Valorization of Palm Oil Fuel Ash Into Cu‐Doped Fibrous Nanosilica for Efficient Photocatalytic Degradation of Methylene Blue: RSM‐CCD Optimization

ABSTRACT This study explores the optimization of methylene blue (MB) photodegradation using a copper‐doped fibrous nano‐silica (Cu/FNS) photocatalyst synthesized from palm oil fuel ash (POFA), an agricultural waste material. The Cu/FNS composite was prepared through an ultrasonic‐assisted impregnation method, with its morphological and surface characteristics analyzed via scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) techniques. To optimize degradation performance, a central composite design (CCD) under response surface methodology (RSM) was employed, evaluating the influence of three main variables, namely catalyst dosage, pH, and initial MB concentration. The CCD framework designed 20 experimental trials, enabling the creation of a predictive model for photocatalytic efficiency. Statistical validation showed the model's strong fit and reliability, supported by high coefficients of determination ( R 2 = 0.9995, adjusted R 2 = 0.9990, and predicted R 2 = 0.9959) and a highly significant p ‐value (< 0.0001). Among the examined factors, pH was identified as the most critical, significantly impacting the electrostatic interactions between the catalyst surface and dye molecules, as well as the formation of reactive oxygen species. Optimal degradation conditions were determined to be pH 8.0, MB concentration of 30 mg/L, and catalyst loading of 5.0 g/L, resulting in a maximum removal efficiency of 92.83%. Furthermore, the photocatalyst demonstrated consistent reusability, maintaining notable activity across five cycles, thus highlighting its potential for practical and sustainable wastewater treatment applications.