Heterogeneous catalysts have been widely used for photocatalysis, which is a highly important process for energy conversion, owing to their merits such as easy separation of catalysts from the ...reaction products and applicability to continuous chemical industry and recyclability. Yet, homogenous photocatalysis receives tremendous attention as it can offer a higher activity and selectivity with atomically dispersed catalytic sites and tunable light absorption. For this reason, there is a major trend to combine the advantages of both homogeneous and heterogeneous photocatalysts, in which coordination chemistry plays a role as the bridge. In this article, we aim to provide the first systematic review to give a clear picture of the recent progress from taking advantage of coordination chemistry. We specifically summarize the role of coordination chemistry as a versatile tool to engineer catalytically active sites, tune light harvesting and maneuver charge kinetics in heterogeneous photocatalysis. We then elaborate on the common fundamentals behind various materials systems, together with key spectroscopic characterization techniques and remaining challenges in this field. The typical applications of coordination chemistry in heterogeneous photocatalysis, including proton reduction, water oxidation, carbon dioxide reduction and organic reactions, are highlighted.
This review elucidates the roles of coordination chemistry in the design of heterogeneous photocatalysts, which can engineer catalytically active sites, tune light harvesting and maneuver charge kinetics.
Sonochemical synthesis of nanomaterials Xu, Hangxun; Zeiger, Brad W; Suslick, Kenneth S
Chemical Society reviews,
2013-Apr-07, Volume:
42, Issue:
7
Journal Article
Peer reviewed
Open access
High intensity ultrasound can be used for the production of novel materials and provides an unusual route to known materials without bulk high temperatures, high pressures, or long reaction times. ...Several phenomena are responsible for sonochemistry and specifically the production or modification of nanomaterials during ultrasonic irradiation. The most notable effects are consequences of acoustic cavitation (the formation, growth, and implosive collapse of bubbles), and can be categorized as primary sonochemistry (gas-phase chemistry occurring inside collapsing bubbles), secondary sonochemistry (solution-phase chemistry occurring outside the bubbles), and physical modifications (caused by high-speed jets or shock waves derived from bubble collapse). This tutorial review provides examples of how the chemical and physical effects of high intensity ultrasound can be exploited for the preparation or modification of a wide range of nanostructured materials.
Two-dimensional (2D) covalent organic frameworks (COFs) are promising metal-free materials for photocatalytic water splitting because of their high surface area and predictability to assemble various ...molecules with tunable electronic properties. Unfortunately, 2D COFs capable of visible-light-driven photocatalytic overall water splitting are rare, partly due to rigorous requirements to their band alignments and coexistence of catalytic sites for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, 12 2D nitrogen-linked COFs are designed based on first-principles calculations and topological assembly of molecular segments with catalytic activities toward either HER or OER, respectively. The electronic band structures calculated with HSE06 method indicate that 2D COFs are semiconductors with a widely tunable bandgap ranging from 1.92 to 3.23 eV. The positions of both conduction and valence band edges of nine 2D COFs match well with the chemical reaction potential of H2/H+ and O2/H2O, which are capable of photocatalytic overall water splitting. Of particular importance is that three of them based on 2,4,6-tris(4-methylphenyl)-1,3,5-triazine (TST) can split water into hydrogen and oxygen under visible light. Our results agree with respect to the literature, with three of them having been studied for photocatalytic HER or CO2 reduction. In addition, we further experimentally demonstrate that I-TST presents both HER and OER activity under visible light. Our findings present a route to design practical 2D COFs as metal-free and single-material photocatalysts for overall water splitting under visible light.
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Extensive efforts have been devoted to synthesizing photothermal agents (PTAs) that are active in the first near-infrared (NIR) region (650–950 nm). However, PTAs for photothermal therapy in the ...second NIR window (1000–1350 nm) are still rare. Here, it is shown that two-dimensional ultrathin polypyrrole (PPy) nanosheets prepared via a novel space-confined synthesis method could exhibit unique broadband absorption with a large extinction coefficient of 27.8 L g–1 cm–1 at 1064 nm and can be used as an efficient PTA in the second NIR window. This unique optical property is attributed to the formation of bipolaron bands in highly doped PPy nanosheets. The measured prominent photothermal conversion efficiency could achieve 64.6%, surpassing previous PTAs that are active in the second NIR window. Both in vitro and in vivo studies reveal that these ultrathin PPy nanosheets possess good biocompatibility and notable tumor ablation ability in the second NIR window. Our study highlights the potential of ultrathin two-dimensional polymers with unique optical properties in biomedical applications.
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Converting solar energy into storable and transportable chemical fuels using artificial photosynthetic systems can provide an alternative route to the current unsustainable use of fossil fuels, ...addressing the worldwide energy crisis and environmental issues. Recently, semiconducting polymers have emerged as a very promising class of photocatalysts for water splitting as their electronic and structural properties can be conveniently controlled and systematically designed at a molecular level. Among the various polymer photocatalysts that are reported so far, 2D polymer nanosheets are particularly interesting and gaining more attention. The 2D planar structure offers unique features such as high surface area, abundant surface active sites, efficient charge separation, and facile formation of heterostructures. The design and synthesis of 2D polymer nanosheets have greatly advanced the research in photocatalytic overall water splitting. Here, recent advances in developing photocatalysts based on 2D polymer nanosheets for photocatalytic overall water splitting are highlighted. Specifically, the existing approaches to tune their electronic structures and surface active sites for photocatalysis are discussed. Future opportunities and challenges for developing 2D polymers for photocatalytic overall water splitting are also included.
2D polymer nanosheets have received increasing attention in converting solar energy into chemical fuels due to their tunable electronic and optical properties. Recent progress in developing heterogeneous photocatalysts based on polymer nanosheets for overall water splitting is reviewed. 2D polymer nanosheets are shown to be very promising for solar fuel generation using sunlight as the only energy input.
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Inspired by natural photosynthesis, Z‐scheme photocatalytic systems are very appealing for achieving efficient overall water splitting. Developing metal‐free Z‐scheme photocatalysts for overall water ...splitting, however, still remains challenging. The construction of polymer‐based van der Waals heterostructures as metal‐free Z‐scheme photocatalytic systems for overall water splitting is described using aza‐fused microporous polymers (CMP) and C2N ultrathin nanosheets as O2‐ and H2‐evolving catalysts, respectively. Although neither polymer is able to split pure water using visible light, a 2:1 stoichiometric ratio of H2 and O2 was observed when aza‐CMP/C2N heterostructures were used. A solar‐to‐hydrogen conversion efficiency of 0.23 % was determined, which could be further enhanced to 0.40 % by using graphene as the solid electron mediator to promote the interfacial charge‐transfer process. This study highlights the potential of polymer photocatalysts for overall water splitting.
After all, you're my van der Waal: A metal‐free Z‐scheme photocatalytic system was prepared for efficient overall water splitting. 2D van der Waals heterostructures composed of ultrathin polymer nanosheets facilitate charge separation and consequently enhance the lifetime and density of photogenerated excitons.
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Harnessing solar energy to generate hydrogen peroxide (H2O2) from H2O and O2 via artificial photosynthesis is an attractive route, as this approach only uses sunlight as the energy input. Organic ...polymers have emerged as a promising class of materials for solar-driven H2O2 production, owing to their virtually unlimited molecular building blocks and rich bond-forming reactions. This distinctive feature leads to the existence of different reaction pathways characterized by different electron transfer numbers. For the overall photosynthesis of H2O2, the O2 reduction reaction and the H2O oxidation reaction must occur concurrently. Thus, in-depth insights into these reaction pathways are crucial for solar-driven H2O2 production, with the eventual aim of steering these pathways to optimize efficiency. In this perspective, we primarily focus on the state-of-the-art progress in developing polymer photocatalysts for the overall photosynthesis of H2O2 via coupling different O2 reduction and H2O oxidation reactions. We also present key challenges and opportunities in developing polymer photocatalysts for H2O2 production in the future. Organic polymers offer an ample molecular-level design space. They have now found extensive applications in solar-driven photochemical reactions. Therefore, this perspective serves as a guideline for designing polymer photocatalysts toward sustainable photosynthesis of H2O2 and has significant implications for the future development of polymer materials in the broad area of solar-to-chemical energy conversion research.
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Metal‐free polymer photocatalysts have shown great promise for photocatalytic H2O2 production via two‐electron reduction of molecular O2. The other half‐reaction, which is the two‐electron oxidation ...of water, still remains elusive toward H2O2 production. However, enabling this water oxidation pathway is critically important to improve the yield and maximize atom utilization efficiency. It is shown that introducing acetylene (CC) or diacetylene (CCCC) moieties into covalent triazine frameworks (CTFs) can remarkably promote photocatalytic H2O2 production. This enhancement is inherent to the incorporated carbon–carbon triple bonds which are essential in modulating the electronic structures of CTFs and suppressing charge recombinations. Furthermore, the acetylene and diacetylene moieties can significantly reduce the energy associated with OH* formation and thus enable a new two‐electron oxidation pathway toward H2O2 production. The study unveils an important reaction pathway toward photocatalytic H2O2 production, reflecting that precise control over the chemical structures of polymer photocatalysts is vital to achieve efficient solar‐to‐chemical energy conversion.
Covalent triazine frameworks incorporated with acetylene and diacetylene moieties exhibit a unique two‐electron water oxidation pathway toward H2O2 production in addition to the two‐electron oxygen reduction pathway. Both experimental and theoretical investigations reveal that carbon–carbon triple bonds are critical to modulate the electronic structures and provide active sites for photocatalytic H2O2 production.
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Two-dimensional covalent organic frameworks (2D COFs) featuring periodic frameworks, extended π-conjugation and layered stacking structures, have emerged as a promising class of materials for ...photocatalytic hydrogen evolution. Nevertheless, the layer-by-layer assembly in 2D COFs is not stable during the photocatalytic cycling in water, causing disordered stacking and declined activity. Here, we report an innovative strategy to stabilize the ordered arrangement of layered structures in 2D COFs for hydrogen evolution. Polyethylene glycol is filled up in the mesopore channels of a β-ketoenamine-linked COF containing benzothiadiazole moiety. This unique feature suppresses the dislocation of neighbouring layers and retains the columnar π-orbital arrays to facilitate free charge transport. The hydrogen evolution rate is therefore remarkably promoted under visible irradiation compared with that of the pristine COF. This study provides a general post-functionalization strategy for 2D COFs to enhance photocatalytic performances.
Two‐dimensional covalent organic frameworks (2D COFs), an emerging class of crystalline porous polymers, have been recognized as a new platform for efficient solar‐to‐hydrogen energy conversion owing ...to their pre‐designable structures and tailor‐made functions. Herein, we demonstrate that slight modulation of the chemical structure of a typical photoactive 2D COF (Py‐HTP‐BT‐COF) via chlorination (Py‐ClTP‐BT‐COF) and fluorination (Py‐FTP‐BT‐COF) can lead to dramatically enhanced photocatalytic H2 evolution rates (HER=177.50 μmol h−1 with a high apparent quantum efficiency (AQE) of 8.45 % for Py‐ClTP‐BT‐COF). Halogen modulation at the photoactive benzothiadiazole moiety can efficiently suppress charge recombination and significantly reduce the energy barrier associated with the formation of H intermediate species (H*) on polymer surface. Our findings provide new prospects toward design and synthesis of highly active organic photocatalysts toward solar‐to‐chemical energy conversion.
A series of isostructural Py‐XTP‐BT‐COFs (X=H, F, Cl) are systematically investigated as the catalysts for photocatalytic H2 production under visible light irradiation. The halogen modulation of Py‐HTP‐BT‐COFs realizes effective regulation of proper electronic structures, boosting the photo‐charge separation and reduction of the energy barrier for achieving highly efficient H2 production.
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