A high-performance NiMoO4/g-C3N4 direct Z-scheme heterojunction photocatalyst for the degradation of organic pollutants

Photocatalytic degradation of harmful organic pollutants in water has been considered an important research subject due to its efficient and cost–effective handling of toxic substances for ecosystems protection. We report a direct Z–scheme heterojunction photocatalyst made up of NiMoO4/g–C3N4 (NMOCN) nanocomposite for degrading the antibiotic, i.e., ciprofloxacin (CIP) and the organic dye, i.e., malachite green (MG). The nanocomposites were systematically prepared, and their structural, morphological, optical, and photoelectrochemical properties were analyzed. XRD analysis verified that NiMoO4 had a monoclinic crystal structure. The FESEM and HRTEM images showed that NMOCN composites were comprised of NiMoO4 nanorods coupled with g-C3N4 nanosheets. UV−VIS absorbance spectral analyses showed that NMOCN composites had a narrow band gap with good visible light absorption properties. Mott–Schottky and EIS measurements revealed that NMOCN composites had an optimum band structure and low charge transfer resistance for heterojunction formation. Increasing the relative mass content of g–C3N4 in NMOCN composites improved the photocatalytic degradation efficiency. NMOCN–30 (30 wt.% of g–C3N4) composite provided a maximum degradation efficiency, i.e., 90.82% for CIP (in 75 min) and 98.84% for MG (in 120 min), while showing excellent stability against CIP and MG up to six consecutive cycles. In addition, the EPR measurement and trap test results proved that all •OH, •O2–, and h+ participated in photodegradation activity. Thus, the presented nanocomposite photocatalysts with a Z–scheme heterojunction can help to build up a viable strategy for water pollution treatment with enhanced photocatalytic degradation capabilities.