Ammonium Niobium Oxalate Research Articles

Fabrication of conductive Nb-doped anatase TiO2 thin films by mist chemical vapor deposition using aqueous solutions of water-soluble Ti and Nb compounds

Electrically conductive Nb-doped anatase TiO2 (Ti1−x Nb x O2: TNO) films can be fabricated through mist CVD using aqueous precursor solutions of water-soluble oxo-peroxo-glycolato titanium complex and ammonium niobium oxalate. Post-deposition annealing in vacuum crystallizes the as-deposited amorphous films into a conductive anatase phase, leading to the fabrication of conductive TNO films. Notably, the addition of H2O2 to the precursor solutions enhances both the crystallinity and conductivity of the annealed TNO films. A Ti0.77N0.23O2 film, annealed at 700 °C, exhibits a resistivity of 2.0 × 10−2 Ω cm at ambient temperature. In general, the solution-based fabrication of TiO2 films relies on organic solvents, which are sometimes toxic and explosive. Here, we demonstrate for the first time that conductive TNO films can be prepared from less toxic and nonflammable aqueous solutions. These findings mark a significant advancement towards a more environmentally compatible process for fabricating TNO films with sufficient conductivity.

Ammonium niobium oxalate (ANO) as an efficient catalyst in the Paal–Knorr synthesis of N-substituted pyrroles

Ammonium niobium oxalate (ANO) has been proven to be an outstanding cheap, low-toxicity and readily available Lewis acid catalyst for carbonyl activation reactions.

Correction: Ammonium niobium oxalate (ANO) as an efficient catalyst in the Paal–Knorr synthesis of N-substituted pyrroles

Correction for ‘Ammonium niobium oxalate (ANO) as an efficient catalyst in the Paal–Knorr synthesis of N-substituted pyrroles’ by Luiz H. Dapper et al., RSC Sustain., 2024, https://doi.org/10.1039/d3su00395g.

Proizvodnja niobijuma - prikaz procesa od rudnika do proizvoda

A number of industrial and technology sectors have been paying attention to a particular chemical element in recent years, namely niobium (Nb). There are many niobium deposits scattered around the world, and for each deposit different technologies are applied for extraction and processing due to the singular characteristics present at each site. In this paper, a review of the many technologies for niobium production will be presented starting at the mine, through techniques of niobium ore beneficiation and refining, technologies to produce ferroniobium alloy, oxides, special oxides, ammonium niobium oxalate, the separation of niobium from tantalum, and techniques to reduce and purify metallic niobium.

Surface engineering with ammonium niobium oxalate: A multifunctional strategy to enhance electrochemical performance and thermal stability of Ni-rich cathode materials at 4.5V cutoff potential

Ni-rich layered oxides with high energy density and low costs are among the most promising candidate cathode materials for the next-generation lithium-ion batteries. However, the intrinsic issues of lithium residuals on particle surface and structural degradation with cycling deteriorate the electrochemical performance and cause safety issues. In this work, a facile and scalable Nb-modification strategy is proposed to remove the surface lithium residuals and in situ form Li-ion conductive LiNbO3 on Ni-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) particle surface with small amount of Nb diffusing into surface lattice and doping at Li sites. The surface Nb-modification is performed with water soluble ammonium niobium oxalate by a wet chemistry route. The reconstructed LiNbO3-coated/Nb-doped hybrid surface structure of NCM622 enables a unique combination of significantly improved cycling stability, superior rate performance and excellent thermal stability. This developed strategy can be applied to modulate the surface chemistry of other Li-containing materials.

Ammonium Niobium Oxalate (ANO)

Niobium is a metal whose major reserves are found in Brazil. Ammonium Niobium Oxalate (ANO) is a stable, cheap, readily available and water-soluble niobium acid catalyst still underrepresented in literature. This manuscript highlights some interesting applications of ANO as a promising catalyst to Green and Sustainable Chemistry.

Methylene blue and metformin photocatalytic activity of CeO2-Nb2O5 coatings is dependent on the treatment time of plasma electrolytic oxidation on titanium

Despite UV photolysis is common industrial water treatment, existent approaches are still not fully effective nor practical due to the growing amount of discharged effluents. Titanium dioxide (TiO2) has been used as a semiconductor for photocatalytic degradation of pollutants, but its efficiency is limited due to its rapid reverse reaction. Thus, novel approaches are needed to improve the quality and cost benefits of photocatalysts. In this study, the processing time effect of CeO2-Nb2O5 coatings on titanium synthesized via a one-step method of Plasma Electrolytic Oxidation (PEO) in an electrolytic solution containing ammonium niobium oxalate salt [NH4NbO(C2O4)2] and cerium oxide (CeO2) powder at 300, 450, and 600 s. The structural and optical properties, morphology, wettability, coating thickness, and elemental chemical composition were investigated. The performance of CeO2-Nb2O5 coatings regarding the photocatalytic activity was evaluated under UV irradiation, using methylene blue (MB) and metformin as model pollutants. Energy Dispersive Spectroscopy confirmed the incorporation of Ce and Nb into the oxide film. The Scanning Electron Microscopy demonstrated that the PEO process produced CeO2-Nb2O5 coatings with a thickness from 9.6 to 55.8 µm and irregular and porous structures that changed in proportion and size according to treatment time. X-ray diffraction (XRD) analysis revealed that the coatings demonstrated crystallization corresponding to CeO2 and Nb2O5 phases. All the experimental groups presented an estimated band gap of 3.3 eV, suggesting that the obtained coatings could be active in the UV light range. Also, such coatings showed an increased surface area that varied from 3.93 to 5.62 cm2 as high it was the treatment time, which could facilitate the degradation of pollutants. These results were consistent with the photocatalytic activity assay, where samples treated for 600 s showed the most significant degradation of MB under UV irradiation, especially at 15 and 30 min of irradiation when compared to untreated titanium and photolysis process (p < 0.05). Regarding metformin, after 120 min of UV exposure, 27% was degraded due to photolysis. Whereas after 210 min, 67% of the pharmaceutical degradation was observed on the 600 s-treated CeO2-Nb2O5 coating. A crystalline CeO2-Nb2O5 coating with improved surface characteristics and photocatalytic activity was synthesized by tailoring the treatment time process. This study makes advantageous for degrading pollutants and medicines, since sewage treatment systems are sometimes slow or not fully effective.

Synthesis, characterization and evaluation of iron oxides and niobium in the removal of dyes in Fenton type reactions and photocatalysis

In this work, catalysts based on niobium oxide modified with iron oxide were developed for the photocatalytic treatment of effluents contaminated with dyes. The catalysts were prepared, in different proportions of niobium and iron, using niobium ammonium oxalate salts, iron nitrate and ammonium acetate and calcination at 400 °C. The solids were characterized by X-ray diffraction, infrared spectroscopy with Fourier transform, measured at zero point charge and evaluated in adsorption, Fenton reaction type advanced oxidation and methylene blue heterogeneous photocatalysis. It was observed that the increase in niobium concentration increased the values of point of zero charge and decreased the reaction system final pH. The solid with Fe/Nb2 ratio showed the best performance as an adsorbent and in oxidation reaction, followed by the one with Fe / Nb1.5 ratio. The solids showed practically the same result (1.8 eV), in addition, the presence of iron niobite (Fe/Nb1) favored the photocatalytic system.

Nb2O5 nanoparticles obtained by microwave assisted combustion synthesis under different conditions

The microwave assisted combustion synthesis (MACS) as a new, quick and low cost synthesis method was used for preparation of niobium pentoxide (Nb2O5) powders. The present paper investigated the effect of reactant concentrations (ammonium niobium oxalate, urea and ammonium nitrate) on the characteristics of Nb2O5 nanoparticles. Three samples were synthesized with stoichiometric ratio between the fuel and oxidant (C1), excess of oxidant (C2) and excess of fuel (C3). In all samples, Nb2O5 crystalline nanoparticles with irregular morphology were detected. The synthesis of nanoparticles with smaller diameter in the C2 and C3 samples was confirmed by greater values of band gap energy measured through UV-Visible diffuse reflectance spectroscopy (indicating quantum confinement) and by the Rietveld refinement of X-ray diffraction patterns. The results showed that the amounts of oxidant and fuel can change synthesis temperature, influencing the final characteristics of the particles, such as size and existent phases. In these cases the excess of oxidant and fuel in the C2 and C3 samples, respectively, decreases the average synthesis temperature and decelerates the particle growth and the formation of the monoclinic phase.

Effective Factor on Catalysis of Niobium Oxide for Magnesium.

Magnesium is a promising hydrogen storage material but requires an efficient catalyst to enhance the sluggish kinetics of its hydrogen desorption/absorption reactions. Niobium catalysts have been shown to accomplish this, but the effective factors for catalysis on hydrogen desorption/absorption of Mg are not well understood. In order to investigate these aspects, various types of Nb oxides were synthesized and mixed with Mg, and their catalytic properties were investigated. The spray pyrolysis synthesis of Nb oxides at different temperatures produced homogeneous spherical particles with different degrees of crystallinity, while Nb oxide particles synthesized by simple calcination of ammonium niobium oxalate were nonuniform. These Nb oxides show significant catalytic activities for the hydrogen desorption/absorption of Mg, with amorphous oxides being more effective catalyst precursors than crystalline precursors. Metastable, amorphous Nb oxide is more easily converted to the reduced state, which is the catalytically active state for the reactions. In addition, Nb in the deactivated sample is in the oxidized state compared with the initially activated sample, and the catalytically active (reduced) state is recovered by reactions with hydrogen. Based on these findings, it is concluded that the chemical state of Nb is an important factor in catalyzing the desorption/absorption of hydrogen by Mg, and the catalytically active state can be preserved without further treatments.

Niobium Pentoxide Nanoparticles and Their Self-Assembled in Building Blocks for Gas Sensors

Niobium pentoxide (Nb2O5) is characterized by an outstanding chemical stability, high corrosion resistance and color changing chemistry. Nb2O5 can adopt different crystal structures (pseudohexagonal, orthorhombic and monoclinic), depending on the temperature [1]. Still, it is one of the least studied metal oxides. [2], [3]. Thus, exploring new synthetic methods and the physicochemical properties of the resulting oxide nanoparticles (NPs) could open new opportunities in different applications such as electrocatalysis, electrochromic displays, Surface-enhanced Raman spectroscopy and gas, humidity, and biological/chemical sensing. For gas sensing applications, nanostructured individual NPs of Nb2O5 with uniform shape, narrow size distribution along with high surface area are required to facilitate the adsorption of the target gas molecules. [1], [3], [4], [5]. Hydrothermal and solvothermal methods are widely used to produce metal oxides NPs with various morphologies. [1] These methods are easily scaled up and produce materials with high purity. Due to the high autogenous pressure inside the reactor, the nanoparticles are usually crystalline; and depending on the temperature and the time of reaction, the crystal phase can be controlled. However, the control of the size and the shape of the NPs with hydrothermal synthesis is a challenge because after nucleation, the nuclei precipitate and agglomerate forming microstructures with ill-defined shapes. [3] ,[5] In this work, we report the synthesis of spherical-like niobium oxide nanoparticles by one-pot hydrothermal synthesis using as a precursor ammonium niobium oxalate aqueous solution, Figures 1.A and 1.B. The kinetics of the NPs growth was investigated by Dynamic Light Scattering (DLS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Figure 1.B. shows that the Nb2O5 NP grow according to the Oswald ripening mechanism, with the size of the nanoparticles increasing from 2 nm to 80 nm with the reaction time. However, the nanoparticles tend to coalesce forming larger nanostructures with uncontrollable size landing to unstable suspensions. A comparative study between different charged ligands, revealed citric acid as the best ligand to ensure the stability of the Nb2O5 suspensions and to control the nanoparticles’ size. Indeed, using citric acid the size of the size of the aggregates in the suspensions is reduced by the factor of 10, from 200 to around 20 nm of diameter. The control of the size and shape of the NPs was found to be critical to form 3D superlattices and to maximize the surface area once the nanoparticles form thin films, Figure 1.C. The kinetic of the NPs growth and the physicochemical properties of the NPs and films will be discussed in detail.AcknowledgementsThe authors would like to thank the funding from NSERC (Strategic partnership program, Canada).

Photoactive Basic Bismuth Nitrate/Nb2O5 Nanocomposites

Basic bismuth nitrates (BBN) are generated from the incomplete hydrolysis of bismuth nitrate pentahydrate, it is a n-type semiconductor, and it was initially used as precursor of bismuth oxides and for medical applications. BBN also can be employed as photocatalysts, but usually exhibit low quantum efficiency due to the fast recombination of photogenerated charge carriers. In order to improve their photocatalytic performance, semiconductor composites have been proposed, being niobium pentoxide (Nb2O5) a promising candidate to be coupled with BBN. Hence, two different and promising photoactive nanocomposites (Nb-BBN) of BBN (Bi6O5(OH)3(NO3)5.3H2O and Bi2O2(OH)(NO3)) and Nb2O5 were obtained by the oxidant peroxide method followed by crystallization under mild hydrothermal conditions. Ammonium niobium oxalate and bismuth nitrate were the sources of Nb and Bi, respectively. Hydrogen peroxide was used as oxidant, and deionized water was used to prepare all solutions. Bismuth nitrate in contact with water forms immediately a highly hydrated basic bismuth nitrate precipitate (Bi6O5(OH)3(NO3)5.3H2O), named P-BBN. Hydrogen peroxide (10:1 molar ratio H2O2:M, M = Bi + Nb) and ammonium niobium oxalate (3:1 molar ratio Bi:Nb) were added into the suspension containing P-BBN, and the synthesis medium was poured in a teflon-lined hydrothermal reactor with autogenous pressure to promote the crystallization under two different procedures. The first nanocomposite (Nb-BBN120) was obtained using one single step: heating at 1 °C min-1 up to 120 ºC (maintained for 12 h), with a final pressure ca. 7 atm. The second nanocomposite (Nb-BBN230) was synthesized using three consecutive steps: 1) heating at 4 °C min-1 up to 150 ºC, with a final pressure ca. 10 atm; 2) heating at 2 °C min-1 up to 200 ºC, with a final pressure ca. 20 atm; and 3) heating at 1 °C min-1 up to 230 ºC (maintained for 12 h), with a final pressure ca. 31 atm. The photocatalytic performance was evaluated, under ultraviolet irradiation at room temperature, towards the discoloration of an aqueous solution of 10 mg L-1 rhodamine B (RhB) using 10 mL of a suspension containing 10 mg mL-1 photocatalyst. No direct photolysis and adsorption were observed. It was also evaluated the photocatalytic stability of the as-synthesized samples after four consecutives RhB discoloration 2-hour-cycles. XRD patterns revealed that the crystallographic structure of the samples Nb-BBN120 and Nb-BBN230 have a monoclinic Bi6O5(OH)3(NO3)5.3H2O (ICSD 00-2406) and orthorhombic Bi2O2(OH)(NO3) (ICSD 15-4359) phases, respectively. No significant peaks assigned to any Nb2O5 second phase are observed, probably due to its low content and high dispersion or the shielding effect of the strong diffraction signals from BBN. Although any XRD peak has been observed for Nb2O5, its presence in the nanocomposites was confirmed by XRF, ICP-OES, and XPS. The kinetics of RhB photodegradation shows that the hydrothermal treatment in presence of Nb2O5 is of paramount importance to enhance the BBN photoactivity. Although Nb-BBN120 and P-BBN have the same BBN phase, the first one has higher activity than the pristine material. Furthermore, despite of Nb-BBN230 shows the best photocatalytic activity, after performing three reuse cycles there was a loss of ~ 50% of its initial photoactivity, suggesting that the lamellar structure is a key factor on the photocatalyst stability. On the other hand, Nb-BBN120 or even the pristine P-BBN retained their initial photocatalytic activity after reuse. In summary, these novel BBN/Nb2O5 nanocomposites provide new insights into the synthesis of promising BBN photocatalysts for oxidation reactions.

Facile Synthesis of Nb2O5 as a Visible Light-Sensitive Photocatalyst

Niobium pentoxide (Nb2O5) is a promising semiconductor in catalysis due to its chemical and physical properties, availability, and non-toxicity. However, because of its large bandgap energy (Eg= 3.1 – 4.0 eV), Nb2O5 does not work as a photocatalyst under visible light, which makes its use of solar light limited. Even though Nb2O5 presents this drawback, its photocatalytic activity under visible light radiation can be enhanced due to the presence of surface groups, known as niobium peroxo complexes, formed by the treatment with hydrogen peroxide. In general, the modified niobia is synthetized in multi-step processes which allow the generation of strongly reactive oxygen species (ROS) (i.e. peroxo and superoxo) on its surface. In contrast, in this study, the peroxo-niobium oxide was prepared by a facile combination of the oxidant peroxide method (OPM) and hydrothermal treatment. The ability of Nb2O5 to form the ROS using this method was investigated in respect to the different Nb:H2O2 molar ratio (1:2 or 1:10) added in the metal oxide synthesis. For this purpose, ammonium niobium oxalate was dissolved in distilled water and hydrogen peroxide was then added to the reaction medium. The niobium precursor in contact with H2O2 forms instantaneously the niobium peroxo complex that was crystallized at 120 ⁰C with a heating ramp of 1 oC/min, for 12h in a home-made teflon lined autoclave. When the desired temperature was reached, the internal pressure of the reactor varied from ca. 10 to 27 atm, depending upon the amount of hydrogen peroxide used to prepare each material. The oxidative properties of the reactive oxygen species formed on the surface of metal oxides were tested in photodegradation of caffeic acid (CA) under visible light. In addition, reuse tests were performed in order to investigate the loss of photoactivity of the best photocatalyst in the CA degradation. XRD patterns revealed that the crystallographic structures of the samples Nb2H and Nb10H contain the Nb2O5 pseudohexagonal-type phase (JCPDS 28-317) and hydrated niobium oxide. Although no changes in the crystalline structure of both materials were observed, the presence of peroxo and superoxo species in the photocatalysts was confirmed by XPS and FTIR. The composites Nb2H and Nb10H presented band gap energies of 3.20 and 3.16 eV, respectively. However, Nb10H sample absorbs visible light at more than 400 nm, suggesting that the synthesis of the Nb2O5 with excess of H2O2 shifts the absorption edge of this material to the visible range, as well as reduces the energy required to the photoactivation of the catalyst. It was found that the photocatalytic activity increased with increasing oxidant concentration in the synthesis medium due to formation of a higher amount of oxygen reactive species on the surface of niobia. The peroxo-niobium groups on the Nb2O5 surface allowed the photocatalysts to be activated by visible light, and the superoxo groups formed can be also be responsible to improve its photocatalytic efficiency. The reuse tests of the Nb10H oxide indicated that the CA removal capacity remained practically constant even after four consecutive cycles. Therefore, the possibility of using solar irradiation to supply energy to active the photocatalyst make this material promising for use in low-cost photocatalytic systems for treatment of wastewater.

Simple Niobium Catalysts Applied in Reflux and Ultrasound-Assisted Systems for Biofuel Synthesis

Using niobium compounds as heterogeneous catalysts in biodiesel production is a promising methodology from economic and environmental viewpoints. However, the application of niobium catalysts still is a challenge due to the high temperatures and pressures for moderate biofuel yields. Therefore, easily handled and applied materials have been developed to optimize biofuel production, which is the goal of this study. Nb2O5 and ammonium niobium oxalate (AmNO) were activated in reflux and ultrasound-assisted system. Nb2O5 showed better activity under reflux, using methanol. The characterizations conclude that the Lewis-acid sites are determinant for higher conversion rather than surface area. AmNO has better activity also in the reflux system at 70 oC, against 170 oC for Nb2O5, reaching above 70% conversion. In addition, reactions in ultrasound-assisted systems are also appealing due to the lower time and temperature, with conversion rates above 40%. Both catalysts showed interesting results under milder conditions than those in the literature.

A niobium-catalyzed coupling reaction of α-keto acids with ortho-phenylenediamines: synthesis of 3-arylquinoxalin-2(1H)-ones

A general methodology to access valuable 3-arylquinoxalin-2(1H)-ones was developed, by the reaction of α-keto acids with ortho-phenylenediamines in the presence of ammonium niobium oxalate (ANO) as a catalyst.

Synthesis of CeNb3O9 perovskite by Pechini method

Pechini method was applied for the first time to synthesize CeNb3O9 perovskite at different calcination temperatures (600, 800 and 1000 °C). A solution of water, citric acid, ethylene glycol, ammonium niobium oxalate and cerium ions was polymerized and calcined at 300 °C for 2 h. The precursor gels were submitted to a second calcination at 600, 800 and 1000 °C to obtain perovskite at different temperatures. These materials were characterized through X-ray diffraction (XRD), thermogravimetric analysis (TGA), N2 physisorption, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS-UVvis) and Fourier transform infrared spectroscopy (FTIR). Results showed the formation of perovskite only at 1000 °C and Nb2O5-CeO2 mixed oxides at lower temperatures with some interesting characteristics. Pechini technique allows the synthesis of cerium niobate perovskite at lower temperatures than those presented in the literature (prepared by different methods).

Liquid Phase Direct Synthesis of H2O2: Activity and Selectivity of Pd-Dispersed Phase on Acidic Niobia-Silica Supports

In this work, acidic niobia-silica (NbS, 4–14 wt % Nb) materials used as supports of dispersed Pd particles (1.0–2.0 wt % Pd) have been prepared from different Nb-precursors (niobium ethoxide, NBE, and ammonium niobium oxalate, ANBO) and techniques (coprecipitation and deposition), characterized, and tested in the direct synthesis of H2O2 in water and methanol solvents. In particular, on a typical NbS sample, the evolution of morphology (by N2-adsorption–desorption), crystalline-phase (by XRD), electronic structure (by UV–vis-DRS), and surface acidity with time/temperature of treatment (350–800 °C for 4–100 h) has been investigated. Surface acidity was measured by titrations with 2-phenylethylamine adsorption in various liquids: cyclohexane, for the intrinsic acidity, and water, methanol, and water–methanol mixtures for the effective acidities. Direct H2O2 synthesis reaction was performed in semibatch slurry reactor with continuous feeding of the gaseous mixture (H2, O2, and N2), under pressure (5 × 103 k...

Synthesis characterization and acid properties of niobium-containing MCM-41

In the current work, the incorporation of niobium onto the nanostructured MCM-41 material was studied. The syntheses were carried out by the hydrothermal method using cetyltrimethylammonium bromide (CTMABr) as structural template, sodium silicate and water as solvent. Niobium was introduced in the reactive medium in the form of ammonium niobium oxalate, for obtaining Nb-MCM-41 materials. In order to verify the influence of the niobium content on the properties of the material, the samples were synthesized at Si/Nb molar ratios of 15, 30, 45 and 60. The materials were calcined and characterized by BET surface area, X-ray diffraction, Fourier transform infrared spectroscopy, X-rays fluorescence, for the determination of chemical composition, and scanning electron microscopy. The acidity properties of the MCM-41 and Nb-MCM-41, as determined by n-butylamine adsorption, were investigated by thermogravimetry in the temperature range of room temperature up to 600 °C, under nitrogen gas. From TG/DTG data, the acidity values were of 3.1–3.3 mmol g−1, for materials with Si/Nb molar ratio of 60, 45 and 30. The lower value of acidity of 0.6 mmol g−1, observed for Si/Nb = 15, suggests that at this molar ratio, Nb is not incorporated in the MCM-41 structure.

Alternative route for the synthesis of high surface-area η-Al2O3/Nb2O5 catalyst from aluminum waste

This paper describes an alternative route for the production of a high-surface-area ɳ-Al2O3/Nb2O5 catalyst synthesized from aluminum waste and niobium ammonium oxalate (NH4H2[NbO(C2O4)3]·3H2O). The effects of thermal treatment on the morphology and crystal structure were examined by X-ray powder diffraction (XPD), surface area measurements (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence, dynamic scanning calorimetry (DSC) and thermogravimetry (TG) measurement. The catalysts were evaluated in the glycerol dehydration reaction. Catalytic tests were carried out with reactants in gas-phase with a fixed-bed reactor at 300° and 400 °C.

Biocerâmicas aditivadas com nióbio (V): avaliação da rota hidrotérmica modificada com ácido cítrico e ureia para obtenção de hidroxiapatitas modificadas

Resumo A hidroxiapatita sintética (Ca10(PO4)6(OH)2; HA) devido à propriedade de biocompatibilidade com o tecido ósseo tornou-se um material cerâmico amplamente utilizado na reconstrução óssea. A biocompatibilidade assim como outras propriedades físico-químicas da hidroxiapatita podem ser modificadas por meio da adição de diferentes íons na sua estrutura. O íon nióbio (V) não tem sido empregado comumente na síntese de hidroxiapatitas. O objetivo deste trabalho foi verificar o emprego da rota hidrotérmica na síntese de hidroxiapatita dopada com íon nióbio (V). A rota empregada utiliza o complexo di-hidrogeno tris(oxalato) oxiniobato (V) de amônio trihidratado (NH4H2[NbO(C2O4)3].3H2O), como precursor de íon nióbio (V). A adição de ácido cítrico e ureia na rota hidrotérmica é usada para o controle do pH da síntese e da taxa de precipitação. Amostras pura e aditivada com 5,3 ppm de íon nióbio (V) foram obtidas. A coexistência de outras fases além da hidroxiapatita não foi observada em ambas amostras por meio dos empregos das técnicas de difração de raios X e espectroscopia no infravermelho. Por meio da técnica de FTIR observou-se a presença de grupos funcionais característicos da hidroxiapatita. Na análise por microscopia eletrônica de varredura, verificou-se a formação de aglomerados compostos por partículas arredondadas confirmadas pela técnica de microscopia eletrônica de transmissão. A análise espectroscópica de fluorescência de raios X detectou a presença de nióbio na amostra aditivada obtida. Os resultados apontam que podem ser sintetizadas hidroxiapatitas aditivadas com íon nióbio (V) por meio da rota hidrotérmica, podendo ser considerado como enorme o potencial para a aplicação em biocerâmicas.