Mechanism of enhanced photocatalytic activity of Cr-doped ZnO nanoparticles revealed by photoluminescence emission and electron spin resonance

Abstract

In this work, we successfully synthesized Cr 3+ doped ZnO nanoparticles using a sol-gel method, and elucidated how Cr 3+ dopant is critical for enhancing photocatalytic activity. The nature of the point defect analyzed by electron spin resonance (ESR), and photoluminescence (PL) emission revealed the role of the Cr 3+ dopant. When introducing Cr 3+ ions in ZnO, the PL emission intensity decreased, indicating a reduction of the radiative recombination rate due to the heterojunction formation between the dopant and the host. The Cr 3+ doped ZnO nanostructures showed that the typical ESR signal with g-factor value ∼1.96 was completely passivated, indicating the diffusion of electrons near the conduction band into the dopant ions. The doped Cr 3+ ion acts as an electron trap in the ZnO crystal described as3 2The mechanism for enhancing the photocatalytic activity of heterogeneous ZnO:Cr 3+ was proposed in respect of point defect evolution through the manner of Cr 3+ doping. As a result, the photocatalytic efficiency investigated by measuring methylene blue degradation under 210 min of direct sunlight irradiation reached 93.5% for 1 at % Cr 3+ doped ZnO, which was significantly improved compared to 59.8% of the pure ZnO.

ON THE CONTRIBUTION FACTORS OF ENHANCED PHOTOCATALYTIC ACTIVITY OF DOPED SEMICONDUCTORS: STRUCTURAL AND OPTICAL INTVESTIGATION OF CU2+ DOPED ZnO NANOPARTICLE

“…The Zn1-xCuxO samples with x = 0.0 and 0.01 were prepared by sol-gel method similar to previous reports [10,11]. Typically, the zincnitratehexahydrate -Zn(NO3)2.6H2O (Sigma-Aldrich) and copper(II) nitrate trihydrate -Cu(NO 3 )2.3H2O (Sigma-Aldrich) were mixed with citric acid -C6H8O7.H2O 1M (Sigma-Aldrich) with a molar ratio of metal ions : acid = 1:3.…”

“…After 150 min of exposure to visible light, the MB degradation efficiencies were about 54.95 % and 76.65 % for ZnO and ZnO:Cu, respectively. The doping effect on the enhanced photocatalytic activity could be from various reasons such as ZnO bandgap reduction [19], enhanced light absorption [20], and excited carriers separation [11] which all affect photoelectron-hole generation/recombination processes.…”

Titanate Tubular Loaded Diatom Fabricated by a Facial Hydrothermal Method for Photocatalytic Enhancement under Visible Light Irradiation

“…Organic ingredients in textile wastewater are very difficult to biodegrade and toxic to the environment [1]. Consequently, scientists around the world are studying to find ways to handle organic components in wastewater [2]. TiO2 nanomaterials with tubular structure (TNT) have shown superiority in the treatment of textile wastewater by photocatalytic ability [3].…”

Photoluminescence Emission and Raman Vibration Properties of Asymmetric Nanoparticle ZnO Doped Mn2+ Fabricated by a Solvothermal Method

“…However, in the natural sunlight, there is a small amount of UV-light ~3%. Hence the bandgap engineering of ZnO has been intensively investigated such as doping ZnO with other elements [5][6][7][8][9], coating ZnO with other materials [10,11]. Recently, S. Choi et al [7] found that when ZnO doped with transition metal ion Cu 2+ , the photocatalytic activity of ZnO was improved thanks to the separation of the excited carrier.…”

“…Recently, S. Choi et al [7] found that when ZnO doped with transition metal ion Cu 2+ , the photocatalytic activity of ZnO was improved thanks to the separation of the excited carrier. Recently, we have shown that the Cr 3+ could be play as an electron trap center in the hydrothermal ZnO doped Cr samples [5]. It means that the photoelectrons were trapped then would leave holes without recombination.…”