Aqueous and solid phase photocatalytic degradation of perfluorooctane sulfonate by carbon- and Fe-modified bismuth oxychloride.

In this study, we prepared and tested a carbon-modified, Fe-loaded bismuth oxychloride (Fe-BiOCl/CS) photocatalyst for photocatalytic degradation of perfluorooctane sulfonate (PFOS). Structural analyses revealed a (110) facet-dominated sheet-type BiOCl crystal structure with uniformly distributed Fe and confirmed carbon modification of the photocatalyst. The presence of d-glucose facilitated the growth control of BiOCl particles and enhanced the adsorption of PFOS via added hydrophobic interaction. Adsorption kinetic and equilibrium tests showed rapid uptake rates of PFOS and high adsorption capacity with a Langmuir Qmax of 1.51 mg/g. When used for directly treating PFOS in solution, Fe-BiOCl/CS was able to mineralize or defluorinate 83% of PFOS (C0 = 100 µgL-1) under UV (254 nm, intensity = 21 mW cm-2) in 4 h; and when tested in a two-step mode, i.e., batch adsorption and subsequent photodegradation, Fe-BiOCl/CS mineralized 65.34% of PFOS that was pre-concentrated in the solid phase under otherwise identical conditions; while the total degradation percentages of PFOS were 83.48% and 80.50%, respectively, for the two experimental modes. The photoactivated electrons and/or hydrated electrons and superoxide radicals primarily initiated the desulfonation of PFOS followed by decarboxylation and defluorination, through a stepwise chain-subsiding mechanism. The elevated photocatalytic activity can be attributed to the effective separation of e-/h+ pairs facilitated by the (110) interlayer electrostatic field, Fe doping, and the presence of oxygen vacancies. This work reveals the potential of carbon-modified and Fe-co-catalyzed BiOCl for concentrating and degrading PFOS and possibly other persistent organic pollutants.

Photoelectrochemical sewage treatment by a multifunctional g-C3N4/Ag/AgCl/BiVO4 photoanode for the simultaneous degradation of emerging pollutants and hydrogen production, and the disinfection of E. coli.

This study describes the photoelectrochemical (PEC) treatment of authentic sewage from Hong Kong for H2 production and degradation of emerging pollutants (EP's) simultaneously, and disinfection of E. coli. The g-C3N4/Ag/AgCl/BiVO4 (CAB-1) coated thin film acted as the photoanode in a three-electrode configuration PEC cell and real sewage as the electrolyte. Electrochemical studies revealed the near reversible, diffusion-controlled and high electron transfer reaction at the electrode-electrolyte surface. For CAB-1, the achieved photocurrent density was 0.1-0.2 mA cm-2 at 1.23 V vs. RHE exhibiting the highest PEC degradation efficiency (11.15% h-1 cm-2) compared to other base materials like g-C3N4/BiVO4 (6.88% h-1 cm-2) or Ag/AgCl/BiVO4 (4.06% h-1 cm-2). During the same reaction, the evolved 118 µmol of H2 gas corresponds to a Faradic efficiency of 69.38%. The composition of sewage was found to influence the overall PEC efficiency. The higher amount of total suspended solids, turbidity, and anionic species decreased the efficiency while as the other parameters like alkaline pH increased the PEC efficiency. Photo-electrochemically, the CAB-1 also effectively disinfected the E. coli present in the sewage with a final discharge of ≤1000 CFU/mL which is within the permissible discharge limits (≤1500 CFU/mL), in Hong Kong.

Morphology Dependent Photocatalytic Activity of CuO/CuO-TiO2 Nanocatalyst for Degradation of Methyl Orange Under Sunlight.

CuO nanoparticles have been extensively used as a photocatalyst because of their superior activity, selectivity and stability properties. The catalytic efficiency of these oxide nanoparticles can be improved by varying the size and shape of nanoparticles. Here, we report the synthesis of different shaped CuO nanoparticles and their impregnation on TiO2. Optical analysis revealed that a considerable red shift (420 nm to 550 nm) in absorption spectra of CuO-TiO2 nanocomposites was observed compared to bare CuO nanoparticles. DLS measurements showed that the average hydrodynamic size of CuO nanostars was increased from 160 nm to 584 nm after deposition on TiO2. These nanocomposites were examined for photocatalytic degradation of methyl orange under sunlight radiation. It was observed that CuO-TiO2 nanostars exhibited superior photocatalytic efficiency compared to CuO-nanoneedles, nanocrumbles and bare CuO nanoparticles. The CuO nanoparticles act as co-catalyst on the surface of TiO2 and alter the physicochemical properties of TiO2. The higher activity arises due to the fact that the doping of CuO reduces the recombination of charge carries (e--h+) and creates the intra-gap states which result in higher absorption of light radiations. Therefore, CuO nanoparticles impregnated on TiO2 found to be an effective and ideal catalyst for the photodegradation of methyl orange dye.

Photocatalytic Degradation of Methylene Blue by Plasmonic Metal-TiO2 Nanocatalysts Under Visible Light Irradiation.

This study demonstrates photocatalytic activity of 1 wt% plasmonic metal (Au, Ag and Cu)­TiO2 nanocatalysts prepared via photodeposition method for the photo oxidative decomposition of methylene blue (MB 0.01 mM) under visible light (50 mWcm−2) irradiation. Plasmonic metal loaded-TiO2 photocatalysts absorb with an absorption maximum at localized surface plasmon resonance wavelengths (500­785 nm). It has been observed that pH altered the surface charge (ζ) of TiO2 (ζ = ­4.98, ­4.0 and +9.16 at pH = 10, 7 and 3, respectively). The point of zero charge (PZC) at pH 6.3 has been determined from a correlation plot between pH and ζ. Higher rate of degradation was observed at pH = 10 because of electrostatic interaction of cationic MB with anionic TiO2. Higher photocatalytic activity was shown by Cu­TiO2 followed by Au­TiO2 and Ag­TiO2 photocatalysts in comparison to TiO2-P25. This enhancement in photocatalytic efficiency is attributed to the plasmonic effect and effective charge separation at the interface between nano size metal deposits and TiO2 particles. The overall photocatalytic reaction followed pseudo first order kinetics as per Langmuir Hinshelwood kinetic equation. GC and GC-MS studies suggested the formation of thionin after demethylation and derivatives of benzene sulphonic acid which are subsequently degraded to CO2 after prolonged irradiation time.