Abstract
This study synthesized and characterized Ag-doped ZnO thin films. Doped ZnO powders were synthesized using the sol-gel method, and thin films were fabricated using the doctor blade technique. The Ag content was determined by optical emission spectrometers with inductively coupled plasma (ICP plasma). Additionally, X-ray diffraction, Raman spectroscopy, Atomic Force Microscopy (AFM), diffuse reflectance, and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. Finally, the photocatalytic degradation of methylene blue (MB) was studied under visible irradiation in aqueous solution. The Langmuir-Hinshelwood model was used to determine the reaction rate constant of the photocatalytic degradation. The physicochemical characterization showed that the samples were polycrystalline, and the diffraction signals corresponded to the ZnO wurtzite crystalline phase. Raman spectroscopy verified the ZnO doping process. The AFM analysis showed that roughness and grain size were reduced after the doping process. Furthermore, the optical results indicated that the presence of Ag improved the ZnO optical properties in the visible range, and the Ag-doped ZnO thin films had the lowest band gap value (2.95 eV). Finally, the photocatalytic degradation results indicated that the doping process enhanced the photocatalytic activity under visible irradiation, and the Ag-doped ZnO thin films had the highest MB photodegradation value (45.1%), as compared to that of the ZnO thin films (2.7%).
Highlights
The high concentration of organic dyes in wastewater has been a problem; synthetic dyes are recalcitrant compounds and are not completely degraded by conventional water treatments [1, 2]
For the Ag-doped Zinc oxide (ZnO) films with different silver contents, Figure 2 shows a signal shift located at 581 cm-1 towards lower wavenumber values near to 572 cm-1, and this change can be attributed to the dispersion contributions of the A1LO process outside the Brillouin area
All results corroborated the doping process; the red shift in the band gap values was detected after the doping process, from 3.22 eV (ZnO) to 2.95 eV (ZnO:Ag 1%)
Summary
The high concentration of organic dyes in wastewater has been a problem; synthetic dyes are recalcitrant compounds and are not completely degraded by conventional water treatments [1, 2]. The search for efficient, cheap, and green treatment processes for wastewater is a challenge around the world. In this context, the field of heterogeneous photocatalysis is aimed at synthesizing materials for the achievement of solar photodegradation processes (solar energy as a primary energy source) [3, 4]. Despite the fact that ZnO has been recognized as a promising photocatalyst, it has a high band gap value (~3.3 eV)—only 4% of the solar spectrum is effective to activate it. The doping process can modify the band gap of ZnO, generating electronic state intragap inside of the semiconductor ensuring the photoactivity redshift; on that topic, different authors have reported that ZnO changed photoresponse after the doping process [22]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
