The presence of microplastics (MPs) in marine environments has become increasingly apparent. Owing to the lack of effective solid waste management, Indonesia is the second largest producer of ocean plastic waste after China. Currently, information about pollution of MPs in the sediments of East Surabaya, Indonesia, is not available, and this issue is addressed in this study for the first time. Sediment samples were collected from 16 sampling sites along urban and mangrove coastal areas. MPs were observed in most of the sampling sites, with abundances ranging from ND (not detected) to 598 items/kg. MP shapes constituted fragments (30%), foam (28%), granules (22%), and fibers (20%). The 500–1000 µm fraction was the dominant size of MPs. Polypropylene was the major polymer constituent, followed by high-density polyethylene and polyethylene. Findings from Spearman’s correlation coefficients, principal component analysis, and hierarchical cluster analysis reveal that the spatial pattern of MPs is closely related to coastal characteristics and population density. MPs in different coastal regions were assessed by the polymer risk index. Results reveal that coastal areas in the Bulak district exhibit the highest risk. Our results confirm the prevalence of MPs as anthropogenic pollutants in East Surabaya and highlight the importance of management action and education on environmental protection for the mitigation of MP pollution.

Heavy metal wastewater pollution has become an environmental and industrial challenge worldwide. Hexavalent chromium (Cr(VI)) is one of the most common forms of chromium metal. Hexavalent chromium pollution is a concern because it was hazardous and can accumulate in the tissues of living organisms and the environment. The adsorption method using activated carbon can be one of the methods to treat hexavalent chromium waste. This study selected Samanea saman as the activated carbon because it contains hemicellulose, lignocellulose, and lignin, which are the requirements for an excellent activated carbon. The study’s objective is to analyze Samanea saman activated carbon (SSAC) to remove hexavalent chromium, measure the adsorption capacity, and determine the appropriate type of adsorption isotherm layer based on the maximum [ ] and minimum [ ] values. The process of making activated carbon was activated using K₂CO₃ through a pyrolysis process and using batch adsorption. The SEM results as characterization of SSAC depicted that the high pore was well developed. The optimal conditions for Samanea saman indicated high efficiency toward hexavalent chromium ions within the following process parameters; pH value 5, adsorbent dosage 5 g, and initial concentration 20 mg/L. The findings demonstrate that SSAC leads to the removal efficiency of hexavalent chromium being 99.90%, with the greatest adsorption capacity of 0.8949 mg/g. Based on the maximum [ ] and minimum [ ] values, the most suitable adsorption isotherm model in SSAC was the Freundlich isotherm existing in the monolayer ([ ]). The experimental results demonstrated that adsorption of Cr(VI) was well performed by SSAC. Thus, the SSAC material is an appropriate adsorbent for the removal of hexavalent chromium in the water and has the potential to be industrial applied.

The new catalyst (La/Bi₂S₃) applies for the photodegradation of Acid Yellow 42 (AY42) dye under visible light in this study. The La/Bi₂S₃ material is the motivating catalyst due to the excellent ability of Lanthanum (La) to increase the adsorption capacity and electron‐hole separation of Bi₂S₃ for enhancing the degradation of AY42. The characterization analysis of the prepared material confirms a successful synthesis using the hydrothermal method. The efficiency of photodegradation AY42 using La/Bi₂S₃ is higher than pure Bi₂S₃. La on Bi₂S₃ (doped at 3%), which is devised on adsorption (40.24%) and photodegradation (51.86%), has the best degradation efficiency (92.1%). The trapping experiment and the analysis of electron spin resonance (ESR) spectra explain that the hydroxyl radical is the most active species in this photocatalytic process due to the total degradation efficiency decreasing from 92.1% to 57.16% by the scavenger using isopropyl alcohol (IPA). The hole (h⁺) shows its importance in the photodegradation of AY42 by detecting that OH^- is the intermediate species. The new material (La/Bi₂S₃) also shows excellent photostability in the reusability test. Finally, the result confirms that La is a suitable doping metal for Bi₂S₃ and is interesting for practical application under visible light. The new catalyst (La/Bi₂S₃) applies for the photodegradation of Acid Yellow 42 (AY42) dye under visible light in this study. The La/Bi2S3 material is the motivating catalyst due to the excellent ability of Lanthanum (La) to increase the adsorption capacity and electron‐hole separation of Bi₂S₃ for enhancing the degradation of AY42. The characterization analysis of the prepared material confirms a successful synthesis using the hydrothermal method. The photodegradation efficiency of AY42 using La/Bi₂S₃is higher than pure Bi₂S₃. The doping of 3% weight of La on Bi₂S₃ shows the optimum degradation efficiency of 92.1%, devised on adsorption (40.24%) and photodegradation (51.86%). The pure Bi₂S₃ (46.7%) contains 17.1% of adsorption and 29.6% of photodegradation. The trapping experiment and the analysis of electron spin resonance (ESR) spectra explain that the hydroxyl radical is the most active species in this photocatalytic process due to the total degradation efficiency decreasing from 92.1% to 57.16% by the scavenger using isopropyl alcohol (IPA). The hole (h⁺) shows its importance in the photodegradation of AY42 by detecting that OH^- is the intermediate species. The new material (La/Bi₂S₃) also shows excellent photostability in the reusability test. Finally, the result confirms that La is a suitable doping metal for Bi₂S₃ and is interesting for practical application under visible light.

The mining and electroplating industries have resulted in the contamination of the environment with heavy metal. This has resulted in a serious threat to the ecological environment and human health due to the presence of copper pollution. To address this issue, extensive efforts have been made to develop effective methods for removing contaminants, particularly heavy metal, and Samanea saman (SS) was selected as precursor production of activated carbon. Therefore, this study is aimed at investigating Samanea saman-activated carbon (SSAC) to remove copper from an aqueous solution. SS was chemically activated by potassium carbonate and carbonized at 600°C for 5 hours, while SSAC was characterized by scanning electron microscopy-energy dispersive X-ray (SEM-EDS), Fourier-transform infrared (FTIR), and proximate tests. Copper adsorption on SSAC was evaluated by the Langmuir, Freundlich, Langmuir, Freundlich, Redlich-Peterson, Harkin-Jura, and Jovanovic models. Pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models were used to identify adsorption process mechanism. SEM-EDS results presented that the pore of SSAC was heterogeneous, irregular in shape, and mesopore. In addition, FTIR analysis identified the main functional groups present in SSAC as C-H, C-O-C, and C-O. The proximate test conducted on SSAC determined the water content, volatile matter, ash content, and fixed carbon to be 0.61%, 22.26%, 9.77%, and 67.97%, respectively. The results showed that SSAC exhibited exceptional performance with copper removal efficiency of 99.49% under an adsorbent mass of 0.25 g, a reaction time of 30 minutes, and a concentration of 10 mg/L. Isotherm adsorption of SSAC followed the Redlich-Peterson model with an adsorption capacity (Qm) of 0.663 mg/g, correlation value () of 0.9992, and pseudo-second-order pattern . Therefore, SSAC can be proposed as a potential and economical biomaterial to treat heavy metal in wastewater.