Food-waste-derived hydrochar to a low-cost p-type semiconducting photocatalyst (Zn–Al@HC): multifunctional role in real wastewater treatment and environmental sustainability

Abstract

The present investigation demonstrates the effectiveness of a novel Zn–Al@HC photocatalyst supported by anaerobically digested food waste-derived hydrochar (HC) for the photocatalytic activation of peroxydisulphate (PDS) and abatement of salicylic acid (SA) in the UV/PDS/Zn–Al@HC system. The morphological and photo-electrochemical characterization of Zn–Al@HC supported the formation of ZnAl₂O₄ crystals and the contraction of band gap energy from 3.80 eV (ZnAl₂O₄) to 2.36 eV (Zn–Al@HC) by the inclusion of HC (1.86 eV) as a carbon-based support material. Moreover, a remarkable reduction in recombination of photogenerated e⁻/h⁺ was witnessed in response to UV irradiation in the UV/PDS/Zn–Al@HC system for SA degradation. Under optimal operating conditions, the proposed treatment system achieved 94.45 ± 0.65% degradation of SA. Furthermore, the radical scavenging test revealed the dominance of hydroxyl radical followed by sulphate radicals in the UV/PDS/Zn–Al@HC system, and a potential mechanism was deduced. Cyclic voltammetry for 20 repetitive cycles in a harsh medium affirms the photo-stability of Zn–Al@HC, even under real environmental conditions. The energy-economic valuation of the as-synthesized photocatalyst unveiled the total operating cost and electrical energy per order of UV/PDS/Zn–Al@HC to be 0.1536 $ per m⁻³ order⁻¹ and 0.0130 kW h m⁻³ order⁻¹, respectively. Thus, the system proves to be a sustainable and economical option for the management of waste and remediation of chemicals of emerging concern, which can be implemented as future large-scale technology for wastewater treatment.