RESUMEN
Real-time detection of formaldehyde in the atmosphere remains challenging. The available gaseous formaldehyde sensing methods offer limited sensitivity, selectivity, and robustness. We modified a quartz crystal microbalance (QCM) system for selective detection of formaldehyde in air. The QCM surface was functionalized with polyvinyl acetate (PVAc) nanofibers and doped with 2, 4, and 6 wt% aniline to improve the selectivity and sensitivity of the sensor. The chemical content and morphological structure of PVAc nanofibers doped with aniline were confirmed by Fourier-transform infrared (FTIR) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, and scanning electron microscopy (SEM). The results showed that the modified QCM sensor had a sensitivity of 0.056 Hz ppm-1 with a response and recovery times of 200 s and 90 s, respectively. It gave limits of detection (LOD) and limit of quantification (LOQ) of 28 ppm and 96 ppm, respectively. Moreover, the modified QCM was selective towards formaldehyde compared to the other gases. The current workplace exposure limit (WEL) for formaldehyde is 2 ppm, with a time-weighted average over eight hours. Future work will focus on improving the reported QCM sensor to meet the required LOD for formaldehyde detection in the environment and industrial sites.
RESUMEN
Background: Urea is a fertilizer widely used by farmers, especially vegetable farmers, due to its high nitrogen content, around 46 %. However, plants only use a small amount of nitrogen, a maximum of 35 %, while the remaining nitrogen is wasted and released into the environment. Undeniably, it causes increases production costs and environmental problems. A slow-release urea fertilizer (SRF) has been formulated to resolve these issues. Methods: In this study, the membrane was made of chitosan with several crosslinking agents such as Tripolyphosphate (TPP). In addition, calcium ion bonds are expected to increase the interaction with urea fertilizer through the encapsulation process. The results: Our data showed that urea slow-release fertilizer (SRF) with the chitosan/TPP/Ca membrane, was successfully synthesized. This membrane has the characteristics of a thin white layer that is transparent. The physical and chemical characterization of SRF membranes with various coating membrane variations showed that the chitosan/TPP/Ca-urea membrane has Young's modulus of 7.75-22.05 N/mm2, swelling of 109.52-132.62 % and porosity of 0.756-1.06 %. Functional group analysis shows that several spectral changes indicate the presence of crosslinking process between the chitosan functional groups and TPP. The urea release results show that the membrane is released through a diffusion mechanism. Furthermore, SEM results show that these membranes have pores with various shapes and sizes. Conclusion: Based on the result, it can be concluded that chitosan membrane modification with the addition of TPP and calcium oxide provides improved membrane characteristic cs including degree of development, hydrophobicity, membrane stress, and nitrogen release on the membrane. This membrane shows is indicating suitability as a slow-release fertilizer.