Synthesis-acidity modulated TiO2@GO with enriched functional groups for efficient photodegradation of trace contaminant

As environmental pollution gets increasingly severe, the removal of trace contaminants has become a critical challenge in the field of water treatment. TiO₂@GO-based catalysts have exhibited excellent photodegradation performance, but so far, current research mainly focuses on investigating the function of oxygen vacancies while overlooking other potential factors, such as the role of GO, which hindered comprehensive understanding of TiO₂@GO-based catalysts. To address this, we propose a simple one-pot sol-gel method, where the catalyst properties are tuned by adjusting the synthesis acidity. Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), and Raman spectroscopy were employed to comprehensively characterize the physicochemical properties of the synthesized catalysts. Both the oxygen vacancy and surface functional group densities of the serial TiO₂@GO catalysts, as well as their photodegradation performance of indigo carmine are investigated. With increasing synthesis acidity, the surface oxygen vacancy proportion showed an increase–decrease pattern with a maximum at 0.1 mol l^-1 HCl, while the surface functional group density and photocatalytic efficiency toward indigo carmine exhibited a decrease-increase-decrease trend, also peaking at 0.1 mol l^-1 HCl but following a different overall pattern. Besides the common understanding that oxygen vacancies enhance photocatalytic degradation, the adsorption effects of functional groups on TiO₂@GO surface proved to be more significant. Additionally, TiO₂@GO also exhibits promoted photodegradation performance and a hydroxyl radical degradation mechanism via a common trace contaminant and radical probe, para-chlorobenzoic acid (pCBA). Density functional theory calculations further reveal that the surface functional groups would significantly enhance the adsorption of pCBA on TiO₂@GO, thereby improving their photodegradation performance. Our study provides new perspectives on understanding how enhancing the surface functionalization of TiO₂@GO-based catalysts helps to improve photocatalytic activity.