Photocatalytic Activity of Silver-Based Biomimetics Composites

Abstract

Different Ag@TiO2 and Ag@ZnO catalysts, with nanowire (NW) structure, were synthesized containing different amounts of silver loading (1, 3, 5, and 10 wt.%) and characterized by FE-SEM, HRTEM, BET, XRD, Raman, XPS, and UV–vis. The photocatalytic activity of the composites was studied by the production of hydrogen via water splitting under UV–vis light and the degradation of the antibiotic ciprofloxacin. The maximum hydrogen production of all the silver-based catalysts was obtained with a silver loading of 10 wt.% under irradiation at 500 nm. Moreover, 10%Ag@TiO2 NWs was the catalyst with the highest activity in the hydrogen production reaction (1119 µmol/hg), being 18 times greater than the amount obtained with the pristine TiO2 NW catalyst. The most dramatic difference in hydrogen production was obtained with 10%Ag@TiO2-P25, 635 µmol/hg, being 36 times greater than the amount reported for the unmodified TiO2-P25 (18 µmol/hg). The enhancement of the catalytic activity is attributed to a synergism between the silver nanoparticles incorporated and the high surface area of the composites. In the case of the degradation of ciprofloxacin, all the silver-based catalysts degraded more than 70% of the antibiotic in 60 min. The catalyst that exhibited the best result was 3%Ag@ZnO commercial, with 99.72% of degradation. The control experiments and stability tests showed that photocatalysis was the route of degradation and the selected silver-based catalysts were stable after seven cycles, with less than 1% loss of efficiency per cycle. These results suggest that the catalysts could be employed in additional cycles without the need to be resynthesized, thus reducing remediation costs.

Hydrogen Production and Degradation of Ciprofloxacin by Ag@TiO2-MoS2 Photocatalysts

“…Huerta-Aguilar and group [21] assigned the spacing measured to the (111) plane of the Ag lattice. Previous works [16,[22][23][24][25] reported similar results when sodium borohydride (NaBH4) was used as a reducing agent. The MoS2 (see Figure 3d) presented a spacing of ca.…”

“…For the commercial catalyst, the highest surface area (172 m 2 g −1 ) was also obtained with the catalysts containing a MoS 2 loading of 20 wt.% (5%Ag@TiO 2 -P25-20%MoS 2 ). Previous works [16,[22][23][24][25] have shown a direct relationship between the surface area and the amount of hydrogen produced. Table 1 shows the BET surface area of the composites containing silver and MoS2 ( 10 and 20 wt.%).…”

“…This difference is mainly attributed to the difference of surface areas of the catalysts (see Table 1). In fact, previous works [16,[22][23][24][25] have documented a direct relationship between hydrogen production and catalyst surface area. This behavior has been justified on the basis that higher surface areas provide charge separation in the form of trapping sites for photo-generated charge carriers [16,25].…”

“…As was shown in the P25-based catalysts, the fact that no saturation in hydrogen production was observed indicates that an increase in MoS 2 loading could lead to even higher hydrogen productions than those observed. When irradiated with visible light (λ > 400 nm), the electrons of the AgNPs are excited due to the plasmon resonance and injected into the CB of the TiO 2 [17], producing holes in the AgNPs that serve as oxidation agents that could lead to oxygen production or to their being quenched by a sacrificial electron donor [25]. The electrons that were injected to the conduction band of TiO 2 are gained by the water molecules, and hydrogen is produced.…”

“…As was described previously, these electrons can go to the MoS 2 or AgNPs. Once there, the electrons serve as catalytic sites for the production of hydrogen [25,50,51]. The holes that were created in the conduction band of the semiconductor act as oxidizing agents, producing oxygen.…”