Manasi Mulay stands in front of a poster which explains how to use chemistry to treat water micropollutants.

Using chemistry to treat water micropollutants: Manasi Mulay

Manasi Mulay’s latest paper reveals how to better use chemistry to treat water micropollutants. Called ‘micro’ because they occur in small concentrations, these pollutants nevertheless have serious negative impacts – such as antimicrobial resistance. In order to better understand Manasi’s paper we spoke to her about her research and what it means for water pollution.

Read the paper: Interaction of organic pollutants with TiO2: a density functional theory study of carboxylic acids on the anatase (101) surface.

1 Being a Grantham Scholar

Like all the Grantham Scholars (we’ve had 90+ so far) Manasi took part in a special training programme to help create the sustainability leaders of the future. Now that she’s finished her PhD, she’s returned to her family home in India. 

What was the Grantham Centre experience like for you?

At the Grantham Centre we get to learn about all sorts of different sustainability work. It’s inspiring. And also you have a ‘Grantham Centre family’. Even during the pandemic, the support provided by the Grantham Centre family was helpful. And I am very, very grateful.

A PhD is not just about studying, it’s also about overall development. So we are not just learning through our research but from human interactions too. Plus all the training at the Grantham Centre and the University of Sheffield. The Grantham Scholar experience was a comprehensive journey that I feel has prepared me well for the future .

Now I see why a PhD is ‘called a Doctor of Philosophy’. It’s truly been a philosophical journey.

How is it being home after such a long time?

I missed my friends and family and it’s so good to be back with them. I just want to take a break and relax and enjoy it. It’s great to have so many options of vegetarian food to eat and wear locally made fabrics. I missed all of that while in Sheffield.

But I do love Sheffield, it’s beautiful, and I miss it already. I miss the nature walks and the Peak District especially.

Do you know what you’re going to do now?

I’m still working on the corrections and taking some time off travelling.

It’s been a long journey since my undergrad (then my Masters and PhD). So now I feel I have travelled a lot for work. Now I am travelling within India but not for work. I’m spending some time painting, it’s so soothing to play with colours.


Grantham Scholar Manasi Mulay on a visit to parliament in the UK.
Grantham Scholar Manasi Mulay on a visit to parliament in the UK. Credit: Reena Sayani.

2 The problem: Water micropollutants

Manasi’s PhD research focused on a type of water micropollutant that have carboxylic acids. 

Why is it so important to remove micropollutants from water?

Even though the concentration is less, micropollutants have major impacts on people.

Firstly, they can have long-term impact on hormones.

Secondly, they cause antimicrobial resistance. So if antibiotics are going into our drinking water frequently then bacteria can get used to them.

Additionally there are some hazards that are still not known. It’s like an iceberg, we only know the very tip of the trouble.

Antimicrobial resistance alone is a huge problem isn’t it?

Yes. And it needs more attention because we are creating that pollution when we take medicine. I mean we can’t do anything about it, we need the medicine, but we must find a process to treat it.

It’s like that with pollution, some can be stopped at the pollution level, but some can’t. So we have to clean it up instead.

Interestingly other kinds of micropollutants are pesticides, as Nicole Kennard’s POSTnote outlines. That is an example where some of the pollution can be controlled, by not letting it into water channels for example.

3 The solution: Titanium dioxide

Manasi’s paper looks at the use of titanium dioxide in removing micropollutants from water. Specifically, she looked at a modification to current uses of titanium dioxide to see if they can be improved.

Can you tell us something about titanium dioxide?

Titanium is an element, in the periodic table it is ‘Ti’. When it is oxidised, that is titanium dioxide. This oxide has a different form and is useful for many things.

For example, titanium dioxide is present in a lot of cosmetics. And it is used as a pigment. If you go into an art shop and look at a tube of white acrylic paint, you will likely see it listed as an ingredient.

We are in contact with titanium dioxide regularly in our sunscreen lotions. And then comes this interesting use as a photocatalyst.

What uses has it been put to as a photocatalyst?

It has been used to remove air pollution. For example, in Sheffield we have seen it used to coat a banner on the side of a building as a ‘catalytic poem’.

It has also been used as self-cleaning glass for windows. And it is used to remove pollution from water, which is the use my paper focuses on.

Where does the oxide come from?

It is naturally available through the minerals but also for particular functional applications it is generated. ‘Functional’ means for particular usage, like we want to treat water micropollutants. These are particular applications in contrast to pigment or cosmetics.

And for the functional applications, we need some particular properties of that material. It cannot be simply used as it is available in nature. Instead we need to make it in a particular form and so make it functional towards a particular property for a particular application. For these reasons we may synthesise it in a laboratory.

So what are these properties of synthesised titanium dioxide which makes it useful?

One thing is how it reacts with the pollutant.

But the most important thing – because it is a photocatalyst – is how it reacts with light.

Manasi Mulay - young Indian woman in an orange pinafore - stands in a botanical park in Sheffield. Behind her are trees, deciduous without leaver and one tall evergreen. She stands on a grass lawn and near her is a stone plant pot.
Manasi at the Botanical Gardens in Sheffield. Back home in India, Manasi misses Sheffield and the Peak District.

4 Photocatalysis: How light can help clean up pollution

Here Manasi explains how her paper reveals an easy way to make titanium dioxide a better photocatalyst and so remove more micropollutants.  

What is a photocatalyst?

As a lot of people learn at school, a chemical catalyst is something that allows a reaction to occur, or helps it go faster, without being changed itself.

And a photocatalyst is a catalyst that needs a light source to get activated. Without a light source, it doesn’t function.

So the most important thing for us to work out is how it reacts with light. And second, how it interacts with the pollutants.

So what did you learn about photocatalysis in your work?

There is a twist here. As you know, sunlight has different wavelengths, for example ultraviolet (UV) or visible light. It is in the visible range we see colours. Whereas UV light we can’t see with our own eyes, right? And that’s the twist.

Pure titanium dioxide can only receive the UV light. As a result, it’s not fully harnessing the potential that the sun provides.

And you improved titanium dioxide’s use of sunlight

Yes. We wanted to modify titanium dioxide so that we can get all of the blessings that the Sun is giving.

That’s what the last part of my paper says: if this photocatalyst is modified with carboxylic acids, then it successfully makes it work in the visible range of light as well.

And this increases the efficiency of titanium dioxide as a photocatalyst?

Yes. Now it can work in the visible range.

As a result, it is now more effective related to cost and time. So now the same exposure to sunlight may destroy more micropollutants.

5 Computational chemistry

Partly due to the pandemic, Manasi’s project at the University of Sheffield used computational chemistry rather than lab work. 

You used computer simulations rather than worked in a lab didn’t you?

Yes. I’m not synthesising things in the lab, I’m considering a model.

Initially the focus was also synthesis but during the pandemic we had to adapt and it became totally computational.

What is computational chemistry like?

You need to be considerate of the computer time, so for example you can’t run random calculations.

In fact, you have to really plan and design the number of calculations what will give you the required data to positively or negatively answer your hypothesis.

Do results have to be physically verified as well?

That’s a good question and I get asked it a lot.

Of course there is experimental backup, there is literature to benchmark the results. And this is coming from the theory, which is the robust ground on which these calculations are based.

6 Applications of chemistry to treat water micropollutants

Though it might sound obscure, Manasi’s results could have big impacts on water pollution. 

Manasi Mulay, a young Indian chemistry researcher with medium black hair and a read scarf around her neck, in her office. Behind her in a periodic table and a computer screen showing sciencey stuff.
Manasi in her office where she did her PhD research in computational chemistry and water pollution.

How is the titanium dioxide used to treat water pollution?

There are different options. For example, it can be used as a paint on films. It can be put on a film inside the water, and then that film can be taken out once the job is done.

Or other options are in a powder or particle form, then it can be in a powder bed. This powder bed doesn’t let the powder come out and mix with the water itself but still it interacts with the light and it does the work it needs to do.

So will your findings lead to new technology for water purification, or do they build on existing work?

It adds to what exists, like the Google Scholar tagline ‘standing on the shoulders of giants’.

We are adding a small bit on giant shoulders. Research is usually like that. It’s a continuous process: all of us together work towards a greater goal.

And how quickly do you think it will be used?

What we have discovered is a simple thing that can be done easily. It can be done by anyone who is already doing this.

They can just add carboxylic acid to titanium dioxide. And they can use this work as a reference for their understanding.

Your work shows how useful chemistry can be for sustainability

Exactly. How we treat pollutants depends on their chemistry. How well they bind, how they react with each other, how well they adsorb and so on.

These characteristics govern whether it is better to destroy them, change them into simplified forms or separate them out as a whole chemical. In this specific case, the micropollutants we talk about in this paper, are better destroyed . Whereas the PFAS pollutants [better known as ‘forever chemicals‘] are better filtered than destroyed.

One thing that needs to be considered is that it should not create secondary pollution. So what you are using for treatment should not actually create more pollution.

What is the by-product of titanium dioxide?

Interestingly, one thing we talk about in this paper, is an intermediate of one of the widely used pharmaceuticals carbamazepine that cause micropollutants. What I mean by intermediates are chemicals formed during the process of treating these micro pollutants.

The intermediates can create  a coating on the surface of the catalyst, which could prevent light coming in. But we found that rather than acting as a curtain and blocking light they actually make it more active in the visible region.

Access Manasi’s paper about titanium dioxide and water pollution.

And if you want more from Manasi on this subject, you might be interested in 2 more of her papers.

Water Pollution and Advanced Water Treatment Technologies.

TiO2 Photocatalysts for Degradation of Micropollutants in Water.

Photo credit for the main image of Manasi is Phebe Bonilla.