Nanotech for Water Purification – 2. Silver Nanoparticles



In this episode I talk about Silver Nanoparticles, and how they are helpful in killing harmful bacteria.

Silver and also Ag(1) group
Silver has valence state of +1 in general, though it also exhibits +2 and +3 states as well – these are the oxidation states coliform bacteria is found in wastewater – indicator used in assessing the sanitary quality of foods and water – they are Gram-negative – generally present in feces of warm blooded animals. They don’t cause serious problems, but their presence is an indicator of existence of other pathogens, bacteria, viruses etc. One of the types of coliform bacteria is Escherichia coli.

What are biocides – they destroy, deter or render harmless those organisms which are harmful. Enter silver nanotech particles. They are highly antibacterial because of their size and shape, low toxicity – these are effective biocides. Their applications have been increasing in industrial, environmental as well as medical applications. These days, silver nanofibers are used as first aid bandages, in self-cleaning fabrics. These fabrics don’t need to be washed again. Silver nanoparticles are used as active biocides against Gram positive and Gram negative bacteria, Escherichia coli – most strains don’t cause diseases, but virulent strains are a problem.

They cause gastroenteritis, urinary tract infections, neonatal meningitis etc. Staphylococcus aueras – Gram positive – bacteria – it is mostly commensal bacterium – which means that it feeds on humans without affecting us positively or negatively. But it can cause diseases too. A lot of skin infections happen due to this bacteria. A lot of boils, folliculitis, cellulitis happens due to these.

Food poisoning also happens due to Staphylococcus auerus, the illness due to the toxins it generates can last anywhere from thirty minutes to three days. Bone and joint infections are also caused by this bacteria. Three ways this can happen – osteomyelitis, septic arthritis and infection from a joint replacement surgery. It also affects a lot of animals. This bacteria can be killed using our silver nanoparticles.

Klebsiella pneumoniae is another bacteria which is gram negative. The infections caused by this are generally seen in those with a weakened immune system. Pneumonia, in the form of bronchopneumonia and bronchitis is a very commonly caused problem by Klebsiella pneumoniae. The death rate is around 50%, even with antimicrobial therapy, and about 100% for people with alcoholism and bacteremia. This bacteria can be killed by our silver nanoparticles effectively.

Another gram negative bacteria called Pseudomonas aeruginosa exists, which affects both animals and plants. It infects the airway and also causes blood infections. This pathogen is multidrug resistant. It has a lot of associations with serious illnesses, including HAI – which are hospital acquired infections. The organism is also very dangerous and it is categorized as an ‘opportunistic’ one. An opportunistic infection is one where pathogens take advantage of an opportunity not normally available. This bacteria is present in exoskeletons and droppings of domestic cockroaches – and it can reach us very easily.
Ag nanoparticles kill this bacteria effectively.

Silver nanoparticles are spherical or flake like the SSA is larger than 1 m2 per g. The antibacterial activity is dependent on the particle size and shape. An 8nm particle is a better bactericide, compared with the 11-23nm ones. Compared to spherical or rod-shaped particles, the truncated triangular silver nano-plates exhibit higher antibacterial effects. There is but a problem with ag nanoparticles. There is a loss of silver ions over time, due to which there is no long-term efficacy against membrane biofouling. Membrane biofouling means that the particle is deposited on a membrane surface or in membrane pores, so that the membrane’s performance is degraded.

So there is further scope of work in reducing this loss of silver ions over time for long-term control of membrane biofouling. This issue can be solved to an extent by doping the Ag nano-particles with other metallic nano-particles. This also simultaneously removes
inorganic/organic compounds from wastewater. Silver nano-particles, have been incorporated successfully in different polymers, to be used as antibacterial, antifungal, antiviral and antiinflamatory agents.

Silver nanoparticles incorporated into cellulose acetate fibers have been found to be effective against both gram negative and gram positive bacteria. Similarly, those incorporated into polyurethane nanofiber mats showed good microbial properties and also good antibacterial properties against E.coli

Ag nanoparticles, incorporated in polysulfone membranes was used as water filtration membranes, against e.coli, pseudomonas etc.

In this way, Ag nanoparticles are very useful to us.

Nanotechnology in Water Purification by Rocky DeRaze

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