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Municipal wastewater, as well as agricultural drainage wastewater, is the main source of organic pollutants such as drugs and pesticides. Efficient, economically profitable and environmentally acceptable adsorbents for their removal are the subject of intensive research. In this work, a composite based on surfactant-modified zeolite and hydroxyapatite was synthesized. It was in detail characterized and examined as an adsorbent of two organic pollutants: one of the most commonly used antibiotics, ciprofloxacin, and an insecticide necessary in agricultural production, acetamiprid. The results showed that the obtained adsorbent removed 5.3 mg ciprofloxacin g-1 and 0.6 mg acetamiprid g-1 from the aqueous solution.

Low-cost and easily available natural zeolite is a promising adsorbent for metal ions removal in wastewater treatment. The possibility of using zeolitic tuff from Serbia in the form of Na-enriched natural zeolite (Na-Z) for the adsorption of Pb2+, Zn2+, Cu2+, and Ni2+ions from wastewater was investigated in the presented paper. The research included Na-Z characterization and determination of adsorption kinetics in individual ion adsorption tests using Weber-Morris intraparticle diffusion model, non-linear pseudo-first-order (PFO), pseudo-second-order (PSO) and mixed-order (MO) kinetic models. The results indicate that the adsorption processes of metal ions on Na-Z are complex processes dominated by multiple rate-limiting mechanisms and best defined by the MO model. The mechanisms of ion diffusion and adsorption to active sites are equally represented in the Pb2+adsorption process. The mechanism of ion adsorption on the active sites is the rate-limiting step in the Zn2+adsorption process, while in the case of the Cu2+and Ni2+adsorption ion diffusion is the rate-limiting kinetic mechanism. Within the MO model, the PFO rate (external/internal diffusion) and the PSO rate (adsorption on active sites) were calculated and results wereapplied to a multicomponent wastewater sample in order to determine and explain the adsorption efficiency in wastewater treatment. The results show that the rate of adsorption of individual metal ions and the efficiency of ion removal from a multicomponent wastewater sample are influenced by several factors including the radius of the hydrated ion and the free energy of hydration. The achieved removal of metal ions by Na-Z is Pb2+(89%) > Cu2+(72%) > Zn2+(61%) > Ni2+(58%) and defines Na-enriched naturalzeolite as an effective adsorbent in wastewater treatment.

Natural zeolite is a good sorbent for many cations due to its specific porous structure. The degree of sorption efficiency depends on the cation type and the availability of exchange positions in the zeolite lattice. The aim of this work is to examine the synthesis possibility of a new adsorbent based on natural zeolite and hydroxyapatite. The adsorbent was prepared mechanochemically by using clinoptilolite-rich zeolite tuff from the Slanci deposit (Serbia) and hydroxyapatite obtained by the hydrothermal process. The milling process was performed in a ball mill and optimized regarding contact time and milling speed. For the synthesis of zeolite/hydroxyapatite adsorbent (ZHAp), optimal values for these two parameters were 10 min and 250 rpm, respectively. The resulting sample ZHAp was characterized by X-ray powder diffraction, thermal analysis and scanning electron microscopy. Diffraction analysis of the ZHAp confirmed the presence of the most abundant mineral in zeolite tuff - clinoptilolite and hydroxyapatite. Needle-like crystals of hydroxyapatite on the clinoptilolite surface are observed in SEM images. Zeolite/hydroxyapatite sample is thermally stable at 800 °C. Adsorption properties of ZHAp were examined for nickel and chromium ions, towards which natural zeolite shows a low affinity. The presence of hydroxyapatite on the zeolite surface led to an increase in the adsorption capacity more than two times for both tested ions compared to the initial zeolite tuff.

Chitosan/gelatin and chitosan/gelatin/zeolite films prepared by solvent casting method were impregnated with a mixture of thymol and carvacrol using a green solvent, supercritical carbon dioxide at 35 °C and 30 MPa, during 18 h. Proposed method enabled preparation of biocompatible and biodegradable blends with strong antioxidant and antibacterial activity, whereby amounts of loaded thymol/carvacrol mixture were in the range from 3.3-6%. After initial burst release, both types of films exhibited gradual release of bioactive compounds, with around 72 and 96% of impregnated thymol/carvacrol mixture released in water and PBS (pH 7.4) during tested period of 10 days, respectively. Results of water vapor transmission rate (> 76 gm-2 day-1) confirmed that prepared composites are suitable for wound dressing application. Thermal analysis showed superior properties of prepared thymol/carvacrol loaded films compared to control samples. In addition, mechanical and structural properties, as well as solubility and swelling behavior of the obtained films were investigated in detail.

Chitosan/gelatin and chitosan/gelatin/zeolite films prepared by solvent casting method were impregnated with a mixture of thymol and carvacrol using a green solvent, supercritical carbon dioxide at 35 °C and 30 MPa, during 18 h. Proposed method enabled preparation of biocompatible and biodegradable blends with strong antioxidant and antibacterial activity, whereby amounts of loaded thymol/carvacrol mixture were in the range from 3.3-6%. After initial burst release, both types of films exhibited gradual release of bioactive compounds, with around 72 and 96% of impregnated thymol/carvacrol mixture released in water and PBS (pH 7.4) during tested period of 10 days, respectively. Results of water vapor transmission rate (> 76 gm-2 day-1) confirmed that prepared composites are suitable for wound dressing application. Thermal analysis showed superior properties of prepared thymol/carvacrol loaded films compared to control samples. In addition, mechanical and structural properties, as well as solubility and swelling behavior of the obtained films were investigated in detail.

Natural zeolite-clinoptilolite (from Vranjska Banja deposit in Serbia) and synthetic Beta zeolite, were amin-functionalized using (3-aminopropyl)-triethoxysilane (APTES). The results of the Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed the presence of amino groups derived from APTES onto the modified zeolite surface. APTES-enriched zeolite was further used as an adsorbent of silver ions from aqueous solutions. Natural zeolite-clinoptilolite showed a higher adsorption capacity (96 mg Ag/g), compared to beta zeolite (54 mg Ag/g) which is attributed to the presence of exchangeable cations in the structure of clinoptilolite. The kinetic data follows the pseudo-second-order model which indicates a chemical interaction between silver ions and functional amino groups on the surface of the zeolite. Ag-APTES and APTES-enriched zeolites further were studied as antibacterial agents toward the pathogenic bacteria Gram-negative Escherichia coli DSM 498 and Gram-positive Staphylococcus aureus ATCC 25923. Based on the results, it was concluded that the APTES-zeolites do not exhibit antibacterial activity while Ag- APTES enriched zeolites shows antibacterial effect toward both examined bacterial strains. Antibacterial activity is attributed to the presence of silver ions.

Zeolites are inorganic, crystalline aluminosilicates that nowadays has been used as adsorbents, catalysts and carriers of catalytically activated substances, due to the small size of their pores, large internal surface, and well-defined chemical composition. In this paper, the modification of beta zeolite using (3-aminopropyl)-triethoxysilane (APTES) was investigated. The results of the Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed the presence of amino groups derived from APTES onto the modified zeolite surface. APTES-enriched zeolite was further used as an adsorbent of silver ions from aqueous solutions. The obtained results reveal that a zeolite after modification exhibited significantly better adsorption efficiency (97%) in comparison to the unmodified (37%). The kinetic data follows the pseudo-second-order model which indicates a chemical interaction between silver ions and functional amino groups on the surface of the silanizedbeta zeolite. Ag-APTES enriched beta zeolite also was studied as anantibacterial agent toward the pathogenic bacteria Gram-negative Escherichia coliDSM 498 and Gram-positive Staphylococcus aureus ATCC 25923.

The adsorption of the antibiotic ciprofloxacin (CIP) from an aqueous solution by natural zeolite, the calcium-rich clinoptilolite (CLI), and magnetite-coated CLI (MAG-CLI) was investigated. Both CLI and MAG-CLI showed a high adsorption affinity towards CIP at 283, 288 and 293 K at a pH of 5. Adsorption kinetics studied for the initial concentrations of 15-75 mg CIP dm(-3) follow Lagergren's pseudo-second order equation and the adsorption is best represented by the Langmuir model. The adsorption mechanism involves strong electrostatic interactions between negatively charged aluminosilicate lattice and the cationic form of CIP accompanied by an ion-exchange reaction. Magnetite coverage (approx. 12 wt.%) induces magnetism, which can facilitate the separation process. The coverage does not influence the adsorption activity of CLI. The leaching test showed that the MAG coating protects the adsorbent from CIP leaching. This is ascribed to interactions between the CIP carboxyl groups and magnetite nano-particles. Antibacterial tests showed strong antibacterial activity of the ciprofloxacin-containing adsorbents towards pathogenic E. coli and S. aureus.

The aim of this study was to investigate the possibilities and to optimize the conditions for the synthesis of hydroxyapatite (HAP) on calcium-enriched natural and synthetic zeolites as carriers. Two synthetic zeolites were used in the paper: zeolite 4A (Na-form) and zeolite 5A (Ca-form) as well as natural zeolite - clinoptilolite from Slanci deposit in Serbia. Clinoptilolite and zeolite 4A were enriched with calcium ions by ion exchange treatmentin order to enable the source of Ca2+in the crystallization of hydroxyapatite. Phosphorus, necessary for the crystallization of hydroxyapatite, was introduced through a solution of ammonium-hydrogenphosphate. The influence of the concentration of hydrogen phosphate ions, temperature and crystallization time of hydroxyapatite on the morphology of the zeolite surface as well as the degree of its coverage with newly formed hydroxyapatite particles was monitored in the experiments. The obtained powders were characterized by X-ray powder diffraction (XRD), thermal TG-DTG analysis, infrared spectroscopy with Fourier transformation (FTIR) and scanning electron microscopy (SEM). Based on the structural analysis, it was shown that the synthesis of hydroxyapatite did not affect on the structure of the zeolite, except in the case when a very concentrated hydrogen-phosphate solution was used. Thermal analysis showed that all obtained zeolite and HAP samples were stable up to 800 °C. Optimization of the hydrothermal crystallization process showed that temperature and time do not have a crucial influence on the synthesis of the materials (similar results were obtained at 120 °C for 20 hours and at 160 °C for 4 hours). When the concentration of the solution of ammonium hydrogen phosphate was higher, larger crystals of hydroxyapatite were obtained, but the crystal lattice of the zeolite was collapsed. SEM micrography showed that unevenly distributed hydroxyapatite crystals were formed on natural zeolite due to the presence of various impur

In the present study, supercritical solvent impregnation (SSI) has been applied to incorporate thymol into bio-composite polymers as a potential active packaging material. Thymol, a natural component with a proven antimicrobial activity, was successfully impregnated into starch-chitosan (SC) and starch-chitosan-zeolite (SCZ) films using supercritical carbon dioxide (scCO2) as a solvent. Experiments were performed at 35 °C, pressures of 15.5 and 30 MPa, and an impregnation time in the range of 4–24 h. The highest impregnation yields of SC films with starch to chitosan mass ratios of 1:1 and 1:2 were 10.80% and 6.48%, respectively. The addition of natural zeolite (15–60%) significantly increased the loading capacity of films enabling thymol incorporation in a quantity of 16.7–27.3%. FTIR and SEM analyses were applied for the characterization of the films. Mechanical properties and water vapor permeability of films before and after the impregnation were tested as well. Thymol release kinetics in deionized water was followed and modeled by the Korsmeyer-Peppas and Weibull model. SCZ films with thymol loading of approximately 24% exhibited strong antibacterial activity against E. coli and methicillin-resistant Staphylococcus (S.) aureus (MRSA).

Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumannii is nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumannii outside hospital settings including natural soils affected by human waste represents a public-health risk for humans and animals. The aim of this study was to investigate the potential of metal-loaded zeolites to eliminate viable A. baumannii from artificially contaminated natural soils. A. baumannii isolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossa and slightly alkaline red palaeosol. A. baumannii survived in terra rossa and red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossa and red palaeosol shortened the survival of A. baumannii to three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumannii within 1 h of contact, while the total native heterotrophic bacterial counts remained high. Since AgNZ is prepared with a simple modification of cost-effective and environmentally friendly natural zeolite, it is a promising material for the remediation of soils contaminated with pandrug-resistant A. baumannii.

Antibacterial activity of a natural zeolite, clinoptilolite (Z), enriched with about 0.4-0.5 mmol of Ag (Ag-Z), Cu (Cu-Z) or Zn (Zn-Z) was tested toward two strains of Gram-negative bacteria - Escherichia coli and Acinetobacter baumannii - in natural seawater from Adriatic Sea (Croatia). The Ag-Z and Cu-Z exhibited bactericidal activity toward E. coli and A. baumannii after 3 and 6 h of exposure, respectively. The Zn-Z showed antibacterial activity toward both strains, but lacking the bactericidal effect even after 24 h of exposure. All studied samples released metal cations in seawater. Concentration of Ag and Zn leached from Ag-Z and Zn-Z was higher than maximum allowable concentrations (MAC) for drinking water, whereas concentration of Cu was below MAC. Due to high concentration of Na+ in seawater (about 1.2 g Na+ dm(-3)) an ion-exchange process can be responsible for the leaching of the studied cations. The lowest extent of leaching from Cu-Z was ascribed to different position and geometry of sites occupied by Cu(II) in the clinoptilolite lattice. The antibacterial activity of M-Z was attributed to the metal cations leached from the zeolite lattice into seawater. The obtained results indicate that Cu-Z can be considered as a promising disinfectant for treatment of seawater.

Hospital wastewaters can become a route for dissemination of antibiotic-resistant bacteria to the environment if not properly treated. Some of these bacteria are able to survive conventional disinfection treatments (e.g. chlorination, UV irradiation), which evokes the need for novel disinfection methods. The metal-exchanged zeolites were tested as novel antibacterial agents for wastewater treatment. The natural zeolite clinoptilolite enriched with silver (AgNZ) showed far better antibacterial activity towards hospital pathogenic bacterium Acinetobacter baumannii when compared with copper-exchanged zeolite (CuNZ), with minimal bactericidal concentration of 0.25-2 (AgNZ) compared with 32-64 mg L-1 (CuNZ) in a batch system and respective log 5.6 reduction compared with log 0.5 reduction in a flow system with pure bacterial culture. In the flow system with real effluent wastewater from the treatment plant, the removal of carbapenem-resistant bacteria using AgNZ was 90-100% during the 4 days of the experimental run. These results indicate that the AgNZ efficiently removes pathogenic bacteria from the wastewater, including A. baumannii, and is promising as a disinfectant material in a bead filter system.

Two types of zeolites-natural clinoptilolite (NZ) and synthetic zeolite A (A)-were enriched with approx. 0.25 mmol of Cu(II), Zn(II), or Ag(I) ions, and the obtained materials (M-Z) were tested against three different isolates of Escherichia coli. Two isolates were environmental isolates from waters in Serbia whereas the third one was DSM 498. Antibacterial activity was studied in different water media-nutrient-rich media (peptone water), water from Sava Lake, and commercially available spring water. The Ag-containing zeolites showed bactericidal activity in the nutrient-rich peptone water after 1 h of contact. Cu- and Zn-containing zeolites showed bactericidal activity in real water samples. Antibacterial activity of the M-Z decreases in all three examined water media in the following order: Ag-NZ ae Ag-A gt Cu-NZ ae Cu-A gt Zn-NZ gt gt gt Zn-A, suggesting that mainly the metal type and not the zeolite type have a role in the antibacterial activity. Leaching experiments showed small amounts of the leached Cu(II) and Zn(II) ions, indicating that the antibacterial activity is not due to the metal ions but should be attributed to the M-Z itself. However, leached amounts of Ag(I) from Ag-NZ and Ag-A in peptone water indicate that the released Ag(I) could be mainly responsible for the bactericidal effect of the Ag(I)-containing zeolites. Since no loss of cellular material was found, the antibacterial activity is not attributed to cytoplasmic membrane damage.

Sorption of the Zn2+ and Ni2+ ions by the Na+-enriched natural clinoptilolite (Na-CLI) from aqueous solutions containing both Zn2+ and Ni2+ ions at a range of concentrations has been studied at 298, 308, and 318K. It was found that the sorption of a particular ion by Na-CLI increases with the increase in the initial concentration of the solution of that ion. At a given initial concentration, the sorption degree increases with temperature. Also, the sorption of a particular ion is greater when the initial solution contains a second ion than it is when the particular ion is present alone. The sorption kinetics is in accord with the pseudo-second-order reaction rate model. The values of the k(2) rate constant do not show a regular change with the initial Zn2+/Ni2+ concentrations probably because the presence of the second ion has a significant effect on the reaction rate. Thermodynamic study has shown that the sorption is exothermic, occurring spontaneously in the 298-318K range and with a positive entropy change.