Photodegrading hazardous pollutants using black TiO₂ materials with different morphology and estimation of energy requirement

Black TiO₂ materials were synthesized with different morphologies, including nanoparticles (NPs) and nanonails (NNs), and their performance for the photodegradation of hazardous phenols from model palm oil mill wastewater (TPOME) was compared. For the first time, the black TiO₂ NNs were prepared by hydrothermal processing, followed by HCl treatment of the TiO₂ NPs that had already been produced using an improved glycerol-assisted precipitation method. Four phenolic compounds (phenol, caffeic acid, ferulic acid, and gallic acid) were combined to represent the model wastewater based on their relative concentrations in actual TPOME. The TiO₂ NNs outperformed the TiO₂ NPs in the photocatalytic degradation of phenols due to their improved properties, including higher visible light absorption and surface area and lower bandgap and rate of electrons and holes recombination. The removal rate and energy requirements of the TiO₂ NNs were also impactful. The TiO₂ NNs degraded more than 99% of individual phenols in 210 min and 84.22% of the total phenols in 270 min with the least amount of electrical energy used (96.36 kW/m³), the lowest cost of treatment of a unit volume of model TPOME, and the highest removal rate constant.