In-situ ion-exchange synthesis Ag₂S modified SnS₂ nanosheets toward highly photocurrent response and photocatalytic activity

Highlights

• Constructed Ag₂S/SnS₂ heterojunction photocatalysts, by in-situ ion exchange method.

• Ag₂S/SnS₂ composite shows excellent photochemical activity and the high activity.

• h⁺ and OH are active groups in the photocatalytic degradation reaction.

Abstract

Heterojunction photocatalyst systems are deemed to be an excellent option to improve the photocatalytic behavior of a material. In this paper, Ag₂S/SnS₂ heterojunction photocatalysts were prepared by a simple in-situ ion exchange method from SnS₂ nanosheets. The Ag₂S/SnS₂ composite photoanode exhibits 13.99 μA/cm² photocurrent density at 0.7 V (vs. Ag/AgCl) in 0.5 M Na₂SO₄ solution and a significant increase in photocatalytic activity compared to SnS₂ nanosheets. Ag₂S (8 wt%)/SnS₂ composite shows the highest activity (0.0440 mg/min) in the degradation of MO and good stability. The reactive species trapping experiments confirmed hole (h⁺) and hydroxyl radical (OH) are active groups and play key roles in the photocatalytic degradation reaction. The highly effective photoelectrochemical and phocatalytic activities of Ag₂S/SnS₂ heterojunctions are attributed to the efficient separation of photogenerated hole-electron pairs. This work may provide a novel concept for the rational design of high performance SnS₂-based photocatalysts.

Introduction

Photocatalytic technology, with clean, economical and environmentally friendly features, is regarded as a green new technology. It is used not only as an efficient way to degrade environmental pollutants, but also produce hydrogen and oxygen by photolysis of water with the help of semiconductor catalysts [1]. Tin Disulfide (SnS₂) is acknowledged as an emerging metal dichalcogenide semiconductor. SnS₂ is earth-abundant and environmentally friendly as well as presents the layered sandwich structure and high chemical stability. The microstructures of SnS₂ can be shown as nanorod [2], nanotubes [3], [4], nanowires [5], nanobelts [6], [7], nanosheets [8], [9], [10], and nanoflowers [11], [12] by different synthesizing methods. Therefore, its various microstructures and properties aroused tremendously sparking interests of researches and designs for lithium ion batteries [13], [14], [15], [16], solar batteries [17], [18], [19], [20], transistors device [21], photocatalysts [22], [23], [24], [25], visible-light water splitting [26], antibacterial applications [27].

As a kind of photocatalysts, SnS₂ is applied for the degradation of organic dyes and the reduction of multivalent metal ions with the visible light irradiation [28]. All researching works of the above-mentioned literatures focused on the design of nanostructure of SnS₂, and concentrated on morphology controlling of SnS₂, and how the photocatalytic activity was influenced by the nanostructure and morphology of SnS₂. It have been reported that SnS₂ nanoparticles possess higher photocatalytic activity under the process of degrading aqueous formic acid and show an exceptional resistance to photocorrosion that compared with the CdS [28]. Zhong’s research also indicated that SnS₂ nanosheets arrays exhibited excellent photocatalytic property due to ultrathin structure of SnS₂ and rapidly diffusion rate of electron-hole pairs [23]. Tarasankar Pal’s group successfully synthesized SnS₂ nanoflowers and SnS₂ nanoyarns, and they featured out SnS₂ nanoflowers is tremendously efficient under the process of photocatalytic reduction of Cr(VI) than SnS₂ nanoyarns. This is attributed to the differences in their surface chemistry and morphology, which give SnS₂ nanoflowers a big specific surface area and many active sites [24]. However, the photocatalytic activity of SnS₂ is greatly limited by its low electrical conductivity and low absorbance value at the region of visible light. It is an effective way to enhance the photocatalytic property of SnS₂ that they are combined with other semiconductor materials to construct heterojunctions. There are some reports about SnS₂ heterojunctions, such as SnS₂/TiO₂ [29], [30], [31], g-C₃N₄/SnS₂ [32], [33], BiOCl/SnS₂ [34], and SnS₂/SnO₂ [35].

Among promising photocatalysts, silver-containing compounds AgPO₄ [36], [37], [38], [39], AgX(X = Cl, Br, I) [40], AgVO₄ [41], Ag₂MO₄ (M = Cr, Mo, W) [42], AgCO₃ [43], [44] and so on, show great high photocatalytic activity. Silver sulfide (Ag₂S) is a narrow direct band gap semiconductor (E_g = 0.9–1.1 eV). Ag₂S has a very wide absorption spectrum due to its narrow band gap, making it an efficient photocatalyst material. Silver sulfide can be used as a co-catalyst combined with other wide bandgap semiconductor photocatalysts to form heterojunction composite such as ZnS-Ag₂S, ¹¹Ag₂S-ZnO, ¹³Ag₂S/g-C₃N₄¹⁴ and Ag₂S-Ag-TiO₂¹⁷ and so on. However, the exploration of SnS₂-Ag₂S heterojunction photocatalysts is still rare. Herein we report a novel Ag₂S/SnS₂ photocatalyst, in which SnS₂ serves as the main photocatalyst and Ag₂S as the co-catalyst. It was shown that the formation of Ag₂S/SnS₂ heterojunction enhance the photocatalytic and photoelectrochemical (PEC) activity compared to bare SnS₂, along with remarkable stability.