Adsorption of phosphate on iron oxide doped halloysite nanotubes

Dema A Almasri,Navid B Saleh,Muataz A Atieh,Said Ahzi,Gordon Mckay

doi:10.1038/s41598-019-39035-2

Dema A Almasri, Navid B Saleh + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-39035-2

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Abstract

Excess phosphate in water is known to cause eutrophication, and its removal is imperative. Nanoclay minerals are widely used in environmental remediation due to their low-cost, adequate availability, environmental compatibility, and adsorption efficiency. However, the removal of anions with nanoclays is not very effective because of electrostatic repulsion from clay surfaces with a net negative charge. Among clay minerals, halloysite nanotubes (HNTs) possess a negatively charged exterior and a positively charged inner lumen. This provides an increased affinity for anion removal. In this study, HNTs are modified with nano-scale iron oxide (Fe2O3) to enhance the adsorption capacity of the nanosorbent. This modification allowed for effective distribution of these oxide surfaces, which are known to sorb phosphate via ligand exchange and by forming inner-sphere complexes. A detailed characterization of the raw and (Fe2O3) modified HNTs (Fe-HNT) is conducted. Influences of Fe2O3 loading, adsorbent dosage, contact time, pH, initial phosphate concentration, and coexisting ions on the phosphate adsorption capacity are studied. Results demonstrate that adsorption on Fe-HNT is pH-dependent with fast initial adsorption kinetics. The underlying mechanism is identified as a combination of electrostatic attraction, ligand exchange, and Lewis acid-base interactions. The nanomaterial provides promising results for its application in water/wastewater treatment.

Highlights

Excess phosphate in water is known to cause eutrophication, and its removal is imperative
Clearer illustrations of the structure of the raw halloysite nanotubes (HNTs) and 1Fe-HNT are obtained through HRTEM imaging, as shown in Fig. 1a,b, respectively. 1Fe-HNT is chosen for transmission electron microscopy (TEM) characterization since it is used for the equilibrium experiments
For the 1Fe-HNTs shown in Fig. 1b, it is observed that the Fe2O3 nanoparticles are attached on the surface of the HNTs

Summary

Introduction

Excess phosphate in water is known to cause eutrophication, and its removal is imperative. The unique surface properties (i.e., the positively charged inner lumen) of HNTs render it to be a promising material for electrostatic removal of phosphates and other anions. A synergistic removal of phosphate by a positively charged HNT interior and iron oxide modified exterior could prove to be a promising low-cost nano-sorbent alternative.

Results

Conclusion