DFT calculation of hydrothermal mechanism on preparation of MoS 2
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ORIGINAL PAPER
DFT calculation of hydrothermal mechanism on preparation of MoS2 He Huang 1 & Na Liu 1 & Xueying Wang 1 & Qinglong Luo 1 & Xueli Huang 1 & Xuefeng Wang 1 & Mei Zhong 1 & Hongyu Zhang 2 Received: 16 April 2020 / Accepted: 26 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Basing on the simplest hydrothermal system containing deionized water, hexa-ammonium molybdate, and thiourea, hydrothermal mechanism on preparation of MoS2 was studied by DFT calculation. Hydrothermal process was divided into four steps which covered ionization equilibrium, the hydrolysis of CS(NH2)2, the formation of intermediates, and the formation of MoS2. Ionization equilibrium occurs at normal condition and determines the existence of Mo in the form of molybdic acid. Thiourea hydrolysis is rate-determining step in the process of hydrothermal which contains 10 elementary reactions. The formation of intermediates includes hydrogen transfer, dehydration, and vulcanization three steps which contain 18 elementary reactions, and the energy barrier of vulcanization is the highest. The formation of MoS2 is divided into two steps, the first step is that MoO(OH)(SH)3.H2O reacts with MoO (SH)4.H2O to form layer MoS2, and the second step is a very fast process that can affect the morphology of the products. Keywords Hydrothermal mechanism . Preparation of MoS2 . Thiourea hydrolysis . Intermediate
Introduction Since the discovery of graphene, MoS2 has drawn more attention due to graphene-like structure [1]. Various synthetic methods have been established to prepare MoS2 such as hydrothermal, solvothermal [2], template-assisted [3], chemical vapor deposition [4], and liquid exfoliation [5]. Among those methods, hydrothermal is considered as the effective method for preparation of MoS2. Many researches have been carried out on the effects of synthetic temperature, pH, and dosage of S source on the crystallinity, morphology, and electrochemical performance [6–10]. But the study of the hydrothermal mechanism is still in speculative stage, and no comprehensive accepted mechanism has been reported. Basing on the above Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00894-020-04521-2) contains supplementary material, which is available to authorized users. * Xueli Huang [email protected] 1
College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, People’s Republic of China
2
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, People’s Republic of China
previous researches [11–13], Wang [14] divided hydrothermal process into four steps, (1) the hydrolysis of CS(NH2)2 to produce H2S, (2) the formation of intermediate MoOxS(4-x), (3) the generation of MoS3, and (4) the thermal decomposition of MoS3 to produce MoS2. The fourth reaction takes place at 350 °C, and the hydrothermal do not reach such temperature. Ma [15] deemed that H2S acted as reducing agent which could convert MoO42− into MoS2 and S2− int
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