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Phenolic resin (PR) materials exhibit numerous outstanding properties and characteristics, including low cost, simple preparation, high mechanical strength, water resistance, and chemical corrosion resistance. They are widely used in fields such as construction, energy, catalysis, and biomedical materials. In recent years, PR nanomaterials have attracted considerable attention due to their controllable chemical structures and ease of functionalization. However, the conventional synthesis of PR nanomaterials relies heavily on toxic and harmful substances, particularly phenol and formaldehyde. Under the concept of green and sustainable development, it has become imperative to prepare high-performance, environmentally friendly PR nanomaterials using bio-based raw materials and to expand their related applications.

Based on this, Professor Yu Liu’s team from the State Key Laboratory of Bio-based Materials and Green Papermaking at Qilu University of Technology (Shandong Academy of Sciences), in collaboration with Associate Professor Wei-kun Jiang, Director Tao Zhang from Shandong First Medical University, and Associate Professor Ji-liang Ma from Dalian University of Technology, has developed a green method for preparing novel resin nanospheres (TFR) using tannic acid and furfural as raw materials. These TFR nanospheres were subsequently employed as carriers for multifunctional silver-based nanocomposites. Compared to conventional PR nanospheres, the new environmentally friendly TFR nanospheres possess abundant phenolic hydroxyl groups, significantly enhancing their adsorption, reduction, and chelation capacities toward Ag+. The prepared TFR nanospheres exhibit high stability and uniformity; by adjusting the amount of ammonia used during synthesis, their size can be precisely controlled within the range of 280 to 1430 nm. Importantly, these TFR nanospheres can load up to 60.3 wt% of silver nanoparticles (Ag NPs), with the Ag NPs themselves measuring only 10.6 nm in size. Moreover, this resin nanomaterial demonstrates outstanding dispersion stability, recyclability, free-radical scavenging ability, and environmental adaptability. The resulting TFR@Ag nanocomposite exhibits remarkable catalytic activity in the treatment of typical hazardous dye-containing wastewater, with rate constants for the catalytic degradation of methylene blue (MB) and methyl orange (MO) reaching as high as 1.71 min⁻¹ and 2.40 min⁻¹, respectively. In addition, the TFR@Ag nanocomposite also displays excellent antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), serving as an effective antimicrobial agent.

The related work, titled “Green Preparation of Versatile Silver-based Nanocomposites Using Whole Biomass-based Tannin-Furfural as Raw Materials,” has been published in the Chemical Engineering Journal. Wu Chen, a 2022 graduate student at the State Key Laboratory of Qilu University of Technology, is the first author of this work. Associate Professor Jiang Weikun from Professor Liu Yu’s team at Qilu University of Technology serves as the first corresponding author. Director Zhang Tao from Shandong First Medical University and Associate Professor Ma Jiliang from Dalian University of Technology are co-corresponding authors. In addition, graduate students Xia Mengyao and Liu Hui also participated in the experimental work associated with this study.

Image and Text Analysis

In this study, TFR nanospheres were prepared using biomass-derived tannic acid and furfural as raw materials, completely replacing toxic phenolic and aldehyde compounds. The synthesis process of TFR nanomicrospheres is illustrated in Figure 1a: First, tannic acid and furfural coalesce into regularly shaped spherical emulsion droplets, thereby reducing the interfacial energy between them in the ethanol-water mixture. Subsequently, these emulsion droplets undergo alkali-catalyzed crosslinking to form polymeric cores, which gradually solidify into solid polymer spheres—termed TFR. Following that, a one-step redox reaction is employed to synthesize the TFR@Ag nanocomposite. Tannic acid contains abundant reducing groups (such as phenolic -OH groups), which can effectively adsorb Ag+ ions onto their surface via electrostatic adsorption and chelation, creating numerous nucleation sites for Ag. Then, the adsorbed Ag+ ions undergo a redox reaction, rapidly initiating nucleation and forming small-sized Ag nanoparticles. Through the formation of coordination bonds—particularly chelation between the Ag nanoparticles and the catechol groups in tannic acid—these Ag nanoparticles are prevented from agglomeration.

Scheme 1. (a) Schematic showing the formation of TFR@Ag nanocomposites. (b) The mechanism diagram illustrating the interactions between Ag+ and Ag NPs.

The average particle size of TFR nanospheres ranges from 280 to 1430 nm, with PDI values between 0.063 and 0.283. As the amount of NH3·H2O catalyst increases, the diameter of TFR nanospheres also increases, enabling precise control over the nanosphere size within the range of 280 to 1430 nm. The addition of NH3·H2O also enhances the cross-linking degree of TFR nanospheres. With the gradual addition of ammonia water, the 1.0TFR nanospheres attain a stable spherical structure.

Fig. 1. SEM images and dimensions of TFR nanospheres with the adding amount of NH3·H2O as catalyst.

TFR nanoparticles exhibit excellent dispersibility in water, with no precipitation even after 5 hours. Moreover, TFR nanoparticles demonstrate outstanding dispersibility and environmental adaptability across a pH range of 3 to 10, as well as in various organic solvents such as methanol, ethanol, and isopropanol. In addition, TFR nanoparticles possess superior antioxidant activity. Considering the health and safety aspects of phenolic chemicals, the cytotoxicity of TFR nanoparticles toward HepG2 cells was evaluated in vitro using the MTT assay. As the dosage increased, the viability of HepG2 cells treated with TFR nanoparticles remained at approximately 90% even after 24 hours and up to 48 hours, indicating that TFR nanoparticles do not exert any cytotoxic effects.

Fig. 2. (a) Photographs showing the stability of samples in water for 5 h. (b) Tyndall effect and the dispersion stability of 1.0TFR nanospheres in different pH values and organic solutions. (c) The zeta potential of samples. (d) UV absorption spectra of the blends containing DPPH and TFR nanospheres. (e) DPPH scavenging activity. (f) Schematic illustrating the ionization state and surface charge of samples in water. (g - i) MTT assay results of samples after 24 h and 48 h.

The Ag NP loading levels in TFR nanospheres of different particle sizes were 60.3%, 56.1%, 53.2%, and 45.3% by weight, respectively—exceeding those reported for most PR nanomaterials to date. The average size of the Ag nanoparticles was 10.6, 11.2, 12.5, and 13.4 nm, which is comparable to that reported for most PR nanomaterials currently available.

Fig. 3. (a) SEM image and high-resolution SEM image. (b) EDS mapping images. (c) The lattice structure and the spacing of Ag NPs. (d) XRD patterns. (e) Electron diffraction pattern of Ag NPs. (g) The grain size analysis results determined using the Scherrer equation. (h) Ag loading amount. (i) The size distribution of Ag NPs. All the tested sample is 1.0TFR@Ag nanocomposites, unless specifically stated otherwise.

The prepared TFR@Ag nanocomposite exhibits outstanding catalytic activity in the treatment of typical hazardous dye-containing wastewater. As a catalyst, 0.4 mg of TFR@Ag can completely reduce 2 mL of 40 mg·mL⁻¹ MB and MO within just 1 minute, with reaction rate constants of 1.71 min⁻¹ and 2.40 min⁻¹, respectively. Moreover, under solution pH conditions of 3 or 10, the TFR@Ag catalyst achieves complete reaction with MB/MO in only 3 minutes, and the degradation of the MB-MO mixture is completed within just 4 minutes. These results demonstrate that the TFR@Ag catalyst is a highly efficient catalyst capable of simultaneously degrading multiple dye mixtures and exhibits excellent adaptability to harsh environmental conditions.

Fig. 4. Evolution of UV-vis spectra for MB (a, d), MO (b, e), and the mixed solution (c) in the presence of the TFR@Ag catalyst. Evolution of UV-vis spectra for the mixed solution (f) containing TFR nanospheres. Evolution of UV-vis spectra for MB (g, j), MO (h, k), and the mixed solution (i, l) in the presence of the TFR@Ag catalyst at different pH values.

The TFR@Ag nanocomposite can be easily recovered by centrifugation and exhibits excellent reusability. After five cycles of experimentation, the recovery rate of the TFR@Ag nanocomposite reached as high as 90%, with minimal loss of Ag NPs from the surface of the TFR nanospheres. When the recycled TFR@Ag nanocomposite was used as a catalyst, the removal rates of MB and MO remained as high as 90%.

Fig. 5. Apparent k and catalytic efficiency for the reduction of MB (a) and MO (b) over 5 cycles. (c) XRD patterns of the sample after 5 cycles. (d) TEM images of the sample after 5 cycles. (e) Photographs showing the stability of the catalyst in water for 5 hours. (f) The zeta potential of the catalyst.

In addition to their highly efficient applications in the catalytic field, silver-based nanomaterials also exhibit broad-spectrum antibacterial properties. The antimicrobial activities of TFR and TFR@Ag nanospheres/nanocomposites against single strains and co-cultured models of E. coli and S. aureus are shown in Figure 6. As evidenced by the growth patterns on the culture plates, the TFR@Ag nanocomposite demonstrates outstanding antibacterial efficacy against Gram-negative models (such as E. coli), Gram-positive models (such as S. aureus), and mixed cultures composed of both strains.

Fig. 6. Antimicrobial properties against E. coli and S. aureus. (a) Schematic diagram of antibacterial experiment. Antibacterial activity of TFR and TFR@Ag nanospheres/nanocomposites against (b, c) E. coli, (d, e) S. aureus (f, g) and co-culture models of E. coli and S. aureus at different concentrations.

Fluorescent staining was further employed to investigate the impact of the sample on bacterial cell integrity. Moreover, when DCFH-DA was used as a fluorescent probe to assess reactive oxygen species (ROS) levels, the TFR@Ag nanocomposite exhibited prominent green fluorescence after treatment, indicating that the TFR@Ag nanocomposite induces oxidative stress in bacteria. In summary, the TFR@Ag nanocomposite demonstrates strong bactericidal activity by inducing membrane damage and oxidative stress.

Fig. 7. (a) Live/dead fluorescence images of bacteria treated with different agents. Scale bar, 50 µm. (b–e) SEM images of bacteria. Scale bar, 500 nm. (f–i) ROS levels in bacteria. Scale bar, 50 µm.

Summary

Professor Yu Liu’s team from Qilu University of Technology has long been focused on the controlled synthesis and multifunctional applications of novel phenolic resin micro- and nanomaterials. In this study, they successfully prepared multifunctional silver-based resin nanocomposites with controllable size distribution and unique morphologies, using entirely bio-based tannic acid and furfural as raw materials instead of the toxic and harmful phenol and formaldehyde. The resulting TFR nanocomposites exhibit outstanding performance, particularly demonstrating excellent dispersion stability, recyclability, free-radical scavenging ability, and environmental adaptability. The abundant phenolic hydroxyl groups in tannins endow the TFR@Ag catalyst with a higher silver-loading capacity (60.3 wt%), enabling it to serve as an efficient catalyst and antimicrobial agent. It shows remarkable catalytic activity toward wastewater samples containing harmful dyes and exhibits high antibacterial efficacy against Escherichia coli and Staphylococcus aureus. This study proposes a novel approach for synthesizing universally applicable silver-based resin nanocomposites with controllable size distribution and unique morphologies, using entirely biomass-derived tannic acid and furfural as feedstocks. This method holds great application potential in fields such as catalysis, nanomaterials science, and biomedicine.

Paper Information:

Green Preparation of Versatile Silver-based Nanocomposites Using Whole Biomass-based Tannin-Furfural as Raw Materials

Chen Wu, Weikun Jiang*, Mengyao Xia, Hui Liu, Tao Zhang*, Jiliang Ma*, Yu Liu

Chemical Engineering Journal, DOI: 10.1016/j.cej.2024.151407

Original link:

https://authors.elsevier.com/sd/article/S1385-8947(24)02894-8

Original Title: “Non-Grain Technology | Construction of All-Bio-Based Resin Micro- and Nanomaterials and Their Applications in Catalysis and Antibacterial Fields”