Sequential combined adsorption and solid-phase photocatalysis to remove aqueous organic pollutants by H3PO4-modified TiO2 nanoparticles anchored on biochar

Various studies have focused on the photocatalytic remediation of toxic organic contaminants in water, but low light utilization and difficult catalyst recovery hindered the prospect of industrial-scale application of photo-catalytic technology. The dispersion of photocatalysts into the solution is the major cause of these shortcomings. In this work, an alternative strategy of sequential adsorption followed by photocatalytic degradation was veri-fied. This strategy operated photocatalysis on the solid phase saturated with contaminants, which not only avoided the absorption and barrier of light by water, but also the regenerated catalyst can be directly used for the next cycle. For this, H3PO4-modified TiO2 nanoparticles loaded on biochar (P-TiO2/BC) was used to adsorb dyes and then the collected adsorbent was directly illuminated to degrade the adsorbed dyes. P-TiO2/BC was char-acterized by XRD, FTIR, XPS, SEM, UV-Vis DRS and N-2 adsorption-desorption technologies. The influence of solution pH on the adsorption of P-TiO2/BC, as well as the adsorption kinetics, isotherms and desorption was investigated. Photocatalystic experiments showed that the adsorbed dyes can be completely degraded. The free radical trapping experiments and electron spin resonance were performed to examine the mechanism of dye degradation. In the meantime, the adsorbent regenerated by solid-phase photocatalysis can be reused several times with higher regeneration rates (88.1-69.3%). This work should provide an available approach for the photocatalytic treatment of water pollution and the photo-regeneration of adsorbents.