Adsorption behaviors of methylene blue onto tubular cadmium sulfide polycrystals
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ORIGINAL ARTICLE
Adsorption behaviors of methylene blue onto tubular cadmium sulfide polycrystals Dian‑Qian Wang1,2 · Ying‑Sheng Wang1 · Zuo‑Xun Xie1 · Wei‑Min Zhang1 Received: 3 January 2020 / Accepted: 8 October 2020 © Islamic Azad University 2020
Abstract The temporal evolution of methylene blue’s adsorption onto tubularly mesoporous CdS synthesized by templating the fibrous precursor of cadmium oleates is investigated using the batch experiment method. UV–visible measurements on the supernatants at λ = 665 nm reveal the adsorption of methylene blue at 25 and 5 °C exhibits the type IV isotherms, having the typical features of mesoporous materials, and the isotherm can be fitted by Freundlich and Langmuir equation for low and high ce, respectively. The adsorption enthalpy change H, which is estimated − 12 kJ/mol, reveals the H-bond existing between CdS and MB molecules. The first hour of contact has proved to be a quite rapid dynamics, and subsequently, the dye molecules go through a tardy process in 30–36 h to reach the equilibrium. The uptake of methylene blue by tubular CdS is interpreted by pseudo-second-order model better than by pseudo-first-order model, and the experimental data over the whole adsorption process can be described based on the intraparticle diffusion model. Keywords Semiconductor · CdS · Adsorption · Isotherm · Kinetic model
Introduction Cadmium sulfide (CdS) has received much attention due to its direct band gap resulting in highly effective absorption of visible light [1–3]. It can be applied in photo-degrading the organic molecules [4–8], producing hydrogen through photolysis of water [9–11], bioimaging [12], and solar energy conversion [13]. When it is irradiated by the light with energy above 2.42 eV, electrons will be excited from the valence band (VB) to the conduction band (CB), producing pairs of e−–h+ as the charge carriers [14, 15]. The photo-induced electrons migrate from bulk to surface and then transfer to the pre-adsorbed organic species to make them reduced. The pre-adsorbed methylene blue (MB) molecules can prompt the electron transfer process greatly [16]. They absorb visible Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40089-020-00316-8) contains supplementary material, which is available to authorized users. * Wei‑Min Zhang [email protected] 1
School of Chemistry and Chemical Engineering, University of Jinan, Jinan, China
Kweichow Moutai Co., LTD., Renhuai, China
2
light to produce a singlet and/or triplet state, and electrons transfer from the singlet state to CB of CdS, facilitating the degradation process [17]. Previous studies on CdS paid much more attention on preparation, morphology, structure analysis, and photo-catalytic efficiency evaluation than on adsorption behaviors [18–23]. Very few studies are carried out with focus on adsorption mechanism of MB molecules on the surface of CdS, which is closely related with photo-catalyst surface modification and dye-sensitized photo-degradation of o
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