Three-dimensional microspheric g-CN coupled by biochar: facile sodium alginate immobilization and excellent photocatalytic Cr(iv) reduction.

Photocatalysts comprising biochar and g-CN loaded on sodium alginate were prepared and characterized in terms of reusability and photocatalytic Cr(vi) reduction performance. The observed photocurrent responses as well as photoluminescence and UV-visible diffuse reflectance spectra showed that the best-performing catalyst featured the benefits of efficient photogenerated charge separation, superior electron conductance/transfer, and excellent light adsorption ability, which resulted in a higher photocatalytic Cr(vi) reduction performance compared to that of pure g-CN powder. The prepared composite was shown to be reusable and well separable from the reaction mixture, thus being a promising material for the practical photocatalytic removal of Cr(vi) from wastewater. The trapping experiment and XPS spectra of catalysts after reactions confirm that the decontamination of Cr(vi) lies in the photocatalytic reduction of this species into low-toxicity Cr(iii) by photoinduced electrons generated from g-CN, followed by the adsorption of Cr(iii) on biochar or alginate with large specific areas.