Ti4O7/g-C3N4 Visible Light Photocatalytic Performance on Hypophosphite Oxidation: Effect of Annealing Temperature

Abstract

The oxidation of hypophosphite to phosphate is the key to recover the phosphorus resource from the hypophosphite wastewater. In the present work, Ti4O7/g-C3N4 composites were synthesized at two different temperatures (100 and 160°C) and their performance on photocatalytic oxidation of hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C3N4 and Ti4O7 was applied to synthesize the Ti4O7/g-C3N4 composites with their hybrid structure and morphology confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS). The annealing temperature significantly affected the photocatalytic performance of Ti4O7/g-C3N4 that the 160-Ti4O7/g-C3N4 composite (fabricated at 160°C) showed the highest oxidation efficiency of hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h−1 comparing with the 100-Ti4O7/g-C3N4 composite (fabricated at 100°C) and pure g-C3N4. The enhanced photocatalytic performance of 160-Ti4O7/g-C3N4 could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti4O7/g-C3N4 photocatalysts showed the remarkable stability in the repetitive experiments.

Ti4O7/g-C3N4 for Visible Light Photocatalytic Oxidation of Hypophosphite: Effect of Mass Ratio of Ti4O7/g-C3N4

“…Among various compositions of Ti n O 2n−1 , Ti 4 O 7 has the properties of best conductivity (1,500 S cm −1 ) and the robust resistance to aggressive chemical conditions (Ganiyu et al, 2016 ). Construction of g-C 3 N 4 /Ti 4 O 7 heterojunction significantly improved the photocatalytic performance as a result of the effective enhancement of charge separation was reported in our previous work (Guan et al, 2018 ). However, the effect of the mass ratio of Ti 4 O 7 (m): g-C 3 N 4 (m) of the g-C 3 N 4 /Ti 4 O 7 heterojunction on photocatalytic performance is still unknown.…”

“…The electrons on the surface of Ti 4 O 7 could easily react with O 2 adsorbed on the Ti 4 O 7 /g-C 3 N 4 surface to generate · radicals for hypophosphite oxidation. Meanwhile, the active ·OH radicals with high redox potential were generated through · radicals, which further facilitated the oxidation of hypophosphite (Nosaka and Nosaka, 2017 ; Guan et al, 2018 ). Therefore, it can be concluded that the oxidation of hypophosphite was mainly ascribed to ·OH and · radicals generated during the photocatalytic process as shown in Figure 8 .…”

“…After that, the visible light photocatalytic oxidation of hypophosphite was conducted with the above solutions exposing to the visible light irradiation and sampling conducted at 1 h intervals over 6 h experimental period. More detailed information about the photocatalytic experiment can be found in our most recent paper (Guan et al, 2018 ). The oxidation efficiency of hypophosphite (η) was calculated using the following equation (Guan et al, 2017 ): where C 0 and C t represent the concentrations of hypophosphite at initial and given time, respectively.…”

Oxygen Reduction Reaction Activity of Microwave Mediated Solvothermal Synthesized CeO2/g-C3N4 Nanocomposite

“…The peak at 284.8 eV corresponds to sp 2 -bonded C-C (Raymundo-Pinero et al, 2002). The peaks at 286.3 and 288.5 eV (Guan et al, 2018) are ascribed to C = N and N-C-N in g-C 3 N 4 respectively (Figure 3B) (Yan et al, 2012). The main peak of N 1s at 398.5 eV is assigned to sp 2 nitrogen (C=N-C) (pyridinic) present in triazine rings, while the peak at 399.6 eV arises from the tertiary nitrogen bonded to carbon atoms in the form of N–(C) 3 (pyrollic).…”

Preparation and Photoelectrocatalytic Performance of Ti/PbO2 Electrodes Modified with Ti4O7

“…Thus, electrons in the conduction band are flown through the counter electrode via the external circuit, and the holes are improved on the surface. Moreover, the induced electrons in the conduction band of PbO 2 can continually transfer to Ti 4 O 7 , and then were faster moved to the external circuit via electric field. Thus, the induced charge carriers were effectively separated.…”