This document summarizes the results of testing different TiO2 coated substrates for photocatalytic degradation of indigo carmine dye. The best performing sample was a sintered stainless steel mesh coated with P25 TiO2 nanoparticles, which fully degraded the dye within 120 minutes. Other effective substrates were anatase-coated stainless steel mesh and P25-coated fine stainless steel mesh. Glass fiber mesh and grout substrates had poorer performance. The document also describes the preparation, testing methods and goals of the research placement investigating photocatalytic water treatment using TiO2 coatings.

1. All Samples Comparable Degradation Testing
References
Treatment of Methyl Orange by Photocatalysis Floating Bed by Enqiang Wang,
Qiaoli Zheng, Shihong Xu & Dengxin Li
Porous Titanium Dioxide Coatings Obtained by Anodic Oxidation for
Photocatalytic Applications by Hernán Traid & MaríaVera
Effect of metal-doping of TiO2 nanoparticles on their photocatalytic activities
toward removal of organic dyes by M. Khairy
Synthesis of Silica Aerogel by Supercritical Drying Method by Tomasz
Błaszczyński ,Agnieszka Ślosarczyk & Maciej Morawski
Personal Experience
The placement for me has been invaluable and given me the opportunity to
experience a working lab. I have taken part in projects and experiments
containing complex chemistry and learned the practical things you cannot
read in a text book about the workings of a research environment. I must
thank Dr. Ian Mabbett, my Nuffield Project Mentor, Dr. Rachel Woods and Mr.
Ashley Pursglove whose passion for their project was infectious. I could not
help but be drawn into the excitement and enthusiasm that comes along with
a project which has the potential to save many lives and be very successful. I
am sure this project will succeed and am proud to be able to say I was a brief
part of it. More than anything else though, it has re-affirmed my desire to
follow this field as it has shown me the possibility to make a real difference
and revolutionise a practise performed worldwide is available for those who
are ready to work hard for it.
Results
My objective during testing was to gain results that showed the best type of
TiO2 paste and which substrate produced the best samples.The graph below
shows a directly comparable test as the conditions were constant for all of
the samples I made.This is the major test I carried out during my project and
it gives clear and incredibly useful results. The SSM with P25 has
outperformed all of the other samples, next is also SSM with anatase, so I can
say with certainty that the SSM is the best substrate to coat out of all the
substrates used so far. Despite having the fastest initial rate, third is the FSSM
with P25 which comes in before both GFM samples.The final 4 samples are
the grout samples.This means I can suggest that, the best sample is the SSM
then FSSM followed by GFM and finally the grout and overall, the SSM with
P25 paste has ultimately performed the best.
FSSM Sintered GFM Sintered SSM Sintered
Testing and the Set Up
The substrate samples I made for testing were 80x80mm, the materials we
used were either: glass fibre mesh (GFM), stainless steel mesh (SSM), an
extremely fine stainless steel mesh (FSSM) or a ‘self-cleaning’ grout. Next I
made the the TiO2 paste that is in the coating.The paste is made up from a
mixture of water, polymer binder and TiO2 nanoparticle powder. The TiO2
nanoparticles are in the P25 form which is seen as the best photoactive
blend between the rutile phase and anatase phase of TiO2.The paste must be
viscous but also have flowable characteristics. I used a glass rod to coat the
substrate with the paste using the draw down method. Next comes the
sintering stage where you must place the sample in an oven or on a hotplate
for an hour at 500oC, this is to remove any water or polymer binder from
the coating to ensure full dispersion of the nanoparticles which maximises
surface area. The substrate will be left with a thin TiO2 coating in the P25
form and is ready for testing.
To test the samples a shaker plate shook the dish to allow thorough mixing
of the solution during the breaking down of the dye. UV lamps were used to
provide photons to be absorbed by the sample. Distilled water was used for
a zero value for absorbance from the UV/VIS spectrometer. 100ml of 10ppm
indigo carmine dye was broken down in the test. An initial value was
recorded before the sample and dye were placed under the lamps, this
absorbance value was usually around 0.375 at 610nm wavelength. The test
was run until the absorbance value at 610nm was zero or three concordant
values were recorded in succession with an discrepancy of around 0.002
being allowed. Values for absorbance were recorded every minute for the
first ten minutes then every two minutes from thereafter. The degradation
showed a first order decay so this plan was suitable.
L: Samples I Made for Further Testing After My Placement
R: Polymer Binder Instantly Combusting Due to Heat at 750oC
Indigo Carmine Molecule
TiO2 Coatings for Degradation of
Organics by Photocatalysis
by David Sharp
Photocatalysis Process Involving TiO2
Background Research
Titanium dioxide (TiO2) nanoparticles can act as photo catalysts under
certain conditions.They can be sintered at high temperatures onto a surface
when heated in various ways including ovens, hot plate or near infrared (NIR)
machines. If this surface is then irradiated with ultra-violet (UV) light it causes
an electron from the valence metallic band to be excited into the conduction
band. When this electron undergoes relaxation an electron (e-) and a hole
(h+) pair are formed. If the pair survive recombination they will produce a
highly reactive species and will cause further reactions.The h+ in the valence
band will oxidise an anion to form a hydroxyl radical (.OH) whilst the e- can
reduce surface absorbed oxygen molecules to yield superoxide radicals
(O2
.-). These are an extremely reactive species. The hydroxyl radical is the
main species that participates in my investigations by degrading dye that has
contaminated water supplies. The dye we predominantly investigated was
indigo carmine (C16H8N2Na2O8S2). This dye is used as a model dye and has
other uses such as in jeans, milk and biscuits. However in high concentrations
it is an irritant and can cause permanent injury to the cornea and conjunctiva.
During my Nuffield research placement I was part of an investigation into the
treatment of water using photocatalysis after activating titanium dioxide
nanoparticles under UV light.This involved investigating curing and deposition
techniques of coatings with a view to integrating this concept into future
factory builds and design.