Post-synthesis plasma processing and activation of TiO2 photocatalyst for the removal of synthetic dyes from industrial wastewater

Abstract

In this study, TiO2 nanopowders were prepared by combining the surfactant assisted sol–gel method with microwave plasma calcination. Plasma calcination was performed just for 20–30 min for reducing the calcination time and ensuring the energy efficient synthesis of photocatalyst. The mixed anatase–rutile phased TiO2 nanoparticles were obtained under these synthesis conditions. The band gap energy of the photocatalyst decreased by 40% on microwave plasma calcination. The surfactants were found to be ineffective on phase transformations of synthesized TiO2. FTIR analysis confirmed the absorption of O–Ti–O band stretching between 415 and 420 cm−1. The hydroxyl bands (OH) were observed to be less stretched after plasma calcination. The conventionally calcined HA–Ti, NA–Ti and MS–Ti samples showed band gap energies of 5.09 eV, 4.88 eV and 5.06 eV, respectively. The band gap energy of plasma calcined MTHA–Ti, MTNNA–Ti and MTMS–Ti samples was calculated about 4.92 eV, 3.11 eV and 4.96 eV, respectively. The combined effect of photocatalyst, plasma reactive species and UV radiations promoted the degradation efficiency of the methylene blue dye. Under DC plasma jet exposure, the maximum degradation efficiency of 95% was achieved after 30 min of plasma exposure time. The catalyst retained about 93–95% degradation efficiency after five cycles of dye degradation.