Gowhar Ahmad Naikoo

Hierarchically macro/mesostructured porous copper oxide: facile synthesis, characterization, catalytic performance and electrochemical study of mesoporous copper oxide monoliths

Hierarchically macro/meso structured porous copper-oxide monoliths with and without additives (dextran, 1,3,5-trimethylbenzene and silica nanoparticles) were successfully synthesized via a facile sol–gel route and characterized by scanning electron microscopy (SEM/FESEM), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), the Brunauer–Emmet–Teller (BET) adsorption technique and FT-IR study. The results obtained reveal that the effect of additives has enhanced the specific surface area from 0.558 m2 g−1 to 229.5 m2 g−1 and varied the pore size from 8 μm to 39 nm. Furthermore, the hierarchically porous copper-oxide materials have shown excellent catalytic activity towards the wet oxidation of phenol and electrocatalytic performance of mesoporous copper oxide (mpCuO) against p-nitrophenol, demonstrating the significance of the porous nature of copper-oxide monoliths.

Hierarchical synthesis of silver monoliths and their efficient catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol

A novel catalyst Ag/Triton X-705/SiNPs is synthesized by a modified sol–gel method without the use of an acid or a base as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of 0.1 M NaBH4 in aqueous media. The reduction time was found to be 30–35 seconds when the concentration of 4-NP was varied from 0.001 M to 0.009 M while maintaining a constant amount of the Ag/Triton X-705/SiNP catalyst at 0.006 g. Fe3O4NPs, dextran, and trimethylbenzene (TMB) were added separately to Ag/Triton X-705 hydrogels to modify their morphology and catalytic activities against the reduction of 4-NP to 4-AP. The as-synthesized monoliths were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area analysis. The pseudo first order rate constant (k), energy of activation (Ea), and thermodynamic parameters viz. activation enthalpy (ΔH‡), activation Gibbs free energy (ΔG‡) and entropy of activation (ΔS‡) have also been determined. The turnover frequency (TOF) of the Ag/Triton X-705/SiNP catalyst was 9.66 × 1020 molecules per s and the catalyst was used up to nine cycles successfully with greater efficiency, making it a potential and leading candidate for the industrial conversion of 4-NP to 4-AP. We claimed that the Ag/Triton X-705/SiNP catalyst took almost minimum time for the reduction of 4-NP to 4-AP.

Solar-assisted photocatalytic reduction of methyl orange azo dye over porous TiO2 nanostructures

Mixed anatase–rutile and pure anatase mesoporous TiO2 photocatalysts have been synthesized for the first time via a modified greener sol–gel approach at low temperature without the involvement of any acid or base. Non-ionic surfactant Brij-35 was used as a sacrificial agent for the synthesis. The effect of additives like dextran and silica nanoparticles on different physical parameters of catalysts was also studied. The chemical, electronic and physical properties of the as-synthesized catalysts were studied by FTIR, TGA, PXRD, DRS, SEM, EDAX, TEM, and BET techniques and the photocatalytic potentiality was also tested by photocatalytic degradation of methyl orange (MO) azo dye. The photocatalytic activity of the synthesized catalysts was found to be in the order TiO2/Brij-35/Si-NPs > TiO2/Brij-35 > TiO2/Brij-35/dextran. The higher photocatalytic activity of TiO2/Brij-35/Si-NPs provided direct evidence of the surface area-dependent photocatalytic activity. As a comparative study, the catalysts were also tested for other environmentally harmful dyes like Rhodamine B and Congo Red and were proven to be highly efficient catalysts for the photodegradation of these dyes.

Fabrication of hierarchically organized nanocomposites of Ba/alginate/carboxymethylcellulose/graphene oxide/Au nanoparticles and their catalytic efficiency in o-nitroaniline reduction

Composite gels of Ba/alginate(Alg)/carboxymethyl cellulose (CMC) were prepared by a dissipative convective process. Graphene oxide (GO) and Au nanoparticle (Au-NPs) were successfully encapsulated into the polysaccharide matrix. The resulting composite gels were characterized by Fourier transform infrared (FTIR) spectrometry, Raman spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The rheological and mechanical behaviors of the composite gels were also investigated. The composite gels were tested for the reduction of o-nitroaniline (o-NA), to 1,2-benzenediamine in the presence of NaBH4. Ba/Alg/CMC/GO/Au composite gels reduce o-NA within 3 min with a rate constant of 0.45 s−1 and the composite can be recycled for up to 4 successive cycles.

Hierarchically porous metallic silver monoliths: facile synthesis, characterization and its evaluation as an electrode material for supercapacitors

A simple method for exploiting soft template Pluronic P123 and silica nanoparticles for the fabrication of porous silver (pAg) monoliths via modified sol gel route is reported. The pAg monoliths were characterized using FTIR, TGA, XRD, FESEM-EDX and BET techniques. The Brunauer–Emmett–Teller (BET) and field emission scanning electron microscopic techniques (FESEM) were used to study the surface area and porous characteristics. Further, the electrochemical capacitor properties of pAg monoliths were studied using cyclic voltammetry, electrochemical impedance spectroscopy and Galvanostatic charge/discharge techniques. The total capacitive characteristics of pAg monoliths are attributed to the pseudocapacitive characteristics which is due to the redox behavior of Ag/Ag+ and electrochemical double layer capacitance due to its porous nature. Electrochemical measurements show that the maximum specific capacitance, power density and the energy density obtained for pseudocapacitor using pAg modified glassy carbon electrode (pAg/GCE) were 224.0xa0Fg−1, 17.6xa0kWxa0kg−1and 31.0xa0Whxa0kg−1, respectively at the current density of 0.5xa0Ag−1. The fabricated pAg modified glassy carbon electrode (pAg/GCE) exhibited excellent life cycle with 91.3xa0% of the initial specific capacitance retained after 1,000 cycles. The results suggest that this porous material is a promising supercapacitor electrode material.

Surfactant-assisted morphological tuning of porous metallic silver sponges: facile synthesis, characterization and catalytic performance

AbstractnNanoporous sponges have many advantages over bulk catalyst structures in terms of providing regular framework of pores and conformational stability. In this paper, precise tuning of porosity and surface morphology in silver sponges for the catalytic reduction of p-nitro phenol to p-amino phenol was explored. The silver spongy catalysts are reusable and stable. The porous catalysts were characterized before calcination by FTIR and TGA and after calcination by XRD, SEM and BET techniques. Catalytic performance of the silver sponges was confirmed by spectrophotometric technique, and it was concluded that the porosity and adsorption capability of silver sponges were responsible for their outstanding catalytic performance.Graphical AbstractThe calcined silver monoliths displayed a potential catalytic activity against the reduction of 4-nitrophenol which is a serious environmental pollutant to 4-aminophenol which is an important intermediate in the synthesis of various analgesic and antipyretic drugs. Fig. (a)–(e) Time-dependent successive UV–vis spectra showing the reduction of 4-nitrophenol catalyzed by 0.06xa0mg of different silver monolith catalysts (a) Ag/Triton X-100, (b) Ag/Triton X-100/dextran, (c) Ag/Triton X-100/TMB, (d) Ag/Triton X-100/Ludox (HF treated). (e) Plots of A/A0 versus time of different Ag monoliths for catalytic reduction of 4-nitrophenol (A) Ag/Triton X-100 (B) (C) Ag/Triton X-100/dextran Ag/Triton X-100/TM (D) Ag/Triton X-100/Ludox (HF treated).

Hierarchically macro/mesostructured porous Au monoliths: simple synthesis, characterization and catalytic performance

We report an efficient, highly selective and low-temperature three-dimensional hierarchically macro/mesostructured porous gold monoliths catalyzed reaction process for one-step oxidation of benzene to phenol with hydrogen peroxide as the green oxidant. The porous catalysts were characterized before calcination by FTIR and TGA and after calcination by XRD, FESEM-EDX and BET techniques. The selectivity of phenol production from the one-step oxidation of benzene over porous gold catalysts can be enhanced by concise tuning of pore diameter and pore surface morphology. From the results obtained, it was concluded that the balance between the decomposition rate of H2O2 and benzene adsorptionxa0over the catalyst surface is responsible for the outstanding catalytic performance of the three-dimensional macro/mesoporous gold monoliths.Graphical AbstractThe as-synthesized series of nanoporous gold monoliths were evaluated for the first time as alternative heterogeneous catalysts for the direct catalytic oxidation of benzene to phenol at low temperature. Therefore, it is of great interest to “switch-off” other time- and energy-consuming reactions and promote the hydroxylation of benzene with porous Au catalysts.

Fabrication of hierarchically mesoporous CuO nanostructures and their role as heterogenous catalysts and sensors

Tween-80 templated mesoporous CuO (mpCuO) nanostructures were explored via a facile, environmentally friendly and scalable sol–gel route for heterogeneous catalysis and sensor technology. Silica nanoparticles (Si-NPs) were used as structural directing agents (SDAs) for the shape selective morphological changes of porous materials which resulted in the fabrication of nanoflowers of CuO/Si-NPs along with a great change in surface area. The mpCuO nanostructures were well characterized by FTIR, TGA, PXRD, FESEM-EDX, TEM, BET techniques. Interestingly, the as-synthesized mpCuO nanostructures showed excellent catalytic activity against the direct hydrogenation of acetone to isopropanol in the presence of sodium borohydride (NaBH4). In addition, mpCuO nanostructures have proved to be excellent sensor materials for simultaneous detection of some metals and biomolecules.