Engineering Headway Vol. 24

Abstract: Water sources in coastal areas are highly susceptible to seawater intrusion, leading to significant environmental and economic losses. Therefore, advanced treatment methods are required to make seawater suitable for clean water production, particularly in addressing water scarcity in coastal regions. One promising approach is seawater desalination using calcium alginate/graphene oxide (GO) beads. In this study, waste coral skeletons were utilized as a calcium source due to their high calcium content. X-ray fluorescence (XRF) analysis revealed that the calcium content in the coral skeletons was 93.4% before calcination and increased to 94.9% after calcination. These findings suggest that coral skeleton waste has potential as an adsorbent for Na⁺ and Cl⁻ ion removal. The synthesis of calcium alginate/GO was conducted using a droplet method and characterized using Fourier-transform infrared spectroscopy (FTIR). The adsorption process for Na⁺ and Cl⁻ ions was investigated at varying CaCl₂ concentrations (0.5 M, 1 M, and 2 M) to determine the optimal conditions for ion removal. Na⁺ ion analysis was performed using atomic absorption spectroscopy (AAS), while Cl⁻ ion concentration was determined via argentometric titration. The optimal Cl⁻ adsorption was observed at a CaCl₂ concentration of 0.5 M with a contact time of 30 minutes, achieving an adsorption efficiency of 99.8% in a standard NaCl solution and 35.9% in seawater. For Na⁺ ion removal, the highest adsorption efficiency was achieved at a CaCl₂ concentration of 2 M with a 30-minute contact time, resulting in 97.3% adsorption in a standard NaCl solution and 61.9% in seawater. These results highlight the potential of calcium alginate/GO composites, derived from waste coral skeletons, as effective adsorbents for seawater desalination.

Abstract: In this work, the activated biochar from coconut shell have prepared using H₃PO₄ with different concentration as activating agent. The obtained activated biochars were characterized by Fourier transform infrared (FTIR) and Iodine number. Effect contact time on the adsorption capacity was studied through batch adsorption. Equilibrium adsorption data was evaluated by Langmuir dan Freundlich isotherm model. As the result, The FTIR analysis revealed a new peak at 982 cm⁻¹ in the activated biochar, corresponding to a P-O group, which was absent in the pristine biochar. The activated biochar obtained had iodine number range from 761 to 1093 mg/g with the highest iodine number biochar activated by H₃PO₄ of 30%. Different concentrations of H₃PO₄ resulted in different optimum contact times of adsorption ranging from 20-60 minutes. Biochar activated by H₃PO₄ of 30% has the shortest optimum contact time with an adsorption capacity of 4.99 mg/g. Freundlich isotherm model provided better fit than to Langmuir isotherm model. The research results contribute to the development of sustainable and renewable adsorbent materials for the recovery or waste water treatment especially for nitrate.

Abstract: The increasing demand for metals has led to the growth of the metal industry in Indonesia. This has resulted in a rise in the amount of waste generated. Various methods can be used in the treatment of metal waste, such as flotation, flocculation-coagulation, and adsorption. One biopolymer that can be used for metal removal is chitosan. This study aims to synthesize chitosan from shrimp shell waste, which is then modified with silica to enhance its mechanical strength and stability in acidic conditions using the sol-gel method. The chitosan-silica composite is then immobilized using dithizone to increase the adsorption capacity through immersion variations of 4, 6, and 8 hours. The adsorbent, characterized using Fourier Transform Infrared, showed the presence of bonds in chitosan at wavenumbers 3454 cm^-1 (N-H) and 1647 cm^-1 (C=O), chitosan-silica at wavenumbers 966 cm^-1 (Si-O in Si-OH), 798 cm^-1 (Si-O in Si-O-Si), and 466 cm^-1 (Si-O-Si), and chitosan immobilized with dithizone at wavenumbers 2343 cm^-1 (S-H) and 1083 cm^-1 (S=C). Adsorption was performed by mixing the adsorbent with the waste for 1 hour, then the waste was added with 0.25 ml of phosphoric acid and analyzed using a UV-Vis Spectrophotometer. Based on the results of the study, the highest adsorption efficiency was obtained with the adsorbent variation of 8 hours immersion at 59%, while the adsorption efficiency for immersion times of 4 and 6 hours was 0.3% and 6%, respectively.

Abstract: Synthesis of calcium alginate silica gel based on coral skeleton and wedi awu beach sand has the potential to be used as a product to reduce NaCl levels in seawater. This research aims to maximize the potential of natural materials. The materials used in the manufacture of adsorbents are calcium from coral skeletons used as a constituent of CaCl2, silica extracted from Wedi Awu beach sand, and sodium alginate. The three materials were synthesized into a cross-linked calcium alginate silica gel. Silica extracted from beach sand was mixed with sodium alginate, and then the mixture was dripped into CaCl2 solution. The results obtained are white round-shaped adsorbent gel, which occurs because SiO2 reacts with-O-groups on sodium alginate to form a white mixture, and Ca2+ in CaCl2 will crosslink with sodium alginate when dripped, forming an adsorbent gel. In the FTIR analysis of silica calcium alginate adsorbent gel, there are-OH, C=O, C-O groups that can play an active role in NaCl adsorption. Calcium alginate silica adsorbent gel can produce the highest percent adsorption at a CaCl2 concentration of 0.5 M, with an optimum contact time of 60 minutes, namely for Na + obtained a percent adsorption of 95.24% and on Cl-of 99.19%. The results of concentration and time optimization were then tested with real seawater with a percent adsorption of Na + of 69.33% while on Cl-of 37.26%.

Abstract: Caffeine, an alkaloid compound found in coffee, is widely known for its ability to stimulate the human central nervous system. The caffeine content in Sidomulyo robusta coffee was analyzed using a gas chromatography-flame ionization detector (GC-FID) with ultrasound-assisted extraction as a preparation method using methanol solvent for 21 minutes at 32°C. A TR-1MS column (15m x 0.25 mm ID x 0.25 μm film, non-polar column 100% dimethyl poly-siloxane) was used for the GC analysis. The injector temperature was set at 260°C and the detector at 280°C. The initial oven temperature was set at 100°C, held for 1 minute, then gradually increased by 5°C/minute up to 280°C and held for 2 minutes, with the optimal flow rate condition selected at 1.2 mL/min. This method met all verification criteria and exhibited linearity in the 100–600 mg/L range with a high correlation coefficient of 0.9929, demonstrating its reliability and accuracy in determining caffeine content in coffee samples

Abstract: Most of FDM 3D technique use filaments made of plastic as the feeder or raw material. Therefore, its application limited to prototyping purpose. Recently, some filaments made of metal and plastic available in the market, which makes it possible to print functional components. However, there is a very limited number of published papers on mechanical properties and their accuracy. This research aims to find the optimal parameters of tensile strength and dimensional accuracy on 3D printing specimens made of steel-PLA. Some of the combined parameters are infill pattern, raster angle, print speed and bed temperature. This study used a delta-type 3D printer to print out specimens with dimensions according to ASTM D638 Type I. The results of this study are a combination that has optimal tensile strength values infill pattern honeycomb, raster angle 90°, print speed 80 mm/s and bed temperature 45°C. As for the combination with optimal dimensional accuracy, the parameters for infill pattern triangle, raster angle 90°, print speed 80 mm/s and bed temperature 60° are obtained.

Abstract: Copper (II) is an essential heavy metal for living things and is beneficial for the environment if levels are still below permitted limits. Copper (II) levels in the environment can be determined using potentiometric sensors. The sensitivity in measuring the copper (II) potentiometric sensor greatly determines the analysis results. To increase the sensitivity of the potentiometric copper (II) sensor, AuNPs compounds were added to the composition of the membrane material based on S-Methyl N-(Methylcarbamoyloxy) Thioacetimidate or methomyl. In this research, the optimum composition of the membrane for making copper (II) potentiometric sensors based on methomyl has been determined and the effect of AuNPs compounds on the sensitivity of copper (II) potentiometric sensors based on methomyl has been studied. Research variables include the composition of the membrane used and variations in the addition of AuNPs compounds to the optimum membrane composition. The research results show the optimum performance of the copper (II) potentiometric sensor on the membrane composition methomyl: PVC: DOP with a ratio of 17: 17: 66 (%w/w) which produces a Nernst Factor value of 28.09 mV/decade. The addition of AuNPs compounds to the potentiometric copper (II) sensor membrane showed optimum performance when adding 0.1 mL of AuNPs with a Nernst Factor value of 29.55 mV/decade with a detection limit of 0.6 ppm copper (II). The addition of AuNPs compounds to the optimum membrane composition can increase the Nernst Factor value which is close to the theoretical Nernst Factor value.

Abstract: Graphene–ZnO composite thin film was synthesized using Hummer method and prepared using electrodeposition has good potential for supercapacitors applications. However, times of electrodeposition could influence the capacitive behaviour due to concentration of graphene layer. The cyclic-voltametric, CV and impedance spectroscopy, EIS showed significant data on these studies. Five samples with concentration of graphene from 1 mg/ml to 5 mg/ml was prepared, represent from 0.04, 0.08, 0.12, 0.16 and 0.20 g mass of graphene. Deposition time was selected to 20, 40 and 60 minutes at 5V of fixed deposition voltage. Despite cyclic voltammetry, these five sample also was measured on their conductivity. CV characterizations of GZ4-20 shows the best result in CV curve shape with complete charging discharging process at 2.88E-05 Fg^-1 for specific capacitance at 20 minutes. The EIS characterization of GZ5-40 shows series resistance at 523.220 Ω as the best result in EIS characterization for 40 minutes electrodeposition time. Deposition time of Graphene-Zinc Oxide at 40 minutes prove that the time can influence on electrocatalytic performance. However, it can be good candidate for various micro electrical of capacitor devices.

Abstract: This study presents the development and optimization of polypyrrole/graphene oxide (PPy/GO) gas sensors for accurate and reliable coffee aroma detection. By systematically varying the PPy/GO film thickness, we determined the optimal configuration to maximize sensor sensitivity and response time. The optimized sensor demonstrated exceptional performance in distinguishing coffee aromas from different plantations, highlighting its potential for applications in coffee quality control and aroma analysis. The PPy/GO composite was synthesized using a proven method and characterized using Fourier transform infrared spectroscopy (FTIR). Fabrication of the sensor involved a straightforward drop-coating technique that allowed precise control of film thickness. Susceptibility testing was performed under controlled conditions using coffee vapor at various concentrations. To evaluate the performance of the sensor in real-world scenarios, coffee samples from three different plantations were analyzed. Despite minor variations in sensor response due to inherent differences in coffee aroma profiles, the overall reproducibility and consistency of the measurements were extremely satisfactory. The %RSD values between 1.11% and 4.75% demonstrate the precision and reliability of the sensor. Keywords: Graphena Oxide, Polypirrole, gas sensor, coffee aroma, thickness optimization