Hussaini M, Vohra M. LDH-TiO
2 Composite for Selenocyanate (SeCN
-) Photocatalytic Degradation: Characterization, Treatment Efficiency, Reaction Intermediates and Modeling.
NANOMATERIALS 2022;
12:nano12122035. [PMID:
35745375 PMCID:
PMC9227849 DOI:
10.3390/nano12122035]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/02/2022] [Accepted: 06/09/2022] [Indexed: 02/06/2023]
Abstract
Selenium as a nutrient has a narrow margin between safe and toxic limits. Hence, wastewater discharges from selenium-containing sources require appropriate treatment that considers health concerns and stringent selenium-related water treatment standards. This work examined the use of a photocatalysis-cum-adsorption system based on a layered double hydroxide coupled with TiO2 (LDH-TiO2) to remove aqueous phase selenocyanate (SeCN−), which is difficult to treat and requires specific treatment procedures. The synthesized LDH and LDH-TiO2 composite samples were characterized using the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetry analysis (TGA) methods. The XRD results for the uncalcined LDH indicated a hydrotalcite mass with a rhombohedral structure, whereas increasing the calcination temperature indicated transition to an amorphous state. FESEM results for the LDH-TiO2 matrix indicated round titanium dioxide particles and LDH hexagonal layers. The TGA findings for uncalcined LDH showed a gradual decrease in weight up to 250 °C, followed by a short plateau and then a sharp decrease in LDH weight from 320 °C, with a net weight loss around 47%. Based on the characterization and initial selenocyanate adsorption results, the 250 °C calcined LDH-TiO2 matrix was used for the selenocyanate photocatalysis. A ~100% selenium removal was observed using LDH:TiO2 at a 1.5:1 w/w ratio with a 2 g/L dose, whereas up to 80% selenium removal was noted for LDH:TiO2 at a 0.5:1 w/w ratio. The respective difference in the efficiency of selenium treatment was attributed to enhanced LDH-based adsorption sites in the enhanced LDH:TiO2 w/w ratio. Furthermore, the selenite and selenate that occurred during SeCN− photocatalytic degradation (PCD) were also nearly completely removed via adsorption. An optimization exercise using response surface methodology (RSM) for total selenium removal showed R2 values of more than 0.95, with a prediction accuracy of more than 90%. In summary, the present findings show that the use of a photocatalysis-cum-adsorption system based on LDH-TiO2 is a promising technique to treat industrial wastewater discharges for selenocyanate and also remove the resulting intermediates.
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