Electronic Supplementary Material

A metal-organic framework nanocomposite made from functionalized magnetite nanoparticles and HKUST-1 (MOF-199) for preconcentration of Cd(II), Pb(II), and Ni(II)

EbrahimGhorbani-Kalhor*

Department of Chemistry, Tabriz Branch, Islamic AzadUniversity, Tabriz, Iran

*Corresponding author: Fax: +98 9143008253; fax: +98 4113333458, E-mail:

Optimization of the preconcentration procedure

Sorption step

The optimization step for the uptake of metal ions on the magnetic nanocomposite was carried out using Box-Behnken design (BBD). pH of sample, amount of the magnetic nanocomposite, and extraction time were selected as affecting variables. Other parameters involved in the extraction were kept constant, especially the concentration of heavy metal ions (0.5 mg L-1). This design permitted the responses to be modeled by fitting a second-order polynomial, which can be expressed as the following equation:

where, x1, x2, and x3 are the independent variables, β0 is an intercept, β1- β33 are the regression coefficients, and Y is the response (removal% or recovery%). The number of experiments (N) is defined by the expression below:

o

where K is the number of variables and Co is the number of center points [39]. In this study, K and Co were set at 3 and 4 respectively, which meant that 16 experiments had to be done. The levels of the factors are listed in Table 1S. The analysis of variance (ANOVA) results producing the Pareto chart of main and interaction effects which are shown in Fig. 2S. The standard effect was estimated for computing the t-statistic for each effect. The vertical line on the plot shows statistically significant effects. The bar extracting beyond the line corresponds to the effects that are statistically significant at 95% confidence level [24, 40, 41]. Furthermore, the positive or negative sign (corresponding to a colored or colorless response) can enhance or reduce the extraction efficiency, respectively, while increasing from the lowest to the highest level set for the specific factor. According to Pareto chart the pH of the solution has the most significant positive effect on the extraction efficiency. The uptake of heavy metal ions increases as the pH increases. In acidic solution, uptake is very low. This observation is due to the protonation of the magnetic nanocomposite active sites especially O, S and N atoms of TAR. As the pH increases, the protonation of these active sites decreases and the condition becomes more favorable for complex formation and adsorption of heavy metal ions to the magnetic nanocomposite. The response surface methodology (RSM) (Fig. 2S) was applied to analysis simultaneous effects of uptake time and pH variables on the response. The uptake efficiency of heavy metal ions increased along with the increase in pH while the extraction time had a non-significant positive effect on the extraction of these ions. Uptake time and amount of the magnetic nanocomposite both showed positive but non-significant effect on the extraction efficiency. According to the overall results of the optimization study, the following experimental conditions were chosen: pH, 6.2; uptake time, 10 min; amount of the magnetic nanocomposite, 40 mg.

Selection of eluent

In this work several eluents including HCl, HNO3, K2SO4, NaOH, KCl, thiourea, EDTA solution and mixture of them were examined as the desorption solvent. Other factors were kept constant during the optimization (pH, 6.2; extraction time, 10 min; amount of the magnetic nanocomposite, 50 mg; eluent volume, 10 mL; elution time, 20 min). Results showed that HCl, HNO3, and NaOH decompose the structure of magnetic nanocomposite, but EDTA and thiourea can recover the target ions without any structure decomposition. Based on the obtained results, the best quantitative recovery was obtained with EDTA solution as the elution solvent.

Elution step

Three factors were studied in elutionstep using experimental design: eluent volume (mL), elution time (min), and concentration of EDTA (mol L-l). Under these conditions, the response surface design can be done without a previous screening design. The BBD was chosen because it requires the least number of experiments (16 run). The data obtained were evaluated by ANOVA. The results of the experimental design were evaluated at 5 % of significance and analyzed by standardized Pareto chart (Fig. 3S). Based on BBD, eluent concentration and elution time showed positive and significant effects on the recovery of the heavy metal ions while eluent volume has a positive but non-significant effect. As Fig. 3S shows, eluent concentration has the greatest influence on the extraction recovery and a positive effect upon the extraction efficiency. The RSM (Fig. 3S) was applied to analyze simultaneous effects of the eluent concentration and eluent volume variables on the responses. The extraction efficiency of heavy metal ions increased along with the increase in the eluent concentration and its volume. According to the overall results of the optimization study, the following experimental conditions were chosen: eluent volume, 5.0 mL; elution time, 15.2 min; and eluent concentration, 0.6 mol L-l EDTA.

Effect of breakthrough volume

In the analysis of real samples, the sample volume is one of the important parameters affecting the preconcentration factor. The breakthrough volume of sample solutions was investigated by dissolving 1 mg of each Cd(II), Pb(II) and Ni(II) ion in 100, 250, 500, 750, 1000, 1250 and 1500 mL of distilled water. Then the SPE protocol was performed. The results demonstrated that the dilution effect was not significant for sample volumes of 1000 mL for each ion on the magnetic nanocomposite. Thus, the new sorbent enabling an enrichment factor of 200 was obtained for Cd(II), Pb(II) and Ni(II) ions.

Table 1S Experimental variables and levels of the Box Behnken design (BBD) for uptake and elution steps.

/ Level
/ Lower / Central / Upper
A: Sample pH / 4.0 / 6.0 / 8.0
Uptake step / B: Uptake time (min) / 5.0 / 10.0 / 15.0
/ C: Sorbent amount (mg) / 20.0 / 40.0 / 60.0
A: Elution time (min) / 5.0 / 15.0 / 25.0
Elution step / B: Eluent concentration (mol L-1) / 0.1 / 0.55 / 1.0
C: Eluent volume (mL) / 2.5 / 5.0 / 7.5

Table 2S The tolerance limit of various ions on the determination of target metal ions.

Potentially interfering ions / Tolerable Concentration
Ratio Xc/ Cd, Zn, Pb / Ra (%) Sb
Cadmium Zinc Lead
K+ / 10000 / 98.0 ± 2.5 / 99.0 ± 1.0 / 97.0 ± 2.0
Na+ / 10000 / 99.2 ± 3.5 / 99.1 ± 2.8 / 98.2 ± 2.4
Ca2+ / 1000 / 97.0 ± 1.6 / 98.2 ± 2.8 / 97.0 ± 1.9
Al3+ / 1000 / 99.0 ± 2.4 / 98.5 ± 2.2 / 95.5 ± 2.6
Zn2+ / 1000 / 95.0 ± 2.6 / 96.0 ± 3.0 / 96.8 ± 2.2
Fe3+ / 1000 / 97.5 ± 3.4 / 98.1 ± 1.8 / 97.6 ± 2.5
Cr3+ / 1000 / 96.0 ± 2.0 / 97.0 ± 3.0 / 96.4 ± 2.0
Mg2+ / 1000 / 99.2 ± 2.3 / 98.0 ± 1.7 / 98.4 ± 2.1
Mn2+ / 500 / 98.3 1.9 / 98.7 ± 2.4 / 99.1 ± 1.6
Ag+ / 500 / 97.2 ± 2.4 / 98.4 ± 1.9 / 96.1 ± 3.2
Hg2+ / 250 / 95.6 ± 2.9 / 96.0 ± 3.5 / 95.0 ± 2.8
Cu2+ / 250 / 97.1 ± 3.2 / 95.6 ± 2.8 / 94.5 ± 3.0
Co2+ / 200 / 96.1 ± 2.6 / 97.5 ± 3.1 / 96.0 ± 2.8
CrO4- / 1000 / 97.0 ± 1.8 / 98.0 ± 2.6 / 95.0 ± 3.4
PO43- / 1000 / 96.0 2.0 / 97.0 ± 2.4 / 96.0 ± 2.5

a Recovery

bstandard deviation (n = 3)

Conditions: sample pH = 6.2, sample volume = 200 mL, 0.02 mg of Cd(II), Pb(II) and Ni(II) ions uptake time = 10 min; eluent = 0.6 mol L-l EDTA; eluent volume = 5.0 mL, elution time = 15.2 min.

c Concentration of potentially interfering ions.

Table 3S Determination of target metal ions in different real samples under the optimized condition.

Sample / Element / Real sample a (ng g-1) / Added (ng g-1) / Found (ng g-1) a / Recovery (%)
Fish 1a
(muscle) / Cd / 150±9 / 100 / 241±20 / 91.0
Pb / 580±41 / 400 / 963±83 / 95.7
Ni / 646±55 / 400 / 996±94 / 87.5
Fish 1
(skin) / Cd / 170±10 / 100 / 260±22 / 90.0
Pb / 594±48 / 400 / 1043±110 / 112
Ni / 690±72 / 400 / 1076±99 / 96.5
Cd / 207±18 / 200 / 410±38 / 102
Fish 2b
(muscle) / Pb / 310±16 / 200 / 497±53 / 93.5
Ni / 553±50 / 400 / 924±85 / 92.8
Fish 2
(skin) / Cd / 247±28 / 200 / 439±26 / 96.0
Pb / 356±29 / 200 / 564±33 / 104
Ni / 580±50 / 400 / 971±102 / 97.8
Shrimp / Cd / 15.0±1.1 / 10.0 / 23.7±2.6 / 87.0
Pb / 30.2±2.5 / 10.0 / 39.4±3.2 / 92.0
Ni / 49.3±5.2 / 10.0 / 57.6±6.4 / 83.0
Lettuce / Cd / 2.5±0.14 / 10.0 / 12.1±1.0 / 96.0
Pb / 5.6±0.43 / 10.0 / 15.0±0.9 / 94.0
Ni / 13.0±0.7 / 10.0 / 22.1±1.8 / 91.0
Broccoli / Cd / N.D. / 10.0 / 9.5±0.7 / 95.0
Pb / 6.5±0.52 / 10.0 / 16.8±1.5 / 103
Ni / 10.1±0.1 / 10.0 / 20.5±1.6 / 104
Mushroom / Cd / N.D. / 10.0 / 10.2±1.1 / 102
Pb / 8.3±0.6 / 10.0 / 18.0±1.2 / 97.0
Ni / 5.4±0.3 / 10.0 / 14.9±0.6 / 95.0

aMean ± standard deviation (n = 3).

Fig. 1S: (a) XRD patterns of MOF and (b) magnetic MOF nanocomposite.

Fig. 2S: (a) Pareto chart of the main effects in the BBD (uptake step). AA, BB and CC are the quadratic effects of the sample pH, uptake time and sorbent amount, respectively. AB, AC and BC are the interaction effects between sample pH and uptake time; sample pH and sorbent amount and uptake time and sorbent amount, respectively. (b) Response surface obtained by plotting of pH vs. uptake time using the BBD.

Fig. 3S: (a) Pareto chart of the main effects in the BBD (elution step). AA, BB and CC are the quadratic effects of the elution time, eluent concentration and eluent volume, respectively. AB, AC and BC are the interaction effects between elution time and eluent concentration; elution time and eluent volume; and eluent concentration and eluent volume, respectively. (b) Response surface obtained by plotting eluent concentration vs. eluent volume.