The nature of carbon quantum dot (CD) luminescence is still broadly investigated based on different CD synthesis processes. This study aims at investigating the effect of microwave power on optical characteristics of CDs using microwave radiation techniques. CDs are synthesized with citric acid as a source of carbon and urea as a passivation agent. CDs have been successfully synthesized, and an increase in the CD burn-off percentage was observed with an increase in the microwave power. The TEM test results show that the dimensions of the CDs resulted are in the range of 3.4–9.5 nm with an average size of 6 nm at 450 W. The results of the FTIR functional group structural analysis show that a CD has N—H and O—H stretching bonds. According to the results of UV–Vis analysis, the CDs have absorption peaks at 335 nm and 407 nm, which indicates a π → π* electronic transition from the C=C bond and an n → π* transition from the C=O bond. Using the Tauc-plot method, the CD energy bandgap values were found to be 2.47 eV, 2.51 eV, 2.51 eV, 2.52 eV, and 2.53 eV at CD 300, CD 450, CD 600, CD 850, and CD 1000, respectively. The optical multichannel analyzer test results show that the peak emission waves produced by CDs are 536 nm and 532 nm with the strongest bright green light at CD 1000. Time-resolved photoluminescence testing shows that the CD decay time generally ranges from 5 ns. Overall, an increase in the microwave power causes an increase in the percentage of burn-off, energy bandgap, absorption intensity, and CD emission intensity.

ZnO is a popular photocatalyst that is often used for the degradation of dyes and bacteria. However, the catalytic performance of ZnO is only optimal under UV light exposure. This study aims to determine the degradation performance of rhodamine b, methylene blue, and Escherichia coli using 0, 5, 10, 15, and 20% Fe-doped ZnO (ZnO:Fe). Deposition of thin film was carried out using the sol-gel method with a spray-coating technique, while the degradation was carried out under halogen light exposure for 3 h. The optical characterization results show that 20% Fe-doped ZnO has the highest transmittance and the lowest energy band gap of 3.21 eV based on Tauc’s plot method. All thin films are hydrophilic with the largest contact angle of 68.54° by 20% Fe-doped ZnO and the lowest contact angle of 52.96° by 5% Fe-doped ZnO. The surface morphology of the thin film resembles a creeping root that is cracked and agglomerated. XRD test results show that the thin film is dominated by ZnO peaks with a wurtzite structure with a hexagonal plane phase and a crystal size of 115.5 A°. The 20% Fe-doped ZnO thin film had the most efficient degradation performance of 70.79% for rhodamine b, 65.31% for blue, and 67% for E. coli bacteria. Therefore, Fe-doped ZnO is a brilliant photocatalyst material that can degrade various pollutants even under visible light.

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Early detection of heavy metals in drinking water is a fundamental step that must be taken to prevent adverse effects on health. This research aims to develop a heavy metal ion detector by utilizing the fluorescence properties of carbon dots. Cdots were synthesized using the microwave irradiation method based on the central composite design: urea mass 0.31-3.68 gr; reactor power 200-1000 W; synthesis time is 13-46 min, and the response is quantum yield. Material characterization includes PL, TEM, UV-VIS, XRD, and FTIR. The selectivity and sensitivity of Cdots as detectors were tested for Ag+, Bi3+, Ni2+, Al3+, Co2+, Pb2+, Fe3+, Zn2+, Zr4+, and Hg2+ ions at concentrations of 0-10 µM. The results showed that Cdots were successfully synthesized by fluorescent light green at 544 nm. An adequate response model is quadratic with the formulation QY= +58.36+10.41X1+14.06X2+13.59X3–5.57X2X3–4.89X12-8.60X22– 5.40X32. The best Cdots were obtained in the formulation of R9 (3 g, 800 W, 40 min), which resulted in a QY of 74.39%. The characteristics of Cdots are spherical, diameter 6.6 nm, the bandgap of 2.53 eV, and having an amorphous structure. The surface of Cdots contains various functional groups such as O-H, C-H, C=O, C N, and C=C. In the heavy metal detection test, Cdots showed specific sensitivity to Fe- 3+ ions. The addition of Fe3+ concentration and the extinction of Cdots fluorescence intensity formed a linear correlation F0/F=0.08894[Fe3+]+0.99391 (R2=0.99276). The detection ability of Cdots for Fe3+ ions reaches a concentration of 0.016 ppm, much lower than the regulatory threshold limit of SNI, WHO, and IBWA. The detection of Fe3+ ions in drinking water uses a fluorescence technique consistent with the SSA and ICP-OES. Based on these results, the fluorescence technique using Cdots can be an instrument for quality control of the final drinking water product.

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Abstract. In this paper, we analyzed J-V curve of the Dye-Sensitized Solar Cell (DSSC) using numerical calculations. The simulation is based on differential equation of photoelectrochemical in the DSSC. Using internal parameters of the DSSC (L, D, n0, t) appropriate for TiO 2 , we calculate the J-V curve numerically. The analysis is performed by also making variations in temperature, irradiant, absorption constant and photoelectrode thickness. We found that irradiant affect the J-V curve significantly compared to the three other variables. The change in absorption constant needs to be in a factor at least in order of 100 or more to obtain a change, which is considerably high in J-V curve. It is also found that the thickness of photoelectrode should be carefully considered since very thin thickness cannot support DSSC process.

This study aims to synthesize Fe3O4 nanoparticles from natural iron sand as a starting material. The synthesis process was carried out by the coprecipitation method at a synthesis stirring rate of 270 rpm. Fe3O4 nanoparticle samples’ characterization process was carried out using scanning electron microscopy - energy dispersive X-ray (SEM-EDX), which produced a particle size of 10.76nm, and the Fe content of the sample was 60.96%. Characterization using X-ray diffraction resulted in a crystal size of 12.49 nm and a magnetite phase (Fe3O4) content of 48%. XRD characterization also showed the presence of another phase peak of NH4Cl. NH4Cl contaminants can be degraded by repeated washing using distilled water. This study proves that this synthesis can degrade other elements in natural iron sand to produce Fe3O4 nanoparticles.