Nanoparticles to Remove Coral Bleaching Oxybenzone

Sunblocks contain a number of different compounds including oxybenzone which acts as a UV filter. The skeletal structural formula of oxybenzone is shown below:

Oxybenzone is soluble in water.
Before you go snorkeling in the Great Barrier Reef to be amazed by the beautiful corals, fascinating fish and other exciting wonders, you smother yourself in sunblock. When you step into the water, the oxybenzone starts to dissolve. Unfortunately, oxybenzone contributes to coral bleaching, the killing off of the tiny, colourful zooxanthellae marine algae that live inside corals. The result is that the coral loses its colour and appears white, as if it has been bleached.

Researchers have found a way to soak up the oxybenzone from the seawater using magnetite nanoparticles.

Magnetite, Fe₃O₄ , is a mineral made up of iron(II) and iron(III) oxides and is one of the main iron ores, that is, magnetite is mined in order to produce iron. Magnetite is ferromagnetic, that is, it is attracted to a magnet. It is the most magnetic naturally occurring mineral on Earth. If you could get the oxybenzone in the seawater to attach to magnetite nanoparticles then you could pull the oxybenzone out of the water using a magnet.

First, the researchers coated the magnetite nanoparticles with sodium oleate. The skeletal structural formula of sodium oleate is shown below:

Next, they oxidised the oleate coating to increase the number of hydroxyl (OH) functional groups:

Since oxybenzone can interact with other molecules via hydrogen bonds, magnetite nanoparticles  covered in a coating rich with hydroxyl functional groups increases the interactions between oxybenzone and the nanoparticles. Once the oxybenzone has hydrogen bonded to the nanoparticle coating, a magnet can be used to extract the particles from water.

Does it work?
One brave researcher applied sunblock, stepped into the ocean, waited 10 minutes, then collected a sample of the surrounding seawater. Back at the lab, chromatography was used to determine the concentration of oxybenzone in the water, 1.3 ppm. This is a disturbing result since it is known that the concentration needed to bleach coral is measured in parts per billion.
Next, the researchers prepared seawater samples. Some had no magnetite nanoparticles added, others had the nanoparticles added. Then they added 30 ppm oxybenzone to  all the samples. The concentration of oxybenzone in the samples with no nanoparticles did not change in an hour. In the samples that contained the nanoparticles, 95% of the  oxybenzone  was removed within the hour.

Reference
American Chemical Society. "Sopping up sunblock from oceans to save coral reefs." ScienceDaily. ScienceDaily, 21 August 2017.

Further Reading
Solutions Concepts
Water as a Solvent
Transition Metals (magnetism)
Fatty Acids
Carboxylic Acids
Nanoparticles and Nanotechnology
Parts per Million (ppm)
Chromatography
Experimental Design
Variables
2-Dimensional Structural Formula
Skeletal Structural Formula
Molecular Formula

Suggested Study Questions

1. For a molecule of oxybenzone:
• draw the 2-dimensional structural formula
• give the molecular formula
2. On the 2-dimensional structural formula of oxybenzone identify and name each functional group present.
3. Use diagrams to explain why oxybenzone is soluble in water.
4. Draw the 2-dimensional structural formula for oleic acid.
5. On your structural formula of oleic acid, identify and name the functional group(s).
6. Suggest a method by which you could change oleic acid into sodium oleate in the laboratory.
7. Suggest a method by which you could oxidise sodium oleate in the laboratory.
8. Explain the term "nanoparticle".
9. Why do you think the researchers chose nanoparticles of magnetite rather than bulk magnetite for this research?
10. Consider the description of the experiment used to determine the effectiveness of the magnetite nanoparticles in removing oxybenzone from seawater:
• What was the hypothesis being tested?
• What was the aim of the experiment?
• What variables need to be considered in this experiment?
• What is the independent variable in the experiment?
• What is the dependent variable in the experiment?
• Which variables are constant variables in the experiment?
• Why did the experimenters add nanoparticles to some samples but not to others?
• Write out a suitable method for this experiment.

Cyclodextrin

Researchers at Temple University's Water and Environmental Technology (WET) Center have been investigating the use of cyclodextrins in the treatment of waste water.
Cyclodextrins are made up of sugar molecules, bonded together to form a ring. An example of the structure of a cyclodextrin, alpha-cyclodextrin which is a 6-membered sugar ring, is shown below:

Cyclodextrins can be used in water treatment because they can bond to substances such as toxic organic compounds or heavy metals and hold them inside the ring structure. Owing to the many polar OH functional groups, cyclodextrins are water soluble, but the researchers have produced insoluble materials by coating a thin layer of cyclodextrin on sand, glass, silica and filter paper. Doing this allows the absorbent material to be collected, washed and re-used.

Reference:
Temple University (2013, September 24). New adsorbent is more effective and environmentally friendly for treating wastewater. ScienceDaily. Retrieved September 30, 2013, from http://www.sciencedaily.com­ /releases/2013/09/130924174152.htm

Further Reading
Carbohydrates: http://ausetute.com.au/members/sugars.html 
Functional Groups: http://ausetute.com.au/fungroup.html
Solubility: http://ausetute.com.au/intermof.html

Zeolites: http://ausetute.com.au/members/zeolites.html
Polymers: http://ausetute.com.au/members/polymers.html 

Suggested Study Questions:

1. What does the "cyclo" part of the name in cyclodextrin refer to?
2. Use the structure above to determine the molecular formula for alpha-cyclodextrin.
3. Use the molecular formula to determine the empirical formula for alpha-cyclodextrin.
4. Calculate the percentage composition of alpha-cyclodextrin.
5. Draw the structure of alpha-cyclodextrin and locate and identify the functional groups.
6. Use a diagram to explain how alpha-cyclodextrin dissolves in water.
7. Use a diagram to explain how alpha-cyclodextrin could be used to remove lead ions from water.
8. Draw the structure of alpha-cyclodextrin an clearly identify all 6 of the sugar molecules making up the structure. 
9. Activated carbon is commonly used to remove contaminants from water. What benefits do you think there might be in using cyclodextrin-derived absorbant materials instead of activated carbon? 

4 Water Experiments to Download

The International Year of Chemistry may be over, but you can still contribute to the Global Experiment until the end of March.

There are 4 experiments to conduct using water:

1. Acidity
2. Salinity
3. Build a water filtration unit using household materials
4. Using solar energy to purify water

You can download the details of all 4 experiments at

http://water.chemistry2011.org/web/iyc/experiments

You will be able to conduct the 4 experiments in class and submit your results to the website until 31^st March.

Even if you can't upload your results to the website, the 4 experiments above make a terrific teaching and learning resource for the future!

Titanium Dioxide To Treat Water

Scientists have discovered that adding silicone to titanium dioxide increases its ability to degrade aerosol and water-borne viruses.

Titanium dioxide (titanium IV oxide) is a naturally occurring compound that is used as a pigment in white paint, in sunscreens, in food colouring (E171), and as a disinfectant, used to kill viruses and bacteria and decompose organics via photocatalysis.

Silicone sealant is used to join glass plates in aquaria, silicone grease and lubricants are widely used in the automotive industry, silicone is used in cookware, liquid silicone is used as a dry cleaning solvent, silicone in gel form is used in medicine, and silicones are found as ingredients in shampoos, hair conditioners and gels.

Silicones are polymers made up of silicon as well as carbon, hydrogen, oxygen and sometimes other elements. They have the general chemical formula [R₂SiO]_n, where R is an organic group. Silicone polymers have an inorganic silicon-oxygen backbone: -Si-O-Si-O-Si-O-Si- with organic side chains attached to the silicon atoms.

Silicones can be produced from the reaction between chlorosilanes and water:
nSi(CH₃)₂Cl₂ + nH₂O →[Si(CH₃)₂O]_n + 2nHCl

In places where they don't have water treatment plants, water is disinfected using the SODIS method in which water is exposed to sunlight for its heat and ultraviolet radiation, but it takes a very long time to make water safe to drink. Treating titanium dioxide with silicone before adding it to the water sample to be disinfected can drastically reduce the time taken to disinfect the water.

Reference
Huma R. Jafry, Michael V. Liga, Qilin Li, Andrew R. Barron. Simple Route to Enhanced Photocatalytic Activity of P25 Titanium Dioxide Nanoparticles by Silica Addition. Environmental Science & Technology, 2010; 101231104927031 DOI: 10.1021/es102749e

Further Reading
Pure Substances and Mixtures
Elements and Compounds
Percentage Composition
Yield
Gravimetric Analysis
Water Analysis

Study Questions

1. What is the formula for titanium dioxide?
2. Calculate the percentage of titanium in titanium dioxide.
3. Calculate the percentage of oxygen in titanium dioxide.
4. A 100g sample of crude titanium oxide ore was known to contain 70% titanium dioxide. Calculate the mass of titanium present in this ore sample.
5. One method for obtaining pure titanium dioxide is to reduce the crude ore with carbon, then oxidize it with chlorine to produce titanium tetrachloride. The titanium tetrachloride is then distilled, then oxidized in a pure oxygen flame or plasma to produce pure titanium dioxide and regenerate the chlorine. Draw a flow chart to represent this purification process.
   
6. What property of titanium dioxide makes it useful as a pigment in white paint?
7. What is the formula for chlorosilane?
8. Given the general silicone formula [R₂SiO]_{n, calculate the percentage of carbon present in each of the following silicones:}
   
• R = methyl groups
  
• R = ethyl groups
• R = propyl groups
• R = butyl groups
9. Draw a structure for a silicone in which R are methyl groups.