Innovative nickel–alginate materials for efficient removal of nutrient pollutants

An international research team led by Prof Shahabaldin Rezania from Sejong University (South Korea) and researchers from Italy has introduced a novel nickel-doped alginate technology that significantly advances sustainable wastewater treatment. The authors found a new material that can remove both nitrate and phosphate with exceptionally high adsorption capacities, outperforming most existing natural-polymer-based sorbents.

Addressing a Critical Global Need

Nitrate and phosphate are among the most persistent nutrient pollutants worldwide. Their excess contributes to eutrophication, algal blooms, and long-term ecological decline. Besides, a recent study proposed a new way to tackle this problem using a biopolymer-based adsorbent engineered to capture both nitrate (NO₃⁻) and phosphate (PO₄³⁻) from water. The ability to efficiently remove both pollutants using renewable, low-cost material offers a significant advancement for:

• Agricultural runoff management,

• Industrial wastewater treatment, and

• Restoration of polluted rivers and lakes.

The study, published in Process Safety and Environmental Protection (Elsevier), in 2025.

Novelty and Key Innovations

The innovative section of this research lies in the strategic incorporation of Ni²⁺ ions into a natural calcium–alginate matrix, transforming a simple biopolymer into a highly active, multifunctional adsorbent. Based on the findings, the highest adsorption capacities of 169.5 mg/g for nitrate and 238.1 mg/g for phosphate were observed only after 2 hours.

The primary adsorption mechanism is driven by electrostatic interactions between the negatively charged nitrate ions (NO₃⁻) and phosphate (PO43-) and the positively charged nickel ions (Ni²⁺) embedded within the alginate matrix. Both Calcium and Nickel ions act as the primary crosslinking agents due to their ability to coordinate with alginate's functional groups. This combination significantly enhances the adsorption efficiency of the Ni-CaAlg composite for nitrate ions.

The proposed adsorbent had significant differences in its surface area, pore volume, and mean pore diameter, with a surface area of 24.485 m²/g and a pore volume of 7.9231 cm³. Besides, a smooth and uniform bead structure with diameters ranging from 51.53 µm to 1.202 mm, exhibiting consistent and homogenous surface morphology. The nickel-doped calcium alginate beads exhibit a rougher, more irregular surface than alginate, with visible clusters and aggregates of nickel particles dispersed throughout the alginate matrix.

In addition, as alginate is renewable and widely available, and because the beads can be regenerated for ten cycles with an efficiency of 67%. These values demonstrate the proposed materials' performance as one of the highest-performing alginate-based adsorbents in wastewater treatment systems.

What makes these findings significant:

• Dual-contaminant capability: The beads show strong simultaneous affinity for both nitrate and phosphate.

• Nickel-driven enhancement: Introducing Ni²⁺ ions creates new binding sites, increases surface charge density, and strengthens both electrostatic and coordination interactions.

• Improved microstructure: Surface area and pore characteristics improve significantly after nickel modification, enabling faster and stronger pollutant binding.

• Green and scalable: the beads are made from renewable alginate and manufactured through a simple, low-cost process suitable for industrial-scale production.

Institutional and Global Impact

By leading this innovation, Sejong University strengthens its international standing in environmental engineering and sustainable materials development. The study enhances the university's global academic visibility, influence in green technology research, and leadership in cross-continental scientific collaboration.

Lead Researcher's View

Professor Shahabaldin Rezania noted the broader importance of the findings:

"This work demonstrates that natural polymers can be modified with highly efficient materials for solving real environmental challenges. If successfully scaled and integrated into existing treatment trains, nickel-doped calcium alginate beads could become a practical tool for protecting drinking water sources and reducing eutrophication risks in nutrient-rich waters".

More information:
Joolaei Ahranjani, P., Dehghan, K., Farhoudi, S., Esmaeili Bidhendi, M., Sotoudehnia Korrani, Z., & Rezania, S. (2025). Effective removal of nitrate and phosphate ions from water using nickel-doped calcium alginate beads. Process Safety and Environmental Protection, 194, 486–496.

DOI: 10.1016/j.psep.2024.12.034

Provided by Sejong University