Prof Ranjit Thapa and his PhD scholar, Mr Samadhan Kapse from the Department of Physics have reported their euphoric achievement of discovering an economically viable electrocatalyst for effective green urea synthesis. The paper “Selective Electrocatalytic Co-reduction of N2 and CO2 on Copper Phthalocyanine for Green Urea Production” has been published in the highly prestigious Nature indexed journal, ‘Advanced Functional Materials’, having an Impact Factor of 18.81. It was published in collaboration with Jit Mukherjee, and Uttam Kumar Ghorai, from the Department of Industrial Chemistry & Applied Chemistry, Swami Vivekananda Research Centre.

With global annual production of 100 million tons, urea is one of the important nitrogen sources for the fertilizer industry. Industrial urea is synthesized by the following two consecutive steps. First, the reaction of nitrogen and hydrogen (N2 + H2 → NH3) by the Haber-Bosch process at high temperature and pressure (350–550°C, 150–350 bar); followed by the reaction of NH3 and CO2 [NH3 + CO2 → CO(NH2)2] under mild reaction conditions (170–200°C and 200–250 bar). The sequential reactions are carried out for several cycles to increase the conversion efficiency. For the first step, fixation of N2 is an energy as well as a capital intensive process due to difficulty in cleaving the N≡N bond. Extensive research works have been reported on electrochemical N2 fixation to NH3 in water medium under ambient conditions. In this electrochemical method, isolation of NH3 gas with high purity from electrolyte solution is troublesome. In the second step, CO2 fixation on the substrate and its separation is one of the major challenging tasks for the further reaction with NH3 to end up in urea formation. Overall, the two-step process for large scale production of urea consumes high energy and produces greenhouse gases for the environment.

The research team reported copper-phthalocyanine nanotubes (CuPc NTs) having multiple active sites as an efficient electrocatalyst which exhibits a tremendous yield of urea with good durability and long-term stability. DFT calculation predicts that Pyridinic–N1 in CuPc is responsible for N2 reduction and the metal centre plays an important role for CO2 reduction. This study not only provides us with the co-reduction of N2 and CO2 gases using cost-effective CuPc NTs catalyst but also opens a new pathway to the rational design of other transitional metal-based electrocatalysts having multiple active sites for N2 and CO2 gas fixation applications.

This electrochemical method of urea synthesis by the co-reduction of N2 and CO2 [N2 + CO2 + 6H+ + 6e– → CO(NH2)2 + H2O] using an efficient electrocatalyst in a water medium under ambient conditions would be an alternative way in the upcoming days. All the strategies using alloys and heterostructure for urea synthesis forming C–N bond by the co–reduction of N2 and CO2 have not reached the benchmark in terms of urea yield rate and FE for practical applications. To achieve a high urea yield and FE, various factors are to be considered in this work.

Abstract of the Research

Green synthesis of urea under ambient conditions by electrochemical co-reduction of N2 and CO2 gases using effective electrocatalyst essentially pushes the conventional two steps (N2 + H2 = NH3 & NH3 + CO2 = CO (NH2)2) industrial process at high temperature and high pressure, to the brink. The single-step electrochemical green urea synthesis process has hit a roadblock due to the lack of an efficient and economically viable electrocatalyst with multiple active sites for dual reduction of N2 and CO2 gas molecules to urea. Herein, the research reports copper-phthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metal centre, Pyrrolic-N3, Pyrrolic-N2, and Pyridinic-N1) as an efficient electrocatalyst which exhibits urea yield of 143.47 µg h-1 mg-1cat and FE of 12.99% at –0.6 V vs RHE by co-reduction of N2 and CO2. Theoretical calculation suggests that Pyridinic-N1 and Cu centres are responsible to form C–N bonds for urea by co-reduction of N2 to NN* and CO2 to *CO respectively. This study provides new mechanistic insight into the successful electro-reduction of dual gases (N2 and CO2) in a single molecule as well as the rational design of an efficient noble metal-free electrocatalyst for the synthesis of green urea.

Studies and research on air pollution have sparked worldwide interest in the recent decades to overcome the imminent threat of air pollution. The air filtration mechanism is one of the efficient ways to capture particulate matter (PM) and purify the air. An innovatory air filtration mechanism blending polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) polymer nanofibers has been proposed by Prof Ranjit Thapa and his PhD scholar Deepak S Gavali from the Department of Physics.

The paper “Low Basis Weight Polyacrylonitrile/Polyvinylpyrrolidone Blended Nanofiber Membranes for Efficient Particulate Matter Capture” was published in collaboration with Applied NanoPhysics Laboratory, Department of Physics and Nanotechnology, SRM Institute of Science and Technology, Kattankulathur. It was featured in the journal ‘ACS Applied Polymer Materials’ having an Impact Factor of 4.09.

In the twenty-first century, air pollution is a major problem facing human and environmental health. Every year, millions of people die, mostly in developing nations, owing to the aggravating level of air pollution. According to the World Health Organization (WHO), 92 per cent of the people live in places where the air quality level has crossed the WHO limits. Particulate matter (PM) (solid or liquid particles with different aerodynamic diameters), nitrogen dioxide (NO2), ozone (O3), and others are the relevant air contaminants.

In low-income cities, the effect of PM 2.5 pollution is high due to high urban air pollution. Even at very low concentrations, PM 2.5 (particles with an aerodynamic diameter less than 2.5 µm) pollution has health consequences. Air filtration is one of the best remedies to tackle such problems and maintain a clean environment for humans. Among the available air filter materials, fiber-based air filters have proven to be the most potentially effective treatment, due to their high porosity, high surface area, lightweight, etc.

This study relies on a careful design that blends PAN and PVP fibers. The resultant nanofiber material is utilized to overcome the low air pressure resistance issue with high filtration efficiency. Large-scale free-standing nanofibers were obtained by a simple peeling-off process. The morphology, chemical interaction between the filter media and PM pollutant; and filtration properties were investigated. Compared to commercial mask, the semi- high-efficiency particulate air (HEPA) filter media, PAN/PVP filter medium showed superior performance in PM 2.5 filtration. Furthermore, the intermolecular interactions between PMs and nanofibers were analyzed by DFT calculations. With constant optimization of synthesis conditions, the synthesized air filters achieved high filtration efficiency for PM removal and showed great potential for practical application.

Abstract of the Research

Particulate matter (PM) in air frequently poses a serious threat to human health. Smaller PM can easily enter into the alveolus and blood vessels with airflow. This work reports the first polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) polymer blend nanofiber filter media for effectively capturing PM. Density functional theory (DFT) calculations are used to investigate the effect of the blending of two polymers on the dipole moment and the electrostatic potential. Based on the DFT calculations of the intermolecular interactions between nanofibers and PM, the PAN/PVP heteromolecular percentage is considered for experimental synthesis, which can provide better performance in the filtration of pollutants. The composite PAN/PVP fiber network was successfully developed and optimized to cope with complex environments during the actual filtration process. The role of the blending ratio of PAN and PVP in wt % was explored on PM 2.5 capture, and the refined ratio overcame the conflict between high filtration efficiency and low air pressure resistance. The air filter medium PAN/PVP (6:2) possesses an extremely high air filtration efficiency of 92% under a very low pressure drop of 18 Pa for a 0.5 g m–2 basis weight. Both polar and nonpolar functional groups in blend nanofibers promoted significantly the electrostatic attraction and improved the filtration efficiency under static and dynamic airflow. The PAN/PVP nanofiber membranes maintain outstanding air filtration under different temperature and humidity conditions. This study will shed light on the fabrication of high-efficiency low-basis weight nanofiber filter media as an end product.