Facile Synthesis of Gold Nanoparticles with Alginate and Its Catalytic Activity for Reduction of 4-Nitrophenol and H₂O₂ Detection

Abstract

Gold nanoparticles (AuNPs) were synthesized using a facile solvothermal method with alginate sodium as both reductant and stabilizer. Formation of AuNPs was confirmed by UV-vis spectroscopic analysis. The synthesized AuNPs showed a localized surface plasmon resonance at approximately 520-560 nm. The AuNPs were characterized using transmission electron microscopy, X-ray diffraction and dynamic light scattering. Transmission electron microscopy revealed that the AuNPs were mostly nanometer-sized spherical particles. Powder X-ray diffraction analysis proved the formation of face-centered cubic structure of Au. Catalytic reduction of 4-nitrophenol was monitored via spectrophotometry using AuNPs as catalyst, and further a non-enzymatic sensor was fabricated. The results demonstrated that AuNPs presented excellent catalytic activity and provided a sensitive response to H₂O₂ detection.

Keywords: alginate; catalytic activity; gold nanoparticles.

Scheme 1

Schematic illustration of the formation of AuNPs with alginate and its application for the catalytic hydrogenation of 4-NP to 4-AP and the non-enzymatic H₂O₂ sensor.

Figure 1

Effect of reaction parameters on the synthesis of gold nanoparticles. (A) UV-vis spectra of AuNPs prepared using different concentrations of sodium alginate in the presence of HAuCl₄ (2.5 mM) at 90 °C for 60 min; (B) UV-vis spectra of AuNPs prepared using different concentrations of HAuCl₄, sodium alginate (1.0%) at 90 °C for 60 min; (C) UV-vis spectra of AuNPs prepared at different reaction time with sodium alginate 1.0%, HAuCl₄ 1.2 mM at 90 °C; (D) UV-vis spectra of AuNPs prepared with different reaction temperature with sodium alginate 1.0%, HAuCl₄ 1.2 mM, 60 min.

Figure 2

(A–C) TEM images of AuNPs prepared using 0.25, 1.0, 3.5 mM of HAuCl₄, respectively; (D) XRD patterns of AuNPs prepared using different HAuCl₄ concentrations of 0.25 (a); 1.0 (b); 3.5 (c) mM, respectively. The inset is the corresponding particle size analysis histogram of the gold nanoparticles.

Figure 3

(A–C) DLS profile: Size distribution by number of AuNPs prepared using 0.25, 1.0, 3.5 mM HAuCl₄, respectively.

Figure 4

Zeta potential analysis of AuNPs prepared using 0.25 mM HAuCl₄.

Figure 5

(A–C) Time-dependent absorption spectra of the reaction solution of 4-NP into 4-AP over AuNPs prepared using 0.25, 1.0, and 3.5 mM HAuCl₄, respectively; (D) (1), (2), and (3) show the plot of ln(A_t/A₀) against the reaction time over AuNPs prepared using 0.25, 1.0, and 3.5 mM HAuCl₄, respectively.

Figure 6

(A) CV curves of AuNPs/GCE obtained in N₂-saturated 0.1 M PBS (pH 7.2) with different H₂O₂ concentration (from a to g: 0, 1, 2, 3, 4, 5 and 6 mM) at a 50 mV S⁻¹ scan rate, the inset is the linear fitting program of the reduction peak current (0.9 V) versus the H₂O₂ concentration; (B) CV curves of AuNPs/GCE obtained in N₂-saturated 0.1 M PBS (pH 7.2) containing 3 mM H₂O₂ concentration with different scan rate (from J to Q: 50, 100, 150, 200, 250, 300, 350 and 400 mV S⁻¹), the inset is the linear fitting program of the reduction peak current (0.9 V) versus the square root of scan rate.