Recovery of rare earth elements from mine wastewater using alginate microspheres encapsulated with zeolitic imidazolate framework-8.

There is increasing demand and interest in efficient methods for the recovery of rare earth elements (REEs) from wastewater because of the growing concerns associated with the negative impacts of REEs-rich waste discharged on pristine ecosystems. Here, we designed a ZIF-8@ALG composite hydrogel by encapsulating zeolitic imidazolate frameworks-8 (ZIF-8) into sodium alginate and poly (vinyl alcohol) double cross-linked networks (ALG) for the recovery of REEs from mine wastewater. ZIF-8@ALG showed exceptional REEs adsorption performance with the most superior separation factor (Ho/Mn) of 597.5. For the REEs considered, the ZIF-8@ALG composite exhibited a preference for heavy REEs with high adsorption efficiencies (65.3 ∼ 97.2%) and distribution coefficients (2045.5 ∼ 28500.0 mL·g-1). Adsorption involved a combination of electrostatic attraction, complexation and ion exchange mechanisms. REEs adsorbed on ZIF-8@ALG could also be desorbed using sodium citrate via ion-exchange and complexation, thus achieving efficient REEs recovery. In addition, ZIF-8@ALG was stable and reusable, maintaining effective adsorption in wastewater over four consecutive cycles, where the optimal adsorption efficiency reached 80.0%. Overall, this study provided an effective and feasible method for the recovery of REEs in mine wastewater, and confirmed that ZIF-8-based materials have significant potential for REEs recovery applications in wastewater engineering treatment.

Enhanced removal of Pb(II) from acid mine drainage using green reduced graphene oxide/silver nanoparticles.

Mining activities can potentially release high levels of Pb(II) in acid mine drainage (AMD), which thereafter poses a significant threat to ecological security. In this study, green reduced graphene oxide/silver nanoparticles (rGO/Ag NPs) were successfully synthesized via a one-step approach using a green tea extract and subsequently used as a cost-effective absorbent to remove Pb(II) from AMD. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that organic functional groups in the green tea extracts, such as C=O-C, CO, and CC, acted both as reductants and stabilizers in the synthesis of rGO/Ag NPs. In addition, the removal efficiency of Pb(II) by rGO/Ag NPs (84.2 %) was much better than either rGO (75.4 %) or Ag NPs (12.3 %) alone. Also, in real AMD, the distribution coefficient (Kd) of Pb(II) (4528 mL/g), was much higher than other heavy metal indicating the adsorbent had a high selective affinity for Pb(II). Interestingly, after five cycles of use, the removal efficiency of Pb(II) by rGO/Ag NPs from AMD actually increased from 46.4 to 65.2 % due to iron oxides (i.e., Fe2O3 and Fe3O4) being generated when rGO/Ag NPs was exposed to AMD. The removal of Pb(II) via adsorption on the rGO/Ag NPs surface involved formation of hexagonal rod-like precipitates. This work demonstrated the potential of rGO/Ag NPs to be continuously used for the removal of Pb(II) from AMD.

Intensive ammonium fertilizer addition activates iron and carbon conversion coupled cadmium redistribution in a paddy soil under gradient redox conditions.

While over-fertilization and nitrogen deposition can lead to the enrichment of nitrogen in soil, its effects on heavy metal fractions under gradient moisture conditions remains unclear. Here, the effect of intensive ammonium (NH4+) addition on the conversion and interaction of cadmium (Cd), iron (Fe) and carbon (C) was studied. At relatively low (30-80 %) water hold capacity (WHC) NH4+ application increased the carbonate bound Cd fraction (F2Cd), while at relatively high (80-100 %) WHC NH4+ application increased the organic matter bound Cd fraction (F4Cd). Iron­manganese oxide bound Cd fractions (F3Cd) and oxalate-Fe decreased, but DCB-Fe increased in NH4+ treatments, indicating that amorphous Fe was the main carrier of F3Cd. The variations in F1Cd and F4Cd observed under the 100-30-100 % WHC treatment were similar to those observed under low moisture conditions (30-60 % WHC). The C=O/C-H ratio of organic matter in soil decreased under the 30-60 % WHC treatment, but increased under the 80-100 % WHC treatment, which was the dominant factor influencing F4Cd changes. The conversion of NH4+ declined with increasing soil moisture content, and the impact on oxalate-Fe was greater at 30-60 % WHC than at 80-100 % WHC. Correspondingly, genetic analysis showed the effect of NH4+ on Fe and C metabolism at 30-60 % WHC was greater than at 80-100 % WHC. Specifically, NH4+ treatment enhanced the expression of genes encoding extracellular Fe complexation (siderophore) at 30-80 % WHC, while inhibiting genes encoding Fe transmembrane transport at 30-60 % WHC, indicating that siderophores simultaneously facilitated Cd detoxification and Fe complexation. Furthermore, biosynthesis of sesquiterpenoid, steroid, butirosin and neomycin was significantly correlated with F4Cd, while glycosaminoglycan degradation metabolism and assimilatory nitrate reduction was significantly correlated with F2Cd. Overall, this study gives a more comprehensive insight into the effect of NH4+ on activated Fe and C conversion on soil Cd redistribution under gradient moisture conditions.

Improved recovery selectivity of rare earth elements from mining wastewater utilizing phytosynthesized iron nanoparticles.

While rare earth elements (REEs) play key roles in many modern technologies, the selectivity of recovering of REEs from mining wastewater remains a critical problem. In this study, iron nanoparticles (FeNPs) synthesized from euphorbia cochinchinensis extracts were successfully used for selective recovery of REEs from real mining wastewater with removal efficiencies of 89.4% for Y(III), 79.8% for Ce(III) and only 6.15% for Zn(Ⅱ). FTIR and XPS analysis suggested that the high selective removal efficiency of Y(III) and Ce(III) relative to Zn(Ⅱ) on FeNPs was due to a combination of selective REEs adsorption via complexing with O or N, ion exchange with H+ present in functional groups contained within the capping layer and electrostatic interactions. Adsorptions of Y(III) and Ce(III) on FeNPs conformed to pseudo second-order kinetics and the Langmuir isotherm model with maximum adsorption capacities of 5.10 and 0.695 mg∙g-1, respectively. The desorption efficiencies of Y(III) and Ce(III) were, respectively, 95.0 and 97.9% in 0.05 M acetic acid, where desorption involved competitive ion exchange between Y(III), Ce(III) and Zn(Ⅱ) with H+ contained in acetic acid and intraparticle diffusion. After four consecutive adsorption-desorption cycles, adsorption efficiencies for Y(III) and Ce(III) remained relatively high at 52.7% and 50.1%, respectively, while desorption efficiencies of Y(III) and Ce(III) were > 80.0% and 95.0%, respectively. Overall, excellent reusability suggests that FeNPs can practically serve as a potential high-quality selectivity material for recovering REEs from mining wastewaters.

Interface coupling effect in biomass-derived iron sulfide nanomaterials triggering efficient hydrogen peroxide activation.

Slow electron migration in iron sulfide nanoparticles (C-FeS NPs) synthesized by co-precipitation severely limits the activation performance of hydrogen peroxide (H2O2). Herein, a biofunctional FeS NPs (P-FeS NPs) derived from Pinus massoniana Lamb biomass, with interface coupling effect, was used for enhanced H2O2 activation and norfloxacin (NOR) degradation. It was discovered that P-FeS NPs exhibited superior catalytic activity (100%) compared to C-FeS NPs (53.1%). Fe atoms of FeS NPs and hydroxyl groups (-OH) of Pinus massoniana Lamb biomass were mutually coupled to produce Fe-OH interfacial sites, which significantly increased the generation of multi-reactive species by accelerating the transfer of electrons across interfaces. Additionally, radical quenching tests elucidated that singlet oxygen (1O2) (66.6%) played a leading role, while hydroxyl radicals (•OH) (14.5%) and superoxide radicals (•O2-) (18.9%) were secondary oxidants. Finally, P-FeS NPs showed a high tolerance to a wide range of pH conditions and could remove 96.4% NOR from wastewater. Overall, this work generates important insights into understanding how green sustainable interfacial catalysts can accelerate catalytic activity.

Burkholderia cepacia immobilized onto rGO as a biomaterial for the removal of naphthalene from wastewater.

As one of the polycyclic aromatic hydrocarbons (PAHs), naphthalene is of serious environmental concern due to its carcinogenicity, persistence and refractory degradation. In this study, a new functional biomaterial based on Burkholderia cepacia (BK) immobilized on reduced graphene oxide (rGO) was prepared, resulting in the removal of 99.0% naphthalene within 48 h. This was better than the 67.3% for free BK and 55.6% for rGO alone. Various characterizations indicated that reduced graphene oxide-Burkholderia cepacia (rGO-BK) was successfully synthesized and secreted non-toxic and degradable surfactants which participated in the degradation of naphthalene. The adsorption kinetics and degradation kinetics conformed best to non-linear pseudo-second-order and pseudo-first-order kinetic models, respectively. Demonstrated in this work is that removing naphthalene by rGO-BK involved both chemically dominated adsorption and biodegradation. As well, GC-MS analysis revealed two things: firstly, that the degraded products of naphthalene were dibutyl phthalate, diethyl phthalate, phthalic acid, and benzoic acid; and secondly, two potentially viable biodegradation pathways of naphthalene by rGO-BK could be proposed. Finally, for practical application experiment, the rGO-BK was exposed to river water samples and generated 99% removal efficiency of naphthalene, so this study offers new insights into biomaterials that can remove naphthalene.

Predicting the effect of silver nanoparticles on soil enzyme activity using the machine learning method: type, size, dose and exposure time.

In this study, machine learning models predicted the impact of silver nanoparticles (AgNPs) on soil enzymes. Artificial neural network (ANN) optimized with genetic algorithm (GA) (MAE = 0.1174) was more suitable for simulating overall trends, while the gradient boosting machine (GBM) and random forest (RF) were ideal for small-scale analysis. According to partial dependency profile (PDP) analysis, polyvinylpyrrolidone coated AgNPs (PVP-AgNPs) had the most inhibitory effect (average of 49.5%) on soil enzyme activity among the three types of AgNPs at the same dose (0.02-50 mg/kg). The ANN model predicted that enzyme activity first declined and then rose when AgNPs increased in size. Based on predictions from the ANN and RF models, when exposed to uncoated AgNPs, soil enzyme activities continued to decrease before 30 d, but gradually rose from 30 to 90 d, and fell slightly after 90 d. The ANN model indicated the importance order of four factors: dose > type > size > exposure time. The RF model suggested the enzyme was more sensitive when experiments were conducted at doses, sizes, and exposure times of 0.01-1 mg/kg, 50-100 nm, and 30-90 d, respectively. This study presents new insights on the regularity of soil enzyme responses to AgNPs.

One-step simultaneous biomass synthesis of iron nanoparticles using tea extracts for the removal of metal(loid)s in acid mine drainage.

Acid Mine Drainage (AMD) contains various metal/metalloid ions such as Fe, Cu, and As, which all impact seriously on mine ecosystems. Currently, the commonly used chemical methods for treating AMD may cause secondary pollution to appear in the environment. In this study, one-step simultaneous biomass synthesis of iron nanoparticles (Fe NPs) using tea extracts for the removal of heavy metals/metalloids in AMD is proposed. Characterizations revealed that the Fe NPs presented severely agglomerated particles with an average particle size of 119.80 ± 4.94 nm, on which various AMD-derived metal(loid)s, including As, Cu, and Ni, were uniformly dispersed. The biomolecules participating in the reaction in the tea extract were identified as polyphenols, organic acids, and sugars, which acted as complexing agents, reducing agents, covering/stabilizing agents, and promoted electron transfer. Meanwhile, the best reaction conditions (reaction time = 3.0 h, volume ratio of AMD and tea extract = 1.0:1.5, concentration of extract = 60 g/L, and T = 303 K) were obtained. Finally, the simultaneous formation of Fe NPs and their removal of heavy metals/metalloids from AMD was proposed, mainly involving the formation of Fe NPs and adsorption, co-precipitation, and reduction processes of heavy metals/metalloids.

The origins of potentially superior properties and multifunctionalities of carbon-nano zero-valent iron in the carbonization pyrolysis process.

Although carbon-nano zero-valent iron (C@nZVI) composites with unique properties have been used for environmental remediation, the origins of their superior properties and multifunctionalities of C@nZVI still need to be verified. Here, iron precursor nanoparticles (PML-Fe NPs) synthesized by Pinus massoniana Lamb and carbonized C@nZVI were systemically compared to reveal the origins of the structure and performance of C@nZVI composites. Characterizations showed that structure-modulated C@nZVI has favorable properties of good crystallinity, graphite carbon-rich structure but also defects when compared to PML-Fe NPs. The resultant carbon layer fundamentally improved its dispersion and anti-oxidation properties. Further experiments demonstrated that the evolution of material crystallinity, graphitization and defects affected the reaction pathway of hexavalent chromium (Cr(VI)), oxytetracycline hydrochloride (OTC), and 17ß-estradiol (ßE2). The multifunctionalities covered adsorption, reduction and catalytic oxidation. This study explains the origins of multifunctional C@nZVI by understanding the structure-property correlation in the carbonization process.

Impact of coexisting components in acid mine drainage on Sb(â ¢) oxidation by biosynthesized iron nanoparticles.

Despite the oxidation mechanism of antimonite (Sb(Ⅲ)) by biosynthesized iron nanoparticles (Fe NPs) has been reported, the impact of coexisting components in acid mine drainage (AMD) on the Sb(III) oxidation by Fe NPs is unknown. Herein, how the coexisting components in AMD affect Sb(Ⅲ) oxidation by Fe NPs was investigated. Firstly, Fe NPs achieved complete oxidation of Sb(Ⅲ) (100%), while only 65.0% of Sb(Ⅲ) was oxidized when As(Ⅲ) was added, due to competitive oxidation between As(Ⅲ) and Sb(Ⅲ), which was verified by characterization analysis. Secondly, the decline in solution pH improved Sb(Ⅲ) oxidation from 69.5% (pH 4) to 100% (pH 2), which could be attributed to the rise of Fe3+ in solution promoting the electron transfer between Sb(Ⅲ) and Fe NPs. Thirdly, the oxidation efficiencies of Sb(Ⅲ) fell by 14.9 and 44.2% following the addition of oxalic and citric acid, respectively, resulting from the fact that these two acids reduced the redox potential of Fe NPs, thereby inhibiting Sb(Ⅲ) oxidation by Fe NPs. Finally, the interference effect of coexisting ions was studied, where PO43- significantly reduced Sb(Ⅲ) oxidation efficiency due to the occupation of the surface-active sites on Fe NPs. Overall, this study has significant implications for the prevention of Sb contamination in AMD.

Arsenic speciation, oxidation and immobilization in an unsaturated soil in the presence of green synthesized iron oxide nanoparticles and humic acid.

While the availability of arsenic (As) in soil is well known to be highly correlated with the presence of iron (Fe) oxides and humic acid (HA) in the soil, the relationship between Fe oxides and HA and As species in the soil is less well understood. In this study, As speciation in an unsaturated soil in the presence of external HA and green synthesized Fe oxide nanoparticles (FeNPs) showed that As(V) was mainly distributed to the specifically-bound (F2), amorphous and poorly-crystalline hydrous oxides of Fe, Al (F3) and the well-crystallized hydrous oxides of Fe and Al (F4). While As(III). This was the major component in unsaturated soil, and was mainly distributed to F4 and the residual fraction (F5). As bound to F3 and F5 was most sensitive to the addition of HA and FeNPs, while HA/FeNPs treatment increased the F3-bound As(V); however, it decreased the F5-bound As(III). Nonetheless the effect of HA on As is completely different to the HA/FeNPs treatment. The increase of As(V) in F3 resulted from F5-bound As(III) oxidation when treated by HA/FeNPs. Cyclic voltammetry confirmed that HA and Fe3+/Fe2+ redox enhanced As(III) oxidation, while FTIR revealed that HA-bound As(III) was the least available fraction in the soil. Finally, a mechanism involving a combination of HA and FeNPs was proposed for explaining the redistribution of As species in the soil.

Enhanced oxidation and stabilization of arsenic in a soil-rice system by phytosynthesized iron oxide nanomaterials: Mechanistic differences under flooding and draining conditions.

Despite arsenic (As) bioavailability being highly correlated with water status and the presence of iron (Fe) minerals, limited information is currently available on how externally applied Fe nanomaterials in soil-rice systems affect As oxidation and stabilization during flooding and draining events. Herein, the stabilization of As in a paddy soil by a phytosynthesized iron oxide nanomaterials (PION) and the related mechanism was investigated using a combination of chemical extraction and functional microbe analysis in soil at both flooding (60 d) and draining (120 d) stages. The application of PION decreased both specifically bound and non-specifically bound As. The As content in rice root, stem, husk and grain was reduced by 78.5, 17.3, 8.4 and 34.4%, respectively, whereas As(III) and As(V) in root declined by 96.9 and 33.3% for the 1% PION treatment after 120 d. Furthermore, the 1% PION treatment decreased the ratio of As(III)/As(V) in the rhizosphere soil, root and stem. Although PION had no significant effect on the overall Shannon index, the distribution of some specific functional microbes changed dramatically. While no As(III) oxidation bacteria were found at 60 d in any treatments, PION treatment increased As(III) oxidation bacteria by 3-9 fold after 120 d cultivation. Structural equation model analysis revealed that the ratio of Fe(III)/Fe(II) affected As stabilization directly at the flooding stage, whereas nitrate reduction and As(III) oxidation microbial groups played a significant role in the stabilization of As at the draining stage. These results highlight that PION exhibits a robust ability to reduce As availability to rice, with chemical oxidation, reduction inhibition and adsorption dominating at the flooding stage, while microbial oxidation, adsorption and coprecipitation dominant during draining.

Mechanism for the simultaneous removal of Sb(III) and Sb(V) from mining wastewater by phytosynthesized iron nanoparticles.

Since antimony (Sb) is a toxic metalloid cost-effective method for the simultaneous removal of the two major Sb species from mining wastewater has attracted much attention. In this study, phytosynthesized iron nanoparticles (nFe) prepared using a eucalyptus leaf extract were successfully used to simultaneously remove Sb(III) and Sb(V) via an adsorption and oxidation mechanism with removal efficiencies of 100 and 97.7% for Sb(III) and Sb(V), respectively. Advanced analysis using X-ray photoelectron spectroscopy (XPS), ion chromatography-atomic fluorescence spectroscopy (IC-AFS), and electrochemical analysis confirmed that Sb(III) was oxidized to Sb(V) by Fe(III) on the nFe surface while Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) indicated that both Sb(III) and Sb(V) were adsorbed onto nFe. Adsorption of both Sb(III) and Sb(V) best fit the Langmuir adsorption model with R2 of 0.999 and 0.989, respectively and both followed pseudo-second-order kinetics with R2 of 0.999 and 0.981, respectively. Furthermore, the adsorption rate of Sb(III) was faster than that of Sb(V) due to inner-sphere complex formation, and the Fe-O bonds in the asymmetric tetrahedron structure of Sb(III) were easier to break due to a lower energy barrier (0.863 eV). Consequently, a simultaneous removal mechanism of Sb(III) and Sb(V) was proposed. Finally, nFe was used practically to remove Sb in mining wastewater with a removal efficiency of 93.5%, demonstrating that nFe have significant potential to remove Sb in contaminated mining wastewaters.

Simultaneous removal of arsenite and arsenate from mining wastewater using ZIF-8 embedded with iron nanoparticles.

Arsenic contamination is an increasing global environmental problem, especially in mining industry wastewater where both arsenite (As(III)) and arsenate (As(V)) have been routinely detected. In this paper, a novel porous metal-organic framework material (ZIF-8) was composited with iron nanoparticles (FeNPs) to form a functional material (ZIF-8@FeNPs) for the simultaneous removal of As(III)/(V) from wastewater. The material effectively removed both As(III) and As(V) with removal efficiencies of 99.9 and 71.2%, respectively. Advanced characterization techniques including X-ray photoelectron spectroscopy (XPS) and Fourier infrared (FTIR) indicated that removal of As(III) and As(V) involved complex formation. Adsorption kinetics followed a pseudo-second order kinetics indicating adsorption involved chemisorption. After four cycles of reuse the he removal rate of As species was still relatively high at > 60% When ZIF-8@FeNPs were used to remove As from real wastewater from acid mines the removal efficiency was 94.27%. Finally, a As(III) and As(V) removal mechanism was proposed.

Biosynthesis of silver nanoparticles using three different fruit extracts: Characterization, formation mechanism and estrogen removal.

Plant-mediated synthesis of silver nanoparticles (Ag NPs) is a green and economically viable method, which can offer numerous benefits over traditional chemical and physical methods. In this paper, three fruit extracts (tomato, orange, and grapefruit) served simultaneously as stabilizing and reducing agents during the biosynthesis of Ag NPs. The formation of Ag NPs, were monitored using the UV-visible absorption spectra of Ag NPs which exhibited three distinct bands centered at 439, 413, and 410 nm. SEM and TEM analysis indicated that these bands corresponded to three distinct spherical-shaped Ag NPs having average particle sizes of 73, 24, and 31 nm, respectively. XRD and EDS spectral analyses were used to verify the degree of crystallinity, nanostructure, and presence of Ag NPs. Advanced analysis using XPS, FTIR, and GC-MS indicated that the Ag NPs were coated with a variety of organic compounds including acids, aldehydes, esters, and ketones, indicating that fruit derived phytochemicals had a significant role in synthesis, and subsequently a mechanism of Ag NPs formation was proposed. The fabricated nanoparticles were also successfully used in Fenton-like oxidation for the environmental remediation of estrone and estriol, with removal efficiencies of 52.1 and 35.9%, respectively.

Isolation and identification of 17ß-estradiol degrading bacteria and its degradation pathway.

The widespread presence of 17ß-estradiol (E2) in the environment is an emerging problem because it poses a potential threat to human health and aquatic organisms. In this study, a strain of E2 degrading bacteria was isolated from activated sludge. 16s rRNA analysis combined with physiological and biochemical detection confirmed that the bacterium was Ochrobactrum sp. strain FJ1. At an initial E2 concentration of 15 mg L-1, strain FJ1 degraded 98 ± 1% of E2 after 10 days. Furthermore, when methanol was added as an additional carbon source, the biomass of strain FJ1 increased by 35 ± 1%, and E2 degradation efficiency was slightly inhibited. Compared with E2 alone when glucose, sodium acetate, and methanol were added as additional carbon sources, biomass decreased by 20 ± 1, 13 ± 1 and 35 ± 1%, respectively. Analysis of the degradation products of E2 by LC/Q-TOF-MS confirmed that the major degradation products of E2 were estrone (E1) and 4,16-OH-E1, which was further degraded by strain FJ1 to several other unknown compounds. Based on SEM and FTIR analysis, the morphology of the bacteria became thicker and the thickness of the cell walls decreased under initial E2 stress, and thereafter E2 was transported into the bacteria primarily via several proteins on the cell surface. Considering the ability and efficiency of Ochrobactrum sp. strain FJ1 to degrade high E2 content, the strain could provide a new bioremediation technology for the effective biodegradation of E2. Finally, a potential bioremediation pathway of E2 by Ochrobactrum sp. strain FJ1 was proposed.

Removal mechanism of 17ß-estradiol by carbonized green synthesis of Fe/Ni nanoparticles.

Even a small concentration of estrogen released into the environment can cause great damage to the surrounding ecosystem, with potential teratogenic and carcinogenic hazards to many organisms. In this study, carbonized green synthesized Fe/Ni NPs, with a maximum adsorption capacity of 44.32 mg g-1 coupled with over 98.3% removal efficiency, were used to remove 17ß-estradiol (E2) from water. Adsorption best conformed to pseudo-second-order kinetics (R2 = 0.998-0.999) and the Freundlich model (R2 = 0.990-0.997). SEM images reveal that the carbonized material had increased specific surface area and pores. Zeta Potential, FTIR and XPS spectra confirmed that carbonized material was negatively charged and contained functional groups with a high affinity for E2. Liquid chromatography during removal of E2 suggested no new substances were generated. Therefore, the synergistic effect of carbonized-Fe/Ni NPs surface functional groups is a key issue, including dehydration bonds, hydrogen bonds, and the accumulation of Π and Π. In practice the application of carbonized-Fe/Ni NPs demonstrated their ability to remove 51.8% and 48.7% of E2 from domestic sewage and livestock wastewater, respectively. This work provides a strong basis for the practical removal of E2 using carbonized-Fe/Ni NPs material.

Cyclodextrin modified green synthesized graphene oxide@iron nanoparticle composites for enhanced removal of oxytetracycline.

The presence of residual antibiotics will lead to potential environmental risks. Here cyclodextrins (CDs) were successfully used to modify graphene-based iron nanoparticles (GO@Fe NPs) to enhance the absorption of oxytetracycline hydrochloride (OTC). The removal of OTC decreased in the order: γCD-GO@Fe NPs > ßCD-GO@Fe NPs > αCD-GO@Fe NPs > GO@Fe NPs, with better performance than that of bare GO and Fe NPs. Characterization techniques were applied to better understand how CDs impact the structure of GO@Fe NPs and improve removal performance. Raman and X-ray diffraction analysis showed that GO acted as a carrier to support Fe NPs within the grafted cyclodextrin, where GO also participated in the removal process. Cyclodextrin modified GO@Fe NPs had relatively small particle sizes (15 nm), with a high surface area (61.7 m2 · g-1). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy suggested that cyclodextrin acted as both a stabilizing and capping agent during green synthesis, which could protect the reactivity of Fe NPs and simultaneously reduce aggregation. A potential synthesis mechanism of cyclodextrins modified composites was also proposed, and subsequent wastewater testing indicated that γCD-GO@Fe NPs had high potential for practical applications.

How do phytogenic iron oxide nanoparticles drive redox reactions to reduce cadmium availability in a flooded paddy soil?

While soil redox reactions are known to determine heavy metal soil availability, specific information on how iron (Fe) nanomaterials reduce heavy metal availability in bulk soil and in the rice rhizosphere is limited. Here a pot experiment was performed to examine the effect of phytogenic iron oxide nanoparticles (PION) on the availability of cadmium (Cd) in flooded soil. PION significantly reduced soil Cd availability, with Cd in rice shoot being 2.72, 1.21 and 0.40 mg kg-1 for the control, 1 and 5% PION treatments, respectively. In addition, following PION application, Illumina MiSeq sequencing indicated that the abundance of Lentimicrobium and Anaeromyxobacter increased, while the abundance of Geobacter and Thiobacillus decreased. Structural equation model analysis revealed that redox reactions, driven by carbon, nitrogen, iron and sulfur cycling related functional groups, played an important role in the immobilization of Cd in flooded soil. Co-occurrence network analysis showed that the rhizosphere soil was far more complex than the bulk soil. Overall, PION addition enhanced the inherent soil microbe's activity and the involved in reducing Cd availability to rice by converting mobile Cd into stabler forms. This initial result paves the way for establishing a practical low-cost remediation strategy for Cd contaminated paddy soils.

Removal of As(V) by iron-based nanoparticles synthesized via the complexation of biomolecules in green tea extracts and an iron salt.

While iron-based nanoparticles (nFe) prepared using green tea extracts have been successfully used to degrade many organic contaminants, their application to remove As(V) remains limited. Thus, in this work, nFe (GT-1) prepared using a green tea extract was used to removal As(V). The maximum adsorption capacity of GT-1 for As(V) was 19.9 mg g-1 at 298 K. The formation of GT-1 and the removal mechanism of As(V) by GT-1, was examined using XRD, TEM and SEM, which showed that GT-1 was composed of amorphous particulates sized between 50 and 100 nm. GC-MS and LC-MS analysis also showed that biomolecules presented in the green tea extract, including polyphenols and L-theanine, participated in the formation of GT-1. Mössbauer spectral analysis confirmed that an organo-Fe(III) complex was formed due to the reaction between biomolecules and Fe(III). FTIR and XPS showed that the adsorption of As(V) by GT-1 occurred both via complexation with Fe(III) in GT-1 and via coordination of As(V) with free hydroxyl groups on the surface of GT-1. Batch experiments showed that adsorption was spontaneous and conformed to the pseudo-second order kinetic model. Finally, mechanisms for the formation of GT-1 and the removal of As (V) by GT-1 were proposed.