Enhanced photocatalytic removal of Safranin-T dye under sunlight within minute time intervals using heulandite/polyaniline@ nickel oxide composite as a novel photocatalyst.

Natural zeolite heulandite/polyaniline composite (Hu/PANI) was synthesized for the first time as catalyst support for nickel oxide photocatalyst (Hu/PANI@NiO). The structural, chemical, morphological, textural and optical properties were investigated using different techniques. The synthetic NiO crystals showed well developed flaky habits with diameter range 200-400 nm and length range 1-4 µm. The estimated band gap energies of Hu/PANI composite and Hu/PANI@NiO composite are 1.8 eV and 1.46 eV, respectively, which are remarkably smaller than the recorded value for pure nickel oxide. The photocatalytic properties of Hu/PANI@NiO composite for efficient degradation of safranin-T dye were evaluated under sunlight as a function of irradiation time, initial dye concentration, catalyst mass, solution pH, and the catalyst stability. Hu/PANI@NiO composite exhibits amazing photocatalytic degradation efficiency for safranin dye, whereas 80%, 98%, and ~ 100% of 5 mg/l dye were removed after only 1 min of solar irradiation using 0.025, 0.03, and 0.035 g of Hu/PANI@NiO, respectively. The higher concentrations of the dye (10-50 mg/L) can be fully removed within minutes by increasing the solution pH or using higher doses from the Hu/PANI@NiO catalyst. The removal percentage achieved the maximum value at the alkaline conditions. Also, the Hu/PANI@NiO displayed high stability and remain 84.5% of the initial photocatalytic efficiency after 5 runs. Additionally, the composite can be used effectively in the removal of different types of dyes and mixed dyes within the same time intervals. Thus, loading of nickel oxide onto hybrid Hu/PANI composite as a catalyst support achieved amazing photocatalytic degradation capacity.