Optimization of sol-immobilized bimetallic Au–Pd/TiO ₂ catalysts: reduction of 4-nitrophenol to 4-aminophenol for wastewater remediation

Abstract

A sol-immobilization method is used to synthesize a series of highly active and stable Au x Pd 1− x /TiO 2 catalysts (where x = 0, 0.13, 0.25, 0.5, 0.75, 0.87 and 1) for wastewater remediation. The catalytic performance of the materials was evaluated for the catalytic reduction of 4-nitrophenol, a model wastewater contaminant, using NaBH 4 as the reducing agent under mild reaction conditions. Reaction parameters such as substrate/metal and substrate/reducing agent molar ratios, reaction temperature and stirring rate were investigated. Structure-activity correlations were studied using a number of complementary techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The sol-immobilization route provides very small Au–Pd alloyed nanoparticles, with the highest catalytic performance shown by the Au 0.5 Pd 0.5 /TiO 2 catalyst. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

Recent Advances in Supported Bimetallic Pd–Au Catalysts: Development and Applications in Organic Synthesis with Focused Catalytic Action Study

“…The selection of catalyst preparation method and its modification is a deciding factor for final catalyst performance as the preparation of supported BMCs is more tedious than monometallic because of parameters such as the exact desired metal composition and bimetallic formation. Therefore, different methods for supported Pd–Au BMCs preparation have been developed such as deposition precipitation, − wet impregnation, − reduction deposition, − coreduction, , photochemical reduction, sol-immobilization, − coprecipitation, ion-exchange, metal sputtering, , sol–gel, sono-photodeposition, electroless deposition, and so on. The efficacy comparison of various adopted methods for preparation of Pd–Au BMCs is quite difficult as their selection is directly related to the nature of anchoring support.…”

“…Furthermore, a tandem reaction between benzyl alcohol and nitrobenzene catalyzed by Pd–Au/TiO 2 led to formation of imines and secondary amines, and Pd–Au/TiO 2 BMC mounted on polyacrylonitrile and nylon based nanofibrous membranes (PNFM) through electrospinning successfully oxidized 5-HMF to FDCA (Table , entry 13) . In addition to this, the oxidation of cinnamyl alcohol (Table , entry18), benzyl alcohol (Table , entry1–2) , and 1-phenylethanol (Table , entry 19), reduction of 4-nitrophenol (Table , entry 4), acetylene (Table , entry 12–13), , and photocatalytic HDC of TCE , have also been reported with significant enhancements in TON, TOF, and selectivity than the monometallic analogues as well other supports applied for same purpose. After TiO 2 , ceria (CeO 2 ) is the most frequently applied metal support for Pd–Au BMCs preparation because of its affordability, accessibility, acid–base properties, and the ability to bind with a large variety of metals. , Li and co-workers reported CeO 2 supported Pd 1 –Au 1 (wt %) BMC for α-alkylation of ketones with primary alcohols under visible light where unsaturated ketone formation takes place in the absence of visible light irradiation .…”

Synthesis of Layered Double Hydroxides and TiO2 Supported Metal Nanoparticles for Electrocatalysis

“…[11] Among these toxic compounds, nitrophenols are one of the persistent, with 4-nitrophenol (4-NP) being the most hazardous in the phenol group. [12] Due to its toxicity, 4-NP has been studied as a model compound to evaluate the catalytic activity of nanoparticles and other solid state materials [13] by adopting several methods such as mass spectrometry, chromatography and spectrophotometry. [14] However, the complexity of sample preparation and laborious nature makes these methods cumbersome.…”