On the Degradation of Glyphosate by Photocatalysis Using TiO2/Biochar Composite Obtained from the Pyrolysis of Rice Husk

Phuong Thu Le,Thi Mai Thanh Dinh,Marine Herrmann,Luong Lam Nguyen,Thi Hue Nguyen,Dieu Linh Vo,Sylvain Ouillon,Le Anh Pham,Thu Phuong Nguyen,Thi Phuong Quynh Le,Quoc Son Nguyen,Huyen Thuong Bui,Duy Ngoc Le,Thi Thuy Duong,Huong Mai,Thu Hien Dang

doi:10.3390/w13233326

Abstract

In this study, titanium dioxide (TiO2) nanoparticles are immobilized onto rice husk biochar (RHB), as a porous support, for the photodegradation of glyphosate under UV light irradiation. The TiO2/RHB composites are prepared by pyrolysis and the sol-gel method. The SEM, XRD, EDX, and FT-IR results confirm the graphene structure of RHB and the formation of 10.61 nm TiO2 nanoparticles on the catalyst support. The effects of operating conditions, including catalyst dosage (3 g L−1, 5 g L−1, 10 g L−1, and 20 g L−1) and different illumination conditions (9 W lamp, 2 × 9 W lamps), on the removal of glyphosate from aqueous solutions were investigated. The photodegradation efficiency of 15 mg L−1 of commercial glyphosate was up to 99% after 5 h of irradiation at pH 3.0, with a TiO2/RHB dosage of 10 g L−1. However, the mineralization efficiency under this condition was lower than the decomposition efficiency of glyphosate, proving the partial degradation of glyphosate into AMPA and other metabolites after 5 h of reaction.

Highlights

SEM was connected with energy dispersive X-ray spectroscopy (EDXS) for chemical element composition analysis
Biochar is obtained from the pyrolysis of rice husks in an anaerobic environment
The cross-sectional image of the rice husk biochar (RHB) illustrates the appearance of mesopores with an average diameter of about 28 μm

Summary

Introduction

Glyphosate (N-(phosphonomethyl) glycine, known by the trade name Roundup and Rodeo) has been a dominant herbicide worldwide for many years, since its first commercial introduction in 1974 [1]. This herbicide is non-selective, systemic, and postemergent, which is decisive for removing a wide range of weeds. The residue glyphosate from various sources, such as industrial effluents, agricultural runoff, and spilt chemicals [1], was considered as a pollutant, which contaminates the environment. In areas in the USA where genetically modified glyphosate-resistant crops are grown, glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) were found in soil, surface water, and groundwater at levels from 2 to 430 μg L−1 [2,3,4,5]

Methods

Results

Conclusion