Facile Preparation of Haggite by Reducing V2O5 in Guaiacol

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Facile Preparation of Haggite by Reducing V2O5 in Guaiacol/ Methanol Solution Fei Yan,† Yunfei Bai,† Yushuai Sang,† Linhao Yu,† Kai Wu,† Kai Cui,† Zhe Wen,† Fuhang Mai,† Zewei Ma,† Hong Chen,*,‡ and Yongdan Li*,†,§ ‡

School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China State Key Laboratory of Chemical Engineering, Tianjin Key Laboratory of Applied Catalysis Science and Technology, School of Chemical Engineering, Tianjin University and Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China § Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, Kemistintie 1, P.O. Box 16100, Espoo, Aalto FI-00076, Finland

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4.050, 3.510, 3.020, 2.440, 1.959 and 1.815 Å. The reduction occurs at 240 °C and finishes within 6 h. Furthermore, V2O5 is reduced to Haggite within the heating-up process (less than 90 min) when the reaction temperature is set at 280 °C. We used different alcohols to reduce V2O5, and the results are presented in Figure 1. When V2O5 is reduced in methanol for 0

ABSTRACT: Haggite-structured V4O6(OH)4 is prepared via a one-step reduction of V2O5 in a mixture of guaiacol and methanol. Guaiacol delays the overreduction of Haggite to V2O3. The time window for the stable existence of the Haggite phase is enlarged at low temperature.

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oth vanadium oxide and oxyhydroxide exhibit a number of structures with different compositions and valences and are applied in many fields, such as the catalyst for oxidation reactions,1,2 cathode materials for rechargeable Li-ion batteries and the electrode for Na-ion batteries,3−6 sensitive materials in thermo- and electrochromic windows,7,8 and other thermoelectric devices.9 Some vanadium compounds, for example, V2O3, Ca1−xSrxVO3, and BaVS3, VO2, show specific electrical properties, for instance, metal-to-insulator transition, which is utilized in smart control.10 Haggite is a scarce black vanadium mineral found in sandstone drill core from Carlile, WY, in the 1950s.11 The chemical formula of Haggite was described as VIVVIIIO2(OH)3 for about half a century since the report of Evans and Mrose.11 Because of the lack of a synthetic method, its property information only came from its mineral sample until the work of Wu et al.12 and Besnardiere et al.13 Wu et al. reported a multistep and time-consuming, >13 h, method to prepare Haggite, possessing a semiconductor−insulator transition at 66 K with an abrupt change of its conductivity and magnetic response, and proposed a chemical formula of Haggite as V4O6(OH)4 in which all vanadium was V4+. Later on, Besnardiere et al. reported a 4.5-day one-step aqueous method to prepare Haggite. Here, Haggite is easily synthesized with one-step V2O5 reduction inguaiacol/methanol solution (1:47.5, w/w) under mild conditions. The reaction was carried out in an autoclave, and the time started when the autoclave was heated to the desired temperature from room temperature. The prepared Haggite shows XRD peaks at 2θ = 18.469°, 21.928°, 25.354°, 29.554°, 36.805°, 46.308° and 50.225° indexed to the (0 0 1), (−2 0 1), (2 0 1), (4 0 0), (1 1 1), (−6 0 1) and (1 1 2) planes. The corresponding lattice spacings of these planes are 4.800, © XXXX American Chemical Society

Figure 1. XRD patterns of materials obtained by reducing V2O5 in different solvents at 280 °C for different times.

h, the diffraction pattern contains the peaks of V2O3 (PDF 340187) withvery small shift to lower diffraction angle and the peaks of Haggite (PDF 29-1380). In addition, some peaks in this pattern cannot be assigned. In the pattern of the material obtained by reducing V2O5 in methanol for 1.5 h, only the peaks of V2O3 show up with small shift to higher diffraction angle. When V2O5 is reduced in ethanol for 1 h, the diffraction pattern contains the peaks of V2O3 and Haggite. However, a few peaks in Received: April 11, 2018

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DOI: 10.1021/acs.inorgchem.8b00987 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry this pattern cannot be assigned. In the pattern of the material obtained by reducing V2O5 in n-propanol for 1 h, the peaks of Haggite show up, while the other peaks cannot be assigned. When V2O5 is reduced in n-butanol for 1 h, no obvious peak occurs. In the pattern of the material obtained by reducing V2O5 in isopropyl alcohol for 1 h, the weak peaks of Haggite show up, while two strong peaks at 2θ = 41.73° and 54.76° cannot be assigned. The oxidation products of these solvents were detected by gas chromatography−mass spectrometry (GC−MS) (Figure S1). Ethyl acetate, 2-butenal and 1,1-diethoxyethane are the oxidation products of ethanol. 1-propenyl propyl ether, propyl propanoate and 1,1-dipropoxypropane are the oxidation products of n-propanol. n-butanal, 1-butenyl n-butyl ether, butyl butyrate and 1,1-dibutoxybutane are the oxidation products of n-butanol. However, we did not find the oxidation products of isopropyl alcohol with GC−MS. The NMR results of the liquid from the reactions with methanol and isopropyl alcohol as solvents are provided in Figures S2 and S3. Because pure methanol over-reduces V2O5 to V2O3 and it is reported that guaiacol reacts with vanadium oxide,14 we speculate that guaiacol can delay the reduction of Haggite to V2O3. Therefore, the reduction of V2O5 was carried out inguaiacol/methanol solution (1:47.5, w/w) and the XRD patterns of the solid samples both before and after the reaction are shown in Figure 2. Fresh V2O5 shows a well-defined pattern

Figure 3. SEM images of raw V2O5 (a and b) and Haggite obtained by reducing V2O5 in a guaiacol/methanol solution at 280 °C for 0 h (c and d).

Figure 4. (a) GC−MS curve of the liquid obtained in the reduction of V2O5 in a guaiacol/methanol solution. (b) Total yield of alkylphenols when V2O5 was reduced in a guaiacol/methanol solution at 280 °C for different times. Note: Anisole is the internal standard for quantification.

oxidation, and acetal reactions (Figure S4). In addition, methanol is the alkylation reagent for guaiacol. An experiment with only the guaiacol/methanol solution at 280 °C shows that guaiacol cannot be reduced by methanol itself. Hence, the solid connects methanol and guaiacol. That is to say, the solid oxidizes methanol to acetals and reduces guaiacol to alkylphenols. Figure 2 shows that V2O5 was reduced to Haggite in the preheating process. Then Haggite was not further reduced during 0−3 h. After 3 h, Haggite was further reduced to V2O3. Figure 4b shows that the reduction of guaiacol happens from 0 to 3 h when the solid phase is Haggite. In Figure 5, X-ray photoelectron spectroscopy (XPS) shows that both V4+ and V3+ exist on the surface of Haggite with a 62:38 ratio. According to the above-mentioned information, we propose a scheme for the reaction (Scheme 1). V2O5 is first reduced to the Haggite structure by methanol without the interference of guaiacol. Then a superficial lattice oxygen of Haggite is removed to oxidize methanol, while the adjacent V4+ on the surface is reduced to V3+. Later on, the oxygen vacancy is refilled with

Figure 2. XRD patterns of raw V2O5 and the materials obtained by reducing V2O5 in a guaiacol/methanol solution at 280 °C for different times.

of V2O5 (PDF 65-0131). In addition, the raw V2O5 shows a layered structure, as shown in Figure 3a,b. The materials obtained by reducing V2O5 at 280 °C for 0−3 h were determined to be Haggite. The obtained Haggite shows a flower-like morphology composed of numerous sheets (Figure 3c,d). The sample reduced at 280 °C for 6 h presents the peaks of both Haggite and V2O3. (Figure 2) Guaiacol is mainly reduced and alkylated to 2,6-dimethylphenol, 2,3,6-trimethylphenol, 2,3,5,6tetramethylphenol and 6-methyl-2-tert-butylphenol (Figure 4a). The products of methanol oxidation are 1,1-dimethoxyethane, 1,1-dimethoxypropane and 1,1-dimethoxy-2-methylpropane. These products are formed by methanol via the Guerbet,15 B

DOI: 10.1021/acs.inorgchem.8b00987 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 5. XPS of the V 2p energy region of the Haggite derived by reducing V2O5 in a guaiacol/methanol solution at 280 °C for 1 h.

Scheme 1. Reducing Pathways of V2O5 in a Guaiacol/ Methanol Solution

Figure 6. XRD patterns of the materials obtained by reducing V2O5 in a guaiacol/methanol solution at different temperatures for 6 h.

In conclusion, Haggite is prepared by reducing V2O5 in guaiacol/methanol solution. In the solution, methanol reduces V2O5 to Haggite while guaiacol protects Haggite from being overreduced to V3O5. In total, we found two strageties to extend the time window of Haggite phase: 1. Lower the temperature; 2. Add guaiacol to create a protective surface layer on Haggite to delay the reduction of the bulk phase.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00987. Experimental section, oxidation products of different solvents, 1H NMR spectra and proposed reaction paths of methanol (PDF)

oxygen from guaiacol and the superficial V3+ is reoxidized to V4+. Meanwhile, guaiacol is reduced to alkylphenols. In fact, the surface of Haggite is involved in this cycle as a catalyst, which is the reason why the Haggite phase remains stable for 0−3 h. In step 1, the solid changes from V2O5 to V4O6(OH)4, which causes change of the skeleton of the solid. In step 2, the catalytic cycle may cause change of Haggite’s morphology. These two reasons caused the huge morphology difference between V2O5 and Haggite. However, after 3 h, the concentration of guaiacol is too low to retain this cycle, so Haggite is further reduced to V2O3. In contrast, when V2O5 is reduced in pure methanol at 280 °C for 0 h, V2O3 has shown up (Figure 1). Therefore, guaiacol protects Haggite from being overreduced, thus extending the time window for the Haggite. The reduction of V2O5 was then carried out in guaiacol/ methanol solution (1:47.5, w/w) at 240−300 °C for 6 h, and the XRD patterns of the obtained solid materials are plotted in Figure 6. The materials obtained at 240 and 260 °C were confirmed to be Haggite. The material formed at 280 °C shows peaks of both Haggite and V2O3. The sample produced at 300 °C was determined as V2O3. Apparently, the higher the temperature, the higher the chemical reaction rate. Therefore, at 240−260 °C, the Haggite structure can be obtained even after 6 h. At 280 °C, part of V2O5 has already been reduced to V2O3 after 6 h, and at 300 °C, V2O5 has been completely reduced to V2O3 after 6 h. Hence, Haggite can exist for a longer time at lower temperature.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: yongdan.li@aalto.fi. ORCID

Hong Chen: 0000-0002-0325-2786 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Natural Science Foundation of China under Contracts 21336008 and 21690083 and the Ministry of Science and Technology of China under Contract 2011DFA41000 is gratefully acknowledged. This research was also supported, in part, by the Program of Introducing Talents to the University Disciplines under File No. B06006 and the Program for Changjiang Scholars and Innovative Research Teams in Universities under File No. IRT 0641. We sincerely appreciate Dr. Binglin Tao from the University of Warwick for his contribution to the Table of Contents/Abstract graphic.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b00987 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b00987 Inorg. Chem. XXXX, XXX, XXX−XXX