Synthesis of CdS Sensitized TiO₂Photocatalysts: Methylene Blue Adsorption and Enhanced Photocatalytic Activities

Abstract

A series of CdS/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:math>nanocomposites with different Cd to Ti molar ratio were synthesized from P25-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:math>nanopowder using microwave-assisted hydrothermal method. The as-produced powders were characterized by XRD, electron microscopy, EDX, and UV-Vis diffuse reflectance spectroscopy. The adsorption capacity and photocatalytic activity of the samples were investigated using methylene blue as a model pollutant. Sorption tests revealed that the adsorption of MB onto the samples obeys the Freundlich-Langmuir isotherm model. The sorption capacity decreased as follows:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub><mml:mo>&gt;</mml:mo><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mn mathvariant="normal">2</mml:mn><mml:mo>&gt;</mml:mo><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mn mathvariant="normal">1</mml:mn><mml:mo>&gt;</mml:mo><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mn mathvariant="normal">3</mml:mn><mml:mo>&gt;</mml:mo><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:math>. The results of the photocatalytic tests under high-intensity discharge (HID) lamp revealed that CdS/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:math>powders with low Cd to Ti molar ratios exhibited much higher activities than P25-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:math>. The CdS/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:math>sample with 20% CdS/(TCd2) showed the most activity among all these samples. The results also show that the Cd to Ti molar ratio of the nanocomposite has a significant effect on the photodegradation of MB and the enhanced activities exhibited by the nanocomposites are because of the low rate of electron-hole recombination.