A novel ternary heterogeneous TiO2/BiVO4/NaY-Zeolite nanocomposite for photocatalytic degradation of microcystin-leucine arginine (MC-LR) under visible light

Microcystin-leucine arginine (MC-LR) is a carcinogenic toxin, produced by cyanobacteria. The release of this toxin into drinking water sources can threaten public health and environmental safety. Therefore, effective MC-LR removal from water resources is necessary. In the present study, the hydrothermal method was used to synthesize a novel ternary BiVO₄/TiO₂/NaY-Zeolite (B/T/N-Z) nanocomposite for MC-LR degradation under visible light. FESEM, FTIR, XRD, and DRS were performed for characterizing the nanocomposite structure. Also, the Response Surface Methodology (RSM) was applied to determine the impact of catalyst dosage, pH, and contact time on the MC-LR removal. High-performance liquid chromatography was performed to measure the MC-LR concentration. Based on the results, independent parameters, including contact time, catalyst dosage, and pH, significantly affected the MC-LR removal (P < 0.05). In other words, increasing the contact time, catalyst dosage, and acidic pH had positive effects on MC-LR removal. Among these variables, the catalyst dosage, with the mean square and F-value of 1041.37 and 162.84, respectively, had the greatest effect on the MC-LR removal efficiency. Apart from the interaction between the catalyst dosage and contact time, the interaction effects of other parameters were not significant. Also, the maximum MC-LR removal efficiency was 99.88% under optimal conditions (contact time = 120 min, catalyst dosage = 1 g/L, and pH = 5). According to the results, the B/T/N-Z nanocomposite, as a novel and effective photocatalyst could be used to degrade MC-LR from polluted water.

Enhanced photocatalytic removal of Safranin-T dye under sunlight within minute time intervals using heulandite/polyaniline@ nickel oxide composite as a novel photocatalyst

Natural zeolite heulandite/polyaniline composite (Hu/PANI) was synthesized for the first time as catalyst support for nickel oxide photocatalyst (Hu/PANI@Ni₂O₃). The structural, chemical, morphological, textural and optical properties were investigated using different techniques. The synthetic Ni₂O₃ crystals showed well developed flaky habits with diameter range 200-400 nm and length range 1-4 µm. The estimated band gap energies of Hu/PANI composite and Hu/PANI@Ni₂O₃ composite are 1.8 eV and 1.46 eV, respectively, which are remarkably smaller than the recorded value for pure nickel oxide. The photocatalytic properties of Hu/PANI@Ni₂O₃ composite for efficient degradation of safranin-T dye were evaluated under sunlight as a function of irradiation time, initial dye concentration, catalyst mass, solution pH, and the catalyst stability. Hu/PANI@Ni₂O₃ composite exhibits amazing photocatalytic degradation efficiency for safranin dye, whereas 80%, 98%, and ~ 100% of 5 mg/l dye were removed after only 1 min of solar irradiation using 0.025, 0.03, and 0.035 g of Hu/PANI@Ni₂O₃, respectively. The higher concentrations of the dye (10-50 mg/L) can be fully removed within minutes by increasing the solution pH or using higher doses from the Hu/PANI@Ni₂O₃ catalyst. The removal percentage achieved the maximum value at the alkaline conditions. Also, the Hu/PANI@Ni₂O₃ displayed high stability and remain 84.5% of the initial photocatalytic efficiency after 5 runs. Additionally, the composite can be used effectively in the removal of different types of dyes and mixed dyes within the same time intervals. Thus, loading of nickel oxide onto hybrid Hu/PANI composite as a catalyst support achieved amazing photocatalytic degradation capacity.

Removal of crotamiton and its degradation intermediates from secondary effluent using TiO2-zeolite composites

Crotamiton, a scabicide and antipruritic agent persistent during biological treatment processes, is frequently detected in secondary effluent. In this study, titanium dioxide (TiO₂) and high-silica zeolite (HSZ-385) composites were synthesized and applied for the treatment of crotamiton in secondary effluent. Crotamiton was rapidly adsorbed by HSZ-385, and the adsorption performance of crotamiton in the secondary effluent was quite close to that in the test using ultrapure water. Even though the TiO₂-zeolite composites showed lower adsorption rates than that of HSZ-385, similar crotamiton adsorption capacities were revealed using both test materials. The photocatalytic decomposition of crotamiton was significantly inhibited by the water matrix at low initial concentrations. The TiO₂-zeolite composites rapidly adsorbed crotamiton from secondary effluent, and then the crotamiton was gradually decomposed under ultraviolet irradiation. Importantly, when using TiO₂-zeolite composites, coexisting material in the secondary effluent did not markedly inhibit crotamiton removal at low initial crotamiton concentration. The behaviors of the main intermediates during treatment demonstrated that the main degradation intermediates of crotamiton were also captured by the composites.

Preparation of 13X from Waste Quartz and Photocatalytic Reaction of Methyl Orange on TiO2/ZSM-5, 13X and Y-Zeolite

TiO2 photocatalytic reactions not only remove a variety of organic pollutants via complete mineralization, but also destroy the bacterial cell wall and cell membrane, thus playing an important bactericidal role. However, the post-filtration procedures to separate nanometer-levels of TiO2 and the gradual inactivity of photocatalyst during continuous use are defects that limit its application. In this case, we propose loading TiO2 on zeolite for easy separation and 13X is considered as a promising one. In our study, 13X-zeolite was prepared by a hydrothermal method and the source of Si was extracted from waste quartz sand. For comparison, commercial zeolite with different microporous and mesoporous diameters (ZSM-5 and Y-zeolites) were also used as TiO2 supports. The pore size of the three kinds of zeolites are as follows: Y-zeolite > 13X > ZSM-5. Different TiO2 loading content over ZSM-5, 13X and Y-zeolite were prepared by the sol-gel method. XRD, FTIR, BET, UV-vis, TGA and SEM were used for investigation of material characteristics. In addition, the efficiencies of mineralization and photodegradation were studied in this paper. The effects of the loading ratio of TiO2 over zeolites, initial pH, and concentration on photocatalytic performance are investigated. The relationship between best loading content of TiO2 and pore size of the zeolite was studied. The possible roles of the ZSM-5, 13X-zeolites and Y-zeolites support on the reactions and the possible mechanisms of effects were also explored. The best loading content of TiO2 over ZSM-5, 13X and Y-zeolite was found to be 50 wt%, 12.5 wt% and 7 wt%, respectively. The optimum pH condition is 3 with TiO2 over ZSM-5, 13X-zeolites and Y-zeolites. The results showed that the degradation and mineralization efficiency of 12.5 wt%GT13X (TiO2 over 13X) after 90 min irradiation reached 57.9% and 22.0%, which was better than that of 7 wt%GTYZ (TiO2 over Y-zeolites) while much lower than that of 50 wt%GTZ (TiO2 over ZSM-5). The materials were recycled four times while the degradation was remained at a higher level.

Photocatalysis of fenoxycarb over silver-modified zeolites

Two samples of silver doped into zeolite Y were prepared and characterized. ICP and SEM-EDS analysis indicate that the AgY1 sample contains twice the amount of silver compared to the AgY2 sample. Solid state luminescence spectroscopy shows variations in the emission modes of the site-selective luminescence where various luminophores might be excited upon selecting the proper excitation energy. The selected material effectively decomposed the pesticide fenoxycarb in aqueous solution. The photodecomposition of fenoxycarb reached 80 % upon irradiation for 60 min in the presence of the AgY1 catalyst. 2-(4-Phenoxy-phenoxy)ethyl] carbamic acid (1) and 1-amine-2-(phenoxy-4-ol) ethane (2) were identified as products for both uncatalyzed solution and the catalyzed fenoxycarb with AgY2 catalyst. Whereas, compound (2) was the only product identified in the catalyzed reaction with AgY1.

In situ ultrasonic diagnostic of zeolite X crystallization with novel (hierarchical) morphology from coal fly ash

In this paper the applicability of an in situ ultrasonic diagnostic technique in understanding the formation process of zeolite X with a novel morphology was demonstrated. The complexity of the starting fly ash feedstock demands independent studies of the formation process for each type of zeolite since it is not known whether the crystallization mechanism will always follow the expected reaction pathway. The hierarchical zeolite X was noted to follow a solution phase-mediated crystallization mechanism which differs from earlier studies of the zeolite A formation process from unaged, clear solution extracted from fused fly ash. The use of the in situ ultrasonic monitoring system provided sufficient data points which enabled closer estimation of the time of transition from the nucleation to the crystal growth step. In order to evaluate the effect of temperature on the resulting in situ attenuation signal, synthesis at three higher temperatures (80, 90 and 94 °C) was investigated. It was shown, by the shift of the US-attenuation signal, that faster crystallization occurred when higher temperatures were applied. The novel hierarchical zeolite X was comprised of intergrown disc-like platelets. It was further observed that there was preferential growth of the disc-shaped platelets of zeolite X crystals in one dimension as the synthesis temperature was increased, allowing tailoring of the hierarchical morphology.

Efficient removal of toluene and benzene in gas phase by the TiO2/Y-zeolite hybrid photocatalyst

Efficient removal of toluene or benzene molecules thinly diffused in gas phase was achieved by using TiO(2)/Y-zeolite hybrid photocatalysts. TiO(2) of 10 wt% hybridized with a hydrophobic USY zeolite showed higher photocatalytic reactivity as compared to TiO(2) hybridized with hydrophilic H-Y or Na-Y zeolites. This phenomenon can be explained by the fact that the hydrophobic USY zeolite efficiently adsorbs the organic compounds and smoothly supplies them onto the TiO(2) photocatalyst surface. However, the toluene or benzene molecules, which are strongly trapped on the hydrophilic H(+) or Na(+) sites of zeolite, cannot diffuse onto the TiO(2) surfaces, resulting in lower photocatalytic reactivity. Although the adsorption capacity of the pure TiO(2) sample rapidly deteriorated, the TiO(2)/Y-zeolite hybrid system maintained a high adsorption efficiency to remove such aromatic compounds for a long period.

Ultrasound assisted, ruthenium-exchanged FAU-Y zeolite catalyzed alkylation of indoles with epoxides under solvent free conditions

Ruthenium-exchanged FAU-Y zeolite (RuY) was used as a recyclable catalyst for regioselective ring-opening of epoxides with indoles under irradiation of sonic waves. It was found that a solvent free process, under the above mentioned conditions provides good yields of the desired 3-alkylated indole derivatives.

Ultrasonic pretreatment for hydrothermal synthesis of SAPO-34 nanocrystals

Synthesis of SAPO-34 nanocrystals which has been recently considered as a challenging task was successfully performed by sonochemical method using TEAOH as structure directing agent (SDA). The products were characterized by XRD, SEM, EDX, BET and TGA. The average crystal size of the final product prepared sonochemically is 50 nm that is much smaller than that of synthesized under hydrothermal condition and the morphology of the crystals changes from uniform spherical nanoparticles to spherical aggregates of cube type SAPO-34 crystals respectively. In the case of sample synthesized sonochemically with aid of hydrothermal condition, the surface area is significantly upper than that of obtained by the conventional static hydrothermal technology with almost the same crystallinity. SAPO-34 framework synthesized by just ultrasonic treatment is unstable and a significant part of SAPO-34 nanocrystals is transformed to the dense phase of AlPO(4) structure, i.e., Cristobalite. Contrary to hydrothermal method that at least 24h of the synthesis time is required to obtain fully crystalline SAPO-34, sonochemical-assisted hydrothermal synthesis of samples leads to form fully crystalline SAPO-34 crystals taking only 1.5h. In a sonochemical process, a huge density of energy for crystallization is provided by the collapse of bubbles which formed by ultrasonic waves. The fact that small SONO-SAPO-34 crystals could be prepared by the sonochemical method suggests a high nucleation density in the early stages of synthesis and slow crystal growth after nucleation.

Effect of ultrasound on the kinetics of cation exchange in NaX zeolite

In this study, we focused on the effect of ultrasound on ion exchange kinetics to obtain the Li-, Ca- and Ce-rich NaX zeolite. The results were compared to those obtained from the traditional batch exchange method under similar conditions. Contact time and initial cation concentration (fold equivalent excess) were studied. Ultrasound enhanced the replacement of Na(+) ion with Li(+), Ca(2+) and Ce(3+) ions in the extra-framework of zeolite up to 76%, 72% and 66%, respectively. The intraparticle diffusion is the rate limiting step in the ion exchange for both exchange methods. As compared to the traditional exchange method, the ultrasonic method applied in this study was found to be very effective on the exchange amount at equilibrium.

Migrating temperature "thermo-chromatographic" pulses (TCP) initiated by radio-frequency (RF) heating

In the present study, the astonishing influence of water dosage on a purged dry packed bed of NaY zeolite in the presence of an electric field with a frequency of 13.56 MHz was investigated. The injection of a small amount of water to the inlet of the bed led to pronounced selective heating of the inlet zone by more than 150 K. Thus, water represented a very effective coupling medium for dielectric heating. The selectively heated zone then slowly moved through the whole packed bed and a water pulse finally left the zeolite. This effect correlated with a coupled water and heat flux was called thermo-chromatographic pulse (TCP) emphasizing its analogy to chromatography. The phenomenon could not be performed by using conventional (convective) or microwave heating. It was demonstrated under various conditions and explained by a new model based on own experimental results as well as data from literature. The model will be the objective of a forthcoming publication.

Effect of alcaline cations in zeolites on their dielectric properties

The effect on dielectric properties of alkaline cations Li+, Na+ and K+ incorporated in a zeolite Faujasite structure X or Y, has been investigated. Two major phenomena have been proved to occur: ionic conductivity and rotational polarization of the water molecules adsorbed. The polarizability of the cation which is directly linked to its radius, affects ionic conductivity as well as rotational polarization. Li cations are more strongly Linked to the framework than K+ and Na+ and induce a lower ionic conductivity. K+ is weakly fixed and induces a ionic conductivity even at low solvation level. At low water content, the cation nature and number mainly control the free rotation of the water molecules and affect the relaxation frequency. Close to saturation, the water molecules are mainly linked together by H bonds: the cation nature and number do not really affect the global dielectric properties anymore.

Cesium leaching from gamma-irradiated CsA and CsX zeolites

The present study discusses the effect of gamma-irradiation on Cs+-exchanged X and A zeolites. The incorporation of Cs+ ions into A and X zeolites was performed using three different cesium salts (chloride, nitrate or acetate). Cs+ ions immobilized into the vitrified zeolites by thermal treatment are located in different sites of the zeolite networks. It is found that gamma-irradiation favors cesium retention depending on the cesium precursor salt used in the cationic exchange step.

Microwave Effect in the Fast Synthesis of Microporous Materials: Which Stage Between Nucleation and Crystal Growth is Accelerated by Microwave Irradiation?

Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW-MW, MW-CE, CE-MW, and CE-CE (in the order of nucleation-crystal growth). In the case of synthesis by MW-CE or CE-MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW-MW<MW-CE approximately CE-MW<CE-CE synthesis. The fast crystal growth and small crystal size observed in the synthesis from microwave-nucleated precursor can be explained in terms of the fact that the microwave-nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.

[Uhf desorption of carbon dioxide from zeolite in physical/chemical human life support systems]

Experimental tests showed that volumetric no-contact immediate SHF heating (a resonating chamber for approx. 30 liter with a 500 W generator operating at 2450 Hz) makes possible to desorb carbon dioxide from zeolite and to extract water from silica gel within a short time. The process included air pre-dehydration with silica gel and concurrent heating of carbon dioxide and water adsorbents. Simplicity of the SHF energy lead-in is an obvious advantage in the context of intensification and flexible control of regenerative technologies offering the challenge for designing components of adaptive (self-adjusting) life support systems.