High Humic Acid Content Research Articles

Characteristics of Chinese Weathered Coal from Six Geographical Locations and Effects on Urease Activity Inhibition

Weathered coal is known to have potential inhibitory effects on urease activity, thus reducing the loss of nitrogen from fertilizer such as ammonia. This means that it can be used as a urea enhancer to promote urea utilization efficiency. However, the variation in its composition and structure has impeded the optimal utilization of this resource. In this study, we collected Chinese weathered coal from six representative geographical locations and analyzed its elemental and substance composition, as well as determined its chemical structure via Fourier transform infrared spectroscopy and investigated its effects on urease (soybean meal) activity. The results showed evident variation in the composition and structure among the different weathered coal samples, especially in the pH values, humic acid and ash content, and aromaticity. All six weathered coal samples significantly inhibited urease activity, and the inhibitory effect was enhanced with the elevated proportion of weathered coal introduced to urea. When the additive proportion of weathered coal increased, the weathered coal, characterized as having a higher humic acid content and a more aliphatic structure, showed a more rapid increase in the urease activity inhibition rate, while there was only a slight effect when the weathered coal had a low humic acid content and high atomicity. Therefore, the former type of weathered coal was more sensitive to the additive proportion. Furthermore, there was no consistent rule when the same proportion of weathered coal from different geographic locations was blended into urea, which might be attributable to other unexplored factors.

Lignocellulose degradation in Protaetia brevitarsis larvae digestive tract: refining on a tightly designed microbial fermentation production line

BackgroundThe Scarabaeidae insect Protaetia brevitarsis (PB) has recently gained increasing research interest as a resource insect because its larvae can effectively convert decaying organic matter to plant growth-promoting frass with a high humic acid content and produce healthy, nutritional insect protein sources. Lignocellulose is the main component of PB larvae (PBL) feed, but PB genome annotation shows that PBL carbohydrate-active enzymes are not able to complete the lignocellulose degradation process. Thus, the mechanism by which PBL efficiently degrade lignocellulose is worthy of further study.ResultsHerein, we used combined host genomic and gut metagenomic datasets to investigate the lignocellulose degradation activity of PBL, and a comprehensive reference catalog of gut microbial genes and host gut transcriptomic genes was first established. We characterized a gene repertoire comprising highly abundant and diversified lignocellulose-degrading enzymes and demonstrated that there was unique teamwork between PBL and their gut bacterial microbiota for efficient lignocellulose degradation. PBL selectively enriched lignocellulose-degrading microbial species, mainly from Firmicutes and Bacteroidetes, which are capable of producing a broad array of cellulases and hemicellulases, thus playing a major role in lignocellulosic biomass degradation. In addition, most of the lignocellulose degradation-related module sequences in the PBL microbiome were novel. PBL provide organic functional complementarity for lignocellulose degradation via their evolved strong mouthparts, alkaline midgut, and mild stable hindgut microenvironment to facilitate lignocellulosic biomass grinding, dissolving, and symbiotic microbial fermentation, respectively.ConclusionsThis work shows that PBL are a promising model to study lignocellulose degradation, which can provide highly abundant novel enzymes and relevant lignocellulose-degrading bacterial strains for biotechnological biomass conversion industries. The unique teamwork between PBL and their gut symbiotic bacterial microbiota for efficient lignocellulose degradation will expand the knowledge of holobionts and open a new beginning in the theory of holobionts.BPGV8LV-Txp2PAmT3d1J6VVideo

Humic Acid Modified by Being Incorporated Into Phosphate Fertilizer Increases Its Potency in Stimulating Maize Growth and Nutrient Absorption.

Humic acid-enhanced phosphate fertilizer (HAP) is widely applied in Chinese agriculture due to its high efficiency. Although the structural composition and physicochemical properties of humic acid (HA) are significantly altered during HAP production, a clear understanding of the mechanisms underlying the biological effects of HA extracted from HAP fertilizer (PHA) on plant growth is still lacking. In the current study, we extracted PHA from HAP and assessed its effects on the dry biomass, phosphorus (P) and nitrogen (N) uptake, and P absorption rate of maize seedlings when supplied at different concentrations (2.5, 5, 10, and 25 mg C L−1) in the hydroponic culture. The root vigor, root plasma membrane H+-ATPase activity, and root nitrate reductase activity were also determined as the representative indicators of the root capacity for nutrient absorption, and used to clarify the mechanism by which PHA affects the maize growth and nutrient absorption. The results showed that the dry biomass, phosphorus uptake, nitrogen uptake, and average phosphorus absorption rates were significantly higher by 14.7–27.9%, 9.6–35.1%, 17.9–22.4%, and 22.1–31.0%, respectively, in plants treated with 2.5–5 mg C L−1 PHA compared to untreated controls. Application of 10–25 mg C L−1 raw HA resulted in similar stimulatory effects on plant growth and nutrient absorption. However, higher levels of PHA (10–25 mg C L−1) negatively impacted these indicators of plant growth. Furthermore, low PHA or high raw HA concentrations similarly improved root vigor and root plasma membrane H+-ATPase and nitrate reductase (NR) activities. These results indicate that lower concentrations of PHA can stimulate maize seedling growth and nutrient absorption to an extent that is comparable to the effect of higher concentrations of raw HA. Thus, the proportion of HA incorporated into HAP could be lower than the theoretical amount estimated through assays evaluating the biological effects of raw HA.

Screening of hierarchical porous UiO-67 for efficient removal of glyphosate from aqueous solution

Defect engineering is essential for improving the adsorption performance of metal-organic frameworks (MOFs). Herein, hierarchical porous UiO-67(Zr) and analogs with controlled levels of defects were successfully obtained and applied to chemoselectively capture glyphosate (GP) from water. The obtained defective UiO-67 was stable at different pH values. The removal performance of defective UiO-67(Zr) was evaluated systematically as a function of different modulators, water chemistry and interfering ions. The maximum adsorption capacity of defective UiO-67(Zr) reached 322.58 mg/g, superior to most MOFs-based adsorbents. The defective UiO-67(Zr) also showed high selectivity for GP adsorption at high concentrations of humic acids (3 times) and interfering anions (100 times). In addition, the defective UiO-67(Zr) has shown good recovery performance and can effectively remove GP from a variety of contaminated water samples and multi-pollutant systems. The results of batch experiments and microscopic spectral characterization (XPS and FTIR) revealed that GP adsorption was mainly guided by electrostatic action, coordination, pore-filling and hydrogen bonding. These findings verified that the fabrication of defect sites played an important role in promoting the adsorption performance of MOFs. Our work provides a clue to the design of defective MOFs with high adsorption performance.

Ti4O7 reactive electrochemical membrane for humic acid removal: Insights of electrosorption and electrooxidation

Electrochemical advanced oxidation processes (EAOPs) are regarded as a promising technology for the treatment of landfill leachate containing high concentrations of humic acid (HA). Herein, a Ti4O7-based porous reactive electrochemical membrane (REM) system was developed and explored for the rapid and effective removal of HA. The relationship between the electrolyte medium (Na2SO4 or NaCl) and the adsorption/oxidation capacity of the REM system for HA removal was comparatively studied under different ionic strengths. An unprecedented trade-off phenomenon was revealed between the electrosorption and electrooxidation induced by chloride ions. On one hand, the pH value of the aqueous solution increased due to the loss of Cl− (NaCl → NaOH) during the electrolysis process in the NaCl medium, which weakened the electrosorption ability of REM on HA and further led to deterioration of the effluent quality. On the other hand, the introduction of chlorine significantly strengthened the mineralization performance of HA adsorbed on the anode surface because the anode enabled the oxidation of Cl− into powerful active chlorine species. Current density, membrane permeability, solution pH, and initial HA concentration were identified as the key parameters affecting the overall degradation performance. The active radicals (Cl and OH) involved in the REM system were systematically studied and generation pathways were proposed accordingly. This study facilitates understanding of the surface catalytic behavior of the Ti4O7 REM in a NaCl medium and confirms that this is a powerful and efficient technology for HA removal.

Nano-sized polystyrene plastics toxicity to microalgae Chlorella vulgaris: Toxicity mitigation using humic acid.

Polystyrene nanoplastics (PS-NPs) can cause toxicity in aquatic organisms, but presence of natural organic matter (NOM) may alter toxicity of PS-NPs. To better understand effects of NOM on acute toxicity of PS-NPs, humic acid (HA) as a model of NOM was added to green microalga Chlorella vulgaris medium in the presence of amino-functionalized polystyrene nanoplastics (PS-NH2). Acute toxicity tests of PS-NH2 to C. vulgaris biomass and chlorophyll a content showed statistical differences between media treated with different concentrations of PS-NH2 and control groups (p<0.05). HA significantly mitigated PS-NH2 toxicity to C. vulgaris biomass and chlorophyll a end-points (p<0.05). Additionally, high HA concentration was more effective than low concentration (10 vs 5 mg/L), showing a greater ameliorative effect on PS-NH2 acute toxicity (p<0.05). Algae exposed to higher PS-NH2 concentrations showed greater morphological changes (i.e., diminution of photosynthetic pigments, reduction of algal size and formation of more cellular aggregates). Formation of high amounts of algal aggregates under influence of PS-NH2 was presumably related to the high electrostatic tendency of these particles (with positively charged surfaces) to C. vulgaris polysaccharide walls (having negative charge). Formation of aggregates was significantly reduced in the presence of HA. HA with dominant negatively charged functional groups (following sorption by PS-NH2 via reduction of PS-NH2 zeta potential), could decrease electrostatic attraction between PS-NH2 and algae, thereby substantially ameliorating cellular aggregation and cell size reduction.

Mechanism of pH sensitive flocculation for organic load and colour reduction in landfill leachate

Landfill leachate has an important fraction of humic substances, mainly humic acids (HAs), which often represent more than half value of COD, specially in liquids proceeded from composting processes of organic fraction of solid wastes. We propose in this article a new method of pH sensitive flocculation for COD and colour reduction in landfill leachate based on the chemical properties of HAs. Landfill leachate with a high content of humic acids can be efficiently treated by pH sensitive flocculation at pH 2.0, reducing COD value in 86.1% and colour in 84.7%. Mechanism of pH sensitive flocculation is based in protonation first of phenolic groups and later of carboxylic acid groups in the HAs molecules, resulting in a reduction of Zeta potential value. For pH over neutrality, carboxylic acid and phenolic groups are ionized and Zeta potential increases in absolute value, maintaining HAs in suspension as colloids and conducting flocculation to be obstructed. Ionized anionic groups (carboxylates) can interact electrostatically with cations abundant in leachate (site binding) aiding to maintain HAs in suspension. Simulation of this situation and ideal visualization of Zeta potential behavior is described in the paper and aggregation of molecules by H-bonds is proposed as the main step in separation of HAs from leachate and reduction of COD value in this complex liquid. CHNS analysis, FT-IR spectrometry and UV–VIS spectrophotometry show chemical elements content in the range of natural and commercial HAs, clear aromaticity and carboxylic acids and phenolic groups presence in the precipitate from landfill leachate.

Insights into the synergistic removal mechanisms of thallium(I) by biogenic manganese oxides in a wide pH range

The behavior and mechanism of thallium (Tl) adsorption by biogenic manganese oxides (BMnOx) are poorly understood. In this study, BMnOx was applied for Tl(I) removal from aqueous solution, and the adsorption interactions were systematically revealed for the first time. BMnOx was successfully prepared with high productivity by effectively oxidizing Mn(II) with a manganese oxide bacterium in an optimal Mn(II) concentration range of 4.0–28 mg/L. Compared with other adsorbents, the prepared BMnOx achieved high Tl(I) adsorption capacity over a wide pH range from 3.0 to 9.0 and high humic acid (HA) concentration (40 mg/L) interference. The experimental results were well depicted by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that chemisorption played the dominant role during the adsorption process. The adsorption mechanisms were verified as synergetic interactions of oxidation-precipitation, electrostatic attraction, ion exchange and surface complexation. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results suggested that 19.46% of the highly toxic Tl(I) was transformed into the much less toxic product Tl2O3 after adsorption onto BMnOx. This study provides theoretical guidance for high-concentration Tl(I) decontamination from groundwater by biogenic manganese oxides.

Fe3O4 catalytic ozonation of iohexol degradation in the presence of 1-hydroxybenzotriazole: Performance, transformation mechanism, and pathways

This study explored the degradation of an iodine X-ray contrast media, iohexol, under heterogeneous ozone-catalyzed oxidation by adding Fe3O4 and 1-hydroxybenzotriazole (HBT). Results show that increasing the dosages of Fe3O4 catalyst and ozone as well as solution pH were beneficial to the degradation of iohexol. The presence of low background humic acid (HA) concentration (≤10 mg/L) promoted iohexol degradation, but high HA concentration (≥20 mg/L) inhibited it. Adding HBT exhibited a similar effect on iohexol degradation as HA. The degradation rate constant of iohexol was calculated as 0.07108 min−1 in the Fe3O4/O3/HBT process ([HBT] = 5 μM) at pH 7.0, which was approximately 1.5 times higher than that in the Fe3O4/O3 process (0.04533 min−1), and 4 times higher than that in the O3 process (0.01742 min−1). Fe3O4/O3/HBT process was pH-dependent with high degradation efficiency of iohexol at pH 5 or 7. Singlet oxygen (1O2), hydroxyl radical (OH∙), and superoxide radical (O2-∙) have been identified in the Fe3O4/O3/HBT process, and the conversion of Fe2+ to Fe3+ was more obvious on the surface of Fe3O4 compared to that in the Fe3O4/O3 process. Transformation intermediates were identified, and the degradation pathways of iohexol were proposed. Overall, Fe3O4/O3 could enhance iohexol degradation compared with ozone-only system, and adding trace HBT in Fe3O4/O3 system can further enhance heterogeneous ozone-catalyzed process for rapid organic matter degradation.

Mechanisms of the effects of humic acid on antibiotic resistance genes and microbial communities in Cd-contaminated soils

Humic acid (HA) is an organic macromolecular compound that widely exists in nature, but its effect on antibiotic resistance genes (ARGs) in Cd-contaminated soil is unknown. This study investigated the effects of Cadmium (Cd) and HA in soil on ARGs, mobile genetic elements (MGEs), and bacterial communities. The relative abundance of ARGs and MGEs increased 0.89-fold and 1.12-fold after the addition of 2 mg kg−1 Cd to the soil, and 1.06-fold and 1.68-fold after the addition of 8 mg kg−1 Cd. Redundancy analysis further revealed that among environmental factors, available Cd was the dominant factor influencing ARGs. In Cd-contaminated conditions, the addition of high concentrations of HA suppressed the expression of ARGs and MGEs. The abundance of ARGs and MGEs decreased by 0.12-fold and 0.44-fold after the addition of HA (50 mg kg−1) to the soil at a Cd concentration of 2 mg kg−1, and by 0.18-fold and 0.41-fold at a Cd concentration of 8 mg kg−1. IntI1 was significantly associated with all ARGs (sul1, sul2, tetG, tetW), and intI2 was significantly correlated with most ARGs (sul2, tetG, tetW). Network analysis illustrated that Proteobacteria were the main host bacteria causing changes in the abundance of ARGs and MGEs. HA has an important role in agricultural production. To reduce the enrichment of ARGs in Cd-contaminated soil, the addition of higher concentrations of humic acid can be considered to mitigate the environmental and biological hazards.

Constructing magnetically separable manganese-based spinel ferrite from spent ternary lithium-ion batteries for efficient degradation of bisphenol A via peroxymonosulfate activation

A magnetically separable manganese-based spinel ferrite (MFO-LIBs) is synthesized using spent ternary lithium-ion batteries (LIBs) for the first time. The ferrite is used to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA), thus meeting the strategy of “treating waste with waste.” Surprisingly, its degradation activity was 2.8 times that of pure MnFe2O4 (MFO). The characterization of the structure and morphology confirmed that the metals (e.g., Ni and Co) in spent ternary LIBs are doped into MFO, leading to MFO-LIBs with a larger specific surface area (1.3 times that of MFO) and a higher ratio of Mn(II)/Mn(III) (1.4 times that of MFO) and Fe(II)/Fe(III) (1.3 times that of MFO). Electron paramagnetic resonance and quenching experiments confirmed that surface-bound SO4∙-, surface-bound ∙OH, O2∙- and 1O2 are the main reactive oxygen species (ROS) in BPA degradation. Simultaneously, the improved degradation activity of the MFO-LIBs/PMS system can be ascribed to the increase in the number of ROS rather than the change in ROS types. Its outstanding performance can be maintained despite the high-salinity conditions (e.g., Cl-, HCO3- and H2PO4-), high content of humic acid and alkaline conditions. MFO-LIBs can be easily separated in the presence of an external magnetic field and has excellent universality (toward bisphenol F, 2,4-dichlorophenol and 2,4,6-trichlorophenol) and regeneration ability. More importantly, the cost of BPA degradation in the MFO-LIBs/PMS system is much lower than that of the related spinel ferrite activator/PMS systems (e.g., CoFe2O4/PMS and MnFe2O4/PMS systems).

Humic acid addition sequence and concentration affect sulfur incorporation, electron transfer, and reactivity of sulfidated nanoscale zero-valent iron

Nanoscale zero-valent iron (nZVI) is extensively used in field remediation and can be sulfidated in situ with sulfide or sulfate-reducing bacteria to enhance its performance. Humic acid (HA) widely exists in nature, but its influence on both the sulfidation process of nZVI and the reactivity of sulfidated nZVI (S-nZVI) has been rarely reported. Herein, we first synthesized S-nZVI by one-pot (S1-nZVI) and two-step (S2-nZVI) approaches with adding HA before (pre-added) or after (post-added) FexSy generation, respectively. Then, we evaluated their reactivity on Cr(VI) removal and analyzed the effects of HA on sulfidation regarding electron transfer resistance, sulfur incorporation, and structure characterization. Pre-added HA inhibited the Cr(VI) removal by S1-nZVI more seriously than by S2-nZVI and nZVI, and stronger inhibition was observed at higher HA concentrations. The inhibitory effect can be attributed mainly to the adsorbed HA increasing the impedance of the material and the free HA impeding the generation and deposition of FexSy. Different from the inhibition of pre-added HA at all studied HA concentrations, the Cr(VI) removal by both S1-nZVI and S2-nZVI with post-added HA was enhanced at specific HA concentrations. The reason for this phenomenon was that the dispersion and specific surface area of S-nZVI were improved, thereby offsetting the inhibition from both impedance increase and sulfur loss. This work suggests that the presence of HA can affect the sulfidation process and the property of S-nZVI, which is conducive to evaluating the performance of S-nZVI produced both by injection and in situ in the subsurface contaminant remediation.

Humic acids restrict the transformation and the stabilization of Cd by iron (hydr)oxides

Iron (hydr)oxides and their association with organic matter significantly affect the mobility of heavy metals in natural soils and sediments. However, the behavior of cadmium (Cd) during crystalline iron (hydr)oxide formation in the presence of humic acid (HA) is still unknown. In this study, the speciation of Cd in iron (hydr)oxide-HA coprecipitates were studied by extraction, surface complexation model (SCM) calculation and characterization of the composites during the aging. The results showed that aging promoted the stabilization of ~30–50% of the added Cd ions with minerals in the binary iron (hydr)oxide systems. The reduction of Cd occurred earlier than hematite formation, indicating that the aggregation of amorphous iron (hydr)oxide led to the initial immobilization of Cd. The presence of HA restricted the crystallization of iron (hydr)oxide by the formation of tight mineral nanoparticle-HA aggregates, while there were negligible changes in the speciation of Cd and Fe during aging at high HA concentrations. Therefore, HA promoted the adsorption of Cd onto amorphous iron (hydr)oxide but limited the partition of Cd to mineral aggregates. The knowledge about the role of HA in iron (hydr)oxide transformation and Cd speciation is of great significance for the prediction of heavy metal behavior in soils and sediments.

New insights into the cooperative adsorption behavior of Cr(VI) and humic acid in water by powdered activated carbon

Chromium and humic acid often co-exist in wastewater and source waters, and the removal of chromium through sorption by activated carbon may be greatly influenced by humic acid. In this study, we systematically evaluated concurrent adsorption of humic acid (HA) and hexavalent chromium (Cr(VI)) in water by powdered activated carbon (PAC) and further, the effect on conversion to trivalent chromium (Cr(III)). Adsorption of both HA and Cr(VI) was significantly enhanced in the dual adsorbate system as compared to treatments with HA or Cr(VI) alone. The removal of HA increased by 16.0% in the presence of 80 mg/L Cr(VI), while the removal of Cr(VI) similarly increased with increasing levels of HA. However, the promotion effect of HA was found to decrease with increasing pH. With HA at 20 mg/L, removal of Cr(VI) increased from 40.09% to 70.12% at pH 3, which was about twice the increase at pH 10. The cooperative adsorption mechanism was explored using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). Comprehensive analysis of spectra suggested that the mutual promotion between HA and Cr(VI) adsorption was attributable to the formation of Cr(VI)-HA and Cr(III)-HA complexes that were readily adsorbed on the PAC surfaces. The higher HA concentrations increased the reduction of Cr(VI) to Cr(III), which was likely due to the electron transfer provided by the functional groups such as -CO, -OH and -COOH in both PAC and HA. At pH 3, 99.1% of Cr adsorbed on the PAC surface was in the form of Cr(III). These findings imply that the interactions between Cr(VI) and HA in the process of water treatment by PAC provides additional and synergistic benefits, leading to a greater removal of chromium.

Innovative Technology of Accelerated Composting of Chicken Manure to Obtain an Organic Fertilizer with a High Content of Humic Acids

Abstract One of the most important fractions of soil organic matter which has significant environmental and agricultural importance is humus. The specific humus compounds of soil include the complex of amorphous organic humic substances which include humic acids, fulvic acids and humins. The effectiveness of the natural formation of active humic substances during composting processes depends on the chemical composition of organic residues and the environmental conditions influencing the development and activity of native microorganisms. The aim of the project was to build innovative composting boxes for chicken manure that allow to effectively obtain a fertilizer with the highest possible content of humic acids, by creating perfect and controlled conditions for the rapid development of indigenous thermophilic microorganisms and by combining it with the owned bio-acceleration technology. For perfect conditions (temperature, humidity, oxygen, pH) for the controlled growth of microorganisms, an algorithm of the dependence of the box operation parameters on the course of the biological process, was built. The product obtained after composting is an easily digestible complex organic fertilizer of brown-black colour, pH 7.5-8.0 and NPK 5:3:4 and a high content of native humic acids. Its use increases the growth of green mass of plants and improves soil fertility, which has been proved by the conducted pot research.

Reactive Nitrogen Species Generated by Gas-Liquid Dielectric Barrier Discharge for Efficient Degradation of Perfluorooctanoic Acid from Water.

Perfluorooctanoic acid (PFOA) poses a serious threat to the ecological environment and biological health because of its ubiquitous distribution, extreme persistence, and high toxicity. In this study, we designed a novel gas-liquid dielectric barrier discharge (GLDBD) reactor which could efficiently destruct PFOA. PFOA removal efficiencies can be obtained in various water matrices, which were higher than 98.0% within 50 min, with energy yields higher than 114.5 mg·kWh-1. It was confirmed that the reactive species including e-, ONOOH, •NO2, and hydroxyl radicals (•OH) were responsible for PFOA removal. Especially, this study first revealed the crucial role of reactive nitrogen species (RNS) for PFOA degradation in the plasma system. Due to the generation of a large amount of RNS, the designed GLDBD reactor proved to be less sensitive to various water matrices, which meant a broader promising practical application. Moreover, influential factors including high concentration of various ions and humic acid (HA), were investigated. The possible PFOA degradation pathways were proposed based on liquid chromatograph-mass spectrometer (LC-MS) results and density functional theory (DFT) calculation, which further confirmed the feasibility of PFOA removal with RNS. This research, therefore, provides an effective and versatile alternative for PFOA removal from various water matrices.

Ti2O3/TiO2-Assisted Solar Photocatalytic Degradation of 4-tert-Butylphenol in Water

Colored Ti2O3 and Ti2O3/TiO2 (mTiO) catalysts were prepared by the thermal treatment method. The effects of treatment temperature on the structure, surface area, morphology and optical properties of the as-prepared samples were investigated by XRD, BET, SEM, TEM, Raman and UV–VIS spectroscopies. Phase transformation from Ti2O3 to TiO2 rutile and TiO2 anatase to TiO2 rutile increased with increasing treatment temperatures. The photocatalytic activities of thermally treated Ti2O3 and mTiO were evaluated in the photodegradation of 4-tert-butylphenol (4-t-BP) under solar light irradiation. mTiO heated at 650 °C exhibited the highest photocatalytic activity for the degradation and mineralization of 4-t-BP, being approximately 89.8% and 52.4%, respectively, after 150 min of irradiation. The effects of various water constituents, including anions (CO32−, NO3, Cl and HCO3−) and humic acid (HA), on the photocatalytic activity of mTiO-650 were evaluated. The results showed that the presence of carbonate and nitrate ions inhibited 4-t-BP photodegradation, while chloride and bicarbonate ions enhanced the photodegradation of 4-t-BP. As for HA, its effect on the degradation of 4-t-BP was dependent on the concentration. A low concentration of HA (1 mg/L) promoted the degradation of 4-t-BP from 89.8% to 92.4% by mTiO-650, but higher concentrations of HA (5 mg/L and 10 mg/L) had a negative effect.

Dispersion and transport of microplastics in three water-saturated coastal soils

The coastal area is one of the key zones for transport and fate of microplastics (MPs). This study investigated the transport behaviors of different sized MPs in three water-saturated coastal soils, with the aim to explore effects of properties of three different coastal soils on the dispersion and migration of three-sized MPs (0.3, 0.5, and 1 µm). All three-sized MPs had the strongest dispersion in Soil 3 solution, followed by that in Soil 1 solution and then that in Soil 2 solution. The strongest dispersion of MPs in Soil 3 solution was attributed to the lowest ionic strength. Such a high dispersion favored MPs movement in soil solution but readily be sorbed and fixed by rich Fe and Al oxides in Soil 3 solid through strong electrostatic attraction, leading to the lowest transport rate (20.5–41.2%). The high ionic strength in the Soil 1 solution decreased the dispersion of MPs, but the presence of high content of humic acid enhanced the electrostatic repulsion and steric hindrance between MPs and soil particles, resulting in the highest transport ability of MPs in Soil 1 (39.4–72.5%). The large amount of dissolved Ca2+ and Mg2+ in Soil 2 solution favored MPs bridged with fulvic acid, resulting in the highest aggregation of MPs and relatively lower transport ability (34.1–49.6%). Large-sized MPs had higher electrostatic repulsion between the particles, thus increasing the dispersion and transport capacity of MPs in soil. Modeling showed the experiment-consistent results that Soil 3 had the lowest MPs transport after 600 mm of heavy rainfall, with the maximum migration distance of 7.50–10.5 cm, which was smaller than that in Soil 2 (8.10–12.0 cm) and that in Soil 1 (9.00–18.3 cm). These results indicated that MPs transport in coastal soil is significant and soil solution and solid composition plays an important role in the dispersion and transport of MPs, respectively. These findings afforded a great basis for the assessment of the fate and risk of MPs in coastal areas.

Mechanistic Insight into Humic Acid-Enhanced Hydroxyl Radical Production from Fe(II)-Bearing Clay Mineral Oxygenation.

Hydroxyl radical (•OH) production by electron transfer from Fe(II)-bearing clay minerals to oxygen has been increasingly reported. However, the influence of ubiquitous coexisting humic acid (HA) on this process is poorly understood. Here, we investigated the effect of different HA on •OH production during the oxygenation of reduced nontronite NAu-2 (rNAu-2), montmorillonite, and sediment. Results showed that HA could enhance •OH production, and the enhancement was related to the content of reactive Fe(II) in rNAu-2 and the electron-accepting capacity of HA. Coexisting HA leads to a new electron-transfer pathway from Fe(II) in rNAu-2 to HA (instead of the HA-Fe complex) and then to O2, changing the first step of O2 reduction from one- to two-electron transfer process with H2O2 as the main intermediate. Reduced HA decomposes H2O2 to •OH at a higher yield (13.8%) than rNAu-2 (8.8%). Modeling results reveal that the HA-mediated electron-transfer pathway contributes to 12.6-70.2% of H2O2 generation and 13.2-62.1% of •OH formation from H2O2 decomposition, with larger contributions at higher HA concentrations (5-100 mg C/L). Our findings implicate that HA-mediated electron transfer can expand the area of •OH production from the mineral surface to the aqueous phase and increase the yield of •OH production.

Micro-gel thin film molecularly imprinted polymer coating for extraction of organophosphorus pesticides from water and beverage samples

Molecularly imprinted polymers (MIPs) have become an important class of materials for selective and efficient adsorption of target analytes. Despite versatility of MIPs for fabrication in numerous formats, these materials have been primarily reported as solid phase extraction packing materials. An effective thin film MIP prepared on stainless steel substrate is reported here for high throughput enrichment of organophosphorus pesticides (OPPs) from water and beverage samples followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The key factors controlling performance as well as best practices for optimized fabrication of thin film MIPs are presented. A pseudo-phase diagram is introduced to evaluate and predict the effect of the ratio of porogen (solvent, 1-octanol) volume to relative crosslinker mass on the desired polymer features (i.e., porosity, surface area, capacity, and selectivity). At low porogen ratios, a macroporous polymer with insignificant selectivity is formed, whereas at high porogen ratios a micro-gel polymer with superior selectivity towards targets is obtained. The porosity and morphology determined with nitrogen adsorption and scanning electron microscopy were attributed to specific regions in the pseudo-phase diagram. Other factors influencing selectivity and stability of the polymer, such as type of the template and its ratios with monomer (methacrylic acid) and crosslinker (ethylene glycol dimethacrylate) were optimized. The prepared thin film MIPs were characterized using adsorption isotherms and adsorption kinetics, and evaluated for matrix effects (high humic acid content) and cross-reactivity in presence of other pesticides and pharmaceuticals. The optimized method provided limits of quantitation (LOQs) ranged from 0.002 to 0.02 ng mL−1 in water and from 0.095 to 0.48 ng g−1 in apple juice. Regarding inter-device variability (CV∼10% without normalization), excellent linearity (R2 > 0.99), satisfactory accuracies (90–110%) and precisions (<15%) were obtained.