Exploring the Origin of High Dechlorination Activity in Polar Materials M₂B₅O₉Cl (M = Ca, Sr, Ba, Pb) with Built-In Electric Field

Abstract

Polar photocatalyst materials usually exhibit ferroelectric characteristics giving rise to spontaneous polarization behavior which works as a driving force for the separation of photogenerated electrons and holes and mitigates the effect of charge recombination. This study shows that the surface potential changes for a polar phtotocatalyst before and after photoirradiation can be used to predict the photocatalytic activities among different phtotocatalysts. We systematically investigated the correlation among the surface properties, crystal structure, electronic band structure, photocatalytic activity, and stability of four B−O and alkaline earth cations containing photocatalysts, M 2 B 5 O 9 Cl (M = Ca, Sr, Ba, Pb). Among the four studied photocatalysts, Ba 2 B 5 O 9 Cl exhibits the greatest changes in the surface potential after photoirradiation and also shows the highest photocatalytic activity for dechlorination of chlorophenols under UV light irradiation. Its photocatalytic activity is about 1.3, 2.8, 4.4, and 15 times those of Ca 2 B 5 O 9 Cl, Sr 2 B 5 O 9 Cl, Pb 2 B 5 O 9 Cl, and P25 samples, respectively. The results support that the photocatalytic activity of the four photocatalysts strongly depends on the spontaneous polarization power. Overall, these findings demonstrate the utility of Kelvin probe force microscopy that can screen for a highly efficient photodegradation materials in the field of photocatalysis.

High-Efficiency Visible Light Responsive Sulfide KSb5S8 Photocatalyst with a Layered Crystal Structure

“…On the basis of the alignment of the above energy levels, we confirmed the possibility of the oxidation mechanism proposed in Figure 6. Generally, active species, including super radical anion• ( ), free hydroxyl radical• (OH), and photo-induced holes (ℎ ), are related to the photocatalytic degradation reaction [26]. Photo-induced electrons ( ) and holes (ℎ ) can transfer to the surface of crystals and then react with molecular oxygen (O2) and H2O molecules to produce superoxide radical anion (• ) and free hydroxyl radical (• OH), respectively.…”

The Role of Polarization in Photocatalysis

“…Given the absence of symmetric centers in crystal structures,t he accumulation of microcosmic polarization from polar units of NCS materials can result in al arge macroscopic polarization as adriving force for charge transfer and separation, thus benefitting photocatalytic activity.N onlinear optical (NLO) materials with NCS crystal structures produce ap olarization electric field caused by an intrinsic dipole moment, and they were recently reported as efficient [10] K 3 B 6 O 10 X( X = Cl and Br), [11] Na 3 VO 2 B 6 O 11 , [12] M 2 B 5 O 9 Cl (M = Ca, Sr, Ba, Pb), [13] Bi 2 O 2 [BO 2 (OH)], [14] Ag 6 Si 2 O 7 , [15] and Ag 9 (SiO 4 ) 2 NO 3 . [16] wherem is the local dipole moment, n is the total number of electrons, e is the charge of an electron, andr is the difference between the "centroids" of the positive and negative charges.…”

The Role of Polarization in Photocatalysis

“…Given the absence of symmetric centers in crystal structures, the accumulation of microcosmic polarization from polar units of NCS materials can result in a large macroscopic polarization as a driving force for charge transfer and separation, thus benefitting photocatalytic activity. Nonlinear optical (NLO) materials with NCS crystal structures produce a polarization electric field caused by an intrinsic dipole moment, and they were recently reported as efficient photocatalysts: BiOIO 3 , BiOI 0.926 V 0.074 O 3 , Bi 2 O 2 (OH)(NO 3 ), K 3 B 6 O 10 X (X=Cl and Br), Na 3 VO 2 B 6 O 11 , M 2 B 5 O 9 Cl (M=Ca, Sr, Ba, Pb), Bi 2 O 2 [BO 2 (OH)], Ag 6 Si 2 O 7 , and Ag 9 (SiO 4 ) 2 NO 3 . The local dipole moment generated by this particular type of structure can be calculated from the Debye equation [Eq.…”