Progress of electrochemical Synthesis of Nitric Acid: Catalyst Design-Mechanistic insights-Protocol-Challenges

Nitrogen-based fertilizers are necessary to increase the agricultural output since nitrogen is the most frequent rate-limiting product. The main ingredients in almost all nitrogen-based fertilizers are ammonia and nitric acid; demand for these substances is significantly driven by global population and food production. Over the next few decades, the size and value of the ammonia and nitric acid markets will continue to be largely influenced by global population, which will have a significant impact on energy utility. Ammonia is synthesized via the high energy demanding Haber-Bosch process, and in the Ostwald process, ammonia is catalytically oxidized to prepare industrial grade nitric acid. As industrial synthesis of nitric acid requires astronomical units of energy and emits greenhouse gases into the atmosphere at an alarming rate. Hence, there is an immediate need to find an eco–friendlier alternative route to produce nitric acid. In the approaching century, the most advantageous method that has the potential to significantly alter the human lifestyle is the electrochemical production of nitrate/nitric acid by nitrogen oxidation. In this review article, we have discussed designs of catalysts, mechanistic insights and strategy adapted for in the electrochemical nitrogen oxidation reaction (N2OR). Emphasis has been made on the various challenges that exist during N2OR and the possible solution to overcome the hurdles

Advanced insights towards electrochemical urea synthesis: Strategic design and techno–commercial compatibility

The industrial production of urea involves two sequential steps, reaction of nitrogen and hydrogen to form ammonia followed by the reaction of the ammonia with carbon dioxide, so the process is capital expensive, massive energy consuming and complex synthesis process with multiple cycles to increase the production efficiency. The electrocatalytic C–N coupling reaction to specifically produce urea by simultaneous activation followed by co-reduction of carbon dioxide (CO2) and nitrogen sources (N2, NO2– or NO3–) at ambient condition presents a sustainable and eco-friendlier alternate route for urea production by a single step process. However, there are several challenges like adsorption capabilities of the reactants on the substrates followed by activation, suppression of hydrogen evolution reaction and finally effective C–N bond formation to specifically produce urea. In this work we showcase the road map of the electrocatalytic green urea production, with concise yet precise discussion on potential electrocatalyst, electrochemical working cell, mechanistic insight of urea synthesis, techno–commercial aspects and finally conclude with the future prospect of the green urea production

Effect of annealing on the defect-mediated blue phosphorescence in ZnO nanocrystals

Recently, UV/NUV excitable RGB phosphors with precisely tunable PL emission properties have been in high demand for their suitability in the fabrication of white LEDs. In this paper, we report to have tuned the PL intensity, shade, and color temperature of the defect-mediated blue phosphorescence of ZnO nanopowders by systematic annealing at different temperatures. The ZnO nanopowder was prepared by a facile and cost-effective aqueous solution-precipitation method. The as-synthesized nanopowder was annealed at different temperatures ranging from 150 degrees C to 850 degrees C and all these samples were characterized by XRD, FESEM, EDX, BET, Raman spectroscopy, and UV-Vis spectroscopy to have insight into their microstructural, compositional, and band-structure details. Optical studies of the samples were conducted by PL and tau-PL spectroscopy. Color coordinates of the samples were obtained from the CIE plots derived from the PL spectra. The CIE coordinates were further used to calculate the CCT values of the samples. tau-PL spectroscopy was carried out to measure the life-time of the photogenerated electrons. PL studies of the samples revealed that the blue emissions have red, yellow, and blue components originating from crystalline point defects, viz. zinc interstitial (Zn-i), and oxygen interstitial (O-i). Annealing at different temperatures triggered changes in the defect concentrations leading to the corresponding changes in the intensity, shade, and color temperature of the blue phosphorescence

Novel multiple phosphorescence in nanostructured zinc oxide and calculations of correlated colour temperature

The design and development of novel and high quantum efficiency luminescent materials, such as phosphors, having tuneability in properties, have received tremendous interest among scientists. In this paper, we have achieved for the first-time multiple phosphorescence (blue and green) having a life-time of similar to 10 mu s in nanostructured zinc oxide that was synthesized using an easy and facile sol-gel method. Importantly, the photoluminescence (PL) intensity and the phosphorescence life-time could be tuned by controlling the annealing temperature under a reducing atmosphere. Temperature and atmosphere dependent variation of V-O] and V-O(center dot)] has been interpreted by the detailed thermodynamic analysis of defect chemistry, for the first time. These nanostructured zinc oxide particles being sufficiently large in size (around 160 nm) are extremely stable and expected to show photoluminescence for a longer period of time than nanorods and quantum dots. The quantum yield was found to be as high as 13-15% which is comparable to the order of magnitude of that of quantum dots. The calculated correlated colour temperature is found to be suitable for cool lighting applications

Bane to boon: tailored defect induced bright red luminescence from cuprous iodide nanophosphors for on-demand rare-earth-free energy-saving lighting applications

The long standing controversy concerning the defect band in cuprous iodide (CuI) has been addressed in this paper from a technological point of view of its solid state lighting application. Recently, solid state lighting technology using nanophosphors has been proposed as the prime candidate in the energy saving lighting paradigm. Herein, we demonstrate a novel rare-earth free and non-toxic CuI nanophosphor, which has been synthesized via a facile solvothermal route. These nanophosphors are able to show ultra-bright and stable red emission under near UV excitation. The spectral features of this easily derived nanophosphor are not less than any rare-earth or cadmium based conventional phosphor. Furthermore, it has been conclusively verified that the deep red emission is strongly related to the excess iodine induced optimized defect level engineering in the band structure. The concepts and results presented in this paper clearly establish that the CuI nanophosphor is a promising 'green' material for the state-ofthe-art rare-earth free lighting and display applications

Modulation of Co-N4 active sites in 1D-2D heterostructure as bifunctional electrocatalyst for nitrate and nitrogen reduction reaction

Ammonia (NH3) is a key agricultural component and a source of clean energy as a hydrogen mediator. Ammonia is produced by Haber Bosch process, resulting in massive energy consumption and severe environmental impact. It is a thriving challenge to design and develop efficient nitrogen reduction reaction (NRR) and nitrate reduction reaction (NO3RR) electrocatalysts using variable reactants sources for ammonia synthesis at STP. 2D graphene sheets wrapped cobalt phthalocyanine nanotube to obtain (1D-2D) heterostructure, which serve as an active bifunctional electrocatalyst for NRR and NO3RR. At –0.2 V vs RHE, the electrocatalyst displayed NH3 yield rate of 58.82 μg h−1 mg−1 cat and a Faradaic efficiency (FE) of 95.12 % for NO3RR and 143.38 μg h−1 mg−1 cat and 43.69 % for NRR. Isotope tracing experiment confirmed the origin of ammonia synthesis. DFT calculations through Bader charge analysis revealed that charge transfer from the RGO to the Co-N4 sites in CoPc aided in the formation of NNH* @ NRR and *NOH @ NO3RR intermediates while impeding the competitive HER, resulting in high selectivity and FE. This study provides new mechanistic insights on the interfacial charge transfer, effect of work function and overpotential of electrocatalyst for their NO3RR and NRR utility