N (Urea) and C-N (L-Asparagine) doped TiO2-CuO nanocomposites: Fabrication, characterization and photodegradation of direct red 16

Abstract

The N and C-N doped TiO2-CuO nanocomposites with different loadings of urea (25, 40 and 50 wt. %), l-Asparagine (0.5-2.5 wt. %) as dopants and CuO (5-25 wt. %) were synthesized and their optimum composition characterized using different analyses such as XRD, FTIR, DRS, FESEM, and PL analyses. The photodegradation results showed that urea with a TiO2 to urea mass ratio of 3:2, l-Asparagine and CuO with a weight fraction of 2 and 10 % were the optimum amounts of the modifiers in the prepared nanocomposites. The C-N codoped TiO2-CuO indicates the highest photocatalytic activity for Direct red 16 (DR16) as azo dye compared to the other modified nanocomposites. The DR16 photodegradation efficiency of C-N codoped TiO2-CuO nanocomposite was also studied with four variables (DR16 concentration, photocatalyst concentration, initial pH and irradiation time) by central composite design (CCD). Experimental data showed that the pH of the solution has a considerable hindering effect on the dye removal efficiency while the role of photocatalyst concentration is minor in comparison with the other variables. Increasing DR16 concentration and initial pH of solution reduces dye removal efficiency. The photocatalyst concentration improves the photodegradation performance slightly but showed an inhibitory effect at photocatalyst concentration higher than 1.5 g/L. It must also be noted that irradiation time had a remarkable positive impact on the photocatalyst process. DR16 was completely removed at optimum conditions (25 ppm of DR16, 1.5 g/L of C-N codoped TiO2-CuO, pH of 4 after 120 min). © 2020 Elsevier Ltd. All rights reserved.