Enhanced Photocatalytic Ozonation of Phenol by Ag/ZnO Nanocomposites

Abstract

Ag/ZnO nanocomposites were synthesized and applied in the photocatalytic ozonation of phenol. Their crystal, textural, morphological, optical, and electrochemical properties were investigated by XRD, Raman, SEM, TEM, UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoemission spectroscopy (XPS), and photoluminescence (PL) techniques in detail. The results indicated that silver nanoparticles were well dispersed on the surface of porous ZnO and the intimate contacts were formed at the Ag/ZnO interfaces. This prominently favored the separation and transfer of photoinduced electrons from ZnO to Ag nanoparticles for the activation of ozone to produce •OH and •O 2 − . As a result, a significant enhancement in photocatalytic ozonation of phenol was achieved over Ag/ZnO catalysts. It also showed a synergistic effect between photocatalysis and ozonation.Catalysts 2019, 9, 1006 2 of 12 pairs [20][21][22][23]. In addition, the supported metal nanoparticles can work with the semiconductor to cocatalyze chemical reactions [24][25][26]. In this study, Ag nanoparticles were employed to decorate ZnO for photocatalytic ozonation of organic pollutants by means of their unique properties. Experimentally, Ag nanoparticles were deposited onto the ZnO surface via a photochemical approach and the resultant Ag/ZnO catalysts were well investigated by XRD, Brunauer-Emmett-Teller (BET), TEM, SEM, X-ray photoemission spectroscopy (XPS), and electrochemical measurement. Phenol was chosen as a model contaminant to assess the catalytic performance. Electron paramagnetic resonance (EPR), along with quenching experiments, was conducted to probe the role of active species in the phenol removal and mineralization. Furthermore, the possible reaction mechanism over Ag/ZnO nanocomposites was proposed. Results and Discussion Catalysts Characterization

The Adsorption of Ozone on the Solid Catalyst Surface and the Catalytic Reaction Mechanism for Organic Components

“…The role of Ag nanoparticles in Ag/ZnO (Figure 21) was the same as the MnO 2 in TiO 2 /MnO 2 heterojunction catalyst (Figure 20), which prominently favored the separation and transfer of photoinduced electrons from the CB of ZnO to Ag nanoparticles for the activation of ozone to produce ⋅OH and ⋅O 2 À . [37] Bi photocatalysts were a hot spot in the recent decade. Liu and the co-workers [38] used the hydrothermal method to synthesized a hierarchical biomimetic monoclinic bismuth vanadate (BiVO 4 ) with leaves morphology and employed the leaves-shaped BiVO 4 for oxalic acid and penicillin degradation in photocatalytic ozonation.…”

“…The proposed mechanism for the photocatalytic ozonation of phenol over Ag/ZnO. [37] Reprinted from Ref. [37] Copyright 2019, with permission from MDPI.…”

“… The proposed mechanism for the photocatalytic ozonation of phenol over Ag/ZnO [37] . Reprinted from Ref.…”

“…In addition to TiO 2 , having photocatalytic activity, ZnO and bismuth vanadate both were promising candidates for photocatalytic ozonation reactions and have attracted much attention. For ZnO, no matter it was used to modify TiO 2 to prepare Zn‐TiO 2 nanocomposites or silver nanoparticles were dispersed on the surface of porous ZnO to prepare Ag/ZnO nanocomposites, Zn‐TiO 2 [36] and Ag/ZnO [37] nanocomposites showed enhanced catalytic performance in the salicylic acid and phenol removal, respectively.…”

Novel Low Temperature Route to Produce CdS/ZnO Composite Nanofibers as Effective Photocatalysts

“…Among these processes, photocatalytic degradation using semiconductor materials is considered an advanced chemical process and an effective route to reduce the environmental pollution caused by industrial organic pollutants [5,6]. Various photocatalytic semiconductors have been applied to treat organic contaminants (e.g., ZnO, TiO 2 , CdS, and ZnS) [3,[7][8][9][10][11][12][13][14][15][16][17][18][19]. Among them, nanocomposites based on ZnO and CdS have attracted special attention owing to their facile preparation in various shapes and sizes using different techniques (e.g., electrochemical deposition, hydrothermal synthesis, precipitation, and sol-gel process) [8,9,17,[20][21][22][23][24].…”