This document describes a final thesis on using the photocatalyst ZnFe2O4/TiO2 to reduce carbon dioxide into methanol under visible light irradiation. The research objectives were to synthesize and characterize ZnFe2O4/TiO2, and evaluate its activity for CO2 conversion. ZnFe2O4 and TiO2 were synthesized separately then coupled using ultrasonication. Characterization methods included FTIR, UV-Vis, TGA, FESEM. Photocatalytic testing showed the maximum methanol yield was 141.22 μmol/gcat.hr using ZnFe2O4/TiO2 with a 1:1 ratio, illuminated for 5.5 hours. Future work could co-synthesize Zn

1. PHOTO-CATALYTIC REDUCTION OF CARBON DIOXIDE (CO2)
INTO METHANOL USING PHOTOCATLYST (ZnFe2O4/TiO2)
UNDER VISIBLE LIGHT IRRADIATION
M.S Chemical Engineering
Final Thesis Defense

2. DEPARTMENT OF CHEMICAL ENGINEERING
FACULTY OF ENGINEERING AND TECHNOLOGY
UNIVERSITY OF GUJRAT, HAFIZ HAYAT CAMPUS, GUJRAT
2
Presented By,
Numair Manzoor
16064423-021
Supervisor,
Prof. Dr. Muhammad Suleman Tahir
Dean Faculty of Engineering & Technology
Co-Supervisor
Assistant Prof. Dr. Muhammad Saghir
Faculty of Engineering and Technology

3. Problem Statement
3
• Global warming is not only one of the major issue facing by the humanity but also most
adversely effecting phenomenon for the earth, greenhouse gases are the main constituent of
Global Warming, CO2 is the main constituent of Global Warming and Pakistan is the 8th most
effected country by Global Warming.
• AQI of Pakistan (Lahore) is 600, whereas the last level of ‘hazardous’ on the AQI is shown as
between 250- 300.
• Conversion of Carbon into Methanol using visible light driven photocatalyst is not only provide
CO2 emissions control but also provide cheap fuel which can be further utilized as a substrate of
Fossil Fuel.
• Problem is to synthesize/produce a photocatalyst that must be visible light driven and have a
narrow band-gap range between 2.5-3.0 eV.

4. Research Objectives
4
The main objective is to reduce CO2 into methanol using photocatalyst with the following
specific objectives:
• To synthesize ZnFe2O4/TiO2 photocatalyst.
• To characterize ZnFe2O4/TiO2 heterojunction photocatalyst.
• To evaluate the activity of prepared photocatalyst for CO2 conversion into methanol under
visible light.

5. 5
• Photocatalysis has a wide range of engineering applications such as water splitting and waste removal from
water etc. The most attractive application of photocatalysis is the conversion of CO2 into value added
products like methanol, Formic Acid, Formaldehyde etc.
• When photocatalyst exposed under light irradiation having a photon energy higher or equal to the band gap
energy of photocatalyst, then electrons in completely filled valence band became excited and transferred to
the conduction band of semiconductor.
• These excited electrons take part in photocatalytic reduction and oxidation reaction. If band gap of
photocatalyst will be very small, then electrons and holes recombined immediately and heat will release. So
there is a need to reduce electron-hole pair recombination, and excited electrons should move to the surface
of a photocatalyst for oxidation and reduction reaction.
• The photoexcited electrons and holes take part in water oxidation and CO2 reduction. Hence CO2 could be
converted into useful cheap fuel like Methanol, Formaldehyde, Formic Acid etc.
Introduction

6. 6
Methodology of Research
Catalyst
Synthesis
Characterization
Catalyst
Activity,
Photoreaction
Parameters
Studies
Comparing
Mechanism

7. 7
Dark Brown Gel
2.5 Molar
Nitric
Acid
Agar +
Iron
Nitrate
Zinc
Nitrate
Organo Gel
2.5 Molar
Nitric Acid
Agar
Titanium
Butaoxide
Dark
Brown
Gel
(ZnFe2O4)
Organo
Gel
(TiO2)
ZnFe2O4/TiO2
Hetrojunction
Coupled
Photocatlyst
Methodology of Research

8. 8
Methodology of Research
Synthesis
of
ZnFe
2
O
4
Nitrates of Zinc
Metal
+
2.5 M Nitric Acid
Solution
+
Agar
+
Stirring & Heating
Synthesis
of
TiO
2
Titanium Butaoxide
+
2.5 M Nitric Acid
Solution
+
Agar
+
Stirring & Heating
Hetrojuction
Photocatalyst
Synthesized ZnFe2O4
+
Sythesized TiO2
+
Sonicated and
Calcined
=
Desired Photocatlyst

9. 9
Methodology
(Reactor/Photocatalytic Reaction)
 After the characterization, the next step was Photoreaction/photocatalytic activity.
 For this experiment, a continuous-flow reactor will be used.
 A 500 W xenon lamp was used as a source of radiation.
 NaNO2 (2M) solution will be used to cut the UV light.
 First of all, KOH, 0.1 M NaSO3 and 0.1 M Na2S were added in 300 ml of distilled
water.
CO2 was bubbled through the solution in the reactor for 1 hr to ensure that all
dissolved oxygen is eliminated and pH of the solution is maintained at 6.2.
 After that, catalyst was added to the solution making the concentration of catalyst to
be 1 g/L.
 Afterwards, the lamp was turned on to start the photoreaction.
 The temperature of the reactor was maintained at 25 °C with the help of chiller
during the reaction.
 The CO2 continuously flowed through the solution during irradiation.
 Three liquid samples were collected at regular intervals and were analyzed in GC-
FID for product detection.
 The photocatalytic reaction was carried out for 5 h. All experiments were repeated
thrice.

10. 10
Original Setup

11. 12/20/2022 11
Final Results
Fourier Transform Infrared Spectroscopy (FTIR)
FTIR Spectrum of ZnFe2O4
Spectrum Band at 557.5cm^-1and 436.2 cm^-1 represents
Zn2+ and Fe3+ ion.
In the same way, the band at 1487.3 cm^-1 point toward
that sample contains slight amount of water.
The band at 1290.9 cm^-1 is an indication of the presence
of nitrates.
The last peak at 2382.6 cm^-1 indicates the presence of
CO2 that was absorbed into the catalyst synthesized from
the environment.

12. 12
Final Results
UV-Vis Spectroscopy
UV-Vis Spectra, TiO2,
ZnFe2O4:TiO2 with Different Ratios
Results are obtained in the wavelength range of 200-
800 nm shown in Figure
The UV-Vis spectra of synthesized ZnFe2O4, TiO2,
and ZnFe2O4coupled with TiO2 in three different
w/w ratios i-e first 1:1 then 1:2 and 2:1.
When ZnFe2O4 is coupled with TiO2 in 1:1 w/w
ratio, it shows maximum absorbance under region
from 400-800 nm i-e Visible Light.

13. 13
Final Results
Thermo-gravimetric Analysis (TGA)
TGA, Derivative of Weight Loss % of ZnFe2O4
vs
Temperature
TGA Results indicate that pure ZnFe2O4 has been
obtained. TGA represented the weight loss at a higher
temperature which is very helpful to obtain the right
calcination temperature. The TGA analysis of
prepared samples is shown in Figure 7.
Red curve which represents the TGA of calcined
sample seems stable and weight loss from 50-900°C
is negligible i.e. less than 1%. In this curve, the major
weight loss was observed from 600-900 °C which is
almost 0.6%. This weight loss is supposed to come
from the development of ZnFe2O4 and from the
removal of minute quantity of ZnO that still exists.

14. 14
Final Results
Field Emission Scanning Electron Microscopy (FESEM)
Figure (a, b, c, d, e, f) illustrates that synthesized ZnFe2O4 formed
well defined crystalline irregular spherical shapes with particle
sizes in the range of 200-400nm.
The anatase TiO2 is also observed to be more homogeneous with
high crystallinity. The particle size of TiO2 nanoparticles is found
to be in the range of 50-300nm.
It is observed that ZnFe2O4/TiO2 heterojunction with (1:1) ratio
shows high homogeneity and porosity. It is
observed that hydrothermally developed ZnFe2O4:TiO2 (1:1)
hetero junction in higher homogeneity in the Photocatalyst.
The loaded catalyst also shows well defined orthorhombic
crystalline shape.
FE-SEM Images
a,b) ZnFe2O4,
c, d) TiO2,
e, f) ZnFe2O4:TiO2 (1:1)

15. 15
Result
(Stability of Catalyst)
527.4
0
100
200
300
400
500
600
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
Methanol
Yield
(μmol/L.g
cat
)
Time (hrs)
The photocatalytic conversion of CO2 into methanol is studied
for 6 -7 hrs by using ZnFe2O4/TiO2 photocatalysts.
The experimental results reveal that methanol is major product
in liquid.
In current study, the catalyst shows deactivation after 5.5 hrs.
The highest yield is obtained after 5.5 hrs which is
527.4μmol/L.gcat but after that, the yield of methanol decreases
which is due to conversion of CO2 into other products or the
occurrence of backward reaction.
Fig. indicates that the yield is increasing with a passage of time
continuously but after 5.5 hrs, the yield declines suddenly.
The methanol oxidation occurred instead of water oxidation
which is one of the major reason of yield diminution.
Fig. indicates that the maximum/optimum point has been
achieved after 4-7 hrs irradiation

16. 16
Final Results / Yield
Maximum Yield obtained
The most optimized catalyst is ZnFe2O4
(calcined at 900°C) coupled with TiO2 1:1 w/w
ratios (calcined at 450°C) which produced
141.22 μmol/gcat.hr (methanol yield),
7% higher than earlier results.
GC-FID Result
(Gas Chromatography –
Flame Ionization Detector or GC-FID)

17. 12/20/2022 17
Results Comparison
Comparison of Results
Photocatalyst Rate of Methanol
Formation
(μmol/gmcat.hr)
Solvent/Electrolyte Light Source Reference
ZnFe2O4/TiO2 141.22 Na2S, Na2SO3, KOH in Water 500 W Xenon Lamp This Study
15% Bi2S3/CdS 122.6 NaOH and Na2S in Water 500 W Xenon Lamp (Li Xet al., 2011)
CeF3/TiO2 80 Water 500 W Xenon Lamp (M. R. Uddin et al., 2015)
Cu2O/SiC 39 NaOH and Na2SO3 in Water 500 W Xenon Lamp (Li H et al., 2011)

18. 12/20/2022 18
• This research could be a game changer as CO2 which is the main constituent of Global
Warming could not only be control but also can be reduce/convert into cheap fuel for further
utilization.
• Sunlight can be utilized as a visible light for source of photoreduction reaction, renewable
source of energy, hence continues and economical production of methanol could be achieved.
• Can be really helpful in enhancing Air Quality Index of Pakistan specially Lahore which is
currently @ 600 AQI (2nd Highest in the World)
• A Photocatalytic Engine kit could be design which can convert CO2 emissions from fossil fuel
burning directly into fuel and thus enhance engine capacity as well as reduce CO2 emissions
and Fossil Fuel burring.
Research Results Implications

19. 12/20/2022 19
There are some suggestions for the future studies on the synthesis of ZnFe2O4 and
ZnFe2O4/TiO2 for the reduction of CO2 into methanol or some other photocatalytic application
• In this study, ZnFe2O4 prepared separately and then coupled with TiO2 by using ultra
sonication method for proper mixing of both catalysts. ZnFe2O4/TiO2 can also be prepared by
other methods. ZnFe2O4/TiO2 can also be synthesized by using the simultaneous preparation
of both catalysts with each other. In this way, ZnFe2O4 may couple with TiO2 instead of
coupling which may be more active for photocatalytic application.
• ZnFe2O4 is a visible light induced catalyst and form a heterojunction with TiO2 which proved
itself a very suitable technique for CO2 reduction. Other metal ferrites should also be tested.
• Different type of photo reactor should be used to identify the most suitable photoreactor, and
the mechanism should be very clear so kinetic modeling should be done.
Utilization of Research Results
and Future Research

20. THNAKS FOR YOUR PRECIOUS TIME
12/20/2022 20
Questions,
Suggestions and Recommendations ?