Search Results (9)

To obtain sustainable food packaging materials, alternatives to traditional ones must be researched. In this work, two different kinds of zeolites, i.e., a natural one, Clinoptilolite, and a synthetic one, Zeolite Na-X, were mixed with thermoplastic polyurethane for the fabrication of composites. Composite films were prepared via a hot mixing stage and then by means of a hot compression molding process. Several TPU/zeolite composites were produced with a filler concentration ranging from 5% to 10%wt. Finally, the obtained films were characterized by Fourier Transform Spectroscopy (FT-IR, ATR), thermal analysis (TGA and DSC), frequency sweep test, scanning electron microscopy (SEM), mechanical tensile test and oxygen permeability test. For both fillers and at all concentrations, the inclusion of zeolites significantly influenced the analyzed properties. In the TPU/zeolite composites, an overall enhancement was observed compared to the neat polymer, attributed to improved processability, superior barrier properties and the potential to create active materials by loading zeolite combined with various chemicals for specific applications. These findings suggest that the resulting composites hold considerable promise for applications in the food packaging sector. Full article

Ammonium ion is a chemical species that is found in abundance in natural waters, whether underground or surface, but also in wastewater resulting from agricultural and industrial activities. Even if the removal of the ammonium ion from water has been studied for a very long time, it has been found that its removal is far from being solved. In this study, we evaluated the performance of the ammonium ion adsorption process on two adsorbents, zeolite clinoptilolite, ZR, a sustainable material (manufacturer: Zeolite Development SRL, Rupea, Brasov, Romania), and the other granular activated carbon type, Norit GAC 830 W. Zeolite ZR is found in very large deposits in Romania; it is a natural, cheap material with costs between 50 and 100 EUR/ton, compared to other adsorbents that cost over 500 EUR/ton and which can be regenerated and reused in the technological process of water treatment and purification, but also after exhaustion, as an amendment for the soil. In the first step, this paper presents the mineralogic (XRD) and structural (SEM and EDX) characterization of the ZR and the determination of the pH zero-point charge, pH_ZPC, for all the adsorbents. Studies were carried out in equilibrium and kinetic conditions. The efficiency of the adsorbent was investigated in different experimental conditions by varying the initial concentration, particle size, temperature, pH, ionic strength, and contact time. The mathematical models and parameters specific to the adsorption isotherms that best describe the experimental results were identified. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich mathematical models were used for comparison. The Langmuir isotherm proved to be the most appropriate to describe the adsorption of ammonium ions on all types of adsorbents used. The adsorption capacity of ammonium ions from synthetic solutions at 20 °C, pH = 6.09, for the range of initial concentrations 0–50 mg/L for Rupea zeolite is in the range of 10.46 mg/g−12.34 mg/g, and for granular activated carbon GAC W830, it is 16.64 mg/g. It was found that the adsorption capacity of the ammonium ion on both activated carbon and zeolite increases with increasing temperature and pH. Also, it was observed that as the ionic strength increases, the adsorption capacity decreases for all four adsorbents. Kinetic models were also identified that best describe the experimental processes. In this sense, pseudo-first order, pseudo-second order, intra-particle diffusion and the Elovich model were used. The results of the investigation showed that second-order kinetics governs the adsorption process on ZR, and pseudo-first order governs activated carbon. Full article

The avoidance of allergen intake is crucial for persons affected by peanut allergy; however, the cross-contamination of food is common and leads to unpredictable consequences after the consumption of supposedly “safe” food. The aim of the present study was to eliminate harmful traces of peanut allergens from food using purified clinoptilolite-tuff (PCT)—a specially processed zeolite material. Analyses were performed using a peanut ELISA and a Coomassie blue (Bradford) assay. Mimicking conditions of the human gastrointestinal tract demonstrated a higher efficacy of PCT in the intestine (pH 6.8) than in the stomach (pH 1.5). Adsorption rates were fast (<2 min) and indicated high capacities (23 µg and 40 µg per 1 mg of PCT at pH 1.5 and pH 6.8, respectively). Allergenically relevant peanut protein concentrations were sorbed in artificial fluids (32 µg/mL by 4 mg/mL of PCT at pH 1.5 and 80.8 µg/mL by 0.25 mg/mL of PCT at pH 6.8) when imitating a daily dose of 2 g of PCT in an average stomach volume of 500 mL. Experiments focusing on the bioavailability of peanut protein attached to PCT revealed sustained sorption at pH 1.5 and only minor desorption at pH 6.8. Accompanied by gluten, peanut proteins showed competing binding characteristics with PCT. This study therefore demonstrates the potential of PCT in binding relevant quantities of peanut allergens during the digestion of peanut-contaminated food. Full article

Negative temperature coefficient (NTC) materials are usually based on ceramic semiconductors, and electrons are involved in their transport mechanism. A new type of NTC material, adequate for alternating current (AC) applications, is represented by zeolites. Indeed, zeolites are single charge carrier ionic conductors with a temperature-dependent electrical conductivity. In particular, electrical transport in zeolites is due to the monovalent charge-balancing cations, like K⁺, capable of hopping between negatively charged sites in the aluminosilicate framework. Owing to the highly non-linear electrical behavior of the traditional electronic NTC materials, the possibility to have alternative types of materials, showing linearity in their electrical behavior, is very desirable. Among different zeolites, natural clinoptilolite has been selected for investigating NTC behavior since it is characterized by high zeolite content, a convenient Si/Al atomic ratio, good mechanical strength due to its compact microstructure, and low toxicity. Clinoptilolite has shown a rapid and quite reversible impedance change under heating, characterized by a linear dependence on temperature. X-ray diffraction (XRD) has been used to identify the natural zeolite, to establish all types of crystalline phases present in the mineral, and to investigate the thermal stability of these phases up to 150 °C. X-ray photoelectron spectroscopy (XPS) analysis was used for the chemical characterization of this natural clinoptilolite sample, providing important information on the cationic content and framework composition. In addition, since electrical transport takes place in the zeolite free-volume, a Brunauer–Emmett–Teller (BET) analysis of the mineral has also been performed. Full article

Bisphenol A is a remarkable chemical compound as it has many applications, mainly in the plastics industry, but it also has toxic effects on the environment and human health. This article presents a comparative study regarding the adsorption of BPA on Active carbon and zeolitic tuff, ZTC. In this paper, the characterization of the zeolitic tuff, adsorbent, was carried out from an elemental and mineralogical point of view, and it noted the pore size and elemental distribution, using SEM, EDAX, and XRD analysis. The pore size varies from 30 nm to 10 µm, the atomic ratio is Si/Al ≥ 4, and 80% of the mineralogical composition represents Ca Clinoptilolite zeolites and Ca Clinoptilolite zeolites ((Na_1.32K_1.28Ca_1.72Mg_0.52) (Al_6.77Si_29.23O₇₂)(H₂O)_26.84). Moreover, a comparative study of the adsorption capacity of bisphenol A, using synthetic solutions on an activated carbon type—Norit GAC 830 W, GAC—as well as on Clinoptilolite-type zeolitic tuff—ZTC, was carried out. The experiments were carried out at a temperature of 20 °C, a pH of 4.11, 6.98, and 8.12, and the ionic strength was assured using 0.01 M and 0.1 M of KCl. The adsorption capacities of GAC and ZTC were 115 mg/g and 50 mg/g, respectively, at an 8.12 pH, and an ionic strength of 0 M. The Langmuir mathematical model best describes the adsorption equilibrium of BPA. The maximum adsorption capacity for both adsorbents increased with an increasing pH, and it decreased with increasing ionic strength. Full article

Clinoptilolite is one of the most common, widespread and abundant zeolites in nature. Its availability, low cost, and outstanding ion exchange properties make clinoptilolite an excellent candidate for both direct use and various modifications to create new low-cost functional materials for sustainable development. Specific applications in which clinoptilolite is already being used include water treatment and heavy metal ion removal, agricultural purposes, storage and conversion of unwanted gaseous emissions into the atmosphere, production of catalysts and photocatalysts, bioactive materials, and a number of others. Unlike some other zeolites, clinoptilolite is difficult to synthesize, which is why most publications refer to this zeolite in its natural form, either directly from the deposit or after applying various processes to this mineral to improve its properties. Among the modification methods used, ion exchange stands out. This review is devoted to the study of ion exchange processes in natural clinoptilolite with two goals: first, as its strategic property for use in processes in which cation exchange is fundamentally necessary; second, as a way to modify it to create composite materials with predetermined desired properties. Full article

A natural clinoptilolite zeolite was transformed into other zeolites of greater industrial interest, such as zeolites with GIS and LTA structures. The synthesis conditions were studied, and the interzeolitic transformation was characterized by X-ray diffraction (XRD), X-ray fluorescence (FRX), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). From the results, it was possible to observe that the GIS and LTA zeolites were successfully synthesized. Furthermore, the results revealed that a synthesis time of 4 days was enough to obtain the GIS structure, and 4 h was sufficient to obtain LTA. The interzeolitic transformation can be explained by the RBU (Ring Building Unit) approach using C4 units from the HEU topology. The use of clinoptilolite in the synthesis of other zeolites is an innovative, economically viable, and environmentally sustainable process that exploits a material that exists in large quantities and is still little explored by industry. Full article

Excessive use of nitrogen fertilizer and inappropriate fertilization designs have negative results in agricultural ecosystems, such as considerable nitrogen losses through nitrogen dioxide (NO₂) soil leaching and ammonia NH₃ volatilization. In addition, climate change, with rising summer temperatures and reduced precipitation, leads to production declines and water shortages in the soil. This review aims to highlight the characteristics of natural zeolite and focus on their multiple uses in agriculture. These minerals are tectosilicates showing an open three-dimensional structure involving the cations required to balance the framework electrostatic charge of aluminum and silicon tetrahedral units. Different research groups reported more than fifty natural zeolites; chabazite, clinoptilolite, phillipsite, erionite, stilbite, heulandite, and mordenite are the most well-known. Zeolites are great tools to help the farmer and agronomist cope with several issues, such as soil or water pollution, contamination by heavy metals, loss of nutrients, and loss of water-use efficiency (WUE) of drylands. These natural crystalline aluminosilicates are considered soil conditioners to improve soil chemical and physical properties, such as saturated hydraulic conductivity (Ks), infiltration rate, cation exchange capacity (CEC), and water-holding capacity (WHC). Owing to their properties, these materials are able to reduce nitrate leaching and ammonia volatilization. Zeolites are also known for their carrying capacity of slow-release macronutrients, micronutrients, and fertilizers. However, the potential of these materials in agricultural areas is apparent, and zeolites show the promise of contributing directly to improve agricultural ecosystems as a sustainable product. Full article

The search for safer and sustainable management of animal manure is a global and topical challenge, in particular for the reduction of nitrogen (N) content. The use of natural adsorbents as zeolite-rich tuffs is recognized as a valid method to recover N, in the form of ammonium (NH₄⁺), from animal manure. While the scientific literature is rich in studies performed on synthetic solutions and using clinoptilolite zeolites as adsorbent, it lacks information concerning adsorption in real liquid manure and using other types of zeolite-rich tuffs (e.g., chabazite). This work aims at exploring the NH₄⁺ adsorption process from raw liquid swine manure, using a chabazite-rich zeolite tuff as adsorbent. The effects of temperature, contact time, and grain size have been assessed. Isotherms, kinetic models, and thermodynamic parameters have been investigated. Harkins-Jura isotherm correlates well with the observed data, in accordance with the formation of an adsorption multilayer. Kinetic data have been explained by intraparticle diffusion and pseudo-second-order models. In conclusion, the natural chabazite tuff has proven to be a valid material for NH₄⁺ adsorption from raw liquid swine manure. In particular, to reach the highest adsorption capacities and adsorption rates, it is recommended to use it at a fine particle size and with dosages < 6 %. Full article