CO2 Photoreduction Process Research Articles

Local surface plasma resonance effect enhanced Z-scheme ZnO/Au/g-C3N4 film photocatalyst for reduction of CO2 to CO

Local Surface Plasma Resonance (LSPR) effect enhanced Z-scheme ZnO/Au/g-C3N4 micro-needles film (3-ZAC) has been prepared for the photoreduction of CO2 into CO under UV–vis light irradiation. Photoreduction experiments show that 3-ZAC has the excellent photocatalytic performance and reusability. The CO production can be achieved 689.7 μmol/m2 after 8 h reaction time, which is 4.5 higher than that of the pure ZnO film. 13C isotope test shows that CO is produced from CO2 by photoreduction. DFT calculations confirm that build-in electric field formed at g-C3N4/ZnO interface effectively promoted the electron transfer efficiency in Z-scheme interface. FDTD simulations prove that Au NPs not only act as electron-transfer bridge, but also as LSPR excited source to speed up the separation of electron-hole pairs. In-situ FTIR technique was used to investigate the CO2 photoreduction process. The above characteristics together maximize the electron transfer efficiency, which causes the material has enhanced photocatalytic performance.

Rapid microwave-assisted hydrothermal synthesis of CuBi2O4 and its application for the artificial photosynthesis

Strategies for CO2 reforming for hydrocarbon production using ultraviolet or visible radiation are promising to mitigate environmental impacts from other human activities. Semiconductors act as photocatalysts for light-to-fuel conversion, but a rigorous control of their structure and morphology is crucial for high efficiency and selectivity. Thus, CuBi2O4 semiconductors have been synthesized by the microwave-assisted hydrothermal method and studied for the CO2 photoreduction process. This method produced crystalline materials with controlled morphology using low temperatures and short processing time. Moreover, the semiconductors showed excellent catalytic performance and selectivity, approximately 90% in the conversion of CO2 to CH4. Therefore, our new synthesis approach was adequate for CuBi2O4 preparation, providing an essential indication of activity in the CO2 photoreduction process.

Synthesis and Surface Modification of TiO2-Based Photocatalysts for the Conversion of CO2

Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO2 into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO2 photoreduction are thoroughly discussed and the CO2 reduction mechanism and pathways are described. Methods to enhance the adsorption of CO2 on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO2 is currently being widely investigated for its photocatalytic ability in reducing CO2 when suitably modified. The recent TiO2 synthesis and modification strategies that may be employed to enhance the efficiency of the CO2 photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO2 in addition to increasing product yield and selectivity.

Unveiling CuO role in CO2 photoreduction process – Catalyst or reactant?

We systematically investigated CO2 photoreduction catalyzed by CuO from different synthetic methods (solvothermal, coprecipitation and solid-state reaction) to understand which mechanism is prevailing for this reaction. The results showed that CuO acts as a reactant during CO2 reduction through copper carbonate formation rather than a catalyst, but the as-formed Cu2(OH)2CO3 (malachite) is active as catalyst for the same reaction. Significant CO2 conversion was observed during the CuO carbonation process, reducing to lower conversion levels after complete conversion to copper carbonate.

CuO thin films deposited by DC sputtering and their photocatalytic performance under simulated sunlight

CuO thin films were obtained by DC Sputtering varying the deposit time: 10, 20 and 30 min with the thickness of 60, 120 and 180 nm, respectively. These films were used photocatalysts in two different photocatalytic processes: hydrogen production and CO2 photoreduction under simulated sunlight. The film with 120 nm of thickness generated the highest amount of hydrogen (24 μmol) of the films tested. Furthermore, the ellipsometry results showed that this film absorbs the simulated light in the UV-to-IR region, which facilitates their photocatalytic performance. In the CO2 photoreduction process, the CuO film with the lowest thickness exhibited the best performance, yielding 6816 μmol/g CH2O, while the film of 120 nm in thickness generated a mixture of CH3OH (1536 μmol/g) and CH2O (450 μmol/g). It is assumed that the optical properties, such as absorption coefficient, refractive index, and extinction coefficient, of the film favored the production of formaldehyde and methanol.

Photocatalytic Conversion of CO2 into Oxygenate Fuels/Chemicals Using Efficient, Eco-Friendly, Titania/Hematite-Based Nanostructured Solar-Energy Materials

Photocatalytic hydrogenation of carbon dioxide (CO₂), using water feedstock (H source), sunlight and appropriate semiconducting low-cost/eco-friendly/solar-energy materials, is a promising route for sequestration of this greenhouse gas and its conversion into value-added oxygenate fuels (compounds). Herein, by employing three hematite-based nanostructured photocatalyst/solar-energy materials, the CO₂ photoreduction (hydrogenation) process was carried out inside a water photosplitting reactor, and various oxygenate (C/H/O) products [including ethanol, methanol and formaldehyde as well as oxalic, acetic and formic acids] were synthesized in the reaction medium. Concerning the complexity of system and the diversity of products-being photocatalytically synthesized during the photoconversion process, two straightforward problem-solving strategies were proposed [one, focusing on a single/particular product and pursuing its quantity (concentration) at different illumination periods, and the other, simultaneous investigation of various products being produced at a fixed reaction period, in the aqueous or gas-phase medium]. Finally, the matter of CO₂ photoconversion into oxygenate fuels/chemicals was explained in detail from photoelectrochemical [semiconductor band structure and redox potential] as well as mechanistic perspectives.

Insights into the role of CuO in the CO2 photoreduction process

The CO2 photoreduction process to produce light hydrocarbons is known to be influenced by the presence of CuO nanoparticles, but the actual role of this material, whether as a catalyst or a reactant, has not yet been revealed. In this work, we investigate the role of CuO nanoparticles produced by a solvothermal method as a catalyst in CO2-saturated water reaction media under UV light, considering the effects of different electrolytes (Na2C2O4, KBrO3, and NaOH) and temperatures on nanoparticle phase and activity. The electrolyte strongly influenced product selectivity (NaOH led to evolution of CH4, Na2C2O4 to CO, and KBrO3 to O2) and induced CuO phase change. A long-term analysis of these processes indicated that during the initial steps, CuO acted as a reactant, rather than as a catalyst, and was converted to CuCO3.Cu(OH)2, while the as-converted material acted as a catalyst in CO2 photoreduction, with conversion values comparable to those reported in the literature.

Sunfuels from CO2 exhaust emissions: Insights into the role of photoreactor configuration by the study in laboratory and industrial environment

Direct photoconversion of CO2 from exhaust emissions into fuels and chemicals is one of the most ambitious challenges to a greater and more effective use of the solar source. Through an extensive and systematic evaluation of CO2 photoreduction process, both in aqueous media and in gas-vapour stream for over 120 h, this work addresses the role of the photoreactor configuration on the CO2 reduction efficiency, leading the study from laboratory to industrial environment, probably for the very first time. Therefore, the performance of a continuously stirred “semi-batch” (SB) photoreactor, a packed-bed (PB) photoreactor and a multi-tubular (MT) photoreactor has been compared in term of efficiency, products distribution and available energy. The results of the photocatalytic tests demonstrate a strong influence of process conditions on the photocatalyst performance and on the reaction path. The packed-bed (PB) configuration reports a maximum “apparent quantum efficiency” of about 6.0% and a net thermal energy of 0.3 kW h/m2 generated in 120 h.

Liquid vs. Gas Phase CO2 Photoreduction Process: Which Is the Effect of the Reaction Medium?

The use of carbon dioxide, the most concerning environmental issue of the 21st century, as a feedstock for fuels productions still represents an innovative, yet challenging, task for the scientific community. CO2 photoreduction processes have the potential to transform this hazardous pollutant into important products for the energy industry (e.g., methane and methanol) employing a photocatalyst and light as the only energy input. In order to design an effective process, the high sustainability of this reaction should be matched with the perfect reaction conditions to allow the reactant, photocatalyst, and light source to come together: therefore, the choice of reaction conditions, and in particular its medium, is a crucial issue that needs to be investigated. Throughout this paper, a careful study of carbon dioxide photoreduction in liquid and vapour phases are reported, focusing on their effect on catalyst performances in terms of light harvesting, productivity, and selectivity. Different from most papers in the literature, catalytic tests were performed under extremely low light irradiance, in order to minimise the primary energy input, highlighting that this experimental variable has a great effect on the reaction pathway and, thus, product distribution.

A review on adsorption-enhanced photoreduction of carbon dioxide by nanocomposite materials

The large amount of CO2 emissions from the increasing consumption of fossil fuels is a potential cause for global warming. Photocatalytic reduction of CO2 using sunlight is considered as an attractive method for mitigating CO2 emissions. Extensive amount of researches on CO2 photoreduction are available, which tend to focus on the types of photocatalysts, the photocatalytic activity, and photoconversion efficiency. However, CO2 adsorption in the CO2 photoreduction process has been overlooked, despite it being an initial and important step. Recently, there has been an increase in the number of publications investigating the effects of CO2 adsorption on the CO2 photoreduction process. Thus, this review summarizes the research progress in this regard. This review focuses on the different CO2 adsorption modes and characterization methods as well as the factors influencing CO2 adsorption such as surface area, surface basicity, surface functional groups, surface defects, and exposed crystal facets. Furthermore, the design of nanocomposites that consist of photocatalysts and CO2 adsorption promoters are reviewed and discussed. It has been demonstrated that the CO2 photoreduction performance can be increased by utilizing CO2 adsorption in various types of nanocomposites, including metal oxides, chalcogenides, layered double hydroxides, and metal organic frameworks. This review provides a unique perspective in the design of nanocomposite photocatalysts with the goal of efficient CO2 photoreduction.

Facet effect of Pd cocatalyst on photocatalytic CO2 reduction over g-C3N4

The separation and transfer of charge carriers, adsorption of CO2 molecules, and desorption of product molecules are crucial factors that affect the CO2 photoreduction process. Herein, we demonstrate the significant facet effect of Pd cocatalyst toward CO2 photoreduction over graphitic carbon nitride (g-C3N4). The surface atomic structure of Pd cocatalyst can be precisely controlled by adjusting the amount of {111} and {100} facets to modulate the interfacial charge carrier transfer, CO2 adsorption and CH3OH desorption. It is shown that the tetrahedral Pd nanocrystals with exposed {111} facets function as a more efficient cocatalyst as compared to cubic Pd nanocrystals with exposed {100} facets, which is reflected by enhancing the CO2 photoreduction over graphitic carbon nitride. The origin of such remarkable shape-induced effect is explained on the basis of experimental studies of charge transfer dynamics and the atomic-scale DFT modeling of CO2 adsorption and CH3OH desorption.

Unravelling charge carrier dynamics in protonated g-C3N4 interfaced with carbon nanodots as co-catalysts toward enhanced photocatalytic CO2 reduction: A combined experimental and first-principles DFT study

In this work, we demonstrated the successful construction of metal-free zerodimensional/ two-dimensional carbon nanodot (CND)-hybridized protonated g-C3N4 (pCN) (CND/pCN) heterojunction photocatalysts by means of electrostatic attraction. We experimentally found that CNDs with an average diameter of 4.4 nm were uniformly distributed on the surface of pCN using electron microscopy analysis. The CND/pCN-3 sample with a CND content of 3 wt.% showed the highest catalytic activity in the CO2 photoreduction process under visible and simulated solar light. This process results in the evolution of CH4 and CO. The total amounts of CH4 and CO generated by the CND/pCN-3 photocatalyst after 10 h of visible-light activity were found to be 29.23 and 58.82 μmol·g catalyst −1 , respectively. These values were 3.6 and 2.28 times higher, respectively, than the amounts generated when using pCN alone. The corresponding apparent quantum efficiency (AQE) was calculated to be 0.076%. Furthermore, the CND/pCN-3 sample demonstrated high stability and durability after four consecutive photoreaction cycles, with no significant decrease in the catalytic activity. The significant improvement in the photoactivity using CND/pCN-3 was attributed to the synergistic interaction between pCN and CNDs. This synergy allows the effective migration of photoexcited electrons from pCN to CNDs via well-contacted heterojunction interfaces, which retards the charge recombination. This was confirmed by photoelectrochemical measurements, and steady-state and time-resolved photoluminescence analyses. The first-principles density functional theory (DFT) calculations were consistent with our experimental results, and showed that the work function of CNDs (5.56 eV) was larger than that of pCN (4.66 eV). This suggests that the efficient shuttling of electrons from the conduction band of pCN to CNDs hampers the recombination of electron–hole pairs. This significantly increased the probability of free charge carriers reducing CO2 to CH4 and CO. Overall, this study underlines the importance of understanding the charge carrier dynamics of the CND/pCN hybrid nanocomposites, in order to enhance solar energy conversion.

Economic Hydrophobicity Triggering of CO2 Photoreduction for Selective CH4 Generation on Noble-Metal-Free TiO2–SiO2

On the basis of the fact that the competitive adsorption between CO2 and H2O on the catalyst plays an important role in the CO2 photoreduction process, here we develop an economic NH4F-induced hydrophobic modification strategy to enhance the CO2 competitive adsorption on the mesoporous TiO2-SiO2 composite surface via a simple solvothermal method. After the hydrophobic modification, the CO2 photoreduction for the selective generation of CH4 over the noble-metal-free TiO2-SiO2 composite can be greatly enhanced (2.42 vs 0.10 μmol/g in 4h). The enhanced CO2 photoreduction efficiency is assigned to the rational hydrophobic modification on TiO2-SiO2 surface by replacing Si-OH to hydrophobic Si-F bonds, which will improve the CO2 competitive adsorption and trigger the eight-electron CO2 photoreduction on the reaction kinetics.

Copper modified TiO2 and g-C3N4 catalysts for photoreduction of CO2 to methanol using different reaction mediums

In this study, Cu/TiO2 and Cu/g-C3N4 catalysts were tested for CO2 reduction to methanol. The catalysts were prepared by the wet impregnation method and, characterized by XRD and FESEM. The product identification and yield were determined using a GC with FID. The CO2 photoreduction process was performed in each of the following reaction mediums: H2O, NaOH, KOH, Na2CO3, K2CO3, NaHCO3 and KHCO3. The efficiency was studied by comparing the methanol yield for each. A slurry type photoreactor with a UV lamp of 365 nm wavelength was used. CO2 photoreduction to methanol using NaOH as the reaction medium registered the highest yield of 431.65 μmole/g-cat•hr. This is due to the higher solubility of CO2 in the alkali as compared to that of the other reaction mediums, the ability of NaOH to serve as a hole scavenger owing to the formation of OH•ions and the higher selectivity of NaOH solution for CO2 photoreduction to methanol. It was obvious the choice of reaction medium affected the photoreduction of CO2 to methanol. The trend of results indicated the use of NaOH as a reaction medium improved the efficiency of the photoreduction process. The findings from this research could promote research in the field of photocatalysis by improving the yield which will encourage the support for methanol economy.

Photoreduction of CO2 on p-type Silicon Using Re(bipy-But)(CO)3Cl: Photovoltages Exceeding 600 mV for the Selective Reduction of CO2 to CO

Hydrogen-terminated p-type silicon was used as a photocathode for the selective photoreduction of CO2 to CO in the presence of Re(bipy-But)(CO)3Cl (bipy-But = 4,4′-di-tert-butyl-2,2′-bipyridine) as an electrocatalyst. The reduction of CO2 to CO on p-type silicon was achieved at a potential more than 600 mV lower than that required with a Pt electrode. A Faradaic efficiency of 97 ± 3% and an overall efficiency of 9.3% and 10% for the conversion of monochromatic and polychromatic light, respectively, to electricity were observed for the CO2 photoreduction process. A short-circuit quantum efficiency of 61% for light-to-chemical energy conversion was observed for the conversion of CO2 to CO.

Photochemical and Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide Mediated by (2,2′‐Bipyridine)tricarbonylchlororhenium(I) and Related Complexes as Homogeneous Catalysts

Abstract[fac‐Re(bpy) (CO)3Cl] (bpy = 2,2′‐bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO2 to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl− ions. The photochemical process took place under visible‐light irradiation and consumed a tertiary amine as electron donor. A formato‐rhenium complex was isolated in the absence of excess Cl− ions. Substitution by Cl− ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal‐to‐ligand charge‐transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 107M−1S−1. The 19e‐complex [Re(bpy) (CO)3X]− produced either photochemically or electrochemically appears to be the active precursor in the CO‐generation process. Detailed spectroscopic studies on 13C‐enriched carbonyl‐rhenium and formato‐rhenium complexes derived from 13C‐enriched CO2 were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO2 photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)3X] complex plays the role of both the photoactive and the catalytic center.