Effective photocatalytic degradation of dye pollution in synthetic wastewater using nanocomposites of chromium and potassium oxides

In the present work, chromium(III) oxide (Cr 2 O 3 ) and potassium oxide (K 2 O) nanoparticles (NPs) were synthesized using the combustion method. Mixed oxides of varying concentrations in the form of (1–x)Cr 2 O 3 /xK 2 O (x = 0.1, 0.3, 0.5, and 0.7) were prepared. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and optical measurements were used to investigate the properties of NPs. XRD indicates that the grain size of the mixed oxides decreased as the K 2 O content increased. Additionally, HRTEM revealed several types of shapes, such as hexagonally shaped NPs. The optical measurements showed a blue shift, indicating that the band structure was slightly modified during the Cr 2 O 3 /xK 2 O mixing. The optical band gap obeys the direct allowed transition and varies from 2.29 to 2.59 eV as the K 2 O ratio in the composites increases from x = 0.1 to 0.7. The (1–x)Cr 2 O 3 /xK 2 O NPs were used as catalysts in wastewater during a photocatalytic process. Orange G was chosen as an impurity in the water. The absorbance curves of Orange G in the water were measured at different times in the presence of the same quantity of Cr 2 O 3 /xK 2 O NPs. It was found that after 120 min, the efficiency reached 11% and 33% for (1–x)Cr 2 O 3 /xK 2 O NPs with x = 0.1 and 0.7, respectively. Furthermore, the experimental results were analyzed by pseudo-first-order model. A first-order kinetic model had the best fit for the (1–x)Cr 2 O 3 /xK 2 O NPs. The strongest relationship occurred with a composition of 0.1Cr 2 O 3 /0.7K 2 O. The formed composites could be used to degrade organic dyes for water purification.