We are very familiar with cellulose, which is the primary component of the paper we use every day. In nature, it exists in plant cell wall and support the tree from falling down. When cellulose is broken up down to small fibers in nanoscale, it gains some excellent mechanical, thermal and optical properties. We call this small and amazing material nanocellulose. In a recently published paper, we described a some characteristics and uses of nanocellulose.
How can we make nanocellulose?
Nanocellulose can be made by mechanical treatment of cellulose pulp. By this method, we can get nanocellulose with a diameter of 10-40 nm. If we want to get smaller nanocellulose fibers (2-5 nm), we need to add enzymes or catalysts before this mechanical treatment. This method is energy-intensive and needs complex equipment. A greener way to get nanocellulose is by culturing specific bacteria like Gluconacetobacter xylinus. These bacteria only require a culture media in which to grow, very little energy and no complex equipment. The shortcoming of this method is that it is time-consuming.
[Read our blog post on the life cycle assessment of nanocellulose here]
Properties of nanocellulose
Because of its small diameter, nanocellulose exhibits many extraordinary properties. Its mechanical strength is comparable to that of carbon nanotubes and thus can be used for a multitude of applications, such as reinforcing polymers. Compared with cellulose, the ability to scatter visible light of nanocellulose is much weaker. Therefore, nanocellulose can be made into transparent films and paper. Those papers and films have larger porosity and surface area, which provide an excellent support, or substrate for housing guest nanoparticles. Because nanocellulose and nanoparticles have similar size, the nanocellulose/nanoparticle composite is expected to be more homogeneous than cellulose/nanoparticle composites.
Environmental applications of nanocellulose/nanoparticle composites
All kinds of nanoparticles such as gold, silver, palladium, platinum, etc., have been used for their excellent optical, catalytic, and antibacterial properties. However, because these particle tend to aggregate, there are limitations to their application in the real world. Nanocellulose can provide an excellent support for dispersing nanoparticles and keeping them from aggregating, which has the potential to maximize their abilities. As an environmental engineer, I am focused on the environmental science and engineering applications of these nanoparticle/nanocellulose composites, such as these:
A nanocomposite of silver nanoparticles + nanocellulose has the potential to be used as antibacterial filter. This filter has strong potential to overcome the biofouling problems of common filters. Besides, it is expected to have higher filtration efficiency and lower pressure drop in air and water use compared with traditional polymer filters.
Gold, platinum, and palladium nanoparticles have excellent catalytic properties for pollutant degradation. However, these properties only occur in very small and well-dispersed nanoparticles.. Nanocellulose can makes this synthesis easy due to its large surface area and abundant hydroxyl “anchors” on the surface. It was reported that the turnover frequency of gold nanoparticles + nanocellulose for the degradation of 4-nitrophenol was 840 times more powerful than that of a gold + polymer composite.
Nanocellulose can form a jelly-like hydrogel when it is wet. After freeze drying, the hydrogel becomes a sponge-like aerogel, which is super light and has abundant pores. Adding titanium dioxide to this aerogel makes it super hydrophobic. This light and hydrophobic material can float on water and absorb spilt oil from the water’s surface. It can absorb 20 to 40 times its own weight!
A nanocellulose hydrogel can be used to concentrate trace chemicals and create “hot spots” for detection using techniques such as surface-enhanced Raman spectroscopy.
Nanocellulose can be used for the fabrication of fuels and solar cells. Nanocellulose has better capacity to host nanoparticles than common polymers, so a nanoparticle + nanocellulose composite (or nanocomposite) can be used as an excellent anode catalyst in a fuel cell. And nanocellulose paper has the potential to be used as a solar cell substrate because it allows more solar light to reach the energy conversion material because of its amazing transparency.
Nanocellulose is a sustainable nanomaterial and a novel support material for nanoparticles. It opens an avenue for numerous novel nanomaterials which are promising to address the emerging environmental challenges.
Read more about this topic in our recently published paper:
Update: This paper was also featured in the ES:Nano Blog!