Supporting Information

Supporting Information

for

Tracking Surface Electron Shuttle using X-ray Spectroscopies in

La/Zr Hydroxide for Reconciliation of Charge Transfer Interaction

and Coordination towards Phosphate

Chao Xiang,a, b _{Hongjie Wang,*}a _{Qinghua Ji,}b _{Gong Zhang,*}b _{and Jiuhui Qu}b,c

a _{College of Environmental Science and Engineering, Beijing Forestry University, Beijing} 100083, China

b _{Center for Water and Ecology, State Key Joint Laboratory of Environment Simulation} and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China

*Corresponding Author

E-mail address: [email protected] (H.J. Wang)

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Supplementary Notes

Supplementary Materials. Lanthanum nitrate hexahydrate (LNO, La(NO3)3·6H2O, AR) was purchased from Aladdin Industrial Co., China. Zirconium nitrate pentahydrate (ZNO, Zr(NO3)4·5H2O, AR), ethanol (EtOH, AR), Propylene oxide (PO, AR), potassium dihydrogen phosphate (KH2PO4, AR), HCl (AR) and KOH (AR) were all purchased from Sinopharm Chemical Co., China. All the dilutions were conducted by using Milli-Q water with a resistivity higher than 18.2 MΩ. All reagents were used without any further refinement.

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Supplementary Figures

Figure S1. XRD patterns of the as-prepared La-, Zr-, and La/Zr hydroxide adsorbents (LaOH, LZ2:1, LZ1:1 and ZrOH samples). The inset image is the diffraction pattern was obtained with

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XRF

LaOH

LZ2:1

LZ1:1

ZrOH

Figure S2. SEM images of the as-prepared La-, Zr-, and La/Zr hydroxide adsorbents (LaOH, LZ2:1, LZ1:1 and ZrOH samples).

200nm

1μm

200nm

1μm

200nm 200nm

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Figure S3. (a)O 1s, (b) Zr 3d and (c) La 3d XPS for the LZ1:1 sample before and after 2000 eV Ar+ sputtering, comparing with that of spectra in text. Firstly, the spectra for the sample before sputtering and shown in original manuscript are very close both in spectral profile and peak position, showing the effectiveness of XPS technique. After sputtering, the spectral profile of O 1s has changed significantly, and the peaks position of Zr 3d and La 3d shifted to lower energy. The results suggested that the sputtering treatment exposed the bulk composite (lattice oxygen increased) and thus reduce the oxides (the shift to lower energy for Zr 3d and La 3d XPS). Although it is difficult to determine the true chemical state during the depth profiling using the ion sputtering, the elemental composition analysis is still reliable. The results showed that the deeper La/Zr composite is very close to the surface composite for the LZ1:1 sample.

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Figure S4. The qm of Langmuir isotherm model for as-prepared La-, Zr-, and La-Zr hydroxide adsorbents (qm – the maximum P-adsorption capacity).

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Figure S5. (a) N2 adsorption-desorption isotherms and (b) BJH distributions of the as-prepared La-, Zr-, and La-Zr hydroxide adsorbents (LaOH, LZ2:1, LZ1:1 and ZrOH), respectively. Inset table: BET parameters.

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Figure S6. (a) FTIR spectra of the as-prepared La-, Zr-, and La/Zr hydroxide adsorbents before and after P

adsorption. (b) Magnified FTIR spectra of the rectangular area in (a). Experimental conditions: adsorbent dosage = 0.5 g L-1_{; initial P concentration = 50.0 mg L}-1_{; pH = 7.0; adsorption time = 24 h.}

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Figure S7. Schematic polarization interactions for the dipolar of aqueous HPO42-_/H2PO4- _{on surface} of the bimetallic La/Zr hydroxides.

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Figure S8. The analysis of two-splitting composition of La 3d5/2 XPS before and after phosphate adsorbed on La- and La/Zr hydroxide samples. Experimental conditions: adsorbent dosage = 0.5 g L-1_{; initial P concentration = 50.0 mg L}-1_{; pH = 7.0; adsorption time = 24 h.}

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Figure S9. The peak fitting of P K-edge XANES for phosphate adsorbed LaOH (a), LZ2:1 (b), LZ1:1 (c) and ZrOH (d) samples. The detail fitting results were seen in Table S6.

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Figure S10. (a) the comparison of O K-edge XANES spectra for La-, Zr- and La/Zr hydroxide samples before and after phosphate adsorption, and (b) the schematic of their [MO6] MOs before and after phosphate adsorption.

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Supplementary Tables

Table S1. Detailed dosages in the synthesis process for La-, Zr, and La-Zr hydroxide adsorbents.

NO. Samples LNO(mg) ZNO(mg) PO(ml) EtOH(ml)

1 LaOH 5196 0 1.60 80

2 LZ5:1 4330 859 1.60 80

3 LZ2:1 3464 1717 1.60 80

4 LZ1:1 2598 2576 1.60 80

5 LZ1:2 1732 3435 1.60 80

6 LZ1:5 866 4293 1.60 80

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Table S2. Kinetic parameters for phosphate adsorption on La-, Zr-, and La-Zr hydroxide adsorbents. Samples

Models Parametersa

LaOH LZ2:1 LZ1:1 ZrOH

qe,exp (mg g−1_{) 32.7847 34.6487 36.4412 31.8563}

qe,cal (mg g−1_{) 19.2752 24.2661 21.9786 22.9615}

k1(h−1_{) 0.1626 0.1612 0.1893 0.1695}

R2 _{0.8874 0.7597 0.9367 0.9559}

Pseudo-first order model

Rate equation y=-0.0706x+1.285 y=-0.07x+1.385 y=-0.0822x+1.342 y=-0.0736x+1.361 qe,cal(mg g−1_{) 32.6797 34.7222 36.4964 32.0513}

k2 (mg g−1_h−1_{) 0.0620 0.0372 0.0552 0.0388}

R2 _{0.9969 0.9927 0.9974 0.9941}

Pseudo- second

order

model Rate equation y=0.0306x+0.0151 y=0.0288x+0.0223 y=0.0274x+0.0136 y=0.0312x+0.0251

a – qe,exp: the equilibrium adsorption capacity obtained by the adsorption kinetics experiment, mg g-1;

qe,cal: the equilibrium adsorption capacity calculated by the model of adsorption kinetics, mg g-1. Pseudo-first order kinetic model: q_e q_t q_e k t

303 . 2 lg )

lg( _{  } 1

Pseudo-second order kinetic model:

e e t q t q k q t   ₂ 2 1

To better understand the adsorption behavior, the data of kinetic studies were fitted to the pseudo-first-order model and the pseudo-second-order model seen in Table S2. It is known that if the calculated qe does not equate to the experimental qe, then the reaction is not likely to be a first-order reaction. From the experimental data, it can be observed that the calculated qe values are too low compared to experimental qe values and the correlation coefficient R2 _{(0.75-0.97) is bad. Thus, it can} be concluded that adsorption of phosphate by the La/Zr hydroxide adsorbent samples does not follow pseudo first-order kinetics. However, the calculated qe values fit well with the experimental qe values and the correlation coefficient R2 _{is high (＞0.99) for pseudo-second order mode, which indicates} that the phosphate adsorption process by the La/Zr hydroxide adsorbent samples follows pseudo second-order kinetics, suggesting a chemisorption process.

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Table S3. Langmuir isotherm parameters for phosphate adsorption on La-, Zr-, and La-Zr hydroxide adsorbents with initial pH 7.0.

Samples qm

(mg g-1₎

KL

(L mg-1₎ R2

LaOH 39.37 0.10 0.974

LZ5:1 70.42 0.12 0.984

LZ2:1 125.00 0.06 0.952

LZ1:1 163.93 0.04 0.945

LZ1:2 73.53 0.07 0.987

LZ1:5 38.31 0.11 0.980

ZrOH 39.37 0.09 0.992

Langmuir isotherm: qe=qm KLCe /(1+KLCe)

Table S3 shows fitting results the Langmuir adsorption isotherm model for phosphate adsorption on La-Zr hydroxide adsorbents at pH 5.0, 7.0 and 9.0. The fitting results of adsorption isotherm model indicated that the data of phosphate adsorption on the La/Zr hydroxide adsorbent samples were fitted better to the Langmuir model, clearly displaying that P adsorption behavior is a chemisorption process.

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Table S4. Comparisons of P adsorption capacity of various metal composites.

Adsorbents pH&T qm (mg g-1) Ref.

Fe-Mn binary oxide pH 5.6, 25 °C 10.83 Zhang, G. et al.1

Fe–Al binary oxide nanosorbent pH 4.0 16.40 Tofik A S et al.2

Ce-incorporated zinc ferrite no data 41.60 Wei Gu et al.3

Mg/Al-LDHs biochar pH 3.0, 23°C 81.83 Ronghua Lia et al.4

Manganese (Mg) oxide-doped aluminum

(Al) oxide (MODAO) pH 6.0, 25 °C 59.80 Wu, K. et al.

5

Zirconium (IV) hydroxide pH 4.0, 22°C 30.40 M.A.H. Johir et al.6

Am-ZrO2 nanoparticles pH 6.2, 25 °C 32.29 Su, Y. et al.7

ZrO2@Fe3O4 pH 7.0 15.98 Liping Fang et al.8

Fe3O4/ZrO2/ chitosan pH 3.0, 25 °C 26.50 Jiang H et al.9

ACF-ZrFe pH 4.0 26.30 Weiping Xiong et al.10

ZrO2@CMK-3 pH 3.0, 25 °C 29.82 Xiaoqiu Ju et al.11

Fe-Zr binary oxide pH 5.5, 25 °C 33.36 Ren, Z. et al.12

Ce0.8Zr0.2O2 pH 6.2, 25 °C 36.60 Yu Su et al.13

Fe3O4@C@ZrO2 pH 6.0, 25 °C 40.00 Wang W et al.14

Zirconic chitosan beads (ZCB) pH 4.0, 15 °C 61.70 Xin Liu et al.15

Lanthanum-modified zeolite pH 7.0, 40 °C 9.10 He Y et al.16

Lanthanum loaded biochar no data 15.12 ZH Wang et al.17

Flower-like mesoporous La@silica spheres pH 5.0, 25°C 44.80 Weiya Huang et al.18

La-MOFs pH 6.32, 25°C 46.32 Hua Liu et al.19 La(OH)3/ La0.5-PC composite pH 8.2, 25 °C 59.60/32.40 Koilraj P et al.20 Biomass-supported nano-La(III)

(hydr)oxides Ws-N-La pH 6.0, 25 °C 67.10 Qiu H et al.

21

La/Al−hydroxide composite pH 4.0, 25 °C 76.30 Rui Xu et al.22

Fe–Mg–La composite pH 6.0, 25 °C 135.41 Yang Yu et al.23

La hydroxides (LOH sample) pH 7.0, 25 °C 39.37 This study

La-Zr hydroxide

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Table S5. The deconvolution fitting results of O K-edge XANES spectra for the La-Zr bimetallic hydroxides.

Sample

s Eπ* Eσ* Esp Iπ* Iσ* Iπ*/Iσ*

LaOH 532.78 537.29 544.56 3.397 2.331 1.457

ZrOH 532.76 534.93 545.65 2.232 1.483 1.505

The energy positions and intensity of the first two (O 2p + M nd) orbitals (π* and

σ* ) and the broad [O 2p + M (n+1)sp] peak (n+1 sp) are designated as Eπ*, Eσ*, Esp

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Table S6. The fitting results of P K-edge XANES spectra for the phosphate adsorbed La/Zr hydroxides.

Samples EA’ EA EB IA’ IA IB σA' σA σB

LaOH-P 2151.73 2153.24 2155.16 1.773 4.708 1.551 0.548 1.168 0.724

LZ2:1-P 2151.81 2153.10 2154.81 2.492 2.13 2.839 0.574 0.731 0.912

LZ1:1-P 2151.83 2153.15 2154.73 2.287 1.983 2.654 0.601 0.709 0.908

ZrOH-P 2151.02 2153.37 / 0.981 9.102 / 0.574 1.194 /

E – Energy of the fitting peaks; I – Intensity of the fitting peaks; σ– Sigma of the fitting peaks. The peaks are fitted by Gaussian function. All values of La/Zr materials only show the La components owing to the negligible Zr.

Table S7. The comparison of the white-line peak position (EA) in P K-edge XANES spectra for the phosphate adsorbed La-/Zr-hydroxides with KH2PO4.

Samples E_A ΔEA

KH2PO4 2152.60 0

LaOH-P 2153.24 0.64

ZrOH-P 2153.37 0.77

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