Photocatalytic degradation abilities of binary core-shell SiO2@mZrO2/TiO2 nanocomposites: Characterization, kinetic and thermodynamic study of metoclopramide (MCP) eradication for water purification

Abstract

In this work, SiO2@ZrO2/TiO2 nanoparticles have been synthesized and characterized by FTIR, XRD, SEM-EDX, TEM, BET-BJH, TG-DTA and DRS analyses. In addition, the photocatalytic activity of the nanoparticles prepared has been investigated in the photodegradation and photomineralization of metoclopramide (MCP). In particular, hexadecylamine (HDA) was used in the coating process functions as the soft template for the preparation of silica@mesostructured metal oxide core-shell nanosphere. A band gap energy (Eg) of 2.94 eV was found for the SiO2@ZrO2/TiO2 sample, which corresponds to a 421.71 nm absorption edge wavelength. SiO2@ZrO2/TiO2 nanoparticles showed unusually smaller band gap energy in comparison with their parent oxides; namely, TiO2 (3.20 eV) and ZrO2 (5.02 eV), which could be due to the generation of heterojunctions between the two phases. The best photocatalytic activity was obtained at pH 5 (near the pHpzc: 4), 0.7 g/L of the catalyst, and 15 mg/L MCP. A Hinshelwood kinetic analysis of the photodegradation process yielded a rate constant of 0.033 min−1 with a t1/2 value of 21 min. When the photodegraded MCP solutions were subjected to the COD experiment k = 6.76 min−1 (t1/2 = 18.05 min) were obtained for the mineralized MCP molecules. An activation energy of 15.3 kJ/mol was obtained for the process using the Arrhenius equation. A negative ΔS‡ (-0.23 kJ/mol) with positive ΔH‡ and ΔG‡ values were obtained for the MCP photodegradation by the SiO2@ZrO2/TiO2 composite.