Spatial separation of photogenerated carriers and enhanced photocatalytic performance on Ag3PO4 catalysts via coupling with PPy and MWCNTs

Visible-light-driven photocatalysis is a promising technology in the environmental pollutant remediation, and charge separation is crucial for increasing the activity of photocatalysts. In this study, novel photocatalysts Ag3PO4@MWCNTs@PPy with excellent photocatalytic activity and photostability were successfully synthesized. The results of density functional theory (DFT) calculation and photochemical deposition experiments demonstrated that a spatial separation system of photogenerated carriers in Ag3PO4@MWCNTs@PPy composite was successfully constructed. The photogenerated electrons of Ag3PO4 were readily transferred to MWCNTs and the photogenerated holes tended to migrate to the surface of PPy, resulting in superior separation efficiency of photogenerated carriers and great enhancement of photocatalytic activity. The photocatalytic degradation efficiency of phenol and tetracycline hydrochloride (TC) over optimal ternary catalyst could reach 100% with visible light irradiation for 20 min and 5 min, respectively. Simultaneously, 80.12% of TOC removal efficiency was also achieved within 20 min on the mineralization of phenol. The LC-MS and 3D EEMs (three-dimensional excitation-emission-matrix spectra) analyses showed that TC was mainly degraded into small molecule acids, fulvic acids- and humic acids-like matters. In addition, a new method of preparing Ag3PO4 with uniform small sized particles was proposed, by which the large Ag3PO4 polyhedron crystals with a diameter of 10-25 mu m were transformed into particles in a range of 0.2-1.4 mu m in diameter, and the apparent rate constant of phenol degradation by this small-sized Ag3PO4 was 3.8 times of that by the large-sized. In this work a new photocatalyst with great application potential has been fabricated, and the strategy for constructing the carrier spatial separation system is promising and intriguing for designing high efficient photocatalysts.