An Innovative Anion Regulation Strategy for Energy Bands of Semiconductors: a Case From

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An Innovative Anion Regulation Strategy for Energy Bands of Semiconductors: a Case From

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An innovative anion regulation strategy for energy bands of semiconductors: a case from Bi2O3 to Bi2O(OH) 2SO4

Hao Tian,a,b Fei Teng, a,b,c,d* Juan Xu, a,b Sunqi Lou, a,b Na Li, a,b Yunxuan Zhao, a,b Mindong Chen a,b,c,d

a Jiangsu Engineering and Technology Research Center of Environmental Cleaning Materials (ECM);b Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), c Jiangsu Joint Laboratory of Atmospheric Pollution Control (APC); d Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (AEET), School of Environmental Science and Engineering, Nanjing University of Information Science & Technology，219 Ningliu Road, Nanjing 210044, China. Email: (F. Teng); Phone/Fax: +86-25-58731090

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Figure S1.Infrared spectra (IR) of Bi(OH)3, Bi2(SO4)3, Bi2O3and Bi2O(OH)2SO4: (a) OH stretching vibration (3200-3700 cm-1); (b)S-O stretching vibration (1604 cm-1); (c) OH bending vibration (1260-1170 cm-1); (d) CO2coming from ambient environment(2380 cm-1); (f)the out-plane bending ofBi(OH)3 and Bi2O(OH)2SO4 (1390 cm-1); Notes in (a): Wide peak (3200-3500 cm-1): OH stretching vibration of H2O; Weak peak: OH stretching vibration peak of Bi(OH)3

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Figure S2. X-ray diffraction patterns ofthe Bi2O(OH)2SO4 samplebefore andafter photocatalytic reaction

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Figure S3. (a, b) scanning electron microscopy (SEM), (c) transmission electron microscopy (TEM) and (d) electron diffractionpattern (ED) of Bi2O(OH)2SO4

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Figure S4. Ultraviolet-visible diffuse reflectance spectra (UV-DRS) of the samples:(a) commercial rutile TiO2; (b) Bi2O(OH)2SO4

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Figure S5. X-ray diffraction patterns of(a)10 mol% Bi2O(OH)2SO4/Bi2O3 and(b) 20 mol% Bi2O(OH)2SO4/Bi2O3

Bi2O(OH)2SO4-Bi2O3. The Bi2O(OH)2SO4-Bi2O3 composite has been synthesized via a facile hydrothermal method. The Bi2O(OH)2SO4/Bi2O3 composite was obtained as follows: 1mmol commercial Bi2O3 was added into 30-mL distilled water, then 0.2 mmol Bi(NO3)3∙5H2O was added under stirring, until the Bi(III) ions hydrolyzed completely. Then, 1 mmol Na2SO4 was added to the system above. Finally, the mixture was transferred into a 50 mL Teflon-lined autoclave and hydrothermally treated at 110 oC for 6 h.

Figure S5 show the XRD patterns of two Bi2O(OH)2SO4/Bi2O3 samples, which contain 10 mol% and 20 mol% Bi2O(OH)2SO4. For 20 mol% Bi2O(OH)2SO4/Bi2O3, the peaks at 27.8o and 30.5o correspond to (-221) and (131)diffraction planes of Bi2O(OH)2SO4, respectively; and all the other peaks observed can be indexed as Bi2O3.

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Figure S6. Scanning electron microscopy (SEM) of commercial pure Bi2O3 (a) and 20 mol% Bi2O(OH)2SO4/Bi2O3 (b)

Typically, Figure S6 presents the SEM images of Bi2O3 (a) and 20 mol% Bi2O(OH)2SO4/Bi2O3 (b). It is obvious that Bi2O(OH)2SO4 has been successfully supported on the surface of Bi2O3.

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Figure S7. Transient photocurrent responses of commercial pure Bi2O3 and 20 mol% Bi2O(OH)2SO4/Bi2O3 under UV light irradiation (λ < 420 nm) in 0.5 M Na2SO4 aqueous solution

Figure S8. Nyquist plots of 20 mol% Bi2O(OH)2SO4/Bi2O3 and commercial Bi2O3 under UV light on/off (λ< 420 nm) in 0.5 M Na2SO4 aqueous solution

Figure S9.Degradation curves of RhB over the 20mol% Bi2O2/Bi2 (OH)SO4 and commercial Bi2O3samples under ultraviolet light irradiation (λ<420 nm)

Figure S10. The energy bands of Bi2O3 and Bi2O(OH)2SO4 (Bi2O3 possess a VB of 3.13 eV and a CB of 0.33eV, whereas Bi2O(OH)2SO4 have a VB of 4.39eV and a CB of 0.21 eV.)

Photoelectric properties of Bi2O3 and Bi2O(OH)2SO4/Bi2O3are provided in Figures S7 and S8, respectively. Both photocurrent and EIS measurement data show that the 20mol% Bi2O(OH)2SO4/Bi2O3 composite does not show an improved photo performance, compared with Bi2O3, which can be further confirmed by the degradationtest of RhB in Figure S9.

Herein, two main facts can not be ignored: (i) since the energy bands of Bi2O3 and Bi2O(OH)2SO4 do not match (see Figure S10), the separation efficiency of photogenerated electron-hole pairs can not be improved; (ii) the Bi2O(OH)2SO4 supportedon the surface of Bi2O3 would reduce the light absorption of Bi2O3, thus resulting in a lower activity, compare with Bi2O3.

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IPCE measurement.

We have tried to test IPCE data of Bi2O(OH)2SO4. However, the IPCE measurement systems available for us are all performed under the illumination of simulated solar power, in which the used lights are longer than 300nm. Therefore, it is difficult for us to find an effective light source shorter than 300nm to investigate the IPCE of Bi2O(OH)2SO4 (4.18 eV, 295 nm). We finally carried out an IPCE measurement of the Bi2O(OH)2SO4 photoanodeunder air mass (AM) 1.5 illumination coupled with a series of band-pass filters. The Bi2O(OH)2SO4 was implemented as the photoanode material in a photoelectrochemical cell (PEC).

Figure S11. Measured IPCE spectra of Bi2O(OH)2SO4 collected in the incident wavelength range from 300-800nm at a potential of 0 V vs. Ag/AgCl

In Figure S11, it seems that almost no photon-to-electron conversion can be observed in wavelength range of 300-800nm, because there is no response in wavelength range of 300-800nm for the wide band-gap Bi2O(OH)2SO4.

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Figure S12. Schematic of possible photocatalytic processes to drive photo redox processes

Bandara et al.1 reported that both TiO2 and CuO could be simultaneously excited under UV-light irradiation and the excess electrons would accumulate in the CBs of CuO. A negative shift of the Fermi level of CuO would result in the required negative potential required for water splitting as a result of the accumulated excess electrons. Moreover, the others 2-6 have reported that the accumulation of electrons or holes would lead to an extra induced potential (φ), as shown in Figure S12. For example, strontium niobate (ECB = -0.36 eV, EVB = 1.54 eV)5 has a low oxidizing ability according to the EVB value. But it has a high oxidizing ability than the expected, which has been ascribed to the generated induced potential by the accumulation of hole in VB, leading to a high oxidizing ability. Bi2O3 has a positive conduct band at 0.33 eV.3-5 The accumulation or storage of electrons in CB would lead to the upper shift of CB, i.e., increasing the reducing ability of Bi2O3 to some extent. Similarly, the accumulation or storage of holes in VB would lead to the down shift of VB, i.e., increasing the oxidizing ability of Bi2O3 to some extent. An extra induced potential would generate. Also, our previous study 7 has reported that the excess electron accumulation in CB of CuO leads to an extra negative potential, lower than the redox potential of H+/H2. In the case ofBi2O(OH)2SO4, the recombination of the photoexcited holes and electrons can be effectively inhibited by the inner electron field formed due to its unique layer structure. We hold that the accumulation of electrons in CB could also lead to an induced potential, which do help to drive reduction process (Eo(O2/O2-) = -0.28 eV)6.

Moreover, we have performed ESR measurements. Fig. 1(a) gives the 10-line spectrum under irradiation. This signal is due to a primary nitrogen triplet (aN=1.40 mT), each line being further split into a doublet (aH=0.90 mT) from the hydrogen in the b-position with respect to the unpaired electron on the nitrogen atom and with an additional small splitting (aH=0.12 mT) for one proton at the c-position. Based on these ESR parameters, the spin adduct has been characterised as the superoxide spin adduct of DMPO 8,9. Without irradiation, no signal can be detected. The results confirm the formation of superoxide radical anions.

Figure S13 ESR spectrum: (a) DMPO(5,5-Dimethyl-1-pyrroline-Noxide) adduct; (b) Under irradiation; (c) Without irradiation; Spectrometer settings were receiver gain, 1.25104; Scanning time, 2 min; Modulation amplitude, 0.01 mT

ESR measurements. A 0.5 ml of 10 mM sample of spin trap solution sample was transferred to a flat quartz cell (60100.5 mm3). The spectra were recorded at room temperature on a Varian E-12 spectrometer with 100 kHz field modulation, operating at 9.5 GHz microwave frequency. The modulation amplitude was usually 0.1 G, the microwave power level was 1 mW, the time constant was 0.3 s and the scan range was 20.0 mT.

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