Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.

1. 1
Supporting Information
Selective Cellobiose Photoreforming for Simultaneous Gluconic
Acid and Syngas Production in Acidic Conditions
Jiu Wang,a
Heng Zhao,a
Lin Chen,b,
* Jonas Björk,b
Johanna Rosen,b
Pawan Kumar,a
Liquan Jing,a
Jun Chen,c
Md Golam Kibria a,
* and Jinguang Hu a,
*
a
Department of Chemical and Petroleum Engineering, University of Calgary, 2500
University Drive, NW, Calgary, Alberta, T2N 1N4, Canada
b
Materials Design Division, Department of Physics, Chemistry and Biology, IFM,
Linköping University, 581 83, Linköping, Sweden
c
State Key Laboratory of Advanced Technology for Materials Synthesis and
Processing, Wuhan University of Technology, 122 Luoshi Road, 430070 Wuhan,
Hubei, China
Email addresses: lin.chen@liu.se; md.kibria@ucalgary.ca; jinguang.hu@ucalgary.ca

2. 2
H2O2 quantification: The concentration of H2O2 during the photocatalytic reaction has
been determined by iodometry. After a certain time of reaction, the sample solution was
collected, centrifuged, and filtered. After that, 0.1 mol L-1
solution of potassium
hydrogen phthalate (C8H5KO4) and 0.4 mol L-1
solution of potassium iodide (KI) were
ready for use. Then these three solutions were mixed in a ratio of 1:1:1 and left to stand
for 2 h, where H2O2 can react with iodide anions (I-
) under acidic condition to produce
I3
-
(H2O2 + 3I-
+2H+
→ I3
-
+2H2O). The amount of I3
-
is then measured by a UV-visible
spectrometer (Lambda, PerkinElmer) based on the characteristic absorption at 350 nm.
Rotating disk electrode (RDE) measurements. The RDE measurements were carried
out at room temperature using an electrochemical workstation (PGSTAT204/FRA32M,
Metrohm Autolab, B.V., Netherlands) in a three-electrode cell. The cell contains a
working electrode, a Pt counter electrode and an Ag/AgCl (3 M KCl) reference
electrode. In addition, the working electrode is a rotating disk glassy carbon (GC-RDE,
5 mm OD from Pine Instrument) connected with a Model 636A electrochemical
rotating system. The working electrode was modified with catalyst dispersion via a
simple drop coasting method. Typically, 10 mg of prepared photocatalyst was dispersed
in 10 mL of 0.05% Nafion dispersion in ethanol and ultrasonicated for 60 mins. After
that, 20.0 µL catalyst dispersion applied on the GC-RDE (after mirror-like polishing
with alumina powder) and dried at 60°C in an air-oven to form a catalyst film. By this
method, CNKS-OH film-coated electrode was obtained and gently rinsed via
immersing in water for around five minutes to remove the unattached materials from
the surface of electrode. Linear sweep voltammograms (LSVs) were obtained in an O2

3. 3
-saturated 0.5 M Na2SO4 electrolyte solution at a scan rate of 20 mV s−1
and the RDE
were rotated at the specific speed up to 2000 rpm. The number of electrons involved
during the dissolved O2 reduction process was calculated applying Koutecky-Levich
(K-L) equations:
𝑗−1
= 𝑗𝑘
−1
+ 𝐵−1
𝜔−1/2
𝐵 = 0.2𝑛𝐹𝜈−1/6
𝐶𝐷2/3
where j (mA cm-2
) is the measured current density, jk (mA cm-2
) is the kinetics current
density, 𝜔 (rpm) is the rotating speed of the RDE. F (96 485 C mol−1
) is the Faraday
constant, ν (0.01 cm2
s-1
) is the kinetic viscosity of water, C (1.26 × 10−3
mol cm−3
) is
the bulk concentration of O2 in water, and D (2.7 × 10−5 cm2
s−1
) is diffusion coefficient
of O2.

4. 4
Fig. S1. FESEM image (a) MCN and (b) CNKS.

5. 5
Fig. S2. XRD patterns of MCN, CNKS and CNKS-OH.

6. 6
Fig. S3. PL spectra of MCN, CNKS and CNKS-OH.

7. 7
Fig. S4. High-resolution XPS spectra of (a) O 1s of MCN and CNKS-OH, and (b) Cl
2p of CNKS-OH.

8. 8
Fig. S5. Cellobiose conversion and glucose production of CNKS-OH upon 6-h visible
light (>400 nm) irradiation.

9. 9
Fig. S6. Cellobiose conversion and gluconic acid yield of CNKS-OH upon 6-h
photocatalytic reaction by controlling the circulation of condensate water.

10. 10
Fig. S7. Glucose conversion and gluconic acid yield of CNKS-OH under the same
reaction conditions as cellobiose photoreforming upon 6-h irradiation.

11. 11
Fig. S8. HPLC measurements of aqueous solution from CNKS-OH sample upon 6-h
irradiation.

12. 12
Fig. S9. Photograph of the H2O2 test strip measuring the solution before and after
reaction.

13. 13
Fig. S10. The LSV curves of CNKS-OH measured on RDE at different rotating speed
in an O2 -saturated 0.5 M Na2SO4 electrolyte solution at a scan rate of 20 mV s−1
. Inset
are the corresponding Koutecky-Levich plots of CNKS-OH.

14. 14
Fig. S11. Concentration of generated H2O2 curve of CNKS-OH during the 6-h glucose
photoreforming process.

15. 15
Fig. S12. The stability of CNKS-OH for cellobiose photoreforming into gluconic acid
during three cycles for 18 h.

16. 16
Fig. S13. Scavenger experiments of CNKS-OH with the addition of BQ, IPA, EDTA-
2Na and NaN3, respectively.

17. 17
Fig. S14. ESR spectra of DMPO-•O2
−
of MCN for comparison.

18. 18
Fig. S15. ESR spectra of TEMP-1
O2 for CNKS-OH in aqueous solution.

19. 19
Fig. S16. Mott-Schottky plots collected at different frequencies of (a) MCN and (b)
CNKS-OH. (c) Band structure of MCN and CNKS-OH.

20. 20
Fig. S17. Birch–Murnaghan equation of state fitting to the calculated energy-volume
data of (a) pristine CN and (b) K-doped CN. A 2x2 supercell structural representation
for each system is shown as an inset. Color codes: K (purple), N (blue) and C (grey).

21. 21
Fig. S18. (a) Potential Gibbs free energy landscape over CNKS and CNKS-OH by
constructing CN fragments with different sizes. Top view of the investigated structural
model for (b) CNKS and (c, d) CNKS-OH with different sizes. Color codes: C (grey),
N (blue), O (red), S(yellow) and K (purple).

22. 22
Table S1. The elemental and ICP analysis of MCN and CNKS-OH.
Sample N (%) C (%) H (%) K (%) S (%)
MCN 60.42 33.85 1.98 0 0
CNKS-OH 42.97 25.66 1.78 6.09 0.31
Table S2. The fluorescence lifetimes and relative percentage of MCN and CNKS-OH.
Sample τav(ns) τ1(ns)
(rel. %)
τ2(ns)
(rel. %)
MCN 9.69 3.29(45.6) 11.26(54.4)
CNKS-OH 4.31 1.45(63.9) 5.62(36.1)