Visible-light Photocatalytic CO2 Reduction Research Articles

Constructing copper Phthalocyanine/Molybdenum disulfide (CuPc/MoS2) S-scheme heterojunction with S-rich vacancies for enhanced Visible-Light photocatalytic CO2 reduction

Constructing a heterojunction by combining two semiconductors with similar band structures is a successful approach to obtaining photocatalysts with high efficiency. Herein, a CuPc/DR-MoS2 heterojunction involving copper phthalocyanine (CuPc) and molybdenum disulfide with S-rich vacancies (13.66%) is successfully prepared by the facile hydrothermal method. Experimental results and theoretical calculations firmly demonstrated that photoelectrons exhibit an S-scheme charge transfer mechanism in the CuPc/DR-MoS2 heterojunction. The S-scheme heterojunction system has proven significant advantages in promoting the charge separation and transfer of photogenerated carriers, enhancing visible-light responsiveness, and achieving robust photoredox capability. As a result, the optimized 3CuPc/DR-MoS2 S-scheme heterojunction exhibits photocatalytic yields of CO and CH4 at 200 and 111.6 μmol g-1h−1, respectively. These values are four times and 4.5 times greater than the photocatalytic yields of pure DR-MoS2. This study offers novel perspectives on the advancement of innovative and highly effective heterojunction photocatalysts.

BiOCl for efficient visible light photocatalytic CO2 reduction with abundant oxygen vacancies and WO3 as p-n heterojunctions

The development of highly efficient photocatalysts is important for CO2 reduction. In this work, bismuth oxychloride (BiOCl) nanospheres with exposed (110) crystalline surfaces were prepared via the coprecipitation method. Oxygen vacancies (OVs) were generated on the nanosphere surface by adjusting the solution pH. The final product obtained is BiOCl with abundant oxygen vacancies (BiOCl-x). Interfacial OVs have importance in terms of narrow bandgap. WO3 nanotubes were introduced during the growth of BiOCl crystals, and closely contacted WO3 nanotube–loaded BiOCl nanomicrospheres were obtained (WO3/BiOCl-x). The WO3/BiOCl-x photocatalyst showcased a substantial increase in CO production, reaching 27.3 µmol g−1, which indicates a 2.7-fold improvement compared with that of pure BiOCl. The photocatalytic CO2 reduction efficiency of BiOCl improved by combining OVs with p–n heterojunctions, which modulated the energy band structure of BiOCl and increased its photogenerated carrier mobility. This work provides some motivation for exploiting the synergy between defect engineering and heterojunctions to increase the activity of bismuth-based photocatalysts.

Well-designed glucose precursor carbon/g-C3N4 nanocomposite for enhanced visible light photocatalytic CO2 reduction activity

Fabrication of glucose precursor carbon-doped g-C3N4 nanocomposite (C/g-C3N4) for enhancing photocatalytic CO2 reduction into syngas (CO, CH4) has been investigated. The samples were successfully synthesized via a two-step thermal treatment and tested in a fixed bed reactor under visible light. The 0.2 % glucose precursor carbon-doped over g-C3N4 photocatalyst has demonstrated excellent activity in converting CO2 to CO and CH4 under visible light. The main product yield, CO of 898.9 μmol g-cat−1 was produced over 0.2 % C/g-C3N4, which is 4.6 folds the amount of CO obtained over the g-C3N4 (196.8 μmol g-cat−1). The XPS results confirmed the formation of a C-O-C bond between carbon and g-C3N4, resulting in a strong interaction between carbon and g-C3N4. Carbon-doped g-C3N4 possesses a narrow energy band and the ability to effectively absorb solar light, which enables efficient transportation of electrons generated by photon excitation. Possible reaction mechanisms for photoreduction of CO2 over carbon-doped g-C3N4 photocatalyst were proposed in order to understand the movement of electrons and holes. This work provides a simple method for designing highly efficient carbon-based photocatalysts for potential application in photocatalytic CO2 reduction using solar energy.

CdS-assisted ultrathin porous nitrogen-vacancy carbon nitride nanosheets for visible-light photocatalytic CO2 reduction

Obtaining highly active and selective target products is both promising and challenging, and can be achieved by regulating the adsorption and desorption energy of reaction intermediates, as well as the transfer of electrons under visible light. Herein, an efficient CNGA/CdS photocatalyst based on ultrathin porous nitrogen vacancies carbon nitride (CNGA) nanosheets (thickness <1 nm) with CdS nanoparticles was synthesized by a facile route for visible-light photocatalytic CO2 reduction. As a result, the rate of CO production was 32.75 μmol g−1 h−1, which was 17.24 and 32.75 times that of CN and CdS under visible light (λ ≥ 420 nm) without sacrificial agents and cocatalysts. Importantly, introducing CdS nanoparticles into CNGA could improve the selectivity of CO2 to CO by nearly 100% (yield-based selectivity). Finally, the photocatalytic mechanism was explored by in-situ FTIR spectra and DFT calculations, and the results presented that the formation of heterostructures facilitated the generated *CO groups to modulate the reaction pathway of photocatalytic CO2 reduction. This work is expected provide a reference for the design of photocatalysts for photoreduction CO2 with accurate products under visible light.

Highly Efficient and Selective Visible-light Photocatalytic CO2 Reduction to CO Using a 2D Co(II)-Imidazole MOF as Cocatalyst and Ru(bpy)3 Cl2 as Photosensitizer.

The first application of an imidazole MOF, the 2D Co(II)- imidazole framework, {[Co(TIB)2 (H2 O)4 ]SO4 } (TIB stands for 1,3,5-tris(1-imidazolyl) benzene) (CoTIB) in photocatalytic CO2 reduction was carried out, and compared with that of ZIF-67. The CO2 /CoTIB (1.0 mg)/Ru(bpy)3 Cl2 (bpy=2,2'-bipyridine) (11.3 mg)/CH3 CN (40 mL)/TEOA (10 mL)/H2 O (400 μL) system produced 76.9 μmol of CO in 9 h, corresponding to the efficiency of 9.4 mmol g-1 h-1 (TOF: 7.3 h-1 ) with a >99% selectivity. Its catalytic activity is even higher than that of ZIF-67 based on TOF values. However, CoTIB is non-porous and has a very poor CO2 adsorption capacity and poor conductivity. Extensive photocatalytic experiments and energy-level diagrams suggest that the reduction did not depend on the CO2 adsorption by the cocatalyst, but can occur by the direct electron transfer from conduction-band maximum (CBM) of the cocatalyst to the zwitterionic alkylcarbonate adduct formed by the reaction of TEOA and CO2 . In addition, the process utilizes the short-lived singlet state (1 MLCT), not the long-lived triplet state (3 MLCT) of Ru(bpy)3 Cl2 to transfer electrons to the CBM of CoTIB. We found that the high efficiency of a cocatalyst, a photosensitizer, or a photocatalytic system depends on the matching of all related energy levels of the photosensitizer, the cocatalyst, CO2 , and the sacrificial agent in the reaction system.

Nanoarchitecture engineering of crumpled polymeric carbon nitride nanosheets for efficient visible-light photocatalytic CO2 reduction

Polymeric carbon nitride nanosheets with few layers have emerged as a new category of semiconductor materials which are promising for photocatalytic applications because of their unique optical and electronic characteristics. The texture and optical–electronic properties of the nanosheets significantly influence the photocatalytic activities. In this study, a series of crumpled polymeric carbon nitride nanosheets was prepared via a facile stepwise pyrolytic strategy and a time-dependent pyrolysis process. The as-obtained nanosheets exhibit a sequential change in morphology from a continuous-aggregation architecture to discrete nanosheets with prolonged thermal-treatment time. The nanosheets with the continuous-aggregation architecture, consisting of small curved nanosheet subunits are laterally large; thus, they can provide numerous reactive sites for surface reactions and awaken intrinsic n → π* electron transitions to promote photocatalytic activity. The optimum crumpled polymeric carbon nitride nanosheet is formed after 2 h of thermal condensation, and it demonstrates efficient CO2-conversion performance with the highest CO-evolution rate of 1287 µmol g−1h−1, which is 7 times more than that of pristine polymeric carbon-nitride nanosheets. This work provides an opportunity to significantly understand the roles of texture and optical–electronic properties in improving the photocatalytic activities of polymeric carbon-nitride nanosheets.

Construction of CsPbBr3-CdS solid solution for visible light photocatalytic CO2 reduction

Construction of CsPbBr3-CdS solid solution for visible light photocatalytic CO2 reduction

Cu-doped SnS2 nanosheets with superior visible-light photocatalytic CO2 reduction performance.

Photocatalytic CO2 reduction utilizing solar energy is a clean, environment-friendly strategy converting CO2 into hydrocarbon fuels to solve the energy crisis and climate issues. Herein, we report the synthesis of Cu-doped SnS2 nanosheets via a simple hydrothermal method. The prepared Cu-doped SnS2 composite displays superior photocatalytic CO2 reduction activity. The optimized CH3OH yield of the composite is two times higher than that of pure SnS2. The enhanced photocatalytic performance is attributed to effective charge separation resulting from the thinner nanosheets and delocalization of electrons from SnS2 to Cu, high visible light utilization efficiency, enlarged SBET, negative shift of the flat-band potential and reduced charge transfer resistance with the introduction of Cu atoms. This work suggests the potential application of Cu-doped SnS2 in photocatalytic CO2 reduction.

Ag-Doped CuV2O6 Nanowires for Enhanced Visible-Light Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction into chemical fuels is a promising strategy to realize the CO2 conversion and solar energy utilization, yet there remains a great challenge in conversion efficiency. Herein, Ag-ion-doped CuV2O6 nanowires (NWs) with abundant oxygen vacancies were prepared by a simple hydrothermal method and utilized as catalysts for CO2 photoreduction with H2O vapor. It was demonstrated that Ag-ion doping in CuV2O6 resulted in a narrow band gap, enhanced visible-light absorption ability, elevated conduction band, abundant oxygen vacancies, strong CO2 surface-absorption capacity, superior hydrophilicity, and high separation/transfer efficiency of the photoinduced electron–hole pairs. Consequently, the Ag-doped CuV2O6 NWs exhibit excellent photocatalytic performance for CO2 reduction as compared to the pristine CuV2O6 NWs. Remarkably, the optimized Ag-doped CuV2O6 NWs exhibited a significantly enhanced photocatalytic activity with a CO evolution rate of 6.95 μmol g–1 h–1 under visible-light irradiation, which is 8.9 times higher than those of pure CuV2O6 NWs. The present work may provide a valid strategy to engineer CuV2O6 NWs for boosting visible-light photocatalytic CO2 reduction.

Ni2O3-modified SrTiO3 for enhanced visible-light photocatalytic CO2 reduction activity

Low-cost and effective cocatalyst Ni2O3 was loaded on SrTiO3 (STO) via a simple one-step hydrothermal method. The Ni2O3 / SrTiO3 ( m ) photocatalysts were systematically characterized and applied to visible-light-driven CO2 reduction to investigate their photocatalytic activity. The series of the Ni2O3-modified SrTiO3 photocatalysts presented an improved photocatalytic activity and stability. Here, the N5.4STO ( m ) catalyst showed the best photocatalytic activity, with CO and CH4 yielding up to 11.57 and 1.51 μmol / g, respectively, under visible-light irradiation of 3 h, which were 3.15 and 14.84 times higher than that of pure STO(m), respectively. Based on the characterization and experimental results, the enhanced photocatalytic activity might be attributed to the following reasons: (1) Ni2O3 well dispersed on SrTiO3 served as CO2 attachment sites; (2) the modification of Ni2O3 could red shift the absorption edge and broaden the visible-light response ability; and (3) Ni2O3 nanoparticles act as electron traps to capture photogenerated electrons, effectively blocking the recombination of electron–hole pairs. The work offers important insights into the design of non-noble metal oxide cocatalyst modified photocatalysts for electron capture and photoreduction.

BiVO4@WO3 S-scheme nanocomposite for visible light photocatalytic CO2 reduction

Significant efforts have been made in the recent times towards the synthesis of sustainable photocatalyst that are both eco-friendly and cost effective in terms of reduction of CO2. The outstanding properties exerted by bismuth, as BiVO4 in specific with respect to its highly facilitative band gap of 2.4 eV has been gaining considerate attention. In the present study, attempts have been made to dope WO3 onto BiVO4 as a means of reducing the recombination rates thereby facilitating the CO2 process. The characterisation results are indicative of the excellent crystallographic properties exerted by the material in addition to the supremacy over stand-alone BiVO4 (0.97 mA/cm2) and WO3 (0.23 mA/cm2) with respect to photocurrent response (1.69 mA/cm2). The catalyst survived 6 cycles of usage, indicative of its environmental and economic upper hand in addition to the greater rates of CO and H2 evolution (29.14 μmolg−1h−1 & 9.24 μmolg−1h−1)

High-efficiency photoreduction of CO2 to solar fuel on alkali intercalated Ultra-thin g-C3N4 nanosheets and enhancement mechanism investigation

The visible-light photocatalytic reduction of CO2 becomes a vital breakthrough to alleviate the greenhouse effect and achieve carbon neutrality. In this paper, ultrathin g-C3N4 nanosheets of 1.74 nm were constructed, and K+ was successfully doped between layers. The yields of CO and CH4 are 1.65 μmol·g−1·h−1 and 0.15 μmol·g−1·h−1, which are 4.70 and 7.27 times higher than the original g-C3N4, respectively. The ultra-thin nano-lamellar structure shortens the carrier transmission distance, and the intercalation of K+ not only promotes the electron transport between g-C3N4 layers but also changes the original hybrid mode of the catalytic system, thus shortening the band gap and adjusting the energy band structure.In addition, the CO2 adsorption center of the K+ intercalated g-C3N4 is transferred from the coordinated carbon atom to the center of the triazine unit, and the binding energy is obviously increased, which strengthens the CO2 adsorption. Finally, through in-situ DRIFT characterization, it is speculated that the reaction enhancement mechanism is that the modified catalyst promotes the adsorption and activation of CO2, resulting in the production of more intermediates, especially more hydrocarbon intermediates, which is more conducive to the photocatalytic reduction of CO2.

Enhanced visible light photocatalytic CO2 reduction over direct Z-scheme heterojunction Cu/P co-doped g-C3N4@TiO2 photocatalyst

Enhanced visible light photocatalytic CO2 reduction over direct Z-scheme heterojunction Cu/P co-doped g-C3N4@TiO2 photocatalyst

Nanostructure rod-like TiO2-reduced graphene oxide composite aerogels for highly-efficient visible-light photocatalytic CO2 reduction

In response to the worldwide over-standard carbon dioxide emission problem, this work synthesized a series of titanium dioxide/reduced graphene oxide composite aerogels (TiO2-rGO) for photoconversion of CO2 by a one-step hydrothermal and freeze-drying method. The prepared composite aerogel presents a high specific surface area of 287.3 m2/g and pore volume of 0.72 cm3/g, contributing to remarkable absorption capability of reactants and fast intraparticle molecular transfer. In the three-dimensional structure of rGO aerogel, TiO2 with nano-rod shape (10–20 nm × 100–150 nm) is uniformly interspersed. Through applying the composite catalytic aerogel for the photocatalysis reaction, CO2 was efficiently converted to MeOH, CH4, and EtOH, etc. The total yield of carbon generated by G-25Ti (TiO2-rGO with 25 mmol Ti4+) was found 15.7 times higher than that of the pure P25. The corresponding characteristic analysis demonstrated that the photocatalytic performance of TiO2-rGO composite aerogel has been highly improved, originated from two folds: (1) the introduction of 3-D rGO to nano-rod shape TiO2 promoted its light absorption efficiency, and more significantly (2) the specific chemical bonding sites and strong O˭C‒O‒Ti group between rGO and TiO2 effectively mitigate the recombination of photogenerated electron–hole pairs. In this work, rod-like TiO2-rGO composite aerogels prepared by using TiCl4 as precursor for the first time have been found a new application in CO2 reduction using visible sunlight.

A butterfly shaped organic heterojunction photocatalyst for effective photocatalytic CO2reduction

The modification of carbon nitride (CN) for visible light photocatalytic CO2reduction is an important issue to explore in the context of energy and environmental challenges.

Oxygen vacancy-rich BiO2-x: Super-active co-catalyst on g-C3N4 for efficient visible-light photocatalytic CO2 reduction

Photoreduction CO2 to hydrocarbons are the sustainable and green methods to solve energy shortages and environmental pollution problems. Therefore, the development of efficient and environment-friendly photocatalysts remains a huge challenge, while coupling co-catalyst on traditional photocatalysts is a potential approach for improving photocatalytic activity. Here, a novel BiO2-x co-catalyst coupled g-C3N4 photocatalyst was prepared by a simple hydrothermal approach for the photocatalytic reduction of CO2. The experimental results proved that BiO2-x/g-C3N4 composites played a vital part for promoting the photocatalytic capability. The 20 % BiO2-x/g-C3N4 composites exhibited the best photocatalytic capability under the simulated visible-light. A maximum yield of CO (42.29 μmol/gcat) and CH4 (7.2 μmol/gcat) were obtained, which were 3.8 and 2.5 times that over pure g-C3N4, and its apparent quantum yield (AQY) was 1.5 % at 420 nm. According to the characterization results, the significantly increased photocatalytic activity could be ascribed to larger specific surface area, stronger visible-light absorption properties and more effective separation and transfer of photogenerated electron-hole pairs. Our finding provides a certain reference for the development and application of novel co-catalyst.

Extending the visible-light photocatalytic CO2 reduction activity of K2Ti6O13 with the MxOy (M = Co, Ni and Cu) incorporation

Co3O4, NiO, and CuO-K2Ti6O13 composites were successfully grown in-situ by using an ultrasound-assisted sol–gel method. As a result of the synthesis method, the introduction of the metallic cations into the crystalline structure substituting Ti4+ or K+ cations depending on the case was achieved. For instance, Co2+ cations were introduced instead of Ti4+ cations, while Ni2+ and Cu2+ were introduced on both sides. The metal-cation introduction between the tunnels favored the growth of K-poor phases as impurities, especially in the CuO loaded K2Ti6O13 samples. The presence of these metallic oxides modified the structural and optical properties by forming oxygen vacancies in some samples, favoring the photocatalytic CO2 reduction in aqueous media to low-weight compounds, such as formaldehyde, methanol, methane, and hydrogen, under visible-light irradiation. Enhanced selectivity of the evolved product, as a result of the metallic cation nature and the formed impurities, was observed. For instance, Co3O4 favored the evolution of formaldehyde in the most efficient sample (1 Co-KTO; 453.2 μmol g−1) as a result of the low quantity of impurities present in samples; NiO favored the hydrogen evolution reaction (1 Ni-KTO; 201 μmol g−1), possibly due to the photo-reforming of the organic compounds; and CuO enhanced the methanol and hydrogen production (159.7 and 282 μmol g−1, respectively in 1 Cu-KTO) due to the formation of oxygen vacancies as active sites for the photocatalytic process and reducing the photo-generated charge recombination.

Bio-inspired honeycomb-like graphitic carbon nitride for enhanced visible light photocatalytic CO2 reduction activity.

Graphitic carbon nitride (g-C3N4) is paying attention lately owing to its interesting characteristics and substantial application in improving environmental and energy concerns. Nevertheless, the photocatalytic activity of g-C3N4 is constrained by the inertness of the surface and particle aggregation during photocatalytic activity. Herein, we report the preparation of g-C3N4 with honeycomb-like morphology (HC-C3N4) via thermal condensation of prepared SiO2 templates and dicyandiamide. The etching out of the SiO2 templates by NH4HF2 created hollow or macropores in the C3N4 matrix resulting in its structural changes. Similar, to the bulk C3N4, the HC-C3N4 exhibited higher photocatalytic CO2 reduction in hydrocarbons. This improved photocatalytic achievement is associated with higher specific surface area, excellent visible light absorption capability, higher electron donor density, easy mass diffusion of materials for surface reaction, and effective segregation of photogenerated charge carriers. Furthermore, the HC-C3N4 honeycomb structure was deposited with Ni(OH)2 clusters which showed remarkable CO2 reduction activity of 1.48μmolh-1g-1 of CH4 and 0.73μmolh-1g-1 of CH3OH generation which is 3.5 and 4.3 times higher CO2 reduction activity compared with bulk C3N4 clustered with Ni(OH)2 particles. This comprehensive study demonstrated that HC-C3N4 nanostructured polymeric semiconductor is envisaged to have great potential in the application of a variety of fields such as photocatalysis, sensor technology, and nanotechnology.

Two anionic Ni(II) porphyrinic metal−organic frameworks: Syntheses, flexibility and roles in visible-light photocatalytic CO2 reduction to CO in the Ru(bpy)3Cl2/TEA/CH3CN system

A 3D, anionic novel porphyrinic metal-organic framework (PMOF) 1 having [NH2(CH3)2]+ as counterions and Li+ -exchanged version of 1 (Li+-1) were synthesized. A very interesting feature of 1 and Li+-1 is their frameworks can change shape without breaking bonds, causing substantial changes of their PXRD patterns depending on what and how much is in the channels. Li+-1 has much larger surface area (Langmuir: 640 ​m2/g), compared with the 339 ​m2/g of PMOF 1. The CO2 adsorption capacities of 1 and Li+-1 are 38 (7.5 ​wt%) and 45 ​mL/g (8.9 ​wt%), respectively at 1 ​atm and 298 ​K, and 165–167 ​mL/g (33%) at 9.9 ​atm. They are direct-bandgap semiconductors with bandgaps of 1.56 (for 1) and 1.62 (for Li+-1) eV. The conduction and valence band-edge positions were determined in non-aqueous solutions as −0.29 and 1.27 (1), −0.32 and 1.30 ​V (Li+-1) versus NHE. PMOF 1 or Li+-1/Ru(bpy)3Cl2/TEA/CH3CN (bpy ​= ​2,2-bipyridine, TEA ​= ​triethylamine) system photocatalytically reduce CO2 to CO under visible light. PMOFs act as cocatalysts, and the photocatalysts were found to be the triplet excited state of Ru(bpy)32+ (Ru(II)∗) and its photodecomposition products. The TOFs contributed from PMOFs after 2 ​h were 0.091 and 0.097 h−1 (224 and 241 ​μmol ​g−1 ​h−1), respectively for 1 and Li+-1, respectively. In addition, the Ru(bpy)3Cl2/TEA/CH3CN system were found to have an unprecedented high TOF of 0.31 h−1 (412 ​μmol ​g−1 ​h−1) when small amounts of H2O (200 ​μL ​H2O in 40 ​mL CH3CN and 10 ​mL TEA) was added.

Self-templated synthesis of Co3O4 hierarchical nanosheets from a metal-organic framework for efficient visible-light photocatalytic CO2 reduction.

Efficient photocatalytic conversion of CO2 into energy-rich chemicals is of great significance for both environmental conservation and alleviating the energy crisis. However, convenient synthesis of low-cost, durable and eco-friendly photocatalysts with a novel morphology or structure for highly selective photocatalytic CO2 reduction remains a challenge. Herein, Co3O4 hierarchical nanosheets were synthesized by calcination of novel cobalt metal-organic framework (MOF) nanosheets prepared by a facile oil bath method. In such Co MOF nanosheets, 1,4-naphthalenedicarboxylic acid was chosen as the organic linker, rather than the commonly used 2-methylimidazole for ZIF-67. After thermal treatment in air, the obtained Co3O4 inherited the 2D morphology of its MOF template and evolved into hierarchical nanosheets which were composed of small nanoparticles. Benefiting from the large surface area, abundant mesoporous structure and good capability towards the separation and transfer of photo-generated charge carriers induced by less internal oxygen vacancies, the Co3O4 hierarchical nanosheets showed a CO generation rate of 39.70 μmol h-1 in visible-light photocatalytic CO2 reduction, which was superior to that of Co3O4 nanoparticles and commercial Co3O4. What's more, a CO selectivity of 77.3% was achieved, which is among the highest of cobalt-based spinel oxide photocatalysts for CO2 conversion.