Efficient Photocatalytic Reduction Research Articles

Development of direct Z-schemes 2D/2D Bi2O2CO3/ SrTiO3 photocatalyst with interfacial interaction for photocatalytic CO2 reduction

Herein, a two-dimensional/two-dimensional (2D/2D) Bi2O2CO3/SrTiO3 (BOC/STO) direct Z-schemes heterojunction photocatalysts with perfect lattice matching are successfully prepared for efficient photocatalytic CO2 reduction. Results show that as-prepared BOC/STO composites follow the orientation relationship of (020) BOC// (200) STO and both two planes have a lattice spacing of 0.26 nm, resulting in the formation of perfect lattice matching between BOC and STO, which implying BOC/STO heterostructure has an ideal channel for charge transport. In addition, the DFT calculation confirms the direct Z-schemes heterojunction is formed at the BOC/STO interface, which can facilitate efficient migration and separation of photogenerated carriers. Combining the advantage of direct Z-schemes heterojunction and good lattice matching, the optimized BOC/STO catalyst performs the photocatalytic reduction of CO2 to CO and CH4 which are ∼ 2.61 times and ∼ 20.47 times for STO, respectively. The selectivity of 20 %-BOC/STO for CH4 increases to 79 %. The calculations confirm the higher adsorption energy of CHOO– and CO and the lower reaction energy of CHO– on BOC/STO than pure BOC or STO, resulting in the higher selectivity performance of BOC/STO for CO2 photocatalytic reduction.

A CuI Cluster-Based Covalent Metal-Organic Framework as a Photocatalyst for Efficient Visible-Light-Driven Reduction of CO2.

The application of solar energy to convert CO2 into high-value chemicals and fuels has been considered a highly desirable approach to relieving the greenhouse effect and energy crisis. However, the exploration of appropriate photocatalysts remains a major challenge. Combining the respective advantages of covalent organic frameworks and metal-organic frameworks to construct covalent metal-organic frameworks (CMOFs) can be a valid strategy to provide efficient, reliable, and eco-friendly photocatalysts. In this study, a CuI cluster-based CMOF (JNM-2) is used as a photocatalyst for CO2 photoreduction under visible-light irradiation. JNM-2 exhibits remarkable efficiency in photocatalytic CO2 reduction with high production rates of HCOOH (9019 μmol g-1 h-1 ) and CO (835 μmol g-1 h-1 ). The active center, reaction intermediates, and product generation pathways are elucidated by in situ DRIFTS and DFT calculations. This work demonstrates the tremendous possibilities of CMOFs as photocatalysts for CO2 reduction and provides profound insights into the mechanism of CO2 conversion into HCOOH/CO by using a molecularly accurate structural model.

Constructing direct Z-scheme heterojunction g-C3N5/BiOBr for efficient photocatalytic CO2 reduction with H2O

Photocatalytic CO2 reduction with H2O into hydrocarbon fuels represented an appealing approach to mitigate the energy crisis and greenhouse effect. However, isolated BiOBr (BOB) usually possessed rapid recombination of photogenerated carriers and low solar energy utilization, which restricted the elevation of photocatalytic performance. Herein, a direct Z-scheme porous N-rich g-C3N5/BiOBr (pCN/BOB) photocatalyst was fabricated through in situ hydrothermal approach. Furthermore, benefiting from Z-scheme heterojunction and tight surface contact, the pCN/BOB exhibited remarkably enhanced photoreduction ability of CO2 under visible light. Specially, 10% pCN/BOB exhibited the optimized photocatalytic performance for CH3OH production (3.08 μmol·g−1·h−1), approximately four times that of isolated BOB, whose improved photocatalytic performance was ascribed to the separation of photoinduced carriers by Z-scheme heterojunction and intimate interface contact. Meanwhile, the photogenerated charge transfer mechanism was calculated by work function calculation. Moreover, pCN/BOB exhibited good reusability for photocatalytic CO2 reduction. This work provided an efficient strategy for designing and preparing the high-efficiency photocatalysts for converting solar energy.

A highly efficient and stable TiO2@NH2-MIL-125 material for enhanced photocatalytic conversion of CO2 and CH4

At present, there are many difficulties in accomplishing the effective and efficient chemical utilization of CO2, such as low catalyst stability, high energy consumption, limited conversion of CH4 by reforming due to thermal reaction kinetics, high reaction temperature and high demand on reactor material. Here, a novel composite catalyst TiO2/NH2-MIL-125, prepared by three different methods, was applied to the photocatalytic conversion of CO2 with CH4 under visible-light irradiation. The experimental results showed that NH2-MIL-125@TiO2-40 catalyst prepared by ultrasonic impregnation method achieved rapid conversion of CO2 and CH4 at room temperature, and the yield of CO was up to 159 μ mol/g, which was 510% great than the catalytic performance of TiO2. In addition, the photocatalytic reduction efficiency of NH2-MIL-125@TiO2-40 material held stay at 93.7% after continuous operation for 28 h, showing excellent photocatalytic stability. Moreover, a series of characterization techniques were used to study the structure, morphology and photoelectric chemical properties of the photocatalyst. As well, the relationship between the physical and chemical properties of the material and the catalytic performance of CO2 conversion is discussed. Based on the above studies, a possible catalytic mechanism for the photocatalytic conversion of CO2 by NH2-MIL-125@TiO2 hybrid materials is proposed.

Bimetal Cu and Fe modified g-C3N4 sheets grown on carbon skeleton for efficient and selective photocatalytic reduction of CO2 to CO

Excessive consumption of fossil fuels leads to resource shortages and the greenhouse effect. In order to solve these problems, the conversion of CO2 to fuel using photocatalytic technology has attracted extensive attention. In this work, Cu and Fe bimetallic modified g-C3N4 sheets grown on carbonized pomelo peels (Cu/Fe-CNC) for photocatalytic reduction CO2 to CO were synthesized via chemical vapor co-deposition (CVD) method. The modification by Cu and Fe bimetallic has enhanced the transfer and separation efficiency of charge carrier and increased surface reaction sites, thereby significantly enhancing the CO yield. Compared with the bulk g-C3N4, the reduction yield of CO2 to CO is increased by 3 times and compared with C3N4 grown on carbonized pomelo peel (CNC), it increased by 2 times. And Cu/Fe-CNC can achieve 100 % reduction of CO2 to CO in the photocatalytic system. Furthermore, the Cu/Fe-CNC has excellent stability in 5 cycle experiments. This work, from a new perspective, assists in developing high active g-C3N4-based photocatalysts to achieve the efficient and selective CO2 to CO reduction.

Cobalt-Doped MoS2-Integrated Hollow Structured Covalent Organic Framework Nanospheres for the Effective Photoreduction of CO2 under Visible Light

Photocatalytic conversion of CO2 into beneficial raw chemicals has gained a great deal of attention for well over the recent decade due to its prospect for alleviating energy scarcity and global warming. Even though photocatalytic CO2 reduction technique has shown great promise, the successful conversion of CO2 to the intended outputs has remained a key barrier. Here, we present the design synthesis of a hollow nanospherical keto-enamine TpPa-1 covalent organic framework (COF) integrated single-atom Co-1T-MoS2 (TpPa-1/Co-1T-MoS2) composite with the appropriate band edge potential and an enhanced charge separation to improve its CO2 photoreduction efficiency under visible light irradiation. With a selectivity of 93%, the developed TpPa-1/Co-1T-MoS2 nanocomposite exhibits impressive photocatalytic CO2 reduction efficiency of up to ∼196 μmol g–1 h–1 of CO. Bare TpPa-1 and Co-1T-MoS2 both had around 1.23 and 1.6 times lower CO than TpPa-1/Co-1T-MoS2. Parametric analyses show that the TpPa-1 and Co-1T-MoS2 counterparts have a remarkable cumulative influence on the specificity and efficacy of photoreduction of CO2 to CO. TpPa-1/Co-1T-MoS2 composite is one of the handful of notable values cited in the literature, with an apparent quantum yield of 0.7% at 420 nm under ideal conditions. 13C labeling confirms that the selective conversion of CO2 to CO was facilitated by couplings between TpPa-1 and Co-1T-MoS2, which enhanced charge separation and migration to the surface. The findings show that COFs and their single-atom-based composites can be developed for next-generation photocatalytic systems and that this technology may also be interesting for other energy conversion applications.

Tunable Bi-bridge S-scheme Bi2S3/BiOBr heterojunction with oxygen vacancy and SPR effect for efficient photocatalytic reduction of Cr(VI) and industrial electroplating wastewater treatment

Surface plasmon resonance (SPR), oxygen vacancy modification and the construction of S-scheme heterostructure are important strategies to enhance visible-light absorption and improve photocatalytic performance. Here, a Bi-bridge S-scheme Bi2S3/BiOBr heterojunction (Bi2S3/Bi/BiOBr) with oxygen vacancies and SPR effect of Bi metal was prepared by one-pot solvothermal method for Cr(VI) reduction. The 3:10 Bi2S3/Bi/BiOBr exhibited superior visible-light photocatalytic reduction performance with 95.82 % Cr(VI) removal efficiency. Additionally, the 3:10 Bi2S3/Bi/BiOBr showed high stability and good anti-interference ability, and can effectively remove Cr(VI) from industrial electroplating wastewater with 97 % of Cr(VI) removal efficiency and residual Cr(VI) concentration of 0.304 mg/L, meeting the industrial effluent standard, which made it potentially attractive for real wastewater treatment. The enhanced photocatalytic performance of Bi2S3/Bi/BiOBr heterojunction was attributed to Bi metal SPR effect and the role of Bi as e-bridge, the presence of oxygen vacancies, the formation of internal electric field and S-scheme charge transfer, which were confirmed by various experimental results and density functional theory (DFT) calculations. This work provided theoretical and experimental reference for the construction of stable S-scheme heterojunctions with high catalytic activity and anti-interference, and a reliable solution for Cr(VI) removal from electroplating wastewater.

Interfacial chemical bond modulated Z-scheme mechanism in In2−xS3/Cd1+xIn2−xS4 heterojunction for enhanced photocatalytic CO2 reduction and wastewater treatment

An interfacial CdS bond modulated hierarchical Z-scheme heterostructure composed by indium vacancies-rich In2-xS3 and Cd-rich Cd1+xIn2-xS4 (In2-xS3/Cd1+xIn2-xS4) is rationally designed and fabricated by using MIL-68 (In) as precursor and template, and used for efficient photocatalytic wastewater treatment and CO2 reduction. The in-situ ion-exchange derived CdS bond at the heterointerface induced the Z-scheme charge transfer mechanism in hierarchical In2-xS3/Cd1+xIn2-xS4 photocatalyst, which is verified by the X-ray photoelectron spectroscopy, electron paramagnetic resonance and density functional theory calculations. Moreover, the hierarchical ultrathin and loose two-dimensional nanosheet structure is conducive to expose more active sites and adsorb more reactants. By integrating the efficient adsorption capacity and Z-scheme mechanism, the In2-xS3/Cd1+xIn2-xS4 photocatalyst shows superior photocatalytic CO2 reduction activity and high removal efficiency of dyes and heavy metal. For example, under visible light illumination, it removed almost 100 % of various dyes within 10 min operation, and reduced 100 % Cr(VI) within 1 h, and it also manifested state-of-the-art production rates of 132.5 and 392.1 μmol h−1 g−1 for CH4 and CO, respectively, in reducing CO2 without co-catalyst. A useful inspiration on purposive modulating Z-scheme charge transfer by atomic-level interface engineering was proposed to significantly promote the photocatalytic performance.

Synthesis of mesoporous Ag/α-Fe2O3/TiO2 heterostructures with enhanced and accelerated photo/-catalytic reduction of 4-nitrophenol.

4-Nitrophenol (4-NP) is reported to originate disadvantageous effects on the human body collected from industrial pollutants; therefore, the detoxification of 4-NP in aqueous contamination is strongly recommended. In this study, the heterojunction mesoporous α-Fe2O3/TiO2 modulated with diverse Ag percentages has been constructed via a sol-gel route in the occurrence of a soft template P123. The formation of biphasic crystalline TiO2 anatase and brookite phases has been successfully achieved with the average 10nm particle sizes. The photo/-catalytic reduction of 4-NP has been performed utilizing NaBH4 as a reducing agent with and without visible illumination. All Ag/Fe2O3/TiO2 nanocomposites exhibited significantly higher photo/-catalytic reduction efficiency than pure Fe2O3, TiO2 NPs, and Fe2O3/TiO2 nanocomposite. 2.5% Ag/Fe2O3/TiO2 nanocomposite was considered the highest and superior photocatalytic reduction efficiency, and it almost achieved 98% after 9min. Interestingly, the photocatalytic reduction of 4-NP was accelerated 9 times higher than the catalytic reduction over 2.5% Ag/Fe2O3/TiO2; its rate constant value was 709 and 706 times larger than pure TiO2 and Fe2O3 NPs, respectively. The enhanced photocatalytic reduction ability of Ag/Fe2O3/TiO2 nanocomposite might be referred to as significantly providing visible light absorption and a large surface area, and it can upgrade the effective separation and mobility of electron holes. The stability of the synthesized catalysts exhibited that the obtained catalysts can undergo a slight decrease in reduction efficiency after five successive cycles. This approach highlights a novel route for constructing ternary nanocomposite systems with high photo/-catalytic ability.

High-loading single cobalt atoms on ultrathin MOF nanosheets for efficient photocatalytic CO2 reduction

High-loading single cobalt atoms on ultrathin MOF nanosheets for efficient photocatalytic CO2 reduction

Rapid charge transfer in covalent organic framework via through-bond for enhanced photocatalytic CO2 reduction

Charge transfer efficiency between discrete photosensitizers and catalytic sites is a key limiting factor in artificial photosynthesis. It is highly desirable but challenging to efficiently combine the two sections into an integration system and get insight into the kinetics and mechanisms. Here in, the photosensitizer [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) and active cobalt porphyrin (Co-Por) sites were integrated into a covalent organic framework (COF), named COF-RuBpy-Co, for efficient charge transfer and photocatalytic CO2 reduction. The catalyst COF-RuBpy-Co exhibited excellent CO2 photoreduction activity towards CO production with a rate of 547 μmol g−1h−1, which is 1.4-fold enhancement over the physical mixture of Ru(bpy)3Cl2 and COF-Bpy-Co. In situ X-ray photoelectron spectroscopy combined with theoretical calculation results revealed that COF-RuBpy-Co achieved efficient photoelectron transfer from [Ru(bpy)3]2+ to cobalt porphyrin. More importantly, transient absorption spectroscopy indicated that the covalent linking [Ru(bpy)3]2+and Co-Por units realized a faster charge transfer (44.2 ps) over the large π-conjugated system. This work provides vital insights into the charge carrier transfer process and demonstrates the potential of COFs as a platform in artificial photosynthesis.

Manipulating electronic structure and light absorption of carbon nitride via P-doping and local crystallization for efficient photocatalytic reduction of CO2

Graphitic carbon nitride (g-C3N4, CN) with high light harvesting and suppressed charge recombination is desired in photocatalytic reactions. Herein, locally crystalline CN (KP/CN) with photoresponse edge of 648 nm was synthesized by a two-step calcination method. First step was P-doping via calcining phytic acid and nitrogen-containing precursor. Another was local crystallinity tailoring via calcining with KSCN. The obtained KP/CN facilitated the n → π* electronic transition, exhibited improved light utilization and charge mobility. Theoretical calculations confirmed that CO2 adsorption and activation became easy on KP/CN-2. The yields of CO and CH4 under KP/CN catalysis were 58.7 and 29.0 μmol g−1, respectively, after 5 h in the presence of 0.5 mL water. This work demonstrated the synergistic enhancement of light absorption and charge carrier dissociation via doping and partial crystallization.

One-step solid-state-chemistry synthesized layered bismuth oxyiodide crystal for efficient solar-driven CO2 photoreduction

We develop a facile one-step solid-state-chemistry strategy for synthesizing BiOI crystals with layered microstructure. The BiOI photocatalyst shows typical mesoporous feature with available surface area, considerable wide-spectrum light absorption and carriers lifetime properties, and remarkable solar to thermal effect for efficient solar-driven photocatalytic CO2 reduction to CH4. The engineered BiOI displays a superior CH4 formation performance with the space-time yield of 13.1 μmol g−1 h−1 and the selectivity of 82.3% as well as excellent photostability for CO2 photoreduction under solar light irradiation. Furthermore, the versatile BiOI can boost the photo-stimulated efficiency on clean H2 generation and pollutant degradation.

A Tb3+-anchored Zr(iv)-bipyridine MOF to promote photo-induced electron transfer and simultaneously enhance photoluminescence ability and photocatalytic reduction efficiency towards Cr2O72−

The fluorescence sensing sensitivity, accuracy, and photocatalytic reduction efficiency of a bcu topological Zr-MOF have been effectively improved, by firmly anchoring lanthanide Tb3+ ions in the Zr-MOF.

Metalloporphyrins: their multitalented nature as observed in multi-metal complex systems.

Five topics pertaining to the unique chemistry of metalloporphyrins as observed in multi-metal complex systems are introduced. The topics include the following: (i) the unique chromatographic separation of cyclic porphyrins on modified silica gel; (ii) room temperature phosphorescence from the zinc porphyrin part in a zinc porphyrin/rhenium complex hetero dyad; (iii) the substituent effect, in the preparation of a readily soluble special-pair-type zinc porphyrin dimer/rhenium complex having efficient photocatalytic CO2 reduction ability; (iv) assessment of the excited triplet state of a special-pair-type zinc porphyrin dimer in macrocyclic multiporphyrin rings; and (v) solvation/desolvation indicators based on exclusive transformation between the head-head type and head-tail type of supramolecular co-ordination polymers composed of bis(zinc porphyrin)s.

Efficient photocatalytic hydrogen evolution and CO2 reduction by HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures with direct Z-schemes.

The elaborate configuration of the heterostructure is crucial and challenging to achieve high solar-to-hydrogen efficiency or CO2 reduction efficiency . Here, we predict two heterostructures composed of HfSe2, ZrSe2, and GaAs3 monolayers. The maximum of 42.71%/35.12% with the heterostructures can be reached with the perfect match between the bandgap and band edges. The configurations of the heterostructures are discovered from 12 possible stacking types of the three monolayers. The formation energy, potentials of band edges, carrier mobilities, and optical absorption were used to identify the feasibility of the CO2 reduction reaction (CO2RR), the hydrogen evolution reaction (HER), and the oxygen evolution reaction (OER). The and based on overpotentials and bandgaps and the Gibbs free energies (ΔGs) are evaluated to quantificationally access the photocatalytic performance of the constructed heterostructures. The results demonstrate that high can be obtained for the solar photocatalytic Z-schemes with the HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures, and these values can be further enhanced through strain engineering. Moreover, small changes in ΔGs were observed for HER, OER, and CO2RR. Therefore, the two heterostructures have excellent performance in photocatalytic hydrogen evolution and CO2 reduction. The results of the electronic properties revealed that the delicate matching of the projected band edges of the monolayers in the heterostructures is responsible for the high photocatalytic performance.

Iron/cobalt/nickel regulation for efficient photocatalytic carbon dioxide reduction over phthalocyanine covalent organic frameworks.

Using solar photocatalytic CO2 reduction to produce high-value-added products is a promising solution to environmental problems caused by greenhouse gases. Metal phthalocyanine COFs possess a suitable band structure and strong light absorption ability, making them a promising candidate for photocatalytic CO2 reduction. However, the relationship between the electronic structure of these materials and photocatalytic properties, as well as the mechanism of photocatalytic CO2 reduction, is still unclear. Herein, the electronic structure of three MPc-TFPN-COFs (M = Ni, Co, Fe) and the reaction process of CO2 reduction to CO, HCOOH, HCHO and CH3OH were studied using DFT calculations. The calculated results demonstrate that these COFs have a good photo response to visible light and are new potential photocatalytic materials. Three COFs show different reaction mechanisms and selectivity in generating CO2 reduction products. NiPc-TFPN-COFs obtain CO through the reaction pathway of CO2 → COOH → CO, and the energy barrier of the rate-determining step is 2.82 eV. NiPc-TFPN-COFs and FePc-TFPN-COFs generate HCHO through CO2 → COOH → CO → CHO → HCHO, and the energy barrier of the rate step is 2.82 eV and 2.37 eV, respectively. Higher energies are required to produce HCOOH and CH3OH. This work is helping in understanding the mechanism of photocatalytic reduction of CO2 in metallophthalocyanine COFs.

A hydrophilic fully conjugated covalent organic framework for photocatalytic CO2reduction to CO nearly 100% using pure water

The incorporation of hydrophilic groups onto a fully conjugated covalent organic framework (COF) has been observed to enhance the adsorption of H2O and CO2, while enabling efficient CO2photocatalytic reductionviaH2O oxidation.

The synergistic chemical coupling of nanostructured MoS2 with nitrogen-deficient 2-D triazine-based polymeric m-C3Nx for efficient and selective CO2 photocatalytic conversion to CO

The chemically coupled MOS2 with nitrogen deficient 2-D triazine polymeric m-C3Nx photocatalyst drives the selective and efficient photocatalytic reduction of CO2 to CO (FE: 31%), – three folds higher than that of MoS2 decorated mpg-C3N4.

Efficient nitrate reduction in water using an integrated photocatalyst adsorbent based on chitosan-titanium dioxide nanocomposite.

Globally, there exists a huge concern on the increased discharge of nitrates to the natural water resources out of various anthropogenic activities as it causes serious environmental pollution and associated harmful effects. In the present work, sol-gel-derived functional nanocomposites based on silver (Ag) and nitrogen (N)-doped titanium dioxide (TiO2)-coated chitosan nanocomposites were successfully synthesized in the form of beads, and their application for the reduction of nitrates in water was studied. The synthesized nanocomposite beads were characterized for their structural, textural, and morphological features using X-ray diffraction analysis, Fourier transform infrared spectroscopy, UV-visible spectroscopy, BET surface area analysis, Scanning electron microscopy, Transmission electron microscopy, and X-ray photoelectron spectroscopy. A uniform coating of doped titania species on the chitosan porous structure was achieved through electrostatic interaction. Adsorption/photocatalytic reduction of nitrates was further carried out using functional nanocomposite beads by monitoring the nitrate concentration of the model contaminated water, in an adsorption study under dark condition and photocatalytic study under UV/sunlight for a definite time period. Drying conditions of the nanocomposite beads were found to have a significant effect on the adsorption cum photocatalytic efficiencies of the nanocomposite. The freeze-dried chitosan-titania nanocomposite beads containing 0.5mol% Ag exhibited an adsorption efficiency of ~ 43.5% (under dark for 30min) and photocatalytic reduction capability of ~ 95% (under sunlight for 2h), whereas the oven dried beads of the same composition exhibits adsorption and photocatalytic efficiencies of 40% (under dark for 30min) and 70% (under UV light for 2h) respectively, towards the reduction of nitrate ions in an aqueous solution. Continuous flow adsorption cum photocatalytic study using the oven-dried nanocomposite beads was also carried out with the help of an experimental setup fabricated in-house and under varying experimental conditions such as flow rate, bed height, and concentration of feed solution. Nitrate reduction efficiency of 87.6% and an adsorption capacity of 7.9mgg-1 were obtained for the nanocomposite beads in the continuous flow adsorption cum photocatalysis experiment for up to 8h when using an inlet concentration of 100ppm, bed height 12cm, and flow rate 5.0mLmin-1. A representative fixed-bed column adsorption experiment performed with oven dried nanocomposite beads in a real groundwater sample collected from the Palakkad District of Kerala shows promising results for nitrate reduction (85.9% efficiency) along with a significant removal rate for the other anions as well. Thus, the adsorption cum photocatalytic nitrate reduction efficiency of the functional nanocomposite material makes them suitable for the reduction of nitrates from water/wastewater through an integrated nanocomposite approach.