Nickel (II) modified porous boron nitride: An effective adsorbent for tetracycline removal from aqueous solution

Highlights

• Ni (II) modified porous boron nitride (BN) was prepared and characterized.

• The interaction between porous BN and Ni (II) was proved to be B-O-Ni bond.

• BN-Ni-3 shows dramatic removal percentage up to 99.769% for 20 mg L⁻¹ TC.

• The adsorption followed pseudo-second-order kinetics and the Freundlich isotherm.

• DFT calculations reveal the changed electron transfer with the existence of Ni (II).

Abstract

Contamination of aqueous environment caused by various antibiotics has attracted wide attention. It is important to find effective adsorbents for the removal of toxic compounds. Herein, Ni (II) was anchored at the surface of porous boron nitride (BN) by a facile way to enhance the adsorption performance for tetracycline (TC). The interaction between porous BN and Ni (II) was proved to be B-O-Ni bond. It is noteworthy that Ni (II) modified porous BN shows excellent removal percentage up to 99.769% for TC which far exceeds the pristine porous BN (70.853%) and most other reported adsorption materials. The maximum adsorption capacity calculated from the Langmuir model is 429.582 mg g⁻¹, confirming that Ni (II) modified porous BN has a remarkable performance for removing TC. In addition, the adsorption of TC onto Ni (II) modified porous BN followed pseudo-second-order kinetics and the equilibrium data fitted well with the Freundlich isotherm, revealing that chemisorption and multilayer adsorption was dominated. Finally, the results of DFT calculations further demonstrated that the effective adsorption of TC on Ni (II) modified porous BN could be ascribed to cation bridge interaction, π-π interaction, Van de Waals force and electrostatic interaction.

Introduction

Water pollution, which has become a key issue that constrains the sustainable development of economy and endangers human health, is of increasing concern all over the world. Since penicillin had been applied in clinical treatment in 1942, hundreds of antibiotics had been isolated or synthesized for human and animal infections, which played a vital role in the second half of the 20th century. The usage of antibiotics for prevention, infection treatment, and even as a growth promoter to improve the efficiency of livestock has become a common phenomenon in animal husbandry [1], [2], [3]. Because the ingested antibiotics cannot be completely absorbed, more than 70% of the antibiotics are excreted in the urine and feces and released into the environment in an active form [4]. Although the concentration of antibiotics in surface water is mainly in the range of ng L⁻¹ to μg L⁻¹, long-term persistent exposure is likely to cause the emergence of drug-resistant microbial strains [5], [6]. As a non-destructive physical method, adsorption uses porous solid substances to adsorb and fix pollutants on its surface through physical or chemical interaction to separate and remove pollutants. Due to its low cost, simple operation, high efficiency and no by-products, it is one of the most commonly used and researched methods [7], [8].

Conventional adsorbents such as activated carbon, mesoporous silica, zeolites and adsorption resin have difficulties in repairing water environment effectively due to their shortcomings such as low adsorption capacity, poor stability and recyclability [9], [10], [11], [12]. Porous hexagonal boron nitride (h-BN) has attracted much attention due to its special physical and chemical properties including high specific surface area, abundant structural defects, low density, high thermal conductivity, exceptional chemical stability and oxidation resistance [13], [14]. These properties make porous h-BN have great application prospects in many fields, especially adsorption-related gas storage and transportation, pollutant adsorption and catalyst support [15], [16], [17]. The potential application of BN nanomaterials as adsorbents in the adsorption of antibiotics contaminants from water has also been confirmed [18], [19], [20], [21].

However, due to the constraints of adsorption efficiency and production cost, BN nanomaterials have been limited to some extent in practical applications as adsorbents. Therefore, finding a simple and effective method to modify BN nanomaterials and improve their adsorption capacity for antibiotics is of great significance. In recent years, various methods for modifying adsorption materials have emerged steadily. Some previous works have proved that metal ions can complexed with antibiotics by cation-bridge interaction [22], [23], [24]. Among them nickel not only has abundant reserves in nature but also has a large number of empty orbitals which can attract the electron cloud surrounding antibiotics molecule to form the antibiotic-metal complex. Zhang et al. developed nickel alginate particles by combining an alginate matrix with nickel ion and then evaluated its enhanced adsorption performance for ciprofloxacin [23]. Rivera-Jiménez et al. functionalized MCM-41 mesoporous silicate with nickel by thermal monolayer dispersion and grafting techniques, which greatly improved the adsorption capacity for naproxen [24]. All the above researches certified that nickel modifying is an easy and effective method to enhance the adsorption performance of adsorbents for antibiotics contaminants.

In this contribution, porous BN was modified by nickel (II) to improve its adsorption affinity and removal percentage for antibiotics in aqueous solution. A simple adsorption-maturing process was adopted and accomplished the uniform distribution of Ni (II) on the surface of porous BN. The interaction between porous BN and Ni (II) was first investigated and then the adsorption kinetics, isotherms and thermodynamics of Ni (II) modified porous BN for TC were systematically analyzed. Furthermore, first-principle calculations prove that the introduction of Ni (II) successfully improves the adsorption energy of porous BN for TC due to electron transfer and sharing.