High-performance natural-sunlight-driven Ag/AgCl photocatalysts with a cube-like morphology and blunt edges via a bola-type surfactant-assisted synthesis.

Ag/AgCl-based structures have recently been receiving considerable attention as visible-light-driven plasmonic photocatalysts, wherein the fabrication of Ag/AgCl species shaped with an anisotropic morphology is considered to be an efficient way to enhance their performances. While the past decade has witnessed great progress in this direction, it is still strongly desired to initiate a green and low-cost protocol for the synthesis of Ag/AgCl based structures with high catalytic activity. Using a surfactant-assisted synthesis protocol, wherein a cationic bola-type surfactant of chloride counteranions serves both as a reactant (namely, source of chlorine) for the generation of AgCl structures and as a directing template to assist the formation of anisotropic structures, we herein report that cube-like Ag/AgCl with blunt edges could be fabricated simply by dropping an aqueous solution of silver nitrate into an ethanol solution of the hexane-1,6-bis(trimethylammonium chloride) surfactant. Importantly, compared to the sphere-like counterparts manufactured using a conventional tadpole surfactant, the as-fabricated cube-like structures exhibit substantially improved catalytic performances under visible-light or natural-sunlight irradiation. It has been revealed that photogenerated holes might serve as the main active species during the catalytic process. Meanwhile, our results have disclosed that in contrast to the sphere-like Ag/AgCl structures, the as-constructed cube-like structures are relatively enriched with high-index AgCl facets of smaller hole effective mass, which promote a faster carrier transfer, facilitate the migration of the photogenerated holes to the surface to be involved in photocatalytic reactions, and suppress carrier recombination, leading to their enhanced photocatalytic performances. Considering the tremendous diversity of surfactants (bola-, gemini-, polymeric surfactants etc.) with various halide counteranions and their sophisticated template effects, our new strategy might open up new opportunities for silver/silver halide (Ag/AgX, X = Cl, Br, and I)-based plasmonic structures with various morphologies and with superior light-to-chemical energy conversion capability.

Sub-10 nm Ag Nanoparticles/Graphene Oxide: Controllable Synthesis, Size-Dependent and Extremely Ultrahigh Catalytic Activity.

While tremendous advancements in Ag nanoparticle (AgNP)-based materials have been made, the development of a facile protocol for preparing sub-10 nm AgNPs with controllable size and ultrahigh performance remains a formidable challenge. It is shown that AgNPs/graphene oxide (AgNPs/GO) bearing 2.5, 4.3, and 6.2 nm AgNPs (2.5-AgNPs/GO, 4.3-AgNPs/GO, and 6.2-AgNPs/GO, respectively) could be fabricated via light-induced synthesis. Their catalytic activity toward 4-nitrophenol (4-NP) reduction, which is a "gold standard" for evaluating the performance of noble metal-based catalysts, is studied. When normalized by mole and area, the activity exhibits an order of 4.3-AgNPs/GO > 6.2-AgNPs/GO > 2.5-AgNPs/GO and 6.2-AgNPs/GO > 4.3-AgNPs/GO > 2.5-AgNPs/GO, respectively. This trend is a result of GO-induced electron concentration reduction with decreasing AgNP size. Significantly, under similar conditions, the activity of 4.3-AgNPs/GO is substantially superior to that of numerous state-of-the-art noble metal-based catalysts. The ultrafine size of the AgNPs and their surface accommodation on the unobstructed 2D GO scaffolds without capping reagents/covers, which make the abundantly exposed catalytically active sites highly accessible to substrate molecules, play an important role in their extremely ultrahigh performance. This work paves a new avenue for high-performance AgNP-based materials, and by taking 4-NP reduction as a proof-of-concept, provides new scientific insights into the rational design of surface-based advanced materials.

Platinized spherical supramolecular nanoassemblies of a porphyrin: facile synthesis and excellent catalytic recyclability.

Porphyrin-based supramolecular nanoassemblies of a spherical morphology have been attracting broad interest owing to their wide application possibilities in numerous fields of paramount significance. Most of the existing assembly protocols, however, either suffer from the requirement of elaborately-designed yet tediously-synthesized ad hoc porphyrins, the use of surfactant templates, or accurate consideration of the experimental parameters etc. The initiation of a facile surfactant-free fabrication protocol performable under ambient conditions using commercial porphyrins as building blocks is strongly desired. We herein report that a commercial metal-free porphyrins, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TPPNH2), could be facilely organized to form well-defined discrete spherical nanoassemblies at room temperature by means of a simple reprecipitation method. We further find that the as-manufactured TPPNH2 nanospheres could work as photocatalysts towards the reduction of potassium tetrachloroplatinate(ii), leading to their self-platinization and the production of platinum/porphyrin nanosphere nanocomposites, wherein ultrathin Pt nanoparticles of a size of ca. 3 nm are immobilized on the porphyrin nanospheres. Significantly, by taking the advantage of their easy sedimentation from aqueous suspensions, we show that the as-produced composites could serve as qualified heterogeneous nanocatalysts in terms of their excellent catalytic stability and recyclability towards the reduction of 4-nitrophenol, where the catalytic reactivity exhibits only trivial changes even after the reactions have been repeated 8 times continuously. Taking into account the general concerns of porphyrins- and Pt-based nanostructures, this might provide a facile method for the construction of spherical porphyrin nanostructures with self-platinization capability. Meanwhile, considering the high cost and scarcity of Pt, our nanocomposites with excellent stability and recyclability likely have a bright future of potential uses.

Sheet-like and truncated-dodecahedron-like AgI structures via a surfactant-assisted protocol and their morphology-dependent photocatalytic performance.

Silver halide-based structures have been attracting great interest as efficient visible-light-driven photocatalysts towards the photodegradation of organic pollutants, and those studies focusing on their morphology-dependent catalytic performances have received particular attention. While great advancements in this regard have been witnessed in the past few years with respect to AgCl- and AgBr-based photocatalysts, relevant explorations concerning AgI-based species are relatively rare, even though the excellent durability of AgI-based structures renders them attractive candidates for potential photocatalytic uses. By means of chemical reactions between AgNO3 and tetramethylammonium iodide (TMAI), and AgNO3 and tetrabutylammonium iodide (TBAI), we herein report that AgI structures with a sheet-like and a truncated-dodecahedron-like morphology, respectively, could be controllably synthesized via a surfactant-assisted fabrication protocol. In our synthesis systems, AgNO3 works as the silver source, while the TMAI and TBAI surfactants serve not only as an iodine source but also as a directing reagent for controllable fabrication. It has been demonstrated that our AgI structures could work as visible-light-energized photocatalysts towards the photodegradation of methyl orange. We find that compared to their sheet-like counterparts, the truncated-dodecahedron-like AgI architectures exhibit substantially boosted catalytic performances. Moreover, we disclose that our truncated-dodecahedron-like AgI-based species could display excellent photocatalytic stability, wherein their catalytic reactivity displays only trivial fluctuations under visible-light irradiation even after the photoreactions have been repeated 22 times continuously. Our work might not only introduce a facile protocol for the controllable synthesis of AgI structures but also pave an avenue for facile enhancement of their catalytic performances via morphology alterations.

Shape-Controlled Metal-Free Catalysts: Facet-Sensitive Catalytic Activity Induced by the Arrangement Pattern of Noncovalent Supramolecular Chains.

Metal-free catalytic materials have recently received broad attention as promising alternatives to metal-involved catalysts. This is owing to their inherent capability to overcome the inevitable limitations of metal-involved catalysts, such as high sensitivity to poisoning, the limited reserves, high cost and scarcity of metals (especially noble metals), etc. However, the lack of shape-controlled metal-free catalysts with well-defined facets is a formidable bottleneck limiting our understandings on the underlying structure-activity relationship at atomic/molecular level, which thereby restrains their rational design. Here, we report that catalytically active crystals of a porphyrin, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, could be shaped into well-defined cubes and sheet-like tetradecahedrons (TDHD), which are exclusively and predominantly enclosed by {101} and {001} facets, respectively. Fascinatingly, compared to the cubes, the TDHDs display substantially enhanced catalytic activity toward water decontamination under visible-light irradiation, although both the architectures have identical crystalline structure. We disclose that such interesting shape-sensitive catalytic activity is ascribed to the distinct spatial separation efficiency of photogenerated electrons and holes induced by single-channel and multichannel charge transport pathways along noncovalent supramolecular chains, which are arranged as parallel-aligned and 2D network patterns, respectively. Our findings provide an ideal scientific platform to guide the rational design of next-generation metal-free catalysts of desired catalytic performances.