Geochemical and Physicochemical Characteristics of Clay Materials from Congo with Photocatalytic Activity on 4-Nitrophenol in Aqueous Solutions

Efficient Catalytic Degradation of Selected Toxic Dyes by Green Biosynthesized Silver Nanoparticles Using Aqueous Leaf Extract of Cestrum nocturnum L

In the present study, the catalytic degradation of selected toxic dyes (methylene blue, 4-nitrophenol, 4-nitroaniline, and congo red) using biosynthesized green silver nanoparticles (AgNPs) of Cestrum nocturnum L. was successfully performed. These AgNPs are efficiently synthesized when a reaction mixture containing 5 mL of aqueous extract (3%) and 100 mL of silver nitrate (1 mM) is exposed under sunlight for 5 min. The synthesis of AgNPs was confirmed based on the change in the color of the reaction mixture from pale yellow to dark brown, with maximum absorbance at 455 nm. Obtained NPs were characterized by different techniques, i.e., FTIR, XRD, HR-TEM, HR-SEM, SAED, XRD, EDX, AFM, and DLS. Green synthesized AgNPs were nearly mono-dispersed, smooth, spherical, and crystalline in nature. The average size of the maximum number of AgNPs was 77.28 ± 2.801 nm. The reduction of dyes using a good reducing agent (NaBH₄) was tested. A fast catalytic degradation of dyes took place within a short period of time when AgNPs were added in the reaction mixture in the presence of NaBH₄. As a final recommendation, Cestrum nocturnum aqueous leaf extract-mediated AgNPs could be effectively implemented for environmental rehabilitation because of their exceptional performance. This can be utilized in the treatment of industrial wastewater through the breakdown of hazardous dyes.

Sorbent and Photocatalytic Potentials of Local Clays for the Removal of Organic Xenobiotic: Case of Crystal Violet

Natural materials are widely used in the field of environmental remediation and are appreciated for their surface physical and chemical properties. Clay constitutes a typical example. In this work, we report the evaluation of sorbent and photocatalytic potentials of local clay of two irrigated rice field waters in the degradation of crystal violet. The structural, textural and compositional properties of the local clay were investigated by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analysis. The analysis results showed that these materials were composed mainly of quartz and kaolinite. The efficiency of these adsorbents (Y. Clay and L. Clay) to eliminate crystal violet dye from aqueous medium was examined at different initial concentrations, pH, contact time, adsorbent dose and the possible interference of inorganic salts from fertilizers. Kinetic studies showed that the adsorption process was well described by the pseudo-second order model and the equilibrium modelling results fitted adequately to the Freundlich model. The maximum amount of uptake capacity achieved at pH 2.0 was 18.40 (mg·g−1) and 20.40 (mg·g−1), respectively, for Y. Clay and L. Clay. The evaluation of the photocatalytic potential showed that the raw clay samples do not show photocatalytic activities during the 30 min of exposure to UV light. On the other hand, their photocatalytic potential is manifested when loaded with titanium dioxide (TiO2). Clays coupled with TiO2 under UV light showed an improvement in the degradation of the crystal violet dye by 15%. The synergistic effects between the high photocatalytic activity of TiO2 and the strong adsorption capacity of clays can be one promising technique for in situ remediation of contaminated soaked rice field.