Accelerating the Crystallization of Zeolite SSZ-13 with Polyamines

Tailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ-13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in selected cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ-13 formation, leading to a 4-fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light-scattering techniques demonstrate these conditions lead to polymer-induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from the growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ-13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis.

The role of mixed alkali metal cations on the formation of nanosized CHA zeolite from colloidal precursor suspension

A clear understanding of the crystal formation pathways of zeolites remains one of the most challenging issues to date. Here we investigate the synthesis of nanosized chabazite (CHA) zeolites using organic template-free colloidal suspensions by varying the time of aging at room temperature and the time of hydrothermal treatment at 90 °C. The role of mixed alkali metal cations (Na⁺, K⁺, Cs⁺) on the formation of CHA in the colloidal suspensions was studied. Increasing the aging time of the precursor colloidal suspension from 4 to 17 days resulted in faster crystallization of CHA nanocrystals (3 h instead of 7 h at 90 °C) to afford significantly smaller particles (60 nm vs 600 nm). During the crystallization a considerable change in the content of inorganic cations in the recovered solid material was observed to coincide with the formation of the CHA nanocrystals. The Na⁺ cations were found to direct the formation of condensed and pre-shaped aluminosilicate particles in the colloidal precursor suspensions, while K⁺ cations facilitated the formation of secondary building units (SBUs) of the CHA type framework structure such as d6r and cha cages, and the Cs⁺ cations promoted the long-range crystalline order facilitating the crystallization of stable zeolite nanocrystals.

Ammonium and potassium removal from undiluted and diluted hydrolyzed urine using natural zeolites

There is limited research comparing nutrient removal in concentrated and dilute waste streams. Accordingly, the goal of this research was to study the effect of dilution on ammonium and potassium removal from real hydrolyzed urine using natural zeolites. The performance of two natural zeolites, clinoptilolite and chabazite, was studied and compared using batch equilibrium experiments at four dilution levels defined as urine volume divided by total solution volume (expressed as a percent): 100%, 10%, 1% and 0.1%. The adsorption behavior of other exchangeable ions, namely sodium, calcium, and magnesium, in clinoptilolite and chabazite was studied to improve the understanding of ion exchange stoichiometry. Ammonium and potassium removals were highest in undiluted urine samples treated with clinoptilolite or chabazite. This is a key finding as it illustrates the benefit of collecting undiluted urine via source separation. High removal of ammonium and potassium by clinoptilolite and chabazite was also achieved in 10% urine solutions, which are representative of water-efficient flush systems and show that nutrient recovery is possible for diluted urine as well. Chabazite showed higher ammonium and much higher potassium removal than clinoptilolite. Finally, the results showed that clinoptilolite and chabazite demonstrated stoichiometric exchange between ammonium and potassium in urine solutions with mobile cations in the zeolites.

The characterization and methane adsorption of Ag-, Cu-, Fe-, and H-exchanged chabazite-rich tuff from Turkey

In this study, a chabazite-rich tuff (CHA) from the Bala deposit of Ankara region (Turkey) and its modified forms (CuCHA, AgCHA, FeCHA, and HCHA samples) were investigated at 273 and 298 K using volumetric apparatus up to 100 kPa. The chabazite samples were characterized by using thermal analysis (TG-DTG-DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with detector X-ray energy dispersive (SEM-EDX), Fourier transform infrared (FT-IR), and N₂ adsorption methods. It was found that natural chabazite is composed of predominantly chabazite with small amounts of clinoptilolite and erionite. XRD showed that there are major structural changes to Fe- and H-exchanged chabazite samples. Capacity of chabazites for CH₄ ranged from 0.168 and 1.341 mmol/g. Among all the modified forms, it was observed that Ag form of chabazite zeolite had the greatest methane adsorption capacity at both temperatures.

Sorption of benzene derivatives onto a humic acid-zeolitic tuff adduct

The sorption of some benzene derivatives: o-xylene, toluene, phenol, benzyl alcohol, resorcinol and hydroquinone onto a zeolitic tuff-humic acid adduct (PCT-ImHA) was analysed by batch technique at 25 °C and neutral pH. PCT-ImHA was prepared by binding leonardite-extracted humic acids (HA) to a zeolitic tuff sample rich in phillipsite and chabazite and enriched with Ca²⁺ by cation exchange (Ca-PCT). The HA calcium salts were gently mixed with wet Ca-PCT; then, the mixture was heated at 330 °C for 1.5 h. An adduct with almost 2% of HA was obtained. The experimental data were well fitted by the Langmuir adsorption isotherm and showed that saturation capacity (q_Max) increased with the octanol-water repartition coefficient (K_O-W). The comparison with previous data on sorption onto immobilised HA highlights that q_Max values for PCT-ImHA are far higher than the sum of the contributions of the two separate components.

Novel application of nanozeolite for radioactive cesium removal from high-salt wastewater

Finding a striking peculiarity of nanomaterials and evaluating its feasibility for practical use are interesting topics of research. We investigated the application of nanozeolite's outstanding reactivity for a rapid and effective method for radioactive cesium removal in the wastewater generated from nuclear power plant accident, as a new concept. Extremely fast removal of cesium, even without stirring, was achieved by the nanozeolite at efficiencies never observed with bulk materials. The nanozeolite reached an adsorption equilibrium state within 1 min. Cesium adsorption by nanozeolite was demonstrated at reaction rates of orders of magnitude higher than that of larger zeolite phases. This observation was strongly supported by the positive correlation between the rate constant ratio (k2,bulk/k2,nano) and the initial Cs concentrations with a correlation coefficient (R(2)) of 0.99. A potential drawback of a nanoadsorbent is the difficulty of particle settling and separation because of its high dispersivity in solution. However, our results also demonstrated that the nanozeolite could be easily precipitated from the high-salt solution with ferric flocculant. The flocculation index reached a steady state within 10 min. A series of our experimental results met the goal of rapid processing in the case of emergency by applying the well-suited nanozeolite adsorption and flocculation.