© 2022 Elsevier LtdThe sol-gel method is one of the most used methods due to its outstanding capacity to obtain alkaline-earth phosphosilicate bioactive glass with high bioactivity. This efficient synthesis method involves several stages constituted by intermediate chemical reactions, which are governed by mechanisms and kinetic parameters that lead to the formation of the precursor gel of the vitreous matrix. Although the sol-gel method has been widely used for the preparation of materials, some steps are still not completely understood and that affect the final properties of the synthesized materials. For instance, the hydrolysis reaction of triethyl phosphate (TEP) which, similarly to tetraethyl orthosilicate (TEOS), is assumed to be complete in the stage of formation of the precursor gel of the glass matrix. Furthermore, the SN2-type mechanism for the hydrolysis of TEP is widely assumed. However, the absence of studies that support these presumptions fully justifies the use of theoretical methods to gain information about the hydrolysis of TEP within the sol-gel synthesis of 58S bioactive glass. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to study the reaction mechanisms and kinetic behavior of TEP hydrolysis. Our results show that the TEP hydrolysis reaction is very slow in its three stages, occurring not only via the SN2 mechanism with configuration inversion (SN2–I), as is commonly reported in the literature, but also via SN2 with configuration retention (SN2–R). Furthermore, it was found that the hydrolysis reaction via SN2–I occurs with faster kinetics than SN2–R. This behavior was observed for the three stages of TEP hydrolysis, both in protonated and non-protonated solutions. Based on our findings on the mechanisms and kinetics of triethyl phosphate hydrolysis reactions, a simple chemical model for the formation of calcium pyrophosphate crystalline domains in 58S sol-gel bioactive glass was proposed. In our model, TEOS undergoes rapid hydrolysis, followed by immediate condensation leading to the formation of three-dimensional silica gels, that permeate non-hydrolyzed TEP molecules due to their slow kinetic rate. This mismatch between the reactions of precursor alkoxides in acidic medium, results in a strong tendency in the formation of a glassy microstructure with low structural homogeneity characterized by crystalline domains of calcium pyrophosphate permeated by a silica-rich glass matrix.

© 2021The pioneeristic work of Hench led to the development of a calcium sodium phosphosilicate composition called 45S5 Bioglass®, which has been investigated extensively for applications in the field of bone repair and regeneration because of its bioactivity, i.e., ability to form a bond to living bone. The bioactivity of silicate glass is qualitatively associated with the development over time of the apatite layer on a bioactive glass, while quantitatively it would be related to how fast the formation of this crystalline phase occurs. In this work, (Camoltensaltbath2+|Naglass+) ion exchange in a molten salt bath (MSB) was employed for modifying the glass surface aiming to create a more reactive glass in a thin shell that surrounds the vitreous core, which preserves all the bioactivity characteristics of 45S5 Bioglass® composition. The 45S5@Ca45S5 core-shell-structured bioactive glass is characterized by a vitreous matrix enriched with calcium and a highly depolymerized silicate network. The presence of calcium-rich glass composition restricted to a thin shell acts as a catalyst, accelerating all the earlier events that occur at the glass/solution interface. The kinetics of deposition of the silica-gel and apatite layers was investigated by FTIR and 31P MAS NMR, respectively. The results suggest that the modification of the glass surface causes not only a reduction in the formation time of silica-gel and amorphous calcium phosphate on the glass surface but also induced the formation of the apatite phase with a higher degree of crystallinity.

© 2021 Elsevier B.V.Electrospun ultrathin polymer fibers hybridized with bioactive ceramics find use in many biomedical applications due to their unique and versatile abilities to modulate structure–performance relationships at the nano–bio interface. These organic–inorganic hybrid fibers present synergies that are otherwise rare, even when the precursors are used individually, such as bioactivity in polymers and stiffness–toughness balance in bioactive ceramics. Despite these unique advantages, a comprehensive and timely review on this important topic is still missing. Herein we describe the most recent and relevant developments on electrospun ultrathin polymer fibers hybridized with bioactive ceramics, with emphasis on bone tissue regeneration. This review addresses the preparation of bioactive ceramics, particularly (nano) hydroxyapatite (HA; nHA) and bioactive glass (BG), which stand out as the ceramics of interest for bone regeneration. The anatomy and mechanical properties of bone as well as fundamental tissue–scaffold interaction mechanisms are covered. The process–structure–property relationships of electrospun ultrathin fibers are discussed in detail from a technical standpoint, as well as fabrication strategies, process variables, characterization methods, and biological requirements (in vitro and in vivo performances). Finally, we highlight the major challenges and outline perspectives to pave the route for the next-generation hybrid materials for bone tissue engineering.

© 2020 Elsevier B.V.The sol-gel method is versatile and one of the well-established synthetic approaches for preparing bioactive glass with improved microstructure. In a successful approach, alkoxide precursors undergo rapid hydrolysis, followed by immediate condensation leading to the formation of three-dimensional gels. On the other hand, a slow kinetics rate for hydrolysis of one or more alkoxide precursors generates a mismatch in the progression of the consecutive reactions of the sol-gel process, which makes it difficult to form homogeneous multicomponent glass products. The amorphous phase separation (APS) into the gel is thermodynamically unstable and tends to transform into a crystalline form during the calcination step of xerogel. In the present study, we report a combined experimental and theoretical method to investigate the stability towards hydrolysis of triethyl phosphate (TEP) and its effects on the mechanism leading to phase separation in 58S bioactive glass obtained via sol-gel route. A multitechnical approach for the experimental characterization combined with calculations of functional density theory (DFT) suggest that TEP should not undergo hydrolysis by water under acidic conditions during the formation of the sol or even in the gel phase. The activation energy barrier (ΔG‡) showed a height of about 20 kcal·mol−1 for the three stages of hydrolysis and the reaction rates calculated for each stage of TEP hydrolysis were kFHR = 7.0 × 10−3s−1, kSHR = 6.8 × 10−3s−1 and kTHR = 3.5 × 10−3s−1. These results show that TEP remains in the non-hydrolyzed form segregated within the xerogel matrix until its thermal decomposition in the calcination step, when P species preferentially associate with calcium ions (labile species) and other phosphate groups present nearby, forming crystalline domains of calcium pyrophosphates permeated by the silica-rich glass matrix. Together, our data expand the knowledge about the synthesis by the sol-gel method of bioactive glass and establishes a mechanism that explains the role played by the precursor source of phosphorus (TEP) in the phase separation, an event commonly observed for these biomaterials.

© 2019 Wiley Periodicals, Inc.In vitro and in vivo experiments were undertaken to evaluate the solubility, apatite-forming ability, cytocompatibility, osteostimulation, and osteoinduction for a series of Nb-containing bioactive glass (BGNb) derived from composition of 45S5 Bioglass. Inductively coupled plasma optical emission spectrometry (ICP-OES) revealed that the rate at which Na, Ca, Si, P, and Nb species are leached from the glass decrease with the increasing concentration of the niobium oxide. The formation of apatite as a function of time in simulated body fluid was monitored by 31P Magic Angle Spinning (MAS) Nuclear magnetic resonance spectroscopy. Results showed that the bioactive glasses: Bioglass 45S5 (BG45S5) and 1 mol%-Nb-containing-bioactive glass (BGSN1) were able to grow apatite layer on their surfaces within 3 h, while glasses with higher concentrations of Nb2O5 (2.5 and 5 mol%) took at least 12 h. Nb-substituted glasses were shown to be compatible with bone marrow-derived mesenchymal stem cells (BMMSCs). Moreover, the bioactive glass with 1 mol% Nb2O5 significantly enhanced cell proliferation after 4 days of treatment. Concentrations of 1 and 2.5 mol% Nb2O5 stimulated osteogenic differentiation of BMMSCs after 21 days of treatment. For the in vivo experiments, trial glass rods were implanted into circular defects in rat tibia in order to evaluate their osteoconductivity and osteostimulation. Two morphometric parameters were analyzed: (a) thickness of new-formed bone layer and (b) area of new-formed subperiostal bone. Results showed that BGNb bioactive glass is osteoconductive and osteostimulative. Therefore, these results indicate that Nb-substituted glass is suitable for biomedical applications.

© 2019 Wiley Periodicals, Inc.Here, we investigated the biocompatibility of a bioactive sodium calcium silicate glass containing 2.6 mol% Nb2O5 (denoted BGPN2.6) and compare the results with the archetypal 45S5 bioglass. The glass bioactivity was tested using a range of in vitro and in vivo experiments to assess its suitability for bone regeneration applications. in vitro studies consisted of assessing the cytocompatibility of the BGPN2.6 glass with bone-marrow-derived mesenchymal stem cells (BM-MSCs). Systemic biocompatibility was verified by means of the quantification of biochemical markers and histopathology of liver, kidneys, and muscles. The glass genotoxicity was assessed using the micronucleus test. The regeneration of a calvarial defect was assessed using both qualitative and quantitative analysis of three-dimensional microcomputed tomography images. The BGPN2.6 glass was not cytotoxic to BM-MSCs. It is systemically biocompatible causing no signs of damage to high metabolic and excretory organs such as the liver and kidneys. No mutagenic potential was observed in the micronucleus test. MicroCT images showed that BGPN2.6 was able to nearly fully regenerate a critical-sized calvarial defect and was far superior to standard 45S5 Bioglass. Defects filled with BGPN2.6 glass showed over 90% coverage compare to just 66% for 45S5 Bioglass. For one animal the defect was completely filled in 8 weeks. These results clearly show that Nb-containing bioactive glasses are a safe and effective biomaterial for bone replacement.

© The Royal Society of Chemistry 2019.A major challenge exists in the preparation of scaffolds for bone regeneration, namely, achieving simultaneously bioactivity, biocompatibility, mechanical performance and simple manufacturing. Here, cellulose nanofibrils (CNF) are introduced for the preparation of scaffolds taking advantage of their biocompatibility and ability to form strong 3D porous networks from aqueous suspensions. CNF are made bioactive for bone formation through a simple and scalable strategy that achieves highly interconnected 3D networks. The resultant materials optimally combine morphological and mechanical features and facilitate hydroxyapatite formation while releasing essential ions for in vivo bone repair. The porosity and roughness of the scaffolds favor several cell functions while the ions act in the expression of genes associated with cell differentiation. Ion release is found critical to enhance the production of the bone morphogenetic protein 2 (BMP-2) from cells within the fractured area, thus accelerating the in vivo bone repair. Systemic biocompatibility indicates no negative effects on vital organs such as the liver and kidneys. The results pave the way towards a facile preparation of advanced, high performance CNF-based scaffolds for bone tissue engineering.

© 2019 Elsevier LtdThe ternary membrane-forming system based on the silk fibroin (SF), glycerol (GLY) and sol-gel precursor of 58S bioactive glass (BG) was studied for the preparation of novel and multifunctional hybrid membranes. The morphology of membranes was observed by scanning electron microscopy (SEM) and spectral imaging, by X-ray mapping technique, were performed in order to investigate the chemical homogeneity of elements. The results show that there is a critical limit for the concentration of GLY and BG for formation of flexible membranes and without a phase separation. XRD and FTIR data showed that the GLY and BG in the silk matrix modifies the short- and intermediate-range order resulting in changes in the silk conformation, i.e., SF molecules are gradually transformed from random coils toward more stable structures – Silk I and Silk II (β-sheets). The solubility study showed that the hybrid membranes have an excellent chemical stability, confirming that the incorporation of inorganic species in the matrix allowed the preparation of novel well-controlled water-soluble membranes. The release profiles of Ca, P and Si confirmed ability of hybrid membranes to deliver controlled inorganic species, which in critical concentration, control the gene expression of osteoblasts and influences cell metabolism and function.

© 2018 Elsevier B.V.In this research, the mechanism of an efficient strategy for the synthesis of 58S bioglass with high structural homogeneity by a citric acid assisted sol-gel route was investigated. This is an interesting approach to prepare bioactive glass via the sol-gel method with application potential in bone tissue engineering and also for the development of new biomedical devices. Herein, 58S bioglass was synthesized by two routes: conventional sol-gel method (CSG) and citric acid assisted sol-gel route coupled to the self-propagating combustion method (SPC). The effects of citric acid on the temperature required for 58S vitreous consolidation, long- and short-range ordering were investigated by several analysis techniques. Results suggested that citric acid molecules serve as an effective molecular template formed by molecular network raised from intermolecular forces, especially the hydrogen bonds, resulting from the chemical interactions between the COOH and hydroxyl groups (water, ethanol, P–OH, Si–OH). In this scenario, citric acid controls the phase segregation during the drying and combustion steps of the gel in the SPC method by establishing chemical interactions (hydrogen bonds) with the superficial silanol groups present on the small-sized silica nanoparticles present in the sol governing their growth. Besides these mentioned features, the self-propagating combustion behavior exhibited by the nitrate-citrate in the SPC xerogel during the combustion step allowed the removal of the organic load and the consolidation of the vitreous structure at a temperature considerably lower than the sample obtained by the CSG method. Consequently, the SPC method leads to the formation of a glass structure with high homogeneity for the 58S, whereas the conventional sol-gel method produces a matrix enriched with calcium phosphate crystalline nuclei - glass-ceramic.

© 2018, The Author(s).The present work presents and discusses the results of a comprehensive study on the bioactive properties of Nb-substituted silicate glass derived from 45S5 bioglass. In vitro and in vivo experiments were performed. We undertook three different types of in vitro analyses: (i) investigation of the kinetics of chemical reactivity and the bioactivity of Nb-substituted glass in simulated body fluid (SBF) by 31P MASNMR spectroscopy, (ii) determination of ionic leaching profiles in buffered solution by inductively coupled plasma optical emission spectrometry (ICP-OES), and (iii) assessment of the compatibility and osteogenic differentiation of human embryonic stem cells (hESCs) treated with dissolution products of different compositions of Nb-substituted glass. The results revealed that Nb-substituted glass is not toxic to hESCs. Moreover, adding up to 1.3 mol% of Nb2O5 to 45S5 bioglass significantly enhanced its osteogenic capacity. For the in vivo experiments, trial glass rods were implanted into circular defects in rat tibia in order to evaluate their biocompatibility and bioactivity. Results showed all Nb-containing glass was biocompatible and that the addition of 1.3 mol% of Nb2O5, replacing phosphorous, increases the osteostimulation of bioglass. Therefore, these results support the assertion that Nb-substituted glass is suitable for biomedical applications.

© 2018 Elsevier B.V.In this work we synthesized an activated carbon/magnetite composite by a simple co-precipitation method. The activated carbon (AC) was synthesized from the solid waste obtained in the extraction process of the peroxidase enzyme and the magnetic composite was used as support for the immobilization of soybean peroxidase (SP). After the determination of the optimal immobilization parameters, a 100% yield was achieved under the following conditions: support:enzyme proportion of 1.0:0.05 g, equilibration time of 7 h, pH 3.0 (citrate buffer phosphate 0.1 mol L−1) and temperature of 50 °C. The determination of pH to the point of zero charge was also done to assist in the understanding of the immobilization process at different pH values. Several characterization techniques were used, such as thermogravimetric analysis, elemental analysis composition, X-ray powder diffraction, Fourier transform infrared spectroscopy and Scanning electron microscopy. The biocatalyst presented excellent operational stability and was reused for 11 consecutive cycles. The magnetic properties inserted in the AC contributed to the removal of the biocatalyst from the reaction medium without interfering in the adsorptive characteristics of the AC. Thus, the activated carbon/magnetite composite can be applied to different research fields with high performance.

© 2017, Springer Science+Business Media B.V.The heterogeneous catalytic route to produce biodiesel can reduce the amount of effluents generated in the steps of esters purification and allows the reuse of catalysts. Specially, when the catalytic supports are synthesized from biomass wastes the process become even more environmentally friendly. In this work, we have synthesized activate carbons (ACs) from agroindustry waste generated after the extraction of essential oil of Candeia wood residue. These ACs were used to support H3PMo12O40. The performances of all the supported catalysts were evaluated on the lauric acid esterification reactions with methanol. The catalysts were produced through impregnation method, varying the H3PMo12O40 load and the support nature (i.e. commercial AC or produced from agroindustry residue). All materials were characterized by thermal analysis, FT-IR spectroscopy, SEM, EDS, BET surface area and powder X-ray diffraction. The catalysts showed good thermal stability. Data of the X-ray diffraction indicated that regardless support origin, a high dispersion of H3PMo12O40 was achieved. High turnover numbers were achieved by the H3PMo12O40/AC catalysts; 7205 for 10 wt% H3PMo12O40/commercial AC and 3571 for 10 wt% H3PMo12O40/agroindustry waste AC. Tests of reuse and leaching of the catalysts were also carried out. A strong deactivation of the catalyst was observed when it was reused directly, without previous treatment.

© 2017 Elsevier B.V.TiO2, glucose oxidase and carbon nanotube microparticles were ultrasonically formed to provide a large surface area for enzyme immobilisation and a favorable microenvironment for direct electron transfer. This simple architecture nanostructure was used to construct a glucose oxidase biosensor, which demonstrated good analytical performance with high reproducibility, and good detection for pathological glucose level.

© 2017 Elsevier LtdElectrochemical oxygen reduction and methanol oxidation are two important reactions in the development of clean energy technology. Substantial progresses in the design of cheap, robust, and efficient catalysts are still required and remain a significant challenge. Here, we report a double pulse electrodeposition process, capable of controlling the density and the size of silver nanoparticle supported on graphene. We found that this catalyst afforded a current density of 5.5 mA cm−2 at a low potential for ORR, comparing favourably with the state-of-the-art Pt/C catalyst. Additionally, we demonstrate that size and distribution effects are critical parameters for more efficient ORR and MOR catalysis. Our results suggest possibility for the development of effective and robust ORR and MOR electrocatalysts based on cheap silver metal and graphene and as replacements for the commercially available but expensive Pt/C catalysts.

© 2016In this work it is presented a facile and novel method for modification of bioglass surface based on (Camolten salt bath2 +| Naglass+) ion exchange by immersion in molten salt bath. This method allows changing selectively the chemical composition of a surface layer of glass, creating a new and more reactive bioglass in a shell that surrounds the unchanged bulk of the original BG45S5 bioglass (core-shell type system). The modified bioglass conserves the non-crystalline structure of BG45S5 bioglass and presents a significant increase of surface reactivity in comparison with BG45S5. Melt-derived bioactive glasses BG45S5 with the nominal composition of 46.1 mol% SiO2, 24.4 mol% Na2O, 26.9 mol% CaO, and 2.6 mol% P2O5 have been subjected to ion exchange at 480 °C in molten mixture of Ca(NO3)2 and NaNO3 with molar ratio of 70:30 for different time periods ranging from 0 to 60 min. The optimization studies by using XRF and XRD showed that ion exchange time of 30 min is enough to achieve higher changes on the glass surface without alters its non-crystalline structure. The chemical composition, morphology and structure of BG45S5 and bioglass with modified surface were studied by using several analytical techniques. FTIR and O1s XPS results showed that the modification of glass surface favors the formation of Si-ONBO groups at the expense of Si[sbnd]OBO[sbnd]Si bonds. 29Si MAS-NMR studies showed that the connectivity of SiQn species decreases from cross-linked SiQ3 units to chain-like SiQ2 units and finally to depolymerized SiQ1 and SiQ° units after ion exchange. This result is consistent with the chemical model based on the enrichment with calcium ions of the bioglass surface such that the excess of positive charges is balanced by depolymerization of silicate network. The pH changes in the early steps of reaction of bioactive glasses BG45S5 and BG45Ca30, in deionized water or solutions buffered with HEPES were investigated. BG45Ca30 bioactive glass exhibited a significant increase in the pH during the early steps of the reaction compared to BG45S5.

© The Royal Society of Chemistry.The immobilization of enzymes is an excellent alternative to overcome the drawbacks of using these biocatalysts in free form. This process plays a significant role in cost-effective recovery, increased catalyst productivity and in simplifying process operations. After the soybean peroxidase (SP) extraction, a residue at high carbon and low ash content is generated. This residue was used as carbonaceous precursor for production of carbon activated (AC) with high surface area (1603 m2 g−1). The AC produced was used as support for SP immobilization. The immobilization of SP was evaluated in different time conditions, enzyme load, pH and temperature. The samples, before and after immobilization, were characterized by thermogravimetric analysis, elemental analysis composition, specific surface area, X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. In addition, repeated applications of immobilized biocatalyst were made in order to evaluate its operational stability and capacity to recover the reaction medium, in which was observed that after a decline in activity from the first to the second cycle, it remained constant until the tenth application. In the context, the process of material obtainment constitutes a clean route for the development of more sustainable biocatalysts capable of applications in various areas.

© 2016 Elsevier Ltd.This paper investigates the microstructure and the mechanical properties of β-tricalcium phosphate (β-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). β-TCP and β-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of β-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from β-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of β-TCP/5%-BG and β-TCP/7.5%-BG was improved around 200% in comparison to pure β-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24 h through the use of medium conditioned by β-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey[U+05F3]s multiple comparison (p<0.05). The β-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering.

© The Author(s) 2016.Platinum (Pt) based electrocatalysts have electrochemical performance that outperforms many other noble metal and metal oxide based materials. Increasing performance allows a reduction in the platinum load, and thus reduce the cost of various devices such as fuel cells. A double pulse electrochemical approach was developed to nucleate and grow Pt nanoparticles into flower shaped assemblies on graphene sheets. The unique morphology and structure of the Pt were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM). The electrocatalytical activities of the Pt nanoflowers were evaluated using methanol and ethanol oxidation as model reactions. This proposed method has led to the synthesis of Pt nanoflowers with the ability to control, both their density and their size on defect free graphene.

© 2015 American Chemical Society.We have developed a potentiostatic double-pulse technique for silver nanoparticle (Ag NP) deposition on graphene (GRn) with superior electronic and ionic conductivity. This approach yielded a two-dimensional electrocatalyst with a homogeneous Ag NP spatial distribution having remarkable performance in the oxygen reduction reaction (ORR). GRn sheets were reproducibly prepared by the electrochemical exfoliation of graphite (GRp) at high yield and purity with a low degree of oxidation. Polystyrenesulfonate added during exfoliation enhanced the stability of the GRn solution by preventing the restacking of the graphene sheets and increased its ionic conductivity. The potentiostatic double-pulse technique is generally used to electrodeposit Pt nanoparticles and remains challenging for silver metal that exhibits nucleation and growth potentials relatively close to each other. We judiciously exploited this narrow margin of potential, and for the first time we report Ag NP electrodeposited onto graphene with the subsequent ability to control both the density and the size of metallic nanoparticles. Considering the high activity along with the lower cost of Ag compared to Pt, these findings are highly relevant to the successful commercialization of fuel cells and other electrochemical energy devices.

© The Royal Society of Chemistry 2015.Carbonic anhydrase was entrapped in a matrix of ultrasonically bonded hydroxyapatite microparticles coated with β-sheet structured silk fibroin. Transfer of the reactant and product between the enzyme and the assembly surface was evident and the system showed a remarkable operational, storage and thermal stability, with enzymatic activity almost unchanged after a one hour's treatment at 110 °C and the assembly retained 45% of its initial activity after 3 weeks of continuous heating at 80 °C in an amine solution. This thermal stability was excellent compared with described CA immobilization systems and indicates that silk fibroin may limit thermally induced enzyme conformation changes and prevent desorption.

© 2015 BCREC UNDIP. All rights reserved.Textile industries are one of the main sources of water pollution. Wastewater containing dyes present a serious environmental problem because of its high toxicity and possible accumulation in the environment. In this work were explored the characteristics of removal of methylene blue dye employing zeolites modified with transition metals (Cu, Fe). The zeolites with iron or copper were prepared by using Naγ and Naβ zeolites as precursors, replacing part of ion sodium for copper or iron ions through the ion exchange method. All materials were characterized by several analytical techniques, in order to gain information about the structure and catalytic activity. Modified zeolites showed a remarkable activity in H2O2 decomposition and in the discoloration an organic dye in aqueous medium. ESI-MS studies of the methylene blue oxidation showed that the oxidation of the dye occurs via a Fenton type system in which∗OH radicals are formed in situ and added to the ring structure of the organic substrate. In addition, modification of the zeolite with transition metal proved to be an interesting pathway to produce efficient catalysts for the oxidation of organic molecules, i.e. dyes in aqueous media.

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Several methods have been proposed for capturing the CO2 emitted into the atmosphere by human activity. To date, mainly amine-based absorption processes are currently among the more promising systems for postcombustion CO2 capture. Tertiary amine solvents obviate the need for a high solvent regeneration temperature and fast absorption can be achieved with the use of carbonic anhydrase (CA), as an activator. In this study, the capacity of CA immobilization on nanoporous microparticles hierarchically structured to enhance their stability in tertiary amines is investigated. These microstructures allow for an efficient supply and presentation of substrate in the non-aqueous solvent to the enzyme catalytic center and the particles' large size is attractive to make separation and reuse facile. These hierarchically structured particles conserve 70% of their initial activity after 30 d at 50 °C in amine solvent, whereas the free enzyme shows no activity after 1 h in the same conditions. In this work, we have overcome the technical hurdle linked to the recovery of the biocatalyst after operation thereby reducing costs of the system and importantly these micro-bioparticles have shown a remarkable increase of the thermal stability of CA in an amine-based CO 2 sequestration solvent as determined by a para-nitrophenyl acetate assay.

© 2014 The American Ceramic Society.The effects of adding Nb2O5 on the physical properties and glass structure of two glass series derived from the 45S5 Bioglass® have been studied. The multinuclear 29Si, 31P, and 23Na solid-state MAS NMR spectra of the glasses, Raman spectroscopy and the determination of some physical properties have generated insight into the structure of the glasses. The 29Si MAS NMR spectra suggest that Nb5+ ions create cross-links between several oxygen sites, breaking Si-O-Si bonds to form a range of polyhedra [Nb(OM)6-y(OSi)y], where 1 ≤ y ≤ 5 and M = Na, Ca, or P. The Raman spectra show that the Nb-O-P bonds would occur in the terminal sites. Adding Nb2O5 significantly increases the density and the stability against devitrification, as indicated by ΔT(Tx - Tg). Bioglass particle dispersions prepared by incorporating up to 1.3 mol% Nb2O5 by replacing P2O5 or up to 1.0 mol% Nb2O5 by replacing SiO2 in 45S5 Bioglass® using deionized water or solutions buffered with HEPES showed a significant increase in the pH during the early steps of the reaction, compared using the rate and magnitude during the earliest stages of BG45S5 dissolution.

In this article the changes on the surface of the 45S5 bioglass submitted to an enrichment with calcium ions were investigated. The method employed was the immersion of bioglass in calcium molten salt bath at 450°C. Changes in composition were probed by different techniques of chemical analysis. The use of SEM-EDS allowed estimating the thickness modified, as being about 10 μm. X-ray photoelectron spectroscopy enabled to infer over the structural changes on the surface of 45S5 bioactive glass. The entry of calcium in the vitreous network promoted the phase separation of microdomains rich in silica and phosphate on the surface of the glass. The formation of immiscibility region was attributed a depolymerization of silica network and also, to a possible migration of phosphate species from the bulk. The results of this study indicate a great change in the surface properties of this biomaterial. In addition, the method proposed in this study proved to be very promising in the possibility of designing the surface of bioactive glasses, to modulate the desired properties, keeping the bulk unchanged. © 2013 The American Ceramic Society.

Two samples of heterogeneous catalysts were prepared by impregnating a raw-clay, a montmorillonite-rich material, with iron oxides, in order to be used in oxidative reactions of toluene. The starting clay-sample was collected from a pedon in the region of San Juan, Argentina. All catalysts were characterized with X-ray powder diffraction (XRD), infrared spectroscopy, temperature programmed reduction (TPR), scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS), and specific surface area measurements. After impregnating the raw clay material with iron oxides, there was a collapse of basal plane spacing and an increase in surface area, from 17 to 62m2g-1 of montmorillonite. The TPR, EDS, and XRD results evidenced that the dispersion of iron-containing species depended on how the impregnation was made. The catalyst with higher exposure to iron oxides on sample preparation presented a higher catalytic activity on toluene oxidation. © 2010 Elsevier B.V.

The feasibility of using a solid waste (rich in nitrogen) from the leather industry, after chromium extraction, as adsorbent for P and K, for possible utilization as NPK fertilizer was evaluated. The materials, with and without the addition of P and K, were characterized by chemical analyses, infrared spectroscopy, EDS (energy dispersive X-ray spectrometry) and SEM (scanning electronic microscopy). Langmuir and Freundlich equations were used for analyzing the experimental data, which showed a better fit to the Freundlich model, thus suggesting a multilayer adsorption process on the surface of the adsorbent. A preliminary test in greenhouse demonstrates that the P and K incorporation on the matrix rich in nitrogen (collagen) is a interesting alternative to use such material as NPK fertilizer. The application of NcollagenPK formulations, as a source of nutrients for the growth of rice plants, showed promising agronomic results. © 2009 Elsevier B.V. All rights reserved.

A series of Nb-containing hematites, Fe2-xNbxO3 (%Nb = 0.00, 1.49, 5.00 and 9.24) was prepared using the conventional co-precipitation method. Mössbauer and temperature-programmed reduction (TPR) measurements suggested the formation of the crystalline phase with partial substitution of Fe3+ by Nb5+ in the structure. N2 adsorption/desorption revealed that the presence of Nb has a remarkable effect on the textural properties of the material with an increase in the BET surface area. The reactivity of Fe2-xNbxO3 was investigated using the oxidation of the methylene blue dye used as a model pollutant. The obtained results showed that the presence of Nb seems not to act directly promoting the H2O2 decomposition, but improving the dye oxidation. The analysis using the ESI-MS technique showed partial oxidation observed through different intermediates before the mineralization. This suggests the use of Nb-doped hematite as an efficient catalyst in degradation reactions in the presence of H2O2 or ultraviolet light. © 2009 Elsevier B.V. All rights reserved.

Catalytic and adsorptive behaviors of montmorillonite to remove methylene blue were investigated. The clay mineral showed high activity for the oxidation of methylene blue in presence of H2O2 and on removing the organic substrate through reactive adsorption as evidenced from Electrospray Ionization Mass Spectrometry (ESI-MS) data. Montmorillonite was characterized by atomic absorption, powder X-ray diffractometry, scanning electron microscopy coupled with energy dispersive spectroscopy, infra-red spectroscopy and surface area analyses. Results indicated a highly reactive surface with can be regenerated by H2O2, promoting heterogeneous catalytic reaction to oxidize organic compounds from aqueous medium without any previous treatment of the montmorillonite. © 2008 Elsevier B.V. All rights reserved.