Synthesis and Photoelectrocatalytic Applications of TiO2/ZnO/Diatomite Composites

Abstract

ZnO and TiO2 are semiconductor nanomaterials that are widely used in photocatalysis. However, the relatively high recombination rate and low quantum yield of photogenerated electron–hole pairs limit their practical applications. In this study, a series of TiO2/ZnO/diatomite composites with various compositions were successfully prepared via a two-step precipitation method. They exhibited stronger UV–visible absorption properties and substantially lower fluorescence intensities than those of ZnO and ZnO/diatomite, which was mainly due to the low recombination rate of the photogenerated electron–hole pairs in the composite system. The reaction intermediates of methylene blue were detected by liquid chromatography–mass spectrometry, and the degradation process was determined. The best composite catalyst was used for the degradation of gaseous methylbenzene and gaseous acetone. The gaseous acetone degradation product was determined to be acetaldehyde via gas chromatography–mass spectrometry. The results show that the composite catalyst exhibited a good photocatalytic degradation of both liquid pollutants and harmful volatile gases. When applied to the hydrogen and oxygen evolution reactions, the composite catalyst retained a good photoresponsivity and electrolytic efficiency.

Optically Transparent TiO2 and ZnO Photocatalytic Thin Films via Salicylate-Based Sol Formulations

“…While TiO 2 and ZnO photocatalysts are frequently used as nanoparticle suspensions in research [4,13] for practical applications and catalyst reusability, the development of photocatalytic coatings holds greater significance [11]. Typically, highly efficient TiO 2 and ZnO coatings are in the form of thick mesoporous layers to maximize their specific surface area [14].…”

“…The sol formulation contains at least three main components: a metal-ion-containing precursor, an organic solvent, and a stabilizing agent to limit undesired hydrolysis and improve sol stability. In TiO 2 sol formulations, titanium tetrachloride (TiCl 4 ) [13] and titanium (IV) tetraisopropoxide (TTIP, Ti(O-iPr) 4 ) [14,17,21,23] are commonly used as precursors, with the latter preferred due to its lower volatility and absence of toxic HCl released during hydrolysis. Isopropyl alcohol (IPA) is generally used as a solvent in the TTIP case.…”

“…Isopropyl alcohol (IPA) is generally used as a solvent in the TTIP case. As for ZnO deposition sols, while examples based on zinc alkoxides have been demonstrated [23], ionic Zn(II) compounds like zinc nitrate [17,24] and, in the predominant case, zinc acetate dihydrate (ZAD, Zn(CH 3 COO) 2 •2H 2 O), are more commonly employed in the literature [13,[25][26][27]. Formulating ZAD-based ZnO deposition sols presents challenges due to ZAD's poor solubility in organic solvents and proneness for self-hydrolysis, even in anhydrous media, due to the hydration water molecules [28].…”

“…The choice of stabilizing agent in both TiO 2 and ZnO sol formulations significantly impacts the quality and structure of the resulting thin films. Acetylacetone (AcAc) is typically used to stabilize TTIP-based sols [13,21,29], while monoethanolamine (MEA) or other substituted amines are employed in the ZAD case [20,26]. However, some studies have shown the interchangeability of these chelating agents between the two cases [13,30].…”

“…Acetylacetone (AcAc) is typically used to stabilize TTIP-based sols [13,21,29], while monoethanolamine (MEA) or other substituted amines are employed in the ZAD case [20,26]. However, some studies have shown the interchangeability of these chelating agents between the two cases [13,30]. For instance, Verma et al compared the effects of AcAc and diethanolamine (DEA) on TiO 2 films, finding that AcAc-stabilized sols produced films with increased transparency, while DEA led to improved electrochemical performance in terms of ion storage capacity, attributed to enhanced porosity [30].…”