Silver nanoparticles impregnated zeolites derived from coal fly ash : effect of the silver loading on adsorption of mercury (II)

Removal of mercury (II) from aqueous phase is of utmost importance, as it is highly toxic and hazardous to the environment and human health. A promising method for the removal of mercury (II) ions from aqueous solutions is by using adsorbents derived from coal fly ash (CFA), such as synthetic zeolites. In this work we present the hydrothermal production of synthetic zeolites from CFA followed by a modification for impregnation of silver nanoparticles, in solid concentrations from 0.15 to 4.71 wt.%. All produced zeolites and parent materials are characterized by XRD, XRF, BET and PSA to obtain morphological and microstructural data. Moreover, mercury (II) ions removal from aqueous solutions with initial concentration of 10 ppm is studied. According to results, zeolites and Ag-nanocomposites demonstrate much higher removal than parent CFA (up to 98%). In addition to this, we could observe a distinct adsorption behavior depending on the loading of Ag NPs in nanocomposites. A possible removal mechanism for both zeolites and Ag-nanocomposites is discussed

Optimized production of coal fly ash derived synthetic zeolites for mercury removal from wastewater

Coal fly ash (CFA) derived synthetic zeolites have become popular with recent advances and its ever-expanding range of applications, particularly as an adsorbent for water and gas purification and as a binder or additive in the construction industry and agriculture. Among these applications, perpetual interest has been in utilization of CFA derived synthetic zeolites for removal of heavy metals from wastewater. We herein focus on utilization of locally available CFA for efficient adsorption of mercury from wastewater. To this end, experimental conditions were investigated so that to produce synthetic zeolites from Kazakhstani CFAs with conversion into zeolite up to 78%, which has remarkably high magnetite content. In particular, the effect of synthesis reaction temperature, reaction time, and loading of adsorbent were systematically investigated and optimized. All produced synthetic zeolites and the respective CFAs were characterized using XRD, XRF, PSA and porosimetric instruments to obtain microstructural and mineralogical data. Furthermore, the synthesized zeolites were studied for the removal of mercury from aqueous solutions. A comparison of removal eficiency and its relationship to the physical and chemical properties of the synthetic zeolites were analyzed and interpreted

Synthetic coal fly ash-derived zeolites doped with silver nanoparticles for mercury (II) removal from water

Coal fly ash-derived zeolites have attracted considerable interest in the last decade due to their use in several environmental applications such as the removal of dyes and heavy metals from aqueous solutions. In this work, coal fly ash-derived zeolites and silver nanoparticles-impregnated zeolites (nanocomposites) were synthesized and characterized by TEM/EDX, SEM/EDX, XRD, XRF, porosimetry (BET), particle size analysis (PSA) and zeta potential measurements. The synthesized materials were used for the removal of Hg2+ from aqueous solutions. The results demonstrated that nanocomposites can remove 99% of Hg2+, up to 10% and 90% higher than the removal achieved by the zeolite and the parent fly ash, respectively. Leaching studies further demonstrated the superiority of the nanocomposite over the parent materials. The Hg2+ removal mechanism is complex, involving adsorption, surface precipitation and amalgamation

Mineralogical, microstructural and thermal characterization of coal fly ash produced from Kazakhstani power plants

Coal fly ash (CFA) is a waste by-product of coal combustion. Kazakhstan has vast coal deposits and is major consumer of coal and hence produces huge amounts of CFA annually. The government aims to recycle and effectively utilize this waste by-product. Thus, a detailed study of the physical and chemical properties of material is required as the data available in literature is either outdated or not applicable for recently produced CFA samples. The full mineralogical, microstructural and thermal characterization of three types of coal fly ash (CFA) produced in two large Kazakhstani power plants is reported in this work. The properties of CFAs were compared between samples as well as with published values

Hydrothermal synthesis of zeolite production from coal fly ash : a heuristic approach and its optimization for system identification of conversion

Commercialization of synthetic zeolites has given considerable impetus to optimization of its production routes. The preferred production route involves hydrothermal treatment of coal fly ash in a strong alkali solution. The process involves several parameters, such as reaction temperature, time, the concentration and amount of alkali solution, and silica content in the fly ash, all of which strongly and non-monotonically affect the conversion. We herein perform several experiments with the Kazakhstani fly ash, and obtained a highest conversion of zeolites of 78% using 3 M NaOH at 110 °C. Further, we propose a conversion model using zero-order Takagi-Sugeno fuzzy system to analyze the effect of individual process parameters on conversion, and thereby, the reaction mechanism(s) of zeolite formation. The model is designed and developed, using the data, both from literature and our experiments on Kazakhstani fly ash. The obtained results clearly illustrate that the model accurately predict the conversion percentage of zeolite for a given set of reaction parameters. The model is further optimized to provide accurate inferences and an average deviation between the model predictions and experimental values for zeolite yield is observed to be less than 5%

Synthetic sodalite doped with silver nanoparticles : characterization and mercury (II) removal from aqueous solutions

In this work, a novel silver nanoparticles-doped synthetic sodalitic composite was synthesized and characterized using advanced characterization methods, namely TEM-EDS, XRD, SEM, XRF, BET, zeta potential, and particle size analysis. The synthesized nanocomposite was used for the removal of Hg2+ from 10 ppm aqueous solutions of initial pH equal to 2. The results showed that the sodalitic nanocomposites removed up to 98.65% of Hg2+, which is ∼16% and 70% higher than the removal achieved by sodalite and parent coal fly ash, respectively. The findings revealed that the Hg2+ removal mechanism is a multifaceted mechanism that predominantly involves adsorption, precipitation and Hg-Ag amalgamation. The study of the anions effect (Cl−, NO3−, C2H3O2−, and SO42−) indicated that the Hg2+ uptake is comparatively higher when Cl− anions co-exist with Hg2+ in the solution

Synthesis of trans-porphyrin dimers for nonlinear optics

Following the development of the idea of octupolar molecules as nonlinear optical materials a variety of compounds have been reported. Trans-porphyrins have a great potential to self-order into octupolar symmetry. Nonlinear optical properties can be tuned by using strong donor-acceptor groups in porphyrins as well as extention of conjugation. Here we report the syntheses of trans-A2D2-porphyrins and their dimerization into cubic octupoles by lanthanides and organic bidentate ligands. Bulky groups are employed to induce non-centrosymmetric eclipsed or staggered conformations. Effect of donor acceptor groups, dimerization conditions and crystal packing of dimers are studied.Research Grant of Ministry of Education and Science of Kazakhsta

Design and synthesis of organic nonlinear optical materials

Following the development of the idea of octupolar molecules as nonlinear optical materials a variety of compounds have been reported. Trans-porphyrins have a great potential to selforder into octupolar symmetry. Nonlinear optical properties can be tuned by using strong donor-acceptor groups in porphyrins as well as extension of conjugation. Here we report the syntheses of trans-A2D2- porphyrins and their dimerization into cubic octupoles by organic bidentate ligands

Design and synthesis of organic nonlinear optical materials

Following the development of the idea of octupolar molecules as nonlinear optical materials a variety of compounds have been reported. Trans-porphyrins have a great potential to selforder into octupolar symmetry. Nonlinear optical properties can be tuned by using strong donor-acceptor groups in porphyrins as well as extension of conjugation. Here we report the syntheses of trans-A2D2- porphyrins and their dimerization into cubic octupoles by organic bidentate ligands

Mercury reduction and chemisorption on the surface of synthetic zeolite silver nanocomposites : equilibrium studies and mechanisms

This work presents the utilization of a coal power plants waste, namely coal fly ash for the synthesis of zeolites and zeolite silver nanocomposites for the removal of Hg2+ from water. Equilibrium data are derived for all materials for mercury concentration range of 10–500 mg/L and models are applied. The removal mechanisms are discussed in detail and complemented by XRD, XRF, SEM-EDS, and TEM characterizations and water phase mercury speciation modeling. According to findings, the adsorption capacity of zeolites is about 4 mg/g and increased by almost 5 times after the modification with silver nanoparticles to 20.5–22.3 mg/g. Langmuir equilibrium model fits well the experimental data of the nanocomposites indicating monolayer adsorption process. The mechanism is complex, involving Hg2+ reduction to Hg+ and possibly Hg0 followed by formation of calomel and amalgams on the surface of the nanocomposites. The mercury reduction is accompanied by Ag0 oxidation to Ag+ and subsequent formation of silver chloride