INST Mohali Develops Filter to Clean Dye Wastewater

The correct answer is the Institute of Nano Science and Technology, Mohali, which is an autonomous institute of the Department of Science and Technology. Its researchers held zinc oxide nanoparticles, prepared from a natural source, inside porous nanofibres of biodegradable polylactic acid and then applied light along with mechanical shaking to break down dyes in water. The work was published in the journal Advanced Functional Materials. The other three options are respected research institutions, but none of them was credited with this filter, which is why they are wrong. For the examination, link the institute with its parent department, with the two materials used in the membrane and with the laboratory of Aviru Kumar Basu, where the nanoparticles were synthesised from an extract of turmeric.

The correct answer is turmeric extract. The nanoparticles were synthesised in the laboratory of Aviru Kumar Basu using an extract of turmeric, in which naturally occurring compounds such as curcumin, flavonoids and phenolic compounds worked as the reducing and stabilising agents. This green route matters because it avoids the harmful reagents that conventional synthesis of nanoparticles depends on, so the material itself is made in an environment friendly way before it is used to clean water. The other options name plant materials that are often used in green synthesis research in general but were not the source here, which makes them plausible yet incorrect. Candidates should remember the pairing of turmeric with zinc oxide and curcumin's role as a reducing agent in this experiment.

The correct answer is 98.6 per cent in 120 minutes. Under light and ultrasonic excitation applied together, the membrane of polylactic acid and zinc oxide removed the colour of 98.6 per cent of methylene blue in that time. Option C gives the figure for the other dye tested, congo red, which lost 96.7 per cent of its colour in the same period, so it is a close but wrong choice. Options A and B are wrong because those percentages belong to the antibacterial results: the material inactivated about 75 per cent of E. coli and 71 per cent of S. aureus after 6 hours of contact. Keeping the dye results and the germ killing results apart is important, since a paper setter will often swap one figure for the other in the options.

The correct answer is photocatalysis and piezocatalysis. The filter breaks down dyes using light and mechanical vibration at the same time. The vibrations create a piezoelectric polarisation in the material, which holds back the recombination of the electrons and holes generated by light and therefore raises the formation of reactive species that attack dye molecules. Options A and C are wrong because adsorption, flocculation, sedimentation and biological treatment are older approaches: the first group separates pollutants without necessarily destroying them, and biological treatment is slow for highly stable dyes. Option D names processes that were not part of this study. Remember also that putting the catalyst inside an electrospun membrane solves the practical problem of recovering nanoparticle catalysts from treated water.