NEW DELHI — Researchers
at the S. N. Bose National Centre for Basic Sciences, Kolkata, an autonomous
institute under the Department of Science and Technology (DST), have found an
efficient, less energy-intensive, and environmentally friendly way to
synthesise hydrogen peroxide -- a chemical that is crucial to the industry for
disinfection, paper bleaching.
Hydrogen peroxide (H2O2) is a versatile oxidising agent that
is widely used in environmental disinfection, chemical synthesis, paper bleaching,
and fuel cells.
The team designed and prepared a series of covalent organic
frameworks (COFs) having good water affinity through careful control of the
hydrazone linkage density and studied their effect on the photocatalytic
performance for H2O2 generation. COFs are a new class of porous and ordered
polymers with modifiable catalytic sites and light-harvesting properties in the
visible range. It has emerged as a promising photocatalysts.
Currently, the growth in the H2O2 market is driven by the
increasing awareness of disinfection, the rise in the number of surgeries, and
the prevalence of hospital-acquired infections. More than 95 per cent of H2O2
is produced industrially using the anthraquinone oxidation process -- which is
very energy intensive, expensive, and produces many hazardous chemicals as
by-products.
Scientists have therefore been looking for an
environmentally friendly and economical strategy to produce H2O2 from renewable
resources with minimal environmental impact.
The study observed that the hydrazone-linked COFs provide
abundant docking sites for water and oxygen, thereby promoting water oxidation
reaction (WOR) and oxygen reduction reaction (ORR) - two main pathways for
photocatalytic H2O2 generation.
As a result, the hydrazone-linked COF exhibited exceptional
photocatalytic H2O2 production without external sacrificial electron donors
when irradiated with a 40 W blue LED.
Interestingly, “a significant amount of H2O2 was also
produced under sunlight irradiation, which outperforms most organic
photocatalysts under similar conditions, thus demonstrating a clean and
sustainable pathway,” said the team.
They showed that as-synthesized hydrazone-linked COFs can
generate a significant amount of H2O2 using an aqueous benzyl alcohol solution
(water: benzyl alcohol = 90:10).
The method also prevented the degradation of H2O2. The
“strategy of using a mixture of water-benzyl alcohol solution will be helpful
in developing a continuous flow reactor for the sustainable production of H2O2
and will reveal a laboratory-to-industry technology transfer for the benefit of
mankind,” noted the researchers.
