The composite gels of konjac glucomannan (KGM) and corn starch (CS) were prepared and treated by the freeze–thaw method. For KGM–CS gels, as the starch ratio rose from 0 to 100%, storage modulus (G′) decreased by 97.7% (from 3875.69 Pa to 87.72 Pa), degradation temperature decreased from 313.32 °C to 293.95 °C, and crystallinity decreased by 16.7%. For F–KGM–CS gels, G′ decreased by 99.0% (from 20,568.10 Pa to 204.09 Pa), degradation temperature increased from 289.68 °C to 298.07 °C, and crystallinity decreased by 17.1% with more starch content. The peak in infrared spectroscopy shifted to a higher wavenumber with more starch and to a lower wavenumber by freezing the corresponding composite gels. The detected retrogradation of the composite gels appeared for KGM–CS with 80% starch and F–KGM–CS with 40% starch. The endothermic enthalpy of free water rose by 10.6% and 10.1% with the increase in starch for KGM–CS and F–KGM–CS, respectively. The results of moisture distribution found that bound water migrated to free water and the water-binding capacity reduced with more starch. The results demonstrated that the molecular interaction in composite gels was weakened by starch and strengthened by freezing.

Industrial wastewater contains complex pollutants, including toxic dyes, necessitating effective and sustainable remediation strategies. Conventional treatment methods often struggle to remove multiple dyes simultaneously, underscoring the need for innovative adsorbents. This study investigated a clay/carbon composite (SBE/C (500 °C)) derived from spent bleaching earth (SBE) via pyrolysis for the simultaneous removal of methylene blue (MB) and malachite green (MG) dyes. The pyrolysis process significantly enhanced the specific surface area of SBE, improving its adsorption capacity. Using the Box–Behnken design (BBD) and response surface methodology (RSM), we optimized key parameters (pH, contact time, and dosage) at 45 °C and an initial dye concentration of 20 mg/L. The developed quadratic model demonstrated high predictive accuracy, with experimental results closely aligning with predictions (R² = 0.9983 for MB, 0.9955 for MG), along with strong adjusted (R² = 0.9962 for MB, 0.9896 for MG) and predicted (R² = 0.9811 for MB, 0.9275 for MG) values. Under optimal conditions, the maximum adsorption capacities reached 27.77 mg/g for MB and 27.38 mg/g for MG. These findings highlight the potential of SBE/C (500 °C) as a sustainable and cost-effective adsorbent for the simultaneous removal of MB and MG from wastewater, offering a promising solution for environmental remediation.

Biochar has attracted increasing attention for aquatic pollution control, particularly due to its capacity to accelerate the rate-limiting steps of denitrification in wastewater treatment. While early research primarily focused on the adsorption capacity of biochar, recent studies have increasingly investigated its role as a redox-active mediator that facilitates electron transfer. This review critically synthesizes the multifaceted mechanisms of biochar-enhanced denitrification, establishing a link between synthesis parameters (feedstock, pyrolysis kinetics) and physicochemical functionalities (pore architecture, redox-active functional groups). Specifically, we elucidate how precise regulation of pyrolysis temperature dictates the dominant electron transfer pathway: low-temperature biochar (700 °C) promotes direct interspecies electron transfer (DIET) through graphitic conduction. We systematically decouple biochar-mediated electron transfer into three pathways: functional group-driven shuttling, solid-state conductive matrix transfer via conjugated π-electrons, and material-assisted DIET. Crucially, we emphasize that validating true DIET requires direct biological evidence of electroactive machinery. Furthermore, the review details how biochar modulates the biological microenvironment, upregulating key denitrification genes (narG, nirS/K, nosZ) and enriching functional microbial consortia. By integrating advances in surface modification—such as heteroatom doping and metal loading—we propose strategies to engineer biochar for optimized nitrate-to-nitrogen conversion. Future perspectives underscore the need for balancing electron-donating capacity with structural stability, developing low-energy functionalization techniques, and conducting life-cycle assessments to facilitate the scale-up of sustainable, high-efficiency nitrogen removal systems.