The decreasing aggregation of nanoscale zero-valent iron induced by trivalent chromium

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1 , 14, Supplementary material The decreasing aggregation of nanoscale zero-valent iron induced by trivalent chromium Danlie Jiang, A,B Xialin Hu, A,C Rui Wang, A Yujing Wang B and Daqiang Yin A,C,D A Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai , China. B School of Materials and Chemical Engineering, Xi an Technological University, 4 Jinhua Road, Xi an , China. C State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai , China. D Corresponding author. yindq@tongji.edu.cn

2 S1. Equations of the related colloidal theories The ven der wall energy (Uvdw) between two spherical particles is derived from the following expression (Equation S1)[2], where A (N m) is the Hamaker constant obtained from equation S2, in which the A1 and A2 is the Hamaker constant of particle (10-19 N m for iron-related materials) and media ( N m for water) respectively, a1, a2 (m) is the radium of two interacting particles, R (m) is the distance between the center. U aa aa R a a - { ln[ ]} 2 2 A ( 1+ 2) vdw = R -( a1+ a2) R -( a1- a2) R -( a1- a2) (S1) A A A = ( 1-2 ) (S2) The electrostatic interaction energy (U el) between two spheres is calculated with the equation S3[2], where a 1, a 2 (m) is the radius of two particles, H (m) is the distance between surface of two spheres, є r is the relative dielectric constant of the water, є 0 (F/m) is the permittivity of the vacuum, ζ (mv) is the zeta-potential, and к (m -1 ) is the inverse Debye length obtain from equation S4[3], in which N A is Avogadro s constant, M (mol/l) is the molarity of ions of the electrolyte, z is the valence of ions, k b is the Boltzmann (J/K) constant, e (C) is the electronic charge, T (K) is the absolute temperature, є 0 and є r is the same with which in equation S3. U 4π aa 1 2 -κ H el = εεζζ r 0 1 2e a1+ a2 (S3) NAeM κ = (S4) εεkt r 0 b The stability of the suspensions would be affected significantly by the magnetic attractive force between particles. The magnetic attractive energy (U M) between spheres is expressed by the following functions (equation 1 in the manuscript)[4]. The m 1, m 2 is the magnetic moment of particles, which is obtained from equation S5, R (m) is the distance between the centers of the particles, Ř denotes the unit vector parallels to R, μ 0 is the permeability of the vacuum (N/A 2 ). In equation S5, V (m 3 ) stands for volume of particle, M is the spatially homogeneous magnetization [5] (the norm of which equal to M s (A/m) when the particles assemble in line).

3 U m m - 3( m R)( m R) M = 3 4πµ 0R (1 in the manuscript) m= µ VM (S5) 0 S2. Detailed information of the experiment The protocol for determining Cr(VI). Chromium reagent (1,5- diphenylcarbohydrazid) was mixed with 5-10 ml of suspension that being filtrated for 5 min. The absorbance of Cr(VI)-diphenylcarbohydrazide product developed was determined by a UV-vis spectrometer (UV2100c, Unico Co., Shanghai, P. R. China) at the wavelength of 542 nm in 1 cm path length cells. Standards ranging from 0.0 mg/l to 2.0 mg/l of Cr(VI) in solution were used for calibration. The preparation of deoxygenated water. Water was deoxygenated by boiling for about 10 minutes and then aerating nitrogen for about 20 minutes. The dissolved oxygen of deoxygenated water was less than 1 mg/l after preparation, and remained consistently lower than 2 mg/l during the experiments. The preparation of nzvi suspensions with varying proportions of Cr(III). The concentration of total chromium is 0.040±0.003 mmol L -1.The suspensions was prepared by mixing the suspension of Cr(III) prepared by chromic chloride hexahydrate and suspension of Cr(VI) prepared by potassium chromate with difference ratio, both of suspensions contain 0.040±0.003 mmol L -1 of chromium and 20±2 mg Fe L -1 of nzvi. For instance, for suspension with Cr(III)% of 50%, Cr(III) suspension and Cr(VI) suspension were mixed with the ratio of 1:1. The mixture was not stable, thus samples were analyzed immediately after preparation (mostly within 1 hour).

4 (a) (b)

5 (c) Fig. S1. The TEM photographs of nzvi aggregations at 0 h (a), 48 h ((b) ph 5, (c) ph 7) of the reduction of Cr(VI). Graphs for other time points are similar with graph at 48 h.

6 C/C 0 Cr(VI)/Cr Proportion (%) Time (h) Fig. S2. Change of chromium concentration and Cr(VI) concentration with time Cr(III) Cr(VI) intensity (c/s) Binding energy (ev) Fig. S3. Detailed XPS spectrums of nzvi on the regions of Cr 2p, after nzvi reduced Cr(VI). The

7 peaks of ev and ev are assigned to Cr(III) (Cr 2O 3 and Cr(OH) 3 respectively), the peak of ev are assigned to Cr(VI). (a)nzvi+100% Cr(III) ph5

8 (b)nzvi+100% Cr(III) ph7 Fig. S4. The TEM photographs of nzvi aggregations in the 100% Cr(III) suspensions at ph 5 (a) and ph 7 (b), suggesting the significant influences induced by Cr(III). Graphs for suspensions with other concentrations of Cr(III) were similar with the 100% Cr(III) group.

9 20 10 fresh nzvi used nzvi 0 ζ/mv ph Fig. S5. ζ-potential of the freshly prepared nzvi (fresh nzvi) and the nzvi after reducing Cr(VI) (used nzvi) as the function of ph, suggesting the oxidized nzvi is negatively charged at ph7 and lowly positive at ph5, however, which will be changed to highly positive by Cr(III).