Jin-Ook Baeg

A Photocatalyst–Enzyme Coupled Artificial Photosynthesis System for Solar Energy in Production of Formic Acid from CO2

The photocatalyst-enzyme coupled system for artificial photosynthesis process is one of the most promising methods of solar energy conversion for the synthesis of organic chemicals or fuel. Here we report the synthesis of a novel graphene-based visible light active photocatalyst which covalently bonded the chromophore, such as multianthraquinone substituted porphyrin with the chemically converted graphene as a photocatalyst of the artificial photosynthesis system for an efficient photosynthetic production of formic acid from CO(2). The results not only show a benchmark example of the graphene-based material used as a photocatalyst in general artificial photosynthesis but also the benchmark example of the selective production system of solar chemicals/solar fuel directly from CO(2).

Iron complexes of 1,1′-bis(diphenylphosphino)ferrocene (BPPF) as efficient catalysts in the synthesis of carbamates. X-ray crystal structure of (BPPF)Fe(CO)3

Abstract 1,1′-Bis(diphenylphosphino)ferrocene (BPPF) reacts with a 5–10 molar excess of Fe(CO)5 to give three new iron complexes (η2-BPPF)Fe(CO)3 (1), (η1-BPPF)Fe(CO)4 (2), and (μ,η1-BPPF)Fe2(CO)8 (3) with the product distribution depending upon reaction conditions. The structure of 1 has been determined. Crystals are monoclinic, space group P21/c, with a 9.708(1), b 16.195(2), c 19.869(5) A, β 95.75(2)°, V 3108(1) A3, Z = 4, and Dcalc 1.49 g cm−3. The geometry around the central iron is a distorted trigonal bipyramid, with the two phosphorus atoms occupying axial and equatorial positions. All these compounds can catalyze efficiently the reaction of propargyl alcohol with secondary amines in the presence of CO2 to provide corresponding carbamate esters. The yields of some carbamates are among the highest (∼ 65%) ever reported in the literature.

Highly Selective Solar-Driven Methanol from CO2 by a Photocatalyst/Biocatalyst Integrated System

The successful development of a photocatalyst/biocatalyst integrated system that carries out selective methanol production from CO2 is reported herein. The fine-tuned system was derived from a judicious combination of graphene-based visible light active photocatalyst (CCG-IP) and sequentially coupled enzymes. The covalent attachment of isatin-porphyrin (IP) chromophore to chemically converted graphene (CCG) afforded newly developed CCG-IP photocatalyst for this research endeavor. The current work represents a new benchmark for carrying out highly selective methanol formation from CO2 in an environmentally benign manner.

Confinement of nano CdS in designated glass: a novel functionality of quantum dot–glass nanosystems in solar hydrogen production

The present work is the investigation of our novel approach to designing quantum dot–glass nanosystems by confining nano CdS in designated glass and the first employment of such a quantum dot system in solar hydrogen production. The CdS quantum dots were grown in a special glass matrix, which involved a sequence of steps. The obtained glass was of uniformly bright yellow in color and the bulk glass was pulverized to a fine powder of micron size particles. The glass powder was characterized structurally and morphologically. X-Ray diffraction and electron diffraction patterns reveal a hexagonal crystallite system for the CdS quantum dots. Field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy and chemical leaching with HCl studies demonstrate that the 2.5 nm size CdS quantum dots distribute homogeneously in a monodispersed form in the glass domain and on the surface with a “partially embedded exposure” configuration. This disposition imparts an excellent photostability against photocorrosion and also a facile catalytic function. Therefore, even a very small amount of CdS quantum dots (0.005 g per gram of glass powder) is able to photodecompose H2S under visible light (λ ≥ 420 nm) both in alkaline and pure aqueous media and produce solar hydrogen with markedly high quantum yields of 17.5 and 11.4%, respectively at 470 nm. Salient features like reusability after simple washing, corrosionless-stability and remarkable catalytic activity of this quantum dot–glass nanosystem are brought forth by our novel catalyst design and are much acclaimed in large scale solar H2 production.

Graphene–BODIPY as a photocatalyst in the photocatalytic–biocatalytic coupled system for solar fuel production from CO2

The utilization of CO2 for production of solar fuels/chemicals is gaining increasing importance due to worldwide fossil-fuel shortage and global warming. As a means to achieve this, we herein report on the synthesis and development of a graphene-based visible light active photocatalyst (CCG–BODIPY) which is chemically converted graphene (CCG) covalently bonded to a light harvesting BODIPY molecule (1-picolylamine-2-aminophenyl-3-oxy-phenyl-4,4′-difluoro-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene-triazine). The photocatalyst-biocatalyst coupled system developed using CCG–BODIPY as photocatalyst functions in a highly efficient manner, leading to high NADH regeneration (54.02 ± 0.61%), followed by its consumption in exclusive formic acid production (144.2 ± 1.8 μmol) from CO2. The present research endeavour highlights the development and application of a graphene based photocatalyst for direct solar fuel formation from carbon dioxide.

Self assembled CdLa2S4 hexagon flowers, nanoprisms and nanowires: novel photocatalysts for solar hydrogen production

We report here a new ternary chalcogenide material, cadmium lanthanum sulfide (CdLa2S4) produced using a facile hydrothermal method at 433 K. The effect of the solvent on the morphology of the CdLa2S4 was demonstrated for the first time. The prima facie observations revealed the formation of highly crystalline hexagonal structures in the form of flowers in aqueous medium. The flowers comprise hexagonal columns ∼300 nm in diameter and 1–1.2 μm in length. All the hexagonal structures have a sharp tip with a cavity of 10 nm and are almost equal in size. The nanoprisms have an average base size of 35 nm with 35 nm edges, and the nanowires have a diameter of 10–15 nm; both were obtained in methanol. Crystal and electronic structure calculations were performed using the Vienna ab initio simulation package (VASP) based on density functional theory (DFT). Considering the band gap of pristine CdLa2S4 in the visible region (2.3 eV), we have demonstrated CdLa2S4 as a photocatalyst for the production of H2 under solar light. Nanostructured CdLa2S4 prisms gave the maximum hydrogen production, i.e. 2552 μmol h−1. Being a stable ternary nanostructured metal sulfide (with nanohexagons, nanoprisms, nanowires), CdLa2S4 may have other potential prospective applications in solar cells and optoelectronic devices.

A solar light-driven, eco-friendly protocol for highly enantioselective synthesis of chiral alcohols via photocatalytic/biocatalytic cascades

The judicious utilization of solar light for the asymmetric synthesis of optically active compounds by imitating natural photosynthesis introduces a new concept that harnesses this renewable energy in vitro for ultimate transformation into chiral chemical bonds. Herein, we present a comprehensive description of such a biomimetic endeavor towards the design and construction of an asymmetric artificial photosynthesis system that comprises an efficient method of nicotinamide cofactor (NADPH) regeneration under visible light employing a graphene-based light harvesting photocatalyst and its subsequent utilization in an enzyme-catalyzed asymmetric reduction of prochiral ketones to expediently furnish the corresponding chiral secondary alcohols. A detailed optimization study revealed a major dependency of the reaction outcome on the amount of cofactor, photocatalyst and enzyme used, as well as the mode of their addition. A series of structurally diverse ketones bearing an array of (hetero)aryl/alkyl substituents proved to be highly suitable to our photocatalytic–biocatalytic cascade approach, providing (R/S)-1-(hetero)aryl/alkylethanols in excellent enantioselectivities (ee ∼ 95–>99.9%) under mild and environmentally benign conditions. To the best of our knowledge, the synthesis of these enantiopure alcohols employing a visible-light-driven nicotinamide cofactor regeneration strategy has been reported for the first time. Such enantioenriched alcohols act as versatile chiral building blocks for the synthesis of compounds having industrial and pharmaceutical relevance. In addition, this solar-to-chiral chemicals prototype appears advantageous from ecological and economical perspectives. We describe mechanistic pathways to demonstrate how the present catalytic synthesis protocol functions through perfect orchestration between visible-light-driven photocatalysis and biocatalysis to be successively applied in inducing asymmetry in an achiral molecule for the ultimate goal of solar energy utilization in the synthesis of valuable chiral fine chemicals. This work highlights the potential advantages of a bioinspired system to the pertinence of solar energy in asymmetric transformations leading to enantioenriched alcohol precursors, and thus opens up a new field of research that might emerge as an important breakthrough with promising implications towards generating a sustainable and non-fossil/non-nuclear energy future.

A highly efficient covalent organic framework film photocatalyst for selective solar fuel production from CO2

Two-dimensional covalent organic frameworks (2D COFs) are a class of crystalline polymers with a design controllable platform that may be developed into a new type of metal-free photocatalyst. The exploration of new frameworks is, however, critical for further progress in this emerging field. To realize their full potential in practical light harvesting applications, the fabrication of a film type photocatalyst is equally essential. Here, we report the successful development of a triazine based covalent organic framework (2D CTF) as an inexpensive and highly efficient visible light active flexible film photocatalyst for solar fuel production from CO2. For this research work, the condensation polymerization between cyanuric chloride and perylene diimide has been exploited for the first time as a new synthetic approach to the construction of 2D CTFs. The visible light-harvesting capacity, suitable band gap and highly ordered π electron channels contribute to the excellent performance of the film photocatalyst. The current study is a benchmark example of COF based photocatalysts for solar fuel production from CO2 and is expected to trigger further interest in potential solar energy conversion applications such as wearable devices.

Functionalized graphene quantum dots as efficient visible light photocatalysts for selective solar fuel production from CO2

Functionalized graphene quantum dots (fGQDs) as visible‐light‐harvesting photocatalysts for solar fuel production from CO2 is explored for the first time. The highly efficient light‐harvesting fGQDs photocatalyst upon integration with the biocatalyst performs highly selective CO2 reduction to formic acid. The results are a benchmark example of GQD based materials as photocatalysts for selective production of solar fuels from CO2 and opens up possibilities for greener synthesis of other value added chemicals.

In situ fabrication of highly crystalline CdS decorated Bi2S3 nanowires (nano-heterostructure) for visible light photocatalyst application

In situ synthesis of the orthorhombic Bi2S3 nanowires decorated with hexagonal CdS nanoparticles (nano-heterostructure) has been demonstrated by a facile solvothermal method. The tiny 5–7 nm CdS spherical nanoparticles are decorated on the surfaces of 30–40 nm Bi2S3 nanowires, successfully. Structural, morphological and optical studies clearly show the existence of CdS on the nanowires. A possible sequential deposition growth mechanism is proposed on the basis of experimental results to reveal the formation of the nano heterostructure. The heterostructures have been used as a photocatalyst for hydrogen production as well as degradation of methylene blue under solar light. The maximum hydrogen evolution i.e. 4560 and 2340 μmol h−1 0.5 g was obtained from H2S splitting and glycerol degradation for Bi2S3 NWs decorated with CdS nanoparticles (nano-heterostructure) which is higher than that of the Bi2S3 NWs (3000 and 1170 μmol h−1 0.5 g, respectively). The enhanced photocatalytical hydrogen evolution efficiency of the heterostructures is mainly attributed to its nanostructure. In the nano heterostructure, the CdS nanoparticles control the charge carrier transition, recombination, and separation, while the Bi2S3 nanowire serves as a support for the CdS nanoparticles. The photogenerated electrons migration is faster than the holes from the inside of a CdS nanoparticle to its surface or to the phase interface, resulting in a relatively higher hole density inside the CdS nanoparticle leaving electron density at surface of the Bi2S3 NWs. This influences the photocatalytic activity under solar light. Such nano-heterostructures may have potential in other photocatalytic reactions.