Enhancement of sonocatalytic degradation of organic dye by using titanium dioxide (TiO2)/activated carbon (AC) derived from oil palm empty fruit bunch

A novel titanium dioxide/activated carbon (TiO₂/AC) composite where AC derived from oil palm empty fruit bunch (EFB) was synthesised by using sol–gel method. All the samples were characterised by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Fourier transformed infrared (FTIR), thermogravimetric analysis (TGA) and surface analyser. SEM analysis showed that TiO₂ particles were successfully embedded and well distributed on the AC surface. The elemental composition analysis found that the TiO₂/AC composite contained titanium (Ti), oxygen (O) and carbon (C) atoms. Meanwhile, the appearance of new band at about 960 cm⁻¹ which assigned to the Ti–O stretching was observed in the FTIR spectra when the AC was incorporated into TiO₂. TGA analysis showed that the weight loss of 32 wt.% from 150 to 550 °C was due to the decomposition of amorphous carbon layers and loss of hydroxyl groups on TiO₂. It was found that the TiO₂/AC composite had better performance in the sonocatalytic degradation of malachite green as compared to the individual AC and TiO₂ because the TiO₂/AC composite had dual functionality and huge number of active sites which could promote the mass transfer of dye molecules towards catalyst surface. By using 1.5 g/L of TiO₂/AC composite which calcined at 700 °C on 100 mL of 200 mg/L of malachite green at solution pH of 7, a degradation efficiency of 87.11% had been achieved after 30 min of ultrasonic irradiation. A lower chemical oxygen demand (COD) removal (81.75%) was observed because the structured dye molecules underwent mineralisation process during the sonocatalytic degradation to generate intermediate compounds. The TiO₂/AC composite was able to be recycled and still achieved a high degradation efficiency of 76.78% after second catalytic cycle as compared to the fresh TiO₂/AC composite with degradation efficiency of 87.11%. In conclusion, the TiO₂/AC composite had high reusability and promising for practical applications in textile industry.