It’s DYI nanotechnology time again. Previously we’ve discussed a simple method to prepare superhydrophobic (water repellent) fabric coating and procedure to synthesize photo-catalytic zinc oxide nanoparticles. Today we will present a similarly easy method to prepare metal nanoparticles at your home with materials that are easily accessible. Infect, there’s a high chance you have everything you need for this synthesis at your home already. Although, the method can be used to prepare number of different types of nanoparticles including, gold, silver and nickel, we will discuss the synthesis of copper nanoparticles in this article. You may need to tweak the setup slightly to make other types of nanoparticles.
Copper nanoparticles are very interesting, not only because they show unique nanoscale phenomena like plasmonic absorption and high surface to volume ratio, but also due to useful properties like antibacterial and fungicidal activity. Copper nanoparticles and metal oxide nanoparticles of copper have widespread commercial presence, especially as fungicides. Copper fungicides are extremely effective against certain species of fungi that are common agricultural pathogens. Copper nanoparticles show good to great antimicrobial property against many pathogenic microbes and also used as a commercial antimicrobial agent. Liquid copper dispersions are used as an antimicrobial spray or to prepare antimicrobial surfaces. Other copper nanoparticle applications include conductive ink, chemical sensors, bio sensors etc. Some of these applications may be difficult for you to reproduce at home. But you can definitely test what we discuss in this article as an antimicrobial and/or fungicidal agent.
We will use a technique called electrochemical synthesis for the preparation of copper nanoparticles. Usually, copper nanoparticles are not stable and will slowly oxidize in to copper oxide nanoparticles with time. It would usually happen within one to two days. Liquid copper nanoparticle dispersion would appear in beautiful golden yellow color and will slowly turn to reddish black color when it oxidizes in to metal oxide nanoparticles of copper. Here is what you need for the synthesis of copper nanoparticles;
Two copper rods or sheets
A DC power supply ideally with 12 V setting
Two crocodile clips or similar wire connectors
250 ml of water ( great if you can use distilled water)
A beaker or glass cup which you can fill with hot water
A method to stir the water ( I used a magnetic stirrer, but simple DC motor with a propeller is more than enough for the job)
Ascorbic acid 1.0 grams or 5 tablets of Vitamin C (50 mg)
Chitosan 0.1 gram (optional)
Step 1: Add water to the glass beaker and bring it to boil. Then take the heat away and add ascorbic acid (or vitamin C pills) and chitosan (optional) and stir until they dissolve completely.
Step 2: Setup the electrodes and spacer and connect them to the positive and negative wires of the DC power supply.
Step 3: Turn on the power supply and set the voltage to a value between 6-12 V while the solution is still hot. If the connection is right, you would see small bubbles appearing from the cathode (the copper rod connected to the negative wire of the power supply)
Step 4: Keep the solution stirring. You would see the solution will slowly turn to light yellow color which develops in to a beautiful golden yellow color with slight reddish tint. This is when you should turn off the power supply.
Step 5: If everything went well, you will have a nice liquid copper dispersion having diameter in submicron range. It’s usual that you will have some component of particles with diameters higher than 100 nm. But that’s okay for a home experiment. If there are lot of these big particles, liquid copper dispersion would appear as blackish brown in color instead of bright yellow.
How nanoparticles form
In acidic conditions, copper metal (Cu) in the anode (copper rod attached to the positive wire of the power supply) oxidizes (loses electrons) to form copper ions (Cu+2). These copper ions are released to the solution and will slowly travel towards the cathode (copper rod attached to the negative wire of the power supply). At the cathode, these copper ions will gain electrons and reduces back to copper metal, leaving a metal deposit on the cathode side. This is the main concept behind, electrodeposition.
However, our system is bit different. We have ascorbic acid; a reducing agent (chemical that can donate electrons to induce reduction) in our solution. Also we heat up the solution to spice things up. Now, for the copper ions that are traveling across the solutions, the journey would not be as easy. This is because, copper ions present the ideal opportunity for ascorbic acid molecules to give off their electrons and reduce the copper ions to copper metal. Therefore, in our system copper particles will be formed well before copper ions reach to the cathode.
Ascorbic acid, will not only function as a reducing agent but also as a capping agent. This means that when small copper particles are formed, ascorbic acid molecules will cap or surround the particle making it difficult for similar copper particles to come near to each other. This prevents the uncontrolled growth of the particles to micron sized dimensions.
What to do with the solution
So there you have it. A DIY style method to synthesize copper nanoparticles. You can prepare copper nanoparticles as well as other nanoparticles using a similar strategy for a science fair or science exhibition. You can also try using this suspension as an antimicrobial spray. If you have a plant or a crop affected by a fungal disease you can try spraying this solution just to see the effect. You may need to play with the concentration but you will certainly see a big improvement. Also keep reading, you may find many interesting things to do with the copper nanoparticles that you made by yourself.