Deriving Ag_3PO_4–CaO composite as a stable and solar light photocatalyst for efficient ammonia degradation from wastewater

A novel Ag3PO4-CaO composite photocatalyst with enhanced photocatalytic activity was synthesized and utilized for degradation of ammonia from aqueous solution under sunlight. Ag3PO4 was prepared by pre- cipitation method, and the composite of AgjPO4-CaO was prepared via impregnation method. Utilization of eggshell for CaO synthesis provided a cost-effective and environmental friendly way for the hetero- geneous catalyst production. The as-prepared photocatalysts were characterized by FT-IR, FE-SEM, TEM, EDX, UV-vis and PL Results show that the Ag3PO4-CaO samples have excellent photocatalytic perfor- mances in the wide visible-light region. The effect of operating parameters like the content of Ag3PO4 in composite, initial ammonia concentration, pH of solution, catalyst dosage and oxygen supply was investi- gated. The photoeatalyst with 60 wt% content of Ag3PO4 had a high photocatalytic performance, because a low content of Ag3PO4 causes weak light absorption, and the excess amount of it results in serious electron-hole recombination due to the aggregation of AgjPO4 particles. The maximum ammonia degra- dation （about 70%） was achieved in 340 mg/L of ammonia, pH 11, and 1.25 g/L of catalyst in the presence of pure oxygen. In comparison to Ag3PO4, 60 wt% AgjPO4-CaO had a good stability and it could have been easily separated from the solution for recycling.

Enhanced photoelectrocatalytic degradation of ammonia by in situ photoelectrogenerated active chlorine on TiO_2 nanotube electrodes

TiO2 nanotube （TINT） electrodes anodized in fluorinated organic solutions were successfully prepared on Ti sheets. Field-emission scanning electron microscopy （FE-SEM） and X-ray diffraction （XRD） were performed to characterize the TiNT electrodes. The linear voltammetry results under irradiation showed that the TiNT electrode annealed at 450℃ presented the highest photoelectrochemical activity. By combining photocatalytic with electrochemical process, a significantly synergetic effect on ammonia degradation was observed with Na2SO4 as supporting electrolyte at pH 10.7. Furthermore, the photoelectrocatalytic efficiency on the ammonia degradation was greatly enhanced in presence of chloride ions without the limitation ofpH. The degradation rate was improved by 14.8 times reaching 4.98 × 10^-2 min^-1 at pH 10.7 and a faster degradation rate of 6.34 × 10^-2 min^-1 was obtained at pH 3.01. The in situ photoelectrocatalytic generated active chlorine was proposed to be responsible for the improved efficiency. On the other hand, an enhanced degradation of ammonia using TiNT electrode fabricated in fluorinated organic solution was also confirmed compared to TiNT electrode anodized in fluorinated water solution and TiO2 film electrode fabricated by sol-gel method. Finally, the effect of chloride concentration was also discussed.

Bi2WO6 quantum dot-intercalated ultrathin montmo- rillonite nanostructure and its enhanced photocatalytic performance

The kinetic competition between electron-hole recombination and water oxidation is a key limitation for the development of efficient solar water splitting materials. In this study, we present a solution for solving this challenge by constructing a quantum dot-intercalated nanostructure. For the first time, we show the interlayer charge of the intercalated nanostructure can significantly inhibit the electron-hole recombination in photocatalysis. For Bi2WO6 quantum dots （QDs） intercalated in a montmorillonite （MMT） nanostructure as an example, the average lifetime of the photogenerated charge carriers was increased from 3.06 μs to 18.8 Ds by constructing the intercalated nanostructure. The increased lifetime markedly improved the photocatalytic performance of Bi2WO6 both in solar water oxidation and environmental purification. This work not oMy provides a method to produce QD-intercalated ultrathin nanostructures but also a general route to design efficient semiconductor-based photoconversion materials for solar fuel generation and environmental purification.

Preparation of ZnO/Ag Heterostructure Material by One-pot Method for Enhanced Photocatalytic Performance

A porous ZnO/Ag heterostructure photocatalyst was prepared by a simple one-pot method. The photoca- talytic degradation of ammonia and dye indicated that compared with pure ZnO, the photocatalytic activity of ZnO/Ag was significantly improved after Ag modification. The main reason for the improvement of photocatalytic activity is that the recombination process of photoinduced electrons and holes of ZnO was inhibited by interconver- sion of Ag＋ and Ag0 at the surface of ZnO. In addition, the effective separation of the photogenerated carriers can generate more active groups, which can promote the degradation of ammonia and organic dyes.