Catalytic Reduction of p-Nitrophenol Using Chitosan Stabilized Copper Nanoparticles

Catalytic Reduction of p-Nitrophenol on MnO2/Zeolite -13X Prepared with Lawsonia inermis Extract as a Stabilizing and Capping Agent

p-nitrophenol (pNP) is a highly toxic organic compound and is considered carcinogenic and mutagenic. It is a very stable compound with high resistance to chemical or biological degradation. As a result, the elimination of this pollutant has been very challenging for many researchers. Catalytic reduction is one of the most promising techniques, if a suitable catalyst is developed. Thus, this work aims to prepare an eco-friendly catalyst via a simple and low-cost route and apply it for the conversion of the toxic p-nitrophenol (pNP) into a non-toxic p-aminophenol (pAP) that is widely used in industry. Manganese oxide was prepared in an environmentally friendly manner with the aid of Lawsonia inermis (henna) extract as a stabilizing and capping agent and loaded on the surface of 13X molecular sieve zeolite. The UV-Vis spectrum, EDS, and XRD patterns confirmed the formation of the pure MnO₂ loaded on the zeolite crystalline network. The TGA analysis showed that the samples prepared by loading MnO₂ on zeolite (Mn2Z, Mn3Z, and Mn4Z) lost more mass than pure MnO₂ (Mn) or zeolite (Z), which is mainly moisture adsorbed on the surface. This indicates a better dispersion of MnO₂ on the surface of zeolite compared to pure MnO₂, and thus a higher number of active adsorption sites. SEM images and EDS confirmed the dispersion of the MnO₂ on the surface of the zeolite. Results showed a very fast reduction rate, following the order Mn2Z > Mn3Z > Mn4Z > Mn > Z. With sample Mn2Z, 96% reduction of pNP was achieved in 9 min and 100% in 30 min. For Mn3Z, Mn4Z, and Mn, 98% reduction was achieved in 20 min and 100% in 30 min. Zeolite was the slowest, with only a 40% reduction in 30 min. Increasing the amount of zeolite in the synthesis mixture resulted in lower reduction efficiency. The kinetic study indicated that the reduction of p-nitrophenol on the surface of the prepared nanocomposite follows the pseudo-first-order model. The results show that the proposed nanocomposite is very effective and very promising to be commercially applied in water treatment, due to its low cost, simple synthesis procedure, and reusability.

Low-Temperature Sintering of l-Alanine-Functionalized Metallic Copper Particles Affording Conductive Films with Excellent Oxidative Stability

Here, the alpha amino acid l-alanine is employed as both a capping and stabilizing agent in the aqueous synthesis of submicron-sized metallic copper particles under ambient atmospheric conditions. The reduction of the copper(II) precursor is achieved using l-ascorbic acid (vitamin C) as the reducing agent. The nature of the complex formed between l-alanine and the copper(II) precursor, pH of the medium, temperature, and the relative proportion of capping agent are found to play a significant role in determining the size, shape, and oxidative stability of the resulting particles. The adsorbed l-alanine is shown to act as a barrier imparting excellent thermal stability to capped copper particles, delaying the onset of temperature-induced aerial oxidation. The stability of the particles is complemented by highly favorable sintering conditions, rendering the formation of conductive copper films at significantly lower temperatures (T ≤ 120 °C) compared to alternative preparation methods. The resulting copper films are well-passivated by residual surface l-alanine molecules, promoting long-term stability without hindering the surface chemistry of the copper film as evidenced by the catalytic activity. Contrary to the popular belief that ligands with long carbon chains are best for providing stability, these findings demonstrate that very small ligands can provide highly effective stability to copper without significantly deteriorating its functionality while facilitating low-temperature sintering, which is a key requirement for emerging flexible electronic applications.

Eggshell membranes coated chitosan decorated with metal nanoparticles for the catalytic reduction of organic contaminates

This study focusses on the effect of chitosan coating with eggshell membranes for the reduction of different organic pollutants. Chickens eggs were collected from the local market and utilized to extract the enrich eggshell membranes (ESM). The chicken eggshell membranes are abundant waste material which is inexpensive and illustrates remarkable physiognomies for many possible applications. Fresh fibers/strips coated by chitosan (CS) were prepared by mixing the eggshell membranes with CS solution (2 wt%/v) in different proportions i.e., 10 %, 30 %, 50 %, 60 %, 70 %, 80 %, and 90 %. These strips were then templated with copper and iron metal nanoparticles by putting them in their metal ions aqueous solution to adsorb the metals ions and were then reduced to zero-valent metal nanoparticles (MNPS) by using NaBH₄ aqueous solution. These prepared materials (MNPS@ESM-CS) were characterized by using XRD, XPS, FE-SEM, and EDS to confirm the successful preparation of MNPs over the surface of ESM coated with CS. Afterwards, these prepared materials were investigated as a catalyst for the reduction of different organic pollutants, such as 4-nitroaniline (4-NA), 4-nitrophenol (4-NP) and methylene blue (MB) dye. The catalytic efficiency of ESM was enhanced 5.7-fold by adding only 20 % CS solution. It was observed that Cu@ESM-CS-80 % took 7 min for reduction of 4-NA, 6 min for 4-NP, and 7 min for MB dye. The reusability of the catalytic strip was also investigated for four cycles and found efficient and can be easily recovered by simply pulling it from the reaction mixture.

Ruthenium Supported on Ionically Cross-linked Chitosan-Carrageenan Hybrid MnFe2O4 Catalysts for 4-Nitrophenol Reduction

Herein, we report a facile procedure to synthesize the hybrid magnetic catalyst (Ru@CS-CR@Mn) using ruthenium (Ru) supported on ionically cross-linked chitosan-carrageenan (CS-CR) and manganese ferrite (MnFe2O4) nanoparticles with excellent catalytic activity. The ionic gelation of CS-CR is acting as a protecting layer to promote the encapsulation of MnFe2O4 and Ru nanoparticles by electrostatic interactions. The presence of an active metal and a CS-CR layer on the as-prepared Ru@CS-CR@Mn catalyst was well determined by a series of physicochemical analyses. Subsequently, the catalytic performances of the Ru@CS-CR@Mn catalysts were further examined in the 4-nitrophenol (4-NP) reduction reaction in the presence of sodium borohydride (reducing agent) at ambient temperature. The Ru@CS-CR@Mn catalyst performed excellent catalytic activity in the 4-NP reduction, with a turnover frequency (TOF) values of 925 h−1 and rate constant (k) of 0.078 s−1. It is worth to mentioning that the Ru@CS-CR@Mn catalyst can be recycled and reused up to at least ten consecutive cycles in the 4-NP reduction with consistency in catalytic performance. The Ru@CS-CR@Mn catalyst is particularly attractive as a catalyst due to its superior catalytic activity and superparamagnetic properties for easy separation. We foresee this catalyst having high potential to be extended in a wide range of chemistry applications.

One-Pot Green Synthesis of Ag-Decorated SnO2 Microsphere: an Efficient and Reusable Catalyst for Reduction of 4-Nitrophenol

In this paper, hierarchical Ag-decorated SnO2 microspheres were synthesized by a facile one-pot hydrothermal method. The resulting composites were characterized by XRD, SEM, TEM, XPS, BET, and FTIR analysis. The catalytic performances of the samples were evaluated with the reduction of 4-nitrophenol to 4-aminophenol by potassium borohydride (KBH4) as a model reaction. Time-dependent experiments indicated that the hierarchical microspheres assembled from SnO2 and Ag nanoparticles can be formed when the react time is less than 10 h. With the increase of hydrothermal time, SnO2 nanoparticles will self-assemble into SnO2 nanosheets and Ag nanoparticles decorated SnO2 nanosheets were obtained. When evaluated as catalyst, the obtained Ag-decorated SnO2 microsphere prepared for 36 h exhibited excellent catalytic performance with normalized rate constant (κ nor) of 6.20 min-1g-1L, which is much better than that of some previous reported catalysts. Moreover, this Ag-decorated SnO2 microsphere demonstrates good reusability after the first five cycles. In addition, we speculate the formation mechanism of the hierarchical Ag-decorated SnO2 microsphere and discussed the possible origin of the excellent catalytic activity.

In situ reduction of well-dispersed nickel nanoparticles on hierarchical nickel silicate hollow nanofibers as a highly efficient transition metal catalyst

Ni nanoparticles were immobilized on the hierarchically double-shell nickel silicate hollow nanofibers, the composites exhibited an excellent catalytic activity.