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Clays are naturally occurring, environmentally friendly, chemically inert, thermostable, inexpensive resources that are easily modified into materials with tailored properties. As such, they can be used as suitable supports for enzyme immobilization and application in the food industry. Natural polysaccharides starch, xylan, pullulan, and its derivatives obtained by the action of enzymes, have numerous potentials for food industrial applications. In this work the enzyme supports were prepared from bentonite from Coal mine "Bogovina", Serbia by acid activation (AA), pillaring (P), and pillaring followed by acid activation (PAA). The characterization of the obtained materials included chemical and phase composition, surface acidity, and textural properties. After characterization, -amylase from Bacillus paralicheniformis (BliAmy), commercial xylanase from Sigma-Aldrich (Xyl), and pullulanase from B. paralicheniformis (BliPull) were immobilized on bentonite based supports by 24 h adsorption at 25 °C. The obtained biocatalysts BliAmy-AA (106 IU/g), Xyl-P (74 IU/g), and BliPull-PAA (45 IU/g) showed very good storage stability with the activity preserved after 4 weeks of testing. Products of hydrolysis were detected by TLC and indicate a promising application in the food industry.

Catalytic degradation of tartrazine in the presence of Oxone® activated by a catalyst constituted of cobalt supported on a nanocomposite of smectite with chitosan-derived carbon was investigated. The catalyst was synthesized using cobalt impregnation followed by carbonization at 773 K in an inert atmosphere. The synthesized catalyst was previously fully characterized using appropriate characterization methods, including XRPD, XPS, FTIR, HR-TEM, and low-temperature N2-physisorption analysis. The catalytic experiments were performed by varying different experimental parameters (dye concentration, Oxone® concentration, temperature, and initial pH of the reaction solution). The kinetic and thermodynamic parameters were estimated from the experimental results. The kinetics data showed the best fit with the pseudo-first-order kinetics model. The activation energy of the investigated degradation process was calculated according to the Arrhenius equation. The catalyst showed excellent performance at low temperatures even at 298 K, and in the wide range of pH values.

Bentonite clay has shown to be a versatile material that can be easily modified and applied as an adsorbent, (electro)catalyst, or as a support for (electro)catalyst. The carbon-clay composites combine a relatively high specific surface area of the clay with a good electrical conductivity of carbon.In this paper, the effect of the applied carbonization procedure on the electrochemical properties of bentonite-carbon composite was investigated. Chitosan-modified bentonite was carbonized by conventional thermal degradation and by the hydrothermal procedure. The electrochemical characterization was performed by cyclic voltammetry and electrochemical impedance spectroscopy. The response to Fe(CN)63-/4- and Ru(NH3)62+/3+ redox probe showed that the thermally treated sample shows somewhat higher electrochemical activity and lower charge-transfer resistance. However, an investigation of composites activity toward minophenazone, performed in the pH range 3-9 showed that the hydrothermally obtained sample shows higher activity at pH above 5, while the thermally obtained sample was more active at pH below 5.

The employment of compounds obtained from natural sources to produce adsorbents and their application in the elimination of antibiotics from industrial effluents have gained significant attention because of their low production cost and sustainability. Herein, chitosan (biopolymer) and smectite (abundant clay mineral) were used for the low-cost and eco-friendly synthesis of a new type of adsorbent. A low-energy-consumption hydrothermal process was applied to the synthesis of the chitosan-derived carbon–smectite nanocomposite with cobalt (H_Co/C-S). The produced nanocomposite was characterized using elemental analysis, ICP-OES, XRPD, low-temperature N2 adsorption–desorption isotherms, FTIR analysis, and point of zero charge. H_Co/C-S (SBET = 0.73 m2 g−1, d001 = 1.40 nm, pHPZC = 5.3) was evaluated as a ciprofloxacin adsorbent in aqueous solution. Experimental data were fitted with different kinetic models and interpreted by selected adsorption isotherms. The pseudo-second-order model was found to be the most appropriate, while ciprofloxacin adsorption onto H_Co/C-S was best described by the Redlich–Peterson isotherm (R2 = 0.985). The maximum adsorption capacity of H_Co/C-S, according to the Langmuir isotherm (R2 = 0.977), was 72.3 mg g−1. Desorption and thermodynamic studies were performed. The obtained results indicated that the new hierarchically designed H_Co/C-S has promising potential to be further tested for application in real wastewater treatment.

The Briggs-Rauscher oscillatory reaction, which represents the oxidation of malonic acid in the presence of hydrogen peroxide and potassium iodate catalyzed by manganese ion in an acidic environment, proved to be extremely sensitive for testing insoluble materials, such as bronzes and clays. It was shown that origin of bentonite has high impact on the length of the oscillation time. In this work, the influence of different sizes of bentonite particles from the Bogovina deposit on the Briggs-Rauscer oscillatory reaction in the conditions of a closed reactor was investigated. Five particle sizes of bentonite, (< 25 µm, < 50 µm, < 75 µm, < 150 µm and < 300 µm) having identical mass of 0.15 g, were tested. The addition of different particle sizes of Bogovina clay does not significantly influence the basic BR oscillogram.

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.

Wastewaters polluted with high concentration of dyes are produced by various industries. Therefore, it is important to perform treatment of the dye-contaminated waters before their discharge into recipients in order to protect the environment. Sulfate radical-based advanced oxidation processes that involve use ofactivated Oxone® can be used for degradation of dyes. In this work,nanocomposite catalysts constituted ofCo supported on smectite with chitosanderived carbon were used for activation of Oxone. Catalysts were synthetizedusingan impregnation-carbonization procedure and denoted as Co/cCh-S-T (T stands for applied carbonization temperature). The carbonization was performed in the temperature range from 400°C to 700°C in the flow of N2 providing inert atmosphere. The synthesized catalysts were fully characterized using XRPD, XPS, FTIR, HR-TEM, and low-temperature N2- physisorption analysis, and evaluated in the Oxone® induced oxidative degradation of food dye tartrazine. The best performing catalyst was investigated in detail regarding catalytic degradation of tartrazine with respect to degradation time and different experimental parameters (dye concentration, Oxone® concentration, temperature, and initial pH of the reaction solution). The kinetic and thermodynamic parameters were calculated from the experimental results.The selected catalyst showed excellent performance in the Oxone® initiated tartrazine degradationat low temperatures (even at 25°C) and in the wide range of pH values.

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.

Some coal mines suffer from problem of having huge deposits of bentonite that they regard as undesirable, since bentonite can cause problem due to its swelling property. Instead of piling stacks of bentonite and regarding it as ecological problem the bentonite can be used as enzyme support by immobilization of enzymes as the challenging new application in the field of biotechnology. The enzyme catalysts in the industrial application present lower energy costs and are more environmentally friendly in comparison to traditional chemical processes. The advantages of enzymes are even more prominent when enzymes are applied in immobilized form. In this work the enzyme supports were prepared from bentonite from Coal mine "Bogovina", Serbia where bentonite, although valuable resource, is still considered to be tailings. Bentonite was modified by common methods: acid activation (AA), pillaring (P), and pillaring followed by acid activation (PAA) and tested as enzyme support. All the obtained materials were characterized by the X-ray powder diffraction and FTIR spectroscopy. The amylase, xylanase, and pullulanase were immobilized on different bentonite based supports by 24 h adsorption at 25 °C. The experimental results revealed that under the investigated conditions AA, P, and PAA, were the most suitable for amylase (106 IU/g), xylanase (74 IU/g), and pullulanase (45 IU/g) immobilization, respectively.

Chitosan (Ch)-derived from biowaste along with smectite, an abundant clay mineral, were used in a low-cost and eco-friendly synthesis of a new type of catalyst. Nanocomposite catalysts constituted of Co supported on smectite with chitosan-derived carbon loading were obtained using an impregnation‑carbonization procedure and denoted as Co/cCh-S-T (T stands for applied carbonization temperature). The carbonization was performed in the temperature range from 400 °C to 700 °C in the flow of N2 providing inert atmosphere. The temperature of 500 °C was found to be the most suitable for catalyst synthesis regarding catalytic performance in a peroxymonosulfate activated degradation of tartrazine. The incorporation of carbonized chitosan structure within the interlamellar space of the smectite was confirmed using X-ray powder diffraction. The high-resolution transmission electron microscopy confirmed a layered structure of nanocomposites characteristic for smectite, as well as the presence of small spherical cobalt containing nanoformations (confirmed by energy dispersive X-ray spectroscopy) well dispersed within structure. The existance of cobalt in the CoII and CoIII oxidation state was proven by X-ray photoelectron spectroscopy. The Co/cCh-S-500 catalyst was proven to be stable and efficient after 5 consecutive cycles. This work showed that nanocomposite Co-catalysts, based on smectite and biowaste-derived carbon, as peroxymonosulfate activators exhibited a very promising performance in the degradation of water pollutants.

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 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.

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.

Catalytic degradation of Tartrazine in the presence of Oxone® activated by Co-supported chitosan derived carbon-montmorillonite as catalyst was investigated. The catalyst was synthetized using impregnation-carbonization method. The carbonization temperature was 500 °C. The catalytic experiments were performed at different temperatures in range from 25 °C to 40 °C in order to determinate kinetics parameters. The kinetics data showed best fit with the first-order kinetics model. The activation energy of the investigated degradation process was calculated according to the Arrhenius equation.

Catalytic advanced oxidative degradation of organic pollutants in water is a promising technique for the purification of industrial effluents. Cobalt-based catalysts wa proven to be very efficient in peroxymonosulfate activation and generation of SO4•− radicals, species with high oxidative potential [1]. This work, for the first time, reports the hydrothermal procedure in the synthesis of cobalt-containing chitosan-derived carbon-smectite catalyst. The obtained catalyst was used for activation of Oxone® (potassium peroxymonosulfate). Activated Oxone® was applied in catalytic degradation of toxic textile dye - Orange G dye, that was used as a model of the water pollutant. Based on the presented results, the catalyst can be considered as an eco-friendly catalyst that was evaluated as highly efficient in the process of the oxidative degradation of selected organic dye, and potentially for a variety of water pollutants.

In this work cobalt supported on chitosan-derived carbon-smectite composite catalyst was synthetized using impregnation-carbonization method (Co/cCh-S). The carbonization temperature was 400 °C. The obtained catalyst was tested as peroxymonosulfate (in form of Oxone®) activator for the food dye tartrazine degradation. The textural properties were obtained using low temperature N2 physisorption. The calculated textural parameters of the Co/cCh-S catalyst were compared with properties of the carbonized chitosane-smectite composite (cCh-S). The catalytic tests confirmed that neither Oxone® without catalyst nor cCh-S were unable to activate Oxone®. The catalyst Co/cCh-S was found to be effective for tartrazine degradation in presence of Oxone®.