Photocatalysts For CO2 Reduction Research Articles

Construction of AgBr/BiOBr S-scheme heterojunction using ion exchange strategy for high-efficiency reduction of CO2 to CO under visible light

CO2 reduction via photocatalytic is regarded as the excellent strategy to resolve the severe environmental crisis and energy crisis caused by the accelerated utilization of fossil energy like natural gas, oil, and coal. The Ag ion and the Br ion in BiOBr are creatively used in the ion exchange strategy to form AgBr on the surface of BiOBr, and an S-scheme BiOBr/AgBr heterojunction with close interface contact is constructed. The visible light utilization rate and CO2 conversion rate of the obtained heterojunction are both remarkably improved. The reduction rate of CO2 over the catalyst was tested under visible light using pure water as the liquid environment. As obtained results displayed that the transformation efficiency of BA-1 to CO from CO2 in the visible light was 12.43 μ mol g-1h−1, which is about 3 times that the pristine BiOBr. The intermediates during the reaction were studied using in situ DRIFTS. The process by which CO2 was degraded was speculated based on in situ DRIFTS spectra. In addition, TPR, EIS, and PL measurements indicate that BA-1 has a high solar utilization rate and strong photo-generated carrier transfer and separation capability. This work showed a novel direction for preparation of efficient photocatalyst for CO2 reduction.

Evaluating the performance of Cs2PtI6−xBrx for photovoltaic and photocatalytic applications using first-principles study and SCAPS-1D simulation

All inorganic free-lead halide double perovskites are attractive materials in solar energy harvesting applications. In this study, density functional theory calculations have been used to predict the structures, band structures, and density of states of Cs2PtI6−xBrx with (x = 0, 2, 4, and 6). The optical properties (reflectivity, refractive index, absorption, dielectric function, conductivity, and loss function) of these materials have been predicted and discussed. The band edges calculations showed that the Cs2PtI6−xBrx may be an efficient visible-light photocatalyst for water splitting and CO2 reduction. The calculated bandgap value of Cs2PtI6 exhibited a great match with the reported experimental values. It has been seen that increasing the doping content of Br− in Cs2PtI6−xBrx (x = 0, 2, 4, and 6) increases the bandgaps from 1.4 eV to 2.6 eV and can be applied in single junction and tandem solar cells. Using Solar Cell Capacitance Simulator (SCAPS), a 1D device modelling has been performed on Cs2PtI6 inorganic lead-free solar cells. For the fully inorganic device, the effect of replacing organic hole transport materials (HTL) and electron transport materials (ETL) with inorganic ones is investigated while keeping high efficiencies and stabilities of solar cell devices. From the obtained results, it was found that WS2 as ETL and Cu2O as HTL were the most suitable materials compared to the others. Further investigation studies are performed on the effect of changing metal back contact work function, absorber layer thickness, doping density, and defect density on the power conversion efficiency (PCE) of the solar cell. The optimized suggested structure (FTO/WS2/Cs2PtI6/Cu2O/Carbon) obtained a PCE of 17.2% under AM1.5 solar illumination.

Hierarchical ternary layered double hydroxide/graphitic carbon nitride heterostructures as visible-light photocatalysts for efficient reduction of CO2

The development and synthesis of high-efficient, stable, and cost-effective photocatalysts to reduce both world-wide energy and environmental issues are the most significant challenge in CO2 reduction. Herein, we explore the photocatalytic performance over NiFeV layered double hydroxide (LDH) nanosheets, g-C3N4, and NiFeV-LDH/g-C3N4 heterostructures, which convert CO2 into high value-added fuels, such as CO and CH4. The 2D/2D hierarchical flower-like structure created an outstanding heterosystem with close interfaces and prominently exposed catalytic active sites to dramatically improve light-harvesting ability. The charge transfer among the individual components made the separation of photogenerated charge carriers easier and lessened their recombination rate, enhancing the photoreduction of CO2. The ratio of g-C3N4 to NiFeV-LDH in term of weight had a significant impact on the photocatalytic activity of the NiFeV-LDH/g-C3N4 heterostructure. The photocatalyst generated the maximum yields of CH4 (15.2 µmol h−1g−1) when the weight ratio of g-C3N4 to NiFeV-LDHs was 15%, which was 4.04 times that of pure NiFeV-LDH. The yield of CO was 13.05 µmol h−1g−1, 3.15 times that of pure NiFeV-LDH. Furthermore, during cycling experimental runs, the optimized NiFeV-LDH/g-C3N4-15% heterostructure exhibited a remarkable photostability with no discernible change in the amounts of CO and CH4 formation. The significantly improved photocatalytic performance towards CO2 reduction was confirmed by the XPS and HRTEM analyses, which showed strong electronic interactions and promoted charge transfer between heterostructure components. The current study provides a feasible way to enhance the photocatalytic performance of LDH-based heterostructures and opens up new prospects for developing LDH-based photocatalysts towards CO2 reduction.

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Redispersion of exsolved Cu nanoparticles on LaFeO3 photocatalyst for tunable photocatalytic CO2 reduction

Excessive exploitation and depletion of fossil fuels have led to the escalation of CO2 emissions, which are responsible for global climate deterioration. Cu-based solid catalysts can transform CO2 into various hydrocarbons via a sustainable photocatalytic pathway. Herein, we fabricated a Cu-decorated LaFeO3 photocatalyst using a sequential in situ exsolution (in H2)/redispersion (in N2) strategy. The dispersion of Cu was significantly enhanced (∼3 times), i.e., from 13.8 % (exsolved) to 41.4 % (redispersed). The combined theoretical and experimental results confirmed the successful formation of uniformly dispersed Cu active sites for efficient CO2 adsorption and photocatalytic conversion. The enhancement of light absorption and manipulation of the band structure were also collectively achieved, offering an optimized catalyst involving superior CO and CH4 production compared to its counterparts. In addition, photocatalytic water splitting was significantly suppressed, suggesting high selectivity of the photocatalytic pathway. This study offers a new perspective on the design principle of photocatalysts for selective CO2 conversion.

RETRACTED: Promoting the photocatalytic reduction of CO2 and dye degradation via multi metallic Smx modified CuCo2O4 Reverse spinel hybrid catalyst

Structuring a multi-functional photocatalyst of which enable high visible light harnessing so as to address the environmental pollution issues is the need of the hour. In view of this, a combination of catalytically active Cu, Co with enhanced adsorption capacity and Sm dopant that can enrich the catalyst with the defect centres would result in a tailor-made photocatalyst. Samarium (Sm) (1–12 wt %) doped CuCo2O4 were synthesized by simple precipitation route. The synergistic influence of Sm, Cu and Co on the photocatalytic ability has been ascertained by optical, structural and morphological methods like XRD, BET, SEM, XPS, Photocurrent, PL, ESR, fluorescence quenching, NMR methods. Thus prepared catalyst was utilized for the photo-catalytic mineralization of methylene blue and reaction was optimized and also it has been proven robust for the photo-reduction of CO2 into value added products, which are identified by NMR spectral analysis. A comprehensive mechanism has been suggested based on the experimental results. The present research provides the concept of multi-functional photo-catalyst for effluent decontamination and CO2 reduction.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications.

Photocatalytic water splitting, CO2 reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H2 generation potential, and an excellent ability to capture and activate CO2 molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H2 evolution, CO2 reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.

Lead-Free Cs2TeX6 (X = Cl, Br, and I) Perovskite Microcrystals with High Stability for Efficient Photocatalytic CO2 Reduction.

In response to calling for a sustainable and carbon-neutral economy, the conversion of CO2 to useful chemicals using the solar energy is a potential tactic to relieve the global energy dilemma and environmental issues, which has been a hot topic so far. Recently, the lead halide perovskites as novel photocatalysts have attracted researchers' interests. However, they generally encounter poor stability and lead toxicity, restricting their large-scale practical applications. Here, the lead-free Cs2TeX6 (X = Cl, Cl0.5Br0.5, Br, Br0.5I0.5, and I) perovskite microcrystals with strong stability were prepared and used to realize the CO2 photocatalytic reduction efficiently. The prepared Cs2TeBr6 microcrystals delivered stronger photocatalytic ability than many previously reported photocatalysts, with the CO and CH4 yields of 308.63 and 60.42 μmolg-1, respectively, under 3 h of illumination. The presented strategy in our work provides new ideas of designing and preparing efficient and practical CO2 reduction photocatalysts based on nonleaded and high-stability halide perovskites.

Microenvironment Modulation of Imine‐Based Covalent Organic Frameworks for CO2 Photoreduction

Comprehensive SummaryPhotocatalytic CO2 reduction to fuels and chemicals has been considered as the promising avenue to realize carbon resource recycling. Covalent organic frameworks (COFs) with pre‐designed and tailorable structures are promising platforms for studying the influence of the microenvironment of catalysts on photocatalytic CO2 reduction. Herein, we report three isomorphic COFs (TPHH‐COF, TPPD‐COF and TPBD‐COF) as heterogeneous photocatalysts for CO2 reduction and investigate the different levels of conjugation and planarity of COFs effect on the catalytic activity. Photoelectrochemical measurements show that TPPD‐COF has a narrower band gap and faster photocurrent response compared to TPHH‐COF and TPBD‐COF, probably due to the moderate conjugation and planarity. As the photocatalyst, TPPD‐COF showed the most outstanding photocatalytic activity with the production rates of 951 and 157 μmol·g–1·h–1 for CO and H2, respectively. This study illustrates the close relation between microenvironment and photocatalytic activity and provides new insights for designing high‐performance photocatalysts.

Perovskite Photocatalytic CO2 Reduction or Photoredox Organic Transformation?

Metal-halide perovskites have been explored as photocatalysts for CO2 reduction. We report that perovskite photocatalytic CO2 reduction in organic solvents is likely problematic. Instead, the detected products (i.e., CO) likely result from a photoredox organic transformation involving the solvent. Our observations have been validated using isotopic labeling experiments, band energy analysis, and new control experiments. We designed a typical perovskite photocatalytic setup in organic solvents that led to CO production of up to ≈1000 μmol g-1 h-1 . CO2 reduction in organic solvents must be studied with extra care because photoredox organic transformations can produce orders of magnitude higher rate of CO or CH4 than is typical for CO2 reduction routes. Though CO2 reduction is not likely to occur, in situ CO generation is extremely fast. Hence a suitable system can be established for challenging organic reactions that use CO as a feedstock but exploit the solvent as a CO surrogate.

Perovskite Photocatalytic CO2 Reduction or Photoredox Organic Transformation?

Metal-halide perovskites have been explored as photocatalysts for CO2 reduction. We report that perovskite photocatalytic CO2 reduction in organic solvents is likely problematic. Instead, the detected products (i.e., CO) likely result from a photoredox organic transformation involving the solvent. Our observations have been validated using isotopic labeling experiments, band energy analysis, and new control experiments. We designed a typical perovskite photocatalytic setup in organic solvents that led to CO production of up to ≈1000 μmol g−1 h−1. CO2 reduction in organic solvents must be studied with extra care because photoredox organic transformations can produce orders of magnitude higher rate of CO or CH4 than is typical for CO2 reduction routes. Though CO2 reduction is not likely to occur, in situ CO generation is extremely fast. Hence a suitable system can be established for challenging organic reactions that use CO as a feedstock but exploit the solvent as a CO surrogate.

Recent advances on Z-scheme engineered BiVO4-based semiconductor photocatalysts for CO2 reduction: A review

The designs of two or more absorber materials in a Z-scheme charge transfer configuration have paved the way for efficient CO2 photoreduction to high-value chemicals and fuels using the artificial photosynthesis approach. Under visible light irradiation or natural solar illumination, semiconductors that themselves do not satisfy minimum thermodynamic requirements for CO2 reduction or accompanying oxidation reactions can be used for targeted specific half-reactions. In this context, BiVO4 has been extensively investigated for water oxidation showing promising activity under visible-light illumination but is restricted as a single reduction photocatalyst since its conduction band is not negative enough. This review provides an overview of the basic principles and fundamentals of CO2 photoreduction and highlights the recent advances in the literature using BiVO4-based Z-scheme photocatalysts. We show that using BiVO4 as the oxidation photocatalyst, together with a reduction photocatalyst (Cu2O, CdZnS, ZnIn2S4, CuGaS2, g-C3N4, others) and under the Z-scheme charge transfer, is strategic for increasing visible-light absorption and facilitating charge separations while keeping the high redox potentials of the individual semiconductor components. This approach additionally helps to avoid undesired photocorrosion reactions triggered by trapped charges. Finally, some critical comments are raised for future research directions to improve CO2 capture and photocatalytic conversion to green fuels and chemicals.

Nanoarchitectonic composites with direct z-scheme heterojunction of CsPbBr3 quantum dot/CuCo2O4 nanosheet for efficient photocatalytic CO2 reduction

Photocatalytic CO2 reduction has attracted extensive attention because of its abilities to generate renewable clean fuels while immobilizing CO2. However, the widely used CO2 reduction photocatalysts generally have the problems of inadequate light absorption performance and insufficient photocatalytic reaction yield. Here we report 0D/2D CsPbBr3 quantum dot/CuCo2O4 nanosheet composites (CsPbBr3 QD/CuCo2O4 NS composites) synthesized by mechanical mixing method, which are applied for photocatalytic CO2 reduction. Thanks to the narrow bandgaps of CsPbBr3 QD and CuCo2O4 NS, CsPbBr3 QD/CuCo2O4 NS composites represent strong light absorption performance. The p-n heterojunction forms between CsPbBr3 QD and CuCo2O4 NS obviously boosts the charge separation, leading to the photocatalytic activity and stability of CsPbBr3 QD/CuCo2O4 NS composites significantly exceeding that of CsPbBr3 QD and CuCo2O4 NS. After 5 h of photocatalytic reaction, the generation rate for CH4 of CsPbBr3 QD/CuCo2O4 NS composites is 285.93 μmolg−1, which is about 3.2 times and 9.2 times higher than CsPbBr3 QD (88.08 μmolg−1) and CuCo2O4 NS (30.92 μmolg−1), respectively. This work provides a new insight to construct novel heterojunction photocatalysts based on lead halide perovskite QD, which shows the enhanced photocatalytic activity and light absorption performance.

Ionic Liquids as homogeneous photocatalyst for CO2 reduction in protic solvents

The study focuses on the photocatalytic reduction of CO2 in protic solvents such as iPrOH or H2O and in the presence of different imidazolium-based ionic liquids (IL). Under UV–vis irradiation, the dilute IL solution adsorbs light, which allows the generation of radical species via electrons produced at the IL, and thus the reduction of CO2. The nature of the solvent impacts the strength of the interaction between the anion and the cation in the IL. The cation functions as an activated species that produces electrons to give the CO2•− radical, and the anion activates the solvent in a way that weakens the HOR bond. All of this contributes to (i) providing protons needed for CO2 reduction, (ii) reducing the energy barrier to CO2 reduction, and ultimately (iii) promoting its efficiency. The important factors we explored are the light adsorption capacity and the value of the Kamlet-Taft (K-T) β parameter, which both have a synergistic effect on the CO2 reduction efficiency. Finally, in aqueous media, the influence of pH was also studied on the selectivity.

Selective CO2-to-Formate Conversion Driven by Visible Light over a Precious-Metal-Free Nonporous Coordination Polymer

Metal–organic frameworks (MOFs) and coordination polymers (CPs) are potential candidates for high-performance photocatalysts because of their high tunability of electronic and structural properties. For example, MOFs and CPs having a high specific surface area (∼1000 m2 g–1) have been applied as visible-light-driven photocatalysts for CO2 reduction and water splitting. Herein, we show a unique CP possessing a metal–sulfur bond with Pb2+, an earth-abundant metal ion. Different from ordinary high-surface-area MOFs and CPs, this CP is nonporous and has just 0.7 m2 g–1 surface area. Nevertheless, owing to its capability of absorbing visible light up to ∼500 nm, it efficiently photocatalyzes CO2 reduction to formate (HCOO–) under visible-light irradiation with >99% selectivity and an apparent quantum yield of 2.6% at 400 nm, even without postmodification treatment such as cocatalyst loading. These values are the highest yet reported for a precious-metal-free single-component photocatalyst for the visible-light-driven reduction of CO2 to HCOO–. This work may thus shed light on the great potential of nonporous CPs as building units of photocatalytic CO2 conversion systems.

Recent Research Progress and Perspectives on Porphyrin-Based Porous Photocatalysts in the Field of CO2 Reduction

Photocatalytic CO2 reduction with valuable carbon-containing fuel production using abundant light energy resources is conducive to reducing CO2 emissions and fossil fuel combustion. Drawing inspiration from the excellent capabilities of active substances in both light capture and photogenerated charge transfer in natural photosynthesis of porphyrins and their derivatives will help to develop research ideas for CO2 reduction photocatalysts. Porphyrin-based porous structure photocatalysts have excellent light absorption units and porous structures. Its excellent light capture, CO2 capture/adsorption, mass transfer, and more catalytic sites are beneficial for photocatalytic CO2 reduction. To further effectively improve the CO2 reduction performance of porphyrin-based porous photocatalysts, it is necessary to review its recent research progress. With the key processes in the photocatalytic CO2 reduction taken as a path to understand, analyze, and summarize the composition, structure, synthesis method, and performance of porphyrin-based photocatalysts, this review focuses on metal-free porphyrin-based porous photocatalysts with strong CO2 adsorption, porphyrin-based porous photocatalysts with active coordination metals, and porphyrin-based porous composite photocatalysts with strong photogenerated charge separation ability in the photocatalytic CO2 reduction field. Finally, the challenges and prospects of porphyrin-based porous photocatalysts for CO2 reduction are discussed.

Modulating the Selectivity of Photocatalytic CO2 Reduction in Barium Titanate by Introducing Oxygen Vacancies

Artificial photosynthetic reduction of CO2 into valuable chemicals is one of the most promising approaches to solve the energy crisis and decreasing atmospheric CO2 emissions. However, the poor selectivity accompanied by the low activity of photocatalysts limits the development of photocatalytic CO2 reduction. Herein, inspired by the use of oxygen vacancy engineering to promote the adsorption and activation of CO2 molecules, we introduced oxygen vacancies in the representative barium titanate (BaTiO3) photocatalyst for photocatalytic CO2 reduction. We found that oxygen vacancies brought significant differences in the CO2 photoreduction activity and selectivity of BaTiO3. The intrinsic BaTiO3 showed a low photocatalytic activity with the dominant product of CO, whereas BaTiO3 with oxygen vacancies exhibited a tenfold improvement in photocatalytic activity, with a high selectivity of ~ 90% to CH4. We propose that the presence of oxygen vacancies promotes CO2 and H2O adsorption onto the BaTiO3 surface and also improves the separation and transfer of photogenerated carriers, thereby boosting the photocatalytic CO2 reduction to CH4. This work highlights the essential role of oxygen vacancies in tuning the selectivity of photocatalytic reduction of CO2 into valuable chemicals.

Preparation of Ni/Ce Composite Photocatalytic CO2 Heterojunction by Treating Electroplating Nickel Wastewater

AbstractIn the past few years, it was discovered that Ni(OH)2 is an effective photocatalyst for CO2 as a chemical fuel catalyst. Ni(OH)2 nanosheets were prepared by simple wet treatment and electric transformation of nickel‐containing wastewater. The Ni(OH)2/Ce(OH)4 hybrid nanosheets were prepared by Ce doping experiment, and Ni/Ce oxide was prepared by calcination with Ni(OH)2/Ce(OH)4 composite nanosheets. Finally, Ce(OH)4 was prepared by electroconversion with CeCl3 ⋅ 7H2O as raw material, and all the samples were used as CO2 photocatalysts for performance comparison. The diameter and thickness of Ni(OH)2/Ce(OH)4 and NiO/CeO2 nanocrystals are about 1∼50 nm and 1∼10 nm, respectively. The BET‐specific surface area is calculated to be 205.93 m2/g (Ni(OH)2/Ce(OH)4) and 18.93 m2/g (NiO/CeO2). During CO2 photoreduction, bare Ce(OH)4 can only produce CO (1.32 μmol after 4 h). The methane yield of Ni(OH)2/Ce(OH)4 is 11.435 μmol after 4 h, while the CO yield increases to 21.515 μmol after 4 h. Compared with the oxide NiO/CeO2, the electrolytic product Ni(OH)2/Ce(OH)4 showed a higher photocatalytic activity for CO2 reduction, which is attributed to the larger specific surface area of the precursor. We believe this work provides a potential approach for treating nickel‐containing electroplating wastewater to prepare highly efficient and selective CO2 reduction photocatalysts.

Universal Kinetic Mechanism Describing CO2 Photoreductive Yield and Selectivity for Semiconducting Nanoparticle Photocatalysts.

Photocatalytic conversion of CO2 to generate high-value and renewable chemical fuels and feedstock presents a sustainable and renewable alternative to fossil fuels and petrochemicals. Currently, there is a dearth of kinetic understanding to inform better catalyst design, especially at uniform reaction conditions across diverse catalytic species. In this work, we investigate 12 active, stable, and unique but common nanoparticle photocatalysts for CO2 reduction at room temperature and low partial pressure in aqueous phase: TiO2, SnO2, and SiC deposited with silver, gold, and platinum. Our analysis reveals a single consistent chemical kinetic mechanism, which accurately describes the yield and selectivity of all single-carbon containing (C1) products obtained in spite of the diverse catalysts employed. Formaldehyde is predicted as the first product in the reaction network and we report, to the best of our knowledge, the highest selectivity to date toward formaldehyde during CO2 photoreduction when compared against all other C1 products (∼80%) albeit at low CO2 conversion (<0.5 μmol gcat-1 h-1, <16.8 nmol m-2 h-1). Further, we observe a volcano-like relationship between the electron-transfer rate of a given photocatalyst for CO2 reduction and the net rate at which reduced products are produced in the reaction mixture taking into account unfavorable product oxidation. We establish an empirical upper limit for the maximum rate of production of CO2 reduction products for any nanoparticle photocatalyst in the absence of a hole-scavenging agent. These results form the basis for the design and optimization of the next generation of highly efficiency and active photocatalysts for CO2 reduction.

First-principles studies of monolayers MoSi2N4 decorated with transition metal single-atom for visible light-driven high-efficient CO2 reduction by strain and electronic engineering

Solar-driven CO2 reduction into value-added hydrocarbons could promote CO2 utilization and solve related environmental issues, while the key lies in the modulation of the active site’s orbital electronic state. By performing first-principles calculations, we systematically explore MoSi2N4 decorated with 3d and 4d period transition metal single atoms (TMSAs) as efficient CO2 reduction photocatalysts and find that product selectivity is highly correlated with the d-band center of TMSAs. Compressive and tensile strains in mutually perpendicular directions are introduced in the horizontal plane to improve the catalytic performance. After filtering, V, Mn, and Ni were found to be the best TMSAs for CO, HCOOH, and CH4 production, respectively. Ni/MoSi2N4 under −6% tensile strain exhibited the lowest CO2 reduction limiting potential (UL) of 0.24 V. Notably, the time-dependent ab initio nonadiabatic molecular dynamics simulations were carried out to elucidate the photogenerated electron transport properties, where the photo-generated electrons can be efficiently transferred from MoSi2N4 to TMSAs active sites. We also identify that the applied strains affect the CO2 reduction performance by modulating the d-band center and valence electrons. These findings provide pioneering design schemes of precisely tailored photocatalytic systems for CO2 reduction under visible light.