Green synthesis of nitrogen-doped TiO2 nanoparticles with exposed {001} facets using Chromolaena odorata leaf extract for photodegradation of pollutants under visible light

Facet-tailored TiO₂ nanoparticles (NPs) exhibit exceptional properties due to high surface energy. Conventional strategies for the fabrication of such TiO₂ NPs involve harmful chemicals, which necessitates the development of environmentally benign pathways. Plant extract-assisted synthesis has emerged as a promising green alternative to conventional nanomaterial synthesis. This work introduces an innovative method for the synthesis of nitrogen-doped TiO₂ (N-TiO₂) NPs with exposed {001} facets using the leaf extract of a weed plant Chromolaena odorata, which is commonly known as Siam weed. The synthesis was carried out by sol-gel process with triethylamine (TEA), hydrazine hydrate and urea being the nitrogen precursors. The synthesised N-TiO₂ NPs exhibited exposed {001} facets and showed a reduction in band gap. Photo-induced degradation of methylene blue dye was used to analyse the photocatalytic capability of N-TiO₂ NPs in the visible range. The effect of N precursor, N dosage and light exposure time on the catalytic efficacy was studied. N-TiO₂ NPs derived from TEA with 1 mol.% dopant achieved 98 % degradation in 180 minutes, while those synthesized with hydrazine and urea attained 96 % and 93 %, respectively when compared to 90 % degradation for undoped samples. The N-doping leads to significant advancement of photocatalytic effectiveness of the TiO₂ NPs by introducing mid-gap levels in the forbidden energy gap that diminishes the charge carrier-recombination and boost the charge-carrier mobility of TiO₂. This along with the existence of high energy facets causes a substantial advancement in the photocatalytic function in the visible region. The proposed method is a sustainable way for synthesising N-TiO₂ NPs with exposed {001} facets for environment remediation applications.