3 research outputs found
Hybrid Cu<sub><i>x</i></sub>OâTiO<sub>2</sub> Heterostructured Composites for Photocatalytic CO<sub>2</sub> Reduction into Methane Using Solar Irradiation: Sunlight into Fuel
Photocatalytic CO<sub>2</sub> conversion to fuel offers an exciting
prospect for solar energy storage and transportation thereof. Several
photocatalysts have been employed for CO<sub>2</sub> photoreduction;
the challenge of realizing a low-cost, readily synthesized photocorrosion-stable
photocatalytic material that absorbs and successfully utilizes a broad
portion of the solar spectrum energy is as yet unmet. Herein, a mesoporous
p-type/n-type heterojunction material, Cu<sub><i>x</i></sub>OâTiO<sub>2</sub> (<i>x</i> = 1, 2), is synthesized
via annealing of Cu/Cu<sub>2</sub>O nanocomposites mixed with a TiO<sub>2</sub> precursor (TiCl<sub>4</sub>). Such an experimental approach
in which two materials of diverse bandgaps are coupled provides a
simultaneous opportunity for greater light absorption and rapid charge
separation because of the intrinsic pân heterojunction nature
of the material. As detailed herein, this heterostructured photocatalyst
demonstrates an improved photocatalytic activity. With the CO<sub>2</sub> reduction of our optimal sample (augmented light absorption,
efficacious charge separation, and mesoporosity) that utilizes no
metal cocatalysts, a remarkable methane yield of 221.63 ppm·g<sup>â1</sup>·h<sup>â1</sup> is achieved
Elucidation of Active Sites and Mechanistic Pathways of a Heteropolyacid/Cu-MetalâOrganic Framework Catalyst for Selective Oxidation of 5âHydroxymethylfurfural via Ex Situ Xâray Absorption Spectroscopy and In Situ Attenuated Total Reflection-Infrared Studies
Chemoselective
oxidation of 5-hydroxymethylfurfural (HMF) over
non-noble metals to produce a bioplastic monomer, 2,5-furandicarboxylic
acid (FDCA), under alkaline-free conditions is challenging and worthy
of investigation. HMF oxidation into FDCA involves the concurrent
oxidation of primary alcohol and an aldehyde functional group into
carboxylic groups, which therefore demand a bifunctional catalyst
containing dual active sites and chemoselective oxidation of HMF.
The present work demonstrated the formation of new selective active
sites in a composite porous material (Cu-BTC_PMA) that consists of
Cu-BTC (metalâorganic framework (MOF)) and polyoxometalate
(POM). The porous framework provides (Cu-BTC_PMA) the desired chemoselectivity,
while a selective Cu metal center in Cu-BTC (MOF) and CuâOâMo
sites functions as active sites for the concurrent oxidation of HMF
into FDCA. This catalyst exhibited a HMF conversion of 89% and an
FDCA selectivity of 92.3% under base-free and mild reaction conditions.
In detail, X-ray absorption spectroscopy analysis demonstrated the
chemical bond tuning, as well as electronic structural modulations
of MOF and POM at the molecular level, which directs the formation
of new synergistic interfacial active sites and charge transfer states.
This phenomenon causes the generation of the unique redox environment
of copper and the multiple oxidation states along with the oxygen
vacancy in the Cu-BTC_PMA catalyst, which most likely behaves as active
sites for base-free oxidation. A kinetics study of this reaction was
followed using in situ attenuated total reflection-infrared spectroscopy,
demonstrating the stabilization of the specific intermediates that
lead to the formation of FDCA. Moreover, we made comparative density
functional theory and quantum theory of atoms in molecules investigations
on the surface interaction between the reactant (HMF) and two catalyst
models of Cu-BTC and Cu-BTC_PMA to interpret quantitatively the higher
catalytic activity of the Cu-BTC_PMA catalyst. The kinetics study
also evaluates the rate-determining step and activation energy for
the multistep oxidation reactions
Highly Efficient Visible Blue-Emitting Black Phosphorus Quantum Dot: Mussel-Inspired Surface Functionalization for Bioapplications
The preparation of
blue-emitting black phosphorus quantum dots
(BPQDs) is based on the liquid-phase exfoliation of bulk BP. We report
the synthesis of soluble BPQDs showing a strong visible blue-light
emission. Highly fluorescent (photoluminescence quantum yield of â5%
with the maximum emission (λ<sub>max</sub>) at â437 nm)
and dispersible BPQDs in various organic solvents are first prepared
by simple ultrasonication of BP crystals in chloroform in the ambient
atmosphere. Furthermore, simple mussel-inspired surface functionalization
of BPQDs with catechol-grafted polyÂ(ethylene glycol) in basic buffer
afforded water-soluble blue-emitting BPQDs showing long-term fluorescence
stability, very low cytotoxicity, and excellent fluorescence live
cell imaging capability