SEGH Articles

# The nano way to cleaner water

04 April 2012
Nanomaterials provide potential for waste water remediation and metal removal and recycling. We envisage that this composite can cheaply and effectively be incorporated into a variety of configurations to improve water treatment.

Decontaminating polluted waste water costs millions but a new discovery by scientists at the University of Brighton could result in huge savings as well as delivering safer, cleaner water. The research, recently published in the journal Angewandte Chemie International Edition, represents a significant shift in our understanding of (nano)chemistry. Mercury is a serious contaminant so this breakthrough could save millions of pounds.

It is generally accepted that when silver is reduced to nano-sized particles, it can only extract a certain amount of mercury. However, Dr Kseniia Katok, working in the Nanoscience and Nanotechnology Group at Brighton, was able to reduce nanoparticles of silver to below 35 nano-metres in diameter (the equivalent of splitting a single human hair into 3,000 separate strands) and found that this allowed almost twice as much mercury to be removed from water.

The team's breakthrough opens the way for more effective, cheaper ways of cleaning mercury-contaminated water. Existing clean-up methods for mercury-contaminated water have either low mercury removal capabilities, leave a large chemical waste footprint or are not energy efficient.

Mercury is found naturally in the environment, but levels of inorganic mercury have increased significantly in recent decades as a result of industrial processes, and mining activities. If mercury contamination occurs, a hugely expensive decontamination process is required, as occurred in Squamish in Canada where the whole of the waterfront was subject to a huge clean-up starting in the 1990s. The seafront town had been subjected to years of industrial pollution because of its forestry industry which began in the early 20th century. Just the chemicals used to clean the water cost around \$50,000,000. The Brighton scientists say their research shows that using silver nanoparticles would cost a few thousand rather than tens of millions of pounds for the materials, although a device containing the silver nanoparticles capable of processing large quantities of water would need to be developed.

Dr Raymond Whitby, head of the Nanoscience and Nanotechnology Group, said: "The amount of mercury taken into silver nanoparticles defies our current understanding and promises a number of exciting developments. For example, it should lead to improved water treatment, removing greater quantities of selected heavy metals more quickly and perhaps more cheaply than before."

One key element in Dr Katok's discovery is her use of chemically-modified quartz sand, which reduces silver particles to a nanoscale with a high degree of purity. Sergey Mikhalovsky, the university's Professor of Materials Chemistry and Dr Katok's co-supervisor, said: "This is the biggest difference between our silver and that prepared by other commonly-used methods such as citrate reduction, which typically leaves residual chemical groups on the surface of the silver nanoparticles. These can cause unwanted side reactions that may have limited its effectiveness." He anticipates that modified quartz could be used in other chemical groupings and might, in the future, aid the extraction and recycling of precious metals such as platinum, palladium and gold.

Andy Cundy, the university's Professor of Applied Geochemistry and Dr Katok's lead supervisor, said: "These findings enable a major shift towards the use of nanomaterials for waste water remediation and metal removal and recycling. We envisage that this composite can cheaply and effectively be incorporated into a variety of configurations to improve water treatment, initially targeting mercury, which remains one of the key environmental contaminants globally."

Professor Andy Cundy, University of Brighton. a.cundy@brighton.ac.uk

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Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Distribution of metal(loid)s in particle size fraction in urban soil and street dust: influence of population density 2020-01-18

### Abstract

Assessment of street dust is an invaluable approach for monitoring atmospheric pollution. Little information is available on the size distribution of contaminants in street dusts and urban soils, and it is not known how the population density would influence them. This research was carried out to assess the size distribution of trace metal(loid)s in street dust and urban soil, and to understand how population density might influence the size-resolved concentration of metal(loid)s. Three urban areas with a high, medium and low population density and a natural area were selected and urban soil and street dust sampled. They were fractionated into 8 size fractions: 2000–850, 850–180, 180–106, 106–50, 50–20, 20–10, 10–2, and < 2 µm. The concentration of Pb, Zn, Cu, Cd, Cr, Ni, As, and Fe was determined, and enrichment factor and grain size fraction loadings were computed. The results indicated that the concentration of Pb, Zn, Cu, Cd, and Cr was highly size dependent, particularly for particles < 100 µm, especially for street dust. Low concentrations of Ni and As in street dust and urban soil were size and population density independent. Higher size dependency of the metals concentration and the higher degree of elemental enrichment in the street dust fractions than the urban soils indicate higher contribution of human-induced pollution to the dust. Findings also confirm the inevitability of size fractionation when soils or dusts are environmentally assessed, particularly in moderately to highly polluted areas. Otherwise, higher concentrations of certain pollutants in fine-sized particles might be overlooked leading to inappropriate decisions for environmental remediation.

• Soil–plant system and potential human health risk of Chinese cabbage and oregano growing in soils from Mn- and Fe-abandoned mines: microcosm assay 2020-01-17

### Abstract

In Portugal, many abandoned mines are often close to agricultural areas and might be used for plant food cultivation. Soils in the vicinity of two Mn- and Fe-abandoned mines (Ferragudo and Rosalgar, SW of Portugal) were collected to cultivate two different food species (Brassica rapa subsp. pekinensis (Lour.) Hanelt and Origanum vulgare L.). Chemical characterization of the soil–plant system and potential risk of adverse effects for human health posed by plants associated with soil contamination, based on the estimation of hazard quotient (HQ), were assessed in a microcosm assay under greenhouse conditions. In both soils, the average total concentrations of Fe and Mn were above the normal values for soils in the region and their concentration in shoots of both species was very high. Brassica rapa subsp. pekinensis grew better in Ferragudo than in Rosalgar soils, and it behaved as an excluder of Cu, Mn, Fe, S and Zn in both soils. The HQ for Cu, Fe, Mn and Zn in the studied species grown on both soils was lower than unit indicating that its consumption is safe. The high Mn tolerance found in both species might be due in part to the high contents of Fe in the soil available fraction that might contribute to an antagonism effect in the uptake and translocation of Mn. The obtained results emphasize the need of further studies with different food crops before cultivation in the studied soils to assess health risks associated with high metal intake.

• Concentration, fractionation, and ecological risk assessment of heavy metals and phosphorus in surface sediments from lakes in N. Greece 2020-01-13

### Abstract

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, were investigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index Igeo values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as “unpolluted,” while many sediments in lakes Volvi and Kerkini were characterized as “moderately to heavily polluted” with regard to Cd. The descending order of potential ecological risk $$E_{\text{r}}^{i}$$ was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.