Enhanced Visible Light Photocatalytic Degradation of Methylene Blue by CdS-ZnS-BiPO4 Nanocomposites Prepared by a Solvent-Assisted Heating Method

Hsin-Chan Tsai,Yang-Wei Lin,Tsunghsueh Wu,Yu-Hui Peng,Po-Yu Wen

doi:10.3390/catal11091095

Abstract

In this study, a ternary CdS-ZnS-BiPO4 nanocomposite, synthesized by a solvent-assisted heating method, demonstrated the highest visible light-induced photocatalysis towards the degradation of methylene blue (MB) when comparing with BiPO4, CdS-BiPO4, and ZnS-BiPO4. Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) were used to characterize the prepared nanocomposites. From UV-DRS results, the energy band gap of the prepared BiPO4 structures was 4.51 eV. When CdS nanoparticles were deposited on BiPO4 surface by a solvent-assisted heating method, the prepared nanocomposites exhibited visible light-responsive photocatalytic degradation toward MB (20 ppm). At a molar ratio of Cd to Zn as 1:7, the prepared CdS-ZnS-BiPO4 nanocomposites exhibited the best photocatalytic activity in degrading 95% of MB dyes, out-performing pure BiPO4, CdS-BiPO4, and ZnS-BiPO4 due to its enhanced charge separation efficiency and the lowered carrier recombination from the efficient p-n junction of unprecedented ternary composites. The investigations on mechanism conclude that the major reactive species responsible for MB degradation are holes and oxygen radicals. For practicality, the degradation efficiency for different dyestuff (Fast Green FCF, Rhodamine 6G, Acid Blue 1, methyl orange, and methyl red) degradation in the different water matrix samples (pond water, seawater, and lake water) by the prepared CdS-ZnS-BiPO4 nanocomposites was evaluated.

Highlights

Apparel plays an important role in our society and contributes to a large part of the global economy; the typical textile dyeing method involves excess amounts of dyestuffs, which are eventually discharged as wastewater, imposing technical challenges on the wastewater treatment facility [1,2,3]
The results show that the BiPO4–CdS composite (30.1 wt% CdS) performed the best as 98.1% of methyl orange (MO) degraded by a 400 W halogen lamp (>400 nm) within 5 h due to the enhanced visible light absorption
The procedure was similar to the degradation process except hole, oxygen radical- and hydroxyl radical- scavengers were added to the methylene blue (MB) solution prior to the addition of nanocomposite

Summary

Introduction

Apparel plays an important role in our society and contributes to a large part of the global economy; the typical textile dyeing method involves excess amounts of dyestuffs, which are eventually discharged as wastewater, imposing technical challenges on the wastewater treatment facility [1,2,3]. Adsorption, filtration, coagulation, and biodegradation are all traditional processes used in the water treatment industry [4,5,6,7,8,9]. These approaches have limitations in terms of cost, feasibility, time required, and environmental impacts [10]. Despite the fact that adsorption is a common process for removing toxic textile dyes it could be incapable of degrading or mineralizing organic contaminants from the environment [11]. Research efforts in improving photocatalytic materials have been made to meet the current challenge in the textile industry [2]

Methods

Results

Conclusion