Abstract
Photocatalytic reduction of CO2 using solar energy to decrease CO2 emission is a promising clean renewable fuel production technology. Recently, Bi-based semiconductors with excellent photocatalytic activity and carbon-based carriers with large specific surface areas and strong CO2 adsorption capacity have attracted extensive attention. In this study, activated carbon spheres (ACSs) were obtained via carbonization and steam activation of phenolic resin-based carbon spheres at 850 °C synthesized by suspension polymerization. Then, the BiOBr/ACSs sample was successfully prepared via a simple impregnation method. The as-prepared samples were characterized by XRD, SEM, EDX, DRS, PL, EIS, XPS, BET, CO2 adsorption isotherm and CO2-TPD. The BiOBr and BiOBr/ACSs samples exhibited high CO selectivity for photocatalytic CO2 reduction, and BiOBr/ACSs achieved a rather higher photocatalytic activity (23.74 μmol g−1 h−1) than BiOBr (2.39 μmol g−1 h−1) under simulated sunlight irradiation. Moreover, the analysis of the obtained results indicates that in this photocatalyst system, due to their higher micropore surface area and larger micropore volume, ACSs provide enough physical adsorption sites for CO2 adsorption, and the intrinsic structure of ACSs can offer effective electron transfer ability for a fast and efficient separation of photo-induced electron–hole pairs. Finally, a possible enhanced photocatalytic mechanism of BiOBr/ACSs was investigated and proposed. Our findings should provide new and important research ideas for the construction of highly efficient photocatalyst systems for the reduction of CO2 to solar fuels and chemicals.
Highlights
With the rapid development of industrial economy, the global environmental pollution and energy crisis have become extremely signi cant challenges that humans are facing in the short-term.[1]
It has been found that the X-ray diffraction (XRD) patterns of BiOBr obtained a er loading BiOBr onto activated carbon spheres (ACSs) do not shi signi cantly; this implies that the effect of ACSs on the phase structure of the BiOBr sample is negligible
The valence band (VB) electrons of BiOBr are excited to its conduction band minimum (CBM), and CO2 activation is achieved; the holes (h+) le in VBM react with H2O to provide H+
Summary
BiOBr, as one of the Bi-based semiconductors with several advantages, including earth abundance, stability, economy and non-toxicity, exhibits a unique layered structure, excellent electrical and optical properties as well as a suitable indirect band gap ($2.7 eV) to endow effective photocatalytic activity and stability.[12,13,14,15,16,17] It was believed that the Bi 6s and O 2p states could form a large number of dispersed hybridized valence bands, which facilitated the migration and oxidation of photogenerated holes; this induced the efficient separation of photogenerated electron–hole (eÀ–h+) pairs and improved the photocatalytic efficiency.[18]. Prepared a series of activated carbon spheres (ACSs) through the carbonization of phenolic resin spheres using the one-pot modi ed Stober and CO2 activation method, which exhibited high surface areas (from 730 to 2930 m2 gÀ1) and CO2 adsorption capacities at 1 bar (4.55 and 8.05 mmol gÀ1, at 25 C and 0 C, respectively).[32] Rivera-Utrilla et al and Ao et al synthesized TiO2-AC33 and BiOBr-AC26 photocatalysts, respectively, with greatly improved photocatalytic performances owing to the higher BET surface area of the AC support with strong adsorption capacity for pollutants and signi cant in uence on the optical absorption capacity and crystal size of the catalysts. The photocatalytic mechanism of action of the BiOBr/ ACSs sample has been investigated and proposed; the results obtained should provide new and important research ideas and great guiding signi cance for the construction of highly-efficient photocatalyst systems for photocatalytic CO2 reduction
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