Solar photocatalytic activity of nano-ZnO supported on activated carbon or brick grain particles: Role of adsorption in dye degradation

• ZnO was supported on activated carbon (AC) or brick grain particles (BGP).
• ZnO-AC and ZnO-BGP had significant adsorption and photocatalytic activity.
• Photocatalytic dye degradation was significantly influenced by adsorption of dye.
• Simultaneous adsorption and photocatalysis (A + P) was the most efficient process.
• ZnO-AC and ZnO-BGP exhibited significant recycling efficiency and stability.

In precedent work, nano-ZnO was supported on activated carbon or brick grain particles using simple co-precipitation method. Successful formation of ZnO-activated carbon (ZnO-AC) and ZnO-brick grain particle (ZnO-BGP) nanocomposites was ascertained by various spectral techniques. Scanning electron microscope (SEM) images revealed that ZnO particles were highly dispersed in activated carbon/brick grain particles. The size of ZnO-AC and ZnO-BGP was found to be 70 and 80 nm, respectively. Both ZnO-AC and ZnO-BGP exhibited excellent adsorption and photocatalytic activity for malachite green (MG) and congo red dye (CR) degradation. The adsorption data for MG and CR removal followed pseudo second order kinetic model. The adsorption capacity followed the order: ZnO-AC > ZnO-BGP > ZnO. The effect of adsorption on photocatalysis was explored under different reaction conditions. Simultaneous adsorption and photocatalysis (A + P) exhibited promoting effect on dye degradation. While adsorption followed by photocatalysis (A − P) had retarding effect on dye removal. ZnO-AC/A + P system emerged as highly efficient for MG and CR degradation. The rate of photodegradation followed pseudo first order kinetics. Using ZnO-AC/A + P system, 99 and 92% of COD removal was attainted for MG and CR degradation, respectively. The oxidative degradation mainly occurred through hydroxyl radicals. The prepared nanocomposites possessed higher recyclability and could be easily separated from solution by sedimentation.

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