Solvothermal synthesis of amorphous TiO2-BiOBr-Bentonite heterostructures for the abatement of phenol in water under visible light irradiation

Dlamini, Menelisi Celumusa
Journal Title
Journal ISSN
Volume Title
A simplistic solvothermal process has been used to fabricate novel amorphous TiO2-BiOBr Bentonite (A-TiO2-BiOBr-Bt) multidimensional photocatalysts with A-TiO2:BiOBr:Bt mass ratios fixed at 1:3:4, 1:1:2, and 3:1:4 respectively. The obtained photocatalysts were characterized using techniques such as Powder X-Ray Diffraction (PXRD), Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET) analysis, Ultra-Violet Visible (UV-vis) spectroscopy, Photoluminescence spectroscopy (PL), pH drift method, and Thermo Gravimetric Analysis (TGA). The A-TiO2-BiOBr-Bt heterostructure with an A-TiO2:BiOBr:Bt mass ratio of 1:1:2 (Ti1Bi1Bt2) displayed the highest BET surface area, low bandgap, and sufficiently low electron-hole pair recombination rate. The high number of A-TiO2-BiOBr p-n heterojunctions, and the Ti-O-Si and Bi-O-Si bonds between A-TiO2-BiOBr and Bt in Ti1Bi1Bt2 lowered its electron-hole recombination rate and enhanced its visible light-harvesting ability. It is for these reasons that Ti1Bi1Bt2 exhibited the best photocatalytic activity compared to the other ternary heterostructures with different mass ratios. Within 70 min of visible light irradiation, 150 mg of Ti1Bi1Bt2 gave 100% conversion of 100 mL of 20 ppm of phenol with a pseudo-first-order rate constant of 0.0322 min-1 at pH 4.0. Scavenging experiments were conducted and it was demonstrated that superoxide radicals (O2 •−) and electrons (e−) were the most dominant reactive oxidation species (ROS) responsible for the phenol photodegradation process while holes (h+ ) and hydroxyl radicals (OH• ) also exerted appreciable participation.
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Chemistry, University of the Witwatersrand, Johannesburg, 2022