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Meso‐Microporous Nanosheet‐Constructed 3DOM Perovskites for Remarkable Photocatalytic Hydrogen Production

DOI:10.1002/adfm.202112831
Authors:
Heng Zhao at The University of Calgary
Heng Zhao
Jing Liu at Wuhan University of Technology
Jing Liu
Chao‐Fan Li
Chao‐Fan Li
Chao‐Fan Li
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Xu Zhang
Xu Zhang
Xu Zhang
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Abstract and Figures

Three‐dimensionally ordered macroporous (3DOM) structures have been widely utilized to largely enhance a photocatalytic activity. However, the common nanoparticles‐constructed 3DOM photocatalysts possess numerous grain boundaries, unavoidably leading to a fast recombination of photogenerated electrons and holes. Herein, for the first time, a hierarchically two‐dimensional (2D) meso‐microporous perovskite nanosheet‐constructed 3DOM CaTiO3 to significantly reduce the grain boundaries is designed and fabricated. Using carbon quantum dots (CQDs) as a metal‐free co‐catalyst, the 3DOM CQDs‐CaTiO3 exhibits an outstanding photocatalytic activity for hydrogen generation of 0.13 mmol h−1 (20 mg photocatalyst) with remarkable apparent quantum efficiency (QAY) of 14.55% at 365 nm monochromatic light. This unprecedented performance is endowed by the synergy of a macro‐meso‐microporosity architecture, a large surface area, enhanced light harvesting, and improved charge carriers separation and transport. Density functional theory calculations and finite difference time‐domain simulations further reveal the mechanism behind the enhanced separation of photogenerated electrons and holes. The present work demonstrates a trial on rationally designing meso‐microporous nanosheet‐constructed 3DOM perovskites for solar driven hydrogen production. A perovskite meso‐microporous nanosheet‐constructed 3DOM CaTiO3 decorated with CQDs is designed for remarkable photocatalytic hydrogen production in a noble‐metal free system. The as‐synthesized composite exhibits extremely enhanced photocatalytic activity owing to the easy mass transfer by the synergistic effect of macro‐meso‐microporosity, large surface area, enhanced light harvesting, and improved separation of charge carriers.
Schematic illustration of the fabrication process of 3DOM CQDs‐CaTiO3.
Schematic illustration of the fabrication process of 3DOM CQDs‐CaTiO3.
… 
a,b) SEM images of 3DOM CaTiO3, c,d) TEM images of 3DOM CQD‐CaTiO3, e) HRTEM image and corresponding FFT image (inset), and the CQDs indicated by the red dashed circles, f) Nitrogen adsorption–desorption isotherms (insets are the corresponding micropore and mesopore distributions) of 3DOM CQD‐CaTiO3, g) HAADF‐STEM image of 3DOM CQD‐CaTiO3, and h–j) corresponding EDX elemental maps: Ca (green), Ti (blue), and O (yellow).
a,b) SEM images of 3DOM CaTiO3, c,d) TEM images of 3DOM CQD‐CaTiO3, e) HRTEM image and corresponding FFT image (inset), and the CQDs indicated by the red dashed circles, f) Nitrogen adsorption–desorption isotherms (insets are the corresponding micropore and mesopore distributions) of 3DOM CQD‐CaTiO3, g) HAADF‐STEM image of 3DOM CQD‐CaTiO3, and h–j) corresponding EDX elemental maps: Ca (green), Ti (blue), and O (yellow).
… 
a) UV–vis absorption, inset is the corresponding plots of (αhν)1/2 versus photon energy (hν), b) Mott–Schottky plot, c) valence band XPS spectra, d) energy band structure.
a) UV–vis absorption, inset is the corresponding plots of (αhν)1/2 versus photon energy (hν), b) Mott–Schottky plot, c) valence band XPS spectra, d) energy band structure.
… 
High‐resolution XPS core level spectra of a) C 1s, b) N 1s, c) O 1s. d) Constructed crystal models of N,O‐co‐doped CQDs (inset) and calculated differential electron density images of 3DOM CQDs‐CaTiO3, where the blue and yellow zones represent electron density accumulation and depletion. FDTD simulations of 3DOM CQDs‐CaTiO3 under 480 nm monochromatic light in the cases of e) y = 9 nm and f) y = 0 nm.
High‐resolution XPS core level spectra of a) C 1s, b) N 1s, c) O 1s. d) Constructed crystal models of N,O‐co‐doped CQDs (inset) and calculated differential electron density images of 3DOM CQDs‐CaTiO3, where the blue and yellow zones represent electron density accumulation and depletion. FDTD simulations of 3DOM CQDs‐CaTiO3 under 480 nm monochromatic light in the cases of e) y = 9 nm and f) y = 0 nm.
… 
a) Photocatalytic hydrogen evolution rates of CaTiO3, 3DOM CaTiO3, CQDs‐CaTiO3, and 3DOM CQDs‐CaTiO3, b) cycling test of CQDs‐CaTiO3, 3DOM CaTiO3 with co‐catalysts of CQDs, Au NPs, and Pt NPs, c) corresponding hydrogen evolution rates, d) photocatalytic hydrogen evolution rates and AQY values of CaTiO3, 3DOM CaTiO3, CQDs‐CaTiO3, and 3DOM CQDs‐CaTiO3 under 365 nm monochromatic light irradiation. e) Transient photocurrent responses at 0.2 V (vs Ag/AgCl), f) Nyquist plots in 0.5 m Na2SO4 aqueous solution under UV–vis light, g) proposed illustration of photocatalytic hydrogen evolution of 3DOM CQDs‐CaTiO3 under UV–vis light irradiation. Reaction condition: 20 mg photocatalyst, 50 mL water and 50 mL methanol, UV–vis light (320–780 nm).
a) Photocatalytic hydrogen evolution rates of CaTiO3, 3DOM CaTiO3, CQDs‐CaTiO3, and 3DOM CQDs‐CaTiO3, b) cycling test of CQDs‐CaTiO3, 3DOM CaTiO3 with co‐catalysts of CQDs, Au NPs, and Pt NPs, c) corresponding hydrogen evolution rates, d) photocatalytic hydrogen evolution rates and AQY values of CaTiO3, 3DOM CaTiO3, CQDs‐CaTiO3, and 3DOM CQDs‐CaTiO3 under 365 nm monochromatic light irradiation. e) Transient photocurrent responses at 0.2 V (vs Ag/AgCl), f) Nyquist plots in 0.5 m Na2SO4 aqueous solution under UV–vis light, g) proposed illustration of photocatalytic hydrogen evolution of 3DOM CQDs‐CaTiO3 under UV–vis light irradiation. Reaction condition: 20 mg photocatalyst, 50 mL water and 50 mL methanol, UV–vis light (320–780 nm).
… 
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©  Wiley-VCH GmbH
2112831 (1 of 8)
C. F. Li, Z. Y. Hu
Nanostructure Research Centre (NRC)
Wuhan University of Technology
 Luoshi Road, Wuhan, Hubei , China
X. Zhang, B. Li
Research Center for Materials Genome Engineering
Wuhan University of Technology
 Luoshi Road, Wuhan, Hubei , China
E-mail: libei@whut.edu.cn
B. L. Su
Laboratory of Inorganic Materials Chemistry (CMI)
University of Namur
 rue de Bruxelles, Namur B-, Belgium
E-mail: bao-lian.su@unamur.be
ReseaRch aRticle
Meso-Microporous Nanosheet-Constructed 3DOM Perovskites
for Remarkable Photocatalytic Hydrogen Production
Heng Zhao, Jing Liu, Chao-Fan Li, Xu Zhang, Yu Li,* Zhi-Yi Hu, Bei Li,* Zhangxin Chen,
Jinguang Hu,* and Bao-Lian Su*
Three-dimensionally ordered macroporous (3DOM) structures have
been widely utilized to largely enhance a photocatalytic activity. However,
the common nanoparticles-constructed 3DOM photocatalysts possess
numerous grain boundaries, unavoidably leading to a fast recombination of
photogenerated electrons and holes. Herein, for the first time, a hierarchically
two-dimensional (2D) meso-microporous perovskite nanosheet-constructed
3DOM CaTiO3 to significantly reduce the grain boundaries is designed and
fabricated. Using carbon quantum dots (CQDs) as a metal-free co-catalyst,
the 3DOM CQDs-CaTiO3 exhibits an outstanding photocatalytic activity for
hydrogen generation of 0.13mmolh−1 (20mg photocatalyst) with remarkable
apparent quantum eciency (QAY) of 14.55% at 365nm monochromatic
light. This unprecedented performance is endowed by the synergy of a
macro-meso-microporosity architecture, a large surface area, enhanced
light harvesting, and improved charge carriers separation and transport.
Density functional theory calculations and finite dierence time-domain
simulations further reveal the mechanism behind the enhanced separation of
photogenerated electrons and holes. The present work demonstrates a trial
on rationally designing meso-microporous nanosheet-constructed 3DOM
perovskites for solar driven hydrogen production.
DOI: 10.1002/adfm.202112831
H. Zhao, J. Liu, C. F. Li, Y. Li, Z. Y. Hu, B. L. Su
State Key Laboratory of Advanced Technology for Materials Synthesis
and Processing
Wuhan University of Technology
 Luoshi Road, Wuhan, Hubei , China
E-mail: yu.li@whut.edu.cn
H. Zhao, Z. X. Chen, J. G. Hu
Department of Chemical and Petroleum Engineering
University of Calgary
 University Drive, NW, Calgary, Alberta TN N, Canada
E-mail: jinguang.hu@ucalgary.ca
hampers the progress of further maxi-
mizing their photocatalytic performance
as the loose interaction among these nano-
particles always leads to impeded charge
transfer.[12]
Compared with nanoparticles, two-
dimensional (2D) nanostructures hold
intrinsic advantages such as a high sur-
face area, low content of defects and a
minimized migration path of charge car-
riers.[13,14] Calcium titanate (CaTiO3) with
a typical perovskite structure demonstrates
enormous potential for various applications
including photocatalysis.[15–17] Although
its unique perovskite structure consider-
ably reduces the defects and recombina-
tion centers,[18–21] the conventional bulk
CaTiO3 photocatalysts still exhibit unsatis-
fied photocatalytic eciency, because the
common preparation methods including
high temperature sintering and simple
hydrothermal treatment cannot realize the
exfoliation of intrinsic 2D materials.[22–24]
Thus, we foresee that the successful mar-
riage of the 3DOM structure with 2D lay-
ered CaTiO3 perovskites will not only synergistically overcome
their limitations to skyrocket the photocatalytic performance,
but also demonstrate a prospective strategy to further enhance
the conversion eciency of solar energy. By utilizing the nega-
tive surface charge of a polystyrene colloid template, an ultrathin
layer of a CaTiO3 precursor can be formed on a surface of poly-
styrene spheres by an electrostatic interaction via precisely con-
trolling the precursor amount.[25] From this perspective, 3DOM
CaTiO3 with 2D nanosheets as building block is expected to be
synthesized by a colloidal crystal template method.
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/./adfm..
1. Introduction
Three-dimensionally ordered macroporous (3DOM) structure,
also known as a photonic crystal, is a typical hierarchically
porous material with the characteristics of Murray materials.[1–5]
This unique architecture of 3DOM endows photocatalysts supe-
rior light harvesting and electron transport ability,[6–8] and thus
significantly enhances photocatalytic eciency for solar-to-chem-
ical energy conversion.[9–11] So far, the building blocks of 3DOM
materials are usually zero-dimensional nanoparticles, which
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