In situ growth of ZnNiAl-LDHs on floral ZnO with excellent cycling performance for high concentration Congo Red by synergetic adsorption photocatalysis mechanism

Abstract

The synergistic degradation of dye wastewater by adsorption-photocatalysis composites represents a green and efficient strategy for pollutant removal. This study reports three ZnNiAl-LDHs@floral ZnO composites (ZnNiAl-LDHs@floral ZnO-1, −2, −3 with the increase in the content of the ZnO template) for the synergistic adsorption-photocatalytic degradation of Congo red (CR). Specifically, flower-like ZnO, as a typical photocatalyst with a large specific surface area, serves as a substrate for the in-situ growth of ZnNiAl-LDHs, which possess remarkable adsorption capabilities. This synergy between the two components endows the composite material with enhanced performance in the effective degradation of high-concentration CR (up to 600 mg/L). Dark adsorption experiments show that the adsorption efficiency of the composites is negatively correlated with the content of the zinc oxide template: (65.83 % > 62.31 % > 59.71 %). While synergistic degradation efficiencies followed the opposite order: (98.25 % < 99.06 % < 99.16 %). This demonstrates the inhibitory effect of the increase in ZnO content on dark adsorption and the enhancing effect on photocatalytic performance, as well as the photocatalytic rate (0.0355 min⁻¹, 0.0433 min⁻¹ and 0.0444 min⁻¹, respectively). In cycling tests with 200 mg/L CR, the degradation rate remained above 80 % after 10 cycles, indicating stable reusability. These results highlight the promise of in-situ grown ZnNiAl-LDHs@floral ZnO heterojunctions as high-performance photocatalysts for removing high-concentration CR.