4.1. Preparation of Nanomaterials

A composite of TiO₂ nanoparticles and multi-walled carbon nanotubes (MWCNTs/TiO₂) was prepared via sol-gel method [51]. Briefly, a 0.03 g of purified MWCNTs (EPRI) was added to a mixture of titanium (IV) isopropoxide (TTIP, Aldrich, St. Louis, MO, USA) and acidified isopropanol (i-PrOH, Fisher, Hampton, NH, USA) within a ratio 4:5 and pH range ~2. The mixture was sonicated for 40 min followed by adding a diluted i-PrOH under vigorous stirring for 30 min at 25 °C. Stirring for the resulting colloidal solution continued for 1 h until sol was developed, followed by aging overnight to form the corresponding gel. The sample was dried at 120 °C in oven and annealed at 450 °C to induce the phase transformation to crystalline anatase TiO₂ while retaining the structural integrity of the CNTs [52]. Remarkably, the multi-walled carbon nanotubes (MWCNTs), have been synthesized via the Catalytic Chemical Vapor Deposition (CCVD) process [33]. To avoid nanoparticles agglomeration, MWCNTs were purified before through washing by strong acid (37% HCL, Aldrich). Furthermore, Q was immobilized on MWCNTs/TiO₂ by dispersing a known weight of MWCNTs/TiO₂ in the Q [1 × 10⁻³ M] solution under sonication for 5 min followed by shaking (100 rpm) at room temperature over a time range stating from 3 h to 36 h. After the incubation time, Q/MWCNTs/TiO₂ was collected by centrifugation and washed 3 times by water then left for drying at 100 °C.