This team of researchers from Japan has developed an ultrathin membrane with a fouling-resistant silica surface treatment for high performing separation of oil and water. The team was led by Professor Matsuyama Hideto and Professor Yoshioka Tomohisa at Kobe University’s Research Center for Membrane and Film Technology.
The development of technologies to filter oily emulsions in order to increase the amount of available clean water is gaining increasing attention. It is said that by 2025, two thirds of the world’s population won’t have sufficient access to clean water. The method developed by the Japanese team separates oil from water, and is crucial for dealing with oil spills and water pollution generated by various industries.
Membrane separation is considered to be low cost, energy efficient alternative to traditional purification methods such as centrifugation and chemical coagulation. However, some membranes suffer from fouling issues whereby droplets of oil get irreversibly absorbed onto the surface. This leads to membrane pore blocking, which reduces its efficiency.
In this study, researchers succeeded in developing a membrane consisting of a porous polyketone (PK) support with a 10-nanometre-thick silica layer applied on the top surface. This silica layer was formed onto the PK fibrils using electrostatic attraction- the negatively charged silica was attracted to the positively charged PK.
The PK membrane has a high water permeance due to its large pores and high porosity. The silicification process- the addition of silica on the PK fibrils- provides a strong oil-repellent coating to protect the surface modified membrane from fouling issues.
Another advantage of this membrane is that it requires no large pressure application to achieve high water penetration. The membrane exhibited water permeation by gravity- even when a water level as low as 10cm (with a pressure of approx. 0.01atm) was utilised. In addition, the developed membrane was able to reject 99.9% of oil droplets- including those with a size of 10 nanometres. By using this membrane with an area of 1m2, 6000 litres of wastewater can be treated in one hour under an applied pressure of 1atm. It was also shown to be effective at separating water from various different oily emulsions.
As mentioned, the silification provided a strong oil repellent coating. Through the experiments carried out on the membrane to test its durability against fouling, it was discovered that oil did not become adsorbed onto the surface and that the oil droplets could be easily cleaned off. This membrane showed great tolerance against a variety of acidic, alkaline, solvent and salt solutions.
The ultrathin membrane developed by this research group has demonstrated efficient separation of water from oily emulsions, in addition to anti-fouling resistance. Technology to separate emulsions is indispensable in the fight against water pollution and clean water shortages. It is hoped that this development could be utilised in the treatment of industry waste water.