Electron Oxygen Reduction Research Articles

Synergistic Active Heterostructure Design for Enhanced Two Electron Oxygen Reduction via Chemical and Electrochemical Reconstruction of Heterosulfides

AbstractTransition metal sulfides, particularly heterostructures, represent a promising class of electrocatalysts for two electron oxygen reduction (2e− ORR), however, understanding the dynamic structural evolution of these catalysts during alkaline ORR remains relatively unexplored. Herein, NiS2/In2.77S4 heterostructure was synthesized as a precatalyst and through a series of comprehensive ex situ and in situ characterizations, including X‐ray absorption spectroscopy, Raman spectroscopy, transient photo‐induced voltage measurements, electron energy loss spectroscopy, and spherical aberration‐corrected electron microscopy, it was revealed that nickel/indium (oxy)hydroxides (NiOOH/In(OH)3) could be evolved from the initial NiS2/In2.77S4 via both electrochemical and chemical‐driven methods. The electrochemical‐driven phase featured abundant bridging oxygen‐deficient [NiO6]‐[InO6] units at the interfaces of NiOOH/In(OH)3, facilitating a synergistic effect between active Ni and In sites, thus enabling an enhanced alkaline 2e− ORR capability than that of chemical‐driven process. Remarkably, electrochemically induced NiOOH/In(OH)3 exhibited exceptional performance, achieving H2O2 selectivity of >90 % across the wide potential window (up to 0.4 V) with a peak selectivity of >99 %. Notably, within the three‐electrode flow cell, a current density of 200 mA cm−2 was sustained over 20 h, together with an impressive Faradaic efficiency of ~90 % during the whole cycle process.

Synergistic Active Heterostructure Design for Enhanced Two Electron Oxygen Reduction via Chemical and Electrochemical Reconstruction of Heterosulfides.

Transition metal sulfides, particularly heterostructures, represent a promising class of electrocatalysts for two electron oxygen reduction (2e- ORR), however, understanding the dynamic structural evolution of these catalysts during alkaline ORR remains relatively unexplored. Herein, NiS2/In2.77S4 heterostructure was synthesized as a precatalyst and through a series of comprehensive ex situ and in situ characterizations, including X-ray absorption spectroscopy, Raman spectroscopy, transient photo-induced voltage measurements, electron energy loss spectroscopy, and spherical aberration-corrected electron microscopy, it was revealed that nickel/indium (oxy)hydroxides (NiOOH/In(OH)3) could be evolved from the initial NiS2/In2.77S4 via both electrochemical and chemical-driven methods. The electrochemical-driven phase featured abundant bridging oxygen-deficient [NiO6]-[InO6] units at the interfaces of NiOOH/In(OH)3, facilitating a synergistic effect between active Ni and In sites, thus enabling an enhanced alkaline 2e- ORR capability than that of chemical-driven process. Remarkably, electrochemically induced NiOOH/In(OH)3 exhibited exceptional performance, achieving H2O2 selectivity of >90 % across the wide potential window (up to 0.4 V) with a peak selectivity of >99 %. Notably, within the three-electrode flow cell, a current density of 200 mA cm-2 was sustained over 20 h, together with an impressive Faradaic efficiency of ~90 % during the whole cycle process.

Oxygen-doped defects modified C3N5 in enhanced molecule oxygen photoactivation for tetracycline hydrochloride degradation and H2O2 in situ production: Double pathways of 1O2 and O2–· high yield

The study aims to investigate the mechanism by which O-doped defect engineering in C3N5 enhances molecular oxygen photoactivation. A feasible one-step roasting method was adopted to synthesize a novel C3N5 with multiple O-doped defects sites (O-C3N5). The experimental characterizations and DFT analysis reveal that O atoms were doped into the in-plane structure of C3N5 to form O-doped defects located at both linked and terminal positions on triazine units. The O-doped defects transform C3N5 morphologies and diminish the band gap, favoring charge migration and electron accumulation under visible-light irradiation. Furthermore, O-doped defects improve the adsorption performance for molecular oxygen, which provides the prerequisite for photoactivating molecular oxygen. The prominent photoelectric property can high effectively photoactivate the adsorbed O2 to directly generate 1O2 in the energy transfer-mediated pathway and O2–· in the electron oxygen reduction reaction pathway. In addition, the well photoelectric property also facilitates the interconversion between 1O2 and O2–·, which enables diverse reaction applications to be achieved. Hence, the outstanding performance of O-C3N5 can be verified in photoactivating molecular oxygen for TC degradation and H2O2 in situ production. The results not only demonstrate the universality and feasibility of utilizing O-C3N5 photoactivating molecular oxygen for the advanced treatment of the complicated sewage, but also provide a comprehensive understanding on the enhanced molecule oxygen photoactivation of C3N5 through O-doped defects.

Surface state modulation of carbon dots for efficient generation of hydrogen peroxide

Electrocatalytic dual electron oxygen reduction to hydrogen peroxide (2e ORR) is considered a special and sustainable method for on-site continuous production of hydrogen peroxide. Oxygen doped carbon based materials have demonstrated their superiority in the generation of H2O2. However, there is still a lack of direct experimental evidence to determine the true active site on complex carbon surfaces. In this work, we introduce only carboxyl functional groups on the surface of carbon dots by a mild and simple synthesis method to study the specific COOH functional groups on the generation of H2O2. The H2O2 selectivity was correlated with the contents of COOH functional groups. In alkaline environments, the citric acid modified CDs (CA-OCDs) own excellent catalytic ability for 2e ORR, showing a maximum starting potential of 0.829 V (vs. RHE) and a high selectivity of 89.7 % over a wide potential range of 0.2–0.7 V (vs. RHE). In actual H2O2 production, the Faraday efficiency (FE) of CA-OCDs can be up to 97 %, and the yield achieves 838 mmol gcatalyst−1 h−1. This work provides an effective and simple strategy for designing efficient carbon-based catalysts for sustainable H2O2 electrosynthesis.

Tuning active sites of carbon nitride using NiO nanoparticles for efficient photocatalytic generation of hydrogen peroxide

The use of solar photocatalysis to produce H2O2 as a new strategy alternative to the anthraquinone method, is less resource intensive and more environmentally friendly. In this study, carbon nitride (CN) loaded with NiO nanoparticles (CN-NiO) was used as photocatalyst for the generation of H2O2 through two electron oxygen reduction reactions (ORR). The existence of NiO nanoparticles improves both the photoactivity and selectivity of the carbon nitride towards two electron ORR. CN-NiO photocatalyst reaches 86 % selectivity for 2e− ORR, and a yield of 4054.1 μmol g−1h−1 for H2O2 generation under simulated sunlight, which is 2.7 times of that for bare CN. NiO nanoparticles promote the separation efficiency of photogenerated electrons and holes in photocatalysts, and also serve as adsorption sites for O2, enhancing the adsorption of O2. Additionally, DFT calculations show that the loading of NiO nanoparticles greatly reduces the energy barrier for the activation of *O2 to *OOH, which facilitates the efficient 2e− ORR photocatalysis. This study may advance knowledge regarding the function of metal oxide nanoparticles in the photocatalytic synthesis of H2O2.

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering.

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

A quaternary ammonium cyclodextrin polymer for efficient photocatalytic production of hydrogen peroxide from pure water

A photocatalytic system can be used to efficiently produce hydrogen peroxide (H2O2) without introducing a sacrificial agent or oxygen (O2). This system has practical application potential but remains challenging to implement. To increase the H2O2 yield of this system, a quaternary ammonium cyclodextrin polymeric photocatalyst QCD36A1-1350 is successfully synthesized using quaternization modification and low-temperature polycondensation. The photocatalyst is used to produce H2O2 from pure water and air by the one-step two electron oxygen reduction reaction. Under irradiation by visible light, QCD36A1-1350 produces a higher H2O2 yield (of up to 2.51 mmol g−1h−1) than unquaternized polymers and reported metal-free catalysts under similar conditions. Experimental and theoretical studies clearly show that the introduction of quaternary ammonium groups can effectively broaden the visible light absorption of polymer catalysts, while increasing the hydrophilicity, charge transfer efficiency and surface stability. The practicability of efficient photocatalytic production of H2O2 is realized by increasing the activity and selectivity of the polymer photocatalyst.

Boundary-Rich Carbon-Based Electrocatalysts with Manganese(II)-Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide.

Coordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non-toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2 O2 ) production through two electron oxygen reduction (2e-ORR) is a challenge on Mn-centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)-coordinated active environment with reactant enrichment effect on boundary-rich porous carbon-based electrocatalysts, which facilitates the selective and rapid synthesis of H2 O2 through 2e-ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2 O2 productivity up to 15.1 mol gcat -1 h-1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn-based electrocatalyst in H2 O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high-curvature boundaries facilitate oxygen (O2 ) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2 . These merits together ensure the efficient formation of H2 O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

Boundary‐Rich Carbon‐Based Electrocatalysts with Manganese(II)‐Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide

AbstractCoordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non‐toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2O2) production through two electron oxygen reduction (2e‐ORR) is a challenge on Mn‐centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)‐coordinated active environment with reactant enrichment effect on boundary‐rich porous carbon‐based electrocatalysts, which facilitates the selective and rapid synthesis of H2O2 through 2e‐ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2O2 productivity up to 15.1 mol gcat−1 h−1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn‐based electrocatalyst in H2O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high‐curvature boundaries facilitate oxygen (O2) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2. These merits together ensure the efficient formation of H2O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

Effective photo-electrochemical production of H2O2 and green Fenton reaction on hierarchical Fe/C/N @ ZIF-8 @ACF for abatement of antibiotics in water

Heterogeneous photo-electro-Fenton (HPEF) reaction is a highly efficient process using H2O2 produced by in-situ two electron oxygen reduction reaction (2e ORR) after aerating for the elimination of refractory organic pollutants. Herein, an effective MOFs derived Fe/C/N @ ZIF-8 @ACF composite electrode for HPEF was prepared by loading Fe/C/N derived from Fe-based metal-organic frameworks (Fe-MOFs) and zeolitic imidazolate framework-8 (ZIF-8) on activated carbon felt (ACF). By supplying air, solar light, and low external electric current (32 mA·cm−2) to the cathode, ZIF-8 could generate H2O2 by 2e- ORR process, and Fe/C/N could react with H2O2 to form strong oxidative radicals (·OH). Photocatalysis accelerates the Fenton reaction greatly with the abundant photo-generated electrons. The HPEF activity of different systems for the degradation of antibiotics was compared. The results showed that the degradation rate of antibiotics can be greatly increased with the best of ∼100% within 100 min. Moreover, the electrode could still maintain a high activity after reuse for 4 times, which proved to be highly active, stable, and well recyclable for a rapid HPEF oxidation for abatement of antibiotic pollutants in water.

Introduction of electron-deficient unit in resorcinol-formaldehyde resin to construct donor–acceptor conjugated polymer for enhancing photocatalytic H2O2 production

Intramolecular donor–acceptor conjugated polymer was constructed in resorcinol-formaldehyde resin by embedding benzothiadiazole, which can reduce the Gibbs free energy for two-electron oxygen reduction and improve photocatalytic H2O2 evolution.

Oxygen-doped carbon nanotubes with dual active cites to enhance •OH formation through three electron oxygen reduction

The electro-Fenton (EF) process generates H2O2 through the 2e- oxygen reduction reaction (ORR), which is subsequently activated to •OH by iron-based catalysts. To alleviate the potential risk of external Fe-based catalysts, along with metal dissolution in acidic or neutral environments, in this study we employed oxygen-doped carbon nanotubes (OCNT) as a bifunctional, metal-free cathode to establish a metal-free EF process for organic pollutant degradation. The results demonstrate that the metal-free electrode has excellent H2O2 accumulation (12 mg L−1 cm−1) and degrades sulfathiazole (STZ) with 97.05 % efficiency in 180 min with an explanation kinetic of 0.0189 min−1. For the first time, this enhancement came from the dual active site centers in OCNT: Ⅰ) -COOH and defects active sites were responsible for H2O2 production, Ⅱ) then -CO triggered H2O2 into •OH, avoiding the introduction of metal-based catalysts. These findings suggest that the EF system with in situ oxygen-doped cathodes have great potential for treating antibiotic wastewater.

Multicomponent Synthesis of Imidazole‐Linked Fully Conjugated 3D Covalent Organic Framework for Efficient Electrochemical Hydrogen Peroxide Production

AbstractThe semiconducting properties and applications of three dimensional (3D) covalent organic frameworks (COFs) are greatly hampered because of their long‐ranged non‐conjugated skeletons and relatively unstable linkages. Here, a robust imidazole‐linked fully conjugated 3D covalent organic framework (BUCT‐COF‐7) is synthesized through the one‐pot multicomponent Debus‐Radziszewski reaction of the saddle‐shaped aldehyde‐substituted cyclooctatetrathiophene, pyrene‐4,5,9,10‐tetraone, and ammonium acetate. The semiconducting BUCT‐COF‐7, as a metal‐free catalyst, shows excellent two electron oxygen reduction reaction (ORR) activity in alkaline medium with high hydrogen peroxide (H2O2) selectivity of 83.4 %. When the BUCT‐COF‐7 as cathode catalyst is assembled into the electrolyzer, the devices showed high electrochemical production rate of H2O2 up to 326.9 mmol g−1 h−1. The accumulative amount of H2O2 could totally degrade the dye methylene blue via Fenton reaction for wastewater treatment. This is the first report about intrinsic 3D COFs for efficient electrochemical synthesis of H2O2, revealing the promising applications of fully conjugated 3D COFs in the environment‐related field.

Multicomponent Synthesis of Imidazole-Linked Fully Conjugated 3D Covalent Organic Framework for Efficient Electrochemical Hydrogen Peroxide Production.

The semiconducting properties and applications of three dimensional (3D) covalent organic frameworks (COFs) are greatly hampered because of their long-ranged non-conjugated skeletons and relatively unstable linkages. Here, a robust imidazole-linked fully conjugated 3D covalent organic framework (BUCT-COF-7) is synthesized through the one-pot multicomponent Debus-Radziszewski reaction of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene, pyrene-4,5,9,10-tetraone, and ammonium acetate. The semiconducting BUCT-COF-7, as a metal-free catalyst, shows excellent two electron oxygen reduction reaction (ORR) activity in alkaline medium with high hydrogen peroxide (H2 O2 ) selectivity of 83.4 %. When the BUCT-COF-7 as cathode catalyst is assembled into the electrolyzer, the devices showed high electrochemical production rate of H2 O2 up to 326.9 mmol g-1 h-1 . The accumulative amount of H2 O2 could totally degrade the dye methylene blue via Fenton reaction for wastewater treatment. This is the first report about intrinsic 3D COFs for efficient electrochemical synthesis of H2 O2 , revealing the promising applications of fully conjugated 3D COFs in the environment-related field.

ZnO nanocomposites containing Cd are synthesized with high photodegradation potential for wastewater treatment

The zinc oxide (ZnO) nanoparticle on a two - electron oxygen reduction reaction is a particularly promising candidate for in-situ application. Herein, we prepared the Cd doped ZnO nanocomposites through a simple hydrothermal method. The X-ray diffraction (XRD) analysis has been carried out to confirm the structure and size of the nanomaterial. The optical absorption and energy gap of the prepared nanoparticles have been identified by UV–vis-NIR studies. Photoluminescence (PL) studies on the synthesized nanomaterials confirm the characteristic existence of blue and green emission bands. Fourier transform infrared (FTIR) spectroscopy has been studied on the ZnO nanoparticles to analyze the -OH and CO-O vibrations. The structural and surface morphology analysis was inferred by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) microanalysis. Cd doped ZnO nanocomposites are environmentally friendly and can be utilized to quickly remove contaminants from wastewater. The findings from the adsorption equilibrium fit the Brunauer-Emmett-Teller (BET) model very well, showing multi-layer adsorption. The photodegradation studies on Cd doped ZnO nanocomposites were carried out, which is an advanced oxidation process widely used for methylene blue removal. Therefore, the higher photocatalytic performance revealed that Cd doped ZnO nanocomposites could be a promising photocatalyst for environmental remediation applications.

Photocarrier transfer induced by Nδ− → Wδ+ in tungsten trioxide/carbon nitride for dual-path production of hydrogen peroxide towards ciprofloxacin degradation

Photo self-Fenton catalyst is a promising candidate for solar energy conversion and environmental remediation. Here we reported a Tungsten trioxide/carbon nitride (WO3/CN) in which the surficial amino groups on CN are inserted into the WO3 matrix, forming coordinate covalently Nδ− → Wδ+ in construction of an intimate S-scheme heterojunction. The intimantance promotes the transfer of photocarriers under light irradiation. The nanohybrids produced hydrogen peroxide (H2O2) in a rate about 20 times of pristine CN. A dual-path architecture in which H2O2 are produced via hole-water oxidation and electron-oxygen reduction was poposed. It is founded that ciprofloxacin also involved in production of H2O2 by their deprotonation to superoxide anions, and holes and hydroxyl radicals effectively attack the weak sites in skeleton of ciprofloxacin. This work suggests a great significance of strategy in self-producing of H2O2 in utilizing solar energy and molecular oxygen for water, particularly the surface water decontamination.

Efficient hydrogen peroxide production enabled by exploring layered metal telluride as two electron oxygen reduction reaction electrocatalyst

It is of great interest to develop the novel transition metal-based electrocatalysts with high selectivity and activity for two electron oxygen reduction reaction (2e− ORR). Herein, the nickel ditelluride (NiTe2) with layered structure was explored as the 2e− ORR electrocatalyst, which not only showed the highest 2e− selectivity more than 97%, but also delivered a slight activity decay after 5000 cycles in alkaline media. Moreover, when NiTe2 was assembled as the electrocatalyst in H-type electrolyzer, the on-site yield of H2O2 could reach up to 672 mmol h−1 g−1 under 0.45 V vs. RHE. Further in situ Raman spectra, theoretical calculation and post microstructural analysis synergistically unveiled that such a good 2e− ORR performance could be credited to the intrinsic layered crystal structure, the high compositional stability, as well as the electron modulation on the active site Ni atoms by neighboring Te atoms, leading to the exposure of active sites as well as the optimized adsorption free energy of Ni to –OOH. More inspiringly, such telluride electrocatalyst has also been demonstrated to exhibit high activity and selectivity towards 2e− ORR in neutral media.

Activating the PdN4 single-atom sites for 4 electron oxygen reduction reaction via axial oxygen ligand modification

The absence of Pd ensemble sites and weak affinity for O-intermediates in tetracoordinate planar PdN4 sites inhibit O-O bond dissociation and restrict 4e- oxygen reduction reaction (ORR) pathway. Optimizing the adsorption energy between O-intermediates and PdN4 sites is a rational approach for selectively promoting 4e- ORR electrocatalysis. Herein, we propose a molten-salt strategy for introducing axial oxygen ligand into the PdN4 sites to manipulate the electronic structure and create catalytic O-PdN4 sites (one subsurface axial Pd-O configuration on PdN4 plane) on N-doped graphene nanosheets (O-PdN4-NGS). Density functional theory calculations revealed that the axial Pd-O coordination can induce charge redistribution, downshift the d-band center of Pd and enhance the adsorption affinity of PdN4 site for O-intermediates, thereby leading to superior electrocatalysis activity and selectivity for 4e- ORR process compared to conventional PdN4 sites in 0.1 M KOH (with a positive half-wave potential E1/2 of 0.90 V vs RHE). Moreover, zinc-air battery featuring with O-PdN4 sites delivers a peak power density of 178 mW cm−2 at 227.5 mA cm−2 and stable long-term cycling performance, effectively showcasing the advantages of the axial O ligand modification in practical application. This work provides a constructive strategy to activate the reaction activity and specificity of PdN4 single-atom sites by precisely-tuning the local coordination environment of Pd.

Highly efficient electrosynthesis of hydrogen peroxide through the combination of side aeration and vacuum filtration modified graphite felt

The electrocatalytic activity towards two electron oxygen reduction reaction of graphite felt was advanced by incorporating carbon nitride, carbon nanotubes and polytetrafluoroethylene through vacuum filtration, which prevented the cleavage of O-O bond, facilitated the charge transfer, and established more three-phase active sites. To ameliorate the oxygen transfer process, the configuration of side-aeration was proposed, providing forced convection to reduce the thickness of diffusion layer, and increasing the dissolved oxygen. By simplified combination of refining the orientation of gas flow and modified graphite felt, the dual-chamber configuration rendered a qualitative leap in H2O2 generation capacity to 4.44–6.89 mg h−1 cm−2. The alkaline affinity of developed system was discussed in terms of a beneficial outer-sphere electron transfer pathway, the variation on adsorption strength of oxygenated species and working electrode potential range. Finally, Long-term operation stability and successful application in Electro-Fenton indicated great potential of developed system for H2O2 synthesis and environmental remediation.

Hydrogen Peroxide Production by Inorganic Photocatalysts Consisting of Gold Nanoparticle and Metal Oxide toward Oxygen Cycle Chemistry

Hydrogen peroxide (H2O2) is not only a versatile clean and strong oxidant but also a promising fuel for fuel cells. This Feature Article has shown that gold nanoparticle (NP)-loaded metal oxides (Au/MOs) can be promising photocatalysts for H2O2 production via two electron-oxygen reduction reaction (2e–-ORR). The fundamental parts deal with the general requirements for the H2O2 synthesis, electrocatalytic activity of Au NPs for 2e–-ORR, Fermi level control of the Au NP of Au/MOs in the dark and under light irradiation, and the factors for governing the catalytic activity for H2O2 production. Subsequently, an artificial photosynthesis of H2O2 from water and O2 under visible light irradiation at ambient temperature and pressure is described. Finally, the conclusions are summarized with a direction of the future research on the hot topics.