An insight into a novel calixarene-sensitized Calix@Nb₂CT_x/g-C₃N₄ MXene-based photocatalytic heterostructure: Fabrication, physicochemical, optoelectronic, and photoelectrochemical properties

The development of highly efficient and cost-effective multifunctional photocatalysts is of current global interest because these photocatalysts have the potential to address the energy and water crisis. Herein, an efficient calixarene-based Calix@Nb₂CT_x/g-C₃N₄ (Cx–Nb–CN) photocatalyst was prepared through the formation of covalent bonds between the calixarene (Cx–COCl), g-C₃N₄ (CN), and Nb₂CT_x MXene. Enhanced optoelectronic and photoelectrochemical (PEC) properties were observed upon introducing Cx–COCl calixarene and Nb₂CT_x complexes to the g-C₃N₄ (CN) photocatalyst. The XPS valence band measurements demonstrated the narrowing of the energy band gap for the composites due to the downshifting and upshifting of the CB and VB, correspondingly. Due to the sensitization effect, the Cx–CN presented superior photocatalytic properties relative to the pristine CN. Moreover, reduced charge transfer resistance (R_ct = 110.7 Ω cm²) and the highest photocurrent density (J_p = 7.95 mA/cm²) were observed for the Cx–Nb–CN–5 heterostructure. The Schottky-heterostructures Cx–Nb–CN–1, Cx–Nb–CN–3, and Cx–Nb–CN–5 presented high linear sweep current densities (J_LSV) of 8.61, 12.39, 14.04 mA/cm² signifying excellent light utilization and efficient separation of charge carriers, respectively. The fabricated photocatalyst exhibits excellent physicochemical and photocatalytic properties with the potential to facilitate host-guest complexation towards environmental detoxification and energy conversions.