The interactions and adsorption mechanisms of ternary heavy metals on boron nitride

Highlights

• Boron nitrite with a short rod-like structures and chemical groups were synthesized.

• Antagonistic adsorption occurred during the adsorption in the ternary system.

• The difference in initial concentration affects the type of interaction between ions.

• Adsorption mechanisms include complexation, ion exchange and electrostatic adsorption.

Abstract

In this work, the interactions and adsorption mechanisms of Cu²⁺, Cd²⁺, and Ni²⁺ on boron nitride (BN) were tested by the simultaneous removal of metal ions from synthetic wastewater. BN was characterized using XRD, SEM, and FTIR spectroscopy. The adsorption differences between BN and the metal ions were explored through comparative studies in a single and ternary system. In the ternary system, adsorption occurs rapidly in the first 2 min for the metal ions, and the affinity order follows Cu²⁺>Cd²⁺>Ni²⁺. However, adsorption behavior changes due to the interaction between metal ions in the ternary system. Cu²⁺ showed an antagonistic effect on the adsorption of Cd²⁺ and Ni²⁺, while Cd²⁺ and Ni²⁺ produced a synergistic effect on Cu²⁺. In addition, the effect of metal ion concentration on the interaction between ions was studied based on a surface response experiment. An increase in Ni²⁺ or Cd²⁺ concentrations plays a synergistic effect on the adsorption of Cu²⁺, while an antagonistic adsorption for Ni²⁺ occurred with increasing Cu²⁺ or Cd²⁺ concentrations. We also discussed the various adsorption mechanisms as complexation, ion exchange, and electrostatic adsorption based on XPS analysis.

Introduction

Over the years, heavy metal pollution in water has received increasing attention. Copper, cadmium, and nickel are common heavy metals in industrial wastewater. Due to their toxicity and non-biodegradability, they may cause harm to human health and the ecosystem once they are discharged into a receiving water body without appropriate treatment.

Several methods, including chemical precipitation, membrane filtration, and electrochemical treatment have been reported to remove heavy metals from wastewater. Wang et al. (2019) proposed a comprehensive treatment process using hydroxide precipitation coupled with H₂O₂ oxidation and NaHS sulfide precipitation to achieve the selective removal of Cu, Fe, and Zn from wastewater. Duan et al. (2017) studied the reduction/removal of Cr (VI) using electrically conducting carbon nanotube-polyvinyl alcohol composite ultrafiltration membranes. Zhao et al. (2019a) proposed a new type of capacitive deionization-electrodeionization technology for the treatment of low-level Cu (II) wastewater. Compared to these technologies, the adsorption process could avoid producing large volumes of waste sludge, membrane backwashing effluent, or high energy consumption (Giwa et al., 2019).

The most essential aspect in the application of adsorption is the sorbent. Synthetic adsorbents possess high adsorption capacities to heavy metal ions compared to that of natural sorbents (Han et al. 2017; Chi et al., 2009; Bouhamed et al., 2012). For instance, Hayati et al. (2017, 2016) synthesized polyamide/amine dendrimer-modified carbon nanotubes, which had an adsorption capacity of 3333 mg/g and 3900 mg/g for Cu²⁺ and Ni²⁺, respectively. These capacities are much higher than that reported for fly ash-based adsorbents (7 mg/g for Cu²⁺) or natural clay (2.7 mg/g for Ni²⁺, 3.3 mg/g for Cd²⁺) (Duan et al., 2016; Darmayanti et al., 2019; Khan et al., 2019). Boron nitride (BN) has the advantages of excellent thermal stability, superb resistance to oxidation as well as chemical inertness. It has a similar structure to graphene but contains B–N polar bonds. Compared with carbon-based adsorbents, B–N polar bonds have better adsorption capacity (Li et al., 2013). Furthermore, due to BN materials contain the high specific surface area, bulk π systems, defects, and functional groups, recent researches reported shown it has an excellent adsorption performance towards metal ions in the single-contaminant system. (Xue et al., 2016; Mubarak et al., 2018; Liu et al., 2015; Yu et al., 2018).

Generally, industrial wastewater contains a variety of heavy metal ions with different concentrations. For example, the concentrations of Cu²⁺ and Ni²⁺ were 8 mg/L and 14 mg/L in electroplating wastewater; Cu²⁺ and Cd²⁺ concentrations were 9.3 mg/L and 6.1 mg/L in smelting effluent, and 19.5 mg/L and 34.3 mg/L in copper production effluents, respectively (Ajmal et al., 2001; Zhou et al., 2017; Mavrov et al., 2006). In these complex multicomponent systems, different heavy metal ions may interact and affect the adsorption capacities of specific sorbents (Srivastava et al., 2005; Zhang et al., 2017; He et al., 2018). Moreover, differences in ion concentrations may further affect their interactions. Therefore, these factors increase the difficulty of predicting the performance of sorbents. However, most current studies use the same metal ion concentration in multicomponent metal ion adsorption (Zhou et al., 2019a,Zhou et al., 2019b; Zhao et al., 2019c). In addition, the interaction behavior of heavy metal ions at different concentrations are seldom reported.

In this study, we synthesized BN and discuss its adsorption capacity for Cu²⁺, Cd²⁺, and Ni²⁺ in single-comonent systems. Then, the interactions between the three ions in an equi-concentration ternary system were studied. Following this, the effect of metal ion concentration on their interaction with the BN sorbent was studied based in the ternary system. We also explore the different adsorption mechanisms observed in the experiments using X-ray photoelectron spectroscopy (XPS). This paper provides a deeper understanding of the adsorption behavior of heavy metal ions in multi-component systems that more accurately reflect their behavior under more realistic conditions that exist in complex wastewater streams.