Nickel oxide (NiO) nanoparticles were formed using the chemical precipitation method. The efect of the calcination process
on the structural parameters, optical bandgap, and photocatalytic performance was investigated. The structural characteristics
were carried out using X-ray difraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron
microscope (SEM). The XRD analysis reveals that the formed NiO crystallized in an fcc crystal structure and the calcination
process infuences the crystallite size, microstrain, dislocation density, and average surface area. For example, the smallest and
largest particle sizes (19.13 nm and 27.63 nm) were achieved for the samples prepared at 800 °C for 4 h and 900 °C for 2 h,
respectively. Based on the difuse refectance spectroscopy analysis, the energy bandgap has the lowest values (3.33 eV) for

the prepared NiO that calcinated at 800 °C for 2 h compared with other samples. The formation of a Ni–O stretching vibra-
tion mode is revealed by FTIR, and the broadness of the absorption band confrms that the NiO samples are nanocrystals.

The morphology of the prepared NiO reveals the formation of spherical nanoparticles for NiO calcinated at 700 °C, while
dodecahedron-like shapes were observed for NiO calcinated at 800 and 900 °C. The photocatalytic performance of NiO
nanoparticles as catalysts for the degradation of indigo carmine dye was investigated under ultraviolet–visible irradiation
up to 3 h. The best degradation efciency was found to be 76% for NiO calcinated at 800 °C for 4 h, which belonged to the
smallest crystallite size of 19.13 nm, and the highest surface area of 47.02 m2 g−1. The superior and excellent performance
of this sample compared to other samples was confrmed by achieving the highest reaction rate constant (4.51× 10−3 min−1).
The proposed photodegradation mechanism shows the importance of increasing the time required for the recombination
process between the positive holes and the excited electrons, which is the best possible when using the optimum photocatalyst
sample that was prepared at 800 °C for 4 h.

Abstract

The numerical contribution of the natural heat flow of dusty hybrid nanofluid due to a square cavity filled with a porous medium with the effects of internal heat generation and the magnetic field is presented in this paper. The system of the problem equations is divided into hybrid nanofluid (Al₂O₃–Cu) phase equations and dusty phase equations, which are converted to a dimensionless form to be suitable for solving them numerically using the finite difference method. The results manifest in the streamlines, isotherms contours for both hybrid nanofluid phase and dust phase as well in local and average Nusselt numbers profiles. The numerical computations are performed and presented via graphs and tables due to the influence of governing physical parameters like ◂()▸, ◂()▸, ◂()▸, (0 ≤ Σ ≤ �/2), ◂()▸, (0.0≤�≤0.1), ◂()▸, and ◂()▸. The results indicate that increasing of fluid–particle interaction parameter for velocity leads to increment of the streamlines and isotherms of both the dust and hybrid nanofluid phases. A notable enhancement is found in the streamlines of the hybrid nanofluid phase and dust phase for high values of the Rayleigh number. The average Nusslet number ameliorates due to suspended dust particles in the hybrid nanofluid while deteriorates with increasing nanoparticle volume fraction. Furthermore, rising values of Hartmann number lead to reducing streamlines of the hybrid nanofluid and dust phases but an increase occurs with an increment of the inclined angle of the magnetic field. A notable agreement is obtained between the data of the present study and other previously published work.