Journal of Physics and Chemistry of Solids 168 (2022) 110826 Available online 4 June 2022 0022-3697/© 2022 Published by Elsevier Ltd. Microstructure of titania aerogels by reverse Monte Carlo simulations Emil Indrea a , Marcela-Corina Ros ¸u a, * , Ramona-Crina Suciu a , Teofl-Dǎnut ¸ Silipas ¸ a , Virginia Danciu b a National Institute for Research and Development of Isotopic and Molecular Technologies, 67 –103 Donat Street, 400293, Cluj-Napoca, Romania b Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, 11 Arany J´ anos Street, 400028, Cluj-Napoca, Romania A R T I C L E INFO Keywords: Titania aerogels Microstructure X-ray diffraction RMC simulations ABSTRACT The local atomic structure of TiO 2 aerogels calcinated at 450 ◦ C and 550 ◦ C has been studied in comparison with that of well-crystallized TiO 2 anatase by the X-ray diffraction (XRD) method and Reverse Monte Carlo (RMC) simulations. The infuence of calcination temperature on the crystallographic properties and microstructure of TiO 2 aerogels was discussed. The large X-ray line broadening of TiO 2 aerogels was due to the small crystallite size and lattice strain. From the traditional Williamson-Hall (W–H) analysis results, it was observed that the strain value decreased but the particle size increased as calcination temperature was increased. The TiO 2 anatase sample revealed an average particle size of about 62 nm and a very low strain in the nano-crystallite. The experimental X-ray structure factor was derived from the wide-angle X-ray scattering (WAXS) pattern after suitable data reduction. The partial atomic pair correlation functions g ij (r), like the g TiO (r), g OO (r) and g TiTi (r) have been revealed from RMC simulation with a fairly good stability and acceptable statistics. The structure model that best describes both the WAXS data consists of nano-crystalline TiO 2 with a highly distorted shell and a strained anatase-like crystalline core. The pre-existence of the anatase like core may be critical to the formation of single-phase nano-crystalline TiO 2 anatase in crystallization of highly porous TiO 2 aerogels upon heating. 1. Introduction TiO 2 photocatalysis continues to arouse interest for various appli- cations in energy and environmental felds. Bakbolat et al. [1] provided a brief overview (starting from 2017) on the recent advances of TiO 2 -- based photocatalysis in the hydrogen production and the degradation of organic pollutants in water. They had discussed important aspects related to TiO 2 photocatalytic activity, such as the mechanism of pho- tocatalytic processes, factors affecting the photoactivity, and new stra- tegies for improving TiO 2 performance in splitting of water with the evolution of hydrogen and degradation of organic compounds used for wastewater treatment. The photocatalytic water splitting over dope- d-TiO 2 was also reviewed by Ismael [2], explaining the infuence of different types of dopants, synthesis methods and several structural factors (such as crystallite size, phase structure, surface area, particle size distribution) on the enhancement of the photocatalytic activity of TiO 2 . These features can be tuned via controlling synthesis conditions of the TiO 2 -based nanostructures [3,4]. TiO 2 aerogels are one of the most important materials that present advantageous characteristics, including high degree of porosity and specifc surface area. Generally, TiO 2 aerogels are prepared by sol–gel procedure and supercritical drying [4,5]. The resulting TiO 2 aerogels are usually amorphous and do not posses photoactivity. The amorphous phase transformation to crystal- line TiO 2 ones (i.e. anatase or rutile) by calcination leads to an enhanced photocatalytic activity, but also changes in the specifc surface area and pore size distribution [6,7]. However, TiO 2 nano-crystallites may contain unusual forms of structural disorder that can substantially modify materials properties as shown by Deb and Chatterjee [8]. They demonstrated that nanocrystalline anatase TiO 2 prepared by chemical process (sol–gel route) have signifcant static disorder. Further, the phase transformation and the structural/microstructural changes of nano-TiO 2 with the annealing temperature was investigated using modifed Rietveld analysis of X-ray powder diffraction profles and transmission electron microscopy. Based on the experimental observa- tions, they concluded that the phase transformation is associated with a drastic grain growth, strain relaxation and reduced static disorder. Inspired by these fndings, the aim of our work was to investigate the infuence of calcination temperature on the crystallographic properties and microstructure of TiO 2 aerogels using X-ray diffraction technique and reverse Monte Carlo simulations. A comparison of partial atomic * Corresponding author. E-mail address: marcela.rosu@itim-cj.ro (M.-C. Ros ¸u). Contents lists available at ScienceDirect Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs https://doi.org/10.1016/j.jpcs.2022.110826 Received 5 May 2022; Accepted 28 May 2022