Effect of roselle (hibiscus sabdariffa) on sensing properties of chitosan film sensors on fertilizer concentration detection

The aim of this project is to analyze the sensing properties of cbitosan film sensor (CFS) and chitosan-rosellc lilm sensor (CRBFS) toward fertilizers at various concentrations. This project has presented the fabrication and characterization of chitosan and cbitosan blend film sensors. The chitosan concentration of 1.75% w/v was selected as the best concentration to fabricate chitosan film sensor. It has proven from electrical testing that both CFS and CRBFS were able to operate at room temperature and fulfilled all the reqt1ired sensing properties including good response, recovery, sensitivity, repeatability, stability and selectivity upon exposure to wet air, dry air, and different fertilizer concentrations from lOppm until 50ppm. All film sensors were demonstrated well response in the both while in water and soil medium. While for blending, the chitosan concentrations of 1.50% w/v as a ratio 96:4 was selected to be blended with roselle extract which exhibited the best electrical and sensing properties. CRBFS gave better response value compared to CFS with range 80% to 90%. UV-VIS spectra of chitosan and chi to san blends showed the highest of intensity with 1.75% w/v of chitosan concentration for chitosan film and 1.50% w/v of chitosan concentration for blend films. The optical bandgap and conductivity results have proven that the electrical properties of CRBFS is bette than CFS. CRBFS gave the best electrical properties with the conductivity of 3.17 x 10·4 Sm 1 and optical band gap of 2.63eV whereas the conductivity and optical band gap of CFS with 3.02 x l0-5 Sm- 1 and optical band gap of 2.87eV of each. The AFM results showed the chitosan films with increased in concentration lead to the noticeable increase ofthe grain sizes. The chitosan-roselle blend films also showed the increasing on the grain size when increased the quantity of roselle extract. With the increasing in grain size, the surl'acc roughness increased. The AFM images also showed that the rougher surfaces with provided larger interaction area have proven that the Jilms were more sensitive during electrical testing with the fast action and stable. The changes of microstructure and su rf'ace morphology \·Ve re related to the electrical performance, the increase of grain size and surface roughness lead to reduction in number of grain boundaries. SEM images of CFS and CRBFS showed that chitosan and chitosan blend films with different concentration also have di !Terent morphological structure. The images of CFS and CRBFS showed the smooth and compact surface. From the thermal testing (TGA, DTG and DSC'), the results showed that CFS with 1.75% w/v has higher melting temperature than other cbitosan concentrations. This means the chitosan films with concentrations of 1.75% w/v gave higher heat resistance than chitosan film with the other concentrations. The thermal testing for chitosan-roselle blend films also showed that 1.50% with 4% roselle extraction with ratio (96:4) showed the higher melting temperature than other roselle extractions blends. The FTIR results showed that the intensity percentage of functional group exist in CFS were improved by addition of CRBFS with Nl-h and C-0. The XRD results have proven that the CRBFS has higher relative crystallinity percentage COITipare to CFS. The crystallinity was greatly enhanced from .intra and intermolecular interaction, which arc explained by hydrogen bonding in chitosan and chitosan blends. Spectroscopic, morphologicaL thermaL and electrical conduction for entire testing have proven that the CRBFS is better compared to CFS. The entire result from all testing showed CRBFS got the highest response value and more stable compared to CFS. It was proven that both CFS and CRBFS were able to operate at room temperature and fulfil all Lhe sensing properties including fast response, complete recovery, high sensitivity, good repeatability, good stability and good selectivity.