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A facile chemical synthetic route has been demonstrated for the synthesis of copper oxide nanoparticles decorated phosphate functionalized graphene oxide (CuO/PGO). The synthesized nanocatalyst was used as an efficient and active candidate for the synthesis of β-amino carbonyl compounds viaa green synthetic ultrasonic route. The structural properties of the samples were investigated by means of a number of sophisticated techniques like X-ray diffraction (XRD), Fourier-transform Infrared (FTIR) spectroscopy, High Resolution Transmission Electron Microscope (HRTEM), N2 adsorption-desorption measurements, X-ray photoelectron spectroscopy (XPS) analysis, Ammonia temperature programmed desorption analysis (NH3-TPD) and Raman spectroscopy. HRTEM analysis confirmed the presence of spherical CuO nanoparticles distributed uniformly throughout the PGO surface. XPS analysis demonstrated the presence of Cu2+ species and minor reduction of oxygen functional groups on GO. A higher surface area of 162 m2/g for CuO/PGO was found from N2 adsorption-desorption isotherms. Later on, the presence of acidic groups on CuO/PGO that play an essential role in the catalytic activity was examined by NH3-TPD and pyridine adsorbed IR analysis. The total acidity on the surface of synthesized nanocatalyst was found to be of 0.59 mmol g−1 which includes both Lewis as well as Bronsted acidic sites. A higher product yield of 95% in a shorter period of time of 15 min was achieved which is superior to many reported catalytic systems. A combined strategy involving greener and easier ultrasonic route and use of an efficient acidic graphene oxide-based catalyst resulted in higher catalytic activity and stability with good recyclability.

The need for an eco-friendly biocomposite for multi-purpose water treatment has been gaining more attention in recent times. In this regard, bio-polymeric composite materials could be the most suitable candidate. Herein, a novel alumina-based cross-linked chitosan–hydroxypropyl methyl cellulose (HPMC) biocomposite film (CgHA) has been designed and its superior fluoride and azo dye removal capacity from water/wastewater with a user-friendly adsorption procedure is demonstrated. Its physicochemical characteristics were investigated by XRD, FTIR, FESEM, TGA, DSC, and XPS techniques. Tensile strength, swelling test, and contact angle measurements demonstrated the suitable stability and hydrophilicity of the composite CgHA film. The fluoride adsorption capacity of the CgHA biocomposite was compared with chitosan–alumina (CgA) and HPMC–alumina (HgA) composites and the results showed the highest adsorption capacity of the reported biocomposite to be 125.1 mg g−1 for CgHA. Also, an enhanced fluoride removal efficiency of 96% from 5 L of real groundwater was achieved with only 0.1 g of CgHA. Again, 82.7% fluoride removal was achieved in highly concentrated fluoride solution (≥100 mg L−1) which established its large-scale potential. Furthermore, the applicability of CgHA in the removal of methyl orange (MO) dye was also demonstrated with textile wastewater, bolstering its superior adsorption capacity. In the end, a novel experimental set up was illustrated for the simultaneous adsorption and separation from the aqueous medium using novel biocomposite. Overall, this study demonstrates a novel, efficient, user-friendly and sustainable biopolymer-based composite as a potential adsorbent for the purification of drinking water as well as industrial wastewater.

Au Sn/ZnO nanocatalyst was synthesized by a two-step synthetic approach in which Au Sn alloy bimetallic nanoparticles (NPs) were incorporated into presynthesized ZnO in 1-butyl 3-methylimidazolium (BMIMBF4) ionic liquid (IL) via combustion route. The structure, morphology, and optical properties of the above synthesized material were analysed by using various analytical techniques, including X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive Spectroscopy Mapping (EDS), UV–vis Spectroscopy, Photoluminescence, Nitrogen Adsorption–Desorption, photoelectrochemical measurements and X-Ray Photoelectron Spectroscopy (XPS). The average particle size and the homogeneous distribution of Au Sn nanoparticle over the surface of ZnO was analyzed by using TEM. XPS analysis provides information regarding the elemental structure of individual species as well as the possible electronic interaction between the nanoparticles. The photocatalytic activity of the nanocatalyst was studied towards the degradation of organic contaminants such as rhodamine B dye, 2-chlorophenol, phenol, 2,4- dichlorophenol and 2,4-dinitrophenol. After 90 min the complete degradation of Rhodamine B (95%) and phenol (94%) and its derivatives was achieved under visible irradiation. The high photoactivity of 3Au 1Sn/ZnO can be attributed to the combined effect of enhanced light absorption intensity, longer lifetime of electron-hole pair, lower electron-hole recombination rate, increased stability, higher surface area and the synergistic effect between the metal nanoparticles and support material. It is expected that our current work could open promising prospects for the utilization of Sn-based bimetallic system as a potential visible light photocatalyst for environmental applications.

Sensitive and selective detection of NH3 at room temperature is required for proper environmental monitoring and also to avoid any health hazards in the industrial areas. Towards this objective, a low-cost, one-step and combustion route mediated reduced graphene oxide (rGO)-CuFe2O4 nanocomposite was exploited as a high–performance NH3 gas sensor by combining the excellent electrical properties of rGO and sensing capabilities of CuFe2O4. This nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and N2 adsorption-desorption analysis. The TEM images demonstrate the uniform distribution of the nanoparticles on the rGO surface and high-resolution transmission electron microscopy (HRTEM) confirms an average particle size of 15–20 nm. The designed sensor can detect NH3 at low concentrations up to 5 ppm at room temperature. Besides high sensing ability, the designed nanocomposite showed good recyclability suggesting its potential applications for the detection of environmentally toxic gases. The enhanced sensing behavior can be attributed to the synergistic behavior between individual rGO and CuFe2O4 component.

In this study, hydroxyapatite decorated with zirconia nanoparticle (HAp-ZrO2) was prepared using sonochemical method and characterized by various techniques such as BET, TEM, XRD, FTIR, FESEM-EDX, XPS, Raman spectroscopy, finding that the nanoparticles were uniformly distributed on the surface of hydroxyapatite with a mean size of 10 ± 5 nm. It was used as photocatalyst for degradation of phenols and its derivatives under UV light irradiation. The coupling of the ZrO2 and HAp significantly enhanced the separation efficiency of the photogenerated electron–hole pairs and then promoted the activity for the photodegradation of phenolic compounds. The estimation of reactive species involves in the degradation process was done by scavenger study. To determine the degradation efficiency, effect of various parameters such as catalyst dose, pH, and temperature has been investigated. Furthermore, the photoelectricalchemical study was carried out to provide further insight into the photocatalyst activity, which further confirmed the superiority of the HAp-ZrO2 in photocurrent generation. Results found no cytotoxic effects on the THP-1 cell-lines even after 72 h, confirming their excellent biocompatibility and biodegradable nature. High reactive sites on the HAp-ZrO2 made it an effective photocatalyst for degradation of phenols (above 95%). The nanocomposites show good stability without loss of their degradation capacity up to 4 cycle, confirming their practical use in water purification.

Phosphate functionalized graphene oxide (PGO), prepared by covalently bonding triethylphosphite on to the surface of graphene oxide (GO) via Arbuzov reaction has been demonstrated as an efficient catalyst for three component Biginelli condensation reaction with excellent yield (96%) under microwave condition. The PGO nanocatalyst was thoroughly characterized by Fourier transform infrared spectra (FTIR), FT-Raman spectroscopy, Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field-emission Scanning electron microscopy (FE-SEM), Energy dispersive X-ray spectroscopy (EDS), N 2 adsorption/desorption study, Ammonia temperature-programmed desorption analysis (NH 3 -TPD) and Thermogravimetric analysis (TGA). The presence of acidic groups on PGO which play an important role in the catalytic transformation were measured by NH 3 -TPD analysis. Based on the catalytic results, a feasible catalytic mechanism has been proposed. Besides high catalytic activity, this nanocatalyst showed good recyclability, suggesting its potential applications for the synthesis of other important organic molecules.

Graphene oxide as suitable support material was employed for the synthesis of GO-MnO2 nanocatalyst via a greener solution combustion route. Rod-like MnO2 was found to be uniformly adhered to both sides of graphene oxide (GO) sheets. The nanocatalyst was thoroughly characterized using different instrumental methods such as X-ray diffraction (XRD), N2 adsorption-desorption, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) with EDS mapping, UV–visible spectroscopy and Thermogravitometric (TG) analysis. From the experimental results, GO-MnO2 was found to be a potential catalyst for chalcones preparation via Claisen-Schmidt condensation. The catalytic activity of GO-MnO2 nanocatalyst was found to be superior as compared to pure MnO2 and GO. The reaction conditions were varied thoroughly by changing several reaction parameters like the solvent polarity, temperature, and catalyst wt%. High yield of chalcones was obtained in a short period of time at 110 °C under solventless conditions. The catalyst was easy to separate and was reused multiple times with minor change in activity. On comparing the activity with other reported catalyst in literatures it was revealed that GO-MnO2 nanocatalyst has significantly high activity in lesser period of time.

A facile one-step combustion route is used for the synthesis of a magnetically separable GO–CuFe2O4–ZnO (GCZ) ternary nanocomposite photocatalyst with varying ZnO contents. Transmission electron microscope (TEM) observations show the exfoliation of graphene oxide sheets and decoration with well-dispersed ZnO and CuFe2O4 nanoparticles. The photocatalytic activity of the ternary nanocomposite was tested under solar light irradiation for the photodegradation of several dyes such as rhodamine-B (RhB), methylene blue (MB), methyl orange (MO), and neutral phenol. The evaluation results demonstrate that the ternary GCZ photocatalyst exhibits the best performance compared to GO–CuFe2O4 (GC), GO–ZnO (GZ), CuFe2O4, ZnO, and CuFe2O4–ZnO (CZ) photocatalysts towards the photocatalytic degradation of the dyes. Photoelectrochemical measurements were carried out to provide deep insights into the enhanced photocatalytic activity in the novel ternary nanocomposite. The improved photocatalytic activity of the ternary nanocomposite can be ascribed to the superior light assimilation, proficient charge transfer process, synergistic effects, high surface area, and superior durability of the composite. Furthermore, a possible reaction mechanism has been proposed. Our results have demonstrated that by precisely introducing GO with appropriate metal oxides, a highly efficient photocatalyst can be designed that would assimilate a wider range of visible light. Furthermore, CuFe2O4 nanoparticles themselves have excellent magnetic properties, which are largely maintained in the GCZ composite, and can be simply separated from the suspension system by applying a magnetic field.

A novel graphene oxide (GO)–SnO2–TiO2-based ternary nanocomposite was prepared via a one-step solvothermal process. The structure, morphology, and optical properties were characterized by a series of techniques, including X-Ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), UV-vis Diffuse Reflectance Spectroscopy (DRS), Photoluminescence, Raman spectroscopy, Nitrogen Adsorption–Desorption, and X-Ray Photoelectron Spectroscopy (XPS). Various microscopic images of the ternary nanocomposite showed that the SnO2 and TiO2 nanoparticles are firmly covered over GO, thereby increasing the surface area of the resultant nanocomposite. The photocatalytic activity of ternary GO–SnO2–TiO2 and binary GO–SnO2 and GO–TiO2 materials were studied through the photodegradation of congo red and methylene blue under solar radiation. The degradation efficiency of GO–SnO2–TiO2 was found to be 96% for methylene blue dyes within 60 min and 98% for congo red within 70 min, which is much higher than the binary composites. Furthermore, a photoelectrochemical study was performed to provide further insight into the photocatalytic activity, which further confirmed the superiority of the novel ternary nanocomposite in photocurrent generation. The enhanced photocatalytic properties of the ternary nanocomposite can be attributed to enhanced light absorption, efficient charge transfer process, high surface area, as well as superior durability of the composite. In addition, a possible reaction mechanism has been postulated. Our results have demonstrated that by carefully introducing GO with suitable metal oxides, highly efficient photocatalysts can be designed that would absorb a wider range of the solar spectrum.

Ionic liquids (ILs) have attracted huge interest as templates for the fabrication of porous materials, as the possibility exists for the IL to act as both the solvent and porogen in such systems. Towards this objective, in this work, porous silica–graphene oxide nanocomposite(GO-SiO2) was synthesized using IL assisted solvothermal method. The N2 adsorption-desorption isotherm data showed that by using IL as a template highly mesoporous composite with higher surface area of 858 m2/g and average pore diameter of 5.3 nm can be obtained. Various other physiochemical properties of the nanocomposite were investigated by several sophisticated characterization techniques such as UV–Vis, FTIR, XRD, TGA, FESEM, HRTEM, XPS, and Raman spectroscopy. Later on, the synthesized GO-SiO2 nanocomposite was used as a versatile nanoadsorbent for Pb(II) and oxidized As(III) removal from water. Detailed adsorption mechanism was thoroughly studied via XPS. The effect of various parameters on adsorption such as pH, contact time, initial metal concentration and the nanoadsorbent amount was also investigated. The maximum adsorption capacities of our mesoporous nanocomposite towards Pb(II) and As(III) were found to be 527 mg/g and 30 mg/g, respectively. Kinetic studies indicated that the experimental details fit well with the pseudo-second-order kinetic model for both the adsorption process. It was also found that the Langmuir model was more suitable for Pb(II) adsorption whereas the Freundlich model was for oxidized As(III) adsorption. The thermodynamic parameters(ΔG 0, and ΔS > 0) indicate the adsorption process was endothermic in nature and spontaneous. The synthesized GO-SiO2 nanocomposite was reusable without any significant loss for 4 cycles.

The decoration of novel nanostructures such as nano particle and nanorod on the surface of graphene oxide (GO) generate potential heterogeneous nanocatalyst. Highlighting this, in the present work, we have designed a ternary GO-MnO2-Au nanocomposite by decorating MnO2nanorods on the surface of graphene oxide via hydrothermal method, followed by deposition of Au nanoparticles on GO-MnO2 surface. The prepared nanocomposite was thoroughly characterised by different instrumental techniques such as X-Ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR),Raman spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), High resolution Transmission electron microscopy (HRTEM), X-Ray photo electron spectroscopy (XPS), N2 adsorption desorption Brunauer–Emmett–Teller (BET) isotherm and Inductively coupled plasma - optical emission spectrometry (ICP-OES). FESEM and TEM images demonstrated that the MnO2 forms rod like structure having diameter of 60–100 nm and are uniformly distributed over the GO surface. HRTEM image clearly signifies gold (Au) nanoparticles having diameter of 7 ± 1.9 nm homogeneously distributed throughout the GO-MnO2 surface. Elementary state of Au and tetravalent nature of Mn as well as reduction of functional group after the decoration was confirmed from XPS studies. The catalyst GO-MnO2-Au was found to be the superior catalyst for synthesis of biologically active molecules such as Betti bases and Bisamides. The high catalytic activity of the materials can be attributed to the small and homogeneous distribution of gold nanoparticles, high redox potential of rod shaped MnO2 and the synergistic effect between GO, MnO2 and Au. All the reaction conditions were optimised by varying catalyst dosage, effect of solvent and temperature. The GO-MnO2-Au was easily recycled with minimal leaching and the product yield was found to be 85–90% after 4th cycle demonstrating the stability and durability of our nanocomposite.

Semiconductor mediated photocatalysis has got enormous consideration as it has shown immense potential in addressing the overall energy and environmental issues. To overcome the earlier drawbacks concerning quick charge recombination and limited visible-light absorption of semiconductor photocatalysts, numerous methods have been produced in the past couple of decades and the most broadly utilized one is to develop the photocatalytic heterojunctions. In our work, a series of SnO2-CuO nanocomposites of different compositions were synthesized by a combustion method and have been investigated in detail by various characterization techniques, such as wide angle X-ray diffraction (XRD), UV-vis spectroscopy, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The results revealed that the crystal structure and optical properties of the nanocomposites were almost same for all the compositions. FE-SEM images showed that the shape of SnO2-CuO was spherical in nature and the 1: 1 Sn/Cu sample had a well-proportioned morphology. The malachite green dye was used for the photocatalytic studies in a photoreactor and monitored with a UV-visible spectrometer for different composition ratio of metal (Sn: Cu) such as 1:1, 1:2, 2:1, 1:0.5 and 0.5:1. The 1:1 ratio nanocomposite showed excellent photocatalytic degradation of 96 % compared to pure SnO2 and CuO. The mechanism of degradation and charge separation ability of the nanocomposite are also explored using photocurrent measurement study.