LaNiO3/g-C3N4 nanocomposite: An efficient Z-scheme photocatalyst for wastewater treatment using direct sunlight

Abstract The major findings in this report are (i) development of nanocomposite photocatalyst working through Z-scheme charge transfer pathway across the heterojunction, (ii) utilization of direct sunlight as the photo-source, (iii) prospect of ligand-hole in photocatalysis through enhanced sub-band gap absorption. The photocatalysts, namely LaNiO3, g-C3N4 and LaNiO3/g-C3N4 nanocomposites were synthesized via facile route and were characterized for their structure, morphology, microstructure, texture, elemental mapping and surface oxidation states by using several physicochemical techniques. The photocatalytic performance of the nanocomposite was tested through the degradation of hazardous azo dye pollutants, namely reactive black 5 and methylene blue as well as the colorless antibiotic-pollutant tetracycline hydrochloride in aqueous solution in presence of natural sunlight with excellent recycling activity. The 10%LaNiO3/g-C3N4 nanocomposite sample shows best catalytic activity, degrading respectively 94%, 98.6% and 88.1% of reactive black 5, methylene blue and tetracycline hydrochloride in 60 min, 180 min and 120 min. The photocatalytic activity of the nanocomposite phase is several times superior to that of the pure phases. The improvements of photocatalytic activity of g-C3N4 in the nanocomposite have been rationalized through the construction of direct Z-scheme heterojunction and suppression of electron-hole pair recombination efficiency. The enhanced photo-absorption of the nanocomposite can possibly be related to sub-bandgap absorption, which is associated to the midgap state originated from ligand-hole formation or defects in the structure. The photodegradation process is mediated through the formation of super oxide radical (˙O2¯) and hole (h+) as the main responsible species.