High {001} facets dominated BiOBr lamellas: facile hydrolysis preparation and selective visible-light photocatalytic activity

Abstract

Efficient photocatalytic nanocrystals with high-ratio exposure of active facets have aroused a great number of research interests in recent years. However, most preparations of such materials need the addition of special capping agents (like surfactants) or harsh reaction conditions (such as hydrothermal reactions). In this work, a controllable synthesis of BiOBr nanosheets with a thickness from 9 nm to 32 nm was easily achieved in a hydrolysis system through adjusting temperature and solvent, without adding any surfactant or capping agents. As the thickness of the nanosheets decreases from 32 nm to 9 nm, the ratio of exposed {001} facets, the active photocatalysis facets in BiOBr crystals, increases from 83% to 94%, along with an increased photocatalytic efficiency over rhodamine B (RhB) under visible-light.Various methods such as SEM, TEM, AFM, DRS and Raman spectroscopy were used to fully characterize the as-obtained BiOBr nanosheets. More importantly, the obtained BiOBr nanosheets exhibit a selective visible-light photocatalytic behavior as the activity over RhB is much higher than that over Methyl Orange (MO) or Methylene Blue (MB). This phenomenon was studied with in situ electron paramagnetic resonance (EPR) measurements and the potential mechanism was explored.

Thickness-dependent photocatalytic activity of bismuth oxybromide nanosheets with highly exposed (0 1 0) facets

“…6b) also analyzedthe photocatalytic data of BiOBr, [7,20] BiOCl, [17] and Bi 3 O 4 Cl [13] nanosheetsin the literature, and a similar linear relationship was obtained for these literature samples (Fig. S13, Supporting information), although the literature authors ascribed their photoactivity enhancement to either the increasing exposure percentages of photoactive facets or the intensifying IEF.In association with our previous results about the linear dependence of the k on the nanosheet thickness for the BiOBr lamellas with highly exposed (001) facets [20], we can conclude that this inversely linear dependence of the k on the nanosheet thickness is irrelevant to the exposed facets of the nanosheets.Thus, the nanosheet thickness is a crucial factor influencing the photoactivity of 2Dsemiconductor photocatalysts.…”

“…[14][15][16]The controversy of photocatalytic mechanisminstudy of crystal facet engineering of semiconductors prominently resides in bismuth-based photocatalysts, especially bismuth oxyhalide (BiOX, X=Cl, Br or I) with highly exposed (001) facet.For instance, most researchers attributed the photoactivity enhancement of BiOX nanosheets to increasing exposure percentages of photoactive (001) facets; [7,9,17,18]Zhang et al thought the photoactivity of Bi 3 O 4 Cl nanosheets with highly exposed (001) facets and similar structure as BiOX nanosheets relied on themagnitude of internal electric field(IEF); [13]Xie et al ascribed the higher photoactivity of BiOCl nanosheets to the more vacancy associates on the surface of (001) facets. [19]Actually, for these sheet-like photocatalysts with highly exposed (001) facets, a prominent reduction of nanosheet thickness was observed along with the increase of the (001) facet exposure percentage, [7,9,17,18]the IEF magnitude [13]or the vacancy associate amount. [19]Recently, we investigatedthe relationship between the photoactivity of BiOBr lamellasandthe lamella thicknessand found that the photoactivity of the samples depended inversely proportionallyonthe lamella thickness.…”

“…[6][7][8][9][10][11][12]The high photoreactivity of active crystal facets of semiconductorswas traditionally thought to arise from their high surface energy, [13]but recent studies indicated that the charge transfer between different facets with different energyband structures played a more important role. [14][15][16]The controversy of photocatalytic mechanisminstudy of crystal facet engineering of semiconductors prominently resides in bismuth-based photocatalysts, especially bismuth oxyhalide (BiOX, X=Cl, Br or I) with highly exposed (001) facet.For instance, most researchers attributed the photoactivity enhancement of BiOX nanosheets to increasing exposure percentages of photoactive (001) facets; [7,9,17,18]Zhang et al thought the photoactivity of Bi 3 O 4 Cl nanosheets with highly exposed (001) facets and similar structure as BiOX nanosheets relied on themagnitude of internal electric field(IEF); [13]Xie et al ascribed the higher photoactivity of BiOCl nanosheets to the more vacancy associates on the surface of (001) facets. [19]Actually, for these sheet-like photocatalysts with highly exposed (001) facets, a prominent reduction of nanosheet thickness was observed along with the increase of the (001) facet exposure percentage, [7,9,17,18]the IEF magnitude [13]or the vacancy associate amount.…”

Combustion Synthesis of BiOCl with Tunable Percentage of Exposed {001} Facets and Enhanced Photocatalytic Properties

“…5,6 BiOCl has a tetragonal structure with lattice constants of a = b = 0.389 and c = 0.789 nm. In its crystal structure, a layer structure (parallel to {001} facets) characterized by [Bi 2 O 2 ] slabs is interleaved by double slabs of Cl atoms. 7 In general, different crystal facets with different electronic structures and geometric shape exhibit different intrinsic reactivities and surface physical and chemical properties related with the crystallographic orientation.…”

Solvothermal Synthesis of Bi2O2CO3Nanoplates for Efficient Photodegradation of RhB and Phenol under Simulated Solar Light Irradiation

“…Jiang et al 19 selectively synthesized BiOCl single-crystalline nanosheets with exposed {001} and {010} facets via a facile hydrothermal route. Zhang et al 20 synthesized BiOBr nanosheets with thicknesses ranging from 9 to 32 nm by a facile and surfactant-free method, which shown higher photocatalytic activity to RhB under visible-light irradiation. Bi 2 O 2 CO 3 is a typical "Sillén" phase, in which Bi-O layers and (CO 3 ) layers are inter-grown with the plane of the (CO 3 ) group orthogonal to the plane of the Bi-O layer.…”