Green synthesis of copper nanoparticles using plant extractives for coconut wood preservation

Abstract

The global demand for timber has been rising at an unprecedented rate, exerting immense pressure on natural forests. To meet this demand sustainably requires a shift towards alternative timber sources. Although abundant, the use of coconut wood is limited by its low natural durability. Traditional preservatives, such as chromated copper arsenate (CCA), copper chromium borate (CCB), and pentachlorophenol, have been used to enhance wood durability, but they pose significant environmental risks. Consequently, biopreservation techniques and advanced nanoparticle applications have emerged as potential eco-friendly solutions. This study addresses a key research gap between bio-preservation and nanoparticle technologies by exploring the effectiveness of green-synthesized copper nanoparticles (CuNPs) in enhancing the properties of coconut wood. Copper nanoparticles were synthesized using plant extracts from neem (Azadirachta indica), lantana (Lantana camara), senna (Senna spectabilis), and teak (Tectona grandis). Characterization of these nanoparticles through UV-Spectroscopy revealed peak values in the 300-350 nm range. Field Emission Scanning Electron Microscopy (FE-SEM) displayed, both spherical and rod-shaped particles, ranging from 8.84 nm to 95.17 nm. Energy-dispersive X ray spectroscopy (EDS) confirmed the presence of copper and oxygen peaks, indicative of either cuprous oxide (Cu₂O) or cupric oxide (CuO) formation. Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) analyses also revealed significant peaks for copper. Thermogravimetric Analysis (TGA) identified two major weight loss regions between 50–150°C and 200–450°C, showing thermal stability and a weight loss of approximately 60% at approximately 600°C. Following synthesis, CuNPs were impregnated into medium-density coconut wood through a vacuum of 3.99 kPa (1.18 in/Hg), which was initially created and maintained for 30 min. This was followed by applying a pressure of 6 bar (87.12 PSI) for 90 min. Successful impregnation was confirmed by FE-SEM, EDS, FTIR, and XRD. Physical, chemical, and durability tests were conducted, including Weight Percent Gain (WPG), Anti-Swelling Efficiency (ASE), Bulking Effect (BE), Water Uptake (WU), Volumetric Swelling (VS), UV weatherability, and termite resistance. The results indicate that the teak-extracted CuNPs achieved the highest yield and provided superior protection. The CuNP–teak treatment exhibited the highest WPG of 2.22%, indicating effective nanoparticle penetration and integration with the wood matrix. Additionally, CuNP-teak treatment yielded the highest bulking effect (2.04%) and water xxiv resistance, with a minimum absorption rate of 16.69% compared to 52.32% in the untreated control, highlighting significant hydrophobic enhancement. Similarly, CuNP-teak-treated wood demonstrated excellent dimensional stability, with the lowest volumetric swelling (2.00%) and highest ASE (83.54%), substantially outperforming the control sample (12.17% VS). Termite resistance tests revealed that CuNP-teak treated wood experienced minimal degradation, with a weight loss of only 0.61%, compared to 25.36% in untreated wood. Other nanoparticle treatments, such as CuSO₄.5H₂O (1.54%), CuNP-neem (1.65%), and CuNP lantana (1.95%), also caused minimal termite damage. Among the plant extracts, teak extract provided notable protection, with a 1.93% weight loss, which showed the cumulative effect of teak extract and CuNPs against the subterranean termite. UV-weatherability analysis, conducted via a QUV accelerated weathering tester for 278 h, showed that CuNPs provided limited protection against UV-induced color changes, with ΔE* values comparable to those of the control. In conclusion, the green synthesis of copper nanoparticles presents a promising and sustainable approach for enhancing the durability, dimensional stability, and termite resistance of coconut wood. However, additional research is required to ensure the safe and scalable application of nanoparticle-based wood preservation