Nanomaterials recycling – way to the future

The way to the future – from internal recycling to the nanotechnology

Broadly speaking, recycling is a process of transforming waste into new materials. The benefits of this process are immense and mainly means reducing energy consumption by reusing raw materials, preserving natural resources, reducing the amount of residues shipped to landfills and installations of incineration, significant contributions to environmental protection (reducing greenhouse gas emissions due to the burning of millions of tons of plastics is essential, banning the leakage of contaminants from toxic substances), reducing the costs associated with this process. For achieving all these, complex technological chains were developed aiming at the transformation waste into new materials. Converting materials into nanoparticles and recycling them could be the optimum way to allow recycling, which would be impossible otherwise. Nevertheless, the recovery of nanoparticles raises new questions and they generate revolutionary ideas. Here they are, in an easy-to-understand form.

1. Recovery of nanoparticles "for doing good"

This idea relates to the decay of waste at nanoparticle levels and their recycling. Although tempting, only a few recycling and reuse strategies for nanoparticles have been developed until now. Essentially these strategies must be able to be exploited with low cost, to be consistent, fast and energy-efficient. The following experiments have succeeded and are already applied:

- separating nanoparticles containing iron from complex mixtures, using magnets. The technology is applied for purifying waste water.

- Obtaining silica carbide nanoparticles, a material with excellent thermal, chemical and mechanical properties, very often used in the abrasive industry. The technology uses discontinued CDs (electronic waste, with a total accumulation rate three times higher compared to the normal household waste), heated in a special furnace containing sand.

- processing of glass waste for obtaining silica nanoparticles, useful as energy storage elements in lithium-ion batteries. Glass debris is broken into very small pieces, cleaned with isopropanol (a common ingredient in antiseptic, disinfectants and detergents), mixed with salt and warmed in an oven containing magnesium.

Despite some undeniable results, the recovery and recycling of nanoparticles are difficult activities, as they tend to form complex mixtures, difficult to separate. However, the interest of companies is major because nanoparticles are often rare materials, which means that recycling is necessary to prevent a steep increase in the prices of these products over medium term, with the diminishing of resources.

Romania is also interested in recycling and developing studies in which nanoparticles are used for technology with high expectations in the future. In a recent study ("Exploiting thermoplastic polymers – recycled"), article supported by the Romanian Academy, Dr. Ing. Al. Grumezescu offers very interesting data on the results of treating PET-type plastic bottles with nanoparticles of several types. "The purpose of this study was to obtain and identify nanostructured membranes with specific consistency... based on recycled PET and inorganic nanoparticles with antimicrobial effect...". The results obtained by treating regular PET with zinc or silver nanoparticles show a pronounced inhibition of the development of microbial growth (Staphylococcus Aureus and Pseudomonas Aeruginosa) and open up significant perspectives for PET recycling, applied for sanitizing, filtration or air purification systems.

2. Recovery of nanoparticles "for avoid doing bad"

In experiments conducted so far there have been identified also "bad" nanoparticles. Several types of nanomaterials and nanoparticles used in industry but also in some commercial products proved to be toxic when recycling was attempted. These have to be disposed and there are intense studied and to allow the destruction of these nanoparticles. Thus, titanium dioxide nanoparticles, used in sun protection products, in electronics and in the production of paints in certain conditions can penetrate the skin, then penetrate into the bloodstream and affect the central nervous system. Silver nanoparticles in residual waters are one of the 15 elements harmful for biological diversity.

Disputes between partisans and recyclers of nanoparticles are intense and each side has serious scientific arguments, which proves that there are still plenty of areas to investigate. That is why nanotechnology is in the first interest group of emerging technologies, with budgets estimated at 75.8 billion dollars up to 2020.