Photocatalyzed degradation of persistent organic pollutants via black TiO₂ nanomaterials with four distinct morphologies: Energy and treatment cost estimation

For photocatalytic remediation of wastewater on an industrial scale, shaping the morphological properties of black TiO₂ and reducing energy consumption and related treatment cost (t-cost) are essential. In this study, black TiO₂ nanomaterials with four different morphologies—nanoparticles (TNPs), nanowires (TNWs), nanoflowers (TNFs), and nanonails (TNNs)—were produced, and their effectiveness in visible-driven photodegradation of model persistent phenolic compounds (PhCs) was evaluated. For every modification, the amount of energy consumed—primarily electrical energy (EE) and t-cost were estimated. The anatase structure was consistent throughout all the different morphological TiO₂ samples, with a range of bandgaps of 2.4–2.93 eV, crystallite sizes of 13.86–18.49 nm, and significantly varying surface areas from 183.76 to 521.58 m²/g. TNFs were the most effective and versatile black TiO₂ nanomaterials among the samples, as evidenced by their significantly higher removal efficiency of 77.99 % of total phenols (TPs). Furthermore, after 120 minutes of exposure to visible light, TNFs eliminated 100 % of the individual PhCs, including phenol, Ferrulic acid (FA), caffeic acid (CA), and gallic acid (GA). The TNFs required less than 170 kWh/m³ of EE with an estimated t-cost of less than 8 $/m³ for more than 80 % removal of all PhCs and reducing BOD₅ and COD levels of the wastewater by 77.90 and 77.54 %, respectively. The estimated cost of the input materials was 39.52, while the EE cost was 5.045 with a total cost of 44.565 $ for producing 1 kg of the TNFs. Scavenging experiments revealed that the main reactive agents responsible for PhCs degradation were ^•OH radicals. This study provides evidence that adjusting the morphological characteristics of black TiO₂ nanomaterials may be a useful tactic to lower the energy consumption and t-cost of photocatalytic remediation of wastewater contaminated with persistent organic pollutants.