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Review

Inorganic Bismuth Catalysts for Photocatalytic Organic Reactions

by
Hualei He
1,
Qiyan Lv
1,2,* and
Bing Yu
1,*
1
College of Chemistry, School of Life Sciences, Zhengzhou University, Zhengzhou 450001, China
2
National Engineering Research Center of Low-Carbon Processing and Utilization of Forest Biomass, Nanjing Forestry University, Nanjing 210037, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(2), 135; https://doi.org/10.3390/catal15020135
Submission received: 27 October 2024 / Revised: 22 January 2025 / Accepted: 28 January 2025 / Published: 1 February 2025
(This article belongs to the Special Issue Photocatalysis: Past, Present, and Future Outlook)
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Abstract

:
Bismuth (Bi) is recognized as a low-toxicity and environmentally friendly metal. Owing to its diverse oxidation states, Bi-based compounds demonstrate exceptional catalytic activities across numerous organic reactions. In particular, Bi-based inorganic materials have emerged as a promising class of photocatalysts in synthetic chemistry. In this review, the recent applications of inorganic Bi-materials, e.g., Bi2O3, BiVO4, BiCl3, Bi2WO6, and Bi4O5Br2, as photocatalysts in various organic reactions, including C-H oxidation, radical addition of olefins, and coupling reactions, have been summarized. The reaction mechanisms are discussed to reveal the crucial steps for enhancing catalytic performance. Moreover, the current challenges and prospects in this vibrant research area are also outlined, aiming to provide valuable insights and guidance for the development of more efficient Bi-based photocatalysts and their applications in diverse organic synthetic pathways.

1. Introduction

In recent years, photocatalytic organic synthesis reactions have attracted considerable attention due to their mild conditions and high efficiency [1,2,3,4,5,6,7,8]. The role of photocatalysts is vital in these processes. Homogeneous photocatalysts, such as metal complexes and organic small molecule dyes are widely applied in various photocatalytic organic synthesis reactions. However, the inability to recover and reuse these photocatalysts following the reaction not only escalates the reaction costs but also poses risks to both the environment and human health. In contrast, heterogeneous photocatalysts can be easily recovered and reused while maintaining stability after the reaction [9,10,11,12,13,14,15,16]. Therefore, the development of more efficient and stable novel heterogeneous photocatalysts is of significant importance to the fields of green chemistry and organic synthesis.
Bismuth is an element in group 15 of the periodic table and has the atomic number 83. Compared to traditional metal catalysts, it offers advantages such as low cost, non-toxicity, abundant reserves, and good availability [17,18]. Although bismuth ranks 69th in abundance in the Earth’s crust, significant quantities are obtained as a byproduct during the refining of various metals, including copper and tin [19]. Consequently, bismuth and its compounds are relatively inexpensive. Furthermore, bismuth and its derivatives are non-toxic, non-carcinogenic, and exhibit no bioaccumulation properties. They have low solubility in blood and water, posing no harm to human health or the environment, making them truly green elements [20,21,22].
Recent research has demonstrated that bismuth possesses the ability to undergo transitions between multiple oxidation states, which enables the development of innovative redox cycles applicable in organic synthesis. Importantly, various catalytic bismuth redox systems have been discovered, revealing new opportunities within the field of main-group redox catalysis. In this regard, recent progress concerning the utilization of organic Bi compounds via the Bi(II)/Bi(III), Bi(I)/Bi(III), and Bi(III)/Bi(V) redox systems in organic synthesis has been well reviewed [18]. On the other hand, the applications of inorganic bismuth catalysts were also reviewed. For example, in 2021, Huang et al. [23] reviewed the applications of bismuth tungstate (Bi2WO6) in photocatalytic energy conversion and environmental remediation, in which various modification strategies for Bi2WO6, including morphology control, atomic modulation, and composite fabrication, were discussed. In 2022, Zhou et al. [24] summarized the research progress on bismuth-based photocatalysts in environmental and energy applications, emphasizing their roles in removing organic pollutants, H2 production, and O2 generation. In 2023, Chen and colleagues [25] provided a comprehensive overview of bismuth-based oxide photocatalysts in selective organic synthesis. Recently, Ma et al. [26] reviewed the progress on bismuth-based photocatalysts in the fields of energy, environment, and biomedicine, in which functional modification methods are also included.
Despite those above-mentioned achievements, reviews specifically addressing the applications of inorganic Bi-based materials in photocatalytic organic reactions remain relatively scarce. Therefore, we herein document the applications of inorganic bismuth photocatalysts in organic reactions, with an emphasis on analyzing their performance in terms of catalytic efficiency, selectivity, and stability. It aims to provide insights into the advanced application of novel photocatalysts and promote the applications of photocatalytic technology in organic synthesis.

2. Application of Bi2O3 (or Bi2S3) in Photocatalytic Organic Reactions

Metal oxides have long been extensively utilized as semiconductor-type photocatalysts in photocatalytic reactions. For instance, the rutile and anatase forms of TiO2, which possess band gaps of 3.0 eV and 3.2 eV, respectively, exhibit large band gaps that restrict their absorption solely to ultraviolet light. Compared with TiO2, Bi2O3 has a band gap of approximately 2.5–2.8 eV, while Bi2S3 has a low band gap of around 1.3 eV [27,28], enabling a broader absorption spectrum in the visible-light region. Previous studies indicate that the bandgap energies of α-, β-, γ-, and δ-Bi2O3 are approximately 2.8 eV, 2.5 eV, 2.8 eV, and 2.7 eV, respectively [29]. The phase structure of crystals is often recognized as a significant parameter influencing their properties. In this context, the photocatalytic performance of Bi2O3 is closely linked to its crystalline morphology and structural characteristics. Although various phase structures of crystals may be interconverted under certain conditions, it is essential to pay attention to the phase structure of catalysts during catalytic reactions.

2.1. α-Alkylation of Aldehydes

In 2014, Pericàs and Palomares’s group [27] reported an asymmetric α-alkylation of aldehydes 1 which utilized α-bromocarbonyl compounds as alkylating reagents, employing bismuth-based materials as low-bandgap photocatalysts alongside the second-generation MacMillan imidazolidinone as a chiral catalyst 3 (Scheme 1). This reaction system can be applied to aldehyde derivatives with α-H, affording the corresponding products in 56–86% yields with ee values up to 82–98%. The organic photocatalytic α-alkylation of aldehydes occurs in the presence of the semiconductor Bi2O3, which features two cycling mechanisms: the semiconductor cycle and the electron donor–acceptor (EDA) interaction cycle, and the reaction is dominated by the photocatalytic cycle. In the photocatalytic cycle, incident photons excite electrons on the surface of the semiconductor, prompting their transition from the valence band (VB) to the conduction band (CB) and generating holes (h+). The photo-excited electrons enable the reductive cleavage of α-bromocarbonyl, releasing the Br- anion and forming the radical 5. On the other hand, the MacMillan catalyst 3 undergoes a nucleophilic reaction with aldehydes 1, producing the intermediate 4, which subsequently coupling with radical 5 to yield radical 6. Radical 6 is converted into intermediate 7 through a single-electron transfer (SET) process with the holes on VB. Upon decomposition, it generates product 2 and regenerates the MacMillan catalyst 3. Regrettably, in this study, commercially available bismuth oxide was directly applied, and the specific phase structure of the crystals was unclear.
In this reaction, it is believed that the reducing ability of the photo-generated electrons on Bi2O3 is crucial to this photocatalytic process, facilitating the single-electron reduction of bromides to obtain the key alkyl radical. In addition to commercial Bi2O3, Bi2S3 nanoparticles demonstrated notable catalytic activity in this process, indicating that bismuth-based materials, as low-band-gap photocatalysts, possess significant potential for the photocatalytic conversion of bromides. Surprisingly, Bi2O3 did not function as a typical heterogeneous catalyst in this reaction; subsequent literature reports indicated that the process yielded a homogeneous mixture [30,31]. In this context, the in situ-generated homogeneous BinBrm species may function as the real active photocatalyst. This observation partially elucidates why only specific brominated substrates can act as reactants in the reaction; it is likely that only certain brominated compounds like 2-bromomalonates, α-bromocarbonyl compounds, and CBr4 are capable of interacting with the catalyst to generate the species that possesses catalytic activity.

2.2. ATRA Reactions of Olefins

In 2015, Pericàs and coworkers [28] reported a Bi2O3-photocatalyzed atom transfer radical addition (ATRA) reaction of terminal alkenes 8 with bromides 9 in DMSO under visible-light irradiation (Scheme 2). The bifunctionalized product 10 could be obtained in good yields (45–90%) under a low catalyst loading (1 mol%). The photogenerated electrons facilitate the reductive cleavage of organic bromides, leading to the formation of radical 11. The photogenerated radical 11 was added to alkenes 8, producing radical intermediate 12. The intermediate 12 may undergo subsequent transformations through two possible pathways. In route a, a radical–polar crossover process was proposed; i.e., the radical intermediate 12 underwent SET oxidation with the holes of Bi2O3 to give the corresponding carbocation intermediate 13, which ultimately reacted with bromide anion to form the ATRA product 10. In route b, a halogen atom transfer (XAT) process was proposed; i.e., radical 12 extracted a bromine atom from the starting material 9, directly producing compound 10 and releasing another radical 11 to sustain the chain reaction. While routes a and b occur concurrently, the reaction mechanism is more favorably oriented towards route a under the influence of Bi2O3.
In 2021, Pericàs and Noël’s group [30] revealed that in the Bi2O3-photocatalyzed ATRA reaction of olefins with 2-bromomalonates, the Bi2O3 is firstly converted into a homogeneous BinBrm species in the presence of 2-bromomalonates, which served as the real photocatalyst for initiating the photocatalytic process. Diethyl bromomalonate 14 and 5-hexen-1-ol 15 were selected as model substrates for the ATRA reaction to investigate the substances that truly contributed to the photocatalytic process (Scheme 3a). Under identical reaction conditions, Bi2O3 and BiBr3 were employed as photocatalysts, respectively. In the UV–visible spectrum of the Bi2O3 catalytic system, two absorption bands appeared that did not correspond to known compounds in the system. Furthermore, in the UV–visible spectrum of the reaction mixture catalyzed by BiBr3, two similar absorption bands emerged, supporting the notion that Bi2O3 transformed into BinBrm for catalysis during the process. Subsequently, the reaction was conducted in a two-step manner (Scheme 3b). First, 14 reacted with Bi2O3 in DMSO solvent under illumination for 24 h, and then reactant 15 was added to the system under light irradiation for another 10 h. The reaction kinetics of this stepwise Bi2O3-catalyzed reaction exhibited a curve pattern similar to that of the BiBr3-catalyzed reaction. These findings further demonstrated that Bi2O3, as a precursor catalyst, interacted with bromide additives to promote the formation of soluble BinBrm, thereby initiating the photocatalytic process. It is noteworthy that only compounds with strong bromide-leaving ability could facilitate the conversion of Bi2O3 into BinBrm. That is the reason why only certain brominated substrates can serve as reactants in the reaction.
The same group [31] then disclosed that the addition of specific amines could stabilize and accelerate the catalytic active species generated from the precursor catalyst Bi2O3, thereby increasing the rate and yield of the ATRA reaction. Diethyl bromomalonate 14 and 5-hexen-1-ol 15 were utilized as model substrates for the ATRA reaction to investigate the effect of amines (Scheme 4). The study revealed that amines from I to VI could stabilize the soluble BinBrm species formed by the reaction of Bi2O3 with diethyl bromomalonate, thereby accelerating the reaction, with the yield of product 16 reaching 50–100%. Among the examined amines, VII-X could not accelerate the reaction and even resulted in yields of product 16 that were lower than those observed in the absence of amines. With amine II, i.e., TMEDA as a bidentate ligand, a stable complex of BinBrm with TMEDA could be formed in DMF. The bidentate coordination imparts increased stability to BinBrm, facilitating its sustained presence in the solution throughout the reaction. This stability enhances catalytic activity and optimizes the generation of catalytically active species, thereby significantly improving reaction yields.
In 2021, Kappe and Williams’s group [32] reported a large-scale, efficient continuous flow method for the ATRA reaction of terminal alkenes (or alkynes) 17 with organic halides 18 utilizing Bi2O3 as a photocatalyst (Scheme 5). A sustainable solvent system (acetone/PEG400) was applied in an oscillatory flow reactor. The optimization of the reaction and oscillation parameters led to a high throughput (36 g in 4 h, 89% yield, 599 g L−1 h−1) and a process mass intensity (PMI) of just 8.5. The method gave the ATRA products 19 in 52% to 97% yields. In this solvent system, the in situ-generated homogenous BinBrm was estimated to be < 10% of the initial Bi2O3 loading. Therefore, most of the Bi2O3 photocatalyst can be recycled by centrifugation and washing. The recycled photocatalyst can be applied three times without significant loss of activity. This procedure offers an effective strategy for the large-scale ATRA reaction of terminal alkenes/alkynes with organic halides.

3. Application of BiCl3 in Photocatalytic Organic Reactions

Ligand-to-metal charge transfer (LMCT) photocatalysis enables the activation and synthesis of halogens and other heteroatoms within metal complexes [33,34,35,36]. Among various metals, bismuth exhibits outstanding performance in LMCT processes. BiCl3 acts as a photocatalyst facilitating the LMCT process and demonstrates good catalytic activity in the functionalization of C(sp3)-H [33], as well as in alkylation, amination, alkynylation, and cascade cyclization [37]. Such advancements indicate that BiCl3 has significant potential for photocatalytic organic reactions.

3.1. Alkylation of C(sp3)-H

In 2023, König and colleagues [33] applied BiCl3 as the LMCT photocatalyst enabling the coupling of C(sp3)-H bond 20 with various electron-deficient alkenes 21 substituted with electron-withdrawing groups (EWGs) such as cyano, carboxyl, and sulfonyl groups, with yields ranging from 29 to 98% (Scheme 6). Generally, precursors with α-heteroatoms in their C-H bonds give higher yields. In the reaction, BiCl3 serves as a source of chlorine radicals, promoting the functionalization of diverse C(sp3)-H precursors. The addition of tetrabutylammonium chloride (TBACl) to BiCl3 produces the active BiCl52− species. Upon irradiation at 385 nm, this BiCl52− species undergoes LMCT to release chlorine radical (Cl•). The Cl• radical abstracts the hydrogen atom from substrate 20, generating carbon-centered radical 23 (R•). After the radical addition of Cl• and electron-deficient alkenes followed by the SET process, the desired coupling product 22 is generated along with the regeneration of photochemically active Bi(III). This process can be enhanced by an inner-sphere protonation step or outer-sphere SET protonation. The regenerated Bi(III) then allows the Bi(II/III) catalytic cycle to be sustained.

3.2. Functionalization of Diarylphosphine Oxides

BiCl3 catalyst was also applied in phosphorylation reactions as reported by Volla and colleagues in 2024 [37]. The phosphorylation of electron-deficient olefins 26 and alkynyl bromides 28, as well as the cascade phosphorylation cyclization reaction to form 31 and 33 were realized, respectively (Scheme 7). In the reaction, upon adding BiCl3 and TBACl to MeCN, the catalytically active [BiCl5]2− was produced. Under light excitation, [BiCl5]2− undergoes an LMCT process to give [BiCl4]2− along with key chlorine radical Cl•. The chlorine radical then participates in the HAT reaction with phosphorus oxide 25, resulting in the formation of phosphonyl radical 34 and HCl. The resulting radical 34 is added to alkene 26 to form radical 35. Next, 35 is subsequently reduced by Bi(II) species and converted into the final product 27 via protonation.
In the above-mentioned studies, BiCl3 is a homogeneous photocatalyst, which makes it challenging to recover after the reaction. A remarkably similar situation also occurs in the process of photocatalysis using FeCl3. Although these catalysts are not economically burdensome, their recyclability presents a significant attraction from the perspective of green chemistry. Notably, the recent ionic liquid strategy developed by the Yu’s group may serve as an effective approach [38]. We anticipate the potential development of BiCl3-based ionic liquids to facilitate photocatalysis while concurrently enabling the recovery of the photocatalyst.

4. Application of Bi4NbO8Cl in Photocatalytic Organic Reactions

The bismuth-based oxychloride, Bi4NbO8Cl, is prepared via the solid-state reaction method from BiOCl, Bi2O3, and Nb2O5. Bi4NbO8Cl has a band gap of 2.38 eV and demonstrates excellent visible-light response capabilities [39]. Consequently, it has been extensively utilized in the photocatalytic generation of oxygen from water under visible light [40] and in the degradation of environmental contaminants [41]. Recently, Bi4NbO8Cl, with its layered structure, has been recognized as a novel and efficient photocatalyst for organic reactions.

Trifluoromethylation of Olefins and (Hetero)Aromatics

Very recently, Sun and Yu’s group [42] reported a heterogeneous Bi4NbO8Cl-photocatalyzed hydroxytrifluoromethylation of olefins 36 and trifluoromethylation of (hetero)aromatics 39. The preparation of photocatalyst Bi4NbO8Cl involves twice calcining the mixture of BiOCl, Bi2O3, and Nb2O5 at 750 °C. The photocatalytic trifluoromethylation reaction was conducted using Bi4NbO8Cl as a photocatalyst in air at room temperature for 12 h with CF3SO2Na 37 as the trifluoromethyl radical source under the irradiation of blue LED. Olefins 36 and (hetero)aromatic compounds 39 were successfully functionalized to afford the corresponding trifluoromethylated products up to 83% yield (Scheme 8). Notably, the Bi4NbO8Cl catalyst demonstrated exceptional stability and reusability, maintaining its catalytic performance and structural integrity over five reaction cycles, underscoring its economic feasibility and practicality. This photocatalytic system exhibits unprecedented efficiency under mild reaction conditions, effectively addressing the traditional inefficiencies associated with g-C3N4 and CdS semiconductor materials. Under visible-light irradiation, an electron–hole pair is generated on Bi4NbO8Cl. The photogenerated hole then oxidizes CF3SO2Na 37, forming a trifluoromethyl radical (•CF3). This radical adds to the C=C bond of the olefin 36, forming a radical intermediate 41. Radical 41 subsequently captures O2 from the air, generating a peroxy radical 42. Then, 42 potentially undergoes the Russell mechanism, involving a tetraoxide intermediate, to generate radical intermediate 43. Ultimately, 43 is reduced by the photogenerated electron and combines with a proton to yield product 38.

5. Application of BiVO4 in Photocatalytic Organic Reactions

Bismuth vanadate (BiVO4), demonstrates remarkable photocatalytic activity due to its distinctive electronic band structure and adjustable morphology. The hybridization of the Bi 6s and O 2p orbitals within the electronic structure of BiVO4 creates a well-dispersed, advantageous VB, leading to a narrow band gap and an extensive response to visible light. In contrast, the electronic structure of other metal oxides, such as titanium dioxide (TiO2), relies solely on O 2p orbitals, which limits their responsiveness to light [43]. This results in BiVO4 having a broader range of applications compared to traditional photocatalysts.

5.1. Oxidation of C(sp2)-H

In 2019, Cho and Nam’s group [44] reported a Sono-BiVO4 photocatalyst capable of effectively converting styrene derivatives into carbonyl compounds via the cleavage of the C=C bond (Scheme 9). For the preparation of the Sono-BiVO4 photocatalyst, a mixed solution containing Bi(NO3)3·5H2O and VCl3 is subjected to ultrasonic treatment at room temperature to prepare BiVO4 powder. The BiVO4 powder is then calcined at 500 °C for 3 h to obtain crystalline BiVO4, i.e., Sono-BiVO4 crystals. These crystals possess a band gap of 2.4 eV and exhibit a highly uniform cubic structure. Due to its lower band gap and unique structure, Sono-BiVO4 demonstrates good photocatalytic activity, showing higher efficiency as a heterogeneous photocatalyst under visible light, and can be easily separated from the reaction mixture and reused without losing efficiency and yield. The reaction conditions are simple and environmentally friendly. With Sono-BiVO4 as a photocatalyst, molecular oxygen as an oxidant, and water as a solvent, styrene derivatives 44 could be converted into the corresponding carbonyl compounds 45, under visible-light irradiation at room temperature (Scheme 9). Nonetheless, the reaction is constrained by certain limitations, as it is exclusively applicable to terminal alkenes, while internal alkenes are unsuitable substrates for this transformation.

5.2. Functionalization of N,N-Dimethylanilines

In 2023, Yu and Chen’s group [45] reported a BiVO4-photocatalyzed functionalization of various C(sp2)-H bonds under ambient visible-light conditions. A hydrothermal synthesis was initially performed at 180 °C, followed by a calcination process to obtain bismuth vanadate (BiVO4-180). Then, N,N-dimethylanilines 46 and maleimides 47 were utilized as reactants, with BiVO4-180 serving as a photocatalyst (5 mol%), while 2-MeTHF acted as a green solvent. The reactions were performed at room temperature under a 5 W blue LED light (458 nm) in air, yielding a product separation of 35–97% (Scheme 10a). During the reaction, the substituents have an influence on the yield, e.g., the substrates bearing electron-donating groups led to lower yields, while electron-withdrawing groups resulted in higher yields. The reaction could be scaled up to grams, achieving a separation yield of 65% for the target product, highlighting the potential of this photocatalytic method for future large-scale applications. BiVO4-180 can also catalyze the synthesis of tetrahydroquinoline compounds 50 and 3-arylmethylindoles 52 (Scheme 10b,c). Using N,N-dimethylaniline as a mechanism demonstration, when BiVO4-180 is exposed to visible light, an electron in the VB is excited to the CB, leaving a hole (h+) in the VB. Subsequently, an electron from 46 transfers to the hole, forming the N,N-dimethylaniline radical cation 53. Concurrently, an electron from the CB transfers to an oxygen molecule in the air, generating a superoxide radical anion (O2•−). Following this, 53 loses a proton to O2•−, producing the radical 54 and hydrogen peroxide radical (HOO•). The addition of 54 to 47 results in the formation of radical 55, which then undergoes intramolecular cyclization to yield radical 56. This is succeeded by the extraction of hydrogen via HOO·, leading to the product 48 and the release of hydrogen peroxide (H2O2) [12].

6. Application of Bi2WO6 in Photocatalytic Organic Reactions

The band gap of Bi2WO6 is approximately 2.81 eV, and the valence band potential is +1.77 V, suggesting that Bi2WO6 possesses mild oxidizing properties, allowing for selective oxidation reactions [46].

Selective Oxidation of Benzyl Alcohols

In 2014, Xu et al. [46] reported a flower-like semiconductor Bi2WO6-catalyzed selective oxidation of benzylic alcohols to aldehydes using water as a solvent and oxygen as a mild oxidant (Scheme 11). This strategy offers an effective green conversion pathway for the oxidation of benzylic alcohols 57 to benzaldehydes 58. The ultrasonic treatment of Bi(NO3)3·5H2O was conducted in a HNO3 solution. Then, a Na2WO4 solution was added, resulting in the formation of a white precipitate. Afterward, a NaOH solution was added and allowed to react for one day, followed by maintaining the mixture at 160 °C for 8 h to obtain the flower-like Bi2WO6 samples. The flower-like Bi2WO6 exhibits mild oxidation capabilities, allowing benzyl alcohol to be converted to aldehydes instead of acids, while its adsorption affinity for aldehydes is weaker than that for alcohols, facilitating the continuous oxidation of benzyl alcohols to aldehydes. These properties endow Bi2WO6 with high chemical selectivity in the photocatalytic oxidation of benzylic alcohols in water. Despite the flower-like Bi2WO6 demonstrating over 96% selectivity in the photocatalytic reaction of benzyl alcohol compounds, the conversion of the reaction remains low. Further efforts are still required to enhance the photocatalytic efficiency.

7. Application of Bi4O5Br2 in Photocatalytic Oxidation of C(sp2)-H

The [Bi2O2]2+ and double Br– in Bi4O5Br2 form a cross-layered structure that generates an internal electric field, aiding in the separation of photo-generated charge carriers (electrons and holes) and thereby enhancing photocatalytic efficiency [47,48]. Furthermore, due to the bismuth-rich properties, the highly dispersed band structure and elevated conduction band potential promote charge transfer and photoreduction capabilities [49]. As a result, Bi4O5Br2 is suitable for use as a photocatalyst.
In 2022, Liu et al. [50] synthesized the bismuth-rich Bi4O5Br2 and applied it as a heterogeneous photocatalyst for the oxidation of the C=C bond in olefins to produce ketone 60. In a microwave reaction vessel, Bi(NO3)3·5H2O was dissolved in ethylene glycol, and then KBr was added. The reaction was placed under microwave irradiation to obtain Bi4O5Br2. Then, a solvent mixture of water and dioxane was employed by using molecular oxygen as the oxygen source under the illumination of a 10 W white LED, and the terminal C=C double bonds were selectively cleavaged achieving the corresponding ketones in yields of 23–94% (Scheme 12). Furthermore, Bi4O5Br2 could be easily separated using a straightforward centrifugation method and could be reused at least four times while maintaining catalytic performance, showing no significant decline in activity. In the reaction, superoxide radicals, along with photogenerated electrons and holes, play a crucial role in the oxidative cleavage of C=C double bonds. The reaction can proceed through a radical pathway. Initially, the semiconductor photocatalyst Bi4O5Br2 generates electrons and holes when excited by visible light. In the presence of oxygen, superoxide radical (O2•−) is generated via a SET reduction with the photogenerated electron of Bi4O5Br2, which then reacts with 59 to produce the intermediate 61. Next, the superoxide radical anion undergoes a [2+2] cycloaddition reaction with the intermediate 61 to yield dioxetane 62. Finally, dioxetane 62 decomposes to generate the target product 60 and formaldehyde 63.

8. Application of Bi2MoO6 in Photocatalytic Organic Reactions

Bi2MoO6 has a bandgap of 2.83 eV [51] and demonstrates responsiveness to visible light. It is also non-toxic and exhibits excellent chemical durability, making it widely utilized for the degradation of organic pollutants [52,53]. However, the rapid recombination of photogenerated charge carriers in Bi2MoO6 results in relatively low photocatalytic activity. Recently, Bi2MoO6 with enhanced catalytic activity has been developed by structural adjustments, defect modulation, heterogeneous structure construction, and surface/interface modifications [54,55].

Biomass Alcohols Oxidation to Aldehydes

In 2024, Wang’s group [51] reported a VM-Bi2MoO6 photocatalyst enriched with subsurface Mo vacancies, prepared using a surfactant-assisted hydrothermal method. This catalyst exhibited remarkable catalytic efficiency in the photocatalytic conversion of biomass alcohols 64 to aldehydes 65 (Scheme 13). Compared to Bi2MoO6 prepared by conventional methods, VM-Bi2MoO6 contains a higher concentration of molybdenum vacancies. Experimental validation indicated that the oxygen atoms near the abundant Mo vacancies can capture holes, facilitating electron transfer and preventing electron–hole recombination during photocatalytic oxidation, thereby enhancing photocatalytic efficiency. When VM-Bi2MoO6 was utilized for the catalytic conversion of lactate compounds to pyruvate, it demonstrated catalytic efficiency significantly superior to that of pure Bi2MoO6. Additionally, it achieved favorable conversion rates and selectivity for various biomass alcohols, with yields ranging from 13% to 95%. During the reaction, photogenerated electrons lower the energy level of O2 to produce O2•−, which is subsequently oxidized by holes to yield the final oxidant 1O2. Under the oxidation of 1O2, lactate loses α-H, resulting in a carbon-centered radical. This carbon-centered radical then loses H to form pyruvate, with H2O as the sole byproduct. The catalyst remained stable after five cycles, showing no significant loss of activity. Overall, in comparison to traditional Bi2MoO6, the interface-modified VM-Bi2MoO6, rich in subsurface molybdenum vacancies, prevents the recombination of photogenerated electron–hole pairs, thereby enhancing catalytic performance and this is the first catalyst that can stably and efficiently use molecular oxygen as an oxidant to oxidize lactate in a heterogeneous catalytic system.

9. Performance of Bismuth-based Photocatalysts

In the preceding section, we summarized recent advancements in organic photoreactions catalyzed by inorganic bismuth. To facilitate readers’ further understanding of the inorganic bismuth photocatalysts, the properties and their corresponding photocatalytic performances are presented in Table 1.

10. Conclusions

In summary, inorganic bismuth catalysts have shown remarkable catalytic activity and selectivity in organic photocatalysis. Notably, these Bi-based photocatalysts are generally applied in reactions under mild reaction conditions, significantly lowering reaction temperatures and reducing reaction times. When exposed to ultraviolet or visible light, these semiconductor photocatalysts can produce photogenerated electron–hole pairs, facilitating the efficient transformation of organic compounds.
This review primarily summarizes the use of inorganic bismuth catalysts (Bi2O3, BiVO4, BiCl3, Bi2WO6, Bi4O5Br2, etc.) in various organic transformations including α-alkylation reactions, organic radical coupling reactions, atom transfer radical addition reactions, and oxidative reactions. Each catalyst demonstrates excellent photocatalytic performance in its specific reaction, with BiVO4 standing out for its diverse catalytic types and notable recyclability. Moreover, BiVO4 achieves relatively high yields during catalytic processes, making it an ideal photocatalyst. Inorganic bismuth photocatalysts show immense potential in the field of organic synthesis, and future research should focus on several key areas:
(1)
Expanding the range of reaction types and developing novel photo-induced reactions to broaden their applications;
(2)
Optimizing the structure–performance relationship of the catalysts and exploring hierarchical catalysts to enhance selectivity and activity; designing multifunctional catalysts to achieve highly selective synthesis;
(3)
Optimizing reaction conditions to improve product yields and environmental compatibility;
(4)
Enhancing the stability and recyclability of the catalysts, exploring reuse strategies, and investigating the potential of bismuth-based catalysts in pharmaceutical synthesis and the development of novel materials.
Through such research, the widespread application of inorganic bismuth photocatalysts in organic synthesis can be promoted, advancing the development of more efficient, green, and economical synthetic methods. We hope this review will inspire the further exploration and application of Bi-based photocatalysts in photochemical organic synthesis.

Author Contributions

Conceptualization, B.Y.; writing—original draft preparation, H.H. and B.Y.; writing—review and editing, H.H., Q.L., and B.Y.; funding acquisition, B.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (22171249), Science & Technology Innovation Talents in Universities of Henan Province (23HASTIT003), Science and Technology Research and Development Plan Joint Fund of Henan Province (242301420006).

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00135 sch001
Scheme 1. Bi2O3-photocatalyzed α-alkylation of aldehydes.
Scheme 1. Bi2O3-photocatalyzed α-alkylation of aldehydes.
Catalysts 15 00135 sch001
Catalysts 15 00135 sch002
Scheme 2. Bi2O3-photocatalyzed bifunctionalization of olefins with bromides.
Scheme 2. Bi2O3-photocatalyzed bifunctionalization of olefins with bromides.
Catalysts 15 00135 sch002
Catalysts 15 00135 sch003
Scheme 3. Reaction kinetics.
Scheme 3. Reaction kinetics.
Catalysts 15 00135 sch003
Catalysts 15 00135 sch004
Scheme 4. Bi2O3-photocatalyzed ATRA reaction accelerated by amines.
Scheme 4. Bi2O3-photocatalyzed ATRA reaction accelerated by amines.
Catalysts 15 00135 sch004
Catalysts 15 00135 sch005
Scheme 5. Bi2O3-photocatalyzed bifunctionalization of olefins by continuous flow.
Scheme 5. Bi2O3-photocatalyzed bifunctionalization of olefins by continuous flow.
Catalysts 15 00135 sch005
Catalysts 15 00135 sch006
Scheme 6. BiCl3-photocatalyzed alkylation of electron-deficient alkenes.
Scheme 6. BiCl3-photocatalyzed alkylation of electron-deficient alkenes.
Catalysts 15 00135 sch006
Catalysts 15 00135 sch007
Scheme 7. BiCl3-photocatalyzed functionalization of diarylphosphine oxides.
Scheme 7. BiCl3-photocatalyzed functionalization of diarylphosphine oxides.
Catalysts 15 00135 sch007
Catalysts 15 00135 sch008
Scheme 8. Bi4NbO8Cl-photocatalysed trifluoromethylation of olefins and (hetero)aromatics.
Scheme 8. Bi4NbO8Cl-photocatalysed trifluoromethylation of olefins and (hetero)aromatics.
Catalysts 15 00135 sch008
Catalysts 15 00135 sch009
Scheme 9. Sono-BiVO4-photocatalyzed oxidation of C(sp2)-H.
Scheme 9. Sono-BiVO4-photocatalyzed oxidation of C(sp2)-H.
Catalysts 15 00135 sch009
Catalysts 15 00135 sch010
Scheme 10. BiVO4-180-photocatalyzed functionalization of N,N-dimethylanilines.
Scheme 10. BiVO4-180-photocatalyzed functionalization of N,N-dimethylanilines.
Catalysts 15 00135 sch010
Catalysts 15 00135 sch011
Scheme 11. Bi2WO6-photocatalyzed selective oxidation of benzyl alcohols.
Scheme 11. Bi2WO6-photocatalyzed selective oxidation of benzyl alcohols.
Catalysts 15 00135 sch011
Catalysts 15 00135 sch012
Scheme 12. Bi4O5Br2-photocatalysed cleavage of C=C bond.
Scheme 12. Bi4O5Br2-photocatalysed cleavage of C=C bond.
Catalysts 15 00135 sch012
Catalysts 15 00135 sch013
Scheme 13. Bi2MoO6-photocatalysed biomass alcohols oxidation to aldehydes.
Scheme 13. Bi2MoO6-photocatalysed biomass alcohols oxidation to aldehydes.
Catalysts 15 00135 sch013
Table 1. Bi-based photocatalysts and their photocatalytic performance.
Table 1. Bi-based photocatalysts and their photocatalytic performance.
PhotocatalystBandgap (eV)ReactionsRuns of PhotocatalystRef.
Bi2O32.83α-Alkylation Reaction3[27]
ATRA Reaction[28]
BiCl3-C(sp3)-H Alkylation-[33]
Functionalization of Diarylphosphine Oxides[37]
Bi4NbO8Cl2.51Trifluoromethylation Reaction5[42]
Sono-BiVO42.40C(sp2)-H Oxidation5[44]
BiVO4-1802.40Functionalization of N,N-Dimethylanilines8[45]
Bi2WO62.81Selective Oxidation of Benzyl Alcohol-[46]
Bi4O5Br22.93Oxidation of C=C Bonds4[50]
VM-Bi2MoO62.74Oxidation of Alcohols5[51]
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He, H.; Lv, Q.; Yu, B. Inorganic Bismuth Catalysts for Photocatalytic Organic Reactions. Catalysts 2025, 15, 135. https://doi.org/10.3390/catal15020135

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He H, Lv Q, Yu B. Inorganic Bismuth Catalysts for Photocatalytic Organic Reactions. Catalysts. 2025; 15(2):135. https://doi.org/10.3390/catal15020135

Chicago/Turabian Style

He, Hualei, Qiyan Lv, and Bing Yu. 2025. "Inorganic Bismuth Catalysts for Photocatalytic Organic Reactions" Catalysts 15, no. 2: 135. https://doi.org/10.3390/catal15020135

APA Style

He, H., Lv, Q., & Yu, B. (2025). Inorganic Bismuth Catalysts for Photocatalytic Organic Reactions. Catalysts, 15(2), 135. https://doi.org/10.3390/catal15020135

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