AuNPs-Based Thermoresponsive Nanoreactor as an Efficient Catalyst for the Reduction of 4-Nitrophenol

Abstract

A new AuNPs-based thermosensitive nanoreactor (SiO2@PMBA@Au@PNIPAM) was designed and prepared by stabilizing AuNPs in the layer of poly(N,N’-methylenebisacrylamide) (PMBA) and subsequent wrapping with the temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) layer. The new nanoreactor exhibited high dispersibility and stability in aqueous solution and effectively prevented the aggregation of AuNPs caused by the phase transformation of PNIPAM. The XPS and ATR-FTIR results indicated that AuNPs could be well stabilized by PMBA due to the electron transfer between the N atoms of amide groups in the PMBA and Au atoms of AuNPs. The catalytic activity and thermoresponsive property of the new nanoreactor were invested by the reduction of the environmental pollutant, 4-nitrophenol (4-NP), with NaBH4 as a reductant. It exhibited a higher catalytic activity at 20 °C and 30 °C (below LCST of PNIPAM), but an inhibited catalytic activity at 40 °C (above LCST of PNIPAM). The PNIPAM layer played a switching role in controlling the catalytic rate by altering the reaction temperature. In addition, this nanoreactor showed an easily recyclable property due to the existence of a silica core and also preserved a rather high catalytic efficiency after 16 times of recycling.

Synergistic Bonding of Poly(N-isopropylacrylamide)-Based Hybrid Microgels and Gold Nanoparticles Used for Temperature-Responsive Controllable Catalysis of p-Nitrophenol Reduction

“…However, when the temperature increased higher than the VPTT, the red region in Figure d,f, the shrinkage of microgels not only caused the AuNPs to come close to each other on the surface of microgels but also caused the hybrid particles to agglomerate (Figure S4), decreasing the number of catalytic sites. As a result, the catalysis efficiency decreased. , It also could be found from Figure d,f that the maximum k app appeared at approximately 35 °C, in accordance with the results in Figure that PNIPAM-based microgels would shrink in the temperature range of 28–37 °C.…”

“…Hybrid microgels of PNIPAM-Au and SiO 2 @PMBA@Au@PNIPAM with random filled and yolk–shell structures, respectively, sample 3 and sample 4 in Table , were employed as catalysts for the 4-NP reduction reaction. Although both hybrid microgels showed good catalytic performance due to low t 1/2 at a low mole ratio of Au and 4-NP, their poor thermal responsivity led to a reduction in controllability of the catalytic reaction.…”

“…As a result, the catalysis efficiency decreased. 63,64 It also could be found from Figure 7d,f that the maximum k app appeared at approximately 35 °C, in accordance with the results in Figure 3 that PNIPAM-based microgels would shrink in the temperature range of 28−37 °C.…”

“…Comparing AuNPs@MG-OH and AuNPs@MG-SH, AuNPs@MG-SH self-assembled by electrostatic interaction and Au−S bonding has better stability to facilitate the reduction smoothly, further improving the catalysis efficiency than that of AuNPs@MG-OH. 11,32,63,76,77 Competitiveness against Known PNIPAM-Based Materials. The catalytic performance of the AuNPs@MG-SH hybrid microgels (surface-covered) prepared in this study was compared with that of similar works according to the halflife (t 1/2 ), the mole ratio of Au and 4-NP, and the conversion of 4-NP.…”

“…Furthermore, the catalytic reduction might be controlled by temperature. Comparing AuNPs@MG-OH and AuNPs@MG-SH, AuNPs@MG-SH self-assembled by electrostatic interaction and Au–S bonding has better stability to facilitate the reduction smoothly, further improving the catalysis efficiency than that of AuNPs@MG-OH. ,,,, …”