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

Wei Guan,Gaoge Sun,Zhenghua Zhang,Lei Yin,Shichao Tian

doi:10.3389/fchem.2018.00037

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.

Highlights

Hypophosphite is commonly used as a reducing agent in metallurgy industries especially in the processes of plating and surface finishing thereby generating large amounts of hypophosphite wastewater (Bulasara et al, 2011; Li et al, 2015)
The enhancement of Ti4O7/g-C3N4 visible light photocatalytic performance on hypophosphite oxidation and the effect of annealing temperature and the corresponding mechanism were investigated in this study. 160-Ti4O7/g-C3N4 photocatalyst showed the highest oxidation efficiency of hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h−1 comparing with 100-Ti4O7/g-C3N4 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

Summary

Introduction

Hypophosphite is commonly used as a reducing agent in metallurgy industries especially in the processes of plating and surface finishing thereby generating large amounts of hypophosphite wastewater (Bulasara et al, 2011; Li et al, 2015). Phosphorus is a non-renewable resource mainly used as a nutrient in agricultural production (Montangero and Belevi, 2007). Due to an increase in the global demand for phosphorus resource, it will be depleted in the 50–100 years The phosphorus recovery from wastewater is of considerable interest. Phosphate is easier to be recovered than hypophosphite by precipitation. A highly efficient approach for the preoxidation of hypophosphite to phosphate becomes of great importance for phosphorus recovery. Photocatalysis, a nanoenabled technology, has been recognized for its promising applications with the generation of activated radicals such as hydroxyl radicals and superoxide anion radicals, which can be applied for hypophosphite oxidation

Methods

Results

Conclusion