Feasible and Clean Solid-Phase Synthesis of LiNbO3 by Microwave

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A feasible and clean solid-phase synthesis of LiNbO3 by microwave-induced combustion and its application as catalyst for low temperature aniline oxidation Neftali Lenin Villarreal Carreno, Vinicius G Deon, Ricardo Marques Silva, Luiza R Santana, Rodrigo Mendes Pereira, Marcelo O. Orlandi, Wellington M Ventura, Anderson Dias, Jason Guy Taylor, Humberto V. Fajardo, and Marcia F. Mesko ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02921 • Publication Date (Web): 29 Dec 2017 Downloaded from http://pubs.acs.org on December 29, 2017

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ACS Sustainable Chemistry & Engineering

A feasible and clean solid-phase synthesis of LiNbO3 by microwaveinduced combustion and its application as catalyst for low temperature aniline oxidation

Neftali L. V. Carrenoa,*, Vinícius G. Deona, Ricardo M. Silvaa, Luiza R. Santanaa, Rodrigo M. Pereirab, Marcelo O. Orlandic, Wellington M. Venturad, Anderson Diasd, Jason G. Taylord, Humberto V. Fajardod, Marcia F. Meskob, #

a

Graduate Program in Materials Science and Engineering, Technology Development

Center, Federal University of Pelotas, 96010-000, Pelotas, RS, Brazil b

Chemistry, Pharmaceutical and Food Science Center, Federal University of Pelotas,

96160-000, Capão do Leão, RS, Brazil c

Department of Physical Chemistry, Institute of Chemistry, São Paulo State University

(UNESP), 14800-900, Araraquara, SP, Brazil d

Department of Chemistry, Institute of Exact and Biological Sciences, Federal

University of Ouro Preto, 35400-000, Ouro Preto, MG, Brazil

Corresponding author: * E-mail address: [email protected]; Telephone number: +55 53 3284-3880 #

E-mail address: [email protected]; Telephone number: + 55 53 3275 7387

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ABSTRACT In this work, a feasible, fast, clean and efficient microwave-induced combustion method for direct synthesis of LiNbO3 in solid phase was developed. X-ray powder diffraction studies showed that quasi-pure Li-Nb-O phases, such as LiNbO3 and Li3NbO4, or mixtures of LiNbO3, Li3NbO4 and LiNb3O8, could be successfully synthesized. The resulting powders were efficiently applied as catalysts under ambient conditions in the oxidation process of aniline using hydrogen peroxide as oxidant. The proposed method was performed in a commercial system using high-pressure quartz vessels, which allowed safe control of the reactions – that usually occurs in less than one minute. The results showed that the reaction conditions as well as the structural and morphological characteristics of the catalyst influenced the aniline oxidation process. Therefore, the present method for the preparation of LiNbO3 described herein, displayed many advantages when compared to conventional combustion methods, such as the physical characteristics of the obtained compound. Moreover, this new approach is considerably faster, safer and cleaner than other traditional procedures described in literature for LiNbO3 synthesis. This new microwave-induced combustion method is less time consuming, saves energy, as well as affording the stoichiometric formation of inorganic particles.

KEYWORDS: Microwave-induced combustion; Niobium compound synthesis; LiNbO3; Aniline oxidation; Low-temperature reactions.


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INTRODUCTION The oxidation of aniline is an important reaction for the synthesis of valuable

intermediates

in

industry

(such

as

phenylhydroxylamine,

nitrosobenzene, nitrobenzene, azobenzene and azoxybenzene). These molecules are generally used to produce pharmaceuticals, dyes, reducing agents, polymer stabilizers, food additives and liquid crystals for electronic displays.1-3 Stoichiometric quantities of metal oxidants, such as Pb(OAc)4, Hg(OAc)2 and BaMnO4 can be used to obtain the oxidation products of aromatic amines.4 However, they usually generate significant amounts of metal waste and environmental issues. Selective oxidation of aromatic amines is one of the most challenging reactions for heterogeneous catalysis. Achieving a highly selective catalytic process with reasonable substrate conversion for the oxidation of aromatic amines is hampered by competitive oxidation reactions, which form either Nphenylhydroxyamine, nitrosobenzene or nitrobenzene. Also, coupling reactions between nitrosobenzene and N-phenylhydroxyamine can occur and afford azoxybenzene and/or azobenzene.2 Both hydrogen peroxide and molecular oxygen are the best alternative oxidizing agents for satisfying the ideals of green chemistry given that they do not produce any toxic waste. Molecular oxygen is a more environmentally friendly source of oxygen than H2O2, and it has greater oxygen content. Very few heterogeneous systems are capable of activating molecular O2 at normal temperature and pressure although some success, has been achieved with the use of Au/TiO2 catalyst.5



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Considering the difficulty in activating O2, H2O2 is more often the preferred oxidant for oxidizing anilines due to its low cost and greater reactivity. Moreover, H2O2 has been employed for the oxidation of amines to their corresponding oxygen-containing derivatives in industry.6 Methods utilizing heterogeneous catalyst, such as rhenium, molybdenum, cobalt oxide, titanium silicate, heteropolyoxometalates (H3PW12O40), Ag/WO3, CuCr2O4, dimeric [Ln4(H2O)6(b-GeW10O38)2]12- anions, titanium silicalite-1, titanium (IV) oxide, Cu–CeO2, Nb2O5 with hydrogen peroxide as oxidant, have been developed for the oxidation of aromatic amines. 2,4,6-9 Although different heterogeneous systems have been developed for the oxidation of anilines with varying degrees of success in terms of substrate conversion and selectivity, there is still a demand for reusable and efficient heterogeneous catalysts that activates benign oxidants for the selective oxidation of anilines. In this sense, heterogeneous lithium-niobium based catalysts could be applied to the oxidation of aniline. To the best of our knowledge, there are no reports in the literature describing a lithium-niobium heterogeneous catalyst for the oxidation of aniline. Perovskite ferroelectric

structures

materials,

with

like

lithium

excellent

niobate

(LiNbO3)

physical-chemical

are

known

properties

for

applications as piezoelectrics, sensors, electro-optics and photonic devices.10-12 Several methods including sol-gel, polymeric precursors, mechanochemical synthesis, reactive molten salt, high-energy ball milling, co-precipitation and hydrothermal synthesis can be used to obtain these materials.13-16,17 Although these synthetic methods produce the desired products, they also generate hazardous waste products to the environment. In turn, combustion methods, also referred to as self-propagating high-temperature synthesis (SHS), have also been


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developed for the synthesis of LiNbO3 with appropriate chemical composition and homogeneity.18-21 In addition, these methods present some advantages when compared with all wet chemical methods, such as the possibility to use relatively simple equipment; the formation of high-purity products; the stabilization of metastable phases and the formation of virtually any size and shape products.21-22 Several works have reported the synthesis of nanomaterials using a microwave-induced combustion synthesis (MICS) such as ZnO,24 calcium phosphate nanowhiskers,25 nanocrystalline yttria,23 and titanium alumides.26 This method consists of igniting a mixture of desired metal salts and an organic fuel (urea, citric acid, glycine, among others), resulting in a self-sustained reaction that can reach temperatures as high as 1500°C, allowing the use of lower temperatures during the calcination steps and, in some cases, relatively short synthesis times.21 Fan et al.27 developed a MICS for the direct production of LiNbO3 in a few minutes, which resulted in nano-composites with porous structure for electrochemical devices. However, despite the advantages in time and overall quality of the obtained material, the Li-Nb-O precursor used for the combustion was prepared by a sol-gel method, which required a number of time consuming steps. In addition, this method uses large quantities of reactants (metallic nitrates), which are difficult to acquisition and present relatively high costs. Therefore, considering the importance of this issue, we describe herein a single process to develop a new, feasible, fast, clean and efficient microwaveinduced combustion (MIC) method for direct synthesis of LiNbO3 as a powder. Given that Brazil is the world’s largest producer of niobium,31 Nb2O5 was employed as precursor for the preparation of the catalyst. The potential of



LiNbO3-based catalysts for oxidation of aniline was investigated with hydrogen peroxide as oxidizing agent at ambient conditions (room temperature and under atmospheric pressure).

EXPERIMENTAL SECTION

Materials Optical grade niobium oxide (Nb2O5), from Companhia Brasileira de Metalurgia e Mineração (CBMM, Brazil), lithium hydroxide monohydrated (LiOH.H2O), and lithium carbonate (Li2CO3) (Synth, Brazil) were used as precursors. Microcrystalline cellulose and granulated paraffin (Synth) were evaluated as fuel. The paraffin granules were reduced to a fine powder through grinding in liquid nitrogen using a mortar and pestle. Ammonium nitrate (NH4NO3) solution (6 mol L-1), which was used as a combustion igniter, was prepared by dissolving the solid reagent in water. All reactants were ACS grade or superior and were used without any further purification.

Conditions and sample preparation The samples (precursors for the syntheses) were prepared as presented in the Table 1. The samples were labeled from #1 to #4. The mixing steps were performed in a low-energy ball mill using about 50 g of Al2O3 spheres with average diameter of 5 mm.


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Table 1. Preparation conditions of the samples for LiNbO3 synthesis by MIC. Sample #1

#2

#3

#4

Li source Nb source Li2CO3

Li2CO3

Li2CO3

LiOH.H2O

Nb2O5

Nb2O5

Nb2O5

Nb2O5

Li:Nb ratio (mols)

Fuel

(Li:Nb):fuel ratio (w/w)

1:1

cellulose (50%) paraffin (50%)

1:1


1:1


1:1


1:1

2:1

4:1

2:1

Mixing method Nb2O5 + Li2CO3: 30 min (ball milling) (Nb2O5 + Li2CO3) + cellulose: 15 min (ball milling) (Nb2O5 + Li2CO3 + cellulose) + paraffin: 15 min (mortar and pestle) Nb2O5 + Li2CO3: 30 min (ball milling) (Nb2O5 + Li2CO3) + cellulose: 15 min (ball milling) (Nb2O5 + Li2CO3 + cellulose) + paraffin: 15 min (mortar and pestle) Nb2O5 + Li2CO3: 30 min (ball milling) (Nb2O5 + Li2CO3) + cellulose: 15 min (ball milling) (Nb2O5 + Li2CO3 + cellulose) + paraffin: 15 min (mortar and pestle) Nb2O5 + Li2CO3: 30 min (ball milling) (Nb2O5 + Li2CO3) + cellulose: 15 min (ball milling) (Nb2O5 + Li2CO3 + cellulose) + paraffin: 15 min (mortar and pestle)



Microwave-induced combustion synthesis of LiNbO3 LiNbO3 synthesis via MIC started by placing 800 mg of each sample on pieces of polyethylene (PE) film (8 x 8 cm2), which were wrapped as small bags and sealed by heating. The bags were placed in homemade quartz sample holders, especially designed for combustion, over small pieces of paper filter moistened with 50 µL of a 6 mol L-1 NH4NO3 solution. The commercial quartz sample holders (part number 16427, Anton Paar, Austria) could also have been used for this purpose. Then, the holders were transferred into the quartz vessels (part number N3142346, Anton Paar), which were closed, fixed to the rotor (part number 18466, Anton Paar) and pressurized with 20 bar of oxygen (99.6%, White Martins, Brazil). An Erlenmeyer flask (250 mL) was filled with 200 mL of water and positioned in the center of the rotor in order to absorb the exceeding microwave radiation and reduce wear of the magnetron. Finally, the rotor was placed in a microwave oven (Multiwave 3000, Anton Paar), and submitted to a microwave irradiation program to ignite the combustion reaction (1400 W for 25 s). It is worth mentioning that the rotor of the microwave oven used in this work enables the combustion up to eight samples simultaneously. The ﬂame temperature of the combustion reactions was measured using an optical pyrometer (Ultimax UX-20P, IRCON, India). The experimental procedure of the proposed MIC method is summarized in the Figure 1.


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Figure 1. Experimental procedure of the proposed MIC method for direct LiNbO3 synthesis. After the ignition of the combustion reaction on the eight vessels (usually in less than 25 s) the microwave irradiation was stopped and the combustion was self-sustained. The internal pressure was relieved after a cooling step of 3 min. The samples were collected and stored in polypropylene vessels for further characterization.

Characterizations The X-ray diffraction (XRD) patterns of the samples were obtained using a X-ray powder diffractometer (XRD-6000, Shimadzu, Japan) using CuKα



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radiation (λ= 1.5418 Å) with 2θ angles ranging from 10° to 80°. The patterns were compared with the JCPDS files #85-2456 for LiNbO3, #75-0902 for Li3NbO4, and #75-2154 for LiNb3O8. The average crystallite sizes were calculated using the Scherrer’s equation.13

Raman scattering was collected in backscattering configuration by using an Horiba LABRAM-HR spectrometer with the 632.8 nm line of a helium-neon laser as excitation source (effective power of 6 mW at the surface of each sample), diffraction gratings of 600 and 1800 grooves/mm, Peltier-cooled charge coupled device (CCD) detector, confocal Olympus microscope (100x objective was used), and experimental resolution of typically 1 cm-1 for 10 accumulations of 30 s. The resulting spectra were corrected for the Bose-Einstein thermal factor. A transmission electron microscope (TEM, CM200, Philips, USA) was also employed to characterize the morphology and structure of the obtained samples. The TEM was operated at 200 kV and the samples were prepared by dropping two droplets of the sample suspension on a carbon coated copper grid (400 mesh Cu, Ted Pella, USA).

The morphologies of the synthesized materials were characterized by field emission scanning electron microscopy (FESEM; JEOL, model 7500F). Elemental

chemical

characterization

was

performed

by

X-ray

Photoelectron Spectroscopy (XPS), using the Al Kα (1486.6 eV) radiation source (ScientaOmicron ESCA+). Survey was collected with 0.1 eV step and highresolution spectra were obtained for lithium (Li 1s), oxygen (O 1s) and niobium (Nb 3d) using an energy step of 0.05 eV. The acidity of the catalysts was determined by titration method. 20 mL of a sodium hydroxide aqueous solution (0.01 mol·L−1) was added to 0.05g of the


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catalyst. The mixture was stirred for 24 hours at room temperature. Upon separation by centrifugation, the supernatant was then titrated with hydrochloric acid (0.05 mol·L−1) aqueous solution using phenolphthalein as indicator. The quantity of acid sites within the catalysts was determined by: number of acid sites = [initial quantity of NaOH added (moles) − quantity of HCl consumed (moles)] × Avogadro constant.

Procedure for catalytic oxidation of aniline The liquid phase oxidation of aniline was carried out in a one necked round bottom vessels (25 mL) maintained at 25 °C on a hotplate stirrer with an oil bath. To the vessel was added catalyst (10 mg), specific solvent (3 mL), aniline (0.10 mL) and finally the drop wise addition of H2O2 35% v/v (0.25-1.0 mL) and the reaction allowed to stir at 25 °C for 24 h. Regarding the solvent, chloroform, ethanol, THF and acetonitrile were evaluated. Upon completion, the reaction was quenched by the addition of a saturated aqueous solution of NaHCO3 (10 mL) and then taken up into a separator funnel and extracted with chloroform (2 x 10 mL), the organic extractions were combined, dried over anhydrous sodium sulfate, filtered and made up to 25 mL in a volumetric vessel with chloroform. This solution was injected in to the GC for analysis. Analysis was performed on Gas Chromatograph (Shimadzu, GC-2014) connected with a Rtx-Wax capillary column (30 m length. 0.25 mm i.d., 0.25 µm film thickness) and flame ionization detector (FID). Aniline conversion and product formation were quantified with the help of calibration curve, which was obtained by manually injecting authentic samples of known concentrations. Conversion of aniline was calculated by:



Conversion (%) =

moles of reactant reacted initial moles of reactant used

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×100

(1)

whereas selectivity of products using the following expression: Selectivity ሺ%ሻ =

total moles of product formed the sum of total moles of all oxidation products formed

×100

(2)

The obtained products were also confirmed by GC-MS (Shimadzu, GCMSQP2010) and GC (Shimadzu GC-2010 Plus Tracera – BID).

RESULTS AND DISCUSSION

Microwave-induced combustion synthesis of LiNbO3 The commercial system for MIC has not been applied to the synthesis of LiNbO3. MIC have however been used for digestion of food, biological, drugs, and environmental samples for further elemental determination by instrumental techniques.28-30 In this system, small amounts of reactants and only few simple steps are required, proving to be an interesting alternative for direct synthesis of LiNbO3. Thus, the proposed method for direct synthesis of LiNbO3 in a powder form by MIC was initially evaluated considering our knowledge of organic sample combustion and further elemental determination. In these experiments, the following parameters were evaluated: fuel (cellulose or a mixture of cellulose and paraffin) and Li/Nb ratio, as presented in Table 1. Initially, some preliminary experiments were performed in order to verify the most appropriate fuel for the LiNbO3 synthesis. Cellulose was initially chosen as fuel taking into account some reports that highlight its efficiency in aiding sample digestion since it helps to ensure that the required digestion temperature in the sample core and the required ACS Paragon Plus Environment

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burning time are achieved.32-33 Therefore, it was expected that the combustion of the cellulose could provide enough energy for the direct synthesis of LiNbO3. To evaluate the efficiency of this material as a fuel, a test sample containing 400 mg of cellulose and 400 mg of a mixture of the precursors Li:Nb (1:1) was submitted to the experimental procedure described in the Figure 1.

Figure 2. Aspect of the sample during the preliminary evaluation of the fuel for direct synthesis of LiNbO3 by MIC using a Li:Nb ratio of 1:1 (mol): (a) before MIC; (b) after MIC using only cellulose as fuel; (c) after MIC using a mixture of cellulose and paraffin (1:1). Figure 2a-c present the aspect of the sample during the preliminary evaluation of the fuel for direct synthesis of LiNbO3 by the proposed MIC. As



can be observed in the Figure 2b, the combustion reaction was incomplete when only cellulose was used as fuel. This fact is probably related to an inadequate temperature and/or burning time required. In view of this, paraffin was also evaluated as a fuel for direct synthesis of LiNbO3. There are reports showing that paraffin can also be successfully used as combustion aid in sample preparation methods.33 Whereas, as showed in Table 2, the temperature of the paraffin combustion reaction using the proposed MIC was around 1470ºC, which could result in the loss of crystal stoichiometry by lithium volatilization.34 Hence, a paraffin cellulose (1:1) mixture was evaluated. As showed in Figure 2c, the combustion reaction was complete when this mixture was used as fuel in the proposed MIC. The paraffin cellulose (1:1) mixture was an effective fuel for this method, since it provides suitable temperatures (about 1280°C when mixed with the precursors) and relatively high burning times when compared with the use of cellulose by its self (see Table 2). No difference was found between the temperature of the combustion reaction using only the fuel or a mixture (1:1) of precursors (Li:Nb) and fuel. The same behavior was observed when different Li:Nb ratios (mol) were evaluated.


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Table 2. Preliminary evaluation of the fuel for direct synthesis of LiNbO3 by the proposed MICa method.

Sampleb Burning time (s) Temperature (°C) Li:Nb ratio (mol)

Fuel Cellulose

22 ± 3

1090 ± 74

Cellulose:Paraffin

45 ± 5

1280 ± 79

-

Cellulose

24 ± 4

1150 ± 62

-

Paraffin

48 ± 7

1470 ± 90

-

Cellulose:Paraffin (1:1)

42 ± 6

1240 ± 83

1:1

a

Values of burning time and temperature are expressed as mean ± standard deviation, n=5. b Corresponding to combustion of a sample mass of 800 mg [precursors/fuel (1:1)] or of a fuel mass of 400 mg

Based on these results, the mixture of cellulose and paraffin (1:1) was selected as the most suitable fuel for the direct synthesis of LiNbO3 using the proposed MIC. Next, the precursor’s ratio was also evaluated as described in the Table 1. Complete combustion reaction was observed for all the evaluated samples. The ignition of the reaction combustion occurs between 10 and 15 s and the sample remained under heated conditions for 40 to 50 s. Efficient combustion promoted greater reduction in volume of the final materials probably due to the complete oxidation of the organic material (see Figure 2c). These samples also resulted in hard and agglomerated structures with glossy aspect. Therefore, taking into account the aspects of all obtained materials after combustion process, they were characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) as presented in the following section.



Sample characterization Initially, the obtained materials were characterized by XRD and Raman

spectroscopy as showed in Figure 3. Figure 3a presents the XRD patterns for the samples synthesized by MIC. All experimental data can be assigned to Li-Nb-O phases with no presence of starting materials (niobium and lithium sources). As it can be observed, sample #1 was prepared using stoichiometric amounts of Li and Nb (Li:Nb ratio 1:1), which leads to single-phase, impurity free LiNbO3 materials. The samples labeled #2 to #4 can be interpreted as mixtures of LiNbO3, Li3NbO4, and LiNb3O8. In the case of the presence of Li3NbO4, previous work indicated that excess of lithium during synthesis leads to the crystallization of this lithium-rich phase.20 For LiNb3O8, the use of microwave-induced combustion route for the synthesis of LiNbO3 can precipitate this niobium-rich phase.35 Figure 3b presents the Raman spectra for the samples produced by MIC. As verified by XRD, sample 1 exhibits bands related to the LiNbO3 phase. The results are similar to those previously reported and show that this phase is pure and free from contaminants and secondary phases. Samples #2, #3 and #4 show the same Raman bands, which dominate the vibrational spectra. However, additional bands related to the impurity phases Li3NbO4 and LiNb3O8 (belong to different symmetries) can be clearly seen, as also observed in prior studies.35 Comparing the sources of lithium employed in the present work, it was possible to observe that the sample prepared with LiOH.H2O exhibits a greater tendency to yield Li3NbO4 than the materials synthesized using Li2CO3 as lithium source. Kuo et al.20 also reported that the lithium content required to stabilize a pure LiNbO3 phase is in the range of 40-43%, determined from conventional combustion syntheses. This may indicate that LiOH.H2O offers better reactivity and higher Li availability than Li2CO3, although leading to the formation of


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secondary phase. To avoid the formation of secondary phases, an optimized amount of LiOH.H2O sub-stoichiometric and between 40-43% was used. Impurity

free

LiNbO3

had

their

morphological

and

structural

characteristics studied by transmission electron microscopy (TEM). Figure 4a shows a typical TEM image for the material produced when the sample #1 was submitted to MIC at about 1280 ºC. It was observed that nanosized, rounded particles dominate the scenario. The inset shows the SAED pattern for this sample, showing the polycrystalline nature of the LiNbO3 materials obtained by MIC. At the high-resolution TEM image observed at Figure 4b the interplanar spacing was about 3.03 Å corresponding to the (104) plane of the rhombohedral

R3c space group. Figures 4c and d presents the morphological characteristics of Nb compounds observed by FE-SEM. The low magnification image presented in Fig. 4c show that sample #2 present a distinct kind of morphology growing in layers and sample #3 present similar morphology. Samples #1 and #4 also present similar morphology, and SEM micrograph of sample #1 is presented in Fig 4d. In general, these nanoparticles are faceted with a close to rhombohedric geometry, although some rounded particles can also be observed. Energy dispersive X-ray spectroscopy (not shown here) showed that particles are composed by Nb and O atoms, once Li cannot be detected.


LiNb3O8

Li3NbO4

(#4)

Li3NbO4

Intensity (arb.units)

(a)

LiNb3O8

(#3)

(#2)

(#1)

10

20

30

40

50

60

70

80

2θ (°) (#4)

LiNb3O8 LiNb3O8

(#2)

LiNb3O8 Li3NbO4 Li3NbO4

(#3)

LiNb3O8


(b)


Raman intensity (arb.units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Li3NbO4


(#1)

200

400

600

800

1000

-1

Wavenumber (cm )

Figure 3. (a) XRD patterns for the samples synthesized by MIC. Undesirable, secondary phases are indicated in samples #2, #3 and #4; (b) Roomtemperature Raman spectra for all materials, with clear indication of the contaminants present.


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a

100 nm

b

10 nm

Figure 4. (a) TEM image for the LiNbO3 sample produced by MICS at about 1280 ºC. The inset shows the SAED pattern for this sample, evidencing the polycrystalline nature of the sample; (b) High-resolution TEM image for the



same sample, with indication of the calculated interplanar spacing corresponding to the (104) plane; (c) FESEM of sample #2 and (d) FESEM of sample #1.

Figure 5a shows the XRD pattern for the sample 1 (LiNbO3), which was indexed by the ICDD card #85-2456, belonging to the R3c space-group (the main Miller indexes are indicated). Figure 5b presents the respective Raman spectrum, which is constituted by a set of relatively wide bands in the frequency range 100-900 cm-1 (at least 16 modes could be visualized). For this material, many previous works studied the vibrational features besides group-theory calculations.36-39 Using the site symmetry and the site occupation factor of each atom of LiNbO3, the nuclear-site group method of Rousseau et al.,40 was applied to determine the active phonons at the Brillouin-zone center ( Γ). At room temperature, the structure of LiNbO3 belongs to the R3c (#161) space group and rhombohedral 3m point group, with two molecules per unit cell. Accordingly, 18 vibrational modes at zero wavevector are decomposed into 4A1 + 9E + 5A2. Whereas the A2 phonons are Raman and infrared inactive (silent modes), A1 and the doubly degenerate E modes are both Raman and infrared active (a total of 13 Raman phonons are expected).36-39 It appears that in our sample the number of bands is higher than those predicted by group-theory calculations. In the case of ceramic materials, the longitudinal branches of the phonons (usually studied by infrared spectroscopy) could be present in the Raman spectrum (defect induced). Thus, superimposed phonon modes are visualized and peak fitting procedures are then required. In our samples, the experimental data were adjusted by Lorentzian curves after Bose-Einstein and baseline corrections. The results are


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presented in Figure 6 experimental data are solid black squares, Lorentzian lines are displayed as green curves, and the fitting curve was presented by red lines. Table 3 presents the results from fitting, in which 26 bands could be identified and assigned by using the excellent study of Maïmounatou et al.39 In that work, the authors made a rigorous analysis of both experimental and theoretical angular dispersion of the Raman frequencies of the optical polar phonons in LiNbO3 single crystal with the emphasis of the determination without ambiguity of a new and complete set of the normal mode assignments that clarify long-standing debates. Our results showed that all the transversal (TO) and longitudinal (LO) modes could be determined from the experimental data, in perfect agreement with the theory calculations, which can help future studies in similar ceramics.


(116)

20

30

40

50

60

(306) (128) (312)

(208) (1010)

(018) (122) (330) (214)

(113) (202)

(006)

(110)

(024)

(104)

Intensity (arb. units) 10

Page 22 of 42

(a)

70

80

2 Theta (°)

(b)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(012)


200

300

400

500

600

700

800

900

1000

-1

Wavenumber (cm )

Figure 5. (a) XRD pattern and Miller indexes for the LiNbO3 ceramic, indexed according to the ICDD card #85-2456; (b) Raman spectrum for the same ceramic


(a)

150

200

250

300

350

400

-1

Wavenumber (cm )

(b)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 23 of 42

400

500

600

700

800

900

-1

Wavenumber (cm )

Figure 6. Fitting curves (individual Lorentzian lines in green) for the LiNbO3 ferroelectrics. The experimental data are represented by black squares and the adjusted curves by solid red lines. (a) 110-400 cm-1; (b) 400-950 cm-1



Table 3. Experimentally obtained Raman modes for LiNbO3 materialsa

a

Band # Frequency (cm-1) Assignment 1 152.0 E TO1 2 195.2 E LO1 3 224.4 E TO2 4 236.1 E LO2 5 254.3 A1 TO1 6 263.3 E TO3 7 273.0 A1 LO1 8 280.6 A1 TO2 9 298.1 E LO3 10 320.2 E TO4 11 330.1 A1 LO2 12 335.3 A1 TO3 13 348.2 E LO4 14 368.1 E TO5 15 424.4 E LO5 16,17 430.2 E TO6, A1 LO3 18 455.2 E LO6 19 580.5 E TO7 20 628.2 A1 TO4 21 659.3 E LO7 22 694.0 E TO8 23 712.4 E LO8 24 731.1 E TO9 25 873.2 A1 LO4 26 890.3 E LO9 Symmetry attribution and assignment was based upon experimental/calculated

modes.39

The XPS analysis of selected samples presented in Figures 7a and b revealed multiple peaks, which were fully indexed as Li, C, O, Nb surface elements. The carbon peak is a surface contamination inherent to the sample and was used for calibration proposes. Quantification of XPS data indicates various bounding states for Nb and O in the sample #4 (Figure 7a), agreeing with undesirable secondary phases observed by XRD. The spectrum suggests that O/Nb surface ratio for the sample #1 is slightly greater than O/Nb surface ratio for the sample #4 (Figure 7b). It worth mentioning that no surface contaminants


Page 24 of 42

Page 25 of 42

were detected in both samples, therefore achieving an ideal experimental that

furnishes

pure

Nb 3d

Li 1s O 2s

Nb 4p

C 1s

Nb 3p1/2 Nb 3p3/2

Nb 3s

O KLL

Intensity (a.u.)

samples.

(a)

O 1s

condition

1200

1000

800

600

400

200

0

O 1s

Binding Energy (eV)

Li 1s O 2s

Nb 4p

Nb 3d

Nb 3p1/2 Nb 3p3/2

C 1s

(b)

Nb 3s

O KLL

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1200

1000

800

600

400

200

0

Binding Energy (eV)

Figure 7. XPS survey spectrum of samples a) #4 and b) #1, respectively.

The amount of acid sites in samples #1 and #4 was determined by the titration method in aqueous solutions.2 Sample #1 had 60.2 × 1020 H+ sites/g while sample #4 presented a similar value of the 66.2 × 1020 H+ sites/g.



Page 26 of 42

Catalytic Reactions In order to investigate the catalytic activity of the synthesized samples, aniline oxidation reactions were carried out under different conditions. No appreciable aniline conversions were detected for reactions carried out in the absence of Li/Nb oxides, indicating the necessity of the catalyst for the process. It could be observed that the solids were active in the proposed reaction and the results revealed that the catalytic behaviors (aniline conversion and product selectivity) were influenced by the experimental conditions employed (Figures 8, 9,

10,

11

and

12).

Nitrobenzene,

nitrosobenzene,

azoxybenzene

and

phenylhydroxylamine were detected as the main products. Azobenzene was the minor product formed, for which the selectivity was always less than 1%. Figure 8 presents the results of the experiments for the different catalysts carried out in the presence of 0.25mL of H2O2 and acetonitrile as solvent.

Figure 8. Liquid phase oxidation of aniline over the synthesized catalysts in acetonitrile as solvent with 0.25mL of H2O2.


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Catalyst #1 was the most active, achieving 89.9% of aniline conversion, while the other catalysts (#2, #3 and #4) showed lower aniline conversion values, mainly catalysts #3 and #4, which achieved 68.8 and 50.4%, respectively. Regarding the product selectivity, some differences could be observed. Over catalyst #4, phenylhydroxilamine was the only product formed, while catalysts #2 and #3 presented very similar tendency, leading mainly to the formation of phenylhydroxylamine (~90%) and nitrobenzene as a secondary product (~10%). However, it is interesting to note that catalyst #1 showed the highest selectivity toward nitrobenzene (17.5%), the lowest selectivity to phenylhydroxylamine (70.5%) and was unique in that nitrosobenzene was formed (12.0%). Comparing the acidity of the less active and the most active catalysts (#4 and #1, respectively), it could be conclude that this property had only a minor influence on the catalytic performances presented, since they presented similar values of acidity. The catalytic results displayed by these samples can be related to the presence of secondary phases (Li3NbO4 and LiNb3O8). Catalyst #1 is free from secondary phases and this could influence the reactivity of the catalyst toward the advanced oxidation products (nitrosobenzene and nitrobenzene). Probably in this case, the interaction of aniline and hydrogen peroxide molecules with the catalyst surface is more effective, consequently allowing for faster consumption of aniline and also limiting the possibility of under oxidation reactions, leading to higher aniline conversion to form nitrosobenzene and nitrobenzene. In addition, XPS results suggest an increase in surface oxygen content and an enhancement of surface oxygen mobility for catalyst #1 that can be an important factor for achieving high activity and selectivities in oxidation of aniline. This result reinforces that this reaction can be sensitive to the catalyst structure.2,41 The effect



Page 28 of 42

of oxidant quantity has been studied and the variation in the aniline oxidation reaction promoted by catalyst #3 are depicted in Figure 9.

Figure 9. Oxidation of aniline over the catalyst #3 in acetonitrile with 0.25, 0.5 and 1.0 mL of H2O2.

The aniline conversion increased with H2O2 volume, reaching 100% in the presence of 1.0mL of the oxidant, because the reactant has a greater number of active oxidizing species available for catalysis. When 0.5mL of H2O2 was used the selectivity toward nitrobenzene decreased to 3.4% accompanied by an appreciable increase in the formation of nitrosobenzene (26.0%) and a decrease in the phenylhydroxilamine selectivity to 70.3%. Interestingly, on increasing the H 2O 2

volume

up

to

1.0mL,

the

selectivities

to

nitrosobenzene

and

phenylhydroxilamine dropped to 19.2% and 44.2%, respectively, with the increase in nitrobenzene formation (36.6%), pointing to the favoring of phenylhydroxylamine oxidation to nitrobenzene due to the higher amount of oxidizing agent present in the reaction mixture.2,

41

Aniline oxidation reactions

were carried out using different solvents, since the catalyst performance can be influenced by the nature of the solvent used.41 Due to its poorer catalytic ACS Paragon Plus Environment

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performance, sample #4 was chosen to study the solvent effect on the oxidation of aniline. It can be observed from Figure 10 that the solvent affected both the aniline conversion and the product selectivity.

Figure 10. Oxidation of aniline over the catalyst #4 in different solvents with 0.25 mL of H2O2.

Furthermore, catalytic activity increases when solvent polarity decreases and the catalytic selectivity were also dependent on the polarity of the solvent used. In the presence of acetonitrile and THF, the catalyst showed similar behavior,

achieving

approximately

50%

of

aniline

conversion

and

phenylhydroxilamine as the major product formed. This indicates that phenylhydroxylamine oxidation to nitrosobenzene and further to nitrobenzene is slower in the presence of such solvents. However, the extent of aniline



Page 30 of 42

conversion and the selectivity towards the products in the presence of ethanol and chloroform

were

very

different.

In

ethanol,

the

selectivity

towards

phenylhydroxilamine was 89.5% whereas the selectivity towards nitrobenzene was only 10.5%, with poor aniline conversion (27.4%). When chloroform was used as solvent, the aniline conversion and the selectivity to nitrosobenzene were considerably greater than in other solvents (86.2% and 45.3%, respectively) as well as the selectivity to phenylhydroxylamine that reached the lowest value (46.4%). This indicates that the conversion of phenylhydroxylamine to nitrosobenzene is favored in the presence of chloroform. Given the fact that catalyst #1 was found to be the most active of the materials evaluated in our initial screen, the selectivity of the reaction under different reaction conditions was also explored (Figures 11 and 12). For the reactions carried out in acetonitrile as solvent, increasing amounts of H2O2 (0.25. 0.50 and 1.00 mL) were found to favor the formation of nitrobenzene at the detriment of nitrosobenzene which was not formed in the presence of large excesses of the oxidant. In contrast, doubling the volume of H2O2 from 0.25 mL to 0.5 mL afforded more azoxybenzene but selectivity towards azoxybenzene remained unaffected at concentrations greater than 0.5 mL (Figure 11). Regarding the performance of catalyst #1 in different solvents (Figure 12), both protic and aprotic solvents were found to afford different results in terms of selectivity. Although ethanol was selective towards the formation of azoxybenzene, the overall

product

distribution

between

azoxybenzene,

nitrobenzene

and

nitrosobenzene was spread in a roughly 2:1:1 ratio. Selectivity was improved in chloroform which yielded mostly nitrosobenzene and the selectivity of the reaction towards azoxybenzene was notably high in THF as solvent. Moreover,


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high levels of aniline conversions over this catalyst were maintained under all the evaluated reaction conditions.

Figure 11. Oxidation of aniline over the catalyst #1 in acetonitrile with 0.25, 0.5 and 1.0 mL of H2O2.



Figure 12. Oxidation of aniline over the catalyst #1 in different solvents with 0.25 mL of H2O2.

In conclusion, the catalytic results showed that aniline could be oxidized at ambient conditions. The aniline conversion and the distribution of the products were dependent on the experimental parameters employed, in particular the nature of the solvent, oxidant volume and nature of the catalyst. It seems that the catalyst free from secondary phases (#1 – pure LiNbO3) was the preferred choice to promote the process, probably due to the more effective interaction of aniline and hydrogen peroxide molecules with its surface. XPS analyses also suggest that a higher surface oxygen content and an enhancement of surface oxygen mobility for catalyst #1 improved the activity and selectivities for the over oxidation products from aniline. In short, pure LiNbO3 material was successfully and efficiently synthesized using the proposed MIC method under very short times (40 s to 1 min). This method is promising and can


Page 32 of 42

Page 33 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


promote tremendous time and energy savings when compared to the conventional combustion methods and previous work on microwave-induced combustion synthesis of LiNbO3. The XRD results confirm that the rhombohedric ferroelectric phase can be obtained by this simple and fast method.

ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support of CNPq, process 482251/2013-1,

CAPES/PROCAD

2013/2998/2014,

FAPEMIG,

and

the

Companhia Brasileira de Metalurgia e Mineração (CBMM, Brazil) for the donation of Nb2O5. TEM analysis were provided by LME-UNESP and XPS characterization was performed at the Crystal Growth and Ceramic Materials Laboratory (USP).



Page 34 of 42

REFERENCES

1.

Grirrane, A.; Corma, A.; García, H., Gold-Catalyzed Synthesis of Aromatic Azo

Compounds from Anilines and Nitroaromatics. Science 2008, 322 (5908), 1661-1664. DOI 10.1126/science.1166401 2.

Ventura, W. M.; Batalha, D. C.; Fajardo, H. V.; Taylor, J. G.; Marins, N. H.;

Noremberg, B. S.; Tański, T.; Carreño, N. L. V., Low temperature liquid phase catalytic oxidation of aniline promoted by niobium pentoxide micro and nanoparticles. Catalysis

Communications 2017, 99, 135-140. DOI 10.1016/j.catcom.2017.06.004 3.

Lekha, L.; Kanmani Raja, K.; Rajagopal, G.; Easwaramoorthy, D., Schiff base

complexes of rare earth metal ions: Synthesis, characterization and catalytic activity for the oxidation of aniline and substituted anilines. Journal of Organometallic Chemistry 2014, 753, 72-80. DOI 10.1016/j.jorganchem.2013.12.014 4.

Acharyya, S. S.; Ghosh, S.; Bal, R., Catalytic Oxidation of Aniline to

Azoxybenzene Over CuCr2O4 Spinel Nanoparticle Catalyst. ACS Sustainable

Chemistry & Engineering 2014, 2 (4), 584-589. DOI 10.1021/sc5000545 5.

Green, I. X.; Tang, W.; Neurock, M.; Yates, J. T., Low-Temperature Catalytic

H2 Oxidation over Au Nanoparticle/TiO2 Dual Perimeter Sites. Angewandte Chemie

International Edition 2011, 50 (43), 10186-10189. DOI 10.1021/sc5000545 6.

Bäckvall, J. E., Modern Oxidation Methods. 2nd ed.; Wiley-VCH: Weinheim,

Germany, 2011; p 481. 7.

Sakaue, S.; Tsubakino, T.; Nishiyama, Y.; Ishii, Y., Oxidation of aromatic

amines with hydrogen peroxide catalyzed by cetylpyridinium heteropolyoxometalates.

The

Journal

of

Organic

Chemistry

1993,

58

10.1021/jo00066a012


(14),

3633-3638.

DOI

Page 35 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8.

Deng, X.; Wang, Y.; Shen, L.; Wu, H.; Liu, Y.; He, M., Low-Cost Synthesis of

Titanium Silicalite-1 (TS-1) with Highly Catalytic Oxidation Performance through a Controlled Hydrolysis Process. Industrial & Engineering Chemistry Research 2013, 52 (3), 1190-1196. DOI 10.1021/ie302467t 9.

Marinescu, L.; Mølbach, M.; Rousseau, C.; Bols, M., Supramolecular Oxidation

of Anilines Using Hydrogen Peroxide as Stoichiometric Oxidant. Journal of the

American Chemical Society 2005, 127 (50), 17578-17579. DOI 10.1021/ja054457q 10.

Patel, N.; Branch, D. W.; Schamiloglu, E.; Cular, S., Acoustically determined

linear piezoelectric response of lithium niobate up to 1100 V. Applied Physics Letters 2014, 104 (16), 163509 (4 pp). DOI 10.1063/1.4873685 11.

Cai, B.; Zhao, M.; Ma, Y.; Ye, Z.; Huang, J., Bio-inspired Formation of

Mesoporous

LiNbO3

Nanotubes

and

Application

for

Glucose

Biosensor.

Electrochimica Acta 2014, 147, 176-182. DOI 10.1016/j.electacta.2014.09.054 12.

Pitcher, M. W.; He, Y.; Bianconi, P. A., Facile in situ synthesis of oriented

LiNbO3 single crystals in a polymer matrix. Materials Chemistry and Physics 2005, 90 (1), 57-61. DOI 10.1016/j.matchemphys.2004.09.030 13.

Khalameida, S.; Sydorchuk, V.; Leboda, R.; Skubiszewska-Zięba, J.;

Zazhigalov, V., Preparation of nano-dispersed lithium niobate by mechanochemical route. Journal of Thermal Analysis and Calorimetry 2014, 115 (1), 579-586. DOI 10.1007/s10973-013-3343-5 14.

Kamali, A. R.; Fray, D. J., Preparation of lithium niobate particles via reactive

molten salt synthesis method. Ceramics International 2014, 40 (1), 1835-1841. DOI 10.1016/j.ceramint.2013.07.085



15.

Kar, S.; Logad, S.; Choudhary, O. P.; Debnath, C.; Verma, S.; Bartwal, K. S.,

Preparation of Lithium Niobate Nanoparticles by High Energy Ball Milling and their Characterization. Universal Journal of Materials Science 2013, 1 (2), 18-24. DOI 10.13189/ujms.2013.010202 16.

Luo, C.; Xue, D., Mild, Quasireverse Emulsion Route to Submicrometer

Lithium Niobate Hollow Spheres. Langmuir 2006, 22 (24), 9914-9918. DOI 10.1021/la062193v 17.

Kavyashree, D.; Shilpa, C. J.; Nagabhushana, H.; Daruka Prasad, B.; Sreelatha,

G. L.; Sharma, S. C.; Ashoka, S.; Anandakumari, R.; Premkumar, H. B., ZnO Superstructures as an Antifungal for Effective Control of Malassezia furfur, Dermatologically Prevalent Yeast: Prepared by Aloe Vera Assisted Combustion Method. ACS Sustainable Chemistry & Engineering 2015, 3 (6), 1066-1080. DOI 10.1021/sc500784p 18.

Liu, M.; Xue, D.; Luo, C., Facile Synthesis of Lithium Niobate Squares by a

Combustion Route. Journal of the American Ceramic Society 2006, 89 (5), 1551-1556. DOI 10.1111/j.1551-2916.2006.00950.x 19.

Liu, M.; Xue, D., Effect of heating rate on the crystal composition of

ferroelectric lithium niobate crystallites. Journal of Alloys and Compounds 2007, 427 (1), 256-259. DOI 10.1016/j.jallcom.2006.02.065 20.

Kuo, C.-L.; Chen, G.-J.; Chang, Y.-S.; Fu, J.-X.; Chang, Y.-H.; Hwang, W.-S.,

Thermal behavior of the nonstoichiometric lithium niobate powders synthesized via a combustion method. Ceramics International 2012, 38 (5), 3729-3733. DOI 10.1016/j.ceramint.2012.01.017


Page 36 of 42

Page 37 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21.

Patil, K. C.; Aruna, S. T.; Mimani, T., Combustion synthesis: an update. Current

Opinion in Solid State and Materials Science 2002, 6 (6), 507-512. DOI 10.1016/S1359-0286(02)00123-7 22.

Yiin, T.; Barmatz, M., Microwave Induced Combustion Synthesis of Ceramic

and Ceramic-Metal Composites. Ceramic Transactions 1995, 59, 541-547. 23.

Mangalaraja, R. V.; Mouzon, J.; Hedström, P.; Camurri, C. P.; Ananthakumar,

S.; Odén, M., Microwave assisted combustion synthesis of nanocrystalline yttria and its powder

characteristics.

Powder

Technology

2009,

191

(3),

309-314.

DOI

10.1016/j.powtec.2008.10.019

24.

Zhao, Y.; Liao, X.-H.; Hong, J.-M.; Zhu, J.-J., Synthesis of lead sulfide

nanocrystals via microwave and sonochemical methods. Materials Chemistry and

Physics 2004, 87 (1), 149-153. DOI 10.1016/j.powtec.2008.10.019 25.

Jalota, S.; Tas, A. C.; Bhaduri, S. B., Microwave-assisted synthesis of calcium

phosphate nanowhiskers. Journal of Materials Research 2011, 19 (6), 1876-1881. DOI 10.1557/JMR.2004.0230 26.

Jokisaari, J. R.; Bhaduri, S.; Bhaduri, S. B., Microwave activated combustion

synthesis of titanium aluminides. Materials Science and Engineering: A 2005, 394 (1), 385-392. DOI 10.1016/j.msea.2004.11.059 27.

Fan, Q.; Lei, L.; Sun, Y., Facile synthesis of a 3D-porous LiNbO3

nanocomposite as a novel electrode material for lithium ion batteries. Nanoscale 2014,

6 (13), 7188-7192. DOI 10.1039 / C4NR00232F 28.

Mesko, M. F.; Costa, V. C.; Picoloto, R. S.; Bizzi, C. A.; Mello, P. A., Halogen

determination in food and biological materials using plasma-based techniques:



Page 38 of 42

challenges and trends of sample preparation. Journal of Analytical Atomic Spectrometry 2016, 31 (6), 1243-1261. DOI 10.1039 / C5JA00488H 29.

Mesko, M. F.; Teotonio, A. C.; Teixeira Oliveira, D. T.; Rosa Novo, D. L.;

Costa, V. C., A feasible method for indirect quantification of L-T4 in drugs by iodine determination. Talanta 2017, 166, 223-227. DOI 10.1016/j.talanta.2017.01.039 30.

Corazza, G.; Henn, A. S.; Mesko, M. F.; Duarte, F. A.; Flores, E. M. M.; Mello,

P. A., Microwave-Induced Combustion of Coal for Further Sulfur Determination by Inductively Coupled Plasma Optical Emission Spectrometry or Ion Chromatography.

Journal of the Brazilian Chemical Society 2016, 27 (9), 1569-1576. DOI 10.5935/01035053.20160036 31.

Alves, A. R.; Coutinho, A. R., The Evolution of the Niobium Production

in Brazil. Materials Research 2015, 18 (1), 106-112. DOI 10.1590/15161439.276414 32.

Pereira, R. M.; Costa, V. C.; Hartwig, C. A.; Picoloto, R. S.; Flores, E. M.

M.; Duarte, F. A.; Mesko, M. F., Feasibility of halogen determination in noncombustible inorganic matrices by ion chromatography after a novel volatilization method using microwave-induced combustion. Talanta 2016, 147, 76-81. DOI 10.1016 / j.talanta.2015.09.031 33.

Souza, G. B.; Carrilho, E. N. V. M.; Oliveira, C. V.; Nogueira, A. R. A.;

Nóbrega, J. A., Oxygen bomb combustion of biological samples for inductively coupled plasma optical emission spectrometry. Spectrochimica Acta Part B:

Atomic

Spectroscopy

2002,

57

(12),

2195-2201.

8547(02)00180-5


DOI

10.1016/S0584-

Page 39 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


34.

Camargo, E. R.; Kakihana, M., Low temperature synthesis of lithium

niobate powders based on water-soluble niobium malato complexes. Solid State

Ionics 2002, 151 (1), 413-418. DOI 10.1016/S0167-2738(02)00547-7 35.

Ausrine, B.; Valentina, P.; Adulfas, A.; Sandra, S.; Samuel, M.; Pascal, B.;

Kobata, T.; Yoshiaki, U.; Jerome, G., Identification of LiNbO3, LiNb3O8 and Li3NbO4 phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy. Journal of Physics: Condensed Matter 2013, 25 (20), 205901 (8pp). DOI 10.1088 / 0953-8984 / 25/20/205901 36.

Sanna, S.; Neufeld, S.; Rüsing, M.; Berth, G.; Zrenner, A.; Schmidt, W.

G., Raman scattering efficiency in LiTaO3 and LiNbO3 crystals. Physical Review

B 2015, 91 (22), 224302 (9 pp). DOI 10.1103/PhysRevB.91.224302 37.

Rüsing, M.; Sanna, S.; Neufeld, S.; Berth, G.; Schmidt, W. G.; Zrenner,

A.; Yu, H.; Wang, Y.; Zhang, H., Vibrational properties of LiNb1-xTaxO3 mixed crystals.

Physical

Review

B

2016,

93

(18),

184305

(11

pp).

DOI

10.1103/PhysRevB.93.184305

38.

Seiji, K.; Kazuki, K.; Takuya, H.; Takaaki, T., Optical phonons and

polariton dispersions of congruent LiNbO3 studied by far-infrared spectroscopic ellipsometry and Raman scattering. Japanese Journal of Applied Physics 2016,

55 (10S), 10TC02 (5 pp). DOI 10.7567/JJAP.55.10TC02 39.

Maïmounatou, B.; Mohamadou, B.; Erasmus, R., Experimental and

theoretical directional dependence of optical polar phonons in the LiNbO3 single crystal: New and complete assignment of the normal mode frequencies. physica

status solidi (b) 2016, 253 (3), 573-582. DOI 10.1002/pssb.201552428



40.

Rousseau, D. L.; Bauman, R. P.; Porto, S. P. S., Normal Mode

Determination in Crystals Journal of Raman Spectroscopy 1981, 10 (1), 253290. DOI 10.1002 / jrs.1250100152 41.

Gontier, S.; Tuel, A., Oxidation of aniline over TS-1, the titanium

substituted silicalite-1. Applied Catalysis A: General 1994, 118 (2), 173-186. DOI 10.1016/0926-860X(94)80312-9


Page 40 of 42

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For table of contents use only

Synopsis: Microwave-induced combustion showed to be feasible, fast, clean and efficient method for LiNbO3 synthesis. The LiNbO3 was efficient applied as catalyst in the oxidation process of aniline under ambient conditions.


ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

LiNbO3 Synthesis by Microwave-induced Combustion

LiNbO3 Aniline oxidation [o]

[o]

Application

[o]


Catalyst

Page 42 of 42

Feasible and Clean Solid-Phase Synthesis of LiNbO3 by Microwave

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