Transcript Photocatalytic reduction of carbon dioxide over chalcogenide

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Photocatalytic reduction of carbon
dioxide over chalcogenides
Reporter: Chen Jingshuai
Supervisor: Prof.Xin Feng
2013.10.15
Content
Introduction
Experiment
Plan
 Introduction
• Solar energy is the only renewable and carbon neutral
energy source of sufficient scale to replace fossil fuels.
Direct conversion of this energy into clean fuels is one
of the most important scientific challenges of the 21st
century.
• In photocatalysis, both hydrogen production from solar
water splitting and carbon dioxide conversion to
organics are obviously attractive, being potentially
convenient and clean methods to store solar energy in
energy rich molecules which can be employed as
virtually inexhaustible fuel sources.
Introduction
According to the Intergovernmental Panel on Climate Change(IPCC
2001),1 the Earth’s surface temperature has risen by approximately 0.6 K in
the past century, with particularly significant warming trends over the past
two decades. The primary contributor to this phenomenon is carbon dioxide
(CO2) emissions from fossil fuel combustion.
Introduction
• Development of photocatalytic CO2 reduction to useful
chemicals using solarlight systems, should be one of
the best solutions for serious problems , i.e.,shortage
of energy, shortage of carbon resources, and the
global worming problem.
Introduction
hv
CB
Surface
Recombination
VB
A
C
B
D
D+
Volume
Recombination
A-
D
A
Photoexcitation in solid followed
by deexcitation
hv
Introduction
• In 1979, Inoue et al. first reported the
photocatalytic reduction of CO2 in aqueous
solution to produce formaldehyde(HCHO), formic
acid (HCOOH), methyl alcohol (CH3OH), and
trace amounts of methane (CH4) using various
semiconductors, such as tungsten trioxide (WO3),
titanium dioxide (TiO2), zinc oxide (ZnO),
cadmium sulfide (CdS), gallium phosphide
(GaP),and silicon carbide (SiC).
• As well known, titanium oxide is most widely
used photocatalyst for wastewater treatment and
destruction of volatile organic compounds and
photoreduction of CO2.
Introduction
• Some Ti-based heterogeneous catalysts
Photocatalyst used
Reaction medium
Primary product(s)
TiO2/zeolite
Water/CO2
CH4
CdSe/Pt/TiO2
Water/CO2
CH4, with CH3OH, H2,
Pt-loaded TiO2
Water/CO2
CH4
Copper-doped Titania Catalysts
KHCO3 solution
methanol
CoPc/TiO2
NaOH aqueous solution
HCOOH, HCHO, CH3OH
Ti silicalite(TS-1)molecular sieve
methanol
HCO2H,CO,HCO2CH3
Cu,Pt cocatalyzed N-doped TiO2
nanutube arrays
Water /CO2
Methane,H2,CO
Ti-containing porous silica thin film
Water vapor
CH4,CH3OH
Ag–TiO2
Water
CH4
Ru complex or perylene
diimine/TiO2 film/Pt
Water
CH4
• Photocatalysis employing various metal
oxide semiconductors such as
Ga2O3 ,GaP ,InTaO4 ,MgO ,ZrO2 ,
BiVO4 ,and ATaO3 (A =Li, Na, K) have
been reported.
• Metal sulfides such as ZnS, CdS, and
CdxZn1+xS can work as CO2
photoreduction catalysts in the presence
of a sacrificial electron donor.
Although the efficiency of CO2 convertion in this
way ,photocatalysis is a potentially economical and
environmental CO2 removal process.Three general
methods are listed follow for enhancing the efficency.
 The first is choosing semiconductors with
appropriate band-gap energies.
 The second improvement method involves reductant
development.
 The third and last method is to optimize operating
conditions including temperature,pressure,light
intensity,and operating wavelength.
H. Yoneyama / Catalysis Today 39 (1997) 169-175
• It was reported that Cu ,Pb,Ni or Bi-doped ZnS
photocatalysts show high activities for H2 evolution from
aqueous solutions in the presence of a sacrificial reagent
such as sulfite ions under visible-light irradiation (λ > 420
nm) even without a platinum cocatalyst.
• Ternary sulfides ZnIn2S4, as the only member of the
AB2X4 family semiconductor with a layered
structure, has attracted farranging interests because
of its potential applications in different fields such as
charge storage ,thermoelectricity ,photoconduction
and so on. Lei et al. synthesized ZnIn2S4 by a
simple hydrothermal method and firstly treated
ZnIn2S4 as an efficient visible-light-driven
photocatalyst for hydrogen production.Thus,
ZnIn2S4 turned to be a good candidate for
photocatalytic hydrogen production from water under
visible light irradiation.
• The band edge potentials of the semiconductors were
estimated using the equation related to Mulliken
electronegativity. Herein, the electronegativity of an atom
is the arithmetic mean of the atomic electron affinity and
the first ionization energy. The conduction band (CB)
potential at the point of zero charge can be calculated
according to an empirical equation:
ECB = X- Ee +0.5Eg
Eg is 2.2~2.3eV reported in some literatures, Ee is the
energy of free electrons on the hydrogen(4.5eV),EVB is
determined by ECB = EVB –Eg.So the conduction band
and valence band have been calculated to be
ECB=-0.75,EVB=1.45
• In2S3, existing in three different structure forms: i.e., αIn2S3(defect cubic structure), β-In2S3 (defect spinel
structure) and γ-In2S3 (layered hexagonal structure), is an
extensively studied narrow band gap(2.0~2.2) semiconductor
because of its defect structure. The photocatalytic activity is
closely related to its crystal structure, the distorted electric
field in the crystal can enhance the separation of
photoinduced electron–hole pairs .As a result, the defect
structure of In2S3 may promise a good photocatalytic activity.
In fact, β -In2S3 has already been investigated as a visiblelight driven photocatalyst recently.
• The the conduction band and valence band of In2S3 is
• ECB=-0.8,EVB=1.2
Experiment
• 1 wt%Cu-doped ZnS, 0.5%Bi-doped ZnS,0.3%Ni-doped
ZnS and In2S3,1 wt%Cu-doped In2S3,ZnIn2S4 have been
synthesized using hydrothermal method.
• For In2S3:
In(NO3)3.5H2O
+
TAA
+
Deionized water
Stirring 15 min
160℃ for 24hr
Dried at 70~80 ℃
In2S3
Cu/In2S3,ZnIn2S4 and Cu/ZnS,Bi/ZnS,Ni/ZnS
was obtained in similar ways.
Ni/ZnS
Bi/ZnS
Cu/ZnS
1.2
1.0
Absorbance
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
Wavelength (nm)
UV–vis DRS spectra of catalysts
800
20 ml of methanol solution and 20 mg of catalyst powders, 6h
µmol/g/h
MF
DMM
catalysts
In2S3
Cu/In2S3
ZnIn2S4
1.4
1.2
1.0
Absorbance
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
Wavelength (nm)
UV–vis DRS spectra of catalysts
800
20 ml of methanol solution and 20 mg of catalyst powders, 6h
µmol/g/h
MF
DMM
catalysts
Plan
Continue to prepare Ni-doped ZnS(0~2%)
using hydrothermal method and find the
optimal concentration.In addition,their
photocatalytic activity and morphology will be
compared with those prepared with surfactant
such as CTAB.Then observe their stability
after 5 runs.(2012.11~2014.1)
Prepare other metal doped ZnS(Cu,Bi,Mn)
and study dopant effects on the
photocatalytic activity of ZnS.The possible
photocatalytic mechanism will be
presented.(2014.1~2014.3)
Plan
Consider using ZnIn2S4 as photocatalyst
and control its morphology,then enhance its
photocatalytic activity by doping
metal.(2014.4~2014.7)
Investigate photocatalytic reduction of CO2
on In2S3 and its morphology ,
improve its photocatalytic activity by doping
metals or combining with other
catalyst.(2014.8~2014.11)
Develop efficient photocatalyst materials with
visible light response.(2014.12~ )
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