Synthesis of Zn-doped TiO2 nanoparticles by the novel oil-in-water (O/W) microemulsion method and their use for the photocatalytic degradation of phenol

• Zn-doped TiO2 NPs synthesized by the novel O/W microemulsion method is reported.
• Doping with an optimum amount of Zn (5%) inhibits crystallite growth.
• Increased photodegradation of phenol in TiO2 doped with the optimal Zn amount (5%).
• 82% phenol mineralization and 93% degradation after 5 h for sample with 5% Zn.
• A mechanism suggesting tetrahedrally coordinated isolated Ti-oxide is proposed.

This investigation is focused on the synthesis of Zn-doped TiO2 nanomaterials by the O/W microemulsion method and their use for the photodegradation of phenol using a low power UV lamp. TiO2 nanoparticles with a size smaller than 20 nm and 100% anatase phase were obtained by this method. Thus, the Ti/Zn atomic ratio was varied and the nanomaterials were evaluated in the photodegradation of phenol, which was chosen for the photocatalytic test. The materials presented only the anatase phase upon calcination at 400 °C; phases corresponding to ZnO were not observed by HRTEM or SAED technique, which suggests the formation of Zn-doped TiO2. The crystallite size estimated from XRD data were dependent on Zn concentration; the material with the smallest crystallite size was the one with an Ti/Zn atomic ratio of 95/5 (7 nm); the particle size observed by TEM confirm these results. The Eg values obtained by diffuse reflectance did not vary significantly, values around 3.2–3.3 eV for the three samples were obtained. The photocatalytic tests showed that the materials are efficient for the degradation of phenol. The most active sample was the Ti/Zn 95/5 mixed oxide, with a phenol mineralization of 82% and 93% degradation after 5 h under irradiation. A mechanism suggesting the presence of tetrahedrally coordinated isolated Ti-oxide is proposed. The obtained results highlight the potential of the O/W microemulsion reaction method for the synthesis of efficient nanostructured photocatalysts such as TiO2 and Zn-doped TiO2 for the degradation of emerging pollutants.

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