Abstract:

Objective This study aims to develop a high-efficiency perylene diimide/graphene oxide (PDI/GO) photocatalyst for printing and dyeing wastewater treatment, so as to solve the secondary pollution problem caused by heavy metal ions in conventional photocatalysts. Its photocatalytic degradation performance for reactive dyes and its adaptability in saline-alkali environment are systematically evaluated, providing theoretical basis for its practical application.

Method The PDI/GO photocatalyst was prepared by loading perylene diimide (PDI) onto graphene oxide (GO) via recrystallization. Its morphology and chemical structure were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The influences of light/dark environment and catalyst types on reactive blue degradation were investigated. Its photocatalytic performance for single and mixed reactive dyes was evaluated under xenon lamp irradiation, and the influences of initial concentration, salinity and alkalinity on degradation efficiency were explored.

Results SEM, FT-IR, XRD and PL characterizations confirm the successful preparation of PDI/GO photocatalyst, with PDI uniformly loaded on GO surface and significantly suppressed charge carrier recombination. Under simulated sunlight irradiation, PDI/GO exhibited excellent photocatalytic degradation for various types of reactive dyes. Control experiments showed that PDI/GO has good adsorption on reactive blue, while pure PDI, and that pure GO exhibit poor degradation capacities. Among the tested dyes, reactive blue achieved the highest degradation rate of approximately 85% after 200 min treatment at dye concentration of 10 mg/L, because of its anthraquinone ring being readily attacked by photogenerated radicals, whereas reactive red and reactive yellow showed relatively lower efficiency. Initial dye concentration was found to significantly affect the degradation performance, where 5 mg/L reactive blue was almost completely degraded (98% removal) within 70 min, while degradation efficiency decreased markedly at 15 mg/L and 25 mg/L. In saline-alkali tests, NaCl accelerated decolorization through electrostatic shielding and generation of active chlorine species, and NaOH restrained degradation due to enhanced electrostatic repulsion. The mixed NaCl/NaOH system demonstrated inhibited early stage degradation followed by accelerated degradation at a later stage, attributing to the gradual accumulation of photogenerated active chlorine species.

Conclusion This study reports the successful preparation of the PDI/GO photocatalyst and its high-efficiency photocatalytic degradation performance for reactive dyes. Under simulated sunlight irradiation, when the initial concentration of reactive blue dye is 5 mg/L, the decolorization rate of the dye solution reaches 98% after 70 min treatment with the PDI/GO photocatalyst, achieving almost complete degradation. In addition, the PDI/GO photocatalyst also demonstrated that it still maintains good catalytic performance in complex environmental systems and effectively degrades target dyes. These findings provide valuable experimental evidence and theoretical support for the application of PDI/GO photocatalytic materials in the treatment of printing and dyeing wastewater. It is recommended that future research should focus on the study of high-efficiency degradation mechanism of high-concentration dye wastewater and on the optimization of the catalytic system for practical application scenarios with high pollution loads.

Key words: printing and dyeing wastewater, organic semiconductor, graphene oxide, degradation, reactive dye, photocatalysis, wastewater treatment