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Subcritical water extraction (SWE) is a process for extracting phenolic and flavonoid compounds from the skin of the peanut (Arachishypogea). The phenolic and flavonoid compounds of peanut skin were frequently recovered using a hazardous solvent in a traditional extraction procedure. Subcritical water extraction is one of the methods for overcoming the toxicity of solvents. Therefore, the study’s aim was to identify the best extraction conditions for recovering total phenolic compounds (TPC), total flavonoid compounds (TFC), and antioxidant activity from peanut skin. The solubility of TPC and TFC in subcritical water was determined using the Chrastil and Del Valle-Aguilera models. The best conditions were 10.46 MPa pressure, 12.56 mL/min water flowrate, 120 °C temperature, 375.08 mg/100 g TPC, 396.24 mg/100 g TFC, and 87.96% antioxidant activity. The Chrastil model fits the solubility of TPC and TFC in subcritical water effectively since it has the lowest average absolute relative deviation (AARD), which is 2.81% and 4.47%, respectively. The findings demonstrate that a low temperature condition is ideal for increasing TPC and TFC.

The present work was aimed to evaluate the removal of methyl violet dye by potassium hydrox- ide-treated palm kernel shell sorbents. The sorbents were prepared by dried impregnation, carbonization and chemical activation in a muffle furnace. The sorbents were characterized for specific surface area, surface morphology and functional groups. Results show that the activated carbon displayed a specific surface area of 302 m2/g, which was 54 times greater than the impregnated sorbent. However, the latter showed a 42 mg/g maximum adsorption capacity of methyl violet, nearly four times better than the former. The equilibrium data were fitted well with the Langmuir isotherm, while the rate of sorption data obeyed the pseudo-second-order model. Adsorption of methyl violet was not specific surface area-dependent. The rate-limiting step for methyl violet adsorption was mainly driven by film diffusion at lower concentration, and intraparticle diffusion at higher concentration. A simple impregnation using potassium hydroxide was a promising approach to yield sorbent rich in acidic groups for methyl violet removal.

The objective of this work is to evaluate the removal of methylene blue dye by bio-polishing sludge-based adsorbents. The adsorbents were characterized according to the specific surface area, pH upon the treatment and surface functional groups. The adsorption of dye was carried out at room temperature, and the adsorption data were analyzed using the isotherm and kinetics models. The bio-polishing sludge is rich in ash content, and the presence of surface functional groups varied with the treatment strategies. The specific surface area of adsorbents is between 7.25 and 20.8 m2/g. Results show that the maximum removal of methylene blue by sludge adsorbents was observed to have the following order: untreated sludge (SR) > zinc chloride-treated (SZ) > microwave-dried (SW) = potassium carbonate-treated (SK) > acid-washed (SH). The maximum adsorption capacities for SR and SZ as predicted by the Langmuir model are 170 and 135 mg/g, respectively. Although SR demonstrates a higher maximum removal than SZ, the latter exhibits greater removal intensity and rate constant even at high dye concentration. The bio-polishing sludge is a promising adsorbent for dye wastewater treatment.

•An overview of traditional extraction techniques employed in Indonesia.•Discussion of various green extraction techniques, including their fundamentals, benefits, and drawbacks•Identification of obstacles and limitations of green extraction in Indonesia.•recent developments green extraction techniques for Indonesian natural products.•Emphasis on the need for more environmentally responsible and sustainable extraction practices in Indonesia.•Suggestions for future research and development of green extraction for Indonesian natural products.

•SC-CO2 with ETOH/H2O maximized anthocyanin recovery from roselle calyces.•Pressure and co-solvent ratios affected anthocyanins, polyphenol and colour quality.•SC-CO2outperforms the SLE methods in TAC and other polyphenols recovery.•Due to greater co-pigment in extract, SC-CO2 improved anthocyanin stability.