Study On Iron Pillared Clay As A Heterogeneous Photo-fenton Catalyst For Photocatalytic Degradation Of Azo Dye Reactive Brilliant Orange X-gn

Nowadays, synthetic dyes are consumed broadly in textile industries and large volumes of dye wastewater are produced. Advanced oxidation processes (AOPs) have been widely applied to deal with azo dye wastewater in recent years, which are characterized by the generation of highly oxidative hydroxyl radicals (?OH) in the homogeneous or heterogeneous phase. However, iron ions which act as catalyst are dissolved in water in the homogeneous Fenton process. Remained iron ions in the treated water normally exceed 10 mg L-1 and need to be removed. This adds to the cost as well as secondary pollution, thus limiting its industrial application. To overcome such limitations and to synthesize reusable catalysts, efforts have been made to develop hetero-Fenton catalysts, such as Fe-treated laponite, iron exchanged zeolite and iron-loaded resin. Many researchers have reported that pillared clays intercalated by iron cations have been used as active heterogeneous Fenton catalysts in decoloration and mineralization of azo dyes.Attention has been focused on the application of a heterogeneous photo-Fenton process to the photodegradation of reactive dye wastewater under UV irradiation. However, the ultraviolet band occupies only 3～5% of the solar light energy that reaches the earth, while artificial ultraviolet apparatus typically consumes large quantities of electrical power. Therefore, it is accepted that an important issue in the heterogeneous photo-Fenton process is to develop catalysts which efficiently use sunlight or visible light irradiation instead of UV as the light source.In this study, iron pillared vermiculite, which was obtained by exchanging the interlayer cations of layered clays with hydroxyl iron ions, was developed as a photo-heterogeneous catalyst in the decoloration and mineralization of the azo dye X-GN. Decoloration of X-GN by different processes was discussed, and the effects of parameters in heterogeneous photo-Fenton process such as solution pH, H2O2 concentration, catalyst dosage, initial X-GN concentration and reaction temperature, were evaluated, to elucidate their effects on the photocatalytic degradation of X-GN. TOC removal and degradation kinetics were also investigated. The present study reveals that iron pillared vermiculite and iron-pillared montmorillonite have great potential as heterogeneous photo-Fenton catalysts for the treatment of industrial dyeing wastewater.The conclusions are as follows:1. In the present study, a novel heterogeneous photo-Fenton catalyst was prepared by iron-pillared vermiculite (Fe-VT). The catalyst Fe-VT was characterized by Laser particle size analyzer, X-ray diffraction (XRD), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. It was found that hydroxy-Fe of low polymerization degree intercalated into the silicate layers of vermiculite successfully. Under the following experimental conditions: 100mg/L reactive brilliant orange X-GN (named as X-GN) solution, pH 3, 30oC, 3.92 mM H2O2 and 0.5g/L Fe-VT dosage, 98.7% decoloration and 54.4% TOC removal could be achieved with 75 min UV irradiation. The kinetics results showed that decoloration kinetics of X-GN was well fitted by a pseudo-first order equation. In addition, the maximum dissolved iron, determined by atomic absorption spectrophotometer (AAS), was less than 1 ppm. Hence, taking into account the favorable photocatalytic properties and low leaching of iron ions, iron-pillared vermiculite is a promising catalyst for dye wastewater treatment.2. Decolorization and mineralization of reactive brilliant orange X-GN was investigated under visible light irradiation (λ≥420 nm) by using Fe-Mt / H2O2 as the heterogeneous photo-Fenton reagent. The characterization results (XRD,FTIR,XRF,BET,XPS,UV–vis diffuse spectra) of Fe-Mt suggested that small-sized hydrolyzed iron successfully intercalated into the interlayer spaces of the clay via pillaring. The stability of the Fe-Mt catalyst was evaluated according to the decolorization efficiency for X-GN with used catalyst from previous runs and the concentration of iron ions leached from the solid structure into the reaction solution. The catalytic results showed that at a reaction temperature of 30℃, pH 3.0, 4.9mmol/L H2O2 and 0.6 g/L catalyst dosage, 98.6 % discoloration of X-GN were achieved under visible irradiation after 140 min treatment. Furthermore, decoloration efficiency was till higher than 90% after the catalyst Fe-Mt being used for 3 cycles. A halogen lamp as light source has demonstrated that visible radiation can be successfully used for a heterogeneous photo-Fenton process.