Critical roles of sulfidation solvent in controlling surface properties and the dechlorination reactivity of S-nZVI

High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.

Differential and mechanism analysis of sulfate influence on the degradation of 1,1,2- trichloroethane by nano- and micron-size zero-valent iron

The in-situ reduction of zero-valent iron (ZVI) is an effective method for removing chlorinated aliphatic hydrocarbons (CAHs) from groundwater. The heterogeneity of environmental conditions is also crucial in affecting dechlorination efficiency. Until now, the effect of Sulfate (SO42-) on ZVI activity has been debated, and the related mechanism research on SO42- behaviour during the abiotic reduction process of chlorinated alkanes is still lacking. In this study, the impacts of SO42- concentrations (0, 2, 4, 8, 80 mM) on the degradation of 1,1,2-trichloroethane (1,1,2-TCA) by micron-size ZVI (mZVI) and nano-size ZVI (nZVI) were systematically investigated. For mZVI, Kobs increased by 0.6 (2 mM), 0.5 (4 mM), 1.1 (8 mM), and 1.6 times (80 mM). For nZVI, Kobs decreased by 32% (2 mM), 39% (4 mM), 45% (8 mM), and 9% (80 mM). The results showed that SO42- increased the rate of 1,1,2-TCA degradation by mZVI but weakened the reduction performance of nZVI; however, this inhibition was reduced when the concentration reached 80 mM. SO42- controlled the degradation of 1,1,2-TCA mainly through the formation of different iron-sulfate complexes on the ZVI surface: water-soluble bidentate iron-sulfate complexes formed on the mZVI surface promoted the corrosion of the oxide layer and accelerated the reduction of 1,1,2-TCA, monodentate complexes mainly formed on the nZVI surface inhibited the reduction of 1,1,2-TCA by blocking surface sites. These results demonstrate the proof of concept to assist land managers in the field application of ZVI technology for the remediation of CAHs contaminated sites with different background concentrations of SO42-.

Improvement strategy of citrate and biochar assisted nano-palladium/iron composite for effective dechlorination of 2,4-dichlorophenol

Rapid passivation and aggregation of nanoscale zero-valent iron (nZVI) seriously limit its performance in the remediation of different contaminants from wastewater. To overcome such issues, in the present study, nano-palladium/iron (nPd/Fe) was simultaneously improved by biochar (BC) prepared from discarded peanut shells and green complexing agent sodium citrate (SC). For this purpose, a composite (SC-nPd/Fe@BC) was successfully synthesized to remove 2,4-dichlorophenol (2,4-DCP) from wastewater. In the SC-nPd/Fe@BC, BC acts as a carrier with dispersed nPd/Fe particles to effectively prevent its agglomeration, and increased the specific surface area of the composite, thereby improving the reactivity and stability of nPd/Fe. Characterization results demonstrated that the SC-nPd/Fe@BC composites were well dispersed, and the agglomeration was weakened. The formation of the passivation layer on the surface of the particles was inhibited, and the mechanism of SC and BC improving the reactivity of nPd/Fe was clarified. Different factors were found to influence the reductive dichlorination of 2,4-DCP, including Pd loading, Fe:C, SC addition, temperature, initial pH, and initial pollutant concentration. The dechlorination results revealed that the synergistic effect of the BC and SC made the removal efficiency and dechlorination rate of 2,4-DCP by SC-nPd/Fe@BC reached to 96.0 and 95.6%, respectively, which was better than that of nPd/Fe (removal: 46.2%, dechlorination: 45.3%). Kinetic studies explained that the dechlorination reaction of 2,4-DCP and the data were better represented by the pseudo-first-order kinetic model. The reaction rate constants followed the order of SC-nPd/Fe@BC (0.0264 min-1) > nPd/Fe@BC (0.0089 min-1) > SC-nPd/Fe (0.0081 min-1) > nPd/Fe (0.0043 min-1). Thus, SC-nPd/Fe@BC was capable of efficiently reducing 2,4-DCP and the dechlorination efficiency of BC and SC synergistically assisted composite on 2,4-DCP was much better than that of SC-nPd/Fe, nPd/Fe@BC and nPd/Fe. Findings suggested that SC-nPd/Fe@BC can be promising for efficient treatment of chlorinated pollutants.

Carboxymethyl cellulose stabilization induced changes in particle characteristics and dechlorination efficiency of sulfidated nanoscale zero-valent iron

Polymer stabilization, exemplified by carboxymethyl cellulose (CMC), has demonstrated effectiveness in enhancing the transport of nanoscale zero-valent iron (nZVI). And, sulfidation is recognized for enhancing the reactivity and selectivity of nZVI in dechlorination processes. The influence of polymer stabilization on sulfidated nZVI (S-nZVI) with various sulfur precursors remains unclear. In this study, CMC-stabilized S-nZVI (CMC-S-nZVI) was synthesized using three distinct sulfur precursors (S2-, S2O42-, and S2O32-) through one-step approach. The antioxidant properties of CMC significantly elevated the concentration of reduced sulfur species (S2-) on CMC-S-nZVIs, marking a 3.1-7.0-fold increase compared to S-nZVIs. The rate of trichloroethylene degradation (km) by CMC-S-nZVIs was observed to be 2.2-9.0 times higher than that achieved by their non-stabilized counterparts. Among the three CMC-S-nZVIs, CMC-S-nZVINa2S exhibited the highest km. Interesting, while the electron efficiency of CMC-S-nZVIs surged by 7.9-12 times relative to nZVI, it experienced a reduction of 7.0-34% when compared with S-nZVIs. This phenomenon is attributed to the increased hydrophilicity of S-nZVI particles due to CMC stabilization, which inadvertently promotes the hydrogen evolution reaction (HER). In conclusion, the findings of this study underscores the impact of CMC stabilization on the properties and dechlorination performance of S-nZVI sulfidated using different sulfur precursors, offering guidance for engineering CMC-S-nZVIs with desirable properties for contaminated groundwater remediation.

Enhancement of norfloxacin degradation by citrate in S-nZVI@Ps system: Chelation and FeS layer

The degradation of organic pollution by sulfur-modified nano zero-valent iron(S-nZVI) combined with advanced oxidation systems has been extensively studied. However, the low utilization of nZVI and low reactive oxygen species (ROS) yield in the system have limited its wide application. Herein, a natural organic acid commonly found in citrus fruits, citric acid (CA), was combined with the conventional S-nZVI@Ps system to enhance the degradation of norfloxacin (NOR). The addition of CA increased the NOR removal by about 31% compared with the conventional S-nZVI@Ps system under the same experimental conditions. Among them, the enhanced effect of CA is mainly reflected in its ability to promote the release of Fe2+ and accelerate the cycling of Fe2+ and Fe3+ to further improve the utilization of nZVI and the generation of ROS; it also promotes the dissolution of the active substance (FeS) on the surface of S-nZVI to further improve the degradation rate of NOR. More importantly, the chelate of CA and Fe2+ (CA-Fe2+) had higher reactivity than alone Fe2+. Free radical quenching and electron spin resonance (ESR) experiments indicated that the main ROS for the degradation of NOR in the CA/S-nZVI@Ps system were SO4•- and OH•. CA-bound sulfur-modifying effects on NOR degradation was systematically investigated, and the degradation mechanism of NOR in CA/S-nZVI@Ps system was explored by various techniques. Additionally, the effect of common anions in water matrix on the degradation of NOR in CA/S-nZVI@Ps system and its degradation of various pollutants were also studied. This study provides a new perspective to enhance the degradation of pollutants by S-nZVI combined with advanced oxidation system, which can help to solve the application boundary problem of S-nZVI.

Minor chromium passivation of S-ZVI enhanced the long-term dechlorination performance of trichlorethylene: Effects of corrosion and passivation on the reactivity and selectivity

The corrosion and surface passivation of sulfidized zero-valent iron (S-ZVI) by common groundwater ions and contaminants are considered to be the most challenging aspects in the application of S-ZVI for remediation of chlorinated contaminants. This study investigated the impacts of corrosive chloride (Cl-) and passivation of hexavalent chromium (Cr(VI)) on the long-term reactivity, selectivity, corrosion behavior, and physicochemical properties during the 60-day aging process of S-ZVI. Although the co-existing of Cl- promoted the initial reactivity of S-ZVI, the rapid consumption of Fe° content shortened the reactive lifetime owing to the insufficient electron capacity. Severe passivation by Cr(VI) (30 mg L-1) preserved the Fe° content but significantly interfered with the reductive sulfur species, resulting in an increase in electron transfer resistance. In comparison, minor passivated S-ZVI (5.0 mg L-1 Cr(VI)) inhibited the hydrogen evolution while concurrently mitigating the further oxidation of the reductive iron and sulfur species, which significantly enhanced the long-term reactivity and selectivity of S-ZVI. Furthermore, the enhancement effect of minor passivation could be detected in the aging processes of one-step, two-step, and mechanochemically synthesized S-ZVI particles with different S/Fe ratios and precursors, which further verified the advantages of minor passivation. This observation is inspirable for the development of innovative strategies for environmental remediation by S-ZVI-based materials.

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.

From liquid to solid: A novel approach for utilizing sulfate reduction effluent through phase transition - Effluent-induced nanoscale zerovalent iron sulfidation

This study investigated the use of sulfate reduction effluent (SR-effluent) to induce sulfidation on nanoscale zerovalent iron (nZVI). SR-effluent-modified nZVI achieved a 100% improvement in Cr(VI) removal from simulated groundwater, a result comparable to cases where other, more typical sulfur precursors (Na2S2O4, Na2S2O3, Na2S, K2S6, and S0) were used. Through a structural equation model analysis, amendment of nanoparticles' agglomeration (standardized path coefficient (std. path coeff.) = -0.449, p < 0.05) and hydrophobicity (std. path coeff. = 0.100, p < 0.05) and direct reaction between iron-sulfur compounds and Cr(VI) (std. path coeff. ranged from -0.195 to 0.322, p < 0.05) were primarily contributing to sulfidation-induced Cr(VI) removal enhancement. Regarding the property improvement of nZVI, the SR-effluent's corrosion radius played a crucial role in tuning the content and distribution of the iron-sulfur compounds based on the core-shell structure of the nZVI and the redox processes at the aqueous-solid interface.

Tetrabromobisphenol A transformation by biochar supported post-sulfidated nanoscale zero-valent iron: Mechanistic insights from shell control and solvent kinetic isotope effects

Post-sulfidated nanoscale zero-valent iron with a controlled FeS_X shell thickness deposited on biochar (S-nZVI/BC) was synthesized to degrade tetrabromobisphenol A (TBBPA). Detailed characterizations revealed that the increasing sulfidation degree altered shell thickness/morphology, S content/speciation/distribution, hydrophobicity, and electron transfer capacity. Meanwhile, the BC improved electron transfer capacity and hydrophobicity and inhibited the surface oxidation of S-nZVI. These properties endowed S-nZVI/BC with highly reactive (∼8.9-13.2 times) and selective (∼58.4-228.9 times) over nZVI/BC in TBBPA transformation. BC modification improved the reactivity and selectivity of S-nZVI by 1.77 and 1.96 times, respectively. The difference of S-nZVI/BC in reactivity was related to hydrophobicity and electron transfer, particularly FeS_X shell thickness and morphology. Optimal shell thickness of ∼32 nm allowed the maximum association between Fe⁰ core and exterior FeS_X, resulting in superior reactivity. A thicker shell with abundant networks increased the roughness but decreased the surface area and electron transfer. The higher [S/Fe]_surface and [S/Fe]_particle were conducive to the selectivity, and [S/Fe]_particle was more influential than [S/Fe]_surface on selectivity upon similar hydrophobicity. The solvent kinetic isotope effects (SKIEs) exhibited that increasing [S/Fe]_dose tuned the relative contributions of atomic H and electron in TBBPA debromination but failed to alter the dominant debromination pathway (i.e., direct electron transfer) in (S)-nZVI/BC systems. Mechanism of electron transfer rather than atomic H contributed to higher selectivity. This work demonstrated that S-nZVI/BC was a prospective material for the remediation of TBBPA-contaminated groundwater.

Strengthened removal of emerging contaminants over S/Fe codoped activated carbon fabricated by a mild one-step thermal transformation scheme

Thermal transformation of carbonized materials to functional activated carbon (AC) is a simplified, economical and eco-friendly strategy, which has great potential in the practical applications of water purification. Herein, a S/Fe codoped activated carbon (S/Fe@AC) with only 0.90 wt% S and 0.76 wt% Fe was creatively fabricated by one synchronous method of physical activation, carbothermal reduction and sulfidation in the solid phase. The formed iron sulfide shell significantly enhances the antioxidation ability of nanoscale zero-valent iron (NZVI, >180 d) and dramatically improves the hydrophobicity of the composite. Meanwhile, the doped thiophenic S in AC enhances the hydrophobicity and increases the specific surface area to 1194.14 m² g^-1. Incorporating with AC in turn greatly strengthens the dispersibility and stability of sulfurized NZVI particles. Compared to NZVI@AC, AC and NZVI, the removal capacity of S/Fe@AC for the representative hydrophobic contaminant-triclosan (TCS) increases to 519.68 mg g^-1 by 66.60%, 78.60% and 981.21%, respectively, outperforming most of the previously reported materials. The strong hydrophobic and π-π interactions, and weak hydrogen bonding and electrostatic repulsion are responsible for the excellent removal performance for TCS. More importantly, the improved chemical property (29.38%) of the composite caused by the doped S/Fe has a greater effect on TCS removal compared with the changed physical structure (14.56%). Furthermore, the stable S/Fe@AC shows strong anti-interference capability and exceptional regenerability. These intriguing discoveries provide new insights into the design of advanced and sustainable adsorbing materials for emerging contaminants.

A quantitative study of the effects of particle' properties and environmental conditions on the electron efficiency of Pd and sulfidated nanoscale zero-valent irons

Electron efficiency (or electron selectivity, ɛ_e) is an important quantitative criterion for zero-valent iron treatment of organohalide contaminated groundwater. The aim of this quantitative study was the systematic exploration and comparison of the effects of the Pd/Fe and S/Fe molar ratios (i.e., [Pd/Fe] and [S/Fe]), trichloroethylene (TCE) concentrations ([TCE]), pH solution, aging time, and water matrices on the ɛ_e of Pd-nZVI and S-nZVI. To this end, we used TCE as a probe contaminant. The ɛ_e of Pd-nZVI increased and then decreased with [Pd/Fe], while that of S-nZVI increased with [S/Fe], as more hydrophobic FeS₂ was formed on S-nZVI at higher [S/Fe]. The ε_e of S-nZVI and Pd-nZVI increased with increasing [TCE]. Specifically, the ε_e of S-nZVI and Pd-nZVI at [TCE] of 200 ppm increased by 24.9 % and 79.3 %, respectively, compared with that at [TCE] of 10 ppm. As the H₂ evolution reaction (HER) was more sensitive to surface passivation than TCE dechlorination, the ε_e of S-nZVI and Pd-nZVI under alkaline conditions was higher than that under basic conditions, and increased by 11.7 % and 37.8 %, respectively, at pH 10 relative to that at pH 6. The ε_e also increased with the aging time of the S-nZVI and Pd-nZVI particles; the increase was by 27.2 % and 59.6 %, respectively, at aging time of 30 d compared with that of the fresh ones. The ɛ_e of both particles were higher in artificial groundwater (AGW) than in real groundwater (RGW). For all batch experiments, the ε_e of S-nZVI increased over the reaction time and tended to outperform that of Pd-nZVI, even though the ε_e of Pd-nZVI was higher than that of S-nZVI at the initial stage of TCE dechlorination, thereby justifying the longevity of S-nZVI.

Recent advances in bioremediation of heavy metals and persistent organic pollutants: A review

Heavy metals and persistent organic pollutants are causing detrimental effects on the environment. The seepage of heavy metals through untreated industrial waste destroys the crops and lands. Moreover, incineration and combustion of several products are responsible for primary and secondary emissions of pollutants. This review has gathered the remediation strategies, current bioremediation technologies, and their primary use in both in situ and ex situ methods, followed by a detailed explanation for bioremediation over other techniques. However, an amalgam of bioremediation techniques and nanotechnology could be a breakthrough in cleaning the environment by degrading heavy metals and persistant organic pollutants.

Insights into enhanced removal of Cd2+ from aqueous solutions by attapulgite supported sulfide-modified nanoscale zero-valent iron

The sulfidation of nanoscale zerovalent iron (nZVI) has received increasing attention for reducing the oxidizability of nZVI and improving its reactivity toward heavy metal ions. Here, a sulfide (S)-modified attapulgite (ATP)-supported nanoscale nZVI composite (S-nZVI@ATP) was rapidly synthesized under acidic conditions and used to alleviate Cd²⁺ toxicity from an aqueous solution. The degree of oxidation of S-nZVI@ATP was less than that of nZVI@ATP, indicating that the sulfide modification significantly reduced the oxidation of nZVI. The optimal loading ratio was at an S-to-Fe molar ratio of 0.75, and the adsorption performance of S-nZVI@ATP for Cd²⁺ was significantly improved compared with that of nZVI@ATP. The removal of Cd²⁺ by S-nZVI@ATP was 100% when the adsorbent addition was 1 g/L, the solution was 30 mL, and the adsorption was performed at 25 °C for 24 h with an initial Cd²⁺ concentration of 100 mg/L. Kinetics studies showed that the adsorption process of Cd followed the pseudo-second-order model, indicating that chemisorption was the dominant adsorption mechanism. The adsorption of Cd²⁺ by S-nZVI @ATP is dominated by the complexation between the iron oxide or iron hydroxide shell of S-nZVI and Cd²⁺ and the formation of Cd(OH)₂ and CdS precipitates.

Removal of Trichloroethylene from Water by Bimetallic Ni/Fe Nanoparticles

Chlorinated organic solvents (COSs) are a significant threat to human beings. In this study, nanoscale bimetallic Ni/Fe particles were synthesized from the reaction of sodium borohydride (NaBH4) with the reduction of Ni2+ and Fe2+ in an aqueous solution. The synthesized nanoscale zero-valent iron (nZVI) and Ni-nZVI were characterized by SEM (scanning electron microscopy), XRD (X-ray diffractometer), Brunauer–Emmett–Teller (BET), and transmission electron microscopy (TEM). The removal performance of trichloroethylene (TCE) over the nZVI catalyst and Ni-nZVI was evaluated. Ni-nZVI with different Ni contents exhibited good reactivity towards the dechlorination of TCE over a 1h period, and the pseudo-first-order rate constant for TCE dechlorination by Ni-nZVI was 1.4–3.5 times higher than that of nZVI. Ni-nZVI with 5 wt% Ni contents exhibited the best dechlorination effect; the removal rates of TCE and its by-product dichloroethylene (DCE) were 100% and 63.69%, respectively. These results indicated that the Ni nanoparticles as the second dopant metal were better than nZVI for TCE degradation. This determination of the optimal Ni-NZVI load ratio provides a factual and theoretical basis for the subsequent application of nano-metal binding in the environment.

Combining electrokinetic treatment with modified zero-valent iron nanoparticles for rapid and thorough dechlorination of trichloroethene

In situ injection of nanoscale zero-valent iron (nZVI) slurry is a promising method to treat chlorinated solvents represented by trichloroethylene (TCE) in groundwater. In this study, the effects of sulfidation and emulsification treatment on the performance of nZVI reductive dechlorination of TCE under enhancement by an external electric field were evaluated. The hydrophobic oil film on the surface of sulfidized and emulsified zero-valent iron (S-EZVI) can sequestrate more than one-fifth of the unreacted TCE in the early stage of the experiment (at 5 min). The FeS layer formed on the surface of S-EZVI can facilitate the electron-transfer process and reduce the degree of corrosion of Fe⁰ with water by 94.0%. Electric-field-enhanced S-EZVI technology can remove more than 93.1% of TCE in the pH range 6.0-9.0, and the performances in overly acid and overly alkali environments both improved. Under the optimal conditions, the TCE removal rate and reaction constant of the applied electric field group reached 96.7% and 1.6 × 10^-2 L g^-1 min^-1, respectively, which were much higher than those of the group without an electric field (53.2% and 3.3 × 10^-3 L g^-1 min^-1) owing to rapid concurrent hydrogenolysis of dichloroethenes and vinyl chloride, or another transformation pathway, such as direct oxidation by the anode. Thereby, this method avoids accumulation of chlorinated intermediates, especially toxic vinyl chloride. This work shows that combination technology has many characteristics that are favorable for field application, and it is expected to provide a new reference and have application value for development of in situ efficient and thorough treatment of TCE-contaminated groundwater.

Strong influence of degree of substitution on carboxymethyl cellulose stabilized sulfidated nanoscale zero-valent iron

Carboxymethyl cellulose (CMC) has been widely adopted as stabilizer to enhance the subsurface mobility of nanoscale zerovalent iron (nZVI). However, CMC surface modification also cause severe decrease of the longevity and electron utilization efficiency (ε_e) of nZVI, which is still not well understood. In this study, we demonstrate the negative influence of CMC on the properties of sulfidated nZVI (S-nZVI) could be reversed by increasing the degree of substitution (D.S.) of CMC. Consistent with previous study, the sample CMC-S-nZVI prepared with commercial CMC with degree of substitution (D.S.) of 0.75 exhibited a considerable low longevity of 33 days with ε_e of 4.5%, much lower than that of sulfidated nZVI (S-nZVI, 113 days and 13%). In sharp contrast, the sample HCMC-S-nZVI synthesized with CMC with super high D.S. of 1.76 demonstrated significantly enhanced longevity of 139 days and ε_e of 20%. The enhancement was attributed to compatible molecular structure of CMC with super high D.S. Moreover, the HCMC-S-nZVI also exhibited higher mobility in porous media than CMC-S-nZVI. Our work provides a feasible way to prepare S-nZVI with desired properties including high subsurface transportability, high longevity and high ε_e.