Assessing the effectiveness of nanoscale zero-valent iron particles produced by green tea for Cr(VI)-contaminated groundwater remediation

Nanoscale zero-valent iron particles(NZVI) produced by using green tea(GT) extract as a reductant can remove Cr(Ⅵ) from water effectively,which can be utilized in groundwater remediation.In order to define the reaction mechanism and removal effect in the aquifer,in this study,GT-NZVI particles were prepared and measured by some characterization methods to define their surface performance,and then batch and one-dimensional experiments were carried out to reveal the reaction properties of GT-NZVI and Cr(Ⅵ) in groundwater.The results showed that the prepared GT-NZVI particles were regular spherical with a diameter of 10-20 nm,which could disperse in water stably.The main component of GT-NZVI wasα-Fe with superficial polyphenols as a stabilizer.GT-NZVI suspension had good ability to reduce the Cr(Ⅵ) to Cr(Ⅲ) in water.When the concentration of GT-NZVI was 1 g/L,the removal efficiency of Cr(Ⅵ)with an initial concentration of 100 mg/L reached 92.8% in 1 h reaction.In column tests,GT-NZVI passed through the natural sand column successfully with an average outflow percentage of 71.2%.The simulated in-situ reaction zone(IRZ) with GT-NZVI was used to remediate Cr(Ⅵ) contaminated groundwater.The oufflow concentration of Cr(Ⅵ) kept in 0.14-0.32 mg/L corresponding to the outflow rate below 0.32%within 15 days,and the removal efficiency of Cr(Ⅵ) by IRZ with GT-NZVI decreased with the increase of aquifer medium particle size,groundwater flow rate and ionic strength.Most of Cr(Ⅲ) as reduzate was adsorbed or immobilized on the surface or in the lattice of GT-NZVI,which indicated effective immobilization for chromium.

Nanoscale Zero-Valent Iron(nZVI)for Heavy Metal Wastewater Treatment:A Perspective

Industries such as non-ferrous metal smelting discharge billions of gallons of highly toxic heavy metal wastewater(HMW)worldwide annually,posing a severe challenge to conventional wastewater treatment plants and harming the environment.HMW is traditionally treated via chemical precipitation using lime,caustic,or sulfide,but the effluents do not meet the increasingly stringent discharge standards.This issue has spurred an increase in research and the development of innovative treatment technologies,among which those using nanoparticles receive particular interest.Among such initiatives,treatment using nanoscale zero-valent iron(nZVI)is one of the best developed.While nZVI is already well known for its site-remediation use,this perspective highlights its application in HMW treatment with metal recovery.We demonstrate several advantages of nZVI in this wastewater application,including its multifunctionality in sequestrating a wide array of metal(loid)s(>30 species);its capability to capture and enrich metal(loid)s at low concentrations(with a removal capacity reaching 500 mg·g^(-1)nZVI);and its operational convenience due to its unique hydrodynamics.All these advantages are attributable to nZVI’s diminutive nanoparticle size and/or its unique iron chemistry.We also present the first engineering practice of this application,which has treated millions of cubic meters of HMW and recovered tons of valuable metals(e.g.,Cu and Au).It is concluded that nZVI is a potent reagent for treating HMW and that nZVI technology provides an eco-solution to this toxic waste.

Performance of bimetallic nanoscale zero-valent iron particles for removal of oxytetracycline

In this study, bimetallic nanoscale zero-valent iron particles（nZVI）, including copper/nanoscale zero-valent iron particles（Cu/nZVI） and nickel/nanoscale zero-valent iron particles（Ni/nZVI）, were synthesized by one-step liquid-phase reduction and applied for oxytetracycline（OTC） removal. The effects of contact time and initial p H on the removal efficiency were studied. The as-prepared nanoscale particles were characterized by scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and X-ray diffraction（XRD）. Finally, the degradation mechanisms of OTC utilizing the as-prepared nanoparticles were investigated by using X-ray photoelectron spectroscopy（XPS） and mass spectrometry（MS）. Cu/n ZVI presented remarkable ability for OTC degradation and removed71.44% of OTC（100 mg/L） in 4 hr, while only 62.34% and 31.05% of OTC was degraded by Ni/nZVI and nZVI respectively. XPS and MS analysis suggested that OTC was broken down to form small molecules by ·OH radicals generated from the corrosion of Fe0. Cu/nZVI and Ni/n ZVI have been proved to have potential as materials for application in OTC removal because of their significant degradation ability toward OTC.

Biochar Supported Nanoscale Zero-valent Iron Composites for the Removal of Petroleum from Wastewater

Considering the need for efficiently and rapidly treating oily wastewater while preventing secondary pollution,the nanoscale zero-valent iron(nZVI)was supported on biochar prepared by using a spent mushroom substrate(SMS),to produce an iron-carbon composite(SMS-nZVI).The ability of the SMS-nZVI to treat wastewater containing high concentration of oil was then comprehensively evaluated.The morphology,structure,and other properties of the composite were characterized by using scanning electron microscopy,transmission electron microscopy,the Brunauer-Emmett-Teller nitrogen sorption analysis,and the Fourier transform infrared spectroscopy.The results show that the biochar prepared by using the SMS can effectively prevent the agglomeration of nZVI and increase the overall specific surface area,thereby enhancing the absorption of petroleum by the composite.Experiments reveal that compared with the SMS and nZVI,the SMS-nZVI composite removes petroleum faster and more efficiently from wastewater.Under optimized conditions involving an nZVI to biochar mass ratio of 1:5 and a pH value of 4,the efficiency for removal of petroleum from wastewater with an initial petroleum concentration of 1000 mg/L could reach 95%within 5 h.Based on a natural aging treatment involving exposure to air for 30 d,the SMS-nZVI composite retained an oil removal rate of higher than 62%,and this result could highlight its stability for practical applications.

Study of diclofenac removal by the application of combined zero-valent iron and calcium peroxide nanoparticles in groundwater

Diclofenac(DCF)is one of the most frequently detected pharmaceuticals in groundwater,posing a great threat to the environment and human health due to its toxicity.To mitigate the DCF contamination,experiments on DCF degradation by the combined process of zero-valent iron nanoparticles(nZVI)and nano calcium peroxide(nCaO_(2))were performed.A batch experiment was conducted to examine the influence of the adding dosages of both nZVI and nCaO_(2)nanoparticles and pH value on the DCF removal.In the meantime,the continuous-flow experiment was done to explore the sustainability of the DCF degradation by jointly adding nZVI/nCaO_(2)nanoparticles in the reaction system.The results show that the nZVI/nCaO_(2)can effectively remove the DCF in the batch test with only 0.05 g/L nZVI and 0.2 g/L nCaO_(2)added,resulting in a removal rate of greater than 90%in a 2-hour reaction with an initial pH of 5.The degradation rate of DCF was positively correlated with the dosage of nCaO_(2),and negatively correlated with both nZVI dosage and the initial pH value.The order of significance of the three factors is identified as pH value>nZVI dosage>nCaO_(2)dosage.In the continuous-flow reaction system,the DCF removal rates remained above 75%within 150 minutes at the pH of 5,with the applied dosages of 0.5 g/L for nZVI and 1.0 g/L for nCaO_(2).These results provide a theoretical basis for the nZVI/nCaO_(2)application to remove DCF in groundwater.

Corrosion behaviors and kinetics of nanoscale zero-valent iron in water:A review

Knowledge on corrosion behaviors and kinetics of nanoscale zero-valent iron(nZVI)in aquatic environment is particularly significant for understanding the reactivity,longevity and stability of nZVI,as well as providing theoretical guidance for developing a cost-effective nZVI-based technology and designing large-scale applications.Herein,this review gives a holistic overview on the corrosion behaviors and kinetics of nZVI in water.Firstly,Eh-pH diagram is introduced to predict the thermodynamics trend of iron corrosion.The morphological,structural,and compositional evolution of(modified-)nZVI under different environmental conditions,assisted with microscopic and spectroscopic evidence,is then summarized.Afterwards,common analytical methods and characterization technologies are categorized to establish time-resolved corrosion kinetics of nZVI in water.Specifically,stable models for calculating the corrosion rate constant of nZVI as well as electrochemical methods for monitoring the redox reaction are discussed,emphasizing their capabilities in studying the dynamic iron corrosion processes.Finally,in the future,more efforts are encouraged to study the corrosion behaviors of nZVI in long-term practical application and further build nanoparticles with precisely tailored properties.We expect that our work can deepen the understanding of the nZVI chemistry in aquatic environment.

Amino acids modified nanoscale zero-valent iron:Density functional theory calculations,experimental synthesis and application in the Fenton-like degradation of organic solvents

To improve the adsorption and catalytic performance of heterogeneous Fenton-like catalysts for oil wastes,amino acids were used to modify nanoscale zero-valent iron(AA@Fe^(0)),which were applied in the Fenton-like degradation of organic solvents(tributyl phosphate and n-dodecane,named TBP and DD).Twelve amino acids,i.e.,glycine(Gly),alanine(Ala),leucine(Leu),proline(Pro),phenylalanine(Phe),methionine(Met),cysteine(Cys),asparagine(Asn),serine(Ser),glutamic acid(Glu),lysine(Lys)and arginine(Arg),were selected and calculated by density functional theory(DFT).The optimized structure,charge distribution,the highest occupied molecular orbital(HOMO),the lowest unoccupied molecular orbital(LUMO),interaction region indicator(IRI)isosurface map and adsorption energy of AA@Fe^(0),AA@Fe^(0)-TBP and AA@Fe^(0)-DD were studied,which indicated that Fe is more likely to approach and charge transfer with-COO and-NH_(3) on theα-carbon of amino acids.There is strong attraction between Fe and–COO,and Van der Waals force between Fe and-NH_(3),respectively.In the interaction of AA@Fe^(0)with TBP and DD,Van der Waal force plays an important role.AA@Fe^(0)was synthesized in laboratory and characterized to investigate physicochemical properties.In Fenton-like degradation of organic solvents,the change of COD in water phase during the degradation process as well as the volume of the organic phase after the reaction were investigated.The results of calculations combined with experiments showed that Ser-modified Fe^(0)performed the best in these amino acids,with 98%removal of organic solvents.A possible catalytic mechanism was proposed in which amino acids acted a linking role between Fe and organic solvents,activating H_(2)O_(2)to generate hydroxyl radicals for the degradation of organic solvents.

Factors Affecting the Reductive Properties of the Core-Shell SiO2-Coated Iron Nanoparticles

In this study, novel core-shell SiO2-coated iron nanoparticles (SiO2-nZVI) were synthesized using a one-step Stoeber method. The Malachite green degradation abilities of the nanoparticles were investigated. The effects of ethanol/distilled water volume ratio, presence and absence of PEG, tetraethyl orthosilicate (TEOS) dosage, and hydrolysis time used in the nanoparticles preparation process were investigated. The results indicated that the SiO2-coated iron nanoparticles had the highest reduction activity when the particles synthesized with ethanol/H2O ratio of 2:1, PEG of 0.15 ml, TEOS of 0.5 ml and the reaction time was 4 h. The SiO2-nZVI nanoparticles were characterized using Transmission Electron Microscopy (TEM), Energy Dispersive Spectrometry (EDS) and powder X-Ray Diffraction (XRD). The results showed that the average particles diameter of the SiO2-nZVI was 20 - 30 nm. The thickness of the outside SiO2 film is consistent and approximately 10 nm. The results indicated that the nanoparticles coated completely with a transparent SiO2-film. Such nanoparticles could have wide applications in dye decolorization.

Unraveling biochar surface area on structure and heavy metal removal performances of carbothermal reduced nanoscale zero-valent iron

Carbothermal reduction using biochar(BC)is a green and effective method of synthesizing BCsupported nanoscale zero-valent iron(nanoFe^(0))composites.However,the effect of BC surface area on the structure,distribution,and performance such as the heavy metal uptake capacity of nanoFe^(0)particles remains unclear.Soybean stover-based BCs with different surface areas(1.7−1472 m^(2)/g)were prepared in this study.They have been used for in-situ synthesis BCs-supported nanoFe^(0)particlesthrough carbothermal reduction of ferrous chloride.The BCs-supported nanoFe^(0)particles were found to be covered with graphene shells and dispersed onto BC surfaces,forming the BC-supported graphene-encapsulated nanoFe^(0)(BC-G@Fe^(0))composite.These graphene shells covering the nanoFe^(0)particles were formed because of gaseous carbon evolved from biomass carbonization reacting with iron oxides/iron salts.Increasing BC surface area decreased the average diameters of nanoFe^(0)particles,indicating a higher BC surface area alleviated the aggregation of nanoFe^(0)particles,which resulted in higher heavy metal uptake capacity.At the optimized condition,BC-G@Fe^(0)composite exhibited uptake capacities of 124.4,121.8,254.5,and 48.0 mg/g for Cu^(2+),Pb^(2+),Ag^(+),and As^(3+),respectively(pH 5,25℃).Moreover,the BC-G@Fe^(0)composite also demonstrated high stability for Cu^(2+)removal from the fixed-bed continuous flow,in which 1 g of BC-G@Fe^(0)can work for 120 h in a 4 mg/L Cu^(2+)flow continually and clean 28.6 L Cu^(2+)contaminated water.Furthermore,the BC-G@Fe^(0)composite can effectively immobilize the bioavailable As^(3+)from the contaminated soil,i.e.,5%(w)of BC-G@Fe^(0)composite addition can immobilize up to 92.2%bioavailable As^(3+)from the contaminated soil.

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.

Decolorization of Methyl Orange by a new clay-supported nanoscale zero-valent iron:Synergetic effect,efficiency optimization and mechanism

In this study, a novel nanoscale zero-valent iron（n ZVI） composite material was successfully synthesized using a low-cost natural clay, ＂Hangjin 2~#clay＂（HJ clay） as the support and tested for the decolorization of the azo dye Methyl Orange（MO） in aqueous solution by n ZVI particles. According to the characterization and MO decolorization experiments, the sample with 5：1 HJ clay-supported n ZVI（HJ/n ZVI） mass ratio（HJ-n ZVI5） showed the best dispersion and reactivity and the highest MO decolorization efficiency. With the same equivalent Fe0 dosage, the HJ-n ZVI1 and HJ-n ZVI5 samples demonstrated a synergetic effect for the decolorization of MO： their decolorization efficiencies were much higher than that achieved by physical mixing of HJ clay and n ZVIs, or the sum of HJ clay and n ZVIs alone. The synergetic effect was primarily due to the improved dispersion and more effective utilization of the n ZVI particles on/in the composite materials. Higher decolorization efficiency of MO was obtained at larger HJ-n ZVI dosage, higher temperature and under N2 atmosphere, while the MO initial concentration and p H were negatively correlated to the efficiency. HJ clay not only works as a carrier for n ZVI nanoparticles, but also contributes to the decolorization through an ＂adsorption-enhanced reduction＂ mechanism. The high efficiency of HJ-n ZVI for decontamination gives it great potential for use in a variety of remediation applications.

Superior trichloroethylene removal from water by sulfide-modified nanoscale zero-valent iron/graphene aerogel composite

Sulfide-modified nanoscale zero-valent iron(S-nZVI) is a promising material for removal of organic pollutants from water, but S-nZVI nanoparticles(NPs) easily agglomerate and have poor contact with organic contaminants.Herein, we propose a new S-nZVI/graphene aerogel(S-nZVI/GA) composite which exhibits superior removal capability for trichloroethylene(TCE) from water.Three-dimensional porous graphene aerogel(GA) can improve the efficiency of electron transport, enhance the adsorption of organic pollutants and restrain the agglomeration of the core-shell S-nZVI NPs.The TCE removal rates of Fe S, nZVI, GA and S-nZVI were 27.8%, 42%, 63% and 75% in 2 hr, respectively.Furthermore, TCE was completely removed within 50 min by S-nZVI/GA.The TCE removal rate increased with increasing p H and temperature, and TCE removal followed the pseudo-first-order kinetic model.The results demonstrate the great potential of S-nZVI/GA composite as a low-cost,easily separated and superior monolithic adsorbent for removal of organic pollutants.

Nanoencapsulation of arsenate with nanoscale zero-valent iron(nZVI):A 3D perspective

The principal forces driving the efficient enrichment and encapsulation of arsenic(As) into nanoscale zero-valent iron(nZVI) are the disordered arrangement of the atoms and the gradient chemical potentials within the core-shell interface. The chemical compositions and the fine structure of nZVI are characterized with a combination of spherical aberration corrected scanning transmission electron microscopy(Cs-STEM), X-ray energy-dispersive spectroscopy(XEDS), electron energy loss spectroscopy(EELS), and high-resolution X-ray photoelectron spectroscopy(HR-XPS). Atomically resolved EELS at the oxygen K-edge unfolds that the Fe species in nZVI are well stratified from Fe(Ⅲ) oxides in the outermost periphery to a mixed Fe(Ⅲ)/Fe(Ⅱ) interlayer, then Fe(Ⅱ) oxide and the pure Fe(0) phase. Reactions between As(Ⅴ)and nZVI suggest that a well-structured local redox gradient exists within the shell layer, which serves as a thermodynamically favorable conduit for electron transfer from the iron core to the surface-bound As(Ⅴ). HR-XPS with ion sputtering shows that arsenic species shift from As(Ⅴ), As(Ⅲ)/As(Ⅴ) to As(Ⅴ)/As(Ⅲ)/As(0) from the iron oxide shell–water interface to the Fe(0) core. Results reinforce previous work on the efficacy of nZVI for removing and remediating arsenic while the analytical TEM methods are also applicable to the study of environmental interfaces and surface chemistry.

Stabilization of nanoscale zero-valent iron in water with mesoporous carbon(n ZVI@MC)

Two challenges persist in the applications of nanoscale zero-valent iron(nZVI) for environmental remediation and waste treatment: limited mobility due to rapid aggregation and short lifespan in water due to quick oxidation. Herein, we report the nZVI incorporated into mesoporous carbon(MC) to enhance stability in aqueous solution and mobility in porous media. Meanwhile, the reactivity of nZVI is preserved thanks to high temperature treatment and confinement of carbon framework. Small-sized(～16 nm) nZVI nanoparticles are uniformly dispersed in the whole carbon frameworks. Importantly, the nanoparticles are partially trapped across the carbon walls with a portion exposed to the mesopore channels. This unique structure not only is conductive to hold the nZVI tightly to avoid aggregation during mobility but also provides accessible active sites for reactivity. This new type of nanomaterial contains ～10 wt% of iron. The nZVI@MC possesses a high surface area(～ 500 m^2/g) and uniform mesopores(～ 4.2 nm) for efficient pollutant diffusion and reactions. Also, high porosity of nZVI@MC contributes to the stability and mobility of nZVI. Laboratory column experiments further demonstrate that nZVI@MC suspension(～4 g Fe/L) can pass through sand columns much more efficiently than bare nZVI while the high reactivity of nZVI@MC is confirmed from reactions with Ni(II). It exhibits remarkably better performance in nickel(20 mg/L) extraction than mesoporous carbon, with 88.0% and 33.0%uptake in 5 min, respectively.

Humic acid and metal ions accelerating the dechlorination of 4-chlorobiphenyl by nanoscale zero-valent iron

Transformation of polychlorinated biphenyls （PCBs） by zero-valent iron represents one of the latest innovative technologies for environmental remediation. The dechlorination of 4-chlorobiphenyl （4-C1BP） by nanoscale zero-valent iron （NZVI） in the presence of humic acid or metal ions was investigated. The results showed that the dechlorination of 4-C1BP by NZVI increased with decreased solution pH. When the initial pH value was 4.0, 5.5, 6.8, and 9.0, the de.chlorination efficiencies of 4-CIBP after 48 hr were 53.8%, 47.8%, 35.7%, and 35.6%, respectively. The presence of humic acid inhibited the reduction of 4-CIBP in the first 4 hi＇, and then significantly accelerated the dechlorination by reaching 86.3% in 48 hr. Divalent metal ions, Co2＋, Cu2＋, and Ni2＋, were reduced and formed bimetals with NZVI, thereby enhanced the dechlorination of 4-CIBP. The dechlorination percentages of 4-CIBP in the presence of 0.1 mmol/L Co2~, Cuz~ and Niz~ were 66.1%, 66.0% and 64.6% in 48 hr, and then increased to 67.9%, 71.3% and 73.5%, after 96 hr respectively. The dechlorination kinetics of 4-C1BP by the NZVI in all cases followed pseudo-first order model. The results provide a basis for better understanding of the dechlorination mechanisms of PCBs in real environment.

Nanoencapsulation of hexavalent chromium with nanoscale zero-valent iron:High resolution chemical mapping of the passivation layer

Solid phase reactions of Cr（Ⅵ） with Fe（0） were investigated with spherical-aberration-corrected scanning transmission electron microscopy（Cs-STEM） integrated with X-ray energy-dispersive spectroscopy（XEDS）. Near-atomic resolution elemental mappings of Cr（Ⅵ）–Fe（0） reactions were acquired. Experimental results show that rate and extent of Cr（Ⅵ） encapsulation are strongly dependent on the initial concentration of Cr（Ⅵ） in solution. Low Cr loading in nZⅥ（〈1.0 wt%） promotes the electrochemical oxidation and continuous corrosion of n ZⅥ while high Cr loading（〉1.0 wt%） can quickly shut down the Cr uptake. With the progress of iron oxidation and dissolution, elements of Cr and O counter-diffuse into the nanoparticles and accumulate in the core region at low levels of Cr（Ⅵ）（e.g., 〈 10 mg/L）. Whereas the reacted n ZⅥ is quickly coated with a newly-formed layer of 2–4 nm in the presence of concentrated Cr（Ⅵ）（e.g., 〉 100 mg/L）. The passivation structure is stable over a wide range of pH unless pH is low enough to dissolve the passivation layer. X-ray photoelectron spectroscopy（XPS） depth profiling reconfirms that the composition of the newly-formed surface layer consists of Fe（Ⅲ）–Cr（Ⅲ）（oxy）hydroxides with Cr（Ⅵ） adsorbed on the outside surface. The insoluble and insulating Fe（Ⅲ）–Cr（Ⅲ）（oxy）hydroxide layer can completely cover the n ZⅥ surface above the critical Cr loading and shield the electron transfer. Thus, the fast passivation of nZⅥ in high Cr（Ⅵ） solution is detrimental to the performance of nZⅥ for Cr（Ⅵ） treatment and remediation.

Optimizing synthesis conditions of nanoscale zero-valent iron （nZVI） through aqueous reactivity assessment

Nanoscale iron particles （nZVI） is one of the most important engineered nanomaterials applied to environmental pollution control and abatement. Although a multitude of synthesis approaches have been proposed, a facile method to screen the reactivity of candidate nZVI materials produced using different methods or under varying synthesis conditions has yet been established. In this study, four reaction parameters were adjusted in the preparation of borohydride-reduced nZVI. The reductive properties of the resultant nanoparticles were assayed independently using two model aqueous contaminants, Cu （II） and nitrate. The results confirm that the reductive reactivity of nZVI is most sensitive to the initial concentration of iron precursor, borohydride feed rate, and the loading ratio of borohydride to ferric ion during particle synthesis. Solution mixing speed, in contrast, carries a relative small weight on the reactivity of nZVI. The two probing reactions （i.e., Cu（II） and nitrate reduction） are able to generate consistent and quantitative inference about the mass-normalized surface activity of nZVI. However, the nitrate assay is valid in dilute aqueous solutions only （50 mg.L~ or lower） due to accelerated deactivation of iron surface at elevated nitrate concentra- tions. Additional insights including the structural and chemical makeup of nZVI can be garnered from Cu（II） reduction assessments. The reactivity assays investigated in this study can facilitate screening of candidate materials or optimization of nZVI production parameters, which complement some of the more sophisticated but less chemically specific material characterization methods used in the nZVI research.

Sodium citrate and biochar synergistic improvement of nanoscale zero-valent iron composite for the removal of chromium(Ⅵ)in aqueous solutions

Sodium citrate(SC)is a widely-used food and industrial additive with the properties of com-plexation and microbial degradation.In the present study,nano-zero-valent iron reaction system(SC-nZVI@BC)was successfully established by modifying nanoscale zero-valent iron(nZVI)with SC and biochar(BC),and was employed to remove Cr(Ⅵ)from aqueous solu-tions.The nZVI,SC-nZVI and SC-nZVI@BC were characterized and compared using X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),thermogravimetric analy-ses(TGA),vibrating sample magnetometer(VSM),scanning electron microscope(SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The results showed that nZVI was successfully loaded on the biochar,and both the agglomeration and surface pas-sivation problems of nanoparticles were well resolved.The dosage of SC,C∶Fe,initial pH and Cr(Ⅵ)concentration demonstrated direct effects on the removal efficiency.The maximum Cr(Ⅵ)removal rate and the removal capacity within 60 min were 99.7%and 199.46 mg/g,respectively(C∶Fe was 1∶1,SC dosage was 1.12 mol.%,temperature was 25℃,pH=7,and the original concentration of Cr(Ⅵ)was 20 mg/L).The reaction confirmed to follow the pseudo-second-order reaction kinetics,and the order of the reaction rate constant k was as follows:SC-nZVI@BC>nZVI@BC>SC-nZVI>nZVI.In addition,the mechanism of Cr(Ⅵ)removal by SC-nZVI@BC mainly involved adsorption,reduction and co-precipitation,and the reduction of Cr(Ⅵ)to Cr(Ⅲ)by nano Fe0 played a vital role.Findings from the present study demon-strated that the SC-nZVI@BC exhibited excellent removal efficiency toward Cr(Ⅵ)with an improved synergistic characteristic by SC and BC.