Boosting the visible-light photoactivity of Bi2WO6 using acidic carbon additives

Abstract

a b s t r a c tWe have explored the role of the physicohemical properties of carbon materials as additives to bismuth tungstate on its structure, optical properties, and photocatalytic activity for the degradation of rhodamine B under visible light. For this purpose, C/Bi 2 WO 6 hybrid composites were prepared following two different routes: (i) physical mixture of the catalyst components, and (ii) one-pot hydrothermal synthesis of the semiconductor in the presence of the carbon additive. Three carbons with different properties were selected as additives: biomass-derived activated carbon, carbon nanotubes and carbon spheres obtained from polysaccharides. Data has shown the outstanding role of the acidic/basic nature of the carbon additive, and of the synthetic method on the photocatalytic performance of the resulting composites. For a given additive, the degradation rate of RhB is greatly improved for the catalysts prepared through a one-step hydrothermal synthesis, where there is low shielding effect of the carbon matrix. Carbon additives of acidic nature boost the surface acidity of the hybrid photocatalyst, thereby enhancing the photodegradation of RhB under visible light via a coupled mechanism (photosensitization, semiconductor photocatalysis and carbon-photon mediated reactions).

Photoelectrochemical Response of WO3/Nanoporous Carbon Anodes for Photocatalytic Water Oxidation

“…The spectra corresponding to the WO 3 /carbon mixtures showed similar trends regardless of the crystalline phase of WO 3 ; below 500 nm the profiles were similar to those of the corresponding bare semiconductor. In the region between 500-800 nm, the absorbance gradually increased with the amount of the carbon additive ( Figure S1), as a result of the light absorption of the carbon matrix [43,44].…”

Carbon Materials as Additives to WO3 for an Enhanced Conversion of Simulated Solar Light

“…On the contrary, the dependence with the structural order of the carbon additive is not clear, as previously discussed for the conversion of phenol (Figures 5 and 6). A similar behavior has been reported for the degradation of RhB using other semiconductors, and attributed to the degradation via coupled mechanisms (photosensitization, photocatalysis, and carbon-photon mediated reactions) in acidic photocatalysts (Galoppini, 2004;Carmona et al, 2015;Wang et al, 2014). Indeed, acidic catalysts' surfaces favor strong interactions with the adsorbed RhB molecules, boosting the degradation via the photosensitization as a result of a more efficient injection of electrons from the dye to the surface of the catalyst.…”

“…20 nm in the absorption sharp edge was detected as the samples are prepared by physical mixture; it is unlikely (but may not be discarded) to have an optimized interface between both phases of this catalyst that would favor the absorption of low energy photons. However, the profiles of the WO3/carbon catalysts showed a marked increase in the absorbance in the region between 500 and 800 nm, regardless the nature of the carbon, a characteristic feature associated with the strong light absorption of black opaque materials (Araña et al, 2003;Carmona et al, 2015). The trend for the absorption above 500 nm followed the order: CNT > HC > CL.…”

“…A more elaborated discussion on the physicochemical properties of the nanoporous carbons used as additives has been reported in a previous study (Carmona et al, 2015) (see also Supplementary Material); however, selected properties are herein shown for data interpretation purposes. Briefly, the high resolution SEM images and EDX analysis of the WO3/carbon catalysts evidence the homogeneous distribution of the carbon additive within the semiconductor matrix (Figure 1), showing the good contact between both phases (carbon and inorganic particles) despite the low amount of additive and the synthetic procedure by physical mixture.…”

Insights on the Use of Carbon Additives as Promoters of the Visible-Light Photocatalytic Activity of Bi2WO6

“…Various forms of porous carbons have also been used for this purpose, due to the increased mass transfer upon adsorption of the pollutant on the porosity [21,22]. In this regard, recent investigations including our own have reported that the photocatalytic performance of Bi 2 WO 6 can be enhanced by the use of certain amounts of carbon additives; nevertheless, the effect of the carbon additive has been barely addressed, and the optimum nominal carbon content seems to be unclear and dependent on the nature of the carbon additive [23,24,25,26,27].…”