Sulfonated graphitic carbon nitride having both Brønsted base and Brønsted acid sites is used as a heterogeneous catalyst for the selective conversion of different biomass-derived saccharides to 5-hydroxymethylfurfural in green solvents.
The
development of efficient photocatalysts for utilization of
solar energy for water splitting coupled with oxidation of biomass-derivatives
is of utmost importance for the simultaneous production of clean fuel
(H2) and value-added chemicals. Consequently, herein we
report the development of the Z-scheme photocatalytic system, Zn0.5Cd0.5S/xMnO2, which
has the optimum band structure suitable for efficient visible-light-assisted
photocatalytic H2 generation integrated with selective
oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to a more
value-added product, 2,5-diformylfuran (DFF). The electron microscopy
analyses of the samples revealed the presence of Zn0.5Cd0.5S microspheres composed of smaller nanocrystals with the
surface covered by the MnO2 nanostructure and the intimate
contact between Zn0.5Cd0.5S and MnO2. Photocatalytic investigations revealed the highest activity for
Zn0.5Cd0.5S/1%MnO2, affording a DFF
yield of 46% and a simultaneous H2 generation rate of 1322
μmol g–1 in 24 h, which are, respectively,
9 and 4 times higher than those of parent sample, Zn0.5Cd0.5S. Further, the best heterostructure exhibits good
catalytic activity even under natural sunlight irradiation, affording
DFF with a 14% yield and H2 generation rate of 152.6 μmol
g–1 in 6 h. The high catalytic activity of the heterostructure
over the parent materials has been attributed to efficient separation
of photogenerated charge-carriers with the aid of the Z-scheme mechanism
and the synergistic catalysis between Zn0.5Cd0.5S and MnO2. Overall, this work represents a unique demonstration
of noble metal-free selective oxidation of HMF to DFF integrated with
H2 production under mild reaction conditions.
A nanocomposite of two‐dimensional MoS2 supported on graphitic C3N4 nanosheets has been prepared by a facile ultrasonication method followed by demonstrating its ability to catalyze the synthesis of several indole derivatives. The as‐prepared nanocomposite catalyst was characterized in detail by using different microscopic and spectroscopic techniques to understand its structure and physicochemical properties. Subsequently, this nanocomposite catalyst was used as a heterogeneous multifunctional catalyst to synthesize several C3‐functionalized indoles in the aqueous medium. The employed strategy also provided very good catalyst recyclability and versatility for the synthesis of various precursors of medicinally significant indoles, such as serotonin, melatonin, and various β‐carboline alkaloids. In addition, a natural product derivate has been prepared on the gram‐scale by using this methodology. Furthermore, high atom economy (100 %) and lower E‐factor (0.042) makes this strategy a sustainable approach for the synthesis of C3‐functionalized indoles.
A nanocomposite of potassium-functionalized graphitic carbon nitride (KGCN) and reduced graphene oxide (RGO) was fabricated by a facile hydrothermal method and used as a heterogeneous catalyst for Knoevenagel condensation and sustainable synthesis of aryl substituted chromenes. The prepared KGCN−RGO nanocomposite catalyst has been characterized by using various techniques, such as powder Xray diffraction technique (PXRD), Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscope, thermogravimetric analysis, and BET surface area analysis. After detailed characterization, the nanocomposite was used as a heterogeneous catalyst to synthesize various aryl substituted chromenes in ethanol. The developed KGCN−RGO nanocatalyst also rendered good recyclability for the explored catalytic reactions. In addition, a high value of atom economy and a low value of E-factor are also key highlights of this green and sustainable catalytic protocol.
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