Natural iron minerals in an electrocatalytic oxidation system and in situ pollutant removal in groundwater: Applications, mechanisms, and challenges

A new insight into the straw decomposition associated with minerals: Promoting straw humification and Cd immobilization

Organic matter (OM) derived from the decomposition of crop residues plays a key role as a sorbent for cadmium (Cd) immobilization. Few studies have explored the straw decomposition processes with the presence of minerals, and the effect of newly generated organo-mineral complexes on heavy metal adsorption. In this study, we investigated the variations in structure and composition during the rice straw decomposition with or without minerals (goethite and kaolinite), as well as the adsorption behavior and mechanisms by which straw decomposition affects Cd immobilization. The degree of humification of extracted straw organic matter was assessed using excitation-emission matrix (EEM) fluorescence and Ultraviolet-visible spectroscopy (UV-vis), while employing FTIR spectroscopy and XPS to characterize the adsorption mechanisms. The spectra analysis revealed the enrichment of highly aromatic and hydrophobic components, indicating that the degree of straw decomposition and humification were further intensified during incubation. Additionally, the existence of goethite (SG) accelerated the humification of OM. Sorption experiments revealed that the straw humification increased Cd adsorption capacity. Notably, SG exhibited significantly higher adsorption performance compared to the organic matter without minerals (RS) and the existence of kaolinite (SK). Further analysis using FT-IR spectroscopy and XPS verified that the primary mechanisms involved in Cd immobilization were complexion with -OH and -COOH, as well as the formation of Cd-π binds with aromatic C=C on the surface of solid OMs. These findings will facilitate understanding the interactions of the rice straw decomposing with soil minerals and its remediation effect on Cd-contaminated farmland.

The Photocatalytic Degradation of Enrofloxacin Using an Ecofriendly Natural Iron Mineral: The Relationship Between the Degradation Routes, Generated Byproducts, and Antimicrobial Activity of Treated Solutions

The use of ecofriendly natural minerals in photocatalytic processes to deal with the antimicrobial activity (AA) associated with antibiotics in aqueous systems is still incipient. Therefore, in this work, the capacity of a natural iron material (NIM) in photo-treatments, generating reactive species, to remove the antibiotic enrofloxacin and decrease its associated AA from water is presented. Initially, the fundamental composition, oxidation states, bandgap, point of zero charge, and morphological characteristics of the NIM were determined, denoting the NIM's feasibility for photocatalytic processes. Consequently, the effectiveness of different advanced processes such as using solar light with the NIM (Light-NIM) and solar light with the NIM and H2O2 (Light-NIM-H2O2) to reduce AA was evaluated. The NIM acts as a semiconductor under solar light, effectively degrading enrofloxacin (ENR) and reducing its AA, although complete elimination was not achieved. The addition of hydrogen peroxide (NIM-Light-H2O2) enhanced the generation of reactive oxygen species (ROS), thereby increasing the elimination of ENR and AA. The role of ROS, specifically O2•- and HO●, in the degradation of enrofloxacin was distinguished using scavenger species and electron paramagnetic resonance (EPR) analysis. Additionally, the five primary degradation products generated during the advanced processes were elucidated. Furthermore, the relationship between the structure of these products and the persistence or elimination of AA, which was differentiated against E. coli but not against S. aureus, was discussed. The effects of the matrix during the process and the extent of the treatments, including their capacity to promote disinfection, were also studied. The reusability of the natural iron material was examined, and it was found that the NIM-Light-H2O2 system showed an effective reduction of 5 logarithmic units in microbiological contamination in an EWWTP and can be reused for up to three cycles while maintaining 100% efficiency in reducing AA.

Recent Progress in Molecular Oxygen Activation by Iron-Based Materials: Prospects for Nano-Enabled In Situ Remediation of Organic-Contaminated Sites

In situ chemical oxidation (ISCO) is commonly used for the remediation of contaminated sites, and molecular oxygen (O2) after activation by aquifer constituents and artificial remediation agents has displayed potential for efficient and selective removal of soil and groundwater contaminants via ISCO. In particular, Fe-based materials are actively investigated for O2 activation due to their prominent catalytic performance, wide availability, and environmental compatibility. This review provides a timely overview on O2 activation by Fe-based materials (including zero-valent iron-based materials, iron sulfides, iron (oxyhydr)oxides, and Fe-containing clay minerals) for degradation of organic pollutants. The mechanisms of O2 activation are systematically summarized, including the electron transfer pathways, reactive oxygen species formation, and the transformation of the materials during O2 activation, highlighting the effects of the coordination state of Fe atoms on the capability of the materials to activate O2. In addition, the key factors influencing the O2 activation process are analyzed, particularly the effects of organic ligands. This review deepens our understanding of the mechanisms of O2 activation by Fe-based materials and provides further insights into the application of this process for in situ remediation of organic-contaminated sites.

The synergistic effect of adsorption and Fenton oxidation for organic pollutants in water remediation: an overview

Water pollution from industrial sources presents a significant environmental challenge due to the presence of recalcitrant organic contaminants. These pollutants threaten human health and necessitate effective remediation strategies. This article reviewed the synergistic application of adsorption and Fenton oxidation for water treatment. Adsorption, a common technique, concentrates pollutants onto a solid surface, but offers limited degradation. Fenton oxidation, an advanced oxidation process (AOP), utilizes hydroxyl radicals for efficient organic compound breakdown. When adsorption and Fenton oxidation combine, adsorption pre-concentrates pollutants, boosting Fenton oxidation effectiveness. This review delves into the mechanisms and advantages of this integrated approach, highlighting its potential for enhanced removal of organic contaminants. The discussion encompasses the mechanisms of Fenton oxidation and the synergistic effects it has with adsorption. Additionally, various support materials employed in this combined process are explored, including carbon-based supports (activated carbon, graphene, carbon nanotubes and biochar), metal-organic frameworks (MOFs), and clays. Finally, the applicability of this approach to diverse wastewater streams, such as medical and industrial wastewater, is addressed. The review contains 105 references and summarizes the key findings and future perspectives for this promising water remediation technology.

A sustainable method for oxidizing phenanthrene in tropical soil using natural iron as a catalyst in a slurry phase reactor with persulfate assistance

The presence of impurities is a significant restriction to the use of natural iron minerals as catalysts in the advanced oxidation process (AOP), especially if applied for soil remediation. This study evaluated the catalytic activity of tropical soil, which has relatively low impurities and naturally contains iron, for the remediation of phenanthrene (PHE) contamination. The system showed good performance, and the best result was 81% PHE removal after 24 h under experimental conditions of pH 7, [PHE]0 = 300 mg/50 g soil, temperature 55 °C, air flow = 260 mL min-1, and [persulfate]0 = 20 mg kg-1, while the mineralization was 61%. Nevertheless, certain limitations were noted in the soil matrix following the remediation procedure, including the appearance of cracks in the soil aggregate, reduction in the crystal size of the soil particles, and decline in the iron and aluminium contents. The results confirmed that the radicals play a major role in the remediation process. SO4˙- was more dominant than O2˙-, while HO˙ played a minor role. Additionally, the by-products were detected by gas chromatography-mass spectroscopy (GC-MS), and the degradation pathway of PHE is proposed. Toxicity assessment tests were performed by using a computational method. In spite of the challenges, this research achieved notable progress in soil remediation, taking a significant step forward in implementing the AOP without catalysts to activate oxidants and remove PHE within the soil. Also, this approach supports sustainability by reducing the need for extra materials and providing an environmentally friendly way of soil remediation.

Inhibiting effects of humic acid on iron flocculation hindered As removal by electro-flocculation on air cathode iron anode

Activated carbon air cathode combined with iron anode oxidation-flocculation synergistic Arsenic (As) removal was a new groundwater purification technology with low energy consumption and high efficiency for groundwater with high As concentration. The presence of organic matter such as humic acid (HA) had ambiguous effects on formation of organic colloids in the system. The effects of the particle size distribution characteristics of these colloids on the formation characteristics of flocs and the efficiency of As purification was not clear. In this work, we used five different pore size alumina filter membranes to separate mixed phase solutions and studied the corresponding changes in iron and arsenic concentrations in the presence and absence of humic acid conditions. In the presence of HA, the arsenic concentration of < 0.05 µm particle size components was 1.01, 1.28, 3.07, 7.69, 2.85 and 1.24 times of that in the absence of HA. At the same time, the arsenic content in 0.05-0.1 µm and 0.1-0.45 µm particle size components was also higher than that in the system without HA, which revealed that the presence of HA hindered the flocculation behavior of As distribution to higher particle sizes in the early stage of the reaction. The presence of HA affected the flocculation rate of iron flocs from small to large particle size fractions and it had limited effect on the behavior of large-size flocs in adsorption of As. These results provide a theoretical basis for targeted, rapid, and low consumption synergistic removal of arsenic and organic compounds in high arsenic groundwater.

Harnessing the power of natural minerals: A comprehensive review of their application as heterogeneous catalysts in advanced oxidation processes for organic pollutant degradation

The release of untreated wastewater into water bodies has become a significant environmental concern, resulting in the accumulation of refractory organic pollutants that pose risks to human health and ecosystems. Wastewater treatment methods, including biological, physical, and chemical techniques, have limitations in achieving complete removal of the refractory pollutants. Chemical methods, particularly advanced oxidation processes (AOPs), have gained special attention for their strong oxidation capacity and minimal secondary pollution. Among the various catalysts used in AOPs, natural minerals offer distinct advantages, such as low cost, abundant resources, and environmental friendliness. Currently, the utilization of natural minerals as catalysts in AOPs lacks thorough investigation and review. This work addresses the need for a comprehensive review of natural minerals as catalysts in AOPs. The structural characteristics and catalytic performance of different natural minerals are discussed, emphasizing their specific roles in AOPs. Furthermore, the review analyzes the influence of process factors, including catalyst dosage, oxidant addition, pH value, and temperature, on the catalytic performance of natural minerals. Strategies for enhancing the catalytic efficiency of AOPs mediated by natural minerals are explored, mainly including physical fields, reductant addition, and cocatalyst utilization. The review also examines the practical application prospects and main challenges associated with the use of natural minerals as heterogeneous catalysts in AOPs. This work contributes to the development of sustainable and efficient approaches for organic pollutant degradation in wastewater.

Molten Salt-Assisted Catalytic Preparation of MoS2/α-MoO3/Graphene as High-Performance Anode of Li-Ion Battery

We report on the facile and scalable catalytic conversion of natural graphite and MoS2 minerals into α-MoO3 nanoribbons incorporated into hexagonal MoS2 and graphene nanosheets, and evaluate the structural, morphological and electrochemical performances of the hybrid nanostructured material obtained. Mechanochemical treatment of raw materials, followed by catalytic molten salt treatment leads to the formation of nanostructures with promising electrochemical performances. We examined the effect of processing temperature on the electrochemical performance of the products. At 1100 °C, an excellent Li-ion storage capacity of 773.5 mAh g−1 is obtained after 180 cycles, considerably greater than that of MoS2 (176.8 mAh g−1). The enhanced capacity and the rate performance of this electrode are attributed to the well-integrated components, characterized by the formation of interfacial molybdenum oxycarbide layer during the synthesis process, contributing to the reduced electrical/electrochemical resistance of the sample. This unique morphology promotes the charge and ions transfer through the reduction of the Li-ion diffusion coefficient (1.2 × 10−18 cm2 s−1), enhancing the pseudocapacitive performance of the electrode; 59.3% at the scan rate of 0.5 mV s−1. This article provides a green and low-cost route to convert highly available natural graphite and MoS2 minerals into nanostructured hybrid materials with promising Li-ion storage performance.