Porous Polyurea Supported Pd Catalyst: Easy Preparation, Full Characterization, and High Activity and Reusability in Reduction of Hexavalent Chromium in Aqueous System

Abstract

Developing efficient supports for transition-metal nanoparticles (M-NPs) to prevent their agglomeration and to facilitate their handling and recycled use has been a constant objective. Herein, porous polyurea (PPU) is prepared by simple precipitation polymerization of toluene diisocyanate through its reaction with water in water–acetone, followed by Pd­(OAc)2 immobilization on a PPU surface to get Pd­(OAc)2@PPU and by Pd­(OAc)2 reduction to get a hybrid composite Pd@PPU with Pd-NPs on a PPU surface. Multiple characterizations revealed that the porous structure of PPU was retained in Pd­(OAc)2@PPU and Pd@PPU. Pd NPs were well dispersed on the Pd@PPU surface with a mean diameter of 7.18 nm. Pd@PPU was used as catalyst for reduction of toxic hexavalent chromium Cr­(VI) to benign trivalent chromium with formic acid as the reducer. A higher catalytic performance was detected compared to that of reported heterogeneous catalysts under similar conditions. A slight decrease in catalytic activity was detected in recycled use of the catalyst, which is ascribed to CO poisoning, a byproduct in formic acid decomposition. Full regeneration was obtained by heating the catalyst under N2 atmosphere for 2 h at 180 °C. This work provides therefore a novel approach for the preparation of a Pd@PPU catalyst of high performance for Cr­(VI) reduction, featured by low cost, facile synthesis, easy handling, and reusability.

Application of the Cu@PET Composite Track-Etched Membranes for Catalytic Removal of Cr(VI) Ions

“…Photocatalysis is one of the most popular techniques because of the simplicity of the hardware design, high efficiency, and low cost of the process [10,11]. Various types of nanoscale materials have previously been studied as effective catalysts for the removal of chromium(VI) ions [8,[12][13][14][15].…”

Uniform and Fluorescent Poly(urea-siloxane) Microspheres: Preparation and Recyclable Use as Sensors for Cr6+ and Fe3+ Detection

“…Cr 6+ is highly toxic and has been classified as a human respiratory carcinogen. 30,44,45 Fluorescent sensors are extensively used as a powerful means due to their simplicity, rapidity, and excellent sensitivity for Cr 6+ detection. 45−48 In order to explore the possibility to use PUSi3 microspheres as a sensor to detect Cr 6+ in water, the emission of PUSi3 6A, which revealed that, among the 16 ions tested, the emission was distinctly attenuated only by Cr 6+ and Fe 3+ , and practically no effect or a slight decrease in emission intensity was detected for the rest of the ions.…”

“…Cr 6+ is highly toxic and has been classified as a human respiratory carcinogen. ,, Fluorescent sensors are extensively used as a powerful means due to their simplicity, rapidity, and excellent sensitivity for Cr 6+ detection. − In order to explore the possibility to use PUSi3 microspheres as a sensor to detect Cr 6+ in water, the emission of PUSi3 dispersion (10.0 mg/mL) was measured in the presence of Cr 6+ (200 μmol/L). It was found that the emission intensity sharply declined.…”

“…Under this consideration, poly­(urea-siloxane) (PUSi) microspheres were prepared by the precipitation copolymerization of isophorone diisocyanate (IPDI) and APDS without any surfactants. Compared with suspension and emulsion polymerizations, polymer microspheres prepared this way feature a clean surface, because there is no need for any surfactants or stabilizers. − A variety of PU materials, including microspheres − and porous materials, − have been reportedly synthesized and used for dye adsorption, metal ion removal, enzyme immobilization, and Pd nanocatalyst support. − It is to point out that, PUSi as-prepared has neither any conjugation structure nor typical chromophores on the polymer chains, and the microspheres are highly fluorescent in the solid state and as dispersion in water. PUSi was used as a fluorescent probe for Cr 6+ and Fe 3+ detection in aqueous solution, demonstrating these microspheres may serve as a green probe for Cr 6+ and Fe 3+ detection with high performance and good reusability in particular.…”

Single-Step Green Synthesis of Iron Nanoparticles in the Aqueous Phase for Catalytic Application in Degradation of Malachite Green

“…They are difficult to decompose using conventional treatment procedures. Adsorption and flocculation, which are common dye effluent treatment techniques, are inefficient because they produce solid residue, which causes other environmental issues and needs further treatment [17][18][19]. Transition metal-related oxidative methods have demonstrated increased removal efficiency for the degradation of carcinogenic pollutants into lower molecular weight and reduced toxicity [20][21].…”