The influence of crystal structures on the performance of CoMoO4 battery-type supercapacitor electrodes.

CoMoO4 is a promising battery-type supercapacitor electrode material that can offer relatively high storage capacity and cycle stability. In this work, we investigate the role of the crystalline phase of CoMoO4 in determining these performance parameters. The hydrate phase of CoMoO4 was synthesized on a nickel foam substrate via hydrothermal reaction with subsequent annealing under an inert atmosphere leading to the formation of the ß-phase CoMoO4. Similar nanoplate morphologies were observed in all of the samples. The hydrate-phase CoMoO4 demonstrates larger specific capacity than the annealed ß-phase CoMoO4. Besides, the samples synthesized at lower temperatures have better rate capability than the sample annealed at higher temperatures. However, the hydrate phase had worse long-term stability compared to the ß-phase samples.

Bioinspired, Non-Enzymatic, Aqueous Synthesis of Size-Tunable CdS Quantum Dots for Sustainable Optoelectronic Applications.

The enzymatic production of hydrogen sulfide (H2S) from cysteine in various metabolic processes has been exploited as an intrinsically "green" and sustainable mode for the aqueous biomineralization of functional metal sulfide quantum dots (QDs). Yet, the reliance on proteinaceous enzymes tends to limit the efficacy of the synthesis to physiological temperature and pH, with implications for QD functionality, stability, and tunability (i.e., particle size and composition). Inspired by a secondary non-enzymatic biochemical cycle that is responsible for basal H2S production in mammalian systems, we establish how iron(III)- and vitamin B6 (pyridoxal phosphate, PLP)-catalyzed decomposition of cysteine can be harnessed for the aqueous synthesis of size-tunable QDs, demonstrated here for CdS, within an expanded temperature, pH, and compositional space. Rates of H2S production by this non-enzymatic biochemical process are sufficient for the nucleation and growth of CdS QDs within buffered solutions of cadmium acetate. Ultimately, the simplicity, demonstrated robustness, and tunability of the previously unexploited H2S-producing biochemical cycle help establish its promise as a versatile platform for the benign, sustainable synthesis of an even wider range of functional metal sulfide nanomaterials for optoelectronic applications.

Sequential, low-temperature aqueous synthesis of Ag-In-S/Zn quantum dots via staged cation exchange under biomineralization conditions.

The development of high quality, non-toxic (i.e., heavy-metal-free), and functional quantum dots (QDs) via 'green' and scalable synthesis routes is critical for realizing truly sustainable QD-based solutions to diverse technological challenges. Herein, we demonstrate the low-temperature all-aqueous-phase synthesis of silver indium sulfide/zinc (AIS/Zn) QDs with a process initiated by the biomineralization of highly crystalline indium sulfide nanocrystals, and followed by the sequential staging of Ag+ cation exchange and Zn2+ addition directly within the biomineralization media without any intermediate product purification. Therein, we exploit solution phase cation concentration, the duration of incubation in the presence of In2S3 precursor nanocrystals, and the subsequent addition of Zn2+ as facile handles under biomineralization conditions for controlling QD composition, tuning optical properties, and improving the photoluminescence quantum yield of the AIS/Zn product. We demonstrate how engineering biomineralization for the synthesis of intrinsically hydrophilic and thus readily functionalizable AIS/Zn QDs with a quantum yield of 18% offers a 'green' and non-toxic materials platform for targeted bioimaging in sensitive cellular systems. Ultimately, the decoupling of synthetic steps helps unravel the complexities of ion exchange-based synthesis within the biomineralization platform, enabling its adaptation for the sustainable synthesis of 'green', compositionally diverse QDs.

Tailored Coupling of Biomineralized CdS Quantum Dots to rGO to Realize Ambient Aqueous Synthesis of a High-Performance Hydrogen Evolution Photocatalyst.

Nanocomposite photocatalysts offer a promising route to efficient and clean hydrogen production. However, the multistep, high-temperature, solvent-based syntheses typically utilized to prepare these photocatalysts can limit their scalability and sustainability. Biosynthetic routes to produce functional nanomaterials occur at room temperature and in aqueous conditions, but typically do not produce high-performance materials. We have developed a method to produce a highly efficient hydrogen evolution photocatalyst consisting of CdS quantum dots (QDs) supported on reduced graphene oxide (rGO) via enzyme-based syntheses combined with tuned ligand exchange-mediated self-assembly. All preparation steps are carried out in an aqueous environment at ambient temperature. Size-controlled CdS QDs and rGO are prepared through enzyme-mediated turnover of l-cysteine to HS- in aqueous solutions of Cd-acetate and graphene oxide, respectively. Exchange of cysteamine for the native l-cysteine ligand capping the CdS QDs drives self-assembly of the now positively charged cysteamine-capped CdS (CdS/CA) onto negatively charged rGO. The use of this short linker molecule additionally enables efficient charge transfer from CdS to rGO, increasing exciton lifetime and, subsequently, photocatalytic activity. The visible-light hydrogen evolution rate of the resulting CdS/CA/rGO photocatalyst is 3300 µmol h-1 g-1. This represents, to our knowledge, one of the highest reported rates for a CdS/rGO nanocomposite photocatalyst, irrespective of the synthesis method.

Low temperature aqueous synthesis of size-controlled nanocrystals through size focusing: a quantum dot biomineralization case study.

Traditional quantum dot synthesis techniques rely on the separation of nucleation and growth to control nanocrystal size. However, the same goal can be achieved through slow and continuous introduction of reactive precursors to keep the growth mechanism in the size focusing regime throughout synthesis. In this work, we demonstrate the efficacy of this approach within the framework of functional material biomineralization where, despite simultaneous nucleation and growth of particles, this growth mechanism enables size-controlled nanocrystal synthesis. Herein, the single enzyme cystathionine γ-lyase (CSE) is utilized to biomineralize CdS nanocrystals via the slow, but continuous turnover of the amino acid l-cysteine to produce H2S. Nanocrystal nucleation and growth theories confirm that consistent addition of monomers will result in a high supersaturation term, driving the nanocrystal growth mechanism into the size focusing regime. We further confirm this theory by mimicking biomineralization via chemical routes and demonstrate the influence of varying supersaturation, to further control the average nanocrystal size. Finally, altering the chelation strength of the capping agent l-cysteine is found to play a key role in balancing nanocrystal growth in solution and long-term stability.