Heterogeneous photo-fenton oxidation degradation of methyl orange using Alg-m, Alg-HAp, and Alg-mHAp catalysts

Removal of methyl orange (MO) anionic dye was investigated by composite beads of sodium alginate-magnetic hydroxyapatite (Alg-mHAp), sodium alginate-magnetite (Alg-m), and sodium alginate-hydroxyapatite (Alg-HAp) as catalysts of heterogeneous photo-Fenton process. Evaluation of XRD and FT-IR analysis proved the presence of magnetite and hydroxyapatite nanoparticles in the structure of synthesised catalysts. SEM analyses showed that the surface of the Alg-mHAp catalyst is rougher than the other two catalysts. The results demonstrated the effluent discoloration of 79.41%, 71.42, and 84.28% for Alg-m, Alg-Hap, and Alg-mHAp, respectively, at an optimum pH = 3. By increasing the pH to more than 3, the removal rate decreased. In addition, it was found that by increasing the hydrogen peroxide concentration from 0.5 to 3 mM, photo-Fenton activity can be further enhanced to effectively degrade MO. However, with increasing the concentration of H2O2 from 3 to 20 mM, the removal percentage of Alg-m, Alg-HAp, and Alg-mHAp catalysts decreased to 92.70%, 86.20%, and 95.62, respectively. The results revealed with increasing initial dye concentration, the removal percentage decreased for all three catalysts. Also, by increasing the catalyst dosage from 0.5 to 2 g/L, the removal percentage for Alg-m, Alg-HAp, and Alg-mHAp catalysts increased 16, 21, and 12%, respectively. Furthermore, it was determined that as the UV intensity increased, the removal percentage increased by an average of 26%. The first-order kinetic equation was most consistent with the experimental results of MO degradation in all three catalysts. This study confirmed the feasibility of a heterogeneous photo-Fenton system of Alg-mHAp for the highly efficient degradation of MO in wastewater.