Preparation of Highly Uniform Polyurethane Microspheres by Precipitation Polymerization and Pd Immobilization on Their Surface and Their Catalytic Activity in 4-Nitrophenol Reduction and Dye Degradation

Abstract

Polyurethanes (PUNs) have been widely used in many fields. However, there are few reports on their microsphere preparation through precipitation polymerization. Herein, uniform PUN microspheres are prepared by precipitation polymerization of toluene diisocyanate and trimethylolpropane, without any surfactant and stabilizer. Under optimized conditions, monomers are fully polymerized within 2 h at a monomer concentration as high as 25.0 wt %, with a high yield of the microspheres (96.9%). By loading Pd on their surface, composite microspheres Pd@PUN are obtained and used as catalysts. 4-Nitrophenol is completely reduced within 1 min, with a kinetic constant of 4.96 min–1, significantly higher than many reported Pd-loaded catalysts, and with comparable reusability. Used in degradation of dye molecules, the catalytic performance is practically unchanged after 20 recycled uses. This work provides a simple method for the preparation of highly uniform PUN microspheres with a high yield and their Pd-loaded catalysts, both of great potential for various applications.

Preparation of PdAuCu/C as a Highly Active Catalyst for the Reduction of 4‐Nitrophenol by Controlling the Deposition of Noble Metals

“…UV‐Vis spectroscopy was used to monitor the reaction's progress. 4‐NP gave an absorption peak at 318 nm in aqueous solution, and this peak red‐shifted to 400 nm due to the formation of 4‐nitrophenolate after the addition of NaBH 4 solution (Figure S16) [20,62,63] . The Cu/C had low activity for this reduction reaction (Figure S17).…”

“…4-NP gave an absorption peak at nm in aqueous solution, and this peak red-shifted to 400 nm due to the formation of 4-nitrophenolate after the addition of NaBH 4 solution ( Figure S16). [20,62,63] The Cu/C had low activity for this reduction reaction ( Figure S17). As shown in Figure 6a-e, the absorption peaks intensity at 400 nm decreased gradually after the addition of catalysts and a new absorption peak at 298 nm appeared and increased gradually.…”

“…The catalysts could be easily recovered by a small magnet and could be reused at least seven times. Many research papers and reviews have focused on the effective catalytic reduction of 4‐NP to 4‐AP [20–50] …”

“…As a result, many studies have focused on the conversion of 4-NP to 4-AP. Yang et al [20] prepared uniform polyurethane microspheres as support for Pd to obtain microspheres of Pd@PUN for the reduction of 4-NP. The kinetic constant reached a value as high as 4.96 min À 1 .…”

Synthesis of post‐modified poly(ester‐amino) microspheres via aza‐Michael precipitation polymerization and its use for enzyme immobilization

“…However, commercially available monomers for them are too little to endow microspheres with ideal property, making it is difficult to obtain functional groups on the particle surface to meet different requirements for practical applications. Precipitation polymerizations of multi‐functional isocyanates with water, amino or hydroxyl compounds are systematic studied by our group and various solid and porous polyurea or polyurethane beads were obtained 23‐25 . Those particles were widely used as dyes degradation 26 and metal ions absorption, 27,28 and applied as supports of Pd 24,29 and Au 30,31 catalysts, benefiting of their functional surface with abundant amino groups.…”