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Applied Catalysis B: Environmental
journal homepage: www.elsevier.com/locate/apcatb
Double-side solar hydrogen evolution nanopaper
Wenhao Sun
a
, Hongrui Cheng
a
, Nanxi Lin
a
, Yongfeng Lu
a
, Lu Chen
a
, Yi Zhao
a
, Paul S. Francis
b
,
Naifeng Zhuang
a
, Yuanhui Zheng
a,
⁎
a
College of Chemistry, Fuzhou University, Fuzhou, 350116, PR China
b
School of Life and Environmental Sciences, Faculty of Science, Engineering and Built Environment, Deakin University, Waurn Ponds, Victoria 3216, Australia
ARTICLE INFO
Keywords:
g-C
3
N
4
Cellulose nanofibers
Free-standing thin films
Nanopapers
Solar hydrogen evolution
ABSTRACT
Carbon nitride, regarded as a promising, environmentally friendly and sustainable photocatalyst for solar hy-
drogen generation, has shown a gradual improvement of photocatalytic activity with an apparent quantum yield
up to 60%. However, it is still challenging to achieve flexible, efficient and scalable carbon nitride solar hy-
drogen evolution devices, limiting its practical application. Herein we report a visible-light-driven double-side
hydrogen evolution nanopaper that is highly porous, crystalline and chemically stable. The nanopaper was
fabricated via vacuum filtration of electrostatically self-assembled carbon nitride and nanocellulose. This na-
nopaper shows excellent mechanical properties with tensile strength of 18.5 MPa and Young’s modulus of
414 MPa, a high hydrogen evolution rate of 3.9 mmol g
−1
h
−1
(corresponding to 6.5 μmol cm
−2
h
−1
), and re-
markable photostability over 32-h photocatalytic tests.
1. Introduction
Since the discovery of photocatalytic hydrogen evolution over gra-
phitic carbon nitride (g-C
3
N
4
) by Wang et al. [1], it has attracted in-
creasing attention because of its high abundance, good chemical sta-
bility, nontoxicity, and visible-light response [2–8]. The original g-C
3
N
4
shows extremely low visible-light-driven hydrogen evolution activity
due to the limited optical absorption, low surface area and fast photo-
excited carrier recombination [1]. Considerable work has been carried
out to address these issues [9–35]. The visible-light-driven hydrogen
evolution activity of g-C
3
N
4
can be greatly enhanced by rational tai-
loring of its structure [ 9–11], and optical and electronic properties
[12–16]. More specifically, by doping [17–20], amorphization or
polymerization synthesis of g-C
3
N
4
[21–24], its visible-light response
can be extended to 680 nm or even further [25–27]. Moreover, the
creation of porous structures and/or heterojunctions not only promotes
the photogenerated carrier separation, but also provides more catalytic
sites for hydrogen evolution reaction [28–30]. Tight control over these
parameters enables the synthesis of highly active g-C
3
N
4
. For example,
a high solar hydrogen production activity with an apparent quantum
yield (AQY) of 60% at 420 nm has recently been achieved over a novel
g-C
3
N
4
composed of internal triazine-heptazine donor-acceptor het-
erostructures [35].
Generally, g-C
3
N
4
is synthesized by thermal polymerization of cy-
anamide or urea at an elevated temperature (typically 550 °C), forming
a condensed yellow solid [1–36]. To date, their photocatalytic hy-
drogen evolution activity has been tested in the form of milled powders,
but not thin films, due to the lack of reliable methods for the fabrication
of high-quality and highly active g-C
3
N
4
films. This is a major obstacle
for their practical applications in solar hydrogen evolution because it is
difficult to maintain a stable dispersion of powdered g-C
3
N
4
based
photocatalysts in solution and recycle the expensive noble metal (ty-
pically Pt) co-catalyst deposited on the g-C
3
N
4
surface. Therefore, the
ability to fabricate high-quality and highly active g-C
3
N
4
films is a key
requirement towards their practical applications in solar hydrogen
evolution. Common strategies for g-C
3
N
4
thin-film fabrication involve
physical methods under non-equilibrium conditions, such as chemical
vapor deposition and pulsed-laser deposition [36–38]. A general
drawback of these methods, however, is that the resulting films suffer
from poor crystallinity and nitrogen deficiency. An alternative strategy
is to use solution-based thin-film fabrication methods, in which a g-
C
3
N
4
suspension is screen-printed or spin-coated on a solid substrate
(e.g., ITO or FTO glass) [39 –42]. Due to the poor particle-particle and
particle-substrate contact, it is very difficult to achieve high-quality thin
films using the milled g-C
3
N
4
powders as raw materials. Since g-C
3
N
4
is
a polymer composed of heptazine repeating units bridged by the ter-
tiary nitrogen, the carbon-nitride bonds in the linking bridges can be
easily cleaved by a strong oxidizing acid like nitric acid, yielding a
stable g-C
3
N
4
colloid. Using the colloid as a coating material, a g-C
3
N
4
thin-film on FTO electrodes has recently been fabricated [43].
https://doi.org/10.1016/j.apcatb.2019.118083
Received 1 January 2019; Received in revised form 27 July 2019; Accepted 13 August 2019
⁎
Corresponding author.
E-mail address: Yuanhui.Zheng@fzu.edu.cn (Y. Zheng).
Applied Catalysis B: Environmental 260 (2020) 118083
Available online 15 August 2019
0926-3373/ © 2019 Elsevier B.V. All rights reserved.
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