Rajakumar Ananthakrishnan

[Ru(bpy)3]2+ aided photocatalytic synthesis of 2-arylpyridines via Hantzsch reaction under visible irradiation and oxygen atmosphere

A rapid photocatalytic synthesis of unusual Hantzsch products—highly substituted 2-arylpyridines—via Hantzsch reaction has been achieved in the presence of a catalytic amount of [Ru(bpy)3]2+ and molecular oxygen under visible irradiation, using a household white lamp (45 W CFL). Here, the photoredox reaction occurs without the addition of any sacrificial donor. The 1,2-dihydropyridine formed in situ plays the role of a sacrificial donor, and superoxide radicals generated from molecular oxygen help in the aromatization of 1,2-dihydropyridine to yield the corresponding 2-arylpyridine selectively as the sole product. Further, the merging of the Fenton reaction with photoredox catalysis for the aromatization of 1,2-dihydropyridine was found to be efficient enough to enhance the rate of the oxidation, but the selectivity of the process was reduced under such conditions, yielding multiple products as detected by LC-MS analysis.

Development of phosphonate modified Fe(1−x)MnxFe2O4 mixed ferrite nanoparticles: Novel peroxidase mimetics in enzyme linked immunosorbent assay

A highly facile and feasible strategy on the fabrication of advanced intrinsic peroxidase mimetics based on Mn(2+) doped mixed ferrite (Mn(II)(x)Fe(II)(1-x)Fe(III)(2)O(4)) nanoparticles was demonstrated for the quantitative and sensitive detection of mouse IgG (as a model analyte). Mn(2+) doped Fe(1-x)Mn(x)Fe(2)O(4) nanoparticles were synthesized using varying ratios of Mn(2+):Fe(2+) ions and characterized by the well known complementary techniques. The increase of Mn(2+) proportion had remarkably enhanced the peroxidase activity and magnetism. The catalytic activity of mixed ferrites was found to follow Michaelis-Menten kinetics and was noticeably higher than native Fe(3)O(4). The calculated K(m) and K(cat) exhibited strong affinity with substrates which were remarkably higher than similar sized native magnetite nanoparticles and horseradish peroxidase (HRP). These findings stimulated us to develop carboxyl modified Fe(1-x)Mn(x)Fe(2)O(4) nanoparticles using phosphonomethyl immunodiacetic acid (PMIDA) to engineer PMIDA-Fe(1-x)Mn(x)Fe(2)O(4) fabricated enzyme linked immunosorbent assay (ELISA). Results of both PMIDA-Fe(1-x)Mn(x)Fe(2)O(4) linked ELISA revealed that the enhancements in absorbance during the catalysis of enzyme substrate were linearly proportional to the concentration of mouse IgG within the range between 0.1 μg/ml and 2.5 μg/ml. Further, this detection was ten times lower than previous reports and the detection limit of mouse IgG was 0.1 μg/ml. The advantages of our fabricated artificial peroxidase mimetics are combined of low cost, easy to prepare, better stability and tunable catalytic activity. Moreover, this method provides a new horizon for the development of promising analytical tools in the application of biocatalysis, bioassays, and bioseparation.

Porous ZnO/Co3O4 heteronanostructures derived from nano coordination polymers for enhanced gas sorption and visible light photocatalytic applications

Porous ZnO/Co3O4 heteronanostructures are successfully fabricated by a one-step solid state conversion of a novel [(Zn)x–(Co)7−x(BDC)(DHS)]·nH2O (x = 1, 3, 4, 6)] nano coordination polymers (NCPs). The precursor is prepared by one-pot wet chemical approach at room temperature without any surfactant using dihydroxy salophen ligand and 1,4-benzenedicarboxylic acid as the linkers in presence of zinc(II) acetate and cobalt(II) acetate in DMF solvent. Different weight ratios of the Zn/Co are fabricated in situ into the hetero-structures during the preparation of the NCPs to tune their physicochemical properties. The produced ZnO/Co3O4 nanostructure possesses relatively higher surface area (80–140 m2 g−1) and having significant N2 gas sorption capacity in comparison with reported materials. It is suggested that synergistic effect of each component, higher separation of electron and holes, high surface area and porous structure led to the promising visible light photocatalytic properties. The prepared mixed metal oxides show significant reusability in photocatalysis more than five times without losing their properties. Importantly, the mixed-metal NCPs could be applied as an effective route to generate not only binary oxide, but also ternary or quaternary oxide nanostructures with desired morphology and enhanced physicochemical properties.

Bromodimethylsulfonium bromide as a potential candidate for photocatalytic selective oxidation of benzylic alcohols using oxygen and visible light

Selective photooxidation of different benzylic alcohols has been carried out in the presence of molecular oxygen and a catalytic amount of bromodimethylsulfonium bromide (BDMS) under visible light irradiation. The above method was found to be efficient for the oxidation of primary and secondary benzylic alcohols into their corresponding aldehydes and ketones with excellent product yield. Unlike other studies, the advantages of this study are the metal-free green protocol, utilization of a household compact fluorescent lamp (CFL) lamp as the visible light source, and the high selectivity of the reaction. A mechanistic study infers that the carbonyl compound obtained by the process possesses an oxygen atom which comes from molecular oxygen. From the study, we propose that the conversion of the benzylic alcohol to its corresponding aldehyde could be following a peroxy radical intermediate. The first-hand results revealed the photocatalytic potential of BDMS in general and its capability for selective alcohol oxidation, in particular.

A facile preparation of superhydrophobic and oleophilic precipitated calcium carbonate sorbent powder for oil spill clean-ups from water and land surfaces

Fabrication of superhydrophobic and oleophilic materials has attracted environment scientists due their application in oil spill clean-up. Herein, we report the preparation of superhydrophobic and oleophilic precipitated calcium carbonate sorbent via a simple and economical one-step synthetic approach using precipitated calcium carbonate as the substrate and palmitic acid as the surface modifying agent. The material is tested for its selectivity and effectiveness in the removal of spilled oil from both water and land surfaces. Test confirms the superhydrophobic character of the material with a static water contact angle of 166 ± 1°, whereas the oleophilic nature was validated from various oil uptake studies. In addition to being superhydrophobic and oleophilic, the sorbent material was found to be reusable for more than five times. Interestingly, the sorbent has high oil sorption selectivity, suitable buoyancy to float on water and possesses high oil sorption efficiencies (>99%).

Utilization of Ru(II)-complex immobilized ZnO hybrid in presence of Pt(II) co-catalyst for photocatalytic reduction of 4-nitrophenol under visible light

In the present study, an attempt has been made to utilize a Ru(II)-complex (dye)-sensitized ZnO hybrid along with a Pt(II) salt for the visible light aided photoreduction of 4-nitrophenol. The dye, bis(2,2′-bipyridyl)(4,4′-dicarboxy-2,2′-bipyridyl)ruthenium(II) chloride, is used as a sensitizer for ZnO. The photocatalyst, Ru(II) dye–ZnO, has been characterized by XRD, FTIR, DRS, SEM, EDX and XPS. A kinetic study of the photoreduction reaction was carried out under visible light irradiation (CFL 45 W) with different concentrations of Pt(II) ions, without changing the 4-nitrophenol concentration. The reduced percentage reached a maximum of 55–60%, in the presence of the Pt(II) salt at a concentration of 2.5 × 10−4 mol%. Control studies were done (in the presence of light and dark) to establish the photoactivity of the prepared photocatalyst. A series of experiments have been conducted to understand the mechanistic aspects of the photoreduction process, and it is identified that the photoreduction of 4-nitrophenol proceeds through an electron transfer process.

A novel Ag deposited nanocoordination polymer derived porous SnO2/NiO heteronanostructure for the enhanced photocatalytic reduction of Cr(VI) under visible light

The fabrication of a novel porous Ag deposited SnO2/NiO (Ag/SnO2/NiO) heteronanostructure for the photoreduction of toxic aqueous Cr(VI) to non-toxic Cr(III) is reported. The material is prepared by depositing metallic Ag nanoparticles into the SnO2/NiO heteronanostructure by the reduction of Ag+ under UV irradiation. The SnO2/NiO heteronanostructure is obtained by a facile solid-state transformation of the novel nanocoordination polymer (NCP). The prepared Ag/SnO2/NiO is characterized by different techniques such as PXRD, XPS, EDX, FESEM, TEM, HRTEM, BET, UV-Vis DRS and PL measurements. The PXRD and XPS studies confirm the formation of a Sn(IV) state of SnO2 in the heterostructure. TEM images reveal the spherical morphology of Ag nanoparticles with an average particle size of 15 nm, and hexagonal shaped SnO2 and NiO with an average particle size of 10 and 5 nm in Ag/SnO2/NiO, respectively. The incorporation of Ag enhances visible light absorption and higher electron–hole separation of Ag/SnO2/NiO by Surface Plasmon Resonance (SPR). Besides, the material exhibits a high surface area and porous nature, which facilitates the effective photocatalytic reduction of toxic aqueous Cr(VI) to non-toxic Cr(III) under visible light. Furthermore, the photocatalytic reduction of Cr(VI) is optimized under different conditions. The photostability of Ag/SnO2/NiO is tested up to five successive runs indicating its promising applications for wastewater treatment. Finally, a photocatalytic mechanism is proposed for the reduction of aqueous Cr(VI) over Ag/SnO2/NiO under visible light.

A novel ternary CuO decorated Ag3AsO4/GO hybrid as a Z-scheme photocatalyst for enhanced degradation of phenol under visible light

A novel CuO decorated Ag3AsO4/GO (CuO/Ag3AsO4/GO) ternary hybrid system is fabricated by an electrostatically-driven assembly method. The CuO nanostructure is obtained from a nano-coordination polymer by a facile solid-state transformation route. The prepared CuO/Ag3AsO4/GO hybrid shows a well-defined crystalline structure, where nanosized CuO particles (20 nm) are decorated on Ag3AsO4 spheres (150 nm) and further distributed on the GO sheets. The prepared CuO/Ag3AsO4/GO hybrid is characterized by PXRD, FT-IR, XPS, EDX, TEM, HRTEM, FESEM, UV-Vis DRS, BET and PL measurements. The CuO/Ag3AsO4/GO hybrid exhibits improvement in the visible light photodegradation of phenol compared to the CuO/Ag3AsO4 or Ag3AsO4/GO hybrid. The higher catalytic activity of the material can be ascribed to an increase in light harvesting, effective electron–hole separation and high surface area of the material. Furthermore, the CuO/Ag3AsO4/GO photocatalyst exhibits excellent photo-stability and reusability for more than five successive cycles signifying its potential applications in wastewater treatment. Interestingly, a Z-scheme type photocatalytic mechanism is proposed for the CuO/Ag3AsO4/GO hybrid under visible light.

Robust superhydrophobic and oleophilic silk fibers for selective removal of oil from water surfaces

The fabrication of efficient sorbents having high selectivity and sorption capacity from natural products has attracted considerable interest due to practical applications in oil spill clean-ups and recovery of spilled oil. Our work presents the preparation of a natural sorbent material with superhydrophobic character, excellent selectivity and high oil sorption capacity using silk fibroin fibers, where the fibers were surface modified with octadecylamine via a simple synthetic approach. The sorbent fibers were found to possess superhydrophobic character with a static water contact angle of 150 ± 3°. The results of oil sorption experiments on oil–water mixtures infer that the modified fibers possess excellent selectivity as well as oil sorption ability, where the oil sorption capacity (OSC) of the material was found to be 46.83 g g−1 for crude oil and 84.14 g g−1 for motor oil. Moreover, the oil sorption capacity of our fiber for motor oil is almost 8 times higher than natural wool, and twice higher than the silkworm cocoon waste. The modified fibers have significantly higher OSC values for crude oil (3.5 times higher) than any wool based sorbents. The suitability of the material over a wide pH range of 3–11 substantiates its advantage in oil sorption even in any corrosive environment. Further, the oil recovery and reusability of the fibers were tested to investigate their applicability for repeatable usage in oil spill clean-up application.

Facile synthesis of nano-Zn/Bi–reduced graphene oxide for enhanced photocatalytic elimination of chlorinated organic pollutants under visible light

A Zn/Bi mixed metal oxide (MMO) was synthesized by a simple co-precipitation method. Then Zn/Bi-MMO was hydrothermally treated with graphene oxide (GO) to obtain a Zn/Bi–RGO co-assembly. The XRD pattern confirms the formation of highly pure Zn/Bi–RGO nanoparticles. In the co-assembled Zn/Bi–RGO hybrid, GO had converted into RGO, which was evidenced by spectroscopy techniques, such as FT-IR, Raman, XPS, etc. UV-Vis DRS spectra infer that the prepared hybrid has significant absorption in the visible light region. The photocatalytic studies were conducted using 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) and the hybrid offered almost complete degradation of pollutants as compared to pure Zn/Bi-MMO. The enhanced photocatalytic activity of Zn/Bi–RGO hybrids is due to the homogeneous distribution of Zn/Bi-MMO over RGO sheets as well as electron transportation efficacy of the RGO sheets. The mechanism of catalysis is expected to have two key events; namely a charge transfer mechanism, which initiates the reaction, followed by an electron–hole aided radical mechanism.