The ZnO-NiO nano-composite: A brief characterization, kinetic and thermodynamic study and study the Arrhenius model on the sulfasalazine photodegradation

The coupled ZnO–NiO nano-composite (NC) was prepared and identified by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), UV–Vis diffuse reflection spectroscopy (DRS) and Fourier transformation infrared spectroscopy (FTIR) characterization techniques. The crystallite sizes of about 6.7, 36.7 and 29.5 nm were obtained for the NiO, ZnO, and ZnO/NiO samples by the Williamson-Hall equation, and about of 33.5, 33.8 and 39.8 nm by the Scherrer equation, respectively. The energy dispersive X-Ray analysis (EDX) showed a NiO:ZnO mole ratio of 3.1 for the composite. The band gap energies of 3.49, 3.19, and 3.02 eV were estimated for the NiO, ZnO, and ZnO–NiO samples by using the absorption edge wavelengths of 355, 388, and 410, respectively. The pHpzc values of 9.3, 8.8, and 7.6 were also estimated for the NiO, ZnO, and ZnO–NiO samples respectively. At initial steps of the work about 42%, 60%, and 87% of a 10 mg/L SZ solution were degraded by the ZnO and NiO NPs and the ZnO–NiO NC, respectively. The best photocatalytic activity was obtained at pH 6.5 (near the pHpzc: 7.6), 0.7 g/L of the catalyst, and 7 mg/L sulfasalazine (SZ). The rate constants of 0.0904 min−1 (t1/2 = 7.66 min) and 0.0915 min−1 (t1/2 = 7.57 min) were obtained for the SZ photodegradation and mineralization processes, respectively. The frequency factor of 2.131 × 104 min−1 and the activation energy of 15.87 kJ/mol were obtained for the process by the Arrhenius equation. A negative activation ΔS (−0.22 kJ/mol) with the positive ΔH and ΔG values obtained for the SZ photodegradation by the ZnO–NiO composite.