This study was focused on the application of white and blue light emitting diodes (LEDs) as sources for the photocatalytic degradation of organic dyes in liquid phase with visible light. The photocatalytic activity of N-doped titanium dioxide, synthesized by direct hydrolysis of titanium tetraisopropoxide with ammonia, was evaluated by means of a batch photoreactor. The bandgap energy of titanium dioxide was moved in the visible range from 3.3 eV to 2.5 eV. The visible light responsive photocatalysts showed remarkably effective activity in decolorization process and in the removal of total organic carbon. Methylene blue was also used as a model dye to study the influence of several parameters such as catalyst weight and initial concentration. The effect of dye on the photocatalytic performance was verified with methyl orange (MO). The results demonstrated that the right selection of operating conditions allows to effectively degrade different dyes with the N-doped TiO2photocatalysts irradiated with visible light emitted by LEDs.

Due to the exceptional characteristics which resulted from nanoscale size, such as improved catalysis and adsorption properties as well as high reactivity, nanomaterials have been the subject of active research and development worldwide in recent years. Numerous studies have shown that nanomaterials can effectively remove various pollutants in water and thus have been successfully applied in water and wastewater treatment. In this paper, the most extensively studied nanomaterials, zero-valent metal nanoparticles (Ag, Fe, and Zn), metal oxide nanoparticles (TiO2, ZnO, and iron oxides), carbon nanotubes (CNTs), and nanocomposites are discussed and highlighted in detail. Besides, future aspects of nanomaterials in water and wastewater treatment are discussed.

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The aim of the present study was to investigate the antioxidant activity and protective potential of T. tetraptera extracts against ion toxicity. The antioxidant activity of the extracts was investigated spectrophotometrically against several radicals (1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•), hydroxyl radical (HO•), and nitric oxide (NO•)), followed by the ferric reducing power, total phenols, flavonoid, and flavonol contents. The effects of the extracts on catalase (CAT), superoxide dismutase (SOD), and peroxidase activities were also determined using the standard methods as well as the polyphenol profile using HPLC. The results showed that the hydroethanolic extract of T. tetraptera (CFH) has the lowest IC50 value with the DPPH, ABTS, OH, and NO radicals. The same extract also exhibited the significantly higher level of total phenols (37.24 ± 2.00 CAE/g dried extract); flavonoids (11.36 ± 1.88 QE/g dried extract); and flavonols contents (3.95 ± 0.39 QE/g dried extract). The HPLC profile of T. tetraptera revealed that eugenol (958.81 ± 00 mg/g DW), quercetin (353.78 ± 00 mg/g DW), and rutin (210.54 ± 00 mg/g DW) were higher in the fruit than the bark extracts. In conclusion, extracts from T. tetraptera may act as a protector against oxidative mediated ion toxicity.

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In this study, a highly polluted wastewater from tannery industry is treated by photocatalysis using home-made N-doped TiO2 as catalyst. The doping by nitrogen of titania particles leads to a reduction in the absorption threshold from 3.2 to 2.5 eV, permitting the absorption of radiation characterized by a wavelength in the visible spectrum.Experiments were carried out by using different light sources, in particular white LEDs, blue LEDs, and UV lamps, with the aim to evaluate the process efficiency at different operating conditions. The obtained performances were compared with those using an undoped commercial TiO2 catalyst (Degussa P25).Moreover, a simplified mathematical model capable to correlate the power input of the used light sources, the geometrical properties of the reactor, and emitting sources spectra with the performances of the photocatalytic reaction was developed.