Photocatalytic Conversion Of CO2 Research Articles

Environmental aspects of using artificial photosynthesis technology for environmental decarbonization

The increasing levels of carbon dioxide (CO2) in the atmosphere have been recognized as a major contributor to global climate change. As a result, there is a pressing need to develop sustainable and eco-friendly methods for mitigating CO2 emissions. CO2 recycling has emerged as a promising solution, aiming to convert CO2 into valuable products while reducing its impact on the environment. This work uses the CO2 recycling approach, which involves the conversion of CO2 emissions into useful organic compounds. An experiment with artificial photosynthesis is carried out with the help of a special installation, where CO2 undergoes photochemical reactions that contribute to the formation of organic compounds. Photocatalytic conversion of CO2 is environmentally friendly as it uses light energy and renewable raw materials to produce valuable chemicals without producing harmful by-products or waste. It has been established that TiO2 in the form of anatase and rutile is the most common CO2 photocatalyst. As a result of the experiment, the main output products were methanol, acetate aldehyde and acetone. The use of ultraviolet radiation and an electric field significantly affected the synthesis of organic substances and their quantity. It can be used in various industries such as fuel, chemical and pharmaceutical industries. In particular, methanol, acetate aldehyde and acetone are promising substances for the use and production of biofuels.

Utilizing Er-doped ZnIn2S4 for efficient photocatalytic CO2 conversion

In the quest for effective photocatalysts for CO2 reduction, catalysts doped with rare-earth elements have garnered considerable attention due to their unique electronic structures and energy levels, which enable enhanced light absorption and charge transfer capabilities. In this study, we synthesized erbium-doped ZnIn2S4 using a hydrothermal method. Compared with pure ZnIn2S4, the erbium-doped variant displayed a significant boost in photocatalytic performance, improving the efficiency of CO2 reduction to methane by 256 times, with a selectivity exceeding 90 % towards methane. Through DFT analysis, we found that the doping of erbium introduced new energy levels into ZnIn2S4, effectively narrowing the band gap and thereby enhancing light absorption efficiency. Furthermore, our research revealed that erbium-doped ZnIn2S4 introduces a uniquely distinct reaction pathway for CO2 reduction compared to pure ZnIn2S4, significantly reducing the reaction barrier. Moreover, it enhances the adsorption of the key intermediate, *CHO and *CH2O, steering the reaction pathway towards the production of CH4. These findings not only offer valuable insights for the development of efficient and selective photocatalysts but also pave new avenues for research into CO2 conversion.

Synergistic effect of surface modification and effective interfacial charge transfer over faceted g-C3N4/ZnSe heterojunction to enhance CO2 photoreduction activity

Heterojunction and surface modification are promising methods to boost the photocatalytic CO2 conversion efficiency which help to optimize the redox ability of photocatalysts and enhance the separation efficiency of photogenerated charge carriers. Herein, a novel surface-modified and interfacial heterojunction of g-C3N4 (CN) over a faceted ZnSe (ZS) {CN/ZS} composite was developed to accelerate the transfer of photogenerated electrons (e−) and holes (h+) between the CN and ZS photocatalysts. This technology allows faster transfer of a larger quantity of excited reductive electrons to the surface of ZS with a lower CO2 adsorption energy. Based on photocatalytic CO2 reduction to CO and CH4, 3 mmol CN/ZS composite outperformed all as-prepared photocatalysts including pure CN and ZS, with yielding rates of 439 and 203 umolg−1, respectively, with 88 % CO2 selectivity. The improved photocatalytic activity and selectivity were attributed to enhanced visible-light absorption, improved CO2 activation and adsorption on the surface of the photocatalyst and facilitated charge transfer at the interface. This study offers a novel approach for precisely controlling the direction of photogenerated charge separation by constructing a heterostructure for CO2 photoreduction.

Engineering of oxygen vacancy and bismuth cluster assisted ultrathin Bi12O17Cl2 nanosheets with efficient and selective photoreduction of CO2 to CO

AbstractThe photocatalytic conversion of CO2 into solar‐powered fuels is viewed as a forward‐looking strategy to address energy scarcity and global warming. This work demonstrated the selective photoreduction of CO2 to CO using ultrathin Bi12O17Cl2 nanosheets decorated with hydrothermally synthesized bismuth clusters and oxygen vacancies (OVs). The characterizations revealed that the coexistences of OVs and Bi clusters generated in situ contributed to the high efficiency of CO2–CO conversion (64.3 μmol g−1 h−1) and perfect selectivity. The OVs on the facet (001) of the ultrathin Bi12O17Cl2 nanosheets serve as sites for CO2 adsorption and activation sites, capturing photoexcited electrons and prolonging light absorption due to defect states. In addition, the Bi‐cluster generated in situ offers the ability to trap holes and the surface plasmonic resonance effect. This study offers great potential for the construction of semiconductor hybrids as multiphotocatalysts, capable of being used for the elimination and conversion of CO2 in terms of energy and environment.

Construction of ZnO@CDs@Co3O4 sandwich heterostructure with multi-interfacial electron-transfer toward enhanced photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into small-molecule chemical feedstocks can meet the growing demand for energy and alleviate the global warming. Herein, a p-n ZnO@CDs@Co3O4 heterojunction with sandwich structure was constructed by calcination method of self-assembled ZIF-8@CDs@ZIF-67. The ZnO@CDs@Co3O4 with well-defined interfacial structure exhibited the significantly enhanced photocatalytic CO2 reduction activity, and the optimal catalyst indicated the (CO + CH4) evolution rate of 214.53 µmol g−1 h−1 under simulated solar light, which was superior to ZnO, Co3O4 and binary ZnO@Co3O4. The internal cavity, exposed active sites, multiple interfaces and constructed p-n heterojunction can facilitate the light harvesting and photoexcited electron transfer. Besides, after introduction of CDs placed in the middle layer between ZnO and Co3O4, CDs with excellent photoelectric property further promoted charge separation and migration. This work represents an appealing strategy to construct well-defined photocatalysts for boosting CO2 photoreduction.

Spatial charge separation in core-shell dual metal-organic frameworks for enhanced CO2 photoreduction

Flexibly and controllably regulating the functionality of the core–shell system is still challenging, which is largely determined by the shell thickness and core–shell interface. Here, elaborately designed core–shell dual MOFs were constructed via in-situ growth of Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) shell with adjustable thicknesses over CuFe Prussian blue analogue (PBA). The thin-shell CuFe PBA@Cu-HHTP heterojunction (CFH-1) improves charge separation and transfer compared to CuFe PBA and thick-shell heterojunction. Density functional theory results indicate the efficient regulation of electron density near Cu site via constructing heterojunction. The photocatalytic CO2-to-CO activity of CFH-1 is improved (29.3 μmol·g−1) by ∼ 14 times than pristine CuFe PBA. This study provides information on charge separation at the core–shell structure interface to achieve efficient photocatalytic CO2 conversion.

(Invited) Al-Doped SrTiO3 Photocatalyst for Selective CO2 Reduction with Water as a Reductant

Among various strategies toward finding new energy sources to replace conventional fossil fuels, photocatalytic conversion of CO2 into useful chemicals using water as an electron donor and a proton source has been increasingly attracting attentions because it can convert light energy to chemical energy. The photocatalytic conversion of CO2 involves photoabsorption (light harvesting), charge separation, and H2O oxidation, as well as the consumption of the photogenerated electrons for reduction. The evolution of H2 rather than CO is preferred when H2O is used as the electron donor, since the redox potential of CO2/CO (−0.51 V vs NHE, at pH 7) is more negative than that of H+/H2 (−0.41 V vs NHE, at pH 7) in an aqueous solution. Therefore, “high selectivity toward CO2 reduction” is one of the most important requirements for the photocatalytic system to achieve the CO2 conversion in water. Various mixed oxides including tantalum-based NaTaO3, Ta2O5, Sr2KTa5O15, titanium-based BaLa4Ti4O15, CaTiO3, Na2Ti3O7, K2Ti6O13, La2Ti2O7, SrTiO3, gallium-based Ga2O3, and ZnGa2O4, and SrNb2O6 were found to be excellent photocatalysts for the conversion of CO2 into CO in the presence of Ag cocatalyst. However, these materials show significant activity for CO evolution only when irradiated with deep region UV-light (λ < 300 nm). Therefore, a series of photocatalysts which can drive under the photoirradiation with UV-light at λ > 300 nm is strongly desired in the research area of the photocatalytic conversion of CO2. Recently, Domen et al. reported that Al-doped SrTiO3 (Al-STO) with suitable cocatalysts such as MoOy/RhCrOx exhibited a promising photocatalytic activity for overall water splitting under photoirradiation at λ > 300 nm; the apparent quantum efficiency of the MoOy/RhCrOx/Al-STO reached close to 69% at 365 nm. Thus, we herein describe our investigation into the photocatalytic conversion of CO2 by H2O using the Al-STO photocatalyst with Ag and AgCo cocatalysts under photoirradiation with λ > 300 nm. Al-STO photocatalyst was fabricated by a flux method using anhydrous SrCl2 as a flux reagent. A mixture of SrTiO3, Al2O3, and anhydrous SrCl2 was ground for 10 min, and then transferred into an alumina crucible and calcined at 1423 K under air for 15 h. Ag cocatalyst was employed to modify the surface of the as-prepared Al-STO photocatalyst via a chemical reduction method. Al-STO was dispersed in deionized ultrapure water, and AgNO3 and NaH2PO2 were added to the suspension, then it was maintained at 353 K for 1.5 h. Photocatalytic activity of Ag/Al-STO photocatalyst was evaluated by using an inner-irradiation type reaction vessel in a quasi-flowing batch system. The photocatalyst powder was dispersed in 1.0 L of an aqueous NaHCO3 solution, and the dissolved air in this suspension was degassed by a flow of high-purity CO2 gas. CO2 was continuously bubbled into the reaction solution at a flow rate of 30 mL/min. The suspension was irradiated using a 400 W high-pressure Hg lamp with a Pyrex filter equipped with a cooling water system (irradiation wavelength: λ > 300 nm). The gaseous products in the outlet gas, e.g., CO, H2, and O2, were analyzed by gas chromatography (FID-GC with methanizer: CO, TCD-GC: H2 and O2). The attached figure shows a formation rate of CO (red), H2 (blue), and O2 (green) in the photocatalytic conversion of CO2 with H2O using undoped STO and Al-STO in the presence of Ag cocatalyst. It should be noted that the formation rate of CO is significantly increased by the doping of Al into STO. Moreover, the addition of Co species as a second cocatalyst to Ag/Al-STO drastically improved its activity for the photocatalytic conversion of CO2 by H2O as the electron donor, with extremely high selectivity toward CO evolution (99.8%), in which Ag and Co might enable CO2 reduction and H2O oxidation on the Al-STO surface, respectively. The formation rate of CO up to 52.7 μmol/h was observed over AgCo/Al-STO when irradiated with the UV light at wavelengths above 300 nm, which is ten-times higher than that over Ag/Al-STO (4.7 μmol/h). Furthermore, isotope-experiments using 13C-labeled CO2 gas revealed that 13C-labeled CO (m/z = 29) is selectively observed by GC-MS analysis, indicating that the CO evolved over the Ag/Al-STO and AgCo/Al-STO photocatalysts should be derived from the introduced CO2 gas. Figure caption Formation rates of products and selectivity toward CO evolution in the photocatalytic conversion of CO2 using bare Ag/STO (undoped STO), Ag/ and AgCo/Al-STO. Red: CO, green: O2, blue: H2, black circle: selectivity. Loading amount of Ag: 1wt%, Ag : Co = 2 : 1 (mol). Figure 1

Photocatalytic Conversion of CO2 By H2o As an Electron Donor over Mg-Doped SrTiO3

Atmospheric CO2 is considered as the main cause of climate change, which is known as one of the serious problems for the earth, and several approaches are employed to convert CO2 into value-added products, such as CO, HCOOH, CH3OH and CH4. Among those approaches, photocatalysis has been highly attracting the world-wide attention, because photocatalytic conversion of CO2, which is called as “artificial photosynthesis”, can be a solution for climate change in terms of its renewability, harmlessness and low cost. Ga-based mixed oxide photocatalysts such as ZnGa2O4 were reported as superior photocatalysts for the photocatalytic conversion of CO2 by using H2O3. Recently, our group reported that Ag and Co dual cocatalysts-loaded Al-doped SrTiO3 photocatalyst showed relatively high formation rate of CO for the photocatalytic conversion of CO2 by H2O under photoirradiation with a monochromatic light (365 nm)1, although Ga-based photocatalysts exhibited the activity under the photoirradiation with less than 300 nm. In this study, the effect of metal dopant in SrTiO3 on the photocatalytic conversion of CO2 was investigated. It was found that Mg-doped SrTiO3 showed higher formation rate of CO for the photocatalytic conversion of CO2 into CO under photoirradiation at 365 nm than Al-doped SrTiO3.Mg-doped SrTiO3 was synthesized by a flux method. After grinding mixture of SrTiO3, MgO, and SrCl2 flux, the obtained powder was calcined at 1418 K for 15 h. Ag and Co dual cocatalysts were loaded by chemical reduction method. An aqueous solution of NaH2PO2 reductant was added to the suspension containing Mg-doped SrTiO3, AgNO3, and Co(NO3)2, and it was kept at 353 K for 1.5 h with stirring. The photocatalytic conversion of CO2 by H2O was carried out using an external-irradiation-type reaction vessel. Ag and Co-loaded Mg-doped SrTiO3 was dispersed in 0.1 M NaHCO3 aqueous solution, and high purity CO2 gas was bubbled into the suspension at a flow rate of 30 mL min−1. Monochromatic UV LED lamp (365 nm) was used as a light source. The gaseous products were analyzed by TCD–GC (H2, O2) and FID–GC equipped with methanizer (CO).XRD patterns of pristine and Mg-doped SrTiO3 showed that diffraction peaks are shifted to the lower angle by Mg2+ doping, which might be corresponded to Mg2+ doping into Ti4+ site in the bulk of SrTiO3. SEM images displayed that a shape of Mg-doped SrTiO3 is an edge-shaved cube, while that of pristine SrTiO3 is irregular. In other words, {110} facets were observed in Mg-doped SrTiO3 in addition to {100} facets. According to the previous report2, the photoexcited carriers, electrons and holes, were transported to different crystal facets of the perovskite oxide, especially {100} and {110} facets, respectively. This anisotropic charge distribution would decrease the charge recombination rate in Mg-doped SrTiO3, resulting in the high photocatalytic activity for CO2 conversion.The attached figure shows formation rates of H2 (gray), O2 (white) and CO (black) and selectivity toward CO evolution (black diamond) for the photocatalytic conversion of CO2 by H2O over Ag and Co-loaded pristine SrTiO3, Al-doped SrTiO3, and Mg-doped SrTiO3. Mg-doped SrTiO3 exhibited much higher photocatalytic activity than pristine SrTiO3 and Al-doped SrTiO3. The formation rate of CO over Mg-doped SrTiO3 was 20 μmol h−1, which was 2.3 times larger than that over Al-doped SrTiO3. Surprisingly, the selectivity toward CO evolution was almost 100 % over both Al-doped and Mg-doped SrTiO3. Moreover, the stoichiometric amount of O2 evolution was observed during this reaction, indicating that H2O worked as an electron donor for the photocatalytic conversion of CO2.The control experiments revealed that the reduction of CO2 did not proceed in the absence of photocatalyst, photoirradiation, or additive (0.1 M NaHCO3). These results clearly indicated that the significant photocatalytic performance was observed by using the Ag and Co-loaded Mg-doped SrTiO3 photocatalyst under photoirradiation with a NaHCO3 additive in the suspension. To confirm that the generated CO is not derived from any organic contamination, the isotope-labeling experiments using 13CO2 gas was carried out. GC-MS analysis of the outlet gas in the photocatalytic conversion of 13CO2 over Mg-doped SrTiO3 clarified that 13C-labeled CO (m/z = 29) was evolved in priority to 12CO (m/z = 28). Accordingly, we concluded that CO gas evolved in our system is originated from CO2 gas bubbled into the suspension. Wang, et al., Chem. Sci., 2021, 12, 4940–4948Takata, et al., Nature, 2020, 581, 411–414Wang, et al., J. Mater. Chem. A 2015, 3, 11313–11319 Figure 1

Performance analysis of rGO-bridged g-C3N4/ZnV2O6 S-scheme heterojunction for CO2 photoreduction with H2O in an externally reflected photoreactor

The photocatalytic conversion of CO2 with H2O over rGO-bridged g-C3N4/ZnV2O6 S-scheme heterojunction using an externally reflected photoreactor has been investigated. The structure and properties of photocatalysts, prepared via the one-pot solvothermal method, were characterized by XRD, RAMAN, FESEM, EDX, HRTEM, UV–vis and PL spectrophotometry. The 4 % rGO-bridged g-C3N4/ZnV2O6 (1:1) nanocomposite registered the highest CH3OH yield. The maximum yield of CH3OH over 4 % rGO-bridged g-C3N4/ZnV2O6 (1:1) nanocomposite was 6246.1 μmol/g-cat; 1.34 and 1.51 folds higher than g-C3N4/ZnV2O6 (1:1) and ZnV2O6 photocatalysts, respectively. Significant enhancement in quantum efficiency of an externally reflected photoreactor over 4 % rGO-bridged g-C3N4/ZnV2O6 (1:1) nanocomposite was observed compared to the slurry photoreactor. This is obviously because of the greater mobility of charges with hindered recombination rate and higher photonic efficiency. The stability of 4 % rGO-bridged g-C3N4/ZnV2O6 (1:1) nanocomposite was partially reduced after several cyclic runs. It is believed that the photocatalyst consisting of three components has demonstrated improved photocatalytic activity through a S-scheme mechanism, utilizing rGO as an electron mediator to enhance the overall performance of the S-scheme heterojunction.

Tröger's base derived 3D-porous aromatic frameworks with efficient exciton dissociation and well-defined reactive site for near-unity selectivity of CO2 photo-conversion

The overall photocatalytic conversion of CO2 and H2O to fuel and O2 is challenging. In this study, a series of three-dimensional Tröger's base-derived porous aromatic frameworks (3D-X-TB-PAFs (X = TEPE, TEPM, SPF)) featuring designated reaction sites and unique charge transfer properties were developed. The incorporation of V-shaped Tröger's base (TB) units and aromatic alkynes imparts the polymers with permanent porosity, additional photon scattering cross-sections, and enhanced CO2 adsorption/activation capabilities. Density functional theory calculations and optoelectronic measurements revealed the formation of intramolecular built-in polarization and electron-trap sites induced by TB, which modulated charge separation and customized reaction sites in collaboration with 3D networks. In addition, product allocation during the photoreduction of CO2 was regulated by the photooxidation of H2O. Among the as-prepared 3D-PAFs, the most efficient electron transport channel was demonstrated by the TEPE-TB-PAF with fully conjugated TEPE-T. In the absence of cocatalysts and sacrificial agents, TEPE-TB-PAF exhibits a competitive CO formation rate (194.50 μmol g−1 h−1) with near-unity selectivity (99.74%). Significantly, the low energy barrier for CO desorption and the high energy barrier for *CHO formation contribute to the high efficiency of TEPE-TB-PAF, as demonstrated by computational exploration and in situ diffuse reflectance infrared Fourier transform spectra. This work offers efficient building blocks for the synthesis of multifunctional organic photocatalysts and groundbreaking insights into the simultaneous enhancement of photocatalytic reactivity and selectivity.

Atomically dispersed Fe sites on TiO2 for boosting photocatalytic CO2 reduction: Enhanced catalytic activity, DFT calculations and mechanistic insight

The design of photocatalysts for the stable and efficient photocatalytic reduction of CO2 without sacrificial agents remains challenging. In this study, Fe atoms were anchored on the surface of TiO2 with atomic-level dispersion using a novel negative-pressure encapsulation and pyrolysis strategy. The photoelectrochemical test results confirmed that the introduction of single Fe atoms accelerated the separation of photogenerated carriers and enhanced the TiO2 utilization rate of visible light. The optimal catalyst with atomically dispersed Fe showed excellent photocatalytic conversion of CO2 to CO (48.2 μmol·g−1·h−1) and CH4 (113.4 μmol·g−1·h−1), whereas the TiO2 system produced only trace amounts of CO (2.7 μmol·g−1·h−1). The increased CO2 adsorption energy and movement of the d-band center toward the Fermi level confirmed that single Fe sites were more favorable for the adsorption of CO2. The differential charge density distribution of CO2 adsorbed on the catalyst surface confirmed the rapid transfer of electrons along the Ti-O-Fe-C path, and the Gibbs free energy calculation further confirmed that the Fe sites were conducive to reducing the energy barrier required for the reaction. In addition, the key intermediate (*COOH) of CO2 conversion to CH4 was detected by in situ diffuse reflectance infrared Fourier transform spectroscopy, and a possible reaction pathway was proposed. This work provides an effective strategy for designing single-atom catalysts that can efficiently reduce CO2 to high-value-added products.

Investigating S-scheme charge transfer pathways in NiS@Ta2O5 hybrid nanofibers for photocatalytic CO2 conversion

Investigating the charge-transfer behavior of photocatalysts is important to promote the photoreduction of CO2 into solar fuels. Therefore, in this study, hybrid Ta2O5 nanofibers were produced through the in situ growth of freestanding NiS nanosheets. The charge separation and CO2 photoreduction mechanisms of these nanofibers were investigated using in situ X-ray photoelectron spectroscopy and density functional theory calculations. The results suggested that the NiS@Ta2O5 nanohybrids formed an S-scheme heterojunction, which promoted the efficient separation of electron-hole pairs and enhanced CO2 photoreduction. Compared to the pristine Ta2O5 nanofibers, the hybrid nanofibers exhibited a significantly higher CO2-reduction rate (43.27 μmol g−1 h−1 for CO; 6.56 μmol g−1 h−1 for CH4). In situ diffuse reflectance infrared Fourier-transform spectroscopy results confirmed the process of CO2 hydrogenation and S-scheme charge transfer pathways in NiS@ Ta2O5 nanohybrids.

Highly stable and durable ZnIn2S4 nanosheets wrapped oxygen deficient blue TiO2(B) catalyst for selective CO2 photoreduction into CO and CH4

Developing new and highly stable efficient photocatalysts is crucial for achieving high performance and selective photocatalytic CO2 conversion. In this paper, we designed a one-dimensional oxygen-deficient blue TiO2(B) (BT) catalyst for improved electron mobility and visible light accessibility. In addition, hexagonal ZnIn2S4 (ZIS) nanosheets with a low bandgap and great visible light accessibility are employed to produce effective heterostructures with BT. The synthesized materials are tested for photocatalytic conversion of CO2 into solar fuels (H2, CO and CH4). The optimized composite yields 71.6 and 10.3 μmol g−1h−1 of CO and CH4, three and ten times greater than ZIS, respectively. When ZIS nanosheets are combined with a one-dimensional oxygen-deficient BT catalyst, improved electron mobility and visible light accessibility are achieved, charge carriers are effectively segregated, and the transfer process is accelerated, resulting in efficient CO2 reduction. The photocatalytic CO2 conversion activity of the constructed BT/ZIS heterostructures is very stable over a 10-day (240-hour) period, and CO and CH4 production rates increase linearly with time; however, as time goes on, the rates of H2 production decrease. Further, a five-time recycling test confirmed this, revealing essentially equal activity and selectivity throughout the experiment. As a result, CO2 to CO and CH4 conversion has high selectivity and longer durability. The band structure of the BT/ZIS composite is determined using Mott-Schottky measurement, diffuse reflectance spectroscopy, and valence band X-ray photoelectron spectroscopy. This research demonstrates a novel approach to investigating effective, stable, and selective photocatalytic CO2 reduction systems for solar-to-chemical energy conversion.

Photoelectron "Bridge" in Van Der Waals Heterojunction for Enhanced Photocatalytic CO2 Conversion Under Visible Light.

Constructing Van der Waals heterojunction is a crucial strategy to achieve excellent photocatalytic activity. However, in most Van der Waals heterojunctions synthesized by ex situ assembly, electron transfer encounters huge hindrances at the interface between the two components due to the large spacing and potential barrier. Herein, a phosphate-bridged Van der Waals heterojunction of cobalt phthalocyanine (CoPc)/tungsten disulfide (WS2 ) bridged by phosphate (xCoPc-nPO4 - -WS2 ) is designed and prepared by the traditional wet chemistry method. By introducing a small phosphate molecule into the interface of CoPc and WS2 , creates an electron "bridge", resulting in a compact combination and eliminating the space barrier. Therefore, the phosphate (PO4 - ) bridge can serve as an efficient electron transfer channel in heterojunction and can efficiently transmit photoelectrons from WS2 to CoPc under excited states. These excited photoelectrons are captured by the catalytic central Co2+ in CoPc and subsequently convert CO2 molecules into CO and CH4 products, achieving17-fold enhancement on the 3CoPc-0.6PO4 - -WS2 sample compared to that of pure WS2 . Introducing a small molecule "bridge" to create an electron transfer channel provides a new perspective in designing efficient photocatalysts for photocatalytic CO2 reduction into valuable products.

Pt clusters in carbon network to enhance photocatalytic CO2 and benzene conversion of WOx/g-C3N4 nanosheets

Noble metals in carbon networks dramatically improve the carrier separation and transfer efficiencies of layered graphic carbon nitride (g-C3N4) based heterostructures for efficient CO2 and benzene photocatalytic conversion. Here, Pt clusters are homogeneously incorporated into ultrathin g-C3N4 nanosheets via multi-step treatment method using the combinations of mechano-chemical pre-reaction and two-step thermal condensation processes. Small Pt nanoparticles with diameters of less than 5 nm are observed and WOx nanobelts with increased oxygen vacancies (as the active sites) are horizontally grown on the thin Pt-g-C3N4 nanosheets. The photocatalytic activities of the constructed composite materials are evaluated under full solar spectrum irradiation condition including water splitting, CO2 photoreduction, and benzene to phenol conversion. The WOx/Pt-g-C3N4 nanosheet heterostructures with optimized preparation condition and without adding any co-catalyst reveals enhanced H2 generation (5267 μmolg−1h−1) and CO2 photoreduction (5.89 and 3.12 μmolg−1h−1 for CO and CH4 conversion rate, respectively), as well as improved benzene to phenol conversion (89.0%) and selectivity (98.2%). The presence of Pt clusters in the heterostructures improves charge transport in-between g-C3N4 and WOx, thus enhances the charge separation efficiency of the composite material. Detailed photocatalytic mechanisms are discussed on the alteration from S-scheme WOx/g-C3N4 heterostructure to Z-scheme WOx/Pt-g-C3N4 heterostructure.

Synergistic role of Cu-C and Cu-N dual bonding of nanostructured g-C3N4/Cu2SnS3 photocatalysts for efficient CO2 conversion to CO

Herein, a 2D/0D g-C3N4/Cu2SnS3 heterostructure is successfully constructed via the facile calcination method, and its application to photocatalytic CO2 conversion is demonstrated for the first time. The fabricated g-C3N4/Cu2SnS3 nanocomposite is featured with its unique Cu-C and Cu-N dual chemical bond at the interface. The engineered g-C3N4/Cu2SnS3 nanocomposites record a superior CO production rate of 18.2 μmol∙g−1∙h−1 with an apparent quantum yield of 2.2% at 500 nm of light illumination, which is the highest among g-C3N4/ternary metal sulfide photocatalysts to the best of our knowledge. This notable improvement is attributed to the effective incorporation of Cu2SnS3 nanoparicles onto the surfaces of ultra-thin g-C3N4 and, the formation of Cu-N and Cu-C dual bonds at the interface. This helps not only the activation of interface defect-mediated Z-scheme conduction but also supplies highly reactive Cu sites in the Cu2SnS3 nanoparticles for efficient photocatalytic CO2 conversion.

In-situ embedded ultrafine Bi12O17Br2 nanotubes in MOF-derived hierarchical porous carbon for enhanced photocatalytic CO2 conversion to CO

Increasing the utilization efficiency of photogenerated electrons is highly recognized as one of the efficient approaches to boost the photocatalytic CO2 conversion efficiency. Herein, ZIF-67-derived porous carbon (PC) material was employed for the construction of PC@ultrafine Bi12O17Br2 nanotubes (PC@BOB NTs) composites through a facile solvothermal synthesis in order to optimize the use of excited electrons in the BOB NTs. Photoelectrochemical characterization results revealed that the introduction of PC material achieved a faster charge separation rate in the PC@BOB composites, ensuring more photogenerated electrons participate in the CO2 adsorption and activation process. Moreover, the pore structures of ZIF-67-derived PC material provided abundant confined spaces for the enrichment of CO2 molecules. After 5 h of Xenon lamp irradiation, PC@BOB composites exhibited obviously increased photocatalytic CO2 reduction activity in the pure water. When the addition amount of PC was 5 wt%, the PC@BOB-2 composite showed the highest CO evolution rate of 359.70 µmol/g, which was 2.95 times higher than that of the pure BOB NTs. This work provides some independent insights into the applications of Metal-Organic Framework (MOF)-derived hierarchical porous structures to strengthen the CO2 enrichment, as well as the excited charge utilization efficiency, thus achieving a high solar-to-fuel conversion efficiency.

Construction of NH2-MIL-101(Fe)@Bi2MoO6 S‐scheme heterojunction for efficient and selective photocatalytic CO2 conversion to CO

Developing efficient photocatalyst to promote the conversion of CO2 into value-added chemicals remains challenging. Here, novel NH2-MIL-101(Fe)@Bi2MoO6 S-scheme heterojunctions were fabricated via a solvothermal method, in which Bi2MoO6 (BMO) nanoparticles uniformly growing on the NH2-MIL-101(Fe) (NM101) octahedrons with intimate contact interface. The resultant heterojunctions revealed significantly enhanced activity for CO2 photoreduction. The optimal performance was achieved when the content of BMO was 10 wt%, and the formation rate of CO reached 67.0 μmol·g−1·h−1 under visible light illumination (with apparent quantum efficiency of 0.09 % at 450 nm), which was 3.2-fold of individual NM101. The boosting activity benefited from the formation of S-scheme heterojunction at the NM101 @BMO interfaces, which facilitated the separation of photoinduced electron-hole pairs with strong redox ability at the interface. This S-scheme charge transfer mechanism was further validated by the in-situ XPS and fluorescence probe molecular experiment. Besides, the intermediates and preliminary mechanism of photoreaction were unraveled based on in-situ DRIFTS analysis. This work provides some novel insights for designing efficient S-scheme photocatalysts for CO2 photoreduction.

Oxygen Vacancy Induced Atom-Level Interface in Z-Scheme SnO2/SnNb2O6 Heterojunctions for Robust Solar-Driven CO2 Conversion.

The modulation of Z-scheme charge transfer is essential for efficient heterostructure toward photocatalytic CO2 reduction. However, constructing a compact hetero-interface favoring the Z-scheme charge transfer remains a great challenge. In this work, an interfacial Nb-O-Sn bond and built-in electric field-modulated Z-scheme Ov-SnO2/SnNb2O6 heterojunction was prepared for efficient photocatalytic CO2 conversion. Systematic investigations reveal that an atomic-level interface is constructed in the Ov-SnO2/SnNb2O6 heterojunction. Under simulated sunlight irradiation, the obtained Ov-SnO2/SnNb2O6 photocatalyst exhibits a high CO evolution rate of 147.4 μmol h-1 g-1 from CO2 reduction, which is around 3-fold and 3.3-fold of SnO2/SnNb2O6 composite and pristine SnNb2O6, respectively, and favorable cyclability by retaining 95.8% rate retention after five consecutive tests. As determined by electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and density functional theory calculations, Nb-O-Sn bonds and built-in electric field induced by the addition of oxygen vacancies jointly accelerate the Z-scheme charge transfer for enhanced photocatalytic performance. This work provides a promising route for consciously modulating Z-scheme charge transfer by atomic-level interface engineering to boost photocatalytic performance.

Development of a photocatalytic method to convert CO2 into formic acid with fulvic acid complex

Increasing levels of carbon dioxide (CO2) due to natural and anthropogenic activities have led to alarming concerns of global warming. Photocatalytic conversion of CO2 to formic acid (FA) is speculated to provide a long-term solution for CO2 remediation and the production of green energy. Herein, we report the conversion method of CO2 to FA using water, light, and organic RRR catalyst at room temperature in a photocatalytic RK-X reactor. A total of seven experiments were conducted and observed to study the effectiveness of the reaction. The experiments achieved 8.47 g/L of FA concentrate. This photocatalytic conversion of CO2 into FA represents a promising approach to addressing global warming and providing carbon negative hydrogen as an answer to fossil fuel problems. Another possible application of this study is to provide sustainable energy on Mars, where water, light, and CO2 are all available for the reaction.