Phosphate Changes Effect of Humic Acids on TiO 2 Photocatalysis: from Inhibition to Mitigation of Electron-Hole Recombination

Transcription

1 Phosphate Changes Effect of Humic Acids on TiO 2 Photocatalysis: from Inhibition to Mitigation of Electron-Hole Recombination Mingce Long,, Jonathon Brame, Fan Qin $, Jiming Bao $, Qilin Li *, Pedro J.J. Alvarez * School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai , China Civil and Environmental Engineering, Rice University, Houston, Texas 77005, United States $ Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA *Corresponding author: Qilin.Li@rice.edu; alvarez@rice.edu 1

2 Text S1 Calculation of R error using error propagation method = (1) = + (2) The ratio (R) between the reaction rate constants in the absence (k 0 ) and presence of HA (k) was used as a measure of the inhibitory effect of HA. S R, S k0 and S k are the errors of R, k 0 and k, respectively. 2

3 Figure S1 Time dependent adsorption of HA (20mg/L) on TiO 2 (0.5 g/l) at ph 4.8. Text S2 Adsorption of HA reaches equilibrium quickly. In the presence or absence of 0.1 M NaClO 4, the final absorbance of HA is the same (0.015 a.u.), indicating that the influence of NaClO 4 on the adsorption of HA on TiO 2 is negligible. 3

4 Figure S2 Standard curve for the relationship between HA and SUV 254 absorbance 4

5 Figure S3 Three-electrode setup for photoelectrochemical or electrochemical tests. 5

6 Figure S4 Effect of phosphate concentration on phenol degradation rate constants ([phenol] 0 =10 mg/l, [TiO 2 ]=0.5 g/l, ph 6.2) 6

7 Figure S5 Comparison of phenol degradation rate constants at various combinations of phosphate (2 mm) and HA (20 mg/l): control (no phosphate or HA); phosphate alone; HA alone; and both phosphate and HA. 7

8 Figure S6 Phosphate addition (2 mm) significantly decreased the inhibitory effect of humic acids (20 mg/l) during photocatalytic degradation of FFA or cimetidine by TiO 2 (ph=6.20, [FFA] 0 =24.5 mg/l, [Cimetidine] 0 =5.0 mg/l). 8

9 Figure S7 First-order phenol degradation rate constant with H 2 O 2 irradiated by UVC in the absence or presence of 20 mg/l HA and 2 mm phosphate, and the comparison of R 2 values ([H 2 O 2 ] 0 =50 mg/l, [phenol] 0 =10 mg/l) Text S3 Experimental details: Tests were conducted in the same reactor used for the heterogeneous reaction but with a UVC bulb as the light source; 50 ml phenol solution at 10 mg/l with or without HA (20 mg/l) or phosphate (2 mm) was stirred in the reactor. After the first sample was taken, H 2 O 2 was added to the solution to reach a concentration of 50 mg/l. UVC illumination started immediately after addition of H 2 O 2. Sample aliquots of 1 ml were taken at predetermined times for analyses of phenol by HPLC method. In the homogeneous H 2 O 2 /UVC system, the degradation rate constant of phenol decreased greatly with the presence of HA, with an R 2 value as high as In the presence of 2 mm phosphate, the R 2 value increased slightly to

10 Figure S8 Adsorption of HA over TiO 2 in absence or presence of 2 mm phosphate ([TiO 2 ]=0.5 g/l, ph=6.2). Text S4 Experimental details: In 30 ml HA aqueous solutions at various concentrations, 15 mg Degussa P25 was added and the suspensions were stirred at ambient temperature for 2 hours to reach adsorption equilibrium. To consider the influence of phosphate, HA solutions at the same initial concentrations were prepared in 2 mm phosphate solutions. The concentration of HA were measured by the absorbance at 254 nm using an Ultraspec 2100 Pro UV/Vis spectrophotometer. 10

11 Figure S9 Fitting parameters for the photocurrent decay of curve c and d in Figure 2. Text S5 I = + exp + exp (3) The decay curve can be fitted by equation 3 (equation 2 in the paper). I 0 is a constant that could be assigned to the photocatalytic oxidation of water. The two exponential decay terms correspond to the slow interfacial-related and the fast surface-related photocatalytic reactions, respectively. A and B represent the instantaneous initial rate of reactions, whose rate constants are represented by the respective decay rate constants k 1 and k 2. Both the slow and fast reactions are related to photooxidation of organic pollutants by photogenerated holes. We fitted the curves by two I ph values at boundary conditions, that is, initial I ph at t = 0 and final I ph at t (in this work, we use t = 20 s). The initial and final I ph are as followings: I ph (t=0)= and I ph (t )= for curve c; I ph (t=0)= and I ph (t )= for curve d. 11

12 Figure S10 Integrated spike photocurrent of curve c and d in Figure 2. Text S6 Total charges (Q) transferred from the electrode to HA can be obtained by. Q=A (4) Wherein, A is the area of working electrode that was exposed under irradiation (6.25 cm 2 ), J is the current density (µa/cm 2 ), t is the time (second). 12

13 Figure S11 Photocatalytic degradation of phenol with TiO 2 in the presence or absence of 5 mg/l HA at various initial ph values ([phenol] 0 =10 mg/l, [TiO 2 ]=0.5 g/l, [PO 4 3- ]=2 mm) 13

14 Figure S12 Photolytic degradation of FFA using UVA and UVC light in the absence or presence of 10 mg/l HA ([FFA] 0 =24.5 mg/l). 14

15 Figure S13 FTIR spectra of HA adsorption on TiO 2 in absence and presence of phosphate. 15