A highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4 microsphere wrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and used for the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation. Owing to the synergistic effect of the components and to the presence of a thin Fe2O3 layer on Fe3O4, rGO@CuZnO@Fe3O4 4 exhibited higher catalytic activity as compared to the other possible combinations such as CuZnO@Fe3O4 2 and GO@CuZnO@Fe3O4 3 microspheres. The yield of methanol in case of using 2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1 cat, respectively. However, the yield was increased to 2656 mol g−1 cat when rGO@CuZnO@Fe3O4 4 was used as photocatalyst under similar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to the restoration of the sp2 hybridized aromatic system in rGO, which facilitated the movement of electrons and resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily be recovered by external magnet and successfully reused for six subsequent cycles without significant loss in the product yield

1. Core–shell structured reduced graphene oxide wrapped
magnetically
separable rGO@CuZnO@Fe3O4 microspheres as superior
photocatalyst
for CO2 reduction under visible light
Pawan Kumar, Chetan Joshi , Alexandre Barras, Brigitte Sieber, Ahmed Addad,
Luc Boussekey, Sabine Szunerits, Rabah Boukherroub, Suman L. Jain
Chemical Science Division, CSIR - Indian Institute of Petroleum, Dehradun - 248005, India
Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 - IEMN, F-59000 Lille, France
1
Published in: Applied Catalysis B205 (2017) 654–665

2. 2
ABSTRACT
• A highly efficient, recyclable and magnetically separable core-shell structured
CuZnO@Fe3O4 microsphere wrapped with reduced graphene oxide
(rGO@CuZnO@Fe3O4) photocatalyst has been developed and used for the
photoreduction of carbon dioxide with water to produce methanol under visible
light irradiation.
• Owing to the synergistic effect of the components, rGO@CuZnO@Fe3O4 4 exhibited
higher catalytic activity as compared to the other possible combinations such as
CuZnO@Fe3O4 2 and GO@CuZnO@Fe3O4 3 microspheres. The yield of methanol in
case of using 2 and 3 as photocatalyst was found to be 858 and 1749 µmol g-1 cat,
respectively.
• However, the yield was increased to 2656 µmol g–1 cat when rGO@CuZnO@Fe3O4 4
was used as photocatalyst under similar experimental conditions. This superior
photocatalytic activity of 4 was assumed to be due to the restoration of the sp2
hybridized aromatic system in rGO, which facilitated the movement of electrons and
resulted in better charge separation.
• The synthesized heterogeneous photocatalyst could readily be recovered by external
magnet and successfully reused for six subsequent cycles without significant loss in
the product yield.

3. 3
Scheme 1. Synthesis of rGO@CuZnO@Fe3O4 microspheres 4.

4. 4
Fig. 1. FE–SEM images of a) Fe3O4 1, b) CuZnO@Fe3O4 2, c)
GO@CuZnO@Fe3O4 3 and d) rGO@CuZnO@Fe3O4 4.

5. 5
Fig. 2. Low resolution TEM
images of a) Fe3O4 1, b)
CuZnO@Fe3O4 2, c)
rGO@CuZnO@Fe3O4 4, d)
high magnification TEM of 4,
e) high resolution TEM and f)
SAED pattern of
rGO@CuZnO@Fe3O4
microspheres 4 showing
diffraction patterns of Fe3O4
and ZnO.

6. 6
Fig. 3. STEM elemental mapping of rGO@CuZnO@Fe3O4 microsphere 4.

7. 7
Fig. 4. Raman spectra of a) GO@CuZnO@Fe3O4 3, b) rGO@CuZnO@Fe3O4 4. The insets
correspond to the D and G bands of GO and rGO. The sharp peak at 523 cm–1 is due to silicon
substrate.

8. 8
Fig. 5. XRD diffraction patterns of a) Fe3O4 (1), b) CuZnO@Fe3O4 (2), c) GO, d)
GO@CuZnO@Fe3O4 (3), e) rGO and f) rGO@CuZnO@Fe3O4 (4).

9. 9
Fig. 6. C1s high resolution XPS spectra of a) GO@CuZnO@Fe3O4 3, b)
rGO@CuZnO@Fe3O4 4, c) Fe2p and d) Zn2p of rGO@CuZnO@Fe3O4 4.

10. 10
Fig. 7. UV–Vis absorption spectra a) and Tauc plot showing band gap b) of Fe2O3/Fe3O4
1, CuZnO@Fe3O4 2, GO@CuZnO@Fe3O4 3, rGO@CuZnO@Fe3O4 4.

11. 11
0
100
200
300
400
500
600
1.2 1.7 2.2 2.7 3.2
PLIntensity/a.u.
Photon Energy / eV
(r)GO@CuZnO@Fe3O4
ZnO
x 0.1
CuZnO@Fe3O4
2.37 eV
1.76 eV 2 eV
Fig. 8. Photoluminescence spectra of ZnO (red), CuZnO@Fe3O4 (dark red) 2,
GO@CuZnO@Fe3O4 3 (green) and rGO@CuZnO@Fe3O4 4 (blue).

12. 12
Fig. 9. Methanol yield using 0.25, 0.50, 1.00 and 1.50 wt% of copper loaded ZnO (CuZnO).

13. 13
Fig. 10. CO2 conversion to methanol for a) ZnO, b) Fe3O4 1 c) ZnO@Fe3O4
microspheres, d) GO@ZnO@Fe3O4 microspheres, and e) rGO@ZnO@Fe3O4
microspheres.

14. 14
Fig. 11. Yield of methanol, a) blank reaction, b) using 1 wt% CuZnO, c) CuZnO@Fe3O4
2, d) GO@CuZnO@Fe3O4 3, and e) rGO@CuZnO@Fe3O4 4.

15. 15
Entr
y
Catalyst Reactant Methanol
Yield
(μmol g–1cat)
Quantum Yield
(mole einstien–1)
1 Blank CO2 Nilb Nil
2 Fe3O4 1 CO2 278 0.0026
3 ZnO CO2 211 0.0020
4 1wt% CuZnO CO2 383 0.0036
5 GO CO2 470 0.0044
6 rGO CO2 117 0.0011
7 rGO@CuZnO CO2 648 0.0061
8 ZnO@F3O4 CO2 524 0.0049
9 CuZnO@Fe3O4
2
CO2 858 0.0082
10 GO@ZnO@Fe3
O4
CO2 942 0.0089
11 rGO@ZnO@Fe
3O4
CO2 1124 0.0106
12 GO@CuZnO@
Fe3O4 3
CO2 1749 0.0167
13 rGO@CuZnO@
Fe3O4 4
CO2
N2
CO2
2656
Nil
Nil
0.0253
Nil
Nil
Table 1. Photocatalytic reduction of CO2 by using different catalysts.a
aReaction conditions: catalyst: 100 mg, solvent: DMF/water (45/5), visible light irradiation
using 20 Watt LED (λ>400 nm), time: 24 h; bwithout catalyst.

16. 16
Fig. 12: Recycling experiments using rGO@CuZnO@Fe3O4 microspheres 4. Inset showing
magnetic separation experiments: a) rGO@CuZnO@Fe3O4 microspheres 4 dispersed in
water and b) after exposure to 1 tesla magnet for 1 min

17. 17
Scheme 2: Plausible mechanism of CO2 reduction by rGO@CuZnO@Fe3O4 4.

18. 18
Thanks