Abstract
Abstract In this study, a model to improve the degradability of methylene blue (MB) dye using graphene oxide/TiO2/SiO2 nanocomposite under sunlight irradiation is investigated. The effect of operative parameters comprising catalyst concentration, initial dye concentration, and pH on the photocatalytic batch during removal of MB is studied. Fractional factorial design (FFD) and response surface methodology (RSM) are used to design the experiment layout. Graphene oxide (GO)/TiO2/SiO2 nanoparticles are synthesized through sonication and sol–gel methodologies. In the experiments, three levels of catalyst varied in the percentage of TiO2 pointed as (I) TiO2:GO (100%), (II) TiO2:GO:SiO2 (50%), and (III) TiO2:GO:SiO2 (25%) are used. The irradiation interval was 7 h at solar radiation energy 6.35–5.00 kW h/m2/day. In the experiments, three levels of catalyst varied in the percentage of TiO2 pointed as (I) TiO2:GO (100%), (II) TiO2:GO:SiO2 (50%), and (III) TiO2:GO:SiO2 (25%) are used. The synthesized catalysts are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy. ANOVA under 23 FFD is conducted to evaluate the effect of independent factors depending on the value of F as pH of solution, weight of catalyst, and concentration of MB. The adsorption kinetics, experimental design with FFD, and RSM are investigated in this study. The Surface Adsorption kinetics were statistically analyzed, the model that best described the results of each experiment was determined out of the two evaluated kinetics (pseudo-first order, pseudo-second order), for the three photocatalyst composites I, II, and III with the parameters; weight of the catalyst, pH, and initial MB concentration, also percentage degradation is evaluated. RSM results are consistent with the kinetic model; first, the pH is considered as the most significant parameter affecting the removal of the organic pollutant, and second, catalyst II gives the highest percentage removal efficiency of MB. FFD results are consistent with both models where the effect of the independent factor depending on the value of F was pH of solution > weight of catalyst > initial concentration of MB. The percentage removal was in the range from 30 to 99%.
Highlights
Treatment of wastewater becomes essential and mandatory because they contain many contaminated compounds that cause risk to the living beings and environment if released without treatment
Three types of photocatalysis were under study, which varied in the percentage of TiO2 pointed as (I) TiO2:Graphene oxide (GO) (100%), (II) TiO2:GO:SiO2 (50%), and (III) TiO2:GO:SiO2 (25%)
Several adsorption kinetic models are used, among them the Langmuir model, which is the most fitting for the experimental results, two fitting model plotted with experimental data under different conditions
Summary
Treatment of wastewater becomes essential and mandatory because they contain many contaminated compounds (organic and inorganic) that cause risk to the living beings and environment if released without treatment. Many of these compounds are stable and pass through conventional wastewater treatment systems, without major changes in their chemistry [1]. The heterogeneous photocatalytic degradation involves three main steps: adsorption on the surface, surface reaction, and desorption of reacted product from the pores. The common point is the optimization of the process. Optimization of the adsorption process was usually performed in a routine and conventional way [3]
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