Phosphorus-Enhanced and Calcium-Retarded Transport of Ferrihydrite Colloid: Mechanism of Electrostatic Potential Changes Regulated via Adsorption Speciation

Insights on the Contradiction between the Affinity and Capacity of Ferrihydrite toward As(III) and As(V): Surface Reaction Revisited

Ferrihydrite is omnipresent in nature, and its adsorption of As(III/V) decides the migration of arsenic. Although As(III) is commonly recognized as the more mobile species of inorganic arsenic, it sometimes exhibits less mobility in ferrihydrite systems, which calls for further insights. In this study, we elucidated the adsorption behavior and mechanisms of As(III/V) on ferrihydrite under different loading levels (molar ratio As/Fe = 0-0.38), solution pH (3-10), and coexisting ions [P(V) and Ca(II)] based on batch adsorption experiments, surface complexation modeling, density functional theory calculations, and X-ray photoelectron spectroscopy. Our results show that As(III) exhibits weaker adsorption affinity but a larger capacity compared with that of As(V). On ferrihydrite, As(III) and As(V) are adsorbed mainly as bidentate mononuclear complexes at type-a sites [≡Fe(OH-0.5)2] and bidentate binuclear complexes at type-b sites (2≡FeOH-0.5), respectively. As the dosage increases, As(III) further forms mononuclear monodentate complexes at both surface sites, resulting in a higher site utilization efficiency, while As(V) does not due to repulsive electrostatic interaction. The difference in surface species of As(III/V) also leads to complex responses when coexisting with high concentrations of P(V) and Ca(II). This study helps us to understand environmental behavior of As(III/V) and develop remediation strategy in As(III/V) contaminated systems.

In Situ Evolution of Ionic Sites at Clay Mineral Interfaces Facilitates Fluoride and Phosphorus Mineralization

Soil minerals influence the biogeochemical cycles of fluoride (F) and phosphorus (P), impacting soil quality and bioavailability to plants. However, the cooperative mechanisms of soil minerals in governing F and P in the soil environment remain a grand challenge. Here, we reveal the essential role of a typical soil mineral, montmorillonite (Mt), in the cycling and fate of F and P. The results show that the enrichment of metal sites on the Mt surface promotes the mineralization of F to the fluorapatite (FAP) phase, thereby remaining stable in the environment, simultaneously promoting P release. This differential behavior leads to a reduction in the level of F pollution and an enhancement of P availability. Moreover, solid-state NMR and HRTEM observations confirm the existence of metastable F-Ca-F intermediates, emphasizing the pivotal role of Mt surface sites in regulating crystallization pathways and crystal growth of FAP. Furthermore, the in situ atomic force microscopy and theoretical calculations reveal molecular fractionation mechanisms and adsorption processes. It is observed that a competitive relationship exists between F and P at the Mt interface, highlighting the thermodynamically advantageous pathway of forming metastable intermediates, thereby governing the activity of F and P in the soil environment at a molecular level. This work paves the way to reveal the important role of clay minerals as a mineralization matrix for soil quality management and offers new strategies for modulating F and P dynamics in soil ecosystems.

Novel Approach to Photocatalytic Removal of Linezolid by Advanced Nano-Biochar/Bismuth Oxychloride Hybrid

Herein, we introduce an innovative nanohybrid material for advanced wastewater treatment, composed of Corchorus olitorius-derived biochar and bismuth oxychloride (Biochar/Bi12O17Cl2), demonstrated in a solar photoreactor. This work focuses on the efficient degradation of linezolid (LIN), a persistent pharmaceutical pollutant, utilizing the unique (photo)catalytic capabilities of the nanohybrid. Compared with its individual components, the biochar/Bi12O17Cl2 hybrid exhibits a remarkable degradation efficiency of 82.6% for LIN, alongside significant chemical oxygen demand (COD) and total organic carbon (TOC) mineralization rates of 81.3 and 75.8%, respectively. These results were achieved within 3 h under solar irradiation, using an optimal composite dose of 125 mg/L at pH 4.3 ± 0.45, with an initial COD and LIN concentrations of 1605 and 160.8 mg/L and TOC of 594.3 mg/L. The nanohybrid's stability across five cycles of use demonstrates its potential for repeated applications, with degradation efficiencies of 82.6 and 77.9% in the first and fifth cycles, respectively. This indicates the biochar/Bi12O17Cl2 composite's suitability as a sustainable and cost-effective solution for the remediation of heavily contaminated waters. Further, the degradation pathway proposed the degradation of all of the generated intermediates to a single-ring compound. Contributing to the development of next-generation materials for environmental remediation, this research underscores the critical role of nanotechnology in enhancing water quality and ecosystem sustainability and addressing the global imperative for clean water access and environmental preservation.

Quantitative Insights into Phosphate-Enhanced Lead Immobilization on Goethite

Despite extensive study, geochemical modeling often fails to accurately predict lead (Pb) immobilization in environmental samples. This study employs the Charge Distribution MUlti-SIte Complexation (CD-MUSIC) model, X-ray absorption fine structure (XAFS), and density functional theory (DFT) to investigate mechanisms of phosphate (PO4) induced Pb immobilization on metal (hydr)oxides. The results reveal that PO4 mainly enhances bidentate-adsorbed Pb on goethite via electrostatic synergy at low PO4 concentrations. At relatively low pH (below 5.5) and elevated PO4 concentrations, the formation of the monodentate-O-sharing Pb-PO4 ternary structure on goethite becomes important. Precipitation of hydropyromorphite (Pb5(PO4)3OH) occurs at high pH and high concentrations of Pb and PO4, with an optimized log Ksp value of -82.02. The adjustment of log Ksp compared to that in the bulk solution allows for quantification of the overall Pb-PO4 precipitation enhanced by goethite. The CD-MUSIC model parameters for both the bidentate Pb complex and the monodentate-O-sharing Pb-PO4 ternary complex were optimized. The modeling results and parameters are further validated and specified with XAFS analysis and DFT calculations. This study provides quantitative molecular-level insights into the contributions of electrostatic enhancement, ternary complexation, and precipitation to phosphate-induced Pb immobilization on oxides, which will be helpful in resolving controversies regarding Pb distribution in environmental samples.

Effect of calcium and phosphorus on ammonium and nitrate nitrogen adsorption onto iron (hydr)oxides surfaces: CD-MUSIC model and DFT computation

Calcium (Ca2+) and phosphorous (PO43-) significantly influence the form and effectiveness of nitrogen (N), however, the precise mechanisms governing the adsorption of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) are still lacking. This study employed batch adsorption experiments, charge distribution and multi-site complexation (CD-MUSIC) models and density functional theory (DFT) calculations to elucidate the mechanism by which Ca2+ and PO43- affect the adsorption of NH4+-N and NO3--N on the goethite (GT) surface. The results showed that the adsorption of NH4+-N on the GT exhibited an initial increase followed by a decrease as pH increased, peaking at a pH of 8.5. Conversely, the adsorption of NO3--N decreased with rising pH. According to the CD-MUSIC model, Ca2+ minimally affected the NH4+-N adsorption on the GT but enhanced NO3--N adsorption via electrostatic interaction, promoting the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. Similarly, PO43- inhibited the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. However, PO43- boosted NH4+-N adsorption by facilitating the formation of ≡Fe3O-NH4+ via electrostatic interaction and site competition. DFT calculations indicates that although bidentate phosphate (BP) was beneficial to stabilize NH4+-N than monodentate phosphate (SP), SP-NH4+ was the main adsorption configuration at pH 5.5-9.5 owing the prevalence of SP on the GT surface under site competition of NH4+-N. The results of CD-MUSIC model and DFT calculation were verified mutually, and provide novel insights into the mechanisms underlying N fixation and migration in soil.

Iron-containing nanominerals for sustainable phosphate management: A comprehensive review and future perspectives

Adsorption, which is a quick and effective method for phosphate management, can effectively address the crisis of phosphorus mineral resources and control eutrophication. Phosphate management systems typically use iron-containing nanominerals (ICNs) with large surface areas and high activity, as well as modified ICNs (mICNs). This paper comprehensively reviews phosphate management by ICNs and mICNs in different water environments. mICNs have a higher affinity for phosphates than ICNs. Phosphate adsorption on ICNs and mICNs occurs through mechanisms such as surface complexation, surface precipitation, electrostatic ligand exchange, and electrostatic attraction. Ionic strength influences phosphate adsorption by changing the surface potential and isoelectric point of ICNs and mICNs. Anions exhibit inhibitory effects on ICNs and mICNs in phosphate adsorption, while cations display a promoting effect. More importantly, high concentrations and molecular weights of natural organic matter can inhibit phosphate adsorption by ICNs and mICNs. Sodium hydroxide has high regeneration capability for ICNs and mICNs. Compared to ICNs with high crystallinity, those with low crystallinity are less likely to desorb. ICNs and mICNs can effectively manage municipal wastewater, eutrophic seawater, and eutrophic lakes. Adsorption of ICNs and mICNs saturated with phosphate can be used as fertilizers in agricultural production. Notably, mICNs and ICNs have positive and negative effects on microorganisms and aquatic organisms in soil. Finally, this study introduces the following: trends and prospects of machine learning-guided mICN design, novel methods for modified ICNs, mICN regeneration, development of mICNs with high adsorption capacity and selectivity for phosphate, investigation of competing ions in different water environments by mICNs, and trends and prospects of in-depth research on the adsorption mechanism of phosphate by weakly crystalline ferrihydrite. This comprehensive review can provide novel insights into the research on high-performance mICNs for phosphate management in the future.

Physicomechanical, Wettability, Corrosion, Thermal, and Microstructural Morphology Characteristics of Carbonized and Uncarbonized Bagasse Ash Waste-Reinforced Al-0.45Mg-0.35Fe-0.25Si-Based Composites: Fabrications and Characterizations

An effort was being made to incorporate waste bagasse ash (WBA) both in carbonized and uncarbonized form into the formulation of Al6063 matrix-based metal matrix composites (MMC's) by partially substituting ceramic particles for them. In the process of developing composites, comparative research on carbonized WBA and uncarbonized bagasse powder was carried out in the role of reinforcement. Microstructure investigations revealed that carbonized WBA particles were properly distributed throughout the aluminum-base metal matrix alloy. They also had the appropriate level of wettability. The reinforcement of carbonized WBA particles in AA6063-based matrix material had a maximum tensile strength of 110 MPa and a maximal hardness of 39 BHN when 3.75 wt % of the particles were used. The deterioration in tensile strength (6.25 wt % of WBA) and the appearance of porosity and blowholes can be enumerated by tensile fractography-based scanning electron microscopy (SEM) analysis. The reinforcement of carbonized WBA particles in AA6063-based matrix material was found to have a maximal percent elongation of 14.42% and the highest fracture toughness of 15 Joules when 1.25 wt % of the particles were employed. For AA6063/3.75 wt % carbonized WBA-based MMC's, the minimum percent porosity was determined to be 5.83, and the minimum thermal expansion was found to be 45 mm3. As the percentage of reinforcement in bagasse-reinforced composites increases, the density of the material, the amount of corrosion loss, and the cost all decrease gradually. The AA6063 matrix, with a composition of 3.75 wt % carbonized WBA-based MMC's, had satisfactory specific strength and corrosion loss. The AA6063 alloy composite's microstructure analysis revealed that carbonized WBA enhanced the material's mechanical characteristics, contributing to its excellent mechanical capabilities. The results of the corrosion test showed that carbonized WBA-reinforced composites exhibited reduced weight loss due to corrosion, whereas uncarbonized bagasse powder was an inappropriate reinforcement. The SEM analysis of AA6063 alloy/3.75 wt % carbonized WBA ash reinforcement-based MMC's exposed to a 3.5 wt % NaCl solution has exhibited the development of corrosion pits as a result of localized attack by the corrosive environment. The thermal expansion test showed that the composite with uncarbonized bagasse powder as reinforcement have a high shrinkage rate in comparison with the composite with 3.75 wt %. The composite's mechanical characteristics and thermal stability were enhanced by the presence of hard phases like SiO2, Al2O3, Fe2O3, CaO, and MgO, as revealed by X-ray diffraction analysis. This made it suitable for use in a variety of applications.

Optimization of syngas production from co-gasification of palm oil decanter cake and alum sludge: An RSM approach with char characterization

The study explores co-gasification of palm oil decanter cake and alum sludge, investigating the correlation between input variables and syngas production. Operating variables, including temperature (700-900 °C), air flow rate (10-30 mL/min), and particle size (0.25-2 mm), were optimized to maximize syngas production using air as the gasification agent in a fixed bed horizontal tube furnace reactor. Response Surface Methodology with the Box-Behnken design was used employed for optimization. Fourier Transformed Infra-Red (FTIR) and Field Emission Scanning Electron Microscopic (FESEM) analyses were used to analyze the char residue. The results showed that temperature and particle size have positive effects, while air flow rate has a negative effect on the syngas yield. The optimal CO + H2 composition of 39.48 vol% was achieved at 900 °C, 10 mL/min air flow rate, and 2 mm particle size. FTIR analysis confirmed the absence of C─Cl bonds and the emergence of Si─O bonds in the optimized char residue, distinguishing it from the raw sample. FESEM analysis revealed a rich porous structure in the optimized char residue, with the presence of calcium carbonate (CaCO3) and aluminosilicates. These findings provide valuable insights for sustainable energy production from biomass wastes.

Skeletal muscle regeneration with 3D bioprinted hyaluronate/gelatin hydrogels incorporating MXene nanoparticles

There has been significant progress in the field of three-dimensional (3D) bioprinting technology, leading to active research on creating bioinks capable of producing structurally and functionally tissue-mimetic constructs. Ti3C2Tx MXene nanoparticles (NPs), promising two-dimensional nanomaterials, are being investigated for their potential in muscle regeneration due to their unique physicochemical properties. In this study, we integrated MXene NPs into composite hydrogels made of gelatin methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) to develop bioinks (namely, GHM bioink) that promote myogenesis. The prepared GHM bioinks were found to offer excellent printability with structural integrity, cytocompatibility, and microporosity. Additionally, MXene NPs within the 3D bioprinted constructs encouraged the differentiation of C2C12 cells into skeletal muscle cells without additional support of myogenic agents. Genetic analysis indicated that representative myogenic markers both for early and late myogenesis were significantly up-regulated. Moreover, animal studies demonstrated that GHM bioinks contributed to enhanced regeneration of skeletal muscle while reducing immune responses in mice models with volumetric muscle loss (VML). Our results suggest that the GHM hydrogel can be exploited to craft a range of strategies for the development of a novel bioink to facilitate skeletal muscle regeneration because these MXene-incorporated composite materials have the potential to promote myogenesis.

Micro/nanoplastics: Critical review of their impacts on plants, interactions with other contaminants (antibiotics, heavy metals, and polycyclic aromatic hydrocarbons), and management strategies

Microplastic/nanoplastics (MPs/NPs) contamination is not only emerging threat to the agricultural system but also constitute global hazard to the environment worldwide. Recent review articles have addressed the environmental distribution of MPs/NPs and their single-exposure phytotoxicity in various plant species. However, the mechanisms of MPs/NPs-induced phytotoxicity in conjunction with that of other contaminants remain unknown, and there is a need for strategies to ameliorate such phytotoxicity. To address this, we comprehensively review the sources of MPs/NPs, their uptake by and effects on various plant species, and their phytotoxicity in conjunction with antibiotics, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and other toxicants. We examine mechanisms to ameliorate MP/NP-induced phytotoxicity, including the use of phytohormones, biochar, and other plant-growth regulators. We discuss the effects of MPs/NPs -induced phytotoxicity in terms of its ability to inhibit plant growth and photosynthesis, disrupt nutrient metabolism, inhibit seed germination, promote oxidative stress, alter the antioxidant defense system, and induce genotoxicity. This review summarizes the novel strategies for mitigating MPs/NPs phytotoxicity, presents recent advances, and highlights research gaps, providing a foundation for future studies aimed at overcoming the emerging problem of MPs/NPs phytotoxicity in edible crops.

Unlocking the potential of biochar in the remediation of soils contaminated with heavy metals for sustainable agriculture

Agricultural soils contaminated with heavy metals (HMs) impose a threat to the environmental and to human health. Amendment with biochar could be an eco-friendly and cost-effective option to decrease HMs in contaminated soil. This paper reviews the application of biochar as a soil amendment to immobilise HMs in contaminated soil. We discuss the technologies of its preparation, their specific properties, and effect on the bioavailability of HMs. Biochar stabilises HMs in contaminated soil, enhance the overall quality of the contaminated soil, and significantly reduce HM uptake by plants, making it an option in soil remediation for HM contamination. Biochar enhances the physical (e.g. bulk density, soil structure, water holding capacity), chemical (e.g. cation exchange capacity, pH, nutrient availability, ion exchange, complexes), and biological properties (e.g. microbial abundance, enzymatic activities) of contaminated soil. Biochar also enhances soil fertility, improves plant growth, and reduces the plant availability of HMs. Various field studies have shown that biochar application reduces the bioavailability of HMs from contaminated soil while increasing crop yield. The review highlights the positive effects of biochar by reducing HM bioavailability in contaminated soils. Future work is recommended to ensure that biochars offer a safe and sustainable solution to remediate soils contaminated with HMs.

Modeling Cu removal from aqueous solution using sawdust based on response surface methodology

Copper (Cu), as one of the heavy metals widely used in industrial and agricultural activities, has a fundamental role in the pollution of water resources. Therefore, removing Cu from the aqueous solutions is considered an important challenge in the purification of water resources. Thus, in this study, sawdust with a diameter of 260-600 μm was used to remove Cu from the aqueous solutions. At first, sawdust was washed using distilled water and dried at laboratory temperature. Cu absorption experiments in closed conditions were performed based on the central composite design (CCD) model and with a range of initial Cu concentrations equal to 1-25 mgl-1. The amount of changes for other variables, including pH, time, and amount of sawdust, was equal to 2-10, 5-185 (min), and 5-25 (gl-1), respectively. After the completion of each test, the remaining Cu concentration in the solution was measured using atomic absorption, and the percentage of Cu removed was determined from the difference between the initial and final concentrations. The results showed that the CCD model has a favorable ability to predict Cu removal from the aqueous solutions (R2=0.90 and RSME=3.34%). Based on the Pareto analysis, contact time, the amount of sawdust, pH, and the Cu concentration had the most significant effect on removing Cu from the solution. Contact time, amount of sawdust, and pH were directly related, and the amount of dissolved Cu was proportional to the removal of Cu from the solution. Therefore, sawdust is desirable as a natural adsorbent, and the removal efficiency of Cu from solutions with low Cu concentration is very high (94%). In this regard, it is advised to use sawdust in the process of targeting Cu and heavy metals due to its low cost and availability.

Enhanced electrochemical treatment of humic acids and metal ions in leachate concentrate: Experimental and molecular mechanism investigations

Membrane technologies are effective for treating leachate, but they generate leachate concentrates (LCs), which contain elevated humic acids (HAs) and metals. LCs are very challenging and expensive to treat; but in-situ coagulation-electrochemical oxidation (CO-EO) treatment is promising. We previously hypothesized and proved that substituting the widely used graphite cathode with an Al cathode will generate Al(OH)3 floccules that would enhance HAs removal in CO-EO systems. However, the fundamental mechanisms are unclear. Here, we examined this hypothesis using laboratory experiments (using an Al cathode and a Ti/Ti4O7 anode CO-EO system) and performed molecular dynamics (MD) simulation to investigate the underlying mechanisms. Up to 84.2% HAs was removed by the Al-cathode system, which is ∼10% higher than a graphite cathode-based system. Based on MD simulation we found that enhanced HAs removal occurred via two steps: (1) degradation by oxidants produced at the anode, and (2) subsequent coagulation with the Al(OH)3 generated from the Al cathode. This finding challenges the current belief that whole HAs and Al(OH)3 directly flocculate. Meanwhile, metal removal efficiency by the graphite cathode system was only 0.8-13.9%, which increased up to 13-folds at most when in the Al cathode system. This work provides new molecular-level insights into an efficient electrochemical treatment of LC.

Insight into Impact of Phosphate on the Cotransport and Corelease of Eu(III) with Bentonite Colloids in Saturated Quartz Columns

Understanding the fate and transport of radionuclides in porous media reduces the risk of contaminating soils and groundwater systems. While the cotransport of bentonite colloids (BC) with radionuclides in saturated media is well documented, the role of phosphate (P) in the colloid-driven transport of radionuclides in saturated porous media is still unaddressed; in particular, phosphate increases the mobilities of radionuclides in porous media, which should be subjected to an environmental risk assessment and model construction. In this work, the effects of phosphate on the transport and release of Eu(III) in different colloid systems (P-Eu(III), P-BC, P-BC-Eu(III)) was investigated with a fundamental colloid chemistry approach and a range of characterization techniques. The results showed that intrinsic europium colloids with size of 685 nm were formed by precipitation with phosphate, which affected the mobility of Eu(III) due to colloid stability and physical straining. Phosphate enhanced BC and BC-Eu(III) transport, and a high phosphate concentration promoted BC transport by eliminating physical straining and enhancing the electrostatic repulsions. The crystal structure of EuPO4 was not destroyed by the subsequent introduction of BC, which carried EuPO4 for further migration. However, when phosphate, bentonite and Eu(III) coexisted in a colloid suspension, the phosphate promoted Eu(III) transport by preferentially interacting with the BC to form ternary BC-P-Eu(III) pseudo-colloids rather than forming the intrinsic EuPO4 colloids. The synergetic role of P and BC on Eu(III) transport involved a relatively complex process and was not a simply additive effect. The findings in this work highlight the significance of phosphate in controlling the fate and transport of Ln(III)/Am(III) radionuclides in the presence of intrinsic colloids and pseudo-colloids in P-rich colloid-bearing environments.

Enhanced Oxidation of Organic Compounds by the Ferrihydrite-Ferrate System: The Role of Intramolecular Electron Transfer and Intermediate Iron Species

Previous studies mostly held that the oxidation capacity of ferrate depends on the involvement of intermediate iron species (i.e., FeIV/FeV), however, the potential role of the metastable complex was disregarded in ferrate-based heterogeneous catalytic oxidation processes. Herein, we reported a complexation-mediated electron transfer mechanism in the ferrihydrite-ferrate system toward sulfamethoxazole (SMX) degradation. A synergy between intermediate FeIV/FeV oxidation and the intramolecular electron transfer step was proposed. Specifically, the conversion of phenyl methyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2) suggested that FeIV/FeV was involved in the oxidation of SMX. Moreover, based on the in situ Raman test and chronopotentiometry analysis, the formation of the metastable complex of ferrihydrite/ferrate was found, which possesses higher oxidation potential than free ferrate and could achieve the preliminary oxidation of organics via the electron transfer step. In addition, the amino group of SMX could complex with ferrate, and the resulting metastable complex of ferrihydrite/ferrate would combine further with SMX molecules, leading to intramolecular electron transfer and SMX degradation. The ferrate loss experiments suggested that ferrihydrite could accelerate the decomposition of ferrate. Finally, the effects of pH value, anions, humic acid, and actual water on the degradation of SMX by ferrihydrite-ferrate were also revealed. Overall, ferrihydrite demonstrated high catalytic capacity, good reusability, and nontoxic performance for ferrate activation. The ferrihydrite-ferrate process may be a green and promising method for organic removal in wastewater treatment.