2nd February 2018
Optimising Hydrothermal Synthesis
Nanoparticles fascinate researchers since they are rich in applications. There are many methods to synthesise nanoparticles. One of the common methods is to synthesise nanoparticles hydrothermally. However, scientists find it difficult to optimize conditions for hydrothermal synthesis.
Recently, scientists from the IIT-Bombay and the Tata Consultancy Service, Pune have come out with a solution to overcome this issue. They developed a thermodynamic modelling framework for predicting the stability of a chemical species under hydrothermal conditions. Understanding the formation and stability of the chemical species under given process conditions is a necessary condition for designing the hydrothermal synthesis.
During hydrothermal synthesis, a metal precursor undergoes hydrolysis and condensation. The scientists, therefore, developed a model based on reaction temperature, pressure, concentration of reagents and pH. They validated the modelled thermal analysis results with experimentally observed hydrothermal synthesis results using ceric oxide and aluminium oxide, under both subcritical and supercritical temperatures.
The model proves to be useful to predetermine the stability conditions favourable for the hydrothermal synthesis of metal oxides, metals, and metal composite nanoparticles.
In addition, the scientists claim, the model will be helpful to determine the phase and morphology of the materials. “Synthesizing new materials require numerous trials. Our model makes the process time efficient and cost effective compared to the conventional hydrothermal synthesis methods’ they say.
Fluid Ph. Equilibria., 456: 33-45 (2018)
29 October 2017
Transparent SnO2 nanoparticles
Metal oxide nanoparticles – ZnO, SnO2, TiO2, CdO – are important for applications such as solar cells, gas sensing, liquid crystal displays and catalysis. Doping helps to alter the properties of metal oxides for specific applications. Co-doping transition metals also impacts the properties of metal oxides, facilitating even greater advantages in terms of applications.
Among these, SnO2 nanoparticles are a favourite among Indian scientists due to lower cost. Recently, Naseem Ahmad and Shakeel Khan from the Aligarh Muslim University reported doping SnO2 with manganese and cobalt. They examined the structural properties of the Mn-Co doped SnO2 using X-ray diffraction and observed that both lattice parameters and crystal size decrease with increase in doping concentration. This may be because of the smaller atomic radius of the cobalt ion.
Using Scanning Electron Microscopy, they found changes in particle shape and size.
When Co2+ ions displace Mn4+ ions, there are two extra electrons. From the optical property, they observed that the band gap value increases with increasing cobalt concentration. The researchers attribute this to the reduced crystallite size and lattice parameters.
The team also found that Mn and Co elements are present in the SnO2 from a compositional analysis using an Energy Dispersive X-ray spectrophotometer. The scientists say that the incorporation of cobalt atoms affects the photoluminescence properties of the emission spectra.
The evolution of electron charge carriers between conduction and valence band increases with increase in doping elements and thus enhances the electrical conductivity of the doped material. Therefore, it’s very useful for transparent conducting oxide materials and their applications.
J. Alloys Compd., 720: 502-509 (2017)
K Deva Arun Kumar