Photocatalysts For CO2 Reduction Research Articles

Accelerated interfacial charges migration on Z-scheme CoAl-LDH/RGO/InVO4 heterojunction for photocatalytic reduction of CO2

In this work, the Z-scheme layered double hydroxide (LDH)/reduced graphene oxide (RGO)/indium vanadate (InVO4) heterojunction was synthesized by a simple hydrothermal synthesis. RGO, with excellent electron mobility, endowed rapid charge migration and separation between the CoAl-LDH and InVO4. Various characterizations and tests showed that the LDH/RGO/InVO4 heterojunction exhibited superior optical properties, and its carriers’ transfer pathway conformed to Z-scheme mechanism. Under visible light illumination, CO was observed to be the main product during photocatalytic CO2 reduction, and the LDH/RGO/InVO4-15 exhibited the highest CO yield of 204.86 μmol g−1 within 2 h, approximately 2.62 times of pristine CoAl-LDH (78.2 μmol g−1). In addition, LDH/RGO/InVO4-15 showed favorable structure stability and performance stability. In situ fourier infrared spectroscopy (ISFT-IR) analysis demonstrated that the predominant intermediates of CO2 reduction process were carboxylate (COOH*) and bicarbonate (HCO3*). Accordingly, possible pathways of CO2 reduction to CO were deduced. This work can advance the development of efficient Z-scheme heterojunction photocatalysts for CO2 reduction.

Modified NiFe-MOF with defects induced by -NH2 and -SH for enhanced adsorption and photocatalytic reduction of CO2

In this study, a Ni-Fe metal-organic framework modified by –NH2 and –SH was synthesized using a simple hydrothermal process for enhancing photocatalytic CO2 reduction. As expected, the N2S-NiFe (NH2-BDC/H4DSBDC, 2:1) displayed excellent photocatalytic CO2 reduction activity and high CO selectivity (12,412.23 μmol g−1 h−1) under visible light irradiation (λ ≥ 420 nm), which is 5 times that of NiFe-MOF. Notably, the excellent photocatalytic performance of N2S-NiFe can benefit from the rich defect trap site caused by the introduction of amino and sulfhydryl groups, accelerating charge transfer and promoting space charge separation, as supported by the photo-electrochemical properties. To better understand the CO2 adsorption mechanism, density functional theory calculations were performed, which revealed that the Niov site has more negative adsorption energy compared with the Feov site. This study provides a simple strategy to establish efficient photocatalysts for CO2 reduction through the modification of organic ligands.

Lead‐Free Halide Perovskite Photocatalysts for Photocatalytic CO2 Reduction: A Review

Solar‐driven CO2 conversion is a promising strategy for solving energy and environmental crises. Developing photocatalysts with high performance is the key to achieve efficient CO2 conversion. Lead halide perovskite is considered as a promising photocatalyst for solar‐driven CO2 conversion due to its excellent properties. However, the toxicity of Pb significantly limits their practical applications. Therefore, developing the lead‐free perovskite photocatalysts has full scientific significance in greatly expanding their application scenarios and reducing the risk of environmental damage. At present, the lead‐free perovskite photocatalysts are attracting widespread attention from researchers and is currently a research hotspot in the field of photocatalysis. Herein, this review systematically describes the crystal structure, photochemical characteristics, preparation methods, and photocatalytic properties. Then, based on the mechanisms of photocatalytic CO2 reduction, this review explores the structure–activity relationship between the microstructure of perovskite and its photocatalytic performance in detail and introduces the modification strategies of lead‐free halide perovskite. Finally, the development prospects and challenges of lead‐free halide perovskite photocatalysts are discussed to fully explore their inherent potential for efficient photocatalytic CO2 reduction. This work provides insights and reference significance for further development of lead‐free halide perovskite photocatalysts for photocatalytic CO2 reduction.

Photocatalytic CO2 Conversion into Solar Fuels Using Carbon-Based Materials-A Review.

Carbon materials with elusive 0D, 1D, 2D, and 3D nanostructures and high surface area provide certain emerging applications in electrocatalytic and photocatalytic CO2 utilization. Since carbon possesses high electrical conductivity, it expels the photogenerated electrons from the catalytic surface and can tune the photocatalytic activity in the visible-light region. However, the photocatalytic efficiency of pristine carbon is comparatively low due to the high recombination of photogenerated carriers. Thus, supporting carbon materials, such as graphene, CNTs (Carbon nanotubes), g-C3N4, MWCNs (Multiwall carbon nanotubes), conducting polymers, and its other simpler forms like activated carbon, nanofibers, nanosheets, and nanoparticles, are usually combined with other metal and non-metal nanocomposites to increase the CO2 absorption and conversion. In addition, carbon-based materials with transition metals and organometallic complexes are also commonly used as photocatalysts for CO2 reduction. This review focuses on developing efficient carbon-based nanomaterials for the photoconversion of CO2 into solar fuels. It is concluded that MWCNs are one of the most used materials as supporting materials for CO2 reduction. Due to the multi-layered morphology, multiple reflections will occur within the layers, thus enhancing light harvesting. In particular, stacked nanostructured hollow sphere morphologies can also help the metal doping from corroding.

Efficient CO2 photoreduction enabled by the energy transfer pathway in metal‐organic framework

AbstractMany studies in metal‐organic frameworks (MOFs) aiming for high photocatalytic activity resort to self‐assembling both energy donor and acceptor building units in skeleton to achieve effective energy transfer, which, however, usually needs tedious synthetic procedure and design of a new MOF. In this work, we demonstrated that building a Förster resonance energy transfer (FRET) pathway can be realized through suitable molecular doping in a given MOF structure without altering the original porous structure, presenting an alternative strategy to design efficient photocatalysts for CO2 reduction. In situ electron spin resonance, ultrafast transient absorption spectroscopy, and computational studies reveal that the FRET‐induced excitation has dramatically altered the exciton transfer pathway in structure and facilitated electron‐hole separation. As a result, the molecular doped MOFs synthesized through one‐pot reaction show outstanding selectivity (96%) and activity (1314 μmol·g−1·h−1) for CO production versus almost no activity for the pristine MOFs, and this result stands out from existing competitors. Furthermore, the reaction mechanism was proposed and the intermediate signals were detected by in situ diffuse reflectance infrared Fourier transform spectroscopies. This study presents a clear picture of building FRET process in MOFs through molecular doping and provides a new design strategy for MOF‐based photocatalysts.

Recent advances on bismuth oxyhalides for photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into fuels such as CO, CH4, and CH3OH, is a promising approach for achieving carbon neutrality. Bismuth oxyhalides (BiOX, where X = Cl, Br, and I) are appropriate photocatalysts for this purpose due to the merits of visible-light-active, efficient charge separation, and easy-to-modify crystal structure and surface properties. For practical applications, multiple strategies have been proposed to develop high-efficiency BiOX-based photocatalysts. This review summarizes the development of different approaches to prepare BiOX-based photocatalysts for efficient CO2 reduction. In the review, the fundamentals of photocatalytic CO2 reduction are introduced. Then, several widely used modification methods for BiOX photocatalysts are systematacially discussed, including heterojunction construction, introducing oxygen vacancies (OVs), Bi-enrichment, heteroatom-doping, and morphology design. Finally, the challenges and prospects in the design of future BiOX-based photocatalysis for efficient CO2 reduction are examined.

Postsynthetic Annulation of Three-Dimensional Covalent Organic Frameworks for Boosting CO2 Photoreduction.

Three-dimensional covalent organic frameworks (3D COFs), with interconnected pores and exposed functional groups, provide new opportunities for the design of advanced functional materials through postsynthetic modification. Herein, we demonstrate the successful postsynthetic annulation of 3D COFs to construct efficient CO2 reduction photocatalysts. Two 3D COFs, NJU-318 and NJU-319Fe, were initially constructed by connecting hexaphenyl-triphenylene units with pyrene- or Fe-porphyrin-based linkers. Subsequently, the hexaphenyl-triphenylene moieties within the COFs were postsynthetically transformed into π-conjugated hexabenzo-trinaphthylene (pNJU-318 and pNJU-319Fe) to enhance visible light absorption and CO2 photoreduction activity. The optimized photocatalyst, pNJU-319Fe, shows a CO yield of 688 μmol g-1, representing a 2.5-fold increase compared to that of unmodified NJU-319Fe. Notably, the direct synthesis of hexabenzo-trinaphthylene-based COF catalysts was unsuccessful due to the low solubility of conjugated linkers. This study not only provides an effective method to construct photocatalysts but also highlights the unlimited tunability of 3D COFs through structural design and postsynthetic modification.

1D S-scheme heterojunction of urchin-like SiC-W18O49 for enhancing photocatalytic CO2 reduction

Constructing heterojunction is an important method to improve the performance of photocatalyst for CO2 reduction. In this work, W18O49 nanosheets (NSs) were grown on the surface of SiC nanocages (NCs) to form the sea urchin ball morphology by solvothermal method. The SiC-W18O49 composite photocatalyst processes 1D S-scheme heterojunction electron transport pathway. The special urchin morphology provides a large surface area for the contact between photocatalyst and CO2 reactants. Meantime, the S-scheme internal electric field at the heterogeneous interface of SiC-W18O49 composite photocatalyst can effectively promote the separation and migration of photogenerated carrier pairs owing to 1D heterojunction structure. The photocatalytic CO2 reduction products (CO + CH4 + CH3OH) can be produced up to 21.87 μmol g−1 h−1 by SiC-W18O49 composite photocatalyst, which was 3.38 and 3.71 times of the total reduction activity of the parent SiC and W18O49, respectively. This work will provide a new idea for the design of heterojunction morphology and structure for boosting photocatalytic CO2 reduction.

G-C3N4/MnFe2O4 p-n hollow stratified heterojunction to improve the photocatalytic CO2 reduction activity

Graphite carbon nitride (g-C3N4) is considered as a promising photocatalyst for CO2 reduction. However, they have problems such as small surface area and fast electron hole recombination rate, so how to improve the photocatalytic efficiency of g-C3N4 remains a great challenge. In this paper, g-C3N4/MnFe2O4 p-n heterojunction composites were synthesized successfully, and their photocatalytic activity for CO2 reduction was tested. We constructed g-C3N4 nanotubes to increase its specific surface area and increase the active sites available for reaction. The structure of p-n heterojunction promotes electron hole separation. The results indicate that under visible light irradiation, CO yield of g-C3N4/MnFe2O4 composite can reach 1136.8 μmol h−1 g−1 when the molar ratio of g-C3N4 microtubules to MnFe2O4 is 10:3, which is 14 times of g-C3N4 microtubules and 29 times of g-C3N4. This study provides some guidance for the design of g-C3N4 based heterojunction.

Bridging molecular photosensitizer and catalyst on carbon nanotubes toward enhanced selectivity and durability for CO2 photoreduction

Homogenous molecular photocatalysts for CO2 reduction, especially metal complex-based photosensitizer‒catalyst assemblages, have been attracting extensive research interests due to their efficiency and customizability. However, their low durability and recyclability limit practical applications. In this work, we immobilized the catalysts of metal terpyridyl complexes and the photosensitizer of [Ru(bpy)3]Cl2 onto the surface of carbon nanotubes through covalent bonds and electrostatic interactions, respectively, transforming the homogeneous system into a heterogeneous one. Our characterizations prove that these metal complexes are well dispersed on CNTs with a high loading (ca. 12 wt.%). Photocatalytic measurements reveal that catalytic activity is remarkably enhanced when the molecular catalysts are anchored, which is three times higher than that of homogeneous molecular catalysts. Moreover, when the photosensitizer of [Ru(bpy)3]Cl2 is immobilized, the side reaction of hydrogen evolution is completely suppressed and the selectivity for CO production reaches 100%, with its durability also significantly improved. This work provides an effective pathway for constructing heterogeneous photocatalysts based on rational assembly of efficient molecular photosensitizers and catalysts.

Lead-free halide perovskite hollow nanospheres to boost photocatalytic activity for CO2 reduction

Strong photoresponse, efficient charge separation, and high surface activity are three important requirements for an ideal photocatalyst, while few photocatalysts can fully meet these requirements. Herein, we report such a photocatalyst based on lead-free halide perovskite hollow nanospheres (H-Cs3Sb2Br9) by a facile antisolvent-assisted method. The hollow structure of H-Cs3Sb2Br9 improves the light-harvesting performance; The formation of surface shallow trap states contributes to promoting the excited-carrier separation; The ligand-free termination surface of H-Cs3Sb2Br9 facilitates the exposure of Br vacancies and active sites, thus strengthens the CO2 adsorption and accelerates surface reactivity dynamics. As a result, with a dinuclear Co(II) complex as the co-catalyst, H-Cs3Sb2Br9 exhibits a record-high photocatalytic activity for CO2 reduction, with a CO yield of 15,010.4 ± 550.4 μmol g−1 after 8 h of illumination under simulated solar light (100 mW cm−2). This research presents a new way to develop cost-effective photocatalysts for CO2 reduction.

New insight into efficient photocatalytic CO2 reduction without any sacrifice agent over the novel hierarchical structured SiOC whisker aerogel

Photoreduction of CO2 to valuable fuels provides a promising strategy for managing the global carbon balance using renewable solar energy, yet the design of active, cost-effective, highly selective, and stable CO2 reduction photocatalysts remains a big challenge. Herein, we report a novel SiOC aerogel photocatalyst synthesized by a simple one-step sol-gel process, combined with the supercritical drying technique and heat treatment processes. The resulting SiOC aerogel exhibits a large BET specific area with typical hierarchical structures, which is responsible for the enhanced photocatalytic activity. In addition, the formation mechanism of the SiOC whisker aerogel is revealed in this study. The optimized SiOC aerogel exhibits CH4 and CO evolution activity of 5.8 and 20.5 μmol/g under simulated sunlight irradiation, respectively, without any additional co-catalyst or sacrificial agent, which is 6.4 and 3.9 times higher than those of the pristine SiC aerogel. The density functional theory (DFT) calculation confirms that the resulting SiOC aerogel can effectively adsorb and activate CO2 and H2O molecules on the catalyst surface. The Gibbs free energy diagram further verifies the superior performance of the resulting SiOC aerogel over the pristine SiC and SiO2 cluster via the rate-determining step calculations. The high efficiency of CO2 reduction can be attributed to the structural merits and the electronic structures modulation, which greatly achieves fast separation and transfer of charge carriers. The work paves an insight into the rational design of photocatalysts toward simultaneously facilitating carrier separation and CO2 activation from aerogel-based porous materials.

One-step fabrication of unique 3D/2D S, O-doped g-C3N4 S-scheme isotype heterojunction for boosting CO2 photoreduction

Solar irradiation-based CO2 conversion to energy-rich products is an efficient way to reduce excessive CO2 emissions and solve resource depletion. Unfortunately, achieving a cost-effective and dependable method for converting CO2 is still a significant challenge. Here, we introduce a hydrothermal approach followed by calcination to design a new-fashioned 3D S-doped g-C3N4/2D O-doped g-C3N4 (3D/2D SOCN) based step-scheme (S-scheme) heterojunction as an efficient photocatalysts for CO2 reduction. The adjusted sample demonstrated significantly greater CO2 photoreduction conversion rates compared to the blank control, including 3D S-doped g-C3N4 (3D SCN), 2D O-doped g-C3N4 (2D OCN), and bulk g-C3N4 (CN). The exceptional photocatalytic performance can be ascribed to multiple factors, including the S-Scheme isotype heterojunction that suppresses the recombination of photogenerated charge carriers, the material's high specific surface areas, which highly enhance the abundance of active sites, and the synergistic effect of the heteroatom as a dopant. The validity of the S-Scheme photogenerated charge transfer process is supported by measuring the work function and electron paramagnetic resonance (EPR). This research presents a practical method for fabricating multi non-metal-doped S-scheme isotype heterojunction photocatalysts that display remarkable efficiency for solar fuel conversion.

Urchin-like band-matched Fe2O3@In2S3 hybrid as an efficient photocatalyst for CO2 reduction

Herein, an urchin-like Fe2O3@In2S3 hybrid composite is designed and synthesized using a facile process. The composite efficiently harvests light in both the ultraviolet and visible regions, and the unique hierarchical structure provides several advantages for photocatalytic applications: (i) a suitable band-matching structure and broadband-light absorbing capacity enable the reduction of CO2 into hydrocarbon, (ii) the extensive network of interfacial contact between nano-sized Fe2O3 and In2S3 significantly increases the separation of charge carriers and enhances the utilization of photogenerated electron-hole pairs, and (iii) an abundance of surface oxygen vacancies provide numerous active sites for CO2 molecule adsorption. The optimized Fe2O3@In2S3 composite generated CO from the photocatalytic reduction of CO2 at a rate of 42.83 μmol·g−1·h−1, and no signs of deactivation were observed during continued testing for 32 h under 300 W Xe lamp irradiation.

Armchair Janus WSSe Nanotube Designed with Selenium Vacancy as a Promising Photocatalyst for CO2 Reduction.

Photocatalytic conversion of carbon dioxide into chemical fuels offers a promising way to not only settle growing environmental problems but also provide a renewable energy source. In this study, through first-principles calculation, we found that the Se vacancy introduction can lead to the transition of physical-to-chemical CO2 adsorption on Janus WSSe nanotube. Se vacancies work at the adsorption site, which significantly improves the amount of transferred electrons at the interface, resulting in the enhanced electron orbital hybridization between adsorbents and substrates, and promising the high activity and selectivity for carbon dioxide reduction reaction (CO2RR). Under the condition of illumination, due to the adequate driving forces of photoexcited holes and electrons, oxygen generation reaction (OER) and CO2RR can occur spontaneously on the S and Se sides of the defective WSSe nanotube, respectively. The CO2 could be reduced into CH4, meanwhile, the O2 is produced by the water oxidation, which also provides the hydrogen and electron source for the CO2RR. Our finding reveals a candidate photocatalyst for obtaining efficient photocatalytic CO2 conversion.

Highly efficient CO2 photoreduction by ultralow-Ru-Loading ZIF-67

Developing highly efficient and low-cost photocatalysts for CO2 reduction is of critical importance for the conversion of CO2 to value-added chemicals. Here we report a Co-based zeolitic imidazole framework (ZIF-67) based photocatalyst with exceptional photocatalytic activity and durability for CO2 reduction. ZIF-67 is doped with dicyandiamide (DCD), the intermediate link with the trace Ru cocatalyst (0.0127 wt. %). The underlying reduction mechanism was unraveled by the joint experiment-theory study. The strong orbital coupling of ZIF-67-DCD-Ru series structure leads to strong CO2 adsorption, electron enrichment on cocatalyst, and minimum Gibbs free energy barrier of CO generation. The synthesized ZIF-67/DCD/Ru sample exhibits excellent CO2 photoreduction performance with a CO generation rate of 1495 mmol gRu−1 h−1 and achieves a record turnover frequency (TOF) of 151 h−1, representing top-level photocatalytic activity among all reported ZIFs-based photocatalysts. For the first time, our work points out a novel way to achieve high activity of ultralow noble metal loading photocatalyst and provides an in-depth understanding of the advances of the series structure.

UV–vis light responsive Bi2WO6 nanosheet/TiO2 nanobelt heterojunction photo-catalyst for CO2 reduction

A series of Bi2WO6/TiO2 composite photocatalysts with different ratios of Bi2WO6 nanosheets to TiO2 nanobelts (1, ½, ⅓ and ¼) were synthesized by hydrothermal method and evaluated for CO2 photoreduction. The structural and optical properties of these photocatalysts were investigated by XRD, N2-physisorption, EDX, FESEM, Raman, TPD, DRS and PL. Bi2WO6/TiO₂ composite photocatalysts show enhanced CO2 adsorption capacity and coversion performance compared to both pure TiO₂ and bulk Bi2WO6. Loading Bi2WO6 nanosheets on TiO2 nanobelts leads to formation a heterojunction, which enhances the photocatalytic visible light performance by decreasing the recombination rate of photoinduced electron-hole pairs. The maximum CH4 production of 18.95 μmol/gcat in 8 h has been reported for composite with Bi2WO6/TiO₂ ratio of ½, which is 3 times higher than that of bulk Bi2WO6 and pure TiO2.

Quantitative In Situ Monitoring of Cu-Atom Release by Cu2O Nanocatalysts under Photocatalytic CO2 Reduction Conditions: New Insights into the Photocorrosion Mechanism.

Cu2O is among the most promising photocatalysts for CO2 reduction, however its photocorrosion remains a standalone challenge. Herein, we present an in situ study of the release of Cu ions from Cu2O nanocatalysts under photocatalytic conditions in the presence of HCO3 as a catalytic substrate in H2O. The Cu-oxide nanomaterials were produced by Flame Spray Pyrolysis (FSP) technology. Using Electron Paramagnetic Resonance (EPR) spectroscopy in tandem with analytical Anodic Stripping Voltammetry (ASV), we monitored in situ the Cu2+ atom release from the Cu2O nanoparticles in comparison with CuO nanoparticles under photocatalytic conditions. Our quantitative, kinetic data show that light has detrimental effect on the photocorrosion of Cu2O and ensuing Cu2+ ion release in the H2O solution, up to 15.7% of its mass. EPR reveals that HCO3 acts as a ligand of the Cu2+ ions, promoting the liberation of {HCO3-Cu} complexes in solution from Cu2O, up to 27% of its mass. HCO3 alone exerted a marginal effect. XRD data show that under prolonged irradiation, part of Cu2+ ions can reprecipitate on the Cu2O surface, creating a passivating CuO layer that stabilizes the Cu2O from further photocorrosion. Including isopropanol as a hole scavenger has a drastic effect on the photocorrosion of Cu2O nanoparticles and suppresses the release of Cu2+ ions to the solution. Methodwise, the present data exemplify that EPR and ASV can be useful tools to help quantitatively understand the solid-solution interface photocorrosion phenomena for Cu2O.

Tin(II)‐Based Metal–Organic Frameworks Enabling Efficient, Selective Reduction of CO2 to Formate under Visible Light

AbstractCertain metal complexes are known as high‐performance CO2 reduction photocatalysts driven by visible light. However, most of them rely on rare, precious metals as principal components, and integrating the functions of light absorption and catalysis into a single molecular unit based on abundant metals remains a challenge. Metal‐organic frameworks (MOFs), which can be regarded as intermediate compounds between molecules and inorganic solids, are potential platforms for the construction of a simple photocatalytic system composed only of Earth‐abundant nontoxic elements. In this work, we report that a tin‐based MOF enables the conversion of CO2 into formic acid with a record high apparent quantum yield (9.8 % at 400 nm) and >99 % selectivity without the need for any additional photosensitizer or catalyst. This work highlights a new MOF with strong potential for photocatalytic CO2 reduction driven by solar energy.

Tin(II)-Based Metal-Organic Frameworks Enabling Efficient, Selective Reduction of CO2 to Formate under Visible Light.

Certain metal complexes are known as high-performance CO2 reduction photocatalysts driven by visible light. However, most of them rely on rare, precious metals as principal components, and integrating the functions of light absorption and catalysis into a single molecular unit based on abundant metals remains a challenge. Metal-organic frameworks (MOFs), which can be regarded as intermediate compounds between molecules and inorganic solids, are potential platforms for the construction of a simple photocatalytic system composed only of Earth-abundant nontoxic elements. In this work, we report that a tin-based MOF enables the conversion of CO2 into formic acid with a record high apparent quantum yield (9.8 % at 400 nm) and >99 % selectivity without the need for any additional photosensitizer or catalyst. This work highlights a new MOF with strong potential for photocatalytic CO2 reduction driven by solar energy.