In situ fabrication of amorphous TiO2/NH2-MIL-125(Ti) for enhanced photocatalytic CO2 into CH4 with H2O under visible-light irradiation

Acceleration of Photoinduced Electron Transfer by Modulating Electronegativity of Substituents in Stable Zr-Metal-Organic Frameworks to Boost Photocatalytic CO2 Reduction

Photoreduction of CO2 with water into chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Metal-organic frameworks (MOFs) show great potential for CO2 photoreduction. However, poor water stability and sluggish charge transfer could limit their application. Herein, three water-stable MOFs functionalized with electron-donating methyl groups and/or electron-withdrawing trifluoromethyl groups are obtained for the CO2 photoreduction. Compared with UiO-67-o-CF3-CH3 and UiO-67-o-(CF3)2, UiO-67-o-(CH3)2 achieves excellent performance with an average CO generation rate of 178.0 μmol g-1 h-1 without using any organic solvent or sacrificial reagent. The superior photocatalytic activity of UiO-67-o-(CH3)2 is attributed to the fact that compared with trifluoromethyl groups, methyl groups could not only elevate CO2 adsorption capacity and reduction potential but also promote photoinduced charge separation and migration. These are evidenced by gas physisorption, photoluminescence, time-resolved photoluminescence, electrochemical impedance spectroscopy, transient photocurrent characteristics, and density functional theory calculations. The possible working mechanisms of electron-donating methyl groups are also proposed. Moreover, UiO-67-o-(CH3)2 demonstrates excellent reusability for the CO2 reduction. Based on these results, it could be affirmed that the strategy of modulating substituent electronegativity could provide guidance for designing highly efficient photocatalysts.

A review on titanium oxide nanoparticles modified metal-organic frameworks for effective CO2 conversion and efficient wastewater remediation

Environmental pollution has been increasing since last decade due to increasing industrialisation and urbanisation. Various kinds ofenvironmental pollutants including carbon dioxide (CO2), dyes, pharmaceuticals, phenols, heavy metals along with many organic and inorganic species have been discovered in the various environmental compartments which possess harmful impacts tox human health, wildlife, and ecosystems. Thus, various efforts have been made through regulations, technological advancements, and public awareness campaigns to reduce the impact of the pollution. However, finding suitable alternatives to mitigate their impacts remained a challenge. Metal-organic frameworks (MOFs) are one of the advanced materials with unique features such as high porosity and stability which exhibit versatile applications in environmental remediation. Their composites with titanium oxide nanoparticles (TiO2) have been discovered to offer potential feature such as light harvesting capacity and catalytic activity. The composite integration and properties have been confirmed through characterization using surface area analysis, scanning electron/transmission electron microscopy, atomic force microscopy, fourier transformed infrared spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and others. Thus, this work rigorously discussed potential applications of the MOF@TiO2 nanomaterials for the CO2 capture and effective utilization in methanol, ethanol, acetone, acetaldehyde, and other useful products that served as fuel to various industrial processes. Additionally, the work highlights the effective performance of the materials towards photocatalytic degradation of both organic and inorganic pollutants with indepth mechanistic insights. The article will offer significant contribution for the development of sustainable and efficient technologies for the environmental monitoring and pollution mitigation.

Growth of 3D-TNAs@Ti-MOFs by dual titanium source strategy with enhanced photoelectrocatalytic/photoelectro-Fenton performance for degradation of tetracycline under visible light irradiation

Visible-light-active 3D-TNAs@Ti-MOFs composite electrodes were fabricated by decorating nanoscaled Ti-based metal-organic frameworks on three-dimensional TiO₂ nanotube arrays (3D-TNAs) prepared by a facile in situ solvothermal method. The photoelectrocatalytic performance of electrode materials was evaluated by degradation of tetracycline (TC) under visible light irradiation. The experiment results show that Ti-MOFs nanoparticles are highly distributed on the top and side walls of TiO₂ nanotubes. The 3D-TNAs@NH₂-MIL-125 solvothermally synthesized for 30 h exhibited the best photoelectrochemical performance compared with 3D-TNAs@MIL-125 and pristine 3D-TNAs. In order to further enhance the degradation efficiency of TC by 3D-TNAs@NH₂-MIL-125, a photoelectro-Fenton (PEF) system was constructed. The influence of H₂O₂ concentration, solution pH and applied bias potential on TC degradation were explored. The results showed that when pH was 5.5, H₂O₂ concentration was 30 mM, and applied bias was 0.7 V, the degradation rate of TC was 24% higher than the pure photoelectrocatalytic degradation process. The enhanced photoelectro-Fenton performance of 3D-TNAs@NH₂-MIL-125 could be attributed to the large specific surface area, excellent light utilization, efficient interfacial charge transfer, low electron-hole recombination rate and high production of ˙OH as the result of the synergistic effect between TiO₂ nanotubes and NH₂-MIL-125.

Effect of Band Bending in Photoactive MOF-Based Heterojunctions

Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO₂ into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH₂. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO₂ photoreduction activity compared to the physical mixture.

Visible-light driven boosting electron-hole separation in CsPbBr3 QDs@2D Cu-TCPP heterojunction and the efficient photoreduction of CO2

CsPbBr₃ quantum dots (CPB QDs) have great potential in photoreduction of CO₂ to chemical fuels. However, the low charge transportation efficiency and chemical instability of CPB QDs presents a considerable challenge. Herein, we describe the electrostatic assemblies of negatively charged colloidal two dimensional (2D) Cu-Tetrakis(4-carboxyphenyl) porphyrins (Cu-TCPP) nanosheets and positively CPB QDs to construct the hydride heterojunction. The photogenerated electron migration from CPB QDs to Cu-TCPP nanosheets has been witnessed, providing the supply of long-lived electrons for the reduction of CO₂ molecules adsorbed on Cu-TCPP matrix. As a direct result, The CPB@Cu-TCPP-x (x wt% of CPB QDs) photocatalysts exhibit significantly enhanced photocatalytic conversion of CO₂, compared to the parent Cu-TCPP nanosheets or single CPB QDs. Especially, when with 20% CPB QDs, the heterostruture system achieves an evolution yield of 287.08 µmol g^-1 in 4 h with highly CO selectivity (99%) under visible light irradiation, which is equivalent to a 3.87-fold improvement compared to the pristine CPB QDs. Meanwhile, the CH₄ generation rate can be up to 3.25 µmol g^-1. This optimized construction of heterostructure could provide a platform to funnel photoinduced electrons to the reaction center, which can both act as a crucial capture and the reaction actives of CO₂.

Single-step fabrication of highly stable amorphous TiO2 nanotubes arrays (am-TNTA) for stimulating gas-phase photoreduction of CO2 to methane

This study investigates the facile fabrication of interfacial defects assisted amorphous TiO₂ nanotubes arrays (am-TNTA) for promoting gas-phase CO₂ photoreduction to methane. The am-TNTA catalyst was fabricated via a one-step synthesis, without heat treatment, by anodization of Titanium in Ethylene glycol-based electrolyte in a shorter anodizing time. The samples presented a TiO₂ nanostructured array with a nanotubular diameter of 100 ± 10 nm, a wall thickness of 26 ± 5 nm, and length of 3.7 ± 0.3 μm, resulting in a specific surface of 0.75 m² g. The am-TNTA presented prolonged chemical stability, a high exposed surface area, and a large number of surface traps that can reduce the recombination of the charge carriers. The am-TNTA showed promising photoactivity when tested in the CO₂ reduction reaction with water under UV irradiation with a methane production rate of 14.0 μmol g_cat^-1 h^-1 for a pure TiO₂ material without any modification procedure. This enhanced photocatalytic activity can be explained in terms of surface defects of the amorphous structure, mainly OH groups that can act as electron traps for increasing the electron lifetime. The CO₂ interacts directly with those traps, forming carbonate species, which favors the catalytic conversion to methane. The am-TNTA also exhibited a high stability during six reaction cycles. The photocatalytic activity, the significantly reduced time for synthesis, and high stability for continuous CH₄ production make this nanomaterial a potential candidate for a sustainable CO₂ reduction process and can be employed for other energy applications.

Promoting photocatalytic CO2 reduction to CH4 via a combined strategy of defects and tunable hydroxyl radicals

A well-designed photocatalyst with excellent activity and selectivity is crucial for photocatalytic CO₂ conversion and utilization. TiO₂ is one of the most promising photocatalysts. However, its excessive surface oxidation potential and insufficient surface active sites inhibit its activity and photocatalytic CO₂ reduction selectivity. In this work, highly dispersed Bi₂Ti₂O₇ was introduced into defective TiO₂ to adjust its oxidation potential and the generation of radicals, further inhibiting reverse reactions during the photocatalytic conversion of CO₂. Moreover, an in situ topochemical reaction etching route was designed, which achieved defective surfaces, a contacted heterophase interface, and an efficient electron transfer path. The optimized heterophase photocatalyst exhibited 93.9% CH₄ selectivity at a photocatalytic rate of 6.8 μmol·g^-1·h^-1, which was 7.9 times higher than that of P25. This work proposes a feasible approach to fabricating photocatalysts with well-designed band structures, highly dispersed heterophase interfaces, and sufficient surface active sites to effectively modulate the selectivity and activity of CO₂ photoreduction by manipulating the reaction pathways.

The covalent Coordination-driven Bi2S3@NH2-MIL-125(Ti)-SH heterojunction with boosting photocatalytic CO2 reduction and dye degradation performance

Herein, the optional and controllable growth of Bi₂S₃ onto NH₂-MIL-125 via covalent conjunction strategy was reported. The experimental results demonstrate that the obtained heterojunction exhibits boosting photocatalytic reduction CO₂ and organic dye degradation. The 18-Bi₂S₃@NH₂-MIL-125-SH displays the highest yield of 12.46 μmol g^-1h^-1 of CO, >13 times that of pure NH₂-MIL-125. Meanwhile, the reaction kinetic of 18-Bi₂S₃@NH₂-MIL-125-SH in the degradation of methylene blue is uppermost, which is 160 times than that of the commercial P25. The enhancement of photocatalytic performance could be ascribed to the covalent coordination-driven intimate interfacial interaction in n-scheme heterojunction. Meanwhile, the plausible mechanism was also investigated by UV-vis diffuse reflectance (UV-vis), photoluminescence (PL), electrochemical photocurrent, electron spin resonance (ESR) and electrochemical impedance spectroscopy (EIS).

Highly efficient and selective photocatalytic CO2 reduction of MIL-125(Ti) based on LiFePO4 and CuO QDs surface-interface regulation

In this study, the CuO quantum dots was encapsulated MIL-125 (Ti) MOF by a simple oxidation method, and then further formed LiFePO4/CuO@MIL-125(Ti) with LiFePO4 loading. Due to the protection of...

Varied proton conductivity and photoreduction CO2 performance of isostructural heterometallic cluster based metal–organic frameworks

A family of isostructural heterometallic MOFs based on Fe2M clusters serve as potential proton conductors and photocatalysts for CO2 photoreduction.

Fe-MIL tuned and bound with Bi4O5Br2 for boosting photocatalytic reduction of CO2 to CH4 under simulated sunlight

The innovative material synthesized in this experiment can reduce CO₂ to methane under simulated sunlight, solving environmental pollution and energy problems.