Multifunctional Alginate–TiO2/SiO2 Hydrogel–Ceramic Composites for Photocatalytic Soil Remediation and Impedance-Based Diagnostics: A Critical Review and Conceptual Framework

Soil contamination by persistent organic pollutants is a major environmental challenge, whereas conventional remediation approaches often lack effective means for continuous, in situ monitoring of treatment progress. Recent advances in multifunctional materials provide a basis for integrating pollutant degradation with non-destructive environmental monitoring. This review critically examines alginate–TiO2/SiO2 hydrogel–ceramic composites as a potential platform for integrating photocatalytic soil remediation with impedance-based monitoring. TiO2 exhibits photocatalytic activity and promotes the generation of reactive oxygen species; SiO2 contributes to adsorption, dispersion, porosity, and structural stability; while sodium alginate provides a hydrated, biodegradable matrix for particle immobilization, water retention, and mass-transport control. Particular attention is given to electrochemical impedance spectroscopy (EIS) as a non-destructive method for monitoring time-dependent physicochemical changes in soil–composite systems. This review evaluates suitable composite architectures, electrode configurations, calibration strategies, control experiments, and approaches for interpreting complex impedance responses. The potential application of artificial intelligence (AI) and machine learning is also considered, with emphasis on data quality, independent validation, and the limitations of models trained on heterogeneous environmental datasets. Because impedance responses are inherently indirect and non-specific, chemical analysis remains essential for confirming pollutant transformation and identifying transformation products. Standardized ecotoxicological assays, particularly reproduction testing with the springtail Folsomia candida, are considered as an independent biological line of evidence for determining whether physicochemical improvements are accompanied by reduced residual toxicity. Key challenges include heterogeneous soil properties, limited light penetration, mass-transfer limitations, catalyst and hydrogel stability, sensor calibration, matrix effects, and model accuracy. The review proposes an evidence-based framework linking material design, photocatalytic treatment, EIS monitoring, chemical verification, and ecotoxicological assessment. However, the complete integrated platform has not yet been experimentally validated, and its performance in real contaminated soils remains to be established.