Recent advances in application of iron-manganese oxide nanomaterials for removal of heavy metals in the aquatic environment

A novel sodium Iron silicate composite with chitosan for efficient removal of Cd(II) ions from water

Cadmium ions constitute a major threat to human health and the environment owing to their toxicity, bioaccumulation, and persistence in water bodies, causing renal dysfunction, cancer, and cardiovascular diseases. Hence, this study reports the facile fabrication of a novel sodium iron oxide silicate@amorphous sodium iron silicate product (S1) and its chitosan composite (S1@chitosan) for the high-performance separation of Cd(II) ions from aquatic environments. The Brunauer-Emmett-Teller surface area, total pore volume, and mean pore diameter of S1 were 94.97 m2/g, 0.5853 cm3/g, and 25.65 nm, respectively, while those for S1@chitosan were 30.94 m2/g, 0.09518 cm3/g, and 12.31 nm, respectively. The reduction in pore diameter, pore volume, and surface area confirms the successful functionalization of S1 with chitosan, as the chitosan coating partially blocks and fills the pores, reducing the available surface area and porosity. Also, scanning electron microscope (SEM) images revealed an uneven surface morphology for S1 and a more textured and rougher surface for S1@chitosan, supporting the incorporation of chitosan. Besides, energy-dispersive X-ray spectroscopy (EDX) and CHN analyses affirmed the existence of chitosan in the composite through the detection of carbon and nitrogen elements, characteristic of chitosan. The optimum conditions for the removal of Cd(II) ions were determined to be a contact time of 70 min for S1 and 50 min for S1@chitosan, a pH of 7.50, and a temperature of 298 K. The maximum sorption capacities were 284.09 mg/g for S1 and 389.11 mg/g for S1@chitosa. The removal mechanism for S1 primarily involves ion exchange, while S1@chitosan utilizes both ion exchange and complexation through the amino and hydroxyl groups of chitosan. Regeneration using HCl confirmed the effective reusability of both adsorbents over five successive cycles. The adsorption process was found to be chemical, exothermic, and best described by the pseudo-second-order kinetic model and Langmuir isotherm.

Atomic Insights into the Heterogeneous Crystallization of Manganese (Oxyhydr)oxides on Typical Iron (Oxyhydr)oxides: from Adsorption to Oxidation to Crystallization

Heterogeneous crystallization of manganese (oxyhydr)oxides (MnOx) on iron (oxyhydr)oxides (FeOx) is crucial for the biogeochemical cycling of Mn, yet atomic-level insights into this process are important but relatively limited. Herein, we revealed the distinct adsorption, oxidation, and crystallization mechanisms of Mn on hematite (Hem), ferrihydrite (Fhy), and goethite (Gth). Gth exhibited highest ability in Mn(II) removal and oxidation, followed by Hem and Fhy. Manganite and hausmannite were the main MnOx products with distinct proportions, and morphologies cross the systems. MnOx growth mechanisms involve surface-induced nucleation, crystallization by particle attachment (CPA), and self-catalyzed growth. On Fhy, self-catalyzed growth was dominant; for Gth, surface-induced nucleation was prevalent, supplemented by CPA; and Hem combined all three mechanisms. These distinct mechanisms led to nanoparticles primarily of hausmannite on Gth and nanowires of manganite and hausmannite on Hem and Fhy, with those on Hem displaying lower aspect ratios. Differences in MnOx structure and morphology were attributed to Mn(II)-FeOx complexation, FeOx electronic band structure, and crystal structure mismatch between MnOx and FeOx, which respectively influenced the direct and indirect electron transfer and heterogeneous nucleation efficiency. This work advances our understanding of MnOx crystallization on FeOx at the nanoscale, explaining the diverse morphology and structure of MnOx in different environments.

New Insight into a Green Process for Iron Manganese Ore Utilization: Efficient Separation of Manganese and Iron Based on Phase Reconstruction by Vanadium Recycle

The difficulty of separating iron and manganese is a bottleneck issue in the traditional utilization process of iron manganese ore (Fe-Mn ore). In this work, ammonium polyvanadate (APV), an intermediate product in the vanadium industry, was introduced innovatively to convert the manganese-containing phase in Fe-Mn ore into manganese pyrovanadate (Mn2V2O7) and iron and manganese were then separated efficiently through the acid leaching process. The migration of manganese, iron, and vanadium were systematically studied through XRD, SEM, and leaching experiments. Results show that during the mixed roasting process of Fe-Mn ore and APV, V2O5, the decomposition product of APV, reacts with the decomposition product of manganese minerals in Fe-Mn ore, Mn2O3, to produce the target product, acid-soluble Mn2V2O7. Iron and silicon exist in the form of Fe2O3 and SiO2 like in Fe-Mn ore. After the two-step leaching process of the sample roasted at 850 °C with n(MnO2)/n(V2O5) of 2.25, the leaching ratios of manganese, iron and vanadium are 84.57%, 0.046%, and 4.68%, respectively, achieving the efficient separation of manganese with iron and vanadium. MnCO3 obtained by carbonization and precipitation from the manganese-containing leaching solution can be used as an intermediate product of manganese metallurgy or manganese chemical industry. APV obtained by alkaline leaching and precipitation from the vanadium- and iron-containing tailing can be recycled into the roasting system as the roasting additive. The TFe content in the iron-containing tailing reaches 57.21 wt.%, which meets the requirement of iron concentrate. More than 99 wt.% of vanadium from the additive APV can be recovered and recycled back into the Fe-Mn ore utilization process by APV recycling and wastewater recycling, making the Fe-Mn ore utilization with APV roasting a green process.

Preparation of a lanthanum-modified flocculant and its removal performance towards phosphorus and fluoride in yellow phosphorus wastewater

Polysilicate-ferric-calcium-lanthanum (PSFCL) was synthesized through a co-polymerization method in order to treat the yellow phosphorus wastewater. Its morphology, composition and functional group were analyzed by X-ray Diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FTIR), Scanning Electron Microscopic (SEM) and X-ray Photoelectron Spectroscopy (XPS), respectively. The optimization of the flocculant was also investigated, including La/Si molar ratio, pH, agitation time, dosage and sedimentation time. Results showed that PSFCL has reached an excellent removal efficiency of 95% and 97% towards phosphorus and fluoride, respectively. It could be inferred that charge neutralization, bridging effect and ligand exchange were the main coagulation mechanisms. As a whole, after the introduction of lanthanum, PSFCL was found to be a promising flocculant in yellow phosphorus wastewater treatment owing to its high removal efficiency and simple synthesis route.

Green synthesized nanoscale zero-valent iron impregnated tea residue biochar efficiently captures metal(loid)s for sustainable water remediation

Pristine or modified nanoscale zero-valent iron (nZVI) synthesized though conventional chemical reduction have been widely recommended for remediating metal(loid)-contaminated water. However, their eco-friendliness is often challenged with the concomitant bio-toxicity and secondary environmental risks. Alternatively, this study utilized waste tea leaves extract and remaining residue as the reducing agent and pyrolytic matrix to innovatively fabricate a green synthesized nZVI impregnated tea residue biochar (G-nZVI/TB). Since the performances, mechanisms, and potential applications of G-nZVI/TB for simultaneous removal of metal cation and metalloid anion remain unclear, typical synthetic aqueous solutions and real wastewaters were systematically tested. The adsorption isotherms showed that the calculated maximum adsorption capacities of G-nZVI/TB for various meta(loid)s were 1.4-10.7 fold higher than those of TB. Although Cd(II) competed with Pb(II) for adsorption on G-nZVI/TB, they synergistically promoted As(III) sequestration. The SEM and FTIR spectra demonstrated that G-nZVI nanoparticles were uniformly dispersed onto TB framework, whereas newly grafted groups like Fe-O, C=O, and C-N accelerated metal(loid)s bonding. The results of batch experiments, XRD, and XPS comprehensively elucidated that metal(loid)s were predominantly separated from polynary systems via electrostatic adsorption, ion exchange, co-precipitation, cation-π interaction, oxidation-complexation, and B-type ternary complexation. In synthetic industrial wastewater and real paddy field drainage with divergent environmental conditions, 0.5 g L-1 optimized G-nZVI/TB efficiently captured over 92.4% metal(loid)s at their concentrations ranging from 0.04 to 3 mg L-1, indicating its excellent selective adsorption effectiveness and extensive compatibility for practical application in reusing multi-metal(loid)s contaminated wastewater. Overall, these findings provide new insights into developing green nano-functional materials for sustainable water purification.

Advancements in magnetic catalysts: Preparation, modification, and applications in photocatalytic and environmental remediation

Owing to their widely available source materials, simple magnetic separation, and low cost, magnetic catalysts have demonstrated considerable application potential in modern photocatalysis technologies and environmental remediation. This review summarizes the synthesis and modification methods of magnetic catalysts and describes recent advances using different synthesis methods. Several key problems still need to be solved in the existing progress, such as the fact that the catalytic activity of magnetic catalysts decreases over time. Under an external magnetic field, magnetic catalysts exhibit satisfactory energy bandgaps and charge transfer rates for photocatalysis, enabling wide and comprehensive photocatalytic applications. In addition, they are strong candidate materials for wastewater treatment and new-energy applications. In summary, the review provides future directions for the development of novel magnetic catalysts, contaminant removal, and even large-scale practical applications.

A portability self-powered sensor facilitates sensitive Cd2+ detection: Dual mechanism and three quantitative mode

As a common heavy metal contaminant, Cd2+ has adverse effects on food safety and consumer health. It is very important for human health to realize highly sensitive Cd2+ detection methods. The self-powered sensing system based on enzyme biofuel cells (EBFCs) does not need an external power supply, which can simplify the experimental equipment and has great application value in portable detection. Thus, the biosensor is innovatively integrated into the screen-printed electrode to construct a new type of portable sensor suitable for on-site and real-time Cd2+ detection. Hybridization chain reaction (HCR) combined with the Cd2+-dependent deoxyribose (DNAzyme) signal amplification strategy is used to enhance the detection sensitivity while specifically recognizing the Cd2+. Moreover, the self-powered sensor combines with smartphones to realize quantitative Cd2+ detection without other instruments and has the characteristic of Effectively improving the hazard detection technology is essential to ensure food safety. Portability, simplicity, and speed are suitable for real-time Cd2+ detection in the field. The dual mechanism and three quantitative modes combining colorimetric and two electrical signals output modes are adopted to realize the visualization and accurate detection. A series of research results confirm that this strategy is of great significance to strengthen the development of intelligent Cd2+ technology, expand the application of self-powered sensing technology, and improve the safety detection system.

Hematite nanomaterial from a tropical freshwater ecosystem: Geological, environmental, and industrial implications

Synthetic hematite (Fe2O3) nanoparticles are extensively explored for medicine, optics, and environmental remediation. However, natural iron nanoparticles in a freshwater ecosystem have not been well characterized. Here we report the presence of natural iron nanoparticles in a tropical freshwater ecosystem in southern India. These iron nanoparticles that exist as slime in the natural water system were characterized through a multiproxy investigation involving Field-Emission Scanning Electron Microscopy (FE-SEM), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), and Raman spectroscopy and BET analyses. These nanoparticles exist as amorphous hematite (Fe2O3), with the XRD peaks matching that of the iron arsenate compound. Fe2O3 occurs as mesoporous hollow microspheres with a size range of 14.97 to 61.3 nm and a surface area of 48.45m2/g. Further, the identification of Bacillus cereus in the slime suggests its role in iron sequestration, indicating a biogeochemical origin, which we infer is a particularly common phenomenon in tropical river basins where lateritic soils prevail. This study is the first to describe natural iron nanoparticles in a tropical freshwater ecosystem. It identifies their amorphous hematite structure and biogeochemical origin, offering new insights into their ecological roles and potential applications. This discovery presents an opportunity for utilizing this slime as an important source of hematite nanomaterials, with potential industrial applications.

Engineered biochars for simultaneous immobilization of as and Cd in soil: Field evidence

Agricultural soil contamination by potentially toxic elements (PTEs) such as arsenic (As) and cadmium (Cd) poses a serious threat to food security. Immobilization serves as a widely used approach for the remediation of PTEs contaminated soils, nevertheless, the long-term effectiveness for the simultaneous immobilization of both cations and oxyanions remains a challenge. In order to effectively enhance the synergistic immobilization effect of soil As and Cd contaminated by multiple elements and improve the ecological environment of farmland. In this study, a typical polluted tailings area farmland was selected for situ immobilization experiments, and biochar was prepared from cow manure (CMB), rice straw (RSB), and pine wood (PWB) as raw materials. On this basis, the pristine biochar was modified with ferric chloride (F), potassium permanganate (K), magnesium chloride (M), and aluminum chloride (A), respectively. Furthermore, the immobilization effect of modified biochar on As-Cd and the stress effect on soil respiration were investigated. The results showed that CMB and RSB reduced the bioavailability of heavy metals, potassium permanganate has strong oxidizing properties, and the strong oxidability of potassium permanganate stimulated the generation of more oxygen-containing functional groups on the surface of biochar, thereby enhancing the adsorption and complexation effect of modified materials on As and Cd. Among them, the extracted Cd concentration of Diethylenetriamine pentaacetic acid (DTPA) in KCMB and KRSB in 2020 decreased by 8.23-43.12% and 9.67-35.29% compared to other treatments, respectively. Meanwhile, the KCMB and KRSB treatments also reduced the enrichment of As and Cd in plant tissues. In addition, the dissolved organic carbon (DOC) content in KCMB treatment was relatively high, and the carbon stability of the material was weakened. Simultaneously, the soil respiration emission of KCMB treatment was increased by 5.63% and 11.93% compared to KRSB and KPWB treatments, respectively. In addition, the structural equation also shows that DOC has a large positive effect on soil respiration. In summary, the KRSB treatment effectively achieve synergistic immobilization of As-Cd and provide important guiding significance for green and low-carbon remediation of polluted farmland.

A new understanding of the regulatory mechanism by which Fe/Mn nanoparticles boost Bisphenol A removal using Comamonas testosteroni

Green synthesized iron/manganese nanoparticles (Fe/Mn NPs), acted as an exogenous promoter to enhance the lignin-degrading bacteria Comamonas testosteroni FJ17 resulting in more efficient removal of bisphenol A (BPA). Batch experiments demonstrated that removal efficiency of BPA via cells at a BPA concentration of 10 mg·L-1 increased by 20.9 % when exposed to 100 mg·L-1 Fe/Mn NPs after 48 h (93.63 %) relative to an unexposed control group (72.70 %). TEM and 3D-EEM analysis confirmed that the cell membrane thickness increased from 47 to 80 nm under Fe/Mn NPs exposure, and the TB-EPS secretion was promoted. Meanwhile, Fe/Mn NPs facilitated greater electron transfer capacity of c-cytochrome (0.55 V reduction peak) and an unknown cytochrome substance (0.7 V oxidation peak) on the surface of cells. Studies of the effect of Fe/Mn NPs on both the growth and activity of laccase cells showed that both biomass and laccase secretion increased significantly during the logarithmic growth period (6-36 h). LC-MS analysis and toxicity assessment indicated that Fe/Mn NPs decreased the degradation time of BPA and efficiently reduced the toxicity of its by-products. Transcriptomic analysis revealed 315 up-regulation of the key genes associated with energy supply, membrane translocation, and metabolic pathways upon exposure to Fe/Mn NPs. Such as MFS transporter (2.27-fold), diguanylate cyclase (1.76-fold) and protocatechuate-3,4-dioxygenase (1.62-fold). Overall, Fe/Mn NPs accelerated proliferation by enhancing metabolic capacity and nutrient transport processes, which serves to improve the efficiency of BPA removal.

Adsorption of Pb(II) in water by modified chitosan-based microspheres and the study of mechanism

In this study, a fresh three-dimensional microsphere adsorbent (CATP@SA3) was successfully synthesized by Attapulgite (ATP) and combining Chitosan (CS), incorporating them into a Sodium alginate (SA) solution, and crosslinking them in a CaCl2 solution. Multiple analyses, including XRD, TGA, FTIR, XPS, SEM-EDS, and BET were utilized to comprehensively characterize the structural makeup of CATP@SA3. These analyses revealed the presence of beneficial functional groups like hydroxyl, amino, and carboxyl groups that enhance the adsorption efficiency in adsorption procedures. CATP@SA3 was evaluated by studying different factors, including material ratio, contact time, dosage, solution pH, Pb(II) concentration, temperature, ionic strength, and aqueous environment. Three adsorption models, including kinetic, isotherm, and thermodynamic, were fitted to the experimental data. The findings demonstrated that the maximum Pb(II) adsorption capacity of CATP@SA3 was 1081.36 mg/g, with a removal rate that exceeded 70 % even after 5 cycles of use. Furthermore, correlation adsorption models revealed that the adsorption process of Pb(II) with CATP@SA3 was driven by a chemical predominantly reaction.

Investigating the role of poly-γ-glutamic acid in Pennisetum giganteum phytoextraction of mercury-contaminated soil

Farmland mercury (Hg) pollution poses a significant threat to human health, but there is a lack of highly efficient phytoextraction for its remediation at present. This study investigates the impact of poly-γ-glutamic acid (γ-PGA) on the phytoextraction capabilities of Pennisetum giganteum (P. giganteum) in Hg-contaminated soil. Our research indicates that amending γ-PGA to soil markedly enhances the assimilation of soil Hg by P. giganteum and transformation of Hg within itself, with observed increases in Hg concentrations in roots, stems, and leaves by 1.1, 4.3, and 18.9 times, respectively, compared to the control. This enhancement is attributed to that γ-PGA can facilitate the hydrophilic and bioavailable of soil Hg. Besides, γ-PGA can stimulate the abundance of Hg-resistance bacteria Proteobacteria in the rhizosphere of P. giganteum, thus increasing the mobility and uptake of soil Hg by P. giganteum roots. Moreover, the hydrophilic nature of Hg-γ-PGA complexes supports their transport via the apoplastic pathway, across the epidermis, and through the Casparian strip, eventually leading to immobilization in the mesophyll tissues. This study provides novel insights into the mechanisms of Hg phytoextraction, demonstrating that γ-PGA significantly enhances the effectiveness of P. giganteum in Hg uptake and translocation. The findings suggest a promising approach for the remediation of Hg-contaminated soil, offering a sustainable and efficient strategy for environmental management and health risk mitigation.

Simultaneous removal of nitrate, manganese, zinc, and bisphenol a by manganese redox cycling system: Performance and mechanism

The manganese(Mn) redox cycling system in this work was created by combining Mn(IV)-reducing bacteria MFG10 with Mn(II)-oxidizing bacteria HY129. The biomanganese oxides (BMO) generated by strain HY129 were transformed by strain MFG10 to Mn(II), finishing the Mn redox cycling, in which nitrate (NO3--N) was converted to nitrite, which was further reduced to nitrogen gas. The system could achieve 85.7 % and 98.8 % elimination efficiencies of Mn(ⅠⅠ) and NO3--N, respectively, at Mn(ⅠⅠ) = 20.0 mg/L, C/N = 2.0, pH = 6.5, and NO3--N = 16.0 mg/L. The removal of bisphenol A (BPA) and zinc (Zn(II)) at 36 h reached 91.7 % and 89.7 % under the optimal condition, respectively. Furthermore, the Mn redox cycling system can reinforce the metabolic activity and electron transfer activity of microorganisms. The findings showed that the adsorption by bioprecipitation throughout the Mn cycling was responsible for the elimination of Zn(II) and BPA.

Advancing Antimony(III) Adsorption: Impact of Varied Manganese Oxide Modifications on Iron-Graphene Oxide-Chitosan Composites

Antimony (Sb) is one of the most concerning toxic metals globally, making the study of methods for efficiently removing Sb(III) from water increasingly urgent. This study uses graphene oxide and chitosan as the matrix (GOCS), modifying them with FeCl2 and four MnOx to form iron-manganese oxide (FM/GC) at a Fe/Mn molar ratio of 4:1. FM/GC quaternary composite microspheres are prepared, showing that FM/GC obtained from different MnOx exhibits significant differences in the ability to remove Sb(III) from neutral solutions. The order of Sb(III) removal effectiveness is MnSO4 > KMnO4 > MnCl2 > MnO2. The composite microspheres obtained by modifying GOCS with FeCl2 and MnSO4 are selected for further batch experiments and characterization tests to analyze the factors and mechanisms influencing Sb(III) removal. The results show that the adsorption capacity of Sb(III) decreases with increasing pH and solid-liquid ratio, and gradually increases with the initial concentration and reaction time. The Langmuir model fitting indicates that the maximum adsorption capacity of Sb(III) is 178.89 mg/g. The adsorption mechanism involves the oxidation of the Mn-O group, which converts Sb(III) in water into Sb(V). This is followed by ligand exchange and complex formation with O-H in FeO(OH) groups, and further interactions with C-OH, C-O, O-H, and other functional groups in GOCS.

Fabrication of nitrogen-doped carbon dots biomass composite hydrogel for adsorption of Cu (II) in wastewater or soil and DFT simulation for adsorption mechanism

With the increase of Cu (II) content, its bioaccumulation becomes a potential pollution to the environment. It is necessary to design an economical and efficient material to remove Cu (II) without causing other environmental hazards. A novel material of alginate composite bead (ALG@NCDs) was synthesized by embedding N-doped carbon dots into pure alginate bead for the adsorption of Cu (II) from wastewater and contaminated soil. The initial concentration, the amount of adsorbent, temperature, adsorption time, and pH value were optimized for the adsorption of Cu (II). According to the Langmuir isothermal adsorption model, the maximum adsorption amount of the material to Cu (II) was 152.44 mg/g. The results of selective adsorption showed that ALG@NCDs had higher affinity to Cu (II) than to Pb (II), Co (II), Ni (II), and Zn (II). After five adsorption-desorption experiment, adsorption capacity of the ALG@NCDs was kept 89% of the initial adsorption capacity. Its Cu (II) adsorption mechanism was studied by density functional theory calculations. In addition, the material could effectively adsorb Cu (II) and release the phytonutrient Ca (II) simultaneously when applied to actual wastewater and soil. The fabricated ALG@NCDs would be a promising material for the adsorption of Cu (II) from wastewater or soil.

Current progress on manganese in constructed wetlands: Bibliometrics, effects on wastewater treatment, and plant uptake

Constructed wetlands (CWs) are a pollutant treatment design inspired by natural wetlands and are widely utilized for the removal of common pollutants. The research focus lies in the circulation of manganese (Mn) in the environment to enhance pollutant removal within CWs. This paper provides a comprehensive review of recent advancements in understanding the role and effects of Mn in chemical weapons, based on literature retrieval from 2002 to 2021. Ecological risk assessment and heavy metals within CWs emerge as current areas of research interest. Mn sources within CWs primarily include natural deposition, heavy metal wastewater, and intentional addition. The cycling between Mn(II) and Mn(IV) facilitates enhanced wastewater treatment within CWs. Moreover, employing a Mn matrix proves effective in reducing ammonia nitrogen wastewater, organic pollutants, as well as heavy metals such as Cd and Pb, thereby addressing complex pollution challenges practically. To comprehensively analyze influencing factors on the system's performance, both internal factors (biological species, design parameters, pH levels, etc.) and external factors (seasonal climate variations, precipitation patterns, ultraviolet radiation exposure, etc.) were discussed. Among these factors, microorganisms, pollutants, and temperature are the most important influencing factors, which emphasizes the importance of these factors for wetland operation. Lastly, this paper delves into plant absorption of Mn along with coping strategies employed by plants when faced with Mn poisoning or deficiency scenarios. When utilizing Mn for the regulation of constructed wetlands, it is crucial to consider the tolerance levels of associated plant species. Furthermore, the study predicts future research hotspots encompass high-efficiency catalysis techniques, matrix-filling approaches, and preparation of resource utilization methods involving Mn nanomaterials.

The mechanisms of ·OH formation in MnO2 and oxalate system: Implication for ATZ removal

Manganese oxides (MnO2) are commonly prevalent in groundwater, sediment and soil. In this study, we found that oxalate (H2C2O4) dissolved MnO2, leading to the formation of Mn(II)/(III), CO2(aq) and reactive oxygen species (·CO2-/O2·-/H2O2/·OH). Notably, CO2(aq) played a crucial role in ·OH formation, contributing to the degradation of atrazine (ATZ). To elucidate underneath mechanisms, a series of reactions with different gas-liquid ratios (GLR) were conducted. At the GLR of 0.3, 3.76, and + ∞ 79.4 %, 5.32 %, and 5.28 % of ATZ were eliminated, in which the cumulative ·OH concentration was 39.6 μM, 8.11 μM, and 7.39 μM and the cumulative CO2(aq) concentration was 11.2 mM, 4.7 mM, and 2.8 mM, respectively. The proposed reaction pathway was that CO2(aq) participated in the formation of a ternary complex [C2O4-Mn(II)-HCO4·3 H2O]-, which converted to a transition state (TS) as [C2O4-Mn(II)-CO3-OH·3 H2O]-, then decomposed to a complex radical [C2O4-Mn(II)-CO3·3 H2O]·- and ·OH after electron transfer within TS. It was novel to discover the role of CO2(aq) for ·OH yielding during MnO2 dissolution by H2C2O4. This finding helps revealing the overlooked processes that CO2(aq) influenced the fate of ATZ or other organic compounds in environment and providing us ideas for new technique development in contaminant remediation. ENVIRONMENTAL IMPLICATION: Manganese oxides and oxalate are common in soil, sediment and water. Their interactions could induce the formation of Mn(II)/(III), CO2(aq) and ·CO2-/O2·-/H2O2. This study found that atrazine could be effectively removed due to ·OH radicals under condition of high CO2(aq) concentration. The concentrations of Mn (0.0002-8.34 mg·L-1) and CO2(aq) (15-40 mg·L-1) were high in groundwater, and the surface water or rainfall seeps into groundwater and bring organic acids, which might promote the ·OH formation. The results might explain the missing steps of herbicides transformation in these environments and be helpful in developing new techniques in remediation in future.

Polyethyleneimine-modified iron-doped birnessite as a highly stable adsorbent for efficient arsenic removal

Remediation of arsenic contamination is of great importance given the high toxicity and easy mobility of arsenic species in water and soil. This work reports a new and stable adsorbent for efficient elimination of arsenic by coating polyethyleneimine (PEI) molecules onto the surface of iron-doped birnessite (Fe-Bir). Characterization results of surface microstructure and crystalline feature (scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS), etc.) suggest that Fe-Bir/PEI possesses a fine particle structure, inhibiting the agglomeration of birnessite-typed MnO2 and offering abundant active sites for arsenic adsorption. Fe-Bir/PEI is capable of working in a wide pH range from 3 to 11, with an efficient removal capacity of 53.86 mg/g at initial pH (pH0) of 7. Meanwhile, commonly coexisting anions (NO3-, SO42-, and Cl-) and cations (Na+, K+, Ca2+ and Mg2+) pose no effect on the arsenic removal performance of Bir/PEI. Fe-Bir/PEI exhibits a good reusability for arsenic removal with low Mn and Fe ions leaching after 5 cycles. Besides, Fe-Bir/PEI possesses efficient remediation capability in simulated As-contaminated soil. The modification of PEI in Fe-Bir/PEI can adsorb newly formed As(V), which is impossible for the adsorbent without PEI. Further, the arsenic removal mechanism of Fe-Bir/PEI is revealed with redox effect, electrostatic attraction and hydrogen bonding.

Effect of Shape and Size on Synthesized Triple (Co/Ni/Zn)-Doped α-Fe2O3 Nanoparticles on their Photocatalytic and Scavenging Properties

Co/Ni/Zn triple doped [Formula: see text]-Fe2O3 nanoparticles (NPs) have been synthesized via polyvinylpyrrolidone (PVP)/Azadirachta indica (A. Indica) leaf extract coating. XRD, UV–Vis, SEM, TEM, EDS, Raman spectroscopy, FTIR, VSM were used to characterize the synthesized NPs. XRD pattern revealed that the crystallite size of NPs ranges from 14[Formula: see text]nm to 21[Formula: see text]nm. Spherical NPs were found by SEM/TEM examination ranging from 16[Formula: see text]nm to 26[Formula: see text]nm of doped [Formula: see text]-Fe2O3 NPs. Analysis of the magnetic properties of [Formula: see text]-Fe2O3 NPs revealed antiferromagnetic characteristics, convergence between magnetization curves (MS), and switching field distribution dM/dh below an irreversible temperature of [Formula: see text][Formula: see text]K. Produced catalyst was used for the degradation of anionic azo dye Malachite green (MG) and Rhodamine blue (RhB) dyes under the influence of UV radiation. RhB and MG were reduced as a result of the doped [Formula: see text]-Fe2O3 catalyzing the conversion of dissolved O2 to hydroxyl radicals (OH) when exposed to visible light. This shows that the main active radical specifically engaged in the photo-catalytic breakdown of dyes is OH. The most effective photo-catalyst was determined by investigating the proposed doped [Formula: see text]-Fe2O3 NPs reusability over three cycles. The catalyst was retrieved and utilized three times after the reaction without suffering a substantial loss of catalytic activity. The plant-mediated [Formula: see text]-Fe2O3 NPs have significant antioxidant activity due to their higher phenolic content. These have a promising future with potential applications in health, aging, food preservation, cosmetics, agriculture and environmental protection.

Excellent coagulation performance of polysilicate aluminum ferric for treating oily wastewater from Daqing gasfield: Responses to polymer properties and coagulation mechanism

The polysilicate aluminum ferric (PSAF) was synthesized via copolymerization of polysilicic acid (PSi), AlCl3 and FeCl3 for treating oily wastewater from Daqing gas field. This study investigated the effects of key preparation factors such as the degree of PSi's preactivation and the ratio of (Fe + Al)/Si and Al/Fe on both polymerization and coagulation performance exhibited by PSAF. To determine the optimal timing for introducing Al3+ and Fe3+, zeta potential, viscosity and particle size were investigated. Additionally, infrared spectroscopy, X-ray powder diffraction, polarizing microscopy and scanning electron microscope analysis were employed to investigate the structure and morphology of PSAF. The results indicate that under conditions characterized by a SiO2 mass fraction of 2.5% and pH = 4.5, an optimal timing for introducing Al3+ and Fe3+ is at 100 min when PSi exhibits moderate polymerization along with sufficient stability. When considering molar ratios such as (Al + Fe)/Si being 6:4 and Al/Fe being 5:5, respectively, PSAF falls within a "stable zone" enabling storage period up to 32 days. Moreover, Jar test results demonstrate that at a dosage of 200 mg/L PSAF for oily wastewater treatment in gas fields could reach the maximum turbidity removal efficiency up to 99.5% while oil removal efficiency reach 88.6% without pH adjustment. The copolymerization facilitates the formation of larger PSAF aggregates with positive potential, thereby augmenting the coagulants' adsorption bridging and charge neutralization capabilities. As a result, PSAF has great potential as a practical coagulant for treating oil-containing wastewater in industrial settings.

Effect of soil organic matter-mediated electron transfer on heavy metal remediation: Current status and perspectives

Soil contamination by heavy metals poses major risks to human health and the environment. Given the current status of heavy metal pollution, many remediation techniques have been tested at laboratory and contaminated sites. The effects of soil organic matter-mediated electron transfer on heavy metal remediation have not been adequately studied, and the key mechanisms underlying this process have not yet been elucidated. In this review, microbial extracellular electron transfer pathways, organic matter electron transfer for heavy metal reduction, and the factors affecting these processes were discussed to enhance our understanding of heavy metal pollution. It was found that microbial extracellular electrons delivered by electron shuttles have the longest distance among the three electron transfer pathways, and the application of exogenous electron shuttles lays the foundation for efficient and persistent remediation of heavy metals. The organic matter-mediated electron transfer process, wherein organic matter acts as an electron shuttle, promotes the conversion of high valence state metal ions, such as Cr(VI), Hg(II), and U(VI), into less toxic and morphologically stable forms, which inhibits their mobility and bioavailability. Soil type, organic matter structural and content, heavy metal concentrations, and environmental factors (e.g., pH, redox potential, oxygen conditions, and temperature) all influence organic matter-mediated electron transfer processes and bioremediation of heavy metals. Organic matter can more effectively mediate electron transfer for heavy metal remediation under anaerobic conditions, as well as when the heavy metal content is low and the redox potential is suitable under fluvo-aquic/paddy soil conditions. Organic matter with high aromaticity, quinone groups, and phenol groups has a stronger electron transfer ability. This review provides new insights into the control and management of soil contamination and heavy metal remediation technologies.

Induced crystallization for the simultaneous removal of hardness-iron-manganese in groundwater: An experimental study

Hardness, iron, and manganese are common groundwater pollutants, that frequently surpass the established discharge standard concentrations. They can be effectively removed, however, through induced crystallization. This study has investigated the effectiveness of the simultaneous removal of hardness-iron-manganese and the crystallization kinetics of calcium carbonate during co-crystallization using an automatic potentiometric titrator. The impacts pH, dissolved oxygen (DO), and ion concentration on the removal efficiency of iron and manganese and their influence on calcium carbonate induced crystallization were assessed. The results suggest that pH exerts the most significant influence during the removal of hardness, iron, and manganese, followed by DO, and then the concentration of iron and manganese ions. The rate of calcium carbonate crystallization increased with pH, stabilizing at a maximum of 10-10 m/s. Iron and manganese can be reduced from an initial level of 4 mg/L to <0.3 mg/L and 0.1 mg/L, respectively. The removal rate of iron, however, was notably higher than that of manganese. The DO concentration correlates positively with the removal of iron and manganese but has minimal impact on the calcium carbonate crystallization process. During the removal of iron and manganese, competitive interactions occur with the substrate, as increases in the concentration of one ion will inhibit the removal rate of the other. Characterization of post-reaction particles and mechanistic analysis reveals that calcium is removed through the crystallization of CaCO3, while most iron is removed through precipitation as Fe2O3 and FeOOH. Manganese is removed via two mechanisms, crystallization of manganese oxide (MnO2/Mn2O3) and precipitation. Overall, this research studies the removal efficiency of coexisting ions, the crystallization rate of calcium carbonate, and the mechanism of simultaneous removal, and provides valuable data to aid in the development of new removal techniques for coexisting ions.

Understanding the role of manganese oxides in retaining harmful metals: Insights into oxidation and adsorption mechanisms at microstructure level

The increasing intensity of human activities has led to a critical environmental challenge: widespread metal pollution. Manganese (Mn) oxides have emerged as potentially natural scavengers that perform crucial functions in the biogeochemical cycling of metal elements. Prior reviews have focused on the synthesis, characterization, and adsorption kinetics of Mn oxides, along with the transformation pathways of specific layered Mn oxides. This review conducts a meticulous investigation of the molecular-level adsorption and oxidation mechanisms of Mn oxides on hazardous metals, including adsorption patterns, coordination, adsorption sites, and redox processes. We also provide a comprehensive discussion of both internal factors (surface area, crystallinity, octahedral vacancy content in Mn oxides, and reactant concentration) and external factors (pH, presence of doped or pre-adsorbed metal ions) affecting the adsorption/oxidation of metals by Mn oxides. Additionally, we identify existing gaps in understanding these mechanisms and suggest avenues for future research. Our goal is to enhance knowledge of Mn oxides' regulatory roles in metal element translocation and transformation at the microstructure level, offering a framework for developing effective metal adsorbents and pollution control strategies.

Nanotechnology-based analytical techniques for the detection of contaminants in aquatic products

Food safety of aquatic products has attracted considerable attention worldwide. Although a series of conventional bioassays and instrumental methods have been developed for the detection of pathogenic bacteria, heavy metal residues, marine toxins, and biogenic amines during the production and storage of fish, shrimp, crabs et al., the nanotechnology-based analyses still have their advantages and are promising since they are cost-efficient, highly sensitive and selective, easy to conduct, facial design, often require no sophisticated instruments but with excellent detection performance. This review aims to summarize the advances of various biosensing strategies for bacteria, metal ions, and small molecule contaminants in aquatic products during the last five years, The review highlights the development in nanotechnologies applied for biorecognition process, signal transduction and amplification methods in each novel approach, the nuclease-mediated DNA amplification, nanomaterials (noble metal nanoparticle, metal-organic frameworks, carbon dots), lateral flow-based biosensor, surface-enhanced Raman scattering, microfluidic chip, and molecular imprinting technologies were especially emphasized. Moreover, this study provides a view of current accomplishments, challenges, and future development directions of nanotechnology in aquatic product safety evaluation.

Utilization of biochar for remediation of heavy metals in aqueous environments: A review and bibliometric analysis

Biochar usage for removing heavy metals from aqueous environments has emerged as a promising research area with significant environmental and economic benefits. Using the PICO approach, the research question aimed to explore using biochar to remove heavy metals from aqueous media. We merged the data from Scopus and the Web of Science Core Collection databases to acquire a comprehensive perspective of the subject. The PRISMA guidelines were applied to establish the search parameters, identify the appropriate articles, and collect the bibliographic information from the publications between 2010 and 2022. The bibliometric analysis showed that biochar-based heavy metal remediation is a research field with increasing scholarly attention. The removal of Cr(VI), Pb(II), Cd(II), and Cu(II) was the most studied among the heavy metals. We identified five main clusters centered on adsorption, water treatment, adsorption models, analytical techniques, and hydrothermal carbonization by performing keyword co-occurrence analysis. Trending topics include biochar reusability, modification, acid mine drainage (AMD), wastewater treatment, and hydrochar. The reutilization of heavy metal-loaded spent biochar includes transforming it into electrodes for supercapacitors or stable catalyst materials. This study provides a comprehensive overview of biochar-based heavy metal remediation in aquatic environments and highlights knowledge gaps and future research directions.

Removal of methylene blue by acrylic polymer adsorbents loaded with magnetic iron manganese oxides: Synthesis, characterization, and adsorption mechanisms

Dyes pose significant risks for aquatic environments and biological health in general owing to their non-biodegradable nature, carcinogenicity, and toxicity. The effective treatment of dye wastewater has become an important research topic. In this study, acrylic polymers (AP) loaded with magnetic iron manganese oxides (MIMO) (AP/MIMO) were prepared and used for the first time for the adsorption of methylene blue (MB). Carbon in AP/MIMO exists predominantly in the C-H and C-C forms, with its content reaching 50.7%. Oxygen and nitrogen in AP/MIMO exist mainly in the -CO- and -N-C forms, with contents of up to 41.5% and 73.3%, respectively. MB removal by AP/MIMO was consistent with the pseudo-second-order kinetic model (R2 = 0.99), equilibrium was achieved within 20 min, and the highest MB capacity of 2611.23 mg g-1 was predicted by the Langmuir isotherm model (R2 = 0.91-0.94). AP/MIMO exhibited excellent MB adsorption performance in the pH range of 4-10, with a removal efficiency higher than 99.0% (MB = 100 mL 1000 mg L-1; AP/MIMO = 50 mg). Thermodynamic indicators, such as positive entropy (ΔS0; 98.30 J⋅mol-1⋅K-1), negative Gibbs free energy (ΔG0; -29.40, -28.50, and -27.50 KJ⋅mol-1), and positive enthalpy (ΔH0; 2.30 KJ⋅mol-1), demonstrated that MB removal by AP/MIMO was autonomous, favorable, and endothermic. In addition, the integration of experimental results and theoretical calculations verified that electrostatic interactions were the primary mechanism for MB adsorption at carboxyl sites on AP/MIMO. The total interaction energy between AP and MB was -310.43 kJ⋅mol-1, and the electrostatic effect had a decisive contribution to the MB adsorption, with a value of up to -341.06 kJ⋅mol-1. AP and MB were most likely bound by -COO and S atoms. Overall, AP/MIMO exhibits high adsorption capacity and shows potential as a high-performance magnetic polymer for MB removal.

Adsorption potential of orange rind-based nanosorbents for the removal of cadmium(II) and chromium(VI) from contaminated water

Heavy metals (HMs) in water are highly poisonous and carcinogenic agents for human health. To alleviate the toxic impacts of HMs, green remediation technologies are the need of the hour. In this regard, different nanosorbents (CMCG@ORP, ORAC, NiO/NPs, and NiO@ORAC/NCs) were synthesized in the present study, and the percentage removal of heavy metals [chromium(VI) and cadmium(II) ions] was evaluated. The nanosorbents were characterized by using FTIR, SEM, UV-Vis spectroscopy, and XRD. UV-Vis spectroscopy confirmed the synthesis of nanosorbents such as NiO/NPs and NiO@ORAC/NCs at 330.5 nm and 352.55 nm, respectively. The characterization studies show that the surface of synthesized nano-sorbents was highly coarse, uneven, and abrasive. XRD pattern deduced that the sample was of single phase, and no other impurity was detected except the face-centered cubic-phase peak of NiO. The maximum adsorption of Cd (91%) and Cr (92%) was found at initial concentrations of 100 and 60 ppm respectively at contact time = 180 min, temperature 25 °C, and with an adsorbent dose of 0.5 g. Isothermal, kinetic, and thermodynamic studies were also performed to evaluate the adsorption mechanisms and feasibility of the process. Adsorption mostly followed Freundlich isotherm which indicates the multilayer adsorption phenomenon and the negative value of Gibb's free energy showed the spontaneous nature and feasibility of the adsorption reaction. Surface complexation, ion exchange, surface precipitation, and the phenomenon of physical adsorption occurred on the sorbent surface which led to the attachment of Cd and Cr to the tested nanosorbents. In conclusion, NiO@ORAC/NCs were the most effective in the alleviation of Cd(II) and Cr(VI) ions in contaminated water.

Mercapto-based palygorskite modified soil micro-biology and reduced the uptake of heavy metals by Salvia miltiorrhiza in cadmium and lead co-contaminated soil

Salvia miltiorrhiza is an important traditional Chinese medicinal and edible plant that can easily accumulate excessive cadmium (Cd) and lead (Pb) from contaminated soils. The soil contaminated with heavy metals severely threatened the quality of S. miltiorrhiza products. In this study, we investigated the effects of mercapto-based palygorskite (MPAL), a new passivation amendment, on restraining the uptake of Cd and Pb by S. miltiorrhiza, and the impact on soil micro-ecology. Results showed that the application of MPAL prominently enhanced the biomass and antioxidant enzyme activities of S. miltiorrhiza. With the treatment of 4% MPAL, the Cd and Pb contents in the roots were significantly decreased by 81.42% and 69.09%, respectively. The active ingredients of S. miltiorrhiza, including Danshensu, Cryptotanshinone, Tanshinone I and Tanshinone II were remarkedly increased by 1899.46%, 5838.64%, 54.23% and 200.78%, respectively. In addition, MPAL decreased the bio-availability of Cd and Pb by speciation transformation, which simultaneously boosted the activities of cellulase and sucrase. The application of MPAL also improved the bacterial community composition. These findings revealed that the application of MPAL regulated the soil micro-ecology, positively modified the growth and obstructed the Cd and Pb accumulation in S. miltiorrhiza.

Photo-assisted "co-movement catalysis": CoFe2O4/CNS heterojunction based portable electrochemical sensor for simultaneous detection of Pb2+ and Cd2+ in natural water

Heavy metal ions (HMIs) seriously threaten human health even under trace conditions. Therefore, accurate, efficient and simultaneous detection of multiple HMIs is of great significance. Here, a strategy of "co-movement catalysis" based on photo-assisted electrochemical catalysis is proposed by constructing a flexible electrochemical sensor with CoFe2O4/CNS heterojunction-modified nickel foam as the working electrode for simultaneous detection of HMIs. Regarding photo-assisted catalysis, CoFe2O4/CNS nanocomposites formed a p-n type heterojunction, effectively separating photo-generated electron-hole pairs and reducing photo-generated carriers' recombination rate, leading to the catalytic reaction of photogenerated electrons and holes with HMIs and atoms to improve the efficiency of preconcentration and stripping, further amplifying the electrochemical signal. Regarding electrochemical catalysis, the CoFe2O4 spinel contains variable valence transition metal ions Fe2+/Fe3+ and Co2+/Co3+, which can reduce and oxidize HMIs circularly, further enhancing the sensor's sensitivity. The portable sensor based on "co-movement catalysis" exhibited sensitive detection performance. The linear range is 0.100-10.0 μM for Pb2+ and 1.00-10.0 μM for Cd2+, with the detection limit of 0.0310 μM for Pb2+ and 0.219 μM for Cd2+, respectively. The recovery rate of the sensor to natural water samples is between 96% and 105%, which proves its development potential in environmental monitoring.

Functionalization of Silica Nanoparticles by 5-Chloro-8-quinolinol as a New Nanocomposite for the Efficient Removal and Preconcentration of Al3+ Ions from Water Samples

In this work, silica nanoparticles were modified by 5-chloro-8-quinolinol as a new nanocomposite for the efficient elimination and preconcentration of Al³⁺ ions from several water sources. The fabricated composite was characterized utilizing XRD, SEM, FT-IR, TEM, CHN elemental analyzer, and N₂ adsorption/desorption analyzer. The XRD demonstrated the existence of a wide peak at 2θ = 30°. Also, all the peaks of silica were severely reduced, which confirms the success of loading the 5-chloro-8-quinolinol on the surface of the silica. The SEM and TEM images demonstrated that the composite resembled cotton, and this confirms that 5-chloro-8-quinolinol was successfully loaded on the silica surface. The specific surface area, the average pore size, and the total pore volume of the synthesized composite are 80.53 m²/g, 3.26 nm, and 0.185 cc/g, respectively. In addition, the greatest uptake capacity of the synthesized composite toward aluminum ions is 95.06 mg/g. The results indicated that the adsorption of aluminum ions onto the silica/5-chloro-8-quinolinol composite follows the Langmuir isotherm and pseudo-second-order model. Moreover, the adsorption of aluminum ions by the silica/5-chloro-8-quinolinol composite is spontaneous, chemical, and thermodynamically favorable. The values of % recovery were more than 97%, whereas the values of % RSD were less than 3.5%. Hence, this confirms the effectiveness of the proposed method in the determination of aluminum ions in real water samples.

Biologically-induced synthetic manganese carbonate precipitate (BISMCP) for potential applications in heavy metal removal

Heavy metal pollution of water is a burning issue of today's world. Among several strategies involved for heavy metal remediation purpose, biomineralization has shown great potential. Of late, research has been focused on developing effective mineral adsorbents with reduced time and cost consumption. In this present paper, the Biologically-Induced Synthetic Manganese Carbonate Precipitate (BISMCP) was produced based on the biologically-induced mineralization method, employing Sporosarcina pasteurii in aqueous solutions containing urea and MnCl2. The prepared adsorbent was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and BET surface area analyzer. EDX analysis showed the elements in the crystal BISMCP were Mn, C, and O. XRD result of BISMCP determined the crystal structure, which is close to rhodochrosite (MnCO3). Spectral peaks of FTIR at 1641.79 cm-1 confirmed the appearance of C[bond, double bond]O binding, with strong stretching of CO32- in Amide I. From the six kinds of BISMCP produced, sample MCP-6 has the higher specific surface area by BET analysis at 109.01 m2/g, with pore size at 8.76 nm and higher pore volume at 0.178 cm3/g. These specifications will be suitable as an adsorbent for heavy metal removal by adsorption process. This study presents a preliminary analysis of the possibility of BISMCP for heavy metals adsorption using ICP multi-element standard solution XIII (As, Cr, Cd, Cu, Ni, and Zn). BISMCP formed from 0.1 MnCl2 and 30 ml of bacteria volume (MCP-6) produced a better adsorbent material than others concentrations, with the adsorption efficiency of total As at 98.9%, Cr at 97.0%, Cu at 94.7%, Cd at 88.3%, Zn at 48.6%, and Ni at 29.5%. Future work could be examined its efficiency adsorbing individual heavy metals.

Preparation of manganese-oxides-coated magnetic microcrystalline cellulose via KMnO4 modification: Improving the counts of the acid groups and adsorption efficiency for Pb(II)

Herein, the manganese-oxides-coated magnetic microcrystalline cellulose (MnOx@Fe₃O₄@MCC) was prepared by coprecipitation and subsequently modified with KMnO₄ solution at room temperature, which was in turn applied for the removal of Pb(II) from wastewater. The adsorption properties of Pb(II) on MnOx@Fe₃O₄@MCC were investigated. The kinetics and isothermal data of Pb(II) were described well by the Pseudo-second-order model and the Langmuir isotherm model, respectively. At pH = 5, 318 K, the Langmuir maximum Pb(II) adsorption capacity of MnOx@Fe₃O₄@MCC was 446.43 mg/g, which is higher than many documented bio-based adsorbents. The results of Fourier transform infra-red and X-ray photoelectron spectroscopy indicated that the adsorption mechanisms for Pb(II) mainly involved surface complexation, ion exchange, electrostatic interaction and precipitation. Interestingly, the increased amount of carboxyl group on the surface of microcrystalline cellulose modified by KMnO₄ was one of the important reasons for the high Pb(II) adsorption performance of MnOx@Fe₃O₄@MCC. Furthermore, MnOx@Fe₃O₄@MCC exhibited excellent activity (70.6 %) after five consecutive regeneration cycles, indicating its high stability and reusability. Endorsing to the cost-effectiveness, environmentally friendliness, and reusable nature, MnOx@Fe₃O₄@MCC can be counted as a great alternative contender for the remediation of Pb(II) from industrial wastewater.

Modification of Multiwalled Carbon Nanotubes and Their Mechanism of Demanganization

Multiwalled carbon nanotubes (MWCNTs) were modified by oxidation and acidification with concentrated HNO₃ and H₂SO₄, and the modified multiwalled carbon nanotubes (M-MWCNTs) and raw MWCNTs were characterized by several analytical techniques. Then the demanganization effects of MWCNTs and M-MWCNTs were well investigated and elucidated. The experimental data demonstrated that the adsorption efficiency of Mn(II) could be greatly promoted by M-MWCNTs from about 20% to 75%, and the optimal adsorption time was 6 h and the optimal pH was 6. The results of the kinetic model studies showed that Mn(II) removal by M-MWCNTs followed the pseudo-second-order model. Isothermal studies were conducted and the results demonstrated that the experimental data fitted well with the three models. The reliability of the experimental results was well verified by PSO-BP simulation, and the present conclusion could be used as a condition for further simulation. The research results provide a potential technology for promoting the removal of manganese from wastewater; at the same time, the application of various mathematical models also provides more scientific ideas for the research of the mechanism of adsorption of heavy metals by nanomaterials.

Electrocoagulation removal of Pb, Cd, and Cu ions from wastewater using a new configuration of electrodes

A new configuration of aluminum electrodes has been performed in an electrocoagulation reactor (ECR) to remove toxic metals from synthetic wastewater. The ECR contains four concentric-cubic electrodes that were connected to the DC power supply with a bipolar mode. The ability of this reactor to eliminate 200 ppm Pb, 200 ppm Cd and 200 ppm Cu from wastewater was investigated under the effect of pH (4-10), applied current (0.2-2.6 A), and the reaction time of (4-60 min). Two grams of NaCl were added to each experiment to enhance the electrical conductivity and minimize the passivation of cathode surfaces. The experiments, analysis, and optimization were conducted using response surface methodology type Box-Behnken design (RSM-BBD) and the Minitab-statistical software program. The highest elimination of heavy metals was: Pb-99.73%, Cd-98.54%, and Cu-98.92% at pH 10, 1.4 A of the applied current, and 60 min of the reaction time. The total real consumption of anodes under these conditions was 0.55 g, and the energy consumption was 12.71 kWh/m3. All reactions of metal removal that occurred in the present EC reactor obey the kinetic of a first-order reaction. Thermodynamics parameters of present electrocoagulation removal of heavy metals indicate an endothermic, spontaneous nature, and random irregularity at the liquid-solid interaction. The highest values of removal efficiencies and the considerably lowest values of energy and electrode consumption proved that the electrocoagulation technology applies in wastewater treatment containing toxic metals.•The anode electrodes were perforated to decrease the amount of electrode consumption, while the cathode electrodes were not perforated.•The new EC reactor eliminated Pb-99.73%, Cd-98.54%, and Cu-98.92% of 200 mg/l of each metal at pH 10, applied current of 1.4 A, and reaction time of 60 min. Moreover, the consumption of energy and electrodes was significantly low.•The performance indicator (R²) of the studied responses was higher than 0.95.

Multifunctional ZnO:Gd@ZIF-8 hybrid nanocomposites with tunable luminescent-magnetic performance for potential bioapplication

Novel multifunctional ZnO:Gd@ZIF-8 hybrid inorganic-organic nanocomposites with tunable luminescent-magnetic performance were successfully fabricated using wet chemistry synthesis routes. Physico-chemical characterization including crystal structure, phase compositions, morphology, surface properties, as well as photoluminescent and magnetic characteristics was performed using powder X-ray diffraction (XRD), FT-IR analysis, transmission and scanning electron microscopies (TEM/SEM), N₂ adsorption/desorption, SQUID magnetometer, and photoluminescence spectroscopy. The biological studies of obtained materials, such as cytotoxicity profile and in vitro MRI imaging also investigated for potential use as contrast agents. Results showed that the doping with Gd³⁺ in a broad concentration range and the presence of ZIF-8 layer on ZnO affect the physico-chemical properties of the obtained composites. The obtained porous ZnO:Gd@ZIF-8 composites were highly crystalline with a large surface area. The XRD study indicated the formation of hexagonal wurtzite structure for ZnO and ZnO:Gd³⁺ (1-5 at.%). Luminescent studies showed, that ZnO is an ideal matrix for the incorporation of Gd³⁺ ions in a broad concentration range with efficient green luminescence. The PL intensity reached the maximum up to 5 at.% of Gd³⁺. The zeta potential values indicated the good stability of obtained nanoparticles. Proposed new materials with paramagnetic behavior and outstanding MR imaging capability could be used as potential contrast agents for magnetic resonance imaging.

Graphene Synthesis Techniques and Environmental Applications

Graphene is fundamentally a two-dimensional material with extraordinary optical, thermal, mechanical, and electrical characteristics. It has a versatile surface chemistry and large surface area. It is a carbon nanomaterial, which comprises sp² hybridized carbon atoms placed in a hexagonal lattice with one-atom thickness, giving it a two-dimensional structure. A large number of synthesis techniques including epitaxial growth, liquid phase exfoliation, electrochemical exfoliation, mechanical exfoliation, and chemical vapor deposition are used for the synthesis of graphene. Graphene prepared using different techniques can have a number of benefits and deficiencies depending on its application. This study provides a summary of graphene preparation techniques and critically assesses the use of graphene, its derivates, and composites in environmental applications. These applications include the use of graphene as membrane material for the detoxication and purification of water, active material for gas sensing, heavy metal ions detection, and CO₂ conversion. Furthermore, a trend analysis of both synthesis techniques and environmental applications of graphene has been performed by extracting and analyzing Scopus data from the past ten years. Finally, conclusions and outlook are provided to address the residual challenges related to the synthesis of the material and its use for environmental applications.

Enhancing mechanism of arsenic(iii) adsorption by MnO2-loaded calcined MgFe layered double hydroxide

The use of MnO2/MgFe-layered double hydroxide (MnO2/MgFe-LDH) and MnO2/MgFe-layered double oxide (MnO2/MgFe-LDO400 °C) for arsenic immobilization from the aqueous medium is the subject of this research. Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to characterise MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C. Based on our developed method, MnO2 was spread on the clay composites' surfaces in the form of a chemical bond. The clay composite exhibited a good adsorption effect on arsenic. The experimental findings fit the pseudo-second-order model well, indicating that the chemisorption mechanism played a significant role in the adsorption process. Furthermore, the Freundlich model suited the adsorption isotherm data of all adsorbents well. The recycling experiment showed that MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C exhibited good stability and reusability. In summary, MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C are promising for developing processes for efficient control of the pollutant arsenic.

pH and pCl Operational Parameters in Some Metallic Ions Separation with Composite Chitosan/Sulfonated Polyether Ether Ketone/Polypropylene Hollow Fibers Membranes

The development of new composite membranes is required to separate chemical species from aggressive environments without using corrective reagents. One such case is represented by the high hydrochloric acid mixture (very low pH and pCl) that contains mixed metal ions, or that of copper, cadmium, zinc and lead ions in a binary mixture (Cu-Zn and Cd-Pb) or quaternary mixture. This paper presents the obtaining of a composite membrane chitosan (Chi)-sulfonated poly (ether ether ketone) (sPEEK)-polypropylene hollow fiber (Chi/sPEEK/PPHF) and its use in the separation of binary or quaternary mixtures of copper, cadmium, zinc, and lead ions by nanofiltration and pertraction. The obtained membranes were morphologically and structurally characterized using scanning electron microscopy (SEM), high resolution SEM (HR-SEM), energy dispersive spectroscopy analysis (EDAX), Fourier Transform InfraRed (FTIR) spectroscopy, thermogravimetric analysis, and differential scanning calorimetry (TGA-DSC), but also used in preliminary separation tests. Using the ion solutions in hydrochloric acid 3 mol/L, the separation of copper and zinc or cadmium and lead ions from binary mixtures was performed. The pertraction results were superior to those obtained by nanofiltration, both in terms of extraction efficiency and because at pertraction, the separate cation was simultaneously concentrated by an order of magnitude. The mixture of the four cations was separated by nanofiltration (at 5 bars, using a membrane of a 1 m² active area) by varying two operational parameters: pH and pCl. Cation retention could reach 95% when adequate values of operational parameters were selected. The paper makes some recommendations for the use of composite membranes, chitosan (Chi)-sulfonated poly (ether ether ketone) (sPEEK)-polypropylene hollow fiber (Chi/sPEEK/PPHF), so as to obtain the maximum possible retention of the target cation.

Sulfur-doped graphitic carbon nitride nanosheets as a sensitive fluorescent probe for detecting environmental and intracellular Ag

Silver is widely used in medical materials, photography, electronics and other industries as a precious metal. The large-scale industrial production of silver-containing products and liquid waste emissions aggravate the environmental pollution. Silver ion is one of the most toxic metal ions, causing pollution to the environment and damage to public health. Therefore, the efficient and sensitive detection of Ag+ in the water environment is extremely important. Sulfur-doped carbon nitride nanosheets (SCN Ns) were prepared by melamine and thiourea via high-temperature calcination. The morphology, chemical composition and surface functional groups of the SCN Ns were characterized by SEM, TEM, XRD, XPS, and FT-IR. The fluorescence of SCN Ns was gradually quenched as the Ag+ concentration increased. The detection limit for Ag+ was as low as 0.28 nM. The quenching mechanism mainly is attributed to static quenching. In this paper, SCN Ns were used as the fluorescent probe for detecting Ag+. SCN Ns have successfully detected Ag+ in different environmental aqueous samples and cells. Finally, SCN Ns were further applied to the visual quantitative detection of intracellular Ag+.

Nanomaterials for microplastic remediation from aquatic environment: Why nano matters?

The contamination of microplastics in aquatic environment is regarded as a serious threat to ecosystem especially to aquatic environment. Microplastic pollution associated problems including their bioaccumulation and ecological risks have become a major concern of the public and scientific community. The removal of microplastics from their discharge points is an effective way to mitigate the adverse effects of microplastic pollution, hence has been the central of the research in this realm. Presently, most of the commonly used water or wastewater treatment technologies are capable of removing microplastic to certain extent, although they are not intentionally installed for this reason. Nevertheless, recognizing the adverse effects posed by microplastic pollution, more efforts are still desired to enhance the current microplastic removal technologies. With their structural multifunctionalities and flexibility, nanomaterials have been increasingly used for water and wastewater treatment to improve the treatment efficiency. Particularly, the unique features of nanomaterials have been harnessed in synthesizing high performance adsorbent and photocatalyst for microplastic removal from aqueous environment. This review looks into the potentials of nanomaterials in offering constructive solutions to resolve the bottlenecks and enhance the efficiencies of the existing materials used for microplastic removal. The current efforts and research direction of which studies can dedicate to improve microplastic removal from water environment with the augmentation of nanomaterial-enabled strategies are discussed. The progresses made to date have witnessed the benefits of harnessing the structural and dimensional advantages of nanomaterials to enhance the efficiency of existing microplastic treatment processes to achieve a more sustainable microplastic cleanup.

Preparation of Magnetic MIL-68(Ga) Metal-Organic Framework and Heavy Metal Ion Removal Application

A magnetic metal-organic framework nanocomposite (magnetic MIL-68(Ga)) was synthesized through a "one pot" reaction and used for heavy metal ion removal. The morphology and elemental properties of the nanocomposite were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), as well as zeta potential. Moreover, the factors affecting the adsorption capacity of the nanocomposite, including time, pH, metal ion type and concentration, were studied. It was found that the adsorption capacity of magnetic MIL-68(Ga) for Pb²⁺ and Cu²⁺ was 220 and 130 mg/g, respectively. Notably, the magnetic adsorbents could be separated easily using an external magnetic field, regenerated by ethylenediaminetetraacetic acid disodium salt (EDTA-Na₂) and reused three times, in favor of practical application. This study provides a reference for the rapid separation and purification of heavy metal ions from wastewater.