substantially constituting a higher fraction of total organic carbon and UV absorption at 254 nm than LMW HULIS. While both HMW and LMW HULIS shared similar fluorophore types and functional groups, the former exhibited higher levels of humification and a greater presence of polar functional groups (e.g., −COOH; &gt; C=O). HRMS analysis further unveiled that molecular formulas within HMW HULIS generally featured smaller sizes but higher degrees of unsaturation and aromaticity compared to those within LMW HULIS fractions. This observation suggests the possibility of small molecules assembling to form the HMW HULIS through intermolecular weak forces. Moreover, HMW HULIS contained a higher proportion of CHON but fewer CHO compounds than LMW HULIS. In both HMW and LMW HULIS, the unique molecular formulas were primarily characterized by lignin-like species, yet the former displayed a prevalence of N-enriched and highly aromatic species. Additionally, HMW HULIS contained more unique lipid-like compounds, while LMW HULIS exhibited a distinct presence of tannin-like compounds. These findings provide valuable insights into the distribution, optical properties, and molecular-level characteristics of HULIS in atmospheric aerosols, thereby advancing our understanding of their sources, composition, and environmental implications.

The synergistic pyrolysis effects of polyethylene terephthalate with the additive of sewage sludge

Pyrolysis could be one of the promising ways for polyethylene terephthalate (PET) waste-based char production, while the adherence environmental persistent free radicals (EPFRs) brought the risks for the wide application. Co-pyrolysis was employed as the potential way to reduce the EPFRs and improve the char quality simultaneously with the introduction of sewage sludge (SS), and the optimization reaction conditions and the relative mechanisms were proposed in this work. EPFRs in PET-based char were found to decrease from 1.07 × 1018–4.84 × 1018 spins·g−1 to 2.17 × 1017–4.90 × 1017 spins·g−1, with 38.86–48.55% reduction at the mass ratio of 1:1 (PET:SS). The corresponding activation energy decreased by 78.83% with 30.93% higher biochar yield rate due to the synergistic effects. Co-pyrolysis facilitated the decomposition of benzoic acid and its derivatives by enhancing the cleavage of oxygen-containing functional groups and led to the binding of nitrogen with more pyrolysis intermediates, resulting in a reduction of precursors for oxygen/oxygenated-carbon centered radicals. More phenyl radicals were polymerized into carbon-centered radicals through hydride transfer and crosslinking in the mixed system. The additive of SS promoted the aromatization degree, enhanced the defect and pore structure of the biochar, and led to a 43.62-fold increase in the surface area of PET-based char at 400 °C. This work provides a potential approach to reduce EPFRs from the pyrolysis of plastic waste and to deal with multiple waste streams in venous industry park under the implementation of zero waste cities construction.

Fast co-pyrolysis of paper mill sludge and corn stover: Relationships between parameters, product distributions, and synergistic interactions

The co-pyrolysis of paper mill sludge (PS) and biomass has attracted significant attention due to its potential for simultaneous resource utilization and waste disposal. In this work, the co-pyrolysis of PS with corn stover (CS) was carried out in a fixed bed reactor to investigate the effect of temperature and PS to CS ratio on the product characteristics. A comparison between the experimental and calculated values of product yield and composition was performed to obtain a deeper understanding of the synergistic interactions. The results exhibited a positive synergistic effect on bio-oil production at lower CS proportions with higher temperatures. Higher temperatures and lower CS proportions were favorable for the formation of aromatics (up to 45.03%) in co-pyrolysis, while the synergistic interactions promoted the production of phenols and exhibited an inhibitory effect on aromatics production. The interactions also inhibited H2 but promoted CO production due to the enhanced decarbonylation of co-pyrolysis intermediates in the presence of PS internal minerals. Additionally, the characterization of biochars indicated an increasing degree of aromaticity with higher temperatures and CS proportions. The synergistic interactions at higher temperatures facilitated the development of pore structures in the biochar, especially micropores. This study provides valuable insights into the relationship between parameters, products, and synergies in the co-pyrolysis of PS and biomass wastes.

Insights into pyrolysis process of coconut shell waste hydrochar: In-situ structural evolution and reaction kinetics

Coconut shell (CS) can be efficiently utilized by coupling hydrothermal carbonization (HTC) pretreatment with pyrolysis to meet the goal of global green development. In-situ Raman spectroscopy and thermogravimetric analyzer (TGA) were adopted to investigate the structural evolutions and reaction kinetics characteristics of hydrochar during the pyrolysis process. According to the results, the intensity of peak D and peak G in Raman spectrum decreased with increasing hydrothermal degree. Mild HTC treatment (≤200 °C) led to an increase in ID/IG, indicating the formation of large aromatic rings through small ring condensation. In contrast, severe HTC treatment (≥220 °C) reduced the ID/IG ratio, indicating an increased polycondensation of aromatic compounds and a higher degree of aromatization, resulting in larger molecules sizes. The spectral area below 400 °C reduced with increasing pyrolysis temperature due to the reduction of oxygen-containing functional groups and thermal radiation. Above 400 °C, the total area remains stable as the Raman spectrum scattering ability increases due to char formation and aromatization reactions. HTC-200 exhibited an increase in ID/IG from 0.54 to 0.72 and ID/I(Me + Ke + GL) from 0.58 to 0.68 with increasing pyrolysis temperatures. The activation energy during pyrolysis ranged from 194.50 to 238.34 kJ/mol for CS and 217.51–259.51 kJ/mol for HTC-200. Hydrothermal carbonization had a significant effect on pyrolysis behavior of hydrochar, as it was found that the mild HTC hydrochar followed D-type diffusion models when conversion rate was less than 0.65, and transitioned to higher reaction order in the late-stage of pyrolysis.

Thermal pretreatment of willow branches impacts yield and pore development of activated carbon in subsequent activation with ZnCl2via modifying cellulose structure

Development of pore structures of activated carbon (AC) from activation of biomass with ZnCl2 relies on content and structure of cellulose/hemicellulose in feedstock. Thermal pretreatment of biomass could induce dehydration and/or aromatization to change structure of cellulose/hemicellulose. This might interfere with evolution of structures of AC, which was investigated herein via thermal pretreatment of willow branch (WB) from 200 to 360 °C and the subsequent activation with ZnCl2 at 550 °C. The results showed that thermal pretreatment at 360 °C (WB-360) could lead to substantial pyrolysis to form biochar with yield of 31.9%, accompanying with nearly complete destruction of cellulose crystals and remarkably enhanced aromatic degree. However, cellulose residual in WB-360 could still be activated to form AC-360 with specific surface area of 1837.9 m2·g−1, which was lower than that in AC from activation of untreated WB (AC-blank, 2077.8 m2·g−1). Nonetheless, the AC-200 from activation of WB-200 had more developed pores (2113.9 m2·g−1) and superior capability for adsorption of phenol, due to increased permeability of ZnCl2 to the largely intact cellulose structure in WB-200. The thermal pretreatment did increase diameters of micropores of AC but reduced overall yield of AC (26.8% for AC-blank versus 18.0% for AC-360), resulting from accelerated cracking but reduced intensity of condensation. In-situ IR characterization of the activation showed that ZnCl2 mainly catalyzed dehydration, dehydrogenation, condensation and aromatization but not cracking, suppressing formation of derivatives of cellulose and lignin in bio-oil. The thermal pretreatment formed phenolic —OH and C=O with higher chemical innerness, which changed reaction network in activation, shifting morphology of fibrous structures in AC-blank to "melting surface" in AC-200 or AC-280.

Changes in the Physicochemical Characteristics of Humic Acids in a Hydrodynamic Rotor-Pulsation Apparatus

The work presents research results of the change comparison of brown coals and the study of the physicochemical properties of humic substances obtained from brown coals of the Karazhyra, Ekibastuz, and Kyzyl-Kiya deposits after hydrodynamic treatment in a rotary-pulsation apparatus. It is shown that the hydromechanical effect on humic acids leads to a change in their composition, accompanied by a decrease in the degree of aromaticity and an increase in the content of oxygen-containing fragments. Mechanical treatment of brown coals under oxidizing conditions maximizes the efficiency of extraction of water-soluble components and humic acids. The structural parameters and functional composition of humic acid molecules during the treatment of brown coals under oxidation-reduction conditions change depending on the conditions. The elemental and functional composition (using IR spectroscopy and potentiometry) of humic substances in brown coals and their molecular weight distribution using size-exclusion chromatography were studied. The influence of the content of metal-binding centers, dispersity, and ash content of humic substances was studied before and after treatment. At a temperature of 70 ºC a rotation time of 10 s, 98.7% of humic acids passes into the solution, which is the best indicator.

Effects of different aging methods on the ability of biochar to adsorb heavy metal cadmium and its physical and chemical properties.

The aging process can affect the physical and chemical properties as well as adsorption capacity of biochar. This study focuses on the heavy metal cadmium (Cd) as the research object, and artificially ages biochar prepared from rice straw and corn straw through accelerated freeze-thaw cycles, alternating dry wet cycles, and ultraviolet light treatment, in order to evaluate the effects of different aging conditions on the physical and chemical properties of the two different types of biochar and on their adsorption capacities for Cd. After aging, the pH of rice and corn biochar decreased to varying degrees, respectively. The surface structure was ruptured, the average pore diameter was decreased, and the specific surface area was increased by 27.3%, 21.9%, and 9.8% (rice) and 95.4%, 27.7%, and 13.4% (corn). Ultraviolet light aging has the most significant impact on the elemental content of biochar, and the C content was decreased by 12.4% (rice) and 9.3% (corn). The O content was increased by 11.2% (rice) and 44.1% (corn), and the numbers of O/C, H/C, (O + N)/C, and oxygen-containing functional groups were increased. These results demonstrate that the aging process reduces the degree of aromatization of biochar, while enhancing its polarity and Cd adsorption capacity. Rice straw biochar (RSB) has a greater ability to adsorb Cd than corn straw biochar (CSB). In addition, ultraviolet light aging is particularly effective in increasing heavy metal adsorption.

Depth-dependent variations of physicochemical properties of sedimentary dissolved organic matter and the influence on the elimination of typical pharmaceuticals

Sedimentary dissolved organic matter (DOM) could exert a significant influence on the transformation of trace organic contaminants. However, the variations of sedimentary DOM properties with depth and their impact on trace organic contaminants biodegradation remain unclear. In this study, the qualitative changes in DOM properties with depth were assessed using spectral techniques. Specifically, within the sediment range of 0–30 cm, humic acid and fulvic acid fractions exhibited higher degrees of humification and aromatization at 10–20 cm, while hydrophilic fractions showed higher degrees of humification and aromatization at 20–30 cm. Furthermore, electrochemical methods were employed to quantitatively assess the electron transfer capacity of sedimentary DOM at different depths, which displayed consistent variation trend with humification and aromatization degree. The high degree of humification and aromatization, along with strong electron-accepting capability of DOM, significantly enhanced the biodegradation rates of tetracycline and ritonavir. To gain deeper insights into the influence of molecular composition of DOM on its properties, two-dimensional gas chromatography-quadrupole mass spectrometry analysis revealed that quinones and phenolic hydroxyl compounds govern the redox reactivity of DOM. Simulated experiment of DOM-mediated biodegradation of typical pharmaceuticals confirmed the role of quinones and phenolic hydroxyl groups in the redox reactivity of DOM.