Surface-tuning TiO₂ NR photoanodes using CoO_x interlayers and NiFe-LDH cocatalysts for photoelectrochemical wastewater treatment

Increasing multidrug-resistant pathogenic microbial around the world become a global problem, making it imperative to develop effective methods for bacterial inactivation in wastewater. In this study, we propose a multifunctional photoelectrochemical (PEC) system to successfully disinfect microbial cells and degrade orange (II) dyes. CoO_x NP were synthesized by spin-coating onto hydrothermally synthesized TiO₂ nanorod arrays followed by electrodeposited NiFe-LDH to develop the NiFe-LDH/CoO_x NP-TiO₂ NRs. Interestingly, spin-coated CoO_x NP-TiO₂ NRs exhibited a 1.5-fold enhancement in photocurrent (1.384 mA/cm²) than pristine TiO₂ NRs (0.92 mA/cm²). A NiFe-layered double hydroxide (LDH) cocatalysts layer further exhibits the maximum photocurrent density of 1.64 mA/cm² with IPCE of 84.5% at 1.0 V_Ag/AgCl at 380 nm. Furthermore, NiFe-LDH/CoO_x-TiO₂ NR photoanodes were effectually employed for photoelectrochemical bacteria disinfection and organic pollutant removals. With NiFe-LDH/CoO_x-TiO₂ NR, 99% (120 min) bacterial inactivation and 99% (60 min) orange II dye decomposition efficiency was achieved. Superoxide radicals (⁻O₂^•), hydroxyl radicals (HO•), and holes (h⁺) played a critical role in the PEC degradation systems. Due to the synergy between NiFe-LDH cocatalyst and CoO_x interlayer, surface water oxidation reactions were accelerated over NiFe-LDH/CoO_x NP-TiO₂ NRs. The charge transport process in NiFe-LDH/CoO_x NP-TiO₂ NRs photoanode-based PEC system was proposed in detail.