Quality by design approach for SrTiO3 perovskite nanomaterials synthesis

The current environmental and energy concerns at global level drive toward politics of sustainable development for a green economy growth. In this scenario, chemical sensors play an important role in regulating energetic, ecological, and productive efficiency because of their excellent potential to develop technology for online gas emissions monitoring and feedback system control. Since sensor performances are affected by size, morphology, crystalline structure, and stoichiometry of the sensing materials, the aim of this work is to study how the synthesis conditions affect the properties of sensing nanoparticles of strontium titanate perovskite oxide and develop mathematical models with predictive ability for the design of materials. The investigated ranges of operating conditions were pH levels from 2 to 12; CA/NO3 molar ratio from 0.09 to 0.17; CA/M molar ratio from 0.63 to 2.00, where CA, NO3, and M terms are related to citric acid, nitrate ions, and the total metals, including strontium and titanium. The results confirm that fuel-to-oxidizer molar ratio of the initial solution affects the properties of the synthesized nanopowder because of its significant effects on flame temperature, burning rate, and reaction time. Depending on the synthesis conditions, the crystallite size changes from 10 to 30 nm and the grain size from 20 to 50 nm. From reacting solution with stoichiometric amounts of fuels and oxidizers, it was obtained more crystalline, pure, and nanosized perovskite oxide powder. In addition, the solution acidity and the complexing agent amount affects the dissolution of metal ions, reflecting upon the homogeneity of the dried gel and the characteristics of the final products in turn. Finally, a quality by design approach, using multiple regression analysis, was successfully used to study the combustion synthesis process by defining the direct and indirect effects of pH, CA/NO3, and CA/M on synthesized nanomaterial properties.