Fabrication of aluminum-based hybrid nanocomposite for photocatalytic degradation of methylene blue dye: A techno-economic approach

Methylene blue (MB) is one of the most consumed dyes in the textile industry, imposing toxic, mutagenic, and/or carcinogenic effects on human health. The unmanaged disposal of MB-laden wastewater into the aquatic environment is associated with the loss of species and damage to habitats. Because its molecular structure contains a 6-carbon aromatic ring, nitrogen, and sulfur, MB has a non-biodegradable property. Compared with conventional biological processes, advanced oxidation technology is preferable for mineralizing MB into simple and non-toxic species. This study focuses on synthesizing aluminum-based hybrid nanocomposite (AHN) by the co-precipitation technique, followed by its application for photocatalytic degradation of MB under visible light. Material characterization revealed that AHN had an Al₂O₃-MgO chemical formula, with an irregular geometric shape and particle sizes in the 50-60 nm range. XRD analysis showed that AHN had a cubic crystal structure with γ-Al₂O₃ and crystallite size in the range of 15-34 nm. The BET surface area was 750 m²/g, with an average pore diameter of 11 nm and pore volume of 1.9 cm³/g. The AHN band gap was calculated as 5.6 eV. At an initial MB concentration of 11 mg/L, the highest removal efficiency was 72.7±3.41% at pH of 8.4 and photocatalyst dosage of 0.5 g/L within 180 min. It’s supposed that during visible light irradiation in the presence of AHN photocatalyst, there is electron transfer and formation of super-oxide (O₂^•ˉ) and hydroxyl (OH^•) radicals responsible for the efficient degradation of MB dye. Another portion of MB could be removed by deposition on the synthesized AHN material, facilitating the MB photo-degradation pathway. The photodegradation reaction followed the pseudo-first-order kinetic model with (k₁) of 0.0075 min^-1. The electrical energy consumption was evaluated and achieved at 184 kWh/m³, equivalent to an operating cost of 16.5 USD/m³. The removal of MB by the manufactured AHN catalyst showed good agreement with other photocatalytic degradation mechanisms reported in the literature.