Ashish Bahuguna

Two-dimensional carbon-based nanocomposites for photocatalytic energy generation and environmental remediation applications

In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.

Bioinspired Functional Surfaces for Technological Applications

Biological matters have been in continuous encounter with extreme environmental conditions leading to their evolution over millions of years. The fittest have survived through continuous evolution, an ongoing process. Biological surfaces are the important active interfaces between biological matters and the environment, and have been evolving over time to a higher state of intelligent functionality. Bioinspired surfaces with special functionalities have grabbed attention in materials research in the recent times. The microstructures and mechanisms behind these functional biological surfaces with interesting properties have inspired scientists to create artificial materials and surfaces which possess the properties equivalent to their counterparts. In this review, we have described the interplay between unique multiscale (micro- and nano-scale) structures of biological surfaces with intrinsic material properties which have inspired researchers to achieve the desired wettability and functionalities. Inspired by naturally occurring surfaces, researchers have designed and fabricated novel interfacial materials with versatile functionalities and wettability, such as superantiwetting surfaces (superhydrophobic and superoleophobic), omniphobic, switching wettability and water collecting surfaces. These strategies collectively enable functional surfaces to be utilized in different applications such as fog harvesting, surface-enhanced Raman spectroscopy (SERS), catalysis, sensing and biological applications. This paper delivers a critical review of such inspiring biological surfaces and artificial bioinspired surfaces utilized in different applications, where material science and engineering have merged by taking inspiration from the natural systems.

Plant leaves as natural green scaffolds for palladium catalyzed Suzuki–Miyaura coupling reactions

This work presents a novel approach of using natural plant leaf surfaces having intricate hierarchical structures as scaffolds for Pd nanoparticles and demonstrated it as a Green dip catalyst for Suzuki-Miyaura coupling reactions in water. The influence of the topographical texture of the plant leaves on the deposition and catalytic properties of Pd nanoparticles are presented and discussed. The catalytic activity can be correlated to the surface texture of the leaves, wherein it has been found that the micro/nanostructures present on the surface strongly influence the assembly and entrapment of the nanoparticles, and thereby control aggregation and leaching of the catalysts. This approach can provide insights for the future design and fabrication of bioinspired supports for catalysis, based on replication of leaf surfaces.

Recyclable, bifunctional composites of perovskite type N-CaTiO3 and reduced graphene oxide as an efficient adsorptive photocatalyst for environmental remediation

Graphene–semiconductor photocatalysts are of utmost interest for achieving visible light activity but there is ambiguity about the role played by graphene in these photocatalysts. Such photocatalysts exhibit both adsorptive and photocatalytic activities towards pollutant degradation. Herein, we report nitrogen doped CaTiO3 (NCT) perovskite coupled with reduced graphene oxide (RGO), RGO–NCT, composites for the first time and utilize them for environmental remediation as an efficient adsorptive photocatalyst. The adsorption and photocatalytic activity were evaluated by investigating the adsorption/degradation of a model dye, methylene blue (MB). In comparison with bare CT and NCT, the RGO–NCT composites exhibit enhanced photocatalytic activity, which could be attributed to the synergistic effect of the adsorption of dye molecules on the RGO surface followed by their degradation under visible light irradiation. In the degradation mechanism, we propose that the degradation of MB is not only due to the dye photosensitization process but also involves the true photocatalytic action of the RGO–NCT composites. The clear role of graphene as an electron acceptor is demonstrated by photoluminescence spectroscopic study. Also, the degradation of a colorless pollutant thiabendazole (TBZ) under visible light irradiation supports our hypothesis. In addition, the commendable stability and recyclability of RGO–NCT photocatalysts demonstrates that these materials can be used as potential, viable and stable photocatalysts for environmental remediation. In principle, we anticipate that our work paves the way for tailoring the photocatalytic activity of perovskite-type semiconductor materials by coupling with graphene for the design of recyclable bifunctional photocatalysts.

Amorphous titania matrix impregnated with Ag nanoparticles as a highly efficient visible- and sunlight-active photocatalyst material

Abstract Amorphous titania matrix impregnated with Ag nanoparticles has been synthesised based on a facile colloidal synthesis route and has been explored for visible- and sunlight-activated photocatalytic applications. The photocatalytic activity of the material under visible light and sunlight irradiation was demonstrated by investigations on the degradation of a common pollutant, nitrobenzene. In comparison to other TiO2-based nanomaterials, this amorphous titania impregnated with Ag nanoparticles was found to be highly efficient for visible light as well as sunlight-active photocatalytic applications. The superior catalytic activity could be attributed to the efficient charge separation and lessened recombination of the photo-generated electrons and holes at the Ag–titania interface and the presence of multiple metal–metal oxide interfaces due to dispersed impregnation of Ag nanoparticles on amorphous titania matrix. Also, it was found that the photocatalytic activity of the prepared nanocomposites had better efficiency under the sunlight irradiation, which may be attributed to the plasmonic heating of the Ag nanoparticles in the sunlight. Fundamentally, this work illustrates that the dispersed impregnation of noble metal nanoparticles on semiconductor metal oxide matrix can be used to tune the photophysical properties of the final material to enhance its photocatalytic performance.

Hypervalent iodine mediated direct one pot transformation of aldehydes to ketones

An environmentally benign, step economical synthesis of ketones directly from aldehydes has been developed using hypervalent iodine as an oxidant. The key features of this protocol are its mild conditions without the use of any heavy and toxic metals for the synthesis of a wide range of ketones.

2D-2D Nanocomposite of MoS2-Graphitic Carbon Nitride as Multifunctional Catalyst for Sustainable Synthesis of C3-Functionalized Indoles

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.

Ammonia-Doped Polyaniline–Graphitic Carbon Nitride Nanocomposite as a Heterogeneous Green Catalyst for Synthesis of Indole-Substituted 4H-Chromenes

A nanocomposite of polyaniline with graphitic carbon nitride (GCN) nanosheets has been synthesized by a facile oxidative polymerization of an aniline monomer and GCN to demonstrate its potential to catalyze the synthesis of various indole-substituted 4H-chromenes. The synthesized nanocomposite was thoroughly characterized using different spectroscopic techniques to confirm the morphology and composition. Subsequently, the fabricated nanocomposite was used as a heterogeneous catalyst to synthesize several bioactive indole-substituted 4H-chromenes in an aqueous medium. Organic transformation under benign and environmentally sustainable conditions is of paramount importance in the view of growing environmental pollution. Water is the universal Green solvent and has been a preferred choice of nature to perform various reactions. The catalyst developed in this work showed very good recyclability and adaptability for the synthesis of various medicinally significant indole-substituted 4H-chromenes. This multicomponent reaction imparts very high atom economy (94%) and low environmental factor (0.13).