Cu 2 O/g-C 3 N 4 nanocomposites: An insight into the band structure tuning and catalytic efficiencies

Transcription

1 Electronic Supplementary Material (ESI) for Nanoscale. This journal is The Royal Society of Chemistry 216 Cu 2 O/g-C 3 N 4 nanocomposites: An insight into the band structure tuning and catalytic efficiencies Anuradha Mitra, a Promita Howli, a Dipayan Sen, b Biswajit Das, a and Kalyan Kumar Chattopadhyay* a-c S1

2 (22) (311) Intensity (counts) (1) (2) (111) Intensity (counts) Intensity (counts) (22) (111) (111) (111) (2) (A) (111) Cu 2 O CuO Cu hkl 2 (111) 36.5 (111) 35.8 (111) (111) 43.4 (2) 5.5 (22) (B) (C) 5 (22) (D) (E) (F) (2) 2 (degree) g-c 3 N 4 Cu 2 O hkl 2 (1) (2) (111) 36.5 (2) (22) (311) (111) (2) 8 (22) 4 (311) (degree) (degree) Fig. S1. (A) XRD and (B-E) TEM images of CuT. (B, C) Large agglomerated nanoparticles of Cu and Cu oxide HRTEM images shows the presence of lattice fringes corresponding to (E) Cu 2 O(111) and (F) Cu(111). (F) XRD of the physical mixture between Cu 2 O and g-c 3 N 4 (Cu 2 O+g-C 3 N 4 ). (G) TEM images and the XRD (top inset) of the Cu 2 O nanocubes synthesized for preparing the physical mixture. One such nanocube is enlarged (top left inset) showing (111) lattice plane of Cu 2 O (bottom inset). S2

3 1. FTIR spectra..6.5 Absorbance (a.u.) { TCu TCu 2 TCu 5 terminal -NH or -NH2 C=N Aromatic C-N Out-of-plane bending C-N heterocycles C N Wavenumber (cm -1 ) Fig. S2. FTIR of TCu, TCu 2 and TCu 5. The region from 124 to 1635 cm -1 are stretching modes characteristic to heptazine-derived repeating units while the intense band at cm -1 is assigned to the out-of-plane bending vibration of heptazine rings. A weak absorption at 2165 cm -1 related to suggests C N stretching vibration suggests the presence of some defect sites in the g-c 3 N 4 structures. A broad band with a maximum at ~32 cm -1 appears due to the presence of terminal -NH 2 or -NH groups. It has S3

4 been observed that these peak positions remain more or less unaltered after the incorporation of Cu but their intensities decrease considerably. 2. XPS analysis: The C1s spectrum (Fig S1 b) shows the existence of C-NH (286.5 ev), C=N bond of the [(N ) 2 C(=N)] skeletal (287.1 ev), sp 3 and sp 2 hybridized graphitic carbon (284.6 ev and ev) and a π-π* satellite peak (292.5 ev) characteristic of carbon nitrides. 1-3 The N1s spectrum in Fig S1 c has been resolved into three peaks at 397. ev, ev, and 42.9 ev and are ascribed to the sp 2 hybridized N of (C=N C), tertiary N atoms [either N( C) 3 or H N (C) 2 ] and π-π* satellite characteristic to nitrogen-containing aromatic polymers. It is to be noted that these peaks show a downshift of ~1.3 ev with respect to the binding energy of N1s for pure g-c 3 N 4 due to the slight variation in its chemical composition. 1 High resolution O1s spectrum reveal peak at ev indicating the presence of C-O functional group in the g-c 3 N 4. S4

5 Intensity(cps) Intensity(cps) Intensity(cps) Intensity(cps) 2 15 C 41.23% N 53.72% O 5.5% N1s C1s (a) C 1s Deconvoluted profiles 6 ev (b) O1s N 1s Deconvoluted profiles Binding Energy(eV) 397 (c) O 1s Deconvoluted profile Binding Energy(eV) (d) Binding Energy(eV) Binding Energy(eV) Fig. S3. (a) XPS of pure g-c 3 N 4 (TCu ) powder shows the presence of C, N and O. (b) C 1s, (c) N 1s, and (c) O 1s XPS spectra with respective deconvoluted profiles. S5

6 Intensity (cps) Intensity (cps) Intensity (cps) Intensity (cps) Intensity (offset Y values) Cu LMM2 Cu LMM Cu LMM1 Cu 2p O1s N1s C1s TCu 2 TCu Binding Energy(eV) C 1s Deconvoluted profiles N 1s Deconvoluted profiles O 1s Deconvoluted profiles Binding Energy (ev) Cu 2p Deconvoluted profiles Binding Energy (ev) Binding Energy (ev) Binding Energy (ev) S6

7 Fig. S4. (A) XPS of powder TCu 2 and TCu 5 powder samples. (B) High resolution XPS of the individual elements present in TCu 5. Fig. S5. (A) The EDX spectra and FESEM image (inset) of TCu 2 sample drop-casted on Si wafer. Elemental mapping on the selected area (B) shows the presence of (C) silicon (from substrate), (D) carbon, (E) nitrogen, (F) copper and (G) oxygen. S7

8 Intensity (counts) Fig. S6. (A) EDS spectra and FESEM image of TCu 5. Elemental mapping on the selected area (B) of TCu 5 sample showing (C) silicon (from substrate), (D) carbon, (E) nitrogen, (F) copper and (G) oxygen. S8

9 Normalized PDOS Density of States.28 ev 2.92 ev s p TDOS 2.64 ev Energy (ev) C 1 C 2 N 1 N 2 N Energy (ev) Fig. S7. (A) Calculated density of states showing orbital contributions and (B) normalized PDOS of carbon and nitrogen atoms of g-c 3 N 4. The solid and dashed lines represent up- and down spin states, respectively. (C, D) Model showing structure of g-c 3 N 4 with different nature of carbon (marked as C 1 and C 2 ) and nitrogen (represented as N 1, N 2 and N 3 ) atoms. The grey and blue spheres represent the respective C and N atoms (C: top view and D: side view.) S9

10 Normalized PDOS Density of States.32 ev 2.19 ev 2 s p d TDOS ev Energy (ev) C 1 C 4 N 1 N 4 Cu 1 Cu 2 O 1 O Energy (ev) Fig. S8. (A) Top and (inset) side views of the Cu 2 O/CuO/g-C 3 N 4 composite model after geometry optimization. The grey, blue, cyan and red spheres represent the respective C, N, Cu and O atoms. (B) DOS and (C) normalized PDOS showing contributions from carbon (C 1 and C 4 ), nitrogen (N 1, N 3 and N 4 ), copper (Cu 1 and Cu 2 ) and oxygen (N 1 and N 2 ) atoms in (A). The solid and dashed lines represent up- and down spin states, respectively. Normalize to [, 1] of "C Normalize to [, 1] of "C Normalize to [, 1] of "N Normalize to [, 1] of "N Normalize to [, 1] of "C Normalize to [, 1] of "C Normalize to [, 1] of "O Normalize to [, 1] of "O Normalize to [, 1] of "O Normalize to [, 1] of "O Normalize to [, 1] of "N Normalize to [, 1] of "N Normalize to [, 1] of "N Normalize to [, 1] of "N Normalize to [, 1] of "C Normalize to [, 1] of "C Normalize to [, 1] of "C Normalize to [, 1] of "C S1

11 .26 V 1/C 2 (F -2 ) 1/C 2 (F -2 ) -.55 V F(R) 1/C 2 (F -2 ) 4.5 4x TCu 3.5 3x TCu TCu 2 TCu 5 Band Edge (nm) x1 13 1x Wavelength (nm) Potential (V vs Ag/AgCl) 2.4x1 13 TCu 2 2.x1 13 TCu 5 2.x x x x x x x x x Potential (V vs Ag/AgCl) Potential (V vs Ag/AgCl).78 V Fig. S9. (A) UV-visible diffused reflectance spectra of TCu, TCu 2 and TCu 5. (B-D) Mott- Schottky plots of (B) TCu, (C) TCu 2 and (D) TCu 5 recorded at 2. KHz (black) and 2.5 KHz (red). S11

12 Absorbance (a.u.) 314 nm 279 nm 32.5 nm A 249 nm min 4.75 min solvent B Wavelength (nm) C D Fig. S1. (A) UV-visible spectra of MO dye in presence of borohydride just before and after catalysis reaction. FTIR of (B) pure MO dissolved in acetone and (C, D) pure MO, reaction products in upper liquid and the lower oily liquid. The portions of the IR regions has been shown separately in the inset of B and in D for clarity and comparison. S12

13 3. Analysis of the reaction products by FTIR. Although we have carried out the reaction in aqueous medium but for extraction of the products we have used acetone as a solvent. Therefore for better understanding we have carried out FTIR of the pure MO dissolved in pure acetone (see Fig. S1 B) to rule out the peaks from the solvent (acetone and water in the product). 4 The peaks characteristic to the dye has been marked in the figure while the remaining peaks are attributed to the solvent (acetone or acetone+water). The FTIR spectra for pure MO in acetone and the reaction products were similar to those reported by Shen et al. 4 with slight shifting in the peak positions owing to the presence of solvent in the present work. 5 The broad band at 3488 cm -1 corresponds to the respective symmetric stretching vibrations of N H bond of MO dye. 4 The peak at 2926 cm -1 appear due to the alkyl C H stretching of the - CH 3 group while and the ones at 168 and 1551 cm -1 are for the C C vibrations of benzene ring. The characteristic peak of the unsymmetrical para substituted azobenzene possessing an electron-donating group (here, -N=N- stretching of MO) is observed at 142 cm -1. 4, 5 The peak 1357 and 1186 cm -1 are attributed to the C N stretching vibration, and that for the S=O vibration of sulphonate group appeared at 1124 cm -1. The peaks at 133, 848 and 819 cm -1 are due to the out-of-plane C H bending vibration of aromatic ring. The lower oily liquid showed a completely different FTIR pattern (Fig. S1 C). The presence of an intense peak at 3245 cm -1 and 1643 cm -1 correspond to respective N H stretching and bending modes of primary amine group; while the peaks for S=O vibration (of sulphonate group) and C H stretching of benzene ring are observed at 1164 and 91 cm -1, respectively. Presence of signals for the NH 2 and sulphonate groups in the oily lower liquid extract suggest the formation of salt S13

14 of sulphanilic acid. The FTIR pattern of the upper liquid is given in Fig S1 C and D at different magnification for clarity. The upper liquid product shows interesting changes in its FTIR pattern than the MO dye. The sharp and intense peak at 3333 cm -1 appear due to N H stretching mode; however the peak for the N H bending mode was not distinct and must have been obscured by the broad peaks in the region cm The peaks at 1465 and 142 cm -1 may be due to C C vibrations of benzene ring. It must be noted that the peak for aromatic C N vibration is shifted to 1372 and 1163 cm -1 in the product along with the appearance of a new peak at 136 cm -1 while the S=O stretching peak position remained more or less unaffected. The peaks at 947, 876 and 812 cm -1 are for the C C aromatic stretching while the prominent peaks at 6 and 534 cm -1 for the C S stretching mode appear in the product. 4 These observations confirms decomposition of the azo dye into the corresponding amine compounds (scheme 1). References 1. X. Zou, R. Silva, A. Goswami and T. Asefa, Appl. Surf. Sci., 215, 357, Y. Zhang, J. Liu, G. Wu and W. Chen, Nanoscale, 212, 4, F. Zhao, H. Cheng, Y. Hu, L. Song, Z. Zhang, L. Jiang and L. Qu, Sci. rep., 214, 4, T. Shen, C. Jiang, C. Wang, J. Sun, X.Wang and X. Li, RSC Adv., 215, 5, R. M. Silverstein and F. X. Webster, in Spectrometric Identification of Organic Compounds, Wiley, India, 6 th edn, ch. 3, pp S14