Zn-Co layered double hydroxide as a sustainable photocatalyst with structural parameters for the visible-light degradation of Ponceau 4R and tartrazine

Abstract This study generated Zn-Co LDH nanosheets using microwave-assisted co-precipitation at pH 10 and a 1:1 cation ratio. After microwave irradiation for 30, 60, and 120 min (LDH-30, LDH-60, and LDH-120), the materials were filtered, dried at 80 °C (LDH-80), and calcined at 300–500 °C for three hours. The chemical, structural, and morphological features of the synthesized materials were investigated using various characterization methods. The Williamson-Hall and modified Scherrer equations were used to evaluate grain size and lattice strain. The two models revealed that the duration of microwave irradiation significantly affects grain size and lattice strain. FE-SEM revealed flake development. Increasing the microwave irradiation period enhanced flake coalescence. The material was found suitable for visible-light-driven photocatalysis, as indicated by diffuse reflectance spectroscopy (DRS), with a band gap energy of 2.19 eV. LDH samples were tested for photocatalytic degradation of tartrazine (E102), Ponceau 4R (E124), and a combination of the two dyes under simulated solar visible light. Monitoring benzene ring skeleton and azo group degradation, calcined samples showed photocatalytic activity, with LDH-300 performing best. E124 dye exhibited higher removal efficiency than E102. The degradation process was affected by pH, reaction temperature, catalyst dosage, and initial dye concentration. Under optimum conditions, LDH-300 degraded E124 to 98.5% under visible irradiation, with considerable mineralization (~ 85%), confirming effective degradation beyond decolorization during TOC analysis. Control studies with dark adsorption and photolysis showed that neither light nor adsorption alone explains the observed elimination. Adsorption equilibrium was reached after 120 min, with Langmuir behavior demonstrated by isothermal analysis (R² = 0.9772). With pseudo-first-order kinetics, degradation was spontaneous and endothermic. The activation energy for E124 was 17.7 KJ/mol for the skeletal benzene ring and 18.0 KJ/mol for azo group degradation. The Zn-Co catalyst showed good stability and reproducibility. The hydroxyl radical is essential to photodegradation.