In the present study, clay - graphene oxide nanocomposite catalysts were successfully used for the first time in the multicomponent one pot organic synthesis. The facile development of the hybrid clay - graphene oxide nanocomposite has been achieved by a cost-effective method without the use of any surfactants. The partial reduction of graphene oxide, upon incorporation of clay layers and subsequent heat treatment, is evident from the X-ray diffraction patterns and FTIR spectra of the samples. X-ray photoelectron spectroscopy as well as Al-27 and Si-29 NMR spectral analyses provided useful information regarding the interaction between clay layers and graphene oxide through Si-O-C and Al-O-C bonding. The deconvoluted XPS spectrum of O (1s), Al (2p) and Si (2p) indicates the increased availability of acidic functionalities in the hybrid nanocomposite. FESEM and TEM photographs show the random distribution of the clay nano-flakes over the graphene oxide sheets and this may be the reason for the availability of more of the active sites for catalysis. Synthesis of 3,4-dihydropyrimidinones by the one pot Biginelli reaction was done over the present clay - graphene oxide heterogeneous catalysts with high product yield. Short time period of reaction and excellent reusability up to 8 repeated cycles under solvent free conditions are the key advantages of the present highly active hybrid nanocomposite clay - graphene oxide catalysts over most of the other reported catalysts used for Biginelli reaction. (C) 2017 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.

Herein we report an easy, scalable, cost-effective and green synthesis of twisted graphene from bulk graphite by a ball milling technique with the in situ formation of novel coconut husk ash (CHA) -twisted graphene nanocomposite and its catalytic application towards multicomponent Biginelli reaction. Here the ash derived from naturally available waste material (coconut husk) is effectively used as an exfoliating agent for the scissoring of graphene layers from bulk graphite for the first time. The elemental analysis data obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES) provided useful information regarding the composition of CHA and the nanocomposites. The X-ray diffraction (XRD) patterns confirmed the exfoliation of graphite into graphene layers. Raman spectroscopic analysis evaluated the quality and the nature of graphene layers in the composites. X-ray photoelectron spectroscopy (XPS) analysis confirmed the bonding between the graphene layers and CHA particles. Transmission electron microscopy (TEM) images revealed the presence of few layered graphene as well as twisted graphene in the composites. The CHA -twisted graphene nanocomposite is found to be an excellent reusable catalyst for Biginelli reaction with a higher yield of 3,4-dihydropyrimidinones within short duration of reaction.

A one pot synthesis of carbon dot incorporated porous coconut shell char derived sulphonated catalyst is reported here for the first time and is effectively used in the multicomponent synthesis of amidoalkyl naphthol. Macroporous nature of the char is revealed from scanning electron microscopic (SEM) analysis, whereas the dispersion of carbon dots (CDs) on the porous coconut shell char is confirmed from the high resolution transmission electron microscopic (HRTEM) analysis. Fluorescence emission spectrum further confirmed the presence of CDs in the catalyst. Fourier-transform infrared (FTIR) spectral analysis of the materials indicated that sulphonation occurred both to the CD and to the porous char. X-ray photo electron spectroscopic (XPS) analysis of the most active catalyst confirmed the presence of both sulphonic acid and carboxylic acid groups in the catalyst. The coconut shell char derived materials prepared by varying the amount of H2SO4 are successfully utilized as efficient alternative green catalysts for the multicomponent reaction, where excellent activity in amidoalkyl naphthol synthesis is obtained within short periods under solvent free reaction conditions. A maximum yield of 98% is obtained in the synthesis of N-[Phenyl-(2-hydroxy-naphthalen-1-y1)-methyl]-benzamide, the representative amidoalkyl naphthol, with the best catalyst within 3 min of reaction. The catalyst is highly active for the reactions carried out with varieties of aldehydes and amides with a product yield in the range of 88-98%. The best catalyst system retained more than 90% of its initial activity even upto 6th repeated run. (C) 2018 Elsevier Inc. All rights reserved.

Here we report the preparation of novel rice husk ash – reduced graphene oxide nanocomposites and their catalytic application in Biginelli reaction. Hydrothermal treatment is given to a mixture of rice husk ash and graphene oxide for the formation of a uniform composite. XRD and FTIR spectral analyses confirmed the partial reduction of graphene oxide in the nanocomposites during hydrothermal treatment. The binding between rice husk silica particles and graphene sheets through SiOC bonding is revealed from XPS analysis. Graphene is found to be less defective in nature in the composite as evident from the reduced ID/IG value in the Raman spectrum. SEM and TEM images showed the effective dispersion of rice husk SiO2 particles on the wrinkled graphene layers. Present study also exploited the use of a statistical model, response surface methodology, for the optimization of reaction parameters on the catalytic synthesis of dihydropyrimidinones via multicomponent solvent free Biginelli reaction. The cost effective highly efficient rice husk ash - reduced graphene oxide catalyst is found to be reusable till 7 repeated cycles with only about 4% reduction of its initial activity.

Montmorillonite KSF clay was effectively modified by the encapsulation of phosphotungstic acid into the clay layers via sonication followed by incipient wet impregnation method. The prepared catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The catalytic activities of the prepared systems were investigated in the solvent free synthesis of amidoalkyl naphthols by the multicomponent one-pot condensation of an aldehyde, β-naphthol and an amide or urea. Excellent yield, shorter reaction time, easy work-up, and reusability of the catalyst are the main attractions of this green procedure.

A cost effective and efficient method for the preparation of fuel grade biodiesel by the transesterification of jatropha oil at room temperature over a coconut husk derived catalyst under mild reaction conditions without the use of any cosolvent is reported here. Catalyst is prepared by means of controlled heating of coconut husk, without any chemical treatment. The main active component over the catalyst was found to be potassium. When the reaction temperature was increased to 45 degrees C, the catalyst showed excellent performance on the transesterification of Jatropha oil in a range of methanol/oil molar ratios. The important speciality for the present catalytic systems is the comparatively low reaction temperature requirement for effective reaction. For the optimization of different reaction variables including molar ratio of the reactants, reaction time, the catalyst calcination temperatures and the catalyst/oil weight percentage, a series of transesterification reactions were conducted and the results obtained are presented here. (C) 2014 Elsevier Ltd. All rights reserved.