Melia azedarach Activated Carbon and its novel TiO2 Nanocomposite for Chemisorption and Photodecoloration of Reactive Orange 16: Isotherm and Kinetic Modeling

Background: Bulk generated textile wastewater loaded with dyes is posing a stern threat to aquatic health, especially when dumped without prior treatment. Lignocellulosic waste based activated carbon (AC) and Titania (TiO2) suspension can constitute the emerging technological solution. Objectives: Best lignocellulosic precursor biomass, Melia azedarach (Darek sawdust - DSD), was selected for ortho-phosphoric acid impregnated AC production and novel AC-DSD-TiO2 nanocomposite was developed. AC-DSD and AC-DSD-TiO2 nanocomposites were employed for reactive orange 16 (RO16) dye adsorption in batch and decoloration in photocatalytic reactors, respectively. Methods: Materials were characterized by Scanning electron microscope (SEM), energy dispersion X-ray (EDX) spectroscopy and Fourier transform infrared spectroscopy (FTIR). For AC-DSD production, the raw powdered biomass of DSD impregnated (value = 2) with H3PO4 at room temperature and after shaking, was placed in a muffle furnace at 100°C for 12 h in glass tubes and subsequently carbonized at a high temperature of 400°C for 30 min. Batch reactor parameters for the ACDSD- RO16 system were optimized as a function of contact time, adsorbent dose, temperature, initial dye concentration and pH. For AC-DSD-TiO2 nanocomposite synthesis, AC-DSD and TiO2 paste was dried in the furnace at 90°C and calcined at 300°C and stored in a desiccator. Results: AC-DSD exhibited RO16 adsorption capacity of 92.84 mg/g. The experimental data were best described by Langmuir and Dubinin-Radushkevich isotherms with high R2 of 0.9995 and 0.9895 and closeness of predicted adsorption capacities of 94.15 and 88.58 mg/g respectively. This determines the chemisorption nature for RO16 adsorption onto AC-DSD. The experimental data was well explained by the pseudo-second order kinetic model. Thermodynamic parameters also suggest the endothermic, chemisorption and spontaneous adsorption reaction. Photocatalytic studies of novel AC-DSD-TiO2 revealed the higher Kc = 0.1833 value over Kad= 0.0572. Conclusions: Melia azedarach AC-DSD and its novel AC-DSD-TiO2 nanocomposite prove that these materials could provide an optimal solution for treating textile dye solutions effectively as the good adsorbent and photocatalyst.