Photocatalytic oxidation of cationic dyes in single and binary solutions in presence of Zn-Cd oxides obtained from calcined LDH

Adsorption of Cd (II) ions and methyl violet dye by using an agar-graphene oxide nano-biocomposite

In this work, an agar-graphene oxide hydrogel was prepared to adsorb Cd (II) and Methyl Violet (MV) from water. The hydrogel was synthesised and characterised through SEM and EDS. Kinetic, equilibrium and regeneration studies were carried out, in which Langmuir, Freundlich and Sips isotherm models were fitted to the equilibrium experimental data; and regarding the kinetics, studies were conducted by modelling experimental data considering both empirical and phenomenological models. SEM and EDS have shown the composite present a 3D-disordered porous microstructure and that it is mainly constituted of C and O. Sips model fitted well to Cd (II) (R2 = 0.968 and χ2 =  0.176) and MV (R2 = 0.993 and χ2 =  0.783). The qmax values for MV and Cd (II) were 76.65 and 11.70 mg.g-1, respectively. Pseudo-order models satisfactorily described Cd (II) and MV adsorption kinetics with R2 > 0.90. Regeneration experiments revealed an outstanding reuse capacity of the adsorbent after three cycles of adsorption-desorption for both Cd (II) and MV. This study evidences the possibility of a feasible adsorbent for Cd (II) and MV removal from water for successive cycles of use.

Ultrafast photodegradation of textile industry dyes using efficient sulfide based ternary nanocomposites

We developed novel zinc-cadmium-bismuth sulfide (Zn-Cd-Bi₂S₃) and Zn-Cd-SnS nanocomposites to fabricate a heterojunction by an easy chemical technique to improve photocatalytic degradation of textile dye. Crystalline size and lattice parameter are analyzed using X-ray diffraction (XRD) spectrometer. The obtained strong diffraction peaks with various diffraction planes confirm the fabrication of a high crystal quality nanocomposite as well as the identification of its mixed crystal structure. The morphological information is studied using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). Due to its higher surface energy, the as-prepared nanocomposite displayed agglomeration by adjoining to tiny particles. The roughness of surface is studied by atomic force microscopy (AFM). Fourier transform-infrared spectroscopy (FT-IR) used to study about presence of organic functional groups on the surface of nanocomposite. Using UV-Visible and photoluminescence spectra, the impact of shifting the positions of Sn and Bi ions on the optical characteristics is investigated. Thermal property of the nanocomposite is studied by thermogravimetric-differential thermal analysis (TG-DTA) at air atmosphere. We examine and compared the photocatalytic activity of Zn-Cd-Bi₂S₃ and Zn-Cd-SnS nanocomposites for the crystal violet (CV) dye. Under the sun light irradiation Zn-Cd-Bi₂S₃ nanocomposite demonstrated a highest percentage of degradation (88.5%) within a short period (120 min). The obtained photocatalytic results indicate that the active radicals •O_2-, h⁺, and •OH- are favourable for the photocatalytic reaction. A possible photocatalytic mechanism for the dye degradation for the photocatalyst is proposed. Due to the narrow band gap, wide range of incident light captured by the heterostructure nanocomposite and the photogenerated electrons and holes is effectively separated in the Zn-Cd-Bi₂S₃.