High surface area microporous carbons as photoreactors for the catalytic photodegradation of methylene blue under UV–vis irradiation

• Pore texture and surface chemistry are key factors in activated carbons as photoreactors.
• Photodegradation of methylene blue is promoted when it is confined in micropores.
• Micropores enhance the photocatalytic activity of TiO2.
• Combined adsorption-photocatalysis is an efficient method for methylene blue abatement.

High surface area (ca. 1700–3400 m2 g−1) activated carbons (ACs) were prepared from Chinese anthracite by chemical activation with KOH using KOH/Anthracite weight ratios (WKOH/WAnthracite) ranging from 1.6 to 5. The photocatalytic degradation of methylene blue (MB) at high concentration conditions up to 25 ppm under UV–vis irradiation was performed on AC and on TiO2-AC mixtures prepared by slurry methodology. The highest values of both BET surface area and of micropore volume to total pore volume ratio were found with a WKOH/WAnthracite ratio of 4. It was found that ACs developed photocatalytic activity and an important synergistic effect with TiO2. TiO2-AC mixtures showed enhancements in the photocatalytic activity up to 6 times higher than commercial TiO2. The photocatalytic activity of ACs and binary materials was discussed with respect to textural properties and surface functional groups of carbons. The ratio of micropore volume to total pore volume and the surface pH of the ACs play important roles upon the photocatalytic activity of TiO2-AC, and the combination of adsorption followed by photodegradation clearly contributed to the treatment of highly concentrated methylene blue. It was concluded that photochemical reactive microporous ACs have a beneficial influence upon the photocatalytic activity of TiO2.

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