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.

Reusable photocatalytic polyacrylonitrile membrane-supported cadmium sulphide/titanium dioxide hybrid nanoparticles (CdS/TiO₂-PAN) were prepared using a dry-wet phase inversion technique. Scanning electron microscopy (SEM) analysis revealed that the photocatalytic membranes had a porous sublayer, a compact top layer, and that, some of the nanoparticles were not encapsulated by the membranes. The average crystallite sizes of the CdS, TiO₂, and CdS/TiO₂ hybrid nanoparticles were 3.41 nm, 10.47 nm, and 12.17 nm, respectively. The combination of CdS and TiO₂ nanoparticles led to a red shift (band gap; ca. 2.6 eV) of the absorption band and extended the optical absorption spectrum into the visible region relative to TiO₂. The photocatalytic activity of CdS/TiO₂-PAN membranes was explored in the degradation of methylene blue dye under visible light irradiation, and the results revealed that the best photocatalytic performance was achieved by 0.1 g CdS/TiO₂-PAN photocatalytic membrane with 5% loading of the CdS/TiO₂ hybrid nanoparticles, which degraded 66.29% of methylene blue in 210 minutes at 25°C and pH 8.5. It was found that the optimum loading of nanoparticles in the membranes was 0.1 g. All the photocatalytic membranes showed an insignificant decrease in the photocatalytic activity when used repeatedly. According to literature, CdS/TiO₂-PAN photocatalytic membranes have not been prepared before for the purpose of treating simulated wastewater.

The existence of dye effluent in environmental water bodies is becoming a growing concern to environmentalists and civilians due to negative health effects. In this study, a novel poly(acrylonitrile)-membrane-supported carbon-doped titanium dioxide–coal fly ash nanocomposite (C-TiO₂-CFA/PAN) was prepared and evaluated in the removal of textiles dyes (methyl orange and golden yellow) in water. The C-TiO₂-CFA nanocomposite was prepared via sol-gel synthesis and immobilized on PAN membrane prepared via phase inversion technique. The photocatalyst was characterized by FTIR, XRD, BET surface area analysis, SEM, EDX, and DRS. FTIR analysis confirmed the existence of the expected functional groups, and XRD revealed that the C-TiO₂ was predominantly in the anatase phase, which exhibited the highest photocatalytic activity. The optimum C-TiO₂-CFA photocatalyst load on the PAN membrane was 2% w/w, and it achieved degradation efficiencies of 99.86% and 99.20% for MO and GY dyes, respectively, at pH 3.5, using a dye concentration of 10 ppm, under sunlight irradiation, in 300 min. The novel 2% C-TiO₂-CFA/PAN photocatalytic membrane proved to be very effective in the removal of textile dyes’ water. Three reusability cycles were carried out, and no significant changes were observed in the photocatalytic efficiencies. Immobilization on PAN membrane allowed easy recovery and reuse of the photocatalyst.

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.