Tag Archives: urea

Nanoparticle fertilizer and dreams of a new ‘Green’ revolution

There were hints even while it was happening that the ‘Green Revolution’ of the 1960s was not all it was touted to be. (For those who haven’t come across the term before, the Green Revolution was a better way to farm, a way that would feed everyone on earth. Or, that was the dream.)

Perhaps this time, they’ll be more successful. From a Jan. 15, 2017 news item on ScienceDaily, which offers a perspective on the ‘Green Revolution’ that differs from mine,

The “Green Revolution” of the ’60s and ’70s has been credited with helping to feed billions around the world, with fertilizers being one of the key drivers spurring the agricultural boom. But in developing countries, the cost of fertilizer remains relatively high and can limit food production. Now researchers report in the journal ACS Nano a simple way to make a benign, more efficient fertilizer that could contribute to a second food revolution.

A Jan. 25, 2017 American Chemical Society news release on EurekAlert, which originated the news item, expands on the theme,

Farmers often use urea, a rich source of nitrogen, as fertilizer. Its flaw, however, is that it breaks down quickly in wet soil and forms ammonia. The ammonia is washed away, creating a major environmental issue as it leads to eutrophication of water ways and ultimately enters the atmosphere as nitrogen dioxide, the main greenhouse gas associated with agriculture. This fast decomposition also limits the amount of nitrogen that can get absorbed by crop roots and requires farmers to apply more fertilizer to boost production. However, in low-income regions where populations continue to grow and the food supply is unstable, the cost of fertilizer can hinder additional applications and cripple crop yields. Nilwala Kottegoda, Veranja Karunaratne, Gehan Amaratunga and colleagues wanted to find a way to slow the breakdown of urea and make one application of fertilizer last longer.

To do this, the researchers developed a simple and scalable method for coating hydroxyapatite (HA) nanoparticles with urea molecules. HA is a mineral found in human and animal tissues and is considered to be environmentally friendly. In water, the hybridization of the HA nanoparticles and urea slowly released nitrogen, 12 times slower than urea by itself. Initial field tests on rice farms showed that the HA-urea nanohybrid lowered the need for fertilizer by one-half. The researchers say their development could help contribute to a new green revolution to help feed the world’s continuously growing population and also improve the environmental sustainability of agriculture.

Here’s a link to and a citation for the paper,

Urea-Hydroxyapatite Nanohybrids for Slow Release of Nitrogen by Nilwala Kottegoda, Chanaka Sandaruwan, Gayan Priyadarshana, Asitha Siriwardhana, Upendra A. Rathnayake, Danushka Madushanka Berugoda Arachchige, Asurusinghe R. Kumarasinghe, Damayanthi Dahanayake, Veranja Karunaratne, and Gehan A. J. Amaratunga. ACS Nano, Article ASAP DOI: 10.1021/acsnano.6b07781 Publication Date (Web): January 25, 2017

Copyright © 2017 American Chemical Society

This paper is open access.

Astonishing observation about gold nanoparticles and self-assembly

An Aug. 4, 2014 news item on ScienceDaily features research on self-assembling gold nanoparticles from Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) and Humboldt-Universität zu Berlin (HU, Berlin),

Researchers at HZB in co-operation with Humboldt-Universität zu Berlin (HU, Berlin) have made an astonishing observation: they were investigating the formation of gold nanoparticles in a solvent and observed that the nanoparticles had not distributed themselves uniformly, but instead were self-assembled into small clusters.

An Aug. 4, 2014 HZB press release (also on EurekAlert), which originated the news item, provides additional technical information about the equipment used to make the observations,

This was determined using Small-Angle X-ray Scattering (SAXS) at BESSY II. A thorough examination with an [a transmission] electron microscope (TEM) confirmed their result. “The research on this phenomenon is now proceeding because we are convinced that such nanoclusters lend themselves as catalysts, whether in fuel cells, in photocatalytic water splitting, or for other important reactions in chemical engineering”, explains Dr. Armin Hoell of HZB. The results have just appeared in two peer reviewed international academic journals.

“What is special about the new process is that it is extremely simple and works with an environmentally friendly and inexpensive solvent”, explains Professor Klaus Rademann from HU Berlin. The solvent actually consists of two powders that one would sooner expect to find in agriculture that in a research laboratory: a supplement in chicken feed (choline chloride, aka vitamin B), and urea. British colleagues discovered a few years ago that mixing the two powders forms a transparent liquid able to dissolve metal oxides and heavy metals, called deep eutectic solvent (DES). The researchers in Berlin then positioned above the solvent gold foil that they could bombard with ions of noble gas in order to detach individual atoms of gold. This is how nanoparticles initially formed that distributed themselves in the solvent.

The researchers did not expect what happened next (from the press release),

The longer the bombardment (sputtering) of the gold foil lasted, the larger the nanoparticles could become, the scientists reasoned. However, this was not the case: the particles ceased growing at five nanometres. Instead, an increasing number of nanoparticles formed over longer sputtering times. The second surprise: these nanoparticles did not distribute themselves uniformly in the liquid, but instead self-assembled into small groups or clusters that could consist of up to twelve nanoparticles.

These kinds of observations cannot be easily made under a microscope, of course, but require instead an indirect, statistical approach: “Using small-angle X-ray scattering at BESSY II, we were not only able to ascertain that the nanoparticles are all around five nanometres in diameter, but also measure what the separations between them are. From these measurements, we found the nanoparticles arrange themselves into clusters”, explains Hoell.

“We ran computer models in advance of how the nanoparticles could distribute themselves in the solution to better understand the measurement results, and then compared the results of the simulation with the results of the small-angle X-ray scattering”, explains Dr. Vikram Singh Raghuwanshi, who works as a postdoc at HU Berlin as well as HZB. An image from the cryogenic transmission electron microscope that colleagues at HU prepared confirmed their findings. “But we could not have achieved this result using only electron microscopy, since it can only display details and sections of the specimen”, Hoell emphasised. “Small-angle X-ray scattering is indispensable for measuring general trends and averages!”

The press release concludes thusly,

It is obvious to the researchers that the special DES-solvent plays an important role in this self-organising process: various interactions between the ions of the solvent and the particles of gold result firstly in the nanoparticles reaching only a few thousand atoms in size, and secondly that they mutually attract somewhat – but only weakly – so that the small clusters arise. “We know, however, that these kinds of small clusters of nanoparticles are especially effective as catalysts for chemical reactions we want: a many-fold increase in the reaction speed due only to particle arrangement has already been demonstrated”, says Rademann.

Here are links to and citations for the two papers the team has published on their latest work,

Deep Eutectic Solvents for the Self-Assembly of Gold Nanoparticles: A SAXS, UV–Vis, and TEM Investigation by Vikram Singh Raghuwanshi, Miguel Ochmann, Armin Hoell, Frank Polzer, and Klaus Rademann. Langmuir, 2014, 30 (21), pp 6038–6046 DOI: 10.1021/la500979p Publication Date (Web): May 11, 2014

Copyright © 2014 American Chemical Society

Self-assembly of gold nanoparticles on deep eutectic solvent (DES) surfaces by V. S. Raghuwanshi, M. Ochmann, F. Polzer, A. Hoell and K. Rademann.  Chem. Commun., 2014,50, 8693-8696 DOI: 10.1039/C4CC02588A
First published online 10 Jun 2014

Both papers are behind a paywall.

This research is being presented at two conferences, one of which is taking place now (Aug.5, 2014; from the press release),

Dr. Raghuwanshi will give a talk on these results, as well as providing a preview of the catalysis research approaches now planned, at the International conference, IUCr2014, taking place from 5-12 August 2014 in Montreal, Canada.

In the coming year, HZB will incidentally be one of the hosts of the 16th International Small-Angle Scattering Conference, SAS2015.

There you have all the news.