A novel molecularly expanded covalent triazine framework heterojunction with significantly enhanced molecular oxygen activation and photocatalysis performance under visible light.

The activation capacity of molecular oxygen is an important indicator to evaluate the photocatalytic efficiency of photocatalysts. In this paper, WS2 nanosheet was deposited on hyper-crosslinked CTF-1-G (obtained by molecular expansion from covalent triazine framework CTF-1) to form a C-GW heterojunction, which promoted the photodegradation of pollutants and the activation of molecular oxygen. This novel C-GW heterojunction exhibited excellent degradation property for organic pollutants (tetracycline (TC), rhodamine B (RhB)) and activating molecular oxygen under visible light irradiation. Among them, C-GW15 could degrade 98% of 20 ppm TC in 60 min and 99% of 30 ppm RhB in 30 min, and it had the highest hydrogen generation rate and hydrogen production amount in 4 hours, which were 8.74 mmol h-1 g-1 and 34.94 mmol g-1, respectively. Meanwhile, C-GW15 had the strongest 3,3',5,5'-tetramethylbenzidine oxidation capacity and could generate 1.83 µmol of ˙O2- in 60 min and the production of H2O2 was 20.8 µmol L-1 in 40 min. The results of this study clearly indicated that the combination of WS2 and CTF-1-G can enhance the visible light absorption capacity and photogenerated carrier separation efficiency, thus promoting the photocatalytic performance. Finally, a Z-type photocatalytic mechanism was proposed based on radical capture, molecular oxygen activation experiments and electron spin resonance analysis. These findings will extend the fundamental understanding of the Z-type photocatalytic mechanism and provide new opportunities for the rational design of CTF heterojunctions for the treatment of environmental pollution and clean energy conversion.

MOF-derived CdS/CoO S-type heterojunctions for improving the efficiency of photocatalytic evolution.

The aggravating extreme climate changes and environmental pollution problems have stimulated the exploration of green alternatives to conventional fossil fuels and green environmental treatments. Photocatalysis is recognized as an outstanding green tool for solving the energy crisis and environmental rehabilitation issues. Restricted by the high cost of precious metals, researchers expect to obtain low-cost, efficient and stable photocatalysts. Herein, CdS materials were derived through MOFs and subsequently combined with CoO to form CdS/CoO heterojunctions. The catalytic ability was evaluated by the photocatalytic degradation of tetracycline hydrochloride (TC) and the photocatalytic production of hydrogen. With the integration of CoO, in terms of TC degradation, CdS/CoO heterojunctions can degrade over 90% of TC within 1 hour. In terms of hydrogen production, compared to CdS alone, the hydrogen production efficiency of the CdS/CoO heterojunction increased by 1.7 times. The initial analysis of the reasons for the enhancement of photocatalytic efficiency was conducted by TEM, XPS and other characterization means. Density functional theory (DFT) calculations verified the existence of a built-in electric field in the CdS/CoO heterojunction, which was the essential reason for the improved catalytic performance, and finally, the presence of ˙O2- and ˙OH in the photocatalytic system was demonstrated by the ESR technique. Based on the carrier separation/transfer pathway in the heterojunction, a simple and novel S-type heterojunction scheme was proposed.

Construction of a direct Z-scheme CeO2/UiO-66-NH2 heterojunction for boosting photocatalytic organic pollutant degradation and H2 evolution performance.

In this study, hollow CeO2 nanospheres were grown on UIO-66-NH2 nanosheets to form a novel CeO2/UiO-66-NH2 (abbreviation, CUx) Z-scheme heterojunction photocatalyst by calcination and hydrothermal method for hydrogen production and photocatalytic degradation of organic pollutants. Under visible light, the H2 generation rate of the CU0.50 composite was 5662.1 µmol g-1 h-1, which was 22 and 7 fold than that of pure CeO2 and pure UiO-66-NH2, respectively. In addition, compared with CeO2 and UiO-66-NH2, the as-prepared CUx composites exhibited enhanced photo-degradation efficiencies for tetracycline (TC) and 2,4-dichlorophenol (DCP) under simulated solar light irradiation. Among them, the CU0.50 composite demonstrated the highest photocatalytic performance and reached 91.5% for TC, and 94.3% for DCP. In addition, a logical solid-state Z-type electron transfer mechanism is presented with the results of radical scavenging and ESR experiments to illustrate the intensive decomposed ability of the photocatalytic system. The enhanced photocatalytic performance of CUx heterostructures can be attributed to the formation of a band-position-matched hollow structure heterojunction between CeO2 and UIO-66-NH2, which can effectively inhibit the recombination of carriers and increase the specific surface area as well as the light absorption. Moreover, the oxidation and reduction ability of the charge carriers was also increased. This work resulted in a feasible idea for removing organic pollutants and hydrogen production by traditional inorganic semiconductor/MOF-based heterostructured photocatalysts.

Enhanced photocatalytic performance over PANI/NH2-MIL-101(Fe) with tight interfacial contact.

Constructing a suitable heterojunction structure while maintaining a tight interface to promote the separation of photogenerated electrons is of great significance for improving the photocatalytic activity. In this paper, a new PANI/NH2-MIL-101(Fe) II-scheme heterojunction was prepared by a hydrothermal method. PANI with a porous structure was firstly obtained by the template method, and then PANI fragments were loaded on the surface of NH2-MIL-101(Fe) crystals under hydrothermal conditions to obtain a PANI/NH2-MIL-101(Fe) photocatalyst. The photocatalytic degradation of TC under simulated sunlight can reach 90% within an hour, and the maximum hydrogen evolution rate is 7040 µmol g-1 h-1 under visible light. The enhanced catalytic performance of PANI/NH2-MIL-101(Fe) was attributed to the appropriate matching of the VB and CB of PANI and NH2-MIL-101(Fe), and secondly, the coordination bonds formed between PANI and NH2-MIL-101(Fe) provided a channel for charge separation and transfer. Finally, a possible mechanism of the photocatalytic system was proposed through a free radical capture experiment and characterization analysis. More importantly, the experiment proved that the heterojunction formed by PANI and NH2-MIL-101(Fe) can achieve the effect of complementing each other, which provides a feasible idea and method for the design of efficient heterojunction photocatalysts.

Bridging multimedia heterogeneity gap via Graph Representation Learning for cross-modal retrieval.

Information retrieval among different modalities becomes a significant issue with many promising applications. However, inconsistent feature representation of various multimedia data causes the "heterogeneity gap" among various modalities, which is a challenge in cross-modal retrieval. For bridging the "heterogeneity gap," the popular methods attempt to project the original data into a common representation space, which needs great fitting ability of the model. To address the above issue, we propose a novel Graph Representation Learning (GRL) method for bridging the heterogeneity gap, which does not project the original feature into an aligned representation space but adopts a cross-modal graph to link different modalities. The GRL approach consists of two subnetworks, Feature Transfer Learning Network (FTLN) and Graph Representation Learning Network (GRLN). Firstly, FTLN model finds a latent space for each modality, where the cosine similarity is suitable to describe their similarity. Then, we build a cross-modal graph to reconstruct the original data and their relationships. Finally, we abandon the features in the latent space and turn into embedding the graph vertexes into a common representation space directly. During the process, the proposed Graph Representation Learning method bypasses the most challenging issue by utilizing a cross-modal graph as a bridge to link the "heterogeneity gap" among different modalities. This attempt utilizes a cross-modal graph as an intermediary agent to bridge the "heterogeneity gap" in cross-modal retrieval, which is simple but effective. Extensive experiment results on six widely-used datasets indicate that the proposed GRL outperforms other state-of-the-art cross-modal retrieval methods.

A water stable layered Tb(iii) polycarboxylate with high proton conductivity over 10-2 S cm-1 in a wide temperature range.

An unprecedented Tb(iii) polycarboxylate, {[Tb4(TTHA)2(H2O)4]·7H2O}n (1), has been synthesized. It possesses an efficient proton transfer pathway formed by water molecules and carboxyl groups, which exhibits proton conductivity over 10-2 S cm-1 at 295-358 K and 98% relative humidity.

Two novel organic phosphorous-based MOFs: synthesis, characterization and photocatalytic properties.

Two novel metal-organic framework (MOF) photocatalysts with different structures [(Cu(H2L)(4,4'-bipy)0.5(H2O)] (1) and [Co(C14H14O6.5P2)(4,4'-bipy)0.5(H2O)2]·H2O (2) were synthesized using a hydrothermal method using a phosphonate ligand [H4L = 1,1'-biphenylene-4,4'-bis(methylene)-bis(phosphonic acid)] and 4,4'-bipyridine ligand. All the samples were characterized by elemental analysis, thermal analysis, and single crystal X-ray diffraction. As novel porous materials, the two complexes showed active performance for the reduction of Cr(vi) to Cr(iii) and the photodegradation of methylene blue (MB) dye in aqueous solution under UV light. Control experiments showed that the pH value was vital for Cr(vi) reduction, meanwhile, the use of a hole scavenger of methanol promoted the photocatalytic reduction significantly. It was also demonstrated that complexes 1 and 2 were efficient for the degradation of MB. Moreover, the possible reaction mechanism of the reaction was also investigated in detail. Finally, the cyclic experiments indicated the two photocatalysts were stable and reusable, enabling them to be potential candidates for use in environment governance.

Two pure MOF-photocatalysts readily prepared for the degradation of methylene blue dye under visible light.

Two 3D metal-organic frameworks (MOFs) with different structures, [Cu(4,4'-bipy)Cl]n (1) and [Co(4,4'-bipy)·(HCOO)2]n (2), were synthesized by means of a hydrothermal method using a typical ligand (4,4'-bipyridine), and characterized by elemental analyses, thermal analyses and single crystal X-ray diffraction. As MOF materials, the two complexes showed active performance for the photodegradation of methylene blue (MB) dye under visible light. MB degradation over the two MOF-based photocatalysts follows first-order kinetics. The addition of an H2O2 electron acceptor can markedly enhance the photocatalytic MB degradation performance via a ligand-to-metal charge transfer mechanism, especially in complex 1. Complex 1 is better than complex 2 in MB photodegradation performance under the same conditions. Moreover, complex 1 showed a stable activity for MB degradation after four consecutive usages. Owing to the advantages of the visible light response, stable structure, low cost and high yield, these MOF-based photocatalysts will facilitate new efforts in environmental purification.