Supporting Information Synthesis of Mg/ Al Layered Double Hydroxides for Adsorptive Removal of Fluoride from Water: A Mechanistic and Kinetic Study Gautam Kumar Sarma and Md. Harunar Rashid* Department of Chemistry, Rajiv Gandhi University, Rono Hills, Doimukh 791 112, Arunachal Pradesh, India *Corresponding author e-mail: mhr.rgu@gmail.com Characterization of the prepared materials. All the as-prepared LDHs were characterized by different spectroscopic, microscopic and diffractometric techniques. For X-ray diffraction study, the dried solid powder samples were used and the diffractograms were recorded in a Rigaku Ultima IV X-ray diffractometer using Cu k α radiation with wavelength 0.154 nm. Fourier transforms infrared spectra (FTIR) of the powder samples were collected in a Thermo Scientific Nicolet is5 spectrophotometer in the range of 4000 400 cm 1. The pellets for recording the FTIR spectra were prepared by mixing the powder sample with dried KBr in the weight ratio of 1:100. For electron microscopic study, a small amount of the dry powder samples were spread on a carbon tape pasted on an aluminium stub and the micrographs were then recorded in a field emission scanning electron microscope (FE-SEM) (Carl Zeiss Sigma) at an accelerating voltage of 5 kv. For transmission electron microscopic (TEM) studies, a drop of aqueous suspension of individual powder sample was cast on a carbon coated copper grid. The excess solutions were soaked with a tissue paper followed by drying in air. The micrographs were then recorded in a high resolution JEOL electron microscope (JEM 2100EM) at an accelerating voltage of 200 kv. S1
The nitrogen (N 2 ) gas adsorption desorption isotherms of the LDHs were recorded at 77 K (Quantachrome Nova 1000 Instrument) after degassing the powder samples at 150 ºC for 4 h in an inert atmosphere. BET specific surface area and pore diameter was determined from the adsorption-desorption isotherms following the well-known Barrett-Joyner-Halenda (BJH) method. The thermal analysis of the powder samples were carried out on a thermogravimetric analyzer (Mettler Toledo TGA/ DSC 1, Star e system) under N 2 atmosphere. Zeta potential measurement of the colloidal suspension of LDH was performed in a Malvern Zetasizer (Malvern Instruments; Nano-ZS) instrument. Atomic absorption spectroscopic (AAS) study on LDH sample was carried out on a Thermo Scientific AAS instrument (ice-2500) in flame mode using air-acetylene/ nitrous oxide gas. X-ray photoelectron spectroscopy study was carried out on FEI PHI Versa Probe II Instrument using Al k α source under ultra high vacuum condition. Table S1: Experimental conditions for fluoride-ldh interactions ph 4.0-10.0 (at unit interval) Interaction time (min) 5, 10, 15, 20, 30, 45, 60, 90, 120, 150, 180, 240, 300, 360 Amount of LDH (g L 1 ) 1, 2, 3, 4, 5 Fluoride concentration (mg 2, 5, 7, 10, 15, 20, 25, 30 L 1 ) Temperature (K) 303 K S2
Figure S1. Energy dispersive X-ray spectra of LDH (sample Mg_Al-6). S3
30000 O 1s 25000 20000 Mg KLL Intensity (a.u.) 15000 10000 5000 O KLL C 1s Al 2s Mg 2s Al 2p Mg 2p O 2s 0 1200 1000 800 600 400 200 0 BE (ev) Figure S2. XPS survey scan spectrum recorded from sample Mg_Al-6. S4
Figure S3. (a) FTIR spectra recorded from different LDH samples and (b) enlarged view of the region from 900 to 400 cm 1. S5
Figure S4. Plot showing the variation of q t versus. t 0.5 on the basis of intra-particles diffusion rate equation. S6
Figure S5. Plot showing the variation of ln (1 F) versus t on the basis of liquid film diffusion model. S7
Figure S6. Plot showing the variation of ln q e versus ln C e on the basis of Freundlich adsorption isotherm. S8
Figure S7. Temkin isotherm plots (q e versus ln C e ) for fluoride adsorption on LDHs S9
Figure S8. Effect of ph on adsorption of fluoride (10 mg L 1 ) on LDH (sample Mg_Al-6). S10
90 4.5 % Adsorption 80 70 60 50 40 4.0 3.5 3.0 2.5 2.0 1.5 q e (mg/ g) 30 1 2 3 4 5 Adsorbent dose (g/l) 1.0 Figure S9. Plots showing the variations of %adsorption and effective adsorption, q e of fluoride with dose of adsorbent. S11
Figure S10. Variation of adsorption of fluoride in presence of different monovalent and bivalent anions. S12
Figure S11. Variation of adsorption (%) with temperature for removal of fluoride by LDH. S13
Figure S12. Zetal potential curves of LDHs (a) before and (b) after F - ions adsorption. S14
(003) Mg_Al-6-after Mg_Al-6-before Intensity (a.u) (006) (009) (015) (018) (110) (113) 10 20 30 40 50 60 70 80 2θ (degree) Figure S13. XRD patterns of LDH before and after fluoride adsorption. S15
Mg_Al-6-after 84 56 28 % T 0 84 Mg_Al-6-before 56 1628 28 1353 3442 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm -1 ) Figure S14. FTIR spectra of LDH before and after fluoride adsorption. S16
Figure S15. SEM images of recovered LDH (sample Mg_Al-6) after fluoride adsorption. S17