Cenk Gümeci

Tailoring cobalt doped zinc oxide nanocrystals with high capacitance activity: factors affecting structure and surface morphology

Highly crystalline zinc cobaltite (ZnCo2O4) nanocrystals were successfully synthesized through an epoxide driven, sol–gel method using Zn(NO3)·6H2O and CoCl2·6H2O as precursors. The crystal phase, morphology, specific surface areas, porosity, and capacitance activity of the prepared materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), gas sorption techniques, and cyclic voltammetry, respectively. Results reveal that the synthesized nanocrystals are ∼4 nm in diameter. Electron microscopy studies illustrate significant changes brought on by varying the solvent and epoxide. Gas sorption analyses detail high specific surface areas (>200 m2 g−1) and porosities of the as prepared and annealed samples. Cyclic voltammetry experiments show that these zinc cobaltite nanocrystals have exceptional capacitance (∼700 Fg−1) and excellent cycle durability making them an excellent electrode material for supercapacitors.

Aerogel nanocomposites of ZnO–SnO2 as efficient photocatalysts for the degradation of rhodamine B

For the first time, aerogel nanocomposites containing ZnO and SnO2 were successfully prepared through a facile, sol–gel method without the use of a template or supporting matrix. These nanoparticles exhibit high potential for application as a photocatalyst for wastewater remediation.

Synthesis of PtCu3 bimetallic nanoparticles as oxygen reduction catalysts via a sonochemical method

We report a sonochemical synthesis of homogeneous PtCu3 nanoparticles. Ultra-sonication during reduction in a non-aqueous solution is compared with synthesis under identical conditions in the absence of sonication (to form a Rieke alloy). X-ray diffraction (XRD) measurements suggest that the sonochemical procedure produces an amorphous, uniformly alloyed nanomaterial having a composition consistent with the PtCu3 stoichiometry, while the Rieke alloy is polyphasic. Energy dispersive X-ray (EDX) analysis indicates that the composition of the sonochemically prepared PtCu3 material reflects the nominal values. EDX and XRD analyses also provide evidence for the inhibition of oxide formation on sonochemically prepared PtCu3 nanoparticles, but oxide is readily apparent in the Rieke alloy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the sonochemically prepared sample show particles with diameters of ∼2 to 3 nm. As-synthesized PtCu3 particles were activated using an electrochemical de-alloying procedure to prepare an oxygen reduction electrocatalyst. The de-alloyed catalyst consisted of a Pt-rich surface layer, over a core indicated as having a Pt3Cu composition. The de-alloyed sample exhibited ∼3 to 6 fold enhancements in oxygen reduction reaction (ORR) activity when compared to commercial Pt catalysts.

Preparation–Morphology–Performance Relationships in Cobalt Aerogels as Supercapacitors

The ability to direct the morphology of cobalt sol-gel materials by using the simple synthetic parameters in epoxide-driven polycondensations has been dramatically demonstrated, and the influence of such morphological differences upon the supercapacity of the materials has been explored. Precursor salt, epoxide, and solvent all influence the speed of the sol-gel transition and the size and shape of the features observed in the as-prepared materials, thereby leading to highly varied microstructures including spheres, sponge-like networks, and plate assemblies of varied size. These morphological features of the as-prepared cobalt aerogels were observed for the first time by high resolution scanning electron microscopy (HRSEM). The as-prepared aerogel materials were identified by powder X-ray diffraction and thermogravimetry as weakly crystalline or amorphous cobalt basic salts with the general formula Co(OH)(2-n)X(n) where X = Cl or NO3 according to the precursor salt used in the synthesis. For all samples, the morphology was preserved through mild calcining to afford spinel phase Co3O4 in a variety of microstructures. Wide-ranging specific surface areas were determined for the as-prepared and calcined phases by physisorption analysis in agreement with the morphologies observed by HRSEM. The Co3O4 aerogels were evaluated for their supercapacitive performance by cyclic voltammetry. The various specimens exhibit capacitances ranging from 110 to 550 F g(-1) depending upon the attributes of the particular aerogel material, and the best specimen was found to have good cycle stability. These results highlight the epoxide-driven sol-gel condensation as a versatile preparative route that provides wide scope in materials properties and enables the analysis of structure-performance relationships in metal oxide materials.