Response surface optimization of photocatalytic process for degradation of Congo Red using H-titanate nanofiber catalyst

In this study, a new generation H-titanate nanofiber catalyst (TNC) with long fibril morphology and surface covered anatase titanium dioxide (TiO₂) crystals of 10-20 nm was used as the photocatalyst for improved photoactivity, mass transfer resistance and downstream separation. The combined Taguchi method and response surface analysis (RSA) were employed to evaluate the effects of key operational factors of TNC loading, pH, aeration rate and initial Congo Red (CR) concentration on the performances of TNC in an annular slurry photoreactor (ASP). The average CR photocatalytic degradation rate (mg dm^-3 min^-1) was estimated and applied as the response outputs of the L₉ (3)⁴ Taguchi orthogonal array. Results from the RSA interpretations revealed that pH, initial CR concentration and aeration rate were the significant factors, while TNC loading appears to be the least significant factor. On contrary, positive interactions of TNC loading were observed when being coupled with pH and aeration rate. Other interactions of the operation factors were also determined using statistical analysis. A natural logarithmic modified regression equation was developed from multiple regression analysis for response surface modelling. This model predicted that the average photocatalytic degradation rate of CR was 0.1576 mg dm³ min^-1 under the optimal conditions. A subsequent verification experiment showed a photocatalytic degradation rate of 0.1563 ± 0.0282 mg dm^-3 min^-1, which is in good agreement with the model predicted value. This proved the applicability of the developed model as a reliable design and modelling tool for scaling up the photocatalytic reactor process.