CdS/ZnIn₂S₄/TiO₂ 3D-heterostructures and their photoelectrochemical properties

Abstract

We describe the synthesis and application of a three-dimensionally (3D) structured CdS quantum dot / ZnIn 2 S 4 nanosheet / TiO 2 nanotube array (CdS/ZnIn 2 S 4 /TiO 2 ) heterostructured material architecture. TiO 2 nanotube arrays (TiO 2 NTAs) are used as the synthetic template, subsequently sensitized using hydrothermal and successive ion layer adsorption and reaction (SILAR) techniques. The described synthesis approach offers a powerful technique for designing 3D heterostructure systems.Under AM1.5G illumination, the 3D CdS/ZnIn 2 S 4 /TiO 2 samples generate a photocurrent of approximately 4.3mA/cm 2 , with a photoconversion efficiency of 2%. Samples are tested for their ability to photocatalytically degrade target agents; noteworthy is that after 90 min illumination 100% of 2, 4-dichlorophenoxyacetic acid (2, 4-D) is removed. Charge carriers are produced when photons are irradiated onto the photocatalyst in the suspended solution. The bandgap of TiO 2 (3.2 eV), ZnIn 2 S 4 (2.6 eV) and CdS (2.4 eV) reduces progressively with the CB and VB increasing progressively to form a stepwise heterostructure that can absorb visible right. Under irradiation, photo-generated electrons are excited from the valence band (VB) to the conduction band (CB) of CdS, creating positive holes in the VB of CdS.Photo-excited electrons in the CB of CdS transfer to ZnIn 2 S 4 , and then migrating to TiO 2 .Meanwhile, holes are transported in the opposite direction at the heterojunction interface. The separated electrons and holes migrate to the surface as reducing agents and sacrificial reagents, respectively (eq (3), eq (4)). Oxygen molecules dissolved in the suspension capture the electrons in the conduction band, and the holes in the valence band are captured by H 2 O species adsorbed on the surface of the catalysts to produce the •OH radicals(eq (5), eq (6) and eq (7)), which subsequently degrades organic pollutants (eq (9)). 67, 68 Meanwhile, CB electrons may recombine with VB holes (eq (8)). 20 is recorded after irradiation 20 min, and the results are shown in Fig. 11B. From TiO 2 (curve c) to CdS/ZnIn 2 S 4 /TiO 2 (curve a), the PL intensity shows a gradual increase. The results confirm the best photocatalytic performance of CdS/ZnIn 2 S 4 /TiO 2 . ConclusionsA novel CdS/ZnIn 2 S 4 /TiO 2 heterostructure is prepared by a mild hydrothermal method combined with a SILAR technique. The photoelectrical performances of the as prepared materials are carefully investigated; optimal samples demonstrate a solar spectrum photoconversion efficiency of approximately 2.0%. Photocatalytic performance was tested by photodegradation of organic pollutants, with excellent efficiencies obtained; a photodegradation mechanism was proposed on the basis of band alignment to elucidate the enhancement of efficiency seen in the CdS/ZnIn 2 S 4 /TiO 2 material system. Fig.11. PL spectra measured during illumination with CdS/ZnIn 2 S 4/ TiO 2 (A) and different photoelectrodes (B): (a)

Hierarchical Ternary Sulfides as Effective Photocatalyst for Hydrogen Generation Through Water Splitting: A Review on the Performance of ZnIn2S4

“…These structures are called ternary metal chalcogenides. From among the family of AB2S4 semiconductors, ZnIn2S4 is the only member with a layered structure (see Figure 1b) [62]. It is a potentially visible-light-responsive photocatalyst reported with three different polymorphs, including, cubic, hexagonal and rhombohedral phase [63].…”

Using Gd-Enhanced β-NaYF4:Yb,Er Fluorescent Nanorods Coupled to Reduced TiO2 for the NIR-Triggered Photocatalytic Inactivation of Escherichia coli

“…The valid h + /e − pairs afterwards could react with H 2 O and O 2 in an aqueous solution (Equations ( 1)-( 7)) to produce reactive species. As it is known, the generated hydroxyl radical (•OH) species can be used as a strong oxidizer for the non-selective killing of bacteria [37]. The amount of •OH is detected by the fluorescent intensity of 2-hydroxyterephthalic acid (λ = 420 nm) which is a product of the reaction of •OH with terephthalic acid [38].…”

Fabrication of TiO2/Fe2O3/CdS systems: effects of Fe2O3and CdS content on superior photocatalytic activity

“…However, TiO 2 is active only under near-ultraviolet irradiation, only around 4% of the incident solar spectrum energy, due to its wide band gap energy of 3.0-3.2 eV. 4,5 Numerous attempts were made to extend the light absorption of TiO 2 to the visible light range, which accounts for around 48% of the incident solar energy. 6 Fe 2 O 3 is considered to be one of the best co-catalyst candidates due to its appropriate band gap (E g $ 2.2 eV) for solar light harvesting, good photochemical stability, earth abundance, nontoxicity and low cost.…”

“…Previous studies have shown that co-sensitizing TiO 2 with different nanocrystals such as CdS/ZnIn 2 S 4 , 4 CdTe/Mn-CdS, 12 CdS-Mn/MoS 2 /CdTe, 13 CdS/CuInS 2 /Au, 14 Mn-CdS/MoS 2 , 15 and CdS-based photocatalysts [16][17][18] can extend the light absorption to the infrared range, and more importantly align the energy bands of the semiconductor. In summary, combining TiO 2 with Fe 2 O 3 and CdS semiconductors could largely improve the photocatalytic activity of the co-sensitized electrode, as the energy levels of Fe 2 O 3 (bandgap $2.2 eV), CdS ($2.4 eV), and TiO 2 (3.0-3.2 eV) are well suitable to one another, which benets the separation of e À -h + pairs.…”

“…However, TiO 2 is active only under near-ultraviolet irradiation, only around 4% of the incident solar spectrum energy, due to its wide band gap energy of 3.0–3.2 eV. 4,5 …”