Highly Efficient and Rapid Lead(II) Scavenging by ... - ACS Publications

Research Article Cite This: ACS Sustainable Chem. Eng. 2018, 6, 1343−1351

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Highly Efficient and Rapid Lead(II) Scavenging by the Natural Artemia Cyst Shell with Unique Three-Dimensional Porous Structure and Strong Sorption Affinity Bo Wang,∥,§ Junling Xia,†,‡ Liyong Mei,§ Lei Wang,§ and Qingrui Zhang*,†,‡ †

State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P. R. China Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China § Shenzhen-HongKong Institution of Industry, Education Research Environmental Engineering Technique Co., Ltd., 518071 Shenzhen, China ∥ Peking University Shenzhen Graduate School, 518055 Shenzhen, China ‡

S Supporting Information *

ABSTRACT: Heavy metal purification of water is a worldwide issue. In this work, we first find that the discarded Artemia cyst shell exhibits a unique three-dimensional porous structure, which can be recycled for efficient toxic Pb(II) removal. The hierarchical skeleton comprised of the macro−meso−micropore confirmation as well as 17 types of amino acid species provides fast ion accessibility and a strong sorption affinity. The results prove that an extremely rapid Pb capture is obtained in less than 2 min, strong adsorption occurs in the presence of high concentration of Ca/Mg/Na ions, and selectivity is far beyond that of the commercial 001x7 (greater than 50 times). More importantly, an efficient application is achieved with a treatment capacity of 9100 kg wastewater/kg sorbent, which is 45 times greater than the performance of commercially activated carbon and ion-exchange resin. The effluent can be dramatically reduced to below 10 μg/L level (WHO). In addition, we can also regenerate the exhausted biomaterial Artemia shell for several cycles. All the results demonstrate that the unique structure and amino acid skeletons make discarded Artemia shells a new application for trace lead removal at low cost. KEYWORDS: Heavy metal, Artemia, Lead(II), Purification

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carboxyl groups within the protein matrix.5,6 Bolisetty et al.7 first prepared the protein fibrils membrane, which demonstrates an exceedingly large sorption capacity and rapid purification for various toxic metals. In addition, polydopamine, inspired from the mussel-protein, is also proved to be an effective adsorbent and coating substrate for trace heavy metal retention and various applications.8−12 Therefore, protein based materials and their derivatives are potential new reforms for efficient metaladsorbent exploration in water purification. Similar to the protein-bearing materials, chitosan and its derivatives have been emerging as efficient metal scavengers due to their abundance of aminated terminates and environmentally benign properties.13,14 In addition, the chitosan catalogue material can readily attach by morphology or shape confirmation through a cross-linking reaction, which is convenient for sequestering various metals.15,16 However, the obtained biomaterials are always sensitive to some water

INTRODUCTION

Water pollution by heavy metals remains a serious environmental and public health threat, even in trace amounts.1 For instance, trace levels of cadmium can significantly magnify the cancer-causing potential by inhibiting the ability to repair DNA.2 To date, various methods, including chemical precipitation, adsorption, ion exchange, and membrane, have been proposed to conquer the problems, and adsorption technology appears to be an efficient approach,3 due to its simplicity and effectiveness. Developing effective materials, thus, is an important route to sequestering trace metals. The ability to easily apply the adsorbent and the rapid decrease of trace pollutants to safe levels are important criteria. Recently, Zare and his co-workers4 at Stanford University discovered the protein-induced hybrid nanoflowers. The unique 3D molecular structure of various proteins/enzymes (BSA, beta-lactalbumin) and strong amide groups will readily form a powerful Cu complex and then bloom into the flower-shaped hybrid nanostructures. More importantly, the prepared proteinbearing nanomaterials can achieve superior heavy metal sequestration through the preferential reaction of amide or © 2017 American Chemical Society

Received: October 13, 2017 Revised: November 5, 2017 Published: November 20, 2017 1343

DOI: 10.1021/acssuschemeng.7b03667 ACS Sustainable Chem. Eng. 2018, 6, 1343−1351

Research Article

ACS Sustainable Chemistry & Engineering constituents; particularly, the coexistence of high salt content and organic components is a serious threat to its chemical stability in wastewater treatment. Brine shrimp Artemia is important bait and food sources in fish cultivation, e.g., P. monodon, Eriocheir sinensis, prawn etc., which is a representative specie, that lives in most high salt regions (e.g., salts lakes/fields and oceans), such as the famous Great Salt Lake of the U.S.17 According to available statistics, worldwide approximately 18 000 tons of Artemia were consumed for various shrimp or fish feedings in one year18 and several international enterprises (e.g., NUTRI-AD International) have engaged in Artemia cultivation and marketing. Unfortunately, the discarded cyst shells are always disposed as waste after nauplii collection. Thus, the application of the discarded cyst shells is an important research issue. Additionally, it is also an ideal support for self-assembled nanomaterials design.19−24 Considering the hypersaline living environment of Artemia nauplii, the discarded Artemia cyst shells (CSs) exhibit biocompatibility, are environmental friendly, and have a remarkable tolerance to extremely harsh conditions. For instance, Artemia eggs can remain stable at extreme temperatures from −271 to 110 °C, under Χ-ray radiation, in high salt, oxygen-deficient environments and are resistant to oxidative damage while shielding the encysted embryos.25−27 Such excellent properties, far beyond those of other common protein biomaterials, make cyst shells a potentially exceptional material in the environmental remediation realm. Interestingly, Artemia CSs also display a unique hierarchically structured skeleton; the shell of Artemia cysts is composed of an outer surface lamella and three-dimensional interior pore regions (Figure 1c). The outer region is particularly rich in Ca(II), P species, which protects the embryos from severe external environments, while the interior 3D hierarchical structures can be divided into the transitive deep mesoporous/microporous section and the macroporous morphology with a size of 20 nm−1 μm, which favors the rapid metal ion accessibility. More importantly, the unique skeleton with a broad honeycomb-like morphology mainly consists of large amounts of chitin and 17 kinds of natural amino acid;28,29 thus, the thriving amides and carboxyl groups can bond with the target heavy metals. In this work, we first gain a new insight into the discarded Artemia CS wastes for use in heavy metal sequestration. Different from the conventional efficient biomaterials, Artemia CSs have excellent chemical stability against various severe environments.30 The amides and carboxyl components of the matrix can provide a strong affinity to target toxic metals, while the unique 3D transitive pore morphology will further enhance ion accessibility and the utilization of active sites. Therefore, rapid and efficient application performance for heavy metal removal can be assumed. Pb(II), listed in the priority pollutants, is selected as the model heavy metal for evaluation, and XPS investigation is also employed to elucidate the possible sorption mechanism.

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Figure 1. (a) Photo of live Artemia shrimp; (b) SEM image of discarded Artemia CSs; (c) SEM image of inner porous morphology of the Artemia CSs; (d) profile slice of the porous structure by SEM analysis; (e) magnified image of the outer lamella; and (f) magnified image of the inner porous morphology, with the inset image being the further observation for deep pores. mequiv/g capacity; prior to use, complete washing is necessary to remove the possible residues. Treatment of the Artemia CSs. The Artemia CSs are treated by the following procedures. A total of 5 g of raw Artemia CSs were added into a 300 mL water−ethanol mixture (50 wt %) and were stirred for 5 h to wash the raw cyst shells to remove the salt and possible residues. The above procedures were repeated for 3−4 cycles. Afterward, the Artemia CSs were subjected to ultrasonic processing for 30 min to achieve pore perforation and water infiltration. The resultant materials gradually gravitate toward the water bottom, suggesting complete water saturation. Finally, the Artemia CSs were filtrated and then heat treated at 60 °C for 8 h. Batch Sorption Runs. A series of batch sorption experiments were performed through the conventional bottle-point method, and the detailed procedures are listed as follows: Solution pH effect on lead(II) removal: 25.0 mg of Artemia CSs was introduced into a plastic bottle containing a 50 mL solution with 0.25 mM lead(II) ions, and 1% HCl or NaOH was added to adjust the solution to the desired pH. Afterward, the above bottles were transferred to an incubator shaker (SH85, Huxi China) under a constant shaking speed of 200 rpm for 2 h at the desired temperatures. An approximately 2 h reaction is enough to reach the final sorption equilibrium, and then the sorbent was filtrated from the remaining solution concentration and the corresponding pH was determined. In addition, this Pb species distribution is calculated using the software of Visual Minteq with the initial Pb concentration of approximately 0.25 mmol/L, which is equal to the Pb concentration in the section Solution pH Effects on Pb Removal. Zeta potential tests were carried out with the following procedure: Suspensions containing 0.25 g/L Artemia CS (ground into powders) were well stirred at room temperature for 10 h; afterward, it was subjected to an ultrasonic bath for 20 min to ensure good dispersion. The solution pH of the suspension was adjusted to 1.0−7.0 using 0.10 M HCl or NaOH, and next the above suspension was further stabilized

MATERIALS AND METHODS

Materials. All the chemical reagents used in this work are of analytical grade without further purification and were purchased from Tianjin Chemical Reagent Station, China. The Artemia CSs were kindly provided by Shenzhen-HongKong Institution of Industry. The referenced materials of commercial cationic exchange resin 001x7 were obtained from Nanjing Resin Co. with the particle size of 0.6−0.8 mm, and the polystyrene skeleton was modified with SO3−H groups of 3.9 1344


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ACS Sustainable Chemistry & Engineering for 6 h to attach the charge equilibrium. The solution pH at equilibrium was determined, and the samples were used for the measurement of zeta potentials by Zeta-plus 4 instruments (Brookhaven Instrument Co., U.S.A.); the values were tested five times to ensure the reliability The competing experiments were conducted involving adding commonly present Na(I), Mg(II), and Ca(II) at different concentrations, and the initial Pb concentration is around 50 mg/L at 298 K, with 0.5 g/L sorbent, pH = 6.2−6.8. The series bottles were transferred to an incubator shaker for 2 h of shaking to approach sorption equilibrium. Finally, the lead uptakes onto sorbents are calculated by conducting a mass balance before and after the test. Kinetic tests were carried out to evaluate the sorption behaviors. Specifically, 0.5 g of Artemia CSs were introduced into a 500 mL solution containing 30 mg/L of lead ions. Mechanical stirring was performed to ensure an identical reaction and complete mixing, and 0.5 mL of the solution was sampled at different time intervals. The sample concentrations and sampling time were recorded for the calculation sorption capacities. Sorption isotherm tests were conducted to evaluate the maximum sorption capacity at different temperatures. To be specific, 50 mg of treated Artemia CSs were introduced into series bottles containing 50 mL of solution with different concentrations of lead(II) ions at the added dose of 1 g/L. The initial different Pb concentrations were 20 mg/L, 50 mg/L, 100 mg/L, 150 mg/L, 200 mg/L, 400 mg/L, and 600 mg/L, and the solution pH at equilibrium is around 6.2−6.6. The above bottles were transferred to an incubator shaker for 10 h shaking at desired temperatures (20 °C/40 °C/60 °C); afterward, the lead(II) contents in effluent were assayed, and the maximum sorption capacity can be well calculated by the classic Langmuir or Freundlich models. It is noteworthy that the concentration of Pb(II) in this section is very high, which is not in agreement with the real wastewater, but this work aims at reflecting the maximum sorption ability; the actual application tests were performed in the section of fixed-bed column sorption. It is noted that, prior to conducting the experiment, all the treated Artemia CSs were well dried at 333 K in a vacuum for 24 h to avoid the possible effects on weight; besides, the cyst shells are extremely light, and 1 mg of adsorbent contains approximately 20−25 shells. Therefore, at this condition, the dose of 0.5 g/L or 1.0 g/L is believable. Fixed-Bed Column Sorption and Regeneration. Fixed bed column experiments were performed to evaluate the applicability of the given Artemia CSs. A total of 3 mL of sorbents were packed in a glass column (12 mm in diameter and 25 cm in length), which was equipped with a water bath apparatus to maintain a constant temperature. A peristaltic pump (lange-580, China) was employed to ensure the feeding flow rates, and an automatic fraction collector was used to collect the effluents at various time intervals. In addition, the exhausted materials can be readily regenerated using 1% HCl solution to strip the adsorbed Pb(II). Prior to the next adsorption cycles, complete washing of the Artemia CSs is necessary until neutral pH conditions are obtained. The fixed-bed adsorption was performed with the following sorption hydrodynamic conditions: the superficial liquid velocity (SLV), 0.50 m/h, and the empty bed contact time (EBCT), 6 min, and those for regeneration were SLV, 0.15 m/h, and EBCT, 24 min. Analysis and Characterization. The lead(II) ion concentration in the solution was determined using an atomic absorption spectroscope (AAS06800, Shimazu), while the trace level ( 5.5). The interesting behaviors might be partially ascribed to the surface charges of Artemia CS and different Pb species. The zero potential charges of Artemia CS are obtained at pHzpc = 2.53 (Figure 3b), and a positive charge onto the surface of Artemia CS can be approached at pH < 2.53, which is unfavorable for Pb(II) adsorption by the strong electrostatic repulsion. Inversely related, the increased adsorption at pH > 2.5 can be associated with the negative surface adsorption. In addition, the strong complexation between the amides/carboxyl

serine, valine, and tyrosine are the main amino acid components. The amino acid skeleton indicates a possible strong interaction with heavy metals. Next, Fourier transform infrared (FT-IR) spectroscopy was conducted to detect the possible characteristic groups of Artemia CS. The results are displayed in Figure 2. The broad adsorption peaks at ∼3394

Figure 2. FT-IR analysis for the primitive Artemia CS and Ca, Pb loaded samples.

cm−1 are credited to the stretching vibration of O−H and active −NH2,31,32 and a weaker asymmetric stretching vibration at ∼2956 and 2923 cm−1 corresponds to the CH3 and CH2 bands, respectively.8 The peaks at 1396 cm−1 and ∼1448 cm−1 are assigned to the presence of the C−OH group for the stretching or bending vibration, respectively.33 A strong peak at 1656 cm−1 can be assigned to CO stretching in the carboxyl or

Figure 3. (a) Solution pH effects for lead removal (conditions: 0.5 g/L sorbent, initial lead(II) concentration of 50 mg/L at 298 K) ; (b) zeta potential analysis for the Artemia CS samples; (c) lead species distribution at various solution pH values; and (d) sorption kinetics at different time intervals (conditions: 1 g/L sorbent, initial lead(II) concentration of 30 mg/L at 298 K, volume: 500 mL, pH = 6.4 ± 0.1). 1346


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shell is completely different from the common eggshell. In addition, as compared to the most porous materials, the Artemia CS also exhibits an outstanding kinetic adsorption feature. Strong Sorption Affinity. In the application view, the common cations, including the representative Ca, Mg, and Na, are ubiquitous at high concentrations; thus, the influences on Pb uptake are required for selectivity determination and the commercial ion-exchanger 001x7 is also involved as a reference for the results shown in Figure 4a−c. Observably, a decreased tendency toward Pb uptake can be attributed for both sorbents with strong ion strength additions. Particularly for the bivalent Ca and Mg ions, the dramatical sorption decreases onto commercial 001x7 can be attributed to its nonspecific sites of sulfonated groups by weak electrostatic attraction with a final efficiency of nearly zero. Relatively, the Artemia CS exhibits a preferable Pb sequestration by a strong adsorption, and efficient Pb removal can be well achieved, even at 128 times comparative ion additions, suggesting its strong affinity and selectivity. Such selective sequestration might partly be ascribed to the amides and carboxyl component of the skeleton, which was preliminarily proven in the FT-IR analysis and further mechanism elucidation and was verified by the XPS investigation in the following section. To further quantify the sorption selectivity, the distribution ratio Kd (mL/g) was employed with the following equations.47

component of the matrix and target Pb will further promote the powerful sequestration. It is also observed that a monovalent Pb(OH)+ exhibits a gradual increased distribution at pH > 5.0 (Figure 3c); thus, more Pb species can be adsorbed by comparing bivalent Pb2+ ions. It is noteworthy that there is no precipitation occurrence at this pH stage. More importantly, the negligible adsorption at acidic surroundings (pH < 2.5) also suggests the possible regeneration using a diluted acid solution. Rapid Lead(II) Sequestration. Adsorption kinetics was also used to determine the sorption behaviors, and the results are shown in Figure 3d. Notably, a rapid Pb(II) adsorption equilibrium can be approached in less than 2 min for approximately 60% removal efficiency. It is noteworthy that the extremely efficient adsorption is not applied in the classic kinetic models, and similar results were also observed in a recent study.36 The efficient and fast adsorption can be ascribed to the unique 3D hierarchically structured skeleton of the Artemia CSs. The broader pore regions of several micrometers scale can support the Pb(II) rapid sequestration, while the micro-/mesoporous section (SEM observation) can provide further thriving active sites for strong adsorption. In the recently reported porous adsorbent, the low-rate diffusion and slow adsorption are always troublesome problems. For instance, the microporous carbon can achieve a sufficient application for above 10 h,37 Pan and his co-workers38 modified high-charged −SO3−H groups for diffusion enhancement of porous polystyrene matrix, and an improved adsorption can be completed in 300 min. In this work, the unique 3D hierarchical structure can endow strong Pb adsorption and rapid entrapment simultaneously. A detailed comparison is also listed in Table 2.

Kd =

no.

adsorbent

1 2 3 4 5 6

porous crab shell eggshell-rich composite chicken eggshell natural eggshell oyster shell MOF-derived magnetic inorganic sorbents HNO3 modified activated carbon hierarchical mesoporous silica nanoparticles to poly(dopamine) coated polyurethane (PU) sponge porous polystyrene supported zirconium oxide nanocomposite natural Artemia CS

7 8

9 10

kinetics (min)

refs

∼210 ∼23.3 ∼154 ∼4.7 ∼250 ∼344

∼6 h ∼180 ∼20 NA ∼60 ∼50

Kim et al.39 Soares et al.40 Joshi et al.41 Ahmad et al.42 Odoemelam43 Chen et al.44

∼143

∼80

Shen et al.45

∼104.42

∼700

Pan et al.46

∼319

∼300

Pan et al.38

∼320

∼2

in this work

(1)

where C0 (mg/L) is the initial Pb(II) concentration of the solution, V (L) is the volume of the solution, and m (g) is the mass of the adsorbent. The detailed results are shown in Table 3. Evidently, the considerably large Kd values (Table 1) for the biomaterial Artemia CS further confirm its strong selectivity, and it is approximately equal to 50 times greater that of the commercial ion-exchange resin 001x7. Sorption isotherms (Figure 4d) were also performed to evaluate the maximum Pb uptake capacity. It can be seen that Pb removal onto Artemia CS is a temperature-dependent endothermic reaction, and higher temperatures favor the Pb sequestration. The representative Langmuir and Freundlich models are also employed to describe the sorption behaviors, and the detailed equation and fitting data are shown in Table S1. Significantly, a large capability, 320 mg/g, was attached, which is comparable to the porous adsorbent in the literature (Table 2). In addition, we also test Cu and Cd adsorption onto Artemia CS with the results of Figures S5 and S6, and it can be found that the both Cd and Cu can have good adsorption with high selectivity; the maximum adsorption capacities are approximately 60.8 and 24.2 mg/g. meanwhile, high concentration of Ca(II) addition can also lead to a slight effect on removal efficiency; it suggests the wide capture for most heavy metals, but considering for the high toxic and efficient removal of Pb, in this work, we take lead ion removal as a case study. Mechanism Elucidation. XPS investigation was also conducive to gain further insights into the sorption mechanism. Figure 5a shows the XPS spectra onto primitive Artemia CS and Pb loading samples. The distinct C, N, and O peaks suggest the amino acid components, while the observed Pb 4f peak confirms the effective capture of the Pb(II) species. Next the Pb 4f band was further ascertained (Figure 5b). The standard Pb 4f, originated Pb(NO3)2 sample, was found at 139.7 eV (Pb 4f

Table 2. Pb(II) Sorption Capacity and Kinetic Comparisons Based on Shell and Porous Nanostructured Adsorbent in the Literature sorption capacity (mg/g)

(C0 − Ce) V Ce m

It can be seen that the Artemia CS in this work represents obvious advantages in capacity and kinetics; specifically, most egg shells can adsorb heavy metal by Ca-complex interaction, and the capacity for lead removal is not high; however, in this work, the Artemia adsorption can remove Pb ion by the surface amino group, and this point is different. In addition, considering the unique life around in high salt regions, the shell can resist the severe environment. Therefore the Artemia 1347


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Figure 4. (a−c) Effects of Ca, Mg, and Na on lead(II) removal by Artemia CS and commercial 001x7, respectively (conditions: 0.5 g/L sorbent, initial lead(II) concentration of 50 mg/L at 298 K, pH = 6.2−6.8) and (d) sorption isotherms at different temperatures (conditions: 1.0 g/L sorbent, initial different lead(II) concentrations of 20−600 mg/L for 10 h reaction, pH = 6.2−6.6).

Table 3. Kd (mL/g) Values of Lead(II) Adsorption onto Artemia CS and 001x7 at 298 K with Competing Ions at Different Levels Kd (mL/g) at different ratios of M/Pb(II) competing ions (M)

adsorbents

8

16

32

64

128

Ca(II)

Artemia CS 001x7 ratio Artemia CS 001x7 ratio Artemia CS 001x7 ratio

3560 2371 1.50 5756 5489 1.05 9341 29000 0.32

3000 1240 2.42 4158 2297 1.81 6751 22585 0.30

2639 483 5.46 3466 1029 3.37 5441 20265 0.27

2258 122 18.5 2987 481 6.21 5240 21650 0.24

2803 48 58.4 3509 106 33.1 5334 22260 0.24

Mg(II)

Na(I)

and 144.6 eV (Pb 4f 5/2), respectively,48 while Pb uptake onto Artemia CS leads to a significant band shift (∼0.7 eV) to a low energy phase. This finding verifies the strong affinity between the Pb species and Artemia CS skeletons. To further probe the possible active sites, the representative N 1s and O 1s peaks are investigated in detail. As illustrated in Figure 5c, the N 1s spectra of bank Artemia CS is centered at ∼400.1 eV with a broad energy band with a full width at halfmaximum (fwhm) value of ∼2.8 eV. Considering the composition of amination skeletons, it can be envisaged into two peaks, i.e., active −NH2 (∼400.4 eV) and −NH− (∼399.9 eV), and the corresponding area proportions are 62.8% and 37.4% respectively. While Pb adsorption brings about a new emerging peak at ∼400.9 eV (green peak) with 0.6 eV shifts, which might be ascribed to the formation the strong metal− ligand formation of NH−Pb from active NH2. Whereas, the high concentration Ca(II) loadings can lead to slight peak area variations, which are associated with the weak H replacement reaction within −NH2 and Ca(II) ions. Such a phenomenon coincides with the competing adsorption results. We also notice that the peaks of the amino group (−NH−) exhibit a slight

shift during Pb or Ca adsorption; while it is not the main component for Pb uptake, on the contrary, the active-NH2 group is responsible for the selective Pb entrapment. Moreover, the O 1s is further examined, and the wide O 1s can be divided into three components, i.e., ∼531.7 eV (C− OH), ∼532.7 eV (CO or C−O), and ∼533.6 eV (C−O− C).49 The corresponding proportions for the three components are 65.9%, 20%, and 14.1%, respectively. Evidently, the lead(II) uptake can induce a C−OH decrease and a C−O peak enhancement (20% to 32.2%), which is possibly ascribed to the species. It suggests a formation of the C−O−Pb or strong adsorption by the hydroxyl and carbonyl groups. In addition, Ca adsorption can result in slight peak shifts and area variations, further verifying the weak affinity toward Pb sequestration. A colorful illustration of the sorption mechanism is shown in Scheme 1. Superior Application Performances. Packed continuous column tests were performed to evaluate the applicability of Artemia CS (Figure 6). The competitive Ca(II)/Mg(II)/Na(I) was selected as the synthetic feeding solution in the application

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Figure 5. High-resolution XPS spectra. (a) XPS spectra survey of Artemia CS and Pb loaded samples; (b) Pb 4f spectra of lead adsorbed Artemia CS and pure Pb(NO3)2; (c) N 1s spectra of primitive Artemia CS and Ca and Pb loaded samples; and (d) O 1s spectra of primitive Artemia CS and Ca and Pb loaded samples.

Scheme 1. Sorption Mechanism Illustration of Artemia CS

Figure 6. Continuous applicability evaluations for the Artemia CS, commercial activated carbon, and 001x7 (feeding condition: 1.0 mg/L Pb, Ca = 250 mg/L, Mg = 180 mg/L, Na = 370 mg/L, HA= 2.4 mg/L, pH = 6.5−6.8).

criterion recommended by the WHO (10 μg/L). The superior performances equate to 45 times greater than the commercial 001x7 and carbon materials. In addition, we also observed that the maximum Pb uptake of approximately 320 mg/g is a moderate level, while the efficient applicability suggests the possible strong diffusion and high accessibility and utilization for active sites. In addition, regeneration tests were also

view, and the commercial ion-exchanger 001x7 and granular activated carbon (coconut) were used for references. As expected, the resulting biomaterial exhibits superior capability for application with a treated volume of 9100 kg water/kg sorbent. The effluents are also far beyond the drinking water 1349



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conducted using 1% EDTA−2Na with an accumulated desorbed efficiency of above 95.2%. The sorption−regeneration experiments further demonstrate the repeated usage property for five cycles (Figure S7). Furthermore, the cost in preparation and treatment is also well estimated. In fact, the raw Artemia CS is the byproduct in aquiculture, which was kindly provided by Shenzhen-HongKong Institution of Industry. The preparation fees are approximately 101.2 $/ton (Table S2), which is preferential to the commercial ion-exchange resin, carbon, graphene oxide, and activated alumina (Table S3). The comparison for prices was obtained from https://www.alibaba.com/, which is the real price for sale. In view of the treated cost of the wastewater, an average cost for 1 ton of wastewater is approximately 0.022 $/ton (including the sorbent depleting, regeneration fees, labor cost, and electricity paid). The detailed calculation is shown in Table S4. Because the Artemia CS is waste with a simple pretreatment, the price is very low, so the cost for application is significantly decreased, which can make a big profit in real application. Thus, the obtained Artemia CS in this work is a representative low-cost adsorbent with significantly promising applications.

CONCLUSIONS Herein, we find strong lead(II) sequestration by discarded Artemia cyst shells with unique hierarchically structured skeletons. The broad pore regions can provide rapid Pb diffusion, while the microspore regions, containing sufficient amides and carboxyl components, are responsible for the strong Pb adsorption. The results reveal that the Artemia CS exhibits a strong sorption affinity of approximately 30 times, which is approximately 30 times greater Kd than the commercial 001x7, and a fast sorption can be attained in 2 min. More importantly, a superior actual capability of 9100 kg of wastewater per sorbent further demonstrates its applicability with a reduced effluent of below 10 μg/L. In addition the exhausted Artemia CS can be well regenerated and used repeatedly. The results prove that waste Artemia CSs are a low-cost adsorbent with significant application potential for trace Pb removal. ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b03667. XRD pattern, sorption result model fittings and SEMEDS analysis, and Cd and Cu removal tests (PDF)

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REFERENCES

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Research Article

AUTHOR INFORMATION

Corresponding Author

*(Qingrui Zhang). E-mail: [email protected]. Tel.: +86-3358387-741. Fax: +86-335-8061-549. ORCID

Qingrui Zhang: 0000-0002-2070-2179 Funding

This work was financially supported by NSFC (Grant Nos. 51578476), NSF of Hebei Province (B2016203056), and the Support Program for the Top Young Talents of Hebei Province. Notes

The authors declare no competing financial interest. 1350


Research Article


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