Melanins are a family of heterogeneous polymeric pigments that provide ultraviolet (UV) light protection, structural support, coloration, and free radical scavenging. Formed by oxidative oligomerization of catecholic small molecules, the physical properties of melanins are influenced by covalent and noncovalent disorder. We report the use of tyrosine-containing tripeptides as tunable precursors for polymeric pigments. In these structures, phenols are presented in a (supra-)molecular context dictated by the positions of the amino acids in the peptide sequence. Oxidative polymerization can be tuned in a sequence-dependent manner, resulting in peptide sequence-encoded properties such as UV absorbance, morphology, coloration, and electrochemical properties over a considerable range. Short peptides have low barriers to application and can be easily scaled, suggesting near-term applications in cosmetics and biomedicine.

Highly porous gallium oxide was synthesized by reconstructing its surface and body with mesopores and macropores. For the first time, the efficient photocatalytic conversion of CO 2 into a high energy carrier, CH 4 , using the porous gallium oxide was realized without any co-particle or sacrificial reagent. The enhanced photocatalytic activity is mainly attributed to the 300% higher CO 2 adsorption capacity, as well as the 200% increased surface area, compared to the bulk nanoparticles. Furthermore, we propose the new reaction pathway based on the result that the carbon dioxide was converted directly into methane without going through carbon monoxide intermediates.Due to the fact that the earth's current primary energy source is obtained through the combustion of fossil fuels, resulting in pollution and a climate change, the idea of artificial photosynthesis that uses carbon dioxide (CO 2 ) to produce hydrocarbon fuels would offer an alternative durable source of energy. 1-5 Among these hydrocarbon fuels, a promising candidate fuel is methane (CH 4 ), since it carries a high amount of energy per mass (55.7 kJ g À1 ). In order to convert CO 2 into CH 4 , it is important to develop a novel photocatalyst that uses solar energy and has a high affinity for CO 2 . [6][7][8] Grimes et al. 9 studied a photocatalytic conversion of CO 2 using TiO 2 nanotubes, enabling charge carriers to readily reach surface species. Meanwhile, the photoactivity on the titania system was limited by its insufficient reduction potential 5 and high recombination rate of photo-generated electron-hole pairs. 10,11 Therefore, new hetero-structures combining with noble metals 12 such as Pt 13 and Ru 14 have been suggested to be used for the separation of electron-hole pairs, but there is a problem that novel metals are expensive. However, metal oxide photocatalysts with d 10 configurations (In 3+ , Ga 3+ , Ge 4+ , Sn 4+ , Sb 5+ ) 15,16 are of great attention because hybridization between the s and p orbital of metals in the conduction band could enhance the mobility of photogenerated electrons, thus, producing high photocatalytic activity. 17 Among them, gallium oxide (Ga 2 O 3 ) is a promising CO 2 reduction photocatalyst due to its high reduction potential for CO 2 . 18-21 Tanaka et al. 20 carried out the photoreduction of CO 2 using H 2 as a reductant over the bulk crystal of b-Ga 2 O 3 , but found that it gave only CO as the product. Consequently, the further breakthrough on gallium oxide for the conversion of CO 2 into CH 4 has remained unsolved.Herein, we report a novel porous gallium oxide with meso-pores and macropores. The small amount of photocatalytic reaction sites, which is the biggest problem 22 with working with gallium oxide, was solved by reconstructing its surface and body with mesopores and macropores, combining the template method with hydrolysis of gallium nitrate. The synthetic procedures of the new porous Ga 2 O 3 and its CO 2 conversion processes are illustrated in Scheme 1. The efficient photocatalytic conversion of CO 2 ...

Titania decorated on single-wall carbon nanotube aerogels degraded organic dyes under visible-light irradiation at ultrahigh rates.

The separation of lithium from magnesium ions in salt brines is an important step in producing raw lithium for prospective use in electrochemical storage systems. Liquid–liquid extraction of Mg2+ ions from Li+ ions is challenging because of comparable thermodynamic behavior in aqueous solutions. Removing Mg2+ ions from brines using consumable ion‐exchange membranes is also a challenging prospect due to poor chemical selectivity and compromised sustainability. Here, we propose the use of redox‐active catechols in the form of melanin pigments for selective removal of Mg2+ ions from aqueous solutions. Synthetic melanin films are oxidatively polymerized on stainless steel meshes from aqueous solutions of dopamine precursors to create electrochemically functionalized polydopamine membranes. The binding selectivity of redox‐active catechol‐bearing polydopamine melanin for Mg2+ ions in aqueous solutions was measured as a function of electrochemical cycling. The binding kinetics of Mg2+ ions to polydopamine pigments was measured. Mg2+ ions binding selectivity to polydopamine in mixed aqueous solutions containing both Li+ and Mg2+ ions were also measured. Additionally, the equilibrium binding concentrations of Mg2+ ions to polydopamine were achieved very rapidly (<1 min). Redox‐active polydopamine membranes therefore show promise as functional materials for the separation of Mg2+ and Li+ ions in aqueous solutions. © 2016 Society of Chemical Industry

Photoelectrochemical conversion of solar energy is explored for many diverse applications but suffers from poor efficiencies due to limited solar absorption, inadequate charge carrier separation, redox half-reactions occurring in close proximity, and/or long ion diffusion lengths. We have taken a drastically different approach to the design of photoelectrochemical cells (PECs) to spatially isolate reaction sites at the nanoscale to different materials and flow channels, suppressing carrier recombination and back-reaction of intermediates while shortening ion diffusion paths and, importantly, avoiding mixed product generation. We developed massively parallel nano-PECs composed of an array of open-ended carbon nanotubes (CNTs) with photoanodic reactions occurring on the outer walls, uniformly coated with titanium dioxide (TiO), and photocathodic reactions occurring on the inner walls, decorated with platinum (Pt). We verified the redox reaction isolation by demonstrating selective photodeposition of manganese oxide on the outside and silver on the inside of the TiO/CNT/Pt nanotubes. Further, the nano-PECs exhibit improved solar absorption and efficient charge transfer of photogenerated carriers to their respective redox sites, leading to a 1.8% photon-to-current conversion efficiency (a current density of 4.2 mA/cm) under white-light irradiation. The design principles demonstrated can be readily adapted to myriads of photocatalysts for cost-effective solar utilization.