Spatial Confinement Effect Research Articles

Polymer Mechanochemistry in Confined Spaces.

With the development of mechanophores, polymer mechanochemistry has emerged as a powerful tool for creating force-responsive materials with a variety of desired functions, ranging from color change to molecular release. However, it remains challenging to improve the efficiency of mechanochemical activation, especially for mechanophores embedded within polymer networks, which has profound implications for translating mechanochemical responses into materials-centered applications. The physical and chemical conditions under spatial confinement differ significantly from those in the surrounding bulk environment, offering opportunities to facilitate mechanochemical activation. In this Minireview, we discuss and summarize recent progress in polymer mechanochemistry within confined spaces including surfaces/interfaces, polymer assemblies, and other nanostructures, specifically focusing on the effects of spatial confinement on the enhancement of mechanophore activation. We envision that combining confinement effects with advances in molecular and materials engineering will further improve the activation efficiency, capitalizing more fully on the potential of mechanophores toward practical applications.

Smartphone-based dual-mode aptasensor with bifunctional metal-organic frameworks as signal probes for ochratoxin A detection

Ochratoxin A (OTA) poses significant risks to human health, being potentially nephrotoxic, carcinogenic, genotoxic, and immuno-toxic. In this work, we developed a dual-mode aptasensor for OTA analysis, integrating colorimetric, electrochemical, and smartphone-based detection. The bifunctional Fe-MIL-88 metal-organic framework, acting as both a nanozyme capable of catalyzing the 3,3′,5,5′-tetramethylbenzidine substrate and an electrochemical signal amplifier, enabled OTA quantification through current response or changes in color and absorbance intensity. Besides, the spatial confinement effect enhances the local concentration of Fe-MIL-88 signal probes through rolling circle amplification reaction, thereby contributing to a substantial enhancement in sensitivity. The proposed technique is simple, disposable, highly sensitive and selective, enabling OTA detection in the range of 1 fg/mL to 250 ng/mL, with a limit of detection of 0.22 fg/mL (3σ rule). Furthermore, we successfully detected OTA in corn, wheat, and red wine samples, with results good concordance with those obtained using commercial enzyme-linked immunoassay kits.

Fabrication of Cu-BTC@PW12/GO for multivariate sensing dopamine and acetaminophen as electrochemical sensor

Dopamine (DA) and acetaminophen (AP) are closely associated with many physiological and pathological processes, monitoring their levels precisely is of significance in the early diagnosis of diseases. Herein, a polyoxometalate-based metal-organic framework (POMOF) based on phosphotungstate (Cu-BTC@PW12) was immobilized on graphene oxide (GO) to fabricate Cu-BTC@PW12/GO (CPG) as an electrochemical sensor for the quantification of DA and AP. The spatial confinement effect of copper-based MOF (Cu-BTC) remained the catalytic activity phosphotungstate (PW12) avoiding the aggregation, facilitating electro-catalysis performance for detection of DA and AP. The CPG electrochemical sensor achieved the analysis of DA and AP with the limit of detection (LOD) of 24.8 nM and 62.3 nM, respectively. Furthermore, CPG can be applied for the quantification of DA and AP in real human serum and environmental water samples with satisfied recoveries. Therefore, this work expanded the utilization of POMOF in electrochemical analysis and has promising prospects for the early diagnosis of diseases and environmental treatment.

Accelerating gas escape efficiency by parallel alignment of nanosheets arrays for high-current oxygen evolution and urea oxidation

Electrocatalysts play a crucial role in energy production and chemical oxidation. Nonetheless, the efficacy of catalysts in expediting reactions is notably affected by the escape of bubbles and the re-exposure of active sites, particularly under high-current-density conditions. Herein, parallel-aligned Ni(OH)2 nanosheets array is anchored on nickel foam as substrate to verify mass transfer enhancement theory. Compare with disordered and interconnected nanosheets structures, parallel alignment of nanosheets array with superior mass transfer capability, larger exposed surface area, and spatial confinement effects is demonstrated to boost effective removal of in situ generated gas bubbles. Moreover, carbon coating layer with high electrical conductivity and nickel-iron-based composite with high activity is simultaneously anchored on parallel-aligned nanosheets surface (C@FeNi/NF-P). As illustration of application viability, C@FeNi/NF-P exhibits overpotential of 317 mV and potential of 1.45 V at 500 mA cm−2, respectively, for oxygen evolution (OER) and urea oxidation (UOR) with good stability. Moreover, the mass transfer enhancement effect of parallel aligned structure for the high active electrodes is also discussed. This work provides new insight for physical structural modulation of active materials to strengthen electrocatalytic activity with high mass-transfer efficiency, further ensuring high-efficient and stable water splitting and urea oxidation.

Dimeric-molecular beacon based intramolecular strand displacement amplification enables robust analysis of miRNA

Given the critical role of miRNAs in regulating gene expression and their potential as biomarkers for various diseases, accurate and sensitive miRNA detection is essential for early diagnosis and monitoring of conditions such as cancer. In this study, we introduce a dimeric molecular beacon (Di-MB) based isothermal strand displacement amplification (ISDA) system (Di-MB-ISDA) for enhanced miRNA detection. The Di-MB system is composed of two monomeric MBs (Mono-MBs) connected by a double-stranded DNA linker with single-stranded sequences in the middle, facilitating binding with the flexible arms of the Mono-MBs. This design forms a compact, high-density structure, significantly improving biostability against nuclease degradation. In the absence of target miRNA, the Di-MB maintains its stable structure. When target miRNA is present, it binds to the stem-loop regions, causing the hairpin structure to unfold and expose the stem sequences. These sequences serve as templates for the built-in primers, triggering DNA replication through an intramolecular recognition mechanism. This spatial confinement effect accelerates the strand displacement reaction, allowing the target miRNA to initiate additional reaction cycles and amplify the detection signal. The Di-MB-ISDA system addresses key challenges such as poor biostability and limited sensitivity seen in traditional methods. By enhancing biostability and optimizing reaction conditions, this system demonstrates robust performance for miRNA detection with a detection limit of 100 pM. The findings highlight the potential of Di-MB-ISDA for sensitive and accurate miRNA analysis, paving the way for its application in biomedical study and disease diagnosis in complex biological samples.

Carbon quantum dots assemblies integrated with spatial confined Co nanoparticles for antibiotic degradation via peroxymonosulfate activation

Heterogeneous Co-based materials are well-known for their exceptional catalytic properties in activating peroxymonosulfate (PMS) for the degradation of antibiotic pollutants. However, the potential applications of these materials are often hindered by significant Co nanoparticle aggregation and ion leaching. In this study, a carbon quantum dot-mediated self-assembly strategy was used to fabricate three-dimensional porous sponge-like Co@CDs-x (x represents the calcination tempeatures) catalysts with spatially confined Co nanoparticles. Among the samples, Co@CDs-900 exhibited a remarkable 97.8 % removal efficiency of TC in 11 minutes, with an apparent rate constant of 0.313 min−1. The exceptional performance of Co@CDs-900/PMS can be attributed to its large specific surface area, unique porosity, and abundant catalytically active sites, which generate ample reactive oxygen species for TC degradation. The catalyst demonstrated good degradation capabilities across a wide pH range of 3–11 and various organic pollutants such as tetranitrophenol, oxytetracycline, ciprofloxacin, methyl orange, and rhodamine B. Moreover, Co@CDs-900 maintained high activity even after the 5th cycle due to its magnetic property and spatial confinement effect, preventing catalyst loss and ion leaching during recycling tests. The degradation mechanism involved both free-radical and non-free radical pathways, with SO4•− and 1O2 identified as the primary reactive oxygen species. The degradation intermediates of TC were identified and a plausible degradation pathway was proposed. Toxicity assessment revealed that the Co@CDs-900/PMS system effectively reduced the toxicity of TC post-degradation. This study presents an effective approach for developing sponge-like CDs assemblies with spatially confined metal nanoparticles for activating PMS in antibiotic degradation.

High coke resistance Ni-based CH4/CO2 reforming catalysts with strong spatial confinement effect: Effect of CeO2 shell thickness

Ni-based catalysts show promise as candidates for the dry reforming of methane (DRM), yet the susceptibility to sintering and carbon deposition is a major obstacle to industrialization. This work demonstrates a mesoporous Ni-based catalyst with a thickness-tailorable CeO2 shell for enhanced spatial confinement effect for the DRM. The Ni-MCM-41@xCeO2 catalysts are prepared at various CeO2 shell thickness through a two-step hydrothermal reaction. The kinetic studies have shown that the Ni-MCM-41@2CeO2 catalyst has the lowest activation energy, producing a high conversion of CH4 and CO2 as high as around 80 % at 700 °C. Our characterizations reveal that the Ni core is tightly confined in the mesoporous skeleton of MCM-41 and within a CeO2 shell. The Ni-MCM-41@2CeO2 catalyst is able to sustain high activity for more than 10 h of operation, with a remarkably reduced carbon deposition (0.28 %) as compared with a conventional Ni-Ce/MCM-41 catalyst (8.77 %). Furthermore, the density functional theory (DFT) calculation supports that the CeO2 shell layer significantly reduces dissociation potential barrier for CH4 and CO2, hence enhancing the catalytic activity of the DRM.

Construction of Multi-Enzyme Integrated Catalysts for Deracemization of Cyclic Chiral Amines.

Multi-enzyme cascade catalysis has become an important technique for chemical reactions used in manufacturing and scientific study. In this research, we designed a four-enzyme integrated catalyst and used it to catalyse the deracemization reaction of cyclic chiral amines, where monoamine oxidase (MAO) catalyses the enantioselective oxidation of 1-methyl-1,2,3,4-tetrahydroisoquinoline (MTQ), imine reductase (IRED) catalyses the stereo selective reduction of 1-methyl-3,4-dihydroisoquinoline (MDQ), formate dehydrogenase (FDH) is used for the cyclic regeneration of cofactors, and catalase (CAT) is used for decomposition of oxidative reactions. The four enzymes were immobilized via polydopamine (PDA)-encapsulated dendritic organosilica nanoparticles (DONs) as carriers, resulting in the amphiphilic core-shell catalysts. The hydrophilic PDA shell ensures the dispersion of the catalyst in water, and the hydrophobic DON core creates a microenvironment with the spatial confinement effect of the organic substrate and the preconcentration effect to enhance the stability of the enzymes and the catalytic efficiency. The core-shell structure improves the stability and reusability of the catalyst and rationally arranges the position of different enzymes according to the reaction sequence to improve the cascade catalytic performance and cofactor recovery efficiency.

Vertical confinement enhances surface exploration in bacterial twitching motility.

Bacteria are often found in environments where space is limited, and they attach themselves to surfaces. One common form of movement on these surfaces is bacterial twitching motility, which is powered by the extension and retraction of type IV pili. Although twitching motility in unrestricted conditions has been extensively studied, the effects of spatial confinement on this behaviour are not well understood. In this study, we explored the diffusive properties of individual twitching Pseudomonas aeruginosa cells in spatially confined conditions. We achieved this by placing the bacteria between layers of agarose and glass, and then tracking the long-term twitching motility of individual cells. Interestingly, we found that while confinement reduced the immediate speed of twitching, it paradoxically increased diffusion. Through a combination of mechanical and geometrical analysis, as well as numerical simulations, we showed that this increase in diffusion could be attributed to mechanical factors. The constraint imposed by the agarose altered the diffusion pattern of the bacteria from normal to superdiffusion. These findings provide valuable insights into the motile behaviour of bacteria in confined environments.

Flexible CNT-based composite films with amorphous SiBCN-inhibited ultrafine SiC grains for high-temperature electromagnetic shielding

Lightweight, flexible and highly conductive electromagnetic interference (EMI) shielding materials are of great importance for protecting flexible electronics and telecommunication devices under extremely high temperature conditions. A potential solution is to incorporate ceramic phases with highly conductive flexible carbon nanotube films to improve their thermal stability. However, the grain size of the ceramic phase generally increased significantly as the temperature increased which led to brittleness. In this work, a highly flexible carbon nanotube (CNT) film with controllable ceramic nanocrystals was prepared by precursor infiltration and pyrolysis. The silicon carbide (SiC) grain size in the nanocomposites was inhibited by the spatial confinement effects of CNT networks and a second amorphous SiBCN phase. The SiC grain size in the composite film decreased with the increase of the SiBCN content and the elongation at break of the nanocomposites improved significantly by 45 %. Moreover, the initial thermogravimetric temperature of the prepared films has been significantly improved to exceed 600 °C compared to the raw CNT film. Importantly, the nanocomposite film exhibited an average EMI shielding effectiveness of ∼40 dB from 8.2 to 12.4 GHz. Benefiting from the ultrafine grain size, the nanocomposite films could be folded and extended without micro-cracks over 1000 times. Combining the performance and mechanical properties of the nanocomposite film, this approach provides important guidance for designing high-performance CNT-based electromagnetic shielding materials with superior flexibility at elevated temperatures.

Size/Shape-Controllable Carbonized Wood Electrodes Enabled by an MXene Shell with Spatial Confinement and a Traction Effect on the Wood Cell Wall for Shape-Customizable Energy Storage Devices.

The shrinkage and collapse of wood cell walls during carbonization make it challenging to control the size and shape of carbonized wood (CW) through pre- or postprocessing (e.g., sawing, cutting, and milling). Herein, a shape-adaptive MXene shell (MS) is created on the surface of the wood cell walls. The MS limits the deformation of wood cell walls by spatial confinement and traction effects, which is supported by the inherent dimensional stability of the MS and the formation of new C-O-Ti covalent bonds between the wood cell wall and MS. Consequently, the volumetric shrinkage ratio of CW encapsulated by the MS (CW-MS) is significantly reduced from 54.8% for CW to 2.6% for CW-MS even at 800 °C. The harnessing of this collapse enables the production of CW-MS with prolonged stability and high electric conductivity (384 S m-1). These properties make CW-MS suitable for energy storage devices with various designed shapes, matching the increasingly compact and complex structures of electronic devices.

Monolithic Z-scheme NiS2/In2S3@PDMS/NF gas diffusion photocatalyst with strong interfacial O2 accumulation effect for effective H2O2 production and Fenton demulsification

In this work, a monolithic NiS2/In2S3@PDMS/NF gas diffusion photocatalyst is elaborately designed and synthesized. The synergy of structure and component gives advantageous features to NiS2/In2S3@PDMS/NF, including hydrophobic hollow NiS2/In2S3@PDMS tubes and porous Ni foam for O2 confinement/enrichment, strong coupling Z-scheme heterointerface for electron-hole separation, and abundant active sites for H2O2 generation via dual-channel pathway. The monolithic NiS2/In2S3@PDMS/NF gas diffusion photocatalyst exhibits outstanding photocatalytic activity for H2O2 production in dichloromethane/water two-phase system, with a yield of 1435.4 μmol·gcat−1, which is 2.5 times higher than that of NiS2/In2S3@PDMS. This can be attributed to the synergistic effect of spatial confinement effect in hollow tubes, hydrophobic modification of catalyst surface and 3D porous breathable self-support substrate. Additionally, white solid H2O2 powder with strong oxidizing property is obtained for reducing costs and increase safety in storage and transportation. Then, a fast and universal smartphone-assisted colorimetric method is constructed to quantitatively detect H2O2 on-site. Besides, NiS2/In2S3@PDMS/NF also exhibits a remarkable demulsification effect on SDS-stabilized oil-in-water emulsion through photocatalytic-Fenton degradation of SDS with “Two Birds One Stone” strategy, which is important for petroleum industry and environmental remediation.

Spatial confinement and erbium-mediated electronic modulation for enhanced 4-nitrophenol destruction through peroxymonosulfate activation

The development of efficient strategies to modulate the electron structure of active sites in heterogeneous catalysts is crucial but remains challenging for enhancing peroxomonosulfate (PMS) activation to degrade organic contaminants. In this study, Co-Er-N-doped carbon black materials are successfully synthesized by pyrolyzing the CB@Er/Co-complex precursor. Er-doping does not enhance the defect level or graphitization degree of the carbon matrix, but rather regulates the electronic structure of Co sites, thereby generating abundant metallic Co species for activating PMS and yield increased reactive oxygen species towards 4-nitrophenol (4-NP) degradation. The optimal Er/Co@NCB-0.6 catalyst exhibits a removal efficiency of 97.9 % in 20 min. Furthermore, this catalyst exhibits broad degradation capabilities against various organic contaminants. Due to the spatial confinement effect from carbon layers, the encapsulated Co nanoparticles in the Er/Co@NCB-0.6 catalyst demonstrate excellent stability and reusability for the reaction. Radical quenching and electron paramagnetic resonance results indicate that the Er/Co@NCB-0.6/PMS system involves radical and non-radical pathways, and 1O2 and SO4•− play essential role in degrading 4-NP. The pollutant is degraded into seventeen intermediates via two plausible pathways. This study provides a valuable rare metal-mediated strategy to regulate the electronic structure of Co-based catalytic materials towards activating PMS in removing persistent organic pollutants.

Tailoring metal-support interactions via spatial confinement of Ni/CeO2 interfaces on h-BN for efficient CO2 methanation

Modulating metal-support interactions is critical for improving catalytic activity and product selectivity for CO2 hydrogenation. Such modulation can be achieved by modifying the metal nanoparticles as well as the supports. Here, we prepared a novel catalyst, in which Ni nanoparticles were dispersed on CeO2 and hexagonal boron nitride (h-BN) hybrid supports. The introduction of h-BN to Ni/CeO2-BN effectively improves the dispersion of Ni nanoparticles. More importantly, the abundant Ni-CeO2 interfacial sites with enriched oxygen vacancies are formed over h-BN edge sites. The dispersed Ni species are anchored on CeO2 via a unique interfacial structure, with electron-rich Ni (Niδ−) species. At the interfacial sites on Ni/CeO2-BN, the synergy between oxygen vacancies and Niδ−, which enhances CO2 activation and H2 dissociation, respectively, renders superior catalytic performance for CO2 methanation. In situ DRIFTS suggests formate as key rate-limiting intermediates on Ni-CeO2 sites, while the formation of B-H bonds further promotes hydrogen activation and subsequently the catalytic performance. The modulation of metal-support interactions by spatial confinement effect by BN offers a new paradigm for designing metal/oxide catalysts for chemical transformations that requires bifunctionality as CO2 hydrogenation.

Confined Pt and M (M = Fe, Co) nanoparticles on NC with ultralow Pt loading for oxygen reduction reaction

In this work, we have prepared Pt and M nanoparticles on nitrogen-doped carbon catalysts (Pt&M/NC, M = Fe, Co) with an ultralow Pt loading (<3 wt%) from room reduction of Pt and 3d transition metals by sodium borohydride on NC, where NC is firstly from pyrolysis of carbon black together with melamine. In Pt&M/NC (M = Fe, Co), Pt and 3d transition metals are in the individual nanoparticles with the size < 2 nm, where M is conducive to create the spatial confinement effect to anchor Pt nanoparticles. Meanwhile, Pt&M/NC (M = Fe, Co) has more internal defects than those of Pt/NC and M/NC. Owing to the synergistic effect of Pt and M together with NC, electrochemical results show that Pt&Co/NC has the ORR peak potential and half wave potential of 0.863 and 0.840 V vs. RHE, respectively, where they are 0.848 and 0.827 V vs. RHE for Pt&Fe/NC, more positive than that of Pt/NC. The average electron transfer number of Pt&M/NC (M = Fe, Co) is more than 3.8, close to the four-electron transfer way. This work provides a new method to reduce Pt use for ORR catalysts.

Enhancing RNA detection and breast cancer subtyping with a universal 3D-hybridization chain reaction system

Breast cancer, a globally prevalent malignancy, is characterized by pronounced heterogeneity. Accurate subtyping requires the simultaneous detection of different biomarkers, which is crucial for personalized treatment strategies. However, existing methodologies are hindered by limited versatility and sensing performance. To overcome these hurdles, this study presents a universal 3D-Hybridization Chain Reaction (3D-HCR) system for RNA detection and subtype-specific diagnosis of breast cancer. The system integrated a universal trigger for HCR, thereby circumventing the need for complex sequence design and enabling the analysis of various RNA targets. Leveraging the spatial-confinement effect offered by DNA nanocarriers, this system exhibited superior amplification efficiency, achieving detection limits of 3.83 pM and 4.96 pM for PD-L1 mRNA and miR-21, respectively. Importantly, the system could differentiate between triple-negative breast cancer and estrogen receptor-positive breast cancer in both living cells and clinical tissues. These findings underscore the potential of the universal 3D-HCR system as a promising tool in clinical diagnostics. With its proven proficiency in breast cancer diagnostics and versatility in RNA analysis, this system holds the promise of broadening the horizons of precision medicine.

Ultrahigh-Speed 3D DNA Walker with Dual Self-Protected DNAzymes for Ultrasensitive Fluorescence Detection and Intracellular Imaging of microRNA.

Herein, a dual self-protected DNAzyme-based 3D DNA walker (dSPD walker), composed of activated dual self-protected walking particles (ac-dSPWPs) and track particles (TPs), was constructed for ultrasensitive and ultrahigh-speed fluorescence detection and imaging of microRNAs (miRNAs) in living cells. Impressively, compared with the defect that "one" target miRNA only initiates "one" walking arm of the conventional single self-protected DNAzyme walker, the dSPD walker benefits from the secondary amplification and spatial confinement effect and could guide "one" target miRNA to generate "n" secondary targets, thereby initiating "n" nearby walking strands immediately, realizing the initial rate over one-magnitude-order faster than that of the conventional one. Moreover, in the process of relative motion between ac-dSPWPs and TPs, the ac-dSPWPs could cleave multiple substrate strands simultaneously to speed up movement and reduce the derailment rate, as well as combine with successive TPs to facilitate a large amount of continuous signal accumulation, achieving an ultrafast detection of miRNA-221 within 10 min in vitro and high sensitivity with a low detection limit of 0.84 pM. In addition, the DNA nanospheres obtained by the rolling circle amplification reaction can capture the Cy5 fluorescence dispersed in liquids, which achieves the high-contrast imaging of miRNA-221, resulting in further ultrasensitive imaging of miRNA-221 in cancer cells. The proposed strategy has made a bold innovation in the rapid and sensitive detection as well as intracellular imaging of low-abundance biomarkers, offering promising application in early diagnosis and relevant research of cancer and tumors.

An Oxidative Cleavage-Based Cruciform DNA Nanostructure for In Vivo Hypochlorous Acid Visualization to Monitor Intestinal Inflammation.

Ulcerative colitis is a persistent inflammatory bowel disease characterized by inflammation and ulceration in the colon and gastrointestinal tract. It was indicated that the generation of hypochlorous acid (HClO) through the enzymatic activity of myeloperoxidase is significantly linked to ulcerative colitis. In this study, by assembling two hairpins (Hpa and Hpb) onto a quadrivalent cruciform DNA nanostructure, a novel HClO-activatable fluorescent probe was developed based on DNA nanomaterials (denoted MHDNA), which is sensitive, economic, simple, and stable. In the presence of HClO, the Trigger (T) was liberated from the MHDNA probe through a hydrolysis reaction between HClO and phosphorothioate (PS), which is modified on the MHDNA probe and has proved to exhibit particular susceptibility to the HClO. The liberated T subsequently initiated the opening of Hpa and Hpb to facilitate the catalyzed hairpin assembly (CHA) reaction, resulting in the changes of fluorescence and releasing T for recycled signal amplification to achieve sensitive detection of HClO (with a limit of detection 9.83 nM). Additionally, the MHDNA-based spatial-confinement effect shortens the physical distance between Hpa and Hpb and yields a high local concentration of the two reactive hairpins, achieving more rapid reaction kinetics in comparison to conventional CHA methods. Inspirationally, the MHDNA probe was effectively utilized for imaging HClO in ulcerative colitis mice, yielding valuable diagnostic insights for ulcerative colitis.

2D/1D nested hollow porous ZnIn2S4/g-C3N4 heterojunction based on morphology modulation for photocatalytic CO2 reduction

The two-dimensional (2D) composite one-dimensional (1D) heterojunction structure is one of the main strategies for constructing composite photocatalysts for photocatalytic reduction of carbon dioxide (CO2). However, morphology modulation for 2D/1D heterojunction is an important way to enhance performance. In this study, a unique 2D/1D ZnIn2S4/g-C3N4 nested hollow porous heterojunction structure was constructed by an in-situ growth method with spatial confinement effect. The synergy between 1D g-C3N4 and 2D ZnIn2S4, achieved through advanced morphology modulation at an optimal ratio of 3:1, results in the formation of the CZ-3 photocatalyst. This unique configuration enables a simultaneous high yield of carbon monoxide (CO) and methane (CH4), achieving 79.96 μmol/g and 17.33 μmol/g respectively, under visible light irradiation without the need for sacrificial agents. The core of this enhanced photocatalytic performance is attributed to the employment of a type-II heterojunction mechanism, which optimizes the transfer of photogenerated carriers. Ultraviolet-visible diffuse reflection spectrum, photoluminescence spectrum and photoelectrochemical analysis reveal the effect of morphology on photocatalytic performance in terms of visible light absorption, photogenerated carrier pairs separation and electronic band structure of heterojunction. By combining the advantages of 2D/1D structural benefits with the efficient charge dynamics of a type-II heterojunction, this work provides new ideas for improving the morphology of composite heterojunction photocatalysts with 2D/1D structure to enhance the photocatalytic CO2 reduction performance.

Space confinement effect of carbon nanotube-alumina strip support on the Cu-Co catalysts for CO2 methanation

The present work reported the space confinement effect of carbon nanotube-alumina strip (CAS) support on the Cu-Co bimetallic catalyst or the single Cu, Co catalysts for the CO2 methanation. CAS, made by extrusion of nanotubes and Al-based sol and high temperature calcination, was a macroscopic support with sufficient mesopores and hydrophobic property. Cu-Co/CAS catalysts exhibited high catalytic activity for methanation of CO2 (H2/CO2=3:1), where CO2 conversion was 49.62% and CH4 selectivity was 95.98% at temperature as low as 250 ℃ and 1.5 MPa, and showed advantage significantly over those with the supports of individual nanotube or pure Alumina support. The comparison suggested the hydrophobicity of carbon nanotubes can effectively remove water from the metal active sites, enhancing the equilibrium of reverse water gas shift and CO methanation reactions, as compared to alumina support. Additionally, CAS support had a spatial confinement effect that increased the contact time of CO2 or intermediates with the active sites, compared with individual nanotube support. XPS and Raman spectroscopy validated the presence of oxygen vacancies of CAS, promoting the CO2 methanation. H2-TPR results, in combination with DFT calculations, confirmed that the CAS supports enabled the Cu-Co active phase by changing their electronic structures, to possess a strong adsorption activation capacity for H2 at low temperatures with high performance for CO2 methanation.