The main objective of this study was to map (1) the research of metacognition in science learning; (2) learning interventions used and metacognition’s key components that learned, integrated, and investigated; and (3) future research recommendations of metacognition research in science learning. We analyzed 438 scientific documents published in journals and books indexed in the Scopus database using VOSviewer software to visualize research trends and main keywords investigated of metacognition in science learning. The research findings show that research in the field of metacognition in science learning through the metacognition as attribution that integrated into learning interventions and as a learning outcome has increased in the last two decades. Scientific concepts understanding, critical thinking skills, motivation, and attention are the main goals in metacognition research. Inquiry-based learning, such as problem-based learning, is the most frequently used intervention to teach students metacognition. The research gaps found are (1) the cognitive regulations are the most investigated aspect, while cognitive aspects such as declarative knowledge, procedural knowledge, and conditional knowledge have not been widely investigated in science learning; (2) metacognition research on college students has a high frequency compared to school students; and (3) the integration of metacognition in online learning is still less investigated, this is indicated by the recommendations of several research results that encourage the integration of self-regulated learning into online learning.

The discharge of dyes in the textile industry leads to several hazardous effects on the environment. One of the most effective methods on treating dye-contaminated wastewater is photocatalytic degradation. TiO 2 has been widely used as a photocatalyst for wastewater treatment. Since the light absorption of TiO 2 is in the UV light range, however, doping of TiO 2 with a non-metal or metal element is needed to improve its absorption in the visible light range. In this study, TiO 2 photocatalyst was doped with carbon using sucrose as a carbon+e at ratios of 0.75:1 and 1:1. The surface area of TiO 2 after doping with carbon improved to two times the TiO 2 surface area. Additionally, the band gap energy of TiO 2 was successfully reduced to 2.38 eV after doping with carbon. In order to avoid the secondary pollutant problems, the carbon-doped TiO 2 was then immobilized with polyamide fibers at 1wt%, 2wt % and 3wt% to facilitate recollection of the photocatalyst. A photodegradation test was performed by degrading methylene blue under visible light irradiation using 70W halogen lamps with a total of 5 hours of time interval readings. The highest percentage degradation was recorded at 82.67% using immobilized 2wt% 1:1 carbon-doped TiO 2 in polyamide fibers.

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