Direct synthesis of nanostructured TiO2 from inorganic metal salt for heterogeneous photocatalysis

Abstract

Nowadays there is a great concern about the energy crisis and environmental pollution worldwide. As a result, advanced oxidative processes (AOPs) have been studied and used to degrade organic and recalcitrant compounds. Titanium dioxide (TiO2) is the most used for heterogeneous photocatalysis. In general, the TiO2 synthesis by organic routes needs a subsequent heat treatment to eliminate volatile compounds and to obtain the desirable photocatalytic phase. In this work, for the first time, the inorganic synthesis of TiO2 NPs using simple reagents and water was performed in a one-pot reaction and without further heat treatment in order to obtain a photocatalytic semiconductor. A 23 factorial design was used to evaluate the factors (independent variables) that influence the synthesis via controlled precipitation, that is, pH (2 and 8), temperature (25 and 50 °C), and reaction time (5 and 30 min). The NPs were characterized by XRD, FTIR, DTA/TG, BET/BJH techniques, and their photocatalytic performance was determined as the discoloration of methylene blue dye to show the potential degradation of organic matter. The photoactivity of NPs was measured for methylene blue dye decolorization under ultraviolet radiation (UVA, 360 nm). The XRD analysis showed anatase as the only phase for all samples. Ti-O-Ti bonds were observed by infrared analysis (FTIR) and the specific surface area of the samples, determined by N2 adsorption (BET), were 112–118 m2/g, double to that of P25 Evonik (SSA = 50 m2/g). The mass loss was 15–45% due to the presence of water in the samples. However, the non-calcined TiO2 NPs presented 90% degradation of the methylene blue dye (4 ppm) after 3 h under UV radiation (360 nm), showing that the post heat treatment is not necessary for photocatalytic performance. The rate constant for all samples were near 0.0133 min−1. The nanoparticles synthesized via controlled precipitation using a metal salt and ammonium hydroxide proved to be a viable and promising route, because there is no need of a subsequent heat treatment. The route is a fast, one-pot method to obtain photocatalytic TiO2 NPs using simple salts as precursors and water as solvent, without further heat treatment, for the degradation of organic matter.