Work

Surface charge engineering of phosphoric acid-activated geopolymers via hydroxyapatite incorporation for enhanced anionic water pollutant removal

Year: 2025

Type: article

Abstract: Geopolymers have emerged as promising sorbents for environmental applications, particularly in removing cationic pollutants due to their negatively charged surfaces. However, their effectiveness for anionic pollutant removal, such as Congo red (CR) dye, remains limited. This study introduces an innovative approach by integrating hydroxyapatite (HAP) into phosphoric acid-activated geopolymers (PAGP) to optimize the surface charge and enhance the adsorption of anionic dyes. The effects of varying HAP loading (up to 50 wt%) on the structural, thermal, mechanical, and CR dye adsorption properties of PAGP were systematically investigated. The optimal formulation, M-50HAP (50 % HAP), exhibited a five-fold increase in specific surface area (from 14 to 72 m²/g), significantly improved structural integrity with a denser microstructure, and enhanced compressive strength (from 0.70 to 1.88 MPa). Zeta potential measurements confirmed that HAP addition reduced surface negativity, promoting anionic dye adsorption. The M-50HAP sorbent achieved a maximum CR dye adsorption capacity of 15.70 mg/g (pH 3, 100 mg/L initial concentration, 4 g/L adsorbent, 24 h contact time) and demonstrated excellent reusability over 12 cycles without performance degradation. Density functional theory (DFT) simulations revealed that CR protonation enhanced its positive charge distribution, facilitating adsorption onto M-50HAP via hydrogen bonding, electron interactions, and electrostatic forces. This study demonstrates that HAP-modified PAGPs are scalable, mechanically robust adsorbents with tunable surface charge, offering a significant advancement in sustainable wastewater treatment and anionic contaminant remediation.

Source: Colloids and Surfaces A Physicochemical and Engineering Aspects

DOI: 10.1016/j.colsurfa.2025.139377

Authors: Aghilas Brahmi, Nuno P.F. Gonçalves, Belhouchet Rebai Houdhaifa, João A. Labrincha, Rui M. Novais

Institutions: University of Bouira, University of Aveiro, Mohamed-Cherif Messaadia University

Language: English

Topic: Adsorption and biosorption for pollutant removal

Subfield: Water Science and Technology

Field: Environmental Science

Domain: Physical Sciences

SDGs: Clean water and sanitation, Responsible consumption and production

Open Access status: hybrid

Estimated APC paid: $3,200