Halloysite nanotubes (MHNTs) modified S-scheme g-C3N4/γ-Fe2O3 photocatalyst for enhancing charge separation and photocatalytic activity

Abstract

Photocatalysis is a surface process and an increase in the adsorption of target molecules on the surface of a photocatalyst could be of prime necessity in the photodegradation efficiency enhancement of dyes. To attain such a purpose, this study equips g-C3N4 with pores-modified halloysite nanotubes (MHNTs), then gets it wrapped by γ-Fe2O3 nanoparticles with high specific surface area (SSA) and S-scheme mechanism through a one-pot synthesis and co-precipitation, respectively. Characterization of fabricated photocatalysts is conducted to detect physical, chemical, optical, magnetic, and electrical properties by XRD, FT-IR, XPS, FE-SEM, EDX+MAP, TEM, BET, DRS, PL, VSM, Photocurrent, and EIS analyses. This research introduces a novel, ternary nanocomposite (g-C3N4/MHNTs/γ-Fe2O3) with dual functionality towards adsorption of both anionic and cationic dyes. Modified halloysite nanotubes (MHNTs), due to predominant negative charges (Si-O) on their outer surface, perform a significant role in the separation of holes (h+) from the photocatalysts and higher adsorption in MB photodegradation. In contrast, the inner surface of MHNTs through positive charges of AL-OH is beneficial for the electron (e-) separation and MO treatment. MHNTs with mesopores structure (Mean pore diameter: 10.6 nm) and high specific surface area (76.25 m2/g) contribute to higher adsorption and rapid transfer of photoexcited charges to the surface of ternary photocatalyst (g-C3N4/MHNTs/γ-Fe2O3 – 59.06 m2/g). After adding γ-Fe2O3 to g-C3N4/MHNTs, band gap of g-C3N4/MHNTs/γ-Fe2O3 reduces to 2.70 eV from 2.85 eV of g-C3N4/MHNTs, indicating influential role of γ-Fe2O3 nanoparticles in shifting photocatalytic activity of the ternary photocatalyst towards larger wavelengths (≥ 900 nm), and real world’s application (under illumination of sunlight). Among fabricated photocatalysts, g-C3N4/MHNTs/γ-Fe2O3 excels at degrading both MB and MO with the efficiency of %99.99 in 60 min and %89.1 in 120 min, respectively. To recognize the photocatalytic mechanism of the ternary photocatalyst, a trapping experiment was utilized for detecting oxidizing radicals in the photocatalytic process and then a photocatalytic mechanism was proposed.