Critical Role of Mineral Fe(IV) Formation in Low Hydroxyl Radical Yields during Fe(II)-Bearing Clay Mineral Oxygenation.

In subsurface environments, Fe(II)-bearing clay minerals can serve as crucial electron sources for O2 activation, leading to the sequential production of O2•-, H2O2, and •OH. However, the observed •OH yields are notably low, and the underlying mechanism remains unclear. In this study, we investigated the production of oxidants from oxygenation of reduced Fe-rich nontronite NAu-2 and Fe-poor montmorillonite SWy-3. Our results indicated that the •OH yields are dependent on mineral Fe(II) species, with edge-surface Fe(II) exhibiting significantly lower •OH yields compared to those of interior Fe(II). Evidence from in situ Raman and Mössbauer spectra and chemical probe experiments substantiated the formation of structural Fe(IV). Modeling results elucidate that the pathways of Fe(IV) and •OH formation respectively consume 85.9-97.0 and 14.1-3.0% of electrons for H2O2 decomposition during oxygenation, with the Fe(II)edge/Fe(II)total ratio varying from 10 to 90%. Consequently, these findings provide novel insights into the low •OH yields of different Fe(II)-bearing clay minerals. Since Fe(IV) can selectively degrade contaminants (e.g., phenol), the generation of mineral Fe(IV) and •OH should be taken into consideration carefully when assessing the natural attenuation of contaminants in redox-fluctuating environments.

Enhanced Arsenate Immobilization by Kaolinite via Heterogeneous Pathways during Ferrous Iron Oxidation.

Clay minerals are ubiquitous in subsurface environments and have long been recognized as having a limited or negligible impact on the fate of arsenic (As) due to their negatively charged surfaces. Here, we demonstrate the significant role of kaolinite (Kln), a pervasive clay mineral, in enhancing As(V) immobilization during ferrous iron (Fe(II)) oxidation at near-neutral pH. Our results showed that Fe(II) oxidation alone was not capable of immobilizing As(V) at relatively low Fe/As molar ratios (≤2) due to the generation of Fe(III)-As(V) nanocolloids that could still migrate easily as truly dissolved As did. In the presence of kaolinite, dissolved As(V) was significantly immobilized on the kaolinite surfaces via forming Kln-Fe(III)-As(V) ternary precipitates, which had large sizes (at micrometer levels) to reduce the As mobility. The kaolinite-induced heterogeneous pathways for As(V) immobilization involved Fe(II) adsorption, heterogeneous oxidation of adsorbed Fe(II), and finally heterogeneous nucleation/precipitation of Fe(III)-As(V) phases on the edge surfaces of kaolinite. The surface precipitates were mixtures of amorphous basic Fe(III)-arsenate and As-rich hydrous ferric oxide. Our findings provide new insights into the role of clay minerals in As transformation, which is significant for the fate of As in natural and engineered systems.

Uptake and translocation of cadmium and trace metals in common rice varieties at different growth stages.

Rice (Oryza sativa) is an important nutritional grain for the majority of Asian countries, but it is also a major source of cadmium (Cd) accumulation. A pot experiment was carried out to investigate the Cd uptake and translocation of high Cd (IR-50) and low Cd (White Ponni) rice cultivars in Cd-contaminated soils. The findings revealed that Cd impacts on rice development and growth differed depending on rice cultivars. Soil Cd levels in the seedling stage exceeded the critical levels (3-6 mg kg-1) only 5.0 mg kg-1 Cd treatment for the IR-50 (7.47 mg kg-1). At higher Cd treatments (1.0 and 5.0 mg kg-1), morphometric characteristics and yield of grains showed a declining and increasing trend in both rice varieties, respectively. The accumulation of Cd was higher in soil and roots during seedling and tillering stages, whereas in booting and maturity stages increased in stems and leaves in IR-50 and WP rice varieties. Cd levels in rice grains above the maximum allowable limit (0.4 mg kg-1) only in IR-50 (0.51 mg kg-1) rice cultivar at maturity stage. The EF of Cd were classified as minor enrichment to 'moderate enrichment' in both rice cultivars. TF values exhibited > 1 in booting and maturity stages in both rice cultivars at higher Cd treatments. The study concluded that the IR-50 rice variety exhibited increased Cd intake and transported to various parts of rice plants, particularly grains. The findings indicate that WP rice cultivar is more resistant to Cd toxicity, reducing health hazards for persons who preferred the staple food rice.

Progress in enhancing the remediation performance of microbial fuel cells for contaminated groundwater.

Microbial fuel cells (MFCs) have become more prevalent in groundwater remediation due to their capacity for power generation, removal of pollution, ease of assembly, and low secondary contamination. It is currently being evaluated for practical application in an effort to eliminate groundwater pollution. However, a considerable majority of research was conducted in laboratories. But the operational circumstances including anaerobic characteristics, pH, and temperature vary at different sites. In addition, the complexity of contaminants and the positioning of MFCs significantly affect remediation performance. Taking the aforementioned factors into consideration, this review summarizes a bibliography on the application of MFCs for the remediation of groundwater contamination during the last ten decades and assesses the impact of environmental conditions on the treatment performance. The design of the reactor, including configuration, dimensions, electrodes, membranes, separators, and target contaminants are discussed. This review aims to provide practical guidance for the future application of MFCs in groundwater remediation.

Bibliometric analysis and systematic review of electrochemical methods for environmental remediation.

Electrochemical methods are increasingly favored for remediating polluted environments due to their environmental compatibility and reagent-saving features. However, a comprehensive understanding of recent progress, mechanisms, and trends in these methods is currently lacking. Web of Science (WoS) databases were utilized for searching the primary data to understand the knowledge structure and research trends of publications on electrochemical methods and to unveil certain hotspots and future trends of electrochemical methods research. The original data were sampled from 9080 publications in those databases with the search deadline of June 1st, 2022. CiteSpace and VOSviewer software facilitated data visualization and analysis of document quantities, source journals, institutions, authors, and keywords. We discussed principles, influencing factors, and progress related to seven major electrochemical methods. Notably, publications on this subject have experienced significant growth since 2007. The most frequently-investigated areas in electrochemical methods included novel materials development, heavy metal remediation, organic pollutant degradation, and removal mechanism identification. "Advanced oxidation process" and "Nanocomposite" are currently trending topics. The major remediation mechanisms are adsorption, oxidation, and reduction. The efficiency of electrochemical systems is influenced by material properties, system configuration, electron transfer efficiency, and power density. Electro-Fenton exhibits significant advantages in achieving synergistic effects of anodic oxidation and electro-adsorption among the seven techniques. Future research should prioritize the improvement of electron transfer efficiency, the optimization of electrode materials, the exploration of emerging technology coupling, and the reduction in system operation and maintenance costs.

New insights on the enhanced non-hydroxyl radical contribution under copper promoted TiO2/GO for the photodegradation of tetracycline hydrochloride.

TiO2/graphene oxide (GO) as photocatalyst in the photo-degradation of multitudinous pollutants has been extensively studied. But its low photocatalytic efficiency is attributed to the high band gap energy which lead to low light utilization. Cu-TiO2/GO was synthesized via the impregnation methods to enhance the catalytic performance. The Cu-TiO2/GO reaction rate constant for photo-degradation of pollutants (tetracycline hydrochloride, TC) was about 1.4 times that of TiO2/GO. In 90 min, the removal ratio of Cu-TiO2/GO for TC was 98%, and the maximum degradation ratio occurred at pH 5. After five cycles, the removal ratio of Cu-TiO2/GO still exceeded 98%. UV-visible adsorption spectra of Cu-TiO2/GO showed that its band gap was narrower than TiO2/GO. Electron paramagnetic resonance (EPR) spectra test illustrated the generation rate of •O2- and •OH was higher in Cu-TiO2/GO system than TiO2/GO and TiO2 system. The contribution sequence of oxidative species was •O2- > holes (h+) > •OH in both TiO2/GO and Cu-TiO2/GO system. Interestingly, the contribution of •OH in Cu-TiO2/GO was less than that in TiO2/GO during the photo-degradation process. This phenomenon was attributed to the better adsorption performance of Cu-TiO2/GO which could reduce the accessibility of TC to •OH in liquid. The enhanced non­hydroxyl radical contribution could be attributed to that the more other active species or sites on (nearby) the surface of Cu-TiO2/GO generated after doping Cu. These results provide a new perspective for the tradition metal-doped conventional catalysts to enhance the removal of organic pollutants in the environment.

Deciphering the toxic effects of metals in gold mining area: Microbial community tolerance mechanism and change of antibiotic resistance genes.

Mine tailing dumps represent significant threats to ecological environments due to the presence of toxic substances. The present work investigated the relationship among microbial activity, the community, antibiotic resistance genes (ARGs) and trace metals in soil surrounding gold mine tailings. Using microbial metabolic activity and high-throughput sequencing analysis, we found the trace metals Cd and Hg could be main factors influencing the microbial community. According to bacterial co-occurrence pattern analysis, the effects of total cadmium and total mercury on bacterial diversity are potentially mediated by influencing bacteria community in the keystone module II. Additionally, most of metal-resistant bacteria belong to Actinobacteria and Proteobacteria, and the metal tolerance suggested to be linked with various functions including replication, recombination and repair, as well as inorganic ion transport and metabolism based on PICRUSt2 analysis. We also found that metals generated by mining activity may trigger the co-selection of antibiotic resistance in the phyla Actinobacteria and Proteobacteria due to co-resistance or cross resistance. Additionally, PLS-PM analysis revealed that metals could indirectly affect ARGs by influencing bacterial diversity in gold mining areas.

Plasmonic silver/silver oxide nanoparticles anchored bismuth vanadate as a novel visible-light ternary photocatalyst for degrading pharmaceutical micropollutants.

The degradation of pharmaceutical micropollutants is an intensifying environmental problem and synthesis of efficient photocatalysts for this purpose is one of the foremost challenges worldwide. Therefore, this study was conducted to develop novel plasmonic Ag/Ag2O/BiVO4 nanocomposite photocatalysts by simple precipitation and thermal decomposition methods, which could exhibit higher photocatalytic activity for mineralized pharmaceutical micropollutants. Among the different treatments, the best performance was observed for the Ag/Ag2O/BiVO4 nanocomposites (5 wt.%; 10 min's visible light irradiation) which exhibited 6.57 times higher photodegradation rate than the pure BiVO4. Further, the effects of different influencing factors on the photodegradation system of tetracycline hydrochloride (TC-HCl) were investigated and the feasibility for its practical application was explored through the specific light sources, water source and cycle experiments. The mechanistic study demonstrated that the photogenerated holes (h+), superoxide radicals (•O2-) and hydroxyl radicals (•OH) participated in TC-HCl removal process, which is different from the pure BiVO4 reaction system. Hence, the present work can provide a new approach for the formation of novel plasmonic photocatalysts with high photoactivity and can act as effective practical application for environmental remediation.

Adsorptive removal of bisphenol A, chloroxylenol, and carbamazepine from water using a novel ß-cyclodextrin polymer.

The emerging organic micro-pollutants, such as bisphenol A (BPA), chloroxylenol (PCMX) and carbamazepine (CBZ), have raised concerns owing to their adverse impact on human health and ecological security. In this study, a novel cyclodextrin polymer (ß-CDP) has been successfully prepared by nucleophilic substitution of ß-cyclodextrin with tetrafluoroterephthalonitrile (TFP). The removal of three emerging organic micro-pollutants (BPA, CBZ and PCMX) by ß-CDP under a single or mixture adsorption system was examined, and the adsorption behavior was investigated by adsorption kinetics and isotherm study. The maximum adsorption capacity of ß-CDP for BPA, PCMX and CBZ according to Langmuir isotherm in single system was 164.4, 144.1 and 136.4 mg/g, respectively. Compared with single system, the competitive adsorption of each pollutant on ß-CDP in mixture system was only slightly inhibited. Changing the pH, raising the presence of fulvic acid (FA) or ionic strength had no significant influence on the adsorption of BPA, PCMX and CBZ onto ß-CDP. The removal of these three organic micro-pollutants was related to the value of logKow of the contaminants. These results demonstrated remarkable advantages of ß-CDP material relevant to organic micro-pollutants removal in wastewater treatment.

Hyperspectral Image Classification with Capsule Network Using Limited Training Samples.

Deep learning techniques have boosted the performance of hyperspectral image (HSI) classification. In particular, convolutional neural networks (CNNs) have shown superior performance to that of the conventional machine learning algorithms. Recently, a novel type of neural networks called capsule networks (CapsNets) was presented to improve the most advanced CNNs. In this paper, we present a modified two-layer CapsNet with limited training samples for HSI classification, which is inspired by the comparability and simplicity of the shallower deep learning models. The presented CapsNet is trained using two real HSI datasets, i.e., the PaviaU (PU) and SalinasA datasets, representing complex and simple datasets, respectively, and which are used to investigate the robustness or representation of every model or classifier. In addition, a comparable paradigm of network architecture design has been proposed for the comparison of CNN and CapsNet. Experiments demonstrate that CapsNet shows better accuracy and convergence behavior for the complex data than the state-of-the-art CNN. For CapsNet using the PU dataset, the Kappa coefficient, overall accuracy, and average accuracy are 0.9456, 95.90%, and 96.27%, respectively, compared to the corresponding values yielded by CNN of 0.9345, 95.11%, and 95.63%. Moreover, we observed that CapsNet has much higher confidence for the predicted probabilities. Subsequently, this finding was analyzed and discussed with probability maps and uncertainty analysis. In terms of the existing literature, CapsNet provides promising results and explicit merits in comparison with CNN and two baseline classifiers, i.e., random forests (RFs) and support vector machines (SVMs).

Cyclodextrin modified filter paper for removal of cationic dyes/Cu ions from aqueous solutions.

A filter paper was functionalized with ß-cyclodextrin and citric acid via esterification reaction for the removal of dyes and Cu ions from aqueous solutions. The adsorption capacity and removal performance of the modified filter paper (MFP) was investigated using static and dynamic adsorption experiments. The static adsorption data fit well the Langmuir and pseudo-second-order models, and the adsorption capacity of Methylene Blue (MB), Brilliant Green (BG), Rhodamine-B (RB) and Cu(II) over the MFP were 124.6 mg/g, 130.4 mg/g, 99.7 mg/g and 39.1 mg/g, respectively, which are much higher than the unmodified filter paper (below 2 mg/g). Even better, the decolorization performance and Cu(II) removal of MFP are remarkable in dynamic adsorption. The effluent can reach the National Standard for dyeing and finishing of textile industry of China after three cycles in a continuous filtration-adsorption system. This method provides a new pathway to achieve high efficiency removal of dyes and metal ions from wastewater.

Enhanced biocatalytic laccase production using agricultural waste in solid-state fermentation by Aspergillus oryzae for p-chlorophenol degradation.

Agricultural residues are one of the most cost-effective and readily accessible carbon resources for producing commercially significant enzymes. Several enzymes have been used in different industries like pharmaceuticals, foods, textiles, and dyes that can be generated by various species of microbes found in waste from agriculture. The current research investigated laccase production by Aspergillus oryzae utilizing agricultural wastes. Physical and chemical properties, including pH, temperature, sucrose, yeast extract, and copper sulfate levels, were optimized. The utilization of the response surface methodology along with the centralized composite design method, which assesses multiple media parameters and utilizes a two-level experimental approach, aids in determining the variable and its significance in increasing production quality. The centralized composite design enhancement showed that the optimal conditions for highest laccase activity (623.16 U/mL) were pH 7.0, temperature 25 °C, corn cobs as substrate, sucrose (2.0 %), yeast extract (1.0 %), and copper sulfate (0.1 mM) level. The laccase enzyme was optimized using various pH, temperature, metal ions, and inhibitors combinations. The extracted laccase enzyme maximum activity was attained at pH 6.0 and 40 °C. The inclusion of divalent ions can enhance laccase activity, while the use of various inhibitors decreases laccase activity. Under various pH circumstances, the Aspergillus oryzae laccase enzyme can successfully degrade p-chlorophenol. The present study describes statistically validated optimal methodologies for enhancing laccase synthesis, leading to a laccase production technique that is simultaneously highly efficient and economically profitable, with possible use of p-chlorophenol degradation.

Adsorption of oxidized humic acid onto redox-inert mineral surfaces induces formation of hydroxyl radicals and carbon dynamics.

The dark formation of hydroxyl radicals (·OH) from O2 activation by reduced humic substances at oxic-anoxic interfaces has been extensively documented. However, their generation in oxic subsurface environments is typically overlooked due to the scarcity of electron donors, especially in the presence of minerals. In this study, the formation of ·OH during the adsorption of oxidized humic acids (HA) onto redox-inert minerals was investigated under oxic and pH-neutral conditions. Batch experiment results demonstrated that the adsorption of oxidized HA onto aluminum (hydr)oxide and Fe-free clay minerals induces the formation of ·OH (e.g., 16/28 µmol/g C) without the addition of exogenous electron donors. In contrast, the interaction of oxidized HA alone with O2 did not result in measurable ·OH production. The enhanced electron-donating capacity (EDC) and humification of the whole HA (mainly in adsorbed state) were measured after adsorption. The surface-catalyzed polymerization of oxidizable polyphenols in HA is proposed as the plausible mechanism for the observed EDC enhancement, which in turn triggers O2 activation for ·OH production. Furthermore, substantial chemical alterations of lignins and condensed aromatics within HA were observed, producing more compounds exhibiting higher molecular weight, aromaticity, O/C ratio, and nominal oxidation state of carbon. It is indicated that the contribution of oxidative polymerization outweighs ·OH oxidation in the molecular transformation of adsorbed HA. Overall, our findings extend the understanding of HA-induced ·OH production from oxic-anoxic interfaces to the oxic zone and present a novel pathway for the abiotic transformation of recalcitrant organic matter in subsurface environments with extensive surface water-groundwater interactions.

Quality evaluation and health risk assessment of karst groundwater in Southwest China.

Groundwater in karst regions is of immense value due to its vital support for regional ecosystems and residents' livelihoods. However, it is simultaneously threatened by multi-source pollution from agricultural non-point sources, industrial and domestic point sources, and mining activities. This study focuses on the Guangxi of China, which features typical karst topography, aiming to thoroughly assess the groundwater quality and related health risks in Guangxi, especially identifying the impacts of various key pollution sources on the groundwater environment. A total of 1912 groundwater samples were collected, covering an area of approximately 237,600 km2. The spatial distribution of pollutants was analysed using the Nemeroww index method and Kriging interpolation, while multivariate statistical and cluster analysis methods were employed to identify the main types of pollution sources. Furthermore, based on the human health risk assessment model of the U.S. Environmental Protection Agency (US EPA), a risk assessment was conducted for key pollutants. The results revealed widespread heavy metal contamination in Guangxi's groundwater, particularly with concentrations of Mn, As, Al, Pb reaching up to 9.4 mg/L, 2.483 mg/L, 37.95 mg/L, 4.761 mg/L, respectively, significantly exceeding China's national Class III groundwater quality standards. Cluster analysis indicated that mining and industrial activities are the primary sources of pollution. The health risk assessment demonstrated that these activities pose a significant risk to public health. The aim of this study is to provide a scientific basis for the protection of the groundwater environment in Guangxi and other karst areas, the formulation of pollution prevention and control strategies, and the optimization of urban and industrial land use layouts. Future research should focus on advanced isotopic and molecular biological techniques to trace pollution sources more precisely and evaluate the effectiveness of pollution control measures.

Evaluation of groundwater quality with multi-source pollution based on source identification and health risks.

Groundwater is a crucial water supply source in Chengdu City, western China, a region experiencing significant water scarcity. The sources of inorganic pollutants in groundwater and their potential health risks are of great concern. In this study, based on 156 groundwater samples collected in 2021 in the study area were analyzed for hydrochemical characterization and controlling factors. The Positive Matrix Factorization (PMF) model was used for contaminant source analysis, and Monte Carlo Simulation (MCS) combined with the Health Risk Evaluation Model (HREM) was used to quantify the health risks. The results indicate that the groundwater in the study area is predominantly of the Ca·Na-SO4·HCO3, Ca·Na-HCO3·SO4 and Ca-HCO3·SO4 types, mainly influenced by the combination of evaporation-concentration-crystallization and rock leaching-weathering. K+, Na+, and Cl- mainly originate from the weathering and dissolution of potassium feldspar and rock salt, while Ca2+, Mg2+, HCO3-, and SO42- primarily come from the weathering and dissolution of sulfate minerals. The main sources of groundwater pollution and their contributions are as follows: domestic pollution (25.6 %), dissolution-filtration-evaporation-concentration action (22.8 %), hydrogeochemical evolution (15.8 %), water-rock interactions (12.8 %), primary geologic context (12.1 %), and agricultural non-point source pollution (11.0 %). Cl- and As are the primary contributors to non-carcinogenic and carcinogenic risks, respectively. Non-carcinogenic risks are below USEPA standards, while the average carcinogenic risk for arsenic exceeded the maximum acceptable risk level thresholds by 23 and 109 times for adults and children, respectively. Non-carcinogenic and carcinogenic health risks were mainly influenced by pollutant concentrations. The primary geological background and domestic pollution contributed the most to the non-carcinogenic risk for adults (50.3 %) and children (77.1 %), and 38.2 % and 10.3 %, respectively. This study highlights the necessity of establishing a comprehensive groundwater pollution monitoring system, enhancing industrial waste management practices, and raising public awareness to mitigate contamination and ensure the sustainable use of groundwater resources in Chengdu City.

Studies on the transfer effect of aged polyethylene microplastics in soil-plant system.

The widespread use of polyethylene (PE) agricultural films has led to a large accumulation of microplastics in soil, and the environmental effects of microplastics on soil-plants have received increasing attention. In the actual soil environment, microplastics undergo significant changes in their physicochemical properties due to aging, accompanied by complex ecological and environmental effects. However, the quantitative understanding of the environmental effects of microplastic aging in soil-plant systems is still unclear. Therefore, this study investigated the effects of aged and unaged PE microplastics on ecological functions and microplastic transfer mechanisms in soil-plant system, and confirmed the transport behavior of micrometer-sized microplastics (26 µm) within maize plants, expanding the upper size limit of existing studies on microplastic transport within plants. The accumulation of microplastics in maize was also quantitatively assessed in combination with the self-established method of Eu marked PE. The mobility ratio of microplastics from soil to roots, roots to stems, and stems to leaves was 1.07%, 0.76%, and 103.28%, respectively. This study provides a scientific understanding for the environmental effects of microplastics in soil-plants systems quantitatively.

Entrapping of fullerenes, nanotubes, and inorganic nanoparticles by a DNA-chitosan complex: a method for nanomaterials removal.

We report a protocol for entrapping of various water-dispersed nanomaterials: fullerenes, multiwall carbon nanotubes, quantum dots (semiconductor nanoparticles), and gold nanorods, into a DNA-chitosan complex. In contrast to small-size nanomaterial particles, the bulky DNA-chitosan interpolyelectrolyte complex incorporating the dispersed nanomaterials can be easily separated from aqueous media by centrifugation, filtration, or decantation. While the removal of nanoparticles by centrifugation is equally efficient for every type of nanoparticles and reaches 100%, the higher efficiency of the nanomaterials removal by other two methods is favored by larger size of nanoparticles. The application of this entrapping protocol for removal of nanomaterials from water is discussed.

Effects of different fertilization methods on Lolium multiflorum Lam. growth and bacterial community in waste slag.

Waste slag has low nutrient content, so it has insufficient nutrient cycling and transformation in the soil ecosystem. There are few studies on the application of oligotrophic phosphate-solubilizing bacteria and phosphate (P) fertilizer to improve the properties of waste slags. In this study, three oligotrophic bacterial strains with P solubilizing activity, namely, Bacillus subtilis 2C (7.23 µg/mL), Bacillus subtilis 6C (4.07 µg/mL), and Bacillus safensis 2N (5.05 µg/mL), were isolated from waste slags. In the pot experiment, compared with no application of P fertilizer, inoculation of Bacillus subtilis 2C with a 50% recommended dose of P fertilizer significantly increased the available phosphorus (AP), total phosphorus (TP), and total nitrogen (TN) in slag by 33.16%, 76.70%, and 233.33%, respectively. The N, P uptake and fresh weight of Lolium multiflorum Lam. were significantly improved by 114.15%, 139.02%, and 100%, respectively. The analysis of the bacterial community showed that the application of P fertilizer decreased the diversity and richness of the bacterial community, and with the addition of phosphorus fertilizer and Bacillus subtilis 2C, the bacterial community in the slag developed towards eutrophication. Redundancy analysis (RDA) showed that the TP content in the slag was significantly correlated with the bacterial community (P = 0.001, < 0.01), followed by the TN content. This study on different P fertilizer application methods can provide some basic ideas for improving the performance of waste slag.

Molecular structure-dependent contribution of reactive species to organic pollutant degradation using nanosheet Bi2Fe4O9 activated peroxymonosulfate.

Iron-based catalysts have attracted increasing attention in heterogeneous activation of peroxymonosulfate (PMS). However, the activity of most iron-based heterogenous catalysts is not satisfactory for practical application and the proposed activation mechanisms of PMS by iron-based heterogenous catalyst vary case by case. This study prepared Bi2Fe4O9 (BFO) nanosheet with super high activity toward PMS, which was comparable to its homogeneous counterpart at pH 3.0 and superior to its homogeneous counterpart at pH 7.0. Fe sites, lattice oxygen and oxygen vacancies on BFO surface were believed to be involved in the activation of PMS. By using electron paramagnetic resonance (EPR), radical scavenging tests, 57Fe Mössbauer and 18O isotope-labeling technique, the generation of reactive species including sulfate radicals, hydroxyl radicals, superoxide and Fe (IV) were confirmed in BFO/PMS system. However, the contribution of reactive species to the elimination of organic pollutants very much depends on their molecular structure. The effect of water matrices on the elimination of organic pollutants also hinges on their molecular structure. This study implies that the molecular structure of organic pollutants governs their oxidation mechanism and their fate in iron-based heterogeneous Fenton-like system and further broadens our knowledge on the activation mechanism of PMS by iron-based heterogeneous catalyst.

As(III) removal from aqueous solutions using simultaneous oxidation and adsorption process by hierarchically magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite.

In the present study, a magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite was synthesized by hydrothermal method and applied for As(III) removal by oxidation and adsorption process. Individual property of the entire material (i.e. magnetic property of Fe3O4, mesoporous surface property of C-dot and oxidation property of MnO2) make the composite efficient with good adsorption capacity for As(III) adsorption. The Fe3O4@C-dot@MnO2 nanocomposite had a saturation magnetization of 26.37 emu/g and it magnetically separated within 40 s. The Fe3O4@C-dot@MnO2 nanocomposite was able to reduce the 0.5 mg/L concentration of As(III) to 0.001 mg/L in just 150 min at pH 3. Pseudo-second-order kinetic and Langmuir isotherm model agreed with experimental data. The uptake capacity of Fe3O4@C-dot@MnO2 nanocomposite was 42.68 mg/g. The anions like chloride, sulphate and nitrate did not show any effect on removal but carbonate and phosphate influenced the As(III) removal rate. Regeneration was studied with NaOH and NaClO solution and the adsorbent was used for repeated five cycles above 80% removal capacity. The XPS studies proposed that As(III) first oxidized to As(V) then adsorb on the composite surface. This study shows the potential applicability of Fe3O4@C-dot@MnO2 nanocomposite to high extent and gives a suitable path for the proficient removal of As(III) from wastewater.