Microfluidic chip-based one-step fabrication of an
artificial photosystem I for photocatalytic cofactor
regeneration†
Xiaowen Huang,
ac
Jian Liu,
b
Qingjing Yang,
d
Yang Liu,
ac
Yujiao Zhu,
ac
Tenghao Li,
ac
Yuen Hong Tsang
ac
and Xuming Zhang
*
ac
We propose herein, a one-step method to assemble the immobilized artificial photosystem I (IAPSI) in
a microfluidic chip, which integrated a preformed graphitic carbon nitride photocatalyst (g-C
3
N
4
) and
electron mediator (M) in one chip and mimicked the characteristics of photosystem I. The simultaneous
assembly of g-C
3
N
4
and M could efficiently regenerate NADH from NAD
+
under visible light irradiation,
which verified the effectiveness of the assembly method. The in situ assembly method was thought to
outperform traditional methods in several aspects in terms of facile synthesis, promotion of the
combination of g-C
3
N
4
and M through p–p stacking and an enhanced coenzyme regeneration rate. For
comparison, we used the bulk g-C
3
N
4
–slurry and the few-layer g-C
3
N
4
–slurry system as the control to
regenerate the photocatalytic cofactor/coenzyme NADH, and measured the required times of 305 s and
30 s, respectively, to accomplish 63% NAD
+
conversion. In contrast, our IAPSI microreactor takes only
13 s, faster than the other two by factors of 23 and 2.3 times. Therefore, we assert that the simple, yet
highly efficient nature of this technique can act as an important method for artificial photosynthesis,
particularly in the photocatalytic cofactor recycling systems for the production of various valuable
molecules.
1 Introduction
Solar energy is the most abundant energy on earth.
1,2
One of the
challenges for building a sustainable society is to develop
practical materials and devices that can perform solar energy
conversion (i.e., solar fuel or solar electricity).
3–12
Natural
photosynthesis is the fundamental process used by plants,
algae and certain bacteria to harness energy from sunlight and
convert it into chemical energy.
13
In the light reaction of natural
photosynthesis, through a series of photo-induced electron
transfer processes in photosystem I (PSI), an integral membrane
protein complex in photosynthesis, the solar energy (photons) is
rstly transferred into active electrons and is then used to reduce
the coenzyme nicotinamide adenine dinucleotide phosphate
(NADP
+
) to NADPH.
14,15
In view of the importance of NAD(P)H/
NAD(P)
+
in many biochemical conversions, particularly in many
enzymatic redox reactions, mimicking such a process could
provide a new way to design high-efficiency materials and
devices for articial photosynthesis.
16–18
The efficiency of photosynthesis in plants is based on the
high surface-area-to-volume ratio structures of PSI (Fig. 1A)
including a series of light-harvesting complexes, several metal–
protein clusters and a group of redox biocatalysts, which are
logically integrated in the phospholipid bilayer and conned to
certain areas. These immobilized structural features not only
facilitate efficient electron transfer and enhanced photon
absorption, but also the isolation of the reaction substrates and
products providing an ordered reaction chain. Thus, by
mimicking the function of the PSI system, the regeneration of
coenzymes (NADH, NADPH) through solar energy is a prom-
ising, sustainable and economic strategy that has attracted
many research efforts that have contributed to important
improvements.
19–21
However, in the past, most of the work has
focused on the heterogeneous photocatalysis for NADH regen-
eration, which renders the practical application impossible due
to separation and recycling problems. Therefore, it is promising
to develop a high-efficiency PSI arti cial photosynthesis system
on the immobilized system (IAPSI) for coenzyme regeneration,
which would pave the way for practical uses in the near future.
Microuidics, as versatile and promising systems, have
several merits to benet articial photosynthesis in many
ways.
22
They have the advantages of large surface areas, short
a
Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, P.
R. China. E-mail: apzhang@polyu.edu.hk; Fax: +852-23337629; Tel: +852-4003258
b
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
c
The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, P. R.
China
d
Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic
University, Hong Kong, PR China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra21390a
Cite this: RSC Adv.,2016,6,101974
Received 25th August 2016
Accepted 6th October 2016
DOI: 10.1039/c6ra21390a
www.rsc.org/advances
101974 | RSC Adv.,2016,6,101974–101980 This journal is © The Royal Society of Chemistry 2016
RSC Advances
PAPER