A Review on Heteroanionic-Based Materials for Photocatalysis Applications

Abstract

In the last few decades, photocatalysis has been found to be a practical, environmentally friendly approach for degrading various pollutants into non-toxic products (e.g., H2O and CO2) and generating fuels from water using solar light. Mainly, traditional photocatalysts (such as metal oxides, sulfides, and nitrides) have shown a promising role in various photocatalysis reactions. However, it faces many bottlenecks, such as a wider band gap, low light absorption nature, photo-corrosion issues, and quick recombination rates. Due to these, a big question arises of whether these traditional photocatalysts can meet increasing energy demand and degrade emerging pollutants in the future. Currently, researchers view heteroanionic materials as a feasible alternative to conventional photocatalysts for future energy generation and water purification techniques due to their superior light absorption capacity, narrower band gap, and improved photo-corrosion resistance. Therefore, this article summarizes the recent developments in heteroanionic materials, their classifications based on anionic presence, their synthesis techniques, and their role in photocatalysis. In the end, we present a few recommendations for improving the photocatalytic performance of future heteroanionic materials.

Low Carrier Effective Masses in Photoactive Sr2Sb2O2Q3 (Q = S, Se): The Role of the Lone Pair

“…5−8 This has motivated researchers to turn toward mixed-anion materials in the search for stable and efficient visible light photocatalysts. 9,10 On the other hand, the Aurivillius phases Bi 2 MO 6 (M = Mo, W) have smaller band gaps (2.6 and 2.8 eV for Bi 2 MoO 6 and Bi 2 WO 6 , respectively) due in part to the contribution from Bi 3+ 6s 2 states to the top of the valence band, 4 suggesting that "inert pair" ns 2 cations (such as Sb 3+ ) might be advantageous in tuning the band gap in potential photocatalysts.…”

“…However, the use of visible light places constraints on the photocatalytic semiconductor: it must have a band gap in the range of 1.23–3.1 eV, and its conduction band minimum (CBM) and valence band maximum (VBM) must be compatible with the redox potential of water (i.e., the CBM more negative than the reduction potential of H 2 O/H 2 (0 V) and the VBM more positive than the oxidation potential of O 2 /H 2 O (1.23 V)) . While many oxide photocatalysts have shown good performance (such as K 2 La 2 Ti 3 O 10 (2186 and 1131 μmol·h –1 for H 2 and O 2 evolution, respectively) and Bi 2 M O 6 ( k app = 6.3 × 10 –3 and 1.7 × 10 –3 min –1 for W and Mo, respectively, for rhodamine B degradation)), they typically have large band gaps (e.g., 3.5 eV for K 2 La 2 Ti 3 O 10 ) and are only photocatalytically active under UV irradiation. − This has motivated researchers to turn toward mixed-anion materials in the search for stable and efficient visible light photocatalysts. , On the other hand, the Aurivillius phases Bi 2 M O 6 (M = Mo, W) have smaller band gaps (2.6 and 2.8 eV for Bi 2 MoO 6 and Bi 2 WO 6 , respectively) due in part to the contribution from Bi 3+ 6s 2 states to the top of the valence band, suggesting that “inert pair” n s cations (such as Sb 3+ ) might be advantageous in tuning the band gap in potential photocatalysts.…”

Mechanistic Insights into the Phase Formation of an Atypical Iron Oxynitride (FexOyNz) System and Its Multifunctional Photocatalytic Applications

“…Among such various conventional oxide-based photocatalysts, iron oxide is a well-reported material for its photocatalytic applications, including photo-Fenton reactions. , Similarly, iron nitride films are often demonstrated for magnetic and mechanical applications . However, iron oxynitride has not received much attention in research, particularly by oxidizing iron nitride in air ambience.…”

Single-Source Precursors for the Controlled Aqueous Synthesis of Bismuth Oxyhalides

“…Solar water splitting is a promising platform to generate hydrogen as a clean fuel. − Bismuth oxyhalides of the form BiOX (X = Cl, Br, I) are a special class of layered photocatalytic materials for this purpose. − The BiOX crystal structure comprises alternating positively charged Bi 2 O 2 2+ and negatively charged X – double layers. , This structure supports their use as photocatalysts, as a static internal electric field is generated between the layers that spatially separates photogenerated holes and electrons, providing a 2-dimensional path to the surface for these charge carriers to engage in redox reactions.…”

“…11−17 The BiOX crystal structure comprises alternating positively charged Bi 2 O 2 2+ and negatively charged X − double layers. 18,19 This structure supports their use as photocatalysts, as a static internal electric field is generated between the layers that spatially separates photogenerated holes and electrons, providing a 2-dimensional path to the surface for these charge carriers to engage in redox reactions.…”