Natural zeolites as effective adsorbents in water and wastewater treatment

Natural zeolites are abundant and low cost resources, which are crystalline hydrated aluminosilicates with a framework structure containing pores occupied by water, alkali and alkaline earth cations. Due to their high cation-exchange ability as well as to the molecular sieve properties, natural zeolites have been widely used as adsorbents in separation and purification processes in the past decades. In this paper, we review the recent development of natural zeolites as adsorbents in water and wastewater treatment. The properties and modification of natural zeolite are discussed. Various natural zeolites around the world have shown varying ion-exchange capacity for cations such as ammonium and heavy metal ions. Some zeolites also show adsorption of anions and organics from aqueous solution. Modification of natural zeolites can be done in several methods such as acid treatment, ion exchange, and surfactant functionalisation, making the modified zeolites achieving higher adsorption capacity for organics and anions.     

Calcining natural zeolites to improve their effect on cementitious mixture workability

Despite the benefits to long-term concrete durability, the use of natural zeolites as supplementary cementitious materials (SCMs) is uncommon due to their high water demand. The motivation of the research presented here was to better understand how the physical and chemical characteristics of natural zeolites influenced the workability of cementitious mixtures and whether those properties could be modified through calcination to mitigate the high water demand of natural zeolites. In this research, three different natural zeolites were characterized in their original and calcined states using x-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area measurements. Rheology experiments were then conducted on cementitious pastes containing these natural zeolites, in their original and calcined states, to assess mixture viscosity and yield stress. Results showed that calcination destabilized the structure of the natural zeolites and reduced their surface area, which led to an improvement in mixture viscosity and yield stress.     

Influence of the zeolite type on the mechanical–thermal properties and volatile organic compound emissions of natural‐flour‐filled polypropylene hybrid composites

The physicomechanical properties, thermal properties, odor, and volatile organic compound (VOC) emissions of natural‐flour‐filled polypropylene (PP) composites were investigated as a function of the zeolite type and content. The surface area and pore structure of the natural and synthetic zeolites were determined by surface area analysis and scanning electron microscopy, respectively. With increasing natural and synthetic zeolite content, the tensile and flexural strengths of the hybrid composites were not significantly changed, whereas the water absorption was slightly increased. The thermal stability and degradation temperature of the hybrid composites were slightly increased with increasing natural and synthetic zeolite content. At natural and synthetic zeolite contents of 3%, the various odors and VOC emissions of the polypropylene/rice husk flour and polypropylene/wood flour hybrid composites were significantly reduced because of the absorption of the odor and VOC materials in the pore structures of the natural and synthetic zeolites. These results suggest that the addition of natural and synthetic zeolites to natural‐flour‐filled thermoplastic polymer composites is an effective method of reducing their odor and VOC emissions without any degradation of their mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The potential application of natural zeolite for greywater treatment

Natural zeolites are good potential material for water and wastewater treatment. It is due to the advantages of low cost, ion-exchange and adsorption capability of the natural zeolites. It can also be modified and regenerated. This paper thus looks at efforts made in exploring the potential application of natural zeolites and modified natural zeolites in water and wastewater treatment especially for reducing or removing contaminants in greywater, a type of wastewater originated from bathrooms and laundries in household. The material to be reviewed in this paper includes (i) major greywater contaminants and (ii) the potential of natural zeolites for greywater treatment.     

Zeolite-based composite membranes for high temperature direct methanol fuel cells

Composite Nafion membranes containing three natural zeolites (Mordenite, Chabazite and Clinoptilolite) were prepared by using a recast procedure for application in high temperature Direct Methanol Fuel Cells (DMFCs). The Nafion-zeolite membranes have shown good properties for high temperature DMFC application, due to their improved water retention characteristics. A maximum power density of 390 mW cm^–2 was achieved at 140 °C with the mordenite-based composite membranes in the presence of oxygen feed. The electrochemical behaviour of the composite membranes was interpreted in the light of surface properties and acidic characteristics of the fillers.     

DYNAMIC ADSORPTION OF S02 ON ZEOLITE MOLECULAR SIEVES†

Sulfur dioxide is one of the major pollutants resulting from fuel combustion. Numerous dry, semi-dry and wet processes have been developed for pollution control of sulfur dioxide. Solid carbonates, natural and synthetic zeolites, ion exchange resins and carbon based sorbents are the most commonly used dry sorbents for sulfur dioxide removal

In this study, measurements of the adsorption properties of sulfur dioxide on zeolites were investigated. The adsorbents used in this work are 5A, 4A and AW300 type molecular sieve zeolites. Adsorption equilibrium parameters were determined from the pulse chromatographic response to injections of low concentrations of sulfur dioxide. The method of moments were used to evaluate the adsorption equilibrium parameters from pulse chromatographic experiments. Data, such as adsorption equilibrium constants or reaction rate parameters are essential in the design of adsorption systems or reactors in which sulfur dioxide is removed

The experiments were conducted in a temperature range of 523-718 K. The relatively strong adsorption properties of sulfur dioxide on zeolites necessitated the use of high carrier gas flow rates and subsequently non-isobaric operation. Non-isobaric pulse chromatography theory was found to describe accurately the adsorption trends." printpubdate="Adsorption equilibrium constants of S0₂ were found to decrease considerably with increasing temperature. It was also found out that adsorption of SO₂ on the adsorbents investigated were found to decrease in the order of AW300 ≤ 4A ≤ 5A. The adsorption equilibrium parameter of S0₂ on 5A was found as 11.78 at 673 K, whereas it has a value of 157.11 at 523 K. The adsorption equilibrium parameter of S0₂ on 4A zeolite was determined to be 8.63 at 718 K and 213.78 at 523 K.     

沸石在生物医药中的新应用

综述了近年来沸石材料在生物医药方面的应用研究新进展 ,着重介绍了天然沸石在药物载体中的应用和助抗癌作用。     

沸石贮氢技术的研究进展

综述了利用沸石进行贮氢的研究进展。从沸石的晶体结构、氢吸附机理、热物理学性质以及实验和理论等方面讨论了沸石贮氢的机理和性能,预测了沸石作为贮氢介质的应用前景,提出了新的贮氢方法及沸石贮氢在实际应用中存在的问题和今后研究的发展方向。     

Liquid-phase degradation of HDPE over alkali-treated natural zeolite catalysts

Catalytic performance of alkali-treated natural zeolites was studied in the liquid-phase catalytic degradation of HDPE. Alkali treatment of natural zeolite with a moderate NaOH solution brought about the formation of mesopores and a decrease in acid site density, resulting in a considerable improvement of its catalytic activity. However, alkali treatment with highly concentrated NaOH solutions induced zeolite structure destruction, resulting in lower activity. HDPE conversion and product selectivity of alkali-treated natural zeolites were discussed in terms of their pore structures, acidities and the diffusion properties of large molecules.     

微波在沸石分子筛研究中的应用

介绍了微波在常规沸石分子筛、纳米沸石分子筛合成及其制备过程中的应用；评述了微波在沸石分子筛多相催化反应、表征沸石分子筛特性、沸石分子筛自身加热以及分子筛改性中的应用；认为微波所具有的快速、高产率、高反应选择性等特性，为沸石分子筛催化剂的制备和活化提供了一条新途径。     

改性沸石制备及对其铬吸附特性的研究

为了解决天然沸石对废水中重金属吸附能力低的问题,制备出了六种改性沸石并考察了改性沸石对六价铬离子的吸附特性。在这六种改性沸石中,H2 SO4/CuSO4复合改性沸石对铬的吸附性能最佳,其对铬的吸附曲线符合Freundlich方程;其吸附强度是天然沸石的8倍;其吸附动力学曲线符合二级动力学模型,实测值十分接近理论值,这也证明在其对六价铬离子的吸附过程中离子交换起着十分重要的作用。     

Porous Materials for Oil Spill Cleanup: A Review of Synthesis and Absorbing Properties

This paper reviews the synthesis and the absorbing properties of the wide variety of porous sorbent materials that have been studied for application in the removal of organics, particularly in the area of oil spill cleanup. The discussion is especially focused on hydrophobic silica aerogels, zeolites, organoclays and natural sorbents many of which have been demonstrated to exhibit (or show potential to exhibit) excellent oil absorption properties. The areas for further development of some of these materials are identified.     

Effect of desiccant characteristics on the properties of PS/zeolite functional packaging materials

Desiccant composites were prepared from a polystyrene homopolymer (PS) and a high impact copolymer (HIPS). Five zeolites were used as adsorbents, which included the A and X types frequently used in industrial practice. Composites containing zeolites up to 50 vol% were homogenized in an internal mixer and then compression molded to 1 mm thick plates. The results proved that the water adsorption capacity of zeolites depends on the total volume of the pores, whereas the rate of adsorption on thermodynamics, on the equilibrium constant of adsorption. On the other hand, zeolite characteristics influence the moisture adsorption of the composites only marginally; adsorption capacity is determined by zeolite content, whereas the rate of adsorption is determined by the properties of the polymer. Composites prepared with X type zeolites have somewhat smaller water adsorption capacity than those containing their A type counterparts. The dispersion of the zeolite is good both in PS and in HIPS composites. Mechanical properties are excellent mainly because of the good interfacial adhesion between the components. Because of their larger surface energy, composites containing X type zeolites have larger viscosity and they reinforce the polymer more than A type desiccants. Matrix characteristics influence mainly application related properties; reinforcement and ductility is better in HIPS than in PS composites. POLYM. COMPOS., 35:2112–2120, 2014. © 2014 Society of Plastics Engineers     

Investigation of structural properties of clinoptilolite rich zeolites in simulated digestion conditions and their cytotoxicity against Caco-2 cells in vitro

The use of the clinoptilolite rich natural zeolites in biomedical applications such as in anticancer therapy, drug or drug support systems and as nutritive supplement is highly dependent on their behavior in digestive conditions. Aim of this study is to investigate structural stability of clinoptilolite rich natural zeolites in simulated digestion conditions and their interactions with digestive media and with Caco-2 (human colon adenocarcinoma) cells. X-ray Diffraction (XRD), Fourier Transform InfraRed (FTIR), Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analyses of the clinoptilolite rich zeolite samples showed that zeolites preserved their structural stabilities during in vitro digestion. Slight interactions were detected in UV measurements of the digestive liquid media and FTIR spectra of the intestinal digested media powders. SEM results implied that zeolites might have a role in the aggregation of the digestive enzymes. Cytotoxicity test using colon cancer cells showed that clinoptilolite rich natural zeolites have cytotoxic effect against Caco-2 cells and cytotoxicity did not significantly change with respect to simulated digestion process.     

USY分子筛的改性及应用进展

USY分子筛由于其突出的物化性质在石油化工领域得到广泛应用,并表现出优异的催化裂化性能。随着技术的进步,对USY分子筛改性以及拓宽USY分子筛的应用范围成为研究热点。介绍USY分子筛的改性及应用进展,在改性方面,总结对USY分子筛的酸碱改性、金属改性以及多种方法混合改性等改性方式;在应用领域,讨论USY分子筛在有机物的合成、生物质降解与环保、无机物的选择性催化以及在电化学方面的应用。     

MCM-41型中孔分子筛的应用

介绍了MCM-41型中孔分子筛的性能、合成过程和近年来在催化、吸附、纳米、光学材料和环保等领域的应用情况，并对MCM-41的发展前景进行了展望。     

Efficiency evaluation of the photocatalytic degradation of zinc oxide nanoparticles immobilized on modified zeolites in the removal of styrene vapor from air

Styrene monomer is a volatile organic compound that has many applications in plastics, rubber, and paint manufacturing industries. Exposure to styrene vapor has certain effects, including suppression of the central nervous system, loss of concentration, weakness and fatigue, and nausea and there is a possibility of carcinogenesis in long-term exposure. Therefore, it is necessary to control and eliminate this vapor. The aim of this study was to investigate the performance of zinc oxide nanoparticles on modified natural zeolites in removing styrene vapor from the air. Natural zeolites of clinoptilolite were modified using hydrochloric acid and diphenyldichlorosilane. Next, zinc oxide nanoparticles with different ratios of 3, 5, and 10 wt% were stabilized on the zeolites. To determine their characteristics, samples were used from BET, SEM and XRD analyses. The input styrene concentration and the ratio of nanoparticles stabilized on zeolites were studied as effective functional parameters on the removal process. The efficiency results of natural zeolites (Ze) and modified zeolites (Mze) in styrene adsorption from the air show that the styrene breakthrough in the bed of MZe compared to that of Ze increases approximately two times. Also, the results showed that the removal by the process of UV/MZe-ZnO 3%, UV/MZe-ZnO 5%, and UV/MZe-ZnO 10%, was 36.5%, 40%, and 26%, respectively. From the results it can be concluded that MZe can increase the efficiency of photocatalytic degradation. Clinoptilolites of Iran can be used as an adsorbent to remove polluted air in industries that have low concentrations and flow rates.     

Friedel-Crafts酰基化催化剂的研究进展

Friedel-Crafts酰基化反应在有机合成研究与现代工业生产中有着非常重要的作用,其催化剂主要有 Lewis酸、超强酸/盐、离子液体、沸石类以及负载型催化剂。本文分别介绍了上述五类催化剂在F-C酰基化反应中的发展沿革与目前应用情况,分析评价了各类催化剂在该反应中的优缺点,并重点综述了沸石类催化剂和负载型催化剂的研究现状。最后从绿色化学、可持续发展的角度出发,指出沸石类和负载型两类催化剂具有较好的综合催化性能和工业化应用前景,值得进一步研究。     

The Surface Properties of Zeolites as Studied by Infrared Spectroscopy

Although the remarkable structural and surface properties of those crystalline aluminosilicates classified as zeolites have been known for some considerable time, it is only quite recently that their catalytic properties have been recognized and utilized. The properties of zeolites as catalysts have been recently discussed in detail in this journal by Turkevich [1]. Many review articles give details of their structural [2–5] and surface [6–9] properties, as studied by classical methods. This review will be restricted to information on zeolites obtained by applying one of the newer methods of studying the solid-gas interface-infrared spectroscopy.     

The Surface Properties of Zeolites as Studied by Infrared Spectroscopy

Although the remarkable structural and surface properties of those crystalline aluminosilicates classified as zeolites have been known for some considerable time, it is only quite recently that their catalytic properties have been recognized and utilized. The properties of zeolites as catalysts have been recently discussed in detail in this journal by Turkevich [1]. Many review articles give details of their structural [2-5] and surface [6-9] properties, as studied by classical methods. This review will be restricted to information on zeolites obtained by applying one of the newer methods of studying the solid-gas interface-infrared spectroscopy.