Supported Nano Zero-valent Iron Research Articles

High stability and reactivity of porous calcium tartrate supported nano zero-valent iron in aerobic environment and alkaline wastewater

Nano zero-valent iron (nZVI) has remarkable reactivity, but its practical application is severely hindered by its easy aggregation and rapid oxidation after exposure in air. In this study, spherical porous calcium tartrate (CaTr) was synthesized with ultrasound technology and used to support nZVI. It was found that the as-obtained nZVI@CaTr was highly stable and reactive in oxygen-rich water under neutral/alkaline conditions. In the pH range of 4–9, the degradation efficiency of p-nitrophenol (PNP, 50 mg/L) by nZVI@CaTr7 exceeded 98.1 %. Importantly, nZVI@CaTr could be stored in air for a long time without inert gas protection. After 60 days and 120 days of air exposure, the removal efficiency of PNP still reached 83.3 % and 63.3 %, which was 2.8 and 9.7 times that of bare nZVI, respectively. Such an excellent performance could be attributed to two reasons: (i) spherical CaTr effectively inhibited the oxidation and aggregation of nZVI by favorable interactions with nZVI, and (ii) the abundant functional groups on the surface of CaTr acted as electronic mediators to significantly promote charge transfer between nZVI (electron donor) and PNP (electron acceptor). Therefore, cheap, air stable and highly effective nZVI@CaTr7 provided a potential application prospect for the degradation of environmental pollutants in aerobic environment and alkaline wastewater.

Metagenomic analysis reveals the mechanisms of biochar supported nano zero-valent iron in two-phase anaerobic digestion of food waste: microbial community, CAZmey, functional genes and antibiotic resistance genes

The mechanisms of biochar supported nano zero-valent iron (BC/nZVI) on two-phase anaerobic digestion of food waste were investigated. Results indicated that the performance of both acidogenic phase and methanogenic phase was effectively facilitated. BC/nZVI with the amount of 120 mg/L increased methane production by 32.21%. In addition, BC/nZVI facilitated direct interspecies electron transfer (DIET) between Geobacter and methanogens. Further analysis showed that BC/nZVI increased the abundance of most CAZymes in acidogenic phase. The study also found that BC/nZVI had positive effects on metabolic pathways and related functional genes. The abundances of acdA and ackA in acidogenic phase were increased by 151.75% and 36.26%, respectively, and the abundances of pilA and TorZ associated with DIET were also increased. Furthermore, BC/nZVI mainly removed IMP-12, CAU-1, cmeB, ErmR, MexW, ErmG, Bla2, vgaD, MuxA, and cpxA from this system, and reduced the antibiotic resistance genes for antibiotic inactivation resistance mechanisms.

Complete 2,4,6-trichlorophenol degradation by anaerobic sludge acclimated with 4-chlorophenol: Synergetic effect of nZVI@BMPC and sodium lactate as an external nutrient

Ball-milled plastic char supported nano zero-valent iron (nZVI@BMPC) and their application combined with anaerobic sludge for microbial dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) were investigated. The XRD and FTIR analysis proved composition of zero valent states of iron, and the BET and SEM analysis showed that nZVI was uniformly distributed on the surface of BMPC. Successive addition of 1000 mg/L sodium lactate and nZVI@BMPC enhanced the acclamation of anaerobic sludge and resulted in the degradation of 4-CP within 80 days. The acclimated consortium with nZVI@BMPC completely degraded 2,4,6-TCP into CH4 and CO2, and the key dechlorination route was through 4-CP dechlorinaion and mineralization. The degradation rate of 2,4,6-TCP with nZVI@BMPC was 0.22/d, greater than that without nZVI@BMPC. The dechlorination efficiency was enhanced in the Fe2+/Fe3+ system controlled by nZVI@BMPC and iron-reducing bacteria. Metagenomic analysis result showed that the dominant de-chlorinators were Chloroflexi sp., Desulfovibrio, and Pseudomonas, which could directly degrade 2,4,6-TCP to 4-CP, especially, Chloroflexi bacterium could concurrently be used to mineralize 4-CP. The relative abundance of the functional genes cprA, acoA, acoB, and tfdB increased significantly in the presence of the nZVI@BMPC. This study provides a new strategy can be a good alternative for possible application in groundwater remediation.

Efficient U(VI) removal from aerobic solution by synergistic interaction of nano zero-valent iron with g-C3N4 and assessment of toxicity to microorganism

The graphitic carbon nitride (g-C3N4) supported nano zero-valent iron (nZVI) composites (g-Fe) were synthesized to assess the performance of U(VI) removal and bacterial inactivation. Under aerobic conditions at pH 6.0, 97.0 % of U(VI) was removed within 60 min, while only 7.2 % or 22.6 % of U(VI) were removed by pristine g-C3N4 or nZVI. Effects of operating parameters (pH, temperature, initial U(VI) concentration, and g-Fe dosage) on U(VI) removal were also studied under aerobic conditions. The U(VI) adsorption followed a pseudo-second-order kinetic model, and the adsorption process was in accordance with the Langmuir adsorption isotherm model. This indicated that the removal of U(VI) by g-Fe was a chemisorption and homogeneous monolayer adsorption process. The maximum removal capacity of U(VI) was 952.38 mg/g at pH = 6.0. The absorbed uranium on the g-Fe composite were confirmed to be solely U(VI) under aerobic conditions, while both U(VI) and U(IV) were observed under anaerobic conditions. Hence, adsorption rather than reduction serves as the primary mechanism for U(VI) removal in aerobic environments. Escherichia coli or Bacillus subtilis could be inactivated by nZVI and g-Fe composite, but the biotoxicity of g-Fe was much lower than nZVI. Physical isolation reduced the biotoxicity of nZVI, and the residual biotoxicity of nZVI after excluding physical contact should be ascribed to oxidative stress or free reactive oxidative species (ROS). The biotoxicity of g-Fe was irrelevant to physical isolation, proving that oxidative stress or free ROS might dominate the inactivation mechanisms. The g-Fe composite, an eco-friendly, facile and sustainable material, can be developed for U(VI) removal from radioactive wastewater.

Removal of Methylene Blue by Granitic Residual Soil Supported Nano Zero Valent Iron (Gr-nZVI): Kinetic and Equilibrium Studies

The presence of dyes in water sources that act as contaminants is hazardous to human and animal health. Therefore, this research was conducted on the removal of methylene blue (MB) using granitic residual soil-supported nano zero-valent iron (Gr-nZVI), to examine its potential use as an efficient adsorbent. Batch adsorption experiments were conducted in this study to examine the impact of initial dye concentration, contact time, dosage, pH and temperature effets. Based on the results, it can be inferred that Gr-nZVI (with Kd=0.1 L/g and R2 =1) exhibits superior adsorption of MB at higher metal ion concentrations when compared to granitic residual soil (Gr) (with Kd=0.0588 L/g and R2 =0.9267). The removal percentage of Gr-nZVI was found to be 100%, obtained at 100 mg/L MB ion concentration. Sorption data have been correlated with both Langmuir and Freundlich adsorption models. However, the Langmuir isotherm was the only model that showed a good fit for the adsorption of MB on Gr-nZVI. The mechanistic phases of the process were determined through kinetic energy studies. Kinetic data showed the removal of MB was 100% within 5 min for both Gr-nZVI and Gr. This indicates the very fast adsorption of MB and data followed a pseudo-second order. According to adsorption analysis, Gr demonstrated a higher adsorption capacity for MB removal compared to Gr-nZVI and nZVI. This study also highlights that nZVI does not facilitate MB adsorption, making the composite nZVI unnecessary due to Gr is capable of removing MB on its own.

Enhanced chromium (VI) removal: A remediation study employing nano zero-valent iron supported by sawdust

The rapid expansion of industry leads to the emission of heavy metals into the environment, posing a significant global concern presently. The management of heavy metals holds particular significance due to their resilience and persistence in the environment. Removal technologies of heavy metals include physical and chemical treatments. Chromium (VI) was utilized as a representative of heavy metals in this research. Sorption experiments were conducted using a composite material consisting of supported nano zero-valent iron on sawdust, designated as NZVI/SD. The NZVI/SD composite was prepared through a two-step process involving the impregnation of sawdust with ferrous sulfate, followed by a chemical reduction using Sodium borohydride (NaBH4). The adsorbent was characterized with the help of Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX), X-Ray Diffraction analysis (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and chemical test. The adsorption characteristics have been investigated under various conditions, including different pH values, adsorbent dosages, initial metal ion concentrations, contact times, and varying temperatures. The optimal conditions for employing NZVI/SD for the removal of Cr(VI) were observed at a pH of 3.0, an adsorbent dosage of 0.5 g/L, an initial metal ion concentration of 61.45 mg/L, a contact time of 180 min, and a temperature of 50 °C. Sorption of Cr(VI) on NZVI/SD followed Langmuir Isotherm model. The maximum monolayer sorption capacity on NZVI/SD was 39.8 mg/g at 298 K temperature (equilibrium pH of 3.0) estimated from the Langmuir isotherm. Kinetics and thermodynamic studies on the sorption of Cr (VI) on NZVI/SD were done to understand the sorption mechanism. Sorption kinetics of Cr (VI) on NZVI/SD confirmed that pseudo second order reaction kinetics was followed concluding that the rate of adsorption depends on the analyte and the available free site of adsorbent. By employing the Langmuir isotherm model and Van't Hoff equation, the determination of thermodynamic parameters such as Gibbs free energy, enthalpy change, and entropy change of the adsorption process was facilitated. It was found that the sorption of Cr(VI) was spontaneous (∆G° = −10.36 kJ.mol−1) on NZVI/SD and the process was endothermic (∆H = +4.609 kJ/mol). NZVI/SD can be effectively regenerated by elution with 1 M NaOH for 4 h.

Peroxymonosulfate activation by walnut shell activated carbon supported nano zero-valent iron for the degradation of tetracycline: Performance, degradation pathway and mechanism

In this study, activated carbon (WS-AC) was prepared from walnut shell. Nano-zero-valent iron (nZVI) was loaded on walnut shell activated carbon by liquid phase reduction method and used as catalyst (WS-AC/nZVI) to activate peroxymonosulfate (PMS) to efficiently degrade tetracycline (TC) in solution. The composite material with a mass ratio of WS-AC to nZVI of 1:1 has the highest catalytic performance for activating PMS to degrade TC. The results showed that under the conditions of TC concentration of 100 ppm, PMS dosage of 0.2 mM and WS-AC/nZVI dosage of 0.1 g/L, the removal efficiency of TC could reach 81%. Based on quenching experiments and electron spin resonance (EPR), it was verified that •OH, SO4•− and 1O2 bound on the catalyst surface were the main reactive oxygen species during the reaction. The intermediate products of TC were identified by liquid chromatography-mass spectrometry (HPLC-MS) and DFT calculation, and the possible degradation pathway of TC was proposed. The catalyst still maintained high removal efficiency of TC after four cycles of experiments, and the minimal iron loss on the surface of the catalyst indicated that it had good stability. The efficient and stable WS-AC/nZVI activated PMS showed great potential in the degradation of antibiotics.

Degradation of trichloroethylene by biochar supported nano zero-valent iron (BC-nZVI): The role of specific surface area and electrochemical properties

Direct electron transfer and the involvement of atomic hydrogen (H⁎) are considered the main mechanisms for reductive dechlorination promoted by nano zero-valent iron (nZVI) supported on highly conductive carbon. It is still unclear how precisely H⁎, the specific surface area, and the electrochemical characteristics contribute to biochar supported nano zero-valent iron (BC-nZVI) activity in chlorinated hydrocarbon contaminant removal. In this study, a range of BC-nZVIs were prepared by a liquid-phase reduction process, and the contributions of specific surface area and electrochemical performance to H⁎ generation and electron transfer have been assessed. The mechanism of trichloroethylene (TCE) dechlorination by BC-nZVIs has been evaluated in terms of removal efficiency and the ultimate degradation products. The results have demonstrated that BC-nZVIs exhibit a higher specific surface area and TCE degradation efficiency compared with the bare nZVI. Ethane, ethylene, and acetylene were the principal TCE degradation products. The elimination of TCE was not significantly affected by differences in BC-nZVI specific surface area, but electron transfer and sustained generation of H⁎ were dependent on the catalyst electrochemical characteristics. The electrochemical properties of biochar serve to lower the corrosion potential of nZVI, improving electronic transfer capability and reactivity and promoting direct electron transfer for the degradation of TCE. In addition, the enhanced electrochemical properties also facilitate the reaction of nZVI with water and can promote the sustained generation of H⁎. Generation of H⁎ played a key role in reductive dechlorination over BC-nZVIs, which was related to the properties of the biochar support. This study focuses on the role of H⁎ and electrochemical performance in TCE reductive dechlorination, and provides a theoretical foundation and experimental support for the practical application of BC-nZVIs.

Microbial mechanism underlying the effect of biochar supported nano zero-valent iron on the anaerobic digestion of food waste

Anaerobic digestion (AD) is one of the effective methods to treat the food waste (FW). In this study, biochar supported nano zero-valent iron (BC-nZVI) was prepared by carbon thermal reduction process. The effects of concentrations (1, 2 and 3 g/L) of BC-nZVI on methane production, microorganisms and metabolic mechanism during the AD of food waste were investigated. The results showed that 1 g/L of BC-nZVI was the best concentration for methane production. The cumulative methane production was enhanced by 29.54% at BC-nZVI 1 g/L. Microbial community analysis showed that BC-nZVI mainly increased the abundances of hydrolytic bacteria (including Bacteroidetes_vadinHA17, Proteiniphilum, Syntrophobacter) and acetoclast (Methanosaeta). Further exploration of the mechanism using PICRUSt2 version based on 16 S rRNA gene sequence analysis indicated that the addition of BC-nZVI promoted the abundances of enzymes related to methane metabolism such as the phosphate acetyltransferase and the methyl-coenzyme M reductase alpha subunit, which made the AD system stable.

Effects of biochar supported nano zero-valent iron with different carbon/iron ratios on two-phase anaerobic digestion of food waste

The promotion effects of biochar supported nano zero-valent iron (BC/nZVI) with different carbon/iron ratios on two-phase anaerobic digestion (AD) of food waste (FW) were studied. Results suggested that when the carbon/iron ratio was 3:1 AD system showed the best performance, with the concentration of volatile fatty acids (VFAs) in acidogenic phase (AP) and the cumulative methane production in methanogenic phase (MP) increased by 31.4% and 24.8%, respectively. Metagenomic analysis demonstrated that BC/nZVI increased the relative abundance of Defluviitoga in AP, and promoted the growth of Methanothrix in MP. Metabolic pathway analysis in AP indicated that BC/nZVI mainly promoted the abundances of acetate kinase and butyrate kinase to enhance acid production. Methane metabolism pathway analysis in MP revealed that BC/nZVI increased methane production by promoting the module of M00357 and activating related enzymes. The results of this sutdy showed that BC/nZVI promoted AD of FW mainly through acetoclastic methanogenic pathway.

Highly efficient removal of ionic dyes in aqueous solutions using magnetic 3D reduced graphene oxide aerogel supported nano zero-valent iron

This study aims to develop three-dimension reduced graphene oxide aerogel supported nano zero-valent iron (rGOA-nZVI) by hydrothermal and liquid phase reduction approach and applies it to the removal of two typical dyes, methylene blue (MB) and methyl orange (MO) from aqueous solutions. The obtained magnetic rGOA-nZVI composites were characterized by scanning electron microscopy (SEM), atomic force microscopy, Brunauer-Emmett-Teller, X-ray diffraction and Fourier transform infrared spectroscopy, and its removal efficiencies for MB and MO from aqueous solutions were evaluated. The removal processes of MB and MO could be completed within 30 min, which were well described by the pseudo-second order kinetic model. The rGOA-nZVI nanocomposites exhibited remarkable performance for the removal of MB (the maximum adsorption amount, <i>q</i><sub>max</sub> = 3918 mg/g) and MO (<i>q</i><sub>max</sub> = 667 mg/g) in a wide pH range (pH 1.0-10.0). Furthermore, rGOA-nZVI is stable and recyclable with high dye removal efficiencies (> 90%) after five cycles. The removal mechanisms were demonstrated with SEM and XRD analyses before and after MB and MO removal. This study showed that rGOA acts as an excellent carrier for nZVI, and the rGOA-nZVI nanocomposites are efficient materials for the advanced treatment of dye wastewater over a wide pH range.

Effectiveness of Artificially Synthesized Granitic Residual Soil-Supported Nano Zero-Valent Iron (Gr-nZVI) as Effective Heavy Metal Contaminant Adsorbent

Supported nano zero-valent iron is receiving great attention nowadays due to its effectiveness in treating heavy metal pollutants. Therefore, this study aimed to investigate the effectiveness of granitic residual soil-supported nano zero-valent iron (Gr-nZVI) for the removal of the heavy metals Pb2+, Cu2+, Co2+, Cd2+ Ni2+ and Zn2+ in mixture solutions under different experimental conditions of batch equilibrium tests. In this study, Gr-nZVI was successfully synthesized by using the chemical reduction of Ferric Chloride Hexahydrate (FeCl3.6H2O) and Sodium Borohydride (NaBH4). The physical and chemical properties, morphology and mineralogy of all adsorbents were characterized by the Braeuer–Emmett–Teller (BET) method, cation exchange capacity (CEC), X-ray fluorescence (XRF), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Isotherm, kinetic and diffusion model analyses were conducted to fit the experimental data. The results show rapid adsorption within 5 min in the initial adsorption stage for Pb2+ on nZVI (qe.Pb = 17.89 mg/g) and Gr-nZVI (qe.Pb = 15.29 mg/g). nZVI and Gr-nZVI also showed no significant effects on pH and temperature, serving as a good example of an energy-efficient process. The isotherm data fitted better to the Langmuir model and the pseudo-second-order kinetic model for the adsorption of all of the heavy metals. The diffusion models revealed that adsorption was not the only rate-limiting step. In this study, nZVI compared to Gr-nZVI and Gr demonstrated superior adsorption capacity for the heavy metal adsorption selectivity. Hence, these materials can be utilized as alternative energy-efficient adsorbents for the adsorption of metal ions from wastewater.

Adsorption of Methylene Blue by Bentonite Supported Nano Zero Valent Iron (B-nZVI)

Dyes used in textiles, foods, cosmetics, and chemicals have become a major environmental pollution issue around the world. To address this issue, a number of technologies have been created to remove these pollutants from the environment. Due to their superior properties at nanoscale, numerous nanomaterials have been applied to remove dyes from polluted waters. This research presents the findings of the development of bentonite nano zero-valent iron (B-nZVI) for the treatment of synthetic cationic dyes. This study has three objectives: (i) to produce bentonite nano zero-valence iron (B-nZVI), (ii) to characterize its adsorbents (B-nZVI), (iii) to characterize its adsorption capacity. Four main tests were used for this purpose: (i) a physical test (Brunauer–Emmett–Teller (BET) surface area), (ii) a chemical test (cation exchange capacity (CEC) and X-ray fluorescence (XRF)), (iii) morphology (field emission scanning electron microscopy (FESEM) and (iv) mineralogy (Fourier transform infrared spectroscopy (FTIR). The five factors for the batch equilibrium test are adsorbent dose, concentration, kinetic, pH, and temperature. The batch test showed that the optimum dose for all adsorbents is 0.5 g. For the concentration factor, B-nZVI exhibits larger adsorption capacity (KL = 30,314.0536 L/g; R2 = 1) compared to bentonite (Kd = 0.0219 L/g; R2 = 0.8892). The kinetic factor showed that the adsorption capacity by pseudo-second-order model was the best for both adsorbents (qe = 1.2038 mg/g, R2 = 0.9993 for bentonite and qe = 6.9979 mg/g, R2 = 1 for B-nZVI). For B-nZVI, the interparticle diffusion model (Kf = 0.8645 m2 g−1 min L−1; R2 = 0.9) and intraparticle diffusion model (Kd = 2.3829 m2 g−1 min L−1; R2 = 0.9189) showed a good correlation with the adsorption data, while bentonite showed a lower correlation with the interparticle diffusion model (Kf = 0.0002 m2 g−1 min L−1; R2 = 0.6253) and intraparticle diffusion model (Kd = 0.2886 m2 g−1 min L−1; R2 = 0.6026), respectively. The pH factor showed that the adsorption capacity of bentonite (qe = 0.5674 mg/g) and B-nZVI (qe = 5.3284 mg/g) was highest in acidic conditions (pH 2). As for the temperature factor, there was no significant effect on bentonite and B-nZVI. Therefore, tests can be conducted at room temperature, saving energy. It was also concluded that B-nZVI is the best material for removing MB compared to bentonite and can be considered for the treatment materials of contaminated water.

Removal of Naphthalene, Fluorene and Phenanthrene by Recyclable Oil Palm Leaves’ Waste Activated Carbon Supported Nano Zerovalent Iron (N-OPLAC) Composite in Wastewater

Despite keen interest in the development of efficient materials for the removal of polycyclic aromatic hydrocarbons (PAHs) in wastewater, the application of advanced composite materials is still unexplored and needs attention. Therefore, this study focused on the synthesis of the composite of oil palm leaves’ waste activated-carbon (OPLAC) and nano zerovalent iron (NZVI) at Fe:OPLAC = 1:1 (N-OPLAC-1) and 1:2 (N-OPLAC-2). The composite with enhanced surface properties was applied for removal of three PAHs including naphthalene (NAP), fluorene (FLU) and phenanthrene (PHE) in wastewater at various pH, dosages, contact time and initial concentration in batch testing. The PAHs’ removal parameters were optimized using design expert software. The PAHs’ removal efficiency was evaluated in produced water at optimized parameters. The results showed that the N-OPLAC-2 had superior surface properties compared to N-OPLAC-1. The removal of NAP, FLU and PHE was heterogenous, favorable and involved chemisorption proved by Freundlich isotherm and pseudo-second-order kinetic models using N-OPLAC-2. The optimum parameters were as follows: pH of 3, dosage and contact time of 122 mg/L and 49 min, respectively. The application of N-OPLAC-2 in produced water was favorable for removal of NAP, FLU and PHE and showed up to 90% removal efficiency, and higher stability up to 3 cycles. It can be concluded that the NZVI-OPLAC composite was successfully synthesized in this study and the materials showed good removal efficiency for three PAHs (NAP, FLU and PHE) in wastewater.

Remediation and its biological responses to Cd(II)-Cr(VI)-Pb(II) multi-contaminated soil by supported nano zero-valent iron composites

Multi-metal contaminated soil has received extensive attention. The biochar and bentonite-supported nano zero-valent iron (nZVI) (BC-BE-nZVI) composite was synthesized in this study by the liquid-phase reduction method. Subsequently, the BC-BE-nZVI composite was applied to immobilize cadmium (Cd), chromium (Cr), and lead (Pb) in simulated contaminated soil. The simultaneous immobilization efficiencies of Cd, Cr(VI), Crtotal, and Pb were achieved at 70.95 %, 100 %, 86.21 %, and 100 %, respectively. In addition, mobility and bioavailabilities of Cd, Cr, and Pb were significantly decreased and the risk of iron toxicity was reduced. Stabilized metal species in the contaminated soil (e.g., Cd(OH)2, Cd-Fe-(OH)2, CrxFe1-xOOH, CrxFe1-x(OH)3, PbO, PbCrO4, and Pb(OH)2) were formed after the BC-BE-nZVI treatment. Thus, the immobilization mechanisms of Cd, Cr, and Pb, including adsorption, reduction, co-precipitation, and complexation co-exist with the metals. More importantly, bacterial richness, bacterial diversity, soil enzyme activities (dehydrogenase, urease, and fluorescein diacetate hydrolase), and microbial activity were enhanced by applying the BC-BE-nZVI composite, thus increasing the soil metabolic function. Over all, this work applied a promising procedure for remediating multi- metal contaminated soil by using the BC-BE-nZVI composite.

The superior performance of silica gel supported nano zero-valent iron for simultaneous removal of Cr (VI)

Pure nano zero-valent iron (NZVI) was fabricated under optimum conditions based on material production yield and its efficiency toward acid blue dye-25 decolorization. The optimum prepared bare NZVI was immobilized with two different supports of silica and starch to fabricate their composites nanomaterials. The three different prepared zero-valent iron-based nanomaterials were evaluated for removal of hexavalent chromium (Cr(VI)). The silica-modified NZVI recorded the most outstanding removal efficiency for Cr(VI) compared to pristine NZVI and starch-modified NZVI. The removal efficiency of Cr(VI) was improved under acidic conditions and decreased with raising the initial concentration of Cr(VI). The co-existence of cations, anions, and humic acid reduced Cr(VI) removal efficiency. The removal efficiency was ameliorated from 96.8% to 100% after adding 0.75 mM of H2O2. The reusability of silica-modified NZVI for six cycles of Cr(VI) removal was investigated and the removal mechanism was suggested as the physicochemical process. Based on Langmuir isotherm, the maximal Cr(VI) removal capacity attained 149.25 mg/g. Kinetic and equilibrium data were efficiently fitted using the pseudo-second-order and Langmuir models, respectively confirming the proposed mechanism. Diffusion models affirmed that the adsorption rate was governed by intraparticle diffusion. Adsorption thermodynamic study suggested the spontaneity and exothermic nature of the adsorption process. This study sheds light on the technology that has potential for magnetic separation and long-term use for effective removal of emerging water pollutants.

Enhanced nitrogen removal from low C/N municipal wastewater employing algal biochar supported nano zero-valent iron (ABC-nZVI) using A/A/O-MBR: Duration and rehabilitation

To bridge the organic-dependent barrier on nitrogen from low carbon/nitrogen (C/N) municipal wastewater, employing algal biochar supported nano zero-valent iron (ABC-nZVI) was investigated using A/A/O-MBR. Firstly, it can be seen that adequate carbon source is indispensable for the removal, since total nitrogen (TN) removal reached 77.89 % with the influent C/N of 7.8. Secondly, conducted in batch experiments with different doses of ABC-nZVI with/without active sludge, removal efficiency of total inorganic nitrogen (TIN) and the effective time achieved 84.94 % and 24 h with an ABC-nZVI dose of 300 mg/L, respectively. Thirdly, it was found that the duration of high-efficiency denitrification reached 9 h with the addition of 250 mg/L of ABC-nZVI to the anoxic tank of A/A/O-MBR, and the effluent ammonium nitrogen (NH4+-N) also meet the national discharge standard. Besides, biodiversity of both anoxic and aerobic sludge was apparently promoted with the addition of ABC-nZVI, while the lab-scale A/A/O-MBR could also be fully rehabilitated within 12 h. Finally, predicted through PICRUSt2, relevant abundance of functional genes involved in nitrogen metabolism could be enriched by nZVI addition. As an alternative supporting electron donor and mediator, ABC-nZVI can also be participated in the enhanced nitrogen removal in A/A/O-MBR at low C/N.

Facile preparation of activated carbon supported nano zero-valent iron for Cd(Ⅱ) removal in aqueous environment

Activated carbon-supported nano-zero-valent iron (nZVI@AC) is considered to be one of the most promising materials for in-situ remediation of pollutants in aqueous environment, while liquid phase reduction (LPR) is one of the most commonly used preparation methods for nZVI@AC. However, the complex operation and the requirement of various agents limit the practical application of the traditional liquid-phase reduction (TLPR). In this study, an improved liquid phase reduction method (ILPR) was proposed, which was characterized by solid-state dosing of reducing agents. Compared with TLPR, ILPR simplified the preparation process, while there was no requirement of polyethylene glycol and ethanol. When the Cd(II) removal efficiency was used as the evaluation index, the preferred parameters of ILPR were as follows: AC/FeSO4·7H2O mass ratio was 15:1; NaBH4 dosage was 8 g; ultrasonic time was 1 h; stirring time was 20 min. Moreover, the Cd(II) removal efficiency of nZVI@AC prepared by ILPR (nZVI@AC-I) was greater than 92.00%, which was superior to that of nZVI@AC prepared by TLPR (nZVI@AC-T). The characterization results showed that the pore parameters, surface functional groups and iron contents of nZVI@AC-I and nZVI@AC-T were basically the same. However, the distribution of iron-containing particles on the surface of nZVI@AC-I was more uniform. Furthermore, the Fe0 in nZVI@AC-I had a smaller particle size and a higher content. Overall, this study provided a promising approach for nZVI@AC preparation.

Pencil graphite supported nano zero-valent iron for removal of levofloxacin from aqueous solution: Effects of pH, kinetic and biological activity

A highly efficient, and potentially recyclable antibacterial composite was prepared in an efficient simple process. Antimicrobial levofloxacin (LEV) was used to functionalize the surface of nano zero-valent iron (Fe0) supported by pencil graphite (PG). The surface morphology, elemental composition, particle size, and removal efficiency of the PG-Fe0 composite were confirmed by UV, FTIR, EDX, SEM, TEM, and XRD techniques. The potential influence of pH, adsorbate concentration, contact time, and temperature on the removal efficiency of LEV by the magnetic composite (PG-Fe0) from an aqueous solution was investigated. The well-known established models were used to examine the adsorption isotherms, and the results showed that the kinetic adsorption data fit well with the pseudo-second-order model, with the highest removal efficiency achieved from pH 5–7 (85%). The maximum adsorption capacity qmax on the surface of Fe0-PG for LEV was obtained using the Langmuir isotherm at pH 6.5 (66.3 mg/g) and pH 8 (11.4 mg/g). All adsorption thermodynamic parameters at pH 6.5 suggested a chemisorption endothermic natural process ΔHo(44.4 kJ/mol), and the negative value of free Gibbs energy indicated a spontaneous process at an ambient temperature. Furthermore, the removal efficiency of the PG-Fe0 composite was better than that of the Fenton-like catalyst performance for both Fe0 and PG-Fe0. Reusability and antibacterial activity of adsorbed LEV on the surface of PG-Fe0 were investigated against various types of gram-positive bacteria; (E. faecalis, S. epidermidis, and S. aureus) and gram-negative; (E. coli, K. pneumonia, and P. Mirabilia) via agar well diffusion method. Finally, the magnetic feature of the PG-Fe0-LEV composite has numerous potential for recovery and reuse.

Investigation of the degradation and dehalogenation properties of florfenicol by heterogeneous Fenton reaction activated with MIL-53(Al)-supported nano zero-valent iron

The antibiotic florfenicol (FF) discharged into the aquatic environment may cause serious water pollution. Therefore, an effective way to eliminate FF antibiotics from the water bodies should be proposed. Herein, MIL-53(Al)-supported nano zero-valent iron (NZVI@MIL-53(Al)) was synthesized and applied to activate hydrogen peroxide (H2O2) to spark the Fenton reaction for FF antibiotics removal. The characterization results demonstrated the successful loading and good dispersion of NZVI onto MIL-53(Al). 100 % FF antibiotics degradation could be achieved under the optimal reaction conditions, including an initial FF antibiotics concentration of 20 mg L−1, initial solution pH of 3.0, NZVI@MIL-53(Al) dose of 25 mg L−1, and H2O2 concentration of 0.2 mM. And after four cycles, the FF antibiotic degradation efficiency was still 81.18 %. The lowest tolerance for HCO3− was observed while the degradation activity was maintained at the presence of Cl− and HA. EPR measurement and free radical quenching experiment showed that ·OH was the main reactive specie in the NZVI@MIL-53(Al)/H2O2 system. FF antibiotics degradation involved hydroxylation reactions (electrophilic substitution), dehalogenation, hydrolysis, and cleavage based on the UPLC-MS/MS analysis and DFT calculation. Noteworthy, 0.247 mg L−1 of F− and 1.2 mg L−1 of Cl− were detected in the solution after the reaction due to the breakage of the stable C–Cl bond and C–F bond. Finally, this work revealed that the NZVI@MIL-53(Al), with high stability and recyclability, could be a potential heterogeneous catalyst for treating antibiotic wastewater.