In this article, studies on organic solubility and stability in subcritical water reported during the past 25 years have been reviewed. Data on the solubility and decomposition of organic compounds in subcritical water, a green solvent, are needed in environmental remediation, chemistry, chemical engineering, medicine, polymer, food, agriculture, and many other fields. For solubility studies, the experimental systems used to measure solubility, mathematical equations derived and applied for the modeling of the experimentally determined solubility data, and the correlation between the predicated and experimental data have been summarized and discussed. This paper also reviewed organic decomposition under subcritical water conditions. In general, the solubility of organics is significantly enhanced with increasing water temperature. Likewise, the percentage of organic decomposition also increases with higher temperature.

The role of Fe-modified sporopollenin (Fe-Sp) biomass in Pb²⁺ removal from aqueous solutions was investigated by batch biosorption technique. The prepared biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy. The influence of pH, contact time, biosorbent dose, and initial concentration on biosorption process were optimized by using a four factor Box–Behnken design combined with response surface methodology. The results indicated a positive adsorption behavior of Fe-Sp and a strong pH dependency of the process. The optimum predicted parameters were determined as follows: biosorbent dosage 0.5 g, pH of 6.75, contact time 104 min, and initial Pb²⁺ concentration of 25.42 ppm. The Freundlich isotherm model provided a better fit (R² = 0.994) for the experimental data, indicating biosorption on a heterogeneous surface. Maximum biosorption capacity (q_max) was 22.72 mg g⁻¹ as indicated by the Langmuir isotherm. Kinetically, the adsorption process followed a pseudo-second-order model, indicating that chemisorption was the rate-limiting step.