Journal of Applied Spectroscopy, Vol. 87, No. 1, March, 2020 (Russian Original Vol. 87, No. 1, January–February, 2020) SYNTHESIS OF NANO-URCHIN Mo-DOPED VO 2 PARTICLES BY THE HYDROTHERMAL METHOD N. T. Manh, a,b N. T. Thanh, a,c P. D. Tam, a,d* V. T. N. Minh, e UDC 535.42/.44:620.3 C. X. Thang, a and V.-H. Pham a* This paper reports for the first time about the synthesis of nano-urchin Mo-doped VO 2 particles and their degradation properties in the presence of methylene blue (MB). Nano-urchin Mo-doped VO 2 particles were synthesized by the hydrothermal method, and their microstructure was controlled by the concentration of Mo. The Mo-doped VO 2 particles showed fast degradation of methylene blue in a relatively short time of 5–10 min. These results show the potential application of Mo-doped VO 2 particles for decolorization of dyers in environmental water treatment. Keywords: VO 2 , nanoparticle, hydrothermal, 3D structure, synthesis. Introduction. Vanadium dioxide (VO 2 ) nanoparticles have attracted increasing attention because of their wide application in many fields, such as smart window coatings, lithium batteries, catalysts, gas sensors, and lasers [1, 2]. Various methods have been used to synthesize VO 2 nanoparticles, such as thermal reduction [3], sol-gel [4, 5], microemulsion [6, 7], microwave [8], and hydrothermal methods [9, 10]. Among these methods, the hydrothermal method is of particular interest due to its simplicity and cost-effectiveness [11, 12]. It has been reported that V 4 O 9 nanoparticles [13] and V 2 O 5 films [14] can be used in dye degradation for environmental water treatment. In particular, to our knowledge, there are no reports on the decolorization of methylene blue (MB) by nano-urchin Mo-doped VO 2 particles. Herein, a novel, nano-urchin Mo-doped VO 2 particle was synthesized successfully by the hydrothermal method. Nano-urchin VO 2 particles were controlled by modulating the Mo concentration. The nano-urchin Mo-doped VO 2 particle can induce fast degradation of MB in a very short time, 5–10 min. The phase and microstructure of the Mo-doped VO 2 particles were characterized by XRD diffraction and scanning electron microscopy (SEM). The decolorization of blue MB by Mo-doped VO 2 particles was determined by UV–Vis spectrometer. Experimental Procedure. Molybdenum (Mo)-doped VO 2 particles were synthesized through a hydrothermal method as follows: an aqueous solution containing x mol of ammonium molybdate tetrahydrate (NH 4 ) 6 Mo 7 O 24 ·4H 2 O (99.99% purity, Merck), x = 0, 5, 8, 10, 14, and 20, was added to an aqueous solution containing 1 M ammonium metavanadate NH 4 VO 3 (99.99% purity, Aldrich) and 2 M oxalic acid (H 2 C 2 O 4 , 99.99% purity, Aldrich) in order to control the microstructure of the nanoparticles. The solutions were stirred for 0.5 h at room temperature. The mixture was transferred into a 200 mL Teflon- lined autoclave, and then the autoclave was sealed and maintained at 200 o C for 12 h. The resulting precipitates were washed twice and then dried at 80 o C for 2 h. The crystal structures of the Mo-doped VO 2 particles were characterized by X-ray diffraction (XRD, D8 Advance, Bruker, Germany). The microstructure and chemical composition of Mo-doped VO 2 particles were determined by field emission scanning electron microscopy FE-SEM JSM-6700F (JEOL Techniques, Tokyo, Japan). For the MB degradation test, 0.3 mg Mo-doped VO 2 nanoparticles were added to 30 mL methylene blue solution at pH 10 for varying times. The degradation of MB was determined by UV-Vis (Cary 500 spectroscopy). Results and Discussion. Figure 1 shows an XRD diagram of the Mo-doped VO 2 synthesized by the hydrothermal method with different Mo concentrations. The VO 2 specimen showed several strong peaks, which can be indexed to the a Advanced Institute for Science and Technology (AIST), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam; email: vuong.phamhung@hust.edu.vn; b School of Engineering Physics, Hanoi University of Science and Technology (HUST), Hanoi, Vietnam; c Quy Nhon University, Quy Nhon, Binh Dinh, Vietnam; d Faculty of Material Science and Engineering, Phenikaa University, Yen Nghia, Hanoi 1000, Vietnam; e School of Chemical Engineering, Hanoi University of Science and Technology (HUST), Hanoi, Vietnam. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 87, No. 1, pp. 29–32, January–February, 2020. Original article submitted November 5, 2018. 22 0021-9037/20/8701-0022 ©2020 Springer Science+Business Media, LLC _____________________ * To whom correspondence should be addressed. DOI 10.1007/s10812-020-00957-9