The effect of calcination temperature on the phase transformation of titanium dioxide for photodegradation of paraquat dichloride

Abstract

Paraquat dichloride is an herbicide which is harmful and toxic which polluted the water system and give negative impact to the health of ecosystems and human and must be treated. In this research, photocatalytic degradation of paraquat dichloride (PQ) solution using single TiO₂ and coupled TiO₂/ZrO₂ catalysts was conducted and assessed using UV-vis spectrometer measured at λ_max, 257 nm under 365 nm UV light irradiation for 3 hours. This research focused on the effect of calcination temperature on the phase transformation of TiO₂ and their performance on the photodegradation of PQ. Single TiO₂ was synthesized using sol gel method while TiO₂:ZrO₂ (90:10) was prepared using impregnated method. The synthesized catalysts were calcined at 450°C, 700°C, 800°C, 900°C, and 1000°C and were compared with TiO₂ Aldrich and P25 Degussa. The transformation of anatase to rutile phase was increased by increasing the calcination temperature for all the photocatalysts. Zr used as a dopant on the TiO₂ has delayed the formation of the rutile phase. Furthermore, addition of H₂O₂ gave better performance on photodegradation. In this study, TiO₂/ZrO₂ and commercial catalyst (P25 Degussa) those calcined at 700°C and 450°C gave highest percentage of photodegradation with 54.87% and 83.66% respectively at original reaction pH at 7.70. XRD analysis has proven the transformation of 75% anatase to 57% anatase calcined at 450°C for P25 Degussa. FESEM-EDX showed TiO₂/ ZrO₂ and P25 Degussa has a spherical morphology and particle size range between 20 - 35 nm. BET analysis showed surface area for TiO₂/ZrO₂ and P25 Degussa range between 25 - 44 m²/g. The data obtained showed that the best catalyst for degradation of PQ is P25 Degussa calcined at 450°C, pH 7.70 which gave 83.66%.