Supporting Information for:
ElectrochemicalMineralization of Sulfamethoxazole by Ti/SnO2-Sb/Ce-PbO2 anode: Kinetics, Reaction pathways, and Energy Cost Evolution.
HuiLin,Junfeng Niu, JialeXu, Yang Li, Yuhang Pan
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, P. R. China.
* Corresponding author. E-mail: (J.F. Niu);
Tel.: +86-10-5880 7612; Fax: +86-10-5880 7612
Text S1-S4 Pages S1-S2
Text S5 Pages S6
Text S6 Pages S10
Text S7 Pages S12
Table S1-S2 Pages S3
Figure S1-S2 Pages S4-S5
Figure S3-S6 Pages S7-S9
Figure S7 Pages S11
Figure S8-S10 Pages S13-S14
Text S1
Concentrations of inorganic ions including NH4+, NO3-, NO2-, and SO42- in aqueous solution were determined by an ion-chromatograph system (ICS-1000, Dionex, USA). The system was equipped with an autosampler (sample injection volume of25μL), a pump, a degasser, a guard column, and a separation columnoperating at 30 °C. For the determination of the anions, the system was fitted with anIonPac AS4A-SC,separation column (4mm i.d ×200 mm). The mobile phase was composed of 4.5 mmol L-1 of KOH/1.4 mmol L-1 of Na2CO3, and the flow rate was set at 1.0 mLmin-1. For the determination of the anions, the system was fitted with an IonPac AS 12Aseparation column (4mm i.d ×200 mm). A 20 mmol L-1 of KOH solution circulating at 1.0 mL min-1was used as the mobile phase.
Text S2
The concentration of SMX was analyzed by a high performance liquid chromatography (HPLC-UV, Dionex U3000, USA) equipped with a WpH C18 column (4.6 nm × 250mm, 5μm). The following operating conditions were employed: isocratic elution of acetonitrile/water (2:8, V: V), flow rate of 1 mLmin-1, injection volume of 25μL, and UV detector of 270 nm. Under these conditions, theretention time of SMX was 3.4 min and thequantitation limit was less than 0.1 mg L-1.
Text S3
Concentrations ofp-Hydroxybenzenesulfonic acid, SFN, AMI, and BZQwere measured using the same HPLC coupled with a UV detector set at wavelength of 200, 220, 220, and 250 nm, respectively. The HPLC separation was conducted by aWpHC18 column (4.6 nm × 250mm, 5μm) at 40°C using a mobile phase of methanol (20%) and 1% H3PO4(80%) mixture at a flow rate of 0.8 mL min-1 (1). The corresponding retention times for SFN, p-Hydroxybenzenesulfonic acid, AMI, and BZQ were 3.23, 3.95, 7.76, and 11.65 min, respectively. Theinjection volume was 25μL.
Text S4
The HPLC (Dionex U3000, USA) separation system and operation conditions were the same as described previously. Solvent A and B were acetonitrile and water with 0.1% formic acid, respectively, at a flow rate of 0.4 mL min-1. The gradient expressed as the concentration of solvent A was as follows: 0~50 min, a linear increase from 10% to 100%; 50~53 min, held at 100% A; 53~68 min, a linear decrease from 100% to 10%; 68~73 min, held at 10% A. The HPLC system was connected to a tripe-stage quadrupole mass spectrometer (LCQT DUO, Finnegan) coupled with an electrospray ionization (ESI) source operating in the positive ion mode under the following conditions: capillary potential: 3.5 KV; source temperature: 120 °C; desolvation temperature: 300 °C; cone voltage: 30V.
Table S1-Calibration conditions for the quantification of NH4+, NO3-, NO2-, and SO42- by ion chromatography.
ions / Retention time (min) / Concentration range (mgL-1) / Correlation coefficient (R2) / LODa (mg L-1) / LOQb (mgL-1)NH4+ / 6.28 / 0.1~20 / 0.998 / 0.010 / 0.028
NO2- / 7.65 / 0.1~50 / 0.999 / 0.003 / 0.014
NO3- / 9.73 / 0.1~50 / 0.999 / 0.006 / 0.020
SO42- / 11.87 / 0.1~50 / 0.999 / 0.007 / 0.025
aLimit of detection (LOD) was calculated from the concentration of each inorganic ions that yielded a signal-to-noise (S/N) ratio of higher than or equal to 3.
bLimit of quantification (LOQ) was calculated from the concentration of each inorganic ions that yielded a signal-to-noise (S/N) ratio of higher than or equal to 10.
Table S2-Calibration conditions for the quantification of p-Hydroxybenzenesulfonic acid, SFN, AMI, BZQ, and SMX by HPLC.
analyte / Retention time (min) / Concentration range (mgL-1) / Correlation coefficient (R2) / LODa (mg L-1) / LOQb (mgL-1)SFN / 3.23 / 0.2~10 / 0.999 / 0.084 / 0.155
p-Hydroxybenzenesulfonic acid / 3.95 / 0.2~10 / 0.999 / 0.078 / 0.147
AMI / 7.66 / 0.2~10 / 0.999 / 0.030 / 0.072
BZQ / 11.65 / 0.2~10 / 0.999 / 0.022 / 0.050
SMX / 3.43 / 0.2~100 / 0.998 / 0.028 / 0.066
aLimit of detection (LOD) was calculated from the concentration of each compounds that yielded a signal-to-noise (S/N) ratio of higher than or equal to 3.
bLimit of quantification (LOQ) was calculated from the concentration of each compounds that yielded a signal-to-noise (S/N) ratio of higher than or equal to 10.
FigureS1 – The HPLC chromatogram of standard p-Hydroxybenzenesulfonic acid (3.947 min), SFN (3.233 min), AMI (7.660 min), and BZQ (11.647 min) (concentration ofevery compound was 10mg L-1).
FigureS2 – (A) UV-Vis spectral of SMX solutions (diluted 5 fold by volume) for different electrolysis time at 2 mA cm-2; (B)UV-Vis spectral of SMX solutions (diluted 5 fold by volume) for different electrolysis time at 40 mA cm-2. SMX concentration: 100 mg L-1, Plate distance: 3 mm.
Text S5
Since the system is diffusion-controlled, a sufficiently large amount of electrolyte is present in the solution (cNaClO4/cSMX > 25), and the electrode spacing is small enough (d= 3 mm), the diffusion mass transfer coefficient/or rate of SMX at the vicinity of the anode surface (diffusion layer) will determine its oxidation rate. The pKa values of the SMX are: pKa1=1.8 and pKa2=5.6, which mean that the pH can affect the species and hydration of the molecules, thus will have an impact on the diffusivity. SMX can be modeled as a typical diprotic acid by eq 1and standard equilibrium distribution equations for [H2A+] (cationic SMX), [HA] (neutral SMX), and [A-] (anionic SMX) (2):
cSMX=[H2A+] + [HA] +[A-] (1)
The relationship curve of cationic SMX, neutral SMX, and anionic SMX distribution coefficient with the solution pH was shown in Figure S3. The results showed that, at the SMX solutionpH lower than 1.8 or higher than 5.6, SMX was mainly in its non-protonated form (cationic SMX for low pH values and anionic SMX for pH values). On the contrary, at the SMX solution pH between 1.8 and 5.6, SMX was primarily in the protonated (neutral SMX) form, which made SMX less charged and reduced the intramolecular electrical repulsion, thus increasing the mass transfer coefficient. The proportions of neutral SMX are 0.938, 0.799, 0.038, 4.00E-04, and 4.00E-06at pH 3, 5, 7, 9, and 11, respectively.
FigureS3 –pH dependency of distribution coefficient of SMX molecular.
FigureS4 – SMX concentration change as a function of electrolysis time. Current density: 10 mA cm-2; Plate distance: 5 mm.(The corresponding results averaged values from three tests with the standard deviation < 5%, the contaminated lake water was issued from Jishuitan in Beijing, China)
FigureS5 – NO3- concentration change as a function of electrolysis time in 10 mmol L-1 NaClO4, at25°C. Current density: 20 mA cm-2; Plate distance: 3 mm.(The corresponding results averaged values from three tests with the standard deviation < 5%)
FigureS6 – (a) HPLC-UV chromatogram of major identified organic intermediates and corresponding MS spectra; (b) LC-ESI (+)-MS total ion chromatograms (TIC) for the monitoring of the degradation of SMX.
Text S6
Concentrations of the aromatic intermediates including sub-structures analogues (structures identical to different portions of the SMX molecule) such as SFN and AMI,and BZQ were quantified by HPLC. As shown in Figure S6, a typical accumulation-destruction cycle can be seen in all cases. For example, at 40 mA cm-2,SFN was formed at the beginning of the electrolysis, and then reached a maximum concentration that was about 40 times (mass ratio) lower than that of initial SMX concentration at 10 min, finally, disappeared from solutions after a short time (20 min). Thus, low concentrations of SFN, AMI, and BZQwere accumulated, and subsequently,were completelydestroyed. A faster disappearance of the aromatic intermediates was observed at a higher applied current density, for example, the complete destroy of BZQ required 20 and 60 min, SFN required 30 and 60 min, whereas AMI required 30 and 60 min at 40 and 10 mA cm-2, respectively.
FigureS7 – Time course of the concentration of the main aromatic intermediates, SFN (a), AMI (b),and BZQ (c), accumulated during the electrochemical treatment of solutions, under the conditions of Figure 1a.(The corresponding results averaged values from three tests with the standard deviation < 5%).
Text S7
Electrochemical experiments conducted with sub-structural analogues, SFN and AMI, demonstrate that the sub-structural analogues can be rapidly degraded during electrolysis (Figure S7). The degradation of SFN and AMI follows pseudo-first-order kinetics (R2> 0.99), and the values of the relative rate constant (k) were 5.4×10-2min-1 and 8.4×10-2 min-1, respectively. Under the same condition, the k value of SMX was 6.2×10-2min-1.Figure S8 shows the evolution of concentrations of SO42- and NH4+ during SFN mineralization process. The results showed that approximately 100% of SO42- and NH4+ were released after electrolysis for 20 min, which indicated that the structure of SFN was completely destroyed. Figure S9 shows the evolution of the concentration of NH4+ during AMI mineralization process. The results showed that NH4+ release rate was lower than AMI degradation rate, implying that isoxazole aromatic ring was one of the priority attack functional group by hydroxyl radical during AMI mineralization process. However, with such high release ratio of SO42- and NH4+ of sub-structural analogues, it is likely to be sufficient to detoxification of the solutions.
FigureS8 – Electrochemical degradation of 100 mg L-1 SMX, AMI, and SFN as a function of electrolysis time with constant current density of 20 mA cm-2,plate distance of 10 mm, and supporting electrolyte of10 mmol L-1NaClO4. (The corresponding results averaged values from three tests with the standard deviation < 5%).
FigureS9 –Evolution ofconcentration of the SO42-and NH4+released during the electrochemical mineralization of SFN solutions with current density of 20 mA cm-2, plate distance of 3 mm, and supporting electrolyte of 10 mmol L-1 NaClO4. (The corresponding results averaged values from three tests with the standard deviation < 5%)
FigureS10 – Evolution of the concentration of the SO42- released during the electrochemical mineralization of AMIsolutions under the same conditions as Figure S7. (The corresponding results averaged values from three tests with the standard deviation < 5%)
Literature Cited
(1)A. Dirany, I. Sirés, N. Oturan, M.A. Oturan, Electrochemical abatement of the antibiotic sulfamethoxazole from water, Chemosphere 81 (2010) 594
(2)M.C. Dodd, C.H. Huang, Transformation of the antibacterial agent sulfamethoxazole in reactions with chlorine: kinetics, mechanisms, and pathways, Environ. Sci. Technol. 38 (2004) 5607
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