Intermediate formation during photodegradation of phenol using lanthanum doped tin dioxide nanoparticles

The effect of use of Ni/Fe and mZVI on phenol removal with the heterogenous fenton process and in-situ generation of H2O2

To degrade phenol with the heterogeneous Fenton-like process and to compare the results, micro-scale zero-valent iron particles (mZVI) and nickel-coated iron bimetallic particles (Ni/Fe) were used. Oxygen was given to the system and converted to H2O2 and •OH radicals. The changes in the properties of mZVI and Ni/Fe particles after the reaction were determined by scanning electron microscope (SEM), X-ray energy-dispersive spectrometer (EDX), Brunauer-Emmett-Teller (BET), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) before and after the reaction. For phenol removal with an initial phenol concentration of 25 mg/L, initial pH of 3 and air flow rate of 150 L/h, 3 g/L dosage and 360 min reaction time for mZVI, 1.5 g/L dosage and 240 min for Ni/Fe reaction time were sufficient. Under these conditions, 76% and 98% phenol removal and 39% and 47% total organic carbon (TOC) removal were obtained for mZVI and Ni/Fe, while 189 and 85 mg/L H2O2 were produced, respectively. While SO 4 - 2 and PO 4 - 3 caused a slight increase in phenol removal efficiency in the mZVI system, these ionic species and Cl- and NO 3 - caused a decrease in the efficiency in the Ni/Fe system. The possible degradation pathway for phenol was suggested by high performance liquid chromatography (HPLC) analysis and hydroquinone, pyrocatechol, maleic acid, benzoquinone and acetic acid were the main intermediates. According to the cost analysis, when using mZVI to treat 1 m3 25 mg/L phenolic wastewater, the cost was $228.15, which was 1.45 times higher than the cost for Ni/Fe.

Facile Synthesis of Tin Dioxide Nanoparticles for Photocatalytic Degradation of Congo Red Dye in Aqueous Solution

This research work reports an approach used to prepare a SnO2 photocatalyst by precipitation and calcination pathways and describes an investigation of the effects of preparation parameters on SnO2 yield. The SnO2 photocatalyst was further used for the photocatalytic degradation of Congo red (CR) dye, and the removal efficiency was optimized using response surface methodology. The results indicate that the SnO2 photocatalyst yield was the highest in 0.05 M of the precursor, stannous chloride and 28 wt % ammonia as the precipitant, pH 10, at 30 °C. The transmission electron microscopy results of the SnO2 photocatalyst illustrate that the average particle size was mainly around 30–50 nm and had a solid spherical shape. The X-ray diffraction results reveal that the prepared sample had a highly crystalline SnO2 rutile crystal structure. The prediction and experimental results of the Response surface methodology (RSM) indicate that, when the reaction time was 97 min, the operating temperature was 47 °C, the photocatalyst dosage was 751 mg/L, and the optimal degradation rate of the CR dye was 100%. After five consecutive photodegradation reactions, the degradation rate remained at 100%. The results demonstrated that the SnO2 photocatalyst prepared in this study possesses excellent reusability.

Highly Robust and Selective System for Water Pollutants Removal: How to Transform a Traditional Photocatalyst into a Highly Robust and Selective System for Water Pollutants Removal

Highly porous monolithic aerogels based on ZnO photocatalyst and syndiotactic polystyrene (s-PS) were obtained by supercritical CO₂ treatment of ZnO/s-PS gels. The prepared aerogels were characterized and their photocatalytic activity was evaluated using phenol and toluene as water pollutant models. The s-PS nanoporous crystalline phase, able to absorb pollutant molecules, was proven to be necessary to ensure high photocatalytic efficiency as the aerogel acts not only as a support, but also as pollutant pre-concentrator. The reusability of ZnO/s-PS aerogels is also strong showing no decrease in photocatalytic activity after six consecutive degradation trials. Finally, the aerogel matrix prevents ZnO dissolution occurring under acidic conditions and promotes a selective removal of the pollutants. The synergy between the photocatalyst and the innovative polymeric support provides the composite system with robustness, chemical stability, easy recovery after treatment, high efficiency of pollutant removal with a marked selectivity which make these materials promising for large scale applications.

Photocatalytic degradation of phenol in water under simulated sunlight by an ultrathin MgO coated Ag/TiO2 nanocomposite

Phenol is one of the most widespread, toxic and recalcitrant compounds in water sources. Due to its persistent nature, conventional wastewater treatment methods are not effective to remove or degrade phenol from water. In this work, novel photocatalysts were developed to effectively degrade phenol under simulated sunlight. The catalysts were composed of one-dimensional titanium dioxide (TiO₂) nanorods decorated with silver (Ag) nanoparticles, coated by an ultrathin magnesium oxide (MgO) overlayer through atomic layer deposition (ALD). Material properties of prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic performance of phenol degradation under simulated sunlight was evaluated and correlated with the material properties. The Ag nanoparticles promoted light absorption and transfer of photo-induced electron-hole pairs from within TiO₂ nanorods to the catalyst surface. The ultrathin MgO overlayer with a sub-nanometer thickness did not hinder charge transfer to the surface, but rather, it further increased the light absorption and inhibited surface charge recombination through a surface passivation effect, promoting phenol degradation. The photocatalytic reaction mechanism was investigated by examining hydroxyl and superoxide radical production in the photocatalytic system. The results from this work demonstrated a new strategy for fabricating efficient solar-driven photocatalysts for the degradation of persistent water contaminants.

Controlled Defects of Zinc Oxide Nanorods for Efficient Visible Light Photocatalytic Degradation of Phenol

Environmental pollution from human and industrial activities has received much attention as it adversely affects human health and bio-diversity. In this work we report efficient visible light photocatalytic degradation of phenol using supported zinc oxide (ZnO) nanorods and explore the role of surface defects in ZnO on the visible light photocatalytic activity. ZnO nanorods were synthesized on glass substrates using a microwave-assisted hydrothermal process, while the surface defect states were controlled by annealing the nanorods at various temperatures and were characterized by photoluminescence and X-ray photoelectron spectroscopy. High performance liquid chromatography (HPLC) was used for the evaluation of phenol photocatalytic degradation. ZnO nanorods with high surface defects exhibited maximum visible light photocatalytic activity, showing 50% degradation of 10 ppm phenol aqueous solution within 2.5 h, with a degradation rate almost four times higher than that of nanorods with lower surface defects. The mineralization process of phenol during degradation was also investigated, and it showed the evolution of different photocatalytic byproducts, such as benzoquinone, catechol, resorcinol and carboxylic acids, at different stages. The results from this study suggest that the presence of surface defects in ZnO nanorods is crucial for its efficient visible light photocatalytic activity, which is otherwise only active in the ultraviolet region.