Discoloration ofAqueous Direct Blue 71 Solutions using UV/H2O2/Nano-SiO2 Process

The photolytic capability of SiO2 nanoparticles (SiO2-NP) for the discoloration of Direct Blue 71
as an environmentally pollutant dye via UV irradiation in the presence of H2O2was assessed and optimized using
response surface methodology (RSM) with a D-optimal design. The response of DB71 degradation was found to
be sensitive to the independent factors of reaction time, SiO2-NP and H2O2 concentrations. The discoloration
process was not pH-dependent and the pHwas not a significant factor in DB71 discolorationmodel. The approach
provided statistically significant quadratic models, which were adequate to predict responses and to carry out
optimization under the conditions studied. The maximum value of discoloration under the optimum operating
conditions was determined to be 99.03% with a time of16 min of irradiation and concentrations of 220 and 155
mg/L for H2O2 and SiO2-NP respectively. The results showed that the discoloration increased about 11%by
increasing SiO2-NP concentration from10 to 155 mg/L. The possiblemechanism of SiO2-NP catalytic performance
was assessed. The kinetic study was also examined and indicated that the degradation of DB71 dye obeys
Langmuir-Hinshelwoodmodel.