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In the past few years, the quest for visible light active TiO 2 -based photocatalysts has been a hotly debated research topic in both scientific and practical fields. Attempting to meet the same purpose, in this study, a visible-driven nanocomposite, l -Histidine (2 wt%)-TiO 2 -CdS (7:1) nanocomposite, was dip-coated on the glass disc (rough vs. smooth) after the optimum composition was identified by varying the l -Histidine and CdS quantities. The prepared nanoparticles and coated catalyst on the disc were characterized by XRD, FT-IR, X-ray (FE-SEM/EDX), DRS, PL analyses in terms of their structural and optical properties as well as morphology. The coated photocatalyst was tested for photocatalytic degradation of direct red 16 (DR16) as an azo dye. The photodegradation process variables, including disc rotation speed, light intensity, irradiation time, and type of disc (smooth vs. rough glass disc)) were also modeled and optimized by central composite design (CCD). At the optimum conditions obtained, the effects of reaction time, pH, DR16 concentration, and aeration were investigated. After 3 h of using the rough disc (disc II) at a disc rotation speed of 100 rpm as well as a light intensity of 13 lumens per m2, DR16 was completely degraded. The pH and DR16 concentration seemed to have the reverse impact on the photodegradation process, whereas aeration had such a positive effect. By analyzing the effects of various scavengers, the contribution of reactive species in the photodegradation process was thoroughly investigated. Furthermore, the reusability results indicate no significant change in the photodegradation efficiency after four cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

The N and C N doped TiO 2 -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 TiO 2 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 TiO 2 -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 TiO 2 -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 TiO 2 -CuO, pH of 4 after 120 min). [ABSTRACT FROM AUTHOR]