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Relevant academic research and scientific papers

Green synthesis of gold, silver, platinum, and palladium nanoparticles reduced and stabilized by sodium rhodizonate and their catalytic reduction of 4-nitrophenol and methyl orange

Sodium rhodizonate was used as a bifunctional reducing as well as stabilizing agent for the single step synthesis of gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) nanoparticles (NPs) in water. Transmission electron microscopy analysis revealed that Pt, Au, Ag, and PdNPs have average core diameters of about 2, 8, 26, and 39 nm, respectively. The ability of these nanoparticles towards the catalytic reduction of 4-nitrophenol (4-NP) with sodium borohydride (NaBH4) and the dual-catalytic oxidation of formic acid followed by the reduction of methyl orange (MO) was studied. The apparent rate constants (kapp) of the catalytic reduction of 4-NP in the presence of Ag, Au, Pt, and PdNPs were calculated to be 2.1482, 1.1167, 1.088 × 10-1, and 1.65 × 10-2 min-1, respectively. However, for the dual-catalytic oxidation of formic acid followed by the reduction of MO, the kapp values were calculated to be 4.145, 1.25 × 10-2, 6.7 × 10-3, and 9.0 × 10-5 for the Pt, Pd, Au, and AgNPs, respectively.

Photocatalytic methanol assisted production of hydrogen with simultaneous degradation of methyl orange

Platinized TiO2 prepared by photodeposition was evaluated for activity in the simultaneous conversion of methyl orange (MO), and methanol assisted formation of hydrogen. Low concentrations of MO were found ineffective for generation of hydrogen in measurable quantities upon illumination of Pt/TiO2 in water. On the other hand, methanol induced hydrogen formation was significant. Surprisingly, when methyl orange was added to the methanol/water solution, hydrogen formation was significantly suppressed. The origin of this detrimental effect of methyl orange lies in the strong and preferred adsorption of the dye on the Pt sites of the catalyst, resulting in hydrogenation of the azo bond and suppression of the catalyzed formation of hydrogen. The hydrogenation of the azo bond is corroborated by dis-colorization of the solution and the observation of a mass fragment in LC-MS analysis corresponding to a hydrogenated product of MO (m/z = 172). Similar to hydrogen formation, dye dis-colorization is stimulated by the presence of methanol, without the formation of new chemical compounds, confirming the role of methanol as a hole scavenger in the photocatalytic processes. Finally the presence of oxygen (in lean conditions) delays dye hydrogenation and hydrogen formation, which we discuss is due to oxygen adsorption and formation of superoxide anions over the Pt sites (leading to oxidation of methanol), which is preferred over N=N bond hydrogenation, and proton reduction.

Green synthesized AgNPs decorated on Ketjen black for enhanced catalytic dye degradation

The green synthesis of nanoparticles using plant-based materials as an alternative to chemical and physical routes provides economic and environmental benefits. In the present study, silver nanoparticles (AgNPs) were fabricated using Pseudocydonia sinensis fruit extract. The fabricated NPs were then decorated on commercial Ketjen black-300 (AgNPs@KB-300) and Ketjen black-600 (AgNPs@ KB-600). The synthesized materials were characterized via XRD, FTIR, XPS, SEM-EDX, and HR-TEM studies. The SEM and HR-TEM results revealed that the synthesized AgNPs were spherical and successfully decorated on KB-300 and KB-600. Additionally, the catalytic ability of the synthesized samples during the degradation of methyl orange in the presence of NaBH4 was studied. Notably, the catalytic activity of AgNPs@ KB-600 was higher than that of AgNPs@ KB-300.

Borohydride-free catalytic reduction of organic pollutants by platinum nanoparticles supported on cellulose fibers

This study presents hydrogen gas-assisted reduction of organic pollutants viz. 4-nitrophenol (4-NP) and methyl orange (MO) by platinum nanoparticles (PtNPs) immobilized on cellulose fibers (CF). Because sodium borohydride (NaBH4) causes secondary pollution in water by its decomposition products, hydrogen (H2) gas was used as a clean, highly active, and alternative reducing agent. As the catalyst, PtNPs of about 2 nm in diameter were synthesized and supported on CF by employing a facile method. The nanocomposites (PtNPs@CF) demonstrated excellent catalytic activity and cyclic stability in the reduction of 4-NP and MO using H2 gas as the clean, environmentally friendly, highly reactive, and an alternative reducing agent to NaBH4. The catalytic reduction followed the pseudo-first-order reaction kinetic with apparent rate constants of 3.6 × 10?1 min?1 and 5.3?10?1 min?1 for 4-NP and MO, respectively. The results of this study further indicate that the H2 gas (reducing agent) and PtNPs@CF nanocomposite (catalyst) can potentially be used for the reduction of a wide variety of other organic and inorganic compounds in water.

Synthesis of high surface area transition metal sponges and their catalytic properties

We have reported sucrose-mediated facile route for the preparation of high surface area cobalt (Co), nickel (Ni), and copper (Cu) sponges. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the sponge-like and nanoparticle-like morphologies of the metal sponges. The catalytic activity of the metal sponges was studied via the reduction of organic pollutants, including 4-nitrophenol (4-NP), methyl orange (MO) and methylene blue (MB) in water. It was found that the Cu sponge exhibited the fastest rate for the reduction of 4-NP, MO, and MB, followed by the Co and Ni sponges, respectively. The metal sponges exhibited excellent catalytic stability for the reduction of 4-NP for multiple cycles. In addition, due to their magnetic properties, the Co and Ni sponges could be easily recovered and reused by applying an external magnetic field.

A Broader-scope Analysis of the Catalytic Reduction of Nitrophenols and Azo Dyes with Noble Metal Nanoparticles

In addition to the broad environmental implications associated with the removal of nitroaromatics from industrial effluent, the catalytic reduction of 4-nitrophenol (4NP) has emerged as a benchmark model for quantifying catalytic activity of metal nanoparticles. Here we present a series of noble metal nanoparticles immobilized on amorphous carbon (Au@C, Ag@C, Pt@C and Pd@C). All materials show competitive catalytic activity over 4NP, amino-substituted nitrophenols (ANPs) and azo dyes. Overall, Pd@C exhibits superior activity that increases further when exposed to recycling protocol. Moreover, testing all materials synthesized over a broader substrate scope with added functionalities reveals inconsistencies in the prognosticating ability of the ubiquitous 4NP model reaction. By incorporating variably substituted ANPs into the substrate scope and averaging performance, the resulting rank of catalyst activity more accurately reflects activity trends when applied to other reducible functionalities, such as -N=N- groups in azo dyes.

Reaction of Phenylhydroxylamine with Bisulfite. A Possible Model for Amine-Mediated Carcinogenesis

Under anaerobic conditions, phenylhydroxylamine reacts with the model nucleophile (bi)sulfite to form aniline, o- and p-aminophenol, and o- and p-aminobenzenesulfonate.Evidence is presented suggesting that all products result from intermediates formed from nucleophilic attack of both bisulfite and sulfite on the arylhydroxylamine with subsequent covalent addition-elimination processes leading to products.Such a scheme offers a possible alternative pathway for describing the mechanism for carcinogenic arylation of nucleic acid residues by arylhydroxylamines not requiring the intermediacy of short-lived free radicals or nitrenium ions.