The paper involves the heterogeneous photocatalytic degradation of Rhodamine B dye (RhB) employing ZnO and ZnO/CdSe nanocomposites as photocatalysts which was synthesized via chemical bath deposition (CBD) method. Nanocomposite CdSe-ZnO powders have been synthesized by varying CdSe/ZnO molar ratios. The structural, optical, morphological, and topological characteristics of as synthesized materials were investigated using the appropriate characterization instrument such as X-ray diffractometer (XRD), diffuse reflectance spectrophotometer (DRS), atomic force microscope (AFM) and field emission scanning electron microscope (FE-SEM). It seems that the growth of CdSe particles onto ZnO particles in a core-shell like structure. The photocatalytic performance of ZnO/CdSe nanocomposite has been investigated under affecting factors such as catalyst dosage, RhB concentration and initial pH of RhB solution. The photocatalytic degradation reactions were carried out by exposing the aqueous suspension of the dye and ZnO/CdSe system with visible light. The residual concentration of RhB dye was measured using a UV-visible spectrophotometer at maximum wavelength of dye (λmax 554 nm). The decolorization process was found to follow pseudo first-order kinetics which is well expressed by the represented by the Langmuir-Hinshelwood (L-H) kinetic model. The maximum decolonization efficiency of 99% was achieved within 180 min at optimum conditions, dye conc. 10 mg/L, pH 10, CdSe (10%)-ZnO dose 1.5 g/L. The ROS studies indicate that hydroxyl radicals and holes are the predominant reactive species within the same step. Furthermore, CdSe(10%)-ZnO shows a good stability after reuse for 15 successive cycles and hence it expected to be promising in polluted water treatment.
In this study, the carbon nanospheres were synthesized by burning diesel and then treated with hydrogen peroxide (H2O2). The results showed that H2O2 - carbon nanospheres has a higher surface area than carbon nanospheres and therefore it was chosen as an adsorbent surface to remove the Rose Bengal dye from aqueous solutions. The prepared carbon nanospheres were examined by FTIR, XRD, SEM, AFM, TGA, Raman spectroscopy, BET and EDX. The FTIR study reveals the presence of hydroxyl and carboxyl stretching vibration and weak peaks belong to CH3, CH2 and C=C. Results obtained by Raman and XRD analysis are in good agreement thereby indicating the amorphous structure of the carbon nanospheres. Also, SEM images confirm the presence of soot materials as spherical and semispherical nanoparticles with diameter in the range (31-78 nm). Surface roughness calculated from AFM data provided evidence that spiky appearance on both carbon surfaces. TGA data indicate that both carbon samples are thermally unstable. BET and BJH results indicate that the treated sample possesses the highest surface area and mean pore diameter. EDX analysis indicated the presence of pure carbon nanosphere (treated sample) without any contamination. Also, the adsorptive removal of Rose Bengal on synthesized carbon nanospheres was studied. The isotherm adsorption results were found to be described fitted by the Freundlich rather than the Langmuir and Temkin models. Furthermore, the kinetics of dye adsorption were applied better by the pseudo-second-order model.
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