Effective catalysts for wastewater treatment under sunlight: Gas dependent preparation of mesoporous biphasic N-doped TiO2 nanoparticles

Abstract

Photocatalysts are playing an indispensable role in tackling environmental and energy crises; however, they are associated with poor solar energy utilization. In this study, N-doped titanium dioxide (N-TiO2) nanocrystals were successfully prepared using benign N-source, guanidine chloride by simple sol-gel technique. The significance of annealing gases environment (air, argon, and nitrogen) on their physicochemical properties and photocatalytic activity under direct sunlight irradiation was investigated. XRD and Raman data revealed that the crystal structure of spheroidal N-TiO2 nanocrystals was transformed from monophase anatase with less crystallinity in argon, and nitrogen to dual-phase anatase/rutile (A/R) with higher crystallinity in air. Importantly, XPS confirmed the successful incorporation of N in interstitial sites of the bare titania structure. Moreover, DRS and PL results revealed that the introduction of N into the TiO2 matrix not only led to a red shift towards visible-light but also lowered the bandgap energy (2.35 eV) and suppressed charge carriers recombination. BET showed a typical IV isotherm of mesoporous N-TiO2 nanomaterials with a high specific surface area in the range of 80–103 m2 g−1. Furthermore, their rhodamine B (RhB) photodegradation performance and thermal-stability were dictated by the annealing gas type. Nobly, the N-TiO2 prepared in air demonstrated the highest degradation performance (99%) with the fastest rate (0.0158 min−1) which is twice faster as the control TiO2 material. Its real textile wastewater removal was 63% and 56.5% COD and TOC, respectively. These improved performances are mainly attributed to its higher crystallinity, A/R mixed phase, aqueous-dispersion character, and lower recombination rate. Such gas driven-synthesis of photocatalysts has practical applications in designing other solar energy conversion systems.