Photocatalyst Activity of TiO2 Nanotubes

INDEX

Introduction………………………….…………………………… 1

 Problem Summary ……………………………………………….1

 Purpose: Goals and Objectives………………………………………… 2

 Scope……………………………………………………………2

System analysis and design………………………………………. 3

 Study of current system………………………………………………… 3

 Problem and weakness of current system……………………………… 3

 Requirements of new system…………………………………………….. 3

 Functions of newsystem……………………………………………….. 4

2.4.1 Metal oxide semiconductor………………………………………. 5

2.4.2 Usefulness of titania and its phases………………………………..5

2.4.3 Diagram……………………………………………………………6

System Implementation…………………………………………… 7

Summary…………….…………………………………………….8

Conclusion………………………………………………………….9

References………………………………………………………..10

Appendices………………………………………………………….11

ABSTRACT

In this work, we synthesized TiO2 nanotubes by hydrothermal route. The obtained particles were characterized and the photocatalytic activity was measured .In checking the photocatalic activity, dye was added and the absorption and degradation was measured. Various samples were prepared at different temperatures and their data were studied. The so obtained photocatalic activity was applied in water purification by using photocatalyst.

Introduction

1.1           Problem Summary

There has been use of photocatalyst since many decades for various purposes and not only water purification. The working of photocatalyst depends on its minimum wavelength required for its excitation.

Today, when we use photocatalyst for water treatment, it is generally operated under UV light but we’ve tried to do the same in the presence of direct sunlight.

For water treatment by photocatalysts (conventional) tasks like:

UV light source

Power source

Maintenance of the source

Dependency on particular source

So with the old approach it becomes more costly as we are using a UV light source as well as a power source to supply power to UV source. Replacement of the UV source after sometime, as well as the power consumption is the reason by which the process becomes a bit costly.

1.2           Purpose: Goals and Objectives

TiO2 nanotubes have a promising photocatalytic activity where it is able to get excited even in the presence of direct sunlight and hence the requirement of UV light source is no more. Due to removal of UV light source, we can also eliminate power source and hence it will be free from the operational cost.

1.3           Scope

As this system works in the presence of sunlight, it has no need for power supply. It is also pollution free and has more amount of absorption so even in presence of only sunlight it may work better than that of the conventional UV method. As it uses nanomaterials which have higher surface area to volume ratio they give more area for reactivity.

System analysis and Design

2.1           Study of current system

Currently, the water treatment is working on conventional photocatalyst to maintain the following tasks

Photocatalyst excitation by using only UV source

Treatment using RO

Micro membranes

Nano membranes

2.2           Problems or weaknesses of current system

Some drawbacks of current system are as follows:

Low efficient

Photocatalytic effect under presence of UV only

Somewhat towards an expensive side

2.3           Requirements of the new system

Functional requirements

Energy efficient

Low cost

More durable

Low maintenance

More efficiency

Chemical stability

Low toxicity

2.4           Functions of new system

2.4.1     Metal oxide semiconductor

Unlike conventional photocatalysts, nanophotocatalysts provide triumphing properties which includes a vast surface area to volume ratio which is helpful to achieve more reactivity.

Being in nanoscale and especially TiO2 nanotubes, the optical property found here is such that unlike the nanophotocatalysts and other used catalysts, it has ability to work under the presence of sunlight which finally gives a farewell to source of UV light.

Being a metallic semiconductor, there is a valence band (V.B.) and a conduction band (C.B.). By the presence of C.B. and V.B. we can see oxidation and reduction by which unstable compounds can be made stable.

When a photocatalyst is exposed by light with energy equal to or greater than band-gap energy, there is conduction process taking place of electrons from valence band to conduction band leaving a positive hole in the valence band.

The excited electron-hole pairs can recombine, releasing the input energy as heat, with no chemical effect.

If the electrons and holes gets migrated to the surface of the semiconductor without recombination, they can take part in various oxidation and reduction reactions with adsorbed species such as oxygen, water and other inorganic or organic species.

2.4.2     Usefulness of Titania and its phases

In previous researches, many researchers have found that as compared to many other semiconductors such as CdS, ZnO2, SnO2 and many more, TiO2 is more efficient because of better photochemical stability, photocatalytic activity, robustness against photocorossion, low price and nontoxicity.

 Three phases of TiO2 exist.

i)      Anatase

ii)    Rutile

iii) Brookite

Amongst all the three, anatase and rutile are vastly studied whereas brookite has been studied very less.

The position of oxygen ions on the exposed anatase TiO2 particle surface possesses a triangular arrangement which allows significant absorption of organic molecules. Whereas, the orientation of titanium ions in the anatase TiO2 creates an advantageous reaction condition with the absorbed organic pollutants.

Fascinatingly, these favorable structural arrangements of oxygen and titanium ions lacks in the rutile phase of TiO2. Therefore anatase phase of titania shows higher photocatalytic activity than rutile.

Anatase phase is reported to be the most photochemically active form of titaniumdioxide, but several researchers also shows less photocatalytic performance in pure anatase phase.

As there is rutile phase along with anatase TiO2, it brings together a wider pore size distribution and some part of mesoporosity which results to encrement in the photocatalytic activity for this phase.

 From these reports, we can conclude that rutile-anatase composites/mixture can be used to enhance photocatalytic efficiency.

2.4.3     Diagram

System Implementation

As stated earlier, the synthesis of the TiO2 nanotubes was done batch wise. Due to difference in the synthesis temperature, it was found that there was change in the phase.

The absorption was tested and from the studies done before it was known about the formation of phase at a particular temperature. To obtain desired phase, various factors were studied from the research papers and patents.

The further process includes coating this nanophotocatalysts in the inner part of a transparent vessel which can be placed in direct sunlight which will activate photocatalytic activity leading to purification of water filled into that vessel at that time.

The caotings will get degraded with respect to time which is to be tested further.

The degradation of coating also depends on pH, concentration of the photocatalysts (dosage), temperature, light intensity and other factors.

Summary

Advantages

Faster access

Easy to use

Reliable

Nature based service

More efficient as compared to older system

Low operational cost

Added functionalities

Portable

Can be accessed where there is sunlight

Problems Solved

Energy efficient

Portability achieved

Conventional sources removed

Environment friendly

No toxicity

Durability

Conclusion

By using nanophotocatalysts (especially TiO2 nanotubes), we can achieve water purification even if there is sunlight and hence there is no need of UV light source which also need a power source for it. It has no operational cost when compared to conventional method.

It is energy efficient as no energy is used while operation. Any transparent vessel can be coated which gives us liberty to coat small vessels as per requirement and this system can be made portable.

It has non-toxic elements which makes the product environment friendly.

Due to presence of composite phase, there is prominent increment in the photocatalytic activity as well as the reactivity. It provides larger surface area which as a result helps in saving the amount of the material used.

Due to less usage of the material it is again helpful in decrement of cost of making the product.

Degradation of the material cannot be predicted as it depends on temperature, pH, concentration of the nanophotocatalysts, oxygen, light intensity and many others.

References

Appendices

AEIOU Canvas

Empathy Mapping Canvas

Ideation Canvas

Product Development Canvas

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