<p> Electronic Supplementary Material</p><p>A magnetic nanocomposite prepared from chelator-modified magnetite (Fe3O4) and HKUST-1 (MOF-199) for separation and preconcentration of mercury(II)</p><p>Azadeh Tadjarodi*, Abolfazl Abbaszadeh </p><p>Research laboratory of inorganic materials synthesis, Department of Chemistry, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran</p><p>* Corresponding author: Tel.: +98 2177240516; fax: +98 2177491204, E-mail address: [email protected] (A. Tadjarodi)</p><p>Optimization of method</p><p>Sorption step</p><p>The optimization of the step was performed using a central composite design (CCD). Other parameters involved in the extraction were kept constant, particularly the concentration of Hg(II)</p><p>-1 ions (50 μg L ). In a system involving three independent variables x1, x2, x3 the responses of CCD can be expressed by the following quadratic polynomial equation:</p><p> where y is the response, β0 is a constant and β1-β33 are the regression coefficients. The number of experimental points (N) can be defined by the following expression: </p><p> where f is the number of parameters and C0 is the number of center points. In this step f and C0 were set at 3 and 6 respectively, therefore 20 experiments had to be done. The following parameters were optimized in sorption step: (a) sample pH value; (b) sorption time; and (c) amount of the magnetic MOF. Respective data and Figures are given in the Electronic Supporting Material (Table 1S and Fig. 3S). 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 [34-37]. 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 that specific factor. According to the Pareto chart pH of sample causes the most significant positive effect on the extraction efficiency. The uptake of Hg(II) ions increases as the pH value increases. In less acidic solutions, the uptake is quite low. This observation is due to the protonation of the magnetic MOF active sites especially, the N and S atoms of DTIM. As the pH increases, the protonation of these active sites decreases and the condition becomes more favorable for complex formation and sorption of Hg(II) ions to the magnetic nanosorbent. Moreover, the sorption time and the sorbent amount both showed positive significant effect on the extraction efficiency and were the second and third important factors, respectively. The response surface methodology and two-dimensional contour plot (Fig. 3S) was applied to analysis simultaneous effects of the sorption time and magnetic MOF amount on the response plot that displayed the interaction between these independent variables. </p><p>The following experimental conditions were found to give the best results: (a) A sample pH value of 6.0; (b) a sorption time of 8.0 min; and (c) magnetic MOF amount of 24 mg.</p><p>Selection of eluent</p><p>In this work, several acidic eluents including HCl, HNO3, thiourea and mixture of them were examined as the elution solvent. Other factors were kept constant during the optimization (pH, 6.0; uptake time, 8.0 min; the nanosorbent amount, 24 mg; eluent volume, 5.0 mL; elution time, 15 min). Results showed that thiourea and EDTA can recover the Hg(II) ions without degradation of magnetic MOF. In the next step the effect eluent volume and its concentration as well as elution time were opted. Elution step The following parameters were optimized in elution step using CCD: (a) thiourea concentration; (b) eluent volume; and (c) elution time. The data obtained were evaluated by analysis of variance. The results of the experimental design were evaluated at 5 % of significance and analyzed by standardized Pareto chart (Fig. 2S). Based on the results, all the factors showed positive and significant effect on the recovery. As Fig. 4S depicts, thiourea concentration has the greatest influence on the extraction recovery. The response surface methodology and two- dimensional contour plot (Fig. 4S) were applied to analyze simultaneous effects of the eluent concentration and eluent volume on the responses. The recovery percentage of Hg(II) ions increased along with an increase in the eluent volume and also eluent concentration. The significance of quadratic effects (AA, BB, CC) in sorption and elution steps shows that the obtained optimum value for each factor is within the selected range and the obtained model is quadratic that is desirable. Moreover, the significance of quadratic effects leads to curvature in the obtained RSM. </p><p>The statistical parameters of R-squared (R2) and adjusted R-squared were used to test fitting the model. R-squared is related to the amount of variation around the mean explained by the model. The adjusted R-squared, which is more suitable for comparing models with different numbers of independent variables, is a modified version of R2 that is sensitive to the number of terms in the model. In fact, the adjusted R-squared decreases as the number of insignificant terms in the model increases. The obtained R-squared and adjusted R-squared values were 0.9908 and 0.9213 for removal step and 0.9649 and 0.8619 for elution step, respectively.</p><p>The following experimental conditions were found to give the best results: (a) A thiourea of 1.1 mol L-l; (b) an eluent volume of 3.5 mL; and (c) an elution time of 11.0 min. Fig. 1S: (a) XRD patterns of MOF and (b) magnetic MOF nanocomposite.</p><p>Fig. 2S: VSM Curves of Fe3O4@DTIM NPs and magnetic MOF. Fig. 3S: (a) Pareto chart of the main effects in the CCD (sorption step). AA, BB and CC are the quadratic effects of pH, the sorption time and the magnetic MOF amount, respectively. AB, AC and BC are the interaction effects between pH and the sorption time; pH and the magnetic MOF amount and the sorption time and the magnetic MOF amount, respectively. (b) RSM and two- dimensional contour plot obtained by sorption time vs. magnetic MOF amount using the CCD.</p><p>Fig. 4S: (a) Pareto chart of the main effects in the CCD (elution step). AA, BB, and CC are the quadratic effects of thiourea concentration, eluent volume and elution time, respectively. (b) RSM and two-dimensional contour plot obtained by plotting thiourea concentration vs. eluent volume using the CCD. Table 1S Experimental variables and levels of the central composite design (CCD).</p><p>Level Star points (α = 1.68) Lower Central Upper -α +α A: pH 4.0 5.5 7.0 3.0 8.0 B: Uptake time (min) Sorption step 5.0 7.5 10.0 3.3 11.7 C: Magnetic MOF amount (mg) 15.0 22.5 30.0 10.0 35.0</p><p>A: thiourea concentration (mol L-1) 0.5 1.0 1.5 0.16 1.84 Elution step B: Eluent volume (mL) 2.0 3.5 5.0 1.0 6.0 C: Elution time (min) 5.0 10.0 15.0 1.6 18.4</p><p>Table 2S Determination of Hg(II) ions (a) in the certified reference materials and (b) in sea food samples. (a) Concentration (mg kg-1) Relative error Sample Certified Found %</p><p>DOLT-4 2.58 2.66 3.1</p><p>DORM-2 4.64 4.47 -3.7</p><p>(b) Sample Real sample (ng g-1) Added (ng g-1) Found (ng g-1) Recovery (%) RSD (%) Canned tuna 1 48.7 50.0 100 103 5.3</p><p>Canned tuna 2 34.0 30.0 62.3 94.3 5.9</p><p>Canned tuna 3 27.0 25.0 49.8 91.2 7.0</p><p>Canned tuna 4 37.8 35.0 79.5 119 8.3</p><p>Canned tuna 5 51.4 50.0 104 105 6.4</p><p>Canned tuna 6 45.1 50.0 94.6 99.0 6.7</p><p>Fish 1 58.6 50.0 101 84.8 5.5</p><p>Fish 2 202 200 393 95.5 4.9</p><p>Fish 3 42.4 40.0 83.9 104 5.2</p><p>Fish 4 570 500 1025 91.0 4.7 Table 3S Comparison of magnetic metal-organic framework nanocomposite with those of the other sorbent RSD Method Instrument LOD a LOQ a SC b EF c Ref. (%)</p><p>This CVAAS 0.01 0.04 <8.3 254 285 Fe3O4/HKUST-1 nanocomposite work</p><p>[(Fe3O4-2,5-dimercapto-1,3,4-thiadiazole)/ MIL-101(Fe)] magnetic metal-organic CVAAS 0.01 0.05 <10 124 363 [21] framework</p><p>SH@SiO / metal-organic framework 2 CVAAS 0.02 0.1 <7.2 210 167 [20] nanocomposite</p><p>Ion-imprinted polymethacrylic microbeads CVAAS 0.006 0.02 5-9 6.42 50 [3]</p><p>Sodium dodecyle sulphate-coated magnetite ICP-OES 0.04 0.2 <5.2 – 1230 [18] nanoparticles</p><p>DPC-doping magnetic nanoparticles CVAAS 0.16 – 2.2 44.1 100 [4]</p><p> a ng mL-1 b Sorption capacity (mg g-1) c Enrichment factor</p>