INTERNATIONAL BACCALAUREATE
CHEMISTRY EXTENDED ESSAY
Title: Spectrophotometric Investigation of the Photocatalytic Degradation of Tartrazine dye
Research Question: How does a change in the pH, from 4.0 to 11.0, affect the absorbance, and
hence rate of photocatalytic degradation, of 0.005 mol.dm-3 Tartrazine dye, when exposed to UV
light for 60 minutes in the presence of zinc oxide as a catalyst, when measured using a
spectrophotometer?
Word count: 3859
Session: May 2021
i
Table of Contents
1-Introduction ............................................................................................................................................. 1
1.1-Significance........................................................................................................................................ 1
1.2-Scope of research .............................................................................................................................. 2
2-Background Information ........................................................................................................................ 4
2.1-Properties of Tartrazine ................................................................................................................... 4
2.2-Photocatalytic Degradation and its relation to dyes ...................................................................... 5
2.3-Effect of pH on photocatalytic degradation of tartrazine ............................................................. 7
2.4-Spectrophotometry ........................................................................................................................... 8
3-Hypothesis .............................................................................................................................................. 10
4-Methodology ........................................................................................................................................... 10
4.1-Variables .......................................................................................................................................... 10
4.2-Safety and ethical concerns ............................................................................................................ 12
4.3-Experimental Procedure ................................................................................................................ 13
5-Data Collection and Processing ............................................................................................................ 14
5.1-Raw Data ......................................................................................................................................... 14
Qualitative data:................................................................................................................................ 14
Quantitative data .............................................................................................................................. 15
5.2-Calculations and Data processing ............................................................................................. 17
5.3-Data Analysis................................................................................................................................... 19
6-Discussion of results............................................................................................................................... 23
7-Conclusion ............................................................................................................................................ 255
8-Evaluation and extension .................................................................................................................... 255
10-Bibliography: ..................................................................................................................................... 288
10.1-Websites ....................................................................................................................................... 288
10.2-Online Journals ............................................................................................................................. 30
10.3-Books .............................................................................................................................................. 34
11-Appendix................................................................................................................................................ iii
11.1-Materials ......................................................................................................................................... iii
11.2-Preparing the stock solution ......................................................................................................... iv
11.3-Calibration Curve absorbance readings ...................................................................................... iv
ii
List of Figures
Figure 1: Structure of tartrazine .................................................................................................................... 4
Figure 2: Conceptual schematic of photocatalytic oxidation of Tartrazine .................................................. 7
Figure 3: A single beam scanning spectrophotometer .................................................................................. 9
List of Tables
Table 1: Controlled Variables ..................................................................................................................... 10
Table 2: Concentration and absorbance ...................................................................................................... 15
Table 3: Raw Data Table: At varying pH ................................................................................................... 17
Table 4: Processed Data Table .................................................................................................................... 18
Table 5: pH and the corresponding change in absorbance, concentration and the linear rate of
photocatalytic degradation .......................................................................................................................... 20
Table 6: Calibration Curve absorbance readings ......................................................................................... iv
List of graphs
Graph 1: Calibration curve of tartrazine ..................................................................................................... 15
Graph 2: Linear regression for dye concentration against time with varying pH ....................................... 19
Graph 3: Rate of dye photocatalytic degradation with varying pH ............................................................ 21
Graph 4: Rate of photocatalytic degradation with varying pH with revised trendline................................ 22
Graph 5: Rate of photocatalytic degradation with varying pH, for last three data points ........................... 23
1
1-Introduction
1.1-Significance
Colours and dyes fascinate everyone. I have early memories of making ink solutions from
pens to colour chalks blue and purple. Likewise, most people prefer products- food, clothes or
books- which are colourful and vibrant. Hence, synthetic dyes, due to their vivid, photo-resistant
colour, have increased dramatically in production rates since their discovery in 1856. But few
people understand the consequences of prioritizing beauty and profitability over our own health.
This fact struck me while looking at the ingredients on a packet of fresh red cherries and seeing
“FD&C Red 40 present in product, possible hyperactivity and hypersensitivity reactions1”.
Further research revealed that the annual synthetic dye production was almost 1 million tonnes in
20072. Unfortunately, almost 20% of these dyes are released as effluents into water bodies3,
changing their COD, BOD, and pH thereby harming aquatic life. Some synthetic dyes, or their
metabolites, are carcinogenic, damaging not only aquatic ecosystems but also humans drinking
1
Kobylewski S, Jacobson MF. Toxicology of food dyes. Int J Occup Environ Health. 2012;18(3):220-246.
doi:10.1179/1077352512Z.00000000034 (www.Peirsoncenter.com Toxicology article). Accessed July 20 2020
2
Pandey, Anjali, Poonam Singh, and Leela Iyengar. 2007. Bacterial decolorization and degradation of azo dyes.
International biodeterioration & biodegradation 59, no. 2 (2007): 73-84. Accessed June 10 2020
3
Farah Maria Drumond Chequer, Gisele Augusto Rodrigues de Oliveira, Elisa Raquel Anastácio Ferraz,
JulianoCarvalho Cardoso, Maria Valnice Boldrin Zanoni and Danielle Palma de Oliveira. 2012. Textile Dyes:
Dyeing Process and Environmental Impact. March 20. Accessed July 26, 2020.
https://www.intechopen.com/books/eco-friendly-textile-dyeing-and-finishing/textile-dyes-dyeingprocess-and-environmental-impact.
2
that water.4 This inspired me to focus this essay on the degradation of synthetic dyes in aqueous
solutions, to reduce its adverse effects during disposal and sustain a greener future for aquatic life.
1.2-Scope of research
I
decided
to
focus
on
Tartrazine
(trisodium;5-oxo-1-(4-sulfonatophenyl)-4-[(4-
sulfonatophenyl)diazenyl]-4H-pyrazole-3-carboxylate)5, an extremely common dye in the food
and cosmetics industry, which also causes hyperactivity and is a potential cytotoxin6. While
looking for the right method for degrading tartrazine and its intermediates, I initially thought of
using chlorine bleaches, which eliminate conjugated pi-bond systems in dyes to decolourise them7.
However, further research revealed that bleach is dangerous and causes skin and lungs irritation8.
So, I discarded this idea to look for a safer solution.
While studying Bonding, I learned that Ultraviolet light breaks the bonds of ozone and oxygen. I
was then introduced to photocatalytic degradation: a promising way to break down complex dyes
and their metabolites. UV radiation leads to electron-hole pairs being produced from
semiconducting metal oxides (the photocatalyst). In aqueous dye solutions, these pairs react with
4
Sarkar, S., Banerjee, A., Halder, U. et al. 2017. Degradation of Synthetic Azo Dyes of Textile Industry: a
Sustainable Approach Using Microbial Enzymes.Water Conserv Sci Eng 2, 121–131 (2017). Accessed May 29 2020
5
"Tartrazine." National Center for Biotechnology Information. PubChem Compound Database. 2021.
https://pubchem.ncbi.nlm.nih.gov/compound/Tartrazine#section=Names-and-Identifiers.Accessed February 08,
2021
6
Kobylewski S, Jacobson MF. Toxicology of food dyes. Int J Occup Environ Health. 2012;18(3):220-246.
doi:10.1179/1077352512Z.00000000034 (www.Peirsoncenter.com Toxicology article). Accessed July 20 2020
7
Marianna A. Busch, Kenneth W. Busch,. 2019. "Bleaches and Sterilants." Edited by Colin Poole, Alan Townshend,
Manuel Miró, Paul Worsfold. Encyclopedia of Analytical Science (Third Edition) (Academic Press) 300-315.
https://doi.org/10.1016/B978-0-12-409547-2.14033-8. Accessed December 1 2020.
8
Benzoni T, Hatcher JD. Bleach Toxicity. [Updated 2020 Jun 29]. In: StatPearls [Internet]. Treasure Island (FL):
StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441921/ Accessed July
27 2020.
3
various species to produce unstable radicals like hydroxyl radicals, which completely degrade
dyes9.
For developing the methodology, I researched the necessity of the catalyst in this reaction, and
learned that a photocatalyst and a UV source were required for photocatalytic degradation to
occur10. For this, I initially chose titanium (IV) oxide due to its high electron-hole pair maintenance
efficiency11. However, zinc oxide was used instead since it has a greater band gap energy(3.37eV)
than does titanium (IV) oxide (3.2eV), enabling it to absorb more UV radiation12.
There are multiple factors, including temperature, dye concentration, and UV-ray intensity which
influence the rate of dye photocatalytic degradation. However, the effect of pH is highly complex
and variable depending on dye structure, with lower pH increasing H+ concentration, catalyst
charge positivity and hence adsorption of anionic dyes (such as tartrazine) on the catalyst surface13,
but higher pH indicating higher OH- concentration and higher concentration of hydroxyl radicals.
9
Andrew W. Skinner, Anthony M. DiBernardo, Arvid M. Masud, Nirupam Aich, Alexandre H. Pinto,. 2020.
"Factorial design of experiments for optimization of photocatalytic degradation of tartrazine by zinc oxide (ZnO)
nanorods with different aspect ratios." Journal of Environmental Chemical Engineering, 8 (5)..
https://doi.org/10.1016/j.jece.2020.104235. Accessed November 2020
10
Benzoni T, Hatcher JD. Bleach Toxicity. [Updated 2020 Jun 29]. In: StatPearls [Internet]. Treasure Island (FL):
StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441921/ Accessed July
27 2020.
11
Rauf, Muhammad & Ashraf, Syed. 2009. "Fundamental principles and application of heterogeneous
photocatalytic degradation of dyes in solution. " Chemical Engineering Journal. 151. 10-18.
10.1016/j.cej.2009.02.026. 10-18 Accessed July 1 2020
12
M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation of C.I. Acid Yellow
23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133, Issues 1–3, 2006, Pages 226-232,ISSN
0304-3894, https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
13
M.A. Rauf, M.A. Meetani, S. Hisaindee,. 2011. "An overview on the photocatalytic degradation of azo dyes in the
presence of TiO2 doped with selective transition metals." Desalination,Volume 276, Issues 1–3,2011,Pages 1327,ISSN 0011-9164,https://doi.org/10.1016/j.desal.2011.03.071. 13-27. Accessed July 16 2020
4
Hence, this investigation aimed to determine the optimum pH for the rate of photocatalytic
degradation of tartrazine in the presence of UV rays. Tartrazine-zinc oxide solutions with varying
pH values were irradiated for 60 minutes, with the absorbance of aliquots measured in a calibrated
spectrophotometer every 10 minutes. Thus, the research question of this essay is: How does a
change in the pH, from 4.0 to 11.0, affect the absorbance, and hence rate of photocatalytic
degradation, of 0.005 mol.dm-3 Tartrazine dye, when exposed to UV light for 60 minutes in
the presence of zinc oxide as a catalyst, when measured using a spectrophotometer?
2-Background Information
2.1-Properties of Tartrazine
According to their functional groups, many classes of synthetic dyes, such as triphenylmethane or
anthraquinone, exist. Of these, azo dyes are the most common14, constituting about 50-90% of
total synthetic dye production15.
Figure 1: Structure of tartrazine16
14
Lade H, Kadam A, Paul D, Govindwar S. 2015. Biodegradation and detoxification of textile azo dyes by bacterial
consortium under sequential microaerophilic/aerobic processes. . doi:10.17179/excli2014-642. EXCLI J.
2015;14:158-174. Accessed 1 June 2020
15
Chavan, R.B. 2011. Environmentally friendly dyes,Editor(s): M. Clark,In Woodhead Publishing Series in Textiles,
Handbook of Textile and Industrial Dyeing. Woodhead Publishing, Volume 1, 2011, Pages 515-561, ISBN
9781845696955. Accessed 12 July
Simmons, M. 2017. Tartrazine — toxicity, side effects, diseases and environmental impacts. December 21..
https://www.naturalpedia.com/tartrazine-toxicity-side-effects-diseases-and-environmental-impacts.html. Accessed
January 22, 2021
16
5
Tartrazine is an anionic azo dye. All dyes comprise chromophores, conjugated systems of multiple
pi-bonds, that absorb light wavelengths. The azo double-bond (N=N), aromatic rings and
carboxylate group in form the chromophore in tartrazine, which consequently appears yellow.
During photocatalytic degradation, this azo bond is destroyed, splitting the pi-bond system and
rendering the dye unable to absorb visible light. This decolourisation will be used to measure
tartrazine degradation.
2.2-Photocatalytic Degradation and its relation to dyes
Photocatalytic degradation is an Advanced Oxidation Process (AOP): a process involving the
formation of reactive hydroxyl (OH●) radicals, which oxidise and dissociate organic compounds
into simpler molecules like carbon dioxide and water.17
In photocatalytic degradation, when the catalyst (here, zinc oxide) in the aqueous solution is
bombarded with UV photons with energies greater than its band gap energy (3.37eV)18, electrons
are excited from the valence to the conduction band, creating an electron-hole (electron vacancy)
pair.
ZnO + ℎ𝑣(UV) → ZnO(𝑒 − 𝐶𝐵 + ℎ+ 𝑉𝐵 ) (eq-1)19
17
Deng, Yang, and Renzun Zhao. "Advanced Oxidation Processes (AOPs) in Wastewater Treatment." Current
Pollution Reports 1, no. 3 (September 18, 2015): 167-76. Accessed January 01, 2021. doi:10.1007/s40726-0150015-z.
18
Gupta, Vinod K, Rajiv Jain, Arunima Nayak, Shilpi Agarwal, and Meenakshi Shrivastava. 2011. "Removal of the
hazardous dye—Tartrazine by photodegradation on titanium dioxide surface." Materials Science and Engineering:
C, 31 (5): 1062-1067. doi:10.1016/j.msec.2011.03.006. Accessed July 18 2020
19
Ioannis K Konstantinou, Triantafyllos A Albanis,. 2003. "TiO2-assisted photocatalytic degradation of azo dyes in
aqueous solution: kinetic and mechanistic investigations: A review,." Applied Catalysis B: Environmental,Volume
49, Issue 1,2004,Pages 1-14,ISSN 0926-3373,https://doi.org/10.1016/j.apcatb.2003.11.010. 1-14. Accessed July 19
2020
6
where ℎ𝑣(UV) is a UV photon, h+VB the hole in the valence band and e-CB the excited electron in
the conduction band.
The excited electrons either reduce the dye molecule (adsorbed on the catalyst’s surface) itself(eq2), or react with aqueous oxygen to form superoxide(O2●-) ions(eq-3), thereby producing hydrogen
peroxide (eq 6) and, indirectly, hydroxyl radicals(eq 8), which further degrade dye molecules(eq11). Simultaneously, the holes in the valence band either oxidize the adsorbed dye (eq-10) or the
Zinc oxide-bound water or hydroxyl particles to produce hydroxyl radicals (eq-4 and 5).20
e-CB + dye →dye-reduction products (eq-2)
e-CB +O2 → O2●- (eq-3)
h+VB +H2O→ H+ + OH● (eq-4)
h+VB +OH-→ OH● (eq-5)
O2●−+ H+ → HO2● (eq-6)
HO2● + H+→H2O2 (eq-7)
H2O2→ 2OH● (eq-8)
h+VB + dye→ dye-oxidation products (eq-10)
OH● + dye→ dye-degradation products (eq-11)
Below lies a schematic of species involved in the photocatalytic degradation of tartrazine.
20
M.A. Rauf, M.A. Meetani, S. Hisaindee,. 2011. "An overview on the photocatalytic degradation of azo dyes in the
presence of TiO2 doped with selective transition metals." Desalination,Volume 276, Issues 1–3,2011,Pages 1327,ISSN 0011-9164,https://doi.org/10.1016/j.desal.2011.03.071. 13-27. Accessed July 16 2020
7
Figure 2: Conceptual schematic of photocatalytic oxidation of Tartrazine21
2.3-Effect of pH on photocatalytic degradation of tartrazine
The effect of pH on the rate of photocatalytic degradation of this dye is complex, with both H+ as
well as OH- concentrations positively affecting the rate.
The surface charge of the photocatalyst is affected by pH. Zinc oxide in solution exists as particles
bonded to hydrogen ions (ZnO-H+), which critically influence its charge22:
At low pH,
𝑍𝑛𝑂𝐻 + 𝐻 + → 𝑍𝑛𝑂𝐻2 +
At high pH,
𝑍𝑛𝑂𝐻 + 𝑂𝐻 − → 𝑍𝑛𝑂− + 𝐻2 𝑂
21
22
El-Deen, Tarek S. Jamil & S. E. A. Sharaf. 2016. "Removal of persistent tartrazine dye by photodegradation on
TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge under visible light." Separation
Science and Technology, 51:10, 1744-1756, DOI:. doi:10.1080/01496395.2016.1170036. Accessed
October 18 2020
Mashkour, M. & Alkaim, Ayad & Ahmed, Luma & Hussein, Falah. (2011). "Zinc Oxide assisted Photocatalytic
decolorization of reactive red 2 dye." International Journal of Chemical Science (9): 969-979. Accessed January 1,
2021. https://www.tsijournals.com/abstract/zinc-oxide-assisted-photocatalytic-decolorization-of-reactive-red-2-dye10649.html.
8
Tartrazine, an anionic dye (with sulfonate (SO3-) and ethanoate functional groups), adsorbs more
frequently on the positively charged ZnOH2+ compared to the negatively charged ZnO-, leading to
greater catalyst-dye interaction and hence greater rate of degradation, at low pH.
However, as OH- concentration increases, so does rate of OH● formation. As seen in figure 2, OH●
radicals significantly control dye degradation, and hence, higher pH also influences the rate of dye
degradation positively.
Therefore, one would infer that an optimum pH would exist for degrading this dye, close to a
neutral pH: near 7, and not an extreme value, as while one effect is enhanced, the other will be
diminished. Considering that OH● radicals can diffuse throughout the solution and react with dye
molecules unadsorbed on the catalyst surface, OH- ion concentration would affect degradation rate
more be more impactful than greater adsorption rate.
2.4-Spectrophotometry
Measuring absorbance, using spectrophotometers or colorimeters, is one way to measure the
concentration of a dissolved substance. The Beer-Lambert Law states that the absorbance, the
amount of light absorbed at a wavelength23, of a dissolved substance is directly proportional24 to
its concentration in a solution25. Quantitatively,
𝐴 = 𝜀𝑏𝑐
23
Brown, Catrin, and Mike Ford. 2014. "Analysis of the Protein concentration of a sample." Chap. 14 in Pearson
Baccalaureate Higher Level Chemistry, by Catrin Brown and Mike Ford, edited by Tim Jackson, 706-707. Accessed
June 1, 2020.
24
Rafferty, J.P. 2019. Beer's Law. November 20. https://www.britannica.com/science/Beers-law. Accessed August
3, 2020
25
Clark, J, and G Gunawardena. 2020. The Beer-Lambert Law. August 16.
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Mod
ules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electronic_Spectroscopy/Electronic_Spectroscopy_Basic
s/The_Beer-Lambert_Law. Accessed 1 1, 2021
9
Where A is the absorbance of the substance, c the concentration, ε the absorptivity and b the
optical path-length.
A spectrophotometer is a device that electronically measures the transmittance of different
wavelengths of light through a coloured sample. It consists of a visible light source, comprising
all wavelengths, which are diffracted, dispersed and separately transmitted through the sample,
using a diffraction grating and a movable slit, respectively.
Figure 3: A single beam scanning spectrophotometer26
A detector27 at the end of the path of the transmitted light, measures the absorbance of the sample,
with reference to a previously measured colourless solution (usually distilled water) that does not
absorb any light.
26
Vista, Shree. (2015). Use of Humic acid in agriculture, Accessed January 1 2021
Instruments, Shimadzu Scientific. “Uv-Vis Frequently Asked Questions - Instrument Design,” September 25, 2019. Accessed
January 30 2021. https://www.ssi.shimadzu.com/products/uv-vis-spectrophotometers/faqs/instrument-design.html.
27
10
3-Hypothesis
Predictions can be made on the effect of the independent variable on the dependent variable:
The rate of photocatalytic tartrazine degradation will increase up till it reaches pH 8, as the
concentration of hydroxyl radicals will increase; after 8, the rate will decrease, as the adsorption
of dye on the catalyst surface will decrease due to repulsion between the anionic dye and the
negatively charged zinc oxide surface.
4-Methodology
4.1-Variables
Independent variable: The pH was varied from 4.0 to 6.0, 8.0, 10.0 and 11.0 by using buffer
solutions to dilute the dye-zinc oxide solutions of concentration 0.005 mol.dm-3, using a droppipette. This will be measured using a pH sensor.
Dependent variable: The absorbance of the dye solution was recorded every 10 minutes for 60
minutes using a spectrophotometer. From the absorbance, the rate of photocatalytic degradation
will be calculated.
Table 1: Controlled Variables
Variable
Reason for controlling variable
Controlled
Method for controlling
variable
Exposure to
Any external light would affect the rate of
The experiments were
external
degradation of the dye (as an extraneous
conducted in a dark room
radiation
variable) and cause random errors
by shutting the curtains.
The apparatus was placed
in a wooden box.
11
External
Changes in temperature in the surroundings
Experiments were
change in
could change the equilibrium point and rates
conducted at the same
Temperature
of electron-hole recombination, reduction
time every day,
and oxidation, creating random errors.
maintaining temperature at
27°C using air-condition
set up. Beyond that,
however, fluctuations in
room temperature could
affect the results.
pH sensor
Changing this could cause systematic errors.
The same sensor was used
for all experiments.
Distilled
Changes in impurities could affect the
Distilled water from the
water
activity and concentration of reactants and
same source was used for
products and create random and systematic
all solutions.
errors.
Mass of the
Different photocatalyst concentrations would
250 mg of ZnO was added
photo-catalyst
cause changes in catalyst activity and rate of
to all the solutions.
used.
degradation.
Initial dye
Varying initial dye concentration would
The irradiated solutions in
concentration
make the values of absorbance and, hence,
the pH-rate experiment all
rate of degradation, inconsistent and
possessed a concentration
unreliable.
of 5 × 10−5 moldm-3.
12
4.2-Safety and ethical concerns
a) Health hazards

As UV rays are harmful to skin and can cause sunburns or skin cancer, as well as
inflammation of eyes28, the entire apparatus was placed in a hard, black cardboard
box, and safety goggles were used.

Nitrile gloves were used while handling the zinc oxide, tartrazine powder and
aqueous solutions, as these chemicals are irritants29 if inhaled or in contact with skin.
b) Care for apparatus and chemical disposal

Do not place the pH sensor in the beaker while pouring hydrochloric acid or sodium
hydroxide, to prevent damage to the instrument. Take it out of the solution before turning
the UV lamp on.

Dilute all solutions before disposal as zinc oxide30 and tartrazine are toxic for aquatic and
human life.

Dispose the excess acid or alkali after neutralizing and diluting.

Dispose of gloves by removing such that it does not come in contact with skin. They
must be disposed of in a designated waste bin for used gloves.
c) Sustainable solution consumption

Dilute the hydrochloric acid and sodium hydroxide solutions to 0.01 moldm-3 or less as
they are corrosive.
28
Kuijk, F. J Van. "Effects of Ultraviolet Light on the Eye: Role of Protective Glasses." Environmental Health
Perspectives 96 (December 1991): 177-84. Accessed November 2, 2020. doi:10.1289/ehp.9196177.
29
Chemical Info for Zinc Oxide. November 23, 2015. Accessed February 1, 2021.
https://chemicalsafety.com/sds1/sdsviewer.php?id=30469074&name=Zinc oxide.
30
Chemical Info for Zinc Oxide. November 23, 2015.
https://chemicalsafety.com/sds1/sdsviewer.php?id=30469074&name=Zinc oxide. Accessed November 1, 2020
13

Maintain a maximum mass of 250 mg for zinc oxide (per solution) and maximum
concentration of 0.005 moldm-3 for Tartrazine.
4.3-Experimental Procedure
Part A: Determining wavelength of maximum absorbance (λmax) of tartrazine (before UV
exposure) to obtain calibration curve.
1) Prepare a stock solution of 9.0 cm3 0.005 mol∙dm-3 tartrazine dye (as given in
appendix)
2) Prepare 5.0 cm3 of 1.0 × 10−5 moldm-3 dye solution, by pipetting out 0.01 cm3
stock solution in a volumetric flask.
3) Measure out 250mg of zinc oxide using a weigh balance and transfer to the flask.
4) Dilute it up to the mark with distilled water and place it on a magnetic stirrer for 5
minutes.
5) Calibrate the spectrophotometer by placing a 5 cm3 distilled water solution in
the spectrophotometer and set the absorbance to 0.000.
6) Pipette out 5.0cm3 of the 1.0 × 10−5 moldm-3 tartrazine solution in the cuvette to
record maximum absorbance set at different wavelengths from 380nm to 700nm.
7) Record the wavelength that produces maximum absorbance.
8) Repeat recording absorbance with 1.0 × 10−5 moldm-3 tartrazine solution setting
at the wavelength with maximum absorbance recorded in step 7 ,thrice.
9) Repeat step 8, taking 5.0 × 10−5 , 5.0 × 10−5 , 1.0 × 10−4 , 1.5 × 10−5 ,
2.0 × 10−4 moldm-3 dye-catalyst solutions, to obtain a calibration curve.
Note: Conduct experiment in a dark area. When not using zinc oxide solutions, place them in
dark containers to prevent dye degradation which would create inconsistent results.
14
Part B: Determining the effect of pH on rate of photocatalytic degradation
1) Prepare 30cm3 of a 5.0 × 10−5 mol∙dm-3 solution, of tartrazine by adding 0.3cm3
5.0 × 10−5 mol∙dm-3 to a 100 cm3 volumetric flask.
2) Add 250 mg of zinc oxide at the end (to prevent reaction initiation before irradiation),
measured using a digital weigh balance and add to the flask.
3) Dilute with pH 4.0 buffer solution up to the mark.
4) Measure initial absorbance: extract 5 cm3 of solution, set the wavelength to the
maximum-absorbance wavelength found from the previous experiment and set
absorbance of blank solution to 0.000. Then measure the absorbance of the irradiated
aliquot at the same wavelength.
5) Place the solution 10 cm away from the UV lamp.
6) Extract 5 cm3 of the solution obtained in step 3 for every 10 minutes to measure
absorbance in the spectrophotometer for 60 minutes.
7) Repeat steps 4-6 for two more trials.
8) Repeat steps 1-6, using pH 6.0, 8.0, 10.0 and 11.0 in step 3 each time.
5-Data Collection and Processing
5.1-Raw Data
Qualitative data:
The tartrazine solution, initially strongly yellow, faded after all irradiation trials. Basic pH
solutions faded faster than acidic solutions did. The cuvette was also hotter after irradiation, as
some of the light was converted into heat energy. It was also observed that effervescence– due to
evolved carbon dioxide– was present at the cuvette rim.
15
Quantitative data
There was no change in dye absorbance at varying pH (before irradiation). The wavelength of
maximum absorbance was recorded at 428 nm,31 as per procedure in part A. This value was
supported by research32. The average absorbance was plotted against concentration for the
calibration curve.
Table 2: Concentration and absorbance
Dye Concentration 10-5 mol∙dm-3
(±0.01)
1.00
5.00
10.00
15.00
20.00
Average Absorbance (±0.001)
0.351
1.759
3.560
5.350
7.050
Graph 1: Calibration curve of tartrazine
31
M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation of C.I. Acid Yellow
23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133, Issues 1–3, 2006, Pages 226-232,ISSN
0304-3894, https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
32
Gobara, Mohamed & Baraka, Ahmad. (2014). 2014. "Tartrazine Solution as Dosimeter for Gamma Radiation
Measurement." International Letters of Chemistry, Physics and Astronomy. doi:33. 106-117. 10.18052. Accessed
October 1 2020
16
The zero-value y-intercept showed that there was absorbance is directly proportional to
concentration. Hence, results were valid.
By the Beer-Lambert Law, 𝑨 = 𝜺𝒃𝒄 = 𝒎𝒙 × 10−5
Here, A is the absorbance, ε the molar absorptivity, b the path length (cuvette side-length), m the
line slope and x, the dye concentration.
∴ 𝑚 = 𝜀 ∙ 𝑏 ∙ 10−5 ; 𝑠𝑜 𝜀 = 105 ∙
𝑚
0.354
= 105 ∙
= 2.832𝑥104
𝑏
1.25
≈ 2.83𝑥104 𝑑𝑚3 ∙ 𝑚𝑜𝑙 −1 ∙ 𝑐𝑚−1
Although the result is only valid for 3 significant figures, it matched the literature value33,
28321.61, to 4 significant figures, and was hence used for calculations.
The table below gives the absorbance, taken every 10 minutes for 60 minutes, with varying pH
of 4.0, 6.0, 8.0, 10.0 and 11.0. The control conditions were an initial concentration of
5.00 × 10−5 moldm-3, temperature of 250C and 250 mg zinc oxide.
33
food and agricultural organization, UN. n.d. TOTAL COLOURING MATTERS CONTENT (VOLUME 4).Database,
food and agricultural organization. http://www.fao.org/3/a0691e/Total_colouring_matters_volume%204.pdf.
Accessed October 15 2020.
17
Table 3: Raw Data Table: At varying pH
Absorbance of solution (± 0.001)
Time
(minutes)
(±0.1)
pH 4.0 (± 0.1)
pH 6.0 (± 0.1)
pH 8.0 (± 0.1)
pH 10.0 (± 0.1)
pH 11.0 (± 0.1)
0.0
Trial
Trial
1
2
3
1
2
3
1
1.770 1.770 1.770 1.770 1.770 1.770 1.770
Trial
Trial
2
3
1
2
3
1
1.770 1.770 1.770 1.770 1.770 1.770
Trial
2
3
1.770 1.770
10.0
1.667 1.703
1.738 1.591
1.627 1.662
1.267
1.303
1.338
1.248
1.283
1.319
1.108
1.143
1.179
20.0
1.646 1.682
1.717 1.521
1.556 1.591
1.032
1.067
1.103
0.952
0.988
1.023
0.581
0.616
0.651
30.0
1.634 1.669
1.705 1.499
1.535 1.570
0.752
0.788
0.823
0.701
0.736
0.772
0.384
0.425
0.455
40.0
1.621 1.657
1.692 1.464
1.499 1.535
0.501
0.536
0.572
0.499
0.535
0.570
0.280
0.319
0.350
50.0
1.597 1.632
1.667 1.448
1.483 1.519
0.388
0.423
0.458
0.313
0.349
0.384
0.173
0.212
0.244
60.0
1.595 1.630
1.666 1.432
1.467 1.503
0.142
0.177
0.212
0.145
0.181
0.216
0.099
0.142
0.170
5.2-Calculations and Data processing
For the sample calculation, readings at pH 4.0 and 10.0 minutes will be taken.
Calculation of average absorbance
Average Absorbance =
sum of absorbance values for each pH per time interval
3
=
1.667 + 1.703 + 1.738
= 1.703 ± 0.001
3
Calculation of concentration
𝐴 = 𝜀𝑏𝑐,
∴𝑐=
𝐴
1.703
=
= 4.810 × 10−5 𝑚𝑜𝑙 ∙ 𝑑𝑚−3
𝜀𝑏 28312 x 1.25
18
∆𝐴
∆𝑏
Percentage uncertainty in concentration = [ 𝐴 + 𝑏 ], since absolute uncertainty is the product
of the absolute value and the total percentage uncertainty, and as path length cannot be assumed
as infinitely precise.
For the error bars, absolute uncertainty was used:
Δ𝑐
∆𝐴 ∆𝑏
𝐴
∆𝐴 ∆𝑏
= [ + ] ; ∴ Δ𝑐 = × [ + ]
𝑐0
𝐴
𝑏
𝜀𝑏
𝐴
𝑏
Δ𝑐
0.001 0.005
=[
+
] = 0.459% ≈ ±0.5%
𝑐0
1.703 1.25
Δ𝑐 =
1.703
0.001 0.005
+
[
] = ±0.221 × 10−6 mol ∙ dm−3
28320 x 1.25 2.804 1.25
Concentration, being extremely small, was plotted in terms of 10-5 mol∙dm-3. Approximate
uncertainties are shown at acidic and basic pH.
Table 4: Processed Data Table
Concentration x (10-5 mol∙dm-3) at
𝛥𝑐
≈ ±0.5%
𝑐
𝛥𝑐
≈ ±1%
𝑐
Time (minutes)
(±0.1)
0.0
pH 4.0
5.000
pH 6.0
5.000
pH 8.0
5.000
pH 10.0
5.000
pH 11.0
5.000
10.0
4.810
4.595
3.680
3.625
3.230
20.0
4.750
4.395
3.015
2.790
1.740
30.0
4.715
4.335
2.225
2.080
1.190
40.0
4.680
4.235
1.515
1.510
0.893
50.0
4.610
4.190
1.195
0.985
0.593
60.0
4.605
4.145
0.500
0.510
0.387
19
5.3-Data Analysis
To find the change in rate of photocatalytic degradation, average rate values for every pH were
required. Hence, linear trendline graphs of tartrazine concentration against time were obtained,
the gradients of which were taken as the rate of change of dye concentration.
Like the concentration, the rate values were obtained in terms of 10-5 moldm-3min-1.
As the trendline equations were in a 𝑦 = 𝑚𝑥 + 𝑐 format, their slopes were the average linear rate
of change of reactant concentration.
Both vertical and horizontal error bars were to too small to be noticed.
Graph 2: Linear regression for dye concentration against time with varying pH
For pH = 4.0, 𝑦 = −0.0059𝑥 + 4.916
20
∴ 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑑𝑒𝑔𝑟𝑎𝑑𝑎𝑡𝑖𝑜𝑛 = −(𝑟𝑎𝑡𝑒 𝑜𝑓 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛) = −(m)
= +0.0059 ∙ 10−5 𝑚𝑜𝑙 ∙ 𝑑𝑚−3 𝑚𝑖𝑛−1
To calculate rate uncertainties,
Δrate Δ(Δ𝑐) Δt
=
+
𝑟𝑎𝑡𝑒
(Δ𝑐)0
𝑡
Where Δc is change of dye concentration. Δ𝑐 = 𝑐𝑖𝑛𝑖𝑡𝑖𝑎𝑙 − 𝑐𝑓𝑖𝑛𝑎𝑙 = 5.000 ± 0.0228 −
4.605 ± 0.0212 = 0.395 ± 0.0440
∴
Δ(Δ𝑐) 0.0440
Δ(Δ𝑐) Δt
=
≈ ±11.3%; ∴ Δrate = 𝑟𝑎𝑡𝑒0 × (
+ )
(Δ𝑐)0
(Δ𝑐)0
0.395
𝑡
= 0.59 × 10−7 × (0.113 +
0.1
) = ±0.067 × 10−7 𝑚𝑜𝑙 𝑑𝑚−3 ∙ 𝑚𝑖𝑛−1
60
Table 5: pH and the corresponding change in absorbance, concentration and the linear rate of
photocatalytic degradation
pH (±0.1)
Change in Absorbance
Change in concentration
Average linear Rate of photocatalytic
(±0.002)
(10-5 moldm-3) ±0.044
degradation (10-5 moldm-3min-1)
4.0
0.140
0.395
0.0059 ± 0.0007
6.0
0.303
0.855
0.0126 ± 0.0006
8.0
1.593
4.500
0.0713 ± 0.0006
10.0
1.590
4.490
0.0715 ± 0.0006
11.0
1.633
4.613
0.0713 ± 0.0005
21
A graph was then created, taking average degradation rate on the Y-axis and pH on the X-axis.
An estimate of the average rate uncertainty for all rates was added. Plotted error bars were not
visible.
Graph 3: Rate of dye photocatalytic degradation with varying pH
Rate of phtocatalytic degradation (x 10-7
moldm-3 min-1) ± 6 x10-4
0.09
0.08
0.07
0.06
y = 0.0108x - 0.0378
R² = 0.824
0.05
0.04
0.03
0.02
0.01
0
3
4
5
6
7
8
9
10
11
12
pH (±0.1)
However, as the last 3 data points were roughly constant a linear trend was considered an unfit
match. Hence, a polynomial (degree 2) curve was chosen instead.
22
Graph 4: Rate of photocatalytic degradation with varying pH with revised trendline
Rate of phtocatalytic degradation x 10-5
moldm-3 min-1 ± 6 x10-4
0.09
y = -0.0011x2 + 0.0272x - 0.0925
R² = 0.8554
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
3
4
5
6
7
8
9
10
11
12
pH (±0.1)
The rate of degradation and pH was best represented with a polynomial equation:
𝑦 = −0.0011𝑥 2 + 0.0272𝑥 − 0.0925 , with y as rate and x as pH. Although the trendline does
not depict the exact change of rate with pH, it does represent the trend followed by the variables,
of rate increasing with pH 8.0 after which it reaches a constant value.
To determine the significance of the difference between rates at pH 8.0, 10.0 and 11.0, the same
rate-pH graph, only at these three pH values, was plotted.
23
Graph 5: Rate of photocatalytic degradation with varying pH, for last three data points
Rate of photocaalytic degradation (10-5 mol
dm-3 min-1 ± 6 x10-4
0.0722
0.072
0.0718
0.0716
0.0714
0.0712
0.071
0.0708
0.0706
7
8
9
10
11
12
pH (± 0.1)
Although uncertainties appear large in the second graph, since the uncertainty range of the last
three points (approximately (0.02 ± 0.01)× 10−7moldm-3min-1) were minimal compared to the
difference between the acidic (pH 4.0 and 6.0) and basic (pH 8.0 to 11.0) solution degradation
rates (approximately (6.21 ± 0.04) × 10−7 moldm-3min-1). Hence, the rate was concluded to be
roughly constant between pH 8.0 and 11.0.
6-Discussion of results
It was found that, as seen in graph 3, the rate of photocatalytic degradation increased with
increasing pH, but settling at a maximum at pH 10. The high R2 value, 0.86, indicates a strong
relationship between pH and rate34.
34
Agnes Ogee, Mark Ellis, Bruno Scibilia, Cheryl Pammer. 2013. Regression Analysis: How Do I Interpret Rsquared and Assess the Goodness-of-Fit? Edited by Minitab Blog Editor. May 30. Accessed 11 27, 2020.
24
At low pH, H+ concentration is greater, and Hydrogen ions are attracted to the aromatic rings of
the dye, reducing the negative electric attraction between the anionic dye and the hydroxyl
radicals, hindering the relative reactivity between the species and hence, the rate of
photocatalytic degradation.
One research study35 also found that zinc oxide converts into Zn2+ ions in acidic pH,
significantly reducing catalyst activity. As pH increases, greater concentration of hydroxide(OH-)
ions increases the negative charge density, facilitating a greater oxidative effect of OH●36. In
addition, greater OH- concentration will increase the rate of hydroxyl ion (OH●) formation, and
consequently enhance the rate of dye degradation37.
One can reason that the positive effect of greater pH on OH● concentration– and OH● radical
reaction–supersedes the positive effect of H+ ions on rate of photocatalytic degradation.
However, it can be seen in Graph 3 that the curve settles at the last 3 rate values (7.13 ×
10−7 , 7.13 × 10−7 , 7.13 × 10−7 moldm-3min-1).But this similarity in rates is likely due the positive
effect of low pH on the rate of degradation, which counters the positive effect of OH- ions at pH
8.0, 10.0 and 11.0. Although more hydroxyl ions are present at higher pH, they interact less
https://blog.minitab.com/blog/adventures-in-statistics-2/regression-analysis-how-do-i-interpret-r-squared-andassess-the-goodness-of-fit.
35
El-Deen, Tarek S. Jamil & S. E. A. Sharaf. 2016. "Removal of persistent tartrazine dye by photodegradation on
TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge under visible light." Separation Science and
Technology, 51:10, 1744-1756, DOI:. doi:10.1080/01496395.2016.1170036. Accessed October 18 2020
36
Gupta, Vinod K, Rajiv Jain, Arunima Nayak, Shilpi Agarwal, and Meenakshi Shrivastava. 2011. "Removal of the
hazardous dye—Tartrazine by photodegradation on titanium dioxide surface." Materials Science and Engineering:
C, 31 (5): 1062-1067. doi:10.1016/j.msec.2011.03.006. Accessed July 15 2020
25
frequently with anionic dye molecules which are not easily adsorbed on the negatively charged
catalyst-surface, hence leading to negligible increase in rate.
Hence the rate of photocatalytic degradation increases up till reaching pH 8.0, after which it
remains constant.
7-Conclusion
This investigation focused on the determining the effect of pH on the rate of photocatalytic
degradation of the dye tartrazine. It was found that the rate of photocatalytic degradation increased
with pH, with pH 4.0 displaying the smallest linear rate, 5.91 × 10−8 moldm-3min-1 until reaching
a roughly constant value at pH 8.0 till 11.0 of 7.14 × 10−7 moldm-3min-1.
Thus, the hypothesis- that rate of tartrazine degradation will increase up till pH 8.0, after which,
the rate will decrease, is partially proven. The Research Question- “How does a change in the
pH, from 4.0 to 11.0, affect the absorbance, and hence rate of photocatalytic degradation, of
0.005 mol.dm-3 Tartrazine dye, when exposed to UV light for 60 minutes in the presence of
zinc oxide as a catalyst, when measured using a spectrophotometer?” has been successfully
answered through this investigation.
8-Evaluation and extension
To determine the validity of this investigation, results were compared with existing research on
the photocatalytic degradation of Tartrazine with a zinc oxide catalyst38.This also showed that rates
were much greater at high pH, with a nearly constant average rate between 8.0 and 11.0. This
38
M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation of C.I. Acid Yellow
23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133, Issues 1–3, 2006, Pages 226-232,ISSN
0304-3894, https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
26
indicates that this experiment possesses high validity. Another study, El-Deen et al39, which
investigated the optimum factors for photocatalytic degradation of tartrazine using a titanium (IV)
oxide-sludge mixture, under visible light, found that pH 8.0 produced the maximum photocatalytic
degradation rate significantly more than that at pH 10.0, indicating that the results obtained in this
investigation may not be valid when complex mixtures (like sludge) exist in the tartrazine solution.
There were limitations to the results obtained, which could be improved on.

The temperature of the dye solution increased during UV ray exposure. This would affect
the rate of photocatalytic degradation by increasing the frequency of molecule collisions
and rate constant40, and creating inconsistencies in results. This could be reduced by
placing the flask in a thermally insulated chamber during irradiation, to maintain constant
temperature.

The results of this study did not consider extreme pH values beyond the 4.0-11.0, as other
factors– such as the dissolution of zinc oxide in concentrated acidic solutions into zinc
salts41 and, in highly alkaline solutions, into alkali zincate salts– take place in such
conditions. The study could have taken a broader pH range of 2.0 to 13.0 to understand the
optimum pH for degradation.
39
El-Deen, Tarek S. Jamil & S. E. A. Sharaf. 2016. "Removal of persistent tartrazine dye by photodegradation on
TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge under visible light." Separation Science and
Technology, 51:10, 1744-1756, DOI:. doi:10.1080/01496395.2016.1170036. Accessed October 18 2020
40
M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation of C.I. Acid Yellow
23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133, Issues 1–3, 2006, Pages 226-232,ISSN
0304-3894, https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
41
M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation of C.I. Acid Yellow
23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133, Issues 1–3, 2006, Pages 226-232,ISSN
0304-3894, https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
27

Although the rate of tartrazine degradation was measured using absorbance values, no
information on its colourless intermediates was obtained. To determine the rate of the dye’s
mineralization into carbon dioxide and water, and hence the destruction of harmful
products, the rate of change of mass of the solution (which changed with carbon dioxide
effervescence) could be measured over time to measure photocatalytic degradation and
mineralization.

Due to the arrangement of apparatus, UV rays could have been unequally distributed to
different sections of the solution and only irradiated the surface, leading to systematic
errors in absorbance values, and hence calculated rate of photocatalytic degradation. By
placing the dye solution on a magnetic stirrer and simultaneously irradiating it, a more
accurate result could be obtained.

In this investigation, rate of photocatalytic degradation was assumed constant over the
entire reaction duration. However, Table 5 shows that maximum change in concentration
was at pH 11.0, while linear rate of degradation was slightly greater at pH 10, indicating
that average rate (considering the first and last concentrations) and linear rate (considering
all concentration values) are not equal, and that rate changes with time. This indicates that
the effect of pH on rate of photocatalytic degradation changes with reaction duration. To
counter this systematic error in the results, the effect of pH on rate of photocatalytic
degradation, at different times, could be measured to understand how the relationship
between rate and pH changes with time.
The experiment was successful overall, however¸ due to its strengths:

The data involved averages of 3 trials, which would give precise results with diminished
random error.
28

The initial concentration of the dye and the concentration of catalyst were standardised,
which improved the relation between the independent and dependent variables.

The use of sophisticated instruments– a magnetic stirrer, digital pH sensor,
spectrophotometer and Logger Pro software lead to more reliable results.

The procedure successfully facilitated an exploration of the relationship between pH and
rate of photocatalytic degradation, thereby answering the research question of this
investigation, by manipulating pH and measuring the change in absorbance.
As an extension to this investigation, the effect of initial dye concentration, temperature and
catalyst concentration on photocatalytic degradation rate could be investigated, to better
understand the rates and kinetics of such reactions, using theoretical models such as the LangmuirHinshelwood Model42. This would help in better understanding optimum conditions to best
eliminate toxic dyes from aquatic ecosystems and reducing their adverse effects on our
environment.
10-Bibliography:
10.1-Websites
1. Agnes Ogee, Mark Ellis, Bruno Scibilia, Cheryl Pammer. 2013. Regression Analysis: How
Do I Interpret R-squared and Assess the Goodness-of-Fit? Edited by Minitab Blog Editor.
May 30. Accessed 11 27, 2020. https://blog.minitab.com/blog/adventures-in-statistics2/regression-analysis-how-do-i-interpret-r-squared-and-assess-the-goodness-of-fit.
42
Gupta, Vinod K., Rajeev Jain, Alok Mittal, Tawfik A. Saleh, Arunima Nayak, Shilpi Agarwal, and Shalini
Sikarwar. "Photo-catalytic Degradation of Toxic Dye Amaranth on TiO2/UV in Aqueous Suspensions." Materials
Science and Engineering: C 32, no. 1 (2012): 12-17. doi:10.1016/j.msec.2011.08.018. Accessed June 12 2020
29
2. Clark,
J,
and
G
Gunawardena.
2020.
The
Beer-Lambert
Law.
August
16.
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_M
aps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electroni
c_Spectroscopy/Electronic_Spectroscopy_Basics/The_Beer-Lambert_Law.
Accessed
January 1, 2021
3. Chemical
Info
for
Zinc
Oxide.
November
23,
2015.
https://chemicalsafety.com/sds1/sdsviewer.php?id=30469074&name=Zinc oxide. Accessed
November 1, 2020
4. Chemical Info for Zinc Oxide. November 23, 2015. Accessed February 1, 2021.
https://chemicalsafety.com/sds1/sdsviewer.php?id=30469074&name=Zinc oxide.
5. Deng, Yang, and Renzun Zhao. "Advanced Oxidation Processes (AOPs) in Wastewater
Treatment." Current Pollution Reports 1, no. 3 (September 18, 2015): 167-76. Accessed
January 01, 2021. doi:10.1007/s40726-015-0015-z.
6. Rafferty, J.P. 2019. Beer's Law. November 20. https://www.britannica.com/science/Beerslaw. Accessed August 3, 2020
7. Farah Maria Drumond Chequer, Gisele Augusto Rodrigues de Oliveira, Elisa Raquel
Anastácio Ferraz, JulianoCarvalho Cardoso, Maria Valnice Boldrin Zanoni and Danielle
Palma de Oliveira. 2012. Textile Dyes: Dyeing Process and Environmental Impact. March 20.
30
https://www.intechopen.com/books/eco-friendly-textile-dyeing-and-finishing/textile-dyesdyeing-process-and-environmental-impact. Accessed July 26, 2020.
8. Food and agricultural organization, UN. n.d. TOTAL COLOURING MATTERS CONTENT
(VOLUME
4).Database,
food
and
agricultural
organization.
http://www.fao.org/3/a0691e/Total_colouring_matters_volume%204.pdf. Accessed October
15 2020.
9. Instruments, Shimadzu Scientific. “Uv-Vis Frequently Asked Questions - Instrument Design,”
September
25,
2019..
https://www.ssi.shimadzu.com/products/uv-vis-
spectrophotometers/faqs/instrument-design.html. Accessed January 30 2021
10. Simmons, M. 2017. Tartrazine — toxicity, side effects, diseases and environmental impacts.
December 21.. https://www.naturalpedia.com/tartrazine-toxicity-side-effects-diseases-andenvironmental-impacts.html. Accessed January 22, 2021
11. "Tartrazine." National Center for Biotechnology Information. PubChem Compound
Database.
2021.https://pubchem.ncbi.nlm.nih.gov/compound/Tartrazine#section=Names-
and-Identifiers.Accessed February 08, 2021
10.2-Online Journals
31
12. Andrew W. Skinner, Anthony M. DiBernardo, Arvid M. Masud, Nirupam Aich, Alexandre
H. Pinto,. 2020. "Factorial design of experiments for optimization of photocatalytic
degradation of tartrazine by zinc oxide (ZnO) nanorods with different aspect ratios." Journal
of Environmental Chemical Engineering, 8 (5).. https://doi.org/10.1016/j.jece.2020.104235.
Accessed November 1 2020
13. Benzoni T, Hatcher JD. Bleach Toxicity. [Updated 2020 Jun 29]. In: StatPearls [Internet].
Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK441921/ Accessed July 27 2020.
14. Chavan, R.B. 2011. Environmentally friendly dyes,Editor(s): M. Clark,In Woodhead
Publishing Series in Textiles, Handbook of Textile and Industrial Dyeing. Woodhead
Publishing, Volume 1, 2011, Pages 515-561, ISBN 9781845696955. Accessed 12 July 2020
15. El-Deen, Tarek S. Jamil & S. E. A. Sharaf. 2016. "Removal of persistent tartrazine dye by
photodegradation on TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge
under visible light." Separation Science and Technology, 51:10, 1744-1756, DOI:.
doi:10.1080/01496395.2016.1170036. Accessed October 18 2020
16. Gupta, Vinod K., Rajeev Jain, Alok Mittal, Tawfik A. Saleh, Arunima Nayak, Shilpi
Agarwal, and Shalini Sikarwar. "Photo-catalytic Degradation of Toxic Dye Amaranth on
32
TiO2/UV in Aqueous Suspensions." Materials Science and Engineering: C 32, no. 1 (2012):
12-17. doi:10.1016/j.msec.2011.08.018. Accessed June 12 2020
17. Gupta, Vinod K, Rajiv Jain, Arunima Nayak, Shilpi Agarwal, and Meenakshi Shrivastava.
2011. "Removal of the hazardous dye—Tartrazine by photodegradation on titanium dioxide
surface." Materials Science and Engineering: C, 31 (5): 1062-1067.
doi:10.1016/j.msec.2011.03.006. Accessed July 18 2020
18. Ioannis K Konstantinou, Triantafyllos A Albanis,. 2003. "TiO2-assisted photocatalytic
degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations: A
review,." Applied Catalysis B: Environmental,Volume 49, Issue 1,2004,Pages 1-14,ISSN
0926-3373,https://doi.org/10.1016/j.apcatb.2003.11.010. 1-14. Accessed July 19 2020
19. Kobylewski S, Jacobson MF. Toxicology of food dyes. Int J Occup Environ Health.
2012;18(3):220-246. doi:10.1179/1077352512Z.00000000034 (www.Peirsoncenter.com
Toxicology article). Accessed July 20 2020
20. Lade H, Kadam A, Paul D, Govindwar S. 2015. Biodegradation and detoxification of textile
azo dyes by bacterial consortium under sequential microaerophilic/aerobic processes. .
doi:10.17179/excli2014-642. EXCLI J. 2015;14:158-174. Accessed 1 June 2020
33
21. M.A. Behnajady, N. Modirshahla, R. Hamzavi, Kinetic study on photocatalytic degradation
of C.I. Acid Yellow 23 by ZnO photocatalyst, Journal of Hazardous Materials, Volume 133,
Issues 1–3, 2006, Pages 226-232,ISSN 0304-3894,
https://doi.org/10.1016/j.jhazmat.2005.10.022. Accessed August 1 2020
22. M.A. Rauf, M.A. Meetani, S. Hisaindee,. 2011. "An overview on the photocatalytic
degradation of azo dyes in the presence of TiO2 doped with selective transition metals."
Desalination,Volume 276, Issues 1–3,2011,Pages 13-27,ISSN 00119164,https://doi.org/10.1016/j.desal.2011.03.071. 13-27. Accessed July 16 2020
23. Marianna A. Busch, Kenneth W. Busch,. 2019. "Bleaches and Sterilants." Edited by Colin
Poole, Alan Townshend, Manuel Miró, Paul Worsfold. Encyclopedia of Analytical Science
(Third Edition) (Academic Press) 300-315. https://doi.org/10.1016/B978-0-12-4095472.14033-8. Accessed December 1 2020.
24. Mashkour, M. & Alkaim, Ayad & Ahmed, Luma & Hussein, Falah. (2011). "Zinc Oxide
assisted Photocatalytic decolorization of reactive red 2 dye." International Journal of
Chemical Science (9): 969-979. Accessed January 1, 2021.
https://www.tsijournals.com/abstract/zinc-oxide-assisted-photocatalytic-decolorization-ofreactive-red-2-dye-10649.html.
34
25. Pandey, Anjali, Poonam Singh, and Leela Iyengar. 2007. Bacterial decolorization and
degradation of azo dyes. International biodeterioration & biodegradation 59, no. 2 (2007):
73-84. Accessed June 10 2020
26. Rauf, Muhammad & Ashraf, Syed. 2009. "Fundamental principles and application of
heterogeneous photocatalytic degradation of dyes in solution. ." Chemical Engineering
Journal. 151. 10-18. 10.1016/j.cej.2009.02.026. 10-18. Accessed July 1 2020
27. Richardson, Jacob J., and Frederick F. Lange. "Rapid Synthesis of Epitaxial ZnO Films from
Aqueous Solution Using Microwave Heating." J. Mater. Chem. 21, no. 6 (2011): 1859-865.
doi:10.1039/c0jm02907f. Accessed January 1 2021
28. Sarkar, S., Banerjee, A., Halder, U. et al. 2017. Degradation of Synthetic Azo Dyes of Textile
Industry: a Sustainable Approach Using Microbial Enzymes. . Water Conserv Sci Eng 2,
121–131 (2017). Accessed May 29 2020
29. Vista, Shree. (2015). Use of Humic acid in agriculture, Accessed January 1, 2021
10.3-Books
35
29. Brown, Catrin, and Mike Ford. 2014. "Analysis of the Protein concentration of a sample."
Chap. 14 in Pearson Baccalaureate Higher Level Chemistry, by Catrin Brown and Mike
Ford, edited by Tim Jackson, 706-707. Accessed June 1, 2020.11-
iii
11-Appendix
11.1-Materials
Instruments:
1 6 W UV Lamp
An analytical balance (±0.001 g)
Logger Pro software
Spectrophotometer
Vernier spectro-vis (software) for the spectrophotometer
2 Quartz cuvettes (5 cm3)
2 Volumetric flasks (500 cm3)
Pipette (10 cm3)
Rubber gloves
Goggles
6 Test tubes (10cm3)
Magnetic stirrer
Magnetic Stirring rod
Temperature probe (±0.1oC)
Black cardboard box (blackened from both sides)
1 digital pH meter (±0.1)
Stopwatch (±0.01 s)
iv
Chemicals
Tartrazine
20% zinc oxide
0.01 mol dm-3 Hydrochloric acid
0.01 mol dm-3 Sodium Hydroxide
pH 4.0 buffer solution
pH 6.0 buffer solution
pH 8.0 buffer solution
pH 10.0 buffer solution
pH 11.0 buffer solution
distilled water
11.2-Preparing the stock solution
1. Weigh 6.679 g tartrazine powder using an analytical balance.
2. Transfer through funnel into a volumetric flask.
3. Add distilled water solution up till the 500cm3 mark.
4. Place the solution on a magnetic stirrer for 10 minutes.
11.3-Calibration Curve absorbance readings
Table 6: Calibration Curve absorbance readings
Dye
Concentration
(moldm-3)
1.00
5.00
10.00
15.00
20.00
Absorbance (±0.001)
Trial 1
0.353
1.769
3.539
5.309
7.079
Trial 2
0.354
1.770
3.540
5.310
7.080
Trial 3
0.355
1.771
3.541
5.311
7.081
Average
absorbance(±0.001)
0.354
1.770
3.540
5.310
7.080