A comprehensive review on the boosted effects of anion vacancy in the heterogeneous photocatalytic degradation, part I: Focus on sulfur, nitrogen, carbon, and halogen vacancies

The greenest environmental remediation way is the photocatalytic degradation of organic pollutants. However, limited photocatalytic applications are due to poor sunlight absorption and photogenerated charge carriers' recombination. These limitations can be overcome by introducing anion vacancy (AV) (O, S, N, C, and Halogen) defects in semiconductors that enhance light harvesting, facilitate charge separation, modulate electronic structure, and produce reactive radicals. In continuing part A of this review, in this part, we summarized the recent AVs' research, including S, N, C, and halogen vacancies on the boosted photocatalytic features of semiconductor materials, like metal oxides/sulfides, oxyhalides, and nitrides in detail. Also, we outline the recently developed AV designs for the photocatalytic degradation of organic pollutants. The AV creating and analysis methods and the recent photocatalytic applications and mechanisms of AV-mediated photocatalysts are reviewed. AV engineering photocatalysts' challenges and development prospects are illustrated to get a promising research direction.

Solar-Light-Driven Ag9(SiO4)2NO3 for Efficient Photocatalytic Bactericidal Performance

Photocatalytic materials are being investigated as effective bactericides due to their superior ability to inactivate a broad range of dangerous microbes. In this study, the following two types of bacteria were employed for bactericidal purposes: Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The shape, crystal structure, element percentage, and optical properties of Ag9(SiO4)2NO3 were examined after it was successfully synthesized by a standard mixing and grinding processing route. Bactericidal efficiency was recorded at 100% by the following two types of light sources: solar and simulated light, with initial photocatalyst concentration of 2 µg/mL, and 97% and 95% of bactericidal activity in ultra-low photocatalyst concentration of 0.2 µg/mL by solar and simulated light, respectively, after 10 min. The survival rate was studied for 6 min, resulting in 99.8% inhibition at the photocatalyst dose of 2 µg/mL. The mechanism of bactericidal efficiency was found to be that the photocatalyst has high oxidation potential in the valence band. Consequently, holes play a significant part in bactericidal efficiency.

Stable and Efficient Photoinduced Charge Transfer of MnFe2O4/Polyaniline Photoelectrode in Highly Acidic Solution

Tailoring conductive polymers with inorganic photocatalysts, which provide photoinduced electron-hole generation, have significantly enhanced composites leading to excellent photoelectrodes. In this work, MnFe2O4 nanoparticles prepared by a hydrothermal method were combined with polyaniline to prepare mixed (hybrid) slurries, which were cast onto flexible FTO to prepare photoelectrodes. The resulting photoelectrodes were characterized by XRD, FESEM, HRTEM and UV-VIS. The photoelectrochemical performance was investigated by linear sweep voltammetry and chronoamperometry. The photocurrent achieved by MnFe2O4/Polyaniline was 400 μA/cm2 at 0.8 V vs. Ag/AgCl in Na2SO4 (pH = 2) at 100 mW/cm2, while polyaniline alone achieved only 25 μA/cm2 under the same conditions. The best MnFe2O4/Polyaniline displayed an incident photon-to-current conversion efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) of 60% at 405 nm wavelength, and 0.17% at 0.8 V vs. Ag/AgCl, respectively. High and stable photoelectrochemical performance was achieved for more than 900 s in an acidic environment.