Mayakrishnan Gopiraman

Noble metal/functionalized cellulose nanofiber composites for catalytic applications.

In this study, cellulose acetate nanofibers (CANFs) with a mean diameter of 325 ± 2.0 nm were electrospun followed by deacetylation and functionalization to produce anionic cellulose nanofibers (f-CNFs). The noble metal nanoparticles (RuNPs and AgNPs) were successfully decorated on the f-CNFs by a simple wet reduction method using NaBH4 as a reducing agent. TEM and SEM images of the nanocomposites (RuNPs/CNFs and AgNPs/CNFs) confirmed that the very fine RuNPs or AgNPs were homogeneously dispersed on the surface of f-CNFs. The weight percentage of the Ru and Ag in the nanocomposites was found to be 13.29 wt% and 22.60 wt% respectively; as confirmed by SEM-EDS analysis. The metallic state of the Ru and Ag in the nanocomposites was confirmed by XPS and XRD analyses. The usefulness of these nanocomposites was realized from their superior catalytic activity. In the aerobic oxidation of benzyl alcohol to benzaldehyde, the RuNPs/CNFs system gave a better yield of 89% with 100% selectivity. Similarly, the AgNPs/CNFs produced an excellent yield of 99% (100% selectivity) in the aza-Michael reaction of 1-phenylpiperazine with acrylonitrile. Mechanism has been proposed for the catalytic systems.

Synthesized photo-cross-linking chalcones as novel corrosion inhibitors for mild steel in acidic medium: experimental, quantum chemical and Monte Carlo simulation studies

New chalcone derivatives namely (E)-(1-(5-(4-(3-(4-methylphenyl)-3-oxoprop-1-enyl)phenoxy)pentyl)-1H-1,2,3-triazol-4-yl)methyl acrylate (CH-5), (E)-(1-(5-(4-(3-(4-methylphenyl)-3-oxoprop-1-enyl)phenoxy)hexyl)-1H-1,2,3-triazol-4-yl)methyl acrylate (CH-6) and (E)-(1-(5-(4-(3-(4-methylphenyl)-3-oxoprop-1-enyl)phenoxy)decyl)-1H-1,2,3-triazol-4-yl) methyl acrylate (CH-10) were synthesized and characterized by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopic techniques. Ultraviolet-visible (UV-vis) spectra of the synthesized compounds confirmed that the chalcones undergo photo-cross-linking upon irradiation with UV-light. Potentiodynamic polarization measurements showed that both the intact and photo-cross-linked chalcones are mixed-type corrosion inhibitors for mild steel in aqueous hydrochloric acid. The EIS results showed an increase in charge transfer resistance with increasing concentration of the inhibitors. The chalcone derivatives adsorb spontaneously on the mild steel surface and their adsorption obeyed the Langmuir adsorption isotherm. The adsorption mode revealed the possibility of competitive physisorption and chemisorption mechanisms. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) analyses confirmed that the chalcones formed a protective film on the mild steel surface. The overall results showed that the photo-cross-linked chalcones are better corrosion inhibitors than the intact chalcones. The results of quantum chemical calculations and Monte Carlo simulation studies are in good agreement with experimental results.

Silver coated anionic cellulose nanofiber composites for an efficient antimicrobial activity.

Herein, we report a comparative study of silver coated anionic cellulose nanocomposite before (CMC-Ag) and after (AgNPs/CMC) chemical reduction for antibacterial activity. Cellulose nanofibers were prepared by deacetylation of electrospun cellulose acetate nanofibers, which were then treated with sodium chloroacetate to prepare anionic cellulose nanofibers (CMC). Aqueous AgNO3 solution with different concentrations was employed to produce nanofiber composites. To obtain AgNPs/CMC, the resultant Ag/CMC nanofibers were chemically reduced with NaBH4. The nanocomposites were characterized by FE-SEM, FTIR, XPS and SEM-EDS. Antimicrobiality tests were conducted using S. aureus and Escherichia coli bacteria following standard test method JIS L1902, 2008. The EDS results confirmed higher silver content in CMC-Ag nanofibers than AgNPs/CMC nanofibers. The antimicrobial test and EDS results demonstrated higher silver release (larger halo width) by the former in comparison to later which confers better antimicrobiality by CMC-Ag nanofibers.

Catalytic N-oxidation of tertiary amines on RuO(2)NPs anchored graphene nanoplatelets

Ultrafine ruthenium oxide nanoparticles (RuO2NPs) with an average diameter of 1.3 nm were anchored on graphene nanoplatelets (GNPs) using a Ru(acac)3 precursor by a very simple dry synthesis method. The resultant material (GNPs–RuO2NPs) was used as a heterogeneous catalyst for the N-oxidation of tertiary amines for the first time. The transmission electron microscopy (TEM) images of the GNPs–RuO2NPs showed the excellent attachment of RuO2NPs on GNPs. The loading of Ru in GNPs–RuO2NPs was 2.68 wt%, as confirmed by scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The X-ray photoelectron spectrum (XPS) and the X-ray diffraction pattern (XRD) of GNPs–RuO2NPs revealed that the chemical state of Ru on GNPs was +4. After the optimization of reaction conditions for N-oxidation of triethylamine, the scope of the reaction was extended to various aliphatic, alicyclic and aromatic tertiary amines. The GNPs–RuO2NPs showed excellent catalytic activity in terms of yields even at a very low amount of Ru catalyst (0.13 mol%). The GNPs–RuO2NPs was heterogeneous in nature, chemically as well as physically, very stable and could be reused up to 5 times.

Rhus verniciflua as a green corrosion inhibitor for mild steel in 1 M H2SO4

The methanolic extract of the plant Rhus verniciflua was examined as a corrosion inhibitor for mild steel in 1 M H2SO4 through weight loss measurements, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements. The sample surface morphology was analyzed using scanning electron microscopy/energy-dispersive X-ray spectroscopy. The total phenolic content of the R. verniciflua leaf extract was found to be 158 mg g−1, while the total flavonoid content was 19.65 mg g−1. Eleven phenolic compounds, three flavonoid compounds, five derivatives of hydroxycinnamic acid, and four hydroxybenzoic acids were identified in the extract. Polarization studies showed that the R. verniciflua plant extract acts as a good mixed-type inhibitor. The inhibition efficiency was found to increase with an increase in the inhibitor concentration. On the other hand, the inhibition efficiency decreased with an increase in the temperature. The adsorption of the plant extract constituents is discussed based on the Langmuir, Temkin, and El-Awady isotherms. Moreover, the adsorption and thermodynamic parameters corresponding to extract adsorption onto mild steel were calculated and are discussed. The results show that the R. verniciflua plant extract can be employed as an effective corrosion inhibitor with good anticorrosion properties for metals in acidic environments.

A highly hydrophilic water-insoluble nanofiber composite as an efficient and easily-handleable adsorbent for the rapid adsorption of cesium from radioactive wastewater

Herein, we report a new Prussian blue nanoparticle (PBNPs) incorporated polyvinyl alcohol (PVA) composite nanofiber (c-PBNPs/PVA) for the rapid adsorption of cesium (Cs) from radioactive wastewater. Initially, various electrospinning parameters such as solvent, PVA wt%, PBNPs wt% and glutaraldehyde (GA) wt% were extensively optimized to obtain a better physicochemical property of the c-PBNPs/PVA. In order to improve the water insoluble nature of the PVA, post cross-linking was carried out for the c-PBNPs/PVA using glutaraldehyde (GA) and HCl vapor as the cross-linker and catalyst, respectively. SEM images revealed the smooth and continuous morphology of the c-PBNPs/PVA composite nanofibers with diameters of 200–300 nm and lengths up to several millimeters. TEM images confirmed homogeneous dispersion and good incorporation of PBNPs into the PVA matrix. The amorphous nature of the c-PBNPs/PVA was confirmed by the XRD analysis. FT-IR spectra showed successful cross-linking of PVA with GA. It was found that the prepared composite nanofiber is highly hydrophilic and water-insoluble. The c-PBNPs/PVA showed an excellent and faster Cs adsorption rate of 96% after only 100 min. These results are comparable to those previously reported. After the Cs adsorption test, the c-PBNPs/PVA composite nanofiber can be easily separated from the wastewater.

Photodegradation of dyes by a novel TiO2/u-RuO2/GNS nanocatalyst derived from Ru/GNS after its use as a catalyst in the aerial oxidation of primary alcohols (GNS = graphene nanosheets)

Ruthenium nanoparticles (RuNPs) supported on graphene nanosheets (GNS), a composite (Ru/GNS), were prepared by a dry synthesis method and were used as nanocatalysts for the aerial oxidation of various primary alcohols. Ru/GNS was highly efficient, selective, stable and heterogeneous in nature. Owing to the high stability of the used catalyst (u-Ru/GNS), it was further applied in a different catalytic system viz photocatalytic degradation, after suitable modifications. We have obtained a novel TiO2/u-RuO2/GNS catalyst from u-Ru/GNS by the sol-gel method. The catalytic activity of TiO2/u-RuO2/GNS toward the photodegradation of methyl orange (MO) and acridine orange (AO) was found to be excellent. Overall, the sustainable use of these recyclable materials (Ru/GNS and TiO2/u-RuO2/GNS) could lead to economic and environmental benefits.

Handspinning Enabled Highly Concentrated Carbon Nanotubes with Controlled Orientation in Nanofibers.

The novel method, handspinning (HS), was invented by mimicking commonly observed methods in our daily lives. The use of HS allows us to fabricate carbon nanotube-reinforced nanofibers (CNT-reinforced nanofibers) by addressing three significant challenges: (i) the difficulty of forming nanofibers at high concentrations of CNTs, (ii) aggregation of the CNTs, and (iii) control of the orientation of the CNTs. The handspun nanofibers showed better physical properties than fibers fabricated by conventional methods, such as electrospinning. Handspun nanofibers retain a larger amount of CNTs than electrospun nanofibers, and the CNTs are easily aligned uniaxially. We attributed these improvements provided by the HS process to simple mechanical stretching force, which allows for orienting the nanofillers along with the force direction without agglomeration, leading to increased contact area between the CNTs and the polymer matrix, thereby providing enhanced interactions. HS is a simple and straightforward method as it does not require an electric field, and, hence, any kinds of polymers and solvents can be applicable. Furthermore, it is feasible to retain a large amount of various nanofillers in the fibers to enhance their physical and chemical properties. Therefore, HS provides an effective pathway to create new types of reinforced nanofibers with outstanding properties.

Allantoin-loaded porous silica nanoparticles/polycaprolactone nanofiber composites: fabrication, characterization, and drug release properties

The development of biocompatible nanocomposites for biomedical applications such as drug release has attracted increasing attention in recent years. We report porous silica nanoparticles (PSNs) immobilized polycaprolactone (PCL) nanofiber composites (PCL/PSNs) for drug delivery applications. The allantoin (model drug)-loaded PSNs were mixed well with a PCL solution and electrospun to fabricate the PCL/PSNs nanofiber composites. The PSNs were prepared from rice husk. Allantoin was loaded on the PSNs to prepare (allantoin-PSNs), and its three different concentrations (10, 20 and 30 wt%) based on PCL wt% were chosen. The biocompatibility and biodegradability of PCL, higher adsorption and nontoxicity of mesoporous silica nanoparticles and the promising results of the PCL/PSNs composite highlighted their challenging potential for controlled drug delivery applications. The prepared PSNs, PCL nanofibers and PCL/allantoin-PSNs nanofiber composites were characterized by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron microscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and drug release analysis. The results confirmed the successfully synthesis of mesoporous nanoscopic PSNs from rice husk and controlled allantoin release profile by the resulting PCL/allantoin-PSNs nanofiber composites.

Gold, silver and nickel nanoparticle anchored cellulose nanofiber composites as highly active catalysts for the rapid and selective reduction of nitrophenols in water

Highly active metal nanoparticle (MNP) supported cellulose nanofiber (CNF) composites (Au/CNF, Ni/CNF and Ag/CNF) were prepared for the reduction of 4- and 2-nitrophenols (4-NP and 2-NP) in water. Transmission electron microscopy (TEM) images showed that the ultrafine nanoparticles (Au, Ni and Ag NPs) were uniformly deposited on CNFs surface. The content of Au (9.7 wt%), Ni (21.5 wt%) and Ag (22.6 wt%) in Au/CNF, Ni/CNF and Ag/CNF respectively was determined by energy dispersive spectroscopy (EDS) and inductive coupled plasma-mass spectroscopy (ICP-MS) analysis. The chemical state of the MNPs in Au/CNF, Ni/CNF and Ag/CNF was determined by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The significant metal-support interaction was studied by means of XPS. The Au/CNF, Ni/CNF and Ag/CNF demonstrated excellent catalytic activity towards the reduction of nitrophenols to aminophenols in water. To our delight, even a very low amount of catalyst was also found to be good enough to achieve 100% reduction of 4- and 2-NP with a higher reaction rate (within 5 min). The best rate constant (kapp) values were determined for the cellulose nanocomposites. To the best our knowledge, Au/CNF, Ni/CNF and Ag/CNF are the most efficient nanocatalysts for the reduction of 4- and 2-NP reported to date. The catalytic performance of Au/CNF, Ni/CNF and Ag/CNF was compared with previously reported results. A possible mechanism has been proposed for these catalytic systems.