One-pot synthesis and immobilization of urea-derived graphitic carbon nitride onto ceramic foams for visible-light photocatalytic wet peroxide oxidation in water treatment

Abstract

A straightforward one-pot in-situ method was employed to successfully obtain urea-derived graphitic carbon nitride (CN) deposited onto a macro-reticulated ceramic alumina-based foam (AF). The resulting CN-coated foams (CN-F) were characterized by different techniques (SEM, N2 adsorption, DRUV–vis, fluorescence spectroscopy), revealing that CN-F structures have visible light absorption and distinctive photoluminescence properties. Moreover, these CN-F materials were investigated for the first time in water treatment, specifically for the degradation of the antibiotic sulfamethoxazole (SMX) in aqueous solutions under visible-LED irradiation and continuous flow mode with total recirculation. The photocatalytic activity of different CN-F was investigated using various CN loads, without or with addition of H2O2 (i.e. Photocatalysis – PC or photocatalytic wet peroxide oxidation – PCWPO, respectively), at different pH (5.0 – 8.5) and a tentative reaction mechanism was described. Thus CN-F with 13.5 mgCN·gAF−1 performed better than with other loads in PCWPO, as demonstrated by a higher conversion of H2O2 and SMX into reaction by-products (short-chain acids and inorganic ions belonging to organic N- or S-containing species). This photocatalyst also succeeded when tested in continuous dead-end mode operation with SMX in ultrapure water or a mixture of 6 pharmaceutical substances (500 ppb each) spiked in a natural river water sample, demonstrating an excellent visible-light PCWPO activity preventing fouling over the catalyst, achieving lower phytotoxicity for the treated water and showing a prolonged stability under 72 h, without CN detachment or any loss of material.