Electronic waste (e-waste) has become one of the fastest-growing waste streams in the world. However, only 17.4% of it can be collected and recycled in 2019. This study aims to formulate strategies to improve the supply chain of e-waste management in Indonesia. Methods used to develop strategies in this study are the Decision-Making Trial and Evaluation Laboratory (DEMATEL), the Analytical Network Process (ANP), Strength–Weaknesses–Opportunities–Threats (SWOT), and the Quantitative Strategic Planning Matrix (QSPM). The results show that infrastructure criteria have the largest weight, that is 0.267, followed by a social environment with 0.261, regulation with 0.244, stakeholder with 0.122, and economy with 0.054. The top priority of the selected strategies is to improve public education (ST1) and provide socialization of regulations and sanctions to the public (ST2).

In the present research, a modified post-hydrothermal treatment with different temperature of 80-150°C has been applied on as-annealed TiO₂ nanotubes derived from conventional hydrothermal process. The treatment has two-fold objectives, i.e. enhancing the nanocrystallinity of anatase TiO₂, and at the same time maintaining the integrity of nanotube structures. The resulting TiO₂ nanotubes were characterized by using XRD and UV-Vis spectroscopy. The XRD analysis revealed that the as dried TiO₂ nanotubes contain combined crystalline structures of sodium-titanate and anatase. It was also found that by increasing the post-hydrothermal temperature from 80 to 150°C, the nanocrystallinity of nanotubes enhances as indicated by increasing the crystallite size of anatase TiO₂ from 6.93 to 7.81 nm. The anatase crystallite growth affected the optical characteristic of nanotubes, as represented with the reduction of the band gap energy, E_g from 3.75 to 3.67 eV by using Kubelka-Munk analysis for the obtained UV-Vis reflectance spectra. TEM observation confirms that the integrity of nanotubes structure can be well-maintained upon post-hydrothermal treatment.

Research into converting solar light energy into electricity using so-called photovoltaic (PV) technology or solar cells (SCs) was started a long time ago. However, most developing countries tend to lag behind. The present work delivers a bibliometric mapping analysis of 30 years of Indonesian solar energy research papers in the Scopus database. A multidisciplinary point of view is used to cover the findings comprehensively, highlighting the emerging gaps, orientation, and promising future research that will benefit many researchers, governments, and industry. Two essential keywords, “photovoltaic” and “solar cell”, were used to harvest the data. A total of 1886 documents were finally investigated. The VOSviewer was utilized as a proper complement for visualizing and analyzing the publication trends based on the keywords and authorships. Many aspects of solar research have been explored, including the basic science of semiconductors, simulation, lab-scale device fabrication, and the application of technologies and policies. The findings show that the two keywords determined the research characteristics. It also reveals that the geographical location had a remarkable impact on publication distribution. The most striking result is that a minimum of 1146 documents are centralized on Java Island. In addition, the policies related to renewable energy show a strong impact: two years after the policies were announced, the publications exhibited a two-fold increase. The results also suggest that future research should focus on the increasingly significant domestic component of silicon-based solar cells, the various multidisciplinary approaches for making PV utilization more affordable, and on shifting towards the use of perovskite solar cells. Solid national and international collaboration should be continued for the sustainability of Indonesian solar energy research.

Ilmenite (FeTiO₃) is a suitable mineral to produce titanium dioxide (TiO₂) for photocatalyst applications. Therefore, this research was conducted to synthesize TiO₂ material from titanium oxysulfate (TiOSO₄) extracted from Indonesia local ilmenite mineral (FeTiO₃) and to modify this material into TiO₂ nanotubes through a hydrothermal process at 150 °C for 24 hours followed by a post-hydrothermal treatment with temperature variations of 80,100, 120, and 150 °C for 12 hours. The purpose was to investigate the effect of the post-hydrothermal variations on the crystal structure, morphology, and optical properties of the TiO₂ nanotubes produced. It was discovered from the scanning electron microscopy (SEM) observations that the TiO₂ nanotube was successfully derived from the ilmenite precursor. Moreover, the X-Ray diffraction (XRD) analysis of the nanotube crystal structure showed that post-hydrothermal treatment enhanced the crystallinity of the anatase TiO₂ phase even though the sodium titanate phase was observed to exist in the structure. The increase in the post-hydrothermal temperature from 80 to 150 °C was also discovered to have led to: 1) a reduction in the unit cell volume from 136.37 to 132.31 ų and a decrease in the lattice constant c from 9.519 to 9.426 Å; 2) an increase in density from 7.783 to 8.081 gr/cm³ as well as in the crystallite size from 19.185 to 25.745 nm; 3) a decrease in the bandgap energy (Eg), from 3.33 to 3.02 eV. These characteristics further indicate the ability of the photocatalytic performance of the nanotubes to enhance the degradation efficiency from 87.69 to 97.11 %. This means the TiO₂ nanotubes extracted from local FeTiO₃ can provide the expected crystal structure and photocatalytic performance