Electrochemical Performance of Niobium MXenes with Lanthanum.

MXenes are the newest class of two-dimensional nanomaterials characterized by large surface area, high conductivity, and hydrophilicity. To further improve their performance for use in energy storage devices, heteroatoms or functional groups can be inserted into the Mxenes' structure increasing their stability. This work proposes insertion of lanthanum atoms into niobium-MXene (Nb-MX/La) that was characterized in terms of morphogy, structure, and electrochemical behavior. The addition of La to the Nb-MXene structure was essential to increase the spacing between the layers, improving the interaction with the electrolyte and enabling charge/discharge cycling in a higher potential window and at higher current densities. Nb-MX/La achieved a specific capacitance of up to 157 mF cm-2, a specific capacity of 42 mAh cm-2 at 250 mV s-1, a specific power of 37.5 mW cm-2, and a specific energy of 14.1 mWh cm-2 after 1000 charge/discharge cycles at 50 mA cm-2.

Predictive Modeling of Vickers Hardness Using Machine Learning Techniques on D2 Steel with Various Treatments.

Hardness is one of the most crucial mechanical properties, serving as a key indicator of a material's suitability for specific applications and its resistance to fracturing or deformation under operational conditions. Machine learning techniques have emerged as valuable tools for swiftly and accurately predicting material behavior. In this study, regression methods including decision trees, adaptive boosting, extreme gradient boosting, and random forest were employed to forecast Vickers hardness values based solely on scanned monochromatic images of indentation imprints, eliminating the need for diagonal measurements. The dataset comprised 54 images of D2 steel in various states, including commercial, quenched, tempered, and coated with Titanium Niobium Nitride (TiNbN). Due to the limited number of images, non-deep machine learning techniques were utilized. The Random Forest technique exhibited superior performance, achieving a Root Mean Square Error (RMSE) of 0.95, Mean Absolute Error (MAE) of 0.12, and Coefficient of Determination (R2) ≈ 1, surpassing the other methods considered in this study. These results suggest that employing machine learning algorithms for predicting Vickers hardness from scanned images offers a promising avenue for rapid and accurate material assessment, potentially streamlining quality control processes in industrial settings.

Niobium oxyhydroxide as a bioactive agent and reinforcement to a high-viscosity bulk-fill resin composite

Abstract Objective The present in vitro study incorporated niobium oxyhydroxide fillers into an experimental high-viscosity bulk-fill resin composite to improve its mechanical performance and provide it a bioactive potential. Methodology Scanning electron microscopy synthesized and characterized 0.5% niobium oxyhydroxide fillers, demonstrating a homogeneous morphology that represented a reinforcement for the feature. Fillers were weighed, gradually added to the experimental resin composite, and homogenized for one minute, forming three groups: BF (experimental high-viscosity bulk-fill resin composite; control), BF0.5 (experimental high-viscosity bulk-fill resin composite modified with 0.5% niobium oxyhydroxide fillers), and BFC (commercial bulk-fill resin composite Beautifil Bulk U, Shofu; positive control). In total, 10 specimens/groups (8 × 2 × 2 mm) underwent flexural strength (FS) tests in a universal testing machine (Instron) (500N). Resin composites were also assessed for Knoop hardness (KH), depth of cure (DoC), degree of conversion (DC), elastic modulus (E), and degree of color change (ΔE). The bioactive potential of the developed resin composite was evaluated after immersing the specimens into a simulated body fluid in vitro solution and assessing them using a Fourier-transformed infrared spectroscope with an attenuated total reflectance accessory. One-way ANOVA, followed by the Tukey's test (p<0.05), determined FS, DC, KH, and ΔE. For DoC, ANOVA was performed, which demonstrated no significant difference between groups (p<0.05). Conclusions The high-viscosity bulk-fill resin composite with 0.5% niobium oxyhydroxide fillers showed promising outcomes as reinforcement agents and performed well for bioactive potential, although less predictable than the commercial resin composite with Giomer technology.

Remineralizing potential of a fluoride varnish modified by bioactive nanoparticles / Potencial remineralizante de um verniz fluoretado modificado por nanopartículas bioativas

Objective: Evaluate a fluoride varnish modified by nanostructures with the bioactive qualities of silica (SiO2) and niobium pentoxide (Nb2O5), testing its remineralizing potential by surface hardness (SH) and energy-dispersive X-ray spectroscopy (EDX). Material and Methods: Bovine enamel specimens (6×4×2mm) were prepared and submitted to a demineralizing/remineralizing process to produce a subsurface caries-like lesion, evaluated by transversal microradiography image (TMR) and subsequently distributed randomly into three groups: fluoride varnish (VZ); fluoride varnish + silica gelatin (VZ-SiO2) and fluoride varnish + niobium nanoparticles (VZ-Nb2O5). The specimens were subjected to a pH-cycling demineralizing/remineralizing process for 7 days at 37ºC. The %SH loss and %SH recovery (after the pH-cycling regimen) were calculated (n=10/group). The Ca/P weight ratio before and after the pH-cycling regimen was evaluated through SEM/EDX. A two-way ANOVA followed by Tukey's test (p<0.05) was performed for hardness and EDX. Results: TMR image showed the formation of an artificial subsurface lesion, and a significant SH increase was observed in the VZ-Nb2O5 group (p<0.05). Regarding the %SHL and %SHR, the VZ-Nb2O5 and VZ-SiO2 were significantly different compared to the VZ group (p<0.001), but VZ-Nb2O5 presented higher values. The Ca/P ratio showed that blocks treated with VZ-SiO2 and VZ-Nb2O5 showed greater ion deposition, particularly in the presence of Nb. Conclusion: The bioactivity of niobium facilitated greater interaction between the enamel and the varnish, leading to a slow release of nanoparticles and a longer-lasting remineralizing effect (AU)

Objetivo: Avaliar um verniz fluoretado modificado por nanoestruturas com a bioatividade da sílica (SiO2) e pentóxido de nióbio (Nb2O5), testando seu potencial remineralizador pela dureza de superfície (SH) e espectroscopia de energia dispersiva de raios-X (EDX). Material e Métodos: Espécimes de esmalte bovino (6×4×2mm) foram preparados e submetidos à desmineralização/remineralização para produzir uma lesão subsuperficial semelhante a cárie, avaliada por imagem de microrradiografia transversal (TMR) sendo distribuída em três grupos: verniz fluoretado (VZ); verniz fluoretado+gelatina de sílica (VZ-SiO2) e verniz fluoretado+nanopartículas de nióbio (VZ-Nb2O5). As amostras foram submetidas à desmineralização/remineralização por ciclagem de pH durante 7 dias a 37°C. A porcentagem de perda e recuperação de SH foram calculadas (n=10/grupo). A relação em peso Ca/P antes e depois da ciclagem foi avaliada através de MEV/EDX. ANOVA a dois critérios seguida do teste de Tukey (p<0,05) foi realizada para dureza e EDX. Resultados: A TMR mostrou a formação de uma lesão subsuperficial e um aumento significativo de SH foi observado no grupo VZ-Nb2O5 (p<0,05). Em relação ao %SHL e %SHR, o VZ-Nb2O5 e o VZ-SiO2 foram significativamente diferentes em relação ao grupo VZ (p<0,001), mas o VZ-Nb2O5 apresentou valores maiores. A relação Ca/P mostrou que os blocos tratados com VZ-SiO2 e VZ-Nb2O5 apresentaram maior deposição de íons, principalmente na presença de Nb. Conclusão: A bioatividade do nióbio facilitou maior interação entre o esmalte e o verniz, levando a uma liberação lenta de nanopartículas e a um efeito remineralizante mais duradouro (AU)

Effects of experimental bleaching gels containing co-doped titanium dioxide and niobium pentoxide combined with violet light.

OBJECTIVES: The objective of the study is to evaluate the bleaching potential of 6% hydrogen peroxide (6% HP) gels containing NF_TiO2 or Nb2O5 irradiated with a violet LED light and the effects on enamel mineral content and surface morphology. METHODS: Particles were synthesized, and experimental gels were chemically analyzed by preliminary and accelerated stability tests, pH, and HP decomposition rate. Bovine enamel blocks were treated with 6% HP gels containing (n = 10): 5% NF_TiO2, 5% Nb2O5, 2.5% NF_TiO2 + 2.5% Nb2O5 or without particles (6% HP), irradiated or not with LED, and the control was treated with 35% HP. Color (∆E00) and whitening index (∆WID) variations, surface microhardness (SH), average roughness (∆Ra), Ca-P concentration (EDS), and enamel morphology (SEM) were assessed. Bleaching was performed in 3 sessions of 30 min and 7-day intervals. Data were submitted to two- (pH, decomposition rate, ∆E00, and ∆WID) or three-way ANOVA and Bonferroni (SH), Kruskal-Wallis (∆Ra), and Dunnet tests (α = 0.05). RESULTS: No changes in the gel's color, odor, or translucency were observed. The pH (6 to 6.5) remained stable over time, and light irradiation boosted the HP decomposition rate. NF_TiO2 and Nb2O5-containing gels displayed higher ∆E00 and ΔWID when light-irradiated (p < 0.05). Nb2O5 and Nb2O5 + NF_TiO2 decreased enamel SH (p < 0.05), but no SH changes were found among groups (p > 0.05). No differences among groups were noted in ∆Ra, Ca-P content, and enamel morphology after treatments (p > 0.05). CONCLUSION: Experimental light-irradiated 6% HP gels containing NF_TiO2 or Nb2O5 were chemically stable and exhibited bleaching potential comparable with 35% HP. CLINICAL RELEVANCE: Low-concentrated HP gels containing NF_TiO2 or Nb2O5 and light-irradiated stand as a possible alternative to in-office bleaching.

Assessing the Rheological, Mechanical, and Photocatalytic Properties of Niobium Oxide-Incorporated White Cement Pastes.

Niobium oxide (Nb2O5) is a semiconductor that exhibits photocatalytic properties, making it potentially valuable in addressing air pollution, self-cleaning, and self-disinfection in cement-based materials (CBMs). Therefore, this study aimed to evaluate the impact of different Nb2O5 concentrations on various parameters, including rheological characteristics, hydration kinetics (measured using isothermal calorimetry), compressive strength, and photocatalytic activity, specifically in the degradation of Rhodamine B (RhB) in white Portland cement pastes. The incorporation of Nb2O5 increased the yield stress and viscosity of the pastes by up to 88.9% and 33.5%, respectively, primarily due to the larger specific surface area (SSA) provided by Nb2O5. However, this addition did not significantly affect the hydration kinetics or the compressive strength of the cement pastes after 3 and 28 days. Tests focusing on the degradation of RhB in the cement pastes revealed that the inclusion of 2.0 wt.% of Nb2O5 was insufficient to degrade the dye when exposed to 393 nm UV light. However, an interesting observation was made concerning RhB in the presence of CBMs, as it demonstrated a degradation mechanism that was not dependent on light. This phenomenon was attributed to the production of superoxide anion radicals resulting from the interaction between the alkaline medium and hydrogen peroxide.

Mechanical and antibacterial properties of an experimental flowable composite containing Nb2O5 and NF_TiO2 nanoparticles.

This study developed an experimental flowable composite incorporated with niobium pentoxide (Nb2O5) combined or not with titanium dioxide co-doped with fluorine and nitrogen (NF_TiO2) and evaluated the mechanical and antibacterial properties. The experimental flowable composite (TEGDMA + BisGMA 1:1 + 60%wt - inorganic filler - borosilicate 0.7 µm) was formulated according to the type and concentration of Nb2O5 and NF_TiO2 (0.5, 1, 1.5 and 2 wt%) or NF_TiO2 + Nb2O5 (0.25, 0.5, 0.75 and 1 wt% - 1:1). The control groups were formed by the experimental composite without the incorporation of Nb2O5 and/or NF_TiO2 (GC-E) and by a commercial flowable composite (GC). The characterization of the surface of the composite and its particles was carried out using scanning electron microscopy (SEM) and energy dispersive x-rays (EDX). Specimens were manufactured and subjected to mechanical tests of flexural strength (FS) (n = 12), flexural modulus (FM) (n = 12), roughness (Ra) (n = 10), microhardness (n = 10), and contact angle (n = 10); and, to evaluate the antibacterial activity, they were submitted to tests of biofilm formation against S. mutans (CFU/mL) (n = 5), biofilm biomass by dry weight (n = 5) and confocal laser microscopy (%LIVE/DEAD) (n = 5). Data were submitted to one-way ANOVA and Tukey's post-hoc and, those that were not homoscedastic, but with normality, were submitted to Welch's ANOVA and Games-Howell's post-hoc. Dunnet's test was used to compare the controls with the other experimental groups (α = 5). The Nb2O5 particles had an average size of 32.4 µm and the nanoparticles (NPs) of NF_TiO2, 10 nm. EDX analysis identified isolated peaks of N, F, Ti, and Nb confirming the presence of these particles in the resin matrix. The 1.5% NF_TiO2 group had a higher FS and FM than the controls (p < 0.05). GC showed higher microhardness between groups (p < 0.05). There was no difference between the experimental groups regarding contact angle and roughness (p > 0.05), except for GC, which had the highest Ra values and the lowest contact angle between groups (p < 0.05). Composites containing 0.5%, 1%, 1.5%, and 2% Nb2O5, 1%, 1.5%, and 2% NF_TiO2 and 2% Nb2O5 + NF_TiO2 showed lower biofilm formation (p < 0.05), lower total biofilm biomass (p < 0.05), and a higher percentage of dead cells (44%, 52%, 52%, 79%, 42% 43%, 62%, 65%, respectively) than GC and GC-E (5% and 1%, respectively). It is concluded that the incorporation of 1.5% NF_TiO2 promoted a greater FS and FM among the experimental composites and that the addition of Nb2O5 particles (0.5%, 1%, 1.5%, and 2%), NF_TiO2 (1%, 1.5% and 2%) and the combination Nb2O5 + NF_TiO2 (2%) showed significant antibacterial effects.

Safe Etching Route of Nb2SnC for the Synthesis of Two-Dimensional Nb2CTx MXene: An Electrode Material with Improved Electrochemical Performance.

In this study, low-temperature synthesis of a Nb2SnC non-MAX phase was carried out via solid-state reaction, and a novel approach was introduced to synthesize 2D Nb2CTx MXenes through selective etching of Sn from Nb2SnC using mild phosphoric acid. Our work provides valuable insights into the field of 2D MXenes and their potential for energy storage applications. Various techniques, including XRD, SEM, TEM, EDS, and XPS, were used to characterize the samples and determine their crystal structures and chemical compositions. SEM images revealed a two-dimensional layered structure of Nb2CTx, which is consistent with the expected morphology of MXenes. The synthesized Nb2CTx showed a high specific capacitance of 502.97 Fg-1 at 1 Ag-1, demonstrating its potential for high-performance energy storage applications. The approach used in this study is low-cost and could lead to the development of new energy storage materials. Our study contributes to the field by introducing a unique method to synthesize 2D Nb2CTx MXenes and highlights its potential for practical applications.

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives.

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Niobium-containing bioactive glasses modulate alkaline phosphatase activity during bone repair.

This study aimed to evaluate the pre-clinical behavior of niobium-containing bioactive glasses (BAGNb) by their ability to promote bone repair and regulate alkaline phosphatase (ALP) levels in an animal model. BAGNbs were produced as powders and as scaffolds and surgically implanted in the femur of male rats (Wistar lineage n = 10). Glasses without Nb (BAG) were produced and implanted as well. The Autogenous Bone (AB) was used as a control. After 15, 30, and 60 days of surgical implantation, blood serum samples were collected to quantify ALP activity, and femurs were removed to assess bone repair. Bone samples were histologically processed and stained with H&E to quantify the % new bone into defects. No postoperative complications were identified. Early-stage repair (15 days) resulted in increased ALP activity for all groups, with increased values ​​for powdered BAGNb. The maturation of the new bone led to a reduction in serum ALP levels. Histological sections showed the formation of immature bone tissue and vascularization with the progression of bone deposition to mature and functional tissue over time. BAG powder showed less new bone formation in 15 days, while the analysis at 30 and 60 days showed no difference between groups (p > .05). Niobium-containing bioactive glasses safely and successfully induced bone repair in vivo. The modulation of ALP activity may be a pathway to describe the ability of niobium-containing materials to contribute to new bone formation.

Phonon Dominated Thermal Transport in Metallic Niobium Diselenide from First Principles Calculations.

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide material which possesses unique electrical and superconducting properties for future nanodevices. While the superconducting, electrical, and bulk thermal transport properties of NbSe2 have been widely studied, the in-plane thermal transport property of NbSe2, which is important for potential thermoelectric applications, has not been thoroughly investigated. In this report, we study the lattice in-plane thermal transport of 2D NbSe2 by solving the phonon Boltzmann transport equation with the help of the first principles calculation. The thermal conductivity obtained at room temperature is 12.3 W/mK. A detailed analysis shows that the transverse acoustic phonon dominates the lattice thermal transport, and an anomalously small portion of electron contribution to the total thermal conductivity is observed for this metallic phase. The results agree well with experimental measurements and provide detailed mode-by-mode thermal conductivity contribution from different phonon modes. This study can provide useful information for integrating NbSe2 in nanodevices where both electrical and thermal properties are critical, showing great potential for integrating monolayer NbSe2 to thermoelectric devices.

Bleaching effectiveness and cytotoxicity of new experimental formulation of niobium-based bleaching gel.

OBJECTIVES: The development of new bleaching agents with minimum concentration of hydrogen peroxide (HP), without adverse effects, and with bleaching effectiveness, has great clinical relevance. The aim of this study was to evaluate the bleaching efficacy and cytotoxicity of a new niobium-based bleaching gel, compared to already available HP-based gels. MATERIALS AND METHODS: For the bleaching efficacy analysis, 40 bovine incisors were randomly divided into 4 groups according to the established bleaching protocol: control, untreated; 35HP, 35% HP bleaching gel; 6HP, 6% HP bleaching gel; NbHP, niobium gel associated with 3% HP gel. The color variation was measured in a spectrophotometer and the values of ΔL, Δa, Δb, and ΔE obtained. For the cell viability assay by MTT, MC3T3 cells were exposed to bleaching gel extracts (1:500, 1:250, 1:125 dilutions; immediately and 24 h). Statistical tests were performed (P < 0.05). RESULTS: The color alteration for all bleaching gels was significant compared to control (P < 0.05), but the NbHP gel showed a significant ΔE than other gels, with expressive color alteration at 14 days (P < 0.05). The 35HP showed high cytotoxicity regarding control and the most groups in all periods and extracts analyzed (P < 0.05), while the NbHP showed greater cell viability than control in the immediate period, dilution of the 1:500 and superior to 6HP in the most extracts at 24 h. CONCLUSION: The new experimental niobium-based gel has bleaching efficacy similar to that of gels with a high concentration of HP, and it has high cytocompatibility. CLINICAL RELEVANCE: The use of this new generation of niobium-based whitening gel associated with a low concentration of hydrogen peroxide represents the possibility of a tooth whitening with lower dentin sensitivity.

Orthodontic resins loaded with niobium silicate particles: Impact of filler concentration on the physicochemical and biological properties.

OBJECTIVES: White spot lesions (WSL) are prevalent in patients using orthodontic appliances. The presence of ion-releasing compounds in the tooth-appliance interface may limit enamel demineralization to control WSL incidence. Thus, this study aims to evaluate the mineral formation on SiNb-containing experimental orthodontic resins and the influence of these fillers on the physicochemical and biological properties of developed materials. MATERIALS AND METHODS: The SiNb particles were synthesized via the sol-gel route and characterized by their molecular structure and morphology. Photopolymerizable orthodontic resins were produced with a 75 wt% Bis-GMA/25 wt% TEGDMA and 10 wt%, 20 wt%, or 30 wt% addition of SiNb. A control group was formulated without SiNb. These resins were tested for their degree of conversion, softening in solvent, cytotoxicity in fibroblasts, flexural strength, shear bond strength (SBS), and mineral deposition. RESULTS: The addition of 10 wt% of SiNb did not impair the conversion of monomers, cytotoxicity, and flexural strength. All groups with SiNb addition presented similar softening in solvent. The presence of these particles did not affect the bond strength between metallic brackets and enamel, with SBS values ranging from 16.41 to 18.66 MPa. The mineral deposition was observed for all groups. CONCLUSION: The use of niobium silicate as filler particles in resins may be a strategy for the adhesion of orthodontic appliances. The 10 wt% SiNb concentration resulted in a material with suitable physicochemical and biological properties while maintaining the bond strength to tooth enamel and promoting mineral deposition.

Cyto-genotoxicity of crystalline and amorphous niobium (V) oxide nanoparticles in CHO-K1 cells.

Niobium (V) oxide nanoparticles (NINPs) have been widely and increasingly applied in various health products and industrial processes. This merits further study of their toxicity. Here, we investigated the potential of NINPs to induce DNA damage, cytotoxicity, and chromosome instability in cultured CHO-K1 cells. NINPs were physico-chemically characterized. As assessed by comet assay, crystalline and amorphous NINPs were genotoxic at the highest concentrations evaluated. The cytokinesis-block micronucleus assay demonstrated that a 24-h treatment with NINPs, for the crystalline and the amorphous samples, significantly reduced the nuclear division cytotoxicity index. In addition, a 4-h treatment period of crystalline NINPs increased micronucleus (MNi) frequencies. MNi, nucleoplasmic bridges and nuclear buds were detected after exposure of the cells for 24 h to crystalline NINPs. In the amorphous sample, chromosome instability was restricted to the induction of MNi, in the 24-h treatment, detected at all tested concentrations. The fluorescence and dark field microscopy demonstrated the uptake of NINPs by CHO-K1 cells and an intracellular distribution outlining the nucleus. Our data advance understanding of the cytotoxic and genotoxic effects of NINPs and should be taken into consideration when setting up guidelines for their use in industrial or health products.

Avaliação das propriedades físico-químicas e osteogênicas do cimento portland associado ao pentóxido de nióbio / Evaluation of the physicochemical and osteogenic properties of portland cement associated with niobium pentoxide

Este trabalho objetivou desenvolver, caracterizar e avaliar a atividade osteogênica de formulações de CP com diferentes proporções de óxido de Nióbio (Nb2O5), substituindo o Bi2O3. Foram utilizados três grupos, um controle e dois experimentais: GC (MTA Angelus®), F6 (75% CP, 20% Nb2O5 e 5% CaSO4) e F7 (75% CP, 10% Bi2O3, 10% Nb2O5e 5% CaSO4). As formulações foram submetidas às análises de Difração de RaioX (DRX), Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Infravermelho com Transformada de Fourier (FTIR), Espectrometria de Fluorescência de Raios-X (FRX), pH, tempo de presa, radiopacidade, resistência a compressão, citotoxicidade e bioatividade. Os dados obtidos foram avaliados estatisticamente pelo teste de variância (ANOVA) com correção de Bonferroni (p<0,05%). O resultado do teste de pH: Nióbio 10% Imediato (12,205 ±0,304); 24h; (12,770 ± 0,226) 48h: (12,910 ± 0,169). Nióbio 20%: imediato (12,080 ± 0,282); 24 h: (12,350 ± 0,593); 48 h: (12,580 ± 0,73). Para o tempo de presa inicial em segundos: MTA (397,500 ±10,606); Nióbio 10% (294,333 + 90,897) e Nióbio 20% (279,000 + 15,874). O tempo de presa final para os grupos foram: MTA (15,000 + 49,497), Nióbio 10% (560 ±38,587), sendo menor quando comparado ao MTA (p<0,001) e Nióbio 20% (715,666 ± 30,664) (p<0,01). Os valores da radiopacidade em mm Al do Nióbio 10% (3,888 ±0,340); Nióbio 20% (3,713 ± 0,712). A resistência a compressão em MPa foi: Nióbio 10% (694,150 + 78,951) Nióbio 20% (699,295 + 47,672). A viabilidade celular não apresentou diferença entre o MTA e grupos experimentais (p<0,05). Os resultados da capacidade osteogênese das formulações a partir do ensaio da fosfatase alcalina (FAL) em UI/L por grama de proteína para cada grupo foi: MTA (1,9 + 1,227) e Nióbio 20% (1,784 + 1,342) (p>0,05). Nossos achados apontam propriedades relevantes para as formulações com Nb2O5 como, pH alcalino, radiopacidade, resistência a compressão e atividade da fosfatase alcalina (AU).

Work aimed to develop, characterize and evaluate the osteogenic activity of PC formulations with different proportions of Niobium oxide (Nb2O5), replacing Bi2O3. Three groups were used, one control and two experimental: GC (MTA Angelus®), F6 (75% CP, 20% Nb2O5 and 5% CaSO4) and F7 (75% CP, 10% Bi2O3, 10% Nb2O5e 5% CaSO4) . The formulations were submitted to X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Fluorescence Spectrometry (FRX), pH, setting, radiopacity, compressive strength, cytotoxicity and bioactivity. The data obtained were statistically evaluated by the test of variance (ANOVA) with Bonferroni correction (p<0.05%). The pH test result: Niobium 10% Immediate (12.205 ±0.304); 24h; (12.770 ± 0.226) 48h: (12.910 ± 0.169). Niobium 20%: immediate (12.080 ± 0.282); 24h: (12.350 ± 0.593); 48 h: (12.580 ± 0.73). For initial setting time in seconds: MTA (397,500 ±10,606); Niobium 10% (294,333 + 90,897) and Niobium 20% (279,000 + 15,874). The final setting time for the groups were: MTA (15,000 + 49,497), Niobium 10% (560 ± 38,587), being smaller when compared to MTA (p<0,001) and Niobium 20% (715,666 ± 30,664) (p<0 .01). Radiopacity values in mm Al of 10% Niobium (3.888 ±0.340); Niobium 20% (3.713 ± 0.712). The compressive strength in MPa was: Niobium 10% (694.150 + 78.951) Niobium 20% (699.295 + 47.672). Cell viability showed no difference between MTA and experimental groups (p<0.05). The results of the osteogenesis capacity of the formulations from the alkaline phosphatase assay (ALF) in IU/L per gram of protein for each group were: MTA (1.9 + 1.227) and Niobium 20% (1.784 + 1.342) (p> 0.05). Our findings point to relevant properties for Nb2O5 formulations such as alkaline pH, radiopacity, compressive strength and alkaline phosphatase activity (AU).

3D printing of poly(butylene adipate-co-terephthalate) (PBAT)/niobium containing bioactive glasses (BAGNb) scaffolds: Characterization of composites, in vitro bioactivity, and in vivo bone repair.

This study aimed to produce poly(butylene adipate-co-terephthalate) (PBAT)/niobium containing bioactive glasses (BAGNb) composites scaffolds produced by fused deposition modeling (FDM) printing and evaluate their physicochemical and biological properties in vitro and in vivo. The composite filaments were produced by melt-extrusion with the addition of 10 wt% of BAGNb (PBAT/BAGNb). Filaments without BAGNb were produced as the control group (PBAT). The filaments were characterized and were used to produce 3D-printed scaffolds using FDM. The scaffolds' structure and surface properties were assessed. In vitro cell, proliferation, and cell mineralization analysis were performed. In vivo data was obtained in the rat femur model (n = 10), and the bone repair was assessed after 15, 30, and 60 postoperative days. The printed structures presented 69.81% porosity for the PBAT/BAGNb group and 74.54% for the PBAT group. Higher cell mineralization was observed for the PBAT/BAGNb group. The in vivo data showed that the PBAT/BAGNb presented new bone formation comparable to positive controls. The combination of PBAT and BAGNb in 3D-printed scaffolds may be an alternative to produce bioactive materials with controllable shapes and properties for bone regeneration treatments.

Hydrochemical and radiometric evaluation of fresh and thermal waters from Araxá city (Minas Gerais, Brazil).

This paper reports the hydrochemistry and activity concentration of the natural radionuclides 238U, 234U, and 210Po for three compartments of the hydrological/hydrogeological system in Araxá city, Minas Gerais State, Brazil: 1) mineral waters from the prominent springs Dona Beja (DBS) and Andrade Júnior (AJS), occurring at Barreiro area; 2) surface waters from Barreiro area and vicinity; and 3) rainwater. According to the Rule for Mineral Waters in Brazil (Register 7841) for temperature, the DBS water is cold (< 25 °C), while AJS is hypothermal (25-33 °C). The TDS (Total Dissolved Solids) concentration of DBS is low (70 mg/L), but high in AJS (2898 mg/L). The hydrogeochemical facies corresponded to sodium-(bi)carbonate for AJS and sodium/potassium-bicarbonate for DBS. The hydrochemical differences of DBS and AJS waters reflect the distinct characteristics of their respective aquifer systems. The DBS classification for TDS is the same of the Barreiro basin surface waters (mean TDS = 102 mg/L). Such value is somewhat higher than that of the rainwater and surface waters used for human consumption at Araxá city (TDS < 50 mg/L). The dataset reported in this paper indicated that fluoride and barium exceeded the WHO limits proposed in 2011 for drinking water. Among the natural radionuclides analyzed here that offer potential hazards for the human health is 210Po, whose WHO's limiting value of 100 mBq/L in drinking water was exceeded in rainwater, thus, restricting the use of this resource as a possible supply of drinking water for the local community.

Bulk and surface theoretical investigation of Nb-doped δ-FeOOH as a promising bifunctional catalyst.

The development of bifunctional catalysts is of great interest in fine chemistry, since they are capable of promoting multicatalytic reactions involved in several important industrial processes. Iron oxyhydroxides have been identified as low-cost bifunctional catalysts. However, their applications are limited due to their weak acid character. Thus, elaborated modifications of these systems can significantly contribute to increasing their activities and selectivity. This work consists in the study, through DFT calculations, of the properties of the bulk and the surface of feroxyhyte (δ-FeOOH) doped with niobium, as a potential bifunctional catalyst. We identified the formation of stronger van der Waals interactions among the doped δ-FeOOH layers, which can increase the thermal stability of the catalyst. In addition, evidence has been found that the insertion of Nb increases Brönsted acidity and gives rise to new Lewis acid sites on the catalyst surface.

Fast pyrolysis as a tool for obtaining levoglucosan after pretreatment of biomass with niobium catalysts.

Levoglucosan (LGA) is a promising chemical platform derived from the pyrolysis of biomass that offers access to a variety of value-added products. We report an efficient route to produce LGA via the pretreatment of biomass with niobium compounds (oxalate, chloride and oxide) followed by fast pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS) at temperatures of 350-600 °C. Catalytic pretreatment reduces the quantity of lignin in the biomass, concentrates the cellulose and enhance LGA formation during fast pyrolysis. The pretreatment also removes alkaline metals, preventing competitive side reactions. The effect of several parameters such as catalyst weight, time, temperature, and solvent, with the optimal pretreatment conditions determined to be 3 (wt.%) niobium oxalate for 1 h at 23 °C in water. Pretreatment increased the LGA yields by 6.40-fold for sugarcane bagasse, 4.15-fold for elephant grass, 4.13-fold for rice husk, 2.86-fold for coffee husk, and 1.86-fold for coconut husk as compared to the raw biomasses. These results indicate that biomass pretreatment using niobium derivates prior fast pyrolysis can be a promising technique for biomass thermochemical conversion in LGA and others important pyrolytic products.

Nb-MCM-Type Mesoporous Material Synthesis Using Ionic Solid as Structure-Directing Agent for In Situ Lipase Immobilization.

MCM-41 and MCM-48 with niobium were successfully synthesized using 1-tetradecyl-3-methylimidazolium chloride ([C14MI]Cl) as a structure-directing agent. The best Si/Nb molar ratio was chosen (Si/Nb = 20) and the CALB enzyme was immobilized in situ in the synthesized Nb-MCM. SEM micrographs showed the formation of very regular spherical agglomerates with a diameter between 0.25 and 0.75 µm. The material presented a surface area of 954 and 704 m2/g and a pore volume of 0.321 and 0.286 cm3/g, for Nb-MCM-41 and Nb-MCM-48, respectively. Also, both materials showed a pore size of 2.261 nm. The number of recycles obtained for the CALB enzyme immobilized in Nb-MCM-41 and Nb-MCM-48 was 26 recycles with a residual activity of 49.62% and 16 recycles with a residual activity of 53.01%, respectively. For both materials, enzymatic activity remained stable for 5 months of storage at room temperature and refrigeration. The supports were able to catalyze the esterification reaction at 40, 60, and 80 °C, showing industrial application in reactions that require high temperatures. This methodology allows the preparation of new highly active and selective enzyme catalysts using niobium and [C14MI]Cl. Also, the new materials can provide greater viability in processes, ensuring a longer service life of catalysts. Graphical abstract.