Access to clean and drinkable water has now not only become a local problem but global as well. Water contamination is one of the world’s leading causes of death and the problem is only getting worse. To tackle this, our team at Indian Institute of Science Education and Research (IISER), Pune came up with a custom-designed unique molecular sponge-like material — macro/microporous ionic organic framework — which can swiftly clean polluted water by soaking up sinister contaminants. The results were published recently in the journal, Angewandte Chemie.
Systematic studies have identified various organic (organic dyes, antibiotics, pesticides, etc.) as well as inorganic toxic pollutants such as iodides, oxo-pollutants like perrhenate that are carcinogenic in fresh water sources and can pose direct threat to humanity and living organisms.
In general, commonly utilised sorbent materials often trap these pollutants through ion-exchange strategy to purify water but suffer from poor kinetics and specificity. To mitigate this issue, our group prepared a newly engineered material called viologen-unit grafted organic-framework (iVOFm).
The material employs amalgamation of electrostatics driven ion-exchange combined with nanometer-sized macropores and specific binding sites for the targeted pollutants. The size and number of tunable macropores along with the strong electrostatic interaction of iVOFm can quickly remove various toxic pollutants from water.
To develop this unique material, our team employed a make-and-break strategy to grow a charged porous organic polymer (POP) as a sponge-like infinite framework on silica nanoparticles that is used as a template. Following this, the silica nanoparticles were strategically removed to create ordered hierarchical interconnected macro/microporosity throughout the material.
This material features inherent cationic nature and macroporosity to allow fast diffusion of pollutants. When tested for a wide array of water pollutants, it showed ultrafast capture of all the pollutants — both organic and inorganic — with over 93% removal in just 30 seconds.
Among all the tested pollutants, the new material showed ultrafast removal of sulfadimethoxine antibiotic from water almost completely. Even in the presence of other co-existing anions such as nitrates, chloride, and bromide, the removal of sulfadimethoxine antibiotic was extremely high within a minute. The engineered material could remove sulfadimethoxine antibiotic with high efficiency when tested using different real water samples.
The fast pollutant trapping capacity is attributed to faster diffusion of pollutants through the ordered interconnected presence of macropores in the material. We also found this material to be very selective toward toxic pollutants in presence of co-existing ions present in waste water even at low concentration. It can also be used several times to clean contaminated water just like a bath sponge can be utilised to tackle multiple water spills.
This cationic compound is adaptable for sequestering various pollutants and is a possible solution to the water pollution problem. These results open up a new avenue for the creation of numerous sophisticated sorbent materials for practical water filtration.
(Sujit K. Ghosh is Professor at Department of Chemistry, IISER Pune. Sahel Fajal is a research scholar at Department of Chemistry, IISER Pune and the first author of the paper.)