Search

Although silver nanoparticles have long attracted scientists due to their remarkable antibacterial properties, the tendency of AgNPs to agglomerate results in diminished antibacterial activities and increased toxicity against normal cells. Among carbon-based nanomaterials, graphene oxide (GO), the oxidized form of graphene, can be utilized as a base for AgNPs to grow and disperse. Regarding the chemical approach, it is conventional to engage sodium borohydride (NaBH4) or hydrazine to reduce silver ions. However, using excessive amounts of these chemicals raises concerns about toxicity in biomedical applications and environmental issues. Here, this work report the synthesis of AgNPs@GO nanocomposites by reducing silver nitrate on GO using various green reducing agents, including ascorbic acid, Houttuynia cordata Thunb. leaf extract, Coffea robusta L. Linden (Robusta green coffee) bean extract, and Camellia sinensis (L.) Kuntze (green tea) leaf extract. The synthesized AgNPs@GO were characterized by X-ray diffraction spectrum, UV–Vis analysis, and dynamic light scattering, followed by an evaluation of the antibacterial activity using the diffusion agar method. The results demonstrate the high potential of green tea as a green-reducing agent in the synthesis procedure of AgNPs. The synthesized AgNPs@GO using green tea extract showed a similar UV–Vis spectral shape compared to the AgNPs@GO synthesized using NaBH4 with the maximum absorption wavelengths of AgNPs at 428 nm and GO at 203.5 nm. The AgNPs@GO synthesized also had the smallest average diameter (609.67 nm) and the highest magnitude of the zeta potential (29.83 mV) among all synthesized samples. Noteworthy is that AgNPs@GO synthesized with green tea extract demonstrated significant stability over 40 days. Furthermore, the results of the antibacterial experiments reveal that the diameter of the inhibitory zone was approximately 2 mm, half that of the control drug amoxicillin (1 mg/mL). In summary, green tea leaf extract emerged as the most effective reducing agent for the eco-friendly synthesis of stable and durable AgNPs@GO. This indicates a suitable and straightforward process for large-scale antibacterial production with potential applications in biological wastewater treatment.

The public is increasingly concerned about the safety of fruit, so the production and preservation of high-quality fresh fruit is becoming more and more important. This work evaluated the use of a 405 nm light emitting diode (LED) for postharvest preservation of fresh green grapes under tropical temperatures of 29 ± 1 °C. LED exposure to green grapes was done for various lengths of time (0, 24, and 48 hours), corresponding to different dosages of 0, 0.7, and 1.4 kJ/cm2. After 7 days of testing, the results found that 95%, 75%, and 5% of the grapes had been invaded by microorganisms, which matched the pretreatment with LED light at 0 h, 24h, and 48 h. According to the first-order kinetic model, the constant rate of weight loss (k) was 0.039 ± 0.005 (control, LED-0h), 0.037 ± 0.009 (LED-24h), 0.062 ± 0.005 (day−1) (LED-48h), with all p-value < 0.001. Compared to the control condition, weight loss was mostly unaffected by LED-24h. No appreciable color changes were seen for LED-24h and 48h, indicating that the fruit has retained its original color as well as its freshness. In control samples, however, one-third of L* and a* values were reduced from baseline. The control samples are susceptible to fungus infection like Guignardia bidwellii, however, color development and morphology showed that LED-48h with an irradiation dose of 1.4 kJ/cm2 had outstanding anti-fungal effectiveness. These LEDs are a possible replacement for fluorescent lights in fruit market showcase and storage rooms, serving as both a source of illumination and protection against microbial contamination.

Phosphorus (P) is an essential yet non-renewable nutrient, so recovering it from urine is getting more attention since it has a high concentration of nutrients. This study aimed to investigate the impacts of temperature, storage condition on urine's characteristics, and the effects of pH, Mg:P ratio, and calcium (Ca) ion on yielded magnesium phosphate hydrate (Mg3(PO4)2•xH2O) crystallization from fresh urine. The results indicated that the urine stored at 4 °C in a sealed environment created less spontaneous precipitation. The findings showed that the favorable condition for Mg3(PO4)2•xH2O recovery was at pH 10.5 and Mg:P of 1.3. The XRD analysis confirmed that P was crystallized as Mg3(PO4)2•xH2O phase with an average particle size of 0.5 mm. Furthermore, SEM-EDS images suggested the Ca and K might co-precipitate with Mg3(PO4)2•xH2O. These findings indicate that the potential of P recovery from nutrient-rich wastewater can both reduce environmental pollution and profit from phosphate fertilizers.

Applying nanotechnology, particularly nano zero-valent iron encapsulated by carboxymethyl cellulose (CMC-nZVI), is considered less expensive and provides high efficiency for the decolorization of textile wastewater. In this study, Congo red dye (CR) was used in synthesized wastewater to evaluate the treatment performance using different composition ratios of CMC-nZVI. At the initial CR concentration of 500 mg/L, decolorization efficiencies increased with the increase of CMC contents. The removal efficiencies reached almost completely at the CMC:Fe2+ ratio of 0.004 within 10 seconds after adding CMC-nZVI to the CR solution. The optimal decolorization rate was observed at the Fe concentration of 1 g/L, with the CR removal efficiency of approximately 90% and a removal capacity of 8.298 g CR/g nZVI. The core principle of dye decolorization is breaking down the chromophore groups (-NN-), which makes the color of the dye, into N–H bonds. CMC-nZVI is a promising key to solving the issues caused by dye-containing wastewater.