Bifunctional adsorbent/photocatalyst AC/ZnO composite for solar resource intermittency management

Solar photocatalysis faces a significant challenge, the treatment process stops immediately when sunlight is interrupted, such as by clouds or at night. To address this, researchers have begun developing hybrid materials that combine adsorption and photocatalysis at the particle level. In this study, we contribute to this effort by designing and testing a new type of hybrid granular composite, in which a zinc oxide (ZnO) photocatalyst is coated across the activated carbon surface. By carefully adjusting the AC content, from 1 to 30% by weight, we tailored the material to perform two key functions, the AC stores pollutant molecules, while the ZnO nanoparticles break them down using light. The granular composites were structurally and compositionally characterized to confirm the successful ZnO-coated AC architecture. Their performance was evaluated through experimental benches measuring key spectral properties, sorption kinetics (described via Langmuir isotherms), and photocatalytic degradation rates. The feasibility of the AC/ZnO granular material synthesis was confirmed by analyzing the evolution of α as a function of the AC weight fraction (wt%). Composites containing 5% AC exhibited high efficiency, with α reaching 60.5 mg·kJ −1 , whereas those with 30% AC showed a lower α value of 18.45 mg·kJ −1 after approximately 4 h, while exhibiting the highest adsorption capacity (qₘₐₓ = 65 mg·g −1 ). Consequently, the composition can be tailored to the target application by increasing the AC content to enhance adsorption or the ZnO content to promote photo-oxidation, while preserving the intrinsic adsorption properties of AC. By merging storage and oxidation capabilities into a single particle, these AC/ZnO granular composites separates phenol capture from the need for constant sunlight. As a result, it avoids the delays typical of multi-stage treatment systems and offers a more streamlined way to cope with the intermittent nature of solar energy. This makes it a promising, practical option for self-sufficient solar-powered water treatment.