Abstract In this paper, we report about hydrothermal synthesis, structural characterization and photocatalytic properties of beta-silver molybdate ( β -Ag2MoO4) microcrystals obtained at different temperatures (100, 120, 140 and 160 °C) for 2 h. These crystals were characterized structurally using X-ray diffraction (XRD), X-ray fluorescence, Rietveld refinement, micro-Raman (m-Raman) and Fourier-transform infrared (FT-IR) spectroscopies. Experimental and theoretical band gap values were correlated by ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy and periodic first-principles calculations in the framework of density functional theory (DFT) with the B3LYP-D3 hybrid functional. The crystals morphology was observed through field-emission scanning electron microscopy (FE-SEM) images. The photocatalytic properties of these crystals were investigated for degradation of rhodamine B (RhB) dye under UV-light. XRD patterns and Rietveld refinement data indicate that all crystals exhibit a spinel-type cubic structure with space group (Fd3′m) formed by tetrahedral [MoO4] clusters and distorted octahedral [AgO6] clusters. m-Raman spectra exhibited five Raman-active modes in a range from 50 to 1000 cm−1, while FT-IR spectra have three infrared active modes in a range from 400 to 1100 cm−1. The experimental results from Raman and IR modes are in reasonable agreement with theoretically calculated results. Experimental UV–Vis spectra indicate a decrease in optical band gap (Egap = 3.35 eV to 3.32 eV) with the temperature rise. The calculated band structure revealed an indirect optical band gap (Egap) of approximately 3.94 eV. Moreover, theoretical calculations based on density of states and electron density maps were employed to understand the polarization phenomenon induced by structural defects in the β -Ag2MoO4 microcrystals. FE-SEM images revealed that the increase of processing temperatures promotes a change in shape of microcrystals from potatoes-like to coral-like. Finally, photocatalytic measures to degradation of the RhB dye resulted in the best catalytic performance for β -Ag2MoO4 microcrystals synthesized at temperatures of 120 and 140 °C, corresponding to 97.3% and 96.8% in the photodegradation of RhB dye under UV–light up to 2 h. The stability of the β-Ag2MoO4 was investigated by reusing, resulting in f 97.2, 93.9 and 78.8% degradation of the RhB dye for the first, second and third cycle, respectively.

中文翻译：

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β-Ag 2 MoO 4 微晶的水热合成、结构表征和光催化性能：实验数据与理论数据的相关性

摘要 在本文中，我们报告了在不同温度（100、120、140 和 160 °C）下 2 小时获得的 β-钼酸银 (β-Ag2MoO4) 微晶的水热合成、结构表征和光催化性能。使用 X 射线衍射 (XRD)、X 射线荧光、Rietveld 精修、微拉曼 (m-Raman) 和傅里叶变换红外 (FT-IR) 光谱对这些晶体进行结构表征。实验和理论带隙值通过紫外-可见（UV-Vis）漫反射光谱和密度泛函理论（DFT）框架下的周期性第一性原理计算与 B3LYP-D3 混合泛函相关联。通过场发射扫描电子显微镜（FE-SEM）图像观察晶体形态。研究了这些晶体在紫外光下降解罗丹明 B (RhB) 染料的光催化性能。XRD 图案和 Rietveld 精修数据表明，所有晶体均呈现尖晶石型立方结构，具有由四面体 [MoO4] 簇和扭曲八面体 [AgO6] 簇形成的空间群 (Fd3'm)。m-拉曼光谱在 50 至 1000 cm-1 范围内表现出五种拉曼活性模式，而 FT-IR 光谱在 400 至 1100 cm-1 范围内具有三种红外活性模式。拉曼和红外模式的实验结果与理论计算结果非常吻合。实验 UV-Vis 光谱表明光学带隙（Egap = 3.35 eV 至 3.32 eV）随着温度升高而减小。计算出的能带结构揭示了大约 3.94 eV 的间接光学带隙 (Egap)。而且，基于状态密度和电子密度图的理论计算被用来理解由 β -Ag2MoO4 微晶中的结构缺陷引起的极化现象。FE-SEM 图像显示，加工温度的升高促进了微晶形状从马铃薯状变为珊瑚状。最后，光催化降解 RhB 染料的措施导致在 120 和 140 °C 温度下合成的 β -Ag2MoO4 微晶具有最佳催化性能，对应于紫外光下 RhB 染料光降解的 97.3% 和 96.8% 2 小时。通过重复使用来研究 β-Ag2MoO4 的稳定性，导致 RhB 染料在第一、第二和第三个循环中的降解率分别为 97.2、93.9 和 78.8%。