Nanoparticles probably receive more attention as pollution hazards than as pollution solutions. Efforts to reduce urban air pollution dangers have focused heavily on toxic particulates emitted from road vehicles and industrial processes; however, the very qualities that make small particles potentially hazardous enable them to do great things.
Firstly, small particles are penetrating – they quickly disperse into a material by squeezing past obstructions. In the presence of water, they can be carried deep by osmosis. Secondly, small particles give a material greater surface area in proportion to its mass. This means that chemical bonding is optimised, enabling less to do more. This valuable property is already critical for many industries, including medical drug delivery, lubricants, inkjet printing and car tyre production. Carbon black has been added to tyres since the 1930s – larger particles would make tyres weaker.
Applications in land remediation
Nanoparticle materials are likely to grow in importance as a soil remediation service.
Manufacturing facilities, landfills and mining sites are sources of groundwater and soil contamination. Before the 1980s, the attitude to domestic and industrial waste was ‘out of sight, out of mind. Since then, it has become apparent that many landfills, mining areas and watercourses pose a variety of toxic risks. Land that could provide new housing, new employment opportunities or new community facilities often needs lengthy remediation.
A soil remediation service provider often has to change a surface and subsurface chemically, biologically and physically by making the soil more stable or less permeable. Nanomaterials can help in all three scenarios.
Every new nanomaterial is carefully tested to ensure it won’t bond to toxins but instead carry them into the air.
A variety of techniques are used to produce nanoparticles. These include milling, chemical precipitation, gas condensation, hydrothermal processes, electrical spark ablation, and even plasma and lasers.
A soil remediation service always strives to tailor a solution to the specific pollution problem. The nanoparticle arsenal appears to offer great scope to do this; for example, amphiphilic polyurethane acrylate (APU) has a high affinity for phenanthrene, while nanoscale zerovalent iron (nZVI) is very effective against chlorinated solvents.
Other useful nanoparticles include nanoscale zeolites, metal oxides, carbon fibres and nanotubes, enzymes, titanium, and the noble metals. Some can be engineered to persist for up to eight weeks, which is enough time to percolate and flow wherever groundwater flows.