Hydrothermal synthesis of hydroxyapatite-reduced graphene oxide (1D-2D) hybrids with enhanced selective adsorption properties for methyl orange and hexavalent chromium from aqueous solutions.

The presence of organic dye molecules and heavy metal ions in water causes ecological and public health problems. Therefore, remediation of water/wastewater contaminated with organic dye molecules and toxic metal ions is of importance. Herein, a reduced graphene oxide (RGO)-hydroxyapatite (Hat) (1D-2D) hybrid composite was fabricated through a hydrothermal process and applied for the adsorption of methyl orange (MO) and hexavalent chromium (Cr(VI)) from water. The as-fabricated RGO-Hat hybrids were characterized using FTIR, XRD, HR-TEM, SEM, XPS, EDAX, and TGA-DSC analytical techniques. The influencing parameters of adsorption performance, namely solution pH, contact time, and co-interfering ions, were explored to obtain the maximum adsorption capacity of contaminants from the solid-liquid interface. Batch studies revealed that MO and Cr(VI) adsorption followed the pseudo-second-order kinetic and the Langmuir isotherm models. The adsorption capacity was 49.14 and 45.24 mg g-1 for MO and Cr(VI), respectively. The adsorption of such ions over RGO-Hat hybrids was mainly driven by several uptake mechanisms viz, electrostatic force of attraction, π-π interactions, and hydrogen bonding. Thus, this study demonstrated that the RGO-Hat hybrid is a potential candidate for the treatment of MO and Cr(VI) from water.

Magnetic kaolinite immobilized chitosan beads for the removal of Pb(II) and Cd(II) ions from an aqueous environment.

In recent decades, magnetic bead material has attracted considerable attention in water and wastewater purification. In this study, the potential of magnetic kaolinite immobilized in chitosan beads (MKa@CB) to remove Pb(II) and Cd(II) ions from an aqueous environment has been successfully investigated. The addition of magnetic kaolinite generates more active sites, whereas that of chitosan enhances the stability of synthesized bead materials, which enable them to effectively interact with the targeted contaminants. Various factors including agitation time, solution pH, and competitive ions were examined to optimize the removal efficiency of the MKa@CB. The adsorption kinetics and isotherm studies indicated that the adsorption fitted well to the pseudo-second-order kinetic model as well as to the Langmuir isotherm. The prepared adsorbent could be reused up to four cycles without any significant adsorption capacity loss. Thus, the synthesized MKa@4%CB can be a promising adsorbent in effectively removing Pb(II) and Cd(II) from water.

Enhanced photocatalytic response of ZnO embedded chitosan/ß-cyclodextrin towards the detoxification of Cr(VI) under visible light.

The present work focused on the assessment of heterogenous photocatalytic efficacy of ZnO@CS-ß-CD towards the degradation of hexavalent chromium under visible light illumination. The prepared ZnO@CS-ß-CD was extensively characterized using XRD, FTIR, SEM, EDX with mapping, TGA, DSC and UV/vis DRS techniques and the photoreduction of Cr(VI) to Cr(III) was confirmed by X-ray photoelectron spectroscopy. The DRS results revealed that the band gap of ZnO@CS-ß-CD was narrowed than ZnO from 3.23 to 2.01 eV. The photocatalyst hold excellent reusability up to seven cycles and the field trail results demonstrated for the practical application for the treatment of wastewater.

Photocatalytic aptitude of titanium dioxide impregnated chitosan beads for the reduction of Cr(VI).

This article describes the photo-reduction of heavy metal Cr(VI) in aqueous solution using titanium dioxide impregnated chitosan beads (TCB) in the presence of UV irradiation. The synergistic role of TCB results in excellent photocatalytic behavior. The reduction of Cr(VI) by the TCB is mainly due to adsorption coupled photocatalytic reduction mechanism. The characterization of TCB was made by Fourier transform Infrared (FTIR) Spectral studies, Scanning Electron Microscope (SEM), Energy Dispersive Analysis of X-ray (EDAX) and Electron Paramagnetic Resonance (EPR) studies. The kinetics of photo-reduction of Cr(VI) is explained on the basis of Langmuir-Hinshelwood mechanism. A comparative study on the percentage removal of chromium using chitosan (CS), titanium dioxide (TiO2) and titanium dioxide impregnated chitosan beads (TCB) in the presence of UV irradiation at 60 min of contact time have been found to be 19.4%, 54.8% and 91.4% respectively. Effects of experimental parameters such as irradiation time, dose, pH, initial concentration, and co-ions were optimized for Cr(VI) removal. Suitability of TCB at field condition was tested with a sample taken from a nearby industrial area.