Efficient Photocatalytic Reduction Research Articles

Construction of 2D BiOIO3/ rod-shaped Zn-MOF II-scheme heterojunction for enhanced photocatalytic CO2 reduction to CO without sacrificial reagents

The conversion of CO2 into useable energy materials through photocatalytic reactions has attracted much attention. In this paper, 2D BiOIO3/rod-shaped Zn-MOF type II heterojunction was constructed for efficient photocatalytic CO2 reduction. XRD, SEM, TEM, XPS, and photoelectrochemical characterization tests were used to investigate the physicochemical properties of the prepared photocatalysts. Under 300 W Xenon lamp without any sacrificial reagents, the composite material BiOIO3/Zn-MOF-15(BOIOZ-15) showed the best photocatalytic efficiency, with a CO generation rate of 58.82 μmol/g/h, which is 1.7 times that of BiOIO3. The formation of a type II heterojunction between BiOIO3 and Zn-MOF-15 reduced the photogenerated electron-hole pair compounding, enhanced the separation and transport of photogenerated carriers, and improved the photocatalytic reaction performance of the composites.

Enhanced photocatalytic CO2 conversion of a CdS/Co-BDC nanocomposite via Co(ii)/Co(iii) redox cycling.

Photocatalytic CO2 reduction into value-added chemical fuels using sunlight as the energy input has been a thorny, challenging and long-term project in the environment/energy fields because of to its low efficiency. Herein, a series of CdS/Co-BDC composite photocatalysts were constructed by incorporating CdS nanoparticles into Co-BDC using a dual-solvent in situ growth strategy for improving photocatalytic CO2 reduction efficiency. The composites were characterized through XRD, SEM, TEM, XPS, DRS and EPR techniques in detail. 18% CdS/Co-BDC composites showed superior performance for the photocatalytic CO2 reduction to CO, which was 8.9 and 19.6 times higher than that showed by the pure CdS and Co-BDC, respectively. The mechanism of enhanced photocatalytic CO2 reduction performance was analyzed. The CdS/Co-BDC composites showed better adsorption for CO2. Detailed analysis of XPS, transient photocurrent responses, and electrochemical impedance spectroscopy (EIS) shows the existence of strong charge interaction between CdS and Co-BDC and the photo-electrons of CdS can be transferred to Co-BDC. Additionally, Co-oxo of Co-BDC plays the role of a redox-active site and promotes the reduction performance via the method of valence transition of Co(ii)/Co(iii) redox.

Construction of CsPbBr3/carboxyl-modified rGO heterostructures for efficient photocatalytic reduction of CO2 to methanol

Construction of monodispersed CsPbBr3 NCs and carboxyl-modified rGO composites led to the production of CO and CH3OH with an Relectron of 359 μmol g−1 h−1 by photocatalytic CO2 reduction.

A band structure modulated 2D/2D ZnIn2S4@amorphous polymeric g-C3N4 S-scheme heterojunction for efficient photocatalytic reduction of CO2

An S-scheme heterojunction of 2D/2D ZnIn2S4 nanosheets@amorphous polymeric carbon nitride is developed for photocatalytic reduction of CO2.

A novel covalent organic framework for efficient photocatalytic reduction of Cr(vi) and synergistic removal of organic pollutants under visible light irradiation

Polluted wastewater containing organic pollutants and heavy metals is increasing and harms environmental ecosystems and human health.

A series of four-substituted polyoxometalate-thiacalix[4]arene-based materials for the efficient photocatalytic reduction of Cr(vi)

Three isostructural polyoxometalate-thiacalix[4]arene-based materials were employed as efficient photocatalysts for the reduction of Cr(vi).

Au Nanoparticle-Loaded UiO-66 Metal–Organic Framework for Efficient Photocatalytic N2 Fixation

In order to achieve efficient photocatalytic N2 reduction activity for ammonia synthesis, a photochemical strategy was used in this work. UiO-66 was prepared through the solvothermal method and further loaded with Au nanoparticles (Au NPs) onto the UiO-66 (Zr) framework. The experimental results verified that there were metal–support interactions between Au NPs and UiO-66; this could facilitate charge transfer among Au NPs and UiO-66, which was beneficial to enhance the photocatalytic activity. The best N2 fixation effect of Au/UiO-66 with a loading of 1.5 wt% was tested, with a photocatalytic yield of ammonia of 66.28 μmol g−1 h−1 while maintaining good stability. The present work provides a novel approach to enhancing photocatalytic N2 fixation activity by loading NPs onto UiO-66.

Ligand Defect-Induced Active Sites in Ni-MOF-74 for Efficient Photocatalytic CO2 Reduction to CO.

The conversion of CO2 into valuable carbon-based products using clean and renewable solar energy has been a significant challenge in photocatalysis. It is of paramount importance to develop efficient photocatalysts for the catalytic conversion of CO2 using visible light. In this study, the Ni-MOF-74 material is successfully modified to achieve a highly porous structure (Ni-74-Am) through temperature and solvent modulation. Compared to the original Ni-MOF-74, Ni-74-Am contains more unsaturated Ni active sites resulting from defects, thereby enhancing the performance of CO2 photocatalytic conversion. Remarkably, Ni-74-Am exhibits outstanding photocatalytic performance, with a CO generation rate of 1380 µmol g-1 h-1 and 94% CO selectivity under visible light, significantly surpassing the majority of MOF-based photocatalysts reported to date. Furthermore, experimental characterizations reveal that Ni-74-Am has significantly higher efficiency of photogenerated electron-hole separation and faster carrier migration rate for photocatalytic CO2 reduction. This work enriches the design and application of defective MOFs and provides new insights into the design of MOF-based photocatalysts for renewable energy and environmental sustainability. The findings of this study hold significant promise for developing efficient photocatalysts for CO2 reduction under visible-light conditions.

Cayanamide Group Functionalized Crystalline Carbon Nitride Aerogel for Efficient CO2 Photoreduction

AbstractFor photocatalytic CO2 reduction, traditional amorphous polymeric carbon nitride (PCN) has suffered from fast photoexcited electron‐hole recombination and low specific surface area, resulting in low photocatalytic activity. Herein, starting from thermally polymerized PCN, cayanamide groups (─CN) functionalized crystalline carbon nitride (CCN) self‐supporting aerogels are obtained through a molten‐salt and self‐assembly two‐step strategy, which realized efficient photocatalytic CO2 reduction into CO as the main reduction products and O2 as the oxidation product, with CO evolution rate and selectivity reaching 25.7 µmol g−1 h−1 and 93.8%, respectively. It is revealed that the self‐supporting porous aerogel structure can enhance the mass transport of reactants and products, and increase the light absorption ability via multiple photon reflection. With charge carrier separation greatly enhanced in CCN aerogels with high crystallinity as revealed by charge carrier dynamics investigations, theoretical calculations and in situ spectral characterizations evidence that the introduced ─CN groups would act as the active sites for photoreduction of CO2 into CO, with energy barrier greatly reduced for the formation of COOH* intermediates, the rate‐determining step for CO2─to─CO reduction. This work demonstrates a novel and controllable strategy to develop semiconducting polymers with crystal, molecular and morphological structures synergistically modulated for highly efficient and selective photocatalytic CO2 reduction.

(Invited) Dye-Sensitized Molecular Photoelectrodes for CO2 Reduction Using Water as a Reductant

Photocatalytic CO2 reduction using visible light and water as a reductant has been one of the important targets for solving global warming problem and shortage of energy and carbon resources. In this presentation, I talk about two projects, i.e., (1) supramolecular photocatalysts with both functions as photosensitizer and catalysts and (2) photocatalytic CO2 reduction coupled to water oxidation.(1) Highly efficient supramolecular photocatalysts for CO2 reduction1-3 Since CO2 is the most oxidized state of carbon, one-electron reduction of CO2 is an extraordinarily high endergonic reaction. From the viewpoints of low-energy light application, the multi-electron reduction of CO2 via chemical reactions promises to be a more valuable process. This is a main reason why both a photosensitizer and a catalyst are required to promote efficient photocatalytic CO2 reduction. We have developed so-called supramolecular photocatalyts that have both the photosensitizer and the catalyst units. This bonding in the supramolecular photocatalysts can accelerate electron transfer between the two units, which improves the performance of the photocatalytic system, especially on the surface of photofunctional solid materials as described below.(2) Molecular photoelectrodes for photocatalytic CO2 reduction with water as a reductant 1,4 The molecular photocatalytic systems have a weakness, i.e., weak oxidation power in the excited state. For practical application, water should be used as an electron donor. For overcoming this problem, we have developed a hybrid system consisting of the supramolecular photocatalyst and semiconductor electrodes. The hybrid photoelectrochemical cell consisting of this hybrid photocathode and n-type semiconductor photoanode induced visible-light-driven CO2 reduction with water as a reductant to generate CO and O2. References “Photocatalytic Systems for CO2 Reduction: Metal-Complex Photocatalysts and Their Hybrids with Photofunctional Solid Materials” Kumagai, H.; Tamaki, Y.; Ishitani, O., Acc. Chem. Res. 2022, 55, 978-990.“Mechanistic study of photocatalytic CO2 reduction using a Ru(II)-Re(I) supramolecular photocatalyst” Kamogawa, K.; Shimoda, Y.; Miyata, K.; Onda, K.; Yamazaki, Y.; Tamaki, Y.; Ishitani, O., Chem. Sci. 2021, 12, 9682-9693.“Supramolecular Photocatalysts for the Reduction of CO2” Tamaki, Y.; Ishitani, O., ACS Cat. 2017, 7, 3394-3409.“Supramolecular photocatalysts fixed on the inside of the polypyrrole layer in dye sensitized molecular photocathodes: application to photocatalytic CO2 reduction coupled with water oxidation. Kuttassery, F.; Kumagai, H.; Kamata, R.; Ebato, Y.; Higashi, M.; Suzuki, H.; Abe, R.; Ishitani, O., Chem. Sci. 2021, 12, 13216-13232. Figure 1

Top-down synthesis of high-performance lead-free double layer perovskite Cs4CuSb2Cl12 with large specific surface area and rich defects for efficient photocatalytic CO2 reduction

In recent years, there has been significant progress in the field of perovskite research. One area that has garnered attention is lead-free perovskite due to its stability, lack of toxicity, and exceptional optical properties. In this study, we successfully synthesized environmentally friendly, small-sized double-layer perovskites Cs4CuSb2Cl12 using a top-down method involving ball milling. The resulting Cs4CuSb2Cl12 nanoparticles exhibit high photocatalytic capacity, with a 1.60-fold increase in CO yield under full spectrum irradiation for 4 h, from 45.01 μmol/g to 72.17 μmol/g compared to the original material. Additionally, CO evolution under NIR light illumination for 4 h increased from 2.31 μmol/g to 5.37 μmol/g. The top-down treatment resulted in smaller particle size and larger specific surface area, shortened carrier transmission distance, and enhanced electron concentration. Furthermore, the material’s surface presented a high concentration of defects, displayed high absorption capability across the entire spectrum, and abundant photocatalytic active sites. This study introduces an effective and environmentally-friendly strategy to enhance the photocatalytic efficiency of Cs4CuSb2Cl12, providing a new perspective for providing the photocatalytic capability of these materials.

A mechanistic evaluation for total removal of toxic hexavalent and trivalent chromium from water by oxygen vacancy-engineered nanocomposite

Oxygen vacancy-engineered nanocomposites are emerging materials in adsorption and photocatalysis research. This study evaluated total toxic Chromium removal by a nanocomposite of core-shell zeolite A@oxygen-vacant ZnO1−X (ZA@ZnO1−X) from water using its coexisting dual characteristics. ZA@ZnO1−X has removed 98.3% of total Cr, achieving a discharge limit of 0.05 ppm of Cr(VI) after the photoreduction and adsorption simultaneously. The detailed structural and physicochemical properties of synthesized ZA@ZnO1−X nanocomposite show higher BET surface area, oxygen-vacant percentage, and visible light photoactivity than the sole ZnO1−X nanosheet. The photocatalytic reduction efficiency (PRE) effect is systematically studied on varying operational variables like pH, citric acid (CA), Cr(VI) concentration, catalyst load, presence of anions, and radical scavengers. ZA@ZnO1−X removed Cr(VI) and Cr(III) simultaneously by 98.5% PRE with a catalyst load of 4 g/l, CA= 5 mM, pH= 5.06 under halogen light irradiation (300 W, 240 V) for 50 mins. This experimental study evaluates the prominent role of oxygen vacancy of ZA@ZnO1−X for photocatalytic reduction of Cr(VI) and enhanced adsorption of Cr(III). The kinetic study reveals adsorption of both Cr(VI) and Cr(III) follows pseudo-second-order kinetics, whereas photoreduction of Cr(VI) follows pseudo-first-order kinetics. A possible mechanism of total Cr removal is sketched, supporting enhanced adsorption due to unsaturated Zn atoms and unpaired e- at the oxygen defect site, followed by photoreduction by photogenerated e- and CO2-• radical. The ZA@ZnO1−X performance is reduced by only 2.5% after five consecutive runs without deformation. The easy regeneration process makes it suitable for toxic total Cr removal, avoiding any secondary pollution.

Construction and mechanism insights of a novel all-solid-state Z-scheme Mo2C/C/BiOI heterojunction for boosted photocatalytic degradation and reduction efficiency

Interfacial configuration of heterostructured photocatalysts to boost photocarrier separation and transfer is immensely beneficial to acquire great photocatalytic efficiency. Herein, a well-structured Mo2C/C/BiOI heterostructure containing different weight ratios Mo2C instead of noble metal was successfully prepared, where the inter-modified carbon nanosheets subserve as a connective to generate a perfect interface contact between Mo2C and BiOI. The photocatalytic performances of the photocatalysts were appraised by the degradation of indigo carmine and reduction of 4-nitroaniline under visible-light elucidation. The nanocomposite containing 7 % by weight of Mo2C/C showed the highest photocatalytic efficiency by eliminating 99.4 % of indigo carmine and 99.8 % of 4-nitroaniline within 75 min and 13 min, respectively. The boosted photocatalytic activity is attributed to the synergistic interaction between Mo2C/C and BiOI and the all-solid-state Z mechanism, where conductive carbon nanoparticles as an efficient electron mediator enable rapid photocarrier transfer and separation between Mo2C and BiOI. This study accentuates that Mo2C/C-based all-solid-state Z-scheme heterojunction nanocomposites are hopeful candidate photocatalysts for environmental applications.

Novel oxygen vacancy-enriched Bi2MoO6-x/MoS2 S-scheme heterojunction for strengthening photocatalytic reduction CO2 and efficient degradation of levofloxacin hydrochloride: Mechanism, DFT calculations

Constructing new photocatalysts for the photocatalytic reduction of CO2 and efficient degradation of Levofloxacin is of great importance to renewable energy. Here, S-scheme Bi2MoO6-x/MoS2 heterojunction nanospheres containing abundant surface defects (oxygen vacancies) were designed and successfully synthesized to enhance CO2 photoreduction activity in the absence of other sacrificial agents, co-catalysts or photosensitisers. At the same time, it can efficiently degrade organic pollutants (Levofloxacin). This heterogeneous structure with surface defects provides an abundance of reactive sites, accelerates charge separation and improves oxidation capacity. The improved Bi2MoO6-x/MoS2 heterogeneous nanospheres show excellent performance under simulated solar light, with the selectivity and yield of 92.45% and 29.01 µmol h−1, respectively, for the generation of CO. Under visible light, the degradation efficiency of levofloxacin hydrochloride (LVX) reached 96.3% within 25 min and remained as high as 95% after three cycles. This work provides a new idea for the design of new S-scheme photocatalysts and an important reference for the preparation of photocatalysts for the efficient photocatalytic reduction of CO2 and the efficient degradation of organic pollutants at the same time.

Boosting photocatalytic CO2 reduction efficiency by graphene nanoflakes (GNF) decorated ZIF-67 under visible light irradiation

The design and development of sustainable and cost-effective photocatalysts necessitate significant effort for improved CO2 reduction efficiency. Metal-organic frameworks (MOFs), with high surface area, are gaining popularity in photocatalysis, but their high electron-hole (e-, h+) recombination and low light harvesting capacity limit their utility. Graphene nanoflake (GNF) is a novel, low-cost carbon nanomaterial which has received attention owing to its non-toxicity, high aqueous solubility, unique photoluminescence properties, and excellent photostability. In this work, graphene nanoflake (GNF) decorated zeolitic imidazole framework ZIF-67 (GNF(X)/ZIF-67) has been synthesized for improving visible light-driven photocatalytic CO2 reduction performance. The composite GNF6/ZIF-67 decorated with 6% GNF nanoflake achieves the highest methanol generation of 50.93 µmolg−1 and the highest ethanol generation of 33.97 µmolg−1 after 8 h of visible light irradiation, compared to pure ZIF-67 which is 1.93 and 1.59 times respectively. The effect of GNF on boosting the visible-light photocatalytic activity of ZIF-67 was explored based on the UV-Vis DRS spectra, electrochemical impedance spectra (EIS), transient photocurrent response, and photoluminescence (PL) experiment. This work may discover a new way to synthesize photocatalysts for applying CO2 photoreduction.

Facile Synthesis of Ni3+/Co3+ Ion-Doped Zn2SnO4 Microspheres toward Efficient Photocatalytic CO2 Reduction

The photocatalytic reduction of CO2 into hydrocarbons is a promising solution for the energy crisis and greenhouse gas emissions. Thus, the fabrication and development of a new type of photocatalyst is of great importance for the practical application of CO2 reduction. Herein, we report a facile synthesis of Zn2SnO4 (ZTO) microspheres doped with Co3+ ions or Ni3+ ions. The doped Co3+/Ni3+ ions substitute the lattice Zn/Sn ions. DFT calculations and experimental results reveal that the doped Co3+/Ni3+ ions would induce new doping energy levels in the band gap, extend the light response from the UV to the visible region, and separate the charge carriers. As a result, compared with pure ZTO, the photocatalytic activity of a CO2 reduction into CH4 is significantly improved for Co-doped ZTO (Co-ZTO) and Ni-doped ZTO (Ni-ZTO).

Water-activation-facilitated photocatalytic CO2 reduction by a heterogeneous synergetic single-atomic Zn sites and Pd nanocrystals

Enhancing the photoreduction of carbon dioxide (CO2) to produce valuable chemicals, such as carbon monoxide (CO), is of significant importance. The bottleneck in developing advanced catalysts lies in the rational design of catalytic centers with efficient CO2 activation and hydrogen proton production. In this work, palladium nanoparticles (Pd NPs) were successfully modified on UiO-66-NH2-Zn SAs (UN-Zn SAs) by a photo-deposition method. The optimized photocatalyst, 4 Pd NPs-UN-0.7Zn SAs, demonstrated exceptional performance in converting CO2 to CO, exhibiting approximately 1.4-fold and 7.8-fold enhancements compared to UN-0.7Zn SAs and UN, respectively. A combination of time-resolved photoluminescence spectroscopy and electron paramagnetic resonance results unveiled that the introduction of Pd NPs effectively promoted the photogenerated charge separation and facilitated water activation to produce more hydrogen protons. The generated hydrogen protons were subsequently coupled with nearby CO2 that was activated by Zn SAs, thus achieving the facile water-activation-induced CO2 reduction process. Theoretical calculations further confirmed that the heterogeneous synergistic effects between Zn SAs and Pd NPs lowered the energy barrier for the rate-limiting step of CO2 conversion to COOH* , thereby achieving efficient photocatalytic CO2 reduction reactions. This work provides a new perspective on the development of efficient catalysts for the effective conversion of CO2.

Tungsten and oxygen dual vacancies regulation of the S-scheme ZnSe/ZnWO4 heterojunction with local polarization electric field for efficient CO2 photocatalytic reduction

Inefficient separation and sluggish transfer of photogenerated charges on the photocatalyst is one of the bottlenecks for CO2 photocatalytic reduction. In this study, the ZnSe/ZnWO4 heterojunction with tungsten vacancies and oxygen vacancies (ZZ-30%-Vw,o) was synthesized by hydrothermal process and post-etching method for CO2 reduction. Various characterizations showed superior structural and optical properties of the ZZ-30%-Vw,o heterojunction; results of ESR and work function calculation demonstrated that the heterojunction conformed to S-scheme charge transfer mechanism. Results of various tests and density functional theory (DFT) calculation confirmed the existence of W and O vacancies, as well as the locally polarized electric field (PEF). The PEF and the built-in electric field (IEF) could not only accelerate carriers separation and transfer, but also enhance CO2 adsorption and activation, thus enhancing photocatalytic activity toward CO2 reduction. The ZZ-30%-Vw,o composite exhibited the highest CO yield of 96.91 µmol/g/h, approximately 21.0 times of the ZnSe. Moreover, the ZZ-30%-Vw,o possessed favorable structure-performance stability. The COOH* was the most important intermediate during CO2 reduction, and possible CO2 reduction pathways and mechanism were proposed. This work paves a feasible way for improving photocatalytic activity via introducing dual surface vacancies on heterojunction photocatalysts.

Multicomponent Self-assembly of a Multinuclear Heterometal–Organic Polymer for CO2 Reduction

To address the greenhouse effect, scientists have never stopped exploring efficient photocatalytic CO2 reduction systems, and metal-organic compounds have recently emerged as a solution for overcoming global warming and climate issues. Under the irradiation of visible light, the catalytic activity, stability, and selectivity of most of the non-noble metal complexes reported so far are unsatisfactory. To efficiently fix CO2, Ru multinuclear heterometal–organic compound was obtained for carbon dioxide reduction. The as-synthesized M-Zn complex (M =Ru) catalysts exhibit special catalytic activity for the reduction of CO2 because of the immobilized metal ions serving as active sites during the reaction. This study proposes a general strategy for CO2 reduction through high levels in metal-organic polymers to achieve effective environmental protection and governance.

Facile fabrication of binary g-C3N4/NH2-MIL-125(Ti) MOF nanocomposite with Z-scheme heterojunction for efficient photocatalytic H2 production and CO2 reduction under visible light

A binary g-C3N4/NH2-MIL-125(Ti) MOF nanocomposite was fabricated through a facile sonochemical-assisted thermal approach for enhanced photocatalytic H2 production and CO2 reduction under visible light. Compared to pure g-C3N4, the g-C3N4/MOF photocatalyst showed enhanced visible light absorption with promoted charge carrier separation which increased the H2 production rate and the CO2 reduction into CH4 and CO. This enhancement was attributed to the successfully constructed Z-scheme heterojunction in addition to the visible-active, large surface area and highly CO2 adsorbable NH2-MIL-125(Ti) MOF. The highest H2 production of 480 µmol g−1 was exhibited over the g-C3N4/NH2-MIL-125(Ti) nanocomposite with 20 wt% MOF. Similarly, the highest CO production rate of 338 µmol g−1 was achieved with 20 wt% MOF composite. However, for the CH4 product gas, it was observed that the highest production rate was attained with pure g-C3N4 which reveals the NH2-MIL-125(Ti) MOF selectivity towards CO production instead of CH4. Among all the investigated sacrificial agents for H2 production, methanol was the best. The performance of CO2 reduction process was found to be increasing with the pressure increase. Furthermore, the stability investigations revealed continuous productions of H2, CO and CH4 over the C3N4/MOF photocatalyst in multiple cyclic runswithout any significant photocatalyst deactivation. This study provides new ideas for the fabrication of cheap, efficient and easy-synthesized nanomaterials for energy production and environmental remediation applications.