Photocatalytic degradation of tetracycline aqueous solutions by nanospherical \u03b1-Fe2O3 supported on 12-tungstosilicic acid as catalyst: using full factorial experimental design

Majid Saghi,Kazem Mahanpoor

doi:10.1007/s40090-016-0108-6

Abstract

In this paper, spherical α-Fe2O3 nanoparticles (NPs) were supported on the surface of 12-tungstosilicic acid (12-TSA·7H2O) using two different solid-state dispersion (SSD) and forced hydrolysis and reflux condensation (FHRC) methods. Photocatalytic activity of supported α-Fe2O3 NPs (α-Fe2O3/12-TSA·7H2O) for tetracycline (TC) degradation in aqueous solution was investigated using UV/H2O2 process and the results were compared with that of pure α-Fe2O3 NPs. α-Fe2O3 and 12-TSA·7H2O were synthesized according to previous reports and all products were characterized by using FTIR, SEM, EDX and XRD. Design of experiments (DoEs) was utilized and photocatalytic degradation process was optimized using full factorial design. The experiments were designed considering four variables including pH, the initial concentration of TC, catalyst concentration and H2O2 concentration at three levels. TC concentration reduction in the medium was measured using UV/Vis spectroscopy at λmax = 357 nm. The results of experiments indicated that supporting α-Fe2O3 NPs on the surface of 12-TSA·7H2O through SSD and FHRC methods caused to improve the filtration, recovery and photocatalytic activity of NPs. Also, it was indicated that those NPs supported through SSD method, have better photocatalytic performance than those supported through FHRC method. The statistical analyses revealed that the maximum TC degradation (97.39%) is obtained under those conditions in which pH and catalyst concentration variables are at maximum levels and the initial concentration of TC and H2O2 concentration variables are at minimum levels (pH 8, catalyst concentration = 150 ppm, initial concentration of TC = 30 ppm, H2O2 concentration = 0.1 ppm). A first order reaction with k = 0.0098 min−1 was observed for the photocatalytic degradation reaction.

Highlights

From the perspective of green chemistry, degradation of chemical pollutants in wastewater has attracted a lot of attention
X-ray diffraction (XRD) is one of the most important characterization tools used in solid state chemistry and materials science
The results revealed that: 1. Spherical a-Fe2O3 NPs had been successfully synthesized and supported on the surface of 12-TSAÁ7H2O through solid-state dispersion (SSD) and forced hydrolysis and reflux condensation (FHRC) methods with no decrease of

Summary

Introduction

From the perspective of green chemistry, degradation of chemical pollutants in wastewater has attracted a lot of attention. Antibiotics are one of the larger groups of these pollutants in wastewater released from pharmaceutical industries [1]. TC is one broad spectrum of antibiotics repeatedly detected in urban and industrial wastewaters, drinking water, surface water and groundwater [2,3,4,5,6]. Metal oxide NPs, i.e., iron oxides, have a special position in the science and technologies because of having wide applications and unique properties [8]. A-Fe2O3 (hematite) which is the most common form of iron oxides, has the rhombohedral structure and it is an attractive compound because of its applications in data storage, gas sensor, magnets materials, pigment, catalysis and photocatalysis [9,10,11,12,13,14]. Various techniques including co-precipitation, sol– gel, thermal decomposition, Micelle synthesis, sonochemical synthesis, hydrothermal synthesis and FHRC have

H H3C OH

12 Na2WO4 þ Na2SiO3 þ 26 HCl ð1Þ

Results and discussion

Result

Conclusions