Tailoring porosity and band gap of pistachio shell–derived carbons via different activation strategies for efficient photodegradation

A series of activated carbons was fabricated from a biomass precursor using physical (steam) and chemical activation routes (H₃PO₄, KOH, and ZnCl₂), and their photocatalytic performance toward methylene blue (MB) degradation under visible-light irradiation was systematically investigated. The activation strategy strongly influenced the textural characteristics, optical properties, and charge-carrier dynamics of the resulting materials. Chemical activation, particularly with KOH and ZnCl₂, led to the development of hierarchical micro–mesoporous structures, significantly larger specific surface areas (750–976 m2/g), and narrowed optical band gaps (2.95–2.74 eV), enabling enhanced light absorption and improved adsorption capability. Among the samples, AC–ZnCl₂ exhibited the highest photocatalytic efficiency, achieving nearly complete MB degradation (98.1%) with a superior apparent rate constant (k = 0.0498 min⁻¹), attributed to reduced electron–hole recombination as evidenced by pronounced PL quenching. AC–ZnCl₂ maintained over 89% MB degradation efficiency after four reuse cycles, demonstrating excellent stability for practical wastewater treatment. These findings demonstrate that tailoring the activation chemistry provides a highly effective approach to optimizing the photocatalytic properties of biomass-derived activated carbons for environmental remediation applications.