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Pseudobemit je impregnisan kobaltom postupkom kapilarne impregnacije. Za impregnaciju su korišćene dve koncentracije, 3 mas% i 6 mas% Co 2+ u odnosu na masu pseudobemita. Dobijeni materijali su žareni na 500 ºC. Sintetisani katalizatori su ispitani u procesu oksidativne degradacije boje tartrazina u prisustvu Oksona kao izvora sulfatnih radikal anjona. Ispitivan je uticaj tempreature na efikasnost degradacije boje. Uočeno je da brzina degradacije raste sa porastom temperature. Eksperimentalno dobijeni rezultati su testirani korišćenjem najčešćih kinetičkih modela i dobijeno je da reakcija u svim slučajevima sledi brzinu pseudo-prvog reda. Takođe je uočeno da sa porastom sadržaja kobalta raste efikasnost katalizatora. Da bi se odredilo koja je reaktivna oksidativna vrsta dominantna u ispitivanom procesu, u reakcioni sistem je dodavan tercijalni butanol, odnosno etanol. Utvrđeno je da su sulfatni radikal anjoni dominantna reaktivna vrsta., Pseudoboehmite was impregnated with cobalt using a incipient wetness impregnation method. Two different concentrations of cobalt were used for impregnation: 3 mas% and 6 mas% of Co2+ relative to the mass of pseudoboehmite. The obtained materials were calcined at 500 ºC. The synthesized catalysts were tested in the process of oxidative degradation of tartrazine dye in the presence of Oxon as a source of sulfate anion radicals. The influence of temperature on the dye degradation efficiency was investigated. It was observed that the degradation rate increases with the increasing of temperature. The experimentally obtained results were tested using the most common kinetic models and it was found that the reaction follows a pseudo-first order rate in all cases. It was also observed that with an increase in the cobalt content, the efficiency of the catalyst increases. In order to determine which reactive oxidative species is dominant in the investigated process, tertiary buthalnol and ethanol was added to the reaction system. According to the experimental results sulfate anion radicals were found to be the dominant reactive species.

Two texturally and structurally different Co-doped aluminas were obtained by using the sol-gel method followed by calcination at temperatures of 1000 °C and 1100 °C. The obtained materials were tested as catalysts in anionic textile dye Orange G (OG) degradation using Oxone® as a precursor of sulfate anion radicals, the main reactive oxygen species. Effects of temperature and initial pH on degradation efficiency was investigated. The increase in temperature accelerated the reaction rate and the maximal degradation efficiency was obtained at 60 °C. Different kinetic models were applied and pseudo-first order rate was found to be the most appropriate. Both catalysts showed the optimal performance in the pH range around neutral. Coexisting cations (Ca2+, Mg2+, K+ and Na+) enhanced the OG degra­dation rate, as well as anions: Clˉ and H2PO4ˉ, while NO3ˉ, SO42ˉand HCO3ˉ inhibited the degradation. The catalysts were also proved effective in degradation of the other investi­gated dyes: Methylene blue, Basic blue 41, and Remazol brilliant blue R. Finally, simulta­neous degradation of OG in binary dye mixtures was investigated showing that the synthesized catalysts can be also used in simultaneous processes of dye degradation. However, differences in structural and textural properties of the two catalysts affected their catalytic performance., Dva kobaltom dopirana katalizatora na bazi aluminijum oksida, sa ra zličitim teksturalnim i strukturnim karakteristikama, dobijena su sol-gel postupkom sinteze, nakon koje su uzorci žareni na tempreturi od 1000 °C odnosno 1100 °C. Dobijeni materijali su ispitani kao katalizatori u procesu degradacije anjonske tekstilne boje Orange G (OG) uz korišćenje Oksona kao prekursora sulfatnih anjon radikala, koji su glavna oksidativna vrsta. Ispitan je uticaj temperature i početnog pH na efikasnost degradacije, i uočeno je da porast temperature povećava brzinu reakcije. Maksimalna efikasnost degradacijeje dobijena na 60 °C. Primenjeni su različiti kinetički modeli i pokazalo se da kinetički model pseudo-prvog reda najbolje opisuje kinetiku ispitanog procesa. Takođe je za oba katalizatora utvrđeno da je optimalna vrednost pH za ispitivanu reakciju u oblasti blizu neutralne. Koegzistirajući katjoni (Ca2+, Mg2+, K+ and Na+) i anjoni Clˉ and H2PO4ˉ su ubrzavali degradaciju OG, dok su je anjoni NO3ˉ, SO4 2ˉ i HCO3ˉ usporavali. Katalizatori su se pokazali efikasnii u degradaciji boja: metilensko plavo, osnovno plavo 41 i boje “Remazol brilliant blue”, kao i u degradaciji boja u binarnim smešama. Ipak, razlike u strukturnim i teksturalnim svojstvima su uticale na razlike u katalitičkoj efikasnosti ova dva katalizatora.

Two texturally and structurally different Co-doped aluminas were obtained by using the sol-gel method followed by calcination at temperatures of 1000 °C and 1100 °C. The obtained materials were tested as catalysts in anionic textile dye Orange G (OG) degradation using Oxone® as a precursor of sulfate anion radicals, the main reactive oxygen species. Effects of temperature and initial pH on degradation efficiency was investigated. The increase in temperature accelerated the reaction rate and the maximal degradation efficiency was obtained at 60 °C. Different kinetic models were applied and pseudo-first order rate was found to be the most appropriate. Both catalysts showed the optimal performance in the pH range around neutral. Coexisting cations (Ca2+, Mg2+, K+ and Na+) enhanced the OG degra­dation rate, as well as anions: Clˉ and H2PO4ˉ, while NO3ˉ, SO42ˉand HCO3ˉ inhibited the degradation. The catalysts were also proved effective in degradation of the other investi­gated dyes: Methylene blue, Basic blue 41, and Remazol brilliant blue R. Finally, simulta­neous degradation of OG in binary dye mixtures was investigated showing that the synthesized catalysts can be also used in simultaneous processes of dye degradation. However, differences in structural and textural properties of the two catalysts affected their catalytic performance., Dva kobaltom dopirana katalizatora na bazi aluminijum oksida, sa ra zličitim teksturalnim i strukturnim karakteristikama, dobijena su sol-gel postupkom sinteze, nakon koje su uzorci žareni na tempreturi od 1000 °C odnosno 1100 °C. Dobijeni materijali su ispitani kao katalizatori u procesu degradacije anjonske tekstilne boje Orange G (OG) uz korišćenje Oksona kao prekursora sulfatnih anjon radikala, koji su glavna oksidativna vrsta. Ispitan je uticaj temperature i početnog pH na efikasnost degradacije, i uočeno je da porast temperature povećava brzinu reakcije. Maksimalna efikasnost degradacijeje dobijena na 60 °C. Primenjeni su različiti kinetički modeli i pokazalo se da kinetički model pseudo-prvog reda najbolje opisuje kinetiku ispitanog procesa. Takođe je za oba katalizatora utvrđeno da je optimalna vrednost pH za ispitivanu reakciju u oblasti blizu neutralne. Koegzistirajući katjoni (Ca2+, Mg2+, K+ and Na+) i anjoni Clˉ and H2PO4ˉ su ubrzavali degradaciju OG, dok su je anjoni NO3ˉ, SO4 2ˉ i HCO3ˉ usporavali. Katalizatori su se pokazali efikasnii u degradaciji boja: metilensko plavo, osnovno plavo 41 i boje “Remazol brilliant blue”, kao i u degradaciji boja u binarnim smešama. Ipak, razlike u strukturnim i teksturalnim svojstvima su uticale na razlike u katalitičkoj efikasnosti ova dva katalizatora.

Cobalt-doped alumina catalyst calcined at 500 ºC (CoA-500) was investigated in the degradation of anionic textile dye Orange G in the presence of Oxone®. Different reaction parameters were altered in order to study their influence on Orange G degradation. The increase of the Oxone® dosage, mass of the catalyst and temperature was beneficial for the dye degradation rate. The best catalytic performance was obtained in the range of the initial solution pH = 6–8. Simultaneous degradation of both Orange G and cationic textile dye Basic blue 41, was also tested. The degradation of the Basic blue 41 did not occur while Orange G was present in the system. CoA-500 was found to be efficient catalyst in the Oxone® induced catalytic degradation of textile dyes.

Magnesium (Mg) is an essential element in the human body primarily stored in bones. Mg ions have many potential benefits for bone tissue showing excellent osteogenic inductivity [1]. The aim of this study was to synthesize Mg substituted hydroxyapatite (Mg-HAP) for application in bone tissue engineering and to assess its behaviour in conditions mimicking physiological ones. Mg-HAP was synthesized using reflux method and its structural and morphological characterization was performed by XRD, FTIR and SEM. The changes in local structure and composition after irradiation and immersion in physiological solution and simulated fluid were assessed by electron paramagnetic resonance (EPR) spectroscopy. The results of EPR analysis pointed out that irradiation did not change the composition and structure of Mg-HAP. After immersion in model media (simulated body fluid and saline solution), the small amount of by-product of synthesis disappeared after 24 h and Mg-HAP remained the only phase. Also, the radical signals in EPR spectra faded away after 28 days in model media, showing that the structure and composition of Mg-HAP both went through a kind of stabilization in simulated physiological conditions. These results make the investigated Mg-HAP promising material for application in bone tissue engineering.

Photocatalytic processes have been recognized as promising and sustainable methods for pollutant degradation and energy conversion. Due to the simplicity of the process, capacity for using renewable and pollution-free solar energy, mild reaction conditions, reasonable reaction time, complete pollutant degradation, no harmful byproducts, and cost-effectiveness, photocatalytic degradation processes are more promising than conventional physical methods. Due to its favorable properties, TiO2 semiconductor has been used as an ideal candidate for photocatalytic reactions. However, large band gap, fast e-/h+ recombination, and low light harvesting efficiency are the main obstacles that restrict its practical application. Using g-C3N4 semiconductor in combination with TiO2 is an excellent strategy to enhance the photocatalytic activity under visible light irradiation. In this study, g-C3N4/TiO2photocatalyst was successfully synthesized and used in single and simultaneous photodegradation of cationic Methylene Blue and anionic Orange G dyes. To examine the heterojunction between g-C3N4 and TiO2 and the mechanism of the transport pathway of photogenerated e-/h+, the photoluminescence spectra and radical scavenger study were applied. The present research offers a novel approach in reaction mechanism analysis for degradation of dye pollutants in single/mixed solutions and suggests a strategy for determination of heterojunction type in g-C3N4/TiO2 systems.

Nowadays, environmental pollution caused by antibiotics attracts extensive attention. Adsorption has been successfully applied in the treatment of wastewater loaded by pharmaceutics, while diverse natural and eco-friendly materials have been recognized as promising adsorbents. In this work smectite clay from Bogovina (Serbia) and biopolymer chitosan (derived from waste of crustaceans) were used as eco-friendly starting materials for the adsorbent synthesis. The combination of transition metal, carbon materials, and clay minerals represents a useful way to develop functional nanocomposites with benefiting synergistic properties of all components. Simple, one-step hydrothermal procedure conducted at 180 ℃ for 24h was applied for synthesis of cobalt/smectite/chitosan-derived carbon (H_Co/C-S) nanocomposite. The sample was characterized using XRPD, FTIR, and low-temperature N2-physisorption analysis and tested as adsorbent of ciprofloxacin (CPX). The effects of temperature, initial pH, and CPX concentration on the adsorption process were investigated. The adsorption results were fitted by Langmuir, Freundlich, and Sips adsorption isotherms. Additionally, CPX adsorption was described by appropriate kinetics and thermodynamic parameters. It was found that temperature increase had the beneficial effect on CPX adsorption, while investigated adsorbent was efficient in a broad pH range (4-8). The H_Co/C-S adsorbent was found to be efficient in the removal of CPX antibiotic.

Seawater electrolysis has recently been recognized as a new hope for affordable renewable energy storage. However, its practical application is still limited due to the presence of various electroactive ions in seawater. For example, the chloride ions compete with the oxygen evolution reaction (OER) causing low efficiency of the OER, and corrosion of both the anode and the cathode. To overcome these issues, the development of catalysts with high activity and selectivity towards OER is of primary importance.Herein, Co supported chitosan–derived carbon–smectite nanocomposite (Co/cCh-S) was tested as an electrocatalyst for the OER in alkaline and simulated alkaline seawater solution. Co/cCh-S was previously synthetized using impregnation–carbonization method at 400 °C in an inert atmosphere and characterized in detail. The electrochemical performance of Co/cCh-S modified GCE was studied by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. According to the obtained values for onset potential, overpotential, and Tafel slope, the Co/cCh-S electrode could be considered a good electrocatalyst for OER in an alkaline solution. Moreover, no noticeable change in the performance of the Co/cCh-S electrode was observed in the presence of chloride ions. This work could be a starting point for designing an inexpensive, earth-abundant OER catalyst for seawater electrolysis.

Catalytic oxidative degradation of a textile dye Orange G was investigated in the reaction system where oxidant Oxone® was used as a source of SO4˙ˉ anion radicals. Cobalt-doped alumina was tested as a heterogenous catalysts for Oxone® activation. The catalyst was synthetized and calcined at 500 °C. The influence of different reaction parameters was followed: the Oxone® dosage, Orange G concentration and initial pH of the reaction solution. The Oxone® dosage was varied from 10 mg to 80 mg. Small differences in degradation efficiency were observed but mass of 40 mg of Oxone® was found to be optimal in the first hour of the reaction. The effect of the Orange G concentration was investigated in the range from 20 mg dm-3 to 50mg dm-3. For the concentration of 20 mg dm-3 the reaction was much faster than for other investigated concentrations. The effect of the pH was tested in the range from 2 to 9. The optimal pH range was found to be between 6 and 9, but reaction was feasible also for lower pH. It can be concluded that investigated catalyst is applicable with high efficiency in the wide range of Oxone® dosages, dye concentrations and initial pH values.

Thanks to its similarity with biological apatite found in vertebrate hard tissues, calcium hydroxyapatite is one of the most investigated materials in bone tissue engineering. Since biological apatite is not stoichiometric, ion substituted hydroxyapatites are in the focus of many studies as they more closely mimic the composition of natural bone. Although there are many investigations of the influence of foreign ions on the structure and physico-chemical properties of ionsubstituted hydroxyapatites, there is no much information on their behaviour in different media. In present study, magnesium - which plays a key role in bone metabolism and silicon - which is necessary for normal skeletal development, were used as ion substitutes. The behaviour of Mg and Si substituted hydroxyapatite in simulated body fluid and physiological solution was investigated by XRD, FTIR and SEM. Obtained results confirmed great potential of these substituted hydroxyapatites for biomedical applications.

As magnesium is an important trace element in bone and teeth, and plays a key role in bone metabolism, the aim of this study was to obtain magnesium substituted hydroxyapatite (Mg-HAP) and to assess its application potential. Upon synthesis, the changes in local structure and composition after irradiation and immersion in physiological solution and simulated fluid were followed by electron paramagnetic resonance (EPR) spectroscopy. Samples were also characterized by XRD, FTIR, SEM, EDS, AAS and TGA. The results showed that irradiation did not affect the composition and structure of Mg-HAP. After immersion in model media, the small amount of by-product of synthesis disappeared already after 24 h and Mg-HAP remained as the only phase. Also, the radical signals in EPR spectra faded or completely disappeared after 28 days in model media, which could indicate that the structure and composition of Mg-HAP both went through a kind of stabilization in conditions mimicking physiological ones. All these indicate that investigated Mg-HAP has good potential for biomedical application considering its behaviour in model media which imitate physiological conditions.

The oscillatory Briggs-Rauscher (BR) reaction was applied on solid insoluble materials - bentonite clays from different deposits: Wyoming (Swy-2), Texas (STx-1b), Idaho (SbId-1), Arizona (SAz-2), Bogovina and Mečji Do, last two from Serbia. Under the same BR experimental conditions, the addition of identical masses (0.25 g) of particular clay resulted in different effects on oscillatory dynamics. There is a prolongation, quenching, or no influence on oscillatory dynamics. Additionally, in the case of different masses of clay added, the response of the BR oscillating system resulted in a complex behavior pattern (oscillatory period vs. bentonite mass). This complex behavior pattern (firstly obtained by using clays in BR), could be applied as a fingerprint for bentonite identification. It is supported by facts that montmorillonite/beidellite ratio, cation exchange capacity, principal exchange cation, the extent of iron leaching in the acidic environment of BR reaction, and specific surface area of each used clays were not exclusively responsible for observed behavior in oscillatory reaction. This means that all bentonite’s properties combined are probably responsible for behavior obtained in oscillatory reaction, making BR reaction as an easily available and economical method for the identification of bentonite clay origin

Cobalt-doped alumina catalyst was synthetized using the sol-gel method, gelled and calcined at 500 °C. The synthesized material was previously fully characterized. Cobalt-doped alumina was tested as catalysts in an Orange G degradation in the presence of Oxone®. Oxone® is a precursor of radicals and the role of the investigated catalyst was to activate its decomposition. Sulfate ion radicals act as oxidizing species in dye degradation reaction. The influence of the mass of the catalyst and the reaction temperature was investigated. The catalyst mass and temperature increase were beneficial for the dye degradation rate. The pseudo-first order kinetic model was found to be the most appropriate fit for experimentally obtained data. The adsorption of the dye on Co-doped alumina was also tested, and it was found to be negligible. The investigated catalyst was found to be effective for Orange G degradation in the presence of Oxone®.

Mixed Al, Fe pillared clay (AlFePILC) was synthesized from Na-exchanged Wyoming clay (Na-Wy) rich in montmorillonite. In the pillaring process Na-Wy was modified with a mixed intercalating (Al, Fe) solution with molar ratio of Fe3+/(Al3++Fe3+) = 10%. The obtained AlFePILC was impregnated with cobalt using the incipient wetness impregnation method, dried at 110 ºC and calcined at 450 ºC (Co-AlFePILC). Co-AlFePILC was tested as a catalyst in catalytic oxidation of tartrazine in the presence of Oxone®. Decolorization was monitored at wavelength =426 nm, while degradation of aryl groups was followed at =257 nm using UV-Vis spectroscopy. The influence of the mass of the catalyst on degradation process was followed in the mass range from 10 mg to 50 mg at 30 °C. It was found that mass increase was beneficial for the decolorization rate. The effect of temperature was investigated from 30 ºC to 60 ºC. The decolorization was over 90% after only 10 minutes for the temperature of 60 ºC, while with the temperature decrease, the decolorization rate decreased. Co-AlFePILC was found to be an efficient catalyst in degradation of tartrazine in the presence of Oxone®.

In recent years, mineral oxides (i.e. zeolite, alumina and clay minerals)-supported non-precious transition metals have extensively studied as highly promising sustainable and green glucose-sensing materials (Mudrinić, 2019). The reason for that is their low cost, easiness of synthesis, low negative environmental impact, and desirable electrochemical properties toward glucose oxidation. It is widely accepted that the catalytic activity of the mineral oxides-supported cobalt is strongly influenced by cobalt-mineral oxide interaction. As a consequence of this interaction different cobalt oxides (Wang, 1991) could be formed: Co3O4-contains both cobalt ions in tetrahedral (Co2+Td) and octahedral (Co3+Oh) coordination and CoAl2O4-contains only Co2+Td. However, little is known about the catalytic activity of these cobalt oxides (i.e. cobalt ions) in the reaction of the electro-oxidation of glucose. In this work, cobalt oxides in both tetrahedral (Co2+Td) and octahedral (Co3+Oh) coordination and with only Co2+Td were synthesized on aluminum pillared clay (AP) and alumina (A). The obtained materials were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). Electrochemical measurements were performed in alkaline solution with and without glucose using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). TPR and XPS along with the results of electrochemical measurements in alkaline solutions without glucose confirmed the successful synthesis of the different cobalt oxides on both AP and A. The electrochemical measurements in glucose-containing solutions showed the enhanced electrocatalytic activity of AP and A with Co2+Td in comparison to their counterparts with both Co2+Td and Co3+Oh. This result suggested that the Co2+Td acted as the main active site for the glucose oxidation.

In this work smectite pillared with mixture of aluminium and cobalt poly(hydroxo metal) cations (Al,Co-PILC) was synthesized and tested as catalyst in degradation of food dye tartrazine by peroxymonosulfate. The Al,Co-PILC was obtained using a common procedure consisting of the following steps: grinding, sieving, Na exchange, intercalation, drying and calcination. Co2+ to (Al3++Co2+) molar ratios in the pillaring solution was 10%. Catalytic tests were carried out in a semibatch reactor under stirring and constant temperature maintained by circulation of thermostatic fluid using Julabo MC 4 heating circulator. Initial dye concentration was 50 ppm in the presence of excess of peroxymonosulfate. Decolorization of tartrazine solution was monitored using UV-Vis spectrophotometry at max= 426 nm. The influence of the mass of the catalyst and reaction temperature was investigated. Catalyst mass and temperature increase were beneficial for dye degradation rate. The catalytic process at 30 ºC reached 97% for 120 min and besides decolorization included further degradation of products of tartrazine oxidation. At 50 ºC complete decolorization occurred for only 30 min. This work showed that application of smectite pillared with mixture of aluminium and cobalt poly(hydroxo metal) cations as peroxymonosulfate activators for degradation of water pollutants is very promising.

This work investigated the kinetics of the glucose oxidation reaction on the carbon paste electrode modified with aluminum pillared clay-supported cobalt (CP-CoAP) in alkaline solution. Cyclic voltammetry and double-step chronoamperometry methods were employed for determining the kinetic parameters such as the charge transfer coefficient, the catalytic rate constant, and the diffusion coefficient. The obtained results confirm that the CP-CoAP can be considered as a competitive electrode material for glucose oxidation.

Our previous study demonstrated that cobalt content strongly affected the electro-activity of aluminum pillared clay-supported cobalt (CoAP) toward glucose oxidation. It was found that the electro-activity of CoAP increased with the increase of cobalt loading. However, at the 10 wt.% of cobalt content, the electro-activity significantly decreased. In the present study, the focus is on the investigation of the nature of the surface sites that might cause the difference in the electro-activity of CoAP. For this purpose, CoAP with 3 wt.% and 10 wt.% cobalt contents (x%CoAP, x=3 and 10) were characterized using FE-SEM and HR-TEM with EDX techniques, and XPS. The microscopic techniques coupled with EDX have shown that cobalt oxide nanoparticles were evenly distributed in both samples. However, the higher cobalt loading resulted in cobalt oxide agglomeration that led to larger particle sizes. The results of XPS confirmed the presence of Co (II) in the 3%CoAP. On the other hand, the presence of Co3O4 which contains both Co (II) and Co (III) was confirmed in 10%CoAP. It is clear from this study that the electro-activity of CoAP strongly depends on the oxidation state of cobalt. However, the effect of agglomeration and cobalt oxide particle sizes cannot be ruled out.

Aluminum pillared montmorillonite-supported cobalt (Co/AP) has proven to be a suitable non-enzymatic sensing material (Mudrinić, 2019). Beside low cost, Co/AP exhibited adequate electrocatalytic performance toward glucose. However, further improvements of electrocatalytic performances are needed, especially regarding increasing sensitivity and widening the linear range of glucose detection. In this regard, in addition to the monometallic cobalt oxide catalyst, a series of bimetallic catalysts supported on AP (Co+Cu/AP, Co+Zn/AP, Co+Fe/AP, and Co+Ni/AP) have been synthesized by the incipient wetness impregnation method (Pinna, 1998). The total amount of supported metal was fixed at 4 mass%, while cobalt:dopant molar ratio was 9:1 for all samples. The synthesized materials were prepared in the form of carbon paste electrode (Co+dopant/AP-CPE) with the same mass ratio of Co+dopant/AP to carbon black (CB) and applied as a working electrode. All the electrochemical measurements of each Co+dopant/AP-CPE were conducted using an Autolab PGSTAT302N potentiostat with Nova 2.1 software. The experiments were carried out in a three-electrode cell with prepared electrodes as working, Ag/AgCl (3 M KCl) as a reference electrode, and platinum rod as a counter electrode. Electrochemical behavior of the working electrodes for glucose detection was studied by the cyclic voltammetry and chronoamperometry in alkaline solution, with and without glucose. Among investigated electrodes for glucose electrooxidation, the Co+Fe/AP-CPE exhibited the highest current response with the best sensitivity. These very first results indicated a vital role of Fe in enhancing the glucose-sensing performance of aluminum pillared montmorillonite-supported cobalt. The physical chemical characterization of all Co+dopant/AP materials is ongoing.

Due to its similarity with biological apatite found in vertebrate hard tissues, calcium hydroxyapatite is one of the most investigated materials in bone tissue engineering. As the biological apatite is not stoichiometric, ion substituted hydroxyapatites attract much atention since they more closely mimic the composition of natural bone. Although there are many investigations of the influence of foreign ions on the structure and physico-chemical properties of ion-substituted hydroxyapatites, there is scarse information on their behaviour in different media. In the present study, magnesium (Mg), that plays a key role in bone metabolism and silicon (Si), that is necessary for normal skeletal development, were used as ion substitutes. The behaviour of Mg and Si substituted hydroxyapatite in simulated body fluid was investigated by XRD, FTIR and SEM. Obtained results confirmed great potential of these substituted hydroxyapatites for biomedical applications.

Recently the focus of electrochemical glucose sensing is on the fabrication of enzyme-free electrodes based on non-precious transition metal oxides, especially cobalt oxide [1]. To our best knowledge, these materials were primarily prepared by conventional methods using solutions, while the solvent-free mechanochemical approach was scarcely reported. Therefore, in this work Co3O4 supported on alumina (Co3O4/Al2O3) were prepared by ball milling using different milling times (0.5, 1, and 2 h) and Co3O4 contents (4, 8, and 16 wt. %). Ball to powder ratio was 30:1 and the rotation speed was 300 rpm. The electrodes based on the synthesized material were prepared in the form of a carbon paste electrodes (CP-Co3O4/Al2O3). The particle size distribution, phase, and chemical composition of the obtained materials were determined using LDPSA, XRPD, and XRF, respectively. The electrochemical performance of the CP-Co3O4/A12O3 electrode was tested in an alkaline solution containing glucose using cyclovoltammetry (CV) and chronoamperometry (ChA). CV revealed that milling time affected the electrochemical response. The highest current response was obtained with material milled for 1 h. Both ChA and CV confirmed that the electrochemical performance was further improved by increasing cobalt content. The CP electrode-based mechanochemically prepared samples showed enhanced performance in comparison to hand mixed Co3O4 and alumina. The beneficial effect of ball milling was attributed to the high dispersion of cobalt oxides over alumina even for large cobalt loadings without agglomeration. The obtained experimental results proved that the solvent-free mechanochemical approach is a promising synthetic route for obtaining green and sustainable glucose-sensing material for the fourth generation.