Synthesis and characterization of a g-C3N4/UiO-66/Ag2CrO4 ternary nanocomposite for the photo-catalytic degradation of methyl orange under visible-light irradiation

Abstract

In this study, novel g-C₃N₄/UiO-66/Ag₂CrO₄ ternary nanocomposites with different mass ratios of Ag₂CrO₄ were synthesized effectively via the precipitation method for the treatment of polluted water. Solvothermal and co-precipitation techniques were used to synthesize the UiO-66 and Ag₂CrO₄ nanoparticles, respectively. The precipitation process was also used to produce binary nanocomposites (g-C₃N₄/UiO-66 and UiO-66/Ag₂CrO₄). UV-visible spectrophotometry, photoluminescence (PL) study, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) evidenced ample and efficient interactions between the components within the composites. The photocatalytic activities of each nanocomposite were evaluated using aqueous solutions of model methyl orange (MO) and a real sewage sample solution collected from Hawasa Textile Industry. The photocatalytic efficiencies of the ternary nanocomposites (g-C₃N₄/UiO-66/Ag₂CrO₄, 10%, 20%, and 30% of Ag₂CrO₄) were found to be higher than those of single and binary nanocomposites due to synergistic effects in the composite, which favored efficient interfacial charge transfer and improved separation of photoinduced electron–hole pairs. In particular, the ternary nanocomposite containing 20% of Ag₂CrO₄ exhibited the highest photocatalytic activity. The effect of various experimental parameters, such as pH, initial dye concentration, photocatalyst load and scavengers' effects, on MO degradation was investigated using this g-C₃N₄/UiO-66/Ag₂CrO₄ ternary nanocomposite. Results showed that at optimum pH (2), catalyst load (0.2 g L⁻¹) and initial dye concentration (10 ppm), the percent degradation of MO under visible-light irradiation (indoor system) was found to be 97.0% in 120 min, and in the outdoor system, it was found to be 99.6% in 40 min. The selected photocatalyst was also applied for the degradation of a real sewage sample solution, and a percent degradation of 76.2% was observed. Importantly, the catalytic efficiency did not decrease significantly even after three reaction cycles, showing it had good stability and recyclability. Hydroxide radicals (*OH) and holes (h⁺) were identified as the most active species in the photocatalytic process. Therefore, the g-C₃N₄/UiO-66/Ag₂CrO₄ ternary nanocomposite may be a viable option for industrial photocatalytic applications, particularly in the removal of organic dyes from wastewater.