TiO2 anatase was prepared by a novel preparation approach, combining utilization of titanyl sulphate as a precursor and pressurized water processing. In addition, two different chemical methods for preparation were used - thermal hydrolysis and induced hydrolysis. The photoactivity of developed TiO2 was examined in two environmentally-prospective reactions: azo-dye AO7 photodiscoloration (oxidation) and N2O photodecomposition (reduction). It was revealed that during the processing the temperature has a crucial effect on TiO2 crystallization contrary to pressure. TiO2 anatase of smaller crystallite-size showed significantly higher photoactivity in AO7 photodiscoloration than TiO2 anatase of large crystallite-size. However, in N2O photodecomposition all synthesized materials showed comparable activity. While the TiO2 anatase crystallite-size and surface area are the determining properties in azodye AO7 photodiscoloration, the electronic band structure and recombination rate of electron and holes are determining in N2O photodecomposition. The correlation enabling the estimation of TiO2 anatase crystallite-size from Raman FWHMs was found as well. (C) 2017 Elsevier Ltd. All rights reserved.