Adsorption and visible-light photocatalytic degradation of organic pollutants by functionalized biochar: Role of iodine doping and reactive species.

Here we developed the functionalized biochar as low-cost and heavy metal-free photocatalysts via a facile iodine doping method, which exhibit efficient adsorption and visible-light-driven photocatalytic degradation of representative organic pollutants, phenol and tetracycline. On one hand, iodine doping elevates the adsorption via creating extra pores, e.g., the adsorbed amounts of phenol by iodine-doped WSP and OSR biochar are increased by 161.8% and 146.3%, respectively, which in turn facilitates the photocatalytic oxidation of the adsorbed pollutants. On the other hand, iodine doping leads to the strong photo-induced excitation and remarkably reduced charge carrier transfer resistance, boosting the photocatalytic activity of iodine-doped biochar by more than 20 orders towards organic pollutants (e.g., phenol) degradation. The systematic analysis of reactive species reveals the active roles of O2-, H2O2, 1O2, OH, electrons, and holes in photocatalytic process and identifies O2- to be the major contributor. This work affords a facile approach to generating porous and visible-light-driven photocatalyst from biomass for efficient adsorbing and degrading organic pollutants, opening up an avenue to turn biowaste into biomaterials for sustainable environmental remediation.

Fabrication of magnetic Fe3O4@SiO2@Bi2O2CO3/rGO composite for enhancing its photocatalytic performance for organic dyes and recyclability.

A novel magnetic Fe3O4@SiO2@Bi2O2CO3/rGO composite comprising of uniform core-shell-structured Fe3O4@SiO2@Bi2O2CO3 microspheres mounted on reduced graphene oxide (rGO) sheets was successfully fabricated by using a facile hydrothermal method. The adsorption-desorption isotherm of Fe3O4@SiO2@Bi2O2CO3/rGO belonged to type IV with an H4-type hysteresis loop. The specific surface areas and magnetization saturation value (Ms) of Fe3O4@SiO2@Bi2O2CO3/rGO (x = 0.15 g) were 102.12 m2/g and 25.4 emu/g, respectively. Fe3O4@SiO2@Bi2O2CO3/rGO (x = 0.15 g) exhibited remarkable photocatalytic degradation activity and mineralization effect for MO and decolorization performance for the mixed solution of MO, Rh B, and MB. MO degradation by Fe3O4@SiO2@Bi2O2CO3/rGO conformed to a first-order kinetic reaction, and the corresponding kapp value was 0.05553 min-1. A suitable amount of rGO in Fe3O4@SiO2@Bi2O2CO3/rGO could decrease the energy band gap, inhibit the recombination of photo-induced electron/hole (e-/h+) pair, and broaden and enhance the response of the catalyst to visible light, thereby enhancing the visible-light catalytic degradation of organic dyes. The active species produced in the photocatalysis included •O2-, •OH, and h+, with •O2- being the dominant active species. The as-prepared photocatalyst also showed excellent magnetic separation performance and stability. Results show that the as-prepared Fe3O4@SiO2@Bi2O2CO3/rGO composite is a promising photocatalyst with considerable application potential in organic dyes removal.

pH-dependent synthesis of iodine-deficient bismuth oxyiodide microstructures: Visible-light photocatalytic activity.

Bismuth oxyiodides have exhibited high potential for applications in visible-light photocatalytic environmental remediation and solar energy conversion. In this work, a series of iodine-deficient bismuth oxyiodides (Bi4O5I2, Bi7O9I3, Bi5O7I) can be simply prepared through a pH-dependent aqueous procedure with feeding Bi/I ratio of 2:1. The compositions of the Bi-based oxyiodides are closely related to acid-base circumstances, with Bi4O5I2 formed in weakly acidic medium (pH = 5) and Bi7O9I3, Bi5O7I in basic medium (pH = 8 and 11). Morphology differences of nanosheet-assembled Bi4O5I2, Bi7O9I3 architectures and rod-like Bi5O7I microstructures demonstrate different crystalline characters and construction of Bi-based oxyiodide crystals. UV-vis DRS results revealed good visible-light absorptions of Bi4O5I2 and Bi7O9I3 architectures and appropriate band structures for photocatalytic reactions, on comparison to Bi5O7I microrods. Low electrochemical impedance of Bi7O9I3 microflowers with sheet-like units further facilitated the separation of e--h+ carriers in the degradation process. Accordingly, among the bismuth oxyiodide samples, Bi7O9I3 displayed prominent visible-light degradation performance for colorless bisphenol-A (BPA) due to the direct photoexcitation process.