Facile green synthesis of rGO and NiO, and fabrication of a novel ternary nanoheterostructure NiO@g-C3N4-rGO as earth abundant superior photocatalyst for dye degradation

Synthesis of reduced graphene oxide (rGO), NiO nanoparticle and a novel ternary nanohybrid, NiO@g-C3N4-rGO were performed via eco-friendly green protocol using aqueous extract of a abundantly available marine alga, Ulva sp. The structure, morphology, optical properties and chemical oxidation state of the materials were probed by UV-Vis, FT-IR, XRD, Raman, SEM, EDAX, TEM, XPS, BET and PL techniques. The electronic band gap of NiO NP and NiO@g-C3N4-rGO are found to be 3.54 eV and 2 eV, respectively. The average diameter of NiO NP is 12 nm. The ternary nanohybrid demonstrated superior photocatalytic performance in the degradation of a water soluble congo red dye under scattered sunlight irradiation. The photocatalytic efficiency of the nanohybrid is ascribed to suppressed electron-hole pair recombination. The rate of dye degradation got significantly enhanced with increase in the catalyst loading while higher amount of dye lowered the rate. Radical trapping experiments indicated O2.- to be the active species in photodegradation. The hybrid material could be recovered, reused for five consecutive catalytic cycles and beyond without loss of efficiency indicating high stability of the photocatalyst.