Wet chemical synthesis of ZnO nanocoating on the surface of bamboo timber with improved mould-resistance

A Simple and Effective Method to Enhance the Mechanical Properties, Dimensional Stability, and Mildew Resistance of Bamboo Scrimber

Given the increasingly prominent contradiction between the supply of and demand for wood, the abundant resource of bamboo can be a good substitute. Bamboo scrimber can effectively improve the utilization rate of bamboo and has good mechanical properties. However, bamboo scrimber has the problem of poor mildew resistance, and does not meet the requirements for outdoor applications. In this study, in order to further improve the mildew resistance and mechanical properties of bamboo scrimber, alkali treatment was used to remove some nutrients from the bamboo bundles and change the pH of the bamboo scrimber. The results showed that nutrients such as hemicellulose, lignin, starch, and sugar were notably removed from bamboo bundles, and the pH of bamboo was slightly alkaline. The anti-mildew effect was significantly enhanced, which could allow use in outdoor environments, and the mechanical properties and dimensional stability were also improved. Among them, TB6 bamboo scrimber showed comprehensively excellent properties. The infection time in the laboratory mildew test increased from 3 days to more than 30 days, and the infection time in the outdoor mildew resistance test increased from 1 week to more than 8 weeks; the static bending intensity of TB6 increased by 62.6% to 150 MPa, and the bending modulus increased by 71.7% to 14.2 GPa; the change rate of water absorption thickness was reduced to 0.58%. This modification method effectively improved the mildew resistance of bamboo scrimber, while maintaining high mechanical strength, and provides a new method for the outdoor application of bamboo scrimber.

Preparation of Citral Compound and Its Bamboo Antimildew Properties

To reduce the amount of citral used without reducing the antimildew performance of bamboo, the citral compound preparation process, the distribution of the compound in bamboo, and its antimildew performance were investigated using the Oxford cup method, Fourier-transform infrared spectroscopy, and ultraviolet spectrophotometry. The results revealed that the combination of citral with cinnamaldehyde or thymol may lead to partial chemical reactions, which may change the chemical structure of citral and affect its bacteriostatic properties. The bacteriostatic properties of the citraldehyde thymol compound against common molds of bamboo were considerably superior to those of the citral cinnamaldehyde compound. The limonaldehyde thymol compound showed a low distribution trend outside and vice versa inside in the treated bamboo. The citral thymol compound exhibited good antimildew performance at a concentration of 200 mg/mL. The citral thymol compound could reduce the amount of citral by approximately 67 mg/mL without reducing the antimildew performance of bamboo.

Antioxidant-Mediated Modification of Citral and Its Control Effect on Mildewy Bamboo

To reduce the oxidative degradation of citral and improve its antimildew performance, citral was modified with natural antioxidants such as tea polyphenols, ascorbic acid, and theaflavin in the present study. Additionally, the effects of these natural antioxidants on the citral degradation rate and DPPH radical-scavenging rate, as well as the effectiveness of antioxidant-modified citral in the antimildew treatment of bamboo were investigated. Ascorbic acid, theaflavin, and tea polyphenols improved the antioxidant performance of citral to some extent, and the tea polyphenols exhibited the best antioxidant performance. When the amount of tea polyphenols added to citral reached 1.0%, the oxidative degradation of citral was effectively prevented. Compared with citral, tea-polyphenol-modified citral could reduce the efficacy of the bamboo antimildew treatment against all four mildews and the effectiveness of the antimildew treatment reached 100%. Citral modification with antioxidants reduced the amount of citral required in the treatment, thereby reducing the treatment cost for bamboo mildew.

Surface Functionalization of Bamboo with Silver-Reduced Graphene Oxide Nanosheets to Improve Hydrophobicity and Mold Resistance

A natural polyphenolic compound was used to assemble nanocomposites. Owing to its stable bioactive properties, bamboo has earned significant attention in material science. Its high nutrient content and hydrophilicity makes bamboo more vulnerable to mold attacks and shortened shelf lives. To produce efficient, multipurpose, long-life bamboo products, a novel technique involving an immersion dry hydrothermal process was applied to impregnate the bamboo with polyphenol-assisted silver-reduced graphene oxide nanosheets. Curcumin (Cur), a natural polyphenol found in the rhizome of Curcuma longa, was used in the preparation of curcumin-enhanced silver-reduced graphene oxide nanosheets (Cur-AgrGONSs). The nanocomposites and nanocomposite-impregnated bamboo materials were examined by field emission scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. At the same time, a phytopathogen was isolated from infected bamboo products and identified by internal transcribed spacer (ITS) sequences. The nanocomposites effectively inhibited the growth of the isolated fungus. The mold resistance and moisture content of both the treated and untreated bamboo timbers were also examined to determine the efficiency of the prepared nanocomposite. The antifungal activity and hydrophobicity of the bamboo materials were significantly enhanced after the incorporation of curcumin-enriched silver-loaded reduced graphene oxide nanosheets (B@Cur-AgrGONSs). This research outcome confirms that the nanocomposite is a well-organized antimicrobial material for different advanced domains.

Nano-AgCu Alloy on Wood Surface for Mold Resistance

The mold infection of wood reduces the quality of its surface and potentially endangers human health. One category of the most popular mold inhibitors on the market is water-soluble fungicides. However, easy leaching due to ionic forms is a problem, which reduces the effectiveness of their antimicrobial action, as well as causing environmental pollution. Interestingly, nanometer-sized sterilizing agents present strong permeability and highly fungicidal behavior, and they are not easily leached, due to the unique nanoscale effect, and they have become alternative candidates as marketable anti-mold agents for wood protection. In this study, we first designed and explored a nanoscale alloy (nano silver–copper alloy, nano-AgCu) to treat wood surfaces for mold growth resistance. The results showed that three molds, i.e., Aspergillus niger, Penicillium citrinum and Trichoderma viride, mainly grew on the surface of wood within a depth of 100 μm; and that the nano-AgCu alloy with a particle size of ~15 nm presented improved retention and anti-mold efficiency at a nanomaterial concentration on the wood surface. Its leaching rate increased non-linearly with the increase in nano-AgCu retention and then it showed a gradually decreasing trend. When the concentration reached 1000 mg/L, the nano-AgCu alloy uniformly distributed on the wood surface in a monodispersed state and exhibited a lower retention of 0.342 g/m², with an anti-mold efficiency of more than 75% and a leaching rate of only 7.678%. Such results positioned 1000 mg/L as the toxic threshold concentration of nano-AgCu against the three molds. This study can provide a scientific basis for the analysis of the anti-mold mechanisms of nano-AgCu alloy on wood surfaces and guide the application of nano-metal alloy materials in the field of wood antimicrobials.

Fabrication of core-shell type poly(NIPAm)-encapsulated citral and its application on bamboo as an anti-molding coating

Bamboo is a widely used renewable and degradable biomass material; however, its sustainable utilisation is hindered by its susceptibility to mold. The current bamboo anti-mold technology is mainly based on organic chemical agents; these agents can easily induce mold resistance in bamboo with long-term use, and can even adversely affect human health. In the present study, the poly(N-isopropyl acrylamide) (PNIPAm)/citral nanohydrogel was prepared by encapsulating the natural antibiotic citral in PNIPAm for the anti-mold treatment of bamboo. The results revealed that this nanohydrogel exhibited a core-shell system with citral as the 'core' and PNIPAm as the 'shell', an average hydrodynamic diameter of 88.1 nm, and a low critical solution temperature (LCST) of 35.4 °C. After the high-pressure impregnation with the nanohydrogel, the bamboo strips showed excellent control effects toward common bamboo molds. Therefore, the nanohydrogel demonstrated high efficiency and it may become an ideal alternative to organic chemical anti-mold agents, thus showcasing its significant potential in the field of mold prevention for bamboo.

Investigation of the Release Mechanism and Mould Resistance of Citral-Loaded Bamboo Strips

In the present study, the sustained-release system loading citral was synthesised by using PNIPAm nanohydrogel as a carrier and analysed its drug-release kinetics and mechanism. Four release models, namely zero-order, first-order, Higuchi, and Peppas, were employed to fit the experimental data, and the underlying action mechanism was analysed. The optimised system was applied to treat a bamboo mould, followed by assessment of the mould-proof performance. Our experimental results revealed that the release kinetics equation of the system conformed to the first order; the higher the external temperature, the better the match was. In the release process, PNIPAm demonstrated a good protection and sustained-release effect on citral. Under the pressure of 0.5 MPa, immersion time of 120 min, and the system concentration ratio of 1, the optimal drug-loading parameters were obtained using the slow-release system with the best release parameters. Compared to the other conditions, bamboos treated with pressure impregnation demonstrated a better control effect on bamboo mould, while the control effect on Penicillium citrinum, Trichoderma viride, Aspergillus niger, and mixed mould was 100% after 28 days. Moreover, the structure and colour of bamboo remained unchanged during the entire process of mould control.

Antimildew Treatment and Control Effect of Citral on Bamboo

Presently, chemical agents remain the main antimildew agents for bamboo, which has a certain negative impact on the environment and human health. Therefore, it is urgent to develop new environment-friendly antimildew agents for bamboo. Here, citral, an environment-friendly natural antibacterial agent, was used as an antimildew agent for bamboo. The orthogonal test was used to explore the effects of citral concentration, impregnation pressure, and pressurization time on the drug loading capacity of treated bamboo strips. The effect of antimildew-treated bamboo strips on bamboo mold was also discussed. Furthermore, the Fourier transform infrared spectroscopy and ultraviolet spectrophotometer were used to investigate the distribution of citral in bamboo strips. Results showed that the optimum technological parameters of citral mildew-proof treatment of bamboo were as follows: citral concentration: 0.795 mg/ml, impregnation pressure: 0.3 MPa, and pressurization time: 90 min. Also, citral was easy to volatilize, which decreased the citral content of bamboo strips after vacuum drying and showed the trend of a lower surface layer and a higher inner layer. The concentration of citral therefore had a significant effect on the drug loading of the antimildew-treated bamboo strips. Thus, it was difficult to achieve effective prevention and control of bamboo mold when bamboo strips were impregnated with a lower concentration of citral solution. When the concentration of citral reached 200 mg/ml, the prevention and antimold efficiency of antimildew bamboo strips reached over 100%. This study will provide references for the development and application of environment-friendly natural antibacterial agents in the field of bamboo mildew prevention.

Visible-Light-Driven Ag-Modified TiO2 Thin Films Anchored on Bamboo Material with Antifungal Memory Activity against Aspergillus niger

A round-the-clock photocatalyst with energy-storage ability has piqued the interest of researchers for removing microbial contaminants from indoor environments. This work presents a moderate round-the-clock method for inhibiting the growth of fungus spores on bamboo materials using Ag-modified TiO₂ thin films. Photoactivated antifungal coating with catalytic memory activity was assembled on a hydrophilic bamboo by first anchoring anatase TiO₂ thin films (TB) via hydrogen bonding and then decorating them with Ag nanoparticles (ATB) via electrostatic interactions. Antifungal test results show that the Ag/TiO₂ composite films grown on the bamboo surface produced a synergistic antifungal mechanism under both light and dark conditions. Interestingly, post-illumination catalytic memory was observed for ATB, as demonstrated by the inhibition of Aspergillus niger (A. niger) spores, in the dark after visible light was removed, which could be attributed to the transfer of photoexcited electrons from TiO₂ to Ag, their trapping on Ag under visible-light illumination, and their release in the dark after visible light was removed. The mechanism study revealed that the immobilized Ag nanoparticles served the role of “killing two birds with one stone”: increasing visible-light absorption through surface plasmon resonance, preventing photogenerated electron–hole recombination by trapping electrons, and contributing to the generation of ●O₂⁻and ●OH. This discovery creates a pathway for the continuous removal of indoor air pollutants such as volatile organic compounds, bacteria, and fungus in the day and night time.

Inhibition mechanism and antibacterial activity of natural antibacterial agent citral on bamboo mould and its anti-mildew effect on bamboo

Bamboo, a natural material, has been widely used in the fields of decoration, architecture and furniture. However, bamboo is easy to mildew and lose its use value. In this paper, the inhibition mechanism and antibacterial activity of a natural antibacterial agent citral on bamboo mould and its anti-mildew effect on bamboo were studied. The results showed that citral could change the shape of mycelium, destroy the integrity of mycelium structure, cell wall and cell membrane structure, thereby causing leakage of nucleic acids, proteins and other substances in the cell, as well as destroy the pH balance of the inside and outside of the cell, to inhibit or kill mould. When the concentration of citral is 100 mg ml-1, the antibacterial rates of citral against Penicillium citrinum (PC), Trichoderma viride (TV), Aspergillus niger (AN) and a hybrid fungi group comprising PC, TV and AN (Hun) were more than 100%. However, compared with the direct effect of citral on mould, the antibacterial property of bamboo treated with citral was significantly reduced, the mildew proof effect can be achieved only if the concentration of citral to treat bamboo is increased to more than twice the concentration of citral directly acting on mould.

Resistance to Growth of Molds for Wood Modified with Hydrophobic Hybrid Silica Gel Containing Copper Amine Complexes

Complexation copper with amine provides an effective strategy for fixation copper in wood, while hydrophobic modification improves the dimensional stability of wood. Thus, a combination of complexation and hydrophobization is expected to enhance the efficiency of copper-based biocides. In this study, hydrophobic hybrid silica gel containing copper amine complexes (MACu) was prepared through an in situ sol-gel process in wood using methyltriethoxysilane (MTES), 3-amino-propyltriethoxysilane (APTES), and copper chloride. The resistance to growth of molds for MACu modified wood (Populus tomentosa) was measured according to ASTM D3273-16. A leaching resistance test was carried out in accordance with AWPA E11-16. The results showed that only Aspergillus niger covered the surface of untreated wood blocks and no mold grew on the MACu surface even after the leaching test. MACu xerogel and MACu wood were further characterized by SEM-EDS, FTIR, and XPS. A possible schematic diagram of the reaction mechanism was proposed to explain the high-efficiency anti-mold performance of MACu wood.

Application of Nanotechnology in Wood-Based Products Industry: A Review

Wood-based industry is one of the main drivers of economic growth in Malaysia. Forest being the source of various lignocellulosic materials has many untapped potentials that could be exploited to produce sustainable and biodegradable nanosized material that possesses very interesting features for use in wood-based industry itself or across many different application fields. Wood-based products sector could also utilise various readily available nanomaterials to enhance the performance of existing products or to create new value added products from the forest. This review highlights recent developments in nanotechnology application in the wood-based products industry.

In situ deposition of MOF199 onto hierarchical structures of bamboo and wood and their antibacterial properties

Tremendous efforts have been dedicated to developing functionalized cellulose materials by synthesis with copper-based metal-organic frameworks (MOF199), also known as HKUST-1. However, few studies have explored the deposition of MOFs on woody materials due to the complex chemical compositions of these materials (cellulose, hemicellulose, lignin) and their difficulty of bonding with MOF crystals. In this article, for the first time, MOF199 was successfully synthesized onto two different woody materials, moso bamboo and balsa wood, via in situ deposition at room temperature. The results show that the diverse surface roughness and the hierarchical structures of woody materials have significant effects on the size of MOF199 crystal. Additionally, bamboo and wood coated with MOF199 exhibited better antibacterial activities against Staphylococcus aureus (S. aureus) than Escherichia coli (E. coli); they could minimize S. aureus colony levels to 2.08 from 8.98 CFU cm^-2. This study provides a facile method for the functionalization of woody materials with MOFs for antibacterial applications.

Facile in-situ growth of Ag/TiO2 nanoparticles on polydopamine modified bamboo with excellent mildew-proofing

Bamboo with the outstanding properties, such as good mechanical strength, fast growth rate and low growth cost, is considered as one of utilitarian structural nature materials. But bamboo is easy to get mildewed resulting in disfiguration and fungi corrosion. In this work, a facile method was developed to improve the mildew-proofing capability of bamboo. Mussel-inspired polydopamine (PDA) with biomimetic adhesion function and highly active functional groups was employed to immobilize highly-dispersed Ag and TiO₂ nanoparticles on the surface of bamboo via an in-situ growth method. Integrating the uniform PDA coating, photocatalytic function of TiO₂ nanoparticles and bactericidal role of Ag nanoparticles, the mildew-proofing capability of bamboo is enhanced significantly. The results show a non-covalent interaction is more likely to account for the binding mechanism of PDA to bamboo. And the prepared bamboo samples show good photocatalytic performance and have excellent resistance leachability. Meanwhile, the mildew-proofing property of prepared bamboo sample was greatly improved.

In Situ Formation of Ag Nanoparticles in Mesoporous TiO2 Films Decorated on Bamboo via Self-Sacrificing Reduction to Synthesize Nanocomposites with Efficient Antifungal Activity

We developed a novel green approach for the in situ fabrication of Ag NPs in mesoporous TiO2 films via the bamboo self-sacrificing reduction of Ag(NH3)2+ ions, which can inhibit fungal growth on the bamboo surface. Mesoporous anatase TiO2 (MT) films were first synthesized on bamboo via a hydrothermal method. Then, Ag NPs with a 5.3 nm mean diameter were incorporated into the pore channels of optimal MT/bamboo (MTB) samples at room temperature without the addition of reducing agents, such that the Ag NPs were almost entirely embedded into the MT films. Our analysis indicated that the solubilized lignin from bamboo, which is rich in oxygen-containing functional groups, serves as a green reductant for reducing the Ag(NH3)2+ ions to Ag NPs. Antifungal experiments with Trichoderma viride under dark conditions highlighted that the antifungal activity of the Ag/MT/bamboo samples were greater than those of naked bamboo, MTB, and Ag/bamboo, suggesting that these hybrid nanomaterials produce a synergistic antifungal effect that is unrelated to photoactivity. The inhibition of Penicillium citrinum effectively followed a similar trend. This newly developed bamboo protection method may provide a sustainable, eco-friendly, and efficient method for enhancing the antifungal characteristics of traditional bamboo, having the potential to prolong the service life of bamboo materials, particularly under dark conditions.

Fabrication of Hydrophobic ZnO/PMHS Coatings on Bamboo Surfaces: The Synergistic Effect of ZnO and PMHS on Anti-Mildew Properties

Poor mildew resistance has limited the application of bamboo materials. In this work, ZnO/PMHS coatings were fabricated on bamboo timber surfaces by hydrothermal synthesis method and hydrophobic modification with poly(methylhydrogen)siloxane (PMHS). The surface chemical characteristics and microstructure of the bamboo before and after modification were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and water contact angle (WCA). The morphology results indicated that ZnO on the surface of bamboo forms flower-like aggregations. The WCA of ZnO/bamboo increased from 65° to 142° after PMHS hydrophobic modification, indicating that the hydrophobicity of bamboo was significantly improved. The original bamboo had poor anti-mildew properties when exposed to Trichoderma viride, Aspergillus niger, and Penicillium citrinum. After depositing ZnO onto the surface of the bamboo, the anti-mildew properties were significantly improved. Furthermore, it was found that after PMHS hydrophobic modification, ZnO/bamboo had excellent anti-mildew properties when exposed to the three mold hyphae, which indicated that PMHS hydrophobic modification had a synergistic effect on the anti-mildew properties of bamboo with a ZnO coating.

Biogenic nanomaterials: Synthesis, characterization, growth mechanism, and biomedical applications

The biosynthesis of nanomaterials is a huge and intensifying field of research due to their application in various areas, in particular the biomedical and pharmaceutical fields. In this review, we focused on the biosynthesis of both metallic and semiconductor nanomaterials and their application in biomedicine and pharmaceutics. In order to meet an exponentially increasing need for nanostructured materials, the biological route for the synthesis of nanomaterials will have to be explored, offering advantages over chemical and physical methods as a simpler, more cost effective, and environmentally friendly method, and for which there is no need to use high pressure and temperatures or toxic chemicals. This review discusses in detail the potential role of bioreducing and capping/stabilizing agents in biosynthesis. This review also investigates the application of various biosynthetic nanomaterials as antimicrobial materials, in clinical detection, for drug delivery and wound-healing, and as anti-diabetic materials.

Colloidal silver nanoparticles: an effective nano-filler material to prevent fungal proliferation in bamboo

Silver nanoparticles (Ag-NPs) are effective nano-filler agents with antifungal activity able to improve bamboo's durability against fungus. Ag-NPs were used to fill up the bamboo biological matrix to obtain an engineered biocomposite material.