The Roles of Graphene and Ag in the Hybrid Ag@Ag2O-Graphene for Sulfamethoxazole Degradation

Abstract

Ag@Ag 2 O-graphene (Ag@Ag 2 O-G) with different concentrations of graphene was synthesized using a facile in situ precipitation method. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS). The antibioticsulfamethoxazole (SMX) degradationunder simulated solar light and visible light irradiationwas investigated to evaluate photocatalytic performance. The composite photocatalyst Ag@Ag 2 O-G with 2.5 wt% graphene presented the highest activity among all the prepared composite photocatalysts. The coupling of graphene and Ag 0 increased the photocatalyticactivity and stability of pure Ag 2 O. Under higher SMX concentrations, the adsorption, not the photocatalytic ability, playeda crucial role during the SMX removal process. On the basis of the characterization and reactive oxygen species (ROS) scavenging experiments, a separation and transfer mechanism of photogenerated carriers was proposed. In the photocatalytic degradation of SMX, the major active species wereidentified as photogenerated holes; photogenerated electrons in the conduction band (CB) of Ag 2 O could not transfer to graphene through Ag 0 due to the more negative reduction potential of graphene. This is an important result regardinggraphene and Ag 0 roles which isdifferent from that for the photocatalytic degradation of dyes. This researchmay provide new insights into photocatalytic processes for the degradation of non-dye pollutants bycomposite materials to guidethe design of highly efficient reaction systems.

Control of Membrane Fouling in Organics Filtration Using Ce-Doped Zirconia and Visible Light

“…As discussed in previous works [27,33,34,42], EPR studies indicated the generation of photo-induced holes and electrons, and the formation of • OH radicals when Ce-doped ZrO 2 was irradiated. Hence, to elucidate HA degradation mechanism with doped zirconia, a series of experiments were performed with disodium ethylenediaminetetraacetate (Na 2 -EDTA) (pointed as scavenger for holes [76] and a chelating agent that prevents HA adsorption on the oxide surface [73,77]) and isopropanol (commonly used as scavenger of • OH radical [77,78]). The results are shown in Figure 11.…”

Enhanced Antibacterial Activity at Ag–Cu Nanojunctions: Unveiling the Mechanism with Simple Surfaces of CuNPs-on-Ag Films

“…Figure 6B depicts Cu 2p XPS spectra with features at 932.0, 932.5, 933.59, and 934.88 eV, which correspond to Cu 2 O, Cu, CuO, and Cu(OH) 2 phases. 43 The oxidization of Ag is followed by a dramatic increase in metallic Cu and a significant rise in the Cu(OH) 45,46 At close interfacial contact, band bending occurs, allowing for charge carrier recombination to take place between the two oxides. 7 Figure 7 depicts a proposed mechanism scheme that represents the different phases involved in the antibacterial process on Ag−Cu film samples.…”

“…Figure 6B depicts Cu 2p XPS spectra with features at 932.0, 932.5, 933.59, and 934.88 eV, which correspond to Cu 2 O, Cu, CuO, and Cu(OH) 2 phases. 43 The oxidization of Ag is followed by a dramatic increase in metallic Cu and a significant rise in the Cu(OH) 45,46 At close interfacial contact, band bending occurs, allowing for charge carrier recombination to take place between the two oxides. 7 Cu(OH) 2 is quite significant since several reports have indicated that the formation of Cu(OH) 2 is directly related to enhanced release of ROS as well as increased amounts of Cu ions, as shown in previous studies, to exhibit the antibacterial effects by disrupting ATP production and impairing bacterial cell wall.…”

Recent Developments in ZnS-Based Nanostructures Photocatalysts for Wastewater Treatment

“…As seen in Figure 10 , the electrons from ZnS CB and GaOOH CB can reduce O 2 to O 2 − • active radicals due to their CB potentials which are more negative than that of O 2 /O 2 − • ( − 0.33 eV). The holes on the GaOOH VB transform OH − ions, adsorbed on the photocatalyst surface from the TC solution, to HO• because the GaOOH VB (2.83 eV) potential is higher than 1.89 eV for OH − /HO• [ 79 ]. Accordingly, the enhanced photocatalytic performance is the result of the efficient charge carriers’ separation and transport, and spatially separated reduction and oxidation sites in ZnS/GaOOH heterojunction, which act as Z-scheme heterojunction photocatalyst (confirmed by photodeposition and the ESR experiments’ results).…”