Green synthesis of Co-doped ZnO via the accumulation of cobalt ion onto Eichhornia crassipes plant tissue and the photocatalytic degradation efficiency under visible light

Abstract

Nowadays, water pollution is a major concern to the globe. For this reason, various research works has been done to access pure water thereby minimizing the effect of pollutants. In this work, the cobalt doped ZnO (Co-doped ZnO) via the accumulation of cobalt ion onto Eichhornia crassipes plant tissue for different days and combined with zinc precursor was synthesized. The resulting catalyst powder samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and Ultraviolet–vis (UV–vis) spectroscopy, and microwave plasma atomic emission spectrometer (MP-AES). The catalysts were also tested for the photocatalytic degradation of methylene blue (MB) in the presence of H2O2 under visible light irradiation. The best catalytic activity was gained by the 8th-days accumulation of cobalt ion onto the Eichhornia crassipes plant tissue and 99.6% of the dye was degraded within 45 min. However, 69.6, 65.7, 73.6, and 94.8% of MB dye was degraded by 1, 2, 4, and 6 days accumulations. Hence, removal of toxic heavy metal by using Eichhornia crassipes plant and recycling in the wastewater treatment gain is highly appreciated. Moreover, the Co-doped ZnO photocatalysts could enhance the photocatalytic activities due to suppressing of the electron and hole recombination and the porosity of the catalysts resulted from the Eichhornia crassipes plant after calcination.

Chromium Ion Accumulations from Aqueous Solution by the Eichorinia crassipes Plant and Reusing in the Synthesis of Cr‐Doped ZnO Photocatalyst

“…The absorption peaks showed at ~3457 and 1643 cm −1 indicate the stretching and bending vibration mode of O-H as a result of water molecule adsorbed on the prepared sample surface. Moreover, the FTIR peak at ~473 cm −1 indicates the stretching vibrational mode of the Zn-O bond [39,48]. The results indicate that the Crdoped ZnO catalyst was synthesized successfully.…”

“…The photogenerated holes can also interact with hydroxyl ion (OH -) or H 2 O to generate hydroxyl radical ( • OH) [15,27,59]. The reactive oxygen species resulting from the reaction will be interacted with MB dye and degrades into smaller degradation products [39,59]. Figure 8 illustrates the mechanism for MB dye oxidation with the Cr-doped ZnO catalyst.…”

“…Moreover, recycling performance of the heavy metals after accumulation on water hyacinth was also studied [38]. In our previous report, the cobalt ion accumulations onto Eichhornia crassipes for the purpose of cobalt doping on ZnO were also studied [39]. However, there was no report on the chromium ion accumulations onto water hyacinth and recycled for organic pollutant degradations.…”

Biogenic Synthesis of Cu‐Doped ZnO Photocatalyst for the Removal of Organic Dye

“…Simultaneously, the holes remained in VB of semiconductors [ 64 ]. After doping of Cu into ZnO, the electrons and holes recombination will be suppressed by trapping of electrons [ 23 , 28 ]. Then, the electrons remained on the surface of the catalyst and interacted with the adsorbed O 2 to generate a superoxide radical anion (O 2 ).…”

“…Due to its high stability, low cost, nontoxicity, great photoelectric conversion efficiency, and controllable material, ZnO is the most efficient semiconductor photocatalyst. However, ZnO requires UV light for photocatalytic activation [ 22 , 23 ].…”