Preparation, Characterization, and Application of Metal Oxide-Doped Zeolitic Imidazolate Framework.

Metal-organic frameworks (MOFs) attract the attention of researchers due to their unique properties, such as high surface area, porosity, and stability. Therefore, in this study, the synthesis of zeolitic imidazole frameworks (ZIF-8), a subclass of MOFs, and copper oxide (Cu2O) and manganese oxide (MnO2) containing ZIF-8 was carried out by a mixing method with methanol. The characterization results show that the polyhedral structure of ZIF-8 was prepared with a surface area of 2088 m2/g and a crystallite size of 43.48 nm. Then, each and mixture of two metal oxides were introduced into the ZIF-8 crystal structure. It was found that the surface area and pore volumes of all metal/ZIF-8 samples decreased with metal loading, depending on the type and ratio of metal oxides. The ZIF-8 containing 4.0 wt % Cu2O and 1.0 wt % MnO2 had the highest surface area (2084 m2/g), which was closest to that of ZIF-8. The polyhedral structure was maintained by the addition of both metal oxides, and the crystal size of the material decreased with the loading of MnO2 to the ZIF-8 structure. All of the synthesized samples were analyzed in supercapacitor applications and a relatively higher value of specific capacitance was obtained for Cu-Mn/ZIF-8 due to higher surface area and improved conductivity. In addition to supercapacitor applications, the properties of metal/ZIF-8 are also promising for applications such as catalysts, membranes, and gas storage.

Structural, dielectric and transport properties of NaxFe1/2Mn1/2O2 (x = 1 and 2/3).

NaxFe1/2Mn1/2O2 (x = 1 and 2/3) layered oxides were prepared by an improved solid-state synthesis method. The XRD analysis confirmed the high purity of these samples. The Rietveld refinement of the crystalline structure illustrated that the prepared materials crystallize in a hexagonal system in the R3̄m space group with the P3 structure for x = 1 and in a rhombohedral system with the P63/mmc space group and P2 structure type for x = 2/3. The vibrational study undertaken using IR and Raman spectroscopy techniques yielded the existence of an MO6 group. Their dielectric properties were determined in frequency range 0.1-107 Hz for a temperature range 333-453 K. The permittivity results indicated the presence of two types of polarization, namely dipolar polarization and space charge polarization. The frequency dependence of the conductivity was interpreted in terms of Jonscher's law. The DC conductivity followed the Arrhenius laws either at low or at high temperatures. The temperature dependence of the power law exponent which corresponds to the grain (s2) suggested that the conduction of the P3-NaFe1/2Mn1/2O2 compound is ascribed to the CBH model, while P2-Na2/3Fe1/2Mn1/2O2 can be attributed to the OLPT model.

Investigation of structural, morphological, and electrical conductivity study for understanding transport mechanisms of perovskite CH3NH3HgCl3.

Along with morphological and structural studies, the temperature and frequency dependence of the electrical and dielectric properties of the CH3NH3HgCl3 (MATM) compound was investigated and analyzed. SEM/EDS and XRPD analyses proved the purity, composition, and perovskite structure of the MATM. DSC analysis reveals the existence of an order-disorder phase transition of a first-order type at about 342 ± 2 K and 320 ± 1 K (heating and cooling, respectively), attributed to the disorder of [CH3NH3]+ ions. The overall results of the electrical study provide arguments for the ferroelectric nature of this compound and aim to broaden the current knowledge on the thermally activated conduction mechanisms of the studied compound via impedance spectroscopy. The electrical investigations have shown the dominant transport mechanisms in different frequency and temperature ranges, proposing the CBH model in the ferroelectric phase and the NSPT model in the paraelectric phase. The temperature dependence of the dielectric study reveals the classic ferroelectric nature of the MATM. As for the frequency dependence, it correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes.

Characterization of persimmon fruit peel and its biochar for removal of methylene blue from aqueous solutions: thermodynamic, kinetic and isotherm studies.

The persimmon fruit peel (PFP) and its biochar (PFP-P) were evaluated for removal of methylene blue (MB) from aqueous solutions and characterized in detail. The pyrolysis of the PFP improved carbon content, surface area, and surface electronegativity of the biochar produced. The effect of initial solution pH, initial MB concentration, contact time, and temperature on the biosorption efficiency of MB on the PFP was investigated through the biosorption experiments in a batch system. The PFP showed higher biosorption removal efficiency than PFP-P due to the existence of hydroxyl and carboxyl functional groups. The maximum biosorption capacity of the PFP was found using 2 g/L of the adsorbent, at a contact time of 180 min and pH of 7. The adsorption kinetics and equilibrium isotherms were well represented by the pseudo-second-order model and the Langmuir model, respectively. The maximum biosorption capacity obtained from the Langmuir isotherm model was 303 mg g-1. Also, the PFP showed an efficient removal efficiency for removal of MB in tap water, seawater, and river water. The high MB biosorption capacity of PFP can be a promising alternative for cationic dye removal at neutral pH.

Effect of alkali-treatment on the characteristics of natural zeolites with different compositions.

A series of natural zeolites with different compositions were modified by post-synthesis modification with sodium hydroxide (NaOH) solution. Natural and modified zeolites were characterized by XRD, SEM, nitrogen adsorption, FTIR, zeta potential and temperature programmed desorption of ammonia (NH3-TPD). The adsorption capacities of these samples were evaluated by the adsorption of manganese from aqueous solution. The treatment with NaOH led to a decrease in the surface area and microporosity of all natural zeolites as well as partly damage of the zeolite structure depending on zeolite composition. In addition, the amount of weak, medium and strong acid sites in the zeolites was changed significantly by NaOH treatment depending on zeolite composition. The NaOH treatment resulted in a four-fold improvement in adsorption capacity of natural zeolite originated from Bigadic and a twofold decrease in that of the natural zeolite originated from Manisa-Gordes. Although the improved adsorption capacity might be mainly due to modification of porosity in the zeolites and formation of hydroxysodalite, the reduced adsorption capacity of the zeolite might be mainly due to a significant deformation of the zeolite structure. The pseudo-second-order kinetic model for the adsorption of manganese on all natural and modified zeolites fits well.

Role of Modification of Natural Zeolite in Removal of Arsenic from Aqueous Solutions.

The adsorption of arsenic from aqueous solution onto natural and modified zeolites was investigated. The natural zeolites were modified by ion-exchange (NH4NO3) and addition of aluminum (Al2(SO4)3). The natural and modified zeolites were characterized by XRF, XRD, N2 sorption, FTIR, NH3-TPD, zeta potential and SEM. Ion-exchange with NH4+ of NZ results in the significant exchange of most cations and an increase in surface area and pore volume of samples as well as surface acidity. While the introduction of aluminum into the zeolite increased its As (V) removal amount, it decreased its As (III) removal. Ion-exchange with NH4+ of the natural zeolite increased significantly its As(III) and As(V) adsorption capacity. The adsorption of both As(III) and As(V) with natural and modified zeolites obeys pseudo second order kinetics. The Langmuir isotherm model for all adsorbents was best fitted to the isotherm data obtained. The highest adsorption capacity for As(III) and As(V) was obtained onto the zeolite modified with ammonia and their calculated qm values are 28.7 mg/g and 36.6 mg/g, respectively. The calculated thermodynamic parameters indicated that the adsorption process was spontaneous and favorable.

Synthesis and characterization of hybrid iron oxide silicates for selective removal of arsenic oxyanions from contaminated water.

A series of hybrid silicates containing iron oxides was synthesized by adding various amounts of iron into silica on the basis of using post precipitation mechanism from aqueous solutions in order to form hydrated iron oxide species (HFO). The obtained materials were characterized by XRD, SEM, TEM, FTIR, Zeta potential and low temperature nitrogen sorption. XRD analysis confirmed that HFO-Si was amorphous and iron oxide crystals in the silica cannot be detected due to the lower size of HFO, which is the probability of its occupied interstitial positions in the silicate matrix. However, TEM image showed the presence of nano-sized HFO located inside the silicate matrix. The adsorption properties and selective efficiency of the synthesized materials were examined with respect to the removal of As(V) and As(III) species from contaminated water under different experimental conditions and in the presence of competing anions. Increasing iron loading enhanced the arsenic adsorption capacity of HFO-Si; the maximum level of arsenic removal was 300mg As/g HFO-Si after 5 successive loads.

The effect of various treatment conditions on natural zeolites: ion exchange, acidic, thermal and steam treatments.

Two different natural zeolites having different phase compositions were obtained from different regions of Turkey and modified by ion-exchange (0.5M NH(4)NO(3)) and acid leaching using 1M HCl. The natural and modified samples were treated at low temperature (LT), high temperature (HT) and steam (ST) conditions and characterised by XRF, XRD, BET, FTIR, DR-UV-Vis, NH(3)-TPD and TGA. Ion-exchange with NH(4)(+) of natural zeolites results in the exchange of the Na(+) and Ca(2+) cations and the partial exchange of the Fe(3+) and Mg(2+) cations. However, steam and acidic treatments cause significant dealumination and decationisation, as well as loss of crystalline, sintering of phases and the formation of amorphous material. The presence of mordenite and quartz phases in the natural zeolites increases the stability towards acid treatment, whereas the structure of clinoptilolite-rich zeolites is mostly maintained after high temperature and steam treatments. The natural and modified zeolites treated at high temperature and in steam were found to be less stable compared with synthetic zeolites, resulting in a loss of crystallinity, a decrease in the surface area and pore volume, a decrease in the surface acidity as well as dealumination, and decationisation.

Heavy metal removal from aqueous solution by Pseudevernia furfuracea (L.) Zopf.

The present study was carried out in a batch system using a lichen (Pseudevernia furfuracea (L.) Zopf) for the sorption of nickel(II) and copper(II) ions from water. Particularly, the effect of pH, contact time and temperature were considered. Pseudevernia furfuracea exhibited nickel(II) and copper(II) uptake of 49.87 and 60.83 mg/g at an initial pH of 4 and 5-6 at 35 degrees C respectively. Both the Freundlich and Langmuir adsorption models were suitable for describing the biosorption of nickel(II) and copper(II) by the biosorbent. Biosorption showed pseudo first order rate kinetics for nickel and copper ions. Using the equilibrium constant values obtained at 25 and 35 degrees C, the thermodynamics properties of the biosorption (deltaG degrees, deltaH degrees and deltaS degrees) were determined. The biosorption of nickel(II) and copper(II) onto Pseudevernia furfuracea was found to be endothermic.