In this study, we prepared alginate composite hydrogel beads containing various compositions of biochar produced from pitch pine (Pinus rigida) for the removal of Cu²⁺ and benzene from model pollutant solutions. The properties of the alginate/biochar hydrogel beads were evaluated using scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer–Emmet–Teller analyses. Adsorption behavior of alginate/biochar hydrogel beads indicated that the adsorption capacities for Cu²⁺ (28.6–72.7 mg/g) were enhanced with increasing alginate content, whereas the adsorption capacities for benzene (20.0–52.8 mg/g) were improved with increasing biochar content. The alginate/biochar hydrogel beads exhibited similar adsorption capacities for Cu²⁺ and benzene in the concurrent system with Cu²⁺ and benzene compared to those in a single pollutant system. Adsorption kinetics and isotherm studies of the alginate/biochar hydrogel beads followed the pseudo-second-order model (r² = 0.999 for Cu²⁺, and r² = 0.999 for benzene), and Langmuir model (r² = 0.999 for Cu²⁺, and r² = 0.995 for benzene). In addition, alginate/biochar hydrogel beads (containing 1 and 4% biochar) exhibited high reusability (>80%). Therefore, alginate/biochar hydrogel beads can be applied as adsorbents for the removal of multiple pollutants with different properties from wastewater.

The present study reports the effective removal of benzene in aqueous phase onto biochar. The adsorption capacity of benzene onto biochars made at different pyrolytic temperatures (e.g., 350, 550, and 750 °C) and from various feedstocks (e.g., grape pomace, rice husk, and Kentucky bluegrass) were investigated. The adsorption capacity of Kentucky bluegrass-derived biochar (KB-BC) prepared at 550 °C for benzene was better than other biochars, owing to the higher surface area and functional groups. The adsorption isotherms and kinetics model for benzene by KB-BC550 fitted the Freundlich and pseudo-first order, respectively. In addition, the results of response surface methodology (RSM) designed with biochar dose, reaction time, and benzene concentration showed the maximum adsorption capacity (ca. 136 mg BZ/g BC) similar to that from kinetic study. KB-BCs obtained as waste grass biomass may be a valuable adsorbent, and RSM may be a useful tool for the investigation of optimal conditions and results.

The ability of biochars derived from fallen (F-BC) and non-fallen (NF-BC) maple leaves to adsorb Cu²⁺ ions from aqueous solutions was examined. Biochars were produced at pyrolysis temperatures of 350, 550, and 750 °C. Higher pyrolysis temperatures resulted in enhanced specific surface areas and promoted CaCO₃ crystallization while limiting MgCO₃ formation. The Cu²⁺ adsorption capacity depended on the biochar type and pyrolysis conditions. Although the Cu²⁺ adsorption efficiency of NF-BCs decreased with increasing pyrolysis temperature, F-BC550 exhibited a higher Cu²⁺ adsorption capacity than F-BC750. Additionally, the Cu²⁺ adsorption performance of both NF-BC350 and F-BC550 improved with increasing solution pH. Cu²⁺ adsorption onto NF-BC350 and F-BC550 followed the two-compartment first-order (involving fast and slow adsorption compartments) and Langmuir (meaning homogeneous monolayer adsorption) models, respectively. The maximum Cu²⁺ adsorption capacity of F-BC550 (147.3 mg Cu/g BC) was 7.8-fold higher than that of NF-BC350 (18.8 mg Cu/g BC), as determined by isotherm studies. The enhanced adsorption performance of F-BC550 may be attributable to physical adsorption facilitated by increased surface area and multiple mechanisms, including cationic attraction via functional groups, ion exchange (Ca and Mg), and van der Waals interaction facilitated by increased surface area. These findings suggest that F-BC550, derived from waste biomass, exhibits superior Cu²⁺ adsorption performance compared to NF-BCs, making it a promising adsorbent for wastewater treatment applications.