Catalytic degradation of P-chlorophenol by muscovite-supported nano zero valent iron composite: Synthesis, characterization, and mechanism studies

Highlights

• Nano zerovalent iron/muscovite (NZVI@muscovite) were synthesized

• NZVI@muscovite composite was characterized in detail

• NZVI@muscovite degraded P-CP at a pollutant: catalyst ratio of 714 mg:1 g

• NZVI@muscovite degraded P-CP was adsorption-Fenton-like reaction

Abstract

P-chlorophenol (P–CP) is a recalcitrant toxicant in wastewater. Recently, the use of composite materials and environmentally friendly technology in the degradation of pollutants in wastewater has attracted widespread attention. For the first time, the nano zerovalent iron nano zerovalent iron (NZVI)-loaded muscovite (NZVI@muscovite), a novel composite material, was synthesized by liquid-phase reduction. The different physicochemical properties of NZVI@muscovite indicated that the muscovite could support NZVI of 40–50 nm sizes. The NZVI@muscovite had a low agglomeration degree, good dispersibility, and improved catalytic activity. In addition, the optimization experiments of P–CP degradation demonstrated that NZVI@muscovite actively degraded P–CP at a pollutant:catalyst ratio of 714 mg:1 g. This ratio was higher than that of the other composite materials under optimal operating conditions. Adsorption and degradation by Fenton-like reaction were the main mechanisms underlying P–CP degradation. This study extended the use of NZVI@muscovite as an efficient composite material for the degradation of P–CP in an aqueous environment.

Introduction

P-chlorophenol (P-CP), a recalcitrant toxicant in wastewater, has attracted the attention of environmentalists because of its high toxicity and solubility (Garba et al., 2019). P–CP is a persistent organic pollutant that promotes biological degradation and has biosuppressive effects on biological treatment processes even at low concentrations (Najafpoor et al., 2018; Garba et al., 2019; Wang et al., 2020), which can change the taste and odor of water resources. Some restrictions and regulations for P–CP concentration in wastewater exist (with a threshold value of 0.1 ppb) (Eslami et al., 2018), and a technique for the rapid removal/degradation of P–CP from wastewater is urgently needed.

Physical and chemical studies on the removal/degradation of P–CP in aqueous solution have been conducted (Sharma et al., 2019). The traditional processes of P–CP removal/degradation from aqueous solutions are ineffective because of their nondestructive nature. These methods can only transfer P–CP from aqueous solution to a solid phase (Eslami et al., 2018). The use of advanced oxidation processes (AOPs) to degrade refractory organic pollutants has been highly recommended (Barbosa et al., 2018; Alcalá-Delgado et al., 2018; Sharma et al., 2019; Duan et al., 2019a, Duan et al., 2019b, Duan et al., 2019c). However, the traditional Fenton reaction (TFR), as an AOP, has certain limitations, such as the formation of iron sludge as a precipitate in practical application (Ghime and Ghosh, 2017; Cai et al., 2018; Barndok et al., 2018; Goncalves et al., 2019). Furthermore, TFR requires the constant addition of iron salts (Duan et al., 2015a, Duan et al., 2015b; Hernández-Francisco et al., 2017; Huang et al., 2018). Considering these factors, the in situ production of Fe²⁺ may be practical (Jamil et al., 2017; Kumar et al., 2018). Therefore, a composite material that generates Fe²⁺ in situ has been developed to solve these problems.

The nano zerovalent iron (NZVI) has been used to remove different types of organic pollutants (Arshadi et al., 2018; Amiri et al., 2018; Bao et al., 2019a, Bao et al., 2019b). NZVI has a high specific surface area and surface activity and can generate Fe²⁺ in situ in wastewater. Therefore, combining NZVI with AOP to fully exploit the potential of NZVI and promote its application to wastewater treatment is necessary (Xi et al., 2014, Duan et al., 2015a, Duan et al., 2015b). However, NZVI has a strong dipole–dipole attraction that causes strong aggregation, reducing the active sites of the catalyst. This limitation can be overcome by using supporting materials for NZVI (Yang et al., 2015; Zhu et al., 2017; Wang et al., 2017; Wang et al., 2017; Vilardi et al., 2018; Yu et al., 2019). As rich natural resources, clay minerals are suitable auxiliary support materials that can adsorb contaminants on their surface, prevent the aggregation of nanometals, and improve the activity of nanometals (Ma et al., 2016; Deng et al., 2017; Ezzatahmadi et al., 2018; Bao et al., 2019a, Bao et al., 2019b; Duan et al., 2019a, Duan et al., 2019b, Duan et al., 2019c). In our previous research, diatomite and bentonite, rectorite, and palygorskite clays have been used as supporting materials for NZVI (Xi et al., 2014; Ma et al., 2016; Deng et al., 2017; Ezzatahmadi et al., 2018; Bao et al., 2019a, Bao et al., 2019b; Duan et al., 2019a, Duan et al., 2019b, Duan et al., 2019c). These minerals can degrade organic pollutants, such as acid orange II, bisphenol a, P-CP and 2, 4-dichlorophenol, by acting as catalysts for the Fenton-like reaction. However, their complete degradation of the pollutants is unsuitable. Therefore, using a suitable clay mineral as a support material is necessary.

Layered silicates have recently attracted researchers'attention, because their charge can change. This ability causes cation exchange, which occupies the interlayer space. This effect is beneficial for the preparation of nanocomposite materials. Muscovite-K{Al₂(AlSi₃O₁₀)(OH)₂} is a typical layered silicate mineral. Muscovite is a natural mineral material used in industrial applications, such as automobiles, electrical appliances, packaging, and absorbents (Dada et al., 2016; Dada et al., 2017; Yuan et al., 2018; Han et al., 2018; Li et al., 2019). However, the use of muscovite as supporting material for NZVI has not been studied.

In the present study, NZVI@muscovite was synthesized using muscovite as a support material. The physicochemical properties of muscovite, NZVI@muscovite, and NZVI were studied using various characterization methods. The degradation of P–CP was also evaluated using NZVI@muscovite. Finally, the mechanism underlying the catalytic degradation of P–CP using NZVI@muscovite was proposed.