Synthesis of a novel visible light responsive γ-Fe2O3/SiO2/C-TiO2 magnetic nanocomposite for water treatment.

This work investigates the preparation of a magnetically recoverable photocatalytic nanocomposite of maghemite nanoparticles coated with silica and carbon doped titanium dioxide. The novel nanocomposite boasts the advantages of efficient photocatalytic degradation of organic pollutants in water and ease of recovery of the fine particles after water treatment. The photocatalytic nanocomposite was successfully synthesized through a stepwise approach via co-precipitation and sol-gel methods. Characterisation by Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) substantiated the existence of the intended structure of the nanocomposite and the particles were found to be in the size range of 15-22 nm with a quasi-spherical shape. Brunauer-Emmett-Teller (BET) surface area analysis revealed an average surface area of 55.20 m2/g, which is higher than that of commercial TiO2 (Degussa P25, 50.00 m2/g), and an average pore diameter of 8.36 nm. A 5 ppm methylene blue solution was degraded with an efficiency of 96.8% after 3 h of solar irradiation, which was 19.7% greater than using the same photo-catalyst under strict UV light irradiation. Photo-catalysis using these nanoparticles was observed to be very effective. The prepared novel visible light active nanocomposite has great potential for incorporation into water treatment systems because it exhibits good stability and magnetism, as well as high photocatalytic efficiency.

Methylene blue removal using a low-cost activated carbon adsorbent from tobacco stems: kinetic and equilibrium studies.

The aim of this study was to prepare activated carbon from tobacco stalks using microwave heating. The prepared activated carbon was applied as an adsorbent in methylene blue (MB) removal from water. The optimum conditions for activated carbon preparation were a radiation power of 280 W for a period of 6 minutes after the impregnation of the precursor material with 30% ZnCl2 for 24 hours. The activated carbon yield and iodine number were 49.43% and 1,264.51 mg/g respectively. The activated carbon also had a point of zero charge of 5.81 with an adsorption capacity of 123.45 mg/g for MB. The optimum conditions for MB adsorption were a pH of 6.5 with an adsorbent dosage of 0.2 g/50 mL at 25 °C. The MB adsorption kinetics followed the pseudo second order kinetic model with the intra-particle diffusion model suggesting a two-step adsorption mechanism. The adsorption data also fitted well within the Langmuir adsorption isotherm model. Tobacco stalks can successfully be turned into an economically important product.

Synthesis and application of a ternary composite of clay, saw-dust and peanut husks in heavy metal adsorption.

The adsorption of a multi-component system of ferrous, chromium, copper, nickel and lead on single, binary and ternary composites was studied. The aim of the study was to investigate whether a ternary composite of clay, peanut husks (PH) and saw-dust (SD) exhibited a higher adsorption capacity than that of a binary system of clay and SD as well as a single component adsorbent of PH alone. The materials were used in their raw state without any chemical modifications. This was done to retain the cost effective aspect of the naturally occurring adsorbents. The adsorption capacities of the ternary composite for the heavy metals Fe2+, Cr3+, Cu2+, Ni2+ and Pb2+ were 41.7 mg/g, 40.0 mg/g, 25.5 mg/g, 41.5 mg/g and 39.0 mg/g, respectively. It was found that the ternary composite exhibited excellent and enhanced adsorption capacity compared with both a binary and single adsorbent for the heavy metals Fe2+, Ni2+ and Cr3+. Characterization of the ternary composites was done using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Kinetic models and adsorption isotherms were also studied. The pseudo second order kinetic model and the Langmuir adsorption isotherm best described the adsorption mechanisms for the ternary composite towards each of the heavy metal ions.

Removal of Pb(2+) and Fe(3+) from water using N-TiO2 blended copolymer grafted asymmetric membranes.

The aim of this study was to evaluate the photo-catalytic properties of nitrogen-doped titanium dioxide nano-particles supported on polymer membranes in the photo-reduction of Fe(3+) and Pb(2+) from synthetic wastewater. The morphology of the prepared N-TiO2 nanoparticles was evaluated using transmission electron microscopy. Successful grafting of methacrylic acid side chains onto poly(vinylidene difluoride) (PVDF) backbone was confirmed by Fourier-transform infrared spectroscopy. The photo-catalytic asymmetric membranes were prepared through the dry-wet phase inversion technique. The asymmetric morphology was evaluated using scanning electron microscopy. The highest Fe(3+) photo-reduction efficiency (76.2%) was achieved in 6 hours using 1% N-TiO2-PMAA-g-PVDF/PAN (PMAA: poly(methacrylic acid); PAN: poly(acrylonitrile)) asymmetric membrane under solar irradiation. Increasing the photo-catalyst loading to 3% was found to negatively impact the photo-reduction of Fe(3+). Very high photo-reduction efficiencies were observed in the photo-reduction of Pb(2+) using 1% N-TiO2-PAN, 1% N-TiO2-PMAA-g-PVDF/PAN and 1% N-TiO2-PVDF membranes (90.5%, 88.9% and 86.9%, respectively) under similar conditions. Increasing the photo-catalyst loading to 3% N-TiO2 was observed to slightly increase the photo-reduction efficiency in the removal of Pb(2+) unlike in the case of Fe(3+). The best support material for the N-TiO2 photo-catalyst was PMAA-g-PVDF/PAN.