Colloidal Polydopamine Beads: A Photothermally Active Support for Noble Metal Nanocatalysts

Abstract

Polydopamine (PDA) is a unique bioinspired synthetic polymer that integrates broadband light absorption, efficient photothermal transduction, and versatile surface-adhesion functions in a single material entity. Here, we utilize colloidal PDA beads in the submicron particle size regime as an easily processable and photothermally active support for sub-10 nm Pd nanocatalysts to construct a multifunctional material system that allows us to kinetically boost thermal catalytic reactions through visible and near-infrared light illuminations. Choosing the Pd-catalyzed nitrophenol reduction by ammonium formate as a model transfer hydrogenation reaction exhibiting temperature-dependent reaction rates, we demonstrate that interfacial molecule-transforming processes on metal nanocatalyst surfaces can be kinetically modulated by harnessing the thermal energy produced through photothermal transduction in the PDA supports.

Pt, Pd, and Rh Nanoparticles Supported on Polydopamine Nanospheres as Catalysts for Transfer Hydrogenolysis

“…The PDA-supported Pt, Pd, and Rh nanocatalysts exhibited strikingly different behaviors when catalyzing the transfer of hydrogen from the hydrogen donors (FA or AF) to the hydrogen-accepting substrate molecules, MO. Noble metal nanoparticles can catalyze the dehydrogenation of FA and AF to produce CO 2 , ,,, and the hydrogen released from FA and AF can be utilized to chemoselectively hydrogenate the azo bond in MO, which eventually leads to the formation of 4-aminobenzenesulfonate and 4- N , N -dimenthylaminobenzene upon the cleavage of the azo bond ,, (see schematic illustrations in Figure A,B). Therefore, the overall molecule-transforming process is essentially a hydrogenolysis process involving a catalytic transfer hydrogenation reaction further coupled with bond cleavage.…”

“…32 This PDA-mediated colloidal synthesis approach could also be adopted to synthesize PDA-supported nanocatalysts composed of other non-Pt noble metal elements. 33 In this work, we focus on the comparative studies of Pt, Pd, and Rh, which constitute the palladium-group platinum-group (PPG) noble metal family. The three PPG metal elements, which are arranged right next to each other in the periodic table, not only share the same face-centered cubic (fcc) crystalline structure with closely matched lattice parameters but are also expected to exhibit similar chemical characteristics.…”

“…Nanoparticles made of noble metal elements constitute a family of catalyst materials that are highly active and durable in catalyzing a variety of important chemical and electrochemical reactions. − Use of sub-5 nm nanoparticulate catalysts with high surface-to-volume ratios provides an effective way to mitigate the cost issues associated with noble metal-driven heterogeneous catalysis. As the size of a metallic nanoparticle varies within the sub-5 nm window, a series of structural characteristics and physicochemical properties, such as the electronic band energies, local surface curvature, and surface atomic coordination, may change drastically, giving rise to intriguing size-dependent catalytic behaviors unobservable in other size regimes. − When utilized for heterogeneous catalysis, sub-5 nm metal nanoparticles are typically dispersed on solid-state support materials, most commonly oxides, polymers, or carbon-based materials. ,− These support materials not only keep the small nanocatalysts from agglomeration and sintering under operando conditions but may also further enhance the overall activities of the catalysts in certain circumstances. − Polydopamine (PDA) has emerged as an ideal support material for sub-5 nm noble metal nanocatalysts owing to its easy processibility, structural robustness, and unique surface properties. − PDA is a bio-inspired synthetic polymer highly sticky to the surfaces of a diverse range of solid-state materials, which mimics the function of the surface-adhesive proteins secreted by the vertebrate mussels. − Benefiting from PDA’s intrinsically adhesive surface properties, we were able to deposit well-dispersed sub-5 nm Pt nanocatalysts onto colloidal PDA supports through a simple one-pot synthetic process in a reaction environment free of any surface-capping molecular ligands . This PDA-mediated colloidal synthesis approach could also be adopted to synthesize PDA-supported nanocatalysts composed of other non-Pt noble metal elements .…”

An Artificial Chameleon Skin for Dynamic Thermoregulation

“…Efficient solar harvest is vital for living organisms to survive in harsh environments, and natural pigments such as melanin, which has unique solar-thermal properties play a variety of key roles in the thermoregulation of ectotherms. In recent years, melanin has attracted much interest for its outstanding properties, such as anti-ultraviolet (UV), [40,41] metal chelating, [42] free radical scavenging, [43,44] and thermoregulation. [45,46] PDA, the most common type of synthetic melanin, has been revealed that its physicochemical properties are generally similar to those of natural melanins, thus PDA has been used as photoprotectors, antioxidants, [43] semiconductors, [47] and biomedical materials.…”

Mechanistic Diversity of Transfer Hydrogenolysis over Noble Metal Nanocatalysts: Pt- and Ru-Catalyzed Azo-Hydrogenolysis by Various Hydrogen Donors

“…In addition, unlike Pt and other noble metal elements that typically crystallize into the face-centered cubic (fcc) structures, the hexagonal close-packed (hcp) phase of Ru is thermodynamically favored over the fcc phase. , Therefore, Pt and Ru represent a pair of contrasting PGM elements well-worthy of systematic comparative studies. We chose colloidal PDA particles as a structurally stable and catalytically inert support material ,− for Pt and Ru nanocatalysts, whose sizes were both carefully tuned to ∼2.3 nm. The unique surface-adhesion function of PDA − enables us to deposit PGM nanoparticles with finely tunable sizes, narrow size distributions, and ligand-free clean surfaces onto the PDA supports through a one-pot PDA-mediated metal deposition process. , Selecting ligand-free Pt and Ru nanoparticles of essentially the same sizes dispersed on the same support material as the model catalysts for detailed kinetic and mechanistic studies enables us to unambiguously decipher the intrinsic composition-dependence of catalytic behaviors without further complications caused by inconsistency in particle sizes, support materials, or surface-capping molecular ligands.…”