Enhanced Visible Light Photocatalytic Degradation of Methylene Blue by CdS-ZnS-BiPO4 Nanocomposites Prepared by a Solvent-Assisted Heating Method

Abstract

In this study, a ternary CdS-ZnS-BiPO4 nanocomposite, synthesized by a solvent-assisted heating method, demonstrated the highest visible light-induced photocatalysis towards the degradation of methylene blue (MB) when comparing with BiPO4, CdS-BiPO4, and ZnS-BiPO4. Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) were used to characterize the prepared nanocomposites. From UV-DRS results, the energy band gap of the prepared BiPO4 structures was 4.51 eV. When CdS nanoparticles were deposited on BiPO4 surface by a solvent-assisted heating method, the prepared nanocomposites exhibited visible light-responsive photocatalytic degradation toward MB (20 ppm). At a molar ratio of Cd to Zn as 1:7, the prepared CdS-ZnS-BiPO4 nanocomposites exhibited the best photocatalytic activity in degrading 95% of MB dyes, out-performing pure BiPO4, CdS-BiPO4, and ZnS-BiPO4 due to its enhanced charge separation efficiency and the lowered carrier recombination from the efficient p-n junction of unprecedented ternary composites. The investigations on mechanism conclude that the major reactive species responsible for MB degradation are holes and oxygen radicals. For practicality, the degradation efficiency for different dyestuff (Fast Green FCF, Rhodamine 6G, Acid Blue 1, methyl orange, and methyl red) degradation in the different water matrix samples (pond water, seawater, and lake water) by the prepared CdS-ZnS-BiPO4 nanocomposites was evaluated.

Defective TiO2 Nanotube Arrays for Efficient Photoelectrochemical Degradation of Organic Pollutants

“…To compare the activities of treated and untreated TiO 2 films, the quantum yield (Φ) during the PEC reaction was studied. The Φ is defined as the ratio between the number of B41 dye molecules being degraded to the number of photons absorbed by the photocatalyst normalΦ = normaln normalu normalm normalb normale normalr 0.25em normalo normalf 0.25em normalm normalo normall normale normalc normalu normall normale normals 0.25em normald normale normalc normalo normalm normalp normalo normals normale normaln normalu normalm normalb normale normalr 0.25em normalo normalf 0.25em normalp normalh normalo normalt normalo normaln normals 0.25em normalo normalf 0.25em normall normali normalg normalh normalt 0.25em normala normalb normals normalo normalr normalb normale normald Based on the literature, the photodegradation rate of dye molecules under the monochromatic light source can also be used for the calculation of quantum yield using the following equation normalΦ = k 2.303 I 0 ε λ l Here I 0 represents the incident light intensity at a specific wavelength (in this study, 370 nm, 20 W, ∼0.7 × 10 –6 Einstein L –1 s –1 ), ε λ is the molar absorptivity of B41 chosen at 610 nm (27 934 cm –1 M –1 ), and l is the path length (3 cm) of the reaction container (75 mL) being illuminated. − The calculated Φ for the treated and untreated TiO 2 are 0.635 and 0.139 mol Einstein –1 , respectively. The Φ of the TiO 2– x film is 3 times higher than the pristine sample.…”

“…To compare the activities of treated and untreated TiO 2 films, the quantum yield (Φ) during the PEC reaction was studied. The Φ is defined as the ratio between the number of B41 dye molecules being degraded to the number of photons absorbed by the photocatalyst Based on the literature, the photodegradation rate of dye molecules under the monochromatic light source can also be used for the calculation of quantum yield using the following equation Here I 0 represents the incident light intensity at a specific wavelength (in this study, 370 nm, 20 W, ∼0.7 × 10 –6 Einstein L –1 s –1 ), ε λ is the molar absorptivity of B41 chosen at 610 nm (27 934 cm –1 M –1 ), and l is the path length (3 cm) of the reaction container (75 mL) being illuminated. − The calculated Φ for the treated and untreated TiO 2 are 0.635 and 0.139 mol Einstein –1 , respectively. The Φ of the TiO 2– x film is 3 times higher than the pristine sample.…”

Tailoring Morphology in Hydrothermally Synthesized CdS/ZnS Nanocomposites for Extraordinary Photocatalytic H2 Generation via Type-II Heterojunction

“…The band gap energy (E g ) usually depends on diffuse reflectance spectra, which can be calculated from the UV-DRS spectra via plotting (αhν) 2 against hν. Therefore, the band gap energy of CdS was 2.26 eV, as estimated by the Tauc plot (Figure 5b) [8]. The pure ZnS sample with a band gap of 3.32 eV exhibited electronic absorption in the UV light region.…”

“…Several approaches, such as morphology control [5], crystal phase control [6], heterojunction formation [7,8], doping with metals [9] and nonmetals [10] have been employed to overcome these limitations. Nowadays, methods to improve the photocatalytic performance of CdS mainly focus on structural engineering or surface modification.…”

Recent advances in bismuth oxyhalides photocatalysts and their applications

“…Recently, bismuth-based photocatalysts have been proven to exhibit high photocatalytic activity [13,14], such as Bi 2 O 3 [15,16], Bi 2 S 3 [17,18], Bi 2 MO 6 (M=W, Cr or Mo) [10,19], BiVO 4 [20,21], BiOX (X=I, Br, Cl) [22,23], BiPO 4 [24,25], (BiO) 2 CO 3 [26,27] and the other Bi 5+ -containing compounds. As shown in figure 1, the band positions of most bismuth-based photocatalysts are suitable for photocatalytic applications, including the removal of toxic substances in water as well as the conversion of fuel production.…”