Xuepin Liao

One-step, size-controlled synthesis of gold nanoparticles at room temperature using plant tannin

Bayberry tannin (BT), a natural plant polyphenol, was used for one-step synthesis of gold nanoparticles (AuNPs) in aqueous solution at room temperature. During the synthetic process, BT simultaneously serves as a reducing agent and stabilizing agent, while no additional reagent (surfactant, template, and capping agent) or treatment (heat and photo-irradiation) is needed. The particle diameter and size distribution of BT-stabilized AuNPs (BT-AuNPs) can be facilely controlled by varying the concentration of BT, and the particle size of BT-AuNPs is as small as 1.8 ± 0.3 nm when the BT concentration was 800 mg L−1. Furthermore, this green approach for the auto-reduction synthesis of AuNPs can be completed in several minutes and exhibits high reproducibility, which shows great potential for practical applications.

Polyphenol-grafted collagen fiber as reductant and stabilizer for one-step synthesis of size-controlled gold nanoparticles and their catalytic application to 4-nitrophenol reduction

A facile method for one-step synthesis of size-controlled gold nanoparticles (AuNPs) supported on collagen fiber (CF) at room temperature was proposed. Epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface to serve as reducing/stabilizing agent, so that the AuNPs were generated on CF surface without introduction of extra chemical reagents or physical treatments. The prepared AuNPs were fully characterized, and the results showed that the dispersed AuNPs were successfully produced and the mean particle size of AuNPs could be effectively controlled in range of 18 to 5 nm simply by varying the grafting degree of EGCG on CF surface. These stabilized AuNPs were found to be active heterogeneous catalysts for the reduction of 4-nitrophenol to 4-aminophenol in aqueous phase. The catalytic behaviors of AuNPs depended on the particle size and the grafting degree of EGCG. A distinct advantage of these catalysts is that they can be easily recovered and reused at least twenty times, because of the high stability of the AuNPs supported by EGCG-grafted CF.

Adsorptive recovery of Au3+ from aqueous solutions using bayberry tannin-immobilized mesoporous silica.

Tannin is well known to be an inexpensive and ubiquitous natural biomass, which has high chelating affinity towards many metal ions. In this study, bayberry tannin (BT) was immobilized on mesoporous silica matrix to prepare a novel adsorbent, which was subsequently used for the adsorptive recovery of Au(3+) from aqueous solutions. It was found that bayberry tannin-immobilized mesoporous silica (BT-SiO(2)) was able to effectively recover Au(3+) from acidic solutions (pH 2.0). The equilibrium adsorption capacity of Au(3+) on BT-SiO(2) was high up to 642.0 mg/g at 323 K. Due to its mesoporous structure, BT-SiO(2) exhibited an extremely fast adsorption rate to Au(3+) as compared with other tannin gel adsorbent. The presence of other coexisting metal ions, such as Pb(2+), Ni(2+), Cu(2+) and Zn(2+), did not decrease the adsorption capacity of Au(3+) on BT-SiO(2), and BT-SiO(2) had almost no adsorption capacity to these coexisting metal ions, which suggested the high adsorption selectivity of BT-SiO(2) to Au(3+). Additionally, about 73% of adsorbed Au(3+) can be desorbed using aqua regia, and the Au(3+) solution was concentrated about 18.0 times as compared with the original solution. Consequently, the outstanding characteristics of BT-SiO(2) provide the possibility of effective recovery and concentration of Au(3+) from diluted solutions.

Synthesis of highly active and reusable supported gold nanoparticles and their catalytic applications to 4-nitrophenol reduction

Gold nanoparticles (AuNPs) are first prepared for the first time by a one-step, green synthesis method using plant tannins as reductant as well as stabilizer. Subsequently, the resultant AuNPs were supported on γ-Al2O3 to prepare a heterogeneous AuNP catalyst (Al2O3-BT-AuNPs). The resultant Al2O3-BT-AuNPs catalyst was well characterized by N2adsorption/desorption, ultraviolet diffusion reflection (UV-DR) spectroscopy and transmission electron microscopy (TEM). It was found that the Al2O3-BT-AuNPs catalyst was highly active and reusable in the catalytic reduction of 4-nitrophenol to 4-aminophenol, and its catalytic activity was dependant on the loading percentage of BT.

One-step room-temperature synthesis of Au@Pd core–shell nanoparticles with tunable structure using plant tannin as reductant and stabilizer

Bayberry tannin (BT), a natural plant polyphenol, is used for the one-step synthesis of Au@Pd core–shell nanoparticles (Au@Pd NPs) in aqueous solution at room temperature. Due to its mild and stepwise reduction ability, BT was able to preferentially reduce Au3+ to Au NPs when placed in contact with an Au3+/Pd2+ mixture, and subsequently, the formed Au NPs served as in situ seeds for the growth of a Pd shell, resulting in the formation of Au@Pd NPs. Importantly, it is feasible to adjust the morphology of the Pd shell by varying the Pd2+/Au3+ molar ratio. Au@Pd NPs with a spherical Pd shell were formed when the Pd2+/Au3+ molar ratio was 1/50, while Au@Pd NPs with cubic Pd shell predominated when the ratio was increased to 2/1. The core–shell structure of synthesized Au@Pd NPs was characterized by TEM, HAADF-STEM, EDS mapping, an EDS line scan, and EDS point scan. Furthermore, density functional theory (DFT) calculations suggested that the localization of BT molecules on the surface of the Au clusters was the crucial factor for the formation of Au@Pd NPs, since the BT molecules increased the surface negative charges of the Au NPs, favoring the attraction of Pd2+ over Au NPs and resulting in the formation of a Pd shell.

Effect of ultrasound on the activity and conformation of α-amylase, papain and pepsin.

The effect of ultrasound on the activity of α-amylase, papain and pepsin was investigated and the mechanism of the effect was explored by determining their conformational changes. With the irradiation of power ultrasound, the activity of α-amylase and papain was inhibited, while the activity of pepsin was activated. According to the analysis of circular dichroism, Fourier transform infrared and fluorescence spectroscopy, the πo → π(∗) amide transitions and secondary structural components, especially β-sheet, of these three enzymes were significantly influenced by ultrasound. The tryptophan fluorescence intensity of the three enzymes was also observed to be affected by sonication. Furthermore, it was found that the pepsin molecule might gradually be resistant to prolonged ultrasonic treatment and recover from the ultrasound-induced damage to its original structure. The results suggested that the activity of α-amylase, papain and pepsin could be modified by ultrasonic treatment mainly due to the variation of their secondary and tertiary structures.

Tannin-immobilized mesoporous silica bead (BT–SiO2) as an effective adsorbent of Cr(III) in aqueous solutions

This study describes a new approach for the preparation of tannin-immobilized adsorbent by using mesoporous silica bead as the supporting matrix. Bayberry tannin-immobilized mesoporous silica bead (BT-SiO2) was characterized by powder X-ray diffraction to verify the crystallinity, field-emission scanning electron microscopy to observe the surface morphology, and surface area and porosity analyzer to measure the mesoporous porous structure. Subsequently, the adsorption experiments to Cr(III) were applied to evaluate the adsorption performances of BT-SiO2. It was found that the adsorption of Cr(III) onto BT-SiO2 was pH-dependent, and the maximum adsorption capacity was obtained in the pH range of 5.0-5.5. The adsorption capacity was 1.30 mmol g(-1) at 303 K and pH 5.5 when the initial concentration of Cr(III) was 2.0 mmol L(-1). Based on proton nuclear magnetic resonance (HNMR) analyses, the adsorption mechanism of Cr(III) on BT-SiO2 was proved to be a chelating interaction. The adsorption kinetic data can be well described using pseudo-first-order model and the equilibrium data can be well fitted by the Langmuir isothermal model. Importantly, no bayberry tannin was leached out during the adsorption process and BT-SiO2 can simultaneously remove coexisting metal ions from aqueous solutions. In conclusion, this study provides a new strategy for the preparation of tannin-immobilized adsorbents that are highly effective in removal of heavy metals from aqueous solutions.

Adsorptive recovery of UO22+ from aqueous solutions using collagen–tannin resin

Collagen-tannin resin (CTR), as a novel adsorbent, was prepared via reaction of collagen with black wattle tannin and aldehyde, and its adsorption properties to UO(2)(2+) were investigated in detail, including pH effect, adsorption kinetics, adsorption equilibrium and column adsorption kinetics. The adsorption of UO(2)(2+) on CTR was pH-dependent, and the optimal pH range was 5.0-6.0. CTR exhibited excellent adsorption capacity to UO(2)(2+). For instance, the adsorption capacity obtained at 303 K and pH 6.0 was as high as 0.91 mmol UO(2)(2+)/g when the initial concentration of UO(2)(2+) was 1.0 mmol/L. In kinetics studies, the adsorption equilibrium can be reached within 300 min, and the experimental data were well fitted by the pseudo-second-order rate model, and the equilibrium adsorption capacities calculated by the model were almost the same as those determined by experiments. The adsorption isotherms could be well described by the Freundlich equation with the correlation coefficients (R(2)) higher than 0.99, the adsorption behaviors of UO(2)(2+) on CTR column were investigated as well. Present study suggested that the CTR can be used for the adsorptive recovery of UO(2)(2+) from aqueous solutions.

Adsorptive removal of Cu(II) from aqueous solutions using collagen-tannin resin.

The collagen-tannin resin (CTR), as a novel adsorbent, was prepared via a reaction of collagen with black wattle tannin and aldehyde, and its adsorption properties to Cu(II) were systematically investigated, including pH effect, adsorption equilibrium, adsorption kinetics, and column adsorption. The adsorption capacity of Cu(II) on CTR was pH-dependent, and it increased with the increase of solution pH. The adsorption isotherms were well described by Langmuir isotherm model with correlating constant (R(2)) higher than 0.99. The adsorption capacity determined at 303 K was high up to 0.26 mmol/g, which was close to the value (0.266 mmol/g) estimated from Langmuir equation. The adsorption capacity was increased with the increase of temperature, and thermodynamic calculations suggested that the adsorption of Cu(II) on CTR is an endothermic process. The adsorption kinetics were well fitted by the pseudo-second-order rate model. Further column studies suggested that CTR was effective for the removal of Cu(II) from solutions, and more than 99% of Cu(II) was desorbed from column using 0.1 mol/L HNO(3) solution. The CTR column can be reused to adsorb Cu(II) without any loss of adsorption capacity.

Fe(III)-loaded collagen fiber as a heterogeneous catalyst for the photo-assisted decomposition of Malachite Green

A heterogeneous catalyst for Fenton reaction was prepared by immobilizing Fe(III) onto collagen fiber and its catalytic activity for the photo-assisted decomposition of Malachite Green (MG) was investigated. The results indicated that this Fe(III)-immobilized collagen fiber (Fe-CF) can effectively catalyse the decoloration and decomposition/mineralization of MG in aqueous solution. Catalysed by Fe-CF, MG solution was completely decolorized in 30 min, while 55.0% of TOC was removed from the dye solution within 120 min in the presence of H(2)O(2) and UVA irradiation (365 nm, 10 W). Fe-CF was recycled for seven times with certain activity loss (32.6% in decoloration, 18.5% in TOC removal), and its catalytic activity can be easily recovered by re-immobilization of Fe(III). Therefore, Fe-CF could act as an efficient and cost-effective catalyst for the photo-assisted decomposition of MG, and shows potential applications in practice.