Eco-friendly nickel-modified titanium dioxide nanotube arrays: A breakthrough in photoelectrochemical degradation of tetramethylammonium hydroxide

• Green Ni/TNAs synthesized using butterfly pea flower and turmeric extract. • Ni/TNAs-BPF showed enhanced visible-light absorption (λ max = 445 nm) and reduced bandgap (2.81 eV). • Achieved high photocurrent density (4.45 mA·cm −2 ) with longer electron lifetime (130.45 ms). • Ni–TNA-BPF PEC system degraded 50 ppm TMAH, 27.3% removal at pH 3 in 4 h. • Hydroxyl radical-driven demethylation yielded TriMA, DiMA, MoMA, NH 4 + , and NO 3 − as intermediates. Titanium dioxide nanotube arrays (TNAs) were synthesized via anodization and modified with nickel nanoparticles (Ni/TNAs) using a green synthesis approach. Natural reducing agents, including butterfly pea flowers (BPF), turmeric (Tur), and their main components anthocyanidin (AC) and curcumin (Cur), were employed. The modified materials were applied in a photoelectrochemical (PEC) system to degrade tetramethylammonium hydroxide (TMAH) and analyze the degradation byproducts. Characterization revealed uniform spherical Ni nanoparticles on TNAs, improved visible light absorption, and retained n-type semiconductor properties. Photocurrent measurements showed enhanced densities for Ni/TNAs-Tur and Ni/TNAs-BPF, with EIS confirming extended electron lifetimes. EPR detected hydroxyl radicals under light irradiation, critical for the degradation process. The PEC system demonstrated optimal TMAH degradation at pH 3 using Ni/TNAs-BPF, achieving efficient demethylation to byproducts such as trimethylamine (TriMA), dimethylamine (DiMA), methylamine (MoMA), ammonium (NH 4 + ), and nitrate (NO 3 − ). This study highlights the potential of green-synthesized Ni/TNAs for sustainable wastewater treatment.