Narrow Results

In this work, small-sized CaO–PdNps nanocomposites were synthesized using Lawsonia inermis leaf extract as a reducing and capping agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to analyze the produced nanocomposites. Based on these investigations, the average particle size was found to be $8\pm 12$nm, with a predominantly spherical morphology. The resulting nanocomposite was then tested for catalytic activity in methylene blue reduction. The mass of the catalyst and dye, the concentration of sodium borohydride ([NaBH4]), and the reaction time were all optimized using a central composite design (CCD). A significant correlation between predicted and experimental degradation percentages was shown by the CCD model ($R^2=0.9901$), which also proved statistically significant (p-$\mathrm{\text{value}}=0.0016$). Furthermore, a deep learning neural network (DLNN) was used to improve the prediction accuracy over and beyond CCD. There was a good connection between the two models as a result of using the CCD output as DLNN validation data. Mean absolute error (MAE), mean squared error (MSE), root mean squared error (RMSE), mean absolute percentage error (MAPE), and $R^2$ were used to assess the performance of the DLNN. The results ($\mathrm{\text{MAE}}=0.001$, $\mathrm{\text{MSE}}=0.01$, $\mathrm{\text{RMSE}}=0.001$, $\mathrm{\text{MAPE}}=0.001$, $R^2=0.999$) validated that all four metrics were successful in forecasting the percentage of degradation.

Catalyst-assisted chemical reduction of P-nitrophenol (PNP) with NaBH₄ is an efficient detoxification method. However, there exist many defects in the use of conventional powdery catalysts. In this work, nickel foam-supported NiO nanosheet array film (NiO@NF), fabricated by the hydrothermal-calcination method, was used as a monolithic catalyst for PNP reduction. A PNP reduction conversion of 91.71% with the reaction rate constant of 0.0995 min${}^{-1}$ was obtained within 25 min at 25${}^{\circ }\text{C}$. Moreover, during 13 continuous cycles, the reduction conversion of PNP always stayed above 80%. The results suggest that NiO@NF is a promising non-noble metal monolithic catalyst for PNP reduction owing to its superb catalytic properties, good stability and facile recovery.

Silver nanoparticles (Ag NPs) were synthesized by one-step process in the presence of kollicoat as capping, reducing and stabilizing mediator. The synthesized NPs were characterized by using FTIR, TEM, DLS, XRD, EDS and UV-Vis spectroscopy. The resulting Ag NPs had an incomparable colloidal stability against the salt addition and change of pH. The effect of different synthesis parameters and the catalytic property of the NPs were examined.

Synthesis of gold nanoparticles dispersed uniformly on mesoporous silica (mAu/SiO₂) by homogeneous deposition–precipitation (HDP) method is used as an effective catalyst for reduction of 4-nitrophenol to 4-aminophenol. Silica provides support and surface area to increase the catalytic activity of gold. X-ray photon spectroscopy revealed binding energy of Au 4$f_{7∕2}$ ($\sim$84.0eV) and Au 4$f_{5∕2}$ ($\sim$87.7eV) which support the formation of Au⁰ on SiO₂ surface. Au/SiO₂ showed Langmuir type-IV isotherms which are the characteristic features of mesoporous materials furthermore, pore size decreases with incorporation of Au NP’s on SiO₂ surface. The enhancement is due to the strong interaction of Au⁰ with silica support. The catalytic conversion was studied by UV-Visible spectroscopy and high performance liquid chromatography (HPLC) quantification method, which shows conversion of nitro group into amino group. In addition, the catalyst was easily separated and reused. The reusability of the catalyst exhibited better reduction of the 4-nitrophenol to 4-aminophenol even after 10 consecutive cycles. In comparison to trisodium citrate capped pure gold nanoparticles mAu/SiO₂ catalysts showed very good catalytic activity toward nitrophenol reduction. Here we conclude that embedment of metal catalysts like Au into high surface area support like silica is a positive step toward development of novel heterogeneous catalysts.

Polydopamine-coated Fe₃O₄ (Fe₃O₄@PDA) nanoparticles (NPs) were prepared as synergistic redox mediators for the catalytic reduction, by NaBH₄, of azo dyes such as methyl orange (MO) and methyl red (MR). Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were applied to determine their surface morphology, surface chemistry and detailed chemical composition, respectively. The latter technique confirmed the presence of quinone moieties. Moreover, a vibrating sample magnetometer (VSM) was used to confirm the superparamagnetic properties of these NPs. The characteristic optical absorption maximum of MO at 462nm was used to monitor the decolorization process. This was employed to determine the catalytic activity in the reaction. An enhancement of the catalytic activity of the magnetic-separable Fe₃O₄@PDA nanocatalyst over that of PDA microspheres (MPs) was observed. Moreover, their reusability and stability were also investigated. A synergistic electron transfer mechanism involving both Fe₃O₄ and PDA moieties was proposed as follows: the quinone moieties and Fe (III) species in Fe₃O₄@PDA NPs served as systematic redox mediators, with quinone receiving an electron from NaBH₄. The reduced quinone next transfers an electron to the Fe (III) moiety, generating an Fe (II) species that in turn transfers an electron to the azo dye. We determined that this process resulted in enhanced reductive degradation of azo dyes when compared with PDA MPs. Moreover, Fe₃O₄@PDA NPs could be magnetically separated and recycled. We therefore concluded that these NPs show great potential in the immobilization of homogeneous catalysts in the chemical reduction processes of azo dyes.

Nickel nanoparticles embedded in mesoporous silica (Ni/SiO${}_2)$ were successfully synthesized by microwave-assisted in situ self-assembly method using colloidal silica, urea and nickel nitrate as precursors and glucose as carbon template, which resulted in mesoporous structure of silica through removal of template. Ni nanoparticles were uniformly well-dispersed within mesoporous silica, which were 3.5–4.0nm in diameter and had a very narrow particle size distribution. In addition, particle size of Ni nanoparticles can be controllably adjusted by microwave power. As-prepared Ni/SiO₂ catalyst exhibited better catalytic activity for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) than Ni/SiO₂-IM catalyst, which was mainly attributed to confinement effect of mesoporous silica support. This simple and versatile method can also be extended to cover many kinds of other supported catalysts for broad applications in many other catalytic reactions in the future.

An efficient and stable catalyst was prepared utilizing reduced graphene oxide, Ag nanoparticles and melamine sponge for the restoration of large volume effluent containing 4-nitrophenol at room temperature. And the as-prepared sample is suitable for continuous flow system. Almost 99% 4-nitrophenol ($1.0\times 10^{-4}$molL${}^{-1}$, 100mL) can be removed within 4min in the presence of the aforementioned sample. Moreover, it also exhibits remarkable stability in continuous flow system. This may offer a new route to the fabrication of efficient flowing catalytic system.

Metal-ferrite/maghemite nanocomposites (NiFe₂O₄/***$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O${}_3)$ were synthesized via doping maghemite with metal salt (NiCl₂ or CoCl${}_2)$ followed by reduction of metal ions using NaBH₄. The synthesized metal-ferrite/maghemite nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) and the amounts of the dopant-metal (Ni/Co) were determined using ICP-OES technique. Results showed that this synthetic route produced nanocomposites with highly active ferrite phases MFe₂O₄. The synthesized nanocomposites exhibited exceptional catalytic activities for the reduction of 4-nitrophenol and 2-nitroaniline as well as the catalytic degradation of methyl orange. Specific activity parameter of NiFe₂O₄/$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O₃ toward reduction of 4-NP reached 993.9 and 929.8s${}^{-1}$g${}_{\mathrm{\text{metal}}}^{-1}$, respectively. These high values of specific activities are higher than most reported metal-ferrite composites prepared via traditional co-precipitation methods. Besides, strong magnetic properties of the prepared metal-ferrite/maghemites facilitates easy separation process for several reuses.

In this work, a foam nickel-loaded Co₃O₄ nanosheet featuring an integral structure (NF@Co₃O₄) was successfully fabricated by a facile hydrothermal-calcination strategy. The catalytic performance of the NF@Co₃O₄ was evaluated using the reduction of P-nitrophenol (PNP) to P-aminophenol (PAP) under NaBH₄ as a model reaction. A reduction rate of 94.44% for PNP was achieved under the following reaction parameters over 25 min at 25°C: two slices of NF@Co₃O₄ monolithic catalysts (3×4cm²), a PNP concentration of 15 mg L ${}^{-1}$ (500mL), and a NaBH₄ dosage of 15 mmol L ${}^{-1}$. Moreover, NF@Co₃O₄ presented a stable performance in PNP reduction, maintaining a reductive conversion above 91% over sixteen consecutive runs. This study suggested that NF-loaded Co₃O₄ is a promising monolithic catalyst for the treatment of phenol-containing wastewater, owe to its superb catalytic performance and ease of recovery.