Photocatalytic Removal of Nitrate from Aqueous Solutions Using Suspended and Immobilized Zinc Oxide

Aim: 
This research aimed to evaluate the efficiency of photocatalytic removal of nitrate from aqueous solutions using suspended and immobilized zinc oxide (ZnO).
Methods: 
A comparison was made between the photocatalytic, suspended, and immobilized ZnO nanoparticles (ZnO NPs) for nitrate removal. In addition, the effect of ZnO NPs either suspended or immobilized was evaluated in the presence of ultraviolet irradiation. The transmission electron microscopy, scanning electron microscopy, and X-ray diffraction analyses were applied to survey the physiochemical properties of ZnO. Photocatalytic degradation of nitrate was investigated using a spectrophotometric approach.
Results: 
The ideal function of removing nitrate (90%) was achieved with the concentration of 25 mg/l and in acidic pH. Immobilized catalysts can be used in continuous reactors due to the possibility of elimination of the phase segregation. The rising concentration of NPs to 0.8 g/L was associated with higher efficiency of the removal process. Maximum reduction performance of photocatalytic removal of nitrate (using immobilized and suspended ZnO) was 90% and 81%, respectively. Nevertheless, according to the findings, the immobilized method is highly more efficient for nitrate removal than the suspended method. The optimal time for the photocatalytic process was obtained at 150 min, and after 150 min, the reaction followed the first-order reaction kinetics.
Conclusions: 
The photocatalytic technique is efficient for nitrate removal from water and wastewater.