Titanium oxide nanoparticles loaded onto activated carbon prepared from bio-waste watermelon rind for the efficient ultrasonic-assisted adsorption of congo red and phenol red dyes from wastewaters

The simultaneous ultrasonic-assisted removal of Congo red (CR) and phenol red (Ph R) dyes from the aqueous solutions was accomplished by using titanium oxide (TiO2) nanoparticles (NPs) loaded onto activated carbon (AC) prepared from bio-waste watermelon rind (WR), referred to as TiO2-NPs-ACWR. The TiO2-NPs-ACWR was characterized by FT-IR, FESEM, SEM, EDX, BET, and TGA techniques. To simplify the optimization process, the pH effect was first studied via one-variable-at-a-time method. The influences of the other parameters such as sonication time, initial dyes concentrations, and adsorbent dosage were then evaluated by central composite design (CCD) combined with desirability function. The optimum conditions consisted of pH 4.3, 0.04 g of TiO2-NPs ACWR, 8.22 min of sonication time, and initial concentrations of 45.9 mg L-1 and 14.7 mg L-1 for Ph R and CR, respectively, which resulted in high removal percentages (100.24% for Ph R and 101.45% for CR). Besides, the adsorption capacities were 55.6 mg g(-1) for Ph R and 17 mg/g for CR. The adsorption equilibrium study showed that Langmuir model had adequate competence for the description and evaluation of the adsorption process. Kinetics study was carried out at various time intervals. The results indicated that adsorption processes can be fitted and predicated by the pseudo-second-order model. (C) 2019 Elsevier Ltd. All rights reserved.