Synergistic effect of TiO₂ size on activated carbon composites for ruthenium N-3 dye adsorption and photocatalytic degradation in wastewater treatment

Abstract

The removal of toxic minerals such as heavy metals from water is critical for wastewater treatment. Adsorptions by activated carbon (AC) is limited by depleted active sites once the adsorbent has bonded to AC. This study aims to explore the properties of AC and enhance its adsorption capability via the addition of TiO2 to produce a photocatalytic AC. Further optimization of AC/TiO2 properties was made by depositing two different sizes of TiO2 (small-sized TiO2 (TS) and big-sized TiO2 (TB)) onto AC. AC/TiO2 composites (AC/TS and AC/TB) were synthesized by wet-impregnation method. The morphology, structure, and properties of the adsorbent catalysts (AC, AC/TS, AC/TB, TS and TB) were investigated using X-ray Diffraction (XRD), Field Emission-Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Diffuse Reflectance Spectroscopy (DRS), Brunauer-Emmett-Teller (BET) surface area and pore size analysis. The capability of modified AC and its adsorbent catalysts were tested for removal of ruthenium N-3 dye. Their kinetics (pseudo-first and pseudo-second order) and isotherm modelling (Langmuir and Freundlich) were also investigated. AC/TiO2 (AC/TS and AC/TB) composites demonstrated an enhanced ruthenium N-3 dye removal by both adsorption and photodegradation, as a result of a synergistic effect. The adsorbent catalysts were more efficient in UV-light compared to dark condition. In this study, the AC/TB composite was more efficient, and resulted in a maximum amount of N-3 dye adsorbed per unit mass (qm) of 523 mg g−1 for about 99% of N-3 dye after 180 min. The composite exhibits overall pseudo-second order reaction kinetics and prefers a Freundlich isotherm where the sorption process was involved in a heterogeneous layer.