Hydrous Niobium Research Articles

Sugarcane bagasse cellulose fibres and their hydrous niobium phosphate composites: synthesis and characterization by XPS, XRD and SEM

Cellulose fibres obtained from sugarcane bagasse were submitted to a purification process, which consisted of an acid hydrolysis for elimination of the major part of lignin and hemicellulose. This was followed by a delignification process carried out in two steps to yield crude cellulose (CCell) fibres in the first one and with a subsequent bleaching in order to yield bleached cellulose fibres (BCell). Composites of crude and bleached cellulose fibres with hydrous niobium phosphate, cell/NbOPO4·nH2O, were subsequently synthesized. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization of the obtained materials showed CCell/NbOPO4·nH2O and BCell/NbOPO4·nH2O are real composites. The nature of the cellulose (CCell or BCell) has an important role on the composites obtained, namely on the niobium salt composition at the composite surface. The synthesis of membranes of both cellulose and mixed matrix cellulose/NbOPO4·nH2O was only possible when the bleached cellulose was used.

Synthesis and Characterization of a Soluble Vanadium‐Containing Keggin Polyoxoniobate by ESI‐MS and 51V NMR: (TMA)9[V3Nb12O42]·18H2O

AbstractThe vanadium‐containing heteropolyoxoniobate (TMA)9[V3Nb12O42]·18H2O was synthesised by hydrothermal reaction of V2O5 and hydrous niobium oxide in tetramethylammonium hydroxide solution. The cluster has an α‐Keggin structure with a central VO4 and two trans‐bicapped VO5. The water‐soluble product was characterised by X‐ray crystallography, ESI‐MS and both liquid‐ and solid‐state 51V NMR spectroscopy. The solid‐ and solution‐phase 51V NMR spectra indicate two major peaks corresponding to one VO4 and two VO5 sites.

Microbial Enzyme: Applications in Industry and in Bioremediation

Microbial Enzyme: Applications in Industry and in Bioremediation

Assessment of the Morphological, Biochemical, and Kinetic Properties forCandida rugosaLipase Immobilized on Hydrous Niobium Oxide to Be Used in the Biodiesel Synthesis

Lipase from Candida rugosa (CRL) was immobilized by covalent attachment on hydrous niobium oxide. The matrix could effectively be attached to the enzyme with high retention of activity and prevent its leakage. Following immobilization, CRL exhibited improved storage stability and performed better at higher incubation temperatures. In addition, the enzyme retained most of its catalytic efficiency after successive operational cycles. The immobilized derivative was also fully characterized with respect to its morphological properties: particle size, surface specific area, and pore size distribution. Structural integrity and conformational changes, such as surface cavities in the support, set by the lipase procedure, were observed by Scanning Electron Microscopy. Additionally, a comparative study between free and immobilized lipases was provided in terms of pH, temperature, and thermal stability. CRL derivative was evaluated for the synthesis of biodiesel employing babassu oil and short chain alcohols. The process was feasible only for oil and butanol reaction system.

Novel cellulose/ NbOPO4.nH2O hybrid material from sugarcane bagasse

In recent years studies concerning the applications of lignocellulosic/ inorganic couples have resulted in the development of an interesting class of functional materials. In this work a cellulose/NbOPO4.nH2O hybrid using cellulose from surgacane bagasse was prepared and characterized in order to test for adsorption applications. The preparation process was conducted by carrying out metallic niobium dilution in hydrofluoric acid in the presence of nitric acid, then adding boric acid to form the complex and, finally, the cellulose sugar cane bagasse was added. Concentrated phosphoric acid was also inserted to precipitate hydrous niobium phosphate particles in the cellulose fiber. This material was characterized by X-ray diffractometry (XRD), thermogravimetry (TG/DTG), and scanning electronic microscopy (SEM) connected to an energy dispersive spectrophotometer (EDS). Results by SEM/EDS show that NbOPO4.nH2O was present in structure of the cellulose. During the preparation of the material, using boric acid it was observed that the formation of precipitate occurred in a shorter time than the material prepared without boric acid.

Adsorção de chumbo, cádmio e prata em óxido de nióbio (V) hidratado preparado pelo método da precipitação em solução homogênea

This paper describes the adsorption of heavy metals ions from aqueous solution by hydrous niobium oxide. Three heavy metals were selected for this study: cadmium, lead and silver. Adsorption isotherms were well fitted by Langmuir model. Maximum adsorption capacity (Q0) for Pb2 +, Ag+ and Cd2 + was found to be 452.5, 188.68 and 8.85 mg g-1, respectively.

Thermodynamic and kinetic investigations of phosphate adsorption onto hydrous niobium oxide prepared by homogeneous solution method

The adsorption kinetics of phosphate onto Nb 2O 5·nH 2O was investigated at initial phosphate concentrations 10 and 50 mg L − 1. The kinetic process was described by a pseudo second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The peak appearing at 1050 cm − 1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The effective desorption could be achieved using water at pH 12.

Adsorption kinetic, thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method

A type of Nb2O5⋅3H2O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-P g−1. The peak appearing at 1050 cm−1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for application to control phosphorus pollution.

Preparation and characterization of cellulose/ hydrous niobium phosphate hybrid

In recent years, increasing attention has been directed to the use of renewable resources, particularly of sugarcane bagasse. Considering the abundant availability of such lignocellulosic materials, relatively few attempts have been made regarding their utilization. Studies about properties and morphology, heavy metal adsorption, and membranes preparation have been conduced by this research group in order to use these materials. In this paper, cellulose fibers obtained from sugarcane bagasse were bleached and modified by hydrous niobium phosphate. Hybrids (cellulose/NbOPO4.nH2O) were prepared from metallic niobium dissolved in a fluoridric/nitric (10:1) mixture, to which cellulose sugarcane bagasse was added. Afterwards a concentrated orthophosphoric acid (85mL, 85% w/w) was added to precipitate hydrous niobium phosphate particles. This material was characterized by X-ray diffraction (XRD), thermogravimetry (TG/DTG), and differential scanning calorimetry (DSC) analyses, as well as scanning electronic microscopy (SEM) coupled to an energy dispersive spectrophotometer (EDS). Morphological studies of bleached cellulose revealed different sizes and arrangement of cells, showing that NbOPO4.nH2O was present in the cellulose structure. Thermal stability of the hybrid was observed up to approximately 200°C, and the cellulose decomposed at 300°C. These data will help finding new uses for these materials.

Quantitative microscopy characterization of hydrous niobium phosphate into bleached cellulose

In this research the spatial distribution characterization of niobium phosphate into bleached cellulose was carried out combining processing and images analysis obtained by SEM and statistical methodologies. The objective is to investigate the deposit composition and phosphate morphology by using complementary analytical techniques. Based on the proposed methodology, parameters of niobium phosphate agglomerates (size and shape) and fiber morphology were evaluated depending on gray-levels (average luminance and fiber type): fiber characteristics (morphology) were measured. For the test method proposed, a specific region of cellulose/NbOPO 4· nH 2O composite was analyzed. This method involves area fraction measuring with a conditional probabilistic analysis. The analyzed fields were divided in different ways, called ‘Scanning’ and as a result, in quantitative terms, the phosphate deposition was described as spatial distribution homogeneous or inhomogeneous. The quantitative microscopy as a non-destructive testing provides relevant information when it is combined with statistic analysis.

Synthesis of Nb 2O 5· nH 2O nanoparticles by water-in-oil microemulsion

Hydrous niobium oxide (Nb 2O 5· nH 2O) nanoparticles had been successfully prepared by water-in-oil microemulsion. They were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTG), Fourier transform infrared spectroscopy (FTIR), BET surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the nanoparticle was exactly Nb 2O 5· nH 2O with spherical shape. Their BET surface area was 60 m 2 g −1. XRD results showed that Nb 2O 5· nH 2O nanoparticles with crystallite size in nanometer scale were formed. The crystallinity and crystallity size increased with increasing annealing temperature. TT-phase of Nb 2O 5 was obtained when the sample is annealed at 550 °C.

Fabrication and characterization of three-dimensionally ordered macroporous niobium oxide

Three-dimensionally ordered macroporous (3-DOM) niobium oxide was fabricated by aqueous organic gel method through the interstitial spaces between polystyrene spheres assembled on glass substrates. Freshly precipitated hydrous niobium oxide (Nb 2O 5· nH 2O), which was prepared starting from Nb 2O 5, was used in combination with citric acid in an aqueous solution and then was transferred as a niobium source to synthesize 3-DOM Nb 2O 5. The morphologies of porous Nb 2O 5 were characterized by scanning electron microscope (SEM). The thermal decomposition and phase composition of 3-DOM Nb 2O 5 were investigated by Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Estudo da adsorção de surfactante catiônico na matriz inorgânica fosfato de nióbio hidratado

This work describes the study the adsorption of a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) in the hydrous niobium phosphate matrix. The matrix was characterized by powder X-ray diffraction (DRX), thermal analysis (TG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and surface area measurements (BET). The Langmuir and Freundlich isothermal models were used in the CTAB adsorption study. The adsorption process wasn`t favorable for the NbOPO4.nH2O in both studied models.

An investigation of phosphate adsorption from aqueous solution onto hydrous niobium oxide prepared by co-precipitation method

The synthetic hydrous niobium oxide has been used for phosphate removal from the aqueous solutions. The kinetic data correspond very well to the pseudo second-order equation. The phosphate removal tended to increase with a decrease of pH. The equilibrium data describe very well the Langmuir isotherm. The peak appearing at 1050 cm −1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The adsorption capacities are high, and increased with increasing temperature. The evaluated Δ G° and Δ H° indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (Δ S° positive) value suggest increase in randomness at the solid–liquid interface during the adsorption. A phosphate desorbability of approximately 60% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent.

Optimised immobilisation of microbial lipase on hydrous niobium oxide

AbstractThe aim of this work was to establish appropriate conditions for immobilising Candida rugosa lipase on a low‐cost inorganic matrix, hydrous niobium oxide, using a multivariate statistical approach. A 23 full factorial design was employed to determine the effects of support activation with glutaraldehyde (concentration 2.5–4.5%, pH 7–10) and lipase loading (200‐700 U g−1 matrix) on the hydrolytic and synthetic activities of the immobilised derivatives. From the results the following conditions were established: lipase loading of 450 U g−1 matrix and niobium oxide activation with glutaraldehyde at a concentration of 2.5% and pH 8. Under these conditions, high activity recovery (47.21%) and esterification yield (86.90%) were attained. The results also show that hydrous niobium oxide can be a valid alternative to replace high‐cost, commercially available inorganic matrices such as controlled pore silica. Copyright © 2006 Society of Chemical Industry

Influência do agente precipitante na preparação do óxido de nióbio (V) hidratado pelo método da precipitação em solução homogênea

This work reports the preparation, characterization and study of the ion exchange behavior of hydrous niobium oxide prepared by a homogeneous precipitation method. The precipitating agent was obtained in aqueous solution by thermal decomposition of urea or ammonium carbonate. The compounds were chemically and physically characterized by X-ray diffractometry, thermal analysis (TG/DTG), surface area measurements and ion exchange behavior with sodium. The materials prepared with ammonium carbonate presented a higher degree of crystallinity and better ion exchange capacity with sodium than materials prepared with urea. In the homogeneous precipitation method, materials were obtained with specific surface area of 123 - 224 m2 g-1. A variation of the preparation process produced hydrous niobium oxide with a different degree of hydration and specific surface area. This provided materials with different physico-chemical properties.

STUDIES OF THE HYDROUS NIOBIUM(V) OXIDE ION EXCHANGER. VII.RATE OF THE ISOTOPIC EXCHANGE OF CESIUM IONS BETWEEN THE EXCHANGER IN THE Cs+FORM AND AQUEOUS SOLUTION

ABSTRACT The isotopic exchange rate of Cs+ between hydrous niobium(V) oxide in the Cs+ form and aqueous solutions was determined radiochemically. The rate was controlled by the diffusion of Cs+ in the exchanger particle at varying pH. The diffusion coefficients at 10°C increased with pH up to pH7; from 3.0x10−11 m2s−1 at pH6 to 4.0×10−11 m2s−1 at pH7, and became constant above pH8 (5.0x10−11 m2s−1). While the diffusion coefficients of Na+ monotonously decrease with increasing pH; from 7.9×l0−11 m2s−1 at pH6.5 to 2.8×l0−11 m2s−1 at pHll. The difference in the dependence of diffusion coefficients on pH between Cs+ and Na+ was interpreted in terms of strength of interaction between counterions and ion-exchange sites since hydrous niobium(V) oxide has selectivity higher for Cs+ than for Na+.

Studies of the Hydrous Niobium(V) Oxide Ion Exchanger. VI. Rate of the Isotopic Exchange of Strontium Ions between the Exchanger in the Sr2+ Form and Aqueous Solution

Abstract The rate of the isotopic exchange of Sr2+ between hydrous niobium(V) oxide in the Sr2+ form and aqueous solution of strontium salts was determined radiochemically. The exchange rate was controlled by the diffusion of Sr2+ in the exchanger particles. The diffusion coefficients of Sr2+ and their activation energy changed with the pH in a solution equilibrated with exchangers. Under the conditions of constant pH, the diffusion coefficients were constant up to a certain concentration of Sr2+ (0.1 mol dm−3, pH 7.5), wherefrom they began to increase. The results were considered in terms of the interaction between the ions and the ion-exchange sites by comparing them with the Na+ isotopic exchange rate on this material.

ChemInform Abstract: The Hydrous Niobium(V) Oxide Ion Exchanger. Part 5. Effect of Heat Treatment on the Sodium Isotopic Exchange Rates Between Hydrous Niobium(V) Oxide in Na+ Form and Aqueous Solutions.

AbstractRadiochemical measurements of the sodium isotopic exchange rates of the Nb2O5 exchanger in Na+ form indicate that the rate is controlled by particle diffusion and increases with increasing temp. of the heat‐treatment in air.

Studies of the Hydrous Niobium(V) Oxide Ion Exchanger. V. Effect of Heat Treatment on the Sodium Isotopic Exchange Rates between Hydrous Niobium(V) Oxide in Na+ Form and Aqueous Solutions

Abstract The effect of a heat treatment was studied on the sodium isotopic exchange rate between the hydrous niobium(V) oxide in the Na+ form and aqueous solutions. The rate was controlled by the particle diffusion of sodium ions and increased with the heat-treatment temperature. The increase in the rate for the exchanger heat-treated at 200 °C was due to a decrease in the effective particle radius brought about by cracks which developed in the particles. A further increase in the rate at temperatures higher than 200 °C could be explained in terms of an increase in the Na+-diffusion coefficient, which was produced by an increase in the pore size responsinble for the movement of sodium ions.