Hydrochar of Prunus persica: green promoter of radical species to degrade methylene blue with visible irradiation

Abstract

The creation of new materials based on metal-free catalysts represents a sustainable alternative in the treatment of water contaminated with dyes. In this context, the use of agro-industrial wastes for the creation of hydrochars with applications in environmental water remediation is an attractive and green option for metal-free catalysts for visible heterogeneous photocatalysis. In this study, hydrochars derived from agro-industrial waste of Prunus persica (peach pit) and their application in visible photodegradation of dyes were performed. The evaluation of the temperature and reaction time of hydrochars showed that 180 °C and 3 h yielded the highest photocatalytic activity and lower energy requirements in their preparation. The electron paramagnetic resonance (EPR) characterization evidenced the presence of persistent free radicals of the oxygen-centered radical type and, together with the oxygenated groups present in the carbonaceous structure of the hydrochar, promoted the generation of radical species such as superoxide and hydroxyl radicals. The visible photodegradation experiments of methylene blue (MB) demonstrated a high degradation efficiency of 92.9% using the following conditions: C_i = 10 mg/L, pH 7.0, hydrochar dosage: 50 mg, V: 50 mL, 120 min of irradiation time, and white-LED irradiation source. In addition, the generation of radicals •OH, O₂^−•, and ¹O₂, was demonstrated, as well as the potential use of the hydrochars for photodegradation in tap water and effluent of wastewater treatment plant matrices. Finally, the valorization of Prunus persica biomass through hydrochar production offers a promising avenue for water treatment and a route for the revalorization of agro-industrial waste.

Graphical abstract