IP: 109.94.223.96 On: Mon, 25 Feb 2019 08:20:37
Copyright: American Scientific Publishers
Delivered by Ingenta
Copyright © 2019 American Scientific Publishers
All rights reserved
Printed in the United States of America
Article
Journal of
Nanoscience and Nanotechnology
Vol. 19, 3237–3243, 2019
www.aspbs.com/jnn
Photocatalytic Conversion of CO
2
into Oxygenate
Fuels/Chemicals Using Efficient, Eco-Friendly,
Titania/Hematite-Based Nanostructured
Solar-Energy Materials
Mohsen Lashgari
1 2 ∗
and Sanaz Soodi
1
1
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
2
Center for Research in Climate Change and Global Warming: Hydrogen and Solar Division, Zanjan 45137-66731, Iran
Photocatalytic hydrogenation of carbon dioxide (CO
2
, using water feedstock (H source), sun-
light and appropriate semiconducting low-cost/eco-friendly/solar-energy materials, is a promising
route for sequestration of this greenhouse gas and its conversion into value-added oxygenate
fuels (compounds). Herein, by employing three hematite-based nanostructured photocatalyst/solar-
energy materials, the CO
2
photoreduction (hydrogenation) process was carried out inside a water
photosplitting reactor, and various oxygenate (C/H/O) products [including ethanol, methanol and
formaldehyde as well as oxalic, acetic and formic acids] were synthesized in the reaction medium.
Concerning the complexity of system and the diversity of products—being photocatalytically syn-
thesized during the photoconversion process, two straightforward problem-solving strategies were
proposed [one, focusing on a single/particular product and pursuing its quantity (concentration) at
different illumination periods, and the other, simultaneous investigation of various products being
produced at a fixed reaction period, in the aqueous or gas-phase medium]. Finally, the matter of CO
2
photoconversion into oxygenate fuels/chemicals was explained in detail from photoelectrochemical
[semiconductor band structure and redox potential] as well as mechanistic perspectives.
Keywords: CO
2
Photoreduction, C/H/O Based Solar-Fuels, Semiconductor Photocatalyst
[Fe
2
O
3
/TiO
2
/Pd] Nanoparticles, Energy Diagram, Eco-Friendly Solar-Energy-
Materials, Water Photosplitting.
1. INTRODUCTION
The challenge of global warming and climate change—
threatening the human life and other living organisms, is
undoubtedly a result of an imbalance between boundless
production and dumping of CO
2
greenhouse gas into the
environment and its limited consumption via photosyn-
thesis process—being naturally done on the bio-globe.
1
Doubtless, a decline in the emission of this greenhouse
gas by decreasing the usage of fossil/C-based fuels and
employing other clean/green energy resources is a promis-
ing route to overcome this energy-related/environmental
issue of the century. Beside the negative sight existing
on the CO
2
issue, this matter can be envisaged as an
opportunity and utilized as a vast feedstock of carbon
∗
Author to whom correspondence should be addressed.
in the nature;
2
through hydrogenation process and apply-
ing a clean energy resource, this notorious material can
be converted to other value-added oxygenate (C/H/O)
chemicals/fuels.
3
Concerning the CO
2
issue, it is worth mentioning that
each fuel compound with this general formula C
l
H
m
O
n
l m n = 1 2, through combustion reaction, is
transformed to carbon dioxide and water molecules and
energy is released. The back-conversion process (Eq. (1)),
i.e., the reaction between CO
2
and H
2
O molecules could
therefore result in the synthesis of a broad spectrum of
oxygenate fuels/chemicals,
3
with carbon oxidation state in
the range of -4 to +4 (the full reductive and oxidative
form of carbon, respectively):
lCO
2
+
m
2
H
2
O + Energy →C
l
H
m
O
n
+
l +
m
4
-
n
2
O
2
(1)
J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 6 1533-4880/2019/19/3237/007 doi:10.1166/jnn.2019.16581 3237