Characterization and physicochemical aspects of novel cellulose-based layered double hydroxide nanocomposite for removal of antimony and fluoride from aqueous solution

Abstract

A series of novel adsorbents composed of cellulose (CL) with Ca/Al layered double hydroxide (CC_xA; where x represent the Ca/Al molar ratio) were prepared for the adsorption of antimony (Sb(V)) and fluoride (F⁻) ions from aqueous solutions. The CC_xA was characterized by Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), elemental analysis (CHNS/O), thermogravimetric analysis (TGA-DTA), zeta potential, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis. The effects of varying parameters such as dose, pH, contact time, temperature and initial concentration on the adsorption process were investigated. According to the obtained results, the adsorption processes were described by a pseudo-second-order kinetic model. Langmuir adsorption isotherm model provided the best fit for the experimental data and was used to describe isotherm constants. The maximum adsorption capacity was found to be 77.2 and 63.1 mg/g for Sb(V) and F⁻, respectively by CC₃A (experimental conditions: pH 5.5, time 60 min, dose 15 mg/10 mL, temperature 298 K). The CC₃A nanocomposite was able to reduce the Sb(V) and F⁻ ions concentration in synthetic solution to lower than 6 μg/L and 1.5 mg/L, respectively, which are maximum contaminant levels of these elements in drinking water according to WHO guidelines.

Introduction

The co-existence of heavy metals, non-metals and metalloids such as fluoride, sulfate, antimony, selenium and nitrate in natural water has posed a global concern for many countries. Over the recent years, and according to World Health Organization (WHO), antimony and fluoride belong to the most significant groundwater pollutants which can cause many environmental and health problems, especially for human beings (He et al., 2014; Wu et al., 2010). Fluoride ions are introduced to groundwater mainly from natural sources. For example, the groundwater can react with the rock aquifer containing fluoride which can result in the enrichment of groundwater by fluoride ions (Bhatnagar et al., 2011). Industrial activities such as fire retardants, pigment, mining industry and ceramic can also contribute to the discharge of various toxic metals and metalloids into aquatic environments (Ayoob and Gupta, 2006; Leng et al., 2012; Li et al., 2016; Meenakshi and Maheshwari, 2006). Some areas such as China, India, Bangladesh, Mexico, Southern Tunisia, Egypt, New Zealand and Japan have suffered from high concentrations of Sb(V) and F⁻ in groundwater (Du et al., 2014; Guissouma and Tarhouni, 2015; Li et al., 2012; Tsering et al., 2019). However, a small amount of fluoride ions of less than 1.5 mg/L in drinking water is essential and beneficial for teeth and dental health. On the other hand, a high concentration of fluoride (> 1.5 mg/L) intake into the body causes many diseases such as skeleton fluorosis, non-skeletal fluorosis and teeth disintegration (Dayananda et al., 2014; Nell and Livanos, 1988). As for antimony, a concentration of more than 6 μg/L in drinking water poses even greater danger than fluoride due to its inherent toxic and possibly carcinogenic nature (Smichowski and Madrid, 1998; Wu et al., 2010; Zhong et al., 2020a, 2020b). The environmental behavior of Sb(V) is often similar to that of arsenic (As) (Wilson et al., 2010). Therefore, there is an urgent need for a suitable method for the removal and preconcentration of Sb(V) and F⁻ from groundwater. Various treatment techniques such as electrodialysis, chemical coagulation, chemical precipitation, membrane separation, photochemical degradation, ion exchange, neutralization, reverse osmosis, biological processes and adsorption have been applied for the separation of Sb(V) and F⁻ ions from contaminated water (Bergmann and Koparal, 2011; Chen et al., 2020; Dorjee et al., 2014; Qiusheng et al., 2015; Wang et al., 2020; Zhang et al., 2014).

Among these methods, the adsorption process has attracted the attention of researchers due to its easy operation, eco-friendliness, good selectivity, high removal efficiency and cost-effectiveness (Bessaies et al., 2020; Iftekhar, 2019; Iftekhar et al., 2018a, 2017a, 2020; Jagtap et al., 2012; Mouelhi et al., 2016; Ramasamy et al., 2019). Different adsorbents such as activated carbon, multi-walled carbon nanotubes, bauxite, hematite, iron oxides and hydroxides, activated alumina, bone charcoal, bentonite and sodium montmorillonite have been investigated for Sb(V) and F⁻ removal (Bhaumik et al., 2011; Das et al., 2005; Loganathan et al., 2013; Rashmi et al., 2011; Salam and Mohamed, 2013; Swain et al., 2009; Yu et al., 2014; Zhao et al., 2010). Several studies have therefore concentrated on finding an effective and low-cost sorbent with uniformly accessible pores, a bead shape, physical and chemical stability, a high surface area and high affinity for both fluoride and Sb(V).

In this context, the synthesis of nanocomposites has attracted a great deal of interest for the adsorption process because of their phenomenal electrical, barrier and mechanical properties (Iftekhar et al., 2018a; Srivastava et al., 2020). They are known as composite materials, which have at least one dimension in the nano-range (1–100 nm). Various nanocomposites have been synthesized based on inorganic and organic matrices like carbon nanotubes (Liao et al., 2017; Rashmi et al., 2011), cadmium sulfide nanoparticles (Mohamed et al., 2014), silica (Peng et al., 2006; Trivinho-Strixino et al., 2004), layered silicate (Kokabi et al., 2007) and cellulose (Zhou et al., 2013).

Cellulose is a well-known effective matrix due to its special properties: hydrophilicity, high surface area, renewability, porosity, biodegradability and low cost in removing toxic pollution (Zhou et al., 2013). Cellulose is a natural polysaccharide endowed with intramolecular hydrogen bonding and good stability and can be derivatized to yield various useful products (Mohanty et al., 2002). Layered double hydroxides (LDHs) have attracted a great deal of interest because of their features: high customization capacity and applications as catalysts, ceramic precursors, ion exchangers, absorbents, drugs, carriers, polymer stabilizers and pollution remediation sorbents. LDHs are bidimensional solids with a positive charge excess in their brucite (Mg(OH)₂)-like layers and balanced with the presence of anions in the interlayer space (Borgiallo and Rojas, 2019; Hudcová et al., 2019; Kameda et al., 2015, 2017; Leroux and Besse, 2001). LDHs capacity as pollutant sorbents has been extensively reported both for inorganic (Park et al., 2007) and organic (Asif et al., 2017, 2016; Gao et al., 2018, 2017; Habib et al., 2017; Hamida et al., 2018; Hammouda et al., 2019, 2017; Koilraj and Srinivasan, 2013; Wang et al., 2019, 2018) anions. However, the application of these LDH-intercalated biopolymer nanocomposites as an adsorbent for the separation of heavy metals, non-metals and metalloids from groundwater is limited.

In this context, the goal of this study is to synthesize a series of nanocomposites (CC_xA) with different molar ratio of Ca:Al and to evaluate their potential for removal of Sb(V) and F⁻ from their aqueous solutions. The prepared nanocomposites were characterized by various techniques viz. Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), elemental analysis (CHNS/O), thermogravimetric analysis (TGA-DTA), zeta potential, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis. After that, the adsorption kinetics for Sb(V) and F⁻ removal have been studied to assess the reaction rate constants. Equilibrium and thermodynamic data were also investigated to understand more about the adsorption mechanism. The stability and affinity of the sorbent were also investigated to establish the environmental application of the synthesized LDH. It should be mentioned that, up to now, CC_xA nanocomposite has not yet been used for Sb(V) and F⁻ ion removal.